Document Modesto_doc_831db6f4eb

Appendix H – Integrated Groundwater Management Plan for the Modesto Subbasin ---PAGE BREAK--- ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Table of Contents 1 Introduction 1 1.1 Introduction 1 1.2 Integrated Regional Water Management Plan Subareas 1 1.3 Stanislaus and Tuolumne Rivers Groundwater Basin Association 2 1.4 Accomplishments of the Stanislaus and Tuolumne Rivers Groundwater Basin Association 2 1.5 Groundwater Management Subareas 5 1.6 Ongoing Groundwater Management-Related Activities 6 2 Need for Groundwater Management Planning 7 2.1 Legislative Requirements 7 2.2 IRGMP Components 8 2.3 Purpose and Goals of the Groundwater Management Plan 8 2.3.1 Water Management Strategies 8 2.4 Authority to Prepare Integrated Regional Groundwater Management Plan 10 3 Water Resources Setting 11 3.1 Land and Water Uses Within the Study Area 11 3.2 Major Water Purveyors in the Basin 11 3.2.1 City of Modesto 11 3.2.2 Modesto Irrigation District 15 3.2.3 City of Oakdale 18 3.2.4 Oakdale Irrigation District 21 3.2.5 City of Riverbank 24 3.3 Stanislaus County 25 3.4 Land Use Planning Activities 27 3.4.1 Agencies’ Spheres of Influence 28 3.4.2 Planning for Growth 28 3.4.3 Potential Future Annexations 28 4 Groundwater Resources in the Modesto Basin 30 4.1 Introduction 31 4.2 Hydrogeology 31 4.2.1 Geology 31 4.2.2 Aquifers 39 4.2.3 Groundwater Levels 40 4.2.4 Groundwater Flow Directions 47 4.2.5 Groundwater Recharge and Discharge Areas 57 4.2.6 Hydraulic Characteristics 58 i ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 4.3 Groundwater Quality 59 4.3.1 Total Dissolved Solids 60 4.3.2 Chloride 63 4.3.3 Sodium 64 4.3.4 Nitrate 64 4.3.5 Iron and Manganese 73 4.3.6 Arsenic 73 4.3.7 Radionuclides 75 4.3.8 Pesticides 75 4.3.9 Herbicides 76 4.3.10 Volatile Organic Chemicals 77 4.3.11 Constituents of Concern 79 4.3.12 Groundwater Quality Protection and Improvement 80 4.4 Groundwater Use 81 4.5 Summary 82 5 Groundwater Management Plan 87 5.1 Definition of Groundwater Basin and Map of Groundwater Basin and Subareas 87 5.2 Basin Management Objectives 87 5.2.1 Maintain Groundwater Levels 87 5.2.2 Control Degradation of Groundwater Quality 88 5.2.3 Protect Against Potential Inelastic Land Surface Subsidence 91 5.2.4 Groundwater Monitoring and Assessment 91 5.2.5 Evaluate Feasible Water Conservation Measures 91 5.2.6 Coordination and Cooperation 92 5.3 Groundwater Management Areas Objectives 92 5.3.1 City of Modesto Management Area 92 5.3.2 Modesto Irrigation District Management Area 94 5.3.3 City of Oakdale Management Area 94 5.3.4 City of Riverbank Management Area 95 5.3.5 Oakdale Irrigation District Management Area 96 5.3.6 Stanislaus County Management Area 96 5.4 Current Groundwater Monitoring Activities 97 5.4.1 Subsidence Monitoring 99 5.5 Facilitating Conjunctive Use Operations 99 6 Groundwater Protection Measures 101 6.1 Identification and Management of Wellhead Protection Area 101 6.1.1 Actions 103 6.2 Regulation of the Migration of Contaminated Groundwater 103 6.2.1 Actions 103 6.3 Identification of Well Construction Policies 104 6.3.1 Actions 105 6.4 Administration of Well Abandonment and Destruction Programs 105 6.4.1 Actions 106 ii ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 6.5 Mitigation of Overdraft Conditions 107 6.5.1 Actions 107 6.6 Replenishment of Groundwater Extracted by Water Producers 107 6.6.1 Actions 108 6.7 Construction and Operation of Recharge, Storage, Conservation, Water Recycling and Extraction Projects 108 6.7.1 Actions 108 6.8 Control of Saline Water Intrusion 109 6.8.1 Actions 109 7 Stakeholder Involvement 111 7.1 Involvement of Other Agencies and Entities 111 7.2 Coordination with Other Agencies 111 7.3 Advisory Committee 111 7.4 Public Involvement 112 7.5 Developing Relationships with State and Federal Agencies 113 7.6 Dispute Resolution Process 114 8 Plan Implementation 115 8.1 Integration of Local, State and Federal Monitoring Activities 115 8.1.1 Integration of Surface and Groundwater Operations 115 8.1.2 Integration of Groundwater Use and Surface Water Delivery 115 8.1.3 Integration of Water Management (MID and City of Modesto) 116 8.1.4 Integration of Water Quality Management for Both Surface Water and Groundwater 116 8.2 Local, Statewide, and Regional Priorities 116 8.2.1 Local Priorities 116 8.2.2 Statewide Priorities 117 8.2.3 Regional Priorities 117 8.2.4 Basin-Wide Water Management Strategies 118 8.3 Implementation Plan 119 8.3.1 Basin-Wide Recommendations 119 8.3.2 Area-Specific Recommendations 126 8.4 Data Management 129 8.5 Annual Implementation Report 129 8.6 Financial Planning for Recommended Actions/Project Implementation 129 8.6.1 Grant Funding 130 8.6.2 Revenues Through Increased Water Rates 130 8.7 Periodic Review of the Integrated Regional Groundwater Management Plan 131 8.8 Schedule and Implementation Sequence 131 References 133 iii ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Tables 2-1 Location of Association Groundwater Management Plan Components 9 3-1 Groundwater Production by the City of Modesto 13 3-2 MID Irrigation Facilities 16 3-3 Description of MID Irrigation and Drainage Wells 17 3-4 Service Connections in the City of Oakdale 19 3-5 Description of City of Oakdale Wells 19 3-6 Distribution of Land Uses in the City of Oakdale 20 3-7 Water Demand Projections for the City of Oakdale 21 3-8 Oakdale Irrigation District Wells 23 3-9 Oakdale Irrigation District Facilities 23 3-10 Service Connections in the City of Riverbank 24 3-11 City of Riverbank's Wells 24 3-12 Major Programs Affecting Groundwater Within the Association's Boundaries 27 3-13 Projected Population Growth in Stanislaus County 28 4-1 Concentrations of Herbicides in Area Wells 76 5-1 Current Level of Monitoring Efforts 98 Figures 1-1 Management Areas and Agencies 3 4-1 Modesto and East San Joaquin Groundwater Subbasins 32 4-2 Geology Map 35 4-3 Nomenclature and Their Depth Beneath the City of Modesto 37 4-4 Corcoran Clay Extent 38 4-5 Schematic Profile of Aquifers—Geologic Section A-A' 41 4-6 Schematic Profile of Aquifers—Geologic Section B-B' 43 4-7 General Location of Aquifers 45 4-8 Shallow Aquifer Groundwater Levels 46 4-9 Groundwater Levels in the Forebay Aquifer 48 4-10 Groundwater Levels in the Mehrten Confined Aquifers 49 4-11 Water Level Contours for the Unconfined Water Body, Spring 1971 51 4-12 Regional Water Level Elevation in Wells and Direction of Groundwater Flow, Spring 1985 53 4-13 Regional Water Level Elevation in Wells and Direction of Groundwater Flow, Spring 1994 55 4-14 TDS Concentration in Water Wells 61 4-15 Chloride Concentrations in the Unconfined Water Body, with Selected Concentrations Shown in the Confined Water Body, 1959–70 65 4-16 Seasonal Variations in Chloride Concentrations 67 4-17 Gas Wells 68 iv ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 4-18 Distribution of Nitrate Concentrations in the Unconfined Water Body, with Selected Concentrations Shown in the Confined Water Body, 1959- 1970 69 4-19 Nitrate (NO3) Concentration in Water Wells in 1990 71 4-20 Trends in Nitrate Concentrations 74 4-21 DBCP Sampling Locations and Concentration in Water Wells 77 5-1 Modesto and East San Joaquin Groundwater Subbasins 89 Appendices A Association Memorandum of Understanding B Memorandum of Understanding Between the Association and the California Department of Water Resources C Current Data Collection Protocol D Groundwater Monitoring Plan E Public Involvement Documentation F Resolutions of Plan Adoption J:\040190 Stanislaus & Tuolumne Rivers Mgmt Plan\Public Draft 04-19-05\R-IRGMP Public Draft.doc v ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Abbreviations and Acronyms AB 3030 Groundwater Management Act Association Stanislaus and Tuolumne Rivers Groundwater Basin Association B-E/GEI Bookman-Edmonston, a Division of GEI Consultants bgs below ground surface BMOs Basin Management Objectives Central Valley Regional Water Quality Control Board DBCP dibromochloropropane DEH San Joaquin County Department of Environmental Health DER Stanislaus County Department of Environmental Resources DWR Department of Water Resources DWSAP Program Drinking Water Source Assessment and Protection Program EC electrical conductivity EDP ethylene dibromide gpd/ft gallons per day per foot gpm gallons per minute IRGMP Integrated Regional Groundwater Management Plan MCL maximum contaminant level mg/l milligrams per liter mgd million gallons per day MID Modesto Irrigation District Modesto Regional Water Treatment Plant OID Oakdale Irrigation District PBE Physical Barrier Effectiveness PCAs Potential Contaminating Activities PCE perchloroethylene SB 1938 Groundwater Management Planning Act of 2002 vi ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N SB 1672 Integrated Regional Water Management Planning Act of 2002 SSJID South San Joaquin Irrigation District TCE trichloroethylene TDS total dissolved solids TID Turlock Irrigation District USGS U.S. Geological Survey VOCs volatile organic compounds WHPA Wellhead Protection Area µg/L micrograms per liter µmhos/cm micromhos per centimeter vii ---PAGE BREAK--- ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 1 Introduction 1.1 Introduction In April 1994, six agencies covering the Modesto Groundwater Subbasin formed the Stanislaus and Tuolumne Rivers Groundwater Basin Association (Association) to provide a forum for coordinated planning and management of the subbasin. These six agencies are: ƒ The City of Modesto ƒ The Modesto Irrigation District (MID) ƒ The City of Oakdale ƒ The Oakdale Irrigation District (OID) ƒ The City of Riverbank ƒ Stanislaus County Since 1994, the Association has been actively engaged in management of the subbasin. In late 2003, the Association began developing an integrated regional groundwater management plan in compliance with the Groundwater Management Planning Act of 2002 (SB 1938) and the Integrated Regional Water Management Planning Act of 2002 (SB 1672). The Association selected Bookman-Edmonston, a Division of GEI Consultants (B-E/GEI), to assist in the preparation of this plan. The six agencies rely on groundwater for some or all of their service area water needs. These agencies share the groundwater resource and, through the Association, provide coordinated planning to make the best use of groundwater to the mutual interests of the inhabitants. Throughout the planning process, other interested parties within the subbasin were encouraged to participate in the development of the plan. The Association coordinates its planning process with other neighboring water agencies as well as state agencies. 1.2 Integrated Regional Water Management Plan Subareas The planning area includes the entire Modesto Groundwater Subbasin and part of the Eastern San Joaquin Groundwater Subbasin and includes all or most of the service areas of the six agencies constituting the Association. The Modesto Groundwater Subbasin underlies all of MID, the City of Oakdale, and the City of Riverbank. However, a portion of OID overlies the Eastern San Joaquin Groundwater 1 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Subbasin, and a portion of the City of Modesto service area overlies the Turlock Groundwater Subbasin. The entire subbasin and planning area is within Stanislaus County. OID’s jurisdictional boundaries reach beyond the boundaries of the Modesto Groundwater Subbasin, and the study area has been extended to include OID’s complete jurisdiction. However, this management plan is simply called the Integrated Resources Groundwater Management Plan (IRGMP) for the Modesto Subbasin. A similar water planning effort is under way in the Turlock Groundwater Subbasin. The portion of the City of Modesto service area within the Turlock Subbasin is covered in the Turlock groundwater planning process. A map of the study area and agencies involved are shown in Figure 1-1. 1.3 Stanislaus and Tuolumne Rivers Groundwater Basin Association This IRGMP is a product of the efforts of the six cooperating agencies noted above that formed the Association through a memorandum of understanding signed in April 1994. The Association was created to provide a forum in which the parties could work cooperatively to combine the available talent and resources of the parties’ respective organizations, to provide coordinated planning to make the best use of available water resources of the subbasin to meet the needs of the parties, and to accomplish the Association’s stated purposes. A copy of the memorandum of understanding is presented in Appendix A. The purposes of the Association are: ƒ To determine and evaluate the subbasin’s groundwater supply ƒ To promote coordination of groundwater management planning activities, including the preparation of the groundwater management plan ƒ To develop a hydrologic groundwater model of the groundwater basin ƒ To determine the subbasin’s need for additional or improved water extraction, storage, delivery, conservation, and recharge facilities ƒ To provide information and guidance for the management, preservation, protection, and enhancement of groundwater quality and quantity in the subbasin 1.4 Accomplishments of the Stanislaus and Tuolumne Rivers Groundwater Basin Association Since its inception, the Association has successfully provided for: ƒ Better understanding of the groundwater basin, its aquifers, geology, water quality, water level fluctuations, and potential sources and mitigation of contaminants. 2 ---PAGE BREAK--- CITY OF MODESTO OAKDALE RIVERBANK OAKDALE I.D MODESTO I.D Tuo lum ne R iver Sta n isla us Ri v er Sa n J oa q u i n Ri ver East San Joaquin Subbasin Modesto Subbasin Turlock Subbasin Modesto Reservoir £ ¤ 132 £ ¤ 120 £ ¤ 33 £ ¤ 5 £ ¤ 99 £ ¤ 59 £ ¤ 108 £ ¤ 219 £ ¤ 49 £ ¤ 165APRIL £ ¤ 205 £ ¤ 108 £ ¤ 120 Empire Salida Waterford JUNE 2005 FIGURE 1-1 Management Areas and Agencies 05-10-04 S:/GIS/Projects/040190/Figure4_1.mxd 4 0 4 2 Miles¥ LEGEND Groundwater Subbasins Modesto I.D. Oakdale I.D. Cities SOURCES: City of Modesto, Modesto Irrigation District, City of Oakdale, Oakdale Irrigation District, City of Riverbank, CA Dept of Water Resources Groundwater Basins, 2002, California Spatial Library. Surface Exposure of Mehrten Formation INTEGRATED REGIONAL GROUNDWATER MANAGEMENT PLAN FOR THE MODESTO BASIN ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ Cooperative working relationship among all agencies, combining their financial strength, and sharing of resources to better managing their groundwater. ƒ A forum for coordinated and uniform data collection, and water management activities. ƒ Regular meeting of the member agencies to share and learn from each other’s experiences to discuss water management issues, and to assist one another to resolve those issues. Some of the Association’s specific accomplishments include: ƒ Six public agencies voluntarily working together under the umbrella of a locally controlled and managed groundwater association. The working relationship is defined by the Memorandum of Understanding Relating to the Formation and Operation of the Stanislaus and Tuolumne Rivers Groundwater Basin Association. Meetings of the Association are held at 2 p.m. on the first Thursday of every month in the MID offices, located at 1231 11th Street, Modesto, California. These meetings are open to the public. ƒ Development of a coordinated groundwater data collection and monitoring program, the extension of groundwater monitoring to selected privately owned wells to provide a more comprehensive view of groundwater elevations throughout the subbasin, and collecting spring and fall water levels throughout the Modesto Subbasin from all participating agencies’ groundwater well networks. ƒ Developing a basin-wide integrated regional groundwater management plan consistent with SB 1938. The updated plan is scheduled for individual public agency adoption in early 2005. ƒ Formation of the Regional Water Management Planning Group consistent with SB 1672 (Costa). ƒ Entered into an agreement with the California Department of Water Resources through a Memorandum of Understanding to Work Cooperatively Together to Improve Surface Water and Groundwater Management and to Promote Conjunctive Use Projects and Programs in the Modesto Groundwater Subbasin (Appendix ƒ The Association provides local share funding for the multi-year, multi-phased study sponsored by the U.S. Geological Survey (USGS) (Modesto Groundwater Basin Characterization, November 2004). The study is entering its third phase. Scientific Investigations Report 2004-5232, published by the USGS in November 2004, summarizes the findings and recommendations from Phase One. 4 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ The Association provided information and other input into the triennial report, Recommendations for Improving Groundwater in Stanislaus County. ƒ Implementation of an agreement between two members of the Association, MID and the City of Modesto, for the delivery of surface water to the City to reduce groundwater pumping, hence reducing localized overdraft and contaminant migration in the subbasin. ƒ Development of a wellfield optimization project. 1.5 Groundwater Management Subareas For the purpose of developing this groundwater management plan, the study area has been divided into six management subareas representing the jurisdictional boundaries of the Association’s member agencies. The groundwater management subareas are: ƒ The City of Modesto management subarea. This area includes the communities of Empire, Del Rio, and Salida and the service area of the City of Modesto that is north of the Tuolumne River. However, the City’s service area south of the Tuolumne River in the Turlock Groundwater Subbasin is covered under a separate groundwater management plan being developed for the Turlock Subbasin. ƒ The Modesto Irrigation District management subarea. This area includes MID’s service area and is entirely located within the Modesto Groundwater Subbasin. ƒ The City of Oakdale management subarea. This area includes the service area of the City of Oakdale and is located entirely within the Modesto Groundwater Subbasin. ƒ The Oakdale Irrigation District management subarea. This area covers OID’s entire service area. About 60 percent of the OID service area is located within the Modesto Groundwater Subbasin and 40 percent is in the Eastern San Joaquin Groundwater Subbasin. ƒ The City of Riverbank management subarea. This area covers the service area of the City of Riverbank and is entirely within the Modesto Groundwater Subbasin. ƒ The Stanislaus County management subarea. This area includes the entire study area within the Modesto Groundwater Subbasin and that part of Stanislaus County in the Eastern San Joaquin Groundwater Subbasin that is not covered by the five management subareas listed above. Figure 1-1 shows the six management subareas as described above. 5 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 1.6 Ongoing Groundwater Management-Related Activities With the exception of some localized areas, groundwater levels are generally stable in the Modesto Groundwater Subbasin and OID service area in the Eastern San Joaquin Groundwater Subbasin. However, increased urban development and changes in irrigation management practices threaten the balance by increasing demand for groundwater and by reducing recharge. It is the objective of the participating agencies to ensure that overall groundwater levels are maintained to provide a reliable long-term source of water. To manage the basin’s groundwater resources, the Association member agencies regularly exchange information and arrange for uniform groundwater data collection and monitoring to better understand the groundwater basin. In 1998, the Association developed a data collection protocol to standardize the data collection procedures among the member agencies. Data is collected in a coordinated fashion biannually. A copy of the current data collection protocol is provided in Appendix C. Conjunctive use management, in-lieu recharge through the local use of surface water for municipal and industrial purposes, and the protection of groundwater quality and water levels are actions that have been discussed for the long-term beneficial use of the basin. To that extent, MID and the City of Modesto developed and executed a treatment and delivery agreement under which MID supplies treated surface water to the City of Modesto, which uses it to augment is drinking water supply. Another avenue for helping to maintain groundwater levels is urban water conservation and the installation of water meters. Implementation of the best management practices, including the installation of water meters, can reduce water consumption, improve the overall water supply reliability, and reduce stress on the groundwater system. A detailed discussion of the water conservation is presented in the various agencies’ urban water management plans. In addition to maintaining groundwater levels, protecting groundwater quality is an important objective for the Association’s member agencies. Actions that are being implemented or considered to achieve this objective include conducting a geological assessment to identify areas of poor water quality; controlling water table elevations to contain poor quality water; sealing and abandoning wells to eliminate pathways for contamination; and protecting natural recharge areas from exposure to pollutants. Land surface subsidence in the basin is not significant. The potential for future land subsidence appears to be remote. 6 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 2 Need for Groundwater Management Planning Groundwater is a precious resource. It is a reliable water source for the agricultural, urban, and industrial needs of the Modesto Subbasin. Increases in population and corresponding increases in groundwater use have resulted in a lower groundwater table in some areas of the Modesto Subbasin and may have contributed to groundwater degradation, especially within the boundaries of the City of Modesto. The water agencies in the subbasin agreed to reevaluate their groundwater management practices and examine opportunities for integration of their surface and groundwater resources. The agencies formed the Association and signed a memorandum of understanding to work cooperatively to resolve their water issues and manage the basin. The signatories also agreed to be involved and cooperate in the development of a groundwater management plan. They have agreed to build upon their recent achievements and prepare a regional and integrated water management plan. Therefore, this IRGMP is being developed as an integrated and regional plan in compliance with SB 1938 and SB 1672. 2.1 Legislative Requirements SB 1938, as passed by California Legislature and signed into law by the Governor in 2002, amended the Water Code section 10750 et seq. to require that new groundwater management plans prepared under the Groundwater Management Act (AB 3030) include the components listed below: ƒ Documentation that a written statement was provided to the public describing the manner in which interested parties might participate in developing the groundwater management plan. This may include appointment of a technical advisory committee of the stakeholders in the basin. ƒ Development of Basin Management Objectives (BMOs). ƒ Adoption of monitoring protocols or a monitoring program capable of tracking changes in conditions for the purpose of meeting BMOs. ƒ Preparation of a map showing the area of the groundwater basin, as defined by the Department of Water Resources’ (DWR) Bulletin 118, with the area of the local agencies subject to the plan as well as the boundaries of other agencies that overlie the basin in which the agency is developing a groundwater management plan. ƒ A description of the components relating to the monitoring and management of groundwater levels, groundwater quality, inelastic land surface subsidence, and 7 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N changes in surface flow and surface water quality that directly affect groundwater levels or groundwater quality. ƒ Preparation of a plan of actions by the managing entity to involve other agencies and that enables the local agencies to work cooperatively with other public entities whose area or boundaries overlie the groundwater basin. ƒ The Groundwater Management Plan must be adopted by the local managing agency. ƒ Provisions for periodic reporting of the groundwater management activities and groundwater basin conditions. In 2002, SB 1672 was also passed by the legislature and signed into law. This law authorizes a regional water management group, as defined, to prepare and adopt a regional plan relating to water supply, water quality, flood protection, or related matters. This law defined procedures to form a regional water management group, to communicate to the public, and to prepare and adopt an integrated regional water management plan. 2.2 IRGMP Components This plan has been prepared in accordance with requirements of SB 1672 and SB 1938. As such, the plan includes components of AB 3030 and SB 1938 (California Water Code Section 10750 et seq.) and SB 1672 (California Water Code Section 10540 et seq.). Table 2-1 lists the sections in which each component is addressed. Appendix D is the Groundwater Monitoring Plan (October 2004). 2.3 Purpose and Goals of the Groundwater Management Plan The purpose of this IRGMP is to provide a framework for coordinating groundwater and surface water management activities into a cohesive set of management objectives and implementing the actions necessary to meet those objectives. The goal of the IRGMP is to provide for the integrated use of groundwater and surface water within the basin to ensure the reliability of a long-term water supply to meet current and future beneficial uses including agricultural, industrial, and municipal water requirements while protecting the environment. 2.3.1 Water Management Strategies The regional management actions, described later in this plan, reflect a comprehensive approach to managing water resources in the Modesto Groundwater Basin. In particular, these actions support the following water management strategies: 8 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Table 2-1 Location of Association Groundwater Management Plan Components 1. Documentation of public involvement statement. 2.1, Section 7 2. Basin Management Objectives (BMOs). 5.4 3. Monitoring and management of groundwater elevations, groundwater quality, inelastic land surface subsidence, and changes in surface water flows and quality that directly affects groundwater levels or quality or are caused by pumping. 5.6, 5.7, 8.2, Appendix A 4. Plan to involve other agencies located within groundwater basin. 1.2, 1.3, 2.3 5. Adoption of monitoring protocols by basin stakeholders. 5.7, Appendix D 6. Map of groundwater basin showing area of agency subject to GMP, other local agency boundaries, and groundwater basin boundary as defined in DWR Bulletin 118. 1.2, 5.3 7. For agencies not overlying groundwater basins, preparation of GMP using appropriate geologic and hydrogeologic principles. NA 1. Management with guidance of advisory committee. 7.3 2. Description of area to be managed under GMP. 1.2, 5.3 3. Creation of link between BMOs and goals and actions of BMP. Section 6, 8.2 4. Description of GMP monitoring program. 5.7, Appendix D 5. Description of integrated water management planning efforts. 2.3 6. Report on implementation of GMP. Section 8 7. Periodical evaluations of GMP. 8.5 1. Control of saline water intrusion. 2.5, 6.8 2. Identification and management of wellhead protection areas and recharge areas. 2.5, 6.1 3. Regulation of the migration of contaminated groundwater. 2.5, 6.2 4. Administration of well abandonment and well destruction program. 2.5, 6.4 5. Mitigation of conditions of overdraft. 2.5, 6.5 6. Replenishment of groundwater extracted by water producers. 2.5, 6.6 7. Monitoring of groundwater levels and storage. 2.5, 5.7, Appendix D 8. Facilitating of conjunctive use operations. 2.5, 6.7 9. Identification of well construction policies. 2.5, 6.3 10. Construction and operation by local agency of groundwater contamination cleanup, recharge, storage, conservation, water recycling, and extraction projects. 2.5, 6.7 11. Development of relationships with state and federal regulatory agencies. 2.5, 8.1 12. Review of land use plans and coordination with land use planning agencies to assess activities that create reasonable risk of groundwater contamination. 2.5, 3.4 1. Integration of water resource managemen activities. 1.2, 5.2, 8.3, 8.6, 8.7 2. Regional planning and management. 1.2, 5.2, 8.3, 8.6, 8.7, 3. Formation of a regional management group Section 7 4. Public involvement. 2.1, Section 7 5. Development of local, regional, and statewide priorities. 8.2, 8.7 D. Integrated Regional Planning (SB 1672) C. CWC § 10750 et seq Voluntary Components (AB 3030) A. CWC § 10750 et seq Required Components (SB 1938) B. DWR's Suggested Components 9 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ Increase local and regional water supply reliability and water use efficiency ƒ Promote groundwater recharge and management ƒ Support water conservation ƒ Implement watershed management programs ƒ Promote water recycling ƒ Foster conjunctive use ƒ Improve water quality ƒ Improve storm water capture and management Other regional water management elements, such as providing for recreation and river restoration, are addressed in other planning documents prepared by the participating agencies. 2.4 Authority to Prepare Integrated Regional Groundwater Management Plan The governing bodies of the Modesto and Oakdale Irrigation Districts and the Cities of Modesto, Oakdale, and Riverbank have elected, through the issuance of resolutions, to prepare this IRGMP to effectively manage the surface and groundwater resources of the basin. The specific authority of each agency is as follows: • MID was formed on July 23, 1887, under the California Irrigation District Act (Wright Act) and is authorized to manage surface and groundwater resources for the benefits of the District landowners. • OID was organized under the Wright Act on November 1, 1909, to manage its water resources, including surface water and groundwater supplies. • The Cities of Modesto, Oakdale, and Riverbank are incorporated and authorized to provide for management and distribution of drinking water to their citizens. • The County of Stanislaus is a water purveyor for a small public water system in the Modesto subbasin. It is a member of the Association and a member of the technical advisory committee to assist in and guide the preparation of the IRGMP. The County may choose, under SB 1672 and as a member of regional management group, to adopt the IRGMP after it is prepared. 10 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 3 Water Resources Setting 3.1 Land and Water Uses Within the Study Area The Modesto Groundwater Subbasin lies between the Stanislaus River to the north and the Tuolumne River to the south and between the San Joaquin River on the west and basement rock of the Sierra Nevada foothills on the east. The surface area of the subbasin is 247,000 acres. The northern, western, and southern boundaries are shared with the Eastern San Joaquin Groundwater, Delta-Mendota, and Turlock Groundwater Subbasins, respectively. The major water purveyors in the planning area include MID, OID, and the Cities of Modesto, Riverbank, and Oakdale. The southern 60 percent of OID is in the Modesto Groundwater Subbasin and 40 percent is in the Eastern San Joaquin Groundwater Subbasin. Modesto is in the southwestern portion of the subbasin, and a portion of the city is located south of the Tuolumne River in the Turlock Groundwater Subbasin. Oakdale and Riverbank lie in the north-central portion. Developed land uses within the Modesto Groundwater Subbasin are concentrated in two major categories, irrigated agricultural and urban land uses. The largest jurisdiction within the subbasin is MID, with a service area of 101,700 acres and an irrigated area of approximately 62,000 acres. Nested within MID is the city of Modesto and the communities of Waterford, Empire, Salida, and parts of Del Rio and Riverbank. Modesto alone occupies approximately 40 square miles or 25,600 acres. OID has a total service area of approximately 72,000 acres, of which approximately 43,200 acres lie within the Modesto Groundwater Subbasin and the remaining 28,800 acres are within the Eastern San Joaquin Groundwater Subbasin. Nested within OID is the city of Oakdale, which covers approximately 2,000 acres and has not been detached from OID, and the city of Riverbank, which covers around 1,760 acres, much of which has been detached. The eastern portion of the subbasin is foothill lands that are primarily rangeland and undeveloped. 3.2 Major Water Purveyors in the Basin 3.2.1 City of Modesto 3.2.1.1 Background The City of Modesto was first incorporated in 1877 and operates as a Charter City. It was originally to be named Ralston after the prominent San Francisco banker, William Ralston. However, when he declined the honor, the name of Modesto was selected. Since its founding, Modesto has grown to a city of over 200,000 people in 2004. 11 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N The City of Modesto has provided potable water service to its urban area since 1985 through the purchase and acquisition of several private water companies. The sole source of water supply until 1995 was groundwater from the Modesto and Turlock Groundwater Basins. Groundwater levels declined from 1924 through 1994 in the downtown area due to increasing urban uses. In the early 1990s, the City, MID and the Del Este Water Company formed a partnership and signed a treatment and delivery agreement to utilize MID’s surface water rights for municipal purposes. The Modesto Domestic Water Project and completion of the Modesto Regional Water Treatment Plant were the result of this partnership. The project consists of a 30-million-gallon-per-day (mgd) surface water treatment plant and storage and delivery facilities, which were completed in January 1995. Its implementation has allowed the City of Modesto to reduce its groundwater pumping, which has led to a recovery in groundwater levels. In the mid-1990s, the City of Modesto acquired the Del Este Water Company, which had previously served approximately 30 percent of the municipal customers in the Modesto area. As a result, the City became the retail water purveyor to the communities of Waterford, Hickman, Del Rio, Salida, Grayson, and parts of Ceres and Turlock, in addition to county islands within Modesto. The Modesto Domestic Water Project provides water to municipal customers served by the City of Modesto north of the Tuolumne River, which is the overlapping service area of both the City and MID. 3.2.1.2 Location Modesto covers approximately 36 square miles in Stanislaus County (see Figure 1-1). The portion of the city north of the Tuolumne River encompasses 34 square miles (94 percent of the service area) and lies within the Modesto Groundwater Subbasin. The portion of the city south of the Tuolumne River encompasses 2 square miles (6 percent of the service area) and lies within the Turlock Groundwater Subbasin. 3.2.1.3 Water Supply Sources of the City’s water within the Modesto Groundwater Subbasin include groundwater from the Modesto Groundwater Subbasin and treated surface water from MID. The City of Modesto supplies approximately 60 percent of its water from City-owned and operated wells. Prior to the completion of the the City of Modesto and the surrounding communities relied solely on groundwater for their domestic supply. The EIR noted that groundwater levels were declining, particularly near the center of Modesto, and that with declining water levels, water quality degradation had been observed. 12 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 3.2.1.4 Facilities The City’s water system includes over 70,000 water connections, 927 miles of water lines system, 118 water wells, and seven water tanks. Of these wells, 108 withdraw water from the Modesto Groundwater Subbasin. The City does not conduct land use planning in the areas it serves that were formerly within the Del Este system outside the City’s Sphere of Influence. Table 3-1 shows groundwater production by the City of Modesto from 1999 through 2003. Average groundwater use from the Modesto Groundwater management subarea during this period was 45,300 acre-feet per year, which, when combined with 33,600 acre-feet of surface water available from the results in a total supply to the joint MID-City of Modesto service area of 78,900 acre-feet. Assuming that the capacity is increased from 30 mgd to 60 mgd, the available normal year water supply for the joint service area would increase to about 112,000 acre-feet in 2008. During supply shortage years, the delivery of treated surface water by MID may be reduced in equal proportions with deliveries to its agricultural customers. The City, however, has the option of receiving its full contract surface water and making up these shortages by delivering groundwater for an amount equal to shortages to the irrigation canal system. The City presently operates 108 drinking water wells in the Modesto Groundwater Subbasin, including the former Del Este wells. Table 3-1 Groundwater Production by the City of Modesto Year Acre-Feet 1999 45,140 2000 42,100 2001 44,900 2002 47,700 2003 46,780 Average 45,300 3.2.1.5 Ongoing Activities The City of Modesto’s partnership with MID to provide domestic water is an important conjunctive use effort. Other ongoing groundwater management activities by the City of Modesto include the following: ƒ Active participation in the Association to manage the basin’s groundwater resources ƒ Conjunctive use of groundwater and surface water supplies ƒ Utilize a SCADA system for the remote operation and monitoring of wells ƒ Test water quality in accordance with Title 22 ƒ Enacted a well ordinance adopting the California Wells Standards (Bulletin 74-81) and all supplements ƒ Implementing provisions of the certified Urban Water Management Plan 13 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ Regulation of wastewater disposal The City received a grant for a feasibility study for the Regional Water Recycling Project. This study investigated the feasibility of collecting the wastewater effluent from a number of cities, including Oakdale and Riverbank. The wastewater from the advanced wastewater treatment plant could be available to the City for non-potable reuse crops and landscape irrigation) or water exchanges with other water agencies within the basin. The City of Modesto Stormwater Program was established in 1993 to meet the objective of effectively eliminating illicit discharges to the storm drain system, reducing the discharge of pollutants from the system, and protecting the groundwater and surface water resources. To meet these objectives, the City prepared a Stormwater Management Plan that has served as the road map for the implementation of the City’s storm water program. The plan consists of seven program elements to control the discharge of pollutants and a monitoring program to characterize storm water discharges and assess the health of the receiving waters. The City currently irrigates approximately 3,000 acres of fodder and feed crops on City- owned land. 3.2.1.6 Issues of Concern Declining water quality, combined with increasingly strict standards from state and federal regulatory agencies, have forced the City to take an average of 2.3 wells out of service each year (West Yost 2004). The City closely monitors groundwater quality and those wells showing high nitrates have remained out of service. The City employs some well-head treatment and uses granular activated carbon to remove organics and chlorination to disinfect the distribution system. The City has also identified four wells that will not currently meet the federal and state arsenic limits of 10 milligrams per liter without treatment (West Yost 2004). Ongoing USGS investigations have also identified uranium as a constituent of concern. Future groundwater production may be limited by water quality issues and the cost and availability of well-head treatment technologies. In addition to arsenic, primary constituents of concern in groundwater are dissolved solids, hardness, major ions (probably iron and manganese), organics, radionuclides, and nitrates. The City’s general plan projects that its population will grow from a current population of approximately 206,200 to approximately 400,000 by build-out of the general plan area. With a limited groundwater supply and groundwater quality issues, meeting the City’s future needs will be challenging and may require the identification of additional surface water supplies and the implementation of water management options, such as water conservation, recycling, and conjunctive use. 14 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 3.2.2 Modesto Irrigation District 3.2.2.1 Background MID is a public utility that supplies surface water, groundwater, and electrical service to agricultural and municipal customers throughout its 101,700-acre service area. MID was formed on July 23, 1887, the second irrigation district to be established under the California Irrigation Districts Act (Wright Act). During its early years, MID developed numerous rights for Tuolumne River water and facilities to irrigate agricultural lands and to generate electricity using this water. The primary economy within the district is agriculture or agriculture-related businesses. The primary crops grown within MID are trees (mostly almonds), vines, grain, row crops, and pasture. The average farm size is approximately 20 acres, and approximately 3,000 farms lie within the district. Currently, MID serves approximately 3,000 irrigation water customers and 62,000 irrigated acres. 3.2.2.2 Location MID is located in eastern Stanislaus County and is bounded on the north by the Stanislaus River, on the south by the Tuolumne River, on the west by the San Joaquin River, and on the east by the Sierra Nevada Mountains (Figure 1-1). The district is located entirely within the Modesto Groundwater Subbasin. 