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TIR-4254
Washington State Auto Dealers Association Addition and Improvements Technical Information Report Prepared for: Washington State Auto Dealers Association 621 Southwest Grady Way Renton, WA 98057 Contact: Vicki Fabrè Phone: (206) 433-6300 Prepared by: Sitts & Hill Engineers, Inc. 4815 Center Street Tacoma, Washington 98409 Contact: Don Davis Phone: (253) 474-9449 April 2023 Revised: October 2023 Job Number 19,682 Washington State Auto Dealers Association Technical Information Report Prepared for: Washington State Auto Dealers Association 621 Southwest Grady Way Renton, WA 98057 Contact: Vicki Fabrè Phone: (206) 433-6300 Prepared by: Sitts & Hill Engineers, Inc. 4815 Center Street Tacoma, Washington 98409 Contact: Don Davis, P.E. Phone: (253) 474-9449 IN COMPLIANCE WITH CITY OF RENTON STANDARDS April 2023 Revised: October 2023 Job Number 19,682 SURFACE WATER UTILITY JFarah 12/11/2023 DEVELOPMENT ENGINEERING SAMorman 12/05/2023 Washington State Auto Dealers Association – Technical Information Report 1 TABLE OF CONTENTS TABLE OF CONTENTS..................................................................................................................... 1 1.0 PROJECT OVERVIEW ................................................................................................................ 3 1.1 Scope ................................................................................................................................................. 3 1.2 Existing Conditions ......................................................................................................................... 3 1.3 Proposed Conditions ...................................................................................................................... 5 2.0 CONDITIONS AND REQUIREMENTS SUMMARY ................................................................... 7 2.1 Discussion of Core and Special Requirements .......................................................................... 7 2.1.1 Core Requirement #1: Discharge at the Natural Location .................................................. 7 2.1.2 Core Requirement #2: Off-site Analysis.................................................................................. 7 2.1.3 Core Requirement #3: Flow-Control Facilities ....................................................................... 7 2.1.4 Core Requirement #4: Conveyance System ........................................................................... 7 2.1.5 Core Requirement #5: Erosion and Sediment Control ......................................................... 7 2.1.6 Core Requirement #6: Maintenance and Operations ........................................................... 7 2.1.7 Core Requirement #7: Financial Guarantees and Liability ................................................... 8 2.1.8 Core Requirement #8: Water Quality Facilities ..................................................................... 8 2.1.9 Core Requirement #9: On-Site BMPs ...................................................................................... 8 2.1.10 Special Requirement #1: Other Adopted Area-Specific Requirements .......................... 9 2.1.11 Special Requirement #2: Flood Hazard Area Delineation ................................................. 9 2.1.12 Special Requirement #3: Flood Protection Facilities ....................................................... 10 2.1.13 Special Requirement #4: Source Control ............................................................................ 10 2.1.14 Special Requirement #5: Oil Control ................................................................................... 10 2.1.15 Special Requirement #6: Aquifer Protection Areas .......................................................... 10 3.0 OFF-SITE ANALYSIS ................................................................................................................ 15 3.1 Define and Map the Study Area ................................................................................................. 15 3.2 Resource Review ........................................................................................................................... 17 3.3 Field Inspection ............................................................................................................................. 17 3.4 Drainage System Description and Problem Descriptions ..................................................... 17 3.5 Mitigation of Existing or Potential Problems .......................................................................... 17 4.0 FLOW CONTROL, LID, AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ......... 18 4.1 Existing Site Hydrology ............................................................................................................... 18 4.2 Developed Site Hydrology .......................................................................................................... 18 4.3 Performance Standards ............................................................................................................... 18 4.4 Flow Control System .................................................................................................................... 19 4.5 Water Quality ................................................................................................................................ 19 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN ............................................................... 21 6.0 SPECIAL REPORTS AND STUDIES ......................................................................................... 22 7.0 OTHER PERMITS ...................................................................................................................... 23 Washington State Auto Dealers Association – Technical Information Report 2 8.0 CSWPPP ANALYSIS AND DESIGN ......................................................................................... 24 9.0 BOND QUANTITIES AND R/D FACILITY SUMMARIES ........................................................ 25 9.1 Bond Quantities ............................................................................................................................ 25 9.2 Facility Summaries ........................................................................................................................ 25 10.0 OPERATIONS AND MAINTENANCE MANUAL ................................................................... 26 10.1 Purpose ........................................................................................................................................ 26 10.2 Permanent Facilities Description ............................................................................................ 26 10.3 Discussion of Maintenance ....................................................................................................... 26 10.4 Maintenance Frequency ............................................................................................................ 27 10.5 Annual Cost Estimate ................................................................................................................ 27 TABLE OF APPENDICES A.1 TIR Worksheet A.2 Bond Quantity Worksheet A.3 Existing and Proposed Surface Coverage Exhibits A.4 Site Historical Aerial Photography A.5 Stormwater Engineering Calculations A.6 Geotechnical Engineering Report A.7 WWHM Reports A.8 2022 CoR SWDM Maintenance Checklists Washington State Auto Dealers Association – Technical Information Report 3 1.0 PROJECT OVERVIEW 1.1 Scope This Technical Information Report (TIR) addresses site improvements associated with the proposed addition to the existing Washington State Auto Dealers Association (WSADA) building located at 621 SW Grady Way, Renton, WA (Parcel No. 3340404730). Please see Figure 1 – Site Location Map for the location of the site. The purpose of this project is to improve the function of spaces within the existing WSADA building. This project will add a stairway, elevator, restrooms, and storage for improved access to the second floor of the building, where WSADA regularly holds training classes. This Technical Information Report has been prepared in accordance with the 2022 City of Renton Stormwater Design Manual (SWDM). A copy of the TIR Worksheet, which provides basic information about the scope of this project, is included with this report in Appendix A.1. 