Document Redmond_doc_81a24dcd38

STORMWATER TECHNICAL NOTEBOOK Issue No. 8 Effective: April 1, 2019 (Amended June 5, 2019) First Adopted: March 18, 1996 Issue No. 2 Effective: April 22, 1996 Issue No. 3 Effective: April 1, 1999 Issue No. 4 Effective: October 1, 2004 Issue No. 5 Effective: January 1, 2007 Issue No. 5A Effective: August 18, 2010 Issue No. 6 Effective: February 23, 2012 Issue No. 7 Effective: January 1, 2017 Issue No. 7A Effective: March 1, 2017 Issue No. 8 Effective: April 1, 2019 ---PAGE BREAK--- 2 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 i Foreword The Stormwater Technical Notebook contains the goals, specifications, and standards for clearing, grading, and stormwater management authorized and required by Chapter 15.24 of the Redmond Municipal Code (RMC). How to Get Printed Copies of the Stormwater Notebook If you would like to receive a copy of the updated manual please stop by the City of Redmond Development Services Center, located on the 2nd floor of City Hall (15670 NE 85th Street). How to Find the Stormwater Technical Notebook Online The Stormwater Technical Notebook is available on the City of Redmond’s website at http://www.redmond.gov/Stormwater. How to Find Corrections, Updates, and Additional Information With a publication of this size and complexity, and with the rapid changes in stormwater management technologies, there may be errors that must be corrected and clarifications that are needed between full document updates. The City publishes corrections, updates, and new technical information on the Stormwater Technical Notebook web page (referenced above). Overview of Changes from Previous Issue • Wellhead Protection Zones are being revised in the Redmond Zoning Code. The Critical Aquifer Recharge Area is revised by new groundwater modeling. Stormwater requirements have been adjusted to align with this change. • Interim facilities are no longer required in Overlake due to recent construction of regional facilities by the City. • New information was added for: o Rainwater Harvesting o Rustic Streets o Artificial Turf o Maintenance Access o Decorative Water Features o Modifying City Stormwater Facilities o Calculating Capital Facilities Charges o Protection of Stormwater Facilities from Temporary Construction Dewatering ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 Revisions Title of Revision Effective Date Section Page Proprietary Treatment Clarification June 05, 2019 Entire document 201 Tree Removal Threshold June 05, 2019 3.2 Clearing and Grading Permits 202 0.1 CFS Flow Control Threshold June 05, 2019 2.6 Analysis 204 ---PAGE BREAK--- ii Table of Contents 1.1. Code Requirements 1 1.2. Permitting Review Process 1 1.3. Vesting 2 1.4. Additional Permit Requirements 3 2.1. Redmond Requirements 5 2.2. Exemptions from Ecology’s Minimum Requirements 5 2.3. Definitions Related to the Minimum Requirements 6 2.4. Applicability of the Minimum Requirements 6 2.4.1 New Development 10 2.4.2 Redevelopment 10 2.5 Minimum Requirements 11 2.5.1 Minimum Requirement Preparation of Stormwater Site Plans (Stormwater Reports) 11 2.5.2 Minimum Requirement Construction Stormwater Pollution Prevention (SWPP) 12 2.5.3 Minimum Requirement Source Control of Pollution 22 2.5.4 Minimum Requirement Preservation of Natural Drainage Systems and Outfalls 22 2.5.5 Minimum Requirement On-Site Stormwater Management 23 2.5.5.1 Flow Control Exempt Areas 24 2.5.5.2 Marymoor – 100% Infiltration 24 2.5.5.3 40th Street Basin 24 2.5.6 Minimum Requirement Runoff Treatment 30 2.5.7 Minimum Requirement Flow Control 33 2.5.8 Minimum Requirement #8 - Wetlands Protection 38 2.5.9 Minimum Requirement Operation and Maintenance 39 2.6 Analysis 40 2.7 Adjustments (Deviations in RMC 15.24 ) 42 2.7.1 Request for Engineering Deviation 43 2.7.2 Criteria for Granting Engineering Deviations 43 2.8 Exceptions (Variances in RMC 15.24) 44 2.9 2014 Modifications in Redmond 45 2.9.1 Volume I. 45 2.9.1.1 Volume I. Chapter 3: Preparation of Stormwater Site Plans 45 2.9.1.2 Volume I. Chapter 4: BMP and Facility Selection Process for Permanent Stormwater Control 45 2.9.2 Volume II: Construction Stormwater Pollution Prevention 46 2.9.3 Volume III: Hydrologic Analysis and Flow Control BMPs 47 2.9.3.1 III-2.1.1 Discussion of Hydrologic Analysis Methods Used for Designing BMPs 47 2.9.3.2 III-3.1 Roof Downspout Controls 48 2.9.3.3 III-3.1.3 Perforated Stub Out Connections (BMP T5.10C) 48 2.9.3.4 III-3.2.1 Detention Ponds 49 2.9.3.5 III-3.2.2 Detention Tanks 50 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 iii 2.9.3.6 III-3.232 Detention Vaults 50 2.9.3.7 III-3.2.5 Other Detention Options 51 2.9.3.8 III-3.3 Infiltration Facilities for Flow Control and for Treatment 51 2.9.3.9 III-3.3.5 Site Characterization 51 2.9.4 Volume IV: Source Control BMPs 52 2.9.4.1 Appendix IVG: Recommendations for Management of Street Wastes 52 2.9.5 Volume V: Runoff Treatment BMPs 52 2.9.5.1 Chapter V-4 - General Requirements for Stormwater 52 2.9.5.2 Chapter V-5 - On-Site Stormwater Management 52 2.9.5.3 Chapter V-7 - Infiltration and Bioretention Treatment Facilities 53 2.9.5.4 Chapter V-9 - Biofiltration Treatment Facilities 53 2.9.5.5 Chapter V-10 - Wetpool 54 3.1 Rough Grade Permits 55 3.2 Clearing and Grading Permits 55 3.3 Small Projects 56 3.4 Medium Projects 56 3.5 Large Projects 56 4.1 Small Project Submittal Requirements 57 4.2 Small Project Construction Stormwater Pollution Prevention Requirements 58 4.3 Permit Process for Small Projects 58 4.4 Fees for Small Projects 61 5.1 Medium Project Submittal Requirements 62 5.2 Project Requirements for Medium Projects 62 5.3 Permit Process for Medium Projects 62 5.4 Fees for Medium Projects 66 6.1 Project Classification 67 6.2 Project Requirements for Large Projects 67 6.3 Permit Process for Large Projects 67 6.4 Fees for Large Projects 71 6.5 Provide Accurate Record Drawings 71 7.1 Provide a Basic System of Drainage 73 7.2 Prevent Flooding of Inhabited Buildings 74 7.3 Minimize Erosion and Sedimentation 74 7.4 Minimize Water Quality Degradation 74 7.5 Don’t Mix Clean and Untreated Stormwater 74 7.6 Protect Water-Related Habitat 74 7.7 Maintain Recharge and Subsurface Flow Patterns 75 7.8 Address “Real-World” Conditions 75 7.9 Provide for Operation and Maintenance 75 7.10 Proceed Based on Clear, Professional Thinking 75 7.11 Meet Standards 75 8.1 Standard Specifications and Details 77 8.2 Proper Drainage 77 8.3 Stormwater Management and Infiltration in Critical Aquifer Recharge Areas 78 8.3.1 Critical Aquifer Recharge Areas 78 8.3.2 Construction in Critical Aquifer Recharge Areas 78 ---PAGE BREAK--- iv 8.3.3 Infiltration in Critical Aquifer Recharge Areas 79 8.3.4 Separation from High Groundwater 79 8.3.5 Defined Bottom of Stormwater Infiltration Facility 80 8.3.6 Using Infiltration as Basic 80 8.4 Conveyance System Design 80 8.4.1 Guidance Documents 80 8.4.2 Pipe Sizing 81 8.4.3 Ditch Sizing 81 8.4.4 Horizontal Clearance and Crossing Angle 81 8.4.5 Vertical Clearance – Utilities 82 8.4.6 Minimum Cover 83 8.4.7 Unstable Soils 83 8.4.8 Maximum and Minimum Slopes 83 8.4.9 Stream Culverts 83 8.4.10 Trees 83 8.4.11 Pump System Requirements 84 8.4.12 Underdrains 84 8.5 Catch Basin and Manhole Requirements 84 8.5.1 Structure Materials 84 8.5.2 Structure Spacing 84 8.5.3 Pipe Connections 85 8.5.4 Spill Prevention Device 85 8.5.5 85 8.5.6 Drop 85 8.5.7 Lot and Area Drains 85 8.5.8 Through-Curb Inlet Frames 85 8.5.9 Catch Basins and Americans with Disabilities Act 86 8.6 Site Design 86 8.6.1 Flood Protection 86 8.6.2 Single Family Residential Plats and Short Plats 86 8.6.3 Drainage Connections for All Lots 86 8.6.4 Single Family Roof and Foundation Drain Requirements 87 8.6.5 Separation of Systems Serving Separate Owners 87 8.6.6 Grading 88 8.6.7 Rockeries/Retaining Walls 88 8.6.8 Easements 88 8.6.8.1 Public Easements 88 8.6.8.2 Private Easements 89 8.6.9 Stormwater 90 8.6.9.1 Maintenance Access 90 8.6.9.2 Facility Maintenance 91 8.6.10 Transfer of Assets to the Public 91 8.6.11 Infiltration Setbacks 91 8.6.13 Artificial Turf 92 8.7 Low Impact Development (LID) 93 8.7.1 LID Overview 93 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 v 8.7.2 Site Assessment for LID 93 8.7.3 Intent of LID 93 8.7.4 Land Use 94 8.7.4.1 Minimize Development Envelope 94 8.7.4.2 Retain Areas of Native Vegetation 94 8.7.4.3 Preserve Native Soils 95 8.7.4.4 Compost Amendment of Soils 95 8.7.4.5 Minimize Impervious Surfaces 95 8.7.4.6 Rustic Street Standard 96 8.7.5 LID BMPs 97 8.7.5.1 Compost Amendment of Soils 97 8.7.5.2 Dispersion 97 8.7.5.3 Bioretention 97 8.7.5.4 Permeable Pavement & Functional Equivalency 98 8.7.5.5 Vegetated Roofs 98 8.7.6 LID in Critical Aquifer Recharge Areas 102 8.7.7 Evaluation and Monitoring 103 8.7.8 Bioretention Limitations 103 8.8 Regional Facilities Program 103 8.8.1 Downtown 104 8.8.2 Overlake 105 8.8.4 Outside Regional Surcharge Areas 107 8.9 Other Development Topics 108 8.9.1 Internal Building Changes as Redevelopment 108 8.9.2 Site Improvements Involving Hazardous Materials 108 8.9.3 Garbage and Recycling Area Stormwater Drainage 108 8.9.4 Water Features 108 8.9.5 Stormwater Fee Calculations 109 8.9.5.1 Citywide Stormwater CFC 109 8.9.5.2 Regional Stormwater CFC 109 8.9.5.3 CFC Fee Calculations 110 8.9.6 Modifications to Stormwater Facilities 110 9.1 Key Points to Address 112 9.2 Contents of Construction Stormwater Pollution Prevention Plan 115 9.3 National Pollutant Discharge Elimination Systems Permit 116 10.1 Introduction 117 10.2 TESC Standards 118 10.3 Special Requirements for Rainy-Season Work 119 10.4 Rough Grading Permits 120 10.5 Explanation of the Rain-Season Clearing/Grading Matrix 120 10.5.1 Location(s) of Work Area(s) 120 10.5.2 Slope of the Land Surface 121 10.5.3 Soil(s) 121 10.5.4 Amount of Land Disturbed 122 10.6 How to Use the Rainy-Season Clearing/Grading Matrix 122 10.6.1 Temporary Erosion and Sediment Control (TESC) Levels 123 ---PAGE BREAK--- vi 10.7 Project Planning Implications 123 10.7.1 General Project Planning Stage 124 10.7.2 Monitoring Requirements 124 10.7.3 Preliminary Design and Application Stage 125 10.7.4 Project Approval Stage 125 10.7.5 Construction Documents Stage 126 10.7.6 Pre-Construction 126 10.7.7 Construction Stage 126 10.8 Appeals: Wet Weather Committee 127 Appendix A - Standard Notes 140 Appendix B - Small Site Template 142 Appendix C - Critical Aquifer 150 Appendix D - Minimum Requirement 5 Map 151 152 Appendix E - Minimum Requirement Map 6 153 Appendix F - Minimum Requirement Map 7 155 Appendix G - SR520 Drainage Basin (North Overlake Flow Control Standard) 157 Appendix H – Map of Historical Land Cover 159 Appendix I - O & M Manual Template 161 Appendix J - Flood Control Zone Application Form 169 Appendix K - Typical Drainage Easement 172 Appendix L - Bill of Sale and Instructions Form 178 Appendix M - Developer Extension Asset Summary Form 182 Appendix N - LID Site Assessment Form 186 Appendix O - Regional Facilities Map 193 Appendix P - Downtown Stormwater Infrastructure Map 195 Appendix Q - Overlake Stormwater Infrastructure Map 197 198 Appendix R - Capital Facilities Charge Form 199 Figure 1 1.2.4.1 Flowchart for Determining Requirements for New Development 8 Figure 2 1.2.4.2 Flowchart for Determining Requirements for Redevelopment 9 Figure 3 1.2.5.1 Flow Chart for Determining LID MR #5 Requirements 29 Figure 4 8.1 Regional Facilities 106 Figure 5 8.2 Downtown Surcharge Area 106 Figure 6 8.3 Overlake Surcharge Area 107 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 vii Table 2.0 On-site Stormwater Management Requirements 25 Table 2.1 Typical Modeling Approaches for Underground Structures 48 Table 4.0 Small Project 61 Table 5.0 Medium Project Requirements 66 Table 6.0 Large Project Requirements 71 Table 8.1 Vertical Clearance – Utilities 82 Table 8.2 CFC Fee Calculations 110 Table 10.1 Hydrologic Groups for Area Soils 128 Table 10.2 Rainy-Season Clearing/Grading Matrix: Work Located in Critical Areas 135 Table 10.3 TESC Requirements 136 Table 10.4 Monitoring Requirements 137 ---PAGE BREAK--- ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 1 Chapter 1 – Introduction The Stormwater Technical Notebook locally modifies the Washington State Department of Ecology’s 2012 Stormwater Management Manual for Western Washington as amended in 2014 (2014 and defines how the 2014 is to be applied in the City of Redmond, and provides information and standards specific to stormwater management in Redmond. The Stormwater Technical Notebook, and Redmond’s Stormwater Management Program, applies to all lands within City limits. The Stormwater Technical Notebook is intended to assist those who prepare and submit applications and construction documents by providing design requirements and permit processing information in Redmond. The methods outlined in the Stormwater Technical Notebook are not the only methods acceptable for use in the City, but any deviations from these must still meet or exceed the intended results and be reviewed and approved by the City. 1.1. Code Requirements Code requirements regarding stormwater management are in the Redmond Municipal Code, Chapter 15.24. The Stormwater Technical Notebook is a supplement to the code and the code should also be reviewed to understand the procedures and requirements. The design, construction, and maintenance of all clearing, grading and stormwater management systems and facilities shall comply with the requirements and design standards contained in all the following documents, and provided in order of precedence: 1. RMC 15.24 2. The Stormwater Technical Notebook 3. City of Redmond Standard Specifications and Details 4. The Washington State Department of Ecology’s 2012 Stormwater Management Manual for Western Washington as amended in 2014. 1.2. Permitting Review Process The permitting review process is a partnership between the applicant and City representatives. Throughout the Stormwater Technical Notebook, there are specific stormwater management alternatives that may be approved for a specific project with the approval of the Stormwater Engineer or the Technical Committee. Private ---PAGE BREAK--- 2 development projects are reviewed by a Stormwater Engineer within the Development Services Division of the Planning Department. Public capital improvement projects are reviewed by a Stormwater Engineer within the Environmental & Utility Services Division of Public Works. In some instances, the City’s Technical Committee will review a project. Chapters 3, 4, 5, and 6 go into more detail about the review process for specific project types. 1.3. Vesting This document is subject to periodic revision. The issue dates are listed below. The version of the Stormwater Technical Notebook that applies to a particular project is the version that is (or was) in effect when the proposed project was “vested.” If a newer version of the Stormwater Technical Notebook is published after a project is vested, the project will have the right to use the newer version of the Stormwater Technical Notebook in its entirety, or the older version in its entirety. Projects are vested when: • A project subject to a Building Permit is vested when a Building Permit Application is submitted and determined to be complete by the City. • A Plat or a Short Plat is vested when the application for the Preliminary Plat or Short Plat is submitted and is deemed complete by the City. • A single-family lot, to be built as part of a plat, is vested as part of the preliminary plat or short plat, provided that its building permit application is submitted within five years of final plat approval. • A project involving only clearing or grading is vested when an application for the clearing and/or grading work is submitted and determined to be complete by the City. • Capital project design standards are vested at the completion of 30% design. For larger projects, this is signified by approval of Phase Gate 2 by the City’s CIP Governance Committee. For smaller projects, this is signified by acceptance by the Stormwater Engineer of the 30% design documents for review. • A project that is in the City’s PREP process, that has submitted a complete PREP Round 1 submittal by March 31, 2019 is vested to the March 1, 2017 Stormwater Technical Notebook. Note that this vesting applies only to the requirements of this Stormwater Technical Notebook. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 3 1.4. Additional Permit Requirements Additional City of Redmond permit requirements and special conditions apply to clearing, grading, or stormwater work in some circumstances. While not necessarily a complete list, the following regulations often apply to clearing, grading, and/or stormwater work in or near Critical Areas or Shorelines (defined in the Redmond Zoning Code). Contact the City of Redmond Development Services Center for more information about work within Shorelines, critical area or their buffers: • Shorelines – Can apply to projects within 200 feet of Bear Creek, Evans Creek, the Sammamish River, Lake Sammamish, and their associated floodplains and wetlands. • Critical Areas – Can apply if your project proposes work (as defined in the Redmond Zoning Code 21.64) within: o fish and wildlife habitat conservation areas; o wetlands; o geologically hazardous areas; o frequently flooded areas; or o critical aquifer recharge areas. Other agencies may also have requirements and permits related to work in Redmond. While not necessarily a complete list, the following agencies and their permits may have permits/regulations that apply to your project: • Washington State Department of Fish and Wildlife – Hydraulic Project Approval (HPA) for work below the Ordinary High Water Mark (OHWM) of surface waters including intermittent streams (work that uses, diverts, obstructs or changes natural flow or bed of State waters). • Washington State Department of Ecology – NPDES Permit(s): programs related to water quality management from construction sites of 1 acre or more. Water Quality Certification (401) ensures that limits placed in a permit on the quantity and concentration of pollutants discharged are not exceeded. • U.S. Army Corps of Engineers – a number of permits (under Section 404 of the Clean Water Act and Section 10 of the Rivers and Harbors Act) related to protection of “waters of the United States” including wetlands, streams and other surface waters. As appropriate the Army Corps will coordinate with the NOAA Fisheries (regarding federally listed anadromous species such as salmon) and U.S. Department of Fish and Wildlife (regarding federally listed land or freshwater species – such as eagles or bull trout) to ensure Endangered Species Act consistency. • U.S. Coast Guard & Washington State Department of Natural Resources are also involved in certain projects involving impacts (such as a bridge) over or adjacent to navigable waters (Class 1 Streams) • Federal Emergency Management Agency – programs related to flood protection near major streams and rivers, including but not limited to Bear ---PAGE BREAK--- 4 Creek, Evans Creek, and the Sammamish River. Compensatory storage may be required for some projects. The Redmond Zoning Code (RZC 21.64.040.C2.A) refers to a City program supporting coordination between private development and capital improvement projects for cooperative compensatory storage. Unfortunately, that program is currently inactive. Also note that any work proposed beyond the applicant’s property limits requires written concurrence of the owners of those properties. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 5 Chapter 2 – Modifications to the Washington State Department of Ecology Stormwater Management Manual for Western Washington 2.1. Redmond Requirements This chapter describes Redmond-specific requirements that may vary from or clarify elements of the Washington State Department of Ecology’s 2012 Stormwater Management Manual for Western Washington as amended in 2014 (2014 Sections 2.2 through 2.8 mirror those sections that appear in Volume I of the 2014 Modifications and additions specific to the City of Redmond are in red italic. Section 2.9 describes modifications in the rest of the 2014 specific to Redmond. 2.2. Exemptions from Ecology’s Minimum Requirements Unless otherwise indicated in this Section, the practices described in this section are exempt from the Minimum Requirements, even if such practices meet the definition of new development or redevelopment. RMC 15.24 requires a clearing and grading permit for some projects that may be exempt from Ecology’s Minimum Requirements. Forest practices: Forest practices regulated under Title 222 WAC, except for Class IV General Forest practices that are conversions from timber land to other uses, are exempt from the provisions of the minimum requirements. Commercial agriculture: Commercial agriculture practices involving working the land for production are generally exempt. However, the conversion from timberland to agriculture, and the construction of impervious surfaces are not exempt. Pavement Maintenance: The following pavement maintenance practices are exempt: pothole and square cut patching, overlaying existing asphalt or concrete pavement with asphalt or concrete ---PAGE BREAK--- 6 without expanding the area of coverage, shoulder grading, reshaping/regrading drainage systems, crack sealing, resurfacing with in-kind material without expanding the road prism, pavement preservation activities that do not expand the road prism, and vegetation maintenance. The following pavement maintenance practices are not categorically exempt. The extent to which the manual applies is explained for each circumstance. • Removing and replacing a paved surface to base course or lower, or repairing the pavement base: If impervious surfaces are not expanded, Minimum Requirements #1 - #5 apply. • Extending the pavement edge without increasing the size of the road prism, or paving graveled shoulders: These are considered new impervious surfaces and are subject to the minimum requirements that are triggered when the thresholds identified for new or redevelopment projects are met. • Resurfacing by upgrading from dirt to gravel, asphalt, or concrete; upgrading from gravel to asphalt, or concrete; or upgrading from a bituminous surface treatment (“chip seal”) to asphalt or concrete: These are considered new impervious surfaces and are subject to the minimum requirements that are triggered when the thresholds identified for new or redevelopment projects are met. Underground utility projects: Underground utility projects that replace the ground surface with in-kind material or materials with similar runoff characteristics are only subject to Minimum Requirement Construction Stormwater Pollution Prevention. 2.3. Definitions Related to the Minimum Requirements Definitions related to minimum requirements have been adopted and not modified by the City as required by the NPDES permit. Those definitions can be found in the glossary of Volume I of the 2.4. Applicability of the Minimum Requirements Not all of the Minimum Requirements apply to every development or redevelopment project. The applicability varies depending on the project type and size. This section identifies thresholds that determine the applicability of the Minimum Requirements to different projects. Use the flow charts in Figure 2.4.1 and 2.4.2 to determine which of the Minimum Requirements apply. The Minimum Requirements themselves are presented in Section 2.5. Project proponents are ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 7 required to submit an annotated copy of the flow charts indicating how they determined the Minimum Requirements applicable to their project. For purposes of applying the thresholds, all single-family developments that include subdivision of property shall be classified as New Development and all their hard surfaces classified as new hard surfaces. Hard surfaces shall be assumed to equal 80% of the maximum impervious area allowed by zoning code. If actual proposed impervious area is unknown, for large single-family lots, 4,200 s.f. of impervious area per lot may be used with approval from the Stormwater Engineer. For the purpose of applying thresholds to artificial turf or shallow soil over underground parking garages or vaults, surfaces shall be classified as they are to be modeled (See Table 2.1 in Section 2.9.3 below). Use the thresholds in Figures 1-2.4.1 and 1-2.4.2 at the time of application for a subdivision, plat, short plat, building permit, or other construction permit. The plat or short plat approval shall identify all stormwater BMPs that are required for each lot. For projects involving only land disturbing activities, clearing or grading), the thresholds apply at the time of application for the permit allowing or authorizing that activity. Note the exemption in Section 2.2 for forest practices other than Class IV General. ---PAGE BREAK--- 8 Figure 1 1.2.4.1 Flowchart for Determining Requirements for New Development ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 9 Figure 2 1.2.4.2 Flowchart for Determining Requirements for Redevelopment ---PAGE BREAK--- 10 2.4.1 New Development All new development shall be required to comply with Minimum Requirement The following new development shall comply with Minimum Requirements #1 through #5 for the new and replaced hard surfaces and the land disturbed: • Results in 2,000 square feet, or greater, of new, replaced, or new plus replaced hard surface area, or • Has land disturbing activity of 7,000 square feet or greater. The following new development shall comply with Minimum Requirements #1 through #9 for the new and replaced hard surfaces and the converted pervious surfaces: • Results in 5,000 square feet, or greater, of new plus replaced hard surface area, or • Converts 3/4 acres, or more, of vegetation to lawn or landscaped areas, or • Converts 2.5 acres, or more, of native vegetation to pasture. 2.4.2 Redevelopment All redevelopment shall be required to comply with Minimum Requirement The following redevelopment shall comply with Minimum Requirements #1 through #5 for the new and replaced hard surfaces and the land disturbed: • Results in 2,000 square feet or more, of new plus replaced hard surface area, or • Has land disturbing activity of 7,000 square feet or greater. The following redevelopment shall comply with Minimum Requirements #1 through #9 for the new hard surfaces and converted pervious areas: • Adds 5,000 square feet or more of new hard surfaces or, • Converts 3/4 acres, or more, of vegetation to lawn or landscaped areas, or • Converts 2.5 acres, or more, of native vegetation to pasture. With approval of the Stormwater Engineer, the Minimum Requirements may be met for an equivalent (flow and pollution characteristics) area within the same site. For public roads’ projects, the equivalent area does not have to be within the project limits, but must drain to the same receiving water. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 11 Additional Requirements for the Project Site For road-related projects, runoff from the replaced and new hard surfaces (including pavement, shoulders, curbs, and sidewalks) and the converted vegetated areas shall meet all the Minimum Requirements if the new hard surfaces total 5,000 square feet or more and total 50% or more of the existing hard surfaces within the project limits. The project limits shall be defined by the length of the project and the width of the right-of-way. Other types of redevelopment projects shall comply with Minimum Requirements #1 through #9 for the new and replaced hard surfaces and the converted vegetated areas if the total of new plus replaced hard surfaces is 5,000 square feet or more, and the valuation of proposed improvements – including interior improvements – exceeds 50% of the assessed value of the existing site improvements. Redmond does not have the “stop-loss” provision described in the 2014 2.5 Minimum Requirements This section describes the Minimum Requirements for stormwater management at development and redevelopment sites. Section 2.4 should be consulted to determine which requirements apply to any given project. Figures 2.4.1 and 2.4.2 should be consulted to determine whether the minimum requirements apply to new surfaces, replaced surfaces or new and replaced surfaces. Volumes II through V of the 2014 present Best Management Practices (BMPs) for use in meeting the Minimum Requirements. 2.5.1 Minimum Requirement Preparation of Stormwater Site Plans (Stormwater Reports) All projects meeting the thresholds in Section 2.4 shall prepare a Stormwater Site Plan for City review. Stormwater Site Plans (Stormwater Reports) shall use site- appropriate low impact development principles, as required and encouraged by development codes, to retain native vegetation and minimize impervious surfaces to the extent feasible. Stormwater Site Plans shall be prepared in accordance with Volume I, Chapter 3 of the 2014 Site Plans shall identify if the proposed project is classified as small, medium, or large. See Chapter 3 of this Stormwater Technical Notebook for site classifications in Redmond. Include Standard Notes (Appendix ---PAGE BREAK--- 12 2.5.2 Minimum Requirement Construction Stormwater Pollution Prevention (SWPP) All new development, redevelopment and maintenance projects are responsible for preventing erosion and discharge of sediment and other pollutants into receiving waters. Projects which result in 2,000 square feet or more of new plus replaced hard surface area, or which disturb 7,000 square feet or more of land must prepare a Construction SWPP Plan and TESC plan sheet as part of the Stormwater Site Plan (see Section 2.5.1). Projects that result in less than 2,000 square feet of new plus replaced hard surface area, or disturb less than 7,000 square feet of land are not required to prepare a Construction but must consider all of the 13 Elements of Construction Stormwater Pollution Prevention and develop controls for all elements that pertain to the project site. Small projects, as classified in Chapter 3 of the Stormwater Technical Notebook, may submit an abbreviated in accordance with the City’s Small Site Abbreviated template (Appendix General Requirements The shall include a narrative and a TESC Plan sheet for civil review. All BMPs shall be clearly referenced in the narrative and marked on the drawings. The narrative shall include documentation to explain and justify the pollution prevention decisions made for the project. Each of the 13 elements must be considered and included in the Construction unless site conditions render the element unnecessary and the exemption from that element is clearly justified in the narrative of the Clearing and grading activities for developments shall be permitted only if conducted pursuant to an approved site development plan subdivision approval) that establishes permitted areas of clearing, grading, cutting, and filling. These permitted clearing and grading areas and any other areas required to preserve critical or sensitive areas, buffers, native growth protection easements, or tree retention areas shall be delineated on the site plans and the development site. The shall be implemented beginning with initial land disturbance and until final stabilization. Sediment and Erosion control BMPs shall be consistent with the BMPs contained in Chapters 3 and 4 of Volume II of the ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 13 Seasonal Work Limitations - From October 1 through April 30, clearing, grading, and other soil disturbing activities shall only be permitted if approved by Redmond’s Wet Weather Committee. An approval to perform work during the wet weather season (October 1 – April 30) shall require a wet weather plan and seasonal suspension plan. See Chapter 10 of the Stormwater Technical Notebook for additional details. Such approval will only be granted if the proposal has shown that silt-laden runoff will be prevented from leaving the site through a combination of the following: 1. Site conditions including existing vegetative coverage, slope, soil type and proximity to receiving waters. 2. Limitations on activities and the extent of disturbed areas. 3. Proposed erosion and sediment control measures. Based on the information provided and/or local weather conditions, the City may expand or restrict the seasonal limitation on site disturbance. Redmond may take enforcement action – such as a notice of violation, seasonal suspension of work, administrative order, penalty, or stop-work order under the following circumstances: • If, during any construction activity or soil disturbance within the seasonal limitation period, sediment or contaminants leave the construction site causing a violation of the Washington State surface water quality standard or groundwater quality standard; or • If clearing and grading limits or erosion and sediment control measures shown in the approved plan are not maintained. The following activities are exempt from the seasonal clearing and grading limitations: 1. Routine maintenance and necessary repair of erosion and sediment control BMPs. 2. Routine maintenance of public facilities or existing utility structures that do not expose the soil or result in the removal of the vegetative cover to soil. 3. Activities where there is one hundred percent infiltration of surface water runoff within the site in approved and installed erosion and sediment control facilities. Project proponents are required to notify the City of Redmond immediately if a turbidity reading of 25 NTU or higher is measured, or a visible sheen or other pollutant is observed entering the stormwater system or receiving water. (Redmond Spill Hotline: 425/556-2868.) Projects discharging such pollutants during construction are required to take immediate action, applying additional temporary erosion and sedimentation control measures, or other applicable BMPS, to reduce pollutant export from the site. If a site discharges directly to a surface water body, the NTU limit is ---PAGE BREAK--- 14 based on the standards in WAC 173-201. In general, projects are not allowed to discharge sediment-laden water to surface waters unless the background turbidity is not increased by more than 5 NTU. Project sites in seasonal suspension are to meet this requirement. If a site requires an NPDES General Construction Stormwater Permit from Washington Department of Ecology, the project will be required to show evidence that they hold a permit prior to project commencement. If requested by the construction inspector, copies of information submitted to Ecology for NPDES construction permit compliance will be given to the City of Redmond. Project Requirements - Construction Elements Element 1: Preserve Vegetation/Mark Clearing Limits • Before beginning land disturbing activities, including clearing and grading, clearly mark all clearing limits, sensitive areas and their buffers, and trees that are to be preserved within the construction area. • Retain the duff layer, native top soil, and natural vegetation in an undisturbed state to the maximum degree practicable. Element 2: Establish Construction Access • Limit construction vehicle access and exit to one route, if possible. • Stabilize access points with a pad of quarry spalls, crushed rock, or other equivalent BMPs, to minimize tracking of sediment onto public roads. • Locate wheel wash or tire baths on site, if the stabilized construction entrance is not effective in preventing tracking sediment onto roads. • If sediment is tracked off site, clean the affected roadway thoroughly at the end of each day, or more frequently as necessary (for example, during wet weather). Remove sediment from roads by shoveling, sweeping, or pick up and transport the sediment to a controlled sediment disposal area. • Street flushing of sediment into stormwater systems is prohibited in Redmond. • Wheel wash station may be required by the City’s construction inspector if track out is not controlled with other measures. Element 3: Control Flow Rates • Protect properties and waterways of development sites from erosion and the associated discharge of turbid waters due to increases in the velocity and peak volumetric flow rate of stormwater runoff from the project site. • Where necessary to comply with the bullet above, construct stormwater retention or detention facilities as one of the first steps in grading. Assure ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 15 that detention facilities function properly before constructing site improvements impervious surfaces). • Permanent infiltration facilities shall not be operational or used to control/treat runoff during construction. Runoff may be infiltrated in locations other than where permanent infiltration and LID facilities will be constructed. Element 4: Install Sediment Controls • Design, install, and maintain effective erosion controls and sediment controls in accordance with the Redmond Standard Specifications and Details to minimize the discharge of pollutants. • Construct sediment control BMPs (sediment ponds, traps, filters, etc.) as one of the first steps in grading. These BMPs shall be functional before other land disturbing activities take place, and shall be maintained and removed once the site is stabilized and the inspector approves removal. • Minimize sediment discharges from the site. The design, installation and maintenance of erosion and sediment controls must address factors such as the amount, frequency, intensity and duration of precipitation, the nature of resulting stormwater runoff, and soil characteristics, including the range of soil particle sizes expected to be present on the site. • Direct stormwater runoff from disturbed areas through a sediment pond or other appropriate sediment removal BMP, before the runoff leaves a construction site or before discharge to an infiltration facility. Runoff from fully stabilized areas may be discharged without a sediment removal BMP, but must meet the flow control performance standard in Element bullet Full stabilization means concrete or asphalt paving; quarry spalls used as ditch lining; or the use of rolled erosion products, a bonded fiber matrix product, or vegetative cover in a manner that will fully prevent soil erosion. Redmond inspectors shall determine if an area is stabilized by means other than pavement or quarry spalls. • Locate BMPs intended to trap sediment on-site in a manner to avoid interference with the movement of juvenile salmonids attempting to enter off-channel areas or drainages. • Where feasible, design outlet structures that withdraw impounded stormwater from the surface to avoid discharging sediment that is still suspended lower in the water column. • Earthen structures such as dams, dikes, and diversions shall be seeded and mulched according to the timing indicated in element 5. Element 5: Stabilize Soils • Stabilize exposed and unworked soils by application of effective BMPs that prevent erosion. Applicable BMPs include, but are not limited to: temporary and permanent seeding, sodding, mulching, plastic covering, erosion control ---PAGE BREAK--- 16 fabrics and matting, the early application of gravel base early on areas to be paved, and dust control. • Soil stabilization measures selected should be appropriate for the time of year, site conditions, estimated duration of use, and potential water quality impacts that stabilization materials may have on waters or groundwater. • Control stormwater volume and velocity within the site to minimize soil erosion. • Control stormwater discharges, including both peak flow rates and total stormwater volume, to minimize erosion at outlets and to minimize channel and stream bank erosion. • Soils must not remain exposed and unworked for more than the time periods set forth below to prevent erosion: o During the dry season (May 1 - Sept. 30): 7 days o During the wet season (October 1 - April 30): 2 days o This condition applies to all soils on site, whether at final grade or not. Redmond inspectors may adjust time limits depending on site conditions, forecasted weather, site characteristics, and to protect human safety, habitat, and property • Stabilize soils at the end of the shift before a holiday or weekend if needed based on the weather forecast. • Stabilize soil stockpiles from erosion, protected with sediment trapping measures, and where possible, be located away from storm drain inlets, waterways and drainage channels. • Minimize the amount of soil exposed during construction activity. • Do not disturb steep slopes. • Minimize soil compaction and, unless infeasible, preserve topsoil. • Linear construction activities, including right-of-way and easement clearing, roadway development, pipelines, and trenching for utilities, shall be conducted to meet the soil stabilization requirement. Contractors