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• <br /> 5. Perforated Stub-Out Connections: Higher priority BMP selected. <br /> Other Hard Surfaces: <br /> 1. Full Dispersion: Not feasible due to not having 65% preserved vegetation. <br /> 2. Permeable Pavement: With a depth to groundwater of over 6 feet and relatively <br /> permeable soils, permeable pavement is feasible. To protect the SFR foundation <br /> and avoid surcharging the foundation drains, standard concrete is being proposed <br /> for the parking pad in front of the garage. See below for drainage details. Permeable <br /> pavement is feasible for the length of driveway along the eastern property line and <br /> is the selected BMP for that surface.The permeable pavement is to be installed per <br /> COE standard details 430 & 431 and per the selected permeable paver product <br /> specifications, with check dams spaced a maximum of 9 feet apart (see drainage <br /> plans for details). <br /> 3. Bioretention/Rain Gardens/Infiltration: Due to site limitations, bioretention/rain <br /> gardens/infiltration are infeasible. The downspout infiltration trench almost entirely <br /> occupies the feasible infiltration area at the front of the lot and increasing the width <br /> of the infiltration trench would increase the risk of groundwater mounding. <br /> 4. Sheet Flow Dispersion: Not feasible due to not having the required 10-foot vegetated <br /> flow path. <br /> 5. Concentrated Flow Dispersion: Infeasible (See above). <br /> This project proposes to collect all runoff from the upper concrete pad in a trench <br /> drain and tightline it approximately 100 feet north and into the main conveyance <br /> system within Viewcrest Avenue. Trench dams will tie into the check dams for the <br /> permeable pavement for the 4" PVC tightline under the permeable pavement (see <br /> drainage plans for detail). A catch basin shall be installed at the connection point. <br /> The foundation drain system will also tie into this tightline and flow into the <br /> conveyance system within Viewcrest Avenue. <br /> 8. RUNOFF TREATMENT <br /> As noted before this project proposes to install a total of 3,401 of PGIS to serve this project <br /> based on the Owner/Applicants plans. <br /> Per the 2014 DOE Stormwater Manual "Minimum Requirements 6: Runoff Treatment — <br /> Requirements" a project is required to provide runoff treatment if: <br /> (a) Projects in which the total effective, pollution-generating impervious surface (PGIS) is <br /> 5,000 square feet or more in a threshold discharge area of the project; or <br /> (b) Projects in which the total of pollution-generating pervious surface (PGPS) is three- <br /> quarters of an acre or more in a threshold discharge area, and from which there is a surface <br /> discharge into a natural or man-made conveyance system from the site. <br /> McCann SFR 19-0913 <br /> September 2019 <br /> Revised:'January-2020 Page 10 <br />