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HomeMy WebLinkAboutRenton Commons_Drainage ReportCONDITIONAL USE PERMIT TECHNICAL INFORMATION REPORT Project:Renton Commons 215 Whitworth Ave Renton, WA 98057 Prepared For:Tonkin Architecture 204 1st Ave South Seattle, WA 98104 Prepared By:Ryan Yokum, EIT Reviewed By:Marc Errichetti, PE Date:June 7, 2016 TABLE OF CONTENTS Section No. Subject Page No. SECTION I PROJECT OVERVIEW........................................................................... 1 SECTION II CONDITIONS AND REQUIREMENTS SUMMARY................................. 9 SECTION III OFFSITE ANALYSIS............................................................................ 11 SECTION IV FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS........................................................................... 16 SECTION V CONVEYANCE SYSTEM ANALYSIS AND DESIGN............................... 19 SECTION VI SPECIAL REPORTS AND STUDIES...................................................... 19 SECTION VII OTHER PERMITS............................................................................... 19 SECTION VIII CSWPPP ANALYSIS AND DESIGN...................................................... 19 SECTION IX BOND QUANTITIES AND DECLARATION OF COVENANTS........................................................ 20 SECTION X OPERATIONS AND MAINTENANCE MANUAL................................... 21 LIST OF FIGURES FIGURE 1 VICINITY MAP..................................................................................... 2 FIGURE 2 TIR WORKSHEET................................................................................. 3 FIGURE 3 EXISTING SITE SOILS........................................................................... 6 FIGURE 4 EXISTING LAND COVER....................................................................... 7 FIGURE 5 DEVELOPED LAND COVER.................................................................. 8 FIGURE 6 OFF-SITE STUDY AREA...................................................................... 11 FIGURE 7 DOWNSTREAM STORMWATER SYSTEM.......................................... 15 LIST OF APPENDIXES APPENDIX A CONVEYANCE CALCULATIONS APPENDIX B FLOW CONTROL APPENDIX C GEOTECHNICAL REPORT APPENDIX D OPERATION AND MAINTENANCE MANUAL Renton Commons Page 1 Project No. 16001 Sitewise Design PLLC SECTION I – PROJECT OVERVIEW General Description: The proposed Renton Commons project is located at 215 Whitworth Avenue in Renton Washington (See Figure 1 for vicinity map). The project consists of the demolition of an existing single family house and associated hardscape, and the construction of a new low income residential building comprising five stories with parking located within the building, on the ground floor. The proposed project also involves the creation of new hardscape walkways and landscaped areas, as well as a small outdoor play area. The proposed redevelopment is designed to meet the requirements of the 2009 King County Surface Water Design Manual (KCSWDM) and the 2010 City of Renton Amendments to the King County Surface Water Design Manual. A summary of the project data is provided in the TIR worksheet (see Figure 2). Predeveloped Conditions: The existing site comprises a 0.32 acre parcel. Approximately .04 acres of the site comprises the existing single family home, while the remaining area is comprised of grass. The underlying soils are silt and silty sand with gravel. (See Figure 3 for soil map). Topography on the majority of the site is characterized by moderately sloping surfaces with slopes ranging from 1-4%. It is surmised that existing roof drainage is collected via roof downspouts and conveyed to the existing PSS in Whitworth Ave S. Runoff from landscaped areas appears to sheet flow off the site; no formal site drainage collection or conveyance system is evident. For a detailed description of the downstream stormwater system see Section III of this report. The predeveloped conditions described above are presented graphically in Figure 4. Developed Conditions: The areas of proposed redevelopment account for 0.32 acres of the 0.32 acre parcel. The proposed site will include a new low income housing building, landscaping, walkways, and a small play area. See Figure 5 for proposed developed surfaces. Stormwater runoff from the proposed