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7. SURFACE DRAINAGE PLANS Grading and drainage systems for the facility are shown on Figure 4 and Sheet 3. The compost pad will drain via surface swales at a minimum grade of 1 percent to a lined evaporation pond. The remainder of the site will drain via ditches and underground storm drain to an on-site retention pond. See Appendix C for the description of proposed drainage systems including design criteria, methodology and calculations. 8. DRAINAGE CONTROL Drainage control systems for the facility are shown on Figure 4 and Sheet 3 and are described in Appendix C. The compost pad will drain via surface swales at a minimum grade of 1 percent to a lined evaporation pond. The remainder of the site will drain via ditches and underground storm drain to an on-site retention pond. See Appendix C for the description of proposed drainage systems including design criteria, methodology, drainage shed map and calculations. 9. COMPOST LEACHATE CONTROL Leachate from the wood and yard waste composting operations will consist of all runoff from the compost pad. Runoff will be generated from precipitation and possibly from water used in moisture conditioning during operations although this portion is considered insignificant. The compost pad is designed, as shown on Figure 4 and on Sheet 3, such that all runoff from the pad will be collected in surface swales and directed to an on-site lined evaporation pond. The compost pad will be constructed of a minimum 6 inches reinforced concrete over a minimum 8 inches aggregate base compacted to 95 percent relative compaction. Pad dimensions for the initial construction will be 200 feet by 300 feet with expansion to occur to the north as necessary for increased material volumes. The liner for the evaporation pond will be a minimum of 3 feet compacted clay with a permeability of 1 x 10' cm per second or less. Perimeter ditches around the compost pad will be constructed to separate runoff from adjacent areas. All runoff from the site except for runoff from the compost pad will be diverted to the on-site retention pond. Drainage swales and perimeter ditches are designed to prevent overtopping during the 25- year/24-hour precipitation event. The evaporation pond will be constructed to an approximate depth of 6 feet with 2:1 sides and a pond bottom sloping at 1 percent. This pond is designed to contain precipitation estimated from the 100-year/24-hour storm event during the most critical L:/PR0JECT/397/MRF/RC14.TCY December 13,1943 12