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• • • Draft Supplemental Environmental Impact Report Page IV.G-18 • Forward Inc. Landfill 2018 Expansion Project • Substantially degrade or deplete groundwater resources; • • Substantially interfere with groundwater recharge, • Cause flooding or subject structures to flood hazards,- * azards;• Substantially modify a local or regional drainage feature (i.e., creek alignment); • • Cause significant erosion or sedimentation; • • Generate more leachate than can be handle by the existing or planned control systems; or • Cause or be subject to substantial flooding, erosion, or siltation. As described in the Project Description, State and Federal standards have been established for the siting, design, construction, operation, closure, and post-closure of Class II landfills. • Similarly, the closed Class I landfill has post-closure monitoring and maintenance requirements. • These standards incorporate state-of-the-art engineering requirements that are intended to reduce the risks associated with waste disposal facilities to an acceptable level. An inconsistency between the proposed project and regulations related to surface or groundwater hydrology and water quality also would have the potential to result in significant impacts. Impact GA: If rainfall runoff was not properly controlled, surface water bodies could become contaminated through contact with the landfill refuse. If rainwater falling on the new landfill area contacts the landfill refuse and picks up dissolved contaminants and is not controlled by the drainage system, surface water could migrate to Littlejohn Creek and flow downsteam to the San Joaquin River. The applicant's geotechnical for the relocation of the South Branch of South Littlejohns Creek report (Questa Engineering • 2017) recommends a project design feature that would control landfill and site drainage run-on • and runoff, so that run-on and run-off would be controlled and channeled to onsite stormwater/sedimentation ponds. The drainage study utilizes San Joaquin County local rainfall data, and the Rational Method was used to estimate maximum potential runoff from a 1,000- year,24-hour event. The 1,000-year,24-hour storm criteria is a RWQCB requirement for Class II • landfills. The surface water control system and drainage control structures for the proposed project are sized to accommodate the calculated peak flows. The proposed surface water control system would also divert run-on from properties surrounding the landfill. The following surface water management procedures are proposed as part of the proposed expansion project: • The drainage study utilizes San Joaquin County local rainfall data, and the Rational Method • would be used to estimate maximum potential runoff from a 1,000-year, 24-hour storm event. The surface water control system and drainage control structures for the proposed project would be sized to accommodate the calculated peak flows. • As part of the design plans for the proposed landfill expansion, Forward has completed calculations of the 1000-year, 24-hour storm event peak discharges. The hydraulic and • drainage study would be used to design appropriate drainage controls. Drainage controls