1.2 Existing Conditions The subject site is zoned as Commercial Arterial (CA), with an area of 0.75 acres. The site was originally developed by WSADA in 2013 as offices for their employees, and as a training facility for area auto dealers. The existing building, which is situated on the westerly extent of the site, includes a first story of approximately 6,300 SF and a second story of approximately 2,700 SF. The easterly two thirds of the parcel is asphalt paved for vehicular circulation and parking of employees and trainees. The site can be accessed from SW Grady Way to the north, or from the alley between Grady and 12th St SW to the south. An auxiliary parking lot is located on the opposite side of the alley to the south of the WSADA site. This parking lot was constructed in 2019 to accommodate for additional parking of trainees, which occurs on weekdays near midday. Storm drainage for the majority of the site is currently collected in catch basins, and conveyed through a Contech Stormceptor pretreatment device and Contech Stormfilter water quality device into a modular detention facility comprised of Stormtech SC-740 units. This system is discharged via a control structure into the public stormwater system in the alley south of the site. The entire building is currently tributary to this system, which is tightlined directly into the detention system from the west. A smaller area at the westerly extent of the site, including runoff from the east side of Raymond Avenue, is tributary via surface flow to a bioretention cell located off the southwest corner of the existing building. After treatment in the bioretention cell, the stormwater is discharged to a 48”Φ detention tank, where it is also released into the public stormwater system in the alley to the south of the site. Based upon our review of available information from the City of Renton, we are not aware of any capacity problems with the existing drainage facilities adjacent to this area. The City of Renton’s Public Works Maps combined with King County GIS together indicate the site is not located within or near any critical areas. In addition, it is located within the Peak Rate Flow Control Standard Zone. Washington State Auto Dealers Association – Technical Information Report 4 Figure 1 – Site Location Map – Proposed Building Washington State Auto Dealers Association – Technical Information Report 5 1.3 Proposed Conditions The primary purpose of this project is to improve the spaces already existing within the WSADA building. The upper floor is currently used for training sessions, which occur regularly for area dealer representatives. Access to the second story is limited, and WSADA would like to improve the accessibility to this floor by adding a supplementary stairway and an elevator. The addition will also provide restrooms and storage within the expanded building footprint. The building addition will encompass a 695 SF footprint (1,390 SF total additional floor area among the two floors). The new addition will largely replace an existing concrete patio located at the northwest corner of the existing building, resulting in minimal new hard surface. Site improvements are strictly limited to accommodation of the proposed expansion. The roof drainage system for the original building will need to be shifted to accommodate the building expansion. The bioretention cell and associated detention tank located near the southwest corner of the building will also need to be renovated to accommodate the building expansion. After investigation, it was determined that the sidewalk along the northern side of the property, adjacent to SW Grady Way, exceeds the cross-slope allowed for ADA access. As such, the sidewalk will be removed and replaced with a code compliant sidewalk. See Table 1 for a description of existing and proposed surface conditions for the addition. The project proposes more than 2,000 SF of combined new and replaced impervious surface, due to the sidewalk replacement, and is subject to a Full Drainage Review. Please see Appendix A.3 for Existing and Proposed Surface Coverage Exhibits. Washington State Auto Dealers Association – Technical Information Report 6 Table 1. Existing and Developed Condition Description – Proposed Addition Description On-site Off-site Total Existing Conditions Total Project Area (ft2) 33,577 9,121 42,698 Existing hard surface (ft2) 26,165 4,211 30,376 Existing landscaping/lawn area (ft2) 7,412 4,910 12,322 Developed Conditions Total Project Area (ft2) 33,577 9,121 42,698 Amount of new hard surface (ft2) 624 10 634 Amount of new pollution generating hard surface (PGHS) (ft2) 0 10 10 Amount of replaced hard surface (ft2) 532 3,344 3,876 Amount of replaced PGHS (ft2) 0 131 131 Amount of new plus replaced hard surface (ft2) 1,156 3,354 4,510 Amount of new plus replaced PGHS (ft2) 0 141 141 Amount of existing hard surfaces converted to vegetation/ landscaping (ft2) 0 0 0 Amount of Land Disturbed (ft2) 2,867 5,018 7,885 Native Vegetation to Pasture (acres) 0 0 0 Existing vegetation area to remain (ft2) 5,530 3,235 8,765 Existing hard surface to remain unaltered (ft2) 25,180 867 26,047 Value of proposed improvements ($) $1.23M 0 $1.23M Amount to be Graded/Approx. FILL (C.Y.) ±40 0 ±40 Washington State Auto Dealers Association – Technical Information Report 7 2.0 CONDITIONS AND REQUIREMENTS SUMMARY 2.1 Discussion of Core and Special Requirements This project will be subject to a Full Drainage Review. This type of drainage review will require compliance with all Core and Special Requirements of the 2022 City of Renton Stormwater Design Manual (SWDM). See Figure 2, Figure 3, and Figure 4 and at the end of this Section for determination of drainage review requirements per the SWDM flow charts. Below is a description of each core requirement and how the project proposes to satisfy each requirement. 2.1.1 Core Requirement #1: Discharge at the Natural Location This requirement will be met by collecting and conveying stormwater to existing private stormwater networks, which discharge into public stormwater networks, ultimately terminating at Springbrook Creek and the Black River. 2.1.2 Core Requirement #2: Off-site Analysis The Off-Site Analysis included in Section 3.0 of this TIR will satisfy this Core Requirement. 2.1.3 Core Requirement #3: Flow-Control Facilities Please see Section 4.0 for a discussion of flow control for the project. The project proposes work within the Peak Rate Flow Control Standards (Existing Site Conditions) Area. The project must match the developed peak discharge rates to the existing site conditions peak discharge rates for the 2-, 10-, and 100-year return periods. The project surfaces currently flow either off- site into the public stormwater system, or into one of two existing on-site systems. The roof of the existing building and area to the north of the building flow into an existing stormwater treatment and detention facility located on the eastern portion of the site. A portion of Raymond Ave flows on-site and is treated by an existing biofiltration pond before entering a storage tank. At the end of the storage tank is a flow control structure currently set to match the historic 2-, 10-, and 100-year storms of the site, assuming a fully forested condition. Runoff from the new addition will go directly to the storage tank. The storage tank will be modified to accommodate the new building addition while providing equivalent storage. The control structure will need to be modified to accommodate the adjusted shape of the storage tank. 2.1.4 Core Requirement #4: Conveyance System Please see Section 5.0 of this TIR for the conveyance system analysis and design. Calculations are provided which demonstrate the sizing and slope of pipes to reroute the existing roof drain pipe around the proposed addition. We have also included calculations to demonstrate the sizing of proposed roof drain pipes to the modified detention tank located near the southwest corner of the existing building. 2.1.5 Core Requirement #5: Erosion and Sediment Control A temporary Erosion and Sediment Control Plan (TESC) will be prepared and included in the construction plan set. Additionally, a CSWPPP under a separate cover, will be provided to satisfy this requirement. 