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Home My WebLink About3719 ENGINEERING REPORT Drainage Report Renton Technical College Building M Parking Lot x/o Renton, WA June 2013 PREPARED FOR: Renton Technical College 3000 NE Fourth St Renton,WA 98101 Barry Baker �l f PREPARED THROUGH: r� Buffalo Design 1520 Fourth Ave#400 n Seattle,WA 98101 43&"7 Julia Cygan It PREPARED BY: COUGHLINPORTERLUNDEEN 413 Pine Street,Suite 300 Seattle,Washington 98101 P: 206/343-0460 Contact: Mr.Alan Jacobson, P.E. COUGH LINPORTERLUNDEEN 0371 Technical Information Report Building M Parking Lot Renton Technical College Coughlin Porter Lundeen Project No.C12 0308-06 June 19,2013 Table of Contents Section Page I. PROJECT OVERVIEW............................................................................................................................2 GENERALDESCRIPTION...........................................................................................................................................2 EXISTING DRAINAGE AND SITE CONDITIONS...........................................................................................................2 PROPOSEDDRAINAGE SYSTEM...............................................................................................................................2 II. PRELIMINARY CONDITIONS..............................................................................................................4 COREREQUIREMENTS.............................................................................................................................................4 SPECIALREQUIREMENTS.........................................................................................................................................4 III. OFF-SITE ANALYSIS...............................................................................................................................6 IV. SITE HYDROLOGY ANALYSIS AND DESIGN..................................................................................7 STORMRUNOFF CONTROL ANALYSIS.....................................................................................................................7 WATERQUALITY ANALYSIS...................................................................................................................................7 V. CONVEYANCE ANALYSIS....................................................................................................................8 VI. SPECIAL REPORTS AND STUDIES.....................................................................................................9 VII. BASIN AND COMMUNITY PLANNING AREAS...............................................................................9 VIII. OTHER PERMITS.....................................................................................................................................9 IX. TEMPORARY EROSION AND SEDIMENT CONTROL..................................................................9 X. BOND QUANTITY WORKSHEET......................................................................................................10 XI. MAINTENANCE AND OPERATIONS MANUAL.............................................................................10 Figures FIGURE 1—CITY FLOW CONTROL REFERENCE MAP FIGURE 2—RECORD STORM SYSTEMS(CITY GIS) FIGURE 3—EXISTING SITE CONDITIONS FIGURE 4—PROPOSED SITE CONDITIONS Appendix APPENDIX A—STORM RUNOFF CONTROL AND WATER QUALITY CALCULATIONS COUGHLIN PORTER LUNDEEN 1 June 19,2013 I. PROJECT OVERVIEW General Description The following Technical Information Report(FIR)provides the technical information and design background required for developing the Drainage and Temporary Erosion and Sedimentation Control(TESC)Plan for the project. The design is for a new 10-car parking lot at Building M on the . Renton Technical College campus.The design is based on the requirements set forth in the 2009 King County Surface Water Design Manual(KCSWDM),as adopted by City of Renton. Building M is located within the Renton Technical College campus,located at 3000 Northeast 4f Street in Renton,Washington(see Figure 2-Site Vicinity Map). The project site is in the north portion of the campus,west of Kirkland Avenue Northeast,and south of Northeast 7th Street. It is within the Lower Cedar River Community Basin and Drainage Sub-basin. The site currently consists of a building with an outdoor play area off to the north.The play area will be removed,and replaced with approximately 4,500-Sf of asphalt parking lot. Additional site improvements will include installing a fire service and landscaping to screen the new parking lot. The project will not provide storm water runoff control per the 2009 King County Surface Water Drainage Manual(KCSWDM)as adopted by City of Renton Surface water from the new pavement will be collected,run through a rain garden for water quality treatment,and discharged to the campus storm system.The campus storm system discharges to City systems to the west,for discharge to Lake Washington. Although run treatment is not required for pollution generating surfaces less than 5,000-Sf,the project will construct a small rain garden to treat the water for oils and metals before discharge from the campus. Existing