3.2.2.3 Water Supply and Storage Facilities MID obtains its surface irrigation water from the Tuolumne River. The river’s 1,880-square- mile watershed extends to the High Sierra and most of the river’s flow comes from snowmelt. Peak flows occur between April and July, when over 60 percent of the annual flow occurs. Annual Tuolumne River runoff average over 1,800,000 acre-feet, varying from a low of 383,000 acre-feet in 1977 to a high of 4,631,000 acre-feet in 1983. MID’s first project as a public entity was the La Grange Dam, completed on December 13, 1893, in conjunction with Turlock Irrigation District (TID). Nearly ten years later, on June 27, 1903, the main canal was completed and farmers along this canal began receiving water. By September of that year, other fields were being served by lateral canals. Storage and the regulation of main canal deliveries began in 1911 with the completion of the 28,000 acre-foot Dallas-Warner Reservoir (now known as Modesto Reservoir). Carryover storage to protect permanent crops from extended drought was unavailable until the completion of Don Pedro Reservoir in 1923. This reservoir allowed MID to store a maximum of 102,000 acre-feet each year and to begin generating electricity from a power plant developed to help defray the cost of irrigation facilities. In 1970, MID and TID enlarged their storage and power generation capacity with the completion of New Don Pedro 15 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Dam and Reservoir, with a storage volume of 2,030,000 acre-feet. New Don Pedro Reservoir is owned, operated, and maintained jointly by MID and TID. 3.2.2.4 Water Distribution Facilities MID distributes a combination of Tuolumne River water and groundwater via a network of storage facilities, canals, pipelines, pumps, water table control wells, and control structures. Table 3-2 provides a summary of these irrigation facilities. Table 3-2 MID Irrigation Facilities Facility Type MID Facilities Improvement District and Private Facilities Canals (lined) 142.2 miles 9.8 miles Canals (unlined) 23.7 miles Pipelines 44.4 miles 152.8 miles Wells/Deep Well Pumps 96 575* Sidegates 1,317 Structures, SCADA-Monitored and/or –Controlled 13 headgates, 5 spills, and 4 flow measurements 0 Structures, Chart-Monitored, Manually Controlled 12 spills and 4 flow measurements 0 *Number of non-MID deep wells with MID represent staff’s best estimate. This number was derived from MID’s electric power records and may not reflect the actual number of private deep wells within the MID service area. Source: MID Final Groundwater Management Plan, Table 2-1. Groundwater management in MID has been influenced by Modesto’s rapid growth. For much of its history, Modesto relied exclusively on groundwater, and thus, its population growth has been accompanied by declining groundwater levels. Between 1924 and 1994, groundwater levels under Modesto declined about 42 feet, with most of this decline occurring after World War II. In 1994, its sole reliance on groundwater ended when MID completed the a 30 mgd domestic water project that treats Tuolumne River water for delivery to the City. This municipal and industrial water treatment plant has helped offset declining groundwater levels in the Modesto area. 3.2.2.5 Groundwater Use MID has both irrigation wells and drainage pumping wells. Prior to widespread urban development, the large influx of surface water for irrigation in MID led to the development of a shallow water table on the west side of the district. To protect crops from the rising water table, groundwater management through shallow groundwater pumping was initiated in 1918. MID now owns and operates 55 water table control wells that are used to maintain groundwater levels below crop root zones. These wells are shallow (usually less than 100 16 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N feet), are perforated throughout their depth, and are generally pumped during the irrigation season. Water table control pumping protects lands by promoting the aeration of the root zone and by allowing naturally occurring salts to leach from the root zone. To the extent feasible, water from the water table control wells is pumped into the irrigation system to supplement surface water. In recent years, water table control pumping has become less important. The reasons for this change include increased groundwater pumping in the urban area, the use of irrigation conservation practices and new irrigation technologies, and increased groundwater pumping for agriculture. The combined effect has resulted in a lowering of groundwater levels, allowing some MID water table control wells to be converted to irrigation wells to augment the district’s surface water supply. Because of the availability of surface water, significant groundwater pumping for irrigated agriculture did not occur in MID until the late 1970s, during one of the most severe droughts on record. MID now owns and operates 44 wells developed for the specific purpose of water supply. These wells are often used to smooth canal flow fluctuations, to improve irrigation delivery service, and to reduce canal spills. Many landowners in MID also operate their own irrigation wells. MID irrigation and water table control wells are tallied in Table 3-3. Table 3-3 Description of MID Irrigation and Drainage Wells Irrigation Wells 44 Water Table Control Wells 55 Well Construction Summary 98 by cable tool 1 by gravel pack Casing Depths 50 to 400 feet Annular Seals? Required after 1985 Typical Depth of Seal 50 to 100 feet Source: MID Final Groundwater Management Plan, Table 3-2. 3.2.2.6 Ongoing Activities The MID partnership with the City of Modesto to provide domestic water is an important conjunctive use effort. Other ongoing activities conducted by MID include: ƒ Active participation in the Association to manage the basin’s groundwater resources ƒ monitoring of all groundwater wells ƒ Estimation of pumping from agricultural wells ƒ Periodic agricultural suitability testing on all irrigation and drainage wells ƒ Periodic mapping of groundwater elevations ƒ Implementation of water conservation projects ƒ Water table control through pumping of water table control wells 17 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 3.2.2.7 Issues of Concern The fundamental issue of concern for MID is maintaining a sustainable balance between groundwater use and groundwater recharge. Municipal and industrial water demand is projected to grow in the basin in response to increasing population. Urban water conservation and reuse practices can help buffer growth in demand. At the same time that groundwater use is expected to grow, some important pathways for groundwater recharge are expected to decline because of the urbanization of farmland and conversion of fields now irrigated using surface irrigation techniques to more intensively managed techniques (such as drip irrigation) that reduce both water applications and deep percolation. Some agencies are concerned that changing irrigation methods from flood irrigation to drip irrigation) will reduce groundwater recharge and contribute to future declines of groundwater levels. Groundwater use in the MID management area varies from year to year and increases significantly during drought years, when groundwater is a more significant component of the water supply. Groundwater quality in some locations in MID has been degraded from urban, industrial, and agricultural operations, and as groundwater recharge is reduced by urban development, less blending of groundwater results. This leads to an increasing concentration of salts and other contaminants and the increased risk of degradation. Agricultural water use efficiency that reduces deep percolation could be detrimental to groundwater levels and groundwater quality in some areas. MID has identified a need to coordinate the operation of its wells to better respond to water supply, water table control, water quality management, and energy use objectives. In addition, identifying and protecting areas that may serve as dedicated groundwater recharge zones are priorities. 3.2.3 City of Oakdale 3.2.3.1 Background The City of Oakdale provided water to a population of approximately 15,800 persons in 2001. The water system also provides potable water to commercial, industrial, and public facilities throughout the city. 3.2.3.2 Location Oakdale is located near the geographical center of OID (Figure 1-1) and lies entirely within the Modesto Groundwater Subbasin. 3.2.3.3 Water Supply The City of Oakdale draws water from nine wells located in the Modesto Groundwater Subbasin. Water pumped from the aquifer meets the standards of Title 22 and is suitable for direct potable use without treatment. The City’s water supply system is operated under a 18 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N permit granted by the California Department of Health Services on August 20, 1964. The permit has been amended as needed to reflect changes in system facilities. 3.2.3.4 Facilities The City’s water system consists of nine deep wells that supply groundwater to a distribution pipe network; two of these wells are newly completed. Currently, there is one 500,000-gallon steel storage reservoir located in northeast Oakdale at the intersection of Valley View Drive and the Stanislaus River bluff. The majority of the water system is controlled and monitored by a remote telemetry system located at the Public Works Center at Fifth and I Streets in southeast Oakdale. Table 3-4 describes the service connections in the city. Table 3-5 describes the characteristics of wells owned and operated by the City. Table 3-4 Service Connections in the City of Oakdale Type Metered Flat Rate Total General and Residential 5,175 5 5,180 Commercial 81 13 94 Industrial 19 0 19 Agricultural (irrigated) 0 0 0 Other Water Systems 8 0 8 Total Active Connections 5,283 18 5,301 Inactive Connections 62 Fire Hydrants ±630 Backflow Prevention Devices ±167 Source: City of Oakdale, Water Master Plan, page 2-1. There are two active booster pumps operating within the distribution system. The Burchell Hill booster station is located in northeast Oakdale and provides the pressure needed to supply the Burchell residential subdivision and an older residential area to the west. The booster station at the site of Well 5A serves a high- pressure zone in the southern part of the city. Table 3-5 Description of City of Oakdale Wells Public Water Supply Wells 9 Well Construction Summary 98 by cable tool 1 by gravel pack Casing Depths Annular Seals? Yes Typical Depth of Seal The water distribution system contains approximately 392,500 feet of mains, ranging in diameter from 2 to 16 inches. The original distribution system was all steel pipe. Over the last 13 years, asbestos cement pipe has been introduced, and most recently, PVC pipe has been used for system extensions and upgrades. 3.2.3.5 Water Use The demand for municipal water depends, generally, on climate, distribution of land use, cost of water, availability of private sources of supply, landscape demand, and cultural attitudes. In Oakdale, nearly all residential, commercial, and industrial users are metered and average 19 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N daily per capita water use for 2000–2001 was estimated to be 248 gallons. This is a typical rate for small San Joaquin Valley cities with metered water supplies. Studies indicate that metering and associated pricing may result in an approximately 10 to 20 percent reduction in a community’s water consumption, an estimate supported by the observation that the average daily per capita water consumption for some San Joaquin Valley communities without meters ranges from 300 to 350 gallons. 3.2.3.6 Influence of Land Use on Water Use The mix of land uses within a city influences water use. Open spaces such as parks or schools also have a smaller water demand than most industrial areas. Table 3-6 presents the distribution of various land use categories in the City of Oakdale. Table 3-6 Distribution of Land Uses in the City of Oakdale Land Use per General Plan Area (acres) Percentage Agricultural 4.39 0.1 Agricultural residential 29.92 1.5 Central business district 101.79 5.1 Estate 0.05 0 General commercial 186.88 9.3 High-density residential 6.58 0.3 Industrial 179.65 9.0 Low-density residential 1,109.31 55.0 Medium-density residential 209.56 10.5 Office 13.50 0.7 Open space 7.95 0.4 Park 46.20 2.3 Public/semi-public 75.37 3.8 School 15.99 0.8 Single/family light-density residential 17.17 0.9 Total 2,004.31 100.0 Source: City of Oakdale, Water Master Plan, page 3-5 Table 3-7 presents the estimated annual average and maximum per capita daily water demands for Oakdale, given a 3 percent rate of population growth and two scenarios for per capita water consumption. 20 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Table 3-7 Water Demand Projections for the City of Oakdale Average Day (gallons per minute) Maximum Day (gallons per minute) Year Estimated Population 2005 17,773 3,086 3,679 5,863 6,990 2015 23,886 4,147 5,884 7,879 11,180 Build-Out per General Plan 7,569 14,381 Source: City of Oakdale, Water Master Plan, page 3-11. Based on population projections and an average water consumption of 250 gallons per capita per day. Based on land use development from the Oakdale Planning Department and corresponding demand coefficients for various land uses. 3.2.3.7 Ongoing Activities Ongoing groundwater management activities by the City of Oakdale include the following: ƒ Active participation in the Association to manage the basin’s groundwater resources ƒ Monitor water levels in all wells ƒ Test water quality in accordance with Title 22 ƒ Enacted a well ordinance adopting the California Wells Standards (Bulletin 74-81) and all supplements 3.2.3.8 Issues of Concern Issues of concern for the City of Oakdale are primarily related to the potential future degradation of groundwater quality and development taking place over recharge areas. Water levels in some wells are impacted by production wells at adjacent industrial plants. 3.2.4 Oakdale Irrigation District 3.2.4.1 Background OID was organized on November 1, 1909, under the Wright Act. In July 1910, the OID and its neighboring district, the South San Joaquin Irrigation District (SSJID), purchased an established ditch system, known as the Tulloch System. This system was developed in the 1880s by Charles H. Tulloch, who had purchased the water rights, a ditch, and a small diversion dam built for working placer gravel near Knights Ferry. Farmers later extended the ditch, known as the Old Tulloch Ditch, into the valley area to serve some 6,000 acres of farmland, including an area around Oakdale. 21 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Currently, OID encompasses approximately 72,345 gross acres that support four major groups of crops—irrigated pasture, oats-corn (double crop), rice, fruits and nuts—and miscellaneous crops such as berries, melons, and onions. 3.2.4.2 Location OID is located in Stanislaus and San Joaquin Counties on the eastern side of the San Joaquin Valley (Figure 1-1). Approximately three-fifths of its service area lies south of the Stanislaus River and is within the Modesto Groundwater Subbasin. The remaining two-fifths of the service area lie north of the Stanislaus River and are within the Eastern San Joaquin Groundwater Subbasin. 3.2.4.3 Water Supply and Storage Facilities By 1912, OID and SSJID had abandoned the old miner’s diversion dam and begun construction of the Goodwin Diversion Dam, an 80-foot-high, double concrete arch dam, which was completed in 1913. Between 1913 and 1925, the service area inflated to 20,000 acres, an increase of more than 300 percent over 12 years. Until 1925, irrigation was dependent upon the natural flow in the Stanislaus River, which was far from adequate to irrigate the 20,000-acre service area. In response to this, OID and SSJID voted $2,200,000 in bonds to finance construction of the 112,500 acre-foot Melones Reservoir, which was completed on December 15, 1926. The districts negotiated a contract with PG&E for the sale of the falling water benefits below the dam for hydropower generation. These payments completely amortized the bond issue without imposing a tax burden upon the landowners in the districts. Between 1931 and 1938, OID constructed 25 deep wells to supplement its surface water supply and to meet the demand for water late in the irrigation season. Nevertheless, by 1938, both OID and SSJID found they were desperately short of irrigation water. To address this water supply problem, the Tri-Dam Project was developed, with power generation as a secondary purpose. In 1948, sites were approved at Donnells and Beardsley on the Middle Fork of the Stanislaus River and at Tulloch, above Goodwin Dam, and the project was completed in 1955. The combined storage capacity for the three reservoirs is 230,400 acre- feet, and the combined annual power generation is approximately 533,000 megawatt-hours. Additionally, in 1984, the Sand Bar Hydroelectric Powerhouse Project, which annually generates approximately 93,000 megawatt-hours, was completed. In 1980, New Melones Dam was completed. With a reservoir capacity of 2.4 million acre- feet, New Melones Reservoir effectively submerges the original Melones project. New Melones Dam was constructed by the U.S. Army Corps of Engineers and transferred to the U.S. Bureau of Reclamation. The dam and the reservoir were then incorporated into the Central Valley Project. Releases from New Melones Dam are now the principal source of irrigation water for OID. 22 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 3.2.4.4 Water Distribution Facilities OID’s distribution facilities include two main canals, one on each side of the Stanislaus River. The North Main Canal extends approximately 15 miles down into the floor of the valley from the joint OID/SSJID diversion of Goodwin Dam. The South Main Canal is approximately 22 miles in length. Approximately 250 miles of lateral and sublateral distribution networks are served from these two main canals. Table 3-8 describes OID’s irrigation facilities. 3.2.4.5 Groundwater Use OID operates 22 groundwater wells. These wells produce an average of about 6,300 acre- feet per year. The District also operates 43 drainage and several reclamation pumps. It is estimated that these facilities discharge around 13,000 acre-feet per year. Most of the private wells in the district are for small farm and domestic use. Table 3-9 summarizes the characteristics of OID wells. Table 3-8 Oakdale Irrigation District Wells Irrigation Wells 22 Drainage Wells 15 Reclamation Wells 28 Well Construction Summary 22 by cable tool Casing Depths 40-250 feet Annular Seals? Required after 1985 Typical Depth of Seal 40-100 feet Table 3-9 Oakdale Irrigation District Facilities District Facilities Canals (lined) 105 miles Canals (unlined) 125 miles Pipelines 100 miles Deep Wells 22 Reclamation/Drainage Pumps 43 Turnouts 3,500 SCADA 8 RTUs Monitored 25 Improvement District Facilities Deep Wells, Domestic 18 Domestic Service Connections 650 3.2.4.6 Ongoing Activities OID’s ongoing groundwater management activities include: ƒ Active participation in the Association to manage the basin’s groundwater resources ƒ water level monitoring of some wells ƒ Estimation of well discharge ƒ Water conservation programs 23 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ Regulation of wastewater disposal 3.2.4.7 Issues of Concern Issues of concern at OID include improving the coordination of groundwater pumping to reduce power consumption and to better manage groundwater levels and water quality. 3.2.5 City of Riverbank 3.2.5.1 Background Located along the Stanislaus River and State Highway 108, Riverbank was incorporated in 1922 and had a population of 17,004 in 2002. 3.2.5.2 Location Riverbank is located approximately five miles west of Oakdale and has, for the most part, been detached from OID (see Figure 1-1). 3.2.5.3 Water Supply The City of Riverbank relies on the Modesto Groundwater Subbasin for its water supply. In 2002, it pumped 3,777 acre-feet of water from the subbasin, using six wells (see Table 3-10). Two additional wells have become operational since 2002. Groundwater from its wells conforms to the requirements of Title 22 and is used directly for domestic supply. 3.2.5.4 Facilities Table 3-10 describes the City of Riverbank’s wells. The City of Riverbank currently has 5,863 active connections, summarized in Table 3-11. Table 3-10 Service Connections in the City of Riverbank Metered Flat Rate Total General and Residential 5,658 7 5,665 Commercial 166 7 173 Industrial 5 2 7 Agricultural (Irrigated) 0 0 0 Other Water Systems 18 0 18 Total Active Connections 5,847 16 5,863 Inactive Connections 78 Table 3-11 City of Riverbank's Wells Well Year Con- structed Annular Seals Well Construction Method #2 (8 th Street) 1956 Yes Cable tool #3 (Jackson) 1965 Yes Cable tool #4 (Pioneer) 1972 Yes Cable tool #5 (River Heights) 1978 Yes Cable tool #6 (Whorten) 1981 Yes Cable tool #7 (Crossroads) 1990 Yes Cable tool #8 (Novi) 2001 Yes Gravel pack #9 (Prospector) 2004 Yes Gravel pack 24 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Groundwater quality is generally good. The City of Riverbank monitors groundwater quality to ensure the delivery of good quality water to its customers. The current level of groundwater monitoring by the City is as follows: ƒ General mineral and general physical every 3 years ƒ Inorganic chemicals every 3 years ƒ Nitrate annually ƒ Regulated VOCs every 3 years ƒ Regulated SOC every 3 years (only DBCP, EDB, simazine, and atrazine) ƒ Gross alpha 4 consecutive quarters every 4 years 3.2.5.5 Ongoing Activities Ongoing groundwater management activities by the City of Riverbank include: ƒ Active participation in the Association to manage the basin’s groundwater resources ƒ Utilize a SCADA system permitting remote operation and monitoring of the wells ƒ Test water quality in accordance with Title 22 ƒ Enacted a well ordinance adopting the California Wells Standards (Bulletin 74-81) and all supplements. ƒ Regulation of wastewater disposal 3.2.5.6 Issues of Concern Two concerns facing the City of Riverbank are the preservation of groundwater quality and the increasing demand for water fueled by its rapid population growth. This growth is illustrated by the increase in population from 1990 through 2002. During these 12 years, the population doubled from 8,547 to 17,004 inhabitants. 3.3 Stanislaus County The participation of Stanislaus County in groundwater management planning is valuable because it encompasses the entire study area of the Modesto Groundwater Subbasin and OID service area within the Eastern San Joaquin Groundwater Subbasin and could represent areas outside the water purveyors’ service areas where water requirements are met by private pumping. It also has oversight responsibility for land use planning activities, water well 25 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N construction and destruction, groundwater contamination remediation, small public water systems, individual on-site sewage disposal systems, and hazardous materials within its jurisdiction. Therefore, the County’s participation in development of this groundwater management plan serves the following functions: ƒ The County could represent water users not served by participating water purveyors. ƒ County participation enables the interaction between groundwater management activities and county land use planning. ƒ The County Department of Environmental Resources (DER) enforces the California Model Well Standards (Bulletin 74-81) and all supplements, as required by the California Water Code, in unincorporated areas. ƒ The DER issues permits for wells that supply small public water systems. ƒ The DER issues permits and inspects well construction and destruction in unincorporated areas and maintains a record of drilling logs of permitted wells. ƒ The DER issues permits to allow the use of hazardous materials. ƒ Groundwater elevations near approximately 150 contamination sites are reported to the DER. ƒ The DER has periodically mapped groundwater levels. ƒ The DER regulates, monitors, and inspects small public water systems for Title 22 compliance to ensure that safe, adequate, and dependable water supplies are available for domestic use. DER maintains a database and file records containing water quality monitoring records for approximately 200 small public water systems. ƒ The DER operates a pilot wellhead protection program. ƒ The DER identifies soil and groundwater contamination associated with leaking underground storage tanks and other point sources. ƒ The DER is responsible for regulating septic tanks and wastewater disposal in unincorporated areas. ƒ The Stanislaus County Public Works Department provides flood control in unincorporated areas. Table 3-12 summarizes major programs that affect groundwater in the area of the Association. 26 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Table 3-12 Major Programs Affecting Groundwater Within the Association's Boundaries Facility or Operation Involved Association Member(s) Conjunctive use for irrigated agriculture MID and OID Domestic water supply MID, Modesto, Riverbank, Oakdale, OID Groundwater monitoring All members Storm water recharge basins Modesto, Oakdale, County Water conservation All members Drainage wells MID and OID Review and permitting of well construction County, Modesto, Oakdale, Riverbank Detection of soil and groundwater contamination County Pilot wellhead protection demonstration project County Regulation of small public water systems County Land use planning County, Modesto, Oakdale, Riverbank Wastewater management County, Modesto, Oakdale, Riverbank Flood control County Source: MID, Final Groundwater Management Plan, Table 3-1. 3.4 Land Use Planning Activities Land use planning is a tool to manage the impacts of various land uses on the quantity and quality of the water supply, especially groundwater resources. The Association does not have any land use planning authority. Therefore, the Association’s role is to review current land use planning activities and guide the water planning efforts of the member agencies in regard to water management activities so that they consider future land development and to encourage land use planning agencies to consider water management issues in their decision-making process. Some members of the Association (Stanislaus County and the three cities) have land use planning roles. In Stanislaus County, land use planning within the incorporated cities is carried out by the respective city. In most cases, Stanislaus County is not involved unless requested by the respective city. Both Stanislaus County and the irrigation districts are permitted to comment on city plans as part of the California Environmental Quality Act process. In unincorporated areas, land use planning is conducted by Stanislaus County’s Planning Department and approved by the Board of Supervisors. In land use planning, an important distinction needs to be made between aquifer (groundwater basin) and groundwater management area. Aquifer protection focuses on the entire groundwater basin. Groundwater management areas are subsets of the basin that can be delineated and prioritized for specific management purposes. 27 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 3.4.1 Agencies’ Spheres of Influence The sphere of influence is the potential area for annexation around an agency’s service area and lands within the sphere of influence are subject to regulation by that agency. However, land within the sphere cannot be annexed until an environmental impact report has been completed and the appropriate Local Agency Formation Commission approves the annexation. Annexation can be used as a tool in groundwater management. If an area currently served by groundwater is annexed by an irrigation district and is provided with surface water, this offers an opportunity for in-lieu recharge. This process can be used to balance the groundwater budget in a basin. 3.4.2 Planning for Growth Stanislaus County is one of the fastest growing counties in California. Based on U.S. Census data, its population during the 1980s climbed from 265,000 to 370,000, for a total increase of 105,000 people (a 40 percent growth rate). This growth continued as the population grew to 454,600 in 2000, an increase of 84,600 (a 23 percent growth rate). Table 3-13 indicates that growth in Stanislaus County is projected to continue. Between 2000 and 2010, the County’s population is expected to increase by 133,000 (29 percent) and between 2010 and 2020, by 124,500 (21 percent). Since 1980, most of the population increase has occurred in the County’s nine incorporated cities rather than the unincorporated area of the County. This concentration of growth in incorporated areas has increased the proportion of the County’s population living in these areas and has fueled substantial increases in the spheres of influence of many incorporated areas. Planning for growth is being facilitated by the County and local agencies by their recognizing that increased cooperation is essential in addressing growth-induced issues. Table 3-13 Projected Population Growth in Stanislaus County Data Source 2000 2005 2010 2015 2020 DOF – 2000 454,600 522,700 587,600 646,800 712,100 DOF - 1998 585,519 708,950 Source: State of California Department of Finance 1998 and 2000. 3.4.3 Potential Future Annexations Annexation by various entities within the Association is a tool for responding to population growth and for managing resources within their spheres of influence. Annexation has the potential to improve water management by: ƒ Better linking the water service required by customers with the type of service available 28 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ By providing service that meets broader water management objectives For example, city annexation that provides city water services to small urban parcels now served by irrigation districts enables the customers to receive the flexible service they desire and enables the irrigation districts to focus their attention on lands best served by agricultural delivery schedules. This type of annexation provides water users with water service that is tailored to fit residential needs, while irrigation districts can focus on the basin’s other water management issues. Irrigation district annexations of lands now being served by private wells allows surface water deliveries to replace groundwater pumping. This process, known as in-lieu recharge, supports aquifers by reducing the demand for groundwater pumping and increasing recharge from deep percolation of surface applied irrigation water. This process increases the overall water supply reliability of a region by enabling water agencies to conjunctively manage their surface and groundwater resources. In addition, water agencies can pump additional groundwater during drought periods without long-term groundwater overdraft in the basin. How annexation projects could impact or benefit a basin’s groundwater levels and groundwater quality should be evaluated on a case-by-case basis. 29 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Page intentionally left blank 30 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 4 Groundwater Resources in the Modesto Basin 4.1 Introduction This chapter describes the geology, aquifers, groundwater quality, and water use in the Modesto Groundwater Subbasin and includes the southeastern portions of the adjacent San Joaquin Groundwater Subbasin. Both subbasins are part of the much larger San Joaquin Valley Groundwater Basin. The locations of the Modesto and East San Joaquin Groundwater Subbasins are shown in Figure 4-1. The Cities of Modesto, Oakdale, and Riverbank and the communities of Salida, Empire, and Waterford use groundwater to supply their residents. MID and OID provide both surface water and groundwater for agricultural use. There are several large industrial water users in the basin. Local residents also rely on groundwater for potable water through numerous small water supply wells. Figure 4-1 shows the service area locations of the cities and irrigation districts. Residential and agricultural interests in the western portions of subbasins are impacted by the presence of shallow groundwater. Historic lowering of the groundwater levels within portions of the basin reversed the natural groundwater balance. Groundwater was depleted in areas near Modesto, which resulted in a cone of depression. Since 1994, when a surface water treatment plant was constructed, groundwater levels within the cone of depression have begun to recover. In addition, there is a potential for increases in the amount of outflow of groundwater from the subbasin, resulting from the anticipated increase in groundwater use outside the subbasin. Groundwater continues to be impacted locally by the increases in industrial and municipal needs. Water quality problems include the presence of salts, uranium, pesticides, and volatile organic chemicals (VOCs). This chapter relates these occurrences and problems to geologic controlling features to allow conceptual planning of groundwater management options. 4.2 Hydrogeology This section describes the geology, aquifers, hydraulic characteristics, groundwater levels, and the direction of groundwater flow. 4.2.1 Geology The Modesto Groundwater Subbasin is located in the northern portion of the San Joaquin Valley, which is a structural trough about 200 miles long and 70 miles wide. The valley is filled with up to 32,000 feet of marine and continental sediments deposited during its periodic inundation by the Pacific Ocean and erosion of the surrounding mountains, 31 ---PAGE BREAK--- # # CITY OF MODESTO OAKDALE RIVERBANK OAKDALE I.D MODESTO I.D Tuo lum ne R iver Sta n isla us Ri v er Sa n J oa q u i n Ri ver East San Joaquin Subbasin Modesto Subbasin Turlock Subbasin Modesto Reservoir £ ¤ 132 £ ¤ 120 £ ¤ 33 £ ¤ 5 £ ¤ 99 £ ¤ 59 £ ¤ 108 £ ¤ 219 £ ¤ 49 £ ¤ 165 £ ¤ 205 £ ¤ 120 £ ¤ 108 Empire Salida Waterford 02S11E29M001 03S10E13C001 JUNE 2005 FIGURE 4-1 Modesto and East San Joaquin Groundwater Subbasins 05-10-04 S:/GIS/Projects/040190/Figure4_1.mxd 4 0 4 2 Miles¥ LEGEND Groundwater Subbasins Modesto I.D. Oakdale I.D. Cities SOURCES: City of Modesto, Modesto Irrigation District, City of Oakdale, Oakdale Irrigation District, City of Riverbank, CA Dept of Water Resources Groundwater Basins, 2002, California Spatial Library. DWR Wells # Surface Exposure of Mehrten Formation INTEGRATED REGIONAL GROUNDWATER MANAGEMENT PLAN FOR THE MODESTO BASIN ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N respectively. Only the upper 800 feet of these sediments contain water that is considered potable or suitable for agricultural use. These sediments are generally categorized as consolidated and unconsolidated sediments. The sediments are generally coarser-grained in the eastern portion of the subbasin, having been deposited as coalescing alluvial fans and rivers near the Sierra Nevada Mountains, and fine-grained to the west. The sediment beds dip toward the west. 4.2.1.1 Consolidated Sediments The consolidated sediment beds that form the fresh water aquifers consist of the Ione, Valley Springs, and Mehrten sediment formations (from oldest to youngest). These sediments are exposed at the ground surface in the eastern portion of the subbasin and dip gently under the basin to the west. Figure 4-2 shows the distribution of these sediments and the locations of ground surface exposure. Figure 4-3 correlates the historic and recent nomenclature and the approximate depths beneath the city of Modesto. The Ione Formation can generally be thought of as continental, lagoons, and marshes with periodic invasions by the ocean (CDMG 1975). The sediments consist of white to red clays, sands, and rounded gravels with layers of black to brown coal. The sands and gravels are locally cemented or have a high clay content. The Valley Spring Formation can generally be considered to be a non-marine sequence of light-colored sediments that were eroded from volcanic rock (rhyolite). Ash and tuff are also present. The sediments consist of sandstone, siltstone, claystone with sandy clay, and sand and gravel generally in a clay matrix. The Mehrten Formation was also eroded from volcanic rocks, but instead of being light- colored, they are typically dark-colored (andesite). The formation is composed of up to 800 feet of sandstone, breccia, conglomerate, tuff, siltstone, and claystone (Page and Balding 1973). This formation is typically identified by well drillers as “black sands.” The sandstone and conglomerate are capable of transmitting large quantities of groundwater. The Mehrten Formation may lie as shallow as 400 feet beneath the city of Modesto (Burow et al. 2004). The top of the Mehrten Formation appears to be an irregular surface with valleys and hills. The reworking and redeposition of the formation sediments make distinguishing the boundary of this formation difficult. 4.2.1.2 Unconsolidated Sediments Historically, the unconsolidated alluvium has been classified as continental deposits (deposited in a freshwater environment), lacustrine and marsh deposits (pertaining to lakes), and Older Alluvium, Younger Alluvium, and flood-basin deposits (Page and Balding 1973). Recent efforts have reclassified these sediments into formations and include, from oldest to youngest, the Laguna, Turlock Lake, Riverbank, and Modesto Formations, Holocene alluvium (associated with stream channel and flood basin deposits) (Burow et al. 2004). 33 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Figure 4-2 shows the distribution of these sediments and where they are exposed on the ground surface. Figure 4-3 correlates the historic and recent nomenclature and their approximate depths beneath the City of Modesto. The Laguna Formation is characterized by alluvial deposits of gravel, sand, and silt in at least two upward-coarsening units separated by a well-developed palesol, a buried soil layer (Marchand and Allwardt 1981). The formation is composed generally of dark-colored volcanic sediments eroded from the Mehrten Formation but also contains some light-colored sediments that are likely derived from the granites (specifically, the granodiotites) from the Sierra Nevada. The Turlock Lake Formation is composed of sediments deposited by rivers from the Sierra Nevada. These sediments consist of two coarsening-upward sequences of silt, sand, and gravel that are likely the result of glacial outwash (Marchand and Allwardt 1981). The lower sequence of the formation contains dark volcanic sediments that were likely eroded from the Mehrten Formation and redeposited (Burow et al. 2004). Portions of the upper sequence are very coarse-grained sand and gravel incised valley fill and are potentially related to deposition from the Tuolumne River (Weissman et al. 2002). The upper and lower sequences are separated in the western portion of the subbasin with a clay layer that formed in a large lake. An areally extensive diatomaceous lake clay occurs at the base of the upper unit of the Turlock Lake Formation and is referred to as the Corcoran clay (correlated to the occurrence of the E-clay in the southern portion of the San Joaquin Valley). This clay layer is regionally extensive with hydrologic significance. Although numerous silt and clay beds occur above and below the Corcoran clay, they cannot be correlated over large areas. Therefore, those beds are of only local importance to the confinement of groundwater (Page 1973). The Corcoran clay is present at a depth of about 200 feet below ground surface (bgs) in the western portion of the subbasin (Page and Balding 1973). The clay is about 20 to 60 feet thick and may be locally eroded. The approximate eastern extent of the Corcoran clay parallels Highway 99 and is shown on Figure 4-4 (Burow et al. 2004). To the east and north, the clay becomes more silty and difficult to recognize along the edges, where the unit either grades into coarser materials of the same age or wedges out (Davis et al. 1959). Near the confluence of the Stanislaus and San Joaquin Rivers, a small portion of the Corcoran clay may be thin or missing and replaced with coarse-grained sediments (Burow et al. 2004). North of the Stanislaus River, the extent of the Corcoran clay aligns with Highway 99. The OID service area does not overlie any areas where the Corcoran clay is present. Overlying the Turlock Lake Formation are the Riverbank and Modesto Formations. These formations consist of river-deposited, light-colored sand, gravel, and silt. These sediments are oxidized and are likely to be derived from granites in the Sierra Nevada. The Modesto 34 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Figure 4-2 Geology Map 35 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Back of 11 x 17 36 ---PAGE BREAK--- Depth Below Ground Surface (feet) 0 to 50 50 to 100 130 to 200 260 450 Ground Surface Younger Alluvium Modesto Formation Riverbank Formation Portions replaced with coarse-grained valley fill Turlock Lake Formation (2 district coarsening upward sequences) Laguna Formation Upper Lower Mehrten Formation Valley Springs Formation Ione Formation Undifferentiated Marine Deposits FIGURE 4-3 JUNE 2005 Nomenclature and Their Depth Beneath The City of Modesto 05-11-04 S:/GIS/Projects/040190/Corel/Figure 4-3.cdr Older Alluvium Continental Deposits Shallow Aquifer Unconsolidated Sediments Consolidated Sediments Deep Aquifer Corcoran -Clay Forebay Aquifers Confined Mehrten Aquifers INTEGRATED REGIONAL GROUNDWATER MANAGEMENT PLAN FOR THE MODESTO BASIN ---PAGE BREAK--- CITY OF MODESTO OAKDALE RIVERBANK STANISLAUS CO. TUOLUMNE CO. SAN JOAQUIN CO. MERCED CO. OAKDALE I.D MODESTO I.D Tuo lum ne R iver Sta n isla us Ri v er Sa n J oa q u i n Ri ver Modesto Reservoir £ ¤ 132 £ ¤ 120 £ ¤ 33 £ ¤ 99 £ ¤ 5 £ ¤ 59 £ ¤ 108 £ ¤ 219 £ ¤ 49 £ ¤ 165 £ ¤ 5 £ ¤ 108 £ ¤ 120 JUNE 2005 FIGURE 4-4 INTEGRATED REGIONAL GROUNDWATER MANAGEMENT PLAN FOR THE MODESTO BASIN 05-10-04 S:/GIS/Projects/040190/Figure4-4.mxd 4 0 4 2 Miles¥ LEGEND Modesto Groundwater Subbasin Modesto I.D. Oakdale I.D. Cities SOURCES: City of Modesto, Modesto Irrigation District, City of Oakdale, Oakdale Irrigation District, City of Riverbank, CA Dept of Water Resources Groundwater Basins, 2002, California Spatial Library. Eastern Extent E-Clay, 2004 Cocoran Clay Extent Eastern Extent E-Clay, 1973 Surface Exposure of Mehrten Formation ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Formation is exposed on the ground surface throughout most of the subbasin. Coarse- grained sediments typically occur in patterns parallel to the Stanislaus and Tuolumne Rivers with finer-grained sediments (clay, silt, and very fine-grained sand) present between the rivers. Relatively discontinuous shallow clay layers may be present in the near-surface sediments. These clay layers may perch percolating water and cause some of the high groundwater conditions in the western part of the subbasin. The USGS has compiled a database with sediment types that could be queried to obtain the depth and extent of these clay layers, along with hardpan layers. A topographic map of the shallow clay and hardpan layers should be constructed for those clays within 20 feet of ground surface. 4.2.2 Aquifers Groundwater is present in the consolidated and unconsolidated sediments. There are two principal aquifers in the western portions of the study area (separated by the Corcoran clay) and one aquifer east of the Corcoran clay. Underlying all of these aquifers is a fourth aquifer. The aquifers are: ƒ The shallow aquifer that is present generally west of Highway 99, above the Corcoran clay. High groundwater levels sometimes cause problems for certain agricultural crops. ƒ The deep aquifer that is also located west of Highway 99, but is below the Corcoran clay and the shallow aquifer. ƒ The forebay aquifers located east of the Corcoran clay and merge with the shallow and deep aquifers west of Highway 99. The eastern extent of the forebay aquifers is where the Mehrten Formation is exposed at the ground surface. Most of OID overlies the forebay aquifers. ƒ The confined aquifers within the Mehrten Formation that underlie all of these aquifers. These aquifers are separated from the overlying aquifers by 60 to 120 feet of clay. Figures 4-5 and 4-6 show a generalized schematic profile of the aquifers. Figure 4-7 shows their locations regionally. The aquifer above the Corcoran clay has been called the shallow aquifer system. This aquifer is about 130 to 220 feet thick (Page 1977). Groundwater in the shallow aquifer ranges from unconfined to semi-confined and is present both in the Modesto and Riverbank Formations and in the upper sequence of the Turlock Lake Formation. 39 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N The aquifer below the Corcoran clay has been designated as the deep aquifer system where groundwater occurs under confined conditions. It is present in the lower sequence of the Turlock Lake and upper Mehrten Formations and extends to the base of fresh water. East of Highway 99, where the Corcoran clay is absent, groundwater occurs under unconfined to semi-confined conditions. This area supplies water to both the shallow and deep aquifers. These recharge areas are typically called forebays. The forebay area extends from the eastern extent of the Corcoran clay to the western limit of the exposed Mehrten Formation, as shown on Figure 4-7. The aquifer generally thickens to the west and thins to the east. Limited data show that the base of the forebay aquifer is a 20- to 40-foot-thick gravel (identified by the USGS as Laguna Formation) that daylights at the western exposure of the Mehrten Formation and dips at about 0.006 feet per foot. Figures 4-5 and 4-6 show the gravel layers in red and possible correlations. Because of the dip and the local occurrence of “lava” (breccia) overlying the gravel, this gravel may be within the Mehrten Formation. The gravel bed is pronounced south of the Stanislaus River, but its presence near the Toulumne River is uncertain. There are a few occurrences of gravel north of the Stanislaus River that could correlate with this marker bed. More data are needed to validate the extent and thickness of this gravel layer. Figures 4-5 and 4-6 show the location of the gravels. The confined aquifer in the Mehrten Formation underlies all of the aquifers listed above. Limited data suggest that the aquifer is separated by a 60- to 120-foot clay layer beneath the area between the Stanislaus and Toulumne Rivers. Groundwater in the forebay and deep aquifers may be perched on top of this clay layer. Recharge to the Merthen Formation confined aquifers occurs in the individual sand beds that are exposed on ground surface or where sand beds intersect river alluvium in the eastern portion of the subbasin. Because of the clay, the aquifers probably receive little vertical recharge. North Stanislaus River clay is thinner and it appears to have been replaced with some sand beds. These beds may allow communication between the forebay and the confined Merthen Formation aquifers. 