CORRESPONDENCE_4/7/22 [REV] APPENDICES W/FIRE PERMIT

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COMPOST FACILITY STORM WATER IMPROVEMNTS 2-1 SECTION 2 Storm Water Conveyance The Compost Facility occupies approximately 39-acres in the southern portion of the Forward Landfill site. Composting is performed using the windrow method. Windrows are located north and south of an east west trending access road. Composting is performed on a 1-ft minimum compacted soil layer with a maximum permeability of 1 x 10-5 cm/sec. Information on the compost pad permeability will be provided in a separate report. Both the north and south compost areas are crowned along a central east-west line and generally slope at a minimum 1 percent grade to the center and perimeter of the compost area. Areas that do not meet the minimum 1 percent grade will be regarded to achieve the minimum required slope as part of the Compost Facility Storm Water Improvements construction project. The natural terrain at the Compost Facility area is relatively flat and there are no adjacent slopes that would cause surface water to run-on to the Compost Facility area. Runoff from the Compost Facility area sheet flows to either the central drainage ditch or to the north and south perimeter ditches. The ditches are sized for the 25-year, 10 minute storm and are a minimum 2.5-ft deep with 3:1 (horizontal:vertical) slopes. A berm is included on the north side of the north ditch as an added runoff protection feature. Storm water calculations are provided in Appendix B. HDPE pipe culverts are incorporated at road crossings. Concrete headwalls are used to transition from the ditches to the pipes. The central ditch combines with the northern ditch on the western side of the site and then transitions via a concrete headwall into a below ground trenched HDPE pipe and into the retention basin. The southern ditch also transitions via a concrete headwall into a below ground HDPE pipe and into the retention basin.