improvements will be collected via roof drains, catch basins, and area drains. Runoff will be routed to a duplex pump chamber and will be discharged to the existing storm main in the SPU ROW to the north of the project site. Per Core Requirement #4 of KCSWDM, the proposed conveyance system has been designed to convey runoff resulting from the peak rates resulting from the 100-year storm event. Renton Commons Page 2 Project No. 16001 Sitewise Design PLLC FIGURE 1 – VICINITY MAP Renton Commons Page 3 Project No. 16001 Sitewise Design PLLC FIGURE 2 TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Part 2 PROJECT LOCATION AND DESCRIPTION Project Owner : Low Income Housing Institute Address : 2407 First Avenue, Seattle, WA Phone : (206) 957-8050 Project Engineer: Marc Errichetti, PE Company: Sitewise Design, PLLC Address/Phone: 206 402 4644 Project Name : Renton Commons LLC Location : 215 Whitworth Ave, Renton, WA 98057 Quarter: SE Section: 18 Township: 23 Range: 5 Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS Subdivision Short Subdivision •Grading •Commercial Other _______________________ _______________________________ DFW HPA Shoreline Management COE 404 Rockery DOE Dam Safety Structural Vaults FEMA Floodplain Other COE Wetlands Part 5 SITE COMMUNITY AND DRAINAGE BASIN Community Renton Drainage Basin Black River Part 6 SITE CHARACTERISTICS Renton Commons Page 4 Project No. 16001 Sitewise Design PLLC River ________________________________ Stream ___________________________ Critical Stream Reach Depressions/Swales Lake Steep Slopes ______________________ Floodplain ______________________ Wetlands Seeps/Springs High Groundwater Table Groundwater Recharge Other __________________________ Part 7 SOILS Soil Type Silt and silty sand with Gravel _________________ _________________ _________________ Slopes 0% to 40% _________________ _________________ _________________ Erosion Potential Moderate _________________ _________________ _________________ Erosive Velocities _________________ _________________ _________________ _________________ Additional Sheets Attached Part 8 DEVELOPMENT LIMITATIONS REFERENCE ______________________________ ______________________________ ______________________________ ______________________________ ______________________________ ______________________________ Additional Sheets Attached LIMITATION/SITE CONSTRAINT _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ Part 9 ESC REQUIREMENTS Renton Commons Page 5 Project No. 16001 Sitewise Design PLLC MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION Sedimentation Facilities •Stabilized Construction Entrance •Perimeter Runoff Control •Clearing and Grading Restrictions •Cover Practices •Construction Sequence Other MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION •Stabilize Exposed Surface •Remove and Restore Temporary ESC Facilities •Clean and Remove All Silt and Debris •Ensure Operation of Permanent Facilities Flag Limits of SAO and open space preservation areas Other Part 10 SURFACE WATER SYSTEM Grass Lined Channel •Pipe System Open Channel Dry Pond Wet Pond Tank Vault Energy Dissipater Wetland Stream Infiltration Depression Flow Dispersal Waiver Regional Detention Method of Analysis KCRTS Compensation/Mitigatio n of Eliminated Site Storage N/A Brief Description of System Operation: Piped conveyance to 12” storm main north of site Facility Related Site Limitations Reference Facility Limitation ____________ ________________ ________________________________________________ ____________ ________________ ________________________________________________ Part 11 STRUCTURAL ANALYSIS Part 12 EASEMENTS/TRACTS Cast in Place Vault Retaining Wall Rockery > 4’ High Structural on Steep Slope Other Drainage Easement Access Easement Native Growth Protection Easement Tract Other Renton Commons Page 7 Project No. 16001 Sitewise Design PLLC FIGURE 3 – EXISTING SITE SOIL CONDITIONS Boring 3: Silt to silty sand Boring 1: Silt with sand Boring 2: Silty sand with gravel designPLLCA CIVIL ENGINEERINGCOMPANY219 First Avenue S.,Suite 401Seattle WA 98104206 402 4644 designPLLCA CIVIL ENGINEERINGCOMPANY219 First Avenue S.,Suite 401Seattle WA 98104206 402 4644 Renton Commons Page 10 Project No. 16001 Sitewise Design PLLC SECTION II – CONDITIONS AND REQUIREMENTS SUMMARY Core and Special Requirements