shall install the bedding materials, roadbeds, structures, pipelines, or utilities and re-stabilize the disturbed soils so that: o From October 1 through April 30 no soils shall remain exposed and unworked for more than 2 days; and o From May 1 to September 30, no soils shall remain exposed and unworked for more than 7 days. Element 6: Protect Slopes • Design and construct cut-and-fill slopes in a manner to minimize erosion. Applicable practices include, but are not limited to, reducing continuous length of slope with terracing and diversions, reducing slope steepness, and roughening slope surfaces (for example, track walking). • Divert off-site stormwater (run-on) or ground water away from slopes and disturbed areas with interceptor dikes, pipes and/or swales. Off-site ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 17 stormwater should be managed separately from stormwater generated on the site. • At the top of slopes, collect drainage in pipe slope drains or protected channels to prevent erosion. • Temporary pipe slope drains must handle the peak volumetric flow rate calculated using a 10-minute time step from a Type 1A, 10-year, 24-hour frequency storm for the developed condition. Alternatively, the 10-year and 1-hour flow rate predicted by an approved continuous runoff model, increased by a factor of 1.6, may be used. The hydrologic analysis must use the existing land cover condition for predicting flow rates from tributary areas outside the project limits. For tributary areas on the project site, the analysis must use the temporary or permanent project land cover condition, whichever will produce the highest flow rates. If using the Western Washington Hydrology Model (WWHM) to predict flows, bare soil areas should be modeled as "landscaped" area. • Place excavated material on the uphill side of trenches, consistent with safety and space considerations. • Place check dams at regular intervals within constructed channels that are cut down a slope. • Provide drainage to remove groundwater intersecting the slope surface of exposed soil areas. • Stabilize soils on slopes, as specified in Element Element 7: Protect Drain Inlets • Protect all storm drain inlets made operable during construction so that stormwater runoff shall not enter the conveyance system without first being filtered or treated to remove sediment. Catch basins are considered operational when stormwater flows are allowed to enter the catch basin. If stormwater is allowed to enter the side of the catch basin, inlet protection is still required for those flows. • All approach roads shall be kept clean. Approach roads shall have inlet protection if they could be impacted by the construction site and at the discretion of the City Inspector. • Clean or remove and replace inlet protection devices when sediment has filled one-third of the available storage (unless a different standard is specified by the product manufacturer). • When projects are completed, removal of inlet protection devices is required. Removal will be done in a way that does not allow the captured sediment to enter or later be washed into the stormwater inlet. Element 8: Stabilize Channels and Outlets • Design, construct, and stabilize all on-site conveyance channels to prevent erosion from the following expected peak flows: ---PAGE BREAK--- 18 o Channels must handle the peak volumetric flow rate calculated using a 10-minute time step from a Type 1A, 10- year, 24-hour frequency storm for the developed condition. Alternatively, the 10-year, 1-hour flow rate indicated by an approved continuous runoff model, increased by a factor of 1.6, may be used. The hydrologic analysis must use the existing land cover condition for predicting flow rates from tributary areas outside the project limits. For tributary areas on the project site, the analysis must use the temporary or permanent project land cover condition, whichever will produce the highest flow rates. If using the Western Washington Hydrology Model (WWHM) to predict flows, bare soil areas should be modeled as "landscaped area. o Provide stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes and reaches at the outlets of all conveyance systems. Element 9: Control Pollutants • Design, install, implement and maintain effective pollution prevention measures to minimize the discharge of pollutants. See Section 8.3 for requirements specific to Critical Aquifer Recharge Areas. • Handle and dispose of all pollutants, including waste materials and demolition debris that occur on-site in a manner that does not cause contamination of soil, groundwater, or stormwater. • Provide cover, containment, and protection from vandalism for all chemicals, liquid products, petroleum products, and other materials that have the potential to pose a threat to human health or the environment. On-site fueling tanks must include secondary containment. Secondary containment means placing tanks or containers within an impervious structure capable of containing 110% of the volume contained in the largest take within the containment structure. Double-walled tanks do not require additional secondary containment. • Conduct maintenance, fueling, and repair of heavy equipment and vehicles using spill prevention and control measures. Clean contaminated surfaces immediately following any spill incident. • Discharge wheel wash or tire bath wastewater to a separate on-site treatment system that prevents discharge to surface water, such as closed- loop recirculation or upland application, or to the sanitary sewer, with City approval. • Apply agricultural chemicals, including fertilizers and pesticides in a manner and at application rates that will not result in loss of chemical to stormwater runoff. Follow manufacturers’ label requirements for application rates and procedures. • Use BMPs to prevent contamination of stormwater runoff by pH modifying sources. The sources for this contamination include, but are not limited to: bulk cement, cement kiln dust, fly ash, new concrete washing and curing ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 19 waters, waste streams generated from concrete grinding and sawing, exposed aggregate processes, dewatering concrete vaults, concrete pumping and mixer washout waters. • Stormwater discharges shall not cause or contribute to a violation of the water quality standard for pH in the stormwater drainage system or receiving water. Allowable runoff pH concentrations shall be within the range of 6.5 to 8.5 pH. • Adjust the pH of stormwater if necessary to prevent violations of water quality standards. • Ensure that washout of concrete trucks is performed off-site or in designated concrete washout areas only. Do not wash out concrete trucks onto the ground, or into storm drains, open ditches, streets, or streams. Do not dump excess concrete on-site, except in designated concrete washout areas. Concrete spillage or concrete discharge to surface waters of the State is prohibited. • Obtain written approval from Ecology before using chemical treatment other than CO2 or dry ice to adjust pH. • In Critical Aquifer Recharge Areas additional care and pollution control BMPs will be required by the City to protect the groundwater aquifer/drinking water supply. Review of TESC civil plans, Seasonal suspension plan, and wet weather plans in Critical Aquifer Recharge Areas will include more scrutiny and strict application of pollution controls. • Spill control materials suitable for applicable chemicals shall be kept on site. Element 10: Control De-Watering • For projects that involve temporary construction dewatering discharges greater than 500 gallons per minute follow the procedures established under City of Redmond Temporary Construction Dewatering Operating Policy authorized by RMC 13.25. Temporary construction dewatering shall not cause flooding or reduce the capacity of a stormwater runoff treatment system. • For projects that involve temporary construction dewatering of less than 500 gallons per minute follow the guidelines below. • Discharge foundation, vault, and trench de-watering water, which has similar characteristics to stormwater runoff at the site, into a controlled conveyance system before discharge to a sediment trap or sediment pond. • Discharge clean, non-turbid de-watering water, such as well-point ground water, to systems tributary to, or directly into surface waters of the State, as specified in Element provided the dewatering flow does not cause erosion or flooding of receiving waters. Do not route clean dewatering water through stormwater sediment ponds. Note that “surface waters of the State” may exist on a construction site as well as off site; for example, a creek running through a site. • Handle highly turbid or otherwise contaminated dewatering water, such as from construction equipment operation, clamshell digging, concrete tremie pour, or work inside a cofferdam, separately from stormwater. ---PAGE BREAK--- 20 • Other treatment or disposal options may include: 1. Infiltration. 2. Transport off-site in a vehicle, such as a vacuum flush truck, for legal disposal in a manner that does not pollute state waters. 3. Ecology-approved on-site chemical treatment or other suitable treatment technologies. 4. Sanitary or combined sewer discharge with City of Redmond and King County approval, if there is no other option. 5. Use of a sedimentation bag that discharges to a ditch or swale for small volumes of localized dewatering. Be prepared for possible bag failure. Element 11: Maintain BMPs • Maintain and repair all temporary and permanent erosion and sediment control BMPs as needed to assure continued performance of their intended function in accordance with BMP specifications. • Remove all temporary erosion and sediment control BMPs within 30 days after achieving final site stabilization or after the temporary BMPs are no longer needed. Element 12: Manage the Project • Phase development projects to the maximum degree practicable and take into account seasonal work limitations. • Inspection and monitoring – Inspect, maintain and repair all BMPs as needed to assure continued performance of their intended function. Projects regulated under the Construction Stormwater General Permit must conduct site inspections and monitoring in accordance with Special Condition S4 of the Construction Stormwater General Permit. • Maintaining an updated construction – Maintain, update, and implement the • Projects that disturb one or more acres must have site inspections conducted by a Certified Erosion and Sediment Control Lead (CESCL). Project sites disturbing less than one acre may have a CESCL or a person without CESCL certification conduct inspections. By the initiation of construction, the must identify the CESCL or inspector, who must be present on-site or on-call at all times. • The CESCL or inspector (project sites less than one acre) must have the skills to assess the: o Site conditions and construction activities that could impact the quality of stormwater. o Effectiveness of erosion and sediment control measures used to control the quality of stormwater discharges. • The CESCL or inspector must examine stormwater visually for the presence of suspended sediment, turbidity, discoloration, and oil sheen. They must ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 21 evaluate the effectiveness of BMPs and determine if it is necessary to install, maintain, or repair BMPs to improve the quality of stormwater discharges. Based on the results of the inspection, construction site operators must correct the problems identified by: o Reviewing the for compliance with the 13 construction elements and making appropriate revisions within 7 days of the inspection, or as directed by the inspector. o Immediately beginning the process of fully implementing and maintaining appropriate source control and/or treatment BMPs as soon as possible, addressing the problems not later than within 10 days of the inspection. If installation of necessary treatment BMPs is not feasible within 10 days, the construction site operator may request an extension within the initial 10-day response period. o Documenting BMP implementation and maintenance in the site log book (sites larger than 1 acre). • The CESCL or inspector must inspect all areas disturbed by construction activities, all BMPs, and all stormwater discharge points at least once every calendar week and within 24 hours of any discharge from the site. (For purposes of this condition, individual discharge events that last more than one day do not require daily inspections. For example, if a stormwater pond discharges continuously over the course of a week, only one inspection is required that week.) The CESCL or inspector may reduce the inspection frequency for temporary stabilized, inactive sites to once every calendar month. Coordination with Utilities and Other Contractors – The primary project proponent shall evaluate, with input from utilities and other contractors, the stormwater management requirements for the entire project, including the utilities, when preparing the Construction Element 13: Protect Low Impact Development BMPs • Protect all Bioretention and Rain Garden BMPs from sedimentation through installation and maintenance of erosion and sediment control BMPs on portions of the site that drain into the Bioretention and/or Rain Garden BMPs. Restore the BMPs to their fully functioning condition if they accumulate sediment during construction. Restoring the BMP must include removal of sediment and any sediment-laden Bioretention/rain garden soils, and replacing the removed soils with soils meeting the design specification. • Prevent compaction of Bioretention and rain garden BMPs by excluding construction equipment and foot traffic. Protect completed lawn and landscaped areas from compaction due to construction equipment. • Control erosion and avoid introducing sediment from surrounding land uses onto permeable pavements. Do not allow muddy construction equipment on the base material or pavement. Do not allow sediment-laden runoff onto permeable pavements or base materials. ---PAGE BREAK--- 22 • Pavement fouled with sediments or no longer passing an initial infiltration test must be cleaned using procedures in accordance with this manual or the manufacturer’s procedures. • Keep all heavy equipment off existing soils under LID facilities that have been excavated to final grade to retain the infiltration rate of the soils. 2.5.3 Minimum Requirement Source Control of Pollution All known, available and reasonable source control BMPs must be applied to all projects. Source control BMPs must be selected, designed, and maintained in accordance with the 2014 “Applicable” and “recommended” source controls in Volume IV of the 2014 are required and shall be documented in the Stormwater Site Plan required by Minimum Requirement and in the Operations and Maintenance Manual if the project triggers Minimum Requirement 2.5.4 Minimum Requirement Preservation of Natural Drainage Systems and Outfalls Natural drainage patterns shall be maintained, and discharges from the project site shall occur at the natural location, to the maximum extent practicable. The manner by which runoff is discharged from the project site must not cause a significant adverse impact to receiving waters and down gradient properties. All outfalls require energy dissipation. Where no conveyance system exists at the adjacent down-gradient property line and the discharge was previously unconcentrated flow or significantly lower concentrated flow, then measures shall be taken to prevent down-gradient significant adverse impacts. Drainage easements from property owners may be needed. If offsite easements are needed, they shall be obtained by the project proponent prior to approval of engineering plans. Any runoff concentrated by the proposed project must be discharged as follows: a. If the 100-year peak discharge is less than or equal to 0.2 cfs (0.3 cfs using 15 minute time steps) under existing conditions and will remain less than or equal to 0.2 cfs under developed conditions, then the concentrated runoff may be discharged onto a rock pad or to any other system that serves to disperse flows. b. If the 100-year peak discharge is less than or equal to 0.5 cfs (0.75 cfs using 15 minute time steps) under existing conditions and will remain less than or equal to 0.5 cfs under developed conditions, then the concentrated runoff may be discharged through a dispersal trench or other dispersal system, provided the applicant can demonstrate that there will be no significant adverse impact to down gradient properties, drainage systems, or natural areas. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 23 c. If the 100-year peak discharge is greater than 0.5 cfs for either existing or developed conditions, or if a significant adverse impact to down-gradient properties or drainage systems is likely, then a conveyance system must be provided to convey the concentrated runoff across the properties to an acceptable discharge point an enclosed drainage system or open drainage feature where concentrated runoff can be discharged without significant adverse impact). Designs for outfall systems to protect against adverse impacts from concentrated runoff are included in Volume V, Chapter 4, of the 2014 Stormwater control or treatment facilities are not permitted within stream or wetland buffers. Conveyance facilities may be permitted. Stormwater control or treatment structures should not be located within the expected 25-year water level elevations for salmonid-bearing waters. Such areas may provide off-channel habitat for juvenile salmonids and salmonid fry. Redmond Stormwater Engineer pre-approval is required for any structure proposed in the 25-year water level elevation of salmonid bearing streams. If the analysis required in Section 2.6 identifies conveyance deficiencies that may be caused or exacerbated by the proposed project, then offsite improvements may be required to avoid significant adverse impact to down gradient properties. 2.5.5 Minimum Requirement On-Site Stormwater Management Projects shall employ on-site stormwater management BMPs in accordance with the following projects thresholds, standards, and lists to infiltrate, disperse, and retain stormwater runoff on- site to the extent feasible without causing groundwater contamination, flooding, or erosion impacts. “Flooding and erosion impacts” include impacts such as flooding of septic systems, crawl spaces, living areas, outbuildings, etc.; increased ice or algal growth on sidewalks/roadways; earth movement/settlement, increased landslide potential; erosion and other potential damage. Section 8.3 describes some clarifications for infiltration in Critical Aquifer Recharge Areas to avoid “groundwater contamination” or other risks to the drinking water aquifer. Appendix C “Critical Aquifer Recharge Areas” provides a planning level map of where infiltrating runoff from pollution generating surfaces is limited and design requirements are locally amended to protect the drinking water aquifer. As is noted below, Minimum Requirement 5 On-Site Stormwater Management requirements are customized in areas draining to flow control exempt waterbodies (Sammamish River and Lake Sammamish) or areas where 100% infiltration is required. See Appendix D for a planning level map of the MR 5 custom areas. The ---PAGE BREAK--- 24 applicant is responsible for confirming that the site meets criteria indicated in the custom area. 2.5.5.1 Flow Control Exempt Areas Projects qualifying as flow control exempt in accordance with 2.5.7 Minimum Requirement Flow Control do not have to achieve the LID performance standard, nor consider bioretention, rain gardens, permeable pavement, or full dispersion if using List #1 or List However, those projects must implement the following: • BMP T5.13: Post-Construction Soil Quality and Depth; • BMP T5.10A: Downspout Full Infiltration, or BMP T5.10B: Downspout Dispersion Systems, or BMP T5.10C: Perforated Stub-out Connections; and • BMP T5.11: Concentrated Flow Dispersion or BMP T5.12: Sheet Flow Dispersion, if feasible. 2.5.5.2 Marymoor – 100% Infiltration Marymoor – 100% Infiltration area mapped in Appendix D has limited conveyance capacity or no conveyance at all. The Marymoor Subarea is shown in Redmond Zoning Code 21.13.060. The area also has highly infiltrative soils. As such, 100% of runoff shall be infiltrated in this area. Projects within this area demonstrate compliance with Minimum Requirement 5 by infiltrating 100% of their runoff. 2.5.5.3 40th Street Basin The 40th Street Basin is a new flow control exempt basin supported by a direct discharge stormwater trunk that was constructed in 2018. The City is adaptively managing the outfall to the lake, gradually increasing flows to the lake to avoid negative impacts to the lake shore environment. The gradual increase of flows at the City’s flow splitter means that the service area of direct discharge will change over time. Project proponents in this area should contact the Stormwater Engineer for specific guidance about use of the flow control exemption during this time of transition. The City estimates that by 2024, the full area noted on the map in Appendix D will be flow control exempt and subject to the requirements described in 2.5.5.1 above. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 25 Table 2.0 1-2.5.1 On-Site Stormwater Management Requirements for Projects Triggering Minimum Requirements #1 - #9 Project Type and Location Requirement New development Low Impact Development Performance Standard and BMP T5.13: Post-Construction Soil Quality and Depth; or List #2 (applicant option). Redevelopment on any parcel inside the UGA, or redevelopment outside the UGA on a parcel less than 5 acres All of Redmond is inside the UGA.) Low Impact Development Performance Standard and BMP T5.13: Post-Construction Soil Quality and Depth; or List #2 (applicant option). Redevelopment outside the UGA on a parcel of 5 acres or larger All of Redmond is inside the UGA.) Low Impact Development Performance Standard and BMP T5.13: Post-Construction Soil Quality and Depth. Note: This table refers to the Urban Growth Area (UGA) as designated under the Growth Management Act (GMA) (Chapter 36.70A RCW) of the State of Washington. If the Permittee is located in a county that is not subject to planning under the GMA, the city limits shall be used. Table 2.0 On-site Stormwater Management Requirements Low Impact Development Performance Standard Stormwater discharges shall match developed discharge durations to pre-developed durations for the range of pre-developed discharge rates from 8% of the 2-year peak flow to 50% of the 2-year peak flow. Refer to the Standard Flow Control Requirement section in Minimum Requirement #7 for information about the assignment of the pre-developed condition. Project sites that must also meet minimum requirement #7 – flow control - must match flow durations between 8% of the 2-year flow through the full 50-year flow. ---PAGE BREAK--- 26 List On-site Stormwater Management BMPs for Projects Triggering Minimum Requirements #1 through #5 For each surface, consider the BMP’s in the order listed for that type of surface. Use the first BMP that is considered feasible. No other On-site Stormwater Management BMP is necessary for that surface. Feasibility shall be determined by evaluation against: 1. Design criteria, limitations, and infeasibility criteria identified for each BMP in this manual; and 2. Competing Needs Criteria listed in Volume V, Chapter 5 of the - On-Site Stormwater Management. Lawn and landscaped areas: • Post-Construction Soil Quality and Depth in accordance with BMP T5.13: Post- Construction Soil Quality and Depth. Roofs: 1. Full Dispersion in accordance with BMP T5.30: Full Dispersion, or Downspout Full Infiltration Systems in accordance with BMP T5.10A: Downspout Full Infiltration 2. Rain Gardens in accordance with BMP T5.14A: Rain Gardens, or Bioretention in accordance with BMP T7.30: Bioretention Cells, Swales, and Planter Boxes. The rain garden or bioretention facility must have a minimum horizontal projected surface area below the overflow which is at least 5% of the area draining to it. 3. Downspout Dispersion Systems in accordance with BMP T5.10B: Downspout Dispersion Systems 4. Perforated Stub-out Connections in accordance with BMP T5.10C: Perforated Stub-out Connections Other Hard Surfaces: 1. Full Dispersion in accordance with BMP T5.30: Full Dispersion 2. Permeable pavement in accordance with BMP T5.15: Permeable Pavements, or Rain Gardens in accordance with BMP T5.14A: Rain Gardens, or Bioretention in accordance with BMP T7.30: Bioretention Cells, Swales, and Planter Boxes. The rain garden or bioretention facility must have a minimum horizontal projected surface area below the overflow which is at least 5% of the area draining to it. Note: If the project identifies permeable pavement as the required element for new or replaced hard surfaces that will be owned and maintained by the City, the project shall instead construct a functionally equivalent alternative to permeable pavement. If the ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 27 hard surfaces will be owned and maintained privately, functionally equivalent alternatives may be used. This policy exists because the goal of permeable pavement is to infiltrate stormwater and it is possible to provide that function without the maintenance burden that comes with permeable pavement. See Chapter 8 of the Stormwater Technical Notebook for discussion of Functional Equivalency. 3. Sheet Flow Dispersion in accordance with BMP T5.12: Sheet Flow Dispersion, or Concentrated Flow Dispersion in accordance with BMP T5.11: Concentrated Flow Dispersion. List On-site Stormwater Management BMPs for Projects Triggering Minimum Requirements #1 through #9 For each surface, consider the BMPs in the order listed for that type of surface. Use the first BMP that is considered feasible. No other On-site Stormwater Management BMP is necessary for that surface. Feasibility shall be determined by evaluation against: 1. Design criteria, limitations, and infeasibility criteria identified for each BMP in this manual; and 2. Competing Needs Criteria listed in Chapter V-5 - On-Site Stormwater Management. Lawn and landscaped areas: • Post-Construction Soil Quality and Depth in accordance with BMP T5.13: Post- Construction Soil Quality and Depth. Roofs: 1. Full Dispersion in accordance with BMP T5.30: Full Dispersion, or Downspout Full Infiltration Systems in accordance with BMP T5.10A: Downspout Full Infiltration. 2. Bioretention (See BMP T7.30: Bioretention Cells, Swales, and Planter Boxes) facilities must have a minimum horizontally projected surface area below the overflow which is at least 5% of the total surface area draining to it. 3. Downspout Dispersion Systems in accordance with BMP T5.10B: Downspout Dispersion Systems 4. Perforated Stub-out Connections in accordance with BMP T5.10C: Perforated Stub-out Connections Other Hard Surfaces: 1. Full Dispersion in accordance with BMP T5.30: Full Dispersion 2. Permeable pavement in accordance with BMP T5.15: Permeable Pavements ---PAGE BREAK--- 28 Note: If the project identifies permeable pavement as the required element for new or replaced hard surfaces that will be owned and maintained by the City, the project shall instead construct a functionally equivalent alternative to permeable pavement. If the hard surfaces will be owned and maintained privately, functionally equivalent alternatives may be used. This policy exists because the goal of permeable pavement is to infiltrate stormwater and it is possible to provide that function without the maintenance burden that comes with permeable pavement. See Chapter 8 of the Stormwater Technical Notebook for discussion of Functional Equivalency. 3. Bioretention BMP’s (BMP T7.30: Bioretention Cells, Swales, and Planter Boxes) that have a minimum horizontally projected surface area below the overflow which is at least 5% of the total surface area draining to it. 4. Sheet Flow Dispersion in accordance with BMP T5.12: Sheet Flow Dispersion, or Concentrated Flow Dispersion in accordance with BMP T5.11: Concentrated Flow Dispersion ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 29 Figure 3 1.2.5.1 Flow Chart for Determining LID MR #5 Requirements ---PAGE BREAK--- 30 2.5.6 Minimum Requirement Runoff Treatment Some areas in Redmond have unique runoff treatment requirements, as noted below. Appendix EE provides a planning level map of “Runoff Treatment Custom Areas.” All areas mapped as “2014 Basic or Enhanced” will use the 2014 to determine which type of runoff treatment is required. The following will discuss what is required in runoff treatment “custom areas” as mapped in Appendix E. The applicant is responsible for confirming that the site meets criteria indicated in the custom area. Critical Aquifer Recharge Areas Section 8.3 describes infiltrating runoff from pollution generating hard surfaces in Critical Aquifer Recharge Areas. Appendix Appendix C “Critical Aquifer Recharge Areas” provides a planning level map of where infiltrating runoff from pollution generating hard surfaces is limited and design requirements are locally amended to protect the drinking water aquifer. Overlake and Downtown Regional Facility Surcharge Areas Regional runoff treatment facilities have been built, or will be built in the Downtown and Overlake regional facility surcharge areas. Participation in the regional facilities is required in Overlake and Downtown (RMC 13.20). In these areas, projects do not need to build basic or enhanced runoff treatment facilities as those are provided for the project in a regional facility, except as noted below. If oil control is triggered by a project, oil control must be installed to treat runoff for the areas of the project that trigger oil control. The map in Appendix E shows the portion of the Downtown Surcharge Area where runoff treatment is addressed by these regional facilities. Some properties drain to streams within the surcharge area and will require runoff treatment if they trigger thresholds. The map in Appendix E shows the portion of the Overlake Surcharge Area where runoff treatment is addressed by these regional facilities. As noted in RMC 13.20, properties south of NE 26th Street are required to provide runoff treatment on site. Document fee calculations in the Stormwater report (Stormwater Site Plan). Provide exhibits to document how the fee is calculated. Phosphorous Control In 1989 a cooperative effort of Washington Department of Ecology, Issaquah, Redmond, King County, and Bellevue published the Lake Sammamish Water Quality Management Project Technical Report. In the report, reducing stormwater loading of ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 31 phosphorous to Lake Sammamish was necessary to preserve water quality in the lake. As such, projects that drain through pipes or streams into Lake Sammamish require phosphorous control treatment. If a project triggers oil control that is still required to treat the runoff that triggers oil control. SE Redmond In this area, regional facilities have been built that provide basic treatment. Some projects within this area may trigger enhanced treatment. This area does not have a mandatory surcharge. Projects proponents within this area are encouraged to contact the Stormwater Engineer to determine if the project can pay into the regional facility to address some or all of its treatment requirements. Otherwise, projects in this area must build runoff treatment facilities on-site. Light Rail The City supports Sound Transit’s position that light rail is non-pollution generating hard surface, with the following caveats: - If Sound Transit changes their proposed methods of operation, equipment, or source control in a way that may increase risk to the drinking water aquifer or receiving waters, then the City’s determination may change. - If Ecology makes a determination, the City will comply with Ecology requirements. - Locations where the light rail guideway is subject to automobile traffic, such as at- grade street crossings, are subject to stormwater runoff treatment based upon the automobile use of the area. Thresholds When assessing a project against the following thresholds, only consider those hard and pervious surfaces that are subject to this minimum requirement as determined in I-2.4 Applicability of the Minimum Requirements. The following require construction of stormwater treatment facilities: • Projects in which the total of pollution generating hard surface (PGHS) is 5,000 square feet or more in a threshold discharge area of the project, or • Projects in which the total of pollution-generating pervious surfaces (PGPS) – not including permeable pavements - is three-quarters (3/4) of an acre or more in a threshold discharge area, and from which there is a surface discharge in a natural or man-made conveyance system from the site. ---PAGE BREAK--- 32 Treatment Facility Sizing Stormwater treatment facilities shall be sized for the entire area that drains to them, even if some of those areas are not pollution-generating, or were not included in the project site threshold decisions (I-2.4 Applicability of the Minimum Requirements) or the treatment threshold decisions of this minimum requirement. Water Quality Design Storm Volume: • The volume of runoff predicted from a 24-hour storm with a 6-month return frequency 6-month, 24-hour storm). Wetpool facilities are sized based upon the volume of runoff predicted through use of the Natural Resource Conservation Service curve number equations in Chapter III-2 - Hydrologic Analysis, for the 6-month, 24-hour storm. Alternatively, when using an approved continuous runoff model, the water quality design storm volume shall be equal to the simulated daily volume that represents the upper limit of the range of daily volumes that accounts for 91% of the entire runoff volume over a multi-decade period of record. Water Quality Design Flow Rate: • Preceding Detention Facilities or when Detention Facilities are not required: The flow rate at or below which 91% of the runoff volume, as estimated by an approved continuous runoff model, will be treated. Design criteria for treatment facilities are assigned to achieve the applicable performance goal 80% TSS removal) at the water quality design flow rate. At a minimum, 91% of the total runoff volume, as estimated by an approved continuous runoff model, must pass through the treatment facility(ies) at or below the approved hydraulic loading rate for the facility(ies). • of Detention Facilities: The water quality design flow rate must be the full 2-year release rate from the detention facility. Treatment Facility Selection, Design, and Maintenance Stormwater treatment facilities shall be: • Selected in accordance with the process identified in Chapter 4 of Volume I of the 2014 as modified by the Stormwater Technical Notebook. • Designed in accordance with the design criteria in Volume V of the 2014 as modified by Chapter 8 of the Stormwater Technical Notebook, and • Maintained in accordance with the maintenance schedule in Volume V of the 2014 as modified by the Stormwater Technical Notebook. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 33 Additional Requirements Treatment facilities applied consistent with this Stormwater Technical Notebook and the 2014 are presumed to meet the requirement of state law to provide all known available and reasonable methods of treatment (RCW 90.52.040, RCW 90.48.010). This technology- based treatment requirement does not excuse any discharge from the obligation to apply whatever technology is necessary to comply with state water quality standards, Chapter 173- 201A WAC; state ground water quality standards, Chapter 173-200 WAC; state sediment management standards, Chapter 173-204 WAC; and the underground injection program, Chapter 173-218 WAC. Additional treatment to meet those standards may be required by the federal government, Washington State or the City of Redmond. Infiltration through use of On-site Stormwater Management BMPs can provide both treatment of stormwater, through the ability of certain soils to remove pollutants, and volume control of stormwater, by decreasing the amount of water that runs off to surface water. Infiltration through engineered treatment facilities that utilize the natural soil profile can also be very effective at treating stormwater runoff, but pretreatment must be applied and soil conditions must be appropriate to achieve effective treatment while not impacting ground water resources. See Section 8.3 for limitations to infiltration in Critical Aquifer Recharge Areas. See Chapter 6 of Volume V of the - Pretreatment for pretreatment design details. Impervious surfaces that are “fully dispersed” in accordance with BMP T5.30: Full Dispersion is not considered effective impervious surfaces. Impervious surfaces that are “dispersed” in accordance with BMP T5.10B: Downspout Dispersion Systems, BMP T5.11: Concentrated Flow Dispersion, and BMP T5.12: Sheet Flow Dispersion are still considered effective surfaces though they may be modeled as pervious surfaces if flow path meet the specified minima. See the 2014 Appendix II-C: Washington State Department of Ecology Low Impact Development Flow Modeling Guidance for a more complete description of hydrologic representation of On-site Stormwater Management BMPs. 2.5.7 Minimum Requirement Flow Control Applicability Projects must provide flow control to reduce the impacts of stormwater runoff from hard surfaces and land cover conversions. The requirement below applies to projects that discharge stormwater directly, or indirectly through a conveyance system, into a fresh waterbody. Flow control is not required for projects that discharge directly to, or indirectly through a conveyance system to Lake Sammamish or the Sammamish River subject to the following restrictions: ---PAGE BREAK--- 34 • Direct discharge to Lake Sammamish or the Sammamish River does not result in the diversion of drainage from any perennial stream classified as Class 1, 2, 3, or 4 in the State of Washington Interim Water Typing System, or Types or “Np” in the Permanent Water Typing System, or from any Category I, II, or III wetland; (“Diversion of Drainage” means removing water from a stream, not intercepting stormwater runoff that drains into a stream.) and • Flow splitting devices or drainage BMPs are applied to route natural runoff volumes from the project site to any Class 5 (in the State of Washington Interim Water Typing System) intermittent stream or Category IV wetland: o Design of flow splitting devices or drainage BMPs will be based on continuous hydrologic modeling analysis. The design will assure that flows delivered to Class 4 intermittent stream reaches will approximate, but in no case exceed, durations ranging from 50% of the 2-year to the 50-year peak flow. o Flow splitting devices or drainage BMPs that deliver flow to Category IV wetlands will also be designed using continuous hydrologic modeling to preserve pre-project wetland hydrologic conditions unless specifically waived or exempted by regulatory agencies with permitting jurisdiction; and, • The project site must be drained by a conveyance system that is comprised entirely of manmade conveyance elements pipes, ditches, outfall protection) and extends to the ordinary high water line of the exempt receiving water; and • The conveyance system between the project site and the exempt receiving water shall have sufficient hydraulic capacity to convey the 50-year storm from future build-out conditions (under current zoning) of the site, and the future build-out condition from non-project areas from which runoff is or will be collected; and • Any erodible elements of the manmade conveyance system must be adequately stabilized to prevent erosion under the conditions noted above. • Use of the manmade conveyance system is subject to restrictions that may be placed by the owner of that system, such as easement requirements or flow limits. • The City of Redmond may require a maximum discharge rate for a site that is flow control exempt. This would typically occur due to existing limits of conveyance capacity. If the discharge is to a stream that leads to a wetland, or to a wetland that has an outflow to a stream, both this minimum requirement (Minimum Requirement and I-2.5.8 Minimum Requirement Wetlands Protection apply. