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Draft Supplemental Environmental Impact Report Page IV.G-17 Forward Inc. Landfill 2018 Expansion Project 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 G.1: 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 Littlejohns Creek and flow downsteam to the San Joaquin River. The applicant's report 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 will complete 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 would be designed to prevent contact between surface water and refuse. Site run-on and run-off control facilities consist of drains and perimeter ditches that channel surface water to holding and evaporation ponds on the site. The surface-water collection drain system would be designed to divert the water to the onsite sedimentation basins. All waste at the proposed Forward Landfill would be separated from the North and South Branches of South Littlejohns Creek by a levee system or other acceptable method designed to protect the site from a 100-year flood event.