Document Redmond_doc_78636eeed2

Overlake Village Station Regional Infiltration Facility Alternatives Analysis Submitted to: Steve Hitch, PE City of Redmond Prepared by: Otak, Inc. 10230 NE Points Drive, Suite 400 Kirkland, WA 98033 Otak Project No. 31470B December, 2013 ---PAGE BREAK--- ---PAGE BREAK--- A l t e r n a t i v e s A n a l y s i s i O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak Table of Contents Overlake Village Station Regional Infiltration Facility Alternatives Analysis Page Section 1—Project Overview 1 Section 2—Design Criteria 5 Section 3—Treatment Alternatives 9 Section 4—Flow Control Alternatives Section 5—Cost Analysis Section 6—Conclusions and Recommendations References Figures Figure 1—Vicinity Map Tables Table 1—Facility Option Summary Table 2—Facility Cost Comparison Exhibits Exhibit 1—Site Layout Exhibit 1 Exhibit 2—Site Layout Exhibit 2 Exhibit 3—Facility Profiles 1 & 2 Exhibit 4—Engineered Soil Vault Typical Section Exhibit 5—UIC Well Typical Section Exhibit 6—Prefered Configuration Typical Section ---PAGE BREAK--- Appendices Appendix A—Treatment Facility Sizing Summary Appendix B—Modeling Output Appendix C—Scenario Preliminary Design Cost Estimates Appendix D—Pre-Manufactured Treatment Schematics Appendix E— Overlake Regional Stormwater Infiltration Facility Design and Performance Criteria Technical Memorandum ---PAGE BREAK--- Section 1—Project Overview A l t e r n a t i v e s A n a l y s i s 1 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak In 2012, Otak assisted Redmond with the development of the Overlake Village Regional Stormwater Alternatives Analysis (Otak 2012b) (referred to as the “2012 Regional Alternatives Analysis”). That plan presented in more detail, the flow control, runoff treatment, and conveyance facilities needed to support full redevelopment of the Overlake neighborhood as envisioned in the City of Redmond’s 2010 Implementation Plan—Overlake Village Stormwater and Park Facilities Conceptual Design (Otak 2010) (referred to as the “2010 Implementation Plan”). The 2012 Regional Alternatives Analysis identified three large regional stormwater facilities along with the use of low impact development infiltration facilities as the most efficient way to meet stormwater requirements while also supporting the neighborhood’s Vision. The proposed facilities include: • Overlake South Detention Vault. This 20 acre-foot detention vault, to be located in the parking lot of Sears will provide flow control for a large portion of the basin. • Overlake Station Infiltration Facility. This large treatment and infiltration facility will collect a large portion of the stormwater coming from north of SR520, treat it, and infiltrate it on site. By infiltrating all the stormwater that comes to it, along with the proposed Central Infiltration Facility, the South Detention Vault will be kept empty more of the time, allowing the combination of the regional facilities to most effectively mimic the predeveloped, forested condition that is the flow target for the basin. This facility is proposed for construction as part of Sound Transit’s proposed light rail station. • Low Impact Development Infiltration Facilities. A key element of the regional plan is the use of smaller scale infiltration facilities that will be incorporated as bioretention and underground infiltration pipes to encourage distributed infiltration throughout the basin. By infiltrating stormwater in these small facilities, the larger regional infiltration vaults are kept empty more of the time, thereby allowing more efficient use of their volume to accommodate the very large storms that come less frequently. • Overlake Central Infiltration Facility. This large infiltration vault will be constructed in the future within a two acre parcel proposed as a future park. With the two-acres available for this use, this regional facility will be designed to provide the final piece that will fully retrofit the basin to Ecology standards for flow control. Because the space is available to increase the size of this facility as needed, it can be used as an adaptive management alternative if the regional facilities or low impact development infiltration facilities do not perform as effectively as is hoped. This facility is proposed for construction in the future as new streets and redevelopment are implemented. The 2012 Regional Alternatives Analysis contemplated various vault sizes, combined with greater or lesser use of low impact development infiltration facilities to find a moderate level of low impact development that would fit well within the proposed urban fabric while optimizing the sizing of the large regional facilities. ---PAGE BREAK--- Section 1—Project Overview Continued A l t e r n a t i v e s A n a l y s i s 2 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak The Overlake Village Station Regional Infiltration Facility (OVSIF) is the subject of this alternatives analysis. As the City has provided greater definition for the proposed Plaza Street to be constructed by Sound Transit in front of the future light rail station, design alternatives considered how this proposed facility could be fit within the proposed right-of- way of that future street (Figure This report validates the conceptual design recommendations of the 2012 Regional Facilities Plan while providing conceptual design and cost information necessary for selection of a preferred design concept for the 30 percent design. The selected, preferred OVSIF configuration will be refined through the 30 percent design plans and performance specifications, including additional geotechnical site data and infiltration testing within the proposed facility footprint. The project’s Performance Specifications and Design Narrative for the OVSIF will be included in the Sound Transit Design-Build Request for Proposal of the East Link Light Rail project, planned for solicitation in early 2014. The 30 percent OVSIF design and cost estimate will be used by the City to negotiate the City’s contribution to the East Link Light Rail Design-Build project, and will be the basis for final design by the selected Design-Build team. For this alternatives analysis, flow control and water quality treatment options were sized based on the flow data (timeseries) developed by NHC using Hydrological Simulation Program-Fortran (HSPF). This data is based on the flow schematic developed in the 2012 Regional Alternatives Analysis and the preferred regional facilities alternative selected in the 2012 Regional Alternatives Analysis, which includes a moderate level of dispersed Low Impact Development (LID) infiltration BMPs. The moderate level of LID assumes five percent LID implementation over the redeveloped area, which provides flow control for approximately 46 percent of the runoff volume from the contributing basins to the OVSIF site. Based on the preferred OVSIF conceptual design per the 2012 Regional Alternatives Analysis, 50 percent of the flow from the upstream contributing Overlake basins to the OVSIF (R-2 subbasins) will flow to the facility; the other 50 percent of the upstream basin flow will be directed to the Central Infiltration Facility, with additional basin flows south of the OVSIF (see Figure Fifty percent of the upstream basin flow represents approximately 94 acres from the R-2 subbasins, as described in the 2012 Regional Alternatives Analysis. Based on the preferred regional facilities configuration recommended in the 2012 Regional Alternatives Analysis, 92 percent of the volume sent to the OVSIF is ultimately infiltrated at the facility with a regional point-of-compliance of the South Detention Facility. The OVSIF is proposed to provide infiltration and water quality treatment for a recommended 70 acres of service area until construction of the Central Infiltration Facility. The OVSIF stormwater treatment alternatives presented in this report are sized based on meeting the Point of Compliance for a given service area, similar to the recommended ---PAGE BREAK--- R-2 0 1,000 2,000 500 Feet¯ SR-520 NE 20TH ST NE 24TH ST NE 40TH ST K:\project\31400\31470A\GIS\mxds\Modified_Vicinity_Vaults.mxd 152nd AVE NE Figure 1 - Vicinity Map Redmond City Limit Infiltration Vault South Detention Vault â â â â â â â â â ââ â â Bellevue Area Tributary to Contibuting Basin ! South Detention Vault ! Future Central Infiltration Vault ! Proposed Station Infiltration Vault Overlake Village Regional Stormwater Facilities Contributing Basin R-2 Subbasins ---PAGE BREAK--- Section 1—Project Overview Continued A l t e r n a t i v e s A n a l y s i s 4 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak approach for the Phase 3 configuration. Both flow control and water quality treatment alternatives for OVSIF are presented in this report. Based on site survey, the connection point from the existing stormwater conveyance invert on 152nd Avenue NE is approximately 15 feet below the existing ground. This is several feet lower than estimated in the conceptual design of the 2012 Regional Alternatives Analysis. The deeper initial depth causes the infiltration vault to be closer to the till and outwash soil interface, which requires additional excavation for OVSIF components but reduces the depth of over-excavation volume needed to connect with the higher infiltration rates within the outwash soils (Exhibit The deeper facility also presents challenges for connecting the vault overflow back to the 152nd Avenue NE conveyance system. Several options for connecting the overflow were evaluated, including the following: 1) a conveyance stub for a future conveyance connection with the future completion of Plaza Street and NE 28th Street; 2) an overflow to a pump station; 3) an automated flow control system at the upstream flow splitter to restrict flows as the OVSIF reaches maximum design depths; and 4) the option of allowing higher ponding depths in the OVSIF to create a tailwater condition at the 152nd Avenue NE flow splitter when the vault reaches maximum ponding depth. Additional geotechnical borings with onsite infiltration testing were completed for the OVSIF design as part of this facility design process. A conservative long-term infiltration rate of 7.5 inches per hour for the planned flow control facility was used for initial facility sizing; this rate is based on onsite infiltration analysis before calibration of the ground water modeling. To meet water quality requirements for a combined treatment and flow control facility, the design infiltration rate of 3.0 inches per hour was initially compared to a 7.5 inches-per-hour rate allowable as a flow control only with upstream water quality treatment. With the completion of the ground water calibration, a variable infiltration rate was evaluated for specific flow control infiltration vault footprints. With the improved site understanding that comes with better site survey, additional geotechnical investigation, and groundwater modeling, this alternatives analysis takes a step closer to design of the proposed facility. A large number of alternatives are considered, seeking to find the sweet spot between better performance for a larger treatment area, lower overall cost, and the ability to fit within a fairly constrained location under a future street. This alternatives analysis selects a preferred alternative that will be used for development of the 30 percent design. ---PAGE BREAK--- Section 2—Design Criteria A l t e r n a t i v e s A n a l y s i s 5 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak The design criteria for the OVSIF project was compiled in the technical memorandum Overlake Regional Stormwater Infiltration Facility Design Parameters and Performance Criteria (Otak 2013) (referred to as the “2013 Regional Parameters and Performance Criteria”) (Appendix This memorandum evaluated design criteria per the City of Redmond Clearing, Grading and Stormwater Management Technical Notebook (referred to as the “2012 Technical Notebook”) and the performance criteria per additional Washington State Department of Ecology (Ecology) design manuals, as summarized below. The design criteria for the OVSIF are primarily based on requirements in the City’s 2012 Technical Notebook, which adapts the requirements of the Ecology 2005 Stormwater Management Manual for Western Washington (referred to as the “2005 Ecology Manual”). Adoption of the Ecology 2012 Stormwater Management Manual for Western Washington (referred to as the “2012 Ecology Manual”) by the City will likely take place prior to the construction of the OVSIF under the Sound Transit Design-Build project for compliance with the City’s 2013-2018 National Pollution Discharge Elimination System (NPDES) Phase II permit. A summary of the differences in the key design requirements under the two manuals is included the 2013 Regional Parameters and Performance Criteria. Some of the design criteria comparisons outlined for the OVSIF in the 2013 Regional Parameters and Performance Criteria are the requirements for the treatment level and criteria for Underground Injection Control (UIC) wells. The 2005 and 2012 Ecology Manuals outline criteria for the level of treatment recommendations. Since the OVSIF is located more than a quarter-mile from fish bearing streams and will infiltrate stormwater, only basic treatment is required by the Ecology Manuals (Volume V, Section 3.5). Additionally, the Manuals require pretreatment upstream of infiltration facilities to prevent them from clogging and to protect groundwater (Ecology Manual Volume V, Section 1.4.3). In addition, the 2013 Regional Parameters and Performance Criteria outlines the design criteria for UIC wells; these stormwater management injection wells are subject to additional design criteria including minimum separation distance above groundwater. The facility is considered a UIC well if it includes a dug hole or shaft that is deeper than it is wide. None of the evaluated facility alternatives meet this definition. Based on initial analysis, the OVSIF will treat a tributary area of between approximately 70 and 100 acres using infiltration to meet flow control standards. In 2012, GeoEngineers coordinated with the City of Redmond and Otak to conduct a groundwater mounding analysis for the Overlake Village South Detention Facility. As part of that work, preliminary infiltration rates were developed for the OVSIF and reported in the Groundwater Mounding Analysis – Overlake Village Stormwater Vaults by GeoEngineers (referred to as the “2012 Groundwater Mounding Report”). This report estimated infiltration rates varying between 2.5 to 9 inches per hour. The initial conceptual design for the OVSIF has a design footprint ---PAGE BREAK--- Section 2—Design Criteria Continued A l t e r n a t i v e