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Page 105 system, and a series of secondary collection trenches beneath the liner and directly under the leachate collection trenches;(d)the operator will remove any hazardous materials spotted during delivery,thus minimizing the potential for leachate contamination if there is a break in the liner or the leachate collection system. Impact K.3: Project activities which increase leachate production from existing landfill materials during various phases could alternatively facilitate the remediation of local groundwater,or result in groundwater contamination. The collection of additional water quality data shows the h-,achate plume to be larger than was thought in 1994. Also, a regulatory cleanup and abatement order has been issued by the lead responsible regulatory agency—the Regional Water Quality Control Board (RWQCB�—for the assessment and-subsequent mitigation of the contaminant plume emanating from the landfill (current RWQCB Order 96-175, superceded Orders 92-143, 90-122, and 77-288). In April 1999, the City of. Stockton completed a Groundwater Corrective Action Engineering Feasibility Study Report (GCE) to evaluate the range of groundwater cleanup alternatives in terms of protection to the environment and consistency with regulatory requirements. In addition, as described above, leachate from part of the landfill's north face has been added to overall leachate collection quantities. Landfill leachate has been collected in a 12,000- gallon storage tank and removed when near full for off-site treatment at a licensed TDS facility. In the fourth quarter of 1998, the most recent data available, 1127 tons or 3,100 gallons of leachate were removed from the 12,000-gallon storage tank for off-site treatment. The GCE was prepared as part of the RWQCB Order, and addresses the requirement of both the RWQCB and California Code of Regulations,Title 27,which include the Waste Management Board requirements. The build-out of Phases V and VI may result in additional leachate generation. Changed conditions in 1999 compared to 1994 show the potential need for amore extensive groundwater extraction system. Additional groundwater extraction and treatment may be necessary in the future. Depