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HomeMy WebLinkAboutRS_Reports_Studies_Drainage Report_190702_v1 TECHNICAL INFORMATION REPORT Brown Bear Car Wash 77 Rainier Avenue South Renton, Washington City of Renton File No. TBD Prepared for: Car Wash Enterprises, Inc. 3977 Leary Way NW Seattle, WA July 2, 2019 Our Job No. 20696 Technical Information Report Barghausen Consulting Engineers, Inc. Brown Bear Car Wash Renton, Washington Our Job No. 20696 20696.001.doc TABLE OF CONTENTS 1.0 PROJECT OVERVIEW Figure 1 – Vicinity Map Figure 2 - Drainage Review Flow Chart 2.0 CONDITIONS AND REQUIREMENTS SUMMARY 2.1 Analysis of the Core Requirements 2.2 Analysis of the Special Requirements 3.0 OFF-SITE ANALYSIS 4.0 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN 4.1 Existing Site Hydrology 4.2 Developed Site Hydrology 4.3 Performance Standards 4.4 Flow Control System 4.5 Water Quality System 4.6 On-site BMPs 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN 6.0 SPECIAL REPORTS AND STUDIES 6.1 Geologic Hazard Area Report 7.0 OTHER PERMITS 8.0 CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN (CSWPP) ANALYSIS AND DESIGN 9.0 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT 10.0 OPERATIONS AND MAINTENANCE MANUAL Tab 1.0 20696.001.doc 1.0 PROJECT OVERVIEW The proposed project site is located within a portion of Section 18, Township 23 North, Range 5 East of the Willamette Meridian. More specifically, the site is located at 77 Rainier Avenue South in Renton, Washington. The site is made up of one (1) Tax Parcel No. 182305-9131. See Figure 1 for the Vicinity Map in this section for the location of the proposed project site. The site consists of an existing 1,836-square-foot car wash structure, an existing gas station with canopy, asphalt and concrete pavement, and landscaping. The proposed improvements include the removal of the existing gas station and appurtenances and the construction of a new auto sentry pay station, which includes a new canopy, new landscaping, and relocation of the dumpster enclosure. The existing car wash building will not be disturbed. The site is relatively level with a rockery wall ranging from about 1½ to 4 feet tall located along the western property line and is the toe of the off-site east-facing slope. The project intends to be completed without any modifications to the existing drainage network on and off site. The developed condition will rely on existing storm and sewer conveyance systems to meet the Core and Special Requirements to satisfy the Full Drainage Review as specified in the 2017 City of Renton Surface Water Design Manual (SWDM) and the City of Renton Municipal Code 4-6-030. Please See Figure 2 for the Flow Chart Determining the review type. A Technical Information Report (TIR) worksheet will be provided upon a subsequent submittal. Figure 1 Vicinity Map VICINTY MAP NTS 99 RAINIER AVE S RENTON, WA Figure 2 Drainage Review Flow Chart SECTION 1.1 DRAINAGE REVIEW 12/12/2016 2017 City of Renton Surface Water Design Manual 1-14 FIGURE 1.1.2.A FLOW CHART FOR DETERMINING TYPE OF DRAINAGE REVIEW REQUIRED Figure 4 Soils Tab 2.0 20696.001.doc 2.0 CONDITIONS AND REQUIREMENTS SUMMARY The project is subject to the Full Drainage Review since it results in greater than 2,000 square feet of new plus replaced impervious surface and is subject to all minimum requirements. Below is an analysis of each core requirement: 2.1 Analysis of the Core Requirements Core Requirement No. 1: Discharge at the Natural Location. Response: The proposed redevelopment will continue to discharge at the natural and existing location and thus not alter and/or adversely impact any downstream basins or facilities. Core Requirement No. 2: Off-Site Analysis. Response: Per the City of Renton SWDM, the proposed project is exempt from Core Requirement #2 as there will be no increase in discharge rate and location of discharge to and from the project site because the proposed condition will contain less impervious area as the existing condition. Core Requirement No. 3: Flow Control. Response: The project site replaces less than 5,000 square feet of impervious surface and less than 3/4 acres of pervious surfaces will be added. Thus, the redevelopment is exempt from providing flow control facilities. Core Requirement No. 4: Conveyance System. Response: The redevelopment has no change in flow characteristics as it will continue to use the existing on-site conveyance system. Therefore, conveyance capacity analysis is not needed. Core Requirement No. 5: Erosion and Sediment Control Response: To satisfy Core Requirement #5, a CSWPP along with a Stormwater Pollution Prevention and Spill Plan (SWPPS) and Erosion Control Plan will be included as part of this report within Section 8.0 upon a subsequent submittal. Core Requirement No. 6: Maintenance and Operations. Response: The redevelopment largely includes regrading for the auto sentry station and does not propose the installation of new drainage facilities. Any new drainage features and/or structures on site shall be included within this report. Core Requirement No. 7: Financial Guarantees and Liability. Response: All Financial Guarantees will be put in place as needed prior to permit issuance. Core Requirement No. 8: Water Quality. Response: The project meets the Surface Area Exemption to install water quality facilities as stated in the City of Renton SWDM, as the proposed replaced pollution- 20696.001.doc generating impervious surfaces are less than 5,000 square feet and there will be less than 3/4 acres of pollution-generating pervious surface added. Core Requirement No. 9: On-site BMPs. Response: The project will install on-site BMPs for the target surfaces as feasible per the Small Lot BMP Requirements detailed within the City of Renton SWDM. Further discussion as to the feasibility of on-site BMPs can be found in Section 5.0. 2.2 Analysis of the Special Requirements Special Requirement No. 1: Other Adopted Area-Specific Requirements. Response: The project will meet any and all requirements as required based on the project location and area-specific requirements therein. Special Requirement No. 2: Flood Hazard Area Delineation. Response: As per the FEMA Flood Map Service Panel 53033C0977F, the area of the project site is located in the 500-year floodplain, Zone X, which largely includes areas of minimal flooding. The project will adhere to any additional requirements as necessary. Special Requirement No. 3: Flood Protection Facilities. Response: The project site does not rely on an existing flood protection facility or modify and construct a new flood protection facility as described in the City of Renton SWDM for a redevelopment to comply Special Requirement No. 3. Thus, the implementation of Flood Protection Facilities is not required. Special Requirement No. 4: Source Control. Response: The proposed project will implement source control measures as required within the King County Stormwater Pollution Control Manual and Renton Municipal Code, Title IV. Special Requirement No. 5: Oil Control. Response: The proposed project will implement source control measures as required within the 2017 City of Renton SWDM. Special Requirement No. 6: Aquifer Protection Area. Response: This redevelopment project is within the Wellhead Protection Zone 2; however, the requirements specified for Zone 2 do not apply to this project because there are no flow control or water quality ponds, infiltration facilities, or open channels proposed for this project. Tab 3.0 20696.001.doc 3.0 OFF-SITE ANALYSIS The proposed project does not intend to change the discharge rate, will maintain the same location of discharge to and from the project site, and shall use the existing drainage network to convey storm runoff to the public storm facilities. It is anticipated that the existing drainage and conveyance system is adequate and has sufficient capacity to serve the site post-development. Tab 4.0 20696.001.doc 4.0 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN 4.1 Existing Site Hydrology The existing site hydrology allows for sheet flow that collects into centralized locations of existing catch basins. The existing drainage network on site consists of three (3) catch basins and pipes that convey stormwater runoff to a 12-inch pipe in the City of Renton storm system. 4.2 Developed Site Hydrology The redevelopment's drainage patterns will largely remain the same. Runoff from impervious surfaces will be conveyed to the storm network through existing drainage and conveyance facilities. The redevelopment incorporates graded concrete and asphalt as a means to convey runoff to the existing storm network. 4.3 Performance Standards The proposed redevelopment includes the replacement of hard surfaces and conversion to pervious surfaces and is within the threshold for a Full Drainage Review as described in the City of Renton SWDM on-site BMPs per the Small Lot BMP requirements. The feasibility of each on-site BMP is explained in Section 5.0. 