s A n a l y s i s 6 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak of 0.42 acres, at a maximum ponding depth of six feet as prescribed by Ecology for combined water quality infiltration facilities, and an operating capacity of 2.5 acre-feet. This conceptual design has been updated as a part of this alternatives analysis report. The design is based the maximum facility footprint per the proposed Plaza Street configuration, with incorporation of additional site survey and geotechnical analysis. Initial geotechnical investigation of the site was conducted in conjunction with creation of the Regional Facilities Plan, which indicated that the site has an approximately 27-foot-deep layer of glacial till, which has poor drainage qualities including low infiltration rates. Outwash soils are located below the glacial till layer that have higher infiltration rates. The water table is approximately 38 feet below the surface and approximately 12 feet below the estimated till and outwash soil interface. Additional soil and infiltration analyses were conducted as part of this alternative analysis for the OVSIF 30 percent design. The results of the infiltration tests and groundwater model calibration for selected facility footprints indicated a variable infiltration rate of 5.60 to 16.20 inches per hour. This variable infiltration rate incorporates a combined factor of safety of 0.5 for heterogeneity (0.75), test method and potential long-term clogging Various configurations were evaluated at both steady and variable infiltration rates, as described below. These parameters were evaluated for a range of service areas to determine the most cost effective combination of treatment options. The infiltration facility was evaluated either as a combined water quality facility (infiltration rates limited to 3 inches per hour) or as a flow control only (infiltration rates based on geotechnical evaluation) with a separate water quality vault. The maximum infiltration vault dimension that could be accommodated on the site was determined to be approximately 50 feet wide by 350 feet long. UIC wells were considered as an optional expansion to the facility configurations for the vault to expedite the rate at which treated runoff would reach outwash soils that have the potential for higher infiltration rates. However, due to the depth of the facility caused by the upstream connection to the existing conveyance main and the elevation drop required for the water quality components, the outwash soils were determined to be located approximately two to four feet below the bottom of the vault. Therefore, the need for UIC wells was diminished. In addition, if UIC wells were implemented, they would extend into the outwash layer and within several feet of the seasonal high groundwater level, with the potential for groundwater mounding into the UIC wells. When the groundwater mound reaches the UIC wells, the advantage of the higher horizontal infiltration rate into the outwash is lost. The use of UIC wells beneath the OVSIF was determined not to be a viable infiltration alternative. ---PAGE BREAK--- Section 2—Design Criteria Continued A l t e r n a t i v e s A n a l y s i s 7 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak The following is a summary of the infiltration rates and other parameters evaluated. Water Quality Infiltration Rate (3 inches per hour) For these facility configurations (FC), the OVSIF was evaluated as a water quality treatment facility at which runoff would be treated by a pretreatment unit prior to flowing into the OVSIF, where basic treatment would be provided by in-situ or engineered soils. With this configuration, the depth of the facility and infiltration rate is limited to 6 feet of ponding depth and 3 inches per hour, based on the 2012 Ecology Manual criteria. The facility configurations were evaluated based on various infiltration criteria: 99.1 percent infiltration (FC 1A); 100 percent infiltration (FC 1B); and meeting Point of Compliance for the target service area through duration analysis at approximately 99.95 percent infiltration (FC 1C). The Point of Compliance scenario was developed as the preferred method of analysis for the subsequent scenarios, as it maximizes the available service area to the facility while adhering to Ecology’s flow control criteria. Constant Infiltration Rate (7.5 inches per hour) A constant infiltration rate of 7.5 inches per hour was used to evaluate sizing of the flow control infiltration facility, based on initial infiltration estimates from the geotechnical team (AMEC) prior to the calibration of the groundwater modeling. The OVSIF was evaluated as a flow control facility with maximum ponding depths of 7 and 18 feet. The service areas were determined based on increasing the dimensions of the facility. A facility that is 310 feet by 32 feet by 7 feet deep and a facility that is 350 feet by 34 feet by 18 feet deep can each infiltrate a 38-acre and 70-acre service area (FC 2 and FC 3A), respectively. Further evaluation of service area was conducted based on evaluation of facility dimensions: a facility that is 350 feet by 34 feet by 18 feet deep and a facility that is 350 feet by 50 feet by 18 feet deep can each infiltrate a 70-acre and 104.9-acre service area (FC 3A and FC respectively. The 350 feet by 50 feet by 18 feet deep facility is the largest footprint that was determined to be feasible to fit within the Plaza Street configuration. Although this facility has the highest potential service area, the cost per service area was higher than the next smallest facility with a 94-acre service area at 7.50 inches per hour infiltration rate. The facility modeling for these facilities was based on the cast-in-place single cell vaults, which do not have inner walls and that maximize the available infiltration area. Variable Infiltration Rate (5.60-15.05 inches per hour) The calibrated infiltration modeling conducted by AMEC (geotechnical engineering consultants) produced results of a variable infiltration rate of 5.60 to 15.05 inches per hour in the location of the proposed infiltration vault for a targeted vault footprint of 345 feet by 45 feet. The rate of infiltration primarily increases based on the amount of head in the vault for the ponding depths up to 18 feet. Various dimensions and service areas were evaluated utilizing this rate; a 320 feet by 34 feet by 18 feet deep facility and a 345 feet by 34 feet by 18 ---PAGE BREAK--- Section 2—Design Criteria Continued A l t e r n a t i v e s A n a l y s i s 8 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak feet deep facility can infiltrate a service area of 70 acres and 75 acres (FC 3C and FC 3D), respectively. These facilities were evaluated using multi-cell units, which do contain an inner wall, but were determined to be more cost-effective than single-cell units. Although the infiltration facility is sized for the corresponding service area, the water quality treatment unit size is based on a 94-acre water quality flow rate (3.0 cfs) to maximize the treatment potential for a future scenario, per the 2012 Regional Alternatives Report with the flow control Point of Compliance of the South Detention Vault. Variable Infiltration Rate (6.00-16.20 inches per hour) The infiltration facility was further evaluated based on the 345 feet by 34 feet by 18 feet deep configuration (FC 3D); the F-table developed by Otak for this facility was sent to AMEC for evaluation in their infiltration models. This facility configuration resulted in a higher infiltration rate due to the long, narrow facility dimensions. The higher infiltration rate was utilized in reevaluating the size of the infiltration facility. The results of this analysis was a facility dimension of 335 feet by 34 feet by 18 feet deep, utilizing a multi-cell precast vault (FC 3E). ---PAGE BREAK--- Section 3—Treatment Alternatives A l t e r n a t i v e s A n a l y s i s 9 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak Pretreatment and basic treatment options were considered in the configuration of the treatment train for the OVSIF. A pretreatment facility is included in all the facility configuration alternatives described in this section. Pretreatment is required per the 2005 and 2012 Ecology Manuals upstream of infiltration facilities. In all scenarios the water quality flow rate was used to size the water quality facility, based on the corresponding facility service area. The basic treatment component can be either a separate water quality vault upstream of the infiltration vault or water quality incorporated into the infiltration vault. Pretreatment technology is not required upstream of a basic treatment technology; however, it is recommended for long-term performance and reduction of maintenance costs. Because most stand-alone pretreatment units are designed for ease of maintenance access, a pretreatment technology is recommended upstream of the OVSIF; therefore, it is included in the cost summaries. Pretreatment All units considered for pretreatment have General Use Level Designation (GULD) from Ecology. The pretreatment alternatives initially considered were a presettling vault, the Defender and Vortech units. The presettling vault requires a large (150 feet by 50 feet) footprint, which exceeds the area available within the proposed Plaza Street upstream of the infiltration vault. Similarly, the Vortech unit has limitations for use due to site constraints. Per communications with the manufacturer (Contech), the Continuous Deflective Separation (CDS) unit was recommended instead of the Vortech unit due to the depth of the facility. The Vortech unit requires three access ports, while the CDS can be installed with a single manhole riser; reducing the facility cost for the estimated depth of this facility. Incorporated Treatment Water quality treatment incorporated within the infiltration vault could provide treatment within in-situ soils beneath the vault if the site suitability requirements are met by testing the cation exchange and organic content of these soils. Otherwise, treatment within the infiltration vault can be provided by adding an amended soil layer consisting of engineered soils meeting the site suitability soil requirement of the in-situ soils with a minimum 18-inch depth (2012 Ecology Manual, Volume III, Section 3.3.7). The use of amended or in-situ soils to provide a basic level of stormwater treatment was also evaluated as an alternative for the OVSIF. Based on the Soil Suitability Criteria (SSC) outlined in Volume III of the 2012 Ecology Manual, in-situ soils can be used to provide basic stormwater treatment if the required Cation Exchange Capacity (CEC) 5 milliequivalents CEC/100 g dry soil) and Organic Content (OC) (minimum 1.0-percent) criteria are met. However, if the in-situ soils ---PAGE BREAK--- Section 3—Treatment Alternatives Continued A l t e r n a t i v e s A n a l y s i s 10 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak do not meet the CEC and OC requirements, engineered soils may be used to meet the basic treatment design criteria (2012 Ecology Manual, Volume III, SSC-6, pg 3-85). The sizing criteria for the infiltration vault differs for combined water quality and flow control or flow control only infiltration facilities. According to the 2005 and 2012 Ecology Manuals, a flow control facility does not need to adhere to a maximum drawdown time. However, a water quality treatment infiltration facility must be sized to infiltrate all flows in 48 hours. The 2005 and 2012 Ecology Manuals differ in maximum infiltration rates. The 2005 Ecology Manual allowed short-term and long-term infiltration rates for water quality treatment of 2.0 and 2.4 inches per hour, respectively (Volume III, pg. 3-83), while the 2012 Ecology Manual allows measured and design water quality treatment infiltration rates of 3.0 and 9 inches per hour, respectively (Vol. III, pg. 3-84). Both documents contain additional site specific criteria regarding the use of these infiltration rates. An alternative was developed to size the OVSIF as a combined water quality facility, where the depth of water in the facility is limited to six feet to meet Ecology's requirement for infiltration in a water quality facility. Except for a presettling vault, most of the separate water quality facilities sizing are based on the design flow rate to the facility rather than a design volume. The time-series developed by NHC was used in the Western Washington Hydrology Model 4 (WWHM4) to determine the treatment flow rates and volume of infiltration at various footprint sizes; infiltration rates used for the analysis were 3 inches per hour for water quality facility and 7.5 inches per hour for flow control facility. A 0.9 reduction factor was incorporated in the model to account for the structural footer that may reduce the amount of flow that can be effectively infiltrated by the facility footprint. An F-table with a more accurate area of infiltration and internal storage volume, representing the estimated footing and internal wall impacts, was developed for the selected facility footprints evaluated with a variable infiltration rate, once this data became available through the design process. The services areas initially targeted for the OVSIF were 70 acres and 94 acres respectively. The service area for the infiltration vault as a water quality treatment facility (3.0 inches per hour infiltration rate per 2012 Ecology Manual) was evaluated based on three levels of infiltration (Facility Configurations 1A, 1B, and 1C), as identified in Table 2. These facility configurations are based on a the maximum allowable infiltration facility footprint with a service area of either 70 acres, infiltrating 100 percent of the runoff volume from the service area (31.6 acres), or meeting Point of Compliance (approximately 99.96 percent infiltration) for the total runoff volume (38.0 acres). A Point of Compliance analysis was used to determine the infiltration vault footprint for the other flow control facility configurations detailed in Table 2. ---PAGE BREAK--- Section 3—Treatment Alternatives Continued A l t e r n a t i v e s A n a l y s i s 11 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak The 3.0-inches-per-hour infiltration rate (with a 0.9 reduction factor) matches the infiltration rate estimated in the 2012 Regional Alternatives Analysis. This rate also matches the long- term infiltration rate recommendation in the 2012 Groundwater Mounding Report. Additionally, for infiltration facilities used for treatment purposes, the 2005 and 2012 Ecology Manuals allow design (long-term) infiltration rates up to 3.0 inches per hour. Because the OVSIF will have a water quality vault placed upstream of the facility; the