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III. Environmental Setting,Impacts, and Mitigations K. Hydrology, Geohydrology, and Water Quality readily through the porous soils. In the event that contaminants were released to the upper aquifer,it could have a potential impact on adjacent beneficial uses of groundwater. Regarding the liner and leachate collection system,a specific listing of the applicable regulations and the project design elements addressing regulatory criteria is included in the Project Design ■ Study(R.W. Beck and Associates, 1992a). The HELP model and leachate generation used on 100-year, 24-hour storm event of 3.2 inches(Appendix B,R.W. Beck and Associates, 1992b). The proposed drainage layer would direct leachate to the collection trenches(a perforated collection pipe surround by drainage gravel) and the gravel would be wrapped in a geotextile filter to separate it from the drainage layer. The leachate is discharged to collection sumps located at low points of the liner system (the preliminary design shows a series of leachate sumps, which may change in the final design). The leachate collection pumps discharge to a perimeter leachate header force main,which transports the leachate to a collection facility northwest of the existing landfill. Leachate would be trucked to the Stockton Municipal Utility District for treatment on an as needed basis. Secondary trenches under the leachate collection trenches are lined with a geomembrane liner and use a drainage gravel and collection pipe system similar to the leachate collection system. The secondary trenches provide a secondary containment beneath the collection trenches and sumps which are critical areas for potential landfill leakage due to concentrated leachate. Mitigation Measure K.5. Proposed as Part of the Proms (a) Landfill design includes a 32 foot separation between the liner and the groundwater. (b) The liner and leachate collection systems for the expansion have been designed to meet or exceed the requirements of the following regulatory sections: • . California Solid Waste Management Regulations;CCR Title 14, Division 7 • California Water Regulations;CCR Title 23,Chapter 15 • Federal Solid Waste Disposal Facility Criteria;40 CFR 257 and 258 (Subtitle D) (c) The project includes a leak detection system,a series of secondary collection trenches beneath the liner and directly under the leachate collection trenches. (d) Removal of any hazardous materials spotted during delivery thus minimizing the potential for leachate contamination if there is a break in the liner or the leachate collection system. IILK.16