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STORMWATER SITE PLAN <br />FEBRUARY 26, 2018 <br />MUKILTEO SCHOOL DISTRICT - TRANSPORTATION <br />PAGE 8 <br />PERMANENT SOURCE CONTROL BMPs <br />Source controls will be those that the site already operated under such as storm maintenance, <br />keeping pavement clean, and vegetative management. <br />MR 4: PRESERVATION OF NATURAL DRAINAGE <br />Currently, runoff is collected and ultimately discharged to the existing wetlands. As the site <br />discharges to the existing storm system, it preserves this drainage system. <br />MR 5: ON -SITE STORMWATER MANAGEMENT <br />Being required to meet Minimum Requirements #1-5, the site will need to meet either the Low <br />Impact Development Performance Standard or List #1 On -site Stormwater Management BMPs. <br />It is proposed to follow the requirements of List #1 as follows: <br />The project proposed to meet the performance standard. "Stormwater discharges shall match <br />developed discharge durations to pre -developed durations for the range of pre -developed <br />discharge rates from 8% of the 2-year peak flow to 50% of the 2- year peak flow." <br />Lawn and Landscaped Areas: <br />BMP T5.13 Post Construction Soil Quality and Depth will be implemented on disturbed and <br />landscaped areas. <br />BMP T5.13 POST CONSTRUCTION SOIL QUALITY AND DEPTH. <br />Post Construction Soil Quality and Depth will be used on the site to recondition those areas that <br />have been compacted by construction traffic. Imported topsoil will be used to cover the <br />disturbed areas. <br />Pavement Areas: <br />1) Full Dispersion: <br />Full dispersion is not feasible on the site due to the previous development. <br />2) Permeable Pavement or Rain gardens: <br />Permeable Pavement: The infeasibility criteria are found under BMP T5.15. <br />Pervious pavement is found infeasible on this site as the new pavement is being placed next to <br />existing pavements that are placed on fill and could compromise that pavement support. <br />Additionally, the new pavement will be constructed on fill material that is the backfill for a <br />retaining wall. <br />Further, the subgrade soils are till and are near to a documented wetland, indicating that <br />infiltration is limited. <br />PAWork\Projects\2012\12-185 Mukilteo SMCMDOCS\Transportation Facility Drainage 12-185_doc <br />