2.1.6 Core Requirement #6: Maintenance and Operations Please see Section 10.0 of this TIR for the Operations and Maintenance Manual, prepared to satisfy this Core Requirement. WSADA will be responsible for maintenance and operation of Washington State Auto Dealers Association – Technical Information Report 8 the proposed on-site stormwater facilities upon completion. The City of Renton will continue to be responsible for operation and maintenance of stormwater systems in the right-of-way. 2.1.7 Core Requirement #7: Financial Guarantees and Liability We anticipate that WSADA will be required to provide a Construction Bond to the City of Renton prior to issuance of the permit. The contractor/owner will be responsible for all erosion and maintenance liabilities during construction. 2.1.8 Core Requirement #8: Water Quality Facilities This project proposes less than 5,000 SF of new plus replaced PGIS, and is therefore exempt from Core Requirement #8. 2.1.9 Core Requirement #9: On-Site BMPs Target surfaces on-site are already being treated by a biofiltration pond, or are discharging onto SW Grady Way. This site qualifies for the Large Lot BMP Requirements per 1.2.9.2.2 of the City of Renton SWDM, since it is larger than 22,000 square feet. These requirements state that all proposed pervious surfaces must implement the soil amendment BMP and roof downspout connections must be perforated pipe connections. The soil amendment BMP will be implemented for every pervious surface affected by construction. The downspout BMP applies and will be used for pipes that are solely roof drains attached to the addition. In addition, these requirements require the consideration of the following BMPs: full dispersion, full infiltration, limited infiltration, bioretention, permeable pavement, basic dispersion, reduced impervious surface credit, native growth retention credit, tree retention credit. None of the listed BMPs are feasible for implementation on the project site, and will therefore not be implemented. Runoff from the roof of the addition is directly connected to the overflow structure of the biofiltration pond via perforated piping. The remainder of this section contains a discussion of infeasibility for each BMP. Full Dispersion – The application of this BMP depends on the sheet flow of runoff through an area of native vegetation. The project site does not contain any native vegetation area (e.g., forested) in the existing or proposed condition. Therefore, full dispersion is infeasible for this project. Full Infiltration – Per Section C.2.2.2 of the Manual, full infiltration requires that “Existing soils must be coarse sands or cobbles or medium sands and cannot be comprised of fill materials where the infiltration device will be located.” Site soils meet this requirement, except for the top layer of soil. Biofiltration is currently being used, and will continue to be used, for treatment with overflow and drain pipe to a nearby storm structure. Water not collected by the underdrain is allowed to infiltrate. Infiltration for roof runoff must be considered for roof runoff, either in a standard infiltration device or the following options: gravel trenches, drywells, or ground surface depressions. Gravel trenches, drywells, or ground surface depressions all require space on-site that is not currently available due to the space used by the biofiltration pond. Limited Infiltration – The infeasibility criteria for limited infiltration are the same as those for full infiltration except that appropriate soils may be fine sands, loamy sands, sandy loams, or loams. Biofiltration is currently being used, and will continue to be used, for treatment with overflow and drain pipe to a nearby storm structure. Water not collected by the underdrain is allowed to infiltrate. Washington State Auto Dealers Association – Technical Information Report 9 Bioretention – A biofiltration cell is presently being used for treatment, and will continue to be used for treatment. The biofiltration cell will also be used to treat the new impervious surface that is not rooftop. The surface is 10 square feet of impervious surface due to the realignment of the stairs accessing the northwest portion of the site. This new surface will drain into the biofiltration pond. Permeable Pavement – The only pavement being treated as part of this project is in the roadway, or a sidewalk. Permeable Pavement does not work for either. It is also not known whether the soil on-site meets the minimum organic matter or cation exchange capacity requirements. Permeable Pavement is infeasible for this project. Basic Dispersion – The implementation of basic dispersion limits the area of impervious surface that can run off to a dispersion structure to 700 square feet per structure. The proposed construction will be adding less than 700 square feet square feet. However, the site is also responsible for runoff from SW Grady way and Raymond Ave SW. It is also required for the dispersed stormwater to flow over a vegetated surface, but there are no existing or proposed vegetated surfaces near the proposed development. Such a flowpath cannot be provided on the project site. We see basic dispersion as infeasible to the project. Reduced Impervious Surface Credit – This BMP presents four possible methods of impervious surface reduction: restricted footprint, wheel strip driveways, minimum disturbance foundation, and open grid decking over pervious surface. The restricted footprint method requires less than 4,000 square feet of impervious area, which is not feasible for an established office building with a parking lot. A wheel strip driveway is not applicable for a commercial parking lot. A minimum disturbance foundation is not feasible for a commercial application. Open grid decking over a pervious surface is also not applicable to a parking lot, sidewalk, or roadway. The reduced impervious surface credit is infeasible for this project. Native Growth Retention Credit – The existing condition of the site does not contain any native growth. Therefore, the native growth retention credit is infeasible for this project. Tree Retention Credit – The existing condition of the site contains approximately 17 within 20 feet of surface modifications. Three of these trees are smaller than 6” dbh, and two trees that are over 6” dbh are being removed. Three trees are being planted as replacements. The majority of the canopy area appears to be covering pervious surface, and not impervious surface, however. While tree retention credits may be available, this project will not be using them. 2.1.10 Special Requirement #1: Other Adopted Area-Specific Requirements The project site is not in a designated critical drainage area or in an area included in an adopted master drainage plan, basin plan, salmon conservation plan, stormwater compliance plan, flood hazard management plan, lake management plan, or shared facility drainage plan. 2.1.11 Special Requirement #2: Flood Hazard Area Delineation N/A. Per the FEMA floodplain map at the end of this Section, Figure 5, the project site lies within an unnamed “Area of Minimal Flood Hazard,” and therefore flood-related delineation on the project site is not required. Washington State Auto Dealers Association – Technical Information Report 10 2.1.12 Special Requirement #3: Flood Protection Facilities This project does not propose to rely on an existing flood protection facility nor does it modify or construct a new flood protection facility. 2.1.13 Special Requirement #4: Source Control WSADA shall implement Operational and Structural Source Control BMPs that include the maintenance of stormwater drainage and treatment systems as described in the Operations and Maintenance Manual, included in Section 10.0 of this report. 2.1.14 Special Requirement #5: Oil Control This project does not propose to develop a high-use site as defined by City of Renton SWDM; therefore, this Special Requirement is not applicable. 