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Draft Environmental Impact Report Page IV.F-24 Forward Inc. Landfill Expansion includes a leachate collection and recovery system, including leachate collection swales and LCRS pipes, collect leachate from the LCRS gravel layer. Spacing of LCRS lateral pipes and headers was determined by HELP2 leachate generation modeling performed by GeoLogic Associates (2008a)and modified by the higher historical G indications of leachate volume. Leachate is collected and discharged to the on-site leachate 4 ponds. If during the service life of the landfill, the demand on the leachate impoundment exceeds capacity, Forward, Inc. would implement an alternative leachate management plan. Leachate in excess of the impoundment's capacity would either be pumped to temporary onsite tanks,trucked for off-site disposal at the City of Stockton Municipal Utility Department wastewater treatment plant or trucked to another off-site licensed Treatment and Disposal Facility. Leachate stored in the temporary on-site tanks may be released back into the impoundment at a later date. i The following measures are proposed as part of theproject: • The Proposed measures to address concerns about additional leachate generation as a F result of the combined landfill have been addressed in the JTD with the presentation of the updated EPA HELP model results based on the projected volumes of refuse, a historical analyses of actual leachate generation volumes (which were at significantly F higher volumes then the model predicted for peak year rainfall) and the description of the leachate collection system designed to meet the maximum probable leachate generated. Engineering control systems (leachate collection system, drainage control, i F, groundwater and gas controls), monitoring programs, and institutional controls have been presented in the JTD, which has been reviewed by the RWQCB. Reporting on leachate generation volume and quality is a requirement of the RWQCB-stipulated j F progress reporting through the various proposed landfilling phases. • The landfill cell anchor trenches will be elevated two to three feet above the surrounding land to minimize the possibility of water from major storm events draining into the cells F and adding to the volume of leachate. i This impact would still be potentialIy significant. Therefore,the followingadditional mitigation measure is suggested by the EIR: g F Mitigation Measure F.4: Continued monitoring of the effectiveness of mitigation measures for leachate shall be performed by the responsible regulatory agencies (currently the RWQCB and, for the WMU-A, the DTSC). These agencies keep abreast of state-of-the-art information on leachate generation mechanisms and appropriate mitigation. If, in the future, monitoring F. demonstrates that the procedures above were insufficient to mitigate the effects of landfill- generated leachate,the agencies will, as appropriate,require additional corrective actions. Implementation of these procedures would reduce the impact to a less-than-significant level. Impact F.5: Surface and/or groundwater contamination could result if differential settlement damaged the liner and/or leachate collection system of the vertical expansion portion of the F� new landfill areas. As the vertical expansion of the proposed expanded landfill progresses, damage to the liner F and/or leachate collection system could result from differential settlement, which would allow the leachate to affect water quality. Landfill material is highly variable and has a high proportion of its material in organic form that can decompose and be reduced in size, causing F 1-,