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Draft Environmental Impact Report Page IV.F-28 Forward Inc. Landfill Expansion There are various methods to mitigate the effects of groundwater extraction, all of which involve infiltration of the groundwater back into the aquifer from which it was withdrawn. # Mitigation Measure F.7: Two infiltration methods are currently used at the landfill. The groundwater currently pumped by the former agricultural well is used onsite;thus, some of it will infiltrate through the unlined parts of the site and migrate back to the groundwater aquifer from where it was extracted. Secondly, the treated groundwater from the groundwater extraction system is discharged into the infiltration basin, which recharges aquifers below and moves offsite. Treated groundwater from the groundwater extraction system is infiltrated back to the aquifer through an infiltration basin located near well MW-11. This has resulted in a dilution of the previous concentrations at MW-11 and may have bifurcated the plume between a northern and northeastern component but has not mitigated the plume from further downgradient. More changes to the current infiltration system and groundwater extraction are currently being reviewed by the applicant. The RWQCB is currently reviewing a Source Control Report by the applicant to address the need for additional groundwater extraction. Mitigation measure F7 should be updated following the Water Board' review and approval. Implementation of Mitigation Measure F.7 would reduce the impact to a less-than-significant level. Impact F.B. Base grade modifications could impact water qualify. Surface water drainage could be affected by base grade changes required by the proposed expansion east of the WMU FU-06. The currently permitted Forward Landfill is designed to drain leachate to the area directly west of the current scale house. However,with the proposed expansion of the Forward Landfill on to the former Brocchini parcel, the leachate risers would not be easily accessible from this location. The base grades in the area east of WMU FU-06 have, therefore, are proposed to be modified to drain to the east. To balance a minimum grade on the east-west trending leachate pipes of one percent and to maintain stability of the refuse fill, the minimum base grades in the area east of WMU FU-06 are proposed to be lowered from the current WDR restriction of 7-ft AMSL(above mean sea level) to-1 ft MSL. Because current groundwater levels are approximately 14-feet BMSL(below mean sea level),the 7-ft AMSL WDR restriction results in an approximately 21-ft separation between waste and groundwater. The 21-foot separation between waste and groundwater is substantially greater than the minimum 5-ft separation required by Title 27, Section 20240(c). IA detailed review of historic groundwater levels in.the area east of WMU FU-06 as analyzed by GLA (GLA, Letter report dated November 21,2007 to Central Valley Regional Water Quality Control Board)has shown that the reasonable historic high groundwater elevation in the area east of WMU FU-06 is 6-ft BMSL. The Central Valley RWQCB concurred with GLA's letter report as noted in their December 14, 2007 response (RWQCB, Letter to Kevin Basso of Forward, dated December 14,2007). FThe historic high groundwater elevation is based on 1984 measurements. Because of the agricultural pumping in the Forward vicinity, the groundwater elevations have been declining and are currently at approximately 14-ft BMSL. Forward is, therefore, proposing establishing the minimum elevation for waste discharge in the area east of WMU FU-06 at 1-ft BMSL,which F allows for a 5-ft separation from historic high groundwater and an approximately 13-ft separation from current groundwater levels. Because this change would still provide the Ft