2.1.15 Special Requirement #6: Aquifer Protection Areas This project is not located within an Aquifer Protection Area per COR Maps. Washington State Auto Dealers Association – Technical Information Report 11 Figure 2 – Drainage Review Flow Chart Washington State Auto Dealers Association – Technical Information Report 12 Figure 3 - Drainage Review Requirements Washington State Auto Dealers Association – Technical Information Report 13 Figure 4 - Drainage Review Requirements (cont.) Washington State Auto Dealers Association – Technical Information Report 14 Figure 5 – FEMA Map Washington State Auto Dealers Association – Technical Information Report 15 3.0 OFF-SITE ANALYSIS Per City of Renton SWDM Section 1.2.2, this project must provide an off-site analysis report that assesses potential off-site drainage and water quality impacts associated with the redevelopment of the project site. The level of analysis required depends on the specific site and downstream conditions. In accordance with Section 1.2.2.1, a Level 1 Downstream Analysis has been performed. 3.1 Define and Map the Study Area Based on the current topographic survey and our observations of the site, the site is mostly tributary to existing, private conveyance systems on-site. The easterly two thirds of the site and the building are tributary to a proprietary stormwater treatment and modular detention system. The westerly third of the site, as well as a portion of the drainage from Raymond Avenue, are tributary to an existing bioretention cell and detention pipe. Both of these on-site stormwater management systems discharge via control structures into the public drainage network in the alley south of the WSADA property. Once in the right-of-way, the stormwater is conveyed north across Grady Way, and then westerly to Spring Brook Creek on the north side of Grady Way. The downstream conveyance system is comprised of pipes ranging in diameter from 12-inch to 66-inch. Springbrook Creek eventually discharges into the Black River, and then on to the Duwamish River. See Figure 6 for an illustration of the downstream flowpath from the project site to the Black River. Figure 6 - Downstream Flowpath See Figure 7 for a partial topographic survey of the project site. Washington State Auto Dealers Association – Technical Information Report 16 Figure 7 – Topographic Survey Washington State Auto Dealers Association – Technical Information Report 17 3.2 Resource Review A thorough review of the resources provided by the City of Renton Maps has been completed for the study area. Research conducted on 04/03/2023 has shown that there are not any adopted basin plans available for the study area. According to the FEMA Map presented in Figure 5 of this report, the project sites lie within a “Zone of Minimal Flood Hazard.” The site is located within the Duwamish – Green River Watershed, the Black River Basin, and the Springbrook Creek Sub Basin. Based on the City of Renton GIS, the project area has not been defined as a sensitive area. To our knowledge, there have not been any reported road drainage problems associated with the roads surrounding the site. It was also found that the site does not have a migrating river study, a 303d listing, or an adopted stormwater compliance plan available. A geotechnical report completed by Migizi Group can be found in Appendix A.6. 3.3 Field Inspection During field inspections, the system appeared to be working sufficiently with no obvious clogs or flooding. We do not anticipate any future problems with the proposed stormwater system. Stormwater flows on the site of the proposed building are expected to increase marginally due to an increase in impervious surface. The control structure for the detention pipe system will not be altered, therefore, the renovated detention pipe system will be designed to accommodate the slight increase in stormwater durations and volumes. Please see Section A.5 for the modeled areas in the predeveloped and mitigated scenarios for both sites. Since it has been determined that there are no anticipated stormwater problems associated with this project, Level 2 and Level 3 downstream analyses are not required. No problems were found related to constrictions, capacity deficiencies, flooding, scouring, overtopping hazards, sedimentation or erosion, aquatic organisms or their habitation. Land use associated with the study area includes commercial/industrial land applications. In addition, the study area includes utilities and roadways. Existing impervious surfaces located within the study area include commercial businesses, paved parking lots, paved driveways, and the paved public right-of-way. Based on existing site topography, stormwater runoff is captured within the on-site stormwater system, treated, detained, and released via control structures to the City’s right-of-way. It is ultimately tributary to the Black River via Springbrook Creek. 3.4 Drainage System Description and Problem Descriptions No drainage system problems were observed during the field inspection. 3.5 Mitigation of Existing or Potential Problems The proposed project area does not have any existing or anticipated drainage problems as outlined in Section 1.2.2.1.1 of the City of Renton SWDM. Washington State Auto Dealers Association – Technical Information Report 18 4.0 FLOW CONTROL, LID, AND WATER QUALITY FACILITY ANALYSIS AND DESIGN 4.1 Existing Site Hydrology The project site was previously developed in 2013 by WSADA, with all of the current site features, including a two-story building, asphalt paved parking lot and driveways, concrete walks, landscaping, and utilities. Stormwater from the easterly two thirds of the site is collected in catch basins and conveyed to a pretreatment device, stormwater quality device, and a series of modular detention tanks located along the southerly margin of the site. The building is also tributary to this detention system, although it bypasses the treatment functions. Stormwater from the westerly third of the site, as well as a portion of the Raymond Avenue road surface, is tributary to a bioretention cell and detention pipe located near the southwest corner of the existing building. Stormwater from both detention facilities currently discharge through independent flow control structures which were sized to match predeveloped conditions. The control structures discharge to the existing public stormwater system in the alley between SW Grady Way and SW 12th Street, immediately south of the WSADA property. This public stormwater system conveys the stormwater across and westerly along Grady Way, discharging into Springbrook Creek, and eventually the Black River. 4.2 Developed Site Hydrology This project includes a two-story building addition at the northwest corner of the existing WSADA building. The footprint of the building will be 695 SF, and will replace the concrete plaza currently situated at this location. Additional new/replaced surfaces will include a new concrete walkway connection to the sidewalk alongside Raymond Ave. The sidewalk along SW Grady Way will also need to be replaced to meet ADA requirements. It is anticipated that the total new/replaced hard surfaces for this project will be more than 1,000 SF. Areas surrounding the new building and sidewalk, as well as all disturbed surfaces adjacent to the bioretention cell and detention tank improvements, will be restored with landscaping similar to existing conditions at the perimeter of the building. The existing concrete plaza at the northwest corner of the building drains via surface flow to the existing bioretention cell and detention pipe system. We are proposing to mimic this drainage scheme with the proposed building addition. The new roof drains will be conveyed directly to the detention pipe, which will be resized (shortened with an increased diameter) to accommodate the building expansion. 4.3 Performance Standards The project site is within the Peak Rate Flow Control Standards (Existing Site Conditions) Area, as illustrated in Figure 8, which requires matching the existing site conditions 2-, 10-, and 100- year peak flows. The predeveloped site is comprised of rooftop surfacing, asphalt pavement, concrete walks, and landscaping. The proposed conditions include a slightly higher quantity of impervious surface than the existing conditions. In areas where conveyance features are required, they have been designed in accordance with Section 1.2.4 of the SWDM. Stormwater from the new roof will be conveyed directly to the Washington State Auto Dealers Association – Technical Information Report 19 detention facility. Downstream of the storage structure is a control structure that is set to match the 2, 10, and 100-year flow conditions prior to development to the WSADA building in 2013. 