facility can be used as a flow control facility and can utilize the higher infiltration rates (5.60 to 16.2 inches per hour). Separate Treatment Ecology approval for new stormwater technologies includes General Use Level Designation (GULD) and Conditional Use Level Designation (CULD). Products with CULD have demonstrated some performance, but require additional analysis before they are approved for widespread, general use. Both GULD and CULD treatment options were considered for basic treatment, as the use of current CULD treatment options could possibly result in considerable cost savings. In addition, construction of the facility will not be taking place in the immediate future, during which time the CULD may be upgraded to a GULD status. StormFilter 27-inch cartridges were considered filled with either ZPG (GULD) or Perlite (CULD) approved media. StormFilter cartridges (27-inch) filled with perlite media (22.5 gpm/cartridge) can handle much higher flow rates than those filled with ZPG media (11.3 gpm/cartridge); therefore, more cartridges and a larger vault is required with GULD approved (ZPG) media (Table Another CULD treatment technology considered was the Contech Jellyfish system. Table 1 shows the size requirements based on the Ecology sizing requirements, vault service area, and corresponding design flow rates for the 70 and 75 acres water quality treatment area. Treatment sizing for the other Facility Configurations are included in Appendix A. Treatment Alternatives Table 1 outlines the various treatment alternatives, sizes, and Ecology approval level (CULD or GULD) for each treatment type; Appendix D contains manufacturer schematics for some of these treatment options. The in-situ compliance with the soil suitability requirements will be evaluated with proposed geotechnical investigations for this project. Conceptual level costs are also included. Based on this analysis, and the City’s experience with Contech products, the CDS was selected for pretreatment and StormFilter ZPG for treatment. ---PAGE BREAK--- Section 3—Treatment Alternatives A l t e r n a t i v e s A n a l y s i s 12 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak Table 1—Facility Option Summary Treatment Level Service Area with Moderate LID (Acres) Stormwater Treatment Alternatives - Pretreatment or Basic Treatment Flowrate (cfs) Unit Type No. of Units Required Ecology Sizing Criteria Size/Model Approval Level Unit Price Installed Pretreatment 70.0 2.3 Defender 1.0 Max. Unit Flowrate, 4.1 cfs 6 ft DIA GULD1 $16,000 $28,800 94.0 3.0 Defender 1.0 Max. Unit Flowrate, 4.1 cfs 6 ft DIA GULD1 $16,000 $28,800 70.0 2.3 CDS 1.0 Max. Unit Flowrate, 3.0 cfs 6 ft DIA / Model CDS3030 GULD1 $28,500 $51,300 94.0 3.0 CDS 1.0 Max. Unit Flowrate, 3.0 cfs 6 ft DIA / Model CDS3030 GULD1 $28,500 $51,300 Basic 70.0 2.3 StormFilter 27" Cartridges (Perlite Media) 45 cartridges 22.5 gpm/cartridge 8'x20' Vault CULD2 $120,695 $217,251 94.0 3 StormFilter 27" Cartridges (Perlite Media) 60 cartridges 22.5 gpm/cartridge 8'x24' Vault CULD2 $185,000 $333,000 70.0 2.3 StormFilter 27" Cartridges (Perlite Media) 45 cartridges 22.5 gpm/cartridge 8'x20' Vault CULD2 $120,695 $217,251 94.0 3.0 StormFilter 27" Cartridges (Perlite Media) 60 cartridges 22.5 gpm/cartridge 8'x24' Vault CULD2 $185,000 $333,000 70.0 2.3 Jellyfish 54" Cartridges 12/3 cartidges4 80 gpm/cartridge 10 ft DIA / Model JF10-12-3 CULD2 $95,478 $171,860 94.0 3.0 Jellyfish 54" Cartridges 15/4 cartidges4 80 gpm/cartridge 10 ft DIA / Model JF10-15-4 CULD2 $117,923 $212,262 94.0 In-Situ or Engineered Soils5 1.0 CEC and OC requirements 350' x 50' Vault N/A $25,000 1GULD - General Use Level Designation (WA DOE Emerging Technologies website) 2CULD - Conditional Use Level Designation (WA DOE Emerging Technologies website) 3PreSettling Vault exceeds available footprint at site 4Fourteen Hi-Flo Cartridges and four Draindown Cartridges required 5In-Situ or Engineered Soils in OVSIF vault provide basic treatment and meet the Ecology Soil Suitability Criteria (Vol. III, Section 3.3.7 and Vol. V, Section 7.4) ---PAGE BREAK--- Section 4—Flow Control Alternatives A l t e r n a t i v e s A n a l y s i s 13 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak Several facility configurations (FC) for the infiltration vault were analyzed to provide stormwater flow control. With the option of water quality treatment provided upstream of the infiltration vault, there is not a limitation on the maximum infiltration rate the in-situ soils can provide. The flow control facilities were sized based on meeting flow duration matching between 50 percent of the 2-year event through the 50-year storm event at the Point of Compliance. Through the 2012 Groundwater Mounding Report, a preliminary variable infiltration rate was developed for the OVSIF. The peak and average infiltration rates over the 60-hour hydrograph were 9.0 inches per hour and 5.67 inches per hour, respectively. The 2012 Groundwater Mounding Report also observed that the infiltration rate dropped to 2.45 inches per hour towards the end of a 60-hour inflow time-series, representing approximately a peak 50-year storm event. Based on initial infiltration analysis from the September 2013 infiltration test and review of the 2012 Groundwater Mounding Report, a conservative infiltration rate of 7.5 inches per hour was used (Table This conservative infiltration rate was used to determine the required facility dimensions for facility configurations with 7-foot and 18-foot depths (FC 2, 3A, 4A, 5A, 6) (Table To improve upon the quality of the soil infiltration assumptions, AMEC conducted additional geotechnical investigation at the site, including new monitoring wells and infiltration tests. Once the results of the infiltration testing were obtained from AMEC, a variable infiltration rate of 5.60 to 15.05 inches/hour was used for facility sizing. Because the infiltration rates increased with head, the 18-foot-deep facility configuration was utilized to maximize the available infiltration rate. The facility dimensions (length and width) were varied, with the constant depth (18-foot depth) based on contributing service area. A service area of 70 acres and 104.9 acres required a facility size of 300 feet by 34 feet by 18 feet deep; and 310 feet by 44 feet by 18 feet deep, respectively (facility configuration [FC] 3B and As the street configuration with 36 feet of vehicle areas was adopted, and based on the results of initial modeling, a footprint size of approximately 345 feet by 34 feet by 18 feet for an approximate 75-acre service area was targeted. The proposed infiltration configuration was given to AMEC to rerun the infiltration analysis. Because the facility is long and narrow, the revised infiltration rates were higher (6.00-16.20 inches/hour). The higher infiltration rates allowed for a narrower facility footprint, resulting in a preferred facility configuration of 335 feet by 34 feet by 18 feet deep (FC 3E). To utilize the infiltration rates available with increased head, the infiltration facility will be allowed to have a tailwater condition through the water quality vault, which will house the proposed StormFilter ZPG units. This tailwater condition will be present only when the stage in the vault is greater than 7 feet; the expected frequency and duration of this ---PAGE BREAK--- Section 4—Flow Control Alternatives Continued A l t e r n a t i v e s A n a l y s i s 14 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak occurrence is expected to be fairly rare and will be investigated in the next phase of the design. According to discussions with the manufacturer, the StormFilter is designed to handle a period of saturation, but must be allowed to completely dry out for approximately a week or more; however, drying time is highly dependent on the surrounding air temperature. ---PAGE BREAK--- Section 5—Cost Analysis A l t e r n a t i v e s A n a l y s i s 15 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak The OVSIF will tie into the existing stormwater system along 152nd Avenue NE, which is located 15 feet below ground. Because this system is deep, the treatment and infiltration vault costs include an increased cost due to more stringent structural requirements, additional access manholes depth, and required excavation. The feasibility of Underground Injection Control (UIC) wells versus infiltration directly through the vault bottom was initially evaluated (Exhibits 4 and The cost of installation of each UIC well is approximately $3,000 per well, which excludes the underdrain manifolds and additional access risers. In comparison to over-excavation to the depth of the outwash soils and replacement with drainage rock at an equivalent cost, approximately ten UIC wells could be installed. However, UIC wells were eliminated from further consideration based on the minimal depth of the facility to the lower outwash soils and the shallow groundwater depth below the facility. A cost matrix was developed to analyze the most effective pretreatment, water quality, and structural vault combinations with consideration for constant and variable infiltration rates. Detail cost sheets are located in Appendix C and show a detail summary of the cost estimates in Table 2. Cost estimates for pretreatment and water quality treatment technologies were obtained from the manufacturer, based on the water quality flow rate for each service area. For example, a 70-acre and 94-acre service area each have a water quality flow rate of 2.26 cfs and 3.00 cfs, respectively. These water quality flow rates were obtained through analysis in WWHM. The preferred pretreatment technology utilized in the detailed cost estimate was the CDS unit, because the City is most familiar with this technology. This unit was recommended by the manufacturer of their General Use Level Designation (GULD) option for ease of maintenance. The selected water quality treatment technology was the StormFilter canisters with ZPG media, as this media type is currently approved for general use (GULD), and the City has experience with this product. Four structural options were analyzed for the infiltration vault which include cast in place and precast single cell and multi cell units. Cast-in-place units can be more cost-effective, while precast units generally take less time to construct. Single cell units offer a larger infiltration area; however, they are more expensive than multi-cell units. The preferred vault structure is the precast multi-cell unit, since it is more cost-effective and easiest to construct when compared to a single span or cast-in-place structure. Property cost was estimated at $900,000 by the City. That cost includes temporary construction permit within and around the facility footprint. It also includes maintenance and inspection access by the City from the time the facility is constructed until such time as ---PAGE BREAK--- Section 5—Cost Analysis Continued A l t e r n a t i v e s A n a l y s i s 16 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak the facility is turned over to the City. It is anticipated that the entire facility will be located within future right-of-way that will be dedicated to the City near the time of opening of the new light rail station. That property cost also includes costs for permanent underground easements limiting construction of new buildings near the vault at depths that impede groundwater infiltration and mounding near the vault. Annual maintenance costs were calculated based on maintaining the infiltration vault and replacing the media in the StormFilter canisters. Maintenance activities in the vault may consist of collecting and removing sediment and solids from the bottom of the vault so that the vault infiltration rates remain optimal. The items highlighted in blue in Table 2 show the selected parameters for which the total facility cost was calculated (listed in second column from the right). The total cost per service area was calculated by dividing the total cost of the facility by the service area. For the preferred facility configuration (FC 3E), the infiltration vault is sized for a 75-acre infiltration area; however, the pretreatment and water quality facilities are sized for a 94-acre water quality flow rate (3.0 cfs) to allow for a large water quality service area in the future. This resulted in an overall cost of $7,331,000 for the preferred facility configuration (FC 3E). ---PAGE BREAK--- POC Area Summary Defender1 CDS1,7 StormFilter 27" Cartridges (Perlite Media)2 StormFilter 27" Cartridges (ZPG Media)1 Jellyfish2 Engineered Soils3 Cast-In-Place (Multi- cell)8,9,10 Cast-In-Place (Single Cell)9,10 PreCast (Multi-Cell Vault)9,10 PreCast (Single Cell - Arched Units)9,10 Property11 Annual Maintainence Cost Facility Configuration 1A 70.0 99.1% below flow control POC 350'x50' 6' 2.26 3.00 $28,800 $51,300 N/A N/A N/A $25,000 $2,783,500 $2,585,000 $2,280,000 $2,705,800 $900,000 $36,000 $6,787,000 $97,000 Facility Configuration 1B 31.6 Meets flow control POC (100% Infiltration) 350'x50' 6' 1.02 3.00 $28,800 $18,900 N/A N/A N/A $25,000 $2,783,500 $2,585,000 $2,280,000 $2,705,800 $900,000 $36,000 $6,755,000 $213,800 Facility Configuration 1C 38.0 Meets flow control POC (99.95% Infiltration) 350'x50' 6' 1.23 3.00 $28,800 $27,400 N/A N/A N/A $25,000 $2,783,500 $2,585,000 $2,280,000 $2,705,800 $900,000 $36,000 $6,763,000 $178,000 Facility Configuration 2 38.0 Meets flow control POC (99.94% 310'x32' 7' 1.23 7.50 $28,800 $27,400 $119,000 $228,400 $86,100 N/A $2,075,700 $1,947,600 $1,599,100 $1,903,000 $900,000 $23,000 $5,829,000 $153,400 Table 2--Facility Comparison - Cost Matrix Facility Configuration Pretreatment Infiltration Vault4 Infiltration Rate (in/hr)12 WQ Flowrate (cfs) Water Quality Service Area with Moderate LID (acres)5 Cost per Service Area Total6 Property & Maintainence Dimensions Depth (ft) 2 Infiltration) Facility Configuration 3A 70.0 Meets flow control POC (99.96% Infiltration) 350'x34' 18' 2.26 7.50 $28,800 $51,300 $217,300 $423,200 $171,900 N/A $2,746,800 $3,016,300 $2,475,600 $2,998,000 $900,000 $36,000 $8,316,000 $118,800 Facility Configuration 3B 70.0 Meets flow control POC (99.96% Infiltration) 300'x34' 18' 2.26 Variable (5.60 - 15.05 in/hr) $28,800 $51,300 $217,300 $423,200 $171,900 N/A $2,631,700 $900,000 $34,000 $7,487,000 $107,000 Facility Configuration 3C 70.0 Meets flow control POC (99.96% Infiltration) 320'x34' 18' 2.26/ 3.00* Variable (5.60 - 15.05 in/hr) $28,800 $51,300 $296,100 $543,000 $212,300 N/A $2,291,600 $900,000 $42,000 $7,131,000 $101,900 Facility Configuration 3D 75.0 Meets flow control POC (99.96% Infiltration) 345'x34' 18' 2.44/ 3.00* Variable (5.60 - 15.05 in/hr) $28,800 $51,300 $296,100 $543,000 $212,300 N/A $2,446,300 $900,000 $43,000 $7,476,000 $99,700 Facility Configuration 3E 75.0 Meets flow control POC (99.96% Infiltration) 335'x34' 18' 2.44/ 3.00* Variable (6.00 - 16.20 in/hr) $28,800 $51,300 $296,100 $543,000 $212,300 N/A $2,383,600 $900,000 $43,000 $7,331,000 $97,800 Facility Configuration 4A 70.0 Meets flow control POC (99.96% Infiltration) 270'x44' 18' 2.26 7.50 $28,800 $51,300 $217,300 $423,200 $171,900 N/A $2,640,500 $2,761,000 $2,629,500 $2,929,300 $900,000 $36,000 $7,743,000 $110,700 Facility Configuration 70 0 Meets flow control POC (99 96% 230' 44' 18' 2 26 Variable (5.60 - $28 800 $51 300 $217 300 $423 200 $171 900 N/A $2 398 500 $900 000 $34 000 $6 967 000 $99 600 y g 4B 70.0 POC (99.96% Infiltration) 230'x44' 18' 2.26 ( 15.05 in/hr) $28,800 $51,300 $217,300 $423,200 $171,900 N/A $2,398,500 $900,000 $34,000 $6,967,000 $99,600 Facility Configuration 5A 94.0 Meets flow control POC (99.96% Infiltration) 315'x50' 18' 3.00 7.50 $28,800 $51,300 $296,100 $543,000 $212,300 N/A $3,071,000 $3,141,300 $2,935,300 $3,278,900 $900,000 $48,000 $7,915,000 $84,300 Facility Configuration 5B 94.0 Meets flow control POC (99.96% Infiltration) 310'x44' 18' 3.00 Variable (5.60 - 15.05 in/hr) $28,800 $51,300 $296,100 $543,000 $212,300 N/A $3,123,600 $900,000 $45,000 $7,814,000 $83,200 Facility Configuration 6 104.9 Meets flow control POC (99.96% Infiltration) 350'x50' 18' 3.35 7.50 $28,800 $57,900 $318,800 $619,900 $222,500 N/A $3,386,400 $3,464,600 $3,235,600 $3,617,400 $900,000 $52,000 $9,663,000 $92,200 (blue highlighted items are used in calculation of total cost for each configuration) 1GULD - General Use Level Designation 2CULD - Conditional Use Level Designation 3Engineered Soils used in Infiltration Vault for treatment - cost includes 18" of amended soils. Cost for additional gravel backfill for drains, excavation and vault depth are included in the total cost. 4Infiltration Vault costs include vault structural cost for concrete vault, footing-slab foundation, vault access, structural excavation and gravel backfill for walls. Facility Configuration 1 includes costs for Engineered Soils and gravel backfill for drains. Additional vault structural costs to meet seismic loading has not been evaluated. 