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 35 Custom Flow Control Areas in Redmond Some areas in Redmond have custom flow control requirements due to regional facilities and known conveyance limitations. Custom flow control areas will be discussed below and a planning level map of the areas can be found in Appendix D. The applicant is responsible for confirming that the site meets criteria indicated in the custom area. Downtown Regional Facility Surcharge Area (Appendix F & O) In the Downtown Surcharge Area, the City has constructed or is constructing stormwater trunk lines that convey 50-year flows to the Sammamish River. Projects may need to construct some conveyance improvements to connect to the Stormwater Trunk. See Section 8.8 for additional information on regional facilities. This does not waive runoff reduction as required in Minimum Requirement Areas that drain to streams within the surcharge area may be required to construct flow control facilities if the project exceeds the minimum thresholds. Document stormwater fee calculations in the Stormwater report (Stormwater Site Plan). Provide exhibits to document how the fee is calculated. Overlake Regional Facility Surcharge Area (Appendix F & O) In the Overlake Surcharge Area, the City is constructing regional detention and infiltration facilities and stormwater trunks to convey flows to those facilities. Projects may need to construct some conveyance improvements to connect to the Stormwater Trunk. See Section 8.8 for additional information on regional facilities. This does not waive runoff reduction as required in Minimum Requirement Document stormwater fee calculations in the Stormwater report (Stormwater Site Plan). Provide exhibits to document how the fee is calculated. SR520 Drainage Basin (North Overlake Flow Control Alternative Area) (Appendix F & G) This portion of the City directly discharges to the Sammamish River, a flow control exempt receiving water. The conveyance to the Sammamish River is largely owned by Washington Department of Transportation (WSDOT). As such, the City is required to limit flows entering WSDOT conveyance to prevent flooding. Appendix GG includes flow restriction information. It is assumed that areas within WSDOT limited access do not require flow control because they have direct discharge within WSDOT’s conveyance pipe. NE 40th Street Basin (Appendix F) ---PAGE BREAK--- 36 The 40th Street Basin is a new flow control exempt basin supported by a new Direct Discharge stormwater trunk that was constructed in 2018. The City is adaptively managing the outfall to the lake, gradually increasing flows to the lake to avoid negative impacts to the lake shore environment. The gradual increase of flows at the City’s flow splitter means that the service area of direct discharge will change over time. Project proponents in this area should contact the Stormwater Engineer for specific guidance about use of the flow control exemption during this time of transition. The City estimates that by 2024, the full area noted on the map in Appendix D will be flow control exempt. SE Redmond (Appendix F) In this area, regional facilities have been built that provide some flow control for specific properties. Projects proponents within this area are encouraged to contact the Stormwater Engineer to determine if the project can pay into the regional facility to address some or all of their flow control requirements. Otherwise, projects in this area must build flow control facilities on-site. Marymoor 100% Infiltration (Appendix D) This portion of the City does not have stormwater conveyance. All sites are required to fully infiltrate stormwater onsite, including the street. Critical Aquifer Recharge Areas (Appendix C) Section 8.3 describes some clarifications for infiltration in Critical Aquifer Recharge Areas to avoid “groundwater contamination” or other risks to the drinking water aquifer. Within CARA I, detention facilities shall be designed with the assumption that the underlying soils are till soils in both the developed and predeveloped condition. (Infiltration facilities will, of course, be designed using the actual soil conditions.) The purpose of this adjustment is to treat areas that may create risk to the drinking water aquifer as if they have a high water table and infiltration is not feasible. This is protective of the drinking water and is consistent with Ecology guidance for high water table areas. Thresholds When assessing a project against the following thresholds, consider only those impervious, hard, and pervious surfaces that are subject to this minimum requirement as determined in I-2.4 Applicability of the Minimum Requirements. The following circumstances require achievement of the standard flow control requirement for western Washington: • Projects in which the total effective impervious surfaces is 10,000 square feet or more in a threshold discharge area; or • Projects that convert 3/4 acres or more of vegetation to lawn or landscape, or convert 2.5 acres or more of native vegetation to pasture in a threshold ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 37 discharge area, and from which there is a surface discharge in a natural or man-made conveyance system from the site; or • Projects that through a combination of hard surfaces and converted vegetation areas cause a 0.10 cubic feet per second increase in the 100-year flow frequency from a threshold discharge area as estimated using the Western Washington Hydrology Model or other approved model and one- hour time step (or a 0.15 cfs increase using 15- minute time steps). Standard Flow Control Requirement Stormwater discharges shall match developed discharge durations to pre-developed durations for the range of pre-developed discharge rates from 50% of the 2-year peak flow up to the full 50-year peak flow. The pre-developed condition to be matched shall be a forested land cover unless: • Reasonable, historic information is available that indicates the site was not forested prior to settlement. A map showing where project proponents may assume pasture for predevelopment conditions (modeled as “pasture” in the Western Washington Hydrology Model) is contained in Appendix H of the Stormwater Technical Notebook; or This standard requirement is waived for sites that will reliably infiltrate all the runoff from hard surfaces and converted vegetation areas. Additional Requirement Flow Control BMPs shall be selected, designed, and maintained in accordance with Volume III of the 2014 Reduction of flows through infiltration decreases stream channel erosion and helps to maintain base flow throughout the summer months. However, infiltration should follow the guidance in this manual to reduce the chance that ground water quality is threatened by such discharges. Volume III of the includes a description of the Western Washington Hydrology Model. The model provides ways to represent On-site Stormwater Management BMPs described in Volumes III and V. Using those BMPs reduces the predicted runoff rates and volumes and thus also reduces the size of the required flow control facilities. Application of sufficient types of On-site Stormwater Management BMPs can result in reducing the effective impervious area and the converted vegetation areas such that a flow control facility is not required. Application of BMP T5.30: Full Dispersion, also results in eliminating the flow control facility requirement for those areas that are “fully dispersed.” See 0.1 CFS Threshold Operational Policy on page 204 ---PAGE BREAK--- 38 See the guidelines in Volume I, Appendix I-D: Guidelines for Wetlands when Managing Stormwater for Minimum Requirement and directions concerning use of the Western Washington Hydrology Model for information about the approach for protecting wetland hydrologic conditions. Diversions of flow from perennial streams and from wetlands can be considered if significant existing pre-project) flooding, stream stability, water quality, or aquatic habitat problems would be solved or significantly mitigated by bypassing stormwater runoff rather than providing stormwater detention and discharge to natural drainage features. Bypassing should not be considered as an alternative to applicable flow control or treatment if the flooding, stream stability, water quality or habitat problem to be solved would be caused by the project. In addition, the proposal should not exacerbate other water quality/quantity problems such as inadequate low flows or inadequate wetland water elevations. The existing problems and their solution or mitigation as a result of the direct discharge should be documented by a stormwater engineer or scientist after review of any available stormwater reports, basin plans, or other relevant literature. The restrictions in this minimum requirement on conveyance systems that transfer water to an exempt receiving water are applicable in these situations. Approvals by all regulatory authorities with relevant permits applicable to the project are necessary. 2.5.8 Minimum Requirement #8 - Wetlands Protection Applicability The requirements below apply only to projects whose stormwater discharges into a wetland, either directly or indirectly through a conveyance system. Thresholds The thresholds identified in I-2.5.6 Minimum Requirement Runoff Treatment, and I-2.5.7 Minimum Requirement Flow Control shall also be applied to determine the applicability of this requirement to discharges to wetlands. Additional requirements to protect wetlands are documented in the Redmond Zoning Code. Standard Requirement Projects shall comply with Guide Sheets #1 through #3 in Volume I of the Appendix I-D: Guidelines for Wetlands when Managing Stormwater. The hydrologic analysis shall use the existing land cover condition to determine the existing hydrologic conditions unless directed otherwise by a regulatory agency with jurisdiction. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 39 Additional Requirements Stormwater treatment and flow control facilities shall not be built within a natural vegetated buffer, except for: • necessary conveyance systems as approved by the Stormwater Engineer; or • as allowed in wetlands approved for hydrologic modification and/or treatment in accordance with Guide Sheet 2 in Volume I of the Appendix I-D: Guidelines for Wetlands when Managing Stormwater if also allowed by the Redmond Zoning Code. An adopted and implemented basin plan, or a Total Maximum Daily Load (TMDL, also known as a Water Clean-up Plan) may be used to develop requirements for wetlands that are tailored to a specific basin. Appendix I-D: Guidelines for Wetlands when Managing Stormwater shall be used for discharges to natural wetlands and wetlands constructed as mitigation. While it is always necessary to pre- treat stormwater prior to discharge to a wetland, there are limited circumstances where wetlands may be used for additional treatment and detention of stormwater. These situations are considered in Guide Sheet 2 of Appendix I-D: Guidelines for Wetlands when Managing Stormwater. Note that if selective runoff bypass is an alternative being considered to maintain the hydroperiod, the hydrologic analysis must consider the impacts of the bypassed flow. For instance, if the bypassed flow is eventually directed to a stream, the flow duration standard, Minimum Requirement applies to the bypass. 2.5.9 Minimum Requirement Operation and Maintenance An operation and maintenance manual that is consistent with the provisions in Volume V of the 2014 shall be provided for all proposed stormwater facilities and BMPs, and the party (or parties) responsible for maintenance and operation shall be identified. At private facilities, a copy of the operation and maintenance manual shall be retained on-site or within reasonable access to the site, and shall be transferred with the property to the new owner. For public facilities, a copy of the operation and maintenance manual shall be retained in the appropriate department. A log of maintenance activity that indicates what actions were taken shall be kept and be available for inspection by the local government. The operations and maintenance manual shall be a stand-alone document prepared in accordance with the City of Redmond O&M Manual Template (Appendix II). The development proposal shall include provisions for maintenance of facilities in perpetuity. At a minimum, the operations and maintenance manual shall include: • the purpose of the facility; • the dimensions and other characteristics of the facility (site map); ---PAGE BREAK--- 40 • description of all BMPs at the facility designed to meet Minimum Requirements 3, 5, 6, 7, and 8; • the party (parties) responsible for maintenance of the facility, with phone numbers and addresses; • list of any proprietary components along with information from the vendor describing maintenance schedule and costs; • except for single-family residential sites, identify potential site activities following site development. “Applicable” and “recommended” source controls in Volume IV of the 2014 are required and shall be documented; • what maintenance activities are required, and proposed schedule; • care and maintenance of any powered devices (aeration); • inspection procedures and how the maintenance schedule will be modified if inspections determine the facility is not operating properly; the minimum requirements for this type of facility as described in Chapter 4 of Volume V of the 2014 as modified in this Stormwater Technical Notebook; • The final O&M manual shall incorporate any written comments made during the development review process, and shall incorporate any field changes made to the facilities during construction. A template Operations and Maintenance Manual is provided in Appendix I. • Any source control measures required by Minimum Requirement 3. 2.6 Analysis Development projects that discharge stormwater off-site shall submit an off-site analysis report that assesses the potential off-site water quality, erosion, slope stability, and drainage impacts associated with the project and that proposes appropriate mitigation of those impacts. An initial qualitative analysis shall extend for the entire flow path from the project site to the receiving water or up to one mile, whichever is less. If a receiving water is within one-quarter mile, the analysis shall extend within the receiving water to one-quarter mile from the project site. The analysis shall extend one-quarter mile beyond any improvements proposed as mitigation. The analysis must extend upstream to a point where any backwater effects created by the project cease. Upon review of the qualitative analysis, the stormwater engineer may require that a quantitative analysis be performed or that the analysis area limits be extended. The existing or potential impacts to be evaluated and mitigated shall include: • Conveyance system capacity problems; • Localized flooding; • Upland erosion impacts, including landslide hazards; • Stream channel erosion at the outfall location; ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 41 • Violations of surface water quality standards as identified in a Basin Plan or a TMDL (Water Clean-up Plan); or violations of ground water quality standards in a Critical Aquifer Recharge Area. Projects shall be required to initially submit, with the permit application, a qualitative analysis of each system leaving a site. The analysis should accomplish four tasks: Task 1 – Define and map the study area Submission of a site map showing property lines; a topographic map (at a minimum a USGS 1:24000 Quadrangle Topographic map) showing site boundaries, study area boundaries, flowpath, and potential/existing problems. Task 2 – Review all available information on the study area This should include all available basin plans, ground water management area plans, drainage studies, floodplain/floodway FEMA maps, wetlands inventory maps, Critical Areas maps, stream habitat reports, salmon distribution reports, infrastructure conditions information available from the City, etc. Task 3 – Field inspect the study area The design engineer should physically inspect the existing on- and off-site drainage systems of the study area for each discharge location for existing or potential problems and drainage features. An initial inspection and investigation should include: • Investigate problems reported or observed during the resource review • Locate existing/potential constrictions or capacity deficiencies in the drainage system • Identify existing/potential flooding problems • Identify existing/potential overtopping, scouring, bank sloughing, or sedimentation • Identify significant destruction of aquatic habitat siltation, stream incision) • Collect qualitative data on features such as land use, impervious surface, topography, soils, presence of streams, wetlands • Collect information on pipe sizes, channel characteristics, drainage structures • Verify tributary drainage areas identified in task 1 • Contact the local government office with drainage review authority (for Redmond, contact the Maintenance Operations Center [PHONE REDACTED]), neighboring property owners, and residents about drainage problems • Note date and weather at time of inspection ---PAGE BREAK--- 42 Task 4 – Describe the drainage system, and its existing and predicted problems For each drainage system component pipe, culvert, bridges, outfalls, ponds, vaults) the following should be covered in the analysis: location, physical description, problems, and field observations. All existing or potential problems ponding water, erosion) identified in tasks 2 and 3 above should be described. The descriptions should be used to determine whether adequate mitigation can be identified, or whether more detailed quantitative analysis is necessary. The following information should be provided for each existing or potential problem: • Magnitude of or damage caused by the problem • General frequency and duration • Return frequency of storm or flow when the problem occurs (may require quantitative analysis) • Water elevation when the problem occurs • Names and concerns of parties involved • Current mitigation of the problem • Possible cause of the problem • Whether the project is likely to aggravate the problem or create a new one. Upon review of this analysis, the Stormwater Engineer may require mitigation measures deemed adequate for the problems, or a quantitative analysis, depending upon the presence of existing or predicted flooding, erosion, or water quality problems, and on the proposed design of the on-site drainage facilities. The analysis should repeat tasks 3 and 4 above, using quantitative field data including profiles and cross-sections. The quantitative analysis should provide information on the severity and frequency of an existing problem or the likelihood of creating a new problem. It should evaluate proposed mitigation intended to avoid aggravation of the existing problem and to avoid creation of a new problem. 2.7 Adjustments (Deviations in RMC 15.24 ) Adjustments to the Minimum Requirements may be granted prior to permit approval and construction. In Accordance with RMC 15.24.084, Deviations, submit a written finding of fact that addresses the following: • The adjustment provides substantially equivalent environmental protection. • The objectives of safety, function, environmental protection and facility maintenance, based upon sound engineering, are met. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 43 A deviation is required for any design or construction alteration from these standards for a development proposal. Deviations from these standards may be granted upon evidence that such deviation is in the public interest and the requirements for safety, function, fire protection, transit needs, appearance, maintainability and long-term maintenance costs, based upon sound engineering and technical judgment, fully meet the intent of the standard. Technical documentation such as reports, engineering drawings and/or calculations, for design proposal or alternative evaluation prepared by or under the direct supervision of Washington State licensed professional engineer shall be stamped and signed. 2.7.1 Request for Engineering Deviation The request for a deviation shall include: • A description of the deviation requested. • The code citation of the Standards from which the application proposes to deviate. • Must demonstrate how the standard can be met. • Provide alternatives to minimize the deviation. • Description of the proposed alternative along with supporting documentation. • Exhibit(s) of the proposed design. • Documentation may include, but not be limited to, a record of use by other agencies, or evidence of meeting criteria for quality such as AASHTO, ASTM, MUTCD, HCM, NACTO, ITE, and AWWA. • Applications for location of utilities by an entity allowed under a franchise agreement must be prepared and submitted by that entity. 2.7.2 Criteria for Granting Engineering Deviations • Applications shall include clear written documentation with exhibits as needed to explain how the proposed deviation(s) address the following criteria: • The deviation produces a comparable or improved result, which is in the public interest. • The deviation meets requirements for safety, public health, function, fire protection, transit needs, appearance, maintainability, and any other criteria deemed relevant by the city. • The deviation provides substantially equivalent (or improved) environmental protection as would be provided if the standard requirements were met. • The deviation needs to reflect sound engineering practices. • The deviation needs to avoid damage to other properties in the vicinity of and of the proposal. ---PAGE BREAK--- 44 • Any deviation from the Standards that does not meet the Fire Code will require concurrence by the City Fire Marshal. 2.8 Exceptions (Variances in RMC 15.24) Exceptions may be allowed in Redmond. See RMC 15.24.089 for details and requirements for variances to be granted in Redmond. Exceptions to the Minimum Requirements may be granted prior to permit approval and construction. The drainage manual administrator (Technical Committee) may grant an exception following legal public notice of an application for an exception, legal public notice of the administrator’s decision on the application, and a written finding of fact that documents the administrator’s decision to grant an exception. The administrator may grant an exception to the minimum requirements if such application imposes a severe and unexpected economic hardship. To determine whether the application imposes a severe and unexpected economic hardship on the project applicant, the administrator must consider and document - with written findings of fact – the following: • The current (pre-project) use of the site, and • How the application of the minimum requirement(s) restricts the proposed use of the site compared to the restrictions that existed prior to the adoption of the minimum requirements; and • The possible remaining uses of the site if the exception were not granted; and • The uses of the site that would have been allowed prior to the adoption of the minimum requirements; and • A comparison of the estimated amount and percentage of value loss as a result of the minimum requirements versus the estimated amount and percentage of value loss as a result of requirements that existed prior to adoption of the minimum requirements; and • The feasibility for the owner to alter the project to apply the minimum requirements. In addition, any exception must meet the following criteria: • The exception will not increase risk to the public health and welfare, nor be injurious to other properties in the vicinity and/or and to the quality of waters of the state; and • The exception is the least possible exception that could be granted to comply with the intent of the Minimum Requirements. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 45 2.9 2014 Modifications in Redmond This section provides Redmond specific changes to the 2014 for all volumes and chapters except Volume I, Chapter 2, which are documented in 2.1-2.8 of this Stormwater Technical Notebook. All information below are local changes to the 2014 2.9.1 Volume I. Below are local modifications to Volume I of the 2014 beyond those described earlier in this chapter. 2.9.1.1 Volume I. Chapter 3: Preparation of Stormwater Site Plans I.3.1.6 - Step 6 – Prepare a Construction Stormwater Pollution Prevention Plan Additional requirements are in Chapter 9 and 10 of the Stormwater Technical Notebook. Additions include wet weather plan and seasonal suspension plan, in addition to the TESC plan and the required in the Stormwater Site Plan requirements if work will occur during the wet weather season. 2014 Volume I.3.1.7 – Complete the Stormwater Site Plan If an Underground Injection Control Well (UIC) is included in the design, proof of registration with the state is required as part of the final Stormwater Site Plan. Document how each of the Minimum Requirements will be met. In addition to the requirements in the 2014 document what applicable or recommended source control BMPs will be applied at the project site. 2.9.1.2 Volume I. Chapter 4: BMP and Facility Selection Process for Permanent Stormwater Control Plans I.4.2 - BMP and Facility Selection Process Note that the City of Redmond has preferences for certain types of stormwater treatment facilities over others. These preferences are based primarily on long-term performance and maintenance cost. Actual selection of facilities must address site- specific constraints. However, these preferences are provided to help the designer in cases where more than one alternative exists. Capital improvement projects shall involve the Stormwater Engineer early in the design process to ensure selection of stormwater treatment facilities that best meet the long-term goals of the City. (see Proprietary Treatment Operational Policy on page 202) ---PAGE BREAK--- 46 Multifamily, commercial and industrial sites: If stormwater facilities will be privately maintained, then any treatment facility approved for that purpose in the 2014 may be used. If facilities will be publicly maintained, then proprietary treatment may be approved by the Stormwater Engineer. Single Family Residential projects: Stormwater facilities: • Infiltration BMPs shall be used with pretreatment, where infiltration is feasible, subject to Critical Aquifer Recharge Area requirements. • Ponds and swales shall be used for most sites, instead of vaults. • Proprietary treatment technologies shall not be allowed. Infiltration BMPs may be limited by Critical Aquifer Recharge Area requirements as noted in section 2.5.5, above. Traffic counts in Redmond are available for some roadways at redmond.gov/Transportation/Resources/Engineering/TrafficCounts/. Follow guidance in the 2014 if traffic counts are not available from Redmond for the project site. 2.9.2 Volume II: Construction Stormwater Pollution Prevention Below are local modifications to Volume II of the 2014 The following list of BMPs have specifications and details unique to Redmond. Use of Redmond specified BMPs is required. • BMP C101 - Preserving Natural Vegetation. No disturbance is allowed within 5 feet of drip lines of trees to be saved unless specifically approved by the City’s Project Planner. • BMP C103 - High visibility plastic or metal fence. Refer to Redmond Standard Specifications and Details. • BMP C105 - Stabilized construction entrance. Refer to Redmond Standard Specifications and Details. • BMP C106 - Wheel wash. Refer to Redmond Standard Specifications and Details. • BMP C121 - Compost mulch may only be used on proposed landscape areas. It is not approved as a general TESC mulch in Redmond. • BMP C140 - Chemical dust suppressants are not approved for use in Redmond. • BMP C202 - Rubble concrete channel lining is not approved in Redmond. • BMP C204 - Pipe slope drain. Note that this is “temporary” only. • BMP C205 - The minimum subsurface drain size shall be 6” diameter. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 47 • BMP C220 - Catch basin filters are required in Redmond for storm drain inlet control. Provisions shall be made to remove filters at the end of the project without dropping accumulated sediment into the catch basin. • BMP C231 - Brush Barrier. Not approved in Redmond. • BMP C233 - Silt fence. Refer to Redmond Standard Specifications and Details. • BMP C234 - Vegetated strips shall have a minimum length of 200 feet. • BMP C240 - Sediment trap shall be sized using the 10-year developed design storm. • BMP C241 - Temporary sediment pond shall be sized using the 10-year design storm. Side slopes shall be 3:1 or flatter (interior and exterior). • BMP C250 - Construction stormwater chemical treatment and other non- standard treatment systems must be approved by the Stormwater Engineer. 2.9.3 Volume III: Hydrologic Analysis and Flow Control BMPs 2.9.3.1 III-2.1.1 Discussion of Hydrologic Analysis Methods Used for Designing BMPs WWHM, the most current version, is preferred. Other models may be accepted with Stormwater Engineer approval. Use one model for a project, without cherry-picking results from one model for one part of a project and a differing model for another part of a project. Conveyance system design is addressed in Chapter 8 of the Stormwater Technical Notebook. Landscaped or artificial turf areas above impervious surfaces like parking garages or vaults shall be modeled to reflect the presence of the impervious surface. Appropriate modeling assumptions depend upon the depth of material above the impervious surface. It may be appropriate to model as a vegetated roof, permeable pavement, impervious surface, or pervious surface, depending on how water is expected to flow through the site. Project proponent shall submit a proposed modeling approach for Stormwater Engineer approval. Small underground vaults (<100 SF in area) may be disregarded. Table 2.1 describes some typical modeling approaches for underground structures. ---PAGE BREAK--- 48 Table 2.1: Typical Modeling Approaches for Artificial Turf or Shallow Soil Over Underground Structures Soil Depth: Where the water goes: Model as: < 3” Soil Drainage over underground structure conveyed to native soils that infiltrate. Permeable Pavement (Impervious surface routed to a Gravel Trench/Bed.) Drainage over underground structure conveyed to stormwater system or surface waters. Impervious Surface 3” to 8” Soil Drainage over underground structure conveyed to native soils that infiltrate. Permeable Pavement (Impervious surface routed to a Gravel Trench/Bed.) Drainage over underground structure conveyed to stormwater system or surface waters. Vegetated Roof (50% till landscaped area; 50% impervious area) to 36” Soil Drainage over underground structure conveyed to native soils that infiltrate. Permeable Pavement (Impervious surface routed to a Gravel Trench/Bed.) Drainage over underground structure conveyed to stormwater system or surface waters. Vegetated Roof (50% till pasture; 50% impervious area) >36” Soil Drainage over underground structure conveyed to native soils that infiltrate. Pervious lawn over underlying soils Drainage over underground structure conveyed to stormwater system or surface waters. Pervious lawn over till Artificial Turf Drainage over underground structure conveyed to native soils that infiltrate. Permeable Pavement (Impervious surface routed to a Gravel Trench/Bed.) Drainage over underground structure conveyed to stormwater system or surface waters. Impervious surface Table 2.1 Typical Modeling Approaches for Underground Structures 2.9.3.2 III-3.1 Roof Downspout Controls Stormwater runoff from roofs may require treatment prior to infiltration if they are subject to venting significant amounts of dust, mist, fumes from manufacturing, commercial, restaurant, or other similar activity. 2.9.3.3 III-3.1.3 Perforated Stub Out Connections (BMP T5.10C) ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 49 The perforated pipe in perforated downspout connections shall not be located where percolating water will encounter and be intercepted by another nearby utility trench or foundation drain. See Section 8.6.11 for infiltration system setback requirements. 2.9.3.4 III-3.2.1 Detention Ponds Proposed slopes shall be 3:1 or flatter. Up to 25% of the pond perimeter may have vertical walls. Anything greater will require approval of the Stormwater Engineer. Modular grid pavement is only allowed if specifically approved by the Stormwater Engineer. Ponds shall be setback a minimum of 10 feet from structures, property lines or required vegetated buffers and 50 feet from the limits of steep slope areas. The setback from steep slopes may be reduced per RZC 21.64.060. Conveyance pipes in steep slope areas shall be installed on the surface of the slope, with the minimum disturbance possible, and shall require applicable City approvals. Minimum setback required for trees is 8 feet. Trees shall be setback from the liner such that the root ball is at least three feet horizontally from the maximum storage elevation to provide maintenance access and liner protection. Trees shall not be planted over any pond liner. Detention ponds in infiltrative soils shall be lined, unless otherwise approved as infiltration facilities. Lining may consist of an impermeable till layer 18 inches or thicker, bentonite or liners approved by the Stormwater Engineer. When a geomembrane is used, provide an analysis demonstrating that the required cover soil will be stable against sliding when saturated. Provide a warning layer, such as colored geotextile to assist maintenance workers protecting the liner during maintenance. Impervious bottoms and sides shall extend up to the stage of the 50- year event. Combination infiltration/detention ponds may be approved by the Stormwater Engineer, subject to the restrictions on infiltration in Critical Aquifer Recharge Areas Section 8.3. Pond control structures shall be accessible by an inductor truck. A backhoe must be able to access each pond for maintenance. The detention pond emergency overflow route must be independent from the primary outflow system. Signs shall be posted at all stormwater ponds using the standard sign format described in City of Redmond Standard Specifications and Details. There are several alternative sign formats, and they shall be selected based on the following: • Ponds greater than 5,000 square feet in size shall receive the large (24 x 48) sign. Smaller ponds may have either the small (12 x 18) or the large sign. ---PAGE BREAK--- 50 • Public ponds shall receive the sign with the City of Redmond logo. Private pond signs shall not include the logo, but shall indicate they are privately owned and maintained. • Ponds with liners shall receive the sign indicating the liner. Ponds that infiltrate shall have the sign indicating the infiltration. Ponds shall be named by the project proponent. The pond name shall be unique to the City of Redmond. In general, the pond name shall be the same as the name of the subdivision in which the pond is located. Pond names are subject to approval by the Stormwater Engineer. 2.9.3.5 III-3.2.2 Detention Tanks Corrugated metal detention tanks are not approved in Redmond. Corrugated metal pipe (CMP) risers are not approved in Redmond. Tank setback requirements from property lines or right-of-way lines must be a minimum of 10 feet, or the distance required to excavate a 1:1 slope from the bottom of the tank to the ground surface at the right-of-way or property line – whichever is greater, and 50 feet from the limits of steep slopes. The setback from steep slope may be reduced per RZC 21.64.060. For limitations on tree planting, see tree separation information for pipes in Chapter 8. Add the following note to drawings that include detention tanks: “Pressure tests may be required by the City Inspector. Tanks that do not pass pressure tests shall be repaired or replaced.” Avoiding leakage is particularly critical in Critical Aquifer Recharge Areas. Maintenance must be feasible and designs should strive to facilitate maintenance (design adjustments to facilitate maintenance may be required during plan review). 2.9.3.6 III-3.232 Detention Vaults Vaults shall be setback a minimum of 10 feet from structures, property lines, required vegetated buffers, and 25 feet from the limits of steep slopes. The setback from steep slopes may be reduced per RZC 21.64.060. Vault setbacks from property lines or right-of-way limits must be a minimum of 10 feet, or the distance required to excavate a 1:1 slope from the bottom of the vault to the ground surface at the right-of-way or property line – whichever is greater. Trees may be as close as 2 feet from concrete vaults provided the trees do not interfere with access for maintenance. Specify shallow rooted trees by species on the project landscape plans for locations closer than 8 feet to vaults. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 51 Maintenance must be feasible and designs should strive to facilitate maintenance (design adjustments to facilitate maintenance may be required during plan review). 2.9.3.7 III-3.2.5 Other Detention Options Parking lot ponding for detention is allowed in Redmond as approved by the Stormwater Engineer and the Fire Department for developments within certain designated flood zones where traditional detention may not be feasible. Roof detention is not allowed in Redmond. 2.9.3.8 III-3.3 Infiltration Facilities for Flow Control and for Treatment Protection of the drinking water resource is a very high priority in Redmond. Therefore, infiltration of stormwater, even with treatment, is limited within Critical Aquifer Recharge Areas. Section 8.3 describes some clarifications for infiltration in Critical Aquifer Recharge Areas to avoid “groundwater contamination” or other risks to the drinking water aquifer. 2.9.3.9 III-3.3.5 Site Characterization Criteria The soil infiltration rate may be determined by a falling head test or other approved testing method in Section 3.3.5 and conducted by a qualified engineer using commonly accepted methods. For Infiltration trenches, ponds, and vaults designed to meet Minimum Requirement infiltration rates less than 1.0 inches/hour shall be considered infeasible. Infiltration rates shall have the appropriate correction factors applied to them and the corrected rate used for sizing the infiltration facilities. Correction factors are identified in Section 3.3.6 of the Ecology Manual. Notify the City of Redmond’s Wellhead Protection Program staff prior to installing groundwater monitoring wells. Wells shall be installed by a certified driller and registered with the state. The City may consider allowing placement of such wells within a public right-of-way if the City wishes to assume responsibility for the wells in the future. All wells shall either be required to be properly abandoned when they are no longer needed, or may be requested to be turned over to the City for ongoing monitoring by City staff. At least 200 feet shall be provided for separation from public drinking water supply wells. Public wells are located within Critical Aquifer Recharge Area I. (Appendix C) Construction plans shall include a note to require field verification during construction of the facility, of soil conditions, and infiltration rates by an engineer with experience in stormwater management and licensed in the State of ---PAGE BREAK--- 52 Washington. The engineer shall provide a written statement to the City of Redmond related to the field verification of the design parameters. Infiltration basins shall meet the same requirements for slopes, fences, signage, etc., as detention ponds. To determine groundwater depth, the average seasonal high water table shall be identified during the wet weather season (Chapter 10). If sufficient data is available, a five-year average may be used. The five-year average seasonal high water table is calculated by taking the average of the highest individual peak groundwater depth for each year of the five-year period. The City has groundwater depth information for areas within Critical Aquifer Recharge Areas that is available upon request. 2.9.4 Volume IV: Source Control BMPs 2.9.4.1 Appendix IVG: Recommendations for Management of Street Wastes Street Waste Liquids Decant liquid shall be discharged to sanitary sewer or otherwise disposed. It shall not be discharged to the storm system, even if it passes through a stormwater treatment BMP. 2.9.5 Volume V: Runoff Treatment BMPs 2.9.5.1 Chapter V-4 - General Requirements for Stormwater Facilities Stormwater Runoff Treatment ponds shall meet the requirements of Section 2.9.3.4 Liners are required for all water quality ponds and most detention ponds (impermeable till layer, liner or bentonite). Concrete liners are not approved in Redmond. Drop structures are not allowed unless specifically approved by the Stormwater Engineer. 