4.2.3 Groundwater Levels Groundwater levels were sorted regionally, based on well screen depths and the three types of aquifers. Groundwater levels in the shallow aquifer, above the Corcoran clay, typically range from about 10 to 30 feet bgs. Figure 4-8 shows the groundwater levels in the shallow aquifer. Figure 4-7 shows the well locations. Groundwater levels from 1969 though 1983 remained relatively stable. Between 1984 and 1994, groundwater levels declined in most wells (MID 39, 40, 61, 103, and 196), while other wells (MID 68 and 102) remained at levels similar to those from before 1983. It is likely that drainage pumping and pumping in the shallow aquifer to augment irrigation water and for the City of Modesto caused the decline in water levels. As shown on Figure 4-7, Well 30E (112 feet deep), is located in Modesto. 40 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Figure 4-5 Schematic Profile of Aquifers—Geologic Section A-A' 41 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Back of 11 x 17 42 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Figure 4-6 Schematic Profile of Aquifers—Geologic Section B-B' 43 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Back of 11 x 17 44 ---PAGE BREAK--- D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D CITY OF MODESTO OAKDALE RIVERBANK STANISLAUS CO. TUOLUMNE CO. SAN JOAQUIN CO. MERCED CO. Tuo lum ne R iver Sta n isla us Ri v er Sa n J oa q u i n Ri ver Forebay Aquifers Shallow Aquifer A A' B' B Modesto Reservoir £ ¤ 132 £ ¤ 120 £ ¤ 33 £ ¤ 99 £ ¤ 5 £ ¤ 59 £ ¤ 108 £ ¤ 219 £ ¤ 49 £ ¤ 165 £ ¤ 120 £ ¤ 5 JUNE 2005 FIGURE 4-7 INTEGRATED REGIONAL GROUNDWATER MANAGEMENT PLAN FOR THE MODESTO BASIN 06-28-04 S:/GIS/Projects/040190/Figure4-6.mxd 4 0 4 2 Miles¥ LEGEND Modesto Groundwater Subbasin Cities SOURCES: City of Modesto, City of Oakdale, City of Riverbank, CA Dept of Water Resources Groundwater Basins, 2002, California Spatial Library. Eastern Extent E-Clay, 2004 General Location of Aquifers Eastern Extent E-Clay, 1973 Approximate Aquifer Extent Surface Exposure of Mehrten Formation D MID Wells ---PAGE BREAK--- Figure 4-8 Integrated Regional Groundwater Management Plan for the Modesto Basin SHALLOW AQUIFER GROUNDWATER LEVELS 0 10 20 30 40 50 60 Nov-69 Nov-71 Nov-73 Nov-75 Nov-77 Nov-79 Nov-81 Nov-83 Nov-85 Nov-87 Nov-89 Nov-91 Nov-93 Nov-95 Nov-97 Nov-99 Nov-01 Nov-03 Depth to Water (feet bgs) MID196 MID 039 MID 040 MID 061 MID 068 MID 102 MID 103 30E ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N The water levels in the deep aquifer, below the Corcoran clay, cannot be assessed at this time because wells reviewed by this plan appear to be constructed in both the shallow and deep aquifers, which would result in an aggregate water level. The USGS recently constructed one monitoring well cluster to assess the groundwater levels in the shallow and deep aquifers. Additional monitoring wells need to be constructed to assess the conditions in the deep aquifer. The water level in deep aquifer may be about 4 to 6 feet deeper than wells in the shallow aquifer (Burow et al. 2004). Groundwater levels in the forebay area range from about 25 to 70 feet bgs. Figure 4-9 shows groundwater levels in wells in this area. The water levels have generally been declining since at least 1969. From late 1982 through 1983, water levels rose, but resumed their downward trend until 1995; between 1995 and 1999, water levels again rose. Since 1999, groundwater levels have resumed a gradual decline. Although there have been two periods of rising groundwater, both associated with wet years, water levels in this area have not returned to their pre-1969 levels. Many of the irrigation wells used by OID and MID in the eastern portion of the subbasin are screened in both the forebay and confined aquifers of the Mehrten Formation. Figures 4-5 and 4-6 illustrate this point. Figure 4-10 shows that few groundwater levels were available from wells solely constructed in the Mehrten Formation confined aquifer. The water levels show trends similar to those of the forebay aquifers. Groundwater levels in the confined aquifer also declined about 20 feet between 1969 and 2004. Groundwater levels were locally depressed (up to 1994) because of municipal pumping for the Modesto urban area and the Riverbank, Oakdale, and Salida areas (MID 1996). The pumping depression resulting from the Modesto urban area pumping extends beneath and south of the Tuolumne River. Since the completion of a surface water treatment plant in 1994, water levels have recovered and the pumping depression has been reduced (Burow et al. 2004). In Figure 4-8, well 30E shows the water level recovery in the shallow aquifer beneath Modesto since 1994. Groundwater levels measured in the City of Riverbank wells are about 60 feet bgs. The groundwater levels have remained relatively consistent over 40 years. MID uses its wells to lower the water levels in the shallow aquifer area. However, from the records reviewed, groundwater levels appear to be 10 feet or more below the ground surface and would not affect crops. More likely, MID’s pumping from the shallow aquifer has been successful at maintaining water levels below 10 feet. 4.2.4 Groundwater Flow Directions Groundwater contour maps show the direction of groundwater flow, recharge areas, and areas of discharge. The groundwater flow direction is typically 90 degrees to the groundwater contour. Groundwater levels in the shallow and forebay aquifers are typically 47 ---PAGE BREAK--- Figure 4-9 Integrated Regional Groundwater Management Plan for the Modesto Basin GROUNDWATER LEVELS IN THE FOREBAY AQUIFER 0 10 20 30 40 50 60 70 80 90 Nov-69 Nov-71 Nov-73 Nov-75 Nov-77 Nov-79 Nov-81 Nov-83 Nov-85 Nov-87 Nov-89 Nov-91 Nov-93 Nov-95 Nov-97 Nov-99 Nov-01 Nov-03 Depth to Water (feet bgs) MID203 MID 209 13C01 ---PAGE BREAK--- Figure 4-10 Integrated Regional Groundwater Management Plan for the Modesto Basin GROUNDWATER LEVELS IN THE MEHRTEN CONFINED AQUIFERS 40 50 60 70 80 90 100 110 120 130 140 Nov-69 Nov-71 Nov-73 Nov-75 Nov-77 Nov-79 Nov-81 Nov-83 Nov-85 Nov-87 Nov-89 Nov-91 Nov-93 Nov-95 Nov-97 Nov-99 Nov-01 Nov-03 Depth to Water (feet bgs) MID230 29M1 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N contoured together. In some instances, a few wells from the deep aquifers may also be contoured with these data, which may provide erroneous results. There are insufficient data at this time to develop a groundwater contour map for the deep aquifer (Burow et al. 2004). Figures 4-11 through 4-13 show groundwater contours in the shallow and forebay aquifers from 1971 through 2000. The maps show different flow directions, and therefore, the interpretation of the data varies considerably. There are also insufficient data near the rivers to determine true gaining and losing reaches and flow direction beneath the rivers. Conditions more likely change seasonally and by water year type. The discussion below is based on very limited available data. In 1971, groundwater contours showed that groundwater generally flows from the east to west-southwest with recharge to the forebay aquifers occurring between the Stanislaus and Tuolumne Rivers (Page and Balding 1973). The contours suggest that groundwater is discharged to the San Joaquin and Tuolumne Rivers (gaining) along most of the reaches of the rivers. Because the contours generally cross the Stanislaus River at 90-degree angles, it suggests that the river is not a gaining stream nor does it recharge the groundwater. The map does not provide sufficient detail to assess whether groundwater is discharging to (gaining reaches) the Stanislaus and San Joaquin Rivers along the western edge of the subbasin. Groundwater level contours were prepared for 1985, a period of relatively high rainfall (wet year), and for 1994, after a prolonged period of relatively low rainfall and runoff (dry year) (MID 1996). Both maps again show that groundwater flow is generally from east to west with recharge occurring between the Stanislaus and Tuolumne Rivers. Both maps show a pumping depression has formed beneath the city of Modesto. The contours show that the rivers have both losing and gaining reaches. Figures 4-12 and 4-13 show these reaches. In 1985, the only losing reach was an approximately five-mile-long reach of the Tuolumne River near central Modesto. By 1994, this reach had extended to the east by approximately five miles. All of the Stanislaus River east of Highway 99 was apparently a losing stream. In 1985 and 1994, apparent gaining reaches include the San Joaquin River and approximately seven miles of the Stanislaus River upstream of the San Joaquin confluence. Changes in the gaining reaches are present from wet year to dry year. In 1985, the gaining portions of the rivers were the Stanislaus River east of Riverbank and the Tuolumne River upstream of Empire. In 1994, the gaining reaches were reduced to a nine-mile-long reach of the Tuolumne River near Waterford and approximately five miles of the Tuolumne River upstream of the confluence with the San Joaquin River. 50 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Figure 4-11 Water Level Contours for the Unconfined Water Body, Spring 1971 51 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Back of 11 x 17 52 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Figure 4-12 Regional Water Level Elevation in Wells and Direction of Groundwater Flow, Spring 1985 53 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Back of 11 x 17 54 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Figure 4-13 Regional Water Level Elevation in Wells and Direction of Groundwater Flow, Spring 1994 55 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Back of 11 x 17 56 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Groundwater contours developed for the spring of 2000 continue to show a general east-west flow direction with recharge occurring between the Stanislaus and Tuolumne Rivers (Burow et al. 2004). The contours show that the Tuolumne River and portions of the Stanislaus River near Oakdale are gaining streams. However, the detail of the graphic does not allow conclusions to be drawn about the city of Modesto’s effects on the river. South of Riverbank, the Stanislaus River does not appear to be affecting groundwater levels by either mounding groundwater, indicating recharge, or draining groundwater, indicating discharge to the river. The recharge and discharge areas may change seasonally. 4.2.5 Groundwater Recharge and Discharge Areas Groundwater recharge to the shallow aquifer occurs from precipitation, applied water, and seasonally from infiltration from the rivers. The forebay also contributes water horizontally to the shallow aquifer. Subsurface recharge may also occur from adjacent subbasins if groundwater gradients are lower in the Modesto subbasin. Groundwater recharge to the deep aquifer is from the shallow aquifer as a result of vertical seepage across the Corcoran clay and horizontally from the forebay aquifers. Groundwater can also exchange between the shallow and deep aquifers in wells with screens in both aquifers. Groundwater recharges the forebay aquifers from precipitation, applied water, and infiltration from the rivers. Groundwater migrates both vertically and horizontally through the sediments. The coarse gravel at the base of the forebay aquifers is exposed at the ground surface, parallel to the western surface exposure of the Mehrten Formation sediments shown on Figure 4-5. The gravels are exposed along an approximately two-mile-wide area. The gravel bed appears to extend beneath and is probably connected to the sediments in the Stanislaus River. Unlined canals that cross this belt also likely provide additional recharge. North of the Stanislaus River and near the Tuolumne River, this gravel belt is poorly defined and needs further definition by a thorough review of well logs or through the USGS database. Groundwater recharge to the Mehrten Formation confined aquifers is from areas between the eastern and western exposure of the Mehrten Formation, as shown on Figure 4-7. For the most part, the recharge is limited to seasonal precipitation that falls directly on the exposed aquifers. Some recharge is likely occurring where the Stanislaus and Tuolumne Rivers cross the aquifers. Recharge also probably occurs from the Modesto and the Woodward Reservoirs. The groundwater contours show that groundwater recharge areas are in the eastern and central portions of the subbasin between the Stanislaus and Tuolumne Rivers. The Stanislaus River provides recharge to the forebay aquifers east of Salida. The Tuolumne River also provides recharge to the forebay aquifers near the cities of Modesto and Empire. For the most part, groundwater discharges to the Tuolumne River and locally controls groundwater levels. Portions of the upper reaches of the Stanislaus River may change from a recharge 57 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N source to a discharge source during wet years. Increased groundwater pumping and the corresponding lowering groundwater levels may result in increased recharge of the basin by the rivers. This induced groundwater recharge may continue until an equilibrium condition has been established. Groundwater recharge based on estimated land use and applied water indicates the highest recharge rates occur in the agricultural areas, which are in the central and western part of the basin (Burow et al. 2004). This water would recharge the shallow aquifers and portions of the forebay aquifers, which contribute water to both the shallow and deep aquifers. There is insufficient data to determine the relative amounts of discharge (outflow) from the subbasin. Outflow likely occurs along the San Joaquin River and lower portions of the Tuolumne and Stanislaus Rivers. The outflow would be from the shallow aquifers. Along these discharge areas, groundwater levels need to be maintained at levels that allow the discharge to the rivers to continue. This will prevent the accumulation of salts within the subbasin and prevent poor quality water from the San Joaquin River and water west of the river from intruding into the subbasin. 4.2.6 Hydraulic Characteristics The hydraulic characteristics of sediments and aquifers are data that provide the foundation for predicting the effects of management options before their implementation. They are basic scientific parameters used to estimate and predict the speed and direction of groundwater movement, groundwater storage, and the potential effects of groundwater pumping on groundwater levels and other wells. These characteristics can be used to answer a number of questions: how should wells be spaced to avoid conflicts; how will the aquifers react to a reduction in recharge resulting from conservation measures; how much water should be removed (in areas with high groundwater table) to lower water levels to benefit agriculture; how much water will a well produce; and how will water quality be affected by the mixing of water from different sources. The hydraulic characteristics of sediments and aquifers use several terms to quantify the ability to store and transmit water. The hydraulic conductivity is the ability of the sediments to transmit water in sediments. Transmissivity, a term applied to aquifers, is the hydraulic conductivity multiplied by the thickness of the sediments capable of conveying water. All sediments have some void space between the particles; this void space is reported as porosity. Water in the void spaces cannot be entirely removed. The storage coefficient is the percentage of water that can be removed from the pores by gravity drainage and is applied when describing unconfined aquifers. Storativity is similar to storage coefficient, but is the percentage of water that can be released from the pores by a decrease in pressure. Storativity is used when referring to semi-confined or confined aquifers. In the eastern portion of the area, consolidated sediments (Ione, Valley Springs, and Mehrten Formations) are exposed on the ground surface. Because of the compact nature of their 58 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N sandstone and conglomerate, an overall clay matrix, and fine ash, sediments of the Ione and Valley Springs Formations result in small-yielding aquifers. No large irrigation wells were found in the Ione Formation in the subbasin (Page and Balding 1973). It is likely the Mehrten Formation will also produce small-yielding wells in this area because the saturated thickness may be small because the formation laps up onto the Valley Springs Formation and the recharge to the area is from limited sources. The Mehrten Formation underlies and is part of both the forebay and confined aquifer systems. Coarse-grained sediments are present in the upper portions of the formation. Wells drilled into the formation produce about 300 to 2,800 gallons per minute (gpm). The hydraulic conductivities ranged from 0.01 to about 67 feet per day (Page and Balding 1973). Transmissivities in the northeastern portion of the study area range from about 11,000 to 32,000 gallons per day per foot (gpd/ft). The shallow and forebay aquifers (unconfined to semi-confined aquifer) yield large amounts of water to wells, with an average yield of 1,900 gpm reported for 96 large-capacity wells (Page and Balding 1973). Transmissivities above or east of the Corcoran clay range between 60,000 and 80,000 gpd/ft. The specific yield or storage coefficient for the shallow aquifer is estimated to be about 7 to 17 percent (Johnson 1967). The deep aquifer has a transmissivity of about 28,000 to 35,000 gpd/ft (Page and Balding 1973). The storativity is estimated to be on the order of 0.0001 to 0.000001 (unitless). The Corcoran clay is a regional layer that restricts movement between the shallow and intermediate aquifers and the underlying deep aquifer. Because the clay is permeable to some degree, water can migrate vertically through the layer but typically at very slow rates. Although this migration rate is very slow, the amount of water moving through the clay can be significant, given the large area covered by the clay and head differences across the clay. No test data are available for the Corcoran clay, but some groundwater models have “backed into” what appear to be reasonable permeability values. The vertical permeability estimated ranged from 0.01 to 0.007 feet per day (Burow et al. 2004). The Corcoran clay’s ability to act as a regional aquitard is uncertain because of the large number of wells. The gravel pack surrounding the wells and the wells themselves act to connect the shallow aquifer with the deep aquifer (Page and Balding 1973). 4.3 Groundwater Quality Groundwater in the Modesto Subbasin is for the most part of good quality. Locally, some problem constituents include total dissolved solids (TDS), nitrates, radionuclides, dibromochloropropane (DBCP), and volatile organic compounds (VOCs). In addition to these constituents, localized areas of man-made contamination (gasoline, solvents, etc.) are present. The following sections discuss these problem constituents, contamination, and their relationship to the aquifers and sediments. 59 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 4.3.1 Total Dissolved Solids TDS is a measure of the amount of salts in the water (typically obtained by evaporating the water and weighing the remaining salts). Electrical conductivity (EC) is also a measure of the salts in the water but uses the water’s ability to pass an electric current. The TDS of water can be approximated by multiplying the EC by 0.55 to 0.70 (Hem 1989). Salts are a concern for both potable and agricultural users. Salt-tolerance thresholds for permanent and vegetable crops may be as low as 600 milligrams per liter (mg/L). Drinking water standards provide recommended maximum contaminant levels (MCLs) of 500 mg/L. An upper limit of 1,000 mg/L is allowed if it is not reasonable or feasible to supply water with levels less than 500 mg/L. TDS concentrations in most wells in the subbasin are low and suitable for potable or agricultural use. The entire Modesto Subbasin is underlain by saline water. The base of fresh water is the boundary between water of specific conductance greater than or less than 3,000 micromhos per centimeter (µmhos/cm) (a TDS of about 2,000 mg/L). In the Modesto Subbasin, the mapped base of fresh water ranges from about 200 feet bgs in the eastern part of the study area where the Mehrten Formation is shallow, to depths of 700 feet beneath the western part of the city of Modesto, and to depths of 400 feet bgs near the confluence of the Stanislaus and San Joaquin Rivers (Page 1973). High salinity water may also be present in Ione Formation sediments exposed on the ground surface in the eastern portion of the subbasin. It appears saline waters may be present at relatively shallow depths beneath Waterford. TDS concentrations in most wells in the forebay aquifers are low and the water is suitable for potable or agricultural use. Figure 4-14 shows the distribution of concentrations in the subbasin. However, two MID wells in the forebay area (wells 3S/10E-26 and 27) have TDS measurements of 1,300 to 1,700 mg/L. Several wells near the town of Empire also have TDS concentrations greater than 500 mg/L but less than 1,000 mg/L. Two wells near Waterford also have reported high TDS levels of about 1,700 mg/L and 8,300 mg/L. Well construction details were not available to assess the potential source of the poor quality water. It is possible that the wells penetrated the Ione or Valley Springs Formations or that the poor water quality is associated with wastewater disposal. Evaporation also may concentrate salts in discharge areas. Water quality data indicate that near Modesto, water from the shallow aquifer (above the Corcoran clay) typically has TDS concentrations less than 500 mg/L (Page 1972). Groundwater from the deep aquifer locally may contain TDS concentrations greater than 500 mg/L. Wells that are screened in both the shallow and deep aquifers typically have TDS concentrations greater than 500 mg/L, suggesting that the deep aquifer may be the source of 60 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Figure 4-14 TDS Concentration in Water Wells 61 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Back of 11 x 17 62 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N the higher salinity water. There also appears to be a geochemical signature that could be used to identify water from the deep aquifer, because chloride concentrations increase significantly in those wells that penetrate below the Corcoran clay. Although there appears to be a regionally downward gradient, it is possible that extended pumping within the deep aquifer could locally create an upward gradient that would allow saline water from below to upwell into the aquifer. Increased groundwater pumping from the 1970s through 1990 has caused the net recharge of salt to be less than the net discharge (MID 1996). The response of the groundwater system to the increased pumping has been a decline in water levels and a slow decrease in salt discharge from the groundwater system to the rivers. Further work is needed to better understand and quantify the spatial and temporal variabilities in salinity and water quality in the Modesto Subbasin and the process affecting water quality. When it is calibrated, the USGS’s groundwater flow model for the Modesto Subbasin could provide valuable salinity and water quality information. 4.3.2 Chloride Chloride is a naturally occurring salt. Concentrations in excess of 100 mg/L can be harmful to plants. Drinking water standards have established a secondary MCL of 250 mg/L. For the most part, chloride concentrations between 1959 and 1970 were below 100 mg/L in the shallow groundwater (Page and Balding 1973). Figure 4-15 shows the chloride concentrations in the area. One area west of Highway 99 and one area near Waterford had chloride concentrations that exceeded 100 mg/L. Only one well, located in the city of Modesto, exceeded the drinking water MCL. This well was screened both above and below the Corcoran clay. Two other wells in the city also had chloride concentrations that exceeded the MCL between 1970 and 1971 (Page 1972). One of these wells extends below the Corcoran clay. Test hole data from the City of Modesto show that chloride concentrations increase with depth, with concentrations exceeding the MCL at a depth of about 250 feet bgs. Short-term, recent data from MID show chloride concentrations are variable and do not appear to be increasing in the area. Seasonal pumping may affect the concentrations produced. Figure 4-16 shows these seasonal variations. Figure 4-17 shows the well locations. Sources of chloride may be from industrial wastewater, a shallow or intermediate source zone of sodium chloride water, the Tuolumne River, an upward flow from the underlying saline water body, or a buried flowing well tapping that body (Page 1972). Historically, improperly destroyed gas exploration wells with artesian conditions have discharged high TDS and chloride water to the Tuolumne River. Also, drill cuttings and mud from the drilling operations could be sources of chloride, sodium, and TDS. Figure 4-17 shows the locations of these wells (California Department of Conservation 2002). 63 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Groundwater with elevated nitrate concentrations also tends to show an increase in chloride. Sulfate also increases, but to a lesser extent. Groundwater underlying agricultural areas may be expected to have higher salinity due to deep percolation of applied water and other agricultural activities. The affected water is characterized by increased concentrations of chloride and sulfate that result from the leaching of nitrogen and potash fertilizers and other agriculture-related compounds and from increased evaporation as groundwater is pumped and reapplied for irrigation. 4.3.3 Sodium Sodium is a naturally occurring salt. Concentrations exceeding 69 mg/L can be harmful to plants. The secondary drinking water MCL for sodium is 250 mg/L. Generally, most wells east of Highway 99 have concentrations below the MCL. Concentrations are typically higher in wells with high TDS concentrations. The sources of sodium are similar to those identified for chloride. 4.3.4 Nitrate Nitrate is an essential element for plant growth. However, some permanent crops, including grapes, may be adversely affected by excess nitrate. High nitrate levels are also detrimental to human health. Drinking water standards establish 45 mg/L nitrate (as nitrate) or 10 mg/L when nitrate is reported as nitrogen as the MCL. Nitrate concentrations in most wells in the subbasin are below the MCL for drinking water. Between 1959 and 1970, only one well in the area, located just south of the Tuolumne River, exceeded the MCL (Page and Balding 1973). Most of the shallow aquifer area contained water with concentrations between 10 to 20 mg/L. Concentrations in a few areas exceeded 20 mg/L. Most of the forebay area had concentrations less than 10 mg/L. Concentrations in the groundwater from the deep aquifer were less than 1 mg/L. Figure 4-18 shows the distribution of the nitrate concentrations. Figure 4-17 shows the location of these wells. By 1990, nitrate concentrations in most of the shallow aquifer area west of Highway 99 had increased to more than 22 mg/L. Figure 4-19 shows the 1990 nitrate concentrations. A large zone of nitrate concentrations ranging from 64 to 96 mg/L was found in seven wells in this area. A second zone of nitrate concentrations exceeding the MCL was present beneath southwestern Modesto. Most of this high nitrate area coincides with Modesto’s former sewage effluent disposal area. Six other wells in north Modesto also had concentrations exceeding the MCL. Nitrate in the forebay area was below the MCL in 1990, except for very high nitrate concentrations (243 to 275 mg/L) in water from wells 3S/10E-26 and 3S/10E-27. The TDS concentrations in these wells also exceeded 1,000 mg/L. Because nitrate is present with the high TDS, it is possible that the source may be related to wastewater disposal. 64 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Figure 4-15 Chloride Concentrations in the Unconfined Water Body, with Selected Concentrations Shown in the Confined Water Body, 1959–70 65 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Back of 11 x 17 66 ---PAGE BREAK--- Figure 4-16 Integrated Regional Groundwater Management Plan for the Modesto Basin SEASONAL VARIATIONS IN CHLORIDE CONCENTRATIONS 0 50 100 150 200 250 300 6/26/2000 8/26/2000 10/26/2000 12/26/2000 2/26/2001 4/26/2001 6/26/2001 8/26/2001 10/26/2001 12/26/2001 2/26/2002 4/26/2002 6/26/2002 8/26/2002 10/26/2002 12/26/2002 2/26/2003 4/26/2003 6/26/2003 8/26/2003 Date Concentration (in mg/L) MID 005 MID 056 MID 235 MID 242 MID 244 ---PAGE BREAK--- k k k k k k k k k k k k k k k k k k k k k k k k k k k k k kk k k k k k k k k k k k k k kk k k k k k k k k k k k k kk kk k k kk k kk k k k k k k k k k k k kk k k k k k k k k k k kk k k k k k k k k CITY OF MODESTO OAKDALE RIVERBANK STANISLAUS CO. TUOLUMNE CO. SAN JOAQUIN CO. MERCED CO. OAKDALE I.D MODESTO I.D Tuo lum ne R iver Sta n isla us Ri v er Sa n J oa q u i n Ri ver A' Modesto Reservoir £ ¤ 132 £ ¤ 33 £ ¤ 120 £ ¤ 5 £ ¤ 99 £ ¤ 59 £ ¤ 108 £ ¤ 219 £ ¤ 165 £ ¤ 49 £ ¤ 205 £ ¤ 120 £ ¤ 108 Empire Salida Waterford NOVEMBER 2004 FIGURE 4-17 INTEGRATED REGIONAL GROUNDWATER MANAGEMENT PLAN FOR THE MODESTO BASIN 05-10-04 S:/GIS/Projects/040190/Figure4_16.mxd 4 0 4 2 Miles¥ LEGEND Modesto Groundwater Subbasin Modesto I.D. Oakdale I.D. Cities SOURCES: City of Modesto, Modesto Irrigation District, City of Oakdale, Oakdale Irrigation District, City of Riverbank, CA Dept of Water Resources Groundwater Basins, 2002, Dept of Conservation, DOG, California Spatial Library. Plugged and Abandoned Gas Wells k Gas Wells APRIL 2005 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Figure 4-18 Distribution of Nitrate Concentrations in the Unconfined Water Body, with Selected Concentrations Shown in the Confined Water Body, 1959-1970 69 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Back of 11 x 17 70 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Figure 4-19 Nitrate (NO3) Concentration in Water Wells in 1990 71 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Back of 11 x 17 72 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N There is insufficient information to assess the nitrate concentrations in the deep aquifer at this time. Future concentrations of nitrate in the area may potentially increase. Water quality samples collected from 2000 through 2003 show a slow increase in nitrate concentrations (MID 2004). Figure 4-20 shows results for several MID wells. The wells obtain water from multiple aquifers so the aquifer with the nitrate cannot be identified at this time. More data are needed to establish any definite trend in nitrate concentrations in the basin. Nitrate concentrations generally decrease with depth because in the recharge areas, groundwater that is deeper in the flow system is generally older. There is a positive correlation between dissolved oxygen and nitrate concentration. Most of the water in the Modesto subbasin is oxic, containing oxygen. Well-oxygenated groundwater likely occurs in areas where the water rapidly infiltrates through coarse-grained sediments. Additional data are necessary to resolve which aquifers contain nitrate and the natural degradation processes that affect its concentrations. 4.3.5 Iron and Manganese Iron and manganese are common elements in sediments and are essential nutrients for humans and plants. An upper limit has not been established for plants. A secondary MCL of 0.3 mg/L for iron and 0.05 mg/L for manganese has been established for drinking water. Groundwater in the western part of the subbasin near the San Joaquin River frequently has high concentrations of naturally occurring iron (MID 1996). Deeper groundwater is also found to have elevated levels of iron and manganese. Shallow groundwater near streams often shows high levels of manganese and occasionally high iron concentrations. The City of Modesto has encountered elevated iron and manganese levels in groundwater in a few test holes in eastern and southern Modesto. The Mehrten Formation typically produces water high in manganese. 4.3.6 Arsenic Arsenic, a naturally occurring element, is used in pesticides and in poultry feed to combat disease. The current primary MCL for drinking water is 50 micrograms per liter (µg/L). The U.S. Environmental Protection Agency has mandated an MCL of 10 µg/L, and California has adopted the revised MCL. Arsenic concentrations in the City of Riverbank wells, in the forebay aquifer, are typically less than 3 µg/L (City of Riverbank 2003). Similar concentrations are present beneath Oakdale, where the concentrations are less than 2 µg/L (City of Oakdale 2003) and at Waterford, where the concentrations range between 3 to 4 µg/L (City of Modesto 2003). The 73 ---PAGE BREAK--- Figure 4-20 Integrated Regional Groundwater Management Plan for the Modesto Basin TRENDS IN NITRATE CONCENTRATIONS 0 20 40 60 80 100 120 140 160 6/26/2000 8/26/2000 10/26/2000 12/26/2000 2/26/2001 4/26/2001 6/26/2001 8/26/2001 10/26/2001 12/26/2001 2/26/2002 4/26/2002 6/26/2002 8/26/2002 10/26/2002 12/26/2002 2/26/2003 4/26/2003 6/26/2003 8/26/2003 Date Concentration (in mg/L) MID 005 MID 056 MID 235 MID 242 MID 244 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N lower concentrations may be the result of the recharge of river water into the aquifers. Arsenic concentrations near Salida are higher, ranging from 7 to 12 µg/L. Concentrations are more variable near Modesto, with levels ranging between non-detectable and 8 µg/L. The wide range may be the result of those wells taking water from two different aquifers, the shallow and deep aquifers. No data were available for the OID service area. Arsenic is typically associated with elevated pH or some specific geochemical conditions. More data on the distribution of redox parameters and pH in the Modesto basin would help predict where elevated arsenic concentrations would be expected. 4.3.7 Radionuclides Radioactive decay of certain elements produces radiation. The drinking water MCL for gross alpha, a general measure of the potential for radioactive substances to be in the water, is 15 picocuries per liter. The MCL for uranium is 20 picocuries per liter. If radiological constituents above the MCL are detected, additional testing is required for specific radioactive species. Sampling in the study area for radiological constituents has generally been limited to large public water system wells. Groundwater with high uranium has been found in parts of Modesto and in Empire. Uranium activities in water from six wells ranged from 20 to 37 picocuries per liter in 1994 (MID 1996). Most of the area with high uranium concentrations is east of Highway 99 and northwest of Dry Creek. In 1994, two other wells in the southern part of this area produced water with alpha activities exceeding the MCL: a well in the Empire area had a uranium activity of 23 picocuries per liter and a small community public water system had uranium above the MCL. More recent data suggest concentrations may be as high as 28 µg/L (City of Modesto 2003). In the northern portions of the forebay, the radiological concentrations are below the MCLs. The City of Oakdale reports a gross alpha between 0.53 and 1.02 picocuries per liter between 2000 and 2003. In Riverbank, the concentrations of gross alpha range from 0 to 7 picocuries per liter. These lower concentrations may be the result of recharge from the Stanislaus River. 4.3.8 Pesticides DBCP, a pesticide usually associated with vineyards or orchards, was banned in 1977. The drinking water MCL is 0.2 µg/L. Water samples collected in 1993 and 1994 detected low levels of DBCP in three localized areas within the subbasin that exceeded the MCL (MID 1996). Figure 4-21 shows sampling locations in the basin. The largest of these areas is between eastern Modesto and Empire and north of the Tuolumne River. The area extends about five to six miles from east to west and about two to three miles from north to south. The concentrations ranged from 0.21 to 0.57 µg/L. A second relatively large area of high DBCP levels is in central Modesto, 75 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N primarily northeast of Highway 99. The third area is south of Del Rio, where the DBCP concentrations ranged from about 0.3 to 0.5 µg/L. The DBCP is in the shallow and forebay aquifers. DBCP concentrations also exceeded the MCL at several scattered wells at different time periods. In the 1990s, DBCP was detected in one well at Salida, in another west of Modesto, and in another in north Modesto. DBCP has also been detected in wells in Waterford and in or near western Modesto but at concentrations below the MCL (MID 1996; City of Modesto 2003). DBCP concentrations in most wells west of Highway 99 were below 0.01 µg/L. The Riverbank and Oakdale areas have not detected DBCP. DBCP contamination is present primarily in the shallow groundwater (MID 1996). Positive correlations of nitrate to the occurrence of pesticides indicate that groundwater susceptible to nitrate contamination may also be susceptible to contamination from pesticides (Burow, Stork, and Dubrovsky 1998). Because DBCP is in the forebay and shallow aquifers and the groundwater flow direction is generally to the west, DBCP may migrate in the shallow aquifer west of Highway 99. It is possible that DBCP could enter the deep aquifer because of a downward flow path, pumping in the deep aquifer, and wells that are screened both in the shallow and deep aquifers. Ethylene dibromide (EDB), another pesticide, has not been detected in groundwater in the area, other than for one unconfirmed incident (MID 1996). 4.3.9 Herbicides Atrazine, cyanazine, deethylatrazine, diuron, ETPC, metolachloro, and simazine have been detected in domestic and monitoring wells located in almond orchards. Most of these herbicides do not have established drinking water MCLs. Those that do have MCLs are listed in Table 4-1. Table 4-1 Concentrations of Herbicides in Area Wells Herbicide MCL (mg/L) Concentration (µg/L) Well Number Land Use Atrazine 0.003 0.008 to 0.059 3S/10E-35K1 3S/11E-30K1 Almond Orchard 76 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Figure 4-21 DBCP Sampling Locations and Concentration in Water Wells 77 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Back of 11 x 17 78 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 4.3.10 Volatile Organic Chemicals VOCs are present in the groundwater near Modesto as the result of industrial activities. VOCs include trichlorofluormethane (freon 11), 1,1,2-trichloro-1,2,2-trifluroethane (freon 113), cis-1,2-dichloroethylene, perchloroethylene (PCE), trichloroethylene (TCE), carbon tetrachloride, disinfection by-products and petroleum fuel products (MID 1996; City of Modesto 2003). Along with these major chemicals are their daughter products, those that have decayed to other compounds. Several of these chemicals have been detected at concentrations above the MCLs, and some have resulted in the closure of municipal supply wells. Water from several wells is being treated. Although most of the contamination is in the shallow aquifer, there is a potential that, with pumping below the Corcoran clay, contaminants could be pulled into the deep aquifer. There is insufficient information at this time to assess whether contaminants have migrated into the deep aquifer. The City of Oakdale has not detected VOCs, except for PCE at 1.5 µg/L. No fuel hydrocarbons have been detected. VOCs have not been detected in the water supply wells at Riverbank. 4.3.11 Constituents of Concern In summary, each of the aquifer systems has water quality problems, as listed below. For the most part, these problems affect only portions of the subbasin. In general, water quality north of the Modesto Subbasin, around the City of Oakdale and Riverbank, is of good quality. The City of Modesto has abandoned some of its wells because of water quality issues. High groundwater levels with high levels of TDS are present in the western portion of the subbasin. ƒ Shallow Aquifer – TDS, nitrate, DBCP, VOCs (localized to Modesto) ƒ Deep Aquifer – TDS, VOCs (localized to Modesto) ƒ Forebay Aquifers – TDS, DBCP, uranium (western part near Modesto and Empire) Although iron and manganese are present, they can be easily removed by treating the water. Additional testing of the agricultural water supply wells and drainage wells should be performed to fully assess the distribution and concentrations in the area. Both sodium and chloride are of local concern and are related to the occurrence of TDS. Nitrate and pesticides also have been correlated. Management actions to improve one of these problems will likely resolve multiple constituents. 79 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 4.3.12 Groundwater Quality Protection and Improvement Groundwater quality problems can be managed through source control and managing the groundwater flow to contain the spread of contaminants in the basin. Improving groundwater quality requires long periods of time. Although active treatment systems can be effective in removing contaminants, they have not been discussed in this report. Sources of TDS, sodium, and chloride include deep percolation from use of water for agriculture, wastewater disposal, naturally occurring water from the Mehrten Formation and below the Corcoran clay, and potentially improperly abandoned or residual wastes from gas wells. Source control can be accomplished by rehabilitating wells. For example, TDS concentrations can be reduced by 100 to 200 mg/L by plugging screen levels in the deep aquifer in wells that obtain water from both the shallow and deep aquifers. Source control may also include an evaluation of each of the gas well sites to assess whether there are artesian flowing conditions or residual wastes. Groundwater flow control can be accomplished by maintaining groundwater outflow to the San Joaquin, Stanislaus, and Tuolumne Rivers. Nitrate sources may include wastewater from animal facilities, urban and agricultural wastewater disposal, and fertilizers. Wastewater control regulations should be supported, and where necessary, mitigating measures implemented by owners. Fertilizer application rates should be strictly followed. Modification of irrigation methods from flooding of fields to drip or spray irrigation may reduce the potential for nitrate to leach into the aquifers; however, this will reduce recharge. Pumping wells with high nitrate levels and reusing the water on vegetation can improve groundwater quality through groundwater flow control. Vegetation is probably the most effective way to remove nitrate from the water. Fertilizer applications may be reduced when using high nitrate waters. An agricultural laboratory should be consulted. Source control of DBCP has already been implemented by banning its use. DBCP is moving through the deeper parts of the system and will degrade over time. DBCP may also be concentrated in the soils near product mixing areas, typically near a water source. Source control is to reduce the amount of leaching of the contaminant from the soils. Localized removal of soils with high concentrations may remove the potential source(s) and prevent further leaching into the groundwater. Groundwater control measures need to be implemented to prevent DBCP from spreading into adjacent portions of the aquifers. Reuse of water tainted with DBCP in the area where it is originally present can allow vegetation to remove the product without spreading the contaminants. However, before implementing this option, local regulatory agencies should be consulted to assess the regulatory and liability aspects of this approach. Uranium is naturally occurring; therefore, source control is limited to identifying its horizontal and vertical extent and preventing its spread into adjacent areas. Anthropogenic activities may enhance its mobility, and therefore, mitigation of those activities may reduce 80 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N the uranium. Passive treatment of the groundwater may be possible; installing filtration barriers may be possible, but would need a detailed assessment. Groundwater flow control may be possible and potable use of the water, likely by dilution with treated surface water, is considered a feasible and cost-effective solution. 