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2-7 Forward Composting Facility SWT Engineering Report of Composting Site Information - January 2022 compost retention basin, which is sized to contain the 25-year, 24-hour rainfall event (2.84 inches), with adequate freeboard. In accordance with WDR Order No. R5 -2014-0006 and WDR Order No. 2020 -0012-DWQ, the compost pond is lined with a geosynthetic clay liner (GCL) overlain with a 60-mil HDPE geomembrane and contains a pan lysimeter. The location of the compost retention basin is shown on Figure 2. All surface water runoff from the Compost Facility will be collected and stored in the compost retention basin and evaporated. Collected runoff may be used to add water to the initial compost mixture to provide the desired initial moisture content, or evaporated. If necessary, collected runoff will be either pumped to a leachate evaporation impoundment or will be collected and removed for off -site disposal. 2.1.5 Pad Composition and Dimensions As detailed in the Lewis Engine ering letter, dated December 14, 2014, compost operations at the facility occur on a compacted pad that has a permeability no greater than the 1 x 10 -5 cm/sec regulatory requirement. The compost pad area is utilized (i.e., the amount of area) based on the selected composting method and materials. The green and wood waste grinding area is approximately 1.56 acres. The material sorting area is approximately 1.07 acres, the windrow areas are approximately 14.8 acres, and the ASP composting area is approximately 3 acres . The windrow curing and product screening area, and final product storage area is approximately 2.97 acres. The remaining acreage is for equipment and vehicle access roads, and the detention pond. The site and pad have a minimum of a one percent slope and windrows will be constructed normal (or perpendicular) to the slope, so there will be no standing water on the pad. Detailed design calculations are presented in Appendix B. 2.1.6 Drainage Control Run-on to the composting site is prevented by existing berms and ditches located on the perimeter of the RRF /Compost site area. S lopes generally decrease from the northeast to the southwest. An existing ditch prevents run -on from the north. The grading and drainage plan (Figure 6) shows the grading of the RRF/Compost Facility. The grading plan is the same for all of the potential composting alternatives. A one percent minimum grade is provided at all points in the composting site. The composting windrows are arranged normal to the slope to allow free drainage and minimize ponding. The site is sloped to drain to two ditches designed to carry the water from the 25 -year, 10- minute duration storm (0.368 inches) assuming all the water that falls on the composting site runs off. The ditches carry the water to the lined compost retention basin designed to contain the 25-year, 24-hour rainfall event (2.84 inches), with adequate freeboard. 2.1.7 Leachate Control (14 CCR, Section 17867(a)(12)) Since additional water will only be applied to the compost when necessary for maintaining adequate internal moisture, significant leachate generation is not anticipated. As stated in Section 3.5.3, the site is in a region of net evaporation. Additionally, compost windrows typically form a light crust on the outside, which repels rainfall. The site's drainage control system, including the lined compost retention basin, was designed to handle all runoff ,