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Draft Supplemental Environmental Impact Report Page IV.G-20 <br /> Forward Inc. Landfill 2018 Expansion Project <br /> Impact GA: If not properly managed,the volume of leachate generated from the expansion <br /> areas could result in potential groundwater impacts. <br /> More refuse would be generated by the expanded landfill than would be under the existing <br /> landfill operating permit, so that there is a potential for more leachate to be produced over time <br /> given the additional 8.12 million cubic yards (CY)of landfilling covered by the expansion. The <br /> base liner system design would be required to be in compliance with the current WDRs for the <br /> existing facilities and in accordance with 27 CCR, Section 20330 requirements for a Class II liner <br /> system. <br /> Spacing of LCRS lateral pipes and headers was evaluated by HELP2 leachate generation <br /> modeling, and modified by the higher historical indications of leachate volume. Leachate would <br /> be collected and discharged to the new onsite leachate ponds in addition to the existing ponds. <br /> If during the service life of the landfill, the demand on the leachate impoundment exceeds <br /> capacity,Forward would implement an alternative leachate management plan. Leachate in <br /> excess of the impoundment's capacity would either be pumped to temporary onsite tanks, <br /> trucked for offsite disposal at the City of Stockton Municipal Utility Department wastewater <br /> treatment plant, or trucked to another offsite licensed treatment and disposal facility. Leachate <br /> stored in the temporary onsite tanks may be released back into the impoundment at a later date. <br /> The following measures are proposed as part of the project: <br /> • The proposed measures to address concerns about additional leachate generation as a result <br /> of the expanded landfill will be addressed in the JTD with the presentation of the updated <br /> EPA HELP model results based on the projected volumes of refuse, a historical analyses of <br /> actual leachate generation volumes (which were at significantly higher volumes than the <br /> model predicted for peak year rainfall)and the description of the leachate collection system <br /> designed to meet the maximum probable leachate generated. Engineering control systems <br /> (leachate collection system, drainage control, groundwater and gas controls),monitoring <br /> programs, and institutional controls have been presented in the JTD, which has been <br /> reviewed by the RWQCB. Reporting on leachate generation volume and quality is a <br /> requirement of the RWQCB-stipulated progress reporting through the various proposed <br /> landfilling phases. <br /> • The landfill cell anchor trenches would be elevated 2 to 3 feet above the surrounding land to <br /> minimize the possibility of water from major storm events draining into the cells and <br /> adding to the volume of leachate. <br /> Implementation of these procedures would reduce the impact to a less-than-significant level. <br /> Mitigation Measure GA:None required. <br /> Impact G.5:The re-routing of the South Branch of South Littlejohns Creek could result in <br /> flooding if the new alignment is not designed to accommodate peak flows. <br /> The updated (April, 2018)design report for the relocation of the South Branch of South <br /> Littlejohns Creek includes objectives to provide adequate flood control(i.e., has capacity to <br />