4.4 Groundwater Use The Modesto Groundwater Subbasin includes more than 247,000 acres, about 68 percent of which is irrigated agricultural land. Surface water supplies for MID are diverted from the Tuolumne River below La Grange Dam. Surface water supplies for OID are diverted from the Stanislaus River at Goodwin Dam. Both irrigation districts have a network of groundwater supply wells to augment their surface water supplies. Since 1977, more than 5,000 wells have been completed in the area between the Stanislaus and Merced Rivers, east of the San Joaquin River. The number of domestic wells constructed during the 1970s through the 1990s increased. In contrast, fewer irrigation wells were constructed in the 1980s and 1990s than during the 1970s. These trends may reflect the increase in population and the decrease in irrigated farm acreage in the region (Burow et al. 2004). The water demand for the Modesto Groundwater Subbasin was estimated at 590,000 acre- feet for water year 2000 (Burow et al. 2004). Surface water deliveries accounted for about 65 percent, or 382,500 acre-feet, of the total water supply. Groundwater accounted for about 35 percent, or about 206,500 acre-feet, of the total supply. Of the approximately 534,000 acre-feet used to meet irrigation demand, 68 percent was surface water and 32 percent was groundwater. Of the approximately 56,000 acre-feet used to meet urban demand, 42 percent was supplied by surface water and 58 percent was supplied by groundwater. Although two-thirds of the wells in the study area are domestic wells, the amount of water pumped has not been quantified. The following quantities of groundwater are supplied to urban customers: ƒ City of Riverbank: 3,800 acre-feet during calendar year 2002 ƒ City of Oakdale: 4,600 acre-feet during calendar year 2002 ƒ City of Modesto: about 46,800 acre-feet during calendar year 2003 The total water recharge in the Modesto Groundwater Subbasin was about 310,000 acre-feet. The largest component of recharge is irrigation (57 percent), whereas precipitation in excess of crop requirements accounted for 41 percent of the recharge (Burow et al. 2004). Recharge in the Modesto urban area totaled 20,000 acre-feet, about 7 percent of the total recharge. 81 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N The highest recharge rates generally occur in the agricultural areas in the western part of the study area, along the canals north of the Tuolumne River and east of Modesto. The lowest recharge rates generally occur in the eastern part of the study area, in the foothills and adjacent uplands, and in the Modesto urban area. The highest pumpage rates generally occur in the agricultural areas in the western part of the study area (Burow et al. 2004). The water supply and demand estimates do not estimate the amount of natural recharge along the Stanislaus or Tuolumne Rivers or the amount of discharge from the basin into the Stanislaus, Tuolumne, and San Joaquin Rivers. Water demands are likely to increase as the area’s population increases. The California Department of Finance projected the population would reach 517,600 in 2000 and 670,000 in 2010 (Stanislaus County 1994). Census data for 2000 showed the population had only reached 245,000; therefore, growth is proceeding slower than anticipated (U.S. Census Bureau 2004). The conversion of agricultural lands to urban development may mitigate some of the water demand. 4.5 Summary Significant basin-wide geologic and hydrogeologic studies have been completed. Information from historic and ongoing studies will be used to focus efforts on resolving uncertainties in the hydrogeologic conditions that govern groundwater movement in the subbasin. Focusing these efforts on limited portions of the subbasin will lead to sound groundwater management options and actions. Based on only two geologic sections, which do not adequately define the three-dimensional nature of the aquifers, the subbasin contains four aquifers. Three are connected (shallow, deep, and forebay) and the fourth, which underlies all of the others, may be relatively isolated from the effects on the other aquifers. Because the three aquifers are interconnected, changes to water supply or demand in one aquifer will affect the other two aquifers. The vertical and horizontal extents of the shallow aquifer and the deep aquifers are relatively well defined. The bottom of the deep aquifer has been less precisely defined. The deep aquifer likely consists of several geologic formations (Turlock Lake, Laguna, and the upper portions of the Mehrten Formation). Although there may be different names for the geologic units, they likely are hydraulically connected. Both the shallow and deep aquifers receive water from the forebay aquifers. In profile, the forebay aquifers represent a triangular wedge that thickens towards the west and thins towards the east. This conceptual picture is based on one geologic section drawn east-west about halfway between the Stanislaus and Tuolumne Rivers. The section showed a gravel bed that coincides with the Mehrten Formation’s western exposure at ground surface. Used by most wells, this gravel occurs to about the center of Modesto and could convey significant amounts of water into the central portion of the subbasin. Because it is exposed on the 82 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ground surface, it can be readily recharged. The gravel bed could be part of the Mehrten Formation because it has a dip of about 0.006 feet per foot and at one location the gravel is overlain by “lava” (“lava” or breccias are commonly associated with the Mehrten Formation). The gravel bed described above is not present in all wells. This is likely the result of historic topography in which the gravels were deposited in valleys but not on the low surrounding hills. The sediments in these hills are more of the typical claystone with thin-bedded sands. Overlying the Mehrten Formation sediments are younger sediments of the Turlock Lake, Riverbank, and Modesto Formations and Holocene alluvium. These sediments were laid down horizontally (or at a slight dip). The dipping sediments of the Mehrten Formation, therefore, will abut these younger sediments and allow water to be conveyed from the younger sediments into the upper Mehrten Formation sediments. The younger sediments act as a reservoir to feed the upper Mehrten Formation aquifers. The horizontal extent of the gravel bed is poorly defined. It appears to extend from about the Stanislaus River to just north of the Tuolumne River. A few well logs from north of the Stanislaus River show gravel at about the right depth, suggesting this marker bed for the forebay aquifers may be present in this area but has not yet been fully defined. Further definition of the extent of this gravel bed is needed to identify potential recharge areas. Underlying the three aquifers are the Mehrten Formation confined aquifers. These aquifers are locally separated from the overlying aquifers by a 60- to 120-foot clay layer. It is possible that the clay has been locally eroded and may allow some interconnectedness of the aquifers, but the current level of information is insufficient to identify those areas. There is currently insufficient information to confirm that the confined Mehrten Formation aquifers are indeed hydraulically separated from the overlying aquifers. The Mehrten Formation confined aquifers conceptually differ greatly from the three other aquifers. Because the younger sediments are not resting over the aquifers and acting as a reservoir, these aquifers receive only local and seasonal recharge. Local recharge to the confined aquifers is likely derived from the Modesto and Woodward Reservoirs and from the area where the Stanislaus and Tuolumne Rivers cut across the surface exposure of the Mehrten Formation. Between these recharge sources, there will be limited seasonal recharge by rain. Groundwater levels between these sources will likely have the greatest changes. At some depth, the Mehrten Formation confined aquifers are likely to contain ancient water that has higher TDS concentrations. All of the City of Oakdale wells, most of the OID wells, and some of the MID wells use these Mehrten Formation confined aquifers. Because recharge is limited, this aquifer needs careful monitoring. Groundwater levels are currently declining about one foot per year, according to the City of Oakdale and hydrographs from the DWR. Groundwater recharge efforts in the forebay aquifers will not have a significant benefit on the Mehrten Formation confined aquifers. 83 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Many of the OID and MID wells are screened in both the forebay and Mehrten Formation confined aquifers. Because sediments in the forebay aquifers have a higher hydraulic conductivity, most of the water pumped from the wells will be derived from these aquifers. However, the forebay aquifers thin to the east and as such will experience the greatest changes in water levels. Increasing the groundwater gradient by pumping wells in the shallow and deep aquifers can easily increase the drawdown. The saturated thickness is directly related to the yield of the wells. When the yield from the forebay aquifers is diminished, greater amounts of water will be obtained from the Mehrten Formation confined aquifers. Most of the current groundwater level monitoring is done in production wells, and because most wells are screened in both aquifers, there is little definition of the groundwater levels and conditions in the forebay aquifers. Groundwater monitoring needs to be improved in the eastern extent of the forebay aquifers to assess the conditions and changes that may occur. Based on the conceptual understanding of the geology and aquifers, we recommend that the following actions be undertaken to secure a more complete understanding of the hydrogeology. Issue Action ƒ Eastern extent of forebay aquifers poorly defined. ƒ Obtain well logs from DWR to prepare additional east-west geologic sections north of the Stanislaus River and near the Tuolumne River. ƒ Monitoring of the forebay aquifers is insufficient where they thin and the greatest changes in water levels may occur. ƒ Review well logs from DWR to identify wells with screens only in the forebay aquifers. Contact well owners to participate in groundwater level monitoring. Where necessary, construct additional monitoring wells. ƒ There is insufficient monitoring along the Stanislaus and Tuolumne Rivers to assess the surface water-to-aquifer interactions. Most wells being monitored are at depths well below the invert of the river. ƒ Review Regional Water Quality Control Board records to assess shallow wells that could provide groundwater gradients near the rivers. ƒ Insufficient monitoring in the Mehrten Formation confined aquifers as most OID wells are screened in both the Mehrten Formation and forebay aquifers. ƒ Review well logs from DWR to identify wells with screens only in the Mehrten Formation confined aquifers. Contact well owners to participate in groundwater level monitoring. Where necessary, construct additional 84 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Issue Action monitoring wells. ƒ Mehrten Formation confined aquifer recharge areas are poorly defined. ƒ Locate significant sand or gravel beds from well logs and project their occurrence to ground surface. Confirm the projections by drilling test holes for sediment types. ƒ Groundwater flow directions are poorly defined, and therefore, interpretations of recharge and discharge areas and of the interactions between aquifers may change greatly. ƒ Implement the groundwater monitoring plan (see Appendix A hydrogeologist should interpret the data and prepare groundwater contour maps. Identify uncertainties, refine the monitoring network, and propose resolution to improve the interpretations. ƒ The recharge areas and the interaction between the forebay and Mehrten Formation confined aquifers are poorly defined. ƒ Conduct oxygen isotope analysis on selected wells in the forebay and Mehrten Formation wells. Supplement where needed with tritium analysis. ƒ The full extent of the 20- to 40-foot gravel layer needs to be explored for potential recharge possibilities and beneficiaries. ƒ Conduct a review of well logs in the area for gravel beds. ƒ Outflow from the basin is poorly understood and needs to be maintained to prevent salt buildup. ƒ Implement monitoring program. Use results to position new monitoring wells. ƒ Drilling of new City production wells within the study area has the potential to yield new and important data, but is not currently being coordinated. ƒ Review well drillings while they are being taken. 85 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N This page left intentionally blank. 86 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 5 Groundwater Management Plan 5.1 Definition of Groundwater Basin and Map of Groundwater Basin and Subareas This regional management plan covers the entire Modesto Subbasin and part of the Eastern San Joaquin Subbasin. DWR Bulletin 118 defines these basins as follows: ƒ The Modesto Subbasin lies between the Stanislaus River to the north and Tuolumne River to the south and between the San Joaquin River on the west and basement rock of the Sierra Nevada foothills on the east. The northern, western, and southern boundaries are shared with the Eastern San Joaquin Valley, Delta- Mendota, and Turlock Groundwater Subbasins, respectively. The subbasin comprises land primarily in MID and the southern two-thirds of OID. The City of Modesto is in the southwestern portion of the subbasin. Average annual precipitation for this subbasin is 11 to 15 inches, increasing eastward. ƒ The Eastern San Joaquin Groundwater Subbasin is defined by the areal extent of unconsolidated to semiconsolidated sedimentary deposits that are bounded by the Mokelumne River on the north and northwest; San Joaquin River on the west; Stanislaus River on the south; and consolidated bedrock on the east. ƒ The Eastern San Joaquin Groundwater Subbasin is bounded on the south, southwest, and west by the Modesto, Delta-Mendota, and Tracy Subbasins, respectively and on the northwest and north by the Solano, South American, and Cosumnes Subbasins. Figure 5-1 shows the Modesto and East San Joaquin Groundwater Subbasins. 5.2 Basin Management Objectives To meet the purposes and goals of the groundwater management plan stated in Section 2.4, the agencies will adopt the following BMOs. Two sets of BMOs have been developed reflecting the integrated and regional nature of this groundwater management plan: the broad BMOs are designed to have basin-wide and regional perspectives, and more specific BMOs have been developed for each management area. 5.2.1 Maintain Groundwater Levels Except for some localized areas, groundwater levels in the basin are generally stable. However, an increase in urban development and reliance of urban areas on groundwater may cause the groundwater table to lower. The Association’s objective is to ensure that the 87 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N overall groundwater levels in the basin are maintained over time to provide long-term reliable sources of water for the economic well-being of the area. Specific actions to achieve this objective include: ƒ Identification and mapping of the basin’s natural recharge areas. ƒ Protection of groundwater recharge areas. This may include communication, coordination, and cooperation with land use planning agencies to encourage them to take actions that would limit incompatible land use development practices in the recharge area. ƒ Development of a water budget to determine if the basin is in overdraft and, if so, to determine the amount of overdraft. ƒ Feasibility evaluation of artificial recharge projects. ƒ Identification and feasibility evaluation of conjunctive use projects. ƒ Support and encourage water conservation programs. ƒ In-lieu recharge through the importation of a surface water supply to areas currently relying on groundwater. 5.2.2 Control Degradation of Groundwater Quality Water quality in the basin is adequate for agricultural use. North of the basin, the Cities of Oakdale and Riverbank enjoy excellent water quality. However, the City of Modesto has lost some of its production wells because of the migration of pollutants into its management area. Specific water quality actions for the basin include: ƒ Maintaining groundwater levels to control the movement of poor quality water into and within the basin. Groundwater pumping that results in the lowering of groundwater levels in part of the basin could alter the natural groundwater flow direction in the basin. In the area with groundwater contamination, this change could result in the movement of poor quality water in the basin. The City of Modesto has reduced groundwater pumping in some parts of the basin, augmenting its groundwater with surface water deliveries to its customers. Other actions may include implementing the actions summarized for the groundwater level BMOs listed above. ƒ Conducting a detailed geologic assessment of the basin, focusing on the areas with poor water quality, to identify the sources of contaminants and poor quality water. Developing actions and projects to mitigate the migration of poor quality water into the basin where practical. 88 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Figure 5-1 Modesto and East San Joaquin Groundwater Subbasins 89 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Back of 11 x 17 90 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ Continuing to support the development of in-lieu recharge projects in urban areas with poor quality water continuing the delivery of additional surface water to the City of Modesto to reduce its reliance on groundwater). ƒ The Association will coordinate and communicate with land use planning. The agencies will work together to discourage land use practices within the recharge areas that may contribute to groundwater degradation. Agencies within the basin, particularly urban water agencies, are concerned about protecting natural recharge areas from pollutants and about the quality of water used for potential future groundwater recharge projects. Such projects within the basin will be developed in a coordinated fashion and through the Association to ensure that the groundwater quality concerns of all management areas are considered. ƒ Evaluating the impact of annexation practices on groundwater levels and groundwater quality. ƒ The Association will coordinate and facilitate implementation of groundwater protection measures. These measures are discussed in more detail in Section 6. 5.2.3 Protect Against Potential Inelastic Land Surface Subsidence Historically land surface subsidence within the basin has not been significant. Given the balanced nature of groundwater storage in the basin, potential future land subsidence is remote. However, the agencies will document and investigate any changes in land surface elevations and take appropriate actions if inelastic subsidence is observed. 5.2.4 Groundwater Monitoring and Assessment The agencies in the Modesto Groundwater Subbasin understand the value of groundwater monitoring and assessment in the management of the basin. Groundwater monitoring is needed to track and assess the potential effects from the water-related activities and the implementation of management objectives in order to protect the quality and quantity of the basin’s groundwater. The Association, therefore, is evaluating its groundwater monitoring needs and has developed (and periodically updated) its groundwater monitoring plan (Appendix A database is being developed to facilitate the storage, retrieval, and archiving of the basin groundwater data. The Association will also develop a groundwater model for the basin that can be used to evaluate the effects of the various proposed projects and management actions on groundwater levels and quality in the basin. 5.2.5 Evaluate Feasible Water Conservation Measures Certain water conservation practices may be evaluated to determine their ability to improve water levels and water quality in the basin. Typical water conservation practices may include: 91 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ Blending: Currently, MID pumps water from the shallow aquifer and blends it with surface water before delivering it to its agricultural water users. The agencies within the basin could evaluate an expansion of the blending program in order to lower the high groundwater table and improve water quality. ƒ Reuse of poor quality water: Groundwater in areas with a high level of nitrates can be pumped for agricultural uses in order to improve water supply availability and groundwater quality. ƒ Water conservation: Water conservation in the form of incentive programs, water audits, water metering, sewage fees, and other measures can be a tool to reduce demand on the basin. 5.2.6 Coordination and Cooperation ƒ Provide and expand existing forum for coordination and cooperation between all water entities to manage the Modesto Subbasin. Assist in formulating regional projects and programs for protection and use of subbasin water resources. ƒ Provide a framework for coordination and cooperation with the state and federal agencies and neighboring water entities such as TID, Stockton East Water District, and SSJID. ƒ A number of industrial plants in the Modesto Subbasin use groundwater. Production wells in these plants frequently affect groundwater levels in neighboring municipal and industrial wells during peak demands in summers. The Association will provide for an education and outreach program to bring industrial water users to the table and to work with them to develop conjunctive use projects to reduce well interference. 5.3 Groundwater Management Areas Objectives This section addresses the specific objectives for each management area. Although specific to each management area, these objectives may limit or constrain activities within other management areas. Therefore, the participation and cooperation of agencies within the basin will be needed for the successful implementation of these objectives. 5.3.1 City of Modesto Management Area Until 1995, the City of Modesto relied solely on groundwater for its service area. Groundwater degradation and more stringent drinking water quality standards resulted in the abandonment of a number of wells within the City’s service area. Currently, the City is augmenting its groundwater supplies in its contingency service area with surface water received from MID. Groundwater quality issues, including elevated levels of uranium and 92 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N arsenic, are threatening the City’s groundwater supply. To protect its groundwater and maintain groundwater as a viable drinking water source, the City of Modesto has formulated the following BMOs for its management area: 5.3.1.1 Groundwater Quality Protection The City proposes to protect groundwater quality by developing and implementing specific actions to identify potential sources of contamination and to develop a management plan to control and curtail movement of contaminants into and within the basin. The specific actions may include the following: ƒ Develop a database and populate it with water quality data. Using the database information, develop tools to map contaminated areas as well as historic movement of the contaminants. ƒ Formulate and implement a geologic assessment to better understand the basin’s aquifer characteristics and water movement and to evaluate and understand the sources of contaminants. Detect potential changes in water quality that could affect the long-term quality and quantity of the drinking water supply. ƒ Develop a well field management plan that will manage groundwater pumping to reduce or eliminate contaminant movement into and within the basin. Develop well design criteria, including proper spacing and screening of wells to manage groundwater pumping and the movement of contaminants. 5.3.1.2 Groundwater Levels Groundwater levels, historically, were declining in this management area. Since 1995 and with the importation of surface water to augment the groundwater supply, groundwater levels have recovered. However, future population growth in and around the management area will increase groundwater use. To maintain groundwater levels in the management area, the City of Modesto formulated the following management objectives: ƒ Work with other entities in the subbasin to identify and protect the groundwater recharge area. ƒ Evaluate feasibility of groundwater recharge and conjunctive use projects including the development of artificial recharge areas, conjunctive use projects, and storage tanks with transmission mains for added reliability to the system. ƒ Work with MID to evaluate the feasibility of developing a cooperative in-lieu recharge and/or water exchange programs including the following: • Increase water treatment capacity and use of surface water to augment the groundwater supply. 93 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N • Develop an exchange program to mix the groundwater of marginal quality (for drinking water) with surface water and deliver it for agricultural use, golf courses, parks, and other open space areas in exchange for a surface water supply for the City of Modesto. 5.3.1.3 Water Conservation and System Improvement The City of Modesto, under its Urban Water Management Planning function, will continue to evaluate water conservation and metering opportunities to reduce water demands in the service area. The City also plans to undertake a conveyance system interconnection improvement project to connect isolated delivery systems to its water delivery network. These actions will add flexibility to the system and enable the City to reduce pumping from the areas of poor water quality and reduce movement of contaminants in the basin. 5.3.2 Modesto Irrigation District Management Area MID plays a major role in the groundwater management of the Modesto Groundwater Subbasin. MID and TID operate Don Pedro Reservoir and divert surface water for agricultural and urban uses to the basin. To manage groundwater levels and protect the basin groundwater quality, MID plans to implement the following BMOs: ƒ Develop a systemwide wellfield optimization program to actively manage MID’s groundwater production and to manage its surface and groundwater resources conjunctively, in real time, to meet its water supply and energy management objectives. ƒ Manage MID’s surface water and groundwater conjunctively in an integrated fashion. This would include importation and treatment of additional surface water supplies from MID to the City of Modesto to reduce pumping groundwater. ƒ Continue working with the City of Modesto to protect the management area from potential overdraft and movement of contaminants to the basin. In cooperation with the City of Modesto, develop a water exchange program to mix the groundwater of marginal quality (as potable water) pumped by the City with surface water and deliver it for agricultural use, golf courses, parks, cemeteries, and other open space areas in exchange for surface water delivery to the City of Modesto. ƒ Evaluate the feasibility of an expanded blending program and the use of shallow water acquired for delivery to agricultural water users. 5.3.3 City of Oakdale Management Area The City of Oakdale relies solely on groundwater for its water supply. The City’s goal is to protect its groundwater levels and quality for a sustainable water supply for its citizens. 94 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 5.3.3.1 Groundwater Levels The City operates nine wells, two of which were recently constructed. Water levels in some wells are impacted by operations of production wells at the Hunts and Hershey industrial plants. To protect its groundwater levels, the City can: ƒ Conduct a systemwide optimization study to determine how its wells can be operated to maximize production while minimizing the impact from the other wells. ƒ Work with plant managers to minimize operation impacts during the City’s peak water demand. Promote and encourage an industrial water conservation program. ƒ Work cooperatively with other water entities in the basin to promote and implement conjunctive management programs. Specifically, investigate the potential of treatment facilities for surface water that could be supplied by OID. ƒ Work cooperatively with other agencies to identify and develop groundwater recharge projects when possible. 5.3.3.2 Groundwater Quality Protection ƒ Construct a sanitary seal on all new wells and work with other groundwater users within the management area to ensure proper well construction methods are used for all new wells. ƒ Abandon wells within the management area in accordance with the Stanislaus County well abandonment ordinance. ƒ Regularly monitor wells adjacent to industrial areas to detect any potential water quality degradation. If degradation is detected, consult with the Regional Water Quality Control Board to encourage the implementation of necessary steps to control the migration of poor quality water. 5.3.4 City of Riverbank Management Area Groundwater is the only source of water for the City of Riverbank. Currently, groundwater levels and water quality are stable within this management area. Groundwater quality protection is the only BMO designated for this management area. To protect the groundwater quality of the management area, the City can take the following actions: ƒ Monitor groundwater quality to ensure that it is not compromised by the operation of industrial facilities such as the wood treatment plant. If water quality degradation is detected, consult with the Regional Water Quality Control Board to encourage the implementation of actions to control the migration of poor quality water in the basin. 95 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ The City is concerned about the operation of a future recharge project and the quality of water used for recharge. The City will work with other water agencies within the basin to ensure that the future recharge project operation will not compromise groundwater quality in the Riverbank management area. 5.3.5 Oakdale Irrigation District Management Area The OID management area is divided between the Modesto Groundwater Subbasin and the East San Joaquin Groundwater Subbasin. About 60 percent of the OID management area is within the Modesto Subbasin. However, the issues of the management area north and south of the Stanislaus River are similar and the BMOs listed below will be applicable for the entire management area. Urbanization within and around the management area has increased groundwater production and the potential for future overdraft. OID plans to implement the following BMOs: ƒ Develop a systemwide well field optimization program to actively manage groundwater production and to manage surface and groundwater resources conjunctively, in real time, to meet OID’s water supply and energy management objectives. ƒ Manage OID’s surface water and groundwater resources conjunctively. This would include: • Investigating the feasibility of developing conjunctive use and groundwater recharge projects. Determine if groundwater recharge is a viable option to reduce the falling water table within the management area. • Promoting programs and actions that protect recharge areas within the management area. • Investigating the feasibility of annexing areas currently on groundwater in order to bring surface water to the area for in-lieu recharge programs. Evaluating the potential benefits of the annexation of adjacent farmland on falling groundwater table within the management area, which is reliant on groundwater, and converting it to surface water. • Investigate impacts of upstream development (urban or agriculture) on the water quality and groundwater level within the OID service area. 5.3.6 Stanislaus County Management Area The County of Stanislaus is represented by the DER at Association meetings. Partnering with the Association in basin-wide groundwater management is consistent with the Board of Supervisors’ priority of ensuring a safe and healthy community, facilitating economic 96 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 97 development, and achieving multijurisdictional cooperation. To meet these priorities, the County promotes and participates in Association programs that: ƒ Preserve and protect the groundwater resource ƒ Enhance the understanding of groundwater resources through the gathering and sharing of information ƒ Provides factual information that may serve as a basis for land use decisions in the groundwater basin 5.4 Current Groundwater Monitoring Activities Groundwater levels in the Modesto Subbasin have been measured in about 230 wells by the DWR and its cooperatives. The wells used for monitoring may be in different aquifers and at times have long screen intervals that make an interpretation of groundwater flow directions and water quality difficult. Some member agencies are reporting data to DWR and are included in this list. The USGS, in partnership with member agencies of the Association, has monitored 17 wells in the area for the National Water Quality Assessment Program. It has also constructed or plans to construct additional monitoring wells in the City of Modesto to define hydraulic characteristics, water levels, and water quality in the shallow and confined aquifers. Appendix D contains a list of these wells. The University of California-Davis with grant funding has constructed several monitoring wells to assess nitrates and nutrient management near dairies. The Association’s members, to varying extents, monitor groundwater production, levels, and quality. Table 5-1 summarizes the current level of monitoring through the member agencies. ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 98 Pumping Member Total Number Totals Water Quality Analyses Agency of Wells Semiannual Annual Quarterly Semiannual Annual Performed MID 104 104 96 15 General Mineral, Boron 104 EC + pH OID 17 17 17 City of Modesto 62 86 14 (VOCs) Per Title 22 and DHS Ceres 4 4 Per Title 22 and DHS Walnut Manor 1 1 Per Title 22 and DHS Salida 7 7 Per Title 22 and DHS Del Rio 3 3 1 Per Title 22 and DHS Waterford 7 7 Per Title 22 and DHS Hickerman 2 2 1 Per Title 22 and DHS City of Oakdale 7 7 Per Title 22 and DHS City of Riverbank 7 7 Per Title 22 and DHS Total 221 245 0 113 0 16 15 104 Source: CCR from City of Modesto; MID e-mail comunication, 2004; OID well location map; Oakdale Water Master Plan, Riverbank production totals Pumping Member Total Number Totals Water Quality Analyses Agency of Wells Semiannual Annual Performed DWR (including Cooperators) 230 230 OID 15 15 Drinking Water Parameters Department of Health 209 Per Title 22 and DHS Services (Including Per Title 22 and DHS Cooperators) Per Title 22 and DHS Total 245 230 224 Source: DWR, 2004, Bulletin 118 Number of Wells Where Groundwater Samples Are Analyzed Number of Wells Where for Water Quality Groundwater Levels Are Measured to Every Three Years Number of Wells Where Groundwater Levels Are Measured Number of Wells Where Groundwater Samples Are Analyzed for Water Quality Table 5-1 Current Level of Monitoring Efforts ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Other groundwater monitoring conducted in the basin assesses releases of hazardous materials to the environment. These wells are typically near metropolitan areas and the resulting data are provided to the Regional Water Quality Control Board. These wells are extremely useful because they typically monitor the first water encountered, which can be correlated with surface water gaging stations to evaluate the aquifer connectedness. 5.4.1 Subsidence Monitoring Land subsidence in the Central Valley has occurred in three areas with an aggregate area of about 4,000 square miles. Subsidence has occurred in the area extending from Los Banos to Wasco, from Arvin to Maricopa, and in the Delta region east of Stockton. Subsidence has also occurred along the west side of the valley in Yolo, Solano, and Colusa Counties. Subsidence can be elastic or inelastic. Elastic subsidence occurs when aquifers are pumped and the pore pressure is decreased. After recharge occurs and the heads increase, the land surface generally recovers. Elastic subsidence in the Sacramento Valley has been reported to be on the order of about 0.2 feet (Borchers et al. 1998). Inelastic subsidence results in permanent, irreversible declines in ground surface. Inelastic subsidence is of three types in the Central Valley: oxidation of peat, lowering of the artesian head in confined aquifer systems, and near-surface compaction of moisture deficient alluvial fan deposits above the water table (Poland and Evenson 1966). Subsidence can also occur in areas where water-level declines in unconsolidated aquifers allow mineral grains to permanently adjust to a denser arrangement (Borchers et al. 1998). The mechanisms of subsidence in unconsolidated aquifers are governed by groundwater levels. If the water levels drop below their lowest historic level, inelastic subsidence may occur. In these cases, inelastic subsidence is generally due to compaction in thick clay beds. The Association is in an area where subsidence has not been reported, although no specific studies have been conducted in the area. The potential for subsidence in the area is low because the sediments lack peat, the sediments were deposited with water, and the Corcoran clay is relatively thin and is not distributed throughout the area. Groundwater levels have declined in unconsolidated sediments through 1995 and may have resulted in some inelastic subsidence. It is not anticipated that groundwater levels will be lowered below these historic levels, and therefore the potential for subsidence in the area is low. 5.5 Facilitating Conjunctive Use Operations The most significant conjunctive use operation in the Modesto basin is the construction of the Modesto Regional Water Treatment Plant and its associated storage and delivery systems, which treats surface water for delivery to areas that had previously relied solely on groundwater. This project has contributed to the recovery of groundwater levels in the Modesto area, improved the delivery system’s reliability, and has reduced pollutant movement in the basin. The program for expanding the treatment plant and its associated 99 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N storage and delivery systems is under way. This conjunctive management of the basin’s surface water and groundwater resources contributes to the protection of the basin, while providing a reliable water supply for the City of Modesto. Other conjunctive use projects will be investigated. One key study to formulate conjunctive use projects will identify recharge areas in the basin. 100 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 6 Groundwater Protection Measures A high priority of the IRGMP is protection of the groundwater resources. This will be accomplished through a series of actions, described below, that will be implemented by the Association members and facilitated by the Association. 6.1 Identification and Management of Wellhead Protection Area The purpose of wellhead protection is to protect the groundwater used for public supply, thereby eliminating costly treatment to meet relevant drinking water quality standards. A Wellhead Protection Area (WHPA), as defined by the Federal Wellhead Protection Program established by Section 1428 of the Safe Drinking Water Act Amendment of 1986, is “the surface and subsurface area surrounding a water well or wellfield supplying a public water system, through which contaminants are reasonably likely to move toward and reach such water well or wellfield.” The WHPA may also be the recharge area that provides the water to a well or wellfield. Unlike surface watersheds that can be easily determined from topography, WHPAs can vary in size and shape depending on subsurface geologic conditions, the direction of groundwater flow, pumping rates, and aquifer characteristics. WHPAs are not directly an agricultural issue. However, in the Modesto Basin, because of the relationship between agricultural and municipal water uses, some important considerations in delineating WHPAs are as follows: ƒ Location of existing public supply wells ƒ Identification of probable locations of future public supply wells ƒ Present direction of groundwater flow ƒ Probable direction of future groundwater flow ƒ Construction characteristics of public supply wells perforated intervals and annular seals) ƒ Subsurface geologic conditions restricting layers, confining beds, and other features) ƒ Rate of current groundwater flow ƒ Pumping from upgradient areas ƒ Potential sources of contamination 101 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ Forecasted future land use Potential areas of water quality risk include: ƒ Areas without improved sewage collection systems ƒ Areas with leaky sewer pipes and septic systems ƒ Wells improperly abandoned ƒ Confined animal feedlots ƒ Agricultural practices where chemicals are used ƒ Areas with potential for spills of hazardous materials Identification of wellhead protection areas is a component of the Drinking Water Source Assessment and Protection Program (DWSAP Program) administered by the Department of Health Services. It set a goal for all water systems statewide to complete Drinking Water Source Assessments by December 31, 2002. The Cities of Modesto, Riverbank, and Oakdale have completed their required assessments by performing the three major required components listed below: ƒ Delineation of capture zones around sources (wells) ƒ Inventory of Potential Contaminating Activities (PCAs) within protection areas ƒ Vulnerability analysis to identify the PCAs to which the source is most vulnerable Delineation of capture zones includes using groundwater gradient and hydraulic conductivity data to calculate the surface area overlying the portion of the aquifer that contributes water to a well within specified time-of-travel periods. Typically, areas are delineated representing and 10-year time-of-travel periods. These protection areas need to be managed to protect the drinking water supply from viral, microbial, and direct chemical contamination. Inventories of PCAs include identifying potential origins of contamination to the drinking water source and protection areas. PCAs may consist of commercial, industrial, agricultural, and residential sites, or infrastructure sources such as utilities and roads. Depending on the type of source, each PCA is assigned a risk ranking, ranging from very high for such sources as gas stations, dry cleaners, and landfills, to low for such sources as schools, lakes, and non- irrigated cropland. Vulnerability analysis includes determining the most significant threats to the quality of the water supply by evaluating PCAs in terms of risk rankings, proximity to the well being surveyed, Physical Barrier Effectiveness (PBE), and whether contaminants have previously 102 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N been detected. PBE takes into account factors that could limit infiltration of contaminants including type of aquifer, aquifer material (for unconfined aquifers), well operation, and well construction. The vulnerability analysis is based on a scoring system that assigns point values for PCA risk rankings, PCA locations within the wellhead protection area, and well area PBE. The PCAs to which drinking water wells are most vulnerable are apparent once vulnerability scoring is complete. 