2.9.5.2 Chapter V-5 - On-Site Stormwater Management BMP T5.13 - Post-Construction Soil Quality and Depth Compost-amended areas shall be marked to prevent vehicle traffic in those areas. BMP T5.20 - Preserving Natural Vegetation ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 53 Preserved areas shall be set aside as native growth protection easements and marked accordingly. No vehicle traffic shall be permitted in preserved areas. 2.9.5.3 Chapter V-7 - Infiltration and Bioretention Treatment Facilities Infiltration area setbacks are described in Section 8.6.11. Section 8.3 describes some clarifications for infiltration in Critical Aquifer Recharge Areas to avoid “groundwater contamination” or other risks to the drinking water aquifer. 2.9.5.4 Chapter V-9 - Biofiltration Treatment Facilities Swales shall be at least 200 feet long. Swale length may be reduced to 150 feet for re- development projects if no feasible alternative exists. Maximum swale bottom width shall be 8 feet (parallel swales are acceptable if needed to provide adequate treatment area). Biofiltration swales and similar water quality facilities in infiltrative soils shall be lined, unless otherwise approved as infiltration facilities. Lining may consist of an impermeable till layer 18 inches or thicker, bentonite or liners approved by the Stormwater Engineer. If biofiltration swales are not able to be located off-line, the swale shall be designed so the maximum flow possible in the swale up to the 50-year does not produce a velocity over 3 feet per second. The size and shape of biofiltration swales (and other surface features) shall be compatible with the terrain and not detract from the landscape value (the latter as determined by the Technical Committee). At least one side of each biofiltration swales shall be accessible for maintenance by a backhoe. Plant no trees within 8 feet of biofiltration swale banks. Their resulting shade and leaves impact the dense vegetated cover required for biofiltration. In designing the landscaping for the area, and placement of the biofiltration swale, take into account the need for sunlight within the swale. Table 9.1 - Sizing Criteria Underdrains are not required. Figure 9.2 - Biofiltration Swale Underdrain Detail Underdrains are not required. ---PAGE BREAK--- 54 2.9.5.5 Chapter V-10 - Wetpool Facilities 10.3 - Best Management Practices (BMPs) for Wetpool Facilities See requirements for Detention Ponds in Volume III. Provide a 5-foot wide level bench around the perimeter of the pond at or up to 1 foot below the permanent water surface. All water quality ponds shall be lined to prevent infiltration. Lining may consist of an impermeable till layer 18 inches or thicker, bentonite or liners approved by the Stormwater Engineer. When a geomembrane is used, provide an analysis demonstrating that the required cover soil will be stable against sliding when saturated. Gravity drains are not required for wet ponds or vaults. Access roads to the pond bottom are not required but are encouraged for wet ponds. Wet ponds that are intended solely for water quality treatment shall have a high flow bypass to divert peak flows above the water quality design storm. Wet ponds shall be setback a minimum of 10 feet from structures, property lines, or required vegetated buffers, and 50 feet from the limits of steep slopes. The setback from steep slopes may be reduced per RZC 21.64.060. A minimum, average depth of 3 feet is required for water quality treatment in vaults and tanks. Storm pipes should discharge into wet ponds at/or above the normal control elevation (elevation of outlet pipe invert). Designs that include pipes discharging below the control elevation must include an analysis demonstrating that sediment will not accumulate within the pipe. To avoid anaerobic conditions, wet ponds should not have permanent pool depths greater than 8 feet, unless aeration is provided. For publicly owned and maintained ponds, aeration requires approval from the Stormwater Engineer. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 55 Chapter 3 – Redmond Permit Types and Project Classifications Projects that involve clearing, grading, installation of new hard surfaces, or modification of drainage patterns are subject to the requirements described in this Stormwater Technical Notebook and the Redmond Municipal Code, Chapter 15.24. Available permits include Rough Grade Permits and Clearing and Grading Permits. Some very small projects may not require permits. See Redmond Municipal Code, Chapter 15.24. 3.1 Rough Grade Permits Rough grading is the stage at which the grade is modified to conform approximately to the proposed final grade. This permit usually covers only earthwork but may also include stormwater systems especially if they are part of the pollution prevention system. It is a prelude to further work on a development proposal that has received conceptual approval from the City. A rough grade permit may be applied for upon completion of the first civil construction review (CCR) debrief meeting. 3.2 Clearing and Grading Permits Projects require a permit if they: • Move over 50 CY of soil; or • Change the topography by more than four feet; or • Perform work within a City of Redmond easement or right-of-way; or • Work with a stormwater pipe 12-inches in diameter or greater; or • Clear 7,000 SF of land; or • Remove 10 or more significant trees; or • Add 2,000 SF or more of impervious surface; or • Work within a fish and wildlife protection area, landslide hazard area or buffer as defined in the RZC 21.64; or • Modify a private water quality or flow control stormwater facility. Projects that exceed the above requirements for a Clearing and Grading Permit are classified as Small, Medium or Large. (see Trees Operational Policy on page 201) ---PAGE BREAK--- 56 3.3 Small Projects Projects are Small Projects if they involve: • Less than 2000 square feet of new and/or replaced impervious surface; and • Less than 7000 square feet of land disturbance; and • Less than 500 CY of grading. Small projects are subject to Minimum Requirement 3.4 Medium Projects Projects are Medium Projects if they involve areas that exceed any of the criteria above for Small Projects and involve: • Less than 5000 square feet of new impervious area; and • Less than ¾ acre of native vegetation converted to lawn or landscaped areas; and • Less than 500 CY of grading; and • Less than 2.5 acres of native vegetation converted to pasture. Medium projects are subject to Minimum Requirements #1-5 in Chapter 2 of the Stormwater Technical Notebook. For these projects, refer to Chapter 5. 3.5 Large Projects Large projects are projects that exceed one or more of the criteria for Medium Projects. Large projects trigger Minimum Requirements #1-9 in Chapter 2 of the Stormwater Technical Notebook. Large projects shall comply with the requirements described in Chapter 6. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 57 Chapter 4 – Small Project Requirements 4.1 Small Project Submittal Requirements The detail required for plans submitted for small projects is extremely variable, from very simple, hand-drawn plans, to detailed engineering drawings and reports. Request a meeting with the Stormwater Engineer to discuss your project specifics. Appendix B includes a template for Small Project Stormwater Site Plan. In general, the plans and narratives submitted shall include: 1. Written description outlining proposed activity. 2. Existing contours (information may be available from the City), shown as dashed lines, or spot elevations. 3. Sketch showing proposed activity. 4. Owner information – name, address and contact. 5. Project and Site information – title, tax parcel or address. 6. Existing utilities – identify type and size (information may be available from the City). 7. Identify slopes 40% or greater. 8. Location and drip lines of trees 6 inch caliper or greater (measured 4 feet above existing grade. (Only those trees to be cleared or trees within 50 feet of cleared areas need to be specifically designated). 9. Existing surface waters (streams, lakes, wetlands, etc.). Proposed drainage (flow arrows). 10. Proposed retaining walls/rockeries (indicate approximate heights). 11. Disturbed area – approximate (identify on the plan and label quantity in square feet). 12. Proposed contours – show as solid lines, or finished grade spot elevations at a minimum. 13. Proposed utilities – identify. 14. Standard Notes (Appendix Note that if the project triggers State Environmental Policy Act (SEPA) thresholds, the permitting process will be more complex. Examples of SEPA thresholds include: • Projects include stormwater pipes greater than 12 inches in diameter. • Projects are located in Critical Areas (See RZC 21.64) such as: o Wetlands o Wetland buffers o Streams o Stream buffers o Critical wildlife habitat areas ---PAGE BREAK--- 58 o Steep slopes o FEMA Floodways o Critical Aquifer Recharge Areas Contact the Development Services Center at [PHONE REDACTED] or the Development Services Division at [PHONE REDACTED] for further information about critical areas. 4.2 Small Project Construction Stormwater Pollution Prevention Requirements Small Projects are required to meet Minimum Requirement #2 - Construction Stormwater Pollution Prevention, as described in the 2014 Small project proponents are also required to review Chapter 10 of this Stormwater Technical Notebook to determine additional requirements for construction monitoring, TESC, and seasonal construction suspension. In addition to those requirements, the following shall apply: • It shall be the responsibility of the contractor to obtain street use and other related permits prior to any construction. • It shall be the responsibility of the contractor to verify the correct locations of utilities to avoid damage or disturbance. • Keep project impacted off-site streets clean at all times. Use sweepers; flushing streets shall not be allowed. • Tie impervious surfaces (roof, streets, driveways, etc.) to completed drainage system as soon as possible. • The City will order stoppage of work and will order sampling and analysis of stormwater discharges if stormwater controls do not meet standards described in this Stormwater Technical Notebook. 4.3 Permit Process for Small Projects The following is an overview of the steps and requirements for projects that require only a Clearing/Grading and Stormwater Management approval (and no other approvals). Projects requiring other permits may have additional steps and requirements. Consult the Development Services Center for additional guidance. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 59 Table 4.0: Small Project Requirements Responsible Party Activity Applicant I. Project Proposal Prepare project submittal – see requirements above. Applicant II. Complete and Submit Applications All the following must be completed and submitted to the Stormwater Engineer for review for the application to be considered complete. Only complete applications will be processed. a. One copy of a completed General Application form of the Stormwater Technical Notebook and available at the Development Services Center. b. One set of plans and computations including the applicable information on the application requirements checklist. City III. City Review Process a. The project engineer or applicant will be contacted when the review is complete. b. The plans and computations are red-lined and one set of each is returned to the applicant. Applicant IV. Revision and Resubmittal, if Required. a. Revise plans per the City’s comments. b. Resubmit the last set of red-lined prints and computations and one set of revised plans and computations as stated above. City V. Review of Revised Plans a. Once all comments have been satisfactorily addressed, the City will proceed with plan approval. b. The project engineer or applicant will be contacted. Applicant VI. Submit Original Plans for City Approval. a. Submit three sets of prints to the Stormwater Engineer for approval. ---PAGE BREAK--- 60 Table 4.0: Small Project Requirements Responsible Party Activity City VII. Permit Preparation and Plan Distribution The Stormwater Engineer prepares the permit letter, signs it, calculates the remaining fee, and determines performance bonds per the standard list. The project engineer or applicant will be contacted when the permit is ready to be issued. Applicant VIII. Obtain Permit When applicant is notified that the permit is ready to issue, applicant needs to come to the Development Services Center and pay any remaining fees and post required bonds. The Permit Letter is then issued. Applicant IX. Pre-Construction Meetings After plan approval and after submitting permit prints, applicant may be required to contact the Construction Division and schedule a Pre- Construction Meeting. Contact the Construction Division at [PHONE REDACTED] for the date, time, and location (the inspector may have the meeting at the site). In addition to permit issuance, construction may not begin before having a Pre-Construction Meeting (unless waived by the Construction Division). Applicant X. Construction The applicant shall complete all activities identified in the approved plans to meet City of Redmond standards. As items are completed, and at appropriate times during construction before utilities are buried) the applicant shall notify the City inspector assigned to the project at the Preconstruction Conference that elements are ready for inspection. Failure to notify the City of readiness for inspection in a timely manner may result in the requirement to remove and replace buried or hidden elements. City XI. Release of Performance Bonds Performance bonds remain in full force and effect until 1) the obligations secured are fully performed to the satisfaction of the City’s inspectors; 2) a bond guaranteeing maintenance of all improvements for a guarantee period have been submitted to the City; and 3) the City has released the bonds in writing. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 61 Table 4.0: Small Project Requirements Responsible Party Activity City XII. Cancellation of Non-Issued Permits a. The permit is only valid for a designated time. It may be to the applicant’s benefit to wait until construction is ready to begin before picking up the permit. b. The permit will be held for a maximum six months without issuance (unless specifically stated otherwise in the conditions of approval) but will then be nullified after this period if not picked up. The permit application would have to be started again, from the beginning, if the project is still desired. A new application may be required by the Public Works Department. Applicant XIII. Permit Extension Request – (Optional) a. If the proposed work cannot be completed within the time covered by the permit an extension may be granted. Additional fees for inspection and renewal are required for extension. b. The applicant must submit a written extension request to the Stormwater Engineer at least two working days before the expiration of the permit. Table 4.0 Small Project Requirements 4.4 Fees for Small Projects Fees are charged for plan review and City inspection. Current fee information is available from the Development Services Center. • Small project fees often include but are not limited to: o Small & Simple Projects: Review o Small & Simple Projects: Inspection Performance security may be required prior to issuance of a permit. Security requirements are determined after application. ---PAGE BREAK--- 62 Chapter 5 – Medium Project Requirements 5.1 Medium Project Submittal Requirements Medium projects are required to develop site plans and a stormwater report (Stormwater Site Plan in accordance with Minimum Requirement 1) addressing all applicable items listed in the Application Checklist available in the Development Services Center. Many items may not apply. Please contact the Development Services Stormwater Engineer for information specific to your project. Additional technical details of engineered plans are in Chapter 7 of this Stormwater Technical Notebook. 5.2 Project Requirements for Medium Projects Medium Projects are required to meet Minimum Requirements #1-5 of the 2014 Note that Chapter 2 of the Stormwater Technical Notebook amends some of those requirements. Medium projects also have more strenuous requirements for construction stormwater pollution prevention, as outlined in Chapters 9 and 10. 5.3 Permit Process for Medium Projects The following is an overview of the steps and requirements for projects that require only a Clearing/Grading and Stormwater Management approval (and no other approvals). Projects requiring other permits may have additional steps and requirements. Consult the Development Services Center for additional guidance. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 63 Table 5.0: Medium Project Requirements Responsible Party Activity Applicant I. Project Proposal a. Prepare project submittal – see requirements below. b. Prepare SEPA Checklist (if required – Consult Stormwater Engineer prior to application). 1. If any work is proposed in a Critical Area the City will require the completion of the SEPA environmental checklist. The Technical Committee may require any project to complete the SEPA process. 2. Checklists are available at the Development Services Center. Redmond has modified the state standard checklist. Therefore, only a City of Redmond SEPA Checklist will be accepted. Complete the checklist to the best of your ability. Applicant II. Complete and Submit Applications All the following must be completed and submitted to the Stormwater Engineer for review for the application to be considered complete. Only complete applications will be processed. a. One copy of a completed General Application form (available at the Development Services Center). (If SEPA is required, submit 8 copies of the General Application form.) b. One set of plans and computations addressing Minimum Requirements #1 through c. Projects that require SEPA approval will be processed through the Technical Committee. Submit nine copies of the SEPA document(s). d. Application fee. City III. City Review Process a. The project engineer or applicant will be contacted when the review is complete. b. The plans and computations are red-lined and one set of each is returned to the applicant with a Plan Review Checklist completed by the City. ---PAGE BREAK--- 64 Table 5.0: Medium Project Requirements Responsible Party Activity Applicant IV. Revision and Resubmittal, if Required a. Revise plans per the City’s comments. b. Resubmit the last set of red-lined prints and computations, the Plan Review Checklist and one set of revised plans and computations as stated above. City V. Review of Revised Plans a. Once all comments have been satisfactorily addressed, the City will proceed with plan approval. b. The project engineer or applicant will be contacted. Applicant VI. Submit Original Plans for City Approval City VII. Plan Approval Plans are approved by signature and returned to the applicant or engineer for reproduction as required. Applicant VIII. Submittal of Permit Prints Submit three sets of prints made from the signed plans to the Stormwater Engineer. City IX. Permit Preparation and Plan Distribution The Stormwater Engineer prepares the permit letter, signs it, calculates the remaining fee, and determines performance bonds per the standard list. The completed permit package is sent to the Development Services Center. The project engineer or applicant will be contacted by the Development Services Center when the permit is ready to be issued. Applicant X. Obtain Permit When applicant is notified that the permit is ready to issue, applicant needs to come to the Development Services Center and pay any remaining fees and post required bonds. The Permit Letter is then issued. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 65 Table 5.0: Medium Project Requirements Responsible Party Activity Applicant XI. Pre-Construction Meetings After plan approval and after submitting permit prints, applicant may be required to contact the Construction Division and schedule a Pre- Construction Meeting. Contact the Construction Division at [PHONE REDACTED] for the date, time, and location (the inspector may have the meeting at the site). In addition to permit issuance, construction may not begin before having a Pre-Construction Meeting (unless waived by the Construction Division). Applicant XII. Construction The applicant shall complete all activities identified in the approved plans to meet City of Redmond standards. As items are completed, and at appropriate times during construction before utilities are buried) the applicant shall notify the City inspector assigned to the project at the Preconstruction Conference that elements are ready for inspection. Failure to notify the City of readiness for inspection in a timely manner may result in the requirement to remove and replace buried or hidden elements. City XIII. Release of Performance Bonds Performance bonds remain in full force and effect until 1) the obligations secured are fully performed to the satisfaction of the City’s inspectors; 2) a bond guaranteeing maintenance of all improvements for a guarantee period have been submitted to the City; and 3) the City has released the bonds in writing. City XIV. Cancellation of Non-Issued Permits a. The permit is only valid for a designated time. It may be to the applicant’s benefit to wait until construction is ready to begin before picking up the permit. b. The permit will be held for a maximum six months without issuance (unless specifically stated otherwise in the conditions of approval) but will then be nullified after this period if not picked up. The permit application would have to be started again, from the beginning, if the project is still desired. A new application may be required by the Public Works Department. ---PAGE BREAK--- 66 Table 5.0: Medium Project Requirements Responsible Party Activity Applicant XV. Permit Extension Request – (Optional) a. If the proposed work cannot be completed within the time covered by the permit an extension may be granted. Additional fees for inspection and renewal are required for extension. b. The applicant must submit a written extension request to the Stormwater Engineer at least two working days before the expiration of the permit. Table 5.0 Medium Project Requirements 5.4 Fees for Medium Projects Fees for Medium Projects are based on the type and number of activities proposed. Fees are charged for plan review and City inspection. Current fee information is available from the Development Services Center. • Medium project fees often include but are not limited to: o Small & Complex Projects: Review o Small & Complex Projects: Inspection Consult the Development Services Center to determine what actual costs you can expect based on the specifics of your project. Performance security may be required prior to issuance of a permit. Security requirements are determined after application. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 67 Chapter 6 – Large Project Requirements 6.1 Project Classification See Chapter 3 for project classification. 6.2 Project Requirements for Large Projects Large Projects are required to meet Minimum Requirements #1 through #9 as detailed in Chapter 2 of the Stormwater Technical Notebook. There are also more strenuous requirements for construction stormwater pollution prevention outlined in Chapters 9 and 10 of the Stormwater Technical Notebook. 6.3 Permit Process for Large Projects The following is an overview of the steps and requirements for projects that require only a Clearing/Grading and Stormwater Management approval (and no other approvals). Projects requiring other permits may have additional steps and requirements. Consult the Development Services Center for additional guidance. Table 6.0 - Large Project Requirements Responsible Party Activity Applicant I. Project Proposal a. Prepare Project Plans – an Application Checklist for Project Plan preparation is found in Appendix F. Large projects are subject to Minimum Requirements #1 through b. Prepare SEPA Checklist 1. All Large Projects are required to submit a SEPA Checklist. The Technical Committee will determine if the proposed activity requires formal SEPA process review. 2. SEPA Checklists are available at the Development Services Center. Redmond has modified the state standard checklist. Therefore, only a City of Redmond SEPA Checklist will be accepted. Complete the checklist to the best of your ability. ---PAGE BREAK--- 68 Table 6.0 - Large Project Requirements Responsible Party Activity Applicant II. Complete and Submit Applications All the following shall be completed and submitted for review for the application to be considered complete. Only complete applications will be processed. a. One copy of a completed General Application Form (available at the Development Services Center). b. Eight sets of Project Plans including the applicable information on the application requirements checklist in Chapter 10. c. Submit nine copies of the SEPA document(s). d. Application fee. City III. City Review Process All Large Projects are processed through the Technical Committee. The Committee reviews the proposed project in concept and makes the SEPA determination. The Committee prepares a letter of conditions to be addressed during preparation of final construction drawings. Applicant IV. Construction Plan Preparation a. Prepare construction drawings based on the letter containing the conditions of approval from the Technical Committee and on Redmond’s design standards. b. Submit three sets of revised plans and supporting calculations to the Development Services Center (include a copy of the Technical Committee letter of conditions). c. Pay construction drawing review fee at the Development Services Center. City V. Construction Plan Review a. Plans are reviewed in house and with City’s contracted consultant. b. The project engineer or applicant will be contacted when the review is complete. c. The plans and computations are red-lined and one set of each is returned to the applicant with a Plan Review Checklist completed by the City. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 69 Table 6.0 - Large Project Requirements Responsible Party Activity Applicant VI. Revision and Resubmittal a. Revise plans per the City’s comments. b. Resubmit the last set of red-lined prints and computations, the Plan Review Checklist and three sets of revised plans and computations. City VII. Review of Revised Plans a. Once all comments have been satisfactorily addressed, the City will proceed with plan approval. b. The project engineer or applicant will be contacted. Applicant VIII. Submit Original Plans for City Approval Submit original plans to the City for approval along with the final the calculations/report that accurately describes the drainage system and function. Plans shall be reproducible Mylar. City IX. Plan Approval Appropriate City staff sign plans and returns them to applicant or engineer. Applicant X. Submittal of Permit Prints For Clear and Grade Applications only: Submit six sets of prints prepared from the signed plans to the Stormwater Engineer. Otherwise, submit prints to Engineering Division. City XI. Permit Preparation and Plan Distribution The Stormwater Engineer completes the permit, signs it, calculates the remaining fee, and determines bonds. The completed package is sent to the Development Services Center. The project engineer or applicant will be contacted by the Development Services Center when the permit is ready. Applicant XII. Obtain Permit When applicant is notified that the Permit is ready to issue, Applicant needs to come to the Development Services Center and: a. Pay any remaining fees and post required bonds, and b. Receive the permit. ---PAGE BREAK--- 70 Table 6.0 - Large Project Requirements Responsible Party Activity Applicant XIII. Pre-Construction Meetings After plan approval and after submitting permit prints, applicant shall contact the Construction Division and schedule a Pre-Construction Meeting. Contact the Construction Division at [PHONE REDACTED] for the date, time, and location (the inspector may have the meeting at the site). In addition to permit issuance, construction may not begin before having a Pre-Construction Meeting. Applicant XIV. Construction The applicant shall complete all activities identified in the approved plans to meet City of Redmond standards. As items are completed, and at appropriate times during construction before utilities are buried) the applicant shall notify the City inspector assigned to the project at the Preconstruction Conference that elements are ready for inspection. Failure to notify the City of readiness for inspection in a timely manner may result in the requirement to remove and replace buried or hidden elements. City XV. Release of Performance Bonds Performance bonds remain in full force and effect until 1) the obligations secured are fully performed to the satisfaction of the City’s inspectors; 2) a bond guaranteeing maintenance of all improvements for a guarantee period have been submitted to the City; and 3) the City has released the bonds in writing. City XVI. Cancellation of Non-Issued Permits a. The permit is only valid for a designated time. It may be to the applicant’s benefit to wait until construction is ready to begin before picking up the permit. b. The permit will be held for six months without issuance (unless specifically stated otherwise in the conditions of approval) but will then be nullified after this period if not picked up. The permit application would have to be started again, from the beginning, if the project is still desired. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 71 Table 6.0 - Large Project Requirements Responsible Party Activity Applicant XVII. Permit Extension Request – (Optional) a. If the proposed work cannot be completed within the time covered by the permit an extension may be granted. Additional fees for inspection and renewal are required for extension. b. The applicant must submit a written extension request to the Development Services Center at least two working days before the expiration of the permit. Table 6.0 Large Project Requirements 6.4 Fees for Large Projects Fees are charged for plan review and City inspection. Current fees are available from the Development Services Center. Large project fees often include but are not limited to: • Large Projects: Review • Large Projects: Inspection There may be additional review fees related to project-specific items. For example, vaults must be designed for appropriate soil, groundwater, and surface loadings. Separate review and permits are required from the Building Department. Consult the Development Services Center to determine what actual costs you can expect based on the specifics of your project. Performance security may be required prior to issuance of a permit. Security requirements are determined after application. 6.5 Provide Accurate Record Drawings As-built records of development projects, including Clear & Grade projects involving stormwater facilities, are maintained by the City. Make sure the records are correct when project information is provided, by submitting accurate record drawings when a project is completed. A record drawing cash bond is required of most projects as part of the final engineering drawing approval process. Before acceptance of improvements, a record drawing shall be prepared by a Professional Land Surveyor or Civil Engineer, licensed in the State of Washington. The record ---PAGE BREAK--- 72 drawing shall include accurate locations, elevations, and sizes of all constructed features. Record drawing documents will bear the signature, stamp, and date of the licensed Land Surveyor preparing them. The process and requirements are found in the City of Redmond publication “Record Drawing Requirements” dated July 2015. This publication is available on- line at the city’s website under the Coordinated Civil Review Process, Resources. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 73 Chapter 7 – Design Goals The purpose of the information in Chapters 7 through 10 is to provide engineers, designers, technicians, inspectors, and others with a reference to City of Redmond’s goals and standards for the planning and design of clearing and grading activities and stormwater management facilities. The following design goals are applied to clearing, grading, and stormwater system designs in Redmond. Design goals are broad targets that indicate desirable outcomes, even though they may not be fully met in specific situations. Failure to completely meet a general design goal minimize erosion and sedimentation) is not intended to constitute a deficiency subject to legal or procedural challenge. The goal must, however, be reasonably addressed in specific situations. If an alternate approach to a project’s stormwater management design would provide a significantly greater achievement of a goal without significant additional cost (monetary, land use, etc.) then the alternative could be considered an alternative that is reasonable and could be required under this chapter. Clearing, Grading, and Stormwater Management goals and design requirements need to be compliant with Redmond Municipal Code 15.24 intent, goals, and requirements. Specific situations can only be evaluated on a case-by-case basis. 7.1 Provide a Basic System of Drainage The drainage system shall: • serve all lots and site improvements that are part of or affected by the project; • reduce stormwater runoff through on-site stormwater management techniques (Minimum Requirement • direct stormwater runoff away from buildings, traveled ways, and other developed surfaces; and • provide stormwater runoff treatment where appropriate (Minimum Requirement Basic systems protect walkways, crosswalks, etc., from concentrated runoff flows (for example, by adding catch basins upslope of the walkways). ---PAGE BREAK--- 74 7.2 Prevent Flooding of Inhabited Buildings Overflow and emergency runoff routes shall be provided. Floodways adjacent to defined channels should accommodate flood flows (to at least the 100-year storm from fully developed upstream conditions). Projects that are located within the floodplain shall submit a Flood Control Zone Application (Appendix J) prior to submittal of final engineering drawings. 7.3 Minimize Erosion and Sedimentation During construction, development activities can have significant and long-term impacts on aquatic ecosystems. Reducing these impacts by meeting all 13 elements of the Temporary Erosion and Sedimentation Control Plan (Minimum Requirement and responding quickly to unforeseen additional erosion and sediment control needs greatly reduces the impacts from construction. In addition, permanent stormwater controls need to control stormwater runoff peaks and durations to reduce adverse hydrologic impacts. 7.4 Minimize Water Quality Degradation Runoff treatment facilities are necessary and required by State law and Redmond Municipal Code to reduce degradation of surface water bodies and groundwater (Minimum Requirement Site layouts and stormwater designs that minimize pollution-generating hard surfaces, inherently reduce pollution (Minimum Requirement Last, source control measures in the site design are required to reduce the quantity of pollution sources contaminating runoff (Minimum Requirement 7.5 Don’t Mix Clean and Untreated Stormwater Stormwater that has been treated for water quality should not be mixed with stormwater that has not been treated for water quality. 7.6 Protect Water-Related Habitat Refer to the Critical Areas Regulations (Redmond Zoning Code 21.64). ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 75 7.7 Maintain Recharge and Subsurface Flow Patterns Maintaining groundwater supplies is important, but do not increase recharge over natural conditions without careful hydro-geologic studies to avoid land stability problems. In areas of existing land stability concerns, recharge should be reduced. Water quality is critical for recharge areas. Infiltration of runoff from PGHS is limited by Critical Aquifer Recharge Areas; infiltration from clean surfaces is encouraged (see Section 8.3). 7.8 Address “Real-World” Conditions Engineering designs should recognize that field conditions, debris, and poor maintenance/repair practices exist which need to be considered so long-term viability is possible. 7.9 Provide for Operation and Maintenance Elements of the system proposed need to be capable of operating in the municipal context, have good access for maintenance and operation, and need to avoid very specialized parts, equipment, and operator qualifications whenever possible (Minimum Requirement 7.10 Proceed Based on Clear, Professional Thinking Engineering documents submitted for approval must have clear concepts (including a narrative description if concepts are non-standard or not obvious) and design explanations, calculations, and other supporting information to show that the construction drawings implement the concepts. 7.11 Meet Standards Designs need to: comply with City regulations and standards; comply with accepted legal principles; apply sound engineering principles; and include alternatives or adjustments to enhance aesthetics. ---PAGE BREAK--- 76 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 77 Chapter 8 – Local Design Standards This chapter contains information on specific issues for projects in Redmond to help define how to meet Redmond’s local codes and regulations and to help define terms in ways that are meaningful to specific engineering design situations in Redmond. 8.1 Standard Specifications and Details All projects shall be designed and constructed to conform to the City of Redmond Standard Specifications and Details, Current Edition. These are available on the City’s website (www.redmond.gov). 8.2 Proper Drainage The Stormwater Technical Notebook describes minimum drainage requirements. These requirements must be addressed in all projects (Small, Medium, or Large) whether or not plans and permits are required. Even though plans and permits are not required for most Small Projects, proper drainage facilities are required with all projects. Proper drainage directs runoff away from structures, meets legally accepted practice, and meets the intent of RMC 15.24. For projects not requiring plans or permits, drainage systems are not required by code to have detention or formally designed runoff treatment facilities. Nevertheless, if conveyance capacity is not adequate, the project proponent may elect to provide detention or infiltration. Drainage systems shall be provided to prevent flooding of developed areas, connect downspouts, and provide positive drainage for footing drains. Runoff from upslope properties must be accepted at natural and established locations at property boundaries and be discharged at natural or established downslope locations along property boundaries or to a constructed drainage system if authorized, subject to required on- site quantity and quality controls. ---PAGE BREAK--- 78 8.3 Stormwater Management and Infiltration in Critical Aquifer Recharge Areas 8.3.1 Critical Aquifer Recharge Areas Critical Aquifer Recharge Areas (CARA) were established based on proximity to City drinking water supply wells and the modeled path of groundwater flow toward these wells. A map of the CARA is available at www.redmond.gov/Map, and Appendix C. CARA I is the land area overlying the aquifer in which it will take a maximum of five years for the groundwater to reach any public water source well owned by the City and is, therefore, the area of greatest concern regarding infiltrating stormwater runoff. CARA II is the land area overlying the aquifer in which it will take over five years to reach any public water source well owned by the City. In CARA I, certain land uses and activities are prohibited, as noted in Redmond Zoning Code 21.64.050. If a project area includes portions that are in more than one Critical Aquifer Recharge Area (CARA), then the Stormwater Engineer will assess, using criteria found in RZC 21.64.050.d.2, whether any portion of the site may be considered to be in the CARA with fewer restrictions. Otherwise, the whole site shall be considered to be within the CARA with more restrictions. 8.3.2 Construction in Critical Aquifer Recharge Areas Projects in CARA I and II shall address the following: A. During construction, if construction vehicles will be refueled onsite and/or the quantity of hazardous materials that will be stored, dispensed, used, or handled on the construction site is in aggregate quantities equal to or greater than 20 gallons liquid or 200 pounds solid, exclusive of the quantity of hazardous materials contained in fuel or fluid reservoirs of construction vehicles, the City may require any or all of the items listed in the Redmond Zoning Code 21.64.050.D. Generally, the following items will be required in writing as part of the TESC Plan: 1. Monitoring plan. 2. Designated project contact. 3. Secondary containment. 4. Provisions to secure hazardous materials. 5. Response to leaking vehicles and equipment. 6. Practices and procedures regarding transfer of flammable and combustible liquids. 7. Practices and procedures regarding masonry and concrete handling and washout to prevent groundwater contamination. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 79 8. On-site cleanup materials (materials are to be listed in the TESC Plan) and other containment and cleanup provisions. All hazardous material releases shall be contained, cleaned up, and reported. B. The Stormwater report required for projects shall include a section describing how each of the items above has been addressed in the plans for the proposed project. 8.3.3 Infiltration in Critical Aquifer Recharge Areas The 2014 allows Redmond to add stormwater requirements to protect the drinking water aquifer (Volume III Section 3.3.7 - Site Suitability Criteria for Infiltration). Infiltrating runoff from pollution generating hard surfaces in Critical Aquifer Recharge Area I is prohibited, with two exceptions. 1) Single-family residential projects in Critical Aquifer Recharge Area I may infiltrate runoff from pollution generating hard surfaces after enhanced treatment using a BMP that is exposed to the surface (such as bioretention visible from public sidewalks or roads). 2) In the Marymoor Subarea there is no stormwater conveyance available, so development is required to infiltrate stormwater, even if it lies within CARA I. As such stormwater shall receive enhanced treatment prior to infiltration. Infiltration of runoff from non-pollution generating surfaces is encouraged where feasible. 8.3.4 Separation from High Groundwater Separation from high groundwater or bedrock for various BMPs is described in the 2014 the Guidance for UIC Wells that Manage Stormwater Runoff (2006) and WAC 173-18. These documents are inconsistent. In light of this issue and Redmond’s attention to groundwater/drinking water supply protection, the following is required when infiltrating runoff in Redmond. In general, the bottom of any infiltrating stormwater facility shall be 5 feet from the seasonal high water table. Section 2.9.3.9 provides detail on how the average seasonal high groundwater elevation can be determined. This can be reduced to 3 feet of separation with a mounding analysis as detailed in the 2014 Exceptions to this rule: 1. Bioretention – with or without an underdrain are not UICs. Bioretention can have 1 foot of separation from the bottom of the facility to the high water ---PAGE BREAK--- 80 table if less than 5,000 square feet of area drain to the facility. If 5,000 square feet or more of area drain to the facility, then 3 feet of separation is required. 2. Single Family roof infiltration – Any type of infiltration facility for the sole purpose of infiltrating runoff from single family roofs is not regulated as a UIC (WAC 173-218) and requires a minimum of 1 foot of separation from the bottom of the facility to the high water table. 3. Permeable pavement – one foot of separation from the bottom of the base course to the high water table is required. (This also applies to functionally equivalent permeable pavement (Section 8.7.5.4).) 8.3.5 Defined Bottom of Stormwater Infiltration Facility It is permissible, with Stormwater Engineer approval, to add clean, free-draining fill below a stormwater facility to replace low permeability soils in an effort to improve function. In that case, the “bottom” of the stormwater facility may be considered to not include this free-draining fill. 8.3.6 Using Infiltration as Basic Treatment The Site Suitability Criteria in Volume III section 3.3.7 shall be used to determine if basic treatment can be achieved by native soil below an infiltration facility. If native soils are to be used for basic treatment, 5 feet of separation from the bottom of the facility to the high water table is mandatory. 8.4 Conveyance System Design 8.4.1 Guidance Documents For basic conveyance system design in Redmond use the latest edition of the Washington State Department of Transportation (WSDOT) “Hydraulics Manual” (M23-03). The manual is available from WSDOT’s website at www.wsdot.wa.gov/publications/manuals/m23-03.htm. Storm drain design (Conveyance Calculations) may be completed using the spreadsheet available from WSDOT’s “Program Downloads: Hydraulic and Hydrologic” website. The spreadsheet uses the rational method as described in the WSDOT “Hydraulics Manual”. Note that the 2014 shall be used for detention sizing and stormwater treatment requirements. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 81 For computation of hydraulic grade lines (Backwater Analyses) in Redmond use one of the following models: 1. King County Surface Water Management Backwater Analysis Program 2. by Computational Hydraulics 3. Equivalent model approved by the Stormwater Engineer 8.4.2 Pipe Sizing All new pipes shall be sized to convey the 50-year fully-developed peak flow without overtopping catch basins. All new culverts shall be sized so that the 50-year fully-developed peak flow should not exceed the allowable headwater of 1.25 times the culvert diameter and should not exceed the elevation of the base course of the roadway. All new culverts should be sized such that there is no roadway overtopping during the 100-year flow event. If the culvert is on a stream that is determined to be fish bearing by the City of Redmond or Washington Department of Fish and Wildlife (WDFW), then the culvert should be designed to be fish passable. Stormwater shall be managed such that the 100-year frequency event does not flood proposed buildings, any existing on-site buildings, or other existing buildings on contiguous parcels. Required conveyance standards may be adjusted by the Stormwater Engineer based on site and conditions. Provide an exhibit to demonstrate the 100-year flow path. For public stormwater pipe, the minimum size shall be 12-inches. For private stormwater pipe, the minimum size shall be 6-inches. To accommodate special installation scenarios, smaller pipe may be used with Stormwater Engineer approval. 8.4.3 Ditch Sizing All ditches shall be sized to convey the 100-year storm with one foot of freeboard. Ditch design should include velocity analysis to ensure stable channels. 8.4.4 Horizontal Clearance and Crossing Angle The minimum horizontal spacing between underground stormwater facilities (pipes, infiltration trenches, Filterra vaults, or stormwater vaults and structures); and other utilities (water mains, gas mains, other underground utility facilities, and all structures) shall be five feet horizontally. Other utilities shall not be placed above and parallel to conveyance or infiltration pipes or tanks. ---PAGE BREAK--- 82 The minimum horizontal distance between any above ground stormwater facilities (swales, open channels, biofiltration swales, etc.) and other utilities (water mains, gas mains, and other underground utility facilities) shall be 10 feet. For pipe crossings, the preferred angle is 90 degrees, but 20 degrees obtuse or acute of 90 degrees is acceptable. To minimize conflicts in the field, all existing utilities at the location of the proposed stormwater pipe shall be potholed using eductor truck prior to approval by the Stormwater Engineer. Document results of potholing on drainage plans and profiles as appropriate where conflicts may arise. A City of Redmond Right-of-Way permit, including an approved traffic control plan, is required before potholing within right- of-way or City easements. 8.4.5 Vertical Clearance – Utilities The minimum vertical clearance spacing between the outside of storm drain pipelines and water mains, gas mains, electrical or communication conduits, and other underground utility facilities, shall be as noted in Table 8.2. It is expected that the “Standard” vertical clearance will be provided. If that is not possible, use of Ethafoam pads or pipe sleeves may be allowed with approval from the Stormwater Engineer. Table 8.1 - Vertical Clearance – Utilities Utility Location (Above or below Storm Pipe) Minimum Clearance Special Requirement Electrical Above or below 12 inches Standard Communications Above or below 12 inches Standard Water main or gas main Above or below 12 inches Standard Water main or gas main Above or below 6 inches Ethafoam pad Sanitary Sewer Below storm pipe 12 inches Standard Sanitary Sewer Above storm pipe 18 inches Standard Sanitary Sewer Above or below storm pipe 6 inches Pipe sleeve and Ethafoam pad Liquid petroleum Above or below See Stormwater Engineer Table 8.1 Vertical Clearance – Utilities An Ethafoam pad is required for some installations to provide additional protection between adjacent utilities. The size of the pad shall be based on the outside ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 83 diameter of the larger crossing pipe. The pad shall be O.D. by O.D. square by 2.5 inches thick minimum or as required to protect the pipes. The pad shall be a strong, resilient, medium-density, closed-cell, polyethylene foam plank (Dow Ethafoam 220, or accepted equivalent.) A pipe sleeve is required for some installations to provide additional protection of stormwater from potential leakage from other utilities. A pipe sleeve shall be a single section of PVC pipe (no joints) with a minimum length of 3 feet to each side of pipe crossing. The pipe sleeve shall be placed around the stormwater pipe with the annular space between the pipe sleeve and the stormwater pipe filled with grout. Additional measures may be necessary to ensure system integrity and may be required as determined by the Stormwater Engineer on a case-by-case basis. 8.4.6 Minimum Cover The standard minimum cover over storm drainage lines is dependent on the pipe material. The Redmond Design Standards and Specifications outline cover requirements. The minimum cover over yard drain lines is 18 inches. 8.4.7 Unstable Soils Unstable soil conditions, such as peat, shall be removed from under pipes unless special measures are approved by the Stormwater Engineer. 8.4.8 Maximum and Minimum Slopes Maximum slope on storm drain lines is 20%, unless approved by the Stormwater Engineer. Minimum slope on storm drain lines is 0.25%, unless approved by the Stormwater Engineer. 8.4.9 Stream Culverts Stream culverts shall be designed to have natural bottom conditions, with 1/3 of the pipe diameter buried. Culverts used for stream conveyance shall be a minimum of 24 inches in diameter. Bridges shall be the first choice for stream crossings. More information can be found in the Redmond Zoning Code 21.64. 8.4.10 Trees Trees shall not be located within 8 feet horizontally from storm drain pipe unless root barriers are provided as approved by the Stormwater Engineer. With root barriers, trees may be no closer than 3 feet to pipes unless approved by the stormwater engineer. ---PAGE BREAK--- 84 8.4.11 Pump System Requirements Pumping stormwater as a permanent practice is the method of last resort, not typically permitted for publicly maintained facilities, and requires Technical Committee approval. When no other alternatives are feasible, pump systems may be considered provided they meet the following: • Pump: 10-year peak flow rate as calculated by the rational method • Backup Pump • Alternative Power Source (Emergency Generator) • Auto-Transfer Switch Disconnecting Generator from Public Grid. Auto-Start Required. • Audio Alarm for High Water/Pump Failure • 3-Hour Flow Storage Volume (may be combined with water quality treatment) In addition to these requirements, a note shall be placed on the plat or title that says, “Property owner is responsible for operation of the stormwater pump, and for any damages to offsite property if the pump fails to transfer stormwater as designed.” 8.4.12 Underdrains Underdrains shall be a minimum of 6” diameter perforated PVC per WSDOT Standard Specification 9-05.2(6). All underdrains shall have cleanouts every 100 feet, or at a minimum at all bends in the underdrain system. 8.5 Catch Basin and Manhole Requirements 8.5.1 Structure Materials The City of Redmond Standard Specifications and Details describes structure material requirements. 8.5.2 Structure Spacing Space catch basins in accordance with best engineering practice and the WSDOT Hydraulics Manual. To accommodate maintenance of the pipes, a manhole or catch basin (structure) shall be placed periodically with the following maximum spacing: • 200 feet for pipes less than 12 inch or with design velocities less than 3 feet per second (fps); otherwise, • 300 feet for pipes less than 30 inch diameter with design velocities greater than 3 fps; or, • 400 feet for pipes equal or greater than 30 inch but less than 42 inch diameter with design velocities greater than 3 fps; or, ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 85 • 600 feet for pipes of 42 inch diameter or larger with design velocities greater than 3 fps; or, • 600 feet for tight lines down steep slopes. Structures shall be installed at the end of all dead end mainlines, at horizontal or vertical pipe bends, at changes in pipe size or material, and at pipe junctions for access. 8.5.3 Pipe Connections Match crowns at structures. Inlet pipe crowns shall not be lower than outlet pipe crowns unless specifically waived by the Stormwater Engineer. Pipe connections shall be water-tight. 8.5.4 Spill Prevention Device Multifamily, commercial, and industrial properties shall include at a minimum a spill prevention device at the last structure on the property before connecting to the public stormwater system. The minimum requirement for a spill prevention device is a downturned elbow, removable for maintenance, located on the outlet pipe leaving a type 2 catch basin. Depending on the uses on the site, the Stormwater Engineer may require additional measures of protection. 8.5.5 Knockouts Knockouts shall be provided in structures where future extensions are anticipated. These shall be shown on the plans. 8.5.6 Drop Structures Drop structures shall only be allowed where approved by the Stormwater Engineer. Generally, drop structures will not be approved if the drop is less than 5 feet. 8.5.7 Lot and Area Drains Lot drains or area drains in excess of 2 feet deep and up to 5 feet deep shall be Type I catch basins. Area drains exceeding 5 feet deep shall be Type 2 catch basins with bolt-down lids. 8.5.8 Through-Curb Inlet Frames Through-curb inlet frames shall be specified on plans at sag points, at any inlet where by- passing runoff would escape the intended control system and at every third inlet on a continuous run along a continuous slope. Through-curb inlet frames may be used at all points except at proposed or likely driveway locations. ---PAGE BREAK--- 86 8.5.9 Catch Basins and Americans with Disabilities Act Storm drains and catch basins are normally placed where they will intercept surface water runoff. Installing a curb ramp at a point of strategic runoff interception can compromise effective drainage. Regrading the section of road or curb ramp location to alter drainage patterns can resolve some situations in which drainage concerns conflict with accessibility requirements. Ideally, inlets should be placed uphill of crossings or curb ramps to drain water before it can puddle where pedestrians are crossing. More frequent drainage inlets, more strategic placement of inlets, and basin pickups will also reduce the frequency of puddles. If catch basins cannot be avoided within ADA accessible pathways, then ADA compliant catch basins grates may be used with approval of the Stormwater Engineer. These are typically maintenance intensive and should be avoided. 8.6 Site Design 8.6.1 Flood Protection All parts of any structure constructed below the 100-year flood elevation of associated waterways shall be protected from flooding using flood-proofing. Flood-proof to the 100-year elevation, plus 1 foot. Flood-proofing shall conform to Federal Emergency Management Agency standards in effect at project vesting. Projects planning work within Flood Control Zones shall submit a Flood Control Zone Application (Appendix 8.6.2 Single Family Residential Plats and Short Plats Projects creating lots for single-family houses (residential plat and short plat projects) shall provide drainage systems for all lots. The drainage systems shall address on-site stormwater management, flow control, and runoff treatment. 8.6.3 Drainage Connections for All Lots All types of plats and short plats (residential, commercial, industrial, and others) shall provide for drainage connections on each lot, unless otherwise approved by the Stormwater Engineer. (On-Site Stormwater Management measures may make the use of lot connections unnecessary.) Drainage connection points are to be located at the low elevation point of the allowable building area of each lot. The connections must be below finished grade so as to allow connection of footing drains, roof drain leaders, and other drains. Providing for drainage connections typically means providing a piped system from the drainage connection points described above to the drainage system in the plat ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 87 or short plat. A maximum of three lots may be connected to a common private collection pipe. Multiple collection pipes may be used. In some cases it may be acceptable to include only the plan for the lot drainage connections as part of the City-approved drainage plan for the plat or short plat and defer construction until building construction on the lots. Infiltration of runoff can reduce hydrologic impacts and water quality impacts and maintain groundwater supplies. Infiltration is generally acceptable where soils and geology are suitable. Infiltration of runoff from pollution generating impervious surfaces is limited based on Critical Aquifer Recharge Areas (Section 8.3). Construction of the lot drainage connection systems must be feasible and allow connection to the proposed plat improvements or to the documented infiltration areas. 8.6.4 Single Family Roof and Foundation Drain Requirements Size and Connection: Roof drain/foundation drain connection from the house, when required based on Figure III-3.1.8 of Volume III of the 2014 shall be 6- inch diameter and shall be extended to a storm drain structure (not connected directly to a stormwater pipe). Foundation drains shall be separate from roof drains around the building foundation. Pipes shall be smooth wall, rigid type (sewer grade). Pipes shall not be corrugated polyethylene (such as flexible ADS). Roof and footing drain connection stubs shall be at least one 1 foot below the lowest existing elevation of the building envelope on all newly-created lots, unless a different elevation is approved or required by the Stormwater Engineer. The minimum cover over yard drain lines is 18 inches. For subdivisions, no more than three roof drain stubs are allowed on a single roof drain collection pipe. Building Footings: Building footings shall be designed, or pipe located, such that the footing shall not bear on the pipe. These requirements shall also be coordinated with the requirements of Section 2.5.5 that addresses roof runoff dispersion and infiltration. 8.6.5 Separation of Systems Serving Separate Owners Stormwater facilities provided to for flow control and runoff treatment generally should be provided within the site they are serving although certain exceptions are acceptable. Facilities for single family plats may be located in common areas (even in public roads that are created by the plat or short plat). ---PAGE BREAK--- 88 Flow control and runoff treatment provided for the private part of a project shall be separate from flow control and runoff treatment for public impervious surfaces that are part of the project. Individual lots within single-family plats and short plats with public road improvements may drain to the public flow control and runoff treatment systems constructed to serve the development. In some circumstances, flow control and runoff treatment requirements for the proposed hard surfaces may be met by adding such control(s) to equivalent existing developed areas of the site, which do not already have such controls. 8.6.6 Grading The maximum ground slope on graded surfaces is 3 horizontal to 1 vertical (3:1) except as approved in association with roadway section in City rights-of-way where the maximum ground slope may be up to 2:1. Proposed contours shall not create undrained, ponding areas where such areas would not be appropriate (onsite or offsite). 8.6.7 Rockeries/Retaining Walls Rockeries or retaining walls should not cross or be near storm-drain pipes. Any crossing of a wall shall be perpendicular to the wall and special construction techniques including steel casings may be required. Rockeries under 4 feet are not regulated. Rockeries over 4 feet shall only be used against cut slopes. Rockeries and retaining walls shall have foundation drains (6 inches in diameter of approved materials) behind the wall connected to a defined conveyance system. Rockeries 48 inches and taller and retaining walls must be designed by a structural or geotechnical engineer. No retaining structure may be higher than 8 feet unless a relief from general design standards is obtained. Refer to Redmond Zoning Code 21.24.030 Height. Structural retaining walls over 4 feet in height are reviewed and permitted by the Building Department following UBC Section 106.2. 8.6.8 Easements 8.6.8.1 Public Easements Where public storm drain line easements are necessary, they shall be 20 feet in width. Easement widths of less than 20 feet may be considered by the Stormwater Engineer, in special situations, but shall not be less than 15 feet in width. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 89 Where public storm drain pipes are to be located across private lots where owners can erect fencing, sheds, and plant landscaping the access for maintenance is severely restricted. An example is a pipeline crossing several single-family lot backyards. City of Redmond standards require an eductor truck to access catch basins for maintenance. See section 8.6.9.1. These pipe installations are to be located in tracts dedicated to the city. Publicly maintained runoff treatment and flow control facilities shall be located in tracts dedicated to the City or City-owned right-of-way. Publicly maintained stormwater facilities may be located within private tracts, provided a public stormwater easement is provided. When located within a private tract, the tract shall be sized to permit a 10-foot minimum maintenance setback, or a 1 to 1 slope setback for excavation from the bottom of the stormwater facility to the property line, whichever is greater. Tracts and easements shall include the entire facility, site access and maintenance area. For facilities in the right-of-way, the entire facility, site access area, and at least 5 feet around the facility should be in the right- of-way. If this is not possible, an easement shall be required. If an easement is permitted, dimensions shall be determined by the Stormwater Engineer. In cases where pipes and/or other facilities are deeper than 8 feet or have other special conditions, larger tracts or easements may be required. All easements needed for City stormwater systems shall be provided by the developer in the name of the City. The required easements shall be shown on the construction drawings and the easement legal description or plat markup shall be submitted for review at the same time construction drawings are submitted for review. Easements shall have language acceptable to the City, similar to the example in Appendix K. An alternative to separately recording a City of Redmond easement form is to record an easement on the face of a plat. If this is the method used, a standard City of Redmond easement statement shall be included in the plat documents. Buildings, structures, garages, carports, dumpster enclosures, decks, rockeries over 4 feet, etc., shall not be located in easement areas. 8.6.8.2 Private Easements In all cases, appropriate easements must be provided, for the specific drainage systems shown on the construction documents. Those documents shall also show anticipated grading, rockeries, retaining walls, etc. The minimum easement for private stormwater BMPs shall include the entire facility, site access area, and at least 10 feet around the facility. Private storm pipe easements shall be a minimum ---PAGE BREAK--- 90 of 15 feet wide, with the storm pipe centered in the easement. Wider private easements will be needed for deep pipe installations. 8.6.9 Stormwater Facilities 8.6.9.1 Maintenance Access Unless specifically waived by the Stormwater Engineer, all stormwater facilities shall be accessible to maintenance vehicles. The Operations & Maintenance manual for the facility shall identify the equipment and access required for maintenance. Eductor trucks are the vacuum excavator trucks used to maintain catch basins, manholes, and other structures. Eductor truck access is required to all entries to vaults, flow splitters, catch basins, manholes, and control structures. Large ponds, stormwater treatment wetlands, sand filters, etc., need access for a track hoe that includes a stabilized ramp into the facility to allow for cleaning and equipment access to the entire facility. Such areas shall be paved from the street to the stormwater facility. Smaller facilities may be allowed to eliminate the ramp if provisions for access are spelled out in the Operations & Maintenance manual. Smaller facilities like rain gardens or biofiltration swales need a work area adjacent to the facility to support maintenance activities. For facilities that require eductor truck maintenance, the preferred configuration is to have the eductor truck approach a structure opening with the front of the vehicle with limited maneuvering required from the nearby street. Access requiring backing maneuvers requires Stormwater Engineer approval. Acceptable access includes an improved roadway surface within 10 feet of a manhole or catch basin with overhead clearance to 20 feet to allow for boom operation. If the manhole is not located within the roadway, then a paved apron for maintenance workers is typically required. Materials for construction of an improved roadway surface can include asphalt concrete or Portland cement concrete. Maintenance access roads shall comply with the current version of Redmond Standard Detail DG-11. Access roads shall have a maximum slope of 10% and a cross slope of Portions of access roads more than 50 feet from structures that require maintenance, turns, or bollards, may be up to 15% slope if constructed with concrete. Either through- access or a turnaround is required. Design drawings shall demonstrate how the City’s eductor trucks can access all areas that require maintenance. Details shall be provided to ensure full clearance of all parts of the vehicle when navigating changes in grade or turning. Special details are required if the access road slope exceeds 10% or if unusual grade transitions exist. The Stormwater Engineer may require maintenance access roads to be located in separate tracts. Facilities that must be located on steep slopes shall be designed to minimize any requirements for maintenance access. A plan for accessing such ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 91 facilities with eductor truck flex hose or measures to minimize required maintenance shall be identified in the Operations & Maintenance manual. Outlet control valves shall be detailed so as to be operable from the surface (not subject to confined space entry requirements) unless approved otherwise by the Stormwater Engineer. The specific detail for these valves depends on the type of valve and shall be subject to approval by the Stormwater Engineer. Gravity-flow draw-down systems (for ponds, vaults, etc.) shall be provided with an outlet control valve. 8.6.9.2 Facility Maintenance Provision shall be made for long-term maintenance of flow control and runoff treatment and low impact development BMP facilities. 8.6.10 Transfer of Assets to the Public When projects include construction of improvements that will be turned over to the public, a Public Utility & Stormwater Facilities Bill of Sale Form (Appendix L) and a Developer Extension Asset Summary (Appendix M) shall be completed and submitted to the Development Services Division of Planning and Community Development. 8.6.11 Infiltration Setbacks Stormwater infiltration facilities shall be located and designed such that the infiltrated stormwater does not cause flooding of buildings or harm existing utilities. Infiltration facilities setbacks shall be observed as follows: • Setback to property line: 10 feet • Setback from off-site structures: As determined appropriate by a registered geotechnical engineer. • Setback to building protected from groundwater: 0 feet • Setback to building of zero feet requires the building design be based upon this location. Provide confirmation from geotechnical and structural engineer of knowledge of proximity of infiltration to building. • Setback to rockeries and retaining walls: 10 feet • Any other setbacks shall conform to Chapter 3 of Volume 3 of the • Setback of infiltration pipes to tree trunks: eight feet. 8.6.12 Dispersion Setbacks ---PAGE BREAK--- 92 Dispersion facilities shall be setback as described in the Department of Ecology Stormwater Management Manual BMP T5.10B. Maintain a setback of at least 5 feet between any edge of the trench and any structure or property line. 8.6.13 Artificial Turf Artificial turf is a fiber surface used in place of grass and is divided into two installation types. Residential projects are single-family residences and commercial projects include areas such as sports fields, golf courses, and parks. Residential projects can typically be installed without an underdrain system, depending on the underlying soil type. Residential applications shall use only sand or a silica sand mix for infill, clean aggregate base, geotextile fabric, and nailer boards at all edges. Commercial projects typically require an underdrain system due to the infill material. Commercial applications are typically comprised of a turf system, made up of turf, infill, shock pad, aggregate base, underdrain, geotextile, etc. Commercial projects shall be installed with an underdrain system if any infill other than sand or silica sand mix is used. Artificial Turf is defined by Ecology as a pollution generating pervious surface, but Ecology does not provide clear guidance for how to consider artificial turf in threshold determinations and sizing treatment and flow control. Therefore, the following guidance shall apply: • When determining minimum requirements, artificial turf shall be considered: o If the surface is underdrained and conveyed to stormwater system or surface water, it is considered a hard surface. o If the surface is underdrained and conveyed to an infiltration system designed to fully infiltrate, or designed to infiltrate directly into the underlying soil, it is considered lawn. • If Minimum Requirement 7 is triggered for a project that includes artificial turf, the artificial turf shall be modeled using the guidance for permeable pavement. • Styrene Butadiene Rubber (Crumb Rubber) is not permitted for an installation that infiltrates within CARA I or II. Outside of CARA I and II, if the infill material or shock pad is crumb rubber, then enhanced treatment is required whether the project triggers Minimum Requirement 6, or not. • If Minimum Requirement 6 is triggered for a project that includes artificial turf, the artificial turf runoff treatment requirement is dependent upon the infill material and what pollutants may leach from that infill material: o Cork, Sand, Silica Sand Blend Infill: No treatment required. o Single family residential application: No treatment required. o Crumb Rubber Infill or shock pad: Enhanced treatment required. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 93 Enhanced treatment is required for artificial turf systems due to the metal concentrations leaching from the various artificial turf infill product(s). A deviation request may be approved for reduced treatment levels. A submitted deviation shall include data documenting pollutant characteristics of stormwater runoff. Basic treatment, or no treatment may be approved, depending upon the data provided for a particular artificial turf system. 8.7 Low Impact Development (LID) 8.7.1 LID Overview Low impact development (LID) (also known as “on-site stormwater management”) is a stormwater management and land development strategy applied at the parcel and subdivision scale that emphasizes conservation and use of on-site natural features integrated with engineered, small-scale hydrologic controls to more closely mimic predevelopment hydrologic functions and provide runoff treatment. Implementation of LID benefits streams, lakes, and Puget Sound by moderating the impacts of stormwater runoff generated by the built environment. These techniques may be accessory or alternative to traditional, structural stormwater management solutions. LID is required by Minimum Requirement Use of LID is one way to implement the following Comprehensive Plan policies: • • NE-9: Encourage environmentally friendly construction practices such as the build green program and low impact development. • • NE-10: Encourage projects which utilize alternative technologies, engineering, and plans which emphasize Low Impact Development strategies through incentives and flexibility in application of regulatory requirements. 8.7.2 Site Assessment for LID All projects that trigger Minimum Requirement #1 are required to submit a Stormwater Site Plan that includes a site assessment. Complete the most recent version of the form in Appendix N as part of this assessment. If infiltration and/or dispersion are not feasible options, the applicant shall provide justification to demonstrate why. 8.7.3 Intent of LID The City encourages the use of LID techniques, including techniques for stormwater management. ---PAGE BREAK--- 94 These goals are to: • Maintain or restore the pre-developed condition surface water flow volumes, durations and frequencies; • Retain or restore native forest cover to capture, infiltrate and evaporate all or a portion of the rainfall on the site; • Cluster development and minimize land disturbance; • Preserve or restore the health and water-holding capacity of soils; • Incorporate natural site features that promote infiltration of stormwater; • Minimize total impervious surfaces and effective impervious surfaces; • Reduce or eliminate piped stormwater conveyance and conventional detention ponds; • Manage stormwater through infiltration, bioretention, and dispersion; and • Manage stormwater runoff as close to its origin as possible. 8.7.4 Land Use LID is not merely the use of specific stormwater management facilities, but is an approach to land development that integrates with and responds to the natural conditions of a site. A low impact development should strive to minimize the impact of development on the pre-developed hydrologic condition. From a land use perspective, this is accomplished by minimizing the development envelope and minimizing impervious surfaces. 8.7.4.1 Minimize Development Envelope Minimizing the development envelope means confining lots and land uses to confine development and activity areas to the smallest impact area. While the City’s development standards are generally designed for conventional development that consumes most or all of a development site with buildings, infrastructure and activity areas, the Redmond Zoning Code provides several mechanisms to focus development on a site. Residential and commercial clustering can be accomplished through provisions of RZC 21.08 and RZC 21.14[SH6] 8.7.4.2 Retain Areas of Native Vegetation Minimizing the development envelope allows retention of a portion of the site in its natural or pre-developed state. In addition to offering an aesthetic amenity and opportunities for passive recreation, preservation of natural open spaces provides areas for dispersion of stormwater generated on the developed portion of the site. The extent to which dispersion to a natural area may be allowed depends on the size of the preserved area relative to the tributary area as well as underlying soil types. Where native forest is preserved or restored to disturbed areas, a portion of the rain that falls on the site will be intercepted and evaporated or absorbed. While preservation of significant natural areas is a challenge in urban areas, conservation ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 95 of existing habitat is a key element of LID. LID projects should preserve or re- establish a minimum of 35 percent of the overall site area in native vegetation. (This 35 percent does not include any critical areas that are already required to be set aside.) Areas retained as native open space are most effective for dispersion when located downslope of proposed development areas. 8.7.4.3 Preserve Native Soils In addition to retention of areas of native vegetation, preservation of native soils is an important aspect of low impact development. Native soils have a significantly higher capacity to absorb, retain and transmit water than soils remaining on a site following conventional development. Commonly, native soils are graded and removed from development sites. In the process, the underlying soils are significantly compressed, resulting in a reduction in the ability of the soils to absorb water from the surface. Prior to any clearing or grading, areas of the site more conducive to infiltration should be identified (see Site Assessment below), and site design should preserve such areas. Ground disturbance should be limited to road, utility, building pad, landscape areas, and the minimum additional area needed to maneuver equipment. A 10-foot perimeter around the building site can provide adequate work space for most activities. The number and extent of construction access roads should be limited and located where future roads and utility corridors will be placed. Where prior clearing or grading has occurred, soils should be restored according to the requirements in the City of Redmond Standard Specifications, Section 9-14.1, in all areas except where impervious surfaces are proposed. 8.7.4.4 Compost Amendment of Soils Compost amendment of soils shall be in accordance with Redmond Standard Specifications and Details, Section 9-14.1[SH7], for disturbed areas of development that will not be impervious surfaces post construction. Amending soils may be a more viable alternative to preservation of native soils for some sites, and can realize many of the same benefits. 8.7.4.5 Minimize Impervious Surfaces Minimizing the development envelope may also limit the extent of new roadways and other impervious surfaces. Limiting impervious surfaces is a primary emphasis of low impact development. Impervious surfaces can be minimized by limiting vehicular and pedestrian infrastructure roads, driveways, parking areas, and sidewalks), to the minimum functional needs of the facilities. The Rustic Street Standards in Appendix 2 of the RZC, while not applicable to all areas or all roadway use conditions, represent a good template for LID road design. LID techniques to minimize impervious surface area also include the use of various pervious paving materials, minimal excavation foundations, and green roofs. These alternatives to ---PAGE BREAK--- 96 conventional development techniques decrease the effective impact of new surfaces and buildings on the pre-developed conditions. 