are listed below along with a discussion of their applicability to this project. Core Requirements: Req. #1 Discharge at Natural Location: The discharge location will be maintained to the public storm drain. Req. #2 Offsite Analysis: See Section III below. Req. #3 Flow Control: Flow control is not required as the project will create less than a 0.1 cfs increase in the existing site condition’s 100 year peak flow. KCRTS results are provided in Appendix B. Req. #4 Conveyance System: The new conveyance system has been designed to provide capacity for the 100 year peak flow. Calculations are provided in Appendix A. Req. #5 Erosion and Sediment Control: Construction BMPs will be implemented to meet this requirement. See Section VIII. Req. #6 Maintenance and Operations: A Declaration of Covenant for flow control BMPs may be necessary for this project. Req. #7 Financial Guarantees: A financial guarantee may be necessary for this project. Bonding may be required for the construction of improvements and will be implemented as required. Renton Commons Page 11 Project No. 16001 Sitewise Design PLLC Req. #8 Water Quality: Water quality is not required as the project will create less than 5,000 SF of new and replaced PGIS and less than 35,000 SF of PGPS. Special Requirements: Req. #1 Area Specific Requirements: No area specific requirements are applicable to this project. Req. #2: Floodplain/Floodway Delineation This project is not adjacent to any floodplains or floodways. Req. #3 Flood Protection Facilities: Not required. Req. #4 Source Controls: This project is a multi family residential project and will provide appropriate source controls. Req. #5 Oil Control: No oil control requirements are applicable to this project. Req. #6 Aquifer Protection Area: The project site is not located within an aquifer protection zone area. Renton Commons Page 12 Project No. 16001 Sitewise Design PLLC SECTION III – OFFSITE ANALYSIS Task 1 – Study Area Definition and Maps The Study Area extends approximately 1 mile downstream from the site and is shown in Figure 6 below. The map below was obtained via King County iMap. Figure 6 – Study Area Renton Commons Page 13 Project No. 16001 Sitewise Design PLLC Task 2 – Resource Review The following resources were reviewed for existing/potential problems in the study area: •Adopted basin plans o King County Watershed: Green/Duwamish River •Floodplain/Floodway (FEMA) Maps o The site is not within a floodplain or floodway per FEMA mapping. •Other Offsite Analysis Reports o No problems identified. •Environmentally Sensitive Areas Map o There are no environmentally sensitive areas mapped within the study area. •DNRP Drainage Complaints o There are no known open drainage complaints within the study area. •Road Drainage Problems o There are no known road drainage problems within the study area. •Soils o A goetech report has been completed; site soils are silt and silty sand with gravel. •Wetlands Inventory Maps o There are no wetlands mapped within the study area. Renton Commons Page 14 Project No. 16001 Sitewise Design PLLC Task 3 – Field Inspection A Level 1 downstream analysis was performed to a point a point located approximately 1/4-mile downstream of the site. The following is a summary of the field inspection: •Investigate any problems reported or observed during the resource review. There were no problems reported or observed during the resource review. •Locate all existing/potential constrictions or lack of capacity in the existing drainage system. There are no known or observed existing/potential constrictions or lack of capacity in the existing drainage system. •Identify all existing/potential downstream drainage problems as defined in Section 1.2.2.1 There are no known or observed existing/potential drainage problems downstream of the site. •Identify existing/potential overtopping, scouring, bank sloughing, or sedimentation. There was no existing/potential overtopping, scouring, bank sloughing, or sedimentation observed downstream of the site. •Identify significant destruction of aquatic habitat or organisms (e.g., severe siltation, bank erosion, or incision in a stream). There were no observed signs of destruction of aquatic habitat or organisms. •Collect qualitative data on features such as land use, impervious surfaces, topography, and soil types. Qualitative