6.1.1 Actions The Association will facilitate the following actions: ƒ A component of the DWSAP Program is an assessment of vulnerability of groundwater sources to quality degradation. The Association member agencies providing drinking water should obtain proper clearances for the release of information and prepare vulnerability summaries from the DWSAP Program to be used for guiding management decisions in the basin. ƒ Contact groundwater basin managers in other areas of the state for technical advice, effective management practices, and “lessons learned” regarding establishing wellhead protection areas. ƒ Attend groundwater conferences and technical workshops and meetings to learn more about groundwater management practices. 6.2 Regulation of the Migration of Contaminated Groundwater The migration and remediation of contaminated groundwater is of primary concern to the Cities of Modesto, Riverbank and Oakdale. Also of concern is the localized contamination of groundwater by industrial point sources such as dry cleaning facilities, food processors and the numerous fuel stations throughout the Modesto Basin and OID service area north of the Stanislaus River. While the Association does not have authority or responsibility for remediation of this contamination, it is committed to coordinating with responsible parties and regulatory agencies to keep Association members informed of the status of known groundwater contamination in the basin. 6.2.1 Actions The Association will take the following actions: ƒ Coordinate with the USGS to expand the network of monitoring wells to provide for an early warning system for public supply wells. 103 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ If detections occur in these monitoring wells, facilitate meetings between the responsible parties and potentially impacted member agency(ies) to develop strategies to minimize the further spread of contaminants. Specifically, the consideration of altering groundwater extraction patterns or altering production wells in the vicinity of a pollutant plume to change the groundwater gradient. ƒ Provide a forum to share all information on mapped contaminant plumes and Leaking Underground Storage Tank sites in order to develop groundwater extraction patterns and in site planning of future production or monitoring wells. ƒ Meet with representatives of the Central Valley Regional Water Quality Control Board to establish a relationship and identify ways to have open and expedient communications with the regarding any new occurrences of contamination, particularly when contamination is believed to have reached the water table. ƒ Track upcoming regulations on septic systems, agricultural discharges and other regulatory programs that pertain to water quality degradation. 6.3 Identification of Well Construction Policies The Stanislaus County Department of Environmental Resources (DER) administers the well permitting program in the unincorporated areas of the Modesto Basin while the San Joaquin County Department of Environmental Health (DEH) administers well construction for the portion of OID lying within San Joaquin County. The standards in both counties for construction are consistent with those recommended in State Water Code Section 13801. This section requires counties, cities, and water agencies to adopt the State Model Well Ordinance as a minimum standard for well construction or a more rigorous standard if desired. Each city in the Association has enacted a well ordinance adopting the California Well Standards, Bulletin 74-81, and all supplements. This ordinance is utilized in wells constructed within the incorporated area of each city. Each city provides a review of well construction plans and specifications within the incorporated area. The Stanislaus County DER and the San Joaquin County DER have enacted well ordinances adopting the California Well Standards, Bulletin 74-81 and all supplements for the unincorporated areas of these counties. The Stanislaus County DER and San Joaquin County DEH staffs also review applications and construction plans and specifications and issue permits for wells constructed or destroyed in unincorporated areas. Both counties require and maintain well logs and water well driller reports for constructed wells. Standards also exist for contractors involved in well construction. Section 13750 of the California Water Code requires that well drillers possess a C-57 Water Well Contractors License, and Section 13751 requires well drillers to file a well completion log with DWR for every production or monitoring well constructed. 104 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N The number of service connections determines whether operating permits for wells used for public drinking water are provided through the Department of Health Services or either the Stanislaus County DER or the San Joaquin County DER. The Department of Health Services has jurisdiction over public water system wells with over 200 service connections. Wells that serve public water systems with fewer than 200 service connections fall under the jurisdiction of the county. 6.3.1 Actions The Association will facilitate the following actions: ƒ Ensure that all member agencies are provided a copy of the applicable county well construction ordinance and understand the proper well construction procedures. ƒ Coordinate with member agencies to provide guidance, as appropriate, on well construction to prevent creating conduits through regionally confining beds. Where feasible and appropriate, this could include the use of USGS lithologic data prior to construction of the well to assist in well design. 6.4 Administration of Well Abandonment and Destruction Programs There are many unknown, obsolete or abandoned water supply and natural gas wells within the Modesto Groundwater Basin. These wells provide potential locations for monitoring of groundwater levels, but more frequently serve as a source of contamination and should be abandoned. One of the primary concerns of local agencies is the groundwater contamination risk posed by unused wells which have not been properly destroyed. Section 21 of DWR Bulletin 74-81 and revisions contained in Part II of Bulletin 74-90 allow classification of unused wells into two types, abandoned and inactive. An abandoned well is defined as one which has not been used for a period of one year, and whose owner has declared the well will not be used again. If the well has not been used during the past year, but the owner demonstrates his/her intention to use the well again for supplying water, the well is considered inactive. Four criteria must be met in order for a well to maintain the inactive, rather than abandoned, classification. These criteria are: ƒ The well has no defects ƒ The well is securely covered ƒ The well is clearly marked ƒ The surrounding area is kept clear of brush and debris 105 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Failure to meet these criteria could result in the well being classified as abandoned under current regulations. All abandoned wells, exploration or test holes, and monitoring wells must be destroyed as stated in Section 22 of Bulletin 74-81 and revisions contained in Bulletin 74-90. An abandonment program should focus on those wells which pose the greatest threat to groundwater; however, numerous factors make the abandonment and destruction of wells difficult. These factors include lack of consistency in records regarding well construction, location and use; cost of well destruction; and the defined classification for abandonment of wells. Well construction within the study area has taken place for nearly a century, with records and standards altered over time. Recent records pertinent to construction and location of new wells are more complete than earlier records which are often inconsistent. The lack of financial incentive for well owners to declare a well as abandoned also reduces the effectiveness of the well abandonment program. Stanislaus County administers the well destruction program in most of the Modesto Basin while San Joaquin County administers the program in the portion of OID that lies within San Joaquin County. The standards for construction are identified in the county codes for these two counties and are based on State of California standards. 6.4.1 Actions The Association members, including Stanislaus County and the cities, will take the following actions for lands within their jurisdictions: ƒ Ensure that all Association members are provided a copy of the code and understand the proper destruction procedures and support implementation of these procedures. ƒ Follow up with Association members on reported abandoned and destroyed wells to confirm information collected from DWR and receive information on abandoned and destroyed wells to fill gaps in county records. ƒ Obtain “wildcat” map from California Division of Oil and Gas to ascertain the extent of historic gas well drilling operations in the area as these wells could function as conduits of contamination if not properly destroyed. ƒ Seek funding to develop and implement a program to assist well owners in the proper destruction of abandoned wells. OID will communicate with San Joaquin County staff to determine the status of abandoned and destroyed wells within the boundaries of OID and will coordinate with San Joaquin County on the procurement of “wildcat” maps from the California Division of Oil and Gas. 106 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 6.5 Mitigation of Overdraft Conditions The Association supports activities such as those undertaken by the City of Modesto and MID providing surface water to areas once wholly dependent on groundwater and eliminating localized overdraft. The Association also supports actions by MID and OID to encourage customers to continue to receive surface water deliveries so that growers do not turn to groundwater as a more flexible source of irrigation supply during periods when surface water is abundant. 6.5.1 Actions The Association will facilitate the following actions: ƒ Support programs that relieve aquifer overdraft through substitution of surface water for groundwater. ƒ Continue implementation of water conservation programs, including the water metering program, that will reduce reliance on groundwater pumping. ƒ Continue and enhance groundwater monitoring and groundwater use to ensure the balanced state of the groundwater basin ƒ Support programs by MID and OID to improve irrigation service to water users who may otherwise irrigate using groundwater because of the greater operational flexibility achievable through pumping. ƒ Seek funding for programs and projects that would identify and mitigate potential condition of overdraft in the basin. 6.6 Replenishment of Groundwater Extracted by Water Producers A component of wellhead protection and an important groundwater management strategy is the protection of major recharge and withdrawal zones. This strategy has far-reaching effects in the Modesto and San Joaquin Basins because of the significant groundwater recharge occurring as a result of agricultural surface irrigation. Groundwater recharge must be adequate to replenish extracted groundwater, while withdrawal zones need protection from upgradient sources to ensure that the quality of extracted groundwater meets the standards established for the intended use. A comprehensive approach to the protection and management of the major recharge and withdrawal zones is much more appropriate than the use of individual zoning techniques. Communities, in concert with neighboring towns and in coordination with the region, must develop comprehensive land and water resource management programs that go beyond simple zoning approaches for the protection of agricultural and urban areas. 107 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N The Association has evaluated surface geology within and directly adjacent to its boundary for the purpose of delineating areas having potentially high recharge rates. The basin contains numerous discontinuous recharge and withdrawal areas that do not allow for easily defined mapping of recharge zones. Nevertheless, a large portion of the study area has been determined to contribute to recharge. The Association supports land use measures that will preserve potential recharge areas from development that would reduce or eliminate their effectiveness as recharge sites. 6.6.1 Actions The Association’s member agencies will take the following actions: ƒ Identify areas having high potential for contributing to aquifer recharge and encourage agencies to communicate with land use planning entities to enact measures that will protect these lands from development that would reduce their value as recharge sites. ƒ Communicate with DWR and other governmental agencies studying groundwater and river interactions. 6.7 Construction and Operation of Recharge, Storage, Conservation, Water Recycling and Extraction Projects Various Association members share responsibility for development and operation of recharge, storage, conservation, water recycling and extraction projects. The role of the Association is to promote cooperation and sharing of information between the agencies sponsoring water management projects and other member agencies. To the extent feasible, the Association will also support measures to coordinate development and optimize operation of facilities to improve the basin-wide effectiveness and efficiency of water management. 6.7.1 Actions The Association will take the following actions: ƒ Encourage sharing of information on project planning, design and operation among member agencies. ƒ Promote a coordinated approach toward project development and operation to lower the costs and increase the benefits of water management efforts. ƒ Seek funding for projects and programs that will contribute to water conservation, recycling, and recharge of the groundwater basin. 108 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 6.8 Control of Saline Water Intrusion Saline water intrusion from the San Joaquin River or from the west side of the San Joaquin Valley (including intrusion from the marine layers) is not well documented in the Modesto Groundwater Basin. Groundwater elevations prevalent in the basin have historically maintained a positive gradient preventing significant migration of saline water associated with groundwater from the western San Joaquin Valley. Maintaining the positive groundwater gradient will continue to prevent induced flow from the river or from groundwater west of the San Joaquin River. 6.8.1 Actions The Association coordinates with member agencies and other local and state agencies to take the following actions: ƒ Continue collecting groundwater quality data along the San Joaquin River, and track the progression, if any, of saline water moving east from the San Joaquin River. This action will include communicating with DWR’s District Office on a biennial basis to check for significant changes to TDS concentrations in wells. DWR has a regular program of sampling water quality in selected domestic, agricultural and monitoring wells throughout the basin. These wells will be augmented by additional monitoring wells to develop an early warning system able to detect saline water intrusion from the river. ƒ The program of monitoring for intrusion of saline water will be supplemented by the Groundwater Monitoring Program described in this plan. The program includes provisions for monitoring groundwater levels and quality. ƒ Observe TDS concentrations in public supply wells that are routinely sampled under the DHS Title 22 Program. 109 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Page left intentionally blank 110 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 7 Stakeholder Involvement The Association’s member agencies initiated a planning process to prepare an IRGMP. This plan is developed to comply with provisions of SB 1938 and SB 1672, including the provisions related to public involvement processes. 7.1 Involvement of Other Agencies and Entities The six agencies forming the Association are the Cities of Modesto, Oakdale, and Riverbank, Stanislaus County, Oakdale Irrigation District, and Modesto Irrigation District. These agencies share the groundwater resources and worked together to formulate this management plan. The Association provides coordinated planning to make the best use of available resources to the mutual interests of the inhabitants and resources of the groundwater subbasin. Throughout this planning process, other interested agencies and entities within the subbasin were encouraged to participate in developing the plan. The Association will work with member agencies and other entities to implement the components of this plan. The County of Stanislaus, a member of the Association and the advisory committee to prepare this management plan, is representing other self-supplied groundwater producers. The Association should encourage a proactive outreach to these groups. One group of suppliers in particular is made up of the industrial groundwater users in the basin. The Association will develop an outreach process to meet with the group and work together for more effective management of the water resources of the basin. 7.2 Coordination with Other Agencies The Association member agencies have also coordinated the planning process with other neighboring water agencies and subbasins. The City of Modesto is also participating in the development of a groundwater management plan for the Turlock Groundwater Subbasin and has been communicating the development of the management plan for the Modesto Subbasin to Turlock Subbasin stakeholders. Similarly, OID has been communicating the development of the management plan with the SSJID for the the Eastern San Joaquin Groundwater Subbasin. The Association plans to provide draft copies of this management plan to the neighboring subbasins. 7.3 Advisory Committee The Association’s member agencies formed an advisory committee to cooperate in the development of an integrated regional groundwater management plan. They met the first Thursday of each month to discuss the water management issues of the basin and guide the planning process to develop the plan. Through detailed discussion, the advisory committee 111 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N has developed BMOs and a related implementation plan. This management plan is the result of the Advisory Committee’s work over a 12-month period. 7.4 Public Involvement An extensive public involvement process was planned for developing the IRGMP. The components of the public involvement process include the following: ƒ Each agency has published a notice informing the public of the intention of the agency to hold a public hearing to determine whether to adopt a resolution to prepare the agency’s groundwater management plan. These notices are included in Appendix E. Stanislaus County, although actively participating in the preparation of the plan, has not published a notice informing the public of the intention of prepare such plan. ƒ The governing bodies of each agency, in their regularly scheduled meeting, held a hearing (after publication of notice) on whether to adopt a resolution of intent to prepare an IRGMP. At the conclusion of the hearing, each agency adopted a resolution to draft the plan and directed the staff to participate with other members of the Association to form a “Regional Water Management Group” to prepare an “Integrated Regional Groundwater Management Plan.” In these hearings, the public was invited to comment on whether the agency should adopt the resolution and on the planning process. The public was informed on how to provide comments to the agency. ƒ At the conclusion of each agency hearing, the agency adopted a resolution of intent. The agency also provided “a written statement describing the manner in which interested parties may participate in developing the IRGMP.” ƒ The Association also published a notice of intent, on behalf of its member agencies, to prepare an IRGMP. The notice included the schedule and location of a public hearing. The Association also acts as an advisory committee of the stakeholders in development of the management plan. ƒ After the publication of notice of intent, the Association held a public hearing to brief the public and interested parties about the planning process, schedule, content, and how the public can participate in the process and provide comments. Interested parties and the general public were invited and encouraged to attend the hearing and provide comments. After the hearing, a regional water management group was formed by the agencies who had decided to prepare an integrated regional groundwater management plan. ƒ When the public draft of the Integrated Regional Management Plan becamse available in April 2005, a notice was given (in the Modesto Bee and on the agency 112 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N website) to notify the public about the availability of the draft plan. Copies of the draft plan were made available to the public upon request. A public meeting was also scheduled. The place, date, and the time of the meeting conducted by the Association was included in the notice. ƒ The governing bodies of the participating agencies will schedule, in their regular meeting, a discussion of the Draft Plan, provide information to the public as to the content of the Draft Plan, and receive comments. The contact person’s name and address will be provided to the public for the submission of any written comments on the Draft Plan. ƒ The Regional Water Management Group will hold a public meeting to brief the public about the draft of the plan and will solicit public comment. It will decide whether to adopt the plan and submit it to the member agencies with a recommendation for its adoption. It will provide the name, phone number, and address of a contact person who will receive written comments from the public. ƒ Upon completion of the IRGMP, each agency will publish a notice of intent to hold a hearing as to whether the agency will adopt the plan. The notice will include a summary of the plan and will state the means of providing copies of the plan to interested parties. ƒ Each agency will hold a hearing to determine whether to adopt the plan. The agency shall consider protests to the adoption of the plan. If the agency determined that “a majority protest” has not been filed, the agency will adopt the IRGMP within 35 days after the conclusion of the hearing. Detailed documentation of the public involvement processes is presented in Appendix E. 7.5 Developing Relationships with State and Federal Agencies In mid-2004, the Association engaged in discussions with the DWR to initiate a cooperative relationship for the conjunctive management of the basin. As a result of these discussions, the Association and DWR signed a Memorandum of Understanding to work together to develop conjunctive use projects. A copy of that document is in Appendix B. For the last several years, the Association has been working cooperatively with the USGS to study the geology and aquifers of the Modesto Subbasin. The Association and the USGS have entered into an agreement, under the National Water-Quality Assessment Program, to map the subsurface geology of the basin and to develop a data network and a three- dimensional model of the basin. The Association member cities are also working with the Department of Health Services on issues related to compliance with Title 22, Drinking Water Quality Standards. 113 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 7.6 Dispute Resolution Process The Association has been used effectively as a tool for the resolution of water management issues in the basin. Discussion of issues in Association meetings, in an open and transparent process, resulted in a cooperative relationship between water users of the basin. The Association will continue to provide a forum for discussion and early resolution of water issues in the basin. 114 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 8 Plan Implementation This section includes a discussion of program integration and local, statewide, and regional water management priorities and illustrates how the structure of the IRGMP addresses these priorities. It then addresses the specifics of plan implementation. Key features of the IRGMP are the linkages that have been established among program actions. These linkages transform a group of isolated measures into a coherent program where the whole is greater than the sum of the parts. Linkages have been established by emphasizing the objective of developing an integrated and regional approach. Specific instances where individual activities have been linked to generate broader, more complementary actions are discussed below. 8.1 Integration of Local, State and Federal Monitoring Activities At present, a number of different agencies are responsible for different aspects of groundwater monitoring in the subbasins. One of the recommendations of the IRGMP is to continue the ongoing process of integrating local monitoring programs and improving access to and management of groundwater data. Local, state and federal entities expected to be involved in this process include DWR, USGS, Department of Health Services, and local water agencies. The objective of the recommendation is to have a groundwater monitoring and data management program that is comprehensive, efficient and provides data in a format that is easy to access to facilitate rapid recognition of problems and to support good management decisions. As a component of this management plan, a groundwater monitoring plan was also developed to ensure adequate data is collected to track the effect of implementation of BMOs. 8.1.1 Integration of Surface and Groundwater Operations This linkage is at the heart of the IRGMP as it requires coordinated operation of surface and groundwater resources to attain the various BMOs. Specific opportunities for integrated surface and groundwater operations include development of recharge basins, increased use of groundwater to respond to fluctuations in irrigation demand, and increased use of surface water to meet growing municipal and industrial requirements, including the expansion of the Modesto Regional Water Treatment Plant and its associated storage and delivery systems. 8.1.2 Integration of Groundwater Use and Surface Water Delivery One of the important recommendations of the IRGMP focuses on the potential to link optimization of groundwater use to surface water deliveries. This concept rests upon the idea that MID and OID could reduce system spillage by managing their use of groundwater to 115 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N respond to fluctuations in demands by irrigators. Use of wells enables water to be introduced into the delivery systems close to the points of demand, thereby reducing the lag time between points of delivery and points where water is introduced into the system in response to changes in delivery orders. The benefits of using groundwater to fine tune surface water deliveries may be further enhanced by making priority use of wells in high water table areas to achieve flow augmentation. In this way, water supply and water table control benefits could be achieved through implementation of one program. Optimization of well field operations and linkage with the surface water deliveries further integrates the districts’ water conservation, energy conservation, and water quality objectives into the districts’ daily operations by reducing operational spillage. 8.1.3 Integration of Water Management (MID and City of Modesto) An example of collaboration between two local agencies has been the effort to supply surface water from MID to the This reallocation has enabled the City of Modesto to expand its capacity to supply treated water without requiring that the City expand pumping of groundwater. MID’s ability to supply water to the City of Modesto has been supported by innovative water management practices within MID that have enabled this reallocation to take place without compromising service to other MID customers. 8.1.4 Integration of Water Quality Management for Both Surface Water and Groundwater Association members have cited declining groundwater quality as one of their major concerns. Coordinated operation of pumps to contain groundwater contamination and recharge of high quality surface water are among the management options available. 8.2 Local, Statewide, and Regional Priorities 8.2.1 Local Priorities The overriding local priority for implementation of the IRGMP is satisfying regional and local water management objectives as they are formulated through the development of BMOs. Local BMOs are specific approaches for achieving water management goals including groundwater supply, groundwater quality, and protecting against inelastic land surface subsidence. Because they are presented within the context of a basin-wide plan, the local BMOs illustrate the degree to which many of the local BMOs are common to more than one of the participating agencies and implementation of local BMOs is best achieved through cooperation among participating agencies. Through their involvement in the development of the IRGMP, participating agencies have demonstrated their conviction that the most effective approach to local water management is through regional actions. Specific local BMOs are discussed later in this section. 116 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 8.2.2 Statewide Priorities Implementation of the IRGMP will enable the Association and its member agencies to respond to a range of statewide water management initiatives. Key among these is the increasing emphasis placed on agencies to develop integrated regional solutions to water management problems and to coordinate the conjunctive management of surface water and groundwater for sustainable water supply reliability and water quality in California. Completion and adoption of the IRGMP will allow participating agencies to satisfy one of the key prerequisites for grant funding through Chapter 8 of Proposition 50, the Integrated Regional Water Management Grant Program. The integrated plan also frames specific water management projects in the context of an integrated regional water management strategy. Although the plan emphasizes groundwater management, elements of the plan address the use of surface water supplies, water conservation, and water recycling and blending to meet demands that have previously been met with groundwater. This integration of surface and groundwater resources leads to a more comprehensive management of water supplies and provides a lucid framework for compliance with state and federal water quality standards. In particular, by promoting effective water use in the Modesto Groundwater Subbasin, implementation of the IRGMP will: ƒ Increase California’s water supply reliability ƒ Reduce conflicts among water users ƒ Contribute to meeting Delta water quality objectives ƒ Assist in the implementation of Regional Water Quality Control Board Watershed Management Initiatives Chapters, plans and policies 8.2.3 Regional Priorities The IRGMP is an effort that recognizes that the most effective approach to managing a basin’s water resources is an integrated plan that enlists the cooperation of the agencies whose political boundaries match the basin’s physical boundaries. As noted above, the IRGMP includes a number of regional BMOs that have been agreed upon by all of the participating agencies. The overarching regional objective of the plan is to foster good stewardship of the resources and to promote wise management of regional resources that responds to regional and local BMOs. Providing reliable good quality water for the basin water users is essential for the economic wellbeing and welfare of the citizens of the region. Specific regional objectives include: ƒ Improve local water supply reliability ƒ Protect the region’s groundwater resources 117 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ Improve water quality ƒ Foster prudent stewardship of water resources ƒ Facilitate compliance with local, state, and federal water quality and public health regulations 8.2.4 Basin-Wide Water Management Strategies The regional water management actions support a comprehensive approach to managing water resources in the Modesto groundwater basin. In particular, these actions provide a framework for developing projects that advance the following water management strategies: ƒ Increase local and regional water supply reliability and water use efficiency: Management actions supporting conjunctive management, policy assessment, and development of a basin-wide water budget will be key to the implementation of this strategy. ƒ Promote groundwater recharge and management: Actions encouraging the identification of natural recharge areas and the evaluation of artificial recharge areas will be used to implement this strategy. ƒ Support water conservation: Development of a basin-wide water budget will be used to identify water conservation opportunities. Management and optimization of well field operations will be used to reduce spillage from irrigation distribution systems. Support the urban water conservation programs and water metering programs. ƒ Implement watershed management programs: This strategy will be implemented through policy assessment, identification of natural recharge areas and evaluation of artificial recharge projects. ƒ Promote water recycling: Management and optimization of well field operations will provide the tools to recycle agricultural returns. Use of groundwater not meeting some of the drinking water standards for landscape irrigation and blending for agricultural use will further promote water recycling in the basin. ƒ Foster conjunctive use. Conjunctive use will be the central management action that serves as the cornerstone for most other activities. The most significant conjunctive use project in the basin is the expansion of the Modesto Regional Water Treatment Plant and its associated storage and delivery systems. This project will reduce pumping by the City of Modesto, improve reliability, and allow the groundwater level in the subarea to recover and reduce the movement of groundwater contaminants. Actions addressing natural and artificial recharge, groundwater 118 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N monitoring, well field optimization, and policy assessment will also contribute to the planning and implementation of groundwater conjunctive use. ƒ Improve water quality: The water quality management, groundwater monitoring and management, and conjunctive use projects the expansion of the Modesto Regional Water Treatment Plant and its associated storage and delivery systems to increase surface water use) will improve groundwater basin water quality. Other projects such as the optimization of well field operations will contribute to improving water quality by reducing agricultural returns to the rivers and the Bay- Delta estuary. ƒ Improve storm water capture and management: Actions supporting public health programs and calling for capturing storm water in dry wells and in natural and artificial recharge facilities will reduce storm water discharges. Other regional water management elements such as provisions for recreation and river restoration are addressed in planning documents prepared by the participating agencies. Water transfer strategies are considered as in-basin projects to help agencies within the Modesto subbasin meet their water needs. Other strategies such as desalting are not applicable to the region. 8.3 Implementation Plan The Implementation Plan presents specific management actions that enable the Association to meet the BMOs. The overarching purpose of the BMOs and the associated management action is to encourage a balance of surface water and groundwater use that will protect the resources of the basin and maximize the reliable supply of high quality water to meet municipal, agricultural, and industrial demands now and in the future. The BMOs reflect issues that the participating agencies have recognized as jeopardizing the reliability or quality of local water supplies; the management actions are designed to resolve these issues. 8.3.1 Basin-Wide Recommendations The following management actions are put forth as recommendations for the implementation of the BMOs: ƒ Protection of natural recharge areas ƒ Development of a calibrated, three-dimensional, basin-wide groundwater model ƒ Feasibility evaluation of artificial recharge projects ƒ Management and optimization of well field operations ƒ Identification and feasibility study of conjunctive use projects 119 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ Support of public health programs ƒ Water quality management ƒ Groundwater monitoring and subsidence monitoring program ƒ Policy assessment ƒ Promoting coordination and cooperation between water entities The first set of actions responds to basin-wide BMOs. These are followed by agency- specific recommendations intended to support the implementation of each agency’s BMOs. 8.3.1.1 Identification of Natural Recharge Areas Groundwater recharge has diminished because of the expansion of urban areas, and trends in agricultural irrigation practices have reduced deep percolation of applied water. These trends underscore the need to identify and map the remaining natural recharge areas and to use this mapping to protect important sources of recharge. The objective is to develop specific planning actions that offer varying degrees of protection, depending upon an area’s significance as a source of recharge. Types of protection could include: ƒ Programs to educate public and planning entities about the importance of protecting recharge areas. ƒ Pricing and incentive programs to encourage the continued use of surface water for flood irrigation. Because irrigation of agricultural land is an important element of recharge in the basin, pricing and incentive programs should be promoted. The first step in implementing this management action would be to identify recharge areas within the cities and the county, to develop a GIS-based map of natural recharge areas, to inform planning entities of the importance of these areas, and to make recommendations for the protection of these areas. 8.3.1.2 Development of a Basin-Wide Groundwater Model To provide quantitative tools for water resource management in the Modesto groundwater basin, a transient optimization groundwater flow model is being developed. This model can be used to help identify the most effective ways to distribute groundwater pumpage, artificial recharge, and surface water deliveries to meet management objectives during normal and drought conditions. Further data collection and analysis are needed to complete the transient groundwater flow model and develop optimization parameters for the analysis of conjunctive use strategies. 120 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N During Phases I and II (Fiscal Years 2002 through 2005) of the Modesto groundwater basin investigations, a “geologic model” and a steady-state regional groundwater flow model were constructed. The geologic model currently consists of the conceptual understanding of the relationship between geologic units in the subsurface (such as the Corcoran clay, the Mehrten formation, and other marker beds), and a three-dimensional spatial interpolation model of “percentage of coarse-grained sediments” was completed, using data from the texture database. Drilling and installation of multilevel monitoring wells at two sites, collection of continuous core and borehole geophysical logs, installation of continuous monitoring devices, collection of aquifer and slug test data to determine aquifer parameters, collection of borehole velocity logs, and stratigraphic analysis of the newly collected core and cuttings data were performed to address the primary data gaps identified in the interpretation of existing data. The regional groundwater flow model was then updated with the new geologic and hydraulic information obtained during Fiscal Year 2004. Currently, long-term data are being collected and formatted for easy import into the transient flow model in preparation for calibration. The tasks required to complete this work include the following: ƒ Quantify Groundwater-Surface Water Interaction: Because the Modesto groundwater basin is surrounded on three sides by major streams, it is expected that changes in pumping stress will significantly affect stream flows. Quantitative data on the interaction between groundwater and surface water are needed to constrain the predictions from the groundwater flow model under scenario testing. Reconnaissance monitoring of temperature and salinity will help identify locations for more detailed data collection. Shallow monitoring wells and drive points will be installed at three to five sites and instrumented for water level and temperature monitoring. These data will be interpreted and used to develop parameters and input to the groundwater flow model, using the new MODFLOW stream flow routing package. ƒ Investigate Incised Valley Fill Deposit: An incised valley fill deposit identified beneath the Modesto urban area constitutes a major pathway for groundwater flow and contaminant transport and may enhance natural or artificial recharge in the basin. Reconnaissance mapping of the known extent of the incised valley fill will be followed by drilling, coring, well installation and monitoring, and characterization of hydraulic properties of the incised valley fill sediments. The more detailed data collected on the incised valley fill feature will be interpreted using stratigraphic modeling and incorporated directly into the groundwater flow model. ƒ Extrapolation of Process-Level Water Quality Findings to Regional Scale: Additional wellbore flow and depth-dependent sampling will be done at selected 121 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N locations throughout the basin. Flow data will be used to improve the regional groundwater flow model. A suite of water quality samples will be collected to evaluate sources and movement of water in the subsurface, including major ions, nitrate, trace elements, and isotopes. ƒ Groundwater Flow Model Transient Calibration: The results of the groundwater-surface water interaction and incised valley-fill deposit aspects of the investigations will be incorporated into the transient model. The transient datasets collected and organized during the last phase of the investigation will be input to the groundwater flow model using the new “farm” package developed for MODFLOW. This package allows the enhanced use of variables in computing crop demands and allows both semi-routed and fully routed surface water diversions. The model will be “nested” within the recently updated USGS Central Valley model to provide a regional context for the local model. This will reduce the uncertainty along the boundaries and in parts of the model where transient data are unavailable (south of the Tuolumne River). ƒ Development of Optimization Parameters and Scenario Testing: Following calibration of the transient groundwater flow model, the USGS will work with the Association to develop the objectives and parameters for optimization. Depending on what optimization parameters are selected, this may require the collection of additional data to include these variables in the groundwater flow model. Following the development of the parameters, the model will be used to perform scenario testing in close communication with Association needs. ƒ Continued Water Level Monitoring: Continuous water level data will be collected in the newly drilled monitoring wells and the data will be input into the USGS’s NWIS database. The Association and the USGS staff will conduct quarterly reviews to discuss progress and results and to address any issues that have come up during that quarter. Preliminary interpretations will be shared with the Association at quarterly meetings. A report documenting the transient groundwater flow model will be completed by the end of Fiscal Year 2008 and a final report on optimization and scenario testing will be completed by the end of Fiscal Year 2009. 