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Draft Supplemental Environmental Impact Report Page IV.G-17 Forward Inc. Landfill 2018 Expansion Project 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. • Channel design features are proposed as part of the expansion project:The project includes r channel reconfiguration and localized flood protection berms to isolate the landfill surfaces from floodwaters. • The project design shall also include provision of replacement floodplain area and storage volume in an easement along the relocated South Branch of South Littlejohns Creek. • The channel and floodplain storage easement are designed to accommodate the 100-year, ' 24-hour storm.The design would also include a three-foot freeboard. All of these measures have been or will be incorporated into the design of the landfill expansion and the relocated South Branch channel.Therefore, potential surface water drainage impacts ' would be reduced to a less than significant level. r