4.4 Flow Control System Although this project is exempt from Core Requirement #3 (flow control facilities), the stormwater from the proposed building will be routed through an existing detention system. We are proposing to alter the control structure. However, the downstream pipe network will experience slightly higher durations and lower volumes of stormwater due to the control structure modifications. 4.5 Water Quality This project is exempt from Core Requirement #8 (water quality facilities). Washington State Auto Dealers Association – Technical Information Report 20 Figure 8- City of Renton Flow Control Application Map Washington State Auto Dealers Association – Technical Information Report 21 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN Proposed conveyance elements include the existing 8” CPEP conveyance piping and a revised storage pipe to accommodate the new addition. The graph below was created with the use of WWHM, using a 15-minute time step to determine the expected 25 year peak flow that would be experienced by the site. Figure 9 - WWHM Using Manning’s Equation: 1.49 Where A = 0.349ft2 for an 8” pipe, n = 13 for PVC or CPEP, and S = 1% to represent the shallowest designed slope, yields a flow, Q, of 1.212cfs. This is above the 25 year peak flow rate of 0.4968cfs. The design of the proposed conveyance systems is discussed in more detail in Appendix A.5. Washington State Auto Dealers Association – Technical Information Report 22 6.0 SPECIAL REPORTS AND STUDIES We are not aware of any site characteristics that are particularly sensitive to stormwater runoff. A geotechnical report by Migizi Group can be found in Appendix A.6 of this report. Washington State Auto Dealers Association – Technical Information Report 23 7.0 OTHER PERMITS In addition to the Civil Construction permit, we anticipate that Site Plan Review, Environmental (SEPA), and Building permits will be required for this project. Washington State Auto Dealers Association – Technical Information Report 24 8.0 CSWPPP ANALYSIS AND DESIGN The Construction Stormwater Pollution Prevention Plan report is included under separate cover. Washington State Auto Dealers Association – Technical Information Report 25 9.0 BOND QUANTITIES AND R/D FACILITY SUMMARIES 9.1 Bond Quantities See Appendix A.2 for a copy of the City of Renton bond report. 9.2 Facility Summaries The project will implement catch basins, conveyance piping, and a new detention pipe. Washington State Auto Dealers Association – Technical Information Report 26 10.0 OPERATIONS AND MAINTENANCE MANUAL 10.1 Purpose The purpose of this manual is to provide guidelines for maintaining the storm drainage system as a part of the construction for the WSADA building addition. The site address is 621 SW Grady Way, Renton, WA 98055. Storm utility improvements that have been proposed as a part of the projects include: o Storm Drainage Piping o Catch Basins o Detention Pipe Each portion of the system has to be maintained in good working condition for the system to function properly. After construction, operations and maintenance of the private drainage system will be the responsibility of WSADA. Vicki Giles Fabré is the contact person. Her contact information is: Vicki Giles Fabré Executive Vice President Washington State Auto Dealers Association 621 SW Grady Way, Renton, WA 98057 (206) 433-6300 The City of Renton will continue to be responsible for the Operation and Maintenance of public improvements. 10.2 Permanent Facilities Description Existing roof drainage conveyance systems will be realigned with new catch basins and piping. Runoff from the proposed building addition will be conveyed to a new detention pipe located near the southwest corner of the existing building. The detention pipe must be renovated to accommodate the new building footprint. The new detention pipe will be shorter with an increased diameter relative to the existing detention pipe. The control structure for the existing detention system will not be altered, however, due to the increased impervious surface, we expect the durations and volumes of stormwater discharged from the site to increase slightly. The project does not propose to alter downstream flow paths and will maintain ultimate discharge to the Black River. 10.3 Discussion of Maintenance Any buildup of sediment, debris, vegetation, or trash that impedes the catch basins will reduce the storm system capacity. As a result, care must be taken to keep all inlets clear of debris. The applicable maintenance checklists and excerpts from the 2022 SWDM have been included in appendix A.8, for review during routine maintenance inspections. Washington State Auto Dealers Association – Technical Information Report 27 10.4 Maintenance Frequency Following construction of the project, the storm drainage system shall be inspected and maintained according to their respective maintenance checklists included at the end of this manual. Facilities will be inspected annually, or after every significant storm event where the precipitation is greater than or equal to one inch in 24 hours When deficiencies are noted, the problems are to be corrected as soon as possible. Any spill of hazardous material (e.g. fuel, lubricant, herbicide, etc.) shall be cleaned up immediately and shall be reported to the Division of Emergency Management (1-800-523-5044). Contaminated material will be disposed of properly. Any questions about the existence of a problem should be directed to a Professional Engineer. 10.5 Annual Cost Estimate Annual maintenance costs for the proposed building addition stormwater conveyance system is expected to increase the current cost private stormwater system maintenance by $1 for every linear foot of new piping. Existing stormwater infrastructure (including the detention pipe) is already accommodated Annual maintenance costs for the proposed stormwater conveyance system on-site for the proposed addition is expected to increase the current costs of maintaining the private stormwater system by $1 for every linear foot of new piping. Approximately 80 linear feet of new pipe will increase the annual cost of maintenance by $80. Washington State Auto Dealers Association – Technical Information Report 28 Cover Sheet for Inspection Forms Name of Inspector: _____________________________________________________________ Date of Inspection: _____________________________________________________________ Number of Sheets Attached: _____________________________________________________________ Inspector’s Signature: _____________________________________________________________ Washington State Auto Dealers Association – Technical Information Report 29 Maintenance Log Action Taken Name Date How Procedure Was Performed Problems Encountered Additional Actions Recommended Washington State Auto Dealers Association – Technical Information Report 30 A.1 TIR Worksheet Washington State Auto Dealers Association – Technical Information Report 31 Washington State Auto Dealers Association – Technical Information Report 32 Washington State Auto Dealers Association – Technical Information Report 33 Washington State Auto Dealers Association – Technical Information Report 34 Washington State Auto Dealers Association – Technical Information Report 35 Washington State Auto Dealers Association – Technical Information Report 36 Washington State Auto Dealers Association – Technical Information Report 37 A.2 Bond Quantity Worksheet The Bond Quantity Worksheet is included under separate cover. Washington State Auto Dealers Association – Technical Information Report 38 A.3 Existing and Proposed Surface Coverage Exhibits Washington State Auto Dealers Association – Technical Information Report 39 Washington State Auto Dealers Association – Technical Information Report 40 Washington State Auto Dealers Association – Technical Information Report 41 Washington State Auto Dealers Association – Technical Information Report 42 Washington State Auto Dealers Association – Technical Information Report 43 A.4 Site Historical Aerial Photography Washington State Auto Dealers Association – Technical Information Report 44 Washington State Auto Dealers Association – Technical Information Report 45 Washington State Auto Dealers Association – Technical Information Report 46 A.5 Stormwater Engineering Calculations As previously mentioned, although this site is exempt from additional flow control requirements, the proposed site will be draining through an existing detention pipe facility that will need to be modified to