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Grade will be' raised approximately 1 to 2 feet in the area of infiltration trenches to <br />allow adequate separation between the bottom -of the trenches and season <br />groundwater table. As shown in the Geotechnical Addendum dated December 21, <br />2020 included in Appendix A of this report, the site was recently, visited, and shallow <br />hand borings were excavated to determine. a groundwater elevation of approximately <br />191.2 in the area of the.,,proposed infiltration trenches.Therefore, as shown on the <br />stormwater site plan,,the infiltration trench bottom shall beinstalled. at an elevation <br />of 192.5, which will provide the minimum required 1-foot separation between bottom <br />of trench and seasonal. groundwater table. <br />4. Downspout Dispersion: Infeasible, as minimum flow paths cannot be provided for <br />the remaining roof area runoff. <br />5. ' Perforated Stub -Out Connections: Feasible,. and selected. As ; shown on the <br />stormwater site plan, ` a ' minimum roof area of 3,332 sf shall drain to 'a ,2x10' <br />perforated' stubout connection that will flow :to the proposed CB near the western <br />property line and into the existing stormwater conveyance system within Baker Dr. <br />Other Hard Surfaces; <br />I.- FuI[ Dispersion: Not feasible due to not having 65% preserved vegetation. <br />2. Permeable Pavement: The:geotechnical report has ruled out infiltration as a feasible <br />flow control BMP for this project with an infiltration rate of 0.21 inches/hour. The <br />proposed driveway is also located directly up -gradient ' of the proposed SFR, so <br />permeable pavement would likely surcharge the foundation drains. <br />3. Bioretention/Rain Gardens: Infeasible due to poor soil infiltration characteristics.` <br />°--Sheet Flow Dispersion: Feasible• and-seleeted.for all driveway. surfaces. <br />Runoff from the driveway shall sheet flow to the west/northwest, flowing through a <br />.2-foot wide transition zone before dispersing .through amended soils with the <br />minimum required flow; paths for sheet flow dispersion.:' <br />5. Concentrated Flow Dispersion: Higher priority BMP selected. <br />.8. RUNOFF. TREATMENT <br />As noted before this project proposes to install a total of 1,577 of PGIS to serve this project <br />based on the Owner/Applicants plans. <br />Per the 2019 DOE Stormwater Manual "Minimum Requirements 6: Runoff Treatment — <br />RequiremenW. a project is required to provide runoff treatment if. <br />Dhaliwal' SFR 19-1208 <br />December 2020 <br />.ReviseiY:"anuarjJ'20�i Page 10 <br />