8.7.4.6 Rustic Street Standard The Rustic Street Standards in Appendix 2 of the RZC, while not applicable to all areas or all roadway use conditions, may represent an opportunity for LID road design. The Rustic Street Standard, as envisioned within the zoning code is not very compatible with dense residential development. Combining these two development techniques results in a heightened challenge as swales along roads are interrupted by closely space driveways, compounding the difficulty of placing fire hydrants, street trees, and other appurtenances. This standard is much more compatible with larger lots with fewer driveways. Techniques like sharing driveways can help offset this conflict. Design of a rustic street requires the designer to develop a large number of details to demonstrate how stormwater will flow through the system. Swales may not fit within the required right-of-way, which will either result in larger right-of-way dedication, or separate stormwater facilities to accommodate the inadequacy of the space available for the swales. One of the largest stormwater challenges for the Rustic Street Standard is how to use the space allocated for the “Landscaped Swale”. Some of the challenges that have been faced by developers so far include: • If the road is not flat, then the landscaped swale may require check dams to prevent erosion. • If the landscaped swale is designed to be too flat, then ponding water may result within the swale. • If driveways frequently interrupt the swale, then the area of the swale is likely not adequate to act as a bioretention facility, and additional facilities will be required to meet stormwater requirements. • Hydrants placed near the swale require an interruption of the swale to accommodate access from the street by fire personnel. • Street trees as required by the Rustic Street standard may require an interruption of the swale and be too close to an underdrain system in the swale. Root barriers may be needed based on placement of trees and proximity (horizontally and vertically) to the underdrain system. • If the swale is too long, it will become deep. This will either require a widening of the swale and associated right-of-way, or frequent short segments of the swale separated by breaks with overflows. • Deep swales become challenging for long term maintenance and may be ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 97 tripping hazards for pedestrians navigating from parking areas to sidewalks. • A pipe system may be required beneath the Landscaped Swale. This pipe may be a bioretention underdrain, or may simply be a parallel conveyance system that is connected to overflow/outlet structure from segments of the landscaped swale. Such overflows may be designed similar to the standard details for such facilities in bioretention. Cleanouts and maintenance access are required. • Maintenance requirements for the swale, the underdrain, etc. must be carefully documented within the O&M manual and in plat documents. Typically, City crews will be responsible for piping, while adjacent homeowners or home owner’s associations will be responsible for the aesthetics of the swales. 8.7.5 LID BMPs To achieve the intent of LID, stormwater should be managed on-site to the greatest extent possible. See Section 2.5.5 for minimum LID requirements. Descriptions of these BMPs, along with design criteria, maintenance standards, and modeling guidance, can be found in Appendix II-B of the Ecology Manual. Other BMPs may be considered for use by the Technical Committee, provided that the committee finds that there is reasonable scientific justification that such BMPs will provide equal or better flow control and water quality results, and that long- term performance is ensured. 8.7.5.1 Compost Amendment of Soils Compost amendment of soils shall be in accordance with Redmond Standard Specifications and Details, Section 9-14.1, for disturbed areas of development that will not be impervious surfaces post construction. Amending soils may be a more viable alternative to preservation of native soils for some sites, and can realize many of the same benefits. 8.7.5.2 Dispersion Areas set aside for dispersion shall comply with requirements in the Ecology Manual, and shall be documented as protected vegetation in the plat or other recorded document. 8.7.5.3 Bioretention Bioretention shall not be located within one-quarter mile of Lake Sammamish. ---PAGE BREAK--- 98 Bioretention with underdrains shall not be allowed if those underdrains discharge to pipes or streams that ultimately drain to Lake Sammamish, due to phosphorous control requirements. Redmond Standard Specifications include approved bioretention mix designs for use within the City. 8.7.5.4 Permeable Pavement & Functional Equivalency Refer to Section 8.3 for limitations or constraints for infiltration from pollution generating hard surfaces in Critical Aquifer Recharge Areas. The primary function of pervious pavement is for it to serve as sidewalk, road, or similar purpose. The secondary function of pervious pavement is to mimic predeveloped hydrology by infiltrating storms over a large area. Pervious pavement represents a larger maintenance burden for owners of the pavement than traditional pavements. It is possible for an alternative BMP to meet the secondary, hydrologic function while also meeting the primary function, without the added maintenance burden. Redmond Standard Details include details for functional equivalents to pervious sidewalks, such as the use of reverse slope sidewalks that drain into landscaped areas or the use of infiltration trenches adjacent to sidewalks. Projects designed to meet the LID Performance Standard shall use modeling to demonstrate how functional equivalency is met. If a project using the Minimum Requirement 5 Lists identifies pervious pavement as a requirement, the project applicant shall model the site assuming pervious pavement, as an alternative. The project applicant shall then design functional equivalent systems and use modeling to document that the proposed alternative meets or exceeds the LID performance standard just for the permeable pavement functionally equivalent BMP. 8.7.5.5 Vegetated Roofs Vegetated roofs may be allowed for commercial development with Stormwater Engineer approval. If vegetated roofs are included in a project design, special inspection will be required during construction by a professional civil engineer who certifies that the green roof was installed properly. This inspection will be the responsibility of the project proponent and this requirement shall appear on the permit drawings. Vegetated roof maintenance shall be included in the project Operation and Maintenance Manual. Easements to allow inspection shall be provided to the City of Redmond. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 99 Vegetated roofs that drain to Lake Sammamish require Phosphorous control. Vegetated roofs shall not be designed to infiltrate into the ground in CARA I. 8.7.5.6 Rainwater Harvesting and Greywater Reuse Rainwater Harvesting for use on-site is permitted, for sub-surface irrigation purposes. Rainwater harvesting for other purposes requires approval from the City of Redmond Water Utility and the City of Redmond Wastewater Utility as described in the City of Redmond Design Requirements for Water and Wastewater Extensions. Such approval is obtained by submitting a proposal to the Public Works Director. Additional regulatory approvals may also be required. 8.7.5.6.1 Permit Requirements a. Rain barrels (up to 60-gallon capacity) for irrigation purposes are allowed without a permit. b. Construction of rainwater harvesting systems larger than a rain barrel requires a clearing and grading permit. Plans and specifications for the rainfall/non-potable cistern water capture, distribution, use and operational practices shall be submitted for review and approval prior to implementation. Depending on the specific proposal, additional permits may be required. c. Greywater reuse systems require approval from the Public Works Director and the King County Department of Health. See the Water / Wastewater Design Requirements for additional information and requirements. 8.7.5.6.2 Water Storage and Source Stormwater runoff from nonpollution generating surfaces like roofs, sidewalks, plazas, and maintenance driveways is permitted for use with rainwater harvesting systems. Stormwater runoff from low-use parking lots may be permitted with Stormwater Engineer approval. Rain barrels collecting roof runoff are permitted. Cisterns may be constructed as dedicated rainwater harvesting storage units. Cisterns used for rainwater harvesting for irrigation shall not be used for other purposes. Cisterns used for irrigation shall include an air-gapped make-up water supply from the potable water supply, delivered through a City irrigation meter. Stormwater ponds or vaults may be used, subject to approval from the Stormwater Engineer. Such use may not impede the primary stormwater function of the facility. 8.7.5.6.3 Separation of Lines In order to minimize construction accidents resulting in pipeline breaks, which may pollute the domestic water supply or accidental cross-connections between ---PAGE BREAK--- 100 rainfall/non- potable cistern water and potable water systems, maximum attainable separation of non- potable cistern water lines and potable water lines is required. • Parallel Construction: There shall be at least a ten-foot (10’) separation for all pressure mains, all distances measured from pipeline outside diameter. In restricted areas where 10-foot separations cannot be met, the use of sleeved pipe is required. • Cross-Over Construction: Perpendicular pipeline installation is set at a one- foot separation, with potable above rainfall/non-potable cistern water, and one full pipe length centered over crossing. • Alternative Cross-Over construction (distance not maintained): Either the rainfall/ non-potable cistern water may be sleeved with the same class piping (usually schedule 40 PVC) for one full pipe length (minimum four feet) centered over the cross-over. • Existing On-site piping – To the extent feasible, maximum separation of rainfall/non-potable cistern water and potable water lines shall be practiced upon system addition or modification. 8.7.5.6.4 Identification of Lines All rainfall/non-potable cistern water main lines, valve boxes and appurtenances shall be identified to clearly distinguish between non-potable cistern water and potable water systems. Specific wording on identification tape shall be required. Evaluation shall be on a case-by-case basis, but with the understanding that the minimum requirement for pipeline identification is per the Uniform Plumbing Code. The following identification tape will be accompanied with respective tags of the same colors and wording for all valve boxes, vaults, control valves, quick couplers, outlets and related appurtenances, if applicable. POTABLE WATER – All potable water lines shall be installed in accordance with the Uniform Plumbing Code and all other governing codes, rules and regulations. Buried potable water lines shall be identified by continuous tape with lettering on three inch minimum width green or blue tape with one-inch black lettering bearing the continuous wording “Potable Water”. Identification tape shall be permanently affixed to the pipeline at five-foot intervals atop all horizontal piping, laterals and mains. Identification tape shall extend to all valve boxes and/or vaults, exposed piping and hydrants. Identification tape is not necessary for extruded colored PVC with continuous wording “Potable Water” printed in contrasting lettering on opposite sides of the pipe. RAINFALL/NON-POTABLE CISTERN WATER – All rainfall/non-potable cistern water lines (pressure/non-pressure) shall be identified by continuous lettering on three inch minimum width YELLOW tape with one-inch black lettering bearing ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 101 the continuous wording “Caution – Non-potable Cistern Water, Subsurface Irrigation Only” permanently affixed at five-foot intervals atop all horizontal piping, laterals and mains. Identification tape shall extend to all valve boxes and/or vaults and exposed piping. NON-POTABLE WATER – All non-potable irrigation water lines (pressure/non- pressure) shall be identified by continuous lettering on three inch minimum width yellow tape with one-inch black lettering bearing the continuous wording “Non-Potable Water” permanently affixed at five-foot intervals atop all piping. Identification tape shall extend to all valve boxes and/or vaults, exposed piping, hydrants and quick couplers. Tags, respective of each water supply, shall be identified with the appropriate wording on both sides with the inclusion of a universal symbol. 8.7.5.6.5 Operational Guidelines and Specifications Irrigation systems utilizing untreated rain-fall/non-potable cistern water shall only be by means of subsurface irrigation. Misting or spraying into the air is prohibited. Irrigation practices shall be controlled to prevent surface runoff. Any pipeline other than potable water that is installed within a structure shall conform to all building code standards and shall be “barber shop” wrapped with the respective continuous identification tape and without any interconnections with the potable water system. Rainfall/runoff non-potable cistern systems shall not be interconnected with water from other sources. Each shall be installed as stand-alone systems completely separate from one another. Rainfall/non-potable cisterns shall not be directly connected to a sewer system. Cisterns/storage vessels shall be adequately covered to prevent mosquito breeding. Contact with untreated rainfall/non-potable cistern should be kept to a minimum. Subsurface irrigation of untreated rain-fall/non-potable cistern water shall meet all the requirements and restrictions for infiltration within Critical Aquifer Recharge Areas I and II. (Infiltration from greywater systems is not permitted in Critical Aquifer Recharge Areas I and II.) To prevent secondary exposure to rainfall/non-potable cistern water, hose bibbs and quick couplers shall not be permitted in order to prevent both the unauthorized use of said water supply and secondary exposure of untreated non-potable water supply. Quick-couplers are presently not allowed on non-potable cistern systems. ---PAGE BREAK--- 102 A pressure test/cross-connection test shall be performed to confirm the physical separation of the stormwater/cistern water and potable water systems before any cistern is placed in service. 8.7.6 LID in Critical Aquifer Recharge Areas Refer to Section 8.3 for limitations or constraints for infiltration from pollution generating impervious surfaces in Critical Aquifer Recharge Areas (Appendix C).8.7.6 Maintenance All BMPs, impervious surface area restrictions, preserved native areas and any project specific LID conditions of approval shall be recorded on a subdivision plat, development covenants, deed restrictions, easements, or other legally binding mechanism approved by the City. Easements shall be provided to the City to allow inspection, maintenance and repair, as necessary, to ensure that approved LID BMPs are preserved and maintained. Maintenance for LID BMPs permitted on private property is the responsibility of the property owners, their heirs and assigns. Subdivision plats shall document who is responsible for maintenance. Native forest or other natural areas preserved or established as part of a permitted dispersion BMP shall be placed in tracts protected. When permitted as part of a development approval, bioretention facilities and pervious pavement on private lots shall be located such that they are available for inspection by the City’s private stormwater inspection program. If they are not adjacent to right-of-way, then they shall be placed within easements providing the City access for future inspection. Title to properties with LID BMPs shall include clear language stating the property owner is responsible for maintenance. Low Impact Development Best Management Practices built for capital projects shall typically be maintained by the City. Bioretention built in the public right-of-way in subdivision projects shall include maintenance provisions that share maintenance responsibility. The City will be responsible for maintaining bioretention facility function, keeping inlets clear, underdrains inspected and clear. The aesthetics of the facilities will be the responsibility of the adjacent land owner or home owner’s association. LID best management practices selected for use on development projects must be maintainable in an urban setting. The designer will provide adequate space for maintenance vehicles, including turn-around capabilities to facilitate the continued operation of each LID facility. Plat documents shall include clear descriptions of all LID facilities and the party responsible for on- going maintenance. The plat will include limitations on property owners from altering approved LID facilities on their properties. The alteration of constructed LID facilities will require written approval from the City, in the form of an approved Clear & Grade Permit. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 103 The Stormwater Engineer may require substitution of alternative LID BMPs for private development projects where long-term maintenance or protection of the BMPs is not supported in an urban setting. An example is proposing a bioretention channel passing through multiple single-family lots; a practice that is not supported. 8.7.7 Evaluation and Monitoring The Stormwater Engineer may require implementation of a monitoring and evaluation program designed to measure the performance of the drainage system or specific elements that are approved for a project under the provisions of this chapter. 8.7.8 Bioretention Limitations Bioretention shall not be located within one-quarter mile of Lake Sammamish. Bioretention with underdrains shall not be allowed if those underdrains discharge to pipes or streams that ultimately drain to Lake Sammamish, due to phosphorous control requirements. Redmond Standard Specifications include approved bioretention mix designs for use within the City. 8.8 Regional Facilities Program As a part of the City’s coordinated, regional approach to managing stormwater City- wide, some projects will have the requirement or option of contributing a fee, in lieu of building site-specific facilities for flow control or runoff treatment. The fee shall be used toward construction of regional stormwater facilities. The City has responsibility for ensuring that: • Potential impacts from all new development or redevelopment within the City are addressed in a manner that meets the City’s obligations on a watershed basis to protect water quality and prevent erosion of streams. • Funds received for construction of regional facilities are used for that purpose. To meet these responsibilities, the City’s program, administered by the Environmental and Utility Services Division of the Public Works Department, includes procedures for: • coordinating with the Development Services Division’s review of development and redevelopment projects; • determining what projects are eligible for “fee in lieu”; • accounting for areas that have been treated by existing regional facilities; • accounting for funds that have been received for construction of new regional facilities; and, ---PAGE BREAK--- 104 • locating, designing, and constructing regional facilities. With the exception of downtown, for new development projects (Section 2.4.2), regional facilities must be operational to be eligible for “fee-in-lieu”. Redevelopment projects (Section 2.4.1) are eligible if associated regional facilities are operational or are on the City’s Six-year Stormwater Capital Improvement Plan. To be eligible for “fee-in-lieu”, project areas must drain to the applicable regional facility. For public road projects, the project area must drain to the same receiving water as the existing or proposed regional facility. A project’s participation in the Regional Facilities Program is dependent upon where the site is located. Appendix O shows a map of the City’s proposed regional facilities and also the City’s Regional Facilities Surcharge Areas. Applicants should review the maps to determine if sites fall within regional surcharge areas, and then use the appropriate flow charts below to determine site requirements related to this program. 8.8.1 Downtown Projects located within the Downtown surcharge area are subject to the Downtown sub-basin stormwater capital facilities charge, per RMC 13.20.045. As described within the RMC, sites located next to the Sammamish River may be eligible to opt out of the regional facilities program with approval of the Technical Committee. There are two small streams within the Downtown surcharge area. Projects that drain to these streams may be required to implement onsite flow control or runoff treatment facilities to protect those streams. Most development in these areas will not trigger runoff treatment or flow control requirements. Contact the Stormwater Engineer in the Environmental & Utility Services Division to discuss alternatives, if a proposed project triggers thresholds. Projects may be required to construct some offsite stormwater improvements such as extending the municipal stormwater system the length of the project site or upsizing existing pipes within the municipal system to prevent flooding. Sites are also required to construct improvements onsite to meet Minimum Requirement and meet infiltration requirements described in Section 2.5.5. The City’s Downtown Facilities Map, shown in Appendix P, identifies pipes that have been confirmed by City modeling to provide direct discharge. Project proponents are responsible for completing a analysis to confirm their project can connect to those stormwater trunks. It may be necessary to improve elements of the conveyance system between the project site and the stormwater trunk. analysis using the City’s model may be required of the applicant. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 105 8.8.2 Overlake Projects located within the Overlake surcharge area are subject to the Overlake sub- basin stormwater capital facilities charge, per RMC 13.20.047. Sites located south of the location of the proposed NE 26th Street are required to construct onsite treatment for all pollution generating surfaces. The requirement for interim stormwater facilities described in RMC 13.20.047 is not required due to the completed construction of the first two regional facilities. Sites are also required to construct improvements onsite to meet Minimum Requirement and meet infiltration requirements described in Section 2.5.5. The City’s Overlake Facilities Plan, shown in Appendix Q, identifies pipes that have been confirmed by City modeling to provide direct discharge. Project proponents are responsible for completing a analysis to confirm their project can connect to those stormwater trunks. It may be necessary to improve elements of the conveyance system between the project site and the stormwater trunk. analysis using the City’s model may be required of the applicant. ---PAGE BREAK--- 106 Figure 8.1 – Regional Facilities Program Figure 4 8.1 Regional Facilities Figure 8.2 – Downtown Surcharge Area Figure 5 8.2 Downtown Surcharge Area Where is the Project Located? Downtown Surcharge Area: See Downtown Flowchart Overlake Surcharge Area: See Overlake Flowchart Outside Regional Surcharge Areas: Contact the City Is the Project Adjacent to the Sammamish River? Yes: Project may be eligible to opt-out, See RMC 13.20.045.D. Do you want to opt out? Yes: Submit a proposal to the Technical Committee No: Pay the Downtown CFC*** No: Pay the Downtown CFC*** Evaluate conveyance between the Project Site and the Stormwater Trunk identified in Appendix P. Offsite improvements to prevent flooding may be required. If project drains to one of the small streams in the surcharge area and triggers thresholds for MR 6 and 7, contact the Stormwater Engineer to discuss alternatives. Onsite treatment for oil control is required if thresholds are triggered. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 107 Figure 8.3 – Overlake Surcharge Area Figure 6 8.3 Overlake Surcharge Area 8.8.4 Outside Regional Surcharge Areas Projects that are not located within the Downtown or Overlake surcharge areas may have the option of negotiating with the City to participate in construction of a regional facility (or use of an existing regional facility) to meet their stormwater requirements. This is effectively a public/private partnership to facilitate private development and public retrofitting of stormwater management. A proposal describing the project will be reviewed by the City to determine if the project may be eligible. This proposal must include: • Full stormwater report • analysis • Discussion of cumulative impacts • Proposed fee • Summary of offsite improvements • Identified location for regional facility • Summary of benefits to the City Is the Project North of NE 26th Street? Yes: Onsite treatment for basic or enhanced treatment is not required. Pay the Overlake Fee No: Onsite runoff treatment is required. Pay the Overlake Fee. Evaluate conveyance between the Project Site and the Stormwater Trunk identified in Appendix Q. Offsite improvements to prevent flooding may be required. Onsite treatment for oil control is required if thresholds are triggered. ---PAGE BREAK--- 108 Due to the large amount of City resources required to accommodate such a request, most sites that lie outside the designated regional surcharge areas are not eligible to participate in this program. Contact the Environmental and Utility Services Division for further information. 8.9 Other Development Topics 8.9.1 Internal Building Changes as Redevelopment Redevelopment projects that are confined to existing interior spaces do not require new drainage controls (except those drainage systems described above as may be required by the City for proper drainage). If redevelopment projects include any work involving the exterior part of the site, the project shall be subject to redevelopment requirements under this Stormwater Technical Notebook. Where exterior work occurs, the value of the interior work shall be included in determining the extent of exterior redevelopment requirements. 8.9.2 Site Improvements Involving Hazardous Materials Site improvements to existing facilities that would otherwise not be subject to stormwater system improvement but involve hazardous materials shall meet the water quality requirements of this Stormwater Technical Notebook, Redmond Municipal Code (RMC) 15.24, RMC 15.06 and RZC 21.64.050. There are also specific source control BMPs in Volume IV of the 2014 8.9.3 Garbage and Recycling Area Stormwater Drainage Stormwater from uncovered garbage and recycling areas (trash enclosures), shall not enter the City’s stormwater system or infiltrate into the ground. These areas shall be covered, with floor drains discharging to the sanitary sewer. 8.9.4 Water Features Water features such as pools, spas, hot tubs, recirculating fountains, recreational splash areas and similar features shall be designed to manage discharge of wastewater. These facilities shall follow Source Control BMP S433. Some key challenges faced by these features include: • If the facility receives rainfall, it shall not be designed to drain to sanitary sewer. • Discharge to groundwater, surface water, or to the stormwater system requires water quality treatment and flow control prior to discharge. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 109 • Maintenance wastewater, such as chlorinated water, backwash residues, algaecides, and acid washes shall be discharged to sanitary sewer with a permit from the local agency receiving the wastewater. • An operation and maintenance manual for the water feature shall document where overflows drain, what maintenance will be provided and how wastewater will be managed. • Discharge to the ground within Critical Aquifer Recharge Area 1 is prohibited. • Discharge of greater than 250 GPM of treated water to the municipal stormwater system requires notice to the City’s Stormwater Utility prior to discharge. 8.9.5 Stormwater Fee Calculations Stormwater Capital Facilities Charges (CFC) (RMC 13.20) are due at the time of permit issuance for permits that allow creation of 200 SF or more of new or replaced impervious surfaces (civil approval, building permit, short plat approval, plat approval, etc.). Stormwater CFCs may be paid early if the applicant prefers. Stormwater CFCs only need to be paid once, however most parcels have not redeveloped since the fees were created so have not paid the Stormwater CFC. For parcels that have paid Stormwater CFCs before, analysis is required to determine what impervious areas were paid for previously, and if additional fees will be owed for the current project based upon that information. It is up to the project proponent to provide evidence of prior payment of impervious units. 8.9.5.1 Citywide Stormwater CFC Citywide Stormwater CFCs apply to the portions of public and private projects that are located on parcels. 8.9.5.2 Regional Stormwater CFC Overlake and Downtown subbasin CFCs are in addition to Citywide Stormwater CFCs and apply to the portions of public and private projects in both parcels and rights-of-way that are located within the respective areas that are shown in Appendix O. ---PAGE BREAK--- 110 8.9.5.3 CFC Fee Calculations Document the following fee calculation in the stormwater report (Appendix The Stormwater Engineer can provide a spreadsheet to help with this calculation. Table 8.2: CFC Fee Calculations Citywide CFC Downtown / Overlake CFC Step 1: Determine the amount of new or replaced impervious area, in square feet. Use impervious within the parcel area after right-of-way dedication. Step 1: Determine the amount of new or replaced impervious area, in square feet. Use total impervious area built by the project. Step 2: Divide the impervious area by 2000 square feet, to get “impervious units Step 3: Truncate IU to the nearest tenth. (Truncated 85.59 = 85.5) Step 4: Citywide CFCs don’t get infiltration credits. Step 4: Determine if any IU are designed to be fully infiltrated in a private facility (document in Stormwater Report). If a designed infiltration facility is not able to infiltrate 100% of the runoff, use modeling to determine what equivalent area the designed facility could fully infiltrate, and that prorated area will be considered the “fully infiltrated area”. Credited IU = IU - (0.8 * fully infiltrated IU) Step 5: Determine if any impervious units previously paid each relevant CFC. Step 6: Determine if any IUs were previously paid. Net IU = IU – Previously Paid IU (may not be less than zero.) Step 7: Final Calculations: Citywide fee = (Net IU) * (Citywide CFC) Step 7: Final Calculations: Downtown/Overlake fee = (Net IU) * (Downtown/Overlake CFC) Table 8.2 CFC Fee Calculations Stormwater CFCs are subject to periodic update, and fees shall be calculated based upon the current fee rate at the time of payment (RMC 13.20). 8.9.6 Modifications to Stormwater Facilities Development projects may request to modify existing stormwater facilities. The Stormwater Engineer will evaluate such requests. Such requests should be made in writing and should address the following design constraints: • Permission from the owner for the proposed modification. • Conveyance capacity of pipes and ditches shall be equal or better than the existing capacity, as demonstrated by modeling the system using or an equivalent model, with no increase to hydraulic grade line permitted ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 111 when comparing the existing condition to the proposed condition. (The increase in HGL attributable to an increase in pipe length may be offset by increasing pipe size, reducing friction through improved pipe materials, adding parallel systems, or other methods.) • Flow Control facilities that are modified shall meet current standards for flow control as demonstrated using WWHM, and shall meet current standards for maintenance access and aesthetics. The proposal may use methodology from Ecology’s 2019 Surface Water Management Manual for Western Washington, Appendix I-D.5, “Sizing Regional Facilities” to support a proposed modification. • Stormwater runoff treatment facilities shall meet current standards for runoff treatment for the areas that drain to the facilities, in terms of treatment capacity and pollutant targets. • Maintenance access shall conform to current standards, including vehicle access, personnel access, and easement requirements. ---PAGE BREAK--- 112 Chapter 9 – Construction Stormwater Pollution Prevention The 2014 provides detailed guidance regarding the plans for stormwater runoff management during construction. That guidance is to be followed in the City of Redmond. Field adjustments, likely to be required as the project construction progresses, must also be consistent with the Stormwater Technical Notebook and the 2014 9.1 Key Points to Address The following are key points to address when formulating a Stormwater Pollution Prevention Plan and Temporary Erosion and Sedimentation Control (TESC) Plan in Redmond: 1. Consider Stormwater Pollution Prevention in the “Bigger Picture” of the project. A. Review Volume II of the 2014 particularly the general principles in Section II-3.1.3. B. Plan the use of the site or adjust critical parts of the site plan (in Critical Areas, for example) to avoid potential issues and problems. As noted in the Rainy-Season Guidelines (Chapter 10 of this document). C. Avoid Rainy-Season work, especially on large and/or weather- sensitive sites. The Rainy-Season Guidelines (Chapter 10 of this document) may show that work can be done in the rainy season but enhanced (and costlier) TESC Plans are typically required. 2. Include a list of Key Contacts on the TESC Plan. Key Contacts related to preparation, implementation, and operation of the TESC measures shall be included on a plan sheet. For each person include the name, title, role in preparing the plan, and phone number(s). The number and skill set of people involved in preparing the plan will typically vary depending on the complexity of the project. For relatively small, straightforward projects, the Key Contact may be just the project CESCL. For complex sites and projects, the list could include: • Project civil engineer • Project CESCL • Project Manager • General Contractor • Grading Contractor ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 113 3. Include the construction Start-up Sequence on the TESC Plan. A. The construction start-up sequence is a list of actions to be followed, in the order presented, to set up the stormwater pollution prevention measures prior to other construction. B. Initial work in the field needs to follow the sequence on the approved plan, with adjustments to fit field conditions that are approved, in advance, by the City Inspector. 4. Delineate Clearing Limits. A. Clearing limits show the area(s) of the site to be left undisturbed. Staging and stockpile areas are considered to be disturbed so they need to be included as cleared area(s). In all cases, disturbed areas shall be the minimum necessary for construction. B. On the TESC Plan, show the Clearing Limits. If there are key dimensions to use in the field for locating the clearing limits, show the dimensions on the plan. Such dimensions involve buffers, setbacks, geotechnical considerations, and other such factors. 5. Include “Disconnection” of Surface Inflows. A. Runoff from areas upslope of the project’s disturbed area(s) must be managed so the upslope runoff does not mix with the disturbed area. B. The basic approach is to: cut off the approaching runoff using lined trenches or barriers (that are erosion-proof); collect that runoff at one or more points (depending on topography and other site circumstances); and convey the water around (or across) the work area (in erosion-proof ditches and/or temporary pipes). 6. Apply all available measures to surface runoff leaving the disturbed area to meet water quality standards. Water quality standards include the State Standards and the City Standards. City Standards include the following: A. At the outflow point(s) from the treatment system(s), the turbidity standard is 25 NTU, maximum. NTU = Nephelometric Turbidity Unit. B. At points of discharge to surface waters, the standard is as follows: runoff from the site is not to cause the turbidity level in the receiving water(s) to increase more than 5 NTU.[AM8] C. At the outflow point(s) from the site, the standard for pH is 6.5, minimum, and 8.5, maximum. D. All available measures can include, but are not necessarily limited to, project phasing, advanced erosion and sediment control measures, ---PAGE BREAK--- 114 and delaying all or part of any project work that has not commenced to avoid working during the rainy season. E. Unless a larger design storm is specified for a specific project or pollution control method, the minimum design storm for construction phase measures is the 10-year return frequency storm. 7. Surface runoff leaving the disturbed area shall be controlled using all available measures to meet water quantity limits where sensitive conveyance situations exist. For discharge(s) to streams or channels subject to erosion, the standards for construction phase discharge are the same as those specified for permanent stormwater management for the project. 8. The TESC Plan must include provisions for other pollutants that are likely to be present on site during construction. The must: • list other potential pollutants that are likely to be present on site and provide basic instructions for their management and control; • list materials and equipment to be onsite to implement the instructions; and • list key emergency phone numbers for resource agencies involved in pollution incidents. The 2014 provides additional information about potential problem areas (Volume II, Chapter 9. Include provisions to prevent mud and dirt from being tracked onto off-site streets in the TESC Plan. The minimum basic provision for controlling mud and dirt is the temporary quarry spall entry/exit pad. This approach is successful only in limited circumstances. A more reliable approach (which may be proposed or required by the City) is a wheel-wash station. At a minimum (unless specifically waived by the City) the TESC Plan must show the standard wheel-wash facility (including site location and related “plumbing”) as an optional measure. The City may stipulate that this measure is required. The City Inspector may require immediate implementation of an optional wheel wash if off-site streets become muddy or dirty from the project. Also see 2014 Volume II, Chapter 4, BMPs C105, C106, and C107. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 115 10. Include provisions to prevent sediment-laden stormwater from draining into areas proposed for infiltration BMPs like infiltration basins or areas designed for on-site stormwater management. 11. Include a Minimum Inspection and Maintenance Schedule for all management practices included on the plan. The Minimum Inspection and Maintenance Schedule is to be a table or matrix listing the management practices on the left and the inspection and maintenance frequencies across the top. Two types of frequencies need to be specified. One type is the minimum time-related frequency once per day, once per week, beginning and end of each work day, etc.). The other type is the event-related frequency after each rainfall, after each larger storm rainfall, after each windstorm, etc.). 12. Comply with other federal, State, and City laws and regulations that relate to the construction phase. Of primary importance under this title is safety. Safety of the project workers and other personnel, City staff, the neighbors, and other people who could be affected by the work is of paramount concern. The should be reviewed by the plan’s designers with safety in mind. Extra features fencing, signs, walkways, etc.) should be considered. Other laws and regulations that typically apply include: A. Noise standards (City) B. Construction work hours (City) C. Dust control (City and the Clean Air Agency) D. Rainy-Season Guidelines (City) E. A Pre-Construction Meeting with the City prior to starting work (City) 13. Post required Performance Securities prior to starting work. The performance securities that are required for a specific project are specified either in the approval conditions for the project or in the requirements for permits that are required for the project. 9.2 Contents of Construction Stormwater Pollution Prevention Plan The 2014 requires a Construction Stormwater Pollution Prevention Plan for Medium and Large Projects. A copy of the is to be submitted to the City of Redmond. The shall follow the outline and include the elements ---PAGE BREAK--- 116 provided in the step by step procedure in Volume II, Chapter 3, of the 2014 9.3 National Pollutant Discharge Elimination Systems Permit A permit is required from the Washington State Department of Ecology for all soil disturbing activities (including clearing, grading, and/or excavation) where one or more acres will be disturbed, and stormwater will be discharged to a receiving water directly wetlands, creeks, unnamed creeks, rivers, marine waters, ditches, estuaries), or to storm drains that discharge to a receiving water. If all stormwater is retained on-site and cannot enter surface waters of the state under any condition, you do not need permit coverage. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 117 Chapter 10 – Rainy Season Clearing / Grading 10.1 Introduction These standards are adopted per Redmond Municipal Code 15.24. These general standards identify which development projects in the City of Redmond can undertake site construction work in the rainy season, what level of Temporary Erosion and Sediment Control (TESC) is necessary and what runoff monitoring is required. Since these are general standards, specific projects and sites may warrant exceptions to these standards. Planning for rainy-season work needs to begin early in a project. The “Permit Processing Implications” section presents important information for those who may be pursuing construction work in the rainy season. It is important to plan ahead if rainy-season work is to occur given that: • The approved for good weather will probably not be adequate for the rainy season. • A Seasonal Suspension Plan will be required for rainy-season work. • Higher levels of TESC require City meetings as these plans are formulated (advance scheduling with City staff is important). • High TESC levels can involve chemical treatment, so the possible use of such measures must be part of SEPA documents. If such measures become necessary for a project and were not included in SEPA reviews, then SEPA processes would need to be amended prior to approval of the special TESC measures. • State Department of Ecology approval is required for some state-of-the- art TESC. Clearing/grading work shall comply with provisions in the Stormwater Technical Notebook and other applicable regulations and standards. Project work shall also comply with City regulations and with requirements developed through SEPA (State Environmental Policy Act) processes, through the City’s site plan review processes, and through other project reviews. These project-specific requirements are in addition to and take priority over the general standards in this document where differences occur. ---PAGE BREAK--- 118 The rest of this chapter contains seven sections: 1. TESC Standards. This section presents the standards that define what constitutes successful Temporary Erosion and Sediment Control for a project. 2. Special Requirements for Rainy-Season Work. This section describes two special requirements that apply to rainy-season project work: the Seasonal Suspension Plan and additional performance security. 3. Rough Grade Permits. This section briefly identifies a permit that allows clearing and grading to get started under certain circumstances, so that such work does not occur in the rainy season. 4. Explanation of the Rainy-Season Clearing/Grading Matrix. This section discusses the elements of the “Matrix” (Table 10.2). 5. How to Use the Rainy-Season Clearing/Grading Matrix. This section describes the steps to follow to use the Matrix. 6. Project Planning Implications. This section outlines the project review and approval implications related to rainy-season work. This section contains information to request an exception to the general standards presented in the Matrix. 7. Appeals: Wet Weather Committee. This section describes the group of City staff that have reviewed these general standards and that considers the Correction Requests and Appeals. This group is called the Wet Weather Committee. There are four tables in this chapter: 1. Table 10.1-Hydrologic Groups for Area Soils 2. Table 10.2-Rainy-Season Clearing/Grading Matrix (consists of five pages) 3. Table 10.3-TESC Requirements 4. Table 10.4-Monitoring Requirements 10.2 TESC Standards Successful TESC will meet all the following standards: 1. Site areas which do not need to be disturbed are not disturbed (clearing limits are defined and maintained). 2. Flows of runoff from areas not under construction are kept off of disturbed soils in the construction areas. 3. Disturbed soil in an area that is not being worked receives temporary cover. 4. The turbidity in runoff from the construction area does not exceed 25 NTU. 5. Run-off from the construction area that reaches receiving waters does not cause the turbidity in the receiving waters to increase more than 5 NTU as a result of the project runoff. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 119 6. Disturbed areas receive final, permanent cover in accordance with the approved project plans without unnecessary delay. 7. Off-site streets are kept free of dirt and mud originating from the construction site. (Using sweeping, not flushing, in the streets and, if appropriate, on-site wheel wash facilities.) 8. Dust is controlled and is in compliance with the Puget Sound Clean Air Agency. 9. Contingency plans for controlling spills and other potential pollutants have been developed and are ready to implement at the construction site. 10. Work in Critical Areas conforms to requirements of the City’s Critical Areas Ordinance (CAO). See Redmond Zoning Code 21.64 for additional information and definitions regarding Critical Areas. 11. 24-hour, 7-day-per-week point(s) of contact is/are designated who can call out and direct crews, obtain materials, and authorize immediate expenditures for on-site temporary erosion and sediment control (TESC) work. 12. Compliance exists with all project approval conditions and permits (including applicable non-City permits such as, but not necessarily limited to, the Hydraulics Project Approval from Washington State Department of Fish and Game and the Washington Department of Ecology NPDES Permit). 10.3 Special Requirements for Rainy-Season Work There are two special requirements that apply specifically to rainy-season clearing and grading: 1. Project must have a City-approved Seasonal Suspension Plan for suspending work until the end of the rainy season if on-site TESC is found to be inadequate. A Seasonal Suspension Plan is a separate outline on the TESC PLAN that describes how the site is closed for the duration of the rainy season if directed by the City. Sites may be closed if they cannot meet the criteria for successful TESC outlined in Section 2. The Seasonal Suspension Plan must have sufficient detail to clearly define the work to be performed under this plan if it is implemented. The Seasonal Suspension Plan can include measures in the TESC Plan and /or additional BMPs. No site work is allowed under the Seasonal Suspension Plan in the rainy season except for work that is necessary to implement the measures in the TESC Plan and the Seasonal Suspension Plan. ---PAGE BREAK--- 120 2. Performance security must be provided in a manner acceptable to the City. Performance security will need to provide for monitoring (Level M2 minimum; discussed later in these General Standards), operation of TESC measures, implementation of the Seasonal Suspension Plan, and site restoration. 10.4 Rough Grading Permits a. Note that a separate permit for clearing and grading may be issued in certain circumstances when such action could allow substantial clearing and grading work to be completed before the rainy season begins. This permit is called a “Rough Grade Permit.” See Chapter 3 of the Stormwater Technical Notebook for requirements. 10.5 Explanation of the Rain-Season Clearing/Grading Matrix Four factors are considered to classify sites and set standards for clearing and grading work during the rainy season: 1. Location of work areas as related to surface waters (streams and lakes) or wetlands and the buffers of these Critical Areas. 2. The slope of the land surface in the work areas. In some instances the direction of the slope relative to nearby surface waters or wetlands is also a factor. 3. The actual soils in the work area expressed as Soil Conservation Service (SCS) Soil Hydrologic Groups designations B, C, or D) (Table 10.1). 4. Amount of land that is disturbed, considering both the cleared area and volume of earth to be moved. 10.5.1 Location(s) of Work Area(s) For purposes of these General Standards, the entire City of Redmond is classified into five types of work areas. Class 1 Work Areas: areas within the banks of a stream, in a lake, in a regulated wetland or on steep slopes (equal to or over 40 percent). Class 2 Work Areas: areas that are the buffers of streams, lakes, regulated wetlands, or steep slopes. Class 3 Work Areas: areas within the current conditions 100-year frequency floodplains of major streams or lakes but outside the buffers of the stream or lake (the Sammamish River, Bear Creek, Evans Creek, and Lake Sammamish). ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 121 Class 4 Work Areas: areas that have “potential hydraulic influence” on a stream, lake, or regulated wetland (See glossary section regarding this term). Class 5 Work Areas: consist of all other areas not included in any of the previous four areas. Work areas are further defined and sub-divided in Table 10.2. 10.5.2 Slope of the Land Surface This factor refers to the general slope of the land in and immediately adjacent to a work area. The slope used in these General Standards generally refers to the steepest gradient before work or during work, prior to final cover. Slopes are considered in categories as shown in Table 10.2. The percent of slope is the vertical rise divided by the horizontal run between two points on the ground surface (measured in the steepest direction) multiplied by 100. 10.5.3 Soil(s) This document is based on soil hydrologic groups as defined by the United States Soil Conservation Service (SCS): Group A (Low runoff potential). Soils having high infiltration rates even when thoroughly wetted. These consist chiefly of deep, well-to- excessively drained sands or gravels. These soils have a high rate of water transmission in that water readily passes through them. Group B Soils having moderate infiltration rates when thoroughly wetted. These consist chiefly of moderately deep-to-deep, moderately well-to-well drained soils with moderately fine to moderately coarse textures. These soils have a moderate rate of water transmission. Group C Soils having slow infiltration rates when thoroughly wetted. These consist chiefly of soils with a layer that impedes downward movement of water or soils with moderately fine- to-fine texture. These soils have a slow rate of water transmission. Group D (High runoff potential) Soils having very slow infiltration rates when thoroughly wetted. These consist chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a claypan or clay layer at or near the surface, and shallow soils over nearly impervious material. These soils have a very slow rate of water transmission. ---PAGE BREAK--- 122 Group A soils have high infiltration capacity in their natural locations because they are associated with permeable underlying geology. In these guidelines, a work area is considered to have Group A soils only if the underlying geology is highly permeable (to a depth of at least 6 feet below the elevation of the lowest project excavation) and only Group A material is used in any filling. A site’s soil types must be determined by a qualified professional engineer based on field observations, borings, and test pits at the site. For reference, Table 10.1 shows hydrologic groups for various soils found in the SCS Soil Survey for King County. 10.5.4 Amount of Land Disturbed The area disturbed is measured in acres and includes all land area that will be cleared at any one time. An area is considered cleared or disturbed until it has the final permanent cover as shown in approved project plans. Permanent cover can include: final landscaping; buildings (at least to pad or first floor stage); and walkways, parking, and roadways (at least to first lift of compacted gravel sub-base or equal). For some projects, project phasing can be part of the TESC Plan so the amount of land disturbed at any one time is reduced (see Table 10.2 to determine how disturbed area can affect requirements for a site). The volume of material to be moved on a site is also a factor in setting standards. The volume of material to be moved is measured in cubic yards, independent of site area. 10.6 How to Use the Rainy-Season Clearing/Grading Matrix Table 10.2 classifies sites, determines if clearing/grading work can occur in the rainy season, determines the level of TESC required, and determines the level of monitoring required. Table 10.3 defines the four levels of TESC shown in Table 10.2. Table 10.4 defines the three levels of monitoring shown in Table 10.2. To use Table 10.2, it is recommended that this document be reviewed to understand site factors and other issues related to rainy-season work. For specific projects, start with the first page of Table 10.2. If any part of the proposed rainy-season work area is in a Class 1 area, then the entire rainy-season work area must comply with requirements for the Class 1 area. If none of the proposed rainy-season work area is in a Class 1 area, do the same review using the second page of Table 10.2. Continue through the table until the ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 123 proposed rainy-season work area is shown in the table. That point in the table defines the class for the proposed work. Once the work area class is found, Table 10.2 shows whether or not work can be undertaken in the rainy season and if so, what levels of TESC and monitoring are required. 10.6.1 Temporary Erosion and Sediment Control (TESC) Levels Table 10.2 requires different levels of TESC for different site circumstances. The TESC Levels are defined in Table 10.3. Level TESC-1 is the most basic level and Level TESC-4 is to be used in critical or sensitive situations. The levels of TESC effort shown in Table 10.3 specify the nature of the TESC Plan and: • The expertise involved in preparation of the TESC Plan. • The expertise and experience of the TESC implementation team (during project construction). Moving large volumes of earth is also a factor in determining the TESC Level required. If rainy- season work involves large quantities of earthwork (over 10,000 cubic yards, as a general threshold), then Level TESC-3 is the minimum required. As experience is obtained by the City concerning TESC-3 and TESC-4 levels, additional guidance will be added to this document. 10.7 Project Planning Implications These standards are intended to protect surface and ground water quality and fisheries resources during construction and keep streets in the vicinity of construction sites safe, free of dirt and mud. Almost all construction sites have the potential to adversely affect water quality and the safety of nearby streets. Such potential greatly increases in the rainy season. It is this increased potential that led to formulation of these general standards for rainy- season work. The best general strategies to avoid the risks associated with rainy-season work are: Strategy One: Plan projects so that major, if not all, site work is done in the dry season. Strategy Two: Plan projects so the site work is phased, if rainy-season work is to be pursued. Work phasing can be applied in two ways as related to these general standards. ---PAGE BREAK--- 124 First, if part of the site is in an area where work would not generally be allowed during the rainy season, a proposed rainy-season work plan might exclude the site work that cannot be constructed in the rainy season. Second, project phasing may be used as a general strategy to reduce the area of bare earth exposed at any one time during the rainy season. Such project phasing can reduce costs and land area required for the more complex TESC measures. This approach can reduce the scope and costs (including bonding) for implementation of the Seasonal Suspension Plan. Even with phasing, some work areas pose such a risk to water quality and fisheries resources that they are not suitable for rainy-season work. These standards identify such work areas. These standards also identify work areas that pose a high risk but one that can be reduced by using exceptional temporary erosion and sediment control (TESC) measures. Further guidance is provided in this document. Even lower risk sites need to carefully plan and implement TESC measures in the rainy season. 10.7.1 General Project Planning Stage 1. The City has significant limitations and conditions regarding clearing and grading work in the rainy season. Is there any way that this project can be scheduled to conduct all clearing and grading activities in the dry weather? This will expedite permitting and reduce the cost of erosion control measures during construction. 2. Can work avoid Critical Areas altogether? A project that avoids or at least minimizes work in Critical Areas also avoids or minimizes permitting issues related to Critical Areas. 3. Can work be phased? This strategy is discussed above. 10.7.2 Monitoring Requirements Table 10.2 requires different levels of monitoring for different site circumstances. The three levels of monitoring are defined in Table 10.4. The monitoring relates to inspection of the TESC measures and to monitoring of site runoff and receiving waters for turbidity levels. Portable, electronic turbidity meters are required TESC tools for Contractors working in this area. If monitoring or other inspections lead to a determination that the TESC measures are not adequate to meet the standards outlined in Section 2, the City may stop work on the entire project and issue further direction. The developer must take actions that are necessary (subject to City approval) to meet the TESC criteria listed in Section 2. Such actions may include compliance with the approved TESC Plan, ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 125 preparation of an improved TESC plan, suspension of work during the rainy season, or other actions depending on the situation. 10.7.3 Preliminary Design and Application Stage 1. If site work is allowed in the rainy season under these general standards, what levels of TESC and Monitoring will be required? See Tables 10.2, 10.3, and 10.4. 2. If state-of-the-art TESC-4 is required, what notifications need to be included in the SEPA documents to allow such TESC options to be used? Note: If chemical treatment options for TESC may be required, this option must be included in the SEPA Environment Checklist (or EIS) for the project. It is possible to amend a SEPA determination at a later date to add the chemical treatment options but initial disclosure is preferable and saves time for the applicant. 3. Are appropriate TESC planning and implementation team members and those with monitoring expertise being brought into the design process? Note: For sites and projects requiring only TESC-1 or TESC-2 levels, the specialized expertise of the team may be less critical. For TESC-3 and TESC-4 levels, the composition, knowledge, and experience of the team will be a major consideration in allowing rainy-season work. See Table 10.3 for requirements regarding team participants. 4. Is adequate scheduling, including lead times, being included to involve the City staff in TESC issues? Note: The TESC-1 and TESC-2 levels require a minimum of City staff involvement in addition to normal project review activities. However, TESC-3 and TESC-4 require additional review by City staff. Joint meetings will likely be needed. As the rainy season approaches in each year, demands for City staff time can increase to the point where scheduling involves significant lead time. Please plan ahead if rainy-season work is a possibility. 10.7.4 Project Approval Stage As part of the City’s initial, written preliminary approval for a project, the Rainy- Season Classification will be included. The City’s classification may be appealed based on specific issues of fact or the project’s context. Appeals may be submitted only after the written preliminary project approval is issued. Appeals are submitted as described in Paragraph 10.9. ---PAGE BREAK--- 126 10.7.5 Construction Documents Stage As construction documents are being developed, it is imperative to apply the expertise of appropriate team members. For most sites, rainy-season TESC will involve significant costs. The TESC measures and their costs are an inherent part of rainy-season work. The design team needs to produce high-quality TESC plans for projects to proceed in the rainy season. 10.7.6 Pre-Construction Stage The main interaction with the City in this stage is the Pre-Construction Meeting. This meeting needs to include members of the TESC and monitoring, planning and implementation team including contractors and sub-contractors. The contractor doing the clearing and grading work must attend. If appropriate parties are not represented at the Pre-Construction Meeting, the City may cancel that meeting and require it to be rescheduled. 10.7.7 Construction Stage The construction stage is the critical stage. It is the responsibility of the developer to meet the standards outlined in Paragraph 10.3 of this chapter. (If the approved plan is not sufficient, the developer must take actions to propose and, after approval by the City, implement additional measures.) If the revised and improved erosion/sediment control plan is found to be inadequate and work is again ordered stopped, then the following shall be required: 1. If it is the rainy season, work will be suspended until the end of the season (until April 30th, or later if weather conditions warrant, and work shall not continue beyond October 1st or earlier if weather conditions warrant). 2. A revised plan shall be required to be submitted to the city public works department. Once approved, work can continue between April 30th and October 1st. 3. An on-site, full-time erosion control inspector (provided by developer) shall be required to monitor all work involving land disturbance. All costs for this inspector shall be paid by the contractor. The inspector shall provide weekly reports to the city regarding all clearing and grading work; monitor all erosion control features; and be a direct contact for the city inspectors. It is the TESC standards—not just the measures on the approved plan—that must be achieved. If TESC (including monitoring) is not being successfully addressed, the City may take action ranging from “Notices of Correction” to “Stop Work Orders” that apply to the whole project including all trades and activities. The ‘Stop Work Order’ can apply for ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 127 the entire rainy-season duration and can require implementation of the Seasonal Suspension Plan. The construction stage does not end under these general guidelines until all disturbed earth surfaces are covered with the final, permanent cover as shown on approved project plans. 10.8 Appeals: Wet Weather Committee After the City has issued the initial written approval or disapproval for a project (which will include the classification of the site and project under these general standards) an appeal may be made based on issues of fact and/or the project’s context. Appeals are to be submitted to the Development Services Division and will be considered by the Wet Weather Committee. The Wet Weather Committee is composed of one representative from each of the following divisions of the Public Works Department: • Construction Division • Development Services Division • Environmental and Utility Services Division Appeals must be in writing (five copies) and must include clearly organized supporting data developed by well-qualified professionals for all key points. Upon reviewing written appeals, the Wet Weather Committee may take one of six actions: • Determine that inadequate or insufficient information has been provided or that information was not developed by appropriate, well-qualified professionals. (The appeal will be returned without action and additional details may or may not be included.) • Approve the appeal. • Approve the appeal with conditions. • Deny the appeal. • Deny the appeal but include information that could be addressed so as to warrant reconsideration. • Request additional information. For sites that require an NPDES permit from the State Department of Ecology, initial review(s) of appeals may be made by the Wet Weather Committee but final approval for rainy-season work will require submittal of the NPDES Permit. ---PAGE BREAK--- 128 For sites that require an HPA from the Washington State Department of Fish and Wildlife, a copy of the state-approved HPA must be submitted with an appeal to the Wet Weather Committee. Table 10.1 Hydrologic Groups for Area Soils* SCS Symbol SCS Soil Name SCS Hydrologic Group Ag Alderwood gravelly sandy loam C Be Beausite gravelly sandy loam B Bh Bellingham silt loam C Br Briscot silt loam B Bu Buckley silt loam B/C Ea Earlmont silt loam B/C Ed Edgewick fine sandy loam B Ev Everett gravelly sandy loam B In Indianola loamy fine sand A Kp Kitsap silt loam C Ks Klaus gravelly loamy sand A Ne Neilton very gravelly loamy sand A Ng Newberg silt loam B Nk Nooksack silt loam B No Norma sandy loam B Or Orcas Peat D Os Oridia silt loam C Ov Ovall gravelly loam C Pc Pilchuck loamy fine sand A Pu Puget silty clay loam C Py Puyallup fine sandy loam B Ra Ragnar fine sandy loam B Table 10.1 Hydrologic Groups for Area Soils * Compiled from Soil Conservation Service information that applies to King County. Note: The terms Outwash and Till are used frequently. “Outwash” soils are A/B soils. “Till” soils are C/D soils. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 129 Table 10.2 Rainy-Season Clearing / Grading Matrix 1 Work Located in Critical Areas Area Class 2 Description 3 Surface Slope Soil Group Work in Rainy Season, General Guidance (Guidance may be modified or waived during City- designated emergencies) 1a • Within the Ordinary High Water mark of a stream (all stream classes) • Within a lake • Within a regulated wetland (all wetland classes) • On steep slopes (equal to or greater than 40 percent) All All No work in rainy season 2a Buffers associated with: • Class I Streams • Class II Streams where native fish are present or could be present during the construction time • All classes of regulated wetlands • The area within 25 feet of Lake Sammamish Ordinary High Water (elevation 27, City Datum) • The area within 15 feet of steep slopes (those equal to or greater than 40 percent) All slopes less than 40 percent All No work in rainy season ---PAGE BREAK--- 130 Area Class 2 Description 3 Surface Slope Soil Group Work in Rainy Season, General Guidance (Guidance may be modified or waived during City- designated emergencies) 2 Buffers associated with: • Class II Streams not included in 2a above • Class III Streams The area within 5 feet of Class IV Streams Ground slopes away from stream (at slope of at least 5 percent at all times before, during, and after project construction) or work area is isolated from stream by dike or equal; slopes less than 40 percent All Work Possible if: • TESC-3 or TESC-4 Plan (as directed by City); M3 monitoring • Separation of work from 100- year stream flows Restoration/mitigation and performance assurances are approved by City 2c All other ground slopes less All No work in rainy season ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 131 Area Class 2 Description 3 Surface Slope Soil Group Work in Rainy Season, General Guidance (Guidance may be modified or waived during City- designated emergencies) 3a Within the current 100- year FEMA Floodplain but outside of stream buffers and wetland buffers (all stream classes, and wetland types) Ground slopes away from stream (at slope of at least 5 percent at all times before, during and after project construction) or work area is isolated from stream by dike or equal; slopes less than 40 percent All Work Possible if: • TESC-3 Plan minimum; M3 monitoring • Separation of work from 100- year stream flows Restoration/mitigati on and performance assurance are approved by City 3b All other ground slopes less than 40 percent All No work in rainy season (unless the work area has been isolated from current 100-year frequency flood flows) ---PAGE BREAK--- 132 4a Potential hydraulic influence; 4 disturbed area for entire project is less than ¼ acre All slopes less than 40 percent A Work possible with: • TESC-1 M1 monitoring Area Class 2 Description 3 Surface Slope Soil Group Work in Rainy Season, General Guidance (Guidance may be modified or waived during City- designated emergencies) 4b All other soils C, and D) • TESC-2 M1 monitoring 4c Potential hydraulic influence;4 two or more phases used so maximum disturbed area does not exceed ¼ acre at any one time All slopes less than 40 percent A Work possible with: • TESC-3  M1 monitoring ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 133 4d All other soils C, and D) • TESC-3 M2 monitoring 4e Potential hydraulic influence;4 disturbed area(s) over ¼ acre All slopes less than 40 percent A Work possible with: • TESC-3 • M2 monitoring Area Class 2 Description 3 Surface Slope Soil Group Work in Rainy Season, General Guidance (Guidance may be modified or waived during City- designated emergencies) 4f All other soils C, and D) • TESC-3 minimum; TESC- 4 approved and ready to implement at site M3 monitoring ---PAGE BREAK--- 134 5a Areas not included in previous types with disturbed area of 1 acre or less 0-10% slope All Work possible if: • TESC-2 plan minimum; M1 monitoring 5b Slopes over 10%, but less than 40% All Work possible if: TESC-2 plan minimum; M2 monitoring 5c Areas not included in previous types with disturbed area over 1 acre 0-10% slope Group A Soils Work possible if: TESC-2 plan minimum; M1 monitoring Area Class 2 Description 3 Surface Slope Soil Group Work in Rainy Season, General Guidance (Guidance may be modified or waived during City- designated emergencies) ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 135 5d Group B, C, or D Soils Work possible if: TESC-3 plan minimum; M2 monitoring 5e Slopes over 10%, but less than 40% All Work possible if: TESC-3 minimum; TESC-4 approved and ready to implement at site; M2 monitoring Table 10.2 Rainy-Season Clearing/Grading Matrix: Work Located in Critical Areas Table Notes: 1. Decisions for a specific project regarding work in the rainy season may be appealed to the Public Works Department’s “Wet Weather Committee.” Contact the Engineering Division for details. For TESC Levels and Monitoring Levels see Tables 3 and 4, respectively. 2. “Area Classes” are labels used to identify sub-parts of a project site that meet the descriptions presented in this table. 3. See Redmond’s Critical Areas Ordinance (RZC 21.64) for additional definitions and information regarding streams, lakes, wetlands, and buffers. “Artificially Created Wetlands” as mitigation to maintain wetland resources are to be treated as closest wetland type. 4. Potential Hydraulic Influence means surface runoff from the site would follow an identifiable conveyance route to a surface water or regulated wetland and would not be infiltrated enroute. Disturbed areas less than ¼ acre typically include: • Trenching/backfill operations • Berm construction/cover work • Small sites, including single family homes • Large sites where work can be phased so as to create only a small disturbed area at any one time. TESC Plans for disturbed areas in Area Classification 4a, 4b, 4c, and 4d must provide methods to cover all disturbed areas and temporarily cease work during rainfall. ---PAGE BREAK--- 136 Table 10.3 TESC Requirements Table Notes: 5 Projects moving over 10,000 cubic yards of earth require TESC-3 or TESC-4. 6 Designated 24-hour, 7-day-per-week contact list is required. 7 TESC Contractor must document prior experience in TESC at level designated. For Level 4, TESC Contractor must document experience in chemical treatment and latest mechanical TESC methods (even if they are not initially included in TESC Plan). Table 10.3 TESC Requirements 5 TESC Level Number Recommended Participants in TESC Plan TESC Plan General Formulation and Features (Note: Seasonal Suspension Plan required for all TESC Levels) TESC Implementation Team (during construction) TESC-1 • Applicant’s Engineer Focus is on standard, common BMPs for site and project type. General sequencing list required. Designated contractor or sub-contractor 6 TESC-2 • Applicant’s Engineer • Applicant’s Project Manager • Designated Contractor or Sub- Contractor for TESC6 Focus is still on standard BMPs. Written summary required outlining how TESC is to be addressed through main construction phases. More detailed sequencing info on plan. Designated contractor or sub- contractor with documented experience 7 TESC-3 • Applicant’s TESC Engineer(s) • Applicant’s Project Manager • General Contractor • Designated Contractor or Sub Contractor6 for TESC • Grading Contractor • City’s Stormwater Engineer • City’s Construction Inspector Plan content similar to Level TESC- 2, above. More attention to all aspects of plan from conceptual to practical considerations included by team during plan formulation so as assure successful TESC. Designated contractor or sub- contractor(s)6 with Level TESC-3 experience7 TESC-4 Same as Level TESC-3 plus: • Representati ve from City’s Environment al and Utility Services Division Same as Level TESC-3 but will include state-of-art stormwater treatment systems, currently including chemical/filtration systems and such systems as “electrofloc”. Designated contractor(s ) or sub- contractor(s ) with Level TESC-4 experience7 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 137 Table 10.4 Monitoring Requirements Table Notes: 8. For all three Monitoring Levels, the minimum inspection frequency of all of the TESC measures shall be: a. After each day of site work (but not less than 3 times per week even if no site work has occurred) b. After each storm c. Twice per day during storms; more frequently if directed by City 9. TESC Contractor must have portable, electronic turbidity meter. At all monitoring levels, a log is to be kept on-site by the TESC Contractor showing monitoring dates, times, locations, weather conditions, estimated discharge rates, monitoring readings, name(s) of those doing the monitoring and equipment used. 10. Frequencies listed are minimum frequencies. More frequent monitoring including continuous monitoring during heavy storms may be required. Table 10.4 Monitoring Requirements 8 Monitoring Level Turbidity Monitoring 9 Monitoring to be by Monitoring What and When Frequency 10 M1 • Contractor or sub- contractor acceptable to City • Monitoring of surface runoff whenever it is leaving the work area • Frequency and details as directed by City; adjusted as project proceeds M2 • City-approved contractor • Supplemental verification, if directed by City, by third party to be approved by City and hired by Developer • Monitoring of surface runoff whenever it is leaving the work area • Monitoring of receiving waters (if applicable) if and when directed by City • Surface runoff to be monitored at least twice per day • Receiving waters to be monitored immediately after surface runoff monitoring M3 • Monitoring to be done by City- approved “third party” hired by Developer • If so specified, monitoring shall be done by “third party” hired by City and paid for by Developer’s advance deposit of funds • Monitoring of surface runoff whenever it is leaving the work area • Monitoring of receiving waters whenever surface runoff is leaving site and is reaching the receiving waters ---PAGE BREAK--- 138 GLOSSARY Clearing - The removal of timber, brush, grass, ground cover or other vegetative matter from a site which exposes the earth’s surface or any actions which disturb the existing ground surface. Engineer - A professional engineer licensed by the State of Washington, who is qualified to practice those aspects of engineering reviewed in Chapter 15.24 RMC, Clearing, Grading and Storm Water Management. (Ord. 1877 (75)) Existing grade - The land surface elevation prior to grading. (Ord. 1877 (95)) French drains - Perforated storm drain pipes used to collect water underground. (Ord. 1877 (97)) Grading - Any action which changes the elevation of the ground surface. Grading includes, but is not limited to, dredging, landfills, excavations, filling, earthwork, embankments, etc. NTU - The letters “NTU” stand for Nephelometric Turbidity Units. These units are a quantitative measure of water clarity based on the scattering of a standard beam of light directed into a standard sample of the water. A higher reading means the sample is less clear (more cloudy/muddy). See also the definition for turbidity. Outwash Soils - Streams flowing from glaciers deposited outwash soils. Water of varying speeds deposits particles of different sizes, sometimes resulting in distinct layers of gravel, sand, and rock in the soil profile. Usually, glacial outwash soils drain rapidly and have low organic matter content. Soils formed from highly permeable sands and gravels. SCS Hydrologic Soil Group A/B soils may be considered Outwash Soils for the purposes of this manual. Potential hydraulic influence - Surface runoff from the project would follow an identifiable conveyance route to surface water (including wetlands) and would not be infiltrated en-route. Quality Control Systems - Stormwater facilities that are intended to reduce the pollutants in runoff. (Ord. 1877 (157)) Quantity Control Systems - Stormwater management facilities that are intended to reduce the rate of runoff. (Ord. 1877 (159)) Rainy season - The period of time starting on October 1 of each year and ending April 30 of the following year. These dates may be adjusted by the Public Works Director based on climatic conditions for a particular year. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 139 Restoration - The re-establishment of the land characteristics and ecological values to pre- development conditions that were lost by alteration, development or catastrophic events. (Ord. 1954; Ord. 1877 (165)) Rough Grading - The stage at which the grade is modified to approximately conform to the proposed final grade. It is a prelude to and shall be based on a known development proposal. (Ord. 1877 (190)) Speculative Clearing and Grading - Clearing or grading without an approved viable site development concept, consisting of a site layout and other appropriate documents, as determined by the City’s Technical Committee. Stormwater Capital Improvement Plan - The Stormwater Capital Improvement Plan is a six-year plan of capital improvements, including facilities, programs, projects necessary to serve the current and future stormwater needs of those who live and work in Redmond. The CIP is a six-year financial planning document of City revenues and expenditures for those improvements. Stormwater Engineer -The Stormwater Engineer is the reviewing authority acting on behalf of the Public Works Director and represents the City for projects that involve stormwater management. City of Redmond Capital Improvement Projects are reviewed by a Stormwater Engineer within the Environmental and Utility Services Division of the Public Works Department. All other public or private projects are reviewed by a Stormwater Engineer in the Development Services Division of the Planning Department. Till Soils - A layer of poorly sorted soil deposited by glacial action that generally has very low infiltration rates. SCS Hydrologic Soil Group C/D soils may be considered Till Soils for the purposes of this manual. Turbidity - The visual cloudiness of runoff, especially as caused by suspended solids and settle-able solids in runoff. Turbidity shall be measured as specified in Method 2130-B of the following reference: Standard Methods for the Examination of Water and Wastewater. Current Edition. Franson, Mary Ann Managing Editor. Clesceri, Lenore S; Greenberg, Arnold E; and Eaton, Andrew D editorial board. Published jointly by the American Public Health Association, the American Water Works Association, and the Water Environment Federation. Turbidity Meter - A portable, electric, hand-held measuring device designed to give a numerical value of the turbidity (cloudiness) of a sample of water. The numerical values are expressed in units known as Nephelometric Turbidity Units (NTUs). ---PAGE BREAK--- 140 Appendix A - Standard Notes ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 141 STANDARD NOTES CLEARING, GRADING AND TEMPORARY EROSION CONTROL PLANS 1. All work and materials to be per City of Redmond Standards. 2. Keep off-site streets clean at all times. Flushing streets shall not be allowed. All streets should be swept. 3. Additional erosion/sediment control measures may be required by City Inspector. 4. When work is stopped/completed in an area, the City Inspector may require post- construction erosion control including seeding or other measures. 5. Locations shown of existing utilities are approximate. It shall be the responsibility of the contractor to verify the correct locations to avoid damage or disturbance. 