8.3.1.3 Feasibility Evaluation of Artificial Recharge Projects The basin-wide water balance, described above, will reveal whether the basin is in overdraft and will illustrate trends in the balance between groundwater recharge and groundwater use. If the water balance demonstrates either that the basin is in overdraft or is likely to fall into an overdraft condition in the near future, two broad options are available for sustaining and protecting basin recharge. The first option is a program to maintain natural recharge by 122 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N protecting natural recharge areas; the second is the augmentation of natural recharge through an artificial recharge program. The evaluation of artificial recharge projects will begin with the mapping of potential recharge sites, which will build on the mapping of natural recharge sites described previously. The enhanced recharge management action will also develop in-lieu recharge projects. These projects would look at opportunities to reduce groundwater demand by supplying surface water to areas now served by groundwater. Such projects could include incentives for OID and MID irrigators to continue to receive surface water, investigations of annexation options to expand the MID and OID service areas, and water conservation programs or other approaches to ensure the districts’ capacity to serve expanded areas. In addition, this management action would continue to support the development and expansion of conjunctive use projects in urban areas with poor groundwater quality supplement the City of Modesto’s water supply with additional surface water in order to reduce its reliance on groundwater, improve groundwater levels, and reduce the movement of contaminants in the basin) as well as program to evaluate the potential for storm water recharge. 8.3.1.4 Management and Optimization of Well Field Operation A component of improved groundwater management is the optimization of well operations to accomplish specified management objectives. For example, each well in a well field can be instrumented and controlled so that the group of wells is operated to meet single or multiple objective functions. Examples of typical objective functions are: ƒ Minimizing the overall costs of pumping ƒ Maintaining groundwater levels within specified ranges ƒ Reducing or eliminating well interference where appropriate ƒ Avoiding the migration of contaminant plumes ƒ Controlling pumping into irrigation canals in response to delivery and cutoff orders, hence creating opportunities to conserve water by reducing spillage In addition, well field optimization would support managing the quality of discharged water to be blended with surface deliveries. For example, MID pumps water from the shallow aquifer and blends it with surface water for delivery to agricultural water users. Similarly, urban wells can be used to deliver water to agricultural users when the urban wells fail drinking water standards. The agencies within the basin could evaluate an expansion of the blending program in order to lower the high groundwater table and improve water quality. 123 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Similarly, wells could be optimized and controlled to manage pumping of high nitrate groundwater as a source of irrigation supply. 8.3.1.5 Identification and Feasibility Study of Conjunctive Use Projects Many of the management actions described above can be viewed as components of a broader conjunctive management program. The goal of this program would be the development of an integrated approach to balancing surface and groundwater use to support the BMOs. Implementation of a conjunctive management strategy may involve reduced groundwater pumping in some parts of the basin and broad controls on pumping to meet groundwater level BMOs. 8.3.1.6 Support of Public Health Programs Well construction and demolition standards are designed specifically to protect groundwater quality. Management actions to assist local agencies in complying with public health standards include the following components: ƒ Installation of sanitary well seals on all new wells in accordance with the California Well Standards ƒ Abandonment of wells in accordance with the California Well Standards This management action will be particularly valuable in unincorporated areas not served by a water purveyor. 8.3.1.7 Water Quality Management The protection of groundwater quality is an increasing concern because the basin’s population is growing. This management action would proceed by conducting a detailed geologic assessment of the basin that would focus on the areas with poor water quality and identify the sources of the contaminants. This assessment would result in coverage on a GIS system for mapping recharge areas and would be used to develop strategies to control the migration and movement of poor quality water into and throughout the basin. 8.3.1.8 Groundwater Monitoring and Subsidence Monitoring Program Groundwater monitoring and analysis and the archiving of collected data are needed to implement several of the recommended management actions conjunctive management and optimized operation of well fields). In addition, groundwater monitoring will be needed to meet the reporting requirements of the plan. The Association is developing a database to facilitate the storage, retrieval, and archiving of groundwater data. Monitoring data will be important in the development and calibration of the basin-wide groundwater model that will be used to evaluate the effects of proposed projects and management actions. 124 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N The Association plans to monitor and measure the rate of inelastic land surface subsidence within the basin. Given the ongoing efforts by Association members to prevent groundwater overdraft and conditions that might lead to subsidence, it appears unlikely that the insignificant subsidence that has occurred historically within the basin will be accelerated. However, the Association plans to monitor and document any future changes in land surface elevations and, if inelastic subsidence is observed, may recommend necessary actions to member agencies. 8.3.1.9 Policy Assessment Several of the technical management actions introduced above have clear policy requirements and implications. For example, effective protection of natural recharge areas will require coordination and communication with entities responsible for land use policies. Similarly, annexations to expand agencies’ service areas as part of an in-lieu recharge program presume clear policies regarding annexation and a process to evaluate the impacts of annexation on groundwater levels and groundwater quality. The development of consistent policies would be assisted by a regional groundwater forum such as the Association. The purpose of this forum would be to foster coordination and cooperation among participating agencies to manage the Modesto Subbasin and to provide a framework for the formulation of regional projects and programs for the protection and use of subbasin water resources. For example, given the mutual concern of agencies within the basin regarding the preservation of natural recharge areas and the protection of these areas from pollutants, local agencies could work through the forum to inform one another about land use practices that may contribute to groundwater degradation and the importance of reducing the occurrence of these land use practices. Similarly, the forum could assist in the formulation of basin-wide water conservation measures including incentive programs, water audits, water metering programs and other measures to reduce demand on the basin. 8.3.1.10 Promoting Cooperation and Coordination Between Water Entities The Association will continue to coordinate water management activities within the basin and to work cooperatively for implementation of agreed-upon BMOs. The Association will also develop an outreach and educational program to engage other water interests for management of the basin. One example of such outreach will be working cooperatively with industrial water users to improve water levels and water quality in the basin and to reduce localized well interference issues. 125 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 8.3.2 Area-Specific Recommendations The following recommendations for management actions are intended to respond to the specific objectives of each of the management areas. 8.3.2.1 City of Modesto Groundwater Quality Protection. The foundation of groundwater management is a good understanding of an area’s hydrogeology. This project would analyze the transport of contaminants using wellbore velocity profiling and depth-dependent sampling in areas of known groundwater quality problems. The well field management and optimization program described above would be valuable for managing pumping to reduce or eliminate contaminant movement into and within the basin. The well field management program would include well design criteria detailing the proper spacing and screening of wells to manage groundwater pumping and the movement of contaminants. It could also provide guidance and information needed to avoid siting new wells in areas of known poor water quality. Groundwater Quality Treatment. The City of Modesto plans to study methods to improve the quality of water pumped from wells that currently experience groundwater quality issues. This investigation would determine, case-by-case, the most economical and effective treatment method for a domestic supply well, based on its location and the type of treatment, such as ion exchange or blending with treated surface water. Groundwater Levels. To maintain groundwater levels, the City of Modesto plans to work with other planning entities to identify, encourage, and promote measures to protect groundwater recharge areas. The City and other members of the Association have agreed to evaluate the feasibility of groundwater recharge and conjunctive use projects, including the development of artificial recharge areas, in-lieu recharge projects, and surface water- groundwater exchange programs. Implementation of surface water-groundwater exchange programs will entail: ƒ Increased water treatment capacity and use of surface water to augment groundwater supplies ƒ Development of exchange programs to mix groundwater of marginal quality with surface water for delivery to agricultural users, golf courses, parks, and other open space areas in exchange for a surface water supply for the City of Modesto Water Conservation and System Improvement. The City of Modesto, under its Urban Water Management Planning function, will implement water conservation and metering opportunities to increase water use efficiency in its service area. 126 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 8.3.2.2 Modesto Irrigation District Management Area MID plays a major role in the groundwater and surface water management of the Modesto Groundwater Subbasin. MID and TID operate Don Pedro Reservoir and bring surface water for agricultural and urban uses to the basin. Development of a system-wide well field optimization program would assist MID in managing groundwater levels, protecting groundwater quality, and managing its energy usage. Conjunctive management actions would enable better control of its surface water and groundwater resources, including the exportation and treatment of additional surface water supplies from MID to the City of Modesto to reduce groundwater pumping. The City of Modesto and MID should work cooperatively to protect the City of Modesto’s management area from potential overdraft and the movement of contaminants to the basin and to continue to develop a water exchange program that mixes City-pumped groundwater of marginal quality (as potable water) with surface water and delivers it for agricultural use and to golf courses, parks, cemeteries, and other open space areas in exchange for surface water delivery to the City of Modesto. MID should also evaluate the feasibility of an expanded blending program and the use of shallow water acquired for delivery to agricultural water users. 8.3.2.3 City of Oakdale Management Area The City of Oakdale relies solely on groundwater for its water supply. The City’s goal is to protect its groundwater levels and quality for a sustainable water supply for its citizens. Groundwater Levels. The City operates nine wells, two of which were recently constructed. Water levels in some wells are impacted by the production wells at the Hunts and Hershey industrial plants. To protect its groundwater levels, the City could pursue the following options: ƒ Participate in a well field management and optimization program to determine how its wells can be operated to maximize production, while minimizing the impact from the other wells ƒ Work with plant managers to minimize impacts during the City’s peak water demand period and encourage industrial water conservation ƒ Work cooperatively with other water entities in the basin to promote and implement conjunctive management programs ƒ Work cooperatively with other agencies to identify and develop groundwater recharge projects 127 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Groundwater Quality Protection. In the area of groundwater protection, the following actions are recommended for compliance with local objectives: ƒ Construct a sanitary seal on all new wells and work with other groundwater users within the management area to ensure proper well construction methods are used for all new wells ƒ Abandon wells within the management area in accordance with the Stanislaus County well abandonment ordinance ƒ Regularly monitor wells adjacent to industrial areas to detect any potential water quality degradation, and if degradation is detected, consult with the Regional Water Quality Control Board to encourage the implementation of necessary steps to control the migration of poor quality water 8.3.2.4 City of Riverbank Management Area Groundwater is the only source of water for the City of Riverbank. Currently, groundwater levels and water quality are stable within this management area. To protect the groundwater quality of the management area, the City can take the following actions: ƒ Develop a monitoring program to ensure that there is no contamination from local industrial facilities. If water quality degradation is detected, consult with the to encourage the implementation of actions to control the migration of poor quality water in the basin. ƒ To address its concerns about the operation of a future recharge project and the quality of water used for recharge, work with other water agencies within the basin to ensure that the future recharge project operation will not compromise groundwater quality in the Riverbank management area. 8.3.2.5 Oakdale Irrigation District Management Area The OID management area is divided between the Modesto Groundwater Subbasin and the East San Joaquin Groundwater Subbasin. About 60 percent of the OID management area is within the Modesto Groundwater Subbasin. However, the issues of the management area north and south of the Stanislaus River are similar and recommended management actions apply to the entire management area. Urbanization within and around the management area has increased groundwater production and the potential for future overdraft. Recommended management actions for OID include: ƒ Participating in well field management and optimization program to actively manage groundwater production to meet OID’s groundwater and energy management objectives. 128 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ Investigating the feasibility of developing conjunctive use and groundwater recharge projects. Determining if groundwater recharge is a viable option to reduce the falling water table within the management area. ƒ Promoting programs and actions that protect recharge areas within the management area. ƒ Evaluating the potential benefits of the annexation of adjacent farmland, which relies on groundwater, and its conversion to surface water as part of an in-lieu recharge program. Assessing the effects of this program on aquifer levels and water quality. ƒ Investigating the impacts of upstream urban or agricultural development on water quality and groundwater levels within OID service area. 8.4 Data Management To manage the basin’s groundwater resources, the Association member agencies regularly exchange information and arrange for uniform groundwater data collection and monitoring to better understand the groundwater basin. In 1998, the Association developed a data collection protocol to standardize the data collection procedures among the member agencies. Data are collected in a coordinated fashion biannually. A copy of the current data collection protocol is provided in Appendix C. Data management practices already initiated by the Association and its member agencies will be expanded and strengthened during implementation of the IRGMP. 8.5 Annual Implementation Report Each year, the Association will prepare a report describing the progress made in implementing management activities and the effects of these activities on meeting basin-wide and local management area BMOs. The report will include maps of spring and fall groundwater elevations and tabular summaries of ongoing management actions. The report narrative will present details of implementation activities and describe developments in the basin that are not part of the groundwater management plan implementation but that impact groundwater conditions in the basin hydrologic conditions, siting of new industrial facilities, newly identified contaminant plumes). 8.6 Financial Planning for Recommended Actions/Project Implementation Progress toward the implementation of the IRGMP is contingent upon securing funding to complete the program. Two avenues that are available for funding are grant funding and funds generated internally by the Association members. 129 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 8.6.1 Grant Funding Identified grant funding opportunities include the following: ƒ U.S. Bureau of Reclamation Challenge Grant Program – The FY 2005 Challenge Grant Program is expected to be better funded than was the FY 2004 program (the program’s initial year) and the goals of the FY 2005 program are expected to encourage water conservation and judicious water management. ƒ CALFED/DWR Water Use Efficiency – This program provides grants for urban and agricultural water conservation projects. ƒ AB 303 Local Groundwater Assistance Program – This DWR-administered program funds groundwater data collection, modeling, monitoring and management studies, basin management and development of information systems. AB 303 is a potential source of funding for a range of management actions. ƒ Chapter 8 of Proposition 50, Integrated Regional Water Management Grant Program (administered jointly by the State Water Resources Control Board and DWR) – This chapter funds integrated water management projects that support water quality and water supply security objectives. Chapter 8 is well suited for funding conjunctive management actions. ƒ Agricultural Water Quality Grant Program – This program, administered by the State Water Resources Control Board, supports baseline monitoring, implementation of management measures, demonstration projects, and effectiveness monitoring. This program has been identified as a potential source of funding for actions that reduce the volume, improve the quality, or control the timing of surface water discharges (such as using groundwater to reduce lateral spillage). 8.6.2 Revenues Through Increased Water Rates Revenue generated internally by local agencies from the sale of water and power is a second source of funding available for implementation of the plan. Internally generated revenues are important because they are controlled by the member entities and represent a local commitment to plan implementation and establishment of the BMOs. Local financial support is often required by grant programs and by other sources of outside financing. Therefore, while local support may be a factor agencies weigh in establishing budgets and reviewing rates, the willingness of local agencies to contribute to plan implementation is likely to aid agencies in their acquisition of outside funding. Successful pursuit of grant funding will, in turn, enable ratepayers to increase the benefits of their investment. 130 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N 8.7 Periodic Review of the Integrated Regional Groundwater Management Plan In addition to the annual reports of implementation progress, there is a need to periodically review and, if necessary, refine the IRGMP. These reviews would be scheduled at five-year intervals and would concentrate on analyzing information presented in the previous annual reports and consolidating the observations of local water managers. The reviews would identify areas where the plan has been successfully implemented as well as areas where deficiencies were apparent. In areas where implementation has proceeded satisfactorily, the plan revision might include increasingly detailed information regarding the specifics of implementation. In areas where progress was less than anticipated, approaches would be discussed to either bring implementation of specific actions back on track or to change course and focus efforts on other actions believed to have a higher likelihood of success. 8.8 Schedule and Implementation Sequence The Regional Water Management Group discussed in detail the prioritization of project, programs, and strategies. The result of the discussions was the identification of phases instead of a specific priority list. Implementation of the actions recommended in the IRGMP is scheduled in three phases: ƒ Phase I-Near Term Projects: These projects are intended to be implemented within the next three years and include: • Management of the well fields: A decision support system to assist the districts to optimize groundwater production from their well fields, based on a set of established objectives. • Increase treatment, storage, and distribution capacities and improve system reliability for the City of Modesto. • Additional water blending projects: To help agencies meet their water quality objectives while increasing the beneficial use of groundwater. • Water conservation projects, including agricultural and urban water conservation projects, and residential water metering programs. • Identification of conjunctive use project concepts • Rockwell monitoring program • Wellhead treatment and remediation projects • Development of a calibrated, three-dimensional groundwater model of the basin 131 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N ƒ Phase II-Mid-Term Projects: These projects are planned for implementation from four to seven years: • Identification of groundwater recharge areas. • Implementation of wastewater treatment and capacity enhancements. • Development of conjunctive use projects. • Development of the in-lieu recharge projects, including evaluation of annexation options to reduce groundwater pumping. • Ongoing development, enhancement, and optimization of the basin-wide groundwater model. • Development of a basin-wide database. • Continue water metering implementation and demand management programs. ƒ Phase III-Long-Term Projects: These projects are scheduled for implementation beyond seven years in the future and include: • Installation of subsidence monitoring station if needed. • Water exchange program. • Update water budget. • Feasibility evaluation of artificial recharge projects. Other water management actions may continue throughout the planning horizon, including: ƒ Association meetings ƒ Preparation of annual progress reports ƒ Groundwater monitoring and data sharing ƒ Coordination and cooperation with water entities, neighboring basins, and state and federal agencies ƒ Periodic review of groundwater monitoring and groundwater management 132 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N References 2000. California Safe Drinking Water Act and Related Laws. Seventh Edition. January 2000. Balding, Gary O. and R. W. Page. 1971. Data for Wells in the Modesto-Merced Area, San Joaquin Valley, California. U.S. Department of the Interior, Geological Survey, Water Resources Division. Prepared in cooperation with the California Department of Water Resources. Open-File Report. Menlo Park, California. Borchers, James M. Gerber, J. Wiley, and H.T. Mitten. 1998. “Using Down-Well Television Surveys to Evaluate Land Subsidence Damage to Water Wells in the Sacramento Valley, California.” In Land Subsidence Case Studies and Current Research: Proceedings of the Dr. Joseph F. Poland Symposium. James W. Borchers, ed. Boyle Engineering Corporation. 2003. Water Master Plan: City of Oakdale. November 2003. Burow, Karen Jennifer L. Shelton, and Neil M. Dubrovsky. 1998. Occurrence of Nitrate and Pesticides in Ground Water Beneath Three Agricultural Land-Use Settings in the Eastern San Joaquin Valley, California, 1993–1995. U.S. Geological Survey. Water- Resources Investigation Report 97-4284. National Water-Quality Assessment Program. Sacramento, California. Burow, Karen Jennifer L. Shelton, Joseph A. Hevesi, and Gary S. Weissmann. 2004. Hydrologic Characterization of the Modesto Area, San Joaquin Valley, California. Preliminary Draft. U.S. Geological Survey. Water-Resources Investigation Report. Prepared in cooperation with Modesto Irrigation District. Burow, Karen Sylvia V. Stork, and Neil M. Dubrovsky. 1998. Nitrate and Pesticides in Ground Water in the Eastern San Joaquin Valley, California: Occurrence and Trends. U.S. Geological Survey. Water-Resources Investigation Report 98-4040a. Available at http://ca.water.usgs.gov/sanj/pub/usgs/wrir98-4040a/wrir98-4040a.html. California Department of Conservation. 2002. California Spatial Library. California Department of Water Resources. 2003. California’s Groundwater: Bulletin 118—San Joaquin Valley Groundwater Basin, Modesto Subbasin. Update of October 1, 2003. California Division of Mines and Geology. 1975. Geophysical Investigations in the Ione Area, Amador, Sacramento, and Calaveras Counties, California. Special Report 117. Sacramento, California. Prepared by Rodger H. Chapman and Charles C. Bishop. 133 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Chapman, Rodger and Charles C. Bishop. 1975. Geophysical Investigations in the Ione Area, Amador, Sacramento, and Calaveras Counties, California. California Division of Mines and Geology. Special Report 117. City of Modesto. 2003. 2003 Consumer Confidence Report. City of Oakdale, California. 2003. Water Master Plan. Prepared by Boyle Engineering Corporation. November 2003. City of Riverbank, California. 2003. 2002 Consumer Confidence Report and supporting data. April 15, 2003. Davis, G.H., J.H. Green, F.H. Olmsted, and D.W. Brown. 1959. Ground-water conditions and storage capacity in the San Joaquin Valley, California. U.S. Geological Survey. Water-Supply Paper 1999-H. Hem, John D. 1989. Study and Interpretation of the Chemical Characteristics of Natural Water. Third Edition. U.S. Geological Survey. Water-Supply Paper 2254. Hotchkiss, W. and G.O. Balding. 1971. Geology, hydrology, and water quality of the Tracy-Dos Palos area, San Joaquin Valley, California. U.S. Geological Survey. Open-File Report. Johnson, A. I. 1967. Specific Yield—Compilati8on of specific Yields for Various Materials. U.S. Geological Survey. Water-Supply Paper 1662-D. Prepared in Cooperation with the California Department of Water Resources. Marchand, D. and A. Allwardt. 1981. Late Cenozoic stratigraphic units, northeastern San Joaquin Valley, California: U.S. Geological Survey Bulletin 1470. MID, see Modesto Irrigation District. Modesto Irrigation District. 1996. Final Groundwater Management Plan for the Modesto Irrigation District (Draft). March 1996. Modesto Irrigation District. 2004. Water quality data spreadsheet. Page, R. W. 1972. Preliminary Appraisal of Ground-Water Conditions in the Vicinity of Modesto, California. U.S. Department of the Interior, Geological Survey, Water Resources Division. Prepared in cooperation with the city of Modesto. Open-File Report. Menlo Park, California. October 2, 1972. Page, R. W. 1973. Base of Fresh Ground Water (Approximately 3,000 Micromhos) in the San Joaquin Valley, California. U.S. Geological Survey. Prepared in cooperation with the California Department of Water Resources. Hydrologic Investigations Atlas HA-489. 134 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Page, R. W. 1977. Appraisal of ground-water conditions in Merced, California, and vicinity. U.S. Geological Survey. Open-File Report. Page, R. W. 1986. Geology of the Fresh Ground-Water Basin of the Central Valley, California, with Texture Maps and Sections: Regional Aquifer-System Analysis. U.S. Geological Survey. Professional Paper 1401-C. Page, R. W. and Balding, G. O. 1973. Geology and Quality of Water in the Modesto- Merced Area, San Joaquin Valley, California, with a Brief Section on Hydrology. U.S. Geological Survey. Prepared in cooperation with the California Department of Water Resources. Water-Resources Investigation 6-73. September 1973. Phillips, Steven Sherrill Beard, and R. J. Gilliom. 1991. Quantity and Quality of Ground- Water Inflow to the San Joaquin River, California. U.S. Geological Survey. Water- Resources Investigations Report 91-4109. Prepared in cooperation with the California Department of Water Resources and the California State Water Resources Control Board. Sacramento, California. Poland, J.F. and R.E. Evenson. 1966. “Hydrogeology and Land Subsidence, Great Central Valley, California.” In Geology of Northern California. Bulletin 190, California Division of Mines and Geology. Edgar H. Bailey, ed. San Francisco, California. Stanislaus County. 1994. 1994 Stanislaus County General Plan. U.S. Census Bureau. 2004. Population Statistics. Available at http://factfinder.census.gov. Accessed May 11, 2004. U.S. Environmental Protection Agency. 2004. EPA Map of Radon Zones. Available at http://www.epa.gov/iaq/radon/zonemap/california.htm. U.S. Geological Survey. 1999. Land Subsidence in the United States. Edited by Devin Galloway, David R. Jones, and S.E. Ignebritsen. Circular 1182. Reston, Virginia. U.S. Geological Survey. 2004. San Joaquin-Tulare Basins NAWQA. Available at http://ca.water.usgs.gov/sanj/gw_cycle1.html. Accessed May 6, 2004. Weissmann, G.S., J.F. Mount, and G.E. Fogg. 2002. Glacially driven cycles in accumulation space and sequence stratigraphy of a stream-dominated alluvial fan, San Joaquin Valley, California. Journal of Sedimentary Research, v. 72, no. 2, March 2002, pp. 240–251. West-Yost. 2004. Engineer’s Report: Justification and Cost Allocation for Proposed Water System Improvements. September 2, 2004. 135 ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Appendix A Association Memorandum of Understanding ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Appendix B Memorandum Between Association and Department of Water Resources ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Appendix C Data Collection Protocols ---PAGE BREAK--- ---PAGE BREAK--- C:\DOCUME~1\SLAMB\LOCALS~1\TEMP\GWMONPRO.DOC Revised June 12, 1998 Page 1 of 6 STANISLAUS & TUOLUMNE RIVERS GROUNDWATER BASIN ASSOCIATION GROUNDWATER MONITORING PROTOCOL FOR MEASURING STATIC GROUNDWATER LEVELS GENERAL The Stanislaus & Tuolumne Rivers Groundwater Basin Association is comprised of the County of Stanislaus, the Cities of Oakdale, Riverbank, and Modesto, and the Oakdale and Modesto Irrigation Districts. The Association’s jurisdiction is defined by the Memorandum of Understand- ing Relating to the Formation and Operation of the Stanislaus and Tuolumne Rivers Groundwater Basin Association (1994, 2002). As recommended by the Groundwater Association Board (See Board Minutes, January 15, 1998), monitoring of spring and fall water levels is to be coordinated among association member agencies and other participating entities within the groundwater basin to facilitate regional mapping of groundwater levels, ensure consistency of data collection, and to channel ongoing work in a cost effective manner. Monitoring spring and fall static water level measurements represents the groundwater association’s first step toward implementation of local groundwater management plans that were developed under Assembly Bill 3030 (1992). The purpose of this work is to preserve and protect the quantity and quality of groundwater for local agencies’ constituents and to ensure local control of groundwater as a valuable resource by showing that prudent groundwater manage- ment practices are being implemented within the local groundwater basin. The development of a groundwater monitoring protocol will continue to be an evolving program as information regarding wells within the basin is developed. Well information, including total depths and screened intervals, location, access, and measuring point elevation, will provide a basis for the development of criteria to select wells best suited for monitoring static water levels. Ultimately, wells selected for the monitoring program must also be accurately surveyed according to a common coordinate system to establish the horizontal and vertical well location. This document as well as its attachments represent procedures for acquiring, recording, and exchanging groundwater level data. To the extent practical, groundwater association members, as well as other participating entities, will strive to collect and record spring and fall groundwater level data consistent with the following protocol. MAPPING The purpose of collecting spring and fall static water level measurements is to develop water level contour maps that display the relationship between hydrologic resources and the cultural resources of the groundwater basin. This mapping tool can then be used by local agencies to better understand the spatial relationships between groundwater recharge and discharge areas, flow ---PAGE BREAK--- C:\DOCUME~1\SLAMB\LOCALS~1\TEMP\GWMONPRO.DOC Revised June 12, 1998 Page 2 of 6 directions, pumping patterns, and land use impacts on groundwater quantity and quality. When water level maps are referenced in time, water level measurements can reveal changes in groundwa- ter flow regimes brought about by natural or human influences. Regional mapping of groundwater levels requires the monitoring of uniformly distributed monitoring wells that capture the vertical extent of the aquifer of interest. This objective is not only technically difficult to accomplish, but also is not economically feasible. A proposed alternative is to utilize production wells currently being monitored by various agencies as representative of average head conditions for that well site. Currently, monitoring of groundwater levels are performed by many agencies and private entities within the basin. Table 1 below shows the agencies and number of wells currently being monitored. Table 1: Summary of Wells Currently Monitored by Local Agencies for Static Groundwater Levels City of Modesto City of Riverbank City of Oakdale Oakdale Irrigation District Modesto Irrigation District Stanislaus County Total Number of Agency Wells in Basin: Irrigation Drainage Public Water Supply 0 0 141 0 0 7 0 0 8 14 0 5 48 53 0 0 0 0 62 53 161 276 As the groundwater monitoring program is further developed, well sites that are better suited to monitoring will be identified and located. Production and monitoring wells not currently in the program will be evaluated based on the monitoring program’s needs, with the ultimate objective of developing a uniform grid of well monitoring sites across the basin. Mapping of groundwater levels will be coordinated with the ongoing local geographic information system. GROUNDWATER MONITORING The acquisition and interpretation of water level data are essential parts of a groundwater monitoring program. Prior to developing these data, a monitoring program must include standard procedures for the acquisition of water level data. This will ensure that groundwater level data is not only consistent between sampling events, but that the data being collected is comparable between different field personnel. Without this, water level data collected during varying months and methods may not be comparable and, if used in a water-level flow analysis, could lead to erroneous conclusions. The following text outlines a proposed water level measurement protocol that will ensure data consistency between the various agencies’ field operations. It is understood that participating Association’s member agencies, as well as other entities, currently have groundwater monitoring programs underway. In recognition of these ongoing programs, the intent of this protocol is not to create additional field work, but to coordinate ongoing monitoring programs to ensure that field data collection efforts share common monitoring program techniques that will best represent depth ---PAGE BREAK--- C:\DOCUME~1\SLAMB\LOCALS~1\TEMP\GWMONPRO.DOC Revised June 12, 1998 Page 3 of 6 to water measured from the ground surface. Once this has been accomplished, depth to groundwater below ground surface can be converted to an elevation referenced to feet above or below mean sea level. Please see Attachments - C and - D, and - E (Figure 1) for the definition of terms, documentation of well-site field notes, and the diagram of a wellhead as they will be referred to through the remain- der of this document. General Preparation Prior to the measurement of static water levels, an inspection of the required equipment is necessary. Electric sounders should be checked for proper battery operation and all cables, regardless of type, should be calibrated quarterly using a graduated steel tape. Transducers also periodically require calibration. Most importantly, all wells, especially public or community supply wells, require standard procedures for field equipment decontamination to guard against the transfer of bacteria, oil lubricants and its by-products, and possible other trace organics, etc. to other wells. While no national standard exists for decontaminating well sampling field equipment, a reasonable guideline to follow would be to immerse or rinse the equipment thoroughly in a mixture of detergent (Alconox) and water or liquid chlorine bleach and water. A final rinse of the equipment with potable water is always required. Locating a Well Well location is important to mapping static water levels. At the present time, over six hundred wells within the groundwater basin have been located for mapping purposes using a global positioning satellite (GPS) system. Because of the success of GPS in measuring well locations, future mapping of wells will likely be located using GPS. Developing a vertical benchmark for the well site measuring point requires additional work in terms of a survey grade GPS system or the use of a traditional survey team to develop a vertical benchmark. In terms of well location accuracy, the following well location criteria should be used: horizontal 3 feet; vertical 0.1 foot. Well location coordinates should be mapped using a recognized coordinate system that allows conversion to other coordinate systems. The current coordinate system being used that facilitates sharing of data with the regional GIS system is: System: United States State Plane 1983 Zone: California Zone 3 0403 Datum: North American Datum - 83 (NAD83 - Western U.S.) Coordinate Units: Feet ---PAGE BREAK--- C:\DOCUME~1\SLAMB\LOCALS~1\TEMP\GWMONPRO.DOC Revised June 12, 1998 Page 4 of 6 Altitude Reference: Mean Sea Level In addition to developing coordinates for the well location site, each well site should have documentation or field notes that physically describe the well site as well as other detailed well information. Please refer to Attachment - D for a breakdown of documentation to be included in the well site’s field notes. Establishing a Permanent Measuring Point A permanent measuring point (MP) is important to ensure consistency and comparability of measured static water level data over time. In addition, the height between the MP and the land surface datum should be accounted for prior to reporting depth to water below ground surface to the regional groundwater mapping entity. Attachment - C provides a detailed definition for establishing a MP at a wellhead site. Static Water Level Measurement Considerations Static water level is the level at which water stands in a well or unconfined aquifer when no water is being removed from the aquifer either by pumping or free flow. It is generally expressed as the distance from the ground surface (or from a measuring point near the ground surface) to the water level in a well. For example, when the static water level in a well is 25 ft, it means that water stands 25 ft below the ground surface or measuring point (datum reference dependent) when there is no pumping. For the Association’s groundwater monitoring work, each participating agency is responsible for developing a measuring point, the distance between the MP and the land surface, if not the MP, and reporting the water level measurement as the SWL. For regional static water level monitoring there are a number of methods and instruments used to collect and record changes in groundwater levels. Several measurement techniques currently utilized by association members include electric sounding, air-line submergence method, and pressure transducers. Each technique requires different information necessary to collect water level data. Details regarding measurement techniques should be well understood by field personnel prior to use of the measurement equipment. Common to each technique, however, are several factors that must be observed in order to maximize the accuracy of the water level data. These factors include: • Ensure that the well being monitored for water level has not been in use for at least 24 hours prior to measuring event. • Annotate nearby pumping wells and approximate distance. • Ensure that the water level measurement is recorded to the tenth of a foot, and is repeatable. ---PAGE BREAK--- C:\DOCUME~1\SLAMB\LOCALS~1\TEMP\GWMONPRO.DOC Revised June 12, 1998 Page 5 of 6 • Account for any factors that may lead to measurement error, such as access port geometry, measuring point above or below ground surface, thick oil layers in oil lubricated wells, etc. Water Level Measurement Precision and Intervals Water level measurement accuracies vary between the different measurement methods. Despite the source of error associated with the different measurement devices, the objective is to measure water levels to the tenth of a foot. This level of accuracy will facilitate water level hydrograph analysis should specific needs arise. Monitoring seasonal fluctuations of water levels in the local groundwater basin require that static water levels should be measured in early spring (late February to mid-March) and again in late fall (late October to mid-November), with emphasis in the spring measurement. Reporting of Data Water level data should be reported as depth to water below ground surface in feet, accurate to a one-tenth of a foot. Attachments - A, and - B are sample spreadsheets that comprise the necessary information required to analyze and interpret water level data collected by field staff. The primary use of the association’s groundwater monitoring program is to monitor water level changes over time. The usual procedure is to plot the location of the wells on a base map, convert the depth-to-water measurements to elevations, plot the water level elevations on the base map, and then construct a groundwater elevation contour map. The direction of groundwater flow can be estimated by drawing groundwater flow lines perpendicular to the groundwater elevation contours. This relatively simple approach to estimating groundwater flow directions is suitable where wells are screened in the same zone and the flow of groundwater is predominantly horizontal. In terms of the associations groundwater monitoring program, these assumptions are generally consistent with regional flow within the basin. As detailed well construction information and geologic strata in which well screens are situated become available, these assumptions will be revised as needed. Water Level Interpretation Interpretation of water level data requires that information regarding the well construction specifications be made available for each well in the monitoring program. This information should be contained in the field notes for each well-site (Attachment - which should include: ---PAGE BREAK--- C:\DOCUME~1\SLAMB\LOCALS~1\TEMP\GWMONPRO.DOC Revised June 12, 1998 Page 6 of 6 • Production or Monitoring Well Installations 1. Geologic sequence. 