Drainage and Site Conditions The project site consists of approximately 0.25-acre in the north end of the Renton Technical College campus. The site is currently comprised of landscape and bark chip covered play area. The site slopes from east to west at approximately 3%with a 5-foot elevation change.Storm water discharges through a private storm system along the western edge of the campus. Runoff is then routed to the public storm system in Kirkland Avenue Northeast. Proposed Drainage System The proposed project will add a new 4,500-SF parking lot to the north end of Building M.No footprint changes to the building will occur with this renovation. Surface runoff generated from the new parking lot will be collected and routed to a new rain garden at the west end of the lot. Storm water runoff will percolate through the rain garden,some of it will infiltrate into surrounding soils, COUGHLIN PORTER LUNDEEN 2 June 19,2013 the remainder will be collected in an under drain for discharge through the existing campus storm system to the Cit/s public system in Kirkland Avenue NE(see Figure 6-Proposed Site Conditions). COUGHLIN PORTER LUNDEEN 3 June 19,2013 II. PRELIMINARY CONDITIONS Core Requirements This section will address the requirements set forth by the Core Requirements listed in Chapter 1 of the 2009 King County Surface Water Design Manual(KCSWDM),as adopted by City of Renton. 1. Discharge at the Natural Location(1.2.1)-All storm runoff from newly developed site areas will be directed to the west side of the building and into existing campus storm drainage systems there. 2. Off-Site Analysis(1.2.2)-A Level 1 off-site analysis is discussed in the"Off Site Analysis-section of this report 3. Flow Control(1.2.3)Peak Rate Runoff Controk The site is in City of Renton mapped"Peak Rabe Flow Control Standard(Existing Conditions).The rate off the site will change by less than 0.1-CF5 in the 100-year storm;no flow control measures are required.No downstream conditions have been identified that would require this site to mitigate beyond minimum requirements. 4. Conveyance System(1.2.4)-The water collected off of the site will be conveyed in minimum 6-inch pipes to the campus storm system,and then to larger pipes in the public street 5. Erosiort/5edimentation Control Plan(1.2.5)-This project will install a series of temporary erosion and sediment control Best Management Practices(BMP's)related to specific conditions on-site. This subject will be addressed in the"Temporanj Erosion and Sediment Control"section of this report 6. Maintenance and Operation(1.2.6)-The proposed on-site storm drainage system will be owned,operated,and maintained by Renton Technical College. A Maintenance and Operation Manual is included in Section XI of this report 7. Financial Guarantees and Liability(1.2.7)-The Owner and Contractor will obtain all necessary permits and obtain required bonds prior to the beginning of construction 8. Water Quality(1.2.8)-Less than 5,000-SF of new impervious pollution-generating area will be developed as part of this project Therefore,water quality treatment will not be required for this project.However,the project will install a small water quality rain garden to treat the collected water before it is discharged from the site. Special Requirements This section will address the requirements set forth by the Special Requirements listed in Chapter 1.3 of the 2009 King County Surface Water Design Manual(KCSWDM)as adopted by City of Renton. 1. OtherAdopted Area Specific Requirements(1.3.1)-The project is not located in an area with special requirements. 2. Flood hazard Delineation(1.3.2)-The project is not located in a flood zone as mapped by FEMA. 3. Flood Protection Facilities(1.3.3)-The project is not located in a flood zone as mapped by FEMA. 4. Source Controls(1.3.4)-No sources of pollutants will be exposed on site as a result of this re-development. COUGHLIN PORTER LUNDEEN 4 June 19,2013 5. Oil Control(1.3.5)-The Site is not a high-use site,and will not generate concentrations of oil. 6. Aquifer Protection Area(1.3.6)-The site is in"Streamflow Source Area"as mapped by the City of Renton It is not in an Aquifer Protection area. COUGHLIN PORTER LUNDEEN 5 June 19,2013 Off-site analysis Upstream Analysis The area upstream of the site is a paved parking lot that drains to a storm system separate from Building M and its surrounding site. No significant water enters the site from off-site.The proposed development will not change this condition. Downstream Analysis The project site is located within Lake Washington East Drainage Basin. Existing land cover on the site consists of approximately 0.25-acres of landscape and bark covered play area. Storm water runoff infiltrates into the landscape and playground bark. There is evidence of a buried area drain/catch basin under the play area.The local on-site storm system at Building M combines with other elements of the Renton Technical College campus piped storm system,which then discharges to the public 18-inch storm main running south,parallel to Kirkland Avenue NE(See Figure 8-City of Renton Storm System Map).This public storm system eventually discharges to Lake Washington near Gene Coulon Park.No evidence of problems with this downstream system has been found. COUGHLIN PORTER LUNDEEN 6 June 19,2013 III. SITE HYDROLOGY ANALYSIS AND DESIGN Storm Runoff Control Analysis The drainage system for the project site was designed in accordance with the 2009 King County Surface Water Design Manual(KCSWDM)as adopted by City of Renton. The peak runoff rates for the hydraulic design were determined using a continuous HPSF model(MGS flood Version 4.31). Stormwater runoff control and water quality will be provided by a small rain garden at the west end of the new parking lot.While neither flow control nor water quality treatment is required by the City code for this level of development(Less than 0.1-cfs change in 100-year event and less than 5,000-SF of new PGIS)the owner wishes to mitigate for the new surface parking. Table 1: Proposed Drainage Basin Areas Land Cover Area acres Impervious Area ac 0.1 Pervious Area ac 0.15 Total Area ac 0.25 The rain garden will have a 4-ft x 23-ft bottom,covered with 12-inches of rain garden soil.An under drain and over flow catch basin will ensure that water that cannot infiltrate has somewhere to go. A minimum infiltration rate of 0.25in/hr has been assumed for the native soils,no infiltration testing has been performed for this site.The water quality function is primarily performed by the imported rain garden soil. Water Quality Analysis Less than 5,000-SF of new pollution generating impervious surface(PGIS)will be installed for the new parking and drive.Per the City's Stormwater code,no treatment is required;however the owner is electing to provide treatment for this new pollution generating area.Per the storm water model,all of the water(100%)entering the rain garden is treated by the rain garden soil. COUGHLIN PORTER LUNDEEN 7 June 19,2013 Conveyance Analysis The proposed conveyance system consists of sheet flow off the parking lot to the rain garden.An under drain or the over flow catch basin will collect water that does not infiltrate,and direct it to the campus storm water system. Flows out of the revised site are expected to be no more than 0.103-cfs in the 100-year storm, The 6-inch pipe at 2%proposed from the site will be able to handle more than 1-cfs.Record systems downstream are steadily larger pipes,and should not notice the change in flow rate. COUGHLIN PORTER LUNDEEN 8 June 19,2013 IV. SPECIAL REPORTS AND STUDIES No special reports have been prepared for this site renovation V. BASIN AND COMMUNITY PLANNING AREAS This site is not part of a special community or planning area VI. OTHER PERMITS No additional permits are required for the project. VII. TEMPORARY EROSION AND SEDIMENT CONTROL To minimize the amount of sediment laden water from leaving the site during the construction process,a temporary erosion and sedimentation control(TESC)plan has been designed for this project in accordance with the current KCSWDM as adopted by the City of Renton. The TESC plan indicates the minimum necessary measures that the contractor shall implement during the construction process. Best Management Practices(BMP's)are defined as physical,structural and/or managerial practices that,when used in combination,prevent or reduce pollution of water caused by construction activities. The TESC plan for the proposed project has been designed to protect off- site properties as well as minimize the quantity of sediment-laden water from entering the public storm system. The following BMP's will be included on the TESC plan for this project: ❑ To ensure that the disturbance of the site is limited to the development area,the clearing limits will be clearly staked prior to any clearing or grading as shown on the TESC plan. ❑ Catch basin protection will be used on existing and future catch basins to reduce sediment-laden water from entering the existing storm system during construction. ❑ Cover measures such as mulch,seeding,or plastic sheeting will be implemented for disturbed areas greater than 5,000 square feet in accordance with the City of Renton Standards. ❑ Perimeter measures such as silt fence or straw wattles will be used at the lower limit of the work to contain and control sediment from leaving the work area. ❑ All construction debris will be promptly removed from the site to minimize demolition and construction impacts on the site. The contractor shall implement additional BMP's as required and/or recommended by the City of Renton inspector or other agencies as required to prevent demolition and construction debris,waste material,fuel,oil,lubricants,and other fluids from entering the public storm system. COUGHLIN PORTER LUNDEEN 9 June 19,2013 VIII. BOND QUANTITY WORKSHEET A Bond Quantity Worksheet is included. IX. MAINTENANCE AND OPERATIONS MANUAL Will be provided later COUGHLIN PORTER LUNDEEN 10 June 19,2013 FIGURES FIGURE 1—CITY FLOW CONTROL REFERENCE MAP FIGURE 2—RECORD STORM SYSTEMS(CITY GIS) FIGURE 3—EXISTING SITE CONDITIONS FIGURE 4—PROPOSED SITE CONDITIONS COUGHLIN PORTER LUNDEEN June 19,2013 Jdi INV INV W, REM Ul OWN MWim- � C� ns Will Vol IN INN PCL XL error Subsystem: TEXT Error: InternaLError Ox50 Operator: Text Position: 311350 S -------- - - up— u -F R NEW PLANTING$ AND SOIL P REP 7' ;,U 7 12'bb-c t r �Lzy p -.1ro / J � . 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