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HomeMy WebLinkAboutRS_Drainage_Assessment_180510_v3 C.E.S. NW Inc. P:\13040.0\!Filing - Chelan Creek PUD-16 Lot\Site Development\Drainage Assessment Lot 12.doc Page | 1 310 29th St. NE, Suite 101 Puyallup, WA 98372 Phone: (253) 848-4282 Fax: (253) 848-4278 Civil Engineering & Surveying February 24, 2017 City of Renton Planning Division Development Engineering Section 1055 S. Grady Way Renton, WA 98057 Project: Chelan Creek - Lot 12 Permit No.: Not Assigned Subject: Drainage Assessment Project Narrative The project is located on Lot 12 of the Chelan Creek PUD (parent APN 102305-9106) with a lot area of 5,507 sq.ft. The lot slopes from north to the south at approximately 1.0% to 5.0% and is surrounded by residential parcels on all sides. The proposed onsite improvements include: 1,248 sq. ft. of driveway and concrete areas, 1,923 sq. ft. of roof area, and 2,336 sq. ft. of landscaped areas. A geotechnical engineering study has been prepared for Chelan Creek PUD by Associated Earth Sciences, Inc., dated June 20, 2013. Exploration test pit EP-1 is proximity of Lot 12. The test pit discovered approximately 1-foot of topsoil overlying 2-feet of Outwash, underlain by dense Vashon till. Till soils are generally not suitable for infiltration. A copy of the geotechnical engineering study is included with the building permit submittal. Flow Control BMP Description The Chelan Creek project utilizes the Flow Control BMP C2.9 Reduced Impervious Surface Credit for the impervious surface on each lot. According to the approved Chelan Creek Technical Information Report the plat is contained within a single drainage basin. This basin accounts for a 65% impervious lot coverage, which is a 10% reduction of the maximum allowable impervious area per the zoning (R-8). The proposed Lot 12 impervious lot coverage is 58%. D08-053 B17005052 V3 REVISION Received: 05/10/2018 / aalexander BUILDING DIVISION APPROVEDBUILDING DIVISION THIS SET OF APPROVED PLANS MUST BE ON THE JOB AT ALLTIMES DURING CONSTRUCTION. THIS BUILDING IS NOT TO BEOCCUPIED UNTIL AFTER FINAL INSPECTION BY THE RENTONBUILDING DIVISION AND RECEIPT OF CERTIFICATE OFOCCUPANCY. APPROVAL SHALL NOT BE CONSTRUED AS THE AUTHORITY TOVIOLATE OR CANCEL ANY PROVISIONS OF CODES, ORDINANCES,OR OTHER REGULATIONS ENFORCED BY THIS CITY. DATE: 05/23/2018 P:\13040.0\!Filing - Chelan Creek PUD-16 Lot\Site Development\Drainage Assessment Lot 12.doc Page | 2 In addition, the Chelan Creek project utilizes the Flow Control BMP C2.4 Basic Dispersion for the roof surface. A dispersion trench exists south of the lot which will disperse the roof area into a 50-foot native vegetated flow path within the existing wetland/stream buffer. The Chelan Creek PUD also provides combined water quality and detention pond for water quality treatment and detention for the residential driveways and roadway elements associated with the project. Erosion and Sediment Control Measures In order to prevent erosion and trap sediment within the project site, the following BMPs will be used approximately as shown on Exhibit “C”:  Clearing limits will be marked by fencing. Clearing shall remain within this limits. The contractor shall not clear any more area than what can be stabilized in a single day.  The driveway will be constructed and graveled immediately.  Cleared areas sheet flowing onto the proposed driveway shall be seeded and mulched.  Runoff shall not be allowed to concentrate and no water will be allowed to point discharge onto any slopes. Silt fencing will be placed following the contours at the downslope limit of clearing.  Mulch will be spread over all cleared areas of the site when they are being worked.  Stockpiles shall be covered or stabilized to prevent sediment laden runoff. Operation and Maintenance Standards The drainage facilities shall be maintained as per the maintenance covenants on file with the City of Renton. A copy of the Chelan Creek PUD Operations and Maintenance Manual can be provided upon request. This Drainage Assessment and Erosion Control Plan for Chelan Creek PUD Lot 12 has been prepared by me or under my supervision and meets the standard of care and expertise which is usual and customary in this community of professional engineers. I understand that the City of Renton does not and will not assume liability for the sufficiency, suitability or performance of drainage facilities prepared by me.