4.4 Flow Control System The project is required to consider Core Requirement #3; however, the City of Renton SWDM presents a basic exemption, which includes the creation of less than 5,000 square feet of impervious surfaces and no addition of pervious surfaces. The redevelopment falls under this criteria and will not propose any flow control facilities. 4.5 Water Quality System Per the City of Renton SWDM, this project is exempt from the provision of water quality facilities and is, therefore, not included in the implementation of this drainage review. 4.6 On-Site BMPs As described in the City of Renton SWDM, Small Lot BMPs are required for project sites under 22,000 square feet. The redevelopment, sized at 21,913 square feet, triggers this requirement for target areas on site where feasible. Discussion of the required on-site BMPs are found below: · Full Dispersion The required length of vegetated flow path over a native vegetated surface required per Appendix C of the Renton SWDM for full dispersion is not available for this project site. Thus, Full Dispersion is infeasible. · Full Infiltration of Roof Runoff The redevelopment does not include any new or modifications to any existing roof downspouts and is, therefore, infeasible for Full Infiltration of Roof Runoff. 20696.001.doc · Full Infiltration The site specific Geotechnical Report by ZipperGeo dated July 27, 2018, found fill material to be present on site. Appendix C of the Renton SWDM states that the existing soils cannot be comprised of fill materials where an infiltration device will be located. Since the site contains fill material, Full Infiltration is not feasible. See Section 6.1 for the Geotechnical Report. · Limited Infiltration The discussion above applies to this BMP; therefore, Limited Infiltration is deemed infeasible. · Rain Gardens/Bioretention Per Appendix C of the 2017 City of Renton SWDM, a rain garden or bioretention facility is infeasible for project sites that are within an erosion hazard zone or steep slope zone and the Geotechnical Report did not consider additions to stormwater facilities in their report. Since the project falls into these zones, the implementation of rain gardens or a bioretention facility is infeasible. · Permeable Pavement The existing project site is classified as 'high-use' due to the use and nature of the existing business. This results in the infeasibility of using permeable pavement. · Basic Dispersion There are no adequate vegetated surfaces or enough flow path length as required within Appendix C of the 2017 Renton SWDM, deeming Basic Dispersion infeasible. · Perforated Pipe Connections The project does not propose any downspout pipe connections and, therefore, this Flow Control BMP does not apply. Based on the existing site characteristics and current use of the site, the implementation of the above BMPs as discussed are infeasible. Tab 5.0 20696.001.doc 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN The redevelopment excludes the construction of new or modification of existing conveyance system elements. Thus, a Conveyance System Analysis and Design is not included in this proposal. Tab 6.0 20696.001.doc 6.0 SPECIAL REPORTS AND STUDIES The following reports are included in this section: 6.1 Geologic Hazard Area Report by ZipperGeo dated July 27, 2018 Geologic Hazard Area Report by ZipperGeo dated July 27, 2018 6.1 20696.001.doc 6.0 OTHER PERMITS All other Permits in conjunction with a Full Drainage Review are listed below: - Building Permit Tab 7.0 20696.001.doc 7.0 OTHER PERMITS All other permits in conjunction with a Full Drainage Review are listed below: · Building Permit Tab 8.0 20696.001.doc 8.0 STORMWATER POLLUTION PREVENTION PLAN (SWPPS) ANALYSIS AND DESIGN A Stormwater Pollution Prevention and Spill Plan and Erosion and Sediment Control Plan will be provided upon a subsequent submittal. Tab 9.0 20696.001.doc 9.0 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT The project will provide all documents pertaining to the Bond Quantities, Facility Summaries, and Declaration of Covenants as required upon final engineering. Tab 10.0 20696.001.doc 10.0 OPERATIONS AND MAINTENANCE MANUAL The project does not propose any new drainage features or systems. Therefore, no Operations and Maintenance Manual will be necessary for this project.