data on features such as land use, impervious surfaces, and topography observed during the field inspection are summarized in Section 1 of this report. •Collect information on pipe sizes, channel characteristics, drainage structures, and relevant critical areas (e.g., wetlands, streams, steep slopes). Information on pipe routes, channel characteristics, drainage structures, and relevant critical areas were obtained from the City of Renton GIS maps and record drawings to establish the downstream conveyance route and potential issues. •Verify tributary basins delineated in Task 1. Basins delineated in Task 1 were confirmed to be consistent with conditions observed during field investigation. •Note the date and weather conditions at the time of the inspection. The Level 1 downstream analysis was performed on the morning of May 25, 2016. Weather conditions consisted of partially cloudy skies and temperatures in the mid- 50s. Renton Commons Page 15 Project No. 16001 Sitewise Design PLLC Figure 7 – Downstream Conveyance System Renton Commons Page 16 Project No. 16001 Sitewise Design PLLC Task 4 – Drainage System Description and Problem Description There are no known problems with the downstream system. Task 5 – Mitigation of Existing or Potential Problems Based on the observations made during the field inspection and the requirements that are being met for the design of the proposed drainage systems, no negative impacts to the systems downstream are anticipated from the proposed project. No existing problems were identified. SECTION IV – FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN Flow Control: Flow control is not required as the project will create less than a 0.1 cfs increase in the existing site condition’s 100 year peak flow. KCRTS results are provided in Appendix B. Flow Control BMPs: The site to be redeveloped is approximately 13,917 SF. This project must therefore address the small lot BMP requirements listed in section C.1.3.1 of the 2009 KCSWDM. See attached figure C.1.3.A for the flowchart used in determining the application of flow control BMPs (following this section). •Full Dispersion – Not feasible due to flow path limitations. •Full Infiltration – Per the geotechnical report, the site soils are not suitable for concentrated infiltration. As full dispersion and full infiltration are not feasible for this project, one or more of the flow control BMPs listed in part A of section C.1.3.1 of the KCSWDM must be implemented to impervious surfaces equal to or greater than 20% of the site/lot, which results in a targeted surface area of 2,780 SF. Proposed application of selected flow control BMPs for the targeted areas is described below, and equals 2,896 SF: •Selected BMPs: -Vegetated Roof: Vegetated roof will be used to mitigate 1,200 SF of targeted impervious surface. -Permeable Pavement: Permeable pavement will be used to mitigate 1,696 SF of targeted impervious surface. Surface collection will also be provided for these permeable pavement areas via catch basins and area drains. Water Quality Water treatment is not required as the project will create approximately 1,110 SF of new plus replaced PGIS. Renton Commons Page 18 Project No. 16001 Sitewise Design PLLC SECTION V – CONVEYANCE SYSTEM DESIGN AND ANALYSIS Surface water runoff from the proposed surfaces will be collected via a system of rain leaders, area drains, and catch basins and conveyed by storm drainage pipes to a duplex pump chamber at the northwest corner of the site. Conveyance calculations are provided in Appendix A. SECTION VI – SPECIAL REPORTS AND STUDIES A geotechnical report for the site was completed and is included in Appendix C. SECTION VII – OTHER PERMITS A building permit will be required for construction of the proposed project. SECTION VIII – CSWPPP ANALYSIS AND DESIGN Part A: ESC Measures will be addressed as follows: •Clearing Limits: Clearing limits will be delineated by perimeter silt fencing and chain link fencing. •Cover Measures: Temporary cover will be installed if an area is to remain unworked for more than seven days during the dry season (May 1 to September 30) or for more than two consecutive working days during the wet season (October 1 to April 30). Any area to remain unworked for more than 30 days shall be seeded, sodded, or protected with plastic