2. Well construction features, especially total well depth, screen and gravel pack length, and geologic strata in which the screen is situated. 3. Depth and elevation of the top and bottom of the screen, or multiple screens, and gravel pack, if used. 4. Measuring point location and elevation y, • Water Level Data 1. Date and time of measurement. 2. Method used to obtain the measurement. 3. Other conditions in the area which might be affecting the water level data such as river stage, well pumping, storm events, irrigation, etc. Performing an analysis of the association’s regional monitoring program entails the evaluation of a large data set. To facilitate this work, computer statistical analysis and contouring will be used to map water-level depths and elevations. Critical review of this approach will be done manually and will require the above individual well construction information. Attachments: A - Sample Well Construction Information Data Table B - Sample Water-Level Data Table C - Groundwater Monitoring Protocol Definitions D - Well Facility Field Notes and Documentation E - Figure of Well Facility ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Appendix D Groundwater Monitoring Plan ---PAGE BREAK--- ---PAGE BREAK--- Groundwater Monitoring Plan Submitted to: Tuolumne and Stanislaus River Groundwater Basin Association Date: October 4, 2004 Project No: 040190 ---PAGE BREAK--- ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N Table of Contents 1 Introduction 1 1.1 Background 1 1.2 Goals and Objectives 2 2 Monitoring Network 4 2.1 Rationale 4 2.1.1 Surface Water 4 2.1.2 Groundwater 4 2.2 Monitoring Network 7 3 Monitoring and Reporting Frequency 10 3.1 Groundwater Production Monitoring 10 3.2 Semiannual Groundwater Level Monitoring 10 3.3 Annual Water Quality Monitoring 10 3.4 Annual Reporting 10 4 Project Organization and Responsibility 12 5 Monitoring 14 5.1 Preparation for Field Work 14 5.2 Meter Reading 14 5.3 PG&E Records 14 5.4 Quality Control 14 6 Semiannual Groundwater Level Monitoring 15 6.1 Preparation for Field Work 15 6.2 Calibration of Field Equipment 15 6.2.1 Electrical Conductivity Meter 16 6.2.2 Groundwater Level Sounder 16 6.3 Monitoring Procedures 16 6.3.1 Groundwater Level Measurements 16 6.3.2 Electrical Conductivity Measurement 17 6.4 Quality Control 17 6.5 Obtain DWR and USGS Records 17 7 Annual Groundwater Quality Monitoring 19 7.1 Preparation for Field Work 19 7.2 Sample Containers 20 7.3 Well Purging and Discharge 20 7.4 Sample Identification and Labeling 20 i ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N 7.5 Sample Collection 20 7.6 Sample Preservation and Storage 21 7.7 Record Keeping and Chain of Custody 21 7.8 Quality Control Samples 21 7.9 Quality Control 21 8 Laboratory Procedures and Reporting of Results 22 8.1 Record Keeping 22 8.2 Quality Assurance 22 8.3 Analytical Methods 23 8.4 Laboratory Reporting of Results 23 9 Recommendations 24 References Tables 1 Current Level of Monitoring Efforts 2 High Groundwater Monitoring Wells 3 Shallow Aquifer Monitoring Wells 4 Deep Aquifer Monitoring Wells 5 Forebay Aquifer Monitoring Wells 6 Mehrten Confined Aquifer Monitoring Wells 7 Modesto Irrigation District Top Producing Wells 8 Aquifer-River Connectedness Monitoring Wells 9 Surface Water Gaging Stations 10 Groundwater Monitoring Summary 11 Typical Production Meter Read Form 12 Semiannual Groundwater Level and Sampling Form 13 Purge Volume Estimation Sheet 14 Analytical Parameters, Test Methods, Holding Times, Sample Containers, Preservation and Approximate Detection Limits for Groundwater Samples 15 Example Chain of Custody Form Figures 1 General Location of Aquifers 2 Geologic Section A-A' 3 Geologic Section B-B' 4 Typical Well Sounding Location Detail 5 Groundwater Level and Quality Monitoring Network 6 Groundwater Production Monitoring Network ii ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N Appendices Wells in the Modesto Subbasin Providing Water Quality Data J:\040190 Stanislaus & Tuolumne Rivers Monitoring Plan\GW Monitoring Plan.doc iii ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N 1 Introduction This Groundwater Monitoring Plan (GMP), prepared for the Stanislaus and Tuolumne Rivers Groundwater Basin Association (Association), provides guidance for the selection of wells for the monitoring network as well as groundwater monitoring and sampling procedures to reduce uncertainties in the monitoring data. This GMP is a starting point for the Association to modify as additional information becomes available to supplement the existing network. The Association’s groundwater monitoring network and data acquisition will provide basic information needed to manage the groundwater resources of the Modesto groundwater subbasin. 1.1 Background Groundwater is present in the consolidated and unconsolidated sediments. There are two principal aquifers, separated by the Corcoran clay, in the western portions of the study area and one aquifer east of the Corcoran clay. Figures 1 through 3 show the location of the aquifer in both plan and profile. The aquifers are defined as: ƒ The shallow aquifer, generally west of Highway 99, above the Corcoran clay. High groundwater levels sometimes cause problems for plants and may be related to a shallow aquitard (clay or hardpan). ƒ The deep aquifer, also located west of Highway 99, below the Corcoran clay and below the shallow aquifer. ƒ The forebay aquifers, east of the Corcoran clay. They merge with the shallow and confined aquifers west of Highway 99. Most of the Oakdale Irrigation District overlies the forebay aquifers. ƒ The confined Mehrten aquifers, which underlie all of these aquifers, are exposed on the ground surface in the eastern portion of the area and dip westward beneath the subbasin. Each of the aquifers has water quality problems, as summarized below: ƒ Shallow aquifer – localized total dissolved solids (TDS), nitrate, dibromochloropropane (DBCP) and volatile organic compounds (VOCs) (western part near Modesto subasin) ƒ Deep aquifer – localized TDS and VOCs (City of Modesto area) 1 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N ƒ Forebay aquifers – localized TDS, DBCP, and uranium (western part near the City of Modesto and Empire) ƒ Mehrten confined aquifer - potentially sodium, chloride, and TDS. For the most part, these problems are localized and affect only portions of the subbasin. In general, the water north of the Modesto subbasin, around the City of Oakdale and Riverbank, is of good quality. The City of Modesto has abandoned some of its wells because of water quality issues. High groundwater levels with high levels of TDS are present in the western portion of the subbasin. Iron and manganese are present in all four aquifers but are typically related to reduced, oxidized soils. At this time, arsenic does not appear to be a water quality issue, based on testing of the municipal supply wells. Groundwater levels in the Modesto subbasin have been measured in about 230 wells by the Department of Water Resources (DWR) and its cooperatives. The wells used for monitoring may be in different aquifers and at times have long screen intervals that make an interpretation of groundwater flow directions and water quality difficult. Appendix A contains a list of these wells. Some member agencies may be reporting data to DWR and are included in this list. The U.S. Geological Survey (USGS) has monitored 17 wells in the area for the National Water Quality Assessment Program. It has also constructed or plans to construct additional monitoring wells in the City of Modesto to define hydraulic characteristics, water levels, and water quality in the shallow and confined aquifers. Appendix A contains a list of these wells. The University of California-Davis (UC-Davis) with grant funding has constructed several monitoring wells to assess nitrates and nutrient management near dairies. The Association’s members, to some varying extents, monitor groundwater production, levels, and quality. Table 1 summarizes the current level of monitoring through the member agencies. Other groundwater monitoring conducted in the basin assesses releases of hazardous materials to the environment. These wells are typically near metropolitan areas and the resulting data are provided to the Regional Water Quality Control Board These wells are extremely useful because they typically monitor the first water encountered, which can be correlated with surface water gaging stations to evaluate the aquifer connectedness. 1.2 Goals and Objectives The goals of this GMP are to develop a plan to track and assess the potential effects from the implementation of basin management objectives (BMOs) and to manage the groundwater in 2 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N the basin to protect the quantity and quality of the groundwater within the subbasin. The GMP goals are to: ƒ Track groundwater levels to identify natural recharge areas, flow directions that govern the movement of contaminants, and potential areas where subsidence may occur. ƒ Develop a better understanding of the spatial variability (both horizontal and vertical) of groundwater quality to control degradation of water quality. ƒ Track groundwater production to develop a water balance. ƒ Monitor changes in water quality over time that indicate impacts to the aquifers. ƒ Obtain consistent and high quality data. ƒ Disseminate the information to the Association members. The objectives of this GMP are to develop a groundwater monitoring network capable of collecting hydraulic measurements that will be used to characterize groundwater occurrence, flow direction, water quality, and recharge areas. Data on groundwater levels, flow directions, and water quality must be gathered from each of the identified aquifers. This GMP describes a preliminary groundwater monitoring network and an approach to assess, justify, and select additional monitoring wells to provide information to address specific issues and BMOs within the subbasin. This plan also designates a responsible party/agency (an Association member) that will coordinate activities and archive, compile, disseminate, and analyze the data. Personnel from member agencies will implement the plan. 3 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N 2 Monitoring Network The following sections describe the rationale for the selection of monitoring points to be included in the monitoring network. Because surface water and groundwater may interact, the monitoring network consists of both groundwater and surface water monitoring through activities of the Association members and other governmental agencies. 2.1 Rationale The Association’s goals are to manage groundwater resources for the long-term sustainability of the resource. Key issues in the subbasin are: ƒ High groundwater in western portion of the subbasin ƒ Groundwater quality ƒ Groundwater recharge and discharge areas ƒ Changes in groundwater levels that affect groundwater in storage The following sections describe the rationale for selecting the monitoring network well sites. 2.1.1 Surface Water The aquifers beneath the subbasin may seasonally discharge to or receive recharge from the Toulumne, Stanislaus and San Joaquin Rivers. Data regarding the stage height of water in these rivers should be obtained from gaging stations and compared to groundwater levels to assess the recharge-discharge relationships. Water quality data should also be obtained to assess the quality of water that may be entering the aquifers in recharge areas. Sources of data include the USGS and DWR websites. The gaging data may also be used to assess the amount of water gained or lost to aquifers by discharge to or recharge by the rivers. 2.1.2 Groundwater Groundwater monitoring wells should be selected to provide regional coverage that can be economically accomplished yet provide high quality, reliable data. These selections will be based on the purpose for which the well will be used and the issues to be defined. The location and spacing of the wells varies, dependent upon the issue. ƒ Groundwater levels and flow directions were selected when they have a rough triangular spacing. The triangular spacing allows the projection of a planar surface, 4 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N thus allowing the development of groundwater contours and their orientation. The contours show recharge areas, discharge areas, and the groundwater flow path. ƒ Groundwater quality monitoring well locations were generally selected with one up- gradient well (to assess the quality of water coming into the area) and a minimum of three down-gradient wells (to detect the horizontal extent of the contaminant). Additional wells are needed to assess the vertical extent (when contaminants may move into different aquifers). ƒ Groundwater discharge or recharge areas were selected, again with a rough triangular spacing, to project the plane into the discharge area. The elevation of the water surface elevation in the discharge or recharge area also provides confirming evidence of the connection of the groundwater surface to the surface water. At least some of these monitoring wells need to be located near the gaging station. ƒ Wells selected to detect groundwater movement between aquifers are typically closely spaced, but screened at different depths. ƒ Wells selected to detect changes in groundwater storage may be screened in multiple aquifers and scattered throughout the basin. These wells are used to account for the major portion of groundwater that is extracted from within the basin. ƒ Wells selected to detect groundwater inflow from outside of the basin generally consist of multiple clusters of three wells with a triangular spacing in the adjacent subbasins, just outside the Modesto groundwater subbasin boundaries. After defining the purpose for monitoring and general areas, a detailed evaluation of potential wells needs to be conducted. Wells selected for monitoring should have: ƒ A well log that describes the well construction details and a description of the sediments encountered ƒ A detailed description of the well’s location ƒ A relatively short screen interval in only one aquifer ƒ A sanitary seal to prevent surface water from entering the well Although the most desirable wells to be included in the monitoring network are wells with short screen intervals completed within a specified aquifer, some wells with longer screen intervals may need to be initially included in the network when there are no wells with short screen intervals to complete the regional interpretation and tracking of groundwater level and water quality. Wells with long screen intervals may also be designated for monitoring because their long historic records provide valuable trending information about the general status of the aquifers. Data obtained from the longer screen wells usually represent an 5 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N aggregate of water quality from two or more aquifers. These wells with longer screen intervals should be replaced with wells with shorter screen intervals if warranted, based on a review and interpretation of the monitoring data. For purposes of this monitoring plan, the following definitions of the well to be used by aquifers are: ƒ High groundwater monitoring wells – wells that are screened to or near the ground surface and overlie the Corcoran clay. ƒ Shallow aquifer monitoring wells – wells that are screened between 30 to 150 feet below ground surface (bgs) in the area where the Corcoran clay is present. ƒ Deep aquifer monitoring wells – wells that are screened 250 feet or more bgs in the area where the Corcoran clay is present. ƒ Forebay aquifer monitoring wells – wells that may be screened as shallow as 30 feet but toward the west, increase in depth to as deep as 400 feet bgs. ƒ Confined Mehrten aquifer monitoring wells- wells that may be screened from as shallow as 30 feet up to 800 feet bgs and will generally increase in depth toward the west. Upon selection of a well to be potentially included in the monitoring network, a site visit will be necessary to assess the field conditions. The conditions necessary for a well to be used in the network include: ƒ A well owner who will allow access for monitoring ƒ All-weather access ƒ Access through the pump or well casing for water level sounders ƒ An assessment to determine if lubrication oil from a turbine pump has accumulated in the well or if there are obstructions in the well that would prevent obtaining repeat and reliable measurements ƒ A pump and electrical service, if the well is to be used for water quality monitoring During the site visit, the investigator should sketch the location and access to the well and the location for measuring water levels and record any special contact information to perform the monitoring. This will ensure consistent monitoring even though monitoring staff may change. Figure 3 shows a typical well sounding location detail. 6 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N Not all wells have to be monitored by the Association members to be included in the network. Potential sources of other monitoring data may include: ƒ DWR monitoring records for about 230 wells (including cooperators) in the Modesto subbasin and an undetermined number in adjacent subbasins. Appendix A lists the wells reported by DWR. Some may be monitored by member agencies. ƒ The USGS monitoring wells near the City of Modesto. ƒ The 15 wells included in the USGS National Water Quality Assessment Program. ƒ UC-Davis and its farm advisory special studies for nitrate and nutrient management near dairies. ƒ Reports submitted to the Regional Water Quality Control Board for releases of hazardous materials to the environment that are affecting groundwater and shallow groundwater levels. These sources have not been assessed for inclusion of additional monitoring wells into this GMP. The Association should assess these potential sources and select wells that would improve this GMP by filling in gaps in the spacing of the network or wells that can provide specific localized information. 2.2 Monitoring Network The proposed groundwater monitoring network consists of gaging stations and wells owned by Association members, private parties, and other governmental bodies. Combined, the network will provide the necessary data to assess groundwater conditions beneath the subbasin. Monitoring will not be performed by any one group, but the data will collected and analyzed by the Association. The monitoring network described below should not be considered as a final network but will provide initial representation of the groundwater conditions within the subbasin. The wells included in this preliminary network were those wells owned or monitored by Association members. An evaluation of wells monitored by other parties has not been included. Additional wells, selected using the rationale presented above, should be added to monitor specific issues. Table 2 identifies groundwater wells that were selected to assess high groundwater conditions (possibly water that is perched on a shallow clay layer) in the western portion of the subbasin. These wells have screen intervals that extend to or near the ground surface. The table also provides well construction details. Figure 4 shows their locations. Table 3 identifies the wells that were selected to assess groundwater levels and water quality in the shallow aquifer, above the Corcoran clay. Data from these wells will also assist in the 7 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N evaluation of the groundwater discharges to the rivers that must be maintained to prevent salt accumulations in the basin. Figure 4 shows their locations. Table 4 identifies the wells that were selected to assess groundwater levels and water quality in the deep aquifer, below the Corcoran clay. The list is short because all of the wells are screened in both the shallow and confined aquifers except for one well south of the Toulumne River (City of Modesto well #19). Replacement wells will need to be found for the long screened wells. Figure 4 shows their locations. These wells should be reevaluated upon the USGS’s release of a report later this year that provides detailed stratigraphy in the subbasin. We understand the USGS plans to construct a new set of wells to monitor this aquifer and to assess vertical gradients. These wells should be added to this list. Table 5 identifies those wells that were selected to assess groundwater levels and water quality in the forebay aquifers. Figure 4 shows their locations. Most of these wells have relatively long screen intervals. Some of the wells on this list have long screen intervals that cross both the forebay and confined Mehrten aquifers but are being used to provide regional coverage. As soon as practical, these wells should be replaced with wells that monitor only the forebay. Table 6 identifies those wells in the eastern portion of the subbasin that monitor only the confined Mehrten aquifers. Figure 4 shows their locations. Groundwater in these wells may or may not be connected to the aquifers in the forebay. Some of the wells on this list have long screen intervals that cross both the forebay and confined Mehrten aquifers but are being used to provide regional coverage. As soon as practical, these wells should be replaced with wells that monitor only the confined aquifer. Table 7 identifies the top ten producing wells in the Modesto Irrigation District service area that could affect the quality of water supplied to agricultural users and may cause problems under the Agriculture Waiver or various Total Maximum Daily Loads Table 8 could potentially be used to identify those wells that could be used to better understand the aquifer-to-river interconnectedness. Wells for this task probably will be obtained from the Additional tables may be created and attached to provide information regarding specific BMOs such as the extent of arsenic, nitrate, uranium, and DBCP. In summary, the groundwater monitoring network will consist of 93 wells (a combination of Association and DWR monitoring wells) designated for groundwater level and quality monitoring. The number of wells by aquifer is summarized below: ƒ High groundwater aquifer (perched aquifer): 21 monitoring wells ƒ Shallow aquifer: 16 monitoring wells 8 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N ƒ Deep aquifer: 6 monitoring wells ƒ Forebay aquifers: 39 monitoring wells Monitoring wells specifically designated to track specific BMOs may add additional wells to this total. All municipal and irrigation wells owned by the Association members are equipped with totalizing flowmeters or power meters and will be included in the monitoring network to measure groundwater production. Six surface water gaging stations along the Toulumne and Stanislaus Rivers continuously monitor the height of water in the rivers. The spacing of the gaging stations on the San Joaquin River was not favorable to assist in evaluating discharge-recharge relationships. Table 9 lists the gaging stations to be included in the monitoring network. The URL for the USGS website is also shown on the table. Figure 4 shows the gaging station locations. 9 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N 3 Monitoring and Reporting Frequency The following sections describe the frequency for monitoring and reporting. Subsequent sections provide a description of the work to be accomplished during each of the designated monitoring periods. Table 10 lists the wells and monitoring types and frequencies. 3.1 Groundwater Production Monitoring Groundwater production from all Association member wells will be measured The measurements should be made within with a two-week period, if possible. 3.2 Semiannual Groundwater Level Monitoring Groundwater levels and electrical conductivity from all designated monitoring wells listed in Table 10 shall be measured in the spring and fall (semiannually). Spring is generally considered to be February through April, prior to the start of irrigation. Fall is generally considered to be October through November, after the irrigation season but prior to the start of the winter rains. If possible, Association member agency personnel should make groundwater level measurements within a two-week period and, if possible, coordinate groundwater level monitoring with DWR and its semiannual measurements. groundwater level measurements should be obtained for those wells to assess aquifer-to- surface water interaction, listed in Table 8. Groundwater levels from the DWR-monitored wells listed in Table 10 (name given as a state well numbers) and river height data from the surface water gaging stations listed in Table 9 should be downloaded from the Internet semiannually and archived. 3.3 Annual Water Quality Monitoring In addition to the and semiannual monitoring requirements, water quality samples from all monitoring wells listed in Table 10 shall be collected each fall. This work can be accomplished concurrently with the work described in Section 3.2. 3.4 Annual Reporting The Association will prepare an annual groundwater monitoring report to summarize the findings of the groundwater level, production, quality, and gaging station data. The report should include an interpretation of the data (including but not limited to groundwater flow directions and the relationship of pumping to water quality and water levels), a discussion of any significant changes from the last reporting period, and groundwater management 10 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N recommendations. Recommendations to improve the monitoring network should also be included. Groundwater contours for each aquifer will be developed, using only those wells that are screened only within the aquifer. The contours can then be used to evaluate recharge and discharge areas, changes in groundwater storage, and the need for additional monitoring wells. 11 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N 4 Project Organization and Responsibility The Association will plan, organize, collect, and archive the groundwater monitoring and sampling data. The following is a summary of the monitoring, sampling, and reporting responsibilities under this GMP. The Association is responsible for: ƒ Coordinating monitoring and sampling schedules with member agencies so that production data and groundwater level measurements occur within the same two- week periods ƒ Archiving sampling and monitoring results ƒ Overseeing quality assurance/quality control (QA/QC) sampling and monitoring methods and procedures ƒ Revising this GMP annually, as necessary ƒ Preparing an annual summary report for distribution to the Association’s members for discussion and development of management options Each member agency will be responsible for: ƒ Scheduling equipment and supplies needed for sampling and monitoring ƒ Measuring and recording groundwater levels ƒ Measuring and recording electric conductivity measurements ƒ Arranging with the laboratory for sample bottles and analysis ƒ Collecting representative groundwater samples ƒ Overseeing quality assurance/quality control (QA/QC) sampling and monitoring methods and procedures The designated contact for making decisions regarding the Association’s GMP is District State-certified laboratories selected by the Association members will be responsible for sample analysis quality control and assurance. The laboratory(s) shall notify the members 12 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N immediately if samples have been compromised during shipment or handling or if the requested analyses cannot be conducted within the designated holding times. 13 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N 5 Monitoring Groundwater production from all Association wells will be measured The measurements shall be made within the same week. 5.1 Preparation for Field Work Field personnel shall prepare for field work by obtaining the following equipment: ƒ A copy of Table 11 or other in-house forms to record the field measurements ƒ Figure 5 showing the location of the wells ƒ Clipboard and ballpoint pen 5.2 Meter Reading Some of the irrigation and municipal wells have been equipped with totalizing flowmeters. The totalizer reading shall be recorded onto Table 11 to provide consistency in the measurements. Field measurements should include all numbers displayed on the meter, including zeros, which provides a level of quality control that the meter was read correctly. Any issues associated with the meter, including ability to read the meter or suggested maintenance, shall also be documented. 5.3 PG&E Records Groundwater production at some wells is estimated from PG&E billings that list the kilowatt- hours used by the pumps on the wells. To accurately estimate the production totals, a pump efficiency test should be performed annually. The billings from PG&E need to be archived 5.4 Quality Control After recording the totalizer readings, the member agencies shall enter the data into an electronic accounting form that will automatically subtract the measurement from the previous month’s reading. The agency managers should review the production data for accuracy within five days of obtaining the initial measurement. Should a measurement appear suspicious, a confirmation reading shall be obtained. Agency personnel should be prepared to maintain the flowmeters. 14 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N 6 Semiannual Groundwater Level Monitoring Groundwater levels and electrical conductivity at all designated monitoring wells shall be measured semiannually, typically in the spring and fall. If possible, groundwater level measurements should be taken within a two-week period. If possible, groundwater level monitoring should be coordinated with DWR. Groundwater level data from the DWR and gaging station data from the USGS should be downloaded from the Internet. 6.1 Preparation for Field Work Prior to collecting semiannual field measurements and before going to the field, the sampling personnel will assemble the following equipment and supplies: ƒ Copy of Table 12, Semiannual Groundwater Level and Sampling Form ƒ Copy of Table 13, Purge Volume Calculations ƒ Copies of Figure 3, Well Sounding Location Details, and Figure 4, Groundwater Level and Quality Monitoring Network ƒ Portable electrical conductivity meter, calibration standards, and manufacturer’s calibration instructions ƒ Electrical water level sounder ƒ Watch or stopwatch ƒ Ballpoint pen and clipboard ƒ Paper towels ƒ Bleach ƒ Spray bottles ƒ Distilled water 6.2 Calibration of Field Equipment Prior to collecting semiannual field measurements and before going to the field, sampling personnel shall clean, maintain, and test the water level sounder and calibrate the electrical conductivity meter, using appropriate standards. 15 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N 6.2.1 Electrical Conductivity Meter The frequency and nature of the electrical conductivity meter calibration shall be consistent with the manufacturer’s recommendations. At a minimum, the meter shall be calibrated every day and when significant changes in climatic conditions occur when the air temperature changes by more than 30°F). The meter type, its manufacturer, model and identification numbers, and calibration information shall be documented in the member agencies’ files. 6.2.2 Groundwater Level Sounder During use of a water level sounder, it is possible for the cable to stretch or to shorten because of tangles and obstructions in wells. Annually, the water level sounder shall be laid out and compared with a steel tape and the results documented. When calibration measurements show that the measurements are greater than 0.10 feet off in 100 feet, the cable shall be replaced. 6.3 Monitoring Procedures The following procedures shall be used to measure the depth to water and electrical conductivity at each designated monitoring well. Water levels and electrical conductivity measurements will be collected semiannually to assess the groundwater flow direction and quality and to detect trends that can lead to improved management of the groundwater resources. 6.3.1 Groundwater Level Measurements Each well has been assigned a unique identification number and a common name. The numbers and names for each well are listed in Table 10. Table 11, Semiannual Groundwater Level and Sampling Form, should be used to record all groundwater level measurements during the semiannual monitoring. Prior to obtaining the water level measurement at each well and between each well site, the electric sounder cable shall be rinsed in a solution of sodium hypochlorite (liquid bleach) and distilled water. The solution shall consist of bleach and distilled water in a one-tablespoon- to-one-quart ratio (a concentration of about 200 parts per million chlorine is desirable). The sounder shall then be rinsed thoroughly three times with distilled water and allowed to air- dry. Thorough cleaning of equipment is necessary to avoid any possibility of cross- contamination and the transport of bacteria between wells. Prior to purging and sampling, the depth to static groundwater level will be obtained at each well, using an electric water level sounder with a cable graduated in increments of 0.01 foot. To obtain a depth to water measurement, the electric sounder cable will be lowered slowly into the well through the access port until the sounder indicates submergence by either a beeping sound or light, depending on the type of signal installed for that particular model. At 16 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N this point, the sampling personnel will note the depth to water (to the nearest 0.01 foot) from the reference point. The depth shall be confirmed by lifting the sounder above the water surface by about 2 to 3 feet and then remeasuring the depth to water. If the depth remains constant, the depth-to-water shall be recorded on Table 12, along with the time and date of the measurement. If the depth changes, the sampling personnel shall indicate that on the form, the variable nature of the measurement, and its possible cause bouncing, recovering water levels). 6.3.2 Electrical Conductivity Measurement A representative sample of the groundwater must be obtained from the well. For purposes of this monitoring plan, a “representative” sample can be collected after at least three well volumes have been pumped from the well. The purge volume and time will be calculated using data from Table 10 and the calculation sheet shown on Table 12. These calculations can be saved and entered into another table that provides approximate purge times. This new spreadsheet will be a quick guide for sampling personnel to use in lieu of having to recalculate the purge time each time the well is sampled. Several different types of electrical conductivity meters may be used by the sampling personnel. Some have a sample cup built into the unit, while others have a probe that requires that the sample be collected in a separate container. Sampling personnel will collect water from as close to the well as possible and place the sample in the electrical conductivity meter sample cup or container. The sample shall be poured into the meter sample cup or container, then discharged and replaced three times before taking a measurement. The measurement shall be recorded on Table 12 and the sampling location noted hose bib, end of discharge pipe, etc.). After the measurement has been taken, the electrical conductivity meter sample cup or probe and container shall be rinsed at least three times with distilled water to maintain the equipment and to prevent false readings in subsequent wells. 6.4 Quality Control After field personnel have completed their work, the member agencies shall enter the data into an electronic spreadsheet or database. The agencies’ managers shall review the groundwater level and electrical conductivity measurements for accuracy within five days of obtaining the measurements. Should a measurement appear suspicious, a confirmation reading shall be obtained. 6.5 Obtain DWR and USGS Records Semiannually, Association personnel shall obtain river gaging data for the six surface water gaging stations listed on Table 9 from the Internet addresses also listed in Table 9. A hard 17 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N copy and an electronic copy of the files shall be made. Should the data be absent, either the USGS or the DWR should be contacted to determine the reason and this conversation documented. The hard copy and/or documentation shall be placed in the project files. After the wells monitored by DWR have been evaluated and if they are selected to be included in the monitoring network, the water level measurements for these wells can be obtained from an Internet search. 18 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N 7 Annual Groundwater Quality Monitoring In the fall of each year, water quality samples will be collected from all wells listed on Table 10 and sent to a laboratory for a more extensive analysis of the water chemistry. These analyses will provide an indication of the source of the water, changes over time, and potential mixing between aquifers. The results will be used to assess the effects of groundwater management actions. The work described below will be performed concurrently with work described in Section 6, Semiannual Groundwater Level Monitoring. 7.1 Preparation for Field Work Prior to water quality sampling, designated sampling personnel shall notify the laboratory when sampling is scheduled, list the sample analysis parameters, and request sample bottles. A copy of Table 14 and Section 8.0 should be faxed to the laboratory to confirm the analytical methods and analytical quality control and assurance requirements. The laboratory should also be provided with the number of wells to be sampled as identified in Table 10 so that they can provide the appropriate number of sample bottles. The laboratory should be requested to deliver these sample containers in clean ice chests to the location chosen by the sampling personnel at least two days before the sampling begins. Upon receipt of the sample bottles, sampling personnel shall inventory the bottles to ensure that an adequate number and proper types of bottles have been provided. The sampling personnel will assemble the following field forms, sampling equipment, and supplies: ƒ Copy of Table 10 ƒ Copy of Table 13, Purge Volumes Calculations ƒ Copy of Table 15, Example Chain-of-Custody, or obtain one from the laboratory ƒ Sample bottles and ice chest from the laboratory ƒ Ballpoint pen and waterproof marking pen ƒ Safety glasses or goggles ƒ Latex or nitrile gloves ƒ Paper towels ƒ Ice 19 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N 7.2 Sample Containers Sample containers will be prepared by the laboratory with both preservative and container type in accordance with the required analysis as presented in Table 14. The containers shall be laboratory-cleaned prior to use, based on the analytes of interest, in accordance with the latest edition of the U.S. Environmental Protection Agency (USEPA), Standard Methods for Examination of Water and Wastewater. Sample containers must be stored in a manner that prevents the accumulation of dust or other contaminants. Prior to shipment to the sampling personnel, the laboratory will be responsible for verifying the cleanliness and integrity of the sample containers, pursuant to its sample container quality assurance and quality control procedures. Each container will have a preprinted identification label that clearly shows the constituent(s) to be analyzed. A laboratory sample number will be assigned by the laboratory upon delivery of the sample(s) to the laboratory for proper identification and tracking. 7.3 Well Purging and Discharge The water quality samples shall be collected after purging the well as described in Section 6.0. The well purge volumes shall be calculated as shown on Table 13 to exchange three well volumes before collecting the sample. 7.4 Sample Identification and Labeling Each well has been assigned a unique identification number as listed in Table 10. This number shall be marked on each sample bottle. All sample containers will be pre-labeled, to the extent possible, prior to each sampling event. Sample containers provided by laboratory will contain waterproof labels that will show the analyte and laboratory identification number. To the extent possible, the designated sampling personnel will inscribe on the label the sample identification, sampler’s name or initials, and date, under dry conditions, using a waterproof marker pen during purging of each well. Immediately before collecting the water sample, sampling personnel will inscribe on the sample bottle label the time the sample was collected. 7.5 Sample Collection Groundwater samples shall be collected from the well discharge water as close to the pump as possible. The sampling location should be the same as that used to collect the electrical conductivity measurements. Sampling personnel will be trained in the use of and exercise care during the handling of acid-preserved sample containers to minimize spillage, damage, and/or injury to the sampler(s) or the field equipment. In addition to latex or nitrile sampling gloves, the designated sampling personnel should wear safety glasses or goggles to minimize potential eye injury. 20 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N Designated sampling personnel will use “clean sampling techniques” to minimize potential contamination of water samples. Prior to the collection of samples, sampling personnel will rinse their hands and don sterilized latex or nitrile gloves. Sample containers and lids will not touch the ground, the sampling personnel’s clothing, or any other potential sources of contamination. Sample container lids will not be removed from a particular container until that container is to be filled. Sample containers shall be rinsed three times with the sample prior to collection unless the container contains a preservative. The sample container shall be filled to the top of the rim to minimize air space between the liquid level and the lid. The lid shall be tightened securely to the container immediately after sample collection is completed. 7.6 Sample Preservation and Storage Chemical preservatives and refrigeration shall be used to maintain sample integrity prior to analysis. Immediately after the sample has been collected, it shall be placed in a clean ice chest containing commercially prepared ice packs to maintain the temperature in the ice chest between 2°C and 6°C until the samples have been delivered to the laboratory. The ice packs will be double-bagged to prevent ice-melt water from touching the sample containers. Samples must be returned to the laboratory within 22 hours of sampling to meet analytical holding time requirements. 7.7 Record Keeping and Chain of Custody Sampling personnel will maintain Table 13 field forms showing the dates and times of sample collections. A chain-of-custody form indicating the sampling site, sampler’s name, date and time sampled, and any special observations shall be filled out by sampling personnel and placed in a sealable plastic bag with the sample(s) in the ice chest. The samples shall remain in the control and custody of a designated sampling team member at all times. A chain-of-custody form is presented in Table 15. When sampling personnel deliver the samples to the laboratory, the laboratory will sign for custody of the samples and provide a copy of the completed chain-of-custody form to the sampling personnel. 