6Total includes Ancillary Items, Mobilization, Tax, Engineering, Management, Permitting, and Property costs. Maintenance costs are not included. 7CDS unit used in cost determination, since the City of Redmond is familiar with the operation and maintainence of this unit. 11Property cost includes a 10 year lease of $25,000 SF easement and a one year construction easement for an additional 55,000 SF around the vault. Final easement cost will be based on selected vault footprint at 30% design. 12Infiltration rates are shown for the OVSIF as a water quality treatment vault (3.0 in/hr), as a flow control facility with a constant infiltration rate (7.5 in/hr), and as a flow control facility with a variable infiltration rate. The infiltration rate for facility 3E is optimized based on the vault dimensions. *Water quality flowrate for Phase 3 and Phase 4 service areas shown, per Phase 4 of the Regional Facilities Plan a service area of 94 acres is planned (3.00 cfs). 5Service area based on Phase 3 of Overlake Village Regional Stormwater Plan with infiltration vault providing flow control for peak flows and duration matching upto the 50-yr storm event at existing forested conditions using WWHM. 8Facility Configurations 3 through 6 include infiltration vault option of hollow-core top slab. At listed depth, hollow core is limited to maximum cover of approximately 11ft; vault requires 2 center walls or columns with additional footing slabs that decrease vault storage volume and infiltration area at bottom of vault. 9Water depth of 18ft is above depth of water quality vault. A float valve is recommended under these scenarios to prevent flooding of water quality structure at storage depths above cartridge height. Additional storage depth within infiltration depth allows overflow to 152nd Avenue stormwater trunk to optimize vault performance. 10Precast hollow-core units and precast 3-sided cell units require interior walls with footings within vault footprint. The interior slab footing decreases the available surface area for infiltration by approximately 20%. The service area is based on a slab reduction of approximately A precast arch unit has a decreased storage area under the 18ft depth configurations due to the curvature of the unit. The facility for hollow-core, precase 3-sided units, and tall precast arch units will need to be increased to meet estimated service area goals. The specific volume adjustment for these units to the target service area will be evaluated for the selected preferred facility configuration with the finalized ground-water mounding analysis. K:\project\31400\31470B\Data\Cost Estimates\Final Alternatives Analysis\ 13_1217_final_Alt_Analysis_CostEst.xlsx Table 4 Otak, Inc. Printed: 12/17/2013 ---PAGE BREAK--- Section 5—Cost Analysis Continued A l t e r n a t i v e s A n a l y s i s 18 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak This Page Intentionally Left Blank ---PAGE BREAK--- Section 6—Conclusions and Recommendations A l t e r n a t i v e s A n a l y s i s 19 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak The OVSIF will be the uppermost regional facility within the Overlake Village Basin (see Figure The targeted design volume of the OVSIF, per the 2012 Regional Alternatives Analysis, is 50 percent of the runoff from the R-2 subbasins, with a moderate level of dispersed LID accounting for approximately 46 percent of the runoff volume from the R-2 subbasins. The remaining 50 percent of the runoff from the R-2 subbasins, also including moderate LID, will bypass towards the future Central Infiltration Facility. The flow splitter upstream of the OVSIF will direct the targeted runoff flow to the facility, while bypassing the remaining flow through the existing conveyance system within 152nd Ave NE. To prevent higher mass loading of sediment and pollutants to the OVSIF than would generally be attributed to a design flow from the targeted service area, the initial storm runoff flows through the peak water quality flow for the R-2 subbasins will be split proportionally to the OVSIF and to the bypass flow sent by the flow splitter. Based on the estimated total facility cost, the most cost-effective OVSIF configuration to meet the water quality and flow control parameters of this project, as defined in the 2012 Regional Alternatives Analysis, was determined to be water quality treatment provided in a separate vault upstream of the infiltration vault. Facility Configurations FC 1C and FC 2 show this comparison (Table 2) at comparable service areas with a point-of-compliance duration matching. According to the duration matching analysis simulation run in WWHM, the facility configuration proposed for Facility 1A (350 feet by 50 feet by 6 feet) does not pass the point of compliance duration test using the water quality infiltration rate (3.0 inches per hour) for a 70 acre service area. However, facility configuration 3C (320 feet by 34 feet by 18 feet) does meet point of compliance with a smaller facility footprint and a variable infiltration rate for the equivalent (70 acre) service area. The soils underneath the proposed facility have been tested to determine if they meet Ecology site suitability requirements for water quality treatment. The soils did not meet the required Cation Exchange Capacity or Organic Content values based on the Ecology thresholds of 5.0 meq/100g and 1 percent, respectively, at an 18-inch depth. However, the treatment capacity of the existing soils could meet treatment requirements over a larger soil depth than Ecology’s 18-inch threshold. The used of engineered soils in FC 1 was the preferred combined water quality and infiltration vault option, rather than reliance on the in- situ treatment capacity. The engineered soil layer would protect the underlying soils from clogging over time, and would allow for a maintenance process of removing and replacing a top depth of the engineered soils. Removing accumulated sediment from the in-situ soils would likely be infeasible, as the clogging depth would be deeper than could be excavated within the vault without impacting the vault footings. Removal over time of any in-situ soils ---PAGE BREAK--- Section 6—Conclusions and Recommendations Continued A l t e r n a t i v e s A n a l y s i s 20 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak would also require a replacement layer of engineered soils to maintain design depth within the facility. The design of the engineered soil layer would follow the general design and maintenance guidelines for a large sand filter as described in the 2012 Ecology Manual. Maintenance of the engineered soils would be similar to the process described in the manual on Best Management Practices for Sand Filters (Volume V, Section 8.5). The maintenance cycle for sand filters can vary greatly based on pollutant loading. Removal of sediment from within the facility would require lowering a light-weight front-end loader or grader into the vault by crane, and lifting the sediment and old sand out with the crane. UIC wells were initially considered in the alternatives analysis as a potential cost savings for the project, as they could potentially limit the amount of over-excavation required by connecting to the higher horizontal conductivity of the underlying soils and thereby maximizing infiltration. Because the existing stormwater system is located approximately 15 feet below ground, the ability to utilize UIC wells is greatly reduced due to proximity to groundwater. Based on the findings in the 2012 Groundwater Mounding Report and evaluation of the depths at which the proposed OVSIF will be located, groundwater mounding may saturate the UIC zone and therefore decrease the UIC wells capacity to infiltrate. Based on this geotechnical information, further evaluation of the UIC well option was not pursued. The depth of the existing stormwater main along 152nd Avenue NE is approximately 15 feet below the existing ground elevation. With the additional elevation drop through the conveyance pipe to the OVSIF and the required drop across the water quality vaults, a pipe overflow connection by to 152nd Avenue is not feasible without running a parallel conveyance pipe approximately 450 feet south. An overflow system within the infiltration vault allows an optimum use of the vault storage depth. Several options were considered to handle flows to the vault that exceeded the infiltration capacity of the OVSIF. The options considered were: 1) Install a riser and conveyance stub at the south end of the vault for a future overflow connection after the existing buildings are removed from the site and the Plaza Street connection is completed. 2) Installation of a pump station and using an actuated valve and programmable logic control (PLC) system was also considered. The pump and PLC system add more complexity and expense to the operations of the infiltration system. The pump and PLC system would allow the infiltration vault to reach maximum ponding depth at higher flows within the 152nd Avenue flow splitter, prior to shutting-off flows to the OVSIF. ---PAGE BREAK--- Section 6—Conclusions and Recommendations Continued A l t e r n a t i v e s A n a l y s i s 21 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak 3) The preferred alternative uses a tall infiltration vault, such that the maximum ponding depth creates a tailwater condition within an upstream flow splitter. When maximum capacity is reached in the OVSIF, flow will be sent down the main stormwater trunk to the Central Infiltration Facility. Selection of the preferred OVSIF alternative and water quality configuration is the primary step in moving forward with development of the 30 percent design and performance specifications. The treatment through a separate water quality vault requires additional depth within the vertical profile of the system, but allows the infiltration vault to utilize the higher infiltration rates available within the in-situ soils without the water quality constraints of a maximum 3-inches-per-hour rate and 6-foot maximum ponding depth. With the upstream deep connection point to the existing stormwater trunk, the bottom of the infiltration vault shown in Exhibit 6 would be near the till and outwash soil interface elevation. By placing the bottom of the infiltration vault below the till soil elevation at approximately 310 foot elevation, the infiltration vault can connect directly to the higher infiltration rates available within the outwash soils. Through cost comparison of Facility Configurations 1C and 2 (see Table the uses of a separate upstream water quality vault and a smaller infiltration vault using higher allowable infiltration rates was determined to have a lower overall cost. The maximum footprint for the OVSIF has been determined to be 350 feet by 50 feet to fit within the proposed Plaza Street; however, based on the design variable infiltration rates per the infiltration modeling, an infiltration vault footprint of approximately 320 feet by 34 feet would meet the target service area of 70 acres, per the 2012 Regional Alternative Analysis. The proposed vault configuration for the 30 percent design is a 335 feet by 34 feet by 18 feet-deep vault, which provides a flow control and water quality treatment for a service area of approximately 75 acres, and at full build-out the facility provides water quality treatment for 94 acres and is optimized for infiltration flows above the water quality depth. The proposed pretreatment is a Contech CDS 5668. The proposed treatment facility is a Contech StormFilter vault with 119 ZPG, 27-inch cartridges, with a vault sized to accommodate up to 125 cartridges. The separate cartridge-style treatment facility has a defined monitoring and maintenance process. Removal of pollutants and replacement of cartridges could be done with surface equipment, including a vactor truck and a crew. Removal of sediment accumulation within the infiltration vault that would limit the infiltration into the in-situ soils will still need to be completed, but on a longer maintenance cycle than would be required for a combined treatment and flow control vault. The proposed vault will include a maintenance access to allow small equipment, such as a bobcat loader or scissor-lift to be lowered into the vault to assist with sediment removal and maintenance inspection. The preferred facility configuration (3E) alternative will be further evaluated in the 30 percent design report. ---PAGE BREAK--- Section 6—Conclusions and Recommendations Continued A l t e r n a t i v e s A n a l y s i s 22 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak This Page Intentionally Left Blank ---PAGE BREAK--- References A l t e r n a t i v e s A n a l y s i s 23 O v e r l a k e V i l l a g e S t a t i o n R e g i o n a l I n f i l t r a t i o n F a c i l i t y otak References Ecology. 2005. Stormwater Management Manual for Western Washington. Washington State Department of Ecology. (2005 Ecology Manual) Ecology. 2012. Stormwater Management Manual for Western Washington. Washington State Department of Ecology. (2012 Ecology Manual) GeoEngineers, 2012. Groundwater Mounding Analysis – Overlake Village Stormwater Vaults. May 2012. (2012 Groundwater Mounding Report) Otak. 2010. Implementation Plan—Overlake Village Stormwater and Park Facilities Conceptual Design, by Otak, Inc. July 2012 (2010 Implementation Plan) Otak. 2012a. Draft - Overlake Village Regional Stormwater Facilities Plan. September 2012. (2012 Regional Facilities Plan) Otak. 2012b. Overlake Stormwater Alternatives Analysis, by Otak, Inc. December 2012. (2012 Regional Alternatives) Otak. 2013. Overlake Regional Stormwater Infiltration Facility Design and Performance Criteria technical memorandum. July 2, 2013. (2013 Regional Parameters and Performance Criteria) Redmond. 2012. City of Redmond Clearing, Grading and Stormwater Management Technical Notebook, effective February 2012. (2012 Technical Notebook) ---PAGE BREAK--- ---PAGE BREAK--- E x h i b i t s ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- A p p e n d i x A — T r e a t m e n t F a c i l i t y S i z i n g S u m m a r y ---PAGE BREAK--- ---PAGE BREAK--- K:\project\31400\31470B\Reports\Alternatives Analysis\FINAL Alternatives Analysis Report\Appendices\Appendix A\AppendixA_Table1.docx Treatment Facility Sizing Summary Flowrate (cfs) Unit Type No. of Units Required DOE Sizing Criteria Size/Model Approval Level Unit Price Installed 31.6 1.02 Defender 1 Max. Unit Flowrate, 4.1 cfs 6 ft DIA GULD1 $16,000 $28,800 38.0 1.23 Defender 1 Max. Unit Flowrate, 4.1 cfs 6 ft DIA GULD1 $16,000 $28,800 70.0 2.26 Defender 1 Max. Unit Flowrate, 4.1 cfs 6 ft DIA GULD1 $16,000 $28,800 94.0 3 Defender 1 Max. Unit Flowrate, 4.1 cfs 6 ft DIA GULD1 $16,000 $28,800 104.9 3.35 Defender 1 Max. Unit Flowrate, 4.1 cfs 6 ft DIA GULD1 $16,000 $28,800 31.6 1.02 CDS 1 Max. Unit Flowrate, 1.1 cfs 5 ft DIA / Model CDS2025 GULD1 $10,450 $18,810 38.0 1.23 CDS 1 Max. Unit Flowrate, 1.6 cfs 5 ft DIA / Model CDS2025 GULD1 $15,200 $27,360 70.0 2.26 CDS 1 Max. Unit Flowrate, 3.0 cfs 6 ft DIA / Model CDS3030 GULD1 $28,500 $51,300 94.0 3 CDS 1 Max. Unit Flowrate, 3.0 cfs 6 ft DIA / Model CDS3030 GULD1 $28,500 $51,300 104.9 3.35 CDS 1 Max. Unit Flowrate, 3.8 cfs 6 ft DIA / Model CDS3035 GULD1 $32,140 $57,852 38.0 1.23 StormFilter 27" Cartridges (Perlite Media) 25 cartridges 22.5 gpm/cartridge 8'x16' Vault CULD2 $66,071 $118,929 70.0 2.26 StormFilter 27" Cartridges (Perlite Media) 45 cartridges 22.5 gpm/cartridge 8'x20' Vault CULD2 $120,695 $217,251 94.0 3 StormFilter 27" Cartridges (Perlite Media) 60 cartridges 22.5 gpm/cartridge 8'x24' Vault CULD2 $185,000 $333,000 104.9 3.35 StormFilter 27" Cartridges (Perlite Media) 67 cartridges 22.5 gpm/cartridge 11'x29' Vault CULD2 $177,071 $318,729 38.0 1.23 StormFilter 27" Cartridges (ZPG Media) 49 cartridges 11.3 gpm/cartridge 8'x22' Vault GULD1 $126,875 $228,375 70.0 2.26 StormFilter 27" Cartridges (ZPG Media) 90 cartridges 11.3 gpm/cartridge 13'x38' Vault GULD1 $235,056 $423,102 94.0 3 StormFilter 27" Cartridges (ZPG Media) 119 cartridges 11.3 gpm/cartridge 13'x38' Vault GULD1 $301,667 $543,000 104.9 3.35 StormFilter 27" Cartridges (ZPG Media) 133 cartridges 11.3 gpm/cartridge 14' ConSpan GULD1 $344,375 $619,875 38.0 1.23 Jellyfish 54" Cartridges 6/2 cartidges4 80 gpm/cartridge 8 ft DIA / Model JF8- 6-2 CULD2 $75,000 $86,097 70.0 2.26 Jellyfish 54" Cartridges 12/3 cartidges4 80 gpm/cartridge 10 ft DIA / Model JF10- 12-3 CULD2 $95,478 $171,860 94.0 3 Jellyfish 54" Cartridges 15/4 cartidges4 80 gpm/cartridge 10 ft DIA / Model JF10- 15-4 CULD2 $117,923 $212,262 104.9 3.35 Jellyfish 54" Cartridges 17/4 cartidges4 80 gpm/cartridge 10 ft DIA / Model JF10- 17-4 CULD2 $123,577 $222,438 94.0 In-Situ or Engineered Soils5 1 CEC and OC requirements 350' x 50' Vault N/A $25,000 1GULD - General Use Level Designation (WA DOE Emerging Technologies website) 2CULD - Conditional Use Level Designation (WA DOE Emerging Technologies website) 3PreSettling Vault exceeds available footprint at site 414 Hi-Flo Cartridges and 4 Draindown Cartridges required 5In-Situ or Engineered Soils in OVSIF vault provide basic treatment and meet the WA DOE Soil Suitability Criteria (Vol. III, Section 3.3.7 and Vol. V, Section 7.4) Basic Pretreatment Treatment Level Phase 3 Service Area with Moderate LID (Acres) Stormwater Treatment Alternatives - Pretreatment or Basic Treatment ---PAGE BREAK--- ---PAGE BREAK--- A p p e n d i x B — M o d e l i n g O u t p u t ---PAGE BREAK--- ---PAGE BREAK--- STORMFILTER WATER QUALITY VAULT SIZING Stormfilter Sizing WATER QUALITY FLOW RATE Qwq = 3.00 CFS 1346 GPM (cfs * 448.8 gal/min/cfs) Description: 15-min Online WQ flow from WWHM3. STORMFILTER VAULT SIZING MINIMUM CARTRIDGES N = Qwq / Qc Qc = 11.3 Cartridges / GPM Description: 27" Cartridges N = 119 Cartridges VAULT SIZE Minimum vault size for 119 cartridges is a 11x36 Vault max cartridges per vault = 125 K:\project\31400\31470B\WaterRes\ 13_0910_StormfilterComparison.xlsx Otak, Inc. Printed: 12/12/2013 Page 1 of 1 ---PAGE BREAK--- STORMFILTER WATER QUALITY VAULT SIZING Stormfilter Sizing WATER QUALITY FLOW RATE Qwq = 2.26 CFS 1014 GPM (cfs * 448.8 gal/min/cfs) Description: 15-min Online WQ flow from WWHM3. STORMFILTER VAULT SIZING MINIMUM CARTRIDGES N = Qwq / Qc Qc = 11.3 Cartridges / GPM Description: 27" Cartridges N = 90 Cartridges VAULT SIZE Minimum vault size for 90 cartridges is a 11x36 Vault max cartridges per vault = 125 K:\project\31400\31470B\WaterRes\ 13_0910_StormfilterComparison.xlsx Otak, Inc. Printed: 12/12/2013 Page 1 of 1 ---PAGE BREAK--- WWHM Output – 345x34x18 Multi-Cell for 70 acres ---PAGE BREAK--- WWHM Output – 345x34x18 Multi-Cell for 75acres ---PAGE BREAK--- WWHM Output – 310x44x18 Multi-Cell for 94 acres ---PAGE BREAK--- ---PAGE BREAK--- A p p e n d i x C — S c e n a r i o P r e l i m i n a r y D e s i g n C o s t E s t i m a t e s ---PAGE BREAK--- ---PAGE BREAK--- PROJECT: Overlake Station Infiltration Facility BY: SR PROJECT ID: 31470B CHECK BY: CSC Facility Configuration 1C: 350'x50'x6' Station Infiltration Vault - Basic Treatment through engineered soils (3.0 in/hr infiltration rate) DATE: 12/17/2013 ITEM NO. ITEM QUANTITY UNIT UNIT PRICE AMOUNT Construction Elements 1 STRUCTURE EXCAVATION CL A INCLUDING HAUL 20,800 CY 20.00 $ 416,000 $ 2 350' x 50' CIP CONC INFILTRATION VAULT 1 LS 1,574,000.00 $ 1,574,000 $ 3 FLOW SPLITTER 1 LS 15,000.00 $ 15,000 $ 4 INFILTRATION VAULT ACCESS 1 LS 90,000.00 $ 90,000 $ 5 AMENDED SOIL (ENGINEERED SOILS FOR TREATMENT) 1,000 CY 25.00 $ 25,000 $ 6 GRAVEL BACKFILL FOR DRAIN 1,600 CY 30.00 $ 48,000 $ 7 GRAVEL BACKFILL FOR WALL & FOUNDATION 2,200 CY 30.00 $ 66,000 $ 8 GRAVEL BORROW 22,200 CY 23.00 $ 510,600 $ 9 CATCH BASIN TYPE 2 72 IN. DIAM. W/FLOW SPLITTER 1 EA 8,000.00 $ 8,000 $ 10 EXCAVATION CL A INCLUDING HAUL (1:1 SLOPES,3 SIDES) 12,800 CY 20.00 $ 256,000 $ 11 SHORING CLASS A (1 SIDE) 2,000 SF 55.00 $ 110,000 $ 12 BACKFLOW PREVENTION VALVE 1 EA 10,000.00 $ 10,000 $ 13 CONVEYANCE PIPE (18 in) 115 60.00 $ 6,900 $ 14 CONVEYANCE PIPE (24 in) 130 LF 70.00 $ 9,100 $ 15 CATCH BASIN TYPE 2 (54 in) 1 EA 3,500.00 $ 3,500 $ 16 PRETREATMENT (CDS) 1 EA 27,400.00 $ 27,400 $ Subtotal Construction Elements 3,175,500 $ Required Ancillary Items 12 EROSION, SEDIMENTATION CONTROL, SITE PREPARATION 1.5% 47,633 $ 13 MOBILIZATION 8% 254,040 $ Subtotal Ancillary 301,673 $ 3,477,173 $ Mobilization 14 CONTINGENCY 20% 695,435 $ Subtotal Construction + Ancillary + Mobilization 4,172,607 $ Tax/Engineering/Management/Permitting/Property 15 SALES TAX 9.5% 396,398 $ 16 ENGINEERING/LEGAL/ADMIN 15% 625,891 $ 17 CONSTRUCTION MANAGEMENT 15% 625,891 $ 18 PERMITTING 1% 41,726 $ 19 PROPERTY 900,000 $ Subtotal 2,589,906 $ Subtotal Construction + Ancillary + Mobilization + Tax/Engineering/Management/Permitting 6,762,513 $ 2013 Dollars Total Estimated Project Cost (Rounded) 6,763,000 $ Notes: 1. The above cost opinion is in 2013 dollars and does not include future escalation, financing, or O&M costs. 3. Estimate assumes that Site Demolition will be completed by others as part of the Sound Transit Station construction. 4. Excavation at 1:1 side slopes assumed for 3 sides, while shoring is assumed on 1 side. 5. If area is available for stockpiling excavated material, Embankment Compaction may be used instead of Gravel Borrow (item 6) at $3 per cubic yard 6. Permanent and construction easement not included in total. PRELIMINARY DESIGN COST ESTIMATE 2. The preliminary design cost opinion has been prepared for guidance in project evaluation from the information available at the time of preparation and for the assumptions stated. The final f E:\Otak\Projects\31470B\Data\Cost Estimates\Final Alternatives Analysis\13_1217_final_Alt_Analysis_CostEst.xlsx ---PAGE BREAK--- PROJECT: Overlake Station Infiltration Facility BY: SR PROJECT ID: 31470B CHECK BY: CSC Facility Configuration 2: 310'x32'x7' Station Infiltration Vault - Facility Configuration 2 - Basic Treatment through StormFilter Canisters (7.5 in/hr infiltration rate) DATE: 12/17/2013 ITEM NO. ITEM QUANTITY UNIT UNIT PRICE AMOUNT Construction Elements 1 STRUCTURE EXCAVATION CL A INCLUDING HAUL 12,800 CY 20.00 $ 256,000 $ 2 310' x 32' CIP SINGLE CELL CONC INFILTRATION VAULT 1 LS 1,210,600.00 $ 1,210,600 $ 3 FLOW SPLITTER 1 LS 15,000.00 $ 15,000 $ 4 INFILTRATION VAULT ACCESS 1 LS 90,000.00 $ 90,000 $ 5 GRAVEL BACKFILL FOR WALL & FOUNDATION 1,900 CY 30.00 $ 57,000 $ 6 GRAVEL BORROW 17,900 CY 23.00 $ 411,700 $ 7 CATCH BASIN TYPE 2 72 IN. DIAM. W/FLOW SPLITTER 1 EA 8,000.00 $ 8,000 $ 8 EXCAVATION CL A INCLUDING HAUL (1:1 SLOPES, 3 SIDES) 11,200 CY 20.00 $ 224,000 $ 9 SHORING OR EXTRA EXCAVATION CLASS A (1 SIDE) 2,000 SF 55.00 $ 110,000 $ 10 BACKFLOW PREVENTION VALVE 1 EA 10,000.00 $ 10,000 $ 11 CONVEYANCE PIPE (18 in) 75 LF 60.00 $ 4,500 $ 12 CONVEYANCE PIPE (24 in) 130 LF 70.00 $ 9,100 $ 13 CATCH BASIN TYPE 2 (54 in) 1 EA 3,500.00 $ 3,500 $ 14 CATCH BASIN TYPE 2 WITH WATER QUALITY FLOW SPLITTER (72 in) 1 EA $4,250.00 4,250 $ 15 PRETREATMENT (CDS) 1 EA 27,400.00 $ 27,400 $ 16 BASIC TREATMENT (CANISTERS WITH ZPG MEDIA, GULD) 1 EA 228,400.00 $ 228,400 $ Subtotal Construction Elements 2,669,450 $ Required Ancillary Items 12 EROSION, SEDIMENTATION CONTROL, SITE PREPARATION 1.5% 40,042 $ 13 MOBILIZATION 8% 213,556 $ Subtotal Ancillary 253,598 $ 2,923,048 $ 14 CONTINGENCY 20% 584,610 $ Subtotal Construction + Ancillary + Mobilization 3,507,657 $ Tax/Engineering/Management/Permitting/Property 15 SALES TAX 9.5% 333,227 $ 16 ENGINEERING/LEGAL/ADMIN 15% 526,149 $ 17 CONSTRUCTION MANAGEMENT 15% 526,149 $ 18 PERMITTING 1% 35,077 $ 19 PROPERTY 900,000 $ Subtotal 2,320,601 $ Subtotal Construction + Ancillary + Mobilization + Tax/Engineering/Management/Permitting 5,828,259 $ 2013 Dollars Total Estimated Project Cost (Rounded) 5,829,000 $ Notes: 1. The above cost opinion is in 2013 dollars and does not include future escalation, financing, or O&M costs. 3. Estimate assumes that Site Demolition will be completed by others as part of the Sound Transit Station construction. 4. Excavation at 1:1 side slopes assumed for 3 sides, while shoring is assumed on 1 side 5. If area is available for stockpiling excavated material, Embankment Compaction may be used instead of Gravel Borrow (item 6) at $3 per cubic yard 6. Construction and permanent easements not included in total. PRELIMINARY DESIGN COST ESTIMATE 2. The preliminary design cost opinion has been prepared for guidance in project evaluation from the information available at the time of preparation and for the assumptions stated. The final E:\Otak\Projects\31470B\Data\Cost Estimates\Final Alternatives Analysis\13_1217_final_Alt_Analysis_CostEst.xlsx ---PAGE BREAK--- PROJECT: Overlake Station Infiltration Facility BY: SR PROJECT ID: 31470B CHECK BY: CSC Facility Configuration 3: 350'x34'x18' Station Infiltration Vault - Facility Configuration 3A - Basic Treatment through StormFilter Canisters (7.5 in/hr infiltration rate) DATE: 12/17/2013 ITEM NO. ITEM QUANTITY UNIT UNIT PRICE AMOUNT Construction Elements 1 STRUCTURE EXCAVATION CL A INCLUDING HAUL 15,100 CY 20.00 $ 302,000 $ 2 350' x 34' CIP SINGLE CELL CONC INFILTRATION VAULT 1 LS 2,174,300.00 $ 2,174,300 $ 3 FLOW SPLITTER 1 LS 15,000.00 $ 15,000 $ 4 INFILTRATION VAULT ACCESS 1 LS 90,000.00 $ 90,000 $ 5 GRAVEL BACKFILL FOR WALL 3,000 CY 30.00 $ 90,000 $ 6 GRAVEL BORROW 20,500 CY 23.00 $ 471,500 $ 7 CATCH BASIN TYPE 2 72 IN. DIAM. W/FLOW SPLITTER 1 EA 8,000.00 $ 8,000 $ 8 EXCAVATION CL A INCLUDING HAUL (1:1 SLOPES, 3 SIDES) 12,500 CY 20.00 $ 250,000 $ 9 SHORING OR EXTRA EXCAVATION CLASS A (1 SIDE) 2,000 SF 55.00 $ 110,000 $ 10 BACK FLOW PREVENTION VALVE 1 EA 10,000.00 $ 10,000 $ 11 CONVEYANCE PIPE (18 in) 75 LF 60.00 $ 4,500 $ 12 CONVEYANCE PIPE (24 in) 130 LF 70.00 $ 9,100 $ 13 CATCH BASIN TYPE 2 (54 in) 1 EA 3,500.00 $ 3,500 $ 14 CATCH BASIN TYPE 2 WITH WATER QUALITY FLOW SPLITTER (72 in) 1 EA 4,250.00 $ 4,250 $ 15 PRETREATMENT (CDS) 1 EA 51,300.00 $ 51,300 $ 16 BASIC TREATMENT (CANISTERS WITH ZPG MEDIA, GULD) 1 EA 423,200.00 $ 423,200 $ Subtotal Construction Elements 4,016,650 $ Required Ancillary Items 12 EROSION, SEDIMENTATION CONTROL, SITE PREPARATION 1.5% 60,250 $ 13 MOBILIZATION 8% 321,332 $ Subtotal Ancillary 381,582 $ 4,398,232 $ 14 CONTINGENCY 20% 879,646 $ Subtotal Construction + Ancillary + Mobilization 5,277,878 $ Tax/Engineering/Management/Permitting/Property 15 SALES TAX 9.5% 501,398 $ 16 ENGINEERING/LEGAL/ADMIN 15% 791,682 $ 17 CONSTRUCTION MANAGEMENT 15% 791,682 $ 18 PERMITTING 1% 52,779 $ 19 PROPERTY 900,000 $ Subtotal 3,037,541 $ Subtotal Construction + Ancillary + Mobilization + Tax/Engineering/Management/Permitting 8,315,419 $ 2013 Dollars Total Estimated Project Cost (Rounded) 8,316,000 $ Notes: 1. The above cost opinion is in 2013 dollars and does not include future escalation, financing, or O&M costs. 3. Estimate assumes that Site Demolition will be completed by others as part of the Sound Transit Station construction. 