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Draft Supplemental Environmental Impact Report Page IV.G-18 Forward Inc. Landfill 2018 Expansion Project Mitigation Measure G.1:None required. Impact G.2: If erosion from soil stockpiles and landfill surfaces are not properly controlled, or inadvertent spills of refuse or other substances onsite occurred,surface water could potentially become contaminated. If erosion from stockpiles and landfill refuse were not properly controlled,this could create sedimentation in Littlejohns Creek and cause contaminants in the refuse to migrate in the surface water and be deposited downstream.Wet Weather Plans and Erosion Control Plans have historically been in place at the Forward Landfill to protect against such uncontrolled erosion and sedimentation. No new regulatory issues have been identified with regard to management of this erosion potential. The following procedures are proposed as part of the proposed expansion project: • The current drainage control structures and monitoring would continue to be implemented to control erosion and sedimentation in the expansion areas.Proposed structural controls include the drainage control system and daily cover. Operational controls include maintenance of the drainage system by keeping ditches clear of debris and excessive vegetation, and making needed repairs to drainage structures. Corrective measures would be implemented if inspections show excessive erosion or damage to drainage channels. Any areas showing erosive effects would be mitigated by removing loose debris followed by replacement, regrading, and compacting the area.Monitoring and protection against sediment from entering the Littlejohns Creek channel would be implemented, including the diversion of part of Littlejohns Creek farther away from the landfilled area. • In order to minimize sediment transport to Littlejohns Creek, landfill slopes, ridgetops, and peripheral areas would be revegetated to inhibit erosion. Implementation of these procedures would reduce the impact to a less-than-significant level. Mitigation Measure G.2:None required. Impact G.3:Potential groundwater impacts could result if the proposed liners and leachate collection systems for the Landfill expansion areas were not properly designed or installed, or if they were to fail. Without a properly designed landfill cell liner and LCRS installed in the project expansion areas, landfill leachate could percolate through the ground underlying the landfill units and potentially contaminate groundwater. To address this potential,the expansion areas would have a leachate collection system installed that will meet the federal and state Class II landfill design requirements. The following groundwater quality protection measures are proposed as part of the project: (as required under CCR Title 27) • A pan lysimeter(secondary liner)would be installed under the sump area, as previously required by the RWQCB;