covering. •Perimeter Protection: Perimeter protection will be implemented by installing silt fencing around the site perimeter where drainage paths require. •Traffic Area Stabilization: A stabilized construction entrance will be provided for construction traffic. •Sediment Retention: Catch basin protection will be provided. •Surface Water Control: Surface water will be collected and conveyed via swales as necessary. Check dams are not warranted as grades are relatively flat. •Dust Control: Dust control, if required, will be provided through the limited use of water trucks. Renton Commons Page 19 Project No. 16001 Sitewise Design PLLC Part B: Anticipated SWPP Activities and the BMPs used to address them are indicated below. The contractor (to be determined later) will be required to provide and maintain a detailed SWPPP on site that will be maintained by the contractor’s CESCL. Stormwater Pollution Prevention Plan - Activity Worksheet Summary #Activity/Category Site Specific Activity Minimum BMP Implemented Add’tl BMB Implemented A-1 Required BMPs for All Commercial Properties Cleanstormdrainagesystem;Eliminate illicitconnectionstostrom drainage system; Stencil storm drains A-4 Storage of Soil, Sand, and Other Erodable Materials Stockpile soil for backfill Cover stockpiles; Routine maintenance Catch basin inserts A-9 Storage of Scrap and Recycling MaterialsConstructionwaste (wood,GWB,metal studs, cardboard, plastic, paper) Designated area for contaminated liquids; Check incoming equipmentforpotentialfluid andbatteries;Removeoldbatteries;Scrap materialstoredofftheground;Coverstockpiles ofmaterial;Routine maintenance Catchbasininserts; OnsiteRecycling A-11 Cleaning or Washing of Tools and Equipment Cleaning small tools Holding tank and disposal into sewer A-1 7 Fueling Operations Fueling lifts Locatefueling toensureleaksdon'tdischarge intostorm,surface,orground;Usedrippans or absorbent pads; Lighting if fueling at night; Routine maintenance Spill control kit onsite A-20 Concrete and Asphalt at Temporary Sites Concrete slurry into backfill pits Drippanswhereappropriate;Stormdraincovers; Containandcollectslurry;Nodischargeinto street,storm,ordrainageditches;Routine maintenance Catch basin inserts A-26 Landscaping Activities Topsoil at landscaping areas No pesticidestosufacewaters;Manufacturer recommendations;Dispose of vegetation properly; Use mulch or erosion control where soilsareexposed;Avoidnoxiousweeds;Routine maintenance Erosioncontrol onsite, including silt fencing A-27 Clearing,Grading,andPreparationof LandforSmallConstruction Projects Grading site Coordinateclearing,grading,anderosion controlrequirementswith City of Samammish Erosion control onsite, includingsilt fencing;Catchbasin inserts A-28 Demolition of Buildings Demolition of existing library Spraywatertocontroldust;Filterfabricat drains;Sweepstreetgutters, sidewalks, drives, and other paved areas Catch basin inserts A-31 Vehicle and Equipment Parking and Storage Vehicles parked onsite Sweep parking lots; Erosion control as required Erosioncontrolplan; Catchbasin inserts; Spill controlkit onsite SECTION IX – BOND QUANTITIES AND DECLARATION OF COVENANT A bond quantity worksheet may be required for this project. A Declaration of Covenant for inspection and maintenance of the proposed flow control BMPs may be required. A draft of the Declaration of Covenant will be included with the final TIR to be submitted for the building permit. Renton Commons Page 20 Project No. 16001 Sitewise Design PLLC SECTION X – OPERATIONS AND MAINTENANCE MANUAL An operation and maintenance manual which outlines required regular maintenance necessary for the proposed stormwater system is provided in Appendix D. The maintenance of the stormwater facilities will by be performed by the Owner. Appendix A Conveyance Calculations Appendix B KCRTS Results EXISTING CONDITIONS MODEL (Hourly time step, reduced) Total Site area: 0.32 Ac. Impervious area: 0.04 Ac. Pervious area: 0.28 Ac. till grass DEVELOPED CONDITIONS MODEL (Hourly time step, reduced) Total Site area: 0.32 Ac. Impervious area: 0.26 Ac. Pervious area: .06 Ac. till grass (.03 grass + .03 grass for flow control BMP credit) SUMMARY 0.133 cfs (Developed) - 0.078 cfs (Existing) = 0.055 cfs < 0.1 cfs NO FLOW CONTROL REQUIRED Appendix C Geotechnical Report Appendix D Operation and Maintenance Manual