4. Excavation at 1:1 side slopes assumed for 3 sides, while shoring is assumed on 1 side 5. If area is available for stockpiling excavated material, Embankment Compaction may be used instead of Gravel Borrow (item 6) at $3 per cubic yard 6. Construction and permanent easements not included in total. PRELIMINARY DESIGN COST ESTIMATE 2. The preliminary design cost opinion has been prepared for guidance in project evaluation from the information available at the time of preparation and for the assumptions stated. The final costs E:\Otak\Projects\31470B\Data\Cost Estimates\Final Alternatives Analysis\13_1217_final_Alt_Analysis_CostEst.xlsx ---PAGE BREAK--- PROJECT: Overlake Station Infiltration Facility BY: SR PROJECT ID: 31470B CHECK BY: CSC Facility Configuration 3: 300'x34'x18' Station Infiltration Vault - Facility Configuration 3B - Basic Treatment through StormFilter Canisters (Variable infiltration rate) DATE: 12/17/2013 ITEM NO. ITEM QUANTITY UNIT UNIT PRICE AMOUNT Construction Elements 1 STRUCTURE EXCAVATION CL A INCLUDING HAUL 13,000 CY 20.00 $ 260,000 $ 2 300' x 34' CIP SINGLE CELL CONC INFILTRATION VAULT 1 LS 1,863,700.00 $ 1,863,700 $ 3 FLOW SPLITTER 1 LS 15,000.00 $ 15,000 $ 4 INFILTRATION VAULT ACCESS 1 LS 90,000.00 $ 90,000 $ 5 GRAVEL BACKFILL FOR WALL 3,000 CY 30.00 $ 90,000 $ 6 GRAVEL BORROW 17,700 CY 23.00 $ 407,100 $ 7 CATCH BASIN TYPE 2 72 IN. DIAM. W/FLOW SPLITTER 1 EA 8,000.00 $ 8,000 $ 8 EXCAVATION CL A INCLUDING HAUL (1:1 SLOPES, 3 SIDES) 10,900 CY 20.00 $ 218,000 $ 9 SHORING OR EXTRA EXCAVATION CLASS A (1 SIDE) 2,000 SF 55.00 $ 110,000 $ 10 BACKFLOW PREVENTION VALVE 1 EA 10,000.00 $ 10,000 $ 11 CONVEYANCE PIPE (18 in) 75 LF 60.00 $ 4,500 $ 12 CONVEYANCE PIPE (24 in) 130 LF 70.00 $ 9,100 $ 13 CATCH BASIN TYPE 2 (54 in) 1 EA 3,500.00 $ 3,500 $ 14 CATCH BASIN TYPE 2 WITH WATER QUALITY FLOW SPLITTER (72 in) 1 EA 4,250.00 $ 4,250 $ 15 PRETREATMENT (CDS) 1 EA 51,300.00 $ 51,300 $ 16 BASIC TREATMENT (CANISTERS WITH ZPG MEDIA, GULD) 1 EA 423,200.00 $ 423,200 $ Subtotal Construction Elements 3,567,650 $ Required Ancillary Items 12 EROSION, SEDIMENTATION CONTROL, SITE PREPARATION 1.5% 53,515 $ 13 MOBILIZATION 8% 285,412 $ Subtotal Ancillary 338,927 $ 3,906,577 $ 14 CONTINGENCY 20% 781,315 $ Subtotal Construction + Ancillary + Mobilization 4,687,892 $ Tax/Engineering/Management/Permitting/Property 15 SALES TAX 9.5% 445,350 $ 16 ENGINEERING/LEGAL/ADMIN 15% 703,184 $ 17 CONSTRUCTION MANAGEMENT 15% 703,184 $ 18 PERMITTING 1% 46,879 $ 19 PROPERTY 900,000 $ Subtotal 2,798,596 $ Subtotal Construction + Ancillary + Mobilization + Tax/Engineering/Management/Permitting 7,486,488 $ 2013 Dollars Total Estimated Project Cost (Rounded) 7,487,000 $ Notes: 1. The above cost opinion is in 2013 dollars and does not include future escalation, financing, or O&M costs. 3. Estimate assumes that Site Demolition will be completed by others as part of the Sound Transit Station construction. 4. Excavation at 1:1 side slopes assumed for 3 sides, while shoring is assumed on 1 side 5. If area is available for stockpiling excavated material, Embankment Compaction may be used instead of Gravel Borrow (item 6) at $3 per cubic yard 6. Construction and permanent easements not included in total. PRELIMINARY DESIGN COST ESTIMATE 2. The preliminary design cost opinion has been prepared for guidance in project evaluation from the information available at the time of preparation and for the assumptions stated. The final costs E:\Otak\Projects\31470B\Data\Cost Estimates\Final Alternatives Analysis\13_1217_final_Alt_Analysis_CostEst.xlsx ---PAGE BREAK--- PROJECT: Overlake Station Infiltration Facility BY: SR PROJECT ID: 31470B CHECK BY: CSC Facility Configuration 3: 320'x34'x18' Station Infiltration Vault - Facility Configuration 3C - Basic Treatment through StormFilter Canisters (Variable infiltration rate) DATE: 12/17/2013 ITEM NO. ITEM QUANTITY UNIT UNIT PRICE AMOUNT Construction Elements 1 STRUCTURE EXCAVATION CL A INCLUDING HAUL 13,800 CY 20.00 $ 276,000 $ 2 320' x 34' PRECAST MULTICELL VAULT 1 LS 1,493,600.00 $ 1,493,600 $ 3 FLOW SPLITTER 1 LS 15,000.00 $ 15,000 $ 4 INFILTRATION VAULT ACCESS 1 LS 90,000.00 $ 90,000 $ 5 GRAVEL BACKFILL FOR WALL 3,000 CY 30.00 $ 90,000 $ 6 GRAVEL BORROW 18,900 CY 23.00 $ 434,700 $ 7 CATCH BASIN TYPE 2 72 IN. DIAM. W/FLOW SPLITTER 1 EA 8,000.00 $ 8,000 $ 8 EXCAVATION CL A INCLUDING HAUL (1:1 SLOPES, 3 SIDES) 11,600 CY 20.00 $ 232,000 $ 9 SHORING OR EXTRA EXCAVATION CLASS A (1 SIDE) 2,000 SF 55.00 $ 110,000 $ 10 BACKFLOW PREVENTION VALVE 1 EA 10,000.00 $ 10,000 $ 11 CONVEYANCE PIPE (18in) 75 LF 60.00 $ 4,500 $ 12 CONVEYANCE PIPE (24 in) 130 LF 70.00 $ 9,100 $ 13 CATCH BASIN TYPE 2 (54 in) 1 EA 3,500.00 $ 3,500 $ 14 CATCH BASIN TYPE 2 WITH WATER QUALITY FLOW SPLITTER (72 in) 1 EA 4,250.00 $ 4,250 $ 15 PRETREATMENT (CDS) 1 EA 51,300.00 $ 51,300 $ 16 BASIC TREATMENT (CANISTERS WITH ZPG MEDIA, GULD) 1 EA 543,000.00 $ 543,000 $ Subtotal Construction Elements 3,374,950 $ Required Ancillary Items 12 EROSION, SEDIMENTATION CONTROL, SITE PREPARATION 1.5% 50,624 $ 13 MOBILIZATION 8% 269,996 $ Subtotal Ancillary 320,620 $ 3,695,570 $ 14 CONTINGENCY 20% 739,114 $ Subtotal Construction + Ancillary + Mobilization 4,434,684 $ Tax/Engineering/Management/Permitting/Property 15 SALES TAX 9.5% 421,295 $ 16 ENGINEERING/LEGAL/ADMIN 15% 665,203 $ 17 CONSTRUCTION MANAGEMENT 15% 665,203 $ 18 PERMITTING 1% 44,347 $ 19 PROPERTY 900,000 $ Subtotal 2,696,047 $ Subtotal Construction + Ancillary + Mobilization + Tax/Engineering/Management/Permitting 7,130,731 $ 2013 Dollars Total Estimated Project Cost (Rounded) 7,131,000 $ Notes: 1. The above cost opinion is in 2013 dollars and does not include future escalation, financing, or O&M costs. 3. Estimate assumes that Site Demolition will be completed by others as part of the Sound Transit Station construction. 4. Excavation at 1:1 side slopes assumed for 3 sides, while shoring is assumed on 1 side 5. If area is available for stockpiling excavated material, Embankment Compaction may be used instead of Gravel Borrow (item 6) at $3 per cubic yard 6. Construction and permanent easements not included in total. PRELIMINARY DESIGN COST ESTIMATE 2. The preliminary design cost opinion has been prepared for guidance in project evaluation from the information available at the time of preparation and for the assumptions stated. The final costs E:\Otak\Projects\31470B\Data\Cost Estimates\Final Alternatives Analysis\13_1217_final_Alt_Analysis_CostEst.xlsx ---PAGE BREAK--- PROJECT: Overlake Station Infiltration Facility BY: SR PROJECT ID: 31470B CHECK BY: CSC Facility Configuration 3: 345'x34'x18' Station Infiltration Vault - Facility Configuration 3D - Basic Treatment through StormFilter Canisters (Variable infiltration rate) DATE: 12/17/2013 ITEM NO. ITEM QUANTITY UNIT UNIT PRICE AMOUNT Construction Elements 1 STRUCTURE EXCAVATION CL A INCLUDING HAUL 14,900 CY 20.00 $ 298,000 $ 2 345' x 34' PRECAST MULTICELL VAULT 1 LS 1,610,300.00 $ 1,610,300 $ 3 FLOW SPLITTER 1 LS 15,000.00 $ 15,000 $ 4 INFILTRATION VAULT ACCESS 1 LS 90,000.00 $ 90,000 $ 5 GRAVEL BACKFILL FOR WALL 3,000 CY 30.00 $ 90,000 $ 6 GRAVEL BORROW 20,300 CY 23.00 $ 466,900 $ 7 CATCH BASIN TYPE 2 72 IN. DIAM. W/FLOW SPLITTER 1 EA 8,000.00 $ 8,000 $ 8 EXCAVATION CL A INCLUDING HAUL (1:1 SLOPES, 3 SIDES) 12,400 CY 20.00 $ 248,000 $ 9 SHORING OR EXTRA EXCAVATION CLASS A (1 SIDE) 2,000 SF 55.00 $ 110,000 $ 10 BACKFLOW PREVENTION VALVE 1 EA 10,000.00 $ 10,000 $ 11 CONVEYANCE PIPE (18 in) 75 LF 60.00 $ 4,500 $ 12 CONVEYANCE PIPE (24 in) 130 LF 70.00 $ 9,100 $ 13 CATCH BASIN TYPE 2 (54 in) 1 EA 3,500.00 $ 3,500 $ 14 CATCH BASIN TYPE 2 WITH WATER QUALITY FLOW SPLITTER (72 in) 1 EA 4,250.00 $ 4,250 $ 15 PRETREATMENT (CDS) 1 EA 51,300.00 $ 51,300 $ 16 BASIC TREATMENT (CANISTERS WITH ZPG MEDIA, GULD) 1 EA 543,000.00 $ 543,000 $ Subtotal Construction Elements 3,561,850 $ Required Ancillary Items 12 EROSION, SEDIMENTATION CONTROL, SITE PREPARATION 1.5% 53,428 $ 13 MOBILIZATION 8% 284,948 $ Subtotal Ancillary 338,376 $ 3,900,226 $ 14 CONTINGENCY 20% 780,045 $ Subtotal Construction + Ancillary + Mobilization 4,680,271 $ Tax/Engineering/Management/Permitting/Property 15 SALES TAX 9.5% 444,626 $ 16 ENGINEERING/LEGAL/ADMIN 15% 702,041 $ 17 CONSTRUCTION MANAGEMENT 15% 702,041 $ 18 PERMITTING 1% 46,803 $ 19 PROPERTY 900,000 $ Subtotal 2,795,510 $ Subtotal Construction + Ancillary + Mobilization + Tax/Engineering/Management/Permitting 7,475,781 $ 2013 Dollars Total Estimated Project Cost (Rounded) 7,476,000 $ Notes: 1. The above cost opinion is in 2013 dollars and does not include future escalation, financing, or O&M costs. 3. Estimate assumes that Site Demolition will be completed by others as part of the Sound Transit Station construction. 4. Excavation at 1:1 side slopes assumed for 3 sides, while shoring is assumed on 1 side 5. If area is available for stockpiling excavated material, Embankment Compaction may be used instead of Gravel Borrow (item 6) at $3 per cubic yard 6. Construction and permanent easements not included in total. PRELIMINARY DESIGN COST ESTIMATE 2. The preliminary design cost opinion has been prepared for guidance in project evaluation from the information available at the time of preparation and for the assumptions stated. The final costs E:\Otak\Projects\31470B\Data\Cost Estimates\Final Alternatives Analysis\13_1217_final_Alt_Analysis_CostEst.xlsx ---PAGE BREAK--- PROJECT: Overlake Station Infiltration Facility BY: SR PROJECT ID: 31470B CHECK BY: CSC Facility Configuration 3: 335'x34'x18' Station Infiltration Vault - Facility Configuration 3E - Basic Treatment through StormFilter Canisters (Variable infiltration rate) DATE: 12/17/2013 ITEM NO. ITEM QUANTITY UNIT UNIT PRICE AMOUNT Construction Elements 1 STRUCTURE EXCAVATION CL A INCLUDING HAUL 14,500 CY 20.00 $ 290,000 $ 2 335' x 34' PRECAST MULTICELL VAULT 1 LS 1,563,600.00 $ 1,563,600 $ 3 FLOW SPLITTER 1 LS 15,000.00 $ 15,000 $ 4 INFILTRATION VAULT ACCESS 1 LS 90,000.00 $ 90,000 $ 5 GRAVEL BACKFILL FOR WALL 3,000 CY 30.00 $ 90,000 $ 6 GRAVEL BORROW 19,600 CY 23.00 $ 450,800 $ 7 CATCH BASIN TYPE 2 72 IN. DIAM. W/FLOW SPLITTER 1 EA 8,000.00 $ 8,000 $ 8 EXCAVATION CL A INCLUDING HAUL (1:1 SLOPES, 3 SIDES) 12,000 CY 20.00 $ 240,000 $ 9 SHORING OR EXTRA EXCAVATION CLASS A (1 SIDE) 2,000 SF 55.00 $ 110,000 $ 10 BACKFLOW PREVENTION VALVE 1 EA 10,000.00 $ 10,000 $ 11 CONVEYANCE PIPE (18 in) 75 LF 60.00 $ 4,500 $ 12 CONVEYANCE PIPE (24 in) 130 LF 70.00 $ 9,100 $ 13 CATCH BASIN TYPE 2 (54 in) 1 EA 3,500.00 $ 3,500 $ 14 CATCH BASIN TYPE 2 WITH WATER QUALITY FLOW SPLITTER (72 in) 1 EA 4,250.00 $ 4,250 $ 15 PRETREATMENT (CDS) 1 EA 51,300.00 $ 51,300 $ 16 BASIC TREATMENT (CANISTERS WITH ZPG MEDIA, GULD) 1 EA 543,000.00 $ 543,000 $ Subtotal Construction Elements 3,483,050 $ Required Ancillary Items 12 EROSION, SEDIMENTATION CONTROL, SITE PREPARATION 1.5% 52,246 $ 13 MOBILIZATION 8% 278,644 $ Subtotal Ancillary 330,890 $ 3,813,940 $ 14 CONTINGENCY 20% 762,788 $ Subtotal Construction + Ancillary + Mobilization 4,576,728 $ Tax/Engineering/Management/Permitting/Property 15 SALES TAX 9.5% 434,789 $ 16 ENGINEERING/LEGAL/ADMIN 15% 686,509 $ 17 CONSTRUCTION MANAGEMENT 15% 686,509 $ 18 PERMITTING 1% 45,767 $ 19 PROPERTY 900,000 $ Subtotal 2,753,575 $ Subtotal Construction + Ancillary + Mobilization + Tax/Engineering/Management/Permitting 7,330,302 $ 2013 Dollars Total Estimated Project Cost (Rounded) 7,331,000 $ Notes: 1. The above cost opinion is in 2013 dollars and does not include future escalation, financing, or O&M costs. 3. Estimate assumes that Site Demolition will be completed by others as part of the Sound Transit Station construction. 4. Excavation at 1:1 side slopes assumed for 3 sides, while shoring is assumed on 1 side 5. If area is available for stockpiling excavated material, Embankment Compaction may be used instead of Gravel Borrow (item 6) at $3 per cubic yard 6. Construction and permanent easements not included in total. PRELIMINARY DESIGN COST ESTIMATE 2. The preliminary design cost opinion has been prepared for guidance in project evaluation from the information available at the time of preparation and for the assumptions stated. The final costs of the project will depend on actual labor and material. E:\Otak\Projects\31470B\Data\Cost Estimates\Final Alternatives Analysis\13_1217_final_Alt_Analysis_CostEst.xlsx ---PAGE BREAK--- PROJECT: Overlake Station Infiltration Facility BY: SR PROJECT ID: 31470B CHECK BY: CSC Facility Configuration 4: 270'x44'x18' Station Infiltration Vault - Facility Configuration 4A - Basic Treatment through StormFilter Canisters (7.5 in/hr infiltration rate) DATE: 12/17/2013 ITEM NO. ITEM QUANTITY UNIT UNIT PRICE AMOUNT Construction Elements 1 STRUCTURE EXCAVATION CL A INCLUDING HAUL 14,500 CY 20.00 $ 290,000 $ 2 270' x 44' CIP SINGLE CELL CONC INFILTRATION VAULT 1 LS 1,988,000.00 $ 1,988,000 $ 3 FLOW SPLITTER 1 LS 15,000.00 $ 15,000 $ 4 INFILTRATION VAULT ACCESS 1 LS 90,000.00 $ 90,000 $ 5 GRAVEL BACKFILL FOR WALL 2,700 CY 30.00 $ 81,000 $ 6 GRAVEL BORROW 18,100 CY 23.00 $ 416,300 $ 7 CATCH BASIN TYPE 2 72 IN. DIAM. W/FLOW SPLITTER 1 EA 8,000.00 $ 8,000 $ 8 EXCAVATION CL A INCLUDING HAUL (1:1 SLOPES, 3 SIDES) 10,100 CY 20.00 $ 202,000 $ 9 SHORING OR EXTRA EXCAVATION CLASS A (1 SIDE) 2,000 SF 55.00 $ 110,000 $ 10 BACKFLOW PREVENTION VALVE 1 EA 10,000.00 $ 10,000 $ 11 CONVEYANCE PIPE (18 in) 75 LF 60.00 $ 4,500 $ 12 CONVEYANCE PIPE (24 in) 130 LF 70.00 $ 9,100 $ 13 CATCH BASIN TYPE 2 (54 in) 1 EA 3,500.00 $ 3,500 $ 14 CATCH BASIN TYPE 2 WITH WATER QUALITY FLOW SPLITTER (72 in) 1 EA 4,250.00 $ 4,250 $ 15 PRETREATMENT (CDS) 1 EA 51,300.00 $ 51,300 $ 16 BASIC TREATMENT (CANISTERS WITH ZPG MEDIA, GULD) 1 EA 423,200.00 $ 423,200 $ Subtotal Construction Elements 3,706,150 $ Required Ancillary Items 12 EROSION, SEDIMENTATION CONTROL, SITE PREPARATION 1.5% 55,592 $ 13 MOBILIZATION 8% 296,492 $ Subtotal Ancillary 352,084 $ 4,058,234 $ 14 CONTINGENCY 20% 811,647 $ Subtotal Construction + Ancillary + Mobilization 4,869,881 $ Tax/Engineering/Management/Permitting/Property 15 SALES TAX 9.5% 462,639 $ 16 ENGINEERING/LEGAL/ADMIN 15% 730,482 $ 17 CONSTRUCTION MANAGEMENT 15% 730,482 $ 18 PERMITTING 1% 48,699 $ 19 PROPERTY 900,000 $ Subtotal 2,872,302 $ Subtotal Construction + Ancillary + Mobilization + Tax/Engineering/Management/Permitting 7,742,183 $ 2013 Dollars Total Estimated Project Cost (Rounded) 7,743,000 $ Notes: 1. The above cost opinion is in 2013 dollars and does not include future escalation, financing, or O&M costs. 3. Estimate assumes that Site Demolition will be completed by others as part of the Sound Transit Station construction. 