6. It shall be the responsibility of the contractor to obtain street use and other related permits prior to any construction. 7. All ground cover is to remain undisturbed outside of clearing areas. 8. The temporary erosion/sediment controls shall be installed, inspected, and operating before any grading or extensive land clearing. These controls must be satisfactorily maintained until construction and landscaping are complete. 9. Tie impervious surfaces (roof, streets, driveways, etc.) to completed drainage system as soon as possible. 10. A Pre-Construction Meeting with the Construction Division and all permits must be completed before start of construction. 11. Clearing limits shall be located by a licensed Civil Engineer or Land Surveyor. 12. Approval of this temporary erosion/sedimentation control (TESC) plan does not constitute an approval of permanent road or drainage design. 13. This approval for TESC is valid for construction between May 1 and September 30. This approval for TESC is not valid for the rainy season (October 1 through April 30). 14. Remove all TESC measures once all work is completed and site is permanently stabilized. ---PAGE BREAK--- 142 Appendix B - Small Site Template ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 143 SMALL SITE PROJECT NUMBER PROJECT NAME PROJECT ADDRESS PREPARED FOR: APPLICANT NAME APPLICANT ADDRESS APPLICANT TELEPHONE APPLICANT EMAIL ADDRESS PREPARED BY: ENGINEER NAME ENGINEER FIRM ENGINEER ADDRESS ENGINEER TELEPHONE ENGINEER EMAIL ADDRESS Washington Engineer Stamp, Signed and Dated ---PAGE BREAK--- 144 Construction Stormwater Pollution Prevention Plan Checklist Project Name: Review Date: 0n-site Inspection Review Date: Construction Reviewer: Section I - Construction Narrative 1. Construction Stormwater Pollution Prevention Elements A. Describe how each of the Construction Stormwater Pollution Prevention Elements has been addressed though the Construction B. Identify the type and location of BMPs used to satisfy the required element. C. Written justification identifying the reason an element is not applicable to the proposal. 13 Required Elements - Construction Stormwater Pollution Prevention Plan 1. Mark Clearing Limits. 2. Establish Construction Access. 3. Control Flow Rates. 4. Install Sediment Controls. 5. Stabilize Soils. 6. Protect Slopes. 7. Protect Drain Inlets. 8. Stabilize Channels and Outlets. 9. Control Pollutants. 10. Control De-Watering. 11. Maintain BMPs 12. Manage the Project. 13. Protect Low Impact Development BMPs 2. Project Description Describe the project; include the items A through D below A. Total project area. B. Total proposed impervious area. C. Total proposed area to be disturbed, including off-site borrow and fill areas. D. Total volumes of proposed cut and fill. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 145 3. Existing Site Conditions Describe the existing site conditions; include the items A through C below A. Description of the existing topography. B. Description of the existing vegetation. C. Description of the existing drainage. 4. Adjacent Areas I. Description of adjacent areas which may be affected by site disturbance a. Streams b. Lakes c. Wetlands d. Residential Areas e. Roads f. Other II. Description of the drainage path leading from the site to the receiving body of water. (Minimum distance of 400 yards.) 5. Critical Areas A. Description of critical areas that are on or adjacent to the site. B. Description of special requirements for working in or near critical areas. 6. Soils Description of on-site soils. A. Soil name(s) B. Soil mapping unit. C. Erodibility D. Settleability E. Permeability F. Depth G. Texture H. Soil Structure 7. Erosion Problem Areas Description of potential erosion problems on site. 8. Construction Phasing A. Construction sequence B. Construction phasing (if proposed) ---PAGE BREAK--- 146 9. Construction Schedule I. Provide a proposed construction schedule. II. Wet Season Construction Activities A. Proposed wet season construction activities. B. Proposed wet season construction restraints for environmentally sensitive/critical areas. 10. Financial/Ownership Responsibilities A. Identify the property owner responsible for the initiation of bonds and/or other financial securities. B. Describe bonds and/or other evidence of financial responsibility for liability associated with erosion and sedimentation impacts. 11. Engineering Calculations Provide Design Calculations. A. Sediment Ponds/fraps B. Diversions C. Waterways D. Runoff/Stormwater Detention Calculations Section II - Erosion and Sediment Control Plans 1. General A. Vicinity Map B. City of Clearing and Grading Approval Block C. Erosion and Sediment Control Notes 2. Site Plan A. Legal description of subject property. B. North Arrow C. Indicate boundaries of existing vegetation, e.g. tree lines, pasture areas, etc. D. Identify and label areas of potential erosion problems. E. Identify any on-site or adjacent surface waters, critical areas and associated buffers. F. Identify FEMA base flood boundaries and Shoreline Management boundaries (if applicable) G. Show existing and proposed contours. H. Indicate drainage basins and direction of flow for individual drainage areas. I. Label final grade contours and identify developed condition drainage basins, ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 147 J. Delineate areas that are to be cleared and graded. K. Show all cut and fill slopes indicating top and bottom of slope catch lines. 3. Conveyance Systems A. Designate locations for swales, interceptor trenches, or ditches. B. Show all temporary and permanent drainage pipes, ditches, or cut-off trenches required for erosion and sediment control. C. Provide minimum slope and cover for all temporary pipes or can out pipe inverts. D. Show grades, dimensions, and direction of flow in all ditches, swales, culverts and pipes. E. Provide details·for bypassing off-site runoff around disturbed areas. F. Indicate locations and outlets of any dewatering systems. 4. Location of Detention BMPs A. Identify location of detention BMPs. 5. Erosion and Sediment Control Facilities A. Show the locations of sediment trap(s), pond(s), pipes and structures. B. Dimension pond berm widths and inside and outside pond slopes. C. Indicate the trap/pond storage required and the depth, length, and width dimensions. D. Provide typical section views through pond and outlet structure. E. Provide typical details of gravel cone and standpipe, and/or other filtering devices. F. Detail stabilization techniques for outlet/inlet. G. Detail control/restrictor device location and details. H. Specify mulch and/or recommended cover of berms and slopes. I. Provide rock specifications and detail for rock check dam(s), if applicable. J. Specify spacing for rock check dams as required. K. Provide front and side sections of typical rock check dams. L. Indicate the locations and provide details and specifications for silt fabric. M. Locate the construction entrance and provide a detail. 6. Detailed Drawings A. Any structural practices used that are not referenced in the Ecology Manual should be explained and illustrated with detailed drawings. 7. Other Pollutant BMPs ---PAGE BREAK--- 148 Indicate on the site plan the location of BMPs to be used for the control of pollutants other than sediment, e.g. concrete wash water. 8. Monitoring Locations Indicate on the site plan the water quality sampling locations to be used for monitoring water quality on the construction site, if applicable. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 149 ---PAGE BREAK--- 150 Appendix C - Critical Aquifer Recharge Areas ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 151 Appendix D - Minimum Requirement 5 Map ---PAGE BREAK--- 152 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 153 Appendix E - Minimum Requirement Map 6 ---PAGE BREAK--- 154 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 155 Appendix F - Minimum Requirement Map 7 ---PAGE BREAK--- 156 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 157 Appendix G - SR520 Drainage Basin (North Overlake Flow Control Standard) ---PAGE BREAK--- 158 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 159 Appendix H – Map of Historical Land Cover ---PAGE BREAK--- 160 Stormwater Technical Notebook Issue No. 6 November 2011 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 161 Appendix I - O & M Manual Template ---PAGE BREAK--- 162 Stormwater Management Facility Operation and Maintenance (O&M) Manual for Insert Development Name Located at: Insert Site Location/Address/contact information Prepared for: Insert Developer Name, Address and Phone # Prepared by: Insert Name, Company Name, Address and Phone # ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 163 Stormwater Management Facility Operation and Maintenance (O&M) Manual Table of Contents I Contact Information II Compliance with Redmond Municipal Code III. Maintenance IV. Preventative Measures to Reduce Maintenance Costs V. Safety VI. General Location and Description of Stormwater Management Facilities VII. Inspecting Stormwater Management Facilities VIII. Maintaining Stormwater Management Facilities IX. Maintenance Documentation Appendices Appendix A – Maintenance Agreements Appendix D – Maintenance Activity Log Appendix C – Site Plan Appendix F – As-Built Drawings Appendix E – Maintenance Standards Appendix F – Pollution Source Control Best Management Practices ---PAGE BREAK--- 164 Stormwater Management Facility Operation and Maintenance (O&M) Manual I Contact Information Owner _ Phone _ _ Email _ Maintenance Responsible Party: _ _ Phone _ _ Email _ Emergency Contact _ _ _ Phone _ _ Email City of Redmond, Stormwater Inspection: [PHONE REDACTED] The above contact information shall be updated any time that the information changes. Notify the City of Redmond Division of Environmental and Utility Services Stormwater Inspector, with this information within 30 days of changes. II Compliance with Redmond Municipal Code In accordance with Redmond Municipal Code 13.06, all property owners are responsible for ensuring that stormwater facilities installed on their property are properly maintained and that they function as designed. The maintenance responsibility for a stormwater facility may be designated on the subdivision plat, the site development plan, and/or within a maintenance agreement for the property. Property owners should be aware of their responsibilities regarding stormwater facility maintenance. Maintenance agreement(s) associated with this property are provided in Appendix A. In accordance with Redmond Municipal Code 13.06, discharging pollutants to the stormwater drainage system is prohibited. No person shall throw, drain, or otherwise discharge, cause or allow others under its control to discharge into a stormwater drainage system any materials other than stormwater. Pollutant discharges shall be reported immediately to the City at [PHONE REDACTED]. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 165 III. Maintenance Maintenance Manuals shall be transferred with the ownership of the property, including from the developer to the first property owner. Maintenance logs shall be provided to the City of Redmond’s Public Works Director or his/her designee upon request. A sample Maintenance Log is provided in Appendix D. You should be in possession of the O&M plan for any stormwater facility on your property. If you are not able to locate your O&M plan, call Joe Capis at [PHONE REDACTED] to receive a copy. IV. Preventative Measures to Reduce Maintenance Costs The most effective way to maintain your water quality facility is to prevent the pollutants from entering the facility in the first place. Common pollutants include sediment, trash & debris, chemicals, dog wastes, runoff from stored materials, illicit discharges into the storm drainage system (like car wash or pressure washing runoff) and many others. A thoughtful maintenance program will include measures to address these potential contaminants, and will save money and time in the long run. Key points to consider in your maintenance program include: ▪ Educate property owners/residents/tenants to be aware of how their actions affect water quality, and how they can help reduce maintenance costs. ▪ Keep properties, streets and gutters, and parking lots free of trash, debris, and lawn clippings. ▪ Ensure the proper handling, storage and disposal of hazardous wastes and chemicals. ▪ Plan landscaping care to minimize the use of chemicals and pesticides. ▪ Sweep paved surfaces and dispose of in the regular solid waste. ▪ Be aware of automobiles leaking fluids. Use absorbents such as clean cat litter to soak up leaked fluids– dispose of properly. ▪ Re-vegetate disturbed and bare areas to maintain vegetative stabilization. ▪ Clean out the upstream components of the storm drainage system, including inlets, storm sewers and outfalls. ▪ Do not store materials outdoors (including landscaping materials) unless properly protected from runoff. ▪ Close the covers on dumpsters to prevent liquids from leaking into the storm system. ▪ Ensure that garbage compactor units are functioning properly and are not leaking, including during pick-up and hauling procedure. ▪ Fleet and commercial car washing should be conducted in an area that drains to sanitary sewer, not stormwater system. Source control best management practices (BMPs) as identified in Volume IV of the current Stormwater Management Manual for Western Washington are required to reduce or eliminate the release of pollution. See Appendix F for examples of common source control best management practices. V. Safety Never enter a confined space (outlet structure, manhole, etc.) without proper training and equipment. A confined space should never be entered without at least one additional person present. If a toxic or flammable substance is discovered, leave the immediate area and call 911. Potentially dangerous fuel, chemicals, hazardous materials) substances found in the ---PAGE BREAK--- 166 areas must be referred to the local Fire Department immediately for response by the Hazardous Materials Unit. The emergency contact number is 911. Vertical drops may be encountered in areas located within and around the facility. Avoid walking on top of retaining walls or other structures that have a significant vertical drop. If any hazard is found within the facility area that poses an immediate threat to public safety, call 911 immediately. Identify site specific hazards here. VI. General Location and Description of Stormwater Management Facilities Insert a description of the stormwater management facilities specific to the site including treatment and flow control facilities, conveyance systems, valves, constructed source controls, green infrastructure, proprietary components, and powered devices (aerators or pumps). Description should include the purpose of each stormwater facility and how it functions. Identify the equipment and access required for maintenance including provisions for access in the absence of a ramp and access for a vactor truck and might require flex hose. Maintenance personnel may use the site plan located in Appendix C containing the locations of the Stormwater Management facilities. VII. Inspecting Stormwater Management Facilities The City of Redmond, Department of Public Works, inspects private stormwater systems. VIII. Maintaining Stormwater Management Facilities Stormwater management facilities must be properly maintained to ensure that they operate correctly and provide the water quality treatment for which they were designed. Routine maintenance performed on a frequently scheduled basis, can help avoid more costly rehabilitative maintenance that results when facilities are not adequately maintained. The Maintenance requirements are contained in Appendix E. These requirements should be updated to reflect changes and updates to these facilities. Routine Work The majority of this work consists of inspection, scheduled mowing, weed control, and trash and debris pickups for stormwater management facilities during the growing season. This includes items such as the removal of debris/material that may be clogging the outlet structure well screens and trash rack, and weed control. These activities normally will be performed numerous times during ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 167 the year. These items can be completed without any prior correspondence with City of Redmond. Minor Work This work consists of a variety of isolated or small-scale maintenance and work needed to address operational problems. Most of this work can be completed by a small crew, with minor tools, and small equipment. These items can be completed without any prior correspondence with City of Redmond. Major Work This work consists of large-scale maintenance and major improvements needed to address failures within the stormwater management facilities. This work may require an engineering design with construction plans to be prepared for review and approval by the City. This work may also require more specialized maintenance equipment, surveying, construction permits or assistance through private contractors and consultants. These items require prior correspondence with City of Redmond and may be subject to permits. IX. Maintenance Documentation The Stormwater Management Facility Maintenance Activity Form provides a record of maintenance activities. Maintenance Forms for each facility type are provided in Appendix,B. Maintenance shall be completed. by the contractor completing the required maintenance items. The form shall then be reviewed by the property owner or an authorized agent of the property owner and kept on site and submitted to the City of Redmond upon request. Appendix A Maintenance Agreements Appendix D Stormwater Facility Maintenance Activity Log ---PAGE BREAK--- 168 Stormwater Facility Maintenance Activity Log Property Address: Inspection Date: Inspection Time: Inspected By: Approximate Date/Time of Last Rainfall: Type of Stormwater Facility: Location of Facility on Site (in relation to building or other permanent structures): Water levels and observations (oil sheen, smell, turbidity, etc.): Sediment accumulation & record of sediment removal: Condition of vegetation (Height, survival rates, invasive species present, etc.) and record of replacement and management (mowing, weeding, etc.): Condition of physical properties such as inlets, outlets, piping, fences, irrigation facilities, and side slopes. Record damaged items and replacement activities: Presence of insects or vectors. Record control activities: Identify safety hazards present. Record resolution activities: ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 169 Appendix J - Flood Control Zone Application Form ---PAGE BREAK--- 170 FLOOD CONTROL ZONE APPLICATION APPLICANT: Name: Company: Address: Telephone: OWNER (if different from applicant): Name: Company: Address: Telephone: PROJECT IDENTIFICATION AND SCHEDULE: Type of Work: Construct Reconstruct Modify Project Description Project Name Construction to commence on and to be completed by Permit if sought for PROJECT LOCATION: Tax parcel number Project address Located in ¼ Section T R E (WM) Within the flood plain of (Body of water) F065 (10/04) ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 171 APPLICANT’S SIGNATURE Applicant, by signature following, herby applies for a Flood Control Zone Permit and stipulates that information provided is correct to the best of applicant’s knowledge: Date Print PERMIT: This document grants permission under provision of Chapter 86.16 RCW when and only when signed below and is subject to all conditions noted: Minimum Finished Elevation shall be NGVD, 1929 Permit Granted City of Redmond Flood Control Date Zone Administration Permit and Conditions: Acknowledged Date Print F065-con’t (10/04) ---PAGE BREAK--- 172 Appendix K - Typical Drainage Easement ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 173 Document Title(s) (or transactions contained therein): EASEMENT Reference Number(s) of Documents assigned or released: Additional reference numbers on page of document Grantor(s): (Last name first, then first name and initials) 1.  Additional names on page of document Grantee(s): (Last name first, then first name and initials) 1. REDMOND, CITY OF  Additional names on page of document Legal Description: (abbreviated form i.e. lot, block, plat name, section-township-range) Ptn  Additional legal on Exhibit of document Assessor's Property Tax Parcel Account Number(s): City of Redmond Reference: Project Number: Permit Number: The Auditor/Recorder will rely on the information provided on the form. The staff will not read the document to verify the accuracy or completeness of the indexing information provided herein. Please Return To: City of Redmond Public Works Adm. MS: 4NPW Attn: D. Wilson P.O. Box 97010 Redmond, WA 98073-9710 ---PAGE BREAK--- 174 EASEMENT THE GRANTOR(S), , a , for Ten and no/100 Dollars ($10.00) or other valuable consideration, in hand paid, receipt of which is hereby acknowledged, conveys and grants to CITY OF REDMOND (Grantee), its successors and assigns, a permanent non-exclusive easement, over, under, in, along, across and upon, that certain land legally described as: Exhibit attached hereto and incorporated herein by reference, and graphically depicted on Exhibit for the purpose of constructing, reconstruction, installing, repairing, replacing, operating and maintaining a public storm drain system, with ordinary and necessary appurtenances, together with the right of ingress and egress thereto without prior institution of any suit or proceedings of law and without incurring any legal obligation or liability therefore. This easement is granted subject to the following terms and conditions: 1. The Grantee shall, upon completion of any work within the property covered by the easement, restore the surface of the easement, and any private improvements disturbed or destroyed during execution of the work, as nearly as practicable to the condition they were in immediately before commencement of the work or entry by the Grantee. 2. Grantor shall retain the right to use the surface of the easement as long as such use does not interfere with the easement rights granted to the Grantee. Grantor shall not, however, have the right to: ) Erect or maintain any building or structures within the easement; or ) Plant trees, shrubs or vegetation having deep root patterns which may cause damage to or interfere with the utilities to be placed within the easement by the Grantee; or ) Develop, landscape, or beautify the easement area in any way which would unreasonably increase the cost to the Grantee of restoring the easement area and any private improvements therein. This easement shall be recorded with the King County Recorder, shall run with the land described herein, and shall be binding upon the parties, their heirs, successors in interest and assigns. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 175 Grantor covenants that he is the lawful owner of the above-described property and has authority to convey such easement. Dated this day of , 20 Grantor: By: Its STATE OF ) ) § COUNTY OF ) I certify that I know or have satisfactory evidence that is the person who appeared before me, and said person acknowledged that he signed this instrument, on oath stated that he was authorized to execute this instrument and acknowledged it as of to be the free and voluntary act of such party for the uses and purposes mentioned in the instrument. Dated this day of , 20 . Notary Signature: Print Name: Notary Public in and for the State of Residing in My Commission Expires: Notary Seal Please stay within block. ---PAGE BREAK--- 176 EXHIBIT EASEMENT KING COUNTY TAX ID # EXHIBIT Map ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 177 ---PAGE BREAK--- 178 Appendix L - Bill of Sale and Instructions Form ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 179 PUBLIC UTILITY & STORMWATER FACILITIES BILL OF SALE FORM INSTRUCTIONS PURPOSE: To transfer ownership of a newly constructed public utility and/or stormwater system and appurtenances that have been newly constructed as part of the following project to the City of Redmond. The project name, as shown on official City approvals is: PROPERTY DESCRIPTION: All constructed stormwater conveyance systems and appurtenances constructed as part of the subject project that: are located in City Rights-of-Way; and any stormwater conveyance systems and appurtenances not in City Rights-of-Way that: have been specifically approved for acceptance by the City in writing and are contained within approved easements granted to the City. SIGNATURE The Bill of Sale shall be signed by the party who paid for the system improvements. Signature shall be notarized. The notary space for individuals or corporations as appropriate. QUESTIONS: If you have any questions about how to complete the form, please contact the Public Works Development Services Division at (425)556-2760. F023 (10/04) ---PAGE BREAK--- 180 BILL OF SALE FOR VALUABLE CONSIDERATION, receipt of which is hereby acknowledged, the undersigned hereby conveys, bargains and sells and transfers to the City of Redmond, hereinafter referred to as the "City", all its present and future right, title and any interest in and to all of the following property: to have and hold the s ame for itself, its successors and assigned forever, free of all liens and encumbrances, or interest of third parties. The undersigned, on behalf of itself and it s successors, and assigns covenants and agrees that the undersigned is the owner of said property and has good right and authority to sell the same and that it will, and does, hereby warrant title to said property and agrees to defend and hold harm less the City, its successors and assigns, against all and every person or persons whom soever lawfully claiming any right, title, or in terest in or to the same. The undersigned warrants that the above-described property is in good operating condition and repair; that the undersigned has not received any citation or warning to the effect that these assets do not comply with all governm ental laws or regulations; and further covenants and agrees with the City to replace, repair and correct any defect in work or materials in respect to the personal property subject to this Bill of Sale arising during a p eriod of o ne year from the date of Acceptance by Public Works Development Services Division, without cost to the City. F023 (10/04) ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 181 DATED this day of 20 By Its STATE OF WASHINGTON ) ) ss. COUNTY OF ) I certify that I know or have satisfactory evidence that signed this instrument, acknowledged it to be his/her free and voluntary act for the uses and purposes mentioned in the instrument. DATED this day of 20 NOTARY PUBLIC My Commission Expires: STATE OF WASHINGTON ) ) ss. COUNTY OF ) I certify that I know or have satisfa ctory evidence that this instrum ent, acknowledged it to be his/her free and voluntar y act for the uses and purposes m entioned in the instrument. DATED this day of 20 NOTARY PUBLIC My Commission Expires: F023 - con’t (10/04) ---PAGE BREAK--- 182 Appendix M - Developer Extension Asset Summary Form ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 183 DEVELOPMENT SERVICES DIVISION DEVELOPER EXTENSION ASSET SUMMARY Project Name: Developer: Contractor: WATER SYSTEM CONSTRUCTION COSTS Land $ Storage Pump Station $ Pressure Reducing Valve $ Water Mains and Appurtenances: Main Size: 4" 6" 8" 12" 16" Other ( ) Length: Type: Lineal Ft Main Cost: Water Mains and Appurtenances Total Service Lines (Line, Meter Box / Vault, Meter Setter) Meter Size Qty Hydrant Q ty Water Total SEWER SYSTEM CONSTRUCTION COSTS Pump Station $ Side Sewer (Within Right of Way) Qty Manholes Q ty Sewer Mains and Appurtenances: Main Size: 8" 8” 10” 10” 12” Other ( ) Length: Type: PVC DI PVC DI Lineal Ft Main Cost Sewer Mains and Appurtenances Total Sewer Total (Combined Water/Sewer) Project Total $ F060 (10/04) ---PAGE BREAK--- 184 PUBLIC STORMWATER SYSTEM CONSTRUCTION COSTS Land $ Pond / Vault / Tank Construction Pipe Storage Size & Water Quality Type $ Stormwater Mains and Appurtenances: Main Size: 8" 12" 18" 24" 36" Other ( ) Length: Type: Lineal Ft Main Cost: Stormwater Mains and Appurtenances Total Stormwater Total NOTES: 1. Include total cost of improvements including sales tax, engineering and administration. 2. As a separate instrument, a Bill of Sale has been provided for the above improvements. ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 185 I hereby certify that all bills pertaining to the installation of the improvements have been paid in full and that the above costs represent the true value of the improvements. HERE AND IN WITNESS WHEREOF, the undersigned have hereunto set their hand and seal. DATED this day of STATE OF WASHINGTON) )ss COUNTY OF KING ) On this da y personally appeared before be known to be the individual as described in and who executed the within and foregoi ng instrument and acknowledged that ( he/she/they) signed the same as (his/hers/their) free and voluntary act and deed of the uses and purposes therein mentioned. GIVEN under my hand and official seal this of Notary Public My commission expires F060 con’t (10/04) ---PAGE BREAK--- 186 Appendix N - LID Site Assessment Form ---PAGE BREAK--- LID Site Assessment and Planning Packet Instructions for completing this packet: This packet is to be completed as part of a preliminary site assessment by the applicant per RZC 21.17.10E and as specified in the Stormwater Technical Notebook (STN). For documentation purposes, all projects that result in 2,000 square feet or greater of new, replaced, or new plus replaced hard surface area or have land disturbing activity of 7,000 square feet or greater must complete an LID assessment and include this packet as an appendix to the project drainage report submitted as part of the site plan entitlement process. This packet is to be completed early in the site development process. Please complete all sections of this packet to the best of your ability. Some sections may not apply. You may state “Not Applicable” only when you can explain why it does not apply and not when the answer is unknown. Consulting with a qualified consultant may be necessary to determine ascertain certain features of the property (i.e. depth to groundwater/ infiltration rates). Please consult with a geotechnical engineer or civil engineer if your project meets the thresholds identified above. This is a fillable PDF form. The forms will expand and allow you to enter more text than the space indicates. If you should run out of space, attach a separate sheet and write “continued from” and include the section and number (i.e. D.1). The goal of this assessment is to: Document how projects propose to minimize: • Impervious areas • Loss of native vegetation • Stormwater runoff Demonstrate how the project proposes to comply with Minimum Requirement On-site Stormwater Management. Some of the below requirements are modified based on whether the project is located within an urban center or an area draining to a flow control exempt water body. To determine how your site’s location in the City influences On-site Stormwater Requirements (Minimum Requirement refer to Map 1- MR 5: Stormwater Management Custom Areas at end of this packet and then look for the corresponding symbol for where requirements are modified. (This map is also found as Appendix F in the Redmond Stormwater Technical notebook). The custom flow control areas in Redmond include: • Downtown • Overlake • SR520 Drainage Basin • 40th Street Basin • SE Redmond (some properties) PROJECT INFORMATION A Project Number: Project Address or Boundaries: Parcel Number: Is the site in a Flow Control Exempt area? (Refer to Section 2.5.7 of the STN): Yes No If yes, note the items that are footnoted in the tables in Section F Potential LID BMP Matrix” and refer to that footnote at the bottom of each table. Is the site located within the Marymoor Subarea as depicted on Map 1? (Refer to Map 1at the end of this packet): Yes No If yes, Sections B, C, D and E do not need to be completed as the intent of this packet will be exceeded through the infiltration of 100% of site runoff. Is the site located within a Critical Aquifer Recharge Area? (Refer to Map 2: Critical Aquifer Recharge Areas at the end of this packet): Yes No If yes, refer to Section 8.3.2 of the STN. Single-family residential projects in Critical Aquifer Recharge Area I may infiltrate runoff from pollution generating hard surfaces only after enhanced treatment using a BMP that is exposed to the surface (such as bioretention visible from public sidewalks or roads). In the Marymoor Subarea there is no stormwater conveyance available, so development is required to infiltrate stormwater, even if it lies within CARA I. Stormwater must receive enhanced treatment prior to infiltration. Infiltration of runoff from non-pollution generating surfaces is encouraged where feasible. Project Type: Residential Commercial Industrial Public New Development Redevelopment Remodel Retrofit Combination (explain) Project Description: APPLICANT INFORMATION Company/Agency/Owner: Contact Person: Address: Phone: Email: Signature: Date: SIGN ---PAGE BREAK--- LOW IMPACT DEVELOPMENT GOALS B In the spaces below, please document project efforts to: Minimize Impervious Surface Coverage: Minimize Loss of Native Vegetation: Minimize Stormwater Runoff: CREATE SITE COMPOSITE MAP C Develop a composite site map as you collect site information in Section D. See the example below. This map must be submitted as part of the completed packet, and will be used as the basis for the site design. Example Site Composite Map EXISTING SITE INVENTORY AND ANALYSIS CHECKLIST D Use this portion of the packet to document the site inventory and analysis. For additional information on each portion of the analysis, refer to Chapter 2 of the City of Redmond Stormwater Technical Notebook 8. 1. PROJECT BOUNDARIES AND STRUCTURES ‰ ‰ Identify/delineate on map: ‰ ‰ Project Site boundaries (limits of disturbance) ‰ ‰ Existing and proposed buildings ‰ ‰ Required Infiltration setbacks (please describe) ‰ ‰ Location and extent of proposed foundations and footing drains 2. SOILS ‰ ‰ Characterize existing soil type(s) (Refer to Section 10.5.3 of the Stormwater Technical Notebook): ‰ ‰ What is the depth to seasonal average high groundwater (feet) as determined by a geotechnical investigation? (Refer to Section 2.9.3.9 of the Stormwater Technical Notebook) ‰ ‰ Is bedrock present? Yes No If yes, depth (feet) ‰ ‰ What is the measured long-term native soil infiltration rate (inch/hour) ‰ ‰ Identify source(s) of information used: 3. CRITICAL AREAS ‰ ‰ Identify and map any Critical Areas and associated buffers located on the project site and within the project vicinity ‰ ‰ Erosion Hazard Areas ‰ ‰ Fish and Habitat Conservation Areas ‰ ‰ Floodplains ‰ ‰ Frequently Flooded Area/Special Flood Hazard Area ‰ ‰ Critical Aquifer Recharge Areas ‰ ‰ Landslide hazard Areas ‰ ‰ Seismic Hazard Areas ‰ ‰ Shoreline Environments ‰ ‰ Streams ‰ ‰ Wetlands ‰ ‰ Other 4. TOPOGRAPHY ‰ ‰ Describe site topography and slopes: ‰ ‰ Identify/Delineate on map: ‰ ‰ Areas of flat(≤5%), moderate moderate-steep (20%-40%) and steep( ≥40%)slopes ‰ ‰ Closed depressions 5. HYDROLOGIC PATTERNS & FEATURES ‰ ‰ Identify/Delineate on map: ‰ ‰ Sub-basin(s) ‰ ‰ Existing drainage swales and ditches (please describe) ‰ ‰ Location(s) if any natural seeps or springs (please describe) ‰ ‰ Existing discharge location(s) from each sub-basin and overall project site: (please describe) ‰ ‰ Signs of existing erosion (please describe) ‰ ‰ Existing flooding or drainage complaints on site or vicinity ‰ ‰ Other 6. VEGETATION ‰ ‰ Native vegetation type(s): ‰ ‰ Approximate tree canopy coverage (acres): ‰ ‰ Number of trees (greater than 6-inch diameter at breast height) ‰ ‰ Identify source(s) of information used: ---PAGE BREAK--- 7. LAND USE CONTROLS ‰ ‰ What is the project site zoning? ‰ ‰ Describe landscaping requirements: ‰ ‰ Describe parking requirements: ‰ ‰ Describe any applicable comprehensive plan designation, zoning classification, and/or overlay districts that apply to the site: ‰ ‰ Does a Shoreline Master Plan apply to the site? Yes No ‰ ‰ If yes, describe 8. ACCESS ‰ ‰ Identify/Delineate on map: ‰ ‰ Roads, driveways, and other points of ingress and egress within 50 feet of the project site ‰ ‰ Identify frontage improvement requirements: 9. UTILITY AVAILABILITY AND CONFLICTS A complete understanding of existing and proposed buried utilities is necessary to properly plan for infiltration. ‰ ‰ Identify/Delineate on map: ‰ ‰ Existing utilities and easements present on and adjacent to the project site, including utility owner. Also note any utility or easement setback requirements that affect site planning: ‰ ‰ Existing utilities that may need to be moved and new utilities that may need to be extended to the site: EXISTING SITE CONDITIONS E EXISTING CONDITIONS PROPOSED CONDITIONS Vegetated Areas Tree Canopy (acres) Landscape (acres) Total project vegetated area Impervious Area Total roof impervious area (sq. feet) Total site impervious area (acres) Change % Increase/decrease in vegetated area % Increase/decrease in impervious area POTENTIAL LID BMP MATRIX F For each of the following surfaces proposed, complete the following matrices evaluating the BMPs in the order as specified in Lists #1 and #2 contained within the Stormwater Technical Notebook: ‰ ‰ Lawn and landscaped areas ‰ ‰ Roofs ‰ ‰ Other hard surfaces SURFACE TYPE: For each LID BMP being evaluated, use the infeasibility criteria for each BMP in the to determine whether the LID BMP is infeasible for your project. You must use the first BMP that is feasible in accordance with Lists #1 and List#2 of the STN. FEASIBILITY/INFEASIBILITY EVALUATION FEASIBLE INFEASIBLE NOT APPLICABLE/ NOT KNOWN If infeasible provide justification as stated by the Infeasibility Criteria in the Post Construction Soil Quality and Depth Full Dispersion1 Downspout Full Infiltration (Roofs, only) Rain Gardens/Bioretention1 Permeable Pavement or Functional Equivalent1 Downspout Dispersion Perforated Stubout Connection (Roofs, only) Sheet Flow Dispersion Concentrated Flow Dispersion 1Not Required in Flow Control Exempt Areas ---PAGE BREAK--- SURFACE TYPE: For each LID BMP being evaluated, use the infeasibility criteria for each BMP in the to determine whether the LID BMP is infeasible for your project. You must use the first BMP that is feasible in accordance with Lists #1 and List#2 of the STN. FEASIBILITY/INFEASIBILITY EVALUATION FEASIBLE INFEASIBLE NOT APPLICABLE/ NOT KNOWN If infeasible provide justification as stated by the Infeasibility Criteria in the Post Construction Soil Quality and Depth Full Dispersion1 Downspout Full Infiltration (Roofs, only) Rain Gardens/Bioretention1 Permeable Pavement or Functional Equivalent1 Downspout Dispersion Perforated Stubout Connection (Roofs, only) Sheet Flow Dispersion Concentrated Flow Dispersion 1Not Required in Flow Control Exempt Areas SURFACE TYPE: For each LID BMP being evaluated, use the infeasibility criteria for each BMP in the to determine whether the LID BMP is infeasible for your project. You must use the first BMP that is feasible in accordance with Lists #1 and List#2 of the STN. FEASIBILITY/INFEASIBILITY EVALUATION FEASIBLE INFEASIBLE NOT APPLICABLE/ NOT KNOWN If infeasible provide justification as stated by the Infeasibility Criteria in the Post Construction Soil Quality and Depth Full Dispersion1 Downspout Full Infiltration (Roofs, only) Rain Gardens/Bioretention1 Permeable Pavement or Functional Equivalent1 Downspout Dispersion Perforated Stubout Connection (Roofs, only) Sheet Flow Dispersion Concentrated Flow Dispersion 1Not Required in Flow Control Exempt Areas Map 1: Onsite Stormwater Management Custom Areas ---PAGE BREAK--- Map 2: Critical Aquifer Recharge Areas ATTACH COMPLETED SITE COMPOSITE MAP HERE. ---PAGE BREAK--- 192 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 193 Appendix O - Regional Facilities Map ---PAGE BREAK--- 194 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 195 Appendix P - Downtown Stormwater Infrastructure Map ---PAGE BREAK--- 196 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 197 Appendix Q - Overlake Stormwater Infrastructure Map ---PAGE BREAK--- 198 ---PAGE BREAK--- Redmond Stormwater Technical Notebook – 4/1/2019 199 Appendix R - Capital Facilities Charge Form ---PAGE BREAK--- 200 This form is available electronically from the Stormwater Engineer. ---PAGE BREAK--- 201 ---PAGE BREAK--- 202 ---PAGE BREAK--- 203 ---PAGE BREAK--- 204 ---PAGE BREAK--- 205