7.8 Quality Control Samples This sampling plan does not require collection of any field quality control samples because the parameters being collected are stable and no volatile samples are being collected. 7.9 Quality Control Within one day after field personnel have completed their work, the member agencies’ managers shall review Tables 13 and 15 to assess if all of the necessary field information has been documented and that adequate purge times were allowed before collecting the samples. Upon receipt of the laboratory analyses, the managers shall compare the results to historic data and identify any anomalous results, and if present, notify the laboratory to confirm the measurement. 21 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N 8 Laboratory Procedures and Reporting of Results The laboratory will select the appropriate sampling containers for the chemical constituents to be analyzed (Table 14) and will meet its internal quality control requirements for duplicate and spike analyses. 8.1 Record Keeping The laboratory will keep appropriate records to indicate the following for each sample: ƒ Date, location, and time of sampling ƒ Name(s) of individuals who performed the water sampling ƒ Date and time that samples were received by the laboratory ƒ Temperature of the ice chest interior upon receipt by the laboratory ƒ Date(s) that the analyses were made ƒ Analytical testing methods used and detection limits ƒ Analytical results 8.2 Quality Assurance The laboratory will adhere to a quality assurance program that follows accepted USEPA protocols. It must maintain state certification for drinking water analyses and perform routine analyses including known, commercially available standards. These QA/QC procedures are to be described in the laboratory’s Quality Assurance and Quality Control Manual. The laboratory shall submit to the agencies a report that describes the quality assurance results, spike recovery, any problems discovered or identified for the analytical period covered at the laboratory, and any subcontract laboratories used. All must be certified or approved to perform the required analyses or have the necessary training. A copy of the certification and training records shall be available to the agencies upon request. 22 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N 8.3 Analytical Methods The laboratory (including any subcontractor laboratory it may use) must use accepted laboratory analytical methods as specified in Table 14 where appropriate. USEPA limits on holding times must also be observed. The laboratory (and any subcontractor laboratory it may use) must be certified by the State of California for the analytical methods used. Written test procedures including quality control practices shall be followed for each analytical method used to measure the parameters listed in Table 14. Detection limits must be equal to or less than the detection limits for reporting purposes or State Action Levels for drinking water set forth by the California Department of Health Services. Table 14 lists the detection limits for each monitoring parameter. 8.4 Laboratory Reporting of Results The laboratory will use a standard reporting form for all water sources listing date(s) of analysis, name(s) of person who analyzed the samples, analytical method(s) used, name of parameter analyzed, detection limit, units of measurement, and results of the analysis. Any analytical result of less than detectable shall be reported as less than the method detection limit. All inorganic constituents analyzed shall be designated as the ion or as calcium carbonate. The laboratory shall submit to the agencies paper and electronic copies of laboratory results and written reports within 30 calendar days of receipt of the samples. Unusual spikes, questionable results, or detection of chemicals not on the list of required constituents will be reported to the designated sampling personnel. The laboratory will maintain records that show the calibration of equipment used in the various analyses for at least three years from the date the analytical reports were submitted to the designated sampling personnel. 23 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N 9 Recommendations A shallow clay layer may be present in the western portion of the subbasin but it is not well defined. This clay layer may be causing high groundwater conditions and may also be limiting river and aquifer interaction. A profile of the sediments needs to be developed to define the geologic controlling conditions as they relate to the high groundwater. The database developed by the USGS should be queried to define the presence and extent of this clay layer. The currently designated monitoring well network for groundwater level, quality, and production was limited to readily available data supplied to us by Modesto Irrigation District, Oakdale Irrigation District, the City of Oakdale, the City of Modesto, and the City of Riverbank. Further development of the monitoring network should be performed by reviewing well logs from DWR, USGS, and UC-Davis and applying the criteria given in Section 2.1.2 to select valid wells. Special interest areas will need focused monitoring. Issues such as DBCP, nitrate, arsenic, and reservoir underflow may need specially designated monitoring wells. It is recommended that a special interest area be considered to evaluate groundwater recharge and discharge areas to the rivers. The current understanding is based on wells with screens starting about 100 feet bgs. Shallow monitoring wells with screens starting where water is first encountered may show different conditions. This detail of information is probably best evaluated through records. If proven to be of value, these wells should be incorporated into the monitoring network and funding obtained for additional wells. Elevations at each of the monitoring wells listed in Table 10 should be surveyed to the nearest 0.01 foot to allow conversions of depth to water to elevations. These elevations can be used to detect subtle differences in groundwater heads between aquifers. The heads will demonstrate whether the different aquifers are connected and will also allow an assessment of the vertical movement of groundwater in the area. Groundwater contours showing the horizontal flow direction of the groundwater can also be developed using the elevations. Additional testing of the agricultural water supply wells and drainage wells should be performed to fully assess the distribution and concentrations of arsenic, uranium, and DBCP in the area. Upon completion of the first water quality sampling, the data should be evaluated and the list of annual groundwater sampling wells revised. The member agencies have limited data on historic groundwater level, water quality, production, and surface water level. With the implementation of this GMP, data will 24 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N accumulate quickly and must be easily retrievable. A data management system should be instituted to archive groundwater level, water quality, groundwater production, and river gage data. Available historic data should be entered to initially populate the database. The database should be capable of producing standard tables and graphics that can aid in the interpretation and presentation of trends in both groundwater level and quality. The development of this GMP should evolve and change as new information and wells become available. As the program evolves, additional wells may be added and other wells may be removed. Preferably all monitoring wells should have well construction details. The figures, tables, and text in this GMP should be updated annually to reflect the changes implemented through the member agencies’ groundwater management actions. 25 ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N Figures 26 ---PAGE BREAK--- ---PAGE BREAK--- D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D CITY OF MODESTO OAKDALE RIVERBANK STANISLAUS CO. TUOLUMNE CO. SAN JOAQUIN CO. MERCED CO. Tuo lum ne R iver Sta n isla us Ri v er Sa n J oa q u i n Ri ver Forebay Aquifers Shallow Aquifer A A' B' B Modesto Reservoir £ ¤ 132 £ ¤ 120 £ ¤ 33 £ ¤ 99 £ ¤ 5 £ ¤ 59 £ ¤ 108 £ ¤ 219 £ ¤ 49 £ ¤ 165 £ ¤ 120 £ ¤ 5 APRIL 2005 FIGURE 1 INTEGRATED REGIONAL GROUNDWATER MANAGEMENT PLAN FOR THE MODESTO BASIN 04-14-05 S:/GIS/Projects/040190/Figure4-6.mxd 4 0 4 2 Miles¥ LEGEND Modesto Groundwater Subbasin Cities SOURCES: City of Modesto, City of Oakdale, City of Riverbank, CA Dept of Water Resources Groundwater Basins, 2002, California Spatial Library. Eastern Extent Cocoran Clay, Burrow 2004 General Location of Aquifers Approximate Aquifer Extent Surface Exposure of Mehrten Formation D MID Wells ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- FIGURE 4 SEPTEMBER 2004 TYPICAL WELL SOUNDING LOCATION DETAIL Claus Road Well DRAWN BY: DATE: 06-11-04 S:/GIS/Projects/040190/Corel/SoundingDetail.cdr ---PAGE BREAK--- ---PAGE BREAK--- "J "J "J "J G "J "J "J "J "J !A !A !A "J !A !A !A !A !A !A !A G hg hg hg !A hg G hg !A hg hg hg hg hg !A !A !A !A !A !A !A !A !A !A !A !A !A hg !A !A !A !A !P !P !P !P !P !P "J G "J "J !A G !A !A "J "J !A !A !A !A !A G "J !A !A CITY OF MODESTO OAKDALE RIVERBANK STANISLAUS CO. TUOLUMNE CO. SAN JOAQUIN CO. MERCED CO. Tuol u m n e Ri ver Stani s laus R iver San Jo a quin R i ve r OAKDALE I.D MODESTO I.D Modesto Reservoir t u 132 t u 120 t u 33 t u 5 t u 99 t u 59 t u 108 t u 219 t u 49 t u 4 t u 165 t u 580 t u 205 t u 120 t u 108 MID243 MID238 MID237 MID232 MID230 MID225 MID223 MID221 MID217 MID216 MID215 MID214 MID209 MID208 MID203 MID201 MID198 MID196 MID195 MID194 MID109 MID108 MID107 MID106 MID103 MID102 MID080 MID068 MID067 MID062 MID061 MID060 MID056 MID055 MID053 MID051 MID050 MID048 MID047 MID046 MID040 MID039 MID037 MID026 MID013 MID012 MID006 MID101 MID082 MID079 Private Well #1 Wemer Deep Well Private Well #9 Private Well #2 Private Well #3 Private Well #4 Private Well #7 Crane Deep Well Private Well #5 Private Well #6 Howard Deep Well Burnett Deep Well Marquis Deep Well Bentley Deep Well Thornton Deep Well Campbell Deep Well Santa Fe Deep Well Steinegul Deep Well Paulsell No.1 Deep Well Paulsell No.2 Deep Well Dry Ck @ Modesto Tuolumne R @ Modesto Stanislaus R @ Ripon Stanislaus R @ Orange Blossom Bridge Tuolumne R BL La Grange Dam NR La Grange Stanislaus R BL Goodwin NR Knights Ferry 6 3 56 52 41 40 39 37 34 29 25 21 19 18 11 10 100 03S10E13C001 02S10E28E001 SEPTEMBER 2004 FIGURE 5 MODESTO GROUNDWATER SUBBASIN 09-29-04 S:/GIS/Projects/040190/Figure_5_11x17.mxd 4 0 4 2 Miles¥ LEGEND Modesto Groundwater Subbasin Cities SOURCES: City of Modesto, City of Oakdale, City of Riverbank, CA Dept of Water Resources Groundwater Basins, 2002, California Spatial Library. Groundwater Level and Quality Monitoring Network Surface Exposure of Mehrten Formation G Deep Aquifer !A Forebay Aquifer High Groundwater hg Confined Mehrten Aquifers "J Shallow Aquifer Monitoring Wells Modesto I.D. Oakdale I.D. USGS Gauging Stations !P Top Producing Wells ---PAGE BREAK--- D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D " " " " CITY OF MODESTO OAKDALE RIVERBANK STANISLAUS CO. TUOLUMNE CO. SAN JOAQUIN CO. MERCED CO. Tu o lu mn e R ive r Stanisl aus Ri v er San Joa q u in R i v er OAKDALE I.D MODESTO I.D Modesto Reservoir t u 132 t u 120 t u 33 t u 99 t u 108 t u 5 t u 59 t u 219 t u 49 t u 165 t u 120 t u 5 MID247 MID300 MID245 MID244 MID243 MID242 MID241 MID240 MID239 MID238 MID237 MID236 MID235 MID234 MID233 MID232 MID231 MID230 MID229 MID228 MID226 MID224 MID223 MID222 MID221 MID217 MID216 MID215 MID214 MID213 MID211 MID210 MID209 MID208 MID206 MID204 MID203 MID200 MID199 MID198 MID197 MID196 MID195 MID194 MID193 MID109 MID108 MID107 MID106 MID103 MID102 MID101 MID100 MID090 MID088 MID083 MID082 MID080 MID079 MID076 MID069 MID068 MID067 MID066 MID062 MID061 MID060 MID059 MID057 MID055 MID053 MID051 MID050 MID047 MID046 MID045 MID040 MID039 MID036 MID030 MID026 MID023 MID018 MID017 MID014 MID013 MID006 MID005 MID002 03S09E30E 03S09E20C Well No. 8 Well No. 7 Well No. 2 Well No. 5A Private Well #1 Private Well #9 Private Well #2 Wyatt Deep Well Allen Deep Well Private Well #3 Private Well #4 Private Well #7 Crane Deep Well Private Well #8 Private Well #5 Private Well #6 Wiemer Deep Well Howard Deep Well Burnett Deep Well Oakdale Deep Well Marquis Deep Well Bentley Deep Well Thornton Deep Well Campbell Deep Well Birnbaum Deep Well Santa Fe Deep Well Steinegul Deep Well Valley Home Deep Well Paulsell No.1 Deep Well Paulsell No.2 Deep Well 8 7 6 4 3 2 1 55 56 53 52 51 49 48 47 46 45 44 43 41 40 39 38 37 36 34 33 30 29 25 24 22 21 19 18 17 16 10 100 SEPTEMBER 2004 FIGURE 6 MODESTO GROUNDWATER SUBBASIN 06-28-04 S:/GIS/Projects/040190/Figure_6_11x17.mxd 3 0 3 1.5 Miles¥ LEGEND SOURCES: City of Modesto, City of Oakdale, City of Riverbank, CA Dept of Water Resources Groundwater Basins, 2002, California Spatial Library. Groundwater Production Monitoring Network MID Wells OID Wells City of Oakdale Wells Modesto Groundwater Subbasin Cities Surface Exposure of Mehrten Formation Modesto I.D. Oakdale I.D. D " City of Modesto Wells ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N Tables 27 ---PAGE BREAK--- ---PAGE BREAK--- TABLE 1 CURRENT LEVEL OF MONITORING EFFORTS Pumping Member Total Number Totals Water Quality Analyses Agency of Wells Semiannual Annual Quarterly Semiannual Annual Performed MID 104 104 96 15 General Mineral, Boron 104 EC + pH OID 17 17 17 City of Modesto 62 86 14 (VOCs) Per Title 22 and DHS Ceres 4 4 Per Title 22 and DHS Walnut Manor 1 1 Per Title 22 and DHS Salida 7 7 Per Title 22 and DHS Del Rio 3 3 1 Per Title 22 and DHS Waterford 7 7 Per Title 22 and DHS Hickerman 2 2 1 Per Title 22 and DHS City of Oakdale 7 7 Per Title 22 and DHS City of Riverbank 7 7 Per Title 22 and DHS Total 221 245 0 113 0 16 15 104 Source: CCR from City of Modesto; MID e-mail comunication, 2004; OID well location map; Oakdale Water Master Plan, Riverbank production totals Pumping Member Total Number Totals Water Quality Analyses Agency of Wells Semiannual Annual Performed DWR (including Cooperators) 230 230 OID 15 15 Drinking Water Parameters Department of Health 209 Per Title 22 and DHS Services (Including Per Title 22 and DHS Cooperators) Per Title 22 and DHS Total 245 230 224 Source: DWR, 2004, Bulletin 118 Number of Wells Where Groundwater Samples Are Analyzed Number of Wells Where for Water Quality Groundwater Levels Are Measured to Every Three Years Number of Wells Where Groundwater Levels Are Measured Number of Wells Where Groundwater Samples Are Analyzed for Water Quality ---PAGE BREAK--- TABLE 2 HIGH GROUNDWATER MONITORING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) MID012 1927 76 0 34 14" Casing Perforated Unknown 34 76 Open Hole 12" dia Open MID013 1927 86 0 40 No. 14 Gauge, 16" dia. Perforated Unknown 40 86 Open Hole 14" dia. Open MID026 1927 85 0 73 16" Casing Perforated Unknown 73 85 Open Hole 14" dia. Open MID036 1927 77 0 40 16" Casing Perforated Unknown 40 77 Open Hole 14" dia. Open MID037 1926 74 0 46 16" Casing Perforated Unknown 46 74 Open Hole 14" dia. Open MID040 1972 106 0 6 1/4" thick, 24" dia. CasingBlank No 0 92 No. 8 Gauge 16" dia. Perforated 92 106 Open Hole 24" dia Open MID047 1927 85 0 43 16" Casing Perforated Unknown 43 85 Open Hole 14" dia. Open MID051 1969 152 0 104 No. 8 Gauge 14" dia. Perforated No 104 117 No. 8 Gauge 14" dia. Blank 117 152 Open Hole 14" dia. Open MID053 1929 110 0 110 16" Casing Perforated Unknown MID055 1930 72 0 48 No. 14 Gauge, 16" dia. DPerforated Unknown 48 72 Open Hole 14" dia. Open MID056 1930 94 0 30 No. 14 Gauge, 16" dia. DPerforated Unknown 30 60 No. 14 Gauge, 14" dia. DPerforated 60 94 Open Hole 12" dia Open ---PAGE BREAK--- TABLE 2 HIGH GROUNDWATER MONITORING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) MID060 1931 95 0 9 No. 14 Gauge, 18" dia. DBlank Unknown 9 42 No. 14 Gauge, 18" dia. DPerforated 45 70 No. 14 Gauge, 14" dia. DPerforated 70 95 Open Hole 12" dia Open MID061 1931 115 0 15 No. 14 Gauge, 18" dia. DBlank Unknown 15 68 No. 14 Gauge, 18" dia. DPerforated 45 90 No. 14 Gauge, 14" dia. DPerforated 90 115 Open Hole 12" dia Open MID067 1933 58 0 21 18" Casing Perforated Unknown 21 45 18" Casing Blank 45 58 16" Casing Perforated MID068 1933 105 0 20 18" Casing Perforated Unknown 20 48 18" Casing Blank 48 72 12" Casing Perforated 72 105 Open Hole 10" dia. Open MID080 1938 155 0 45 18" Casing Perforated Unknown 42 82 16" Casing Perforated 76 81 14" Casing Blank 81 141 14" Casing Perforated 141 155 Open Hole 12" dia Open MID102 1949 154 0 4 16" Casing Blank Unknown 4 25 16" Casing Perforated 25 40 16" Casing Blank 82 85 14" Casing Blank 85 117 Open Hole 12" dia Perforated 117 154 12" Hole, caved in. Open ---PAGE BREAK--- TABLE 2 HIGH GROUNDWATER MONITORING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) MID106 1953 95 0 8 No. 10 Gauge, 14" dia. Perforated No 8 24 No. 10 Gauge, 14" dia. Blank 24 68 No. 10 Gauge, 14" dia. Perforated 68 72 No. 10 Gauge, 14" dia. Blank 72 95 Open Hole 10" dia. Open MID107 1953 76 0 35 14" Casing Perforated No 35 76 Open Hole 12" dia Open MID109 1967 137 0 82 No. 8 Gauge 16" dia. Perforated Unknown 82 100 No. 8 Gauge 16" dia. Blank 100 137 Open Hole 16" dia Open MID196 1948 98 0 66 No. 12 Gauge, 18" dia. DBlank No 0 92 No. 10 Gauge 12" dia. Perforated 92 98 Open Hole 10" dia. Open ---PAGE BREAK--- TABLE 3 SHALLOW AQUIFER MONITORING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) MID006 1924 41 0 32 14" Casing Blank Unknown 31 41 Open Hole 12" dia Open MID014 1923 93 0 56 16" Casing Blank Unknown 56 93 Open Hole 14" dia. Perforated MID034 1973 94 0 80 No. 8 Gauge 14" diaBlank Unknown 80 94 Open Hole 14" dia. Open MID039 1924 74 0 41 16" Casing Blank Unknown 41 74 Open Hole 14" dia. Open MID048 1924 100 0 10 Sump & Drain Blank Unknown 10 28 18" Casing Blank 28 62 12" Casing Blank 62 100 Open Hole 10" dia. Open MID050 1949 67 0 40.5 No. 12 Gauge, 16" Blank Unknown 40.5 67 Open Hole 14" dia. Open MID062 1931 75 0 21 No. 14 Gauge, 16" Blank Unknown 21 56 No. 14 Gauge, 16" Perforated 56 75 Open Hole 14" dia. Open MID103 1949 130 0 54 16" Casing Blank Unknown 53 81 12" Casing Perforated 81 120 Open Hole 10" dia. Open 120 130 10" Hole, caved in. MID108 1955 90 0 70 No. 12 Gauge, 14" Blank None 70 90 Open Hole 14" dia. Open MID201 1949 88 0 36 No. 12 Gauge, 18" Blank Unknown 36 48 Open Hole 16" dia Open 48 58 No. 12 Gauge, 16" Blank 58 74 No. 12 Gauge, 16" Perforated 74 78 No. 12 Gauge, 16" Blank 78 88 Open Hole 12" dia Open ---PAGE BREAK--- TABLE 3 SHALLOW AQUIFER MONITORING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) City of Mod. 1956 138 0 92 14" dia. Steel Blank Unknown Well #3 92 138 Open Hole Open City of Mod. 1939 110 0 ? 24 inch dia. Steel Blank Unknown Well #10 ? ? 20 inch dia. Steel Blank ? 110 10 inch dia. Steel Blank City of Mod. 1936 125 0 ? 24" dia. Steel Blank Unknown Well #11 ? ? 20" dia. Steel Blank ? ? 14" dia. Steel Blank 116 125 Open Hole Open City of Mod. 1964 144 0 138 14" dia.Steel Blank Unknown Well #29 138 144 Open Hole Open City of Mod. 1967 112 0 100 16" dia. Casing Blank Unknown Well #34 112 Open Hole Open City of Mod. 1958 127 0 ? 14" dia. Steel Blank Unknown Well #100 ? 80 12" dia. Steel Blank 80 127 Open Hole Open ---PAGE BREAK--- TABLE 4 DEEP AQUIFER MONITORING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) MID046 1925 240 0 151 12" Casing Blank Unknown 151 240 Open Hole 10" dia. Open MID217 1961 467 0 120 No. 10 Gauge 18" dia. DBlank Unknown 116 124 No. 8 Gauge 16" dia. Blank 124 152 No. 8 Gauge 14" dia. Blank 152 364 No. 8 Gauge 14" dia. Perforated 364 368 No. 8 Gauge 14" dia. Blank 368 467 UNKNOWN MID237 1991 297 0 32 No. 10 Gauge 24" dia. Blank 0-32' 0 164 No. 8 Gauge 18" dia. Blank 155 159 No. 10 Gauge 16" dia. Blank 159 251 No. 10 Gauge 16" dia. Perforated 251 255 No. 10 Gauge 16" dia. Blank 255 297 Open Borehole Open City of Mod. 1921 234 0 175 18" dia. Steel Blank Unknown Well #6 175 234 Open Borehole Open City of Mod. 1957 240 0 240 18" dia. Steel Blank Unknown Well #19 City of Mod. Unknown 255 180 16" dia. Steel Blank Unknown Well #56 180 255 Open Borehole Open Note: Currently only one well is screened solely beneath the Corcoran clay. The other wells should be replaced with wells that are screened solely below the Corcoran clay. Until then, monitor these wells to provide a general indication of the conditions. ---PAGE BREAK--- TABLE 5 FOREBAY AQUIFER MONITORING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) MID194 1948 302 0 106 18" Casing Blank Unknown 100 150 16" Casing Blank 148 182 3/16" thick, 12" dia. Perforated 182 211 3/16" thick, 12" dia. Blank 211 302 Open Hole 10" dia. Open MID195 1948 260 0 136.5 No. 12 Gauge, 18" dia. Blank Unknown 127 140.5 16" Casing Blank 140.5 149.5 16" Casing Perforated 149.5 152.5 16" Casing Blank 152.5 164.5 16" Casing Perforated 164.5 169 16" Casing Blank 170 185 14" Casing Blank 185 210 14" Casing Perforated 210 233 14" Casing Blank 233 260 Open Hole 11" dia. Open MID198 1980 258 0 124 No. 8 Gauge 16" dia. Blank No 105 109 No. 10 Gauge, 14" dia. Blank 109 209 No. 10 Gauge, 14" dia. Perforated 209 213 No. 10 Gauge, 14" dia. Blank MID 202 1949 255 0 78 No. 12 Gauge, 18" dia. DoBlank Unknown 76 92 No. 12 Gauge, 16" dia. Do Perforated 92 152 No. 12 Gauge, 16" dia. Do Blank 131 204 3/16" thick, 14" dia. Perforated 204 222 3/16" thick, 14" dia. Blank 222 255 Open Hole 12" dia Open MID203 1949 384 0 136 No. 12 Gauge, 18" dia. DoBlank Unknown 135 151 No. 12 Gauge, 16" dia. Do Blank 151 175 No. 12 Gauge, 16" dia. Do Perforated 166 187 No. 12 Gauge, 14" dia. Blank 175 180 No. 12 Gauge, 16" dia. Do Blank 187 229 No. 12 Gauge, 14" dia. Perforated 229 250 No. 12 Gauge, 14" dia. Blank 250 259 Open Hole 14" dia. Open 259 277 3/16" thick, 12" dia. Blank 277 313 3/16" thick, 12" dia. Perforated 313 331 3/16" thick, 12" dia. Blank 331 384 Open Hole 10" dia. Open ---PAGE BREAK--- TABLE 5 FOREBAY AQUIFER MONITORING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) MID208 1950 320 0 98 No. 12 Gauge, 18" dia. DoBlank Unknown 79 119 No. 10 Gauge 16" dia. Perforated 119 139 No. 10 Gauge 16" dia. Blank 128 203 No. 12 Gauge, 14" dia. Perforated 196 272 No. 12 Gauge, 12" dia. Perforated 272 276 No. 12 Gauge, 12" dia. Blank 276 320 Open Hole 10" dia. Open MID209 1949 424 0 90 No. 12 Gauge, 18" dia. DoBlank Unknown 78 108 No. 10 Gauge 16" dia. Perforated 108 128 No. 10 Gauge 16" dia. Blank 128 148 No. 10 Gauge 16" dia. Perforated 148 168 No. 10 Gauge 16" dia. Blank 158 230 No. 12 Gauge, 14" dia. Perforated 230 248 No. 12 Gauge, 14" dia. Blank 248 284 Open Hole 14" dia. Open 284 365 No. 12 Gauge, 12" dia. Perforated 365 384 No. 12 Gauge, 12" dia. Blank 384 424 Open Hole 10" dia. Open MID214 1959 480 0 116 No. 10 Gauge 18" dia. DouBlank 0-116' 107 275 No. 8 Gauge 14" dia. Perforated 275 362 Open Hole 11" dia. Open 362 480 Exploratory Borehole 6" diaOpen MID215 1959 476 0 106 No. 10 Gauge 18" dia. Blank Unknown 106 116 Open Hole 18" dia. Open 116 216 No. 12 Gauge, 16" dia. Perforated 198 310 No. 12 Gauge, 14" dia. Perforated 306 400 No. 12 Gauge, 12" dia. Perforated 400 476 Open Hole 10" dia. Open MID216 1960 382 0 114 No. 12 Gauge, 18" dia. DoBlank Unknown 110 128 No. 8 Gauge 14" dia. Blank 128 380 No. 8 Gauge 14" dia. Perforated MID230 1989 412 0 28 No. 8 Gauge 24" dia. Blank 0-30' 0 192 No. 8 Gauge 18" dia. Blank 175 179 No. 10 Gauge 16" dia. Blank 179 283 No. 10 Gauge 16" dia. Perforated 283 287 No. 10 Gauge 16" dia. Blank 287 412 Open Borehole Open ---PAGE BREAK--- TABLE 5 FOREBAY AQUIFER MONITORING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) MID243 1996 346 0 20 No. 10 Gauge 24" dia. Blank 0-20' 0 148 No. 8 Gauge 18" dia. Blank 141 251 No. 10 Gauge 16" dia. Perforated 251 346 Open Borehole Open OID-Bentley OID-Burnett OID-Campbell 1948 502 0 118 18" dia Casing Perforated 118 240 14" dia Casing Perforated OID-Crane OID-Howard Unknown 475 0 ? 18" dia. Casing Blank Unknown ? 102 18" dia Casing Perforated 98 232 14" dia Casing Perforated 232 475 Open Borehole Open OID-Marquis OID Santa Fe OID-Steinegul 1943 500 0 43 18" dia. Casing Blank Unknown 43 53 18" dia Casing Perforated 53 69 18" dia Casing Blank 69 93 18" dia Casing Perforated 93 115 14" dia Casing Blank 115 265 14" dia Casing Perforated 265 362 Open Borehole Open OID-Thornton OID-Wemer OID-Private well #1 OID-Private well #2 OID-Private well #3 ---PAGE BREAK--- TABLE 5 FOREBAY AQUIFER MONITORING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) OID-Private well #4 OID-Private well #5 OID-Private well #6 OID-Private well #7 City of Mod. 1956 250 0 104 20" dia. Steel Casing Blank Unknown Well #18 104 232 14" dia. Steel Casing Perforated 232 250 Open Hole Open City of Mod. 1959 320 0 144 20" dia. Steel casing Blank Unknown Well # 21 144 294 14" dia. Steel Casing Perforated 294 320 12" dia. Open Hole Open City of Mod. 1962 395 0 91 20" dia. Steel casing Blank Unknown Well # 25 91 366 16" dia. Steel Casing Perforated 366 395 12" dia. Open Hole Open City of Mod. 1970 228 0 102 20" dia. Steel casing Blank 110 Well # 37 102 214 18" dia. Well Screen Perforated 214 218 18" dia. Steel casing Blank 218 228 Unknown Unknown City of Mod. 1972 292 0 116 24" dia. Steel casing Blank 50 Well # 39 116 216 18" dia. Well Screen Perforated 216 220 18" dia. Steel casing Blank 220 292 Open Hole Open City of Mod. 1974 275 0 97 24" dia. Steel casing Blank 52 Well # 40 97 229 20" dia. Well Screen Perforated 229 233 20" dia. Steel casing Blank 233 275 18" dia. Open Hole Open City of Mod. 1976 248 0 124 24" dia. Steel casing Blank 52 Well # 41 124 216 20" dia. Well Screen Perforated 216 220 20" dia. Steel casing Blank 220 248 18" dia. Open Hole Open ---PAGE BREAK--- TABLE 5 FOREBAY AQUIFER MONITORING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) City of Mod. 1992 280 0 120 18" dia. Steel casing Blank 100 Well # 52 120 195 18" dia. Well Screen Perforated 195 255 18" dia. Steel casing Blank 255 270 18" dia. Well Screen Perforated 270 280 18" dia. Steel casing Blank 2S/10E-28E1 Unknown 196 0 111 Unknown Blank Unknown 111 196 Open Hole 3S/10E-13C1 1952 108 0 95 7" dia Steel Unknown Unknown Notes: All wells without construction details listed in this table should be evaluated to confirm within the Forebay aquifers These wells may be obtaining water from both the Mehrten Confined and Forebay aquifers. These wells should be replaced with wells that are screened solely within the Forebay aquifers. Until then, monitor these wells to provide a general indication of the conditions. Replacement wells may be found through DWR. Conflicting data regarding well screen interval versus sanitary seal depths ---PAGE BREAK--- TABLE 6 MEHRTEN CONFINED AQUIFER MONITORING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) MID221 1994 510 0 320 1/4" thick, 16" dia. CasinBlank 0-50' 320 500 1/4" thick, 16" dia. CasinPerforated 500 510 1/4" thick, 16" dia. CasinBlank MID225 1960 235 0 104 No. 10 Gauge, 14" dia. Blank Unknown 103 171 No. 12 Gauge, 12" dia. Perforated 160 220 No. 12 Gauge, 10" dia. Perforated 220 235 Open Hole 10" dia. Open MID223 1959 380 0 116 No. 10 Gauge, 14" dia. Blank Unknown 116 168 Open Hole 14" dia. Open 168 208 No. 12 Gauge, 12" dia. Perforated 208 380 Open Borehole Open MID232 1989 460 0 16 No. 10 Gauge 24" dia. Blank 0-20' 0 216 No. 8 Gauge 18" dia. Blank 192 196 No. 10 Gauge 16" dia. Blank 196 288 No. 10 Gauge 16" dia. Perforated 288 292 No. 10 Gauge 16" dia. Blank 292 460 Open Borehole Open MID238 1994 484 0 24 No. 8 Gauge 24" dia. Blank 0-24' 0 196 No. 8 Gauge 18" dia. Blank 196 484 Open Hole 12" dia Open OID - private well #9 Paulsell No. 1 Paulsell No. 2 1945 830 0 54 No. 12 Gauge, 20" dia. Blank Unknown 54 132 No. 12 Gauge, 18" dia. Blank 132 159 16" dia. Blank 159 830 Open Borehole Open ---PAGE BREAK--- TABLE 6 MEHRTEN CONFINED AQUIFER MONITORING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) City of Oakdale #2 1954 565 0 156 Casing Blank 0-164' 156 565 Perforated Perforated City of Oakdale #7 1990 478 0 274 Casing Blank 0-100' 274 478 Perforated Perforated City of Oakdale #8 1990 380 0 240 Casing Blank 0-170' 240 380 Perforated Perforated Notes: This well may be obtaining water from both the Mehrten Confined and Forebay aquifers. This well should be replaced with a well that is screened solely within the Forebay aquifers. Until then, monitor this well to provide a general indication of the conditions. Replacement wells may be found through DWR ---PAGE BREAK--- TABLE 7 MID TOP PRODUCING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) MID018 1965 136 0 24 No. 12 Gauge 24" dia. Blank No 0 36 No. 8 Gauge 14" dia. Blank 36 96 No. 8 Gauge 14" dia. Perforated 96 100 No. 8 Gauge 14" dia. Blank 100 136 Open Borehole Perforated MID034 1973 94 0 80 No. 8 Gauge 14" dia. Blank Unknown 80 94 Open Hole 14" dia. Open MID062 1931 75 0 21 No. 14 Gauge, 16" dia. DBlank Unknown 21 56 No. 14 Gauge, 16" dia. DPerforated 56 75 Open Hole 14" dia. Open MID079 1937 198 0 115.5 16" Casing Perforated Unknown 115.5 198 Open Hole 14" dia. Open MID082 1938 200 0 48 18" Casing Blank Unknown 45 68 16" Casing Perforated 60 79 PVC Blank 79 94 14" Casing Perforated 91 99 12" Casing Perforated 99 120 PVC Blank 120 200 Open Hole 10" dia. Open MID101 1949 64 0 44 16" Casing Blank Unknown 44 64 Open Hole 14" dia. Open MID108 1955 90 0 70 No. 12 Gauge, 14" dia. DBlank No 70 90 Open Hole 14" dia. Open Notes: Seven of the top ten are listed above. The remaining three wells have been incorporated into monitoring network. ---PAGE BREAK--- TABLE 8 AQUIFER-RIVER CONNECTEDNESS MONITORING WELLS Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) Obtain Information From: ---PAGE BREAK--- Table 9 Surface Water Gaging Stations Gaging Station Name Gaging Station ID Monitoring Agency Elevation (feet above mean sea level) Stanislaus River below Goodwin near Knights Ferry SKF USGS 253 Stanislaus River at Orange Blossom Bridge OBB DWR 117 Stanislaus River at Ripon RIP USGS 73 Tuolumne River below La Grange Dam LGN USGS 170 Dry Creek at Modesto DCM DWR 88 Tuolumne River at Modesto MOD DWR 90 Obtain USGS Information at http://waterdata.usgs.gov/ca/nwis/rt Obtain DWR Information at ---PAGE BREAK--- Table 10 Groundwater Monitoring Summary Well Name Production 1 Quarterly Semiannnual Annual Semiannual Annual OID - Paulsell No. 1 X X X X OID - Paulsell No. 2 X X X X OID-Bentley X X X X OID-Burnett X X X X OID-Campbell X X X X OID-Crane X X X X OID-Howard X X X X OID-Marquis X X X X OID-Santa Fe X X X X OID-Steinegul X X X X OID-Thornton X X X X OID-Wemer X X X X OID-Private well #1 X X X X OID-Private well #2 X X X X OID-Private well #3 X X X X OID-Private well #4 X X X X OID-Private well #5 X X X X OID-Private well #6 X X X X OID-Private well #7 X X X X OID - private well #9 X X X X MID006 X X X X MID012 X X X X MID013 X X X X MID014 X X X X MID018 X X X X MID026 X X X X MID034 X X X X MID034 X X X X MID036 X X X X MID037 X X X X MID039 X X X X MID040 X X X X MID046 X X X X MID047 X X X X MID048 X X X X MID050 X X X X MID051 X X X X MID053 X X X X MID055 X X X X MID056 X X X X MID060 X X X X MID061 X X X X MID062 X X X X MID062 X X X X MID067 X X X X MID068 X X X X MID079 X X X X MID080 X X X X MID082 X X X X MID101 X X X X MID102 X X X X MID103 X X X X MID106 X X X X MID107 X X X X MID108 X X X X MID108 X X X X MID109 X X X X Groundwater Level Monitoring Groundwater Quality 1 ---PAGE BREAK--- Table 10 Groundwater Monitoring Summary Well Name Production 1 Quarterly Semiannnual Annual Semiannual Annual Groundwater Level Monitoring Groundwater Quality MID194 X X X X MID195 X X X X MID196 X X X X MID198 X X X X MID201 X X X X MID202 X X X X MID203 X X X X MID208 X X X X MID209 X X X X MID214 X X X X MID215 X X X X MID216 X X X X MID217 X X X X MID221 X X X X MID223 X X X X MID225 X X X X MID230 X X X X MID232 X X X X MID237 X X X X MID238 X X X X MID243 X X X X City of Oakdale #8 X X X X City of Oakdale #7 X X X X City of Oakdale #2 X X X X City of Mod. Well #3 X X X X City of Mod. Well #6 City of Mod. Well #11 X X X X City of Mod. Well #18 X X X X City of Mod. Well #19 X X X X City of Mod. Well #21 X X X X City of Mod. Well #25 X X X X City of Mod. Well #29 X X X X City of Mod. Well #34 X X X X City of Mod. Well #37 X X X X City of Mod. Well #39 X X X X City of Mod. Well #40 X X X X City of Mod. Well #41 X X X X City of Mod. Well #52 X X X X City of Mod. Well #56 X X X X City of Mod. Well #100 X X X X 3S/10E-13C12 X 2S/10E-28E12 X Notes: 1 = Monitor production in all wells including those on this list 2 = Obtain water level measurements from DWR website at http://www.well.water.ca.gov/ 2 ---PAGE BREAK--- TABLE 11 TYPICAL PRODUCTION METER READ FORM Date: WATER METER READINGS Measured by: WELLS - WATER METERS TOTAL WELL NO. COMMON NAME START FINISH (Acre-Feet) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 TOTALS 0 Comments: ---PAGE BREAK--- Semiannual Groundwater Level and Sampling Form Measured by: Well ID Common Name Date Time Depth to Water (Feet) EC (umhos/cm) Comments TABLE 12 ---PAGE BREAK--- TABLE 13 PURGE VOLUME ESTIMATION SHEET 1. WELL SITE ID NO.: TIME: 2. DATE: FIELD TECH(S): 3. YEAR WELL CONSTRUCTED-INSTALLED:________ WEATHER CONDITIONS: hot, cold, clear, etc) 4. CASING REFERENCE POINT (R.P) 5. WELL DIAMETER: (in) top of casing) 6. WELL DEPTH: (ft) 7. DEPTH TO WATER: PH METER (TYPE AND MODEL 8. COLUMN OF WATER (line 7 - line CALIBRATED FIELD CALIBRATED EC METER (TYPE AND MODEL CALIBRATED FIELD CALIBRATED WELL VOLUME CALCULATION 9. ONE WELL VOLUME = Enter Line 5 (in) = / x x line 10. ONE WELL VOLUME (V in gallons) = V(line 9) x 7.48 = 11. THREE WELL VOLUMES (in gallons) = V(line 10) x 3 = WELL PURGE TIME CALCULATION 12 WELL DISCHARGE RATE gallons per minute (gpm) or gpm from meter 13 WELL PURGE TIME (THREE WELL VOLUMES) = V(line 11) / Q(line 12) = ADDITIONAL FIELD NOTES 15 TIME PUMP TURNED "ON": 16 TIME PUMP TURNED "OFF": 17 ELAPSED PURGE TIME: COMMENTS ---PAGE BREAK--- TABLE 14 Analytical Parameters, Test Methods, Holding Times, Sample Containers, Preservation and Approximate Detection Limits For Groundwater Samples Groundwater Monitoring Plan ANALYTICAL MAXIMUM SAMPLE CONTAINER MINIMUM Parameter TESTING HOLDING BOTTLE TYPE SIZE/SET PRESERVATION REPORTING METHOD TIME LIMIT Calcium SM 2340C or SM3500Ca-D 6 Months Plastic 1 Liter HNO3, cool to 4 oC 1.0 mg/L Magnesium EPA 200.7 or SM3500Mg-E 6 Months Plastic 1 Liter HNO3, cool to 4 oC 1.0 mg/L Sodium EPA 200.7 or SM3111B 6 Months Plastic 1 Liter HNO3, cool to 4 oC 1.0 mg/L Potassium EPA 200.7 6 Months Plastic 1 Liter Cool to 4 oC 1.0 mg/L Bicarbonate SM 2320-B 14 Days Plastic or Glass 250 mL Cool to 4 oC 1.0 mg/L Sulfate EPA 300.0 28 Days Plastic or Glass 250 mL Cool to 4 oC 0.50 mg/L Chloride EPA 300.0 28 Days Plastic or Glass 250 mL Cool to 4 oC 1.0 mg/L Nitrate, (Nitrate as NO3) EPA 300.0 48 Hours Plastic or Glass 250 mL Cool to 4 oC 2.0 mg/L pH EPA 150.1 Immediate Plastic 250 mL None Required None Required Total Dissolved Solids (TDS) SM 2450-C 7 Days Plastic 250 mL Cool to 4 oC 1.0 mg/L Specific Conductance (EC) SM 2510-B 28 Days Plastic or Glass 250 mL Cool to 4 oC 10 umhos/cm ---PAGE BREAK--- Table 15: Example Chain of Custody Form PAGE OF 1 CALTEST LAB # CLIENT LAB # COMP. or GRAB Samples: WC MICRO BIO AA SV VOA BD: BIO WC AA CC: AA SV VOA SIL: HP PT QT VOA W/HNO3 H2SO4 NaOH PIL: HNO3 R PR M F ANALYSES REQUESTED REPORT TO: 1885 N. KELLY ROAD NAPA, CA 94558 (707) 258-4000 FAX (707) 226-1001 P.O. NUMBER CLIENT: SAMPLE MATRIX* FAX PHONE NUMBER: DATE SAMPLED TIME SAMPLED NaOH DATE/TIME RELINQUISHED BY HCL H2SO4 DATE/TIME RECEIVED BY RELINQUISHED BY RECEIVED BY REMARKS DUE DATE: SAMPLE IDENTIFICATION / SITE CONTAINER TYPE/ AMOUNT** PRESERVATIVE ZIP SAMPLER (PRINT & SIGN NAME): MAILING ADDRESS: STATE: PHONE NUMBER: STANDARD RUSH pH? Y/N TEMP: Y/N COMMENTS: Y/N INTACT: SEALED: 1 LAB ORDER # BILLING ADDRESS: ATTN: SAMPLE CHAIN OF CUSTODY TURN-AROUND TIME 10/04/04 FOR LAB USE ONLY WHITE - LABORATORY YELLOW - CLIENT COPY TO ACCOMPANY FINAL REPORT PINK - CLIENT COPY AS RECEIPT PROJECT NAME / PROJECT NUMBER: *MATRIX: AQ = Aqueous Nondrinking Water, Digested Metals; FE = Low R.L.s, Aqueous Nondrinking Water, Digested Metals; DW = Drinking Water; SL = Soil Sludge, Solid ; FP = Free Product **CONTAINER TYPES: AL = Amber Liter; AHL = 500 ml Amber; PT = Pint (Plastic); QT = Quart (Plastic); HG = Half Gallon (Plastic); SJ = Soil Jar; B4 = 4oz. BACT; BT = Brass Tube; VOA = 40mL VOA; OTC - Other Type Container ---PAGE BREAK--- G R O U N D W A T E R M O N I T O R I N G P L A N Appendix A Wells in the Modesto Subbasin Providing Water Quality Data A-1 ---PAGE BREAK--- ---PAGE BREAK--- Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) 01S07E01J001M 01S07E02J001M 01S07E03D001M 01S07E05A001M 01S07E06M002M 01S07E08J002M 01S07E09Q001M 01S07E10A001M 01S07E10A001M 01S07E10A001M 01S07E10A001M 01S07E10A001M 01S07E10A001M 01S07E12H001M 01S07E13J001M 01S07E14M001M 01S07E14P003M 01S07E15F002M 01S07E17N002M 01S07E18L001M 01S07E21G001M 01S07E25E001M 01S07E25R001M 01S07E26G001M 01S07E27K001M 01S07E28D001M 01S07E30R001M 01S07E33H001M 01S07E36D001M 01S08E04R001M 01S08E05A001M 01S08E05R001M 01S08E06D001M 01S08E08J001M 01S08E08J001M 01S08E08J001M 01S08E08J001M 01S08E08J001M 01S08E08J001M 01S08E09Q001M 01S08E11F001M 01S08E14B001M 01S08E15A001M 01S08E15P001M 01S08E25Q001M 01S08E27A001M 01S08E29K001M 01S08E30C002M 01S08E34Q001M 01S08E35R002M 01S09E02R001M 01S09E05H002M 01S09E07A001M 01S09E07N001M 01S09E11J001M 01S09E11J002M 01S09E13K001M 01S09E14K001M 01S09E14K001M 01S09E14K001M 01S09E14K001M 01S09E14K001M 01S09E14K001M 01S09E15P001M 01S09E16R001M 01S09E18R003M 01S09E19Q002M 01S09E21J001M 01S09E21J002M 01S09E22L001M 01S09E23A001M 01S09E24R001M 01S09E26A001M 01S09E28M002M 01S09E29M002M ---PAGE BREAK--- Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) 01S09E33J002M 01S09E33P001M 01S09E34A001M 01S10E04C001M 01S10E06Q001M 01S10E08L001M 01S10E16Q001M 01S10E17L001M 01S10E18M001M 01S10E20G001M 01S10E21A001M 01S10E22Q001M 01S10E23H001M 01S10E23J001M 01S10E26J001M 01S10E27Q001M 01S10E28J001M 01S10E33J001M 01S10E34R001M 01S10E35F001M 01S11E25N001M 02S06E25J001M 02S07E07D002M 02S07E07Q001M 02S07E08R001M 02S07E09M001M 02S07E10B002M 02S07E11N002M 02S07E12G001M 02S07E12R001M 02S07E12R001M 02S07E12R001M 02S07E12R001M 02S07E12R001M 02S07E12R001M 02S07E12R002M 02S07E12R002M 02S07E12R002M 02S07E12R002M 02S07E12R002M 02S07E12R002M 02S07E19H001M 02S07E20R002M 02S07E22N002M 02S07E24R002M 02S07E26B001M 02S07E31N001M 02S08E04M001M 02S08E06J001M 02S08E07R001M 02S08E08A001M 02S08E08E001M 02S08E09J001M 02S08E12D001M 02S08E14E001M 02S08E17N002M 02S09E03K001M 02S09E05C001M 02S09E07D001M 02S09E09Q001M 02S09E11K001M 02S09E12R001M 02S09E19B002M 02S09E19B002M 02S09E19B002M 02S09E19B002M 02S09E19B002M 02S09E19B002M 02S10E08H001M 02S10E09E001M 03S07E05J001M 03S07E06Q001M 02S10E01E001M 02S10E02C001M ---PAGE BREAK--- Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) 02S10E02P001M 02S10E10M002M 02S10E22A001M 02S10E22D001M 02S10E23R001M 02S10E24R001M 02S10E25J001M 02S10E26N001M 02S10E27H001M 02S10E28E001M log available 02S10E29B001M 02S10E31C002M 02S10E34M002M 02S10E35M001M no log available 02S10E36A001M 02S11E07J001M 02S11E19K002M 02S11E20N001M 02S11E28J001M 02S11E29M001M 02S11E30C001M 02S11E30M001M 02S11E31N001M 02S11E32H001M 02S12E32P001M 03S08E11K001M 03S08E13C001M 03S08E13J001M 03S08E24K001M 03S08E25J001M 03S09E05J003M 03S09E07C002M 03S09E08K001M 03S09E10E001M 03S09E10M001M 03S09E10P001M 03S09E14G001M 03S09E15L001M 03S09E16D001M 03S09E16N002M 03S09E17D001M 03S09E17P001M 03S09E19C001M 03S09E19E001M 03S09E20C001M 03S09E20J001M 03S09E20K001M 03S09E21H001M 03S09E22F001M 03S09E22N001M 03S09E23E001M 03S09E24F001M 03S09E24M001M 03S09E25D001M 03S09E26K001M 03S09E26M001M 03S09E27D001M 03S09E28C001M 03S09E28J001M 03S09E28K001M 03S09E28M001M 03S09E29B001M 03S09E29D002M 03S09E29G001M 03S09E29P001M 03S09E30E001M 03S09E30Q001M 03S09E31G001M 03S09E32A001M 03S09E32G001M 03S09E33Q001M 03S09E34A001M 03S09E35A001M 03S09E36C001M ---PAGE BREAK--- Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) 03S09E36C002M 03S09E36D001M 03S10E01J001M 03S10E02D001M 03S10E04A001M 03S10E05L001M 03S10E06B001M 03S10E09J001M 03S10E11D001M 03S10E12L001M 03S10E13C001M 03S10E14A001M 03S10E15A001M 03S10E15Q001M 03S10E16A001M 03S10E19E001M 03S10E20F001M 03S10E20R001M 03S10E22G001M 03S10E26E001M 03S10E30H001M 03S10E30R002M 03S10E31F001M 03S10E31J001M 03S10E31K001M 03S10E34D002M 03S11E06C001M 03S11E07C001M 03S11E18D001M 03S11E19C001M 03S11E27L001M 03S11E28M001M 03S11E31K001M 03S11E34C003M 03S11E34N001M 03S12E05C002M 04S08E01C002M 03S12E33L001M 04S08E13P001M 04S08E22R001M 04S08E27H001M 04S08E35J001M 04S08E36B002M 04S09E03M001M 04S09E04K001M 04S09E04N002M 04S09E05H001M 04S09E05J001M 04S09E09Q001M 04S09E16D002M 04S09E19A001M 04S09E20A001M 04S09E21A001M 04S09E21J001M 04S09E22C001M 04S09E22L001M 04S09E24G001M 04S09E27H001M 04S09E28J001M 04S09E29M001M 04S09E30Q001M 04S09E31C001M 04S09E32J001M 04S09E33E001M 04S09E36E002M 04S10E02M001M 04S10E08H001M 04S10E11J001M 04S10E12A001M 04S10E18R001M 04S10E21E001M 04S10E21R002M 04S10E24B001M 04S10E29B001M ---PAGE BREAK--- Well # Yr. Drilled Drilled Depth Top of Casing Bottom of Casing Casing Type Blank or Perf ? Sanitary Seal (ft) (ft) (ft) 04S10E31B001M 04S10E32N002M 04S11E03H001M 04S11E08A001M 04S11E11H001M 04S11E14P001M 04S11E15J001M 04S11E17A001M 04S11E21D001M 04S11E24Q001M 04S11E24Q001M 04S11E28J001M 04S11E28J001M 04S11E31J001M 04S11E32D002M 04S11E32D002M 04S11E33R001M 04S11E33R001M 04S11E35A001M 04S11E36N001M 04S12E03C001M 04S12E03G001M 04S12E06E001M 04S12E06G001M 04S12E07C001M 04S12E07J001M 04S12E08E001M 04S12E08G001M 04S12E09M001M 04S12E16E001M 04S12E17D001M 04S12E17G001M 04S12E18C001M 04S12E19N001M 04S12E21N001M 04S12E27J001M 04S12E30Q001M 04S12E34F001M 04S12E35C001M 04S13E28B001M 04S13E28K001M 04S13E28Q001M ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Appendix E Public Involvement Documentation ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- I N T E G R A T E D R E G I O N A L G R O U N D W A T E R M A N A G E M E N T P L A N Appendix F Resolutions of Plan Adoption ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- 05-06-05 S:/GIS/Projects/040190/Corel/Geology.cdr INTEGRATED REGIONAL GROUNDWATER MANAGEMENT PLAN FOR THE MODESTO BASIN Geology Map JUNE 2005 FIGURE 4-2 SOURCE: USGS, PP 1401-C Plate 2, 1969. ---PAGE BREAK--- APRIL 2005 ---PAGE BREAK--- APRIL 2005 ---PAGE BREAK--- Figure 4-11 05-10-04 S:GIS/Projects/040190/Corel/Figure 4-10.cdr Integrated Regional Groundwater Management Plan for the Modesto Basin ---PAGE BREAK--- Figure 4-12 05-10-04 S:GIS/Projects/040190/Corel/Figure 4-11.cdr Integrated Regional Groundwater Management Plan for The Modesto Basin ---PAGE BREAK--- Figure 4-13 05-10-04 S:GIS/Projects/040190/Corel/Figure 4-12.cdr Integrated Regional Groundwater Management Plan for The Modesto Basin ---PAGE BREAK--- Figure 4-14 05-10-04 S:GIS/Projects/040190/Corel/Figure 4-13.cdr Integrated Regional Groundwater Management Plan for The Modesto Basin ---PAGE BREAK--- Figure 4-15 05-10-04 S:GIS/Projects/040190/Corel/Figure 4-14.cdr Integrated Regional Groundwater Management Plan for The Modesto Basin ---PAGE BREAK--- 05-10-04 S:GIS/Projects/040190/Corel/Figure 4-17.cdr Figure 4-18 Integrated Regional Groundwater Management Plan for The Modesto Basin Distribution of Nitrate Concentrations ---PAGE BREAK--- 05-10-04 S:GIS/Projects/040190/Corel/Figure 4-18.cdr Figure 4-19 Integrated Regional Groundwater Management Plan for The Modesto Basin In 1990 ---PAGE BREAK--- FIGURE 4-21 05-10-04 S:GIS/Projects/040190/Corel/Figure 4-20.cdr Integrated Regional Groundwater Management Plan for The Modesto Basin DBCP Sampling Locations and Concentrations in Water Wells ---PAGE BREAK--- East San Joaquin Subbasin Modesto Subbasin £ ¤ 12 £ ¤ 99 £ ¤ 120 £ ¤ 4 £ ¤ 120 £ ¤ 120 £ ¤ 132 £ ¤ 160 £ ¤ 5 £ ¤ 5 TOULUMNE RIVER STANISLAUS RIVER SAN JOAQUIN RIVER 11-24-04 S:/GIS/Projects/040190/Figure_5_1.mxd 7.5 0 7.5 3.75 Miles ® LEGEND Groundwater Subbasins SOURCES: CA Dept of Water Resources Groundwater Basins, 2002, California Spatial Library. JUNE 2005 FIGURE 5-1 MODESTO AND EAST SAN JOAQUIN GROUNDWATER SUBBASINS INTEGRATED REGIONAL GROUNDWATER MANAGEMENT PLAN FOR THE MODESTO BASIN