4. Excavation at 1:1 side slopes assumed for 3 sides, while shoring is assumed on 1 side 5. If area is available for stockpiling excavated material, Embankment Compaction may be used instead of Gravel Borrow (item 6) at $3 per cubic yard 6. Construction and permanent easements not included in total. PRELIMINARY DESIGN COST ESTIMATE 2. The preliminary design cost opinion has been prepared for guidance in project evaluation from the information available at the time of preparation and for the assumptions stated. The final costs E:\Otak\Projects\31470B\Data\Cost Estimates\Final Alternatives Analysis\13_1217_final_Alt_Analysis_CostEst.xlsx ---PAGE BREAK--- PROJECT: Overlake Station Infiltration Facility BY: SR PROJECT ID: 31470B CHECK BY: CSC Facility Configuration 4: 230'x44'x18' Station Infiltration Vault - Facility Configuration 4B - Basic Treatment through StormFilter Canisters (Variable infiltration rate) DATE: 12/17/2013 ITEM NO. ITEM QUANTITY UNIT UNIT PRICE AMOUNT Construction Elements 1 STRUCTURE EXCAVATION CL A INCLUDING HAUL 12,400 CY 20.00 $ 248,000 $ 2 230' x 44' CIP SINGLE CELL CONC INFILTRATION VAULT 1 LS 1,693,481.48 $ 1,693,481 $ 3 FLOW SPLITTER 1 LS 15,000.00 $ 15,000 $ 4 INFILTRATION VAULT ACCESS 1 LS 90,000.00 $ 90,000 $ 5 GRAVEL BACKFILL FOR WALL 2,700 CY 30.00 $ 81,000 $ 6 GRAVEL BORROW 15,600 CY 23.00 $ 358,800 $ 7 CATCH BASIN TYPE 2 72 IN. DIAM. W/FLOW SPLITTER 1 EA 8,000.00 $ 8,000 $ 8 EXCAVATION CL A INCLUDING HAUL (1:1 SLOPES, 3 SIDES) 8,800 CY 20.00 $ 176,000 $ 9 SHORING OR EXTRA EXCAVATION CLASS A (1 SIDE) 2,000 SF 55.00 $ 110,000 $ 10 BACKFLOW PREVENTION VALVE 1 EA 10,000.00 $ 10,000 $ 11 CONVEYANCE PIPE (18 in) 75 LF 60.00 $ 4,500 $ 12 CONVEYANCE PIPE (24 in) 130 LF 70.00 $ 9,100 $ 13 CATCH BASIN TYPE 2 (54 in) 1 EA 3,500.00 $ 3,500 $ 14 CATCH BASIN TYPE 2 WITH WATER QUALITY FLOW SPLITTER (72 in) 1 EA 4,250.00 $ 4,250 $ 15 PRETREATMENT (CDS) 1 EA 51,300.00 $ 51,300 $ 16 BASIC TREATMENT (CANISTERS WITH ZPG MEDIA, GULD) 1 EA 423,200.00 $ 423,200 $ Subtotal Construction Elements 3,286,131 $ Required Ancillary Items 12 EROSION, SEDIMENTATION CONTROL, SITE PREPARATION 1.5% 49,292 $ 13 MOBILIZATION 8% 262,891 $ Subtotal Ancillary 312,182 $ 3,598,314 $ 14 CONTINGENCY 20% 719,663 $ Subtotal Construction + Ancillary + Mobilization 4,317,977 $ Tax/Engineering/Management/Permitting/Property 15 SALES TAX 9.5% 410,208 $ 16 ENGINEERING/LEGAL/ADMIN 15% 647,697 $ 17 CONSTRUCTION MANAGEMENT 15% 647,697 $ 18 PERMITTING 1% 43,180 $ 19 PROPERTY 900,000 $ Subtotal 2,648,781 $ Subtotal Construction + Ancillary + Mobilization + Tax/Engineering/Management/Permitting 6,966,757 $ 2013 Dollars Total Estimated Project Cost (Rounded) 6,967,000 $ Notes: 1. The above cost opinion is in 2013 dollars and does not include future escalation, financing, or O&M costs. 3. Estimate assumes that Site Demolition will be completed by others as part of the Sound Transit Station construction. 4. Excavation at 1:1 side slopes assumed for 3 sides, while shoring is assumed on 1 side 5. If area is available for stockpiling excavated material, Embankment Compaction may be used instead of Gravel Borrow (item 6) at $3 per cubic yard 6. Construction and permanent easements not included in total. PRELIMINARY DESIGN COST ESTIMATE 2. The preliminary design cost opinion has been prepared for guidance in project evaluation from the information available at the time of preparation and for the assumptions stated. The final costs E:\Otak\Projects\31470B\Data\Cost Estimates\Final Alternatives Analysis\13_1217_final_Alt_Analysis_CostEst.xlsx ---PAGE BREAK--- PROJECT: Overlake Station Infiltration Facility BY: SR PROJECT ID: 31470B CHECK BY: CSC Facility Configuration 5: 315'x50'x18' Station Infiltration Vault - Facility Configuration 5A - Basic Treatment through StormFilter Canisters (7.5 in/hr infiltration rate) DATE: 12/17/2013 ITEM NO. ITEM QUANTITY UNIT UNIT PRICE AMOUNT Construction Elements 1 STRUCTURE EXCAVATION CL A INCLUDING HAUL 18,800 CY 20.00 $ 376,000 $ 2 315' x 50' CIP SINGLE CELL CONC INFILTRATION VAULT 1 LS 2,252,286.00 $ 2,252,286 $ 3 FLOW SPLITTER 1 LS 15,000.00 $ 15,000 $ 4 INFILTRATION VAULT ACCESS 1 LS 90,000.00 $ 90,000 $ 5 GRAVEL BACKFILL FOR WALL 2,700 CY 30.00 $ 81,000 $ 6 GRAVEL BORROW 21,600 CY 23.00 $ 496,800 $ 7 CATCH BASIN TYPE 2 72 IN. DIAM. W/FLOW SPLITTER 1 EA 8,000.00 $ 8,000 $ 8 EXCAVATION CL A INCLUDING HAUL (1:1 SLOPES, 3 SIDES) 11,600 CY 20.00 $ 232,000 $ 9 SHORING OR EXTRA EXCAVATION CLASS A (1 SIDE) 2,000 SF 55.00 $ 110,000 $ 10 BACKFLOW PREVENTION VALVE 1 EA 10,000.00 $ 10,000 $ 11 CONVEYANCE PIPE (18 in) 75 LF 60.00 $ 4,500 $ 12 CONVEYANCE PIPE (24 in) 130 LF 70.00 $ 9,100 $ 13 CATCH BASIN TYPE 2 (54 in) 1 EA 3,500.00 $ 3,500 $ 14 CATCH BASIN TYPE 2 WITH WATER QUALITY FLOW SPLITTER (72 in) 1 EA 4,250.00 $ 4,250 $ 15 PRETREATMENT (CDS) 1 EA 51,300.00 $ 51,300 $ 16 BASIC TREATMENT (CANISTERS WITH ZPG MEDIA, GULD) 1 EA 543,000.00 $ 543,000 $ Subtotal Construction Elements 4,286,736 $ Required Ancillary Items 12 EROSION, SEDIMENTATION CONTROL, SITE PREPARATION 1.5% 64,301 $ 13 MOBILIZATION 8% 342,939 $ Subtotal Ancillary 407,240 $ 4,693,976 $ 14 CONTINGENCY 20% 938,795 $ Subtotal Construction + Ancillary + Mobilization 5,632,771 $ Tax/Engineering/Management/Permitting/Property 15 SALES TAX 9.5% 535,113 $ 16 ENGINEERING/LEGAL/ADMIN 15% 844,916 $ 17 CONSTRUCTION MANAGEMENT 15% 844,916 $ 18 PERMITTING 1% 56,328 $ 19 PROPERTY 900,000 $ Subtotal 2,281,272 $ Subtotal Construction + Ancillary + Mobilization + Tax/Engineering/Management/Permitting 7,914,043 $ 2013 Dollars Total Estimated Project Cost (Rounded) 7,915,000 $ Notes: 1. The above cost opinion is in 2013 dollars and does not include future escalation, financing, or O&M costs. 3. Estimate assumes that Site Demolition will be completed by others as part of the Sound Transit Station construction. 4. Excavation at 1:1 side slopes assumed for 3 sides, while shoring is assumed on 1 side 5. If area is available for stockpiling excavated material, Embankment Compaction may be used instead of Gravel Borrow (item 6) at $3 per cubic yard 6. Construction and permanent easements not included in total. PRELIMINARY DESIGN COST ESTIMATE 2. The preliminary design cost opinion has been prepared for guidance in project evaluation from the information available at the time of preparation and for the assumptions stated. The final costs E:\Otak\Projects\31470B\Data\Cost Estimates\Final Alternatives Analysis\13_1217_final_Alt_Analysis_CostEst.xlsx ---PAGE BREAK--- PROJECT: Overlake Station Infiltration Facility BY: SR PROJECT ID: 31470B CHECK BY: CSC Facility Configuration 5: 310'x44'x18' Station Infiltration Vault - Facility Configuration 5B - Basic Treatment through StormFilter Canisters (Variable infiltration rate) DATE: 12/17/2013 ITEM NO. ITEM QUANTITY UNIT UNIT PRICE AMOUNT Construction Elements 1 STRUCTURE EXCAVATION CL A INCLUDING HAUL 16,600 CY 20.00 $ 332,000 $ 2 310' x 44' CIP SINGLE CELL CONC INFILTRATION VAULT 1 LS 2,282,518.52 $ 2,282,519 $ 3 FLOW SPLITTER 1 LS 15,000.00 $ 15,000 $ 4 INFILTRATION VAULT ACCESS 1 LS 90,000.00 $ 90,000 $ 5 GRAVEL BACKFILL FOR WALL 2,700 CY 30.00 $ 81,000 $ 6 GRAVEL BORROW 20,000 CY 23.00 $ 460,000 $ 7 CATCH BASIN TYPE 2 72 IN. DIAM. W/FLOW SPLITTER 1 EA 8,000.00 $ 8,000 $ 8 EXCAVATION CL A INCLUDING HAUL (1:1 SLOPES, 3 SIDES) 11,400 CY 20.00 $ 228,000 $ 9 SHORING OR EXTRA EXCAVATION CLASS A (1 SIDE) 2,000 SF 55.00 $ 110,000 $ 10 BACKFLOW PREVENTION VALVE 1 EA 10,000.00 $ 10,000 $ 11 CONVEYANCE PIPE (18 in) 75 LF 60.00 $ 4,500 $ 12 CONVEYANCE PIPE (24 in) 130 LF 70.00 $ 9,100 $ 13 CATCH BASIN TYPE 2 (54 in) 1 EA 3,500.00 $ 3,500 $ 14 CATCH BASIN TYPE 2 WITH WATER QUALITY FLOW SPLITTER (72 in) 1 EA 4,250.00 $ 4,250 $ 15 PRETREATMENT (CDS) 1 EA 51,300.00 $ 51,300 $ 16 BASIC TREATMENT (CANISTERS WITH ZPG MEDIA, GULD) 1 EA 543,000.00 $ 543,000 $ Subtotal Construction Elements 4,232,169 $ Required Ancillary Items 12 EROSION, SEDIMENTATION CONTROL, SITE PREPARATION 1.5% 63,483 $ 13 MOBILIZATION 8% 338,573 $ Subtotal Ancillary 402,056 $ 4,634,225 $ 14 CONTINGENCY 20% 926,845 $ Subtotal Construction + Ancillary + Mobilization 5,561,069 $ Tax/Engineering/Management/Permitting/Property 15 SALES TAX 9.5% 528,302 $ 16 ENGINEERING/LEGAL/ADMIN 15% 834,160 $ 17 CONSTRUCTION MANAGEMENT 15% 834,160 $ 18 PERMITTING 1% 55,611 $ 19 PROPERTY 900,000 $ Subtotal 2,252,233 $ Subtotal Construction + Ancillary + Mobilization + Tax/Engineering/Management/Permitting 7,813,303 $ 2013 Dollars Total Estimated Project Cost (Rounded) 7,814,000 $ Notes: 1. The above cost opinion is in 2013 dollars and does not include future escalation, financing, or O&M costs. 3. Estimate assumes that Site Demolition will be completed by others as part of the Sound Transit Station construction. 4. Excavation at 1:1 side slopes assumed for 3 sides, while shoring is assumed on 1 side 5. If area is available for stockpiling excavated material, Embankment Compaction may be used instead of Gravel Borrow (item 6) at $3 per cubic yard 6. Construction and permanent easements not included in total. PRELIMINARY DESIGN COST ESTIMATE 2. The preliminary design cost opinion has been prepared for guidance in project evaluation from the information available at the time of preparation and for the assumptions stated. The final costs E:\Otak\Projects\31470B\Data\Cost Estimates\Final Alternatives Analysis\13_1217_final_Alt_Analysis_CostEst.xlsx ---PAGE BREAK--- PROJECT: Overlake Station Infiltration Facility BY: SR PROJECT ID: 31470B CHECK BY: CSC Facility Configuration 6: 350'x50'x18' Station Infiltration Vault - Facility Configuration 6 - Basic Treatment through StormFilter Canisters (7.5 in/hr infiltration rate) DATE: 12/17/2013 ITEM NO. ITEM QUANTITY UNIT UNIT PRICE AMOUNT Construction Elements 1 STRUCTURE EXCAVATION CL A INCLUDING HAUL 20,800 CY 20.00 $ 416,000 $ 2 350' x 50' CIP SINGLE CELL CONC INFILTRATION VAULT 1 LS 2,502,540.00 $ 2,502,540 $ 3 FLOW SPLITTER 1 LS 15,000.00 $ 15,000 $ 4 INFILTRATION VAULT ACCESS 1 LS 90,000.00 $ 90,000 $ 5 GRAVEL BACKFILL FOR WALL 3,000 CY 30.00 $ 90,000 $ 6 GRAVEL BORROW 23,900 CY 23.00 $ 549,700 $ 7 CATCH BASIN TYPE 2 72 IN. DIAM. W/FLOW SPLITTER 1 EA 8,000.00 $ 8,000 $ 8 EXCAVATION CL A INCLUDING HAUL (1:1 SLOPES, 3 SIDES) 12,800 CY 20.00 $ 256,000 $ 9 SHORING OR EXTRA EXCAVATION CLASS A (1 SIDE) 2,000 SF 55.00 $ 110,000 $ 10 BACKFLOW PREVENTION VALVE 1 EA 10,000.00 $ 10,000 $ 11 CONVEYANCE PIPE (18 in) 75 LF 60.00 $ 4,500 $ 12 CONVEYANCE PIPE (24 in) 130 LF 70.00 $ 9,100 $ 13 CATCH BASIN TYPE 2 (54 in) 1 EA 3,500.00 $ 3,500 $ 14 CATCH BASIN TYPE 2 WITH WATER QUALITY FLOW SPLITTER (72 in) 1 EA 4,250.00 $ 4,250 $ 15 PRETREATMENT (CDS) 1 EA 57,900.00 $ 57,900 $ 16 BASIC TREATMENT (CANISTERS WITH ZPG MEDIA, GULD) 1 EA 619,900.00 $ 619,900 $ Subtotal Construction Elements 4,746,390 $ Required Ancillary Items 12 EROSION, SEDIMENTATION CONTROL, SITE PREPARATION 1.5% 71,196 $ 13 MOBILIZATION 8% 379,711 $ Subtotal Ancillary 450,907 $ 5,197,297 $ 14 CONTINGENCY 20% 1,039,459 $ Subtotal Construction + Ancillary + Mobilization 6,236,756 $ Tax/Engineering/Management/Permitting/Property 15 SALES TAX 9.5% 592,492 $ 16 ENGINEERING/LEGAL/ADMIN 15% 935,513 $ 17 CONSTRUCTION MANAGEMENT 15% 935,513 $ 18 PERMITTING 1% 62,368 $ 19 PROPERTY 900,000 $ Subtotal 3,425,886 $ Subtotal Construction + Ancillary + Mobilization + Tax/Engineering/Management/Permitting 9,662,643 $ 2013 Dollars Total Estimated Project Cost (Rounded) 9,663,000 $ Notes: 1. The above cost opinion is in 2013 dollars and does not include future escalation, financing, or O&M costs. 3. Estimate assumes that Site Demolition will be completed by others as part of the Sound Transit Station construction. 4. Excavation at 1:1 side slopes assumed for 3 sides, while shoring is assumed on 1 side 5. If area is available for stockpiling excavated material, Embankment Compaction may be used instead of Gravel Borrow (item 6) at $3 per cubic yard 6. Construction and permanent easements not included in total. PRELIMINARY DESIGN COST ESTIMATE 2. The preliminary design cost opinion has been prepared for guidance in project evaluation from the information available at the time of preparation and for the assumptions stated. The final E:\Otak\Projects\31470B\Data\Cost Estimates\Final Alternatives Analysis\13_1217_final_Alt_Analysis_CostEst.xlsx ---PAGE BREAK--- A p p e n d i x D — P r e - M a n u f a c t u r e d T r e a t m e n t S c h e m a t i c s ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- ---PAGE BREAK--- A p p e n d i x E — D e s i g n a n d P e r f o r m a n c e C r i t e r i a T e c h n i c a l M e m o r a n d u m ---PAGE BREAK--- ---PAGE BREAK--- Memorandum K:\project\31400\31470B\Reports\Alternatives Analysis\Appendices\Appendix_E\OVSIF Design Criteria Memo_FINAL.docx 10230 NE Points Drive Suite 400 Kirkland, WA 98033 Phone (425) 822-4446 Fax (425) 827-9577 Facility Design and Performance Criteria This memo describes the design parameters and performance criteria for the Overlake Village Station Regional Infiltration Facility (OVSIF). This facility will be the second stormwater control facility built in the Overlake Basin based on the City’s approved Overlake Village Stormwater and Park Facilities Conceptual Design Implementation Plan. The OVSIF will be located within the proposed Sound Transit Overlake Village Station site as part of the future East Link Light Rail Extension. The OVSIF will supply flow control and water quality treatment for the northern portion of the Overlake Basin, with dispersed LID planned throughout the surrounding developable area. General Design and Performance Parameters The identified design and performance criteria for the OVSIF facility include design elements for general facility criteria, flow splitter elements, geotechnical analysis parameters, UIC regulations, flow control standards, and pretreatment requirements. A summary of the OVSIF identified design and performance criteria, descriptions of conceptual design values based on the regional analysis completed to date, and referenced report or design manual are included in the attached table. The general design parameters for the OVSIF are listed below. The OVSIF facility size and site specific long-term infiltration rate recommendations will be evaluated and verified with the design of this project. Treatment tributary area: 94 acres Flow control: infiltration OVSIF conceptual design footprint: 0.42 acres Runoff treatment infiltration rate: 3 inches per hour Estimated flow control infiltration rate: 2.5-8 inches per hour To: Steve Hitch, PE From: Cheyenne Covington, PE Copies: File Date: September 13, 2013 Subject: Overlake Village Station Regional Infiltration Facility Design Parameters and Performance Criteria Project No.: 31470.B ---PAGE BREAK--- Steve Hitch, PE Page 2 Overlake Station Infiltration Facility Design and Performance Criteria K:\project\31400\31470B\Reports\Alternatives Analysis\Appendices\Appendix_E\OVSIF Design Criteria Memo_FINAL.docx Maximum ponding depth: 6 feet OVSIF conceptual operating capacity: 2.5 acre-feet Geotechnical Engineering Criteria As part of the completed conceptual facility sizing, four monitoring wells were installed on the OVSIF proposed site. Planning level geotechnical services for the Overlake Regional Facilities and design level services for the South Detention Vault have been completed