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GLINT CAR WASH - EVERETT <br /> STORMWATER REPORT <br /> Minimum Requirement#5—On-Site Stormwater Management <br /> Onsite Stormwater Management is required of the project since our project requires compliance <br /> with MR1 —MR9. See Figure 1-3.3 of the 2019 SWMMWW. The existing till soils are not conducive <br /> for onsite infiltration to meet the LID Performance Standard. List#2 will be evaluated for feasibility <br /> of possible BMPs to implement. The following is an outline of our landcover area and the viability of <br /> each Onsite Stormwater Management BMP (viability analysis noted in bold): <br /> 2019 SWMM Note: For each surface, evaluate the feasibility of the BMPs in the order listed, and <br /> use the first BMP that is considered feasible. The designer must document the site conditions and <br /> infeasibility criteria used to deem BMPs infeasible. Once a BMP is deemed feasible and used for <br /> a surface, no other BMP from the list is necessary for that surface. <br /> If all BMPs in the list are infeasible,then the designer must document the site conditions and <br /> infeasibility criteria used to deem each BMP infeasible. This documentation will demonstrate <br /> compliance with Minimum Requirement#5. <br /> Feasibility shall be determined by evaluation against: <br /> • Design criteria, limitations, and infeasibility criteria identified for each BMP in this manual, <br /> and, <br /> • Competing Needs Criteria as listed below. <br /> Lawn and Landscaped Areas <br /> Post Construction Soil Quality and Depth in accordance with BMP T5.13 —We have specified <br /> this BMP for our pervious areas on the permit plans. <br /> Roofs <br /> 1. Either(The applicant shall evaluate both a and b for feasibility) <br /> a. Full Dispersion in accordance with BMP T5.13 -Insufficient area for full dispersion, or <br /> b. Downspout Infiltration Systems in accordance with BMP T5.10A — The existing fill and <br /> native Till soils are not suitable for stormwater infiltration. The presence of loose fills <br /> will require cement treatment of the site subgrades which will then render the existing <br /> subgrade too dense and shallow to allow infiltration. <br /> 2. Bioretention in accordance with BMP T7.30 - Not proposed since the existing Till soils are <br /> not suited for full infiltration and the available depth to dense soils will be too shallow. <br /> 3. Downspout Dispersion Systems in accordance with BMP T5.10B — Insufficient available <br /> vegetative flow path. <br /> 4. Perforated Stub-Out Connections in accordance with BMP T5.10C - The existing fill and <br /> native Till soils are not suitable for stormwater infiltration. Insufficient depth separation <br /> to dense subgrade. <br /> No Onsite Stormwater Management BMPs are proposed for the project Roof Surfaces. <br /> Terraforma Design Group, Inc. <br /> Page 14 <br />