ARCHIVED REPORTS_JULY 2014 FINAL RCSI

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2-7 Forward Composting Facility SWT Engineering Report of Composting Site Information - July 2014 z:\projects\allied waste\forward\resource recovery facility\5 yr permit rvw 2013-14\rcsi 2014\text\sec 2.doc water that falls on the site composting runs off. This exceeds the 25-year, 24-hour rainfall event (2.28 inches). The location of the sedimentation basin is shown on Figure 2. All surface water runoff from the Compost Facility will be collected and stored in the sedimentation (retention) basin and evaporated. If necessary, collected runoff that meets water quality criteria for stormwater discharge may be discharged to the South Fork or used to add water to the initial compost mixture to provide the desired initial moisture content, or evaporated. If necessary, collected runoff which does not meet the water quality criteria for stormwater discharge 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 The Compost Facility pad will be constructed of low permeability compacted native soil. It is anticipated that the compacted native soil will provide adequate protection of groundwater. 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, and the windrow areas are approximately 14.8 acres. The curing and screening area, and final product storage area is approximately 2.97 acres. As described above in this section, the composting pad will be constructed of native earth. The permeability of soils below the surface of the composting pad is low. Operations will be suspended, if necessary, during periods of wet weather to prevent damage to the composting pad or the surface will be paved with gravel or asphalt if the economics justify the higher cost. Due to the low-permeability of native soils and depth to groundwater, monitoring of soil moisture is not warranted. In accordance with WDR Order No. R5-2014- 0006, the soil in the upper one foot of the composting pad and compost storage pad areas are tested and if necessary, conditioned and compacted to achieve 1 X 10 -5 cm/sec vertical hydraulic conductivity. The site and pad will 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 an existing berm located on the eastern and a portion of the south edges of the site. Slopes 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 proposed 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 (0.25 inches, 1.5 inches per hour) assuming all the water that falls on the composting site runs off. The ditches will carry the water t o a sedimentation basin designed to hold the net average annual rainfall during months where rainfall exceeds evaporation (5.67 inches) assuming all the water that falls on the site runs off. This exceeds the 25-year, 24-hour rainfall event (2.28 inches).