by GeoEngineers, Inc. As part of the basin wide analysis, a groundwater mounding analysis was completed at the proposed Central Facility site to understand the effects of the infiltration facilities on the seasonal high water table. This information was extrapolated to predict groundwater mounding conditions at the proposed OVSIF site. The GeoEngineers’ Groundwater Mounding Analysis Report (May 2012) provides the preliminary geotechnical engineering criteria and performance criteria for the infiltration facilities. Conceptual geotechnical parameters Site soil borings indicate a thick lens of glacial till (~26 feet) overlaying advanced recessional outwash deposits Site surface elevation: 336 feet NAVD88 Estimated lower extent of glacial till: 310 feet NAVD88 Estimated seasonal high groundwater elevation: 298 feet NAVD88 Groundwater mounding elevation: 313 feet NAVD88 Estimated long term infiltration rate: 2.03 inches per hour The preliminary groundwater mounding analysis was predicated on the assumption that the bottom of the infiltration facility would be at an elevation of 305 feet NAVD88. For constructability and cost alternatives, the proposed OVSIF facility bottom elevation will be further evaluated. A more in-depth geotechnical site specific infiltration test and groundwater mounding analysis will be completed for the OVSIF to better define the site conditions. This information will be used for the design of the infiltration facility. Updated Requirements of the 2012 Ecology Manual Stormwater management for the Overlake Village area is based on the guidance for flow control and runoff treatment as described in the City of Redmond 2012 Stormwater Technical Notebook. The City’s Stormwater Technical Notebook is a supplement to the adopted Department of Ecology 2005 Stormwater Management Manual for Western Washington (2005 Ecology Manual), with relevant ---PAGE BREAK--- Steve Hitch, PE Page 3 Overlake Station Infiltration Facility Design and Performance Criteria K:\project\31400\31470B\Reports\Alternatives Analysis\Appendices\Appendix_E\OVSIF Design Criteria Memo_FINAL.docx modifications for city regulations and procedures. The City's Stormwater Technical Notebook has been used as the basis of design for stormwater management regional facilities design as it is the most current adopted regulatory manual for the City. For the OVSIF project, the City has requested a summary of potential design impacts based on the Department of Ecology’s recently issued 2012 Stormwater Management Manual for Western Washington (2012 Ecology Manual). The primary change with the new 2012 Ecology Manual is the addition of a LID Performance standard for controlling low flows. This standard requires matching pre-developed discharge rates from eight percent of the two-year peak flow to one-half of the two-year peak flow. Therefore, projects triggering Minimum Requirement 7 for flow control, must match pre-developed discharge rates from eight percent of the two-year peak to the full 50-year peak flow. The flow control measures from the 2005 Ecology Manual require the stormwater discharge durations to match the pre-developed durations from one-half of the two-year peak flow up to the full 50-year peak flow. In the hydrologic modeling of the basin the pre-developed condition for the Overlake Village watershed is required to be forested land cover. Determination of meeting the standards is accomplished using an Ecology approved continuous simulation hydrologic model. The new WWHM 2012 model has been update to allow analysis of the LID Performance Standard. This model includes additional rainfall data that was not available with the previous version, including several large storm events. While not a design modification, use of the updated WWHM 2012 model produces larger rainfall volumes for mitigation. The current HSPF modeling for the Overlake Basin, by NHC, provided results that approximately matched estimated flows from the WWHM 2005 program . The Overlake Basin HSPF model may need to be reevaluated. With the proposed infiltration flow control at the OVSIF, matching the low flow discharge rates to eight percent of the two-year flow per the 2012 Ecology Manual should not change the proposed facility size since infiltration of contributing area will already be at or above this predicted runoff volume. On a regional scale, dispersed LID can be used to provide infiltration of the low flow LID Performance Standard to meet basin discharge requirements not accommodated with the larger detention facilities. The Overlake Stormwater Alternatives Analysis Report, December 2012, recommends the use of 'moderate' dispersed LID with 5 percent of the total private development site area including bioretention facilities or equivalent LID. Additional updates between the 2005 and 2012 Ecology Stormwater Manual include pretreatment requirements for infiltration facilities used for flow control and water quality treatment. The 2005 Ecology Manual indicates using infiltration through the soil for treatment purposes is permitted as long as the facility is preceded by a pre-settling basin or a basic treatment BMP. Basic treatment is defined as the removal of at least 80 percent of solids found in runoff. ---PAGE BREAK--- Steve Hitch, PE Page 4 Overlake Station Infiltration Facility Design and Performance Criteria K:\project\31400\31470B\Reports\Alternatives Analysis\Appendices\Appendix_E\OVSIF Design Criteria Memo_FINAL.docx The 2012 Ecology Manual also requires the use of a pre-settlement basin or basic treatment BMP, but adds additional treatment recommendations for ‘high use’ sites. Areas designated as high use sites for roadway and parking lots within commercial and industrial sites are required to include an oil control facility with the capability of removing soluble pollutants, petroleum-based pollutants, and bacteria if Site Suitability Criterion SSC-6 is not met. SSC-6 classifies the physical and chemical suitability for pollutant treatment. Treatment criteria include: cation exchange capacity (5 meq CEC/100g minimum), depth of soil (18 inches minimum), and organic content of treatment soil (one percent minimum). The soil treatment capacity will be evaluated with the OVSIF project. The 2005 and 2012 Ecology Manuals list correction factors that are used to adjust the measured (initial) infiltration rate to a long-term design infiltration rate; however the 2012 Ecology Manual includes test method correction factors for the specific type of test conducted (i.e Large, Small-scale PIT test). The test correction factors adjusted the estimated actual saturated hydraulic conductivity based on the reliability of the test, with the assumption that a larger scale test will produce a more representative result. The Construction Stormwater Pollution Protection Plan with the 2012 Ecology Manual was also revised to include a 13th element for projection of Low Impact Development BMP’s. Compliance with these items would not impact the design or construction of the OVSIF unless the 2012 Ecology Manual is adopted, and these revisions required prior to project completion. UIC Regulations and Considerations Preliminary design alternatives considered for the OVSIF include a deep infiltration facility or drilled deep injection wells within the infiltration facility to facilitate infiltration past the layer of glacial till. These design consideration could define the OVSIF as a Class V underground injection control (UIC) well. These stormwater management injection wells are subject to design regulations outlined in Ecology’s Guidance for UIC Wells that Manage Stormwater (Ecology UIC Manual), Publication No. 05-10-067, December 2006. Design criteria for UIC wells include regulations for the amount of pretreatment required for stormwater prior to infiltration, and the minimum separation distance between the infiltration well and groundwater elevation. According to UIC regulations, all UICs used for flow control require basic pretreatment for solids removal prior to infiltration. Pretreatment helps preserve the long term infiltration rate by reducing the potential of clogging of surface soils by sediments within the facility. Since the OVSIF will be used to satisfy flow control requirements, it would require a minimum of basic pretreatment prior to stormwater entering the facility. Ecology also regulates the minimum separation distance between the UIC facility and the seasonal high groundwater elevation. This distance criterion is dependent on the treatment capacity of the vadose (unsaturated) zone. Generally, silt-based soils are considered to have high treatment capacity, ---PAGE BREAK--- Steve Hitch, PE Page 5 Overlake Station Infiltration Facility Design and Performance Criteria K:\project\31400\31470B\Reports\Alternatives Analysis\Appendices\Appendix_E\OVSIF Design Criteria Memo_FINAL.docx and are allowed to have a minimum separation distance of five feet between the bottom of the well and groundwater. This distance can be reduced to three feet if a groundwater mounding analysis is performed. Sand-based soils are generally considered to have medium treatment capacity, and are allowed a minimum separation distance of ten feet. Gravel-based soils are considered to have low treatment capacity, and a 25-foot minimum separation distance is required. Sand and gravel soils provide high infiltration rates and provide flow control capacity. With potential classification as a UIC facility, additional pretreatment requirements are defined in the Ecology UIC Manual depending on soil treatment capacity and pollutant loading classifications (as defined by Table 5.3 of the Ecology UIC Guidance Manual), varying degrees of pretreatment for UIC wells are required. Table 5.4 of the Ecology UIC Guidance Manual defines the pretreatment requirements for UICs. These vary between no required pretreatment to the removal of oils and solids. Exemptions to the UIC treatment requirements and minimal vadose treatment thickness may be made for local planning efforts with alternative methods to meet the non-endangerment standard and with discharge to a publicly-owned UIC facility with local jurisdictional approval. ---PAGE BREAK--- ---PAGE BREAK--- Overlake Village Station Regional Infiltration Facility - Design Parameters LEGEND 1) DOE 2012 5) Geo Eng-GW Mounding Analysis, May 2012 2) Otak-OV Regional Stormwater Facilities Plan 6) DOE Guidance for UICs that manage stormwater, Dec 2006 3) Otak-Stormwater Alternative Analysis 7) 2012 Redmond Stormwater Technical Notebook 4) NHC-OVSV H&H Modeling Report, Feb 2013 # Section/Page Station Vault Tributary Area 93.6 acres NA Site Condition 2 pg. 2-11 Flow Control Infiltration 2 pg. 2-11 Runoff Treatment Basic Basic Requirement 1 Vol 3 pg 3-84 Facility will be designed to provide basic treatment. Vault Footprint 0.42 acres NA Directive 2 pg. 2-11 Footprint will be adjusted to fit within proposed Plaza Street Max Ponding Depth 6 ft 6ft Requirement 1; 2 Vol 3 pg 3-94; pg. 2-11 Ground Surface Elev. 336ft NAVD88 NA Site Condition 5 pg. 8 To be verified by survey Depth from Ground Surface to bottom 31 ft NA Directive 2 pg. 2-11 Vault Bottom Elev. TBD NA Operating Capacity 2.5 acre-ft NA Directive 2 pg. 3-1 Volume per initial geotech analysis. Proposed facility size will be based onsite constraints Drawndown Time TBD 48 hrs Requirement 1 Vol 3 pg 3-84 48 hour drawdown requirement for 6-month 24-hr precipitation event. Facility Structure TBD NA Facility Roof TBD NA Minimum loading criteria will be H-20 Station Vault Flow Splitter WQ Outlet Pipe Diam. 1.5 ft NA 4 pg. 17 WQ Outlet Pipe Slope 0.006 NA 4 pg. 17 WQ Outlet Pipe I.E. 324.9ft NAVD88 NA 4 pg. 17 WQ Orifice 8-in NA 4 pg. 17 Overflow Weir Length 10.6 ft NA 4 pg. 17 Overflow Weir Crest Elev. Above Pipe Invert 3.75 ft NA 4 pg. 17 Geotech Analysis Seasonal High GW Elev. 298ft NAVD88 NA Site Condition 5 pg. 6 Depth of Till 26ft (Elev 310ft NAVD88) NA Site Condition 5 pg. 8 Bottom of Vault (Model) TBD GW Mounding Elev. 313ft NAVD88 NA Site Condition 5 pg. 16 Long Term Infiltration Rate 2.03 in/hr NA Site Condition 5 pg. 18 Runoff Treatment Infiltration Rate TBD up to 3in/hr Requirement 1; 2 Vol 3 pg 3-84; pg. 2-11 Initial (measured) Infiltration Rate 2.5-8in/hr < 9 in/hr Requirement 1; 2 Vol 3 pg 3-84; pg. 2-11 Long term infiltration rate will be verified through onsite infiltration test and mounding analysis Injection Well Regulations Flow splitter hydraulics will be revised with proposed facility design. Geotech analysis performed under the assumptions of a larger infiltration vault (1.2 acre footprint), and a maximum ponding depth of 13.5ft. These requirements may change when AMEC completes geotech analysis for station vault. Results of conceptual geotech analysis are used. Geotechnical site conditions will be determined at proposed plaza street location. Site infiltration test with revised mounding analysis will verify long term facility infiltration rate. Reference Design Criteria Design Value Code or Agency Required Value Degree of Requirement Notes K:\project\31400\31470B\Reports\Alternatives Analysis\Appendices\Appendix_E\OVSIF Design Critera.xls Otak, Inc. Page 1 of 2 Printed: 9/17/2013 ---PAGE BREAK--- # Section/Page Reference Design Criteria Design Value Code or Agency Required Value Degree of Requirement Notes Needs to be registered as a UIC? Registration need dependent on proposed facility design. See definition NA 6 pg. 2,3 Groundwater Separation TBD 5-ft minimum Required with UIC registration 6 pg. 14 Depends on the treatment capacity of the soils. Separation distance increases with lower treatment soils. Pretreatment TBD Basic Required with UIC registration 6 pg. 24 All UICs used for flow control require basic pretreatment to remove solids. Depending on treatment capacity of the soils and separation from groundwater, additional pretreatment to remove metals and oils may be required. Flow Control Discharge Durations (Redmond) Rates to comply Match predeveloped flows from half of the 2 year peak flow to the full 50-year peak flow Required 7 pg. 29 Redmond SM Notebook created to be in compliance with DOE 2005 Discharge Durations (Ecology) TBD Match predeveloped flows from 8% of the 2 year peak flow to the full 50-year peak flow Required 1 Vol. 1 pg. 2-30 2012 has new LID Performance Standard. Need to confirm if Station Vault will be designed to comply with new flow control standards. Sizing Procedure Design provides compliance with this procedure Continuous simulation hydrologic model, (WWHM) Required 1 Vol. 3 pg. 3-68 Pretreatment Treatment Level TBD Minimum is TSS removal Required 1 Vol. 3 pg. 3-65 K:\project\31400\31470B\Reports\Alternatives Analysis\Appendices\Appendix_E\OVSIF Design Critera.xls Otak, Inc. Page 2 of 2 Printed: 9/17/2013