accommodate the building. The existing detention pipe will need to rotated counterclockwise, in plan view, about the existing control structure in order to provide clearance for the proposed building addition. Also, the pipe will need to be shortened, and increased in diameter to provide the necessary storage volume. We are not proposing to alter the control structure of the existing detention system, as such, the durations and volumes of stormwater released from the site will be slightly increased, due to the increase in impervious surface tributary to the detention pipe. The following calculations illustrate the predeveloped and developed conditions of the detention system (existing and proposed detention pipes, respectively). Predeveloped Conditions: Based on aerial photographs, included in Section A.4, the site had previously been a forested lot before the development of the WSADA office building. As this project is introducing less than 2,000SF, and is modifying an existing stormwater feature, the present WSADA office and coverage will be used as ‘predeveloped conditions’ to demonstrate the modified system will meet the needs of the existing system. See the following excerpt from WWHM indicating the assumptions used in the “Predeveloped” Condition: Washington State Auto Dealers Association – Technical Information Report 47 Mitigated Conditions: The mitigated site coverage is comprised of almost identical surfacing to the existing site coverage, with the exception of the addition covering a slightly larger area than the concrete patio it is replacing. See the following excerpt from WWHM indicating the assumptions used in the “Mitigated” Condition: Washington State Auto Dealers Association – Technical Information Report 48 Flow Frequency Results: As mentioned in Section 4.3, this project does not require flow control. However, due to modifications being made to the detention structure, the control structure must be modified The flow frequency table included below has been included to demonstrate that the modified stormwater detention system does not greatly change the discharge rate for the design storm events. Detention System Modifications: In order to accommodate the proposed building addition, while also matching the existing stormwater discharge characteristics of the current site, we are proposing to replace the existing 35 linear foot segment of 48” diameter detention pipe with a shorter 60” diameter detention pipe. The proposed 24 linear foot 60” diameter detention pipe will provide an equivalent volume. The control structure will also need to be modified since detained water within the 60” pipe will attain a greater elevation head than the 48” pipe. The WWHM report included in A.7 shows that there will be a very minor increase in discharge from the site with the new control structure. Washington State Auto Dealers Association – Technical Information Report 49 Water Quality: A biofiltration cell currently treats stormwater for this portion of the site. The addition will impact its footprint, requiring the cell to be modified. After modification, the biofiltration cell will maintain the same treatment area of at least 169 sqft, by providing 170sqft. While the addition is increasing the amount of non-roof impervious surface on-site, it is only increasing it by 10 sqft. Washington State Auto Dealers Association – Technical Information Report 50 Washington State Auto Dealers Association – Technical Information Report 51 Washington State Auto Dealers Association – Technical Information Report A.6 Geotechnical Engineering Report The Geotechnical Report, prepared by Migizi Group, Inc, dated September 26, 2022, is included under a separate cover. Washington State Auto Dealers Association – Technical Information Report A.7 WWHM Reports WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: 2023-05 WSADA Site Name: Site Address: City : Report Date: 8/3/2023 Gage : Seatac Data Start : 1948/10/01 00:00 Data End : 2009/09/30 00:00 Precip Scale: 1.00 Version Date: 2021/08/18 Version : 4.2.18 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Predev Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Flat .283 Pervious Total 0.283 Impervious Land Use acre ROOF TOPS FLAT 0.169 PARKING FLAT 0.528 Impervious Total 0.697 Basin Total 0.98 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Storage Storage ___________________________________________________________________ Name : Storage Tank Name: Storage Washington State Auto Dealers Association – Technical Information Report Dimensions Depth: 4 ft. Tank Type : Circular Diameter : 4 ft. Length : 35 ft. Discharge Structure Riser Height: 3.99 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 36 in. Elevation: 0.5 ft. Element Flows To: Outlet 1 Outlet 2 Control Structure ___________________________________________________________________ Tank Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 14.790 0.000 0.000 0.000 0.000 14.834 0.000 0.000 0.000 0.000 14.879 0.000 0.000 0.000 0.000 14.923 0.001 0.000 0.000 0.000 14.968 0.001 0.000 0.000 0.000 15.012 0.001 0.000 0.000 0.000 15.057 0.001 0.000 0.000 0.000 15.101 0.001 0.000 0.000 0.000 15.146 0.001 0.000 0.000 0.000 15.190 0.001 0.000 0.000 0.000 15.234 0.002 0.000 0.000 0.000 15.279 0.002 0.000 0.000 0.000 15.323 0.002 0.000 6.421 0.000 15.368 0.002 0.000 9.808 0.000 15.412 0.002 0.001 12.29 0.000 15.457 0.002 0.001 14.35 0.000 15.501 0.002 0.001 16.15 0.000 15.546 0.002 0.001 17.77 0.000 15.590 0.002 0.001 19.26 0.000 15.634 0.002 0.001 20.64 0.000 15.679 0.002 0.001 21.93 0.000 15.723 0.002 0.001 23.15 0.000 15.768 0.002 0.001 24.31 0.000 15.812 0.002 0.002 25.41 0.000 15.857 0.002 0.002 26.47 0.000 15.901 0.002 0.002 27.49 0.000 15.946 0.002 0.002 28.47 0.000 15.990 0.002 0.002 29.42 0.000 16.034 0.003 0.002 30.34 0.000 16.079 0.003 0.002 31.23 0.000 16.123 0.003 0.002 32.10 0.000 16.168 0.003 0.003 32.95 0.000 16.212 0.003 0.003 33.77 0.000 16.257 0.003 0.003 34.57 0.000 16.301 0.003 0.003 35.36 0.000 16.346 0.003 0.003 36.13 0.000 16.390 0.003 0.003 36.88 0.000 16.434 0.003 0.003 37.62 0.000 16.479 0.003 0.004 38.34 0.000 Washington State Auto Dealers Association – Technical Information Report 16.523 0.003 0.004 39.05 0.000 16.568 0.003 0.004 39.75 0.000 16.612 0.003 0.004 40.44 0.000 16.657 0.003 0.004 41.11 0.000 16.701 0.003 0.004 41.77 0.000 16.746 0.003 0.004 42.43 0.000 16.790 0.003 0.005 43.07 0.000 16.834 0.003 0.005 43.70 0.000 16.879 0.003 0.005 44.33 0.000 16.923 0.003 0.005 44.94 0.000 16.968 0.003 0.005 45.55 0.000 17.012 0.003 0.005 46.15 0.000 17.057 0.003 0.005 46.74 0.000 17.101 0.003 0.006 47.33 0.000 17.146 0.003 0.006 47.90 0.000 17.190 0.003 0.006 48.47 0.000 17.234 0.003 0.006 49.04 0.000 17.279 0.003 0.006 49.59 0.000 17.323 0.003 0.006 50.15 0.000 17.368 0.003 0.006 50.69 0.000 17.412 0.003 0.007 51.23 0.000 17.457 0.003 0.007 51.76 0.000 17.501 0.003 0.007 52.29 0.000 17.546 0.003 0.007 52.81 0.000 17.590 0.002 0.007 53.33 0.000 17.634 0.002 0.007 53.85 0.000 17.679 0.002 0.007 54.35 0.000 17.723 0.002 0.007 54.86 0.000 17.768 0.002 0.008 55.36 0.000 17.812 0.002 0.008 55.85 0.000 17.857 0.002 0.008 56.34 0.000 17.901 0.002 0.008 56.83 0.000 17.946 0.002 0.008 57.31 0.000 17.990 0.002 0.008 57.78 0.000 18.034 0.002 0.008 58.26 0.000 18.079 0.002 0.008 58.73 0.000 18.123 0.002 0.009 59.19 0.000 18.168 0.002 0.009 59.66 0.000 18.212 0.002 0.009 60.12 0.000 18.257 0.002 0.009 60.57 0.000 18.301 0.002 0.009 61.02 0.000 18.346 0.002 0.009 61.47 0.000 18.390 0.001 0.009 61.92 0.000 18.434 0.001 0.009 62.36 0.000 18.479 0.001 0.009 62.80 0.000 18.523 0.001 0.009 63.24 0.000 18.568 0.001 0.009 63.67 0.000 18.612 0.001 0.009 64.10 0.000 18.657 0.001 0.010 64.53 0.000 18.701 0.000 0.010 64.95 0.000 18.746 0.000 0.010 65.37 0.000 18.790 0.000 0.010 65.80 0.000 18.834 0.000 0.000 66.34 0.000 ___________________________________________________________________ Name : Control Structure Tank Name: Control Structure Washington State Auto Dealers Association – Technical Information Report Dimensions Depth: 6.27 ft. Tank Type : Circular Diameter : 6.27 ft. Length : 4.5 ft. Discharge Structure Riser Height: 5.77 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 0.6 in. Elevation: 0.5 ft. Orifice 2 Diameter: 0.5 in. Elevation: 3 ft. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Tank Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 14.790 0.000 0.000 0.000 0.000 14.860 0.000 0.000 0.000 0.000 14.929 0.000 0.000 0.000 0.000 14.999 0.000 0.000 0.000 0.000 15.069 0.000 0.000 0.000 0.000 15.138 0.000 0.000 0.000 0.000 15.208 0.000 0.000 0.000 0.000 15.278 0.000 0.000 0.000 0.000 15.347 0.000 0.000 0.002 0.000 15.417 0.000 0.000 0.003 0.000 15.487 0.000 0.000 0.004 0.000 15.556 0.000 0.000 0.005 0.000 15.626 0.000 0.000 0.005 0.000 15.696 0.000 0.000 0.006 0.000 15.765 0.000 0.000 0.006 0.000 15.835 0.000 0.000 0.007 0.000 15.905 0.000 0.000 0.007 0.000 15.974 0.000 0.000 0.008 0.000 16.044 0.000 0.000 0.008 0.000 16.114 0.000 0.000 0.008 0.000 16.183 0.000 0.000 0.009 0.000 16.253 0.000 0.000 0.009 0.000 16.323 0.000 0.000 0.009 0.000 16.392 0.000 0.000 0.010 0.000 16.462 0.000 0.000 0.010 0.000 16.532 0.000 0.000 0.010 0.000 16.601 0.000 0.000 0.011 0.000 16.671 0.000 0.000 0.011 0.000 16.741 0.000 0.000 0.011 0.000 16.810 0.000 0.000 0.012 0.000 16.880 0.000 0.000 0.012 0.000 16.950 0.000 0.001 0.012 0.000 17.019 0.000 0.001 0.012 0.000 17.089 0.000 0.001 0.013 0.000 17.159 0.000 0.001 0.013 0.000 17.228 0.000 0.001 0.013 0.000 17.298 0.000 0.001 0.013 0.000 17.368 0.000 0.001 0.014 0.000 Washington State Auto Dealers Association – Technical Information Report 17.437 0.000 0.001 0.014 0.000 17.507 0.000 0.001 0.014 0.000 17.577 0.000 0.001 0.014 0.000 17.646 0.000 0.001 0.015 0.000 17.716 0.000 0.001 0.015 0.000 17.786 0.000 0.001 0.015 0.000 17.855 0.000 0.001 0.017 0.000 17.925 0.000 0.001 0.018 0.000 17.995 0.000 0.001 0.019 0.000 18.064 0.000 0.001 0.019 0.000 18.134 0.000 0.001 0.020 0.000 18.204 0.000 0.001 0.021 0.000 18.273 0.000 0.001 0.021 0.000 18.343 0.000 0.001 0.022 0.000 18.413 0.000 0.001 0.022 0.000 18.482 0.000 0.002 0.023 0.000 18.552 0.000 0.002 0.023 0.000 18.622 0.000 0.002 0.024 0.000 18.691 0.000 0.002 0.024 0.000 18.761 0.000 0.002 0.024 0.000 18.831 0.000 0.002 0.025 0.000 18.900 0.000 0.002 0.025 0.000 18.970 0.000 0.002 0.026 0.000 19.040 0.000 0.002 0.026 0.000 19.109 0.000 0.002 0.026 0.000 19.179 0.000 0.002 0.027 0.000 19.249 0.000 0.002 0.027 0.000 19.318 0.000 0.002 0.028 0.000 19.388 0.000 0.002 0.028 0.000 19.458 0.000 0.002 0.028 0.000 19.527 0.000 0.002 0.029 0.000 19.597 0.000 0.002 0.029 0.000 19.667 0.000 0.002 0.029 0.000 19.736 0.000 0.002 0.030 0.000 19.806 0.000 0.002 0.030 0.000 19.876 0.000 0.002 0.030 0.000 19.945 0.000 0.002 0.031 0.000 20.015 0.000 0.002 0.031 0.000 20.085 0.000 0.002 0.031 0.000 20.154 0.000 0.002 0.032 0.000 20.224 0.000 0.002 0.032 0.000 20.294 0.000 0.003 0.032 0.000 20.363 0.000 0.003 0.032 0.000 20.433 0.000 0.003 0.033 0.000 20.503 0.000 0.003 0.033 0.000 20.572 0.000 0.003 0.048 0.000 20.642 0.000 0.003 0.282 0.000 20.712 0.000 0.003 0.648 0.000 20.781 0.000 0.003 1.075 0.000 20.851 0.000 0.003 1.494 0.000 20.921 0.000 0.003 1.844 0.000 20.990 0.000 0.003 2.087 0.000 21.060 0.000 0.003 2.239 0.000 21.130 0.000 0.000 2.413 0.000 ___________________________________________________________________ MITIGATED LAND USE Washington State Auto Dealers Association – Technical Information Report Name : Mitigated Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Flat .279 Pervious Total 0.279 Impervious Land Use acre ROOF TOPS FLAT 0.183 PARKING FLAT 0.518 Impervious Total 0.701 Basin Total 0.98 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Storage Storage ___________________________________________________________________ Name : Storage Tank Name: Storage Dimensions Depth: 5 ft. Tank Type : Circular Diameter : 5 ft. Length : 24 ft. Discharge Structure Riser Height: 4.99 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 36 in. Elevation: 1 ft. Element Flows To: Outlet 1 Outlet 2 Control Structure ___________________________________________________________________ Tank Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 14.290 0.000 0.000 0.000 0.000 14.346 0.000 0.000 0.000 0.000 14.401 0.000 0.000 0.000 0.000 14.457 0.001 0.000 0.000 0.000 14.512 0.001 0.000 0.000 0.000 14.568 0.001 0.000 0.000 0.000 14.623 0.001 0.000 0.000 0.000 14.679 0.001 0.000 0.000 0.000 14.734 0.001 0.000 0.000 0.000 Washington State Auto Dealers Association – Technical Information Report 14.790 0.001 0.000 0.000 0.000 14.846 0.001 0.000 0.000 0.000 14.901 0.001 0.000 0.000 0.000 14.957 0.001 0.000 0.000 0.000 15.012 0.001 0.001 0.000 0.000 15.068 0.002 0.001 0.000 0.000 15.123 0.002 0.001 0.000 0.000 15.179 0.002 0.001 0.000 0.000 15.234 0.002 0.001 0.000 0.000 15.290 0.002 0.001 0.000 0.000 15.346 0.002 0.001 8.289 0.000 15.401 0.002 0.001 11.72 0.000 15.457 0.002 0.001 14.35 0.000 15.512 0.002 0.002 16.57 0.000 15.568 0.002 0.002 18.53 0.000 15.623 0.002 0.002 20.30 0.000 15.679 0.002 0.002 21.93 0.000 15.734 0.002 0.002 23.44 0.000 15.790 0.002 0.002 24.86 0.000 15.846 0.002 0.002 26.21 0.000 15.901 0.002 0.003 27.49 0.000 15.957 0.002 0.003 28.71 0.000 16.012 0.002 0.003 29.88 0.000 16.068 0.002 0.003 31.01 0.000 16.123 0.002 0.003 32.10 0.000 16.179 0.002 0.003 33.15 0.000 16.234 0.002 0.003 34.17 0.000 16.290 0.002 0.004 35.16 0.000 16.346 0.002 0.004 36.13 0.000 16.401 0.002 0.004 37.07 0.000 16.457 0.002 0.004 37.98 0.000 16.512 0.002 0.004 38.88 0.000 16.568 0.002 0.004 39.75 0.000 16.623 0.002 0.005 40.61 0.000 16.679 0.002 0.005 41.44 0.000 16.734 0.002 0.005 42.26 0.000 16.790 0.002 0.005 43.07 0.000 16.846 0.002 0.005 43.86 0.000 16.901 0.002 0.005 44.64 0.000 16.957 0.002 0.005 45.40 0.000 17.012 0.002 0.006 46.15 0.000 17.068 0.002 0.006 46.89 0.000 17.123 0.002 0.006 47.61 0.000 17.179 0.002 0.006 48.33 0.000 17.234 0.002 0.006 49.04 0.000 17.290 0.002 0.006 49.73 0.000 17.346 0.002 0.006 50.42 0.000 17.401 0.002 0.007 51.10 0.000 17.457 0.002 0.007 51.76 0.000 17.512 0.002 0.007 52.42 0.000 17.568 0.002 0.007 53.07 0.000 17.623 0.002 0.007 53.72 0.000 17.679 0.002 0.007 54.35 0.000 17.734 0.002 0.007 54.98 0.000 17.790 0.002 0.008 55.60 0.000 17.846 0.002 0.008 56.22 0.000 17.901 0.002 0.008 56.83 0.000 17.957 0.002 0.008 57.43 0.000 Washington State Auto Dealers Association – Technical Information Report 18.012 0.002 0.008 58.02 0.000 18.068 0.002 0.008 58.61 0.000 18.123 0.002 0.008 59.19 0.000 18.179 0.002 0.009 59.77 0.000 18.234 0.002 0.009 60.34 0.000 18.290 0.002 0.009 60.91 0.000 18.346 0.002 0.009 61.47 0.000 18.401 0.002 0.009 62.03 0.000 18.457 0.002 0.009 62.58 0.000 18.512 0.002 0.009 63.13 0.000 18.568 0.001 0.009 63.67 0.000 18.623 0.001 0.010 64.21 0.000 18.679 0.001 0.010 64.74 0.000 18.734 0.001 0.010 65.27 0.000 18.790 0.001 0.010 65.79 0.000 18.846 0.001 0.010 66.31 0.000 18.901 0.001 0.010 66.83 0.000 18.957 0.001 0.010 67.34 0.000 19.012 0.001 0.010 67.85 0.000 19.068 0.001 0.010 68.35 0.000 19.123 0.001 0.010 68.85 0.000 19.179 0.000 0.010 69.35 0.000 19.234 0.000 0.010 69.84 0.000 19.290 0.000 0.010 70.34 0.000 19.346 0.000 0.000 71.00 0.000 ___________________________________________________________________ Name : Control Structure Tank Name: Control Structure Dimensions Depth: 6.27 ft. Tank Type : Circular Diameter : 6.27 ft. Length : 4.5 ft. Discharge Structure Riser Height: 5.77 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 0.9 in. Elevation: 1 ft. Orifice 2 Diameter: 0.5 in. Elevation: 3 ft. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Tank Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 14.290 0.000 0.000 0.000 0.000 14.360 0.000 0.000 0.000 0.000 14.429 0.000 0.000 0.000 0.000 14.499 0.000 0.000 0.000 0.000 14.569 0.000 0.000 0.000 0.000 14.638 0.000 0.000 0.000 0.000 14.708 0.000 0.000 0.000 0.000 14.778 0.000 0.000 0.000 0.000 Washington State Auto Dealers Association – Technical Information Report 14.847 0.000 0.000 0.000 0.000 14.917 0.000 0.000 0.000 0.000 14.987 0.000 0.000 0.000 0.000 15.056 0.000 0.000 0.000 0.000 15.126 0.000 0.000 0.000 0.000 15.196 0.000 0.000 0.000 0.000 15.265 0.000 0.000 0.000 0.000 15.335 0.000 0.000 0.004 0.000 15.405 0.000 0.000 0.007 0.000 15.474 0.000 0.000 0.009 0.000 15.544 0.000 0.000 0.011 0.000 15.614 0.000 0.000 0.012 0.000 15.683 0.000 0.000 0.013 0.000 15.753 0.000 0.000 0.015 0.000 15.823 0.000 0.000 0.016 0.000 15.892 0.000 0.000 0.017 0.000 15.962 0.000 0.000 0.018 0.000 16.032 0.000 0.000 0.018 0.000 16.101 0.000 0.000 0.019 0.000 16.171 0.000 0.000 0.020 0.000 16.241 0.000 0.000 0.021 0.000 16.310 0.000 0.000 0.022 0.000 16.380 0.000 0.000 0.022 0.000 16.450 0.000 0.001 0.023 0.000 16.519 0.000 0.001 0.024 0.000 16.589 0.000 0.001 0.025 0.000 16.659 0.000 0.001 0.025 0.000 16.728 0.000 0.001 0.026 0.000 16.798 0.000 0.001 0.027 0.000 16.868 0.000 0.001 0.027 0.000 16.937 0.000 0.001 0.028 0.000 17.007 0.000 0.001 0.028 0.000 17.077 0.000 0.001 0.029 0.000 17.146 0.000 0.001 0.029 0.000 17.216 0.000 0.001 0.030 0.000 17.286 0.000 0.001 0.031 0.000 17.355 0.000 0.001 0.033 0.000 17.425 0.000 0.001 0.034 0.000 17.495 0.000 0.001 0.035 0.000 17.564 0.000 0.001 0.036 0.000 17.634 0.000 0.001 0.037 0.000 17.704 0.000 0.001 0.038 0.000 17.773 0.000 0.001 0.039 0.000 17.843 0.000 0.001 0.040 0.000 17.913 0.000 0.001 0.041 0.000 17.982 0.000 0.002 0.041 0.000 18.052 0.000 0.002 0.042 0.000 18.122 0.000 0.002 0.043 0.000 18.191 0.000 0.002 0.043 0.000 18.261 0.000 0.002 0.044 0.000 18.331 0.000 0.002 0.045 0.000 18.400 0.000 0.002 0.045 0.000 18.470 0.000 0.002 0.046 0.000 18.540 0.000 0.002 0.047 0.000 18.609 0.000 0.002 0.047 0.000 18.679 0.000 0.002 0.048 0.000 18.749 0.000 0.002 0.049 0.000 18.818 0.000 0.002 0.049 0.000 Washington State Auto Dealers Association – Technical Information Report 18.888 0.000 0.002 0.050 0.000 18.958 0.000 0.002 0.050 0.000 19.027 0.000 0.002 0.051 0.000 19.097 0.000 0.002 0.052 0.000 19.167 0.000 0.002 0.052 0.000 19.236 0.000 0.002 0.053 0.000 19.306 0.000 0.002 0.053 0.000 19.376 0.000 0.002 0.054 0.000 19.445 0.000 0.002 0.054 0.000 19.515 0.000 0.002 0.055 0.000 19.585 0.000 0.002 0.055 0.000 19.654 0.000 0.002 0.056 0.000 19.724 0.000 0.002 0.056 0.000 19.794 0.000 0.003 0.057 0.000 19.863 0.000 0.003 0.057 0.000 19.933 0.000 0.003 0.058 0.000 20.003 0.000 0.003 0.058 0.000 20.072 0.000 0.003 0.073 0.000 20.142 0.000 0.003 0.308 0.000 20.212 0.000 0.003 0.674 0.000 20.281 0.000 0.003 1.101 0.000 20.351 0.000 0.003 1.520 0.000 20.421 0.000 0.003 1.871 0.000 20.490 0.000 0.003 2.114 0.000 20.560 0.000 0.003 2.266 0.000 20.630 0.000 0.000 2.440 0.000 ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.283 Total Impervious Area:0.697 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.279 Total Impervious Area:0.701 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.18952 5 year 0.242077 10 year 0.278836 25 year 0.327619 50 year 0.365719 100 year 0.405374 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.189457 Washington State Auto Dealers Association – Technical Information Report 5 year 0.241825 10 year 0.278431 25 year 0.326992 50 year 0.364903 100 year 0.404349 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.195 0.196 1950 0.274 0.263 1951 0.195 0.196 1952 0.160 0.161 1953 0.147 0.148 1954 0.179 0.180 1955 0.190 0.191 1956 0.182 0.182 1957 0.213 0.214 1958 0.189 0.189 1959 0.144 0.145 1960 0.184 0.185 1961 0.159 0.159 1962 0.159 0.156 1963 0.152 0.147 1964 0.185 0.186 1965 0.163 0.164 1966 0.164 0.164 1967 0.245 0.246 1968 0.274 0.275 1969 0.150 0.151 1970 0.164 0.165 1971 0.156 0.157 1972 0.235 0.235 1973 0.149 0.150 1974 0.157 0.158 1975 0.223 0.216 1976 0.151 0.152 1977 0.183 0.184 1978 0.237 0.238 1979 0.196 0.200 1980 0.206 0.204 1981 0.225 0.226 1982 0.313 0.314 1983 0.219 0.220 1984 0.168 0.161 1985 0.155 0.156 1986 0.207 0.208 1987 0.271 0.272 1988 0.127 0.128 1989 0.130 0.140 1990 0.333 0.334 1991 0.307 0.308 1992 0.169 0.169 1993 0.113 0.113 1994 0.133 0.133 1995 0.171 0.172 1996 0.217 0.218 Washington State Auto Dealers Association – Technical Information Report 1997 0.204 0.204 1998 0.191 0.181 1999 0.407 0.409 2000 0.209 0.210 2001 0.170 0.171 2002 0.212 0.212 2003 0.175 0.167 2004 0.376 0.377 2005 0.170 0.170 2006 0.145 0.140 2007 0.326 0.324 2008 0.303 0.304 2009 0.198 0.199 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.4071 0.4087 2 0.3762 0.3774 3 0.3329 0.3339 4 0.3260 0.3239 5 0.3130 0.3143 6 0.3071 0.3081 7 0.3034 0.3043 8 0.2743 0.2754 9 0.2741 0.2721 10 0.2710 0.2626 11 0.2455 0.2465 12 0.2371 0.2382 13 0.2346 0.2354 14 0.2252 0.2261 15 0.2233 0.2201 16 0.2191 0.2175 17 0.2169 0.2157 18 0.2132 0.2140 19 0.2115 0.2124 20 0.2087 0.2095 21 0.2070 0.2078 22 0.2061 0.2043 23 0.2036 0.2036 24 0.1981 0.1998 25 0.1961 0.1989 26 0.1952 0.1959 27 0.1952 0.1958 28 0.1906 0.1908 29 0.1900 0.1894 30 0.1886 0.1862 31 0.1854 0.1852 32 0.1844 0.1841 33 0.1832 0.1825 34 0.1816 0.1815 35 0.1789 0.1796 36 0.1745 0.1719 37 0.1710 0.1706 38 0.1699 0.1705 39 0.1697 0.1693 40 0.1687 0.1669 Washington State Auto Dealers Association – Technical Information Report 41 0.1676 0.1645 42 0.1639 0.1644 43 0.1636 0.1638 44 0.1631 0.1613 45 0.1600 0.1608 46 0.1592 0.1594 47 0.1590 0.1576 48 0.1570 0.1566 49 0.1559 0.1559 50 0.1549 0.1558 51 0.1518 0.1518 52 0.1512 0.1508 53 0.1502 0.1496 54 0.1489 0.1477 55 0.1471 0.1469 56 0.1454 0.1449 57 0.1442 0.1402 58 0.1327 0.1401 59 0.1301 0.1331 60 0.1271 0.1278 61 0.1129 0.1135 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility FAILED Facility FAILED duration standard for 1+ flows. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0948 1313 1299 98 Pass 0.0975 1198 1185 98 Pass 0.1002 1089 1092 100 Pass 0.1030 1015 1022 100 Pass 0.1057 933 943 101 Fail 0.1084 870 876 100 Pass 0.1112 801 814 101 Fail 0.1139 731 736 100 Pass 0.1167 671 681 101 Fail 0.1194 622 631 101 Fail 0.1221 576 579 100 Pass 0.1249 537 541 100 Pass 0.1276 497 506 101 Fail 0.1303 457 472 103 Fail 0.1331 422 439 104 Fail 0.1358 389 406 104 Fail 0.1386 366 377 103 Fail 0.1413 339 348 102 Fail 0.1440 312 325 104 Fail 0.1468 293 309 105 Fail 0.1495 271 282 104 Fail 0.1522 253 265 104 Fail 0.1550 239 247 103 Fail 0.1577 219 227 103 Fail 0.1604 204 209 102 Fail 0.1632 193 197 102 Fail 0.1659 178 181 101 Fail 0.1687 169 171 101 Fail Washington State Auto Dealers Association – Technical Information Report 0.1714 157 161 102 Fail 0.1741 146 150 102 Fail 0.1769 139 141 101 Fail 0.1796 130 132 101 Fail 0.1823 124 126 101 Fail 0.1851 114 117 102 Fail 0.1878 108 109 100 Pass 0.1906 100 102 102 Pass 0.1933 93 96 103 Pass 0.1960 83 85 102 Pass 0.1988 77 80 103 Pass 0.2015 72 74 102 Pass 0.2042 71 70 98 Pass 0.2070 68 67 98 Pass 0.2097 62 63 101 Pass 0.2124 60 61 101 Pass 0.2152 57 58 101 Pass 0.2179 56 56 100 Pass 0.2207 53 54 101 Pass 0.2234 52 52 100 Pass 0.2261 49 51 104 Pass 0.2289 48 49 102 Pass 0.2316 47 46 97 Pass 0.2343 44 43 97 Pass 0.2371 41 42 102 Pass 0.2398 39 40 102 Pass 0.2426 39 39 100 Pass 0.2453 37 38 102 Pass 0.2480 34 35 102 Pass 0.2508 33 33 100 Pass 0.2535 32 32 100 Pass 0.2562 31 32 103 Pass 0.2590 30 30 100 Pass 0.2617 27 27 100 Pass 0.2645 26 26 100 Pass 0.2672 26 26 100 Pass 0.2699 24 25 104 Pass 0.2727 23 22 95 Pass 0.2754 18 21 116 Fail 0.2781 18 18 100 Pass 0.2809 18 18 100 Pass 0.2836 18 18 100 Pass 0.2863 15 16 106 Pass 0.2891 15 15 100 Pass 0.2918 14 14 100 Pass 0.2946 13 13 100 Pass 0.2973 12 13 108 Pass 0.3000 12 12 100 Pass 0.3028 11 12 109 Pass 0.3055 9 10 111 Fail 0.3082 8 8 100 Pass 0.3110 8 8 100 Pass 0.3137 7 8 114 Fail 0.3165 7 7 100 Pass 0.3192 7 7 100 Pass 0.3219 6 6 100 Pass 0.3247 6 5 83 Pass 0.3274 5 5 100 Pass Washington State Auto Dealers Association – Technical Information Report 0.3301 5 5 100 Pass 0.3329 5 5 100 Pass 0.3356 4 4 100 Pass 0.3383 4 4 100 Pass 0.3411 4 4 100 Pass 0.3438 4 4 100 Pass 0.3466 4 4 100 Pass 0.3493 4 4 100 Pass 0.3520 4 4 100 Pass 0.3548 4 4 100 Pass 0.3575 3 3 100 Pass 0.3602 3 3 100 Pass 0.3630 3 3 100 Pass 0.3657 3 3 100 Pass _____________________________________________________ The development has an increase in flow durations from 1/2 Predeveloped 2 year flow to the 2 year flow or more than a 10% increase from the 2 year to the 50 year flow. The development has an increase in flow durations for more than 50% of the flows for the range of the duration analysis. ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.0939 acre-feet On-line facility target flow: 0.1114 cfs. Adjusted for 15 min: 0.1114 cfs. Off-line facility target flow: 0.0613 cfs. Adjusted for 15 min: 0.0613 cfs. ___________________________________________________________________ LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Control Structure POC N 119.22 N 0.00 Storage N 119.22 N 0.00 Total Volume Infiltrated 238.44 0.00 0.00 0.00 0.00 0% No Treat. Credit Compliance with LID Standard 8 Duration Analysis Result = Failed ___________________________________________________________________ Perlnd and Implnd Changes No changes have been made. ___________________________________________________________________ This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2023; All Rights Reserved. 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