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HomeMy WebLinkAboutC_WrittenDrainageAssesment_190430_V1Builder / Owner Classic Concepts VIII LLC PO Box 146, Renton WA 98057 425-228-9750 Site Address 16000 SE 140th Street Renton WA 98059 Mindy’s Place (Estates) lot 1 Parcel # 554754-0010 DRAINAGE ASSESSMENT PROJECT NARRATIVE The project is located on16000 SE 140th Street Renton WA 98059 which is been developed as an lot short plat on a 7,200 sq. ft. lot zoned R-4. The lot has been cleared during development with no native vegetation on site. The lot has about three feet of fall from North to Southeast. There are no drain fields or other improvements and utilities on the lot. There is no steep slope, wetlands or other buffers on the lot. The Reduced Impervious Surface credit BMP is a maximum of 3,564 sq. ft. as proposed for the Mindy’s Place Plat development conditions. House and porch including overhangs, patio and driveway cover approximately 3,145 ft. making total lot coverage 43.6% Lot 1 is part of the Mind’s Place (Estates). The storm water and house drainage was considered in the current storm water and retention system design. Due to the size of the lot it is subject to the Small Project Drainage Review and the development requirements. The size of the lot does not allow for any of the following BMP’s; Ground Surface Depression Infiltration, Downspout Dispersal or Rain Gardens. All native vegetation is cleared and Native Growth Retention is not possible. The soils are hardpan clay limiting the effectiveness of Drywells, other in-ground dispersal trenches and Permeable Pavement. The storm connection to the existing Plat/Development storm system will be via a Perforated Pipe Connection per details and Section C.2.11. The subdivision storm system has been adequately designed to receive the anticipated storm water and roof run off of the individual lots. EROSION AND SEDIMENT CONTROL MEASURES The lot is cleared and silt fence was installed during development. Additional silt fence shall be installed on the east downhill side of the lot. A construction rock entrance shall be installed in front of the garage and all exposed soils shall be covered as needed to prevent run off into the storm system. Downhill catch basins shall have Stream Guard Filtration Socs. PR13000037 B19003029 V1 RECEIVED 06/06/2019 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: 07/16/2019 EXHIBIT B Perforated pipe connection as required Page 5 of 6 . FLOW CONTROL MAINTENANCE INSTRUCTIONS Site Address 16000 SE 140th Street Renton WA 98059 Mindy’s Place (Estates) lot 1 Parcel # 554754-0010 The Development Conditions of Mindy’s Place plat requires a Reduced Impervious Surface credit BMP of a maximum of 3,564 square feet for this lot. This lot 8 House, porch, patio and driveway cover approximately 3,145 ft. at no time can the impervious surfaces be increased to more than the maximum of 3,564 sq. ft. The square footage of any sheds, additional patios or building additions cannot cover more than the remaining 419 square feet. This property contains a storm water management flow control BMP (Best Management Practice) called a "perforated pipe connection," which was installed to reduce the storm water runoff impacts of some or all of the impervious surface on your property. A perforated pipe connection is a length of drainage conveyance pipe with holes in the bottom, designed to "leak" runoff, conveyed by the pipe, into a gravel filled trench where it can be soaked into the surrounding soil. The connection is intended to provide opportunity for infiltration of any runoff that is being conveyed from an impervious surface (usually a roof) to the local drainage system designed for the plat Per King County 2009 SWDM Appendix C.2.11 see attached drawing. Infiltration devices must be inspected annually and after major storm events to identify and repair any physical defects. Maintenance and operation of the system should focus on ensuring the system's viability by preventing sediment-laden flows from entering the device. Excessive sedimentation will result in a plugged or non-functioning facility. If the infiltration device has a catch basin, sediment accumulation must be removed on a yearly basis or more frequently if necessary. Prolonged ponding around or atop a device may indicate a plugged facility. If the device becomes plugged, it must be replaced. Keeping the areas that drain to infiltration devices well swept and clean will enhance the longevity of these devices. For roofs, frequent cleaning of gutters will reduce sediment loads to these devices. Minimum Page 6 of 6 .