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7. ON -SITE STORMWATER MANAGEMENT <br />As documented in Section 1 of this report this project is required to meet Minimum <br />Requirements 1-5. As a result, this project is required. to use the On -Site Stormwater <br />Management BMP's from the 2019 DOE SWMMWW. <br />Per the DOE SWMMWW, the BMP's must be evaluated in the order they are listed. <br />BMP's for roofs: <br />1. Full Dispersion: Not feasible due to the 65:35 requirement. <br />2. Downspout Infiltration Systems: <br />Per Section. 8.1.5 of the geotechnical report (see Appendix A), "the infiltration rate was <br />determined to be 0.24 inches per hour. This rate is lower than what is considered to be <br />feasible for widespread infiltration." Therefore, infiltration is infeasible. <br />3. Downspout Dispersion Systems: <br />Minimum flow paths cannot be achieved, therefore downspout dispersion is infeasible. <br />4. :Perforate.d,Stub-out Connections: <br />Feasible and selected. The roof runoff shall be directed to a perforated stubout <br />connection before 'connecting to the existing stormwater stub on -site that drains to the <br />detention vault. <br />BMP's for other hard surfaces: <br />1. Full Dispersion: Not feasible due to not having 65% preserved vegetation. <br />2. :- -Permeable Pavement: The geotechnical -engineer -states.-thatthe•-design. infiltration <br />rate is 0.24 inches per hour. Section 8.1.5 of the geotechnical report also states <br />"Depending on the final site layout and grading, it may be possible to utilize <br />permeable pavements for new driveways. Thus, permeable pavement is feasible - <br />and is being proposed for the new driveway. The permeable pavement section was <br />modeled using the 2012WWHM with an infiltration rate of 0.24 inches per hour. <br />With a 6-inch pavement thickness1-inch layer of leveling course and 6-inch layer <br />of reservoir course, the permeable pavement is shown to infiltrate 100 percent of <br />runoff (See Appendix A for WWHM printout). <br />3. Bioretention/Rain Gardens: Higher priority BMP selected. <br />4. Sheet Flow Dispersion Higher priority BMP selected. <br />5. Concentrated flow Dispersion: Higher priority BMP selected. <br />Finally, any area of the site not proposed to .be covered with impervious surfaces but <br />graded or compacted will be treated to meet the criteria for BMP 12.20. Please refer to <br />the engineering plans for basic soil amendment notes. <br />Moir SP Lot 6 20-0108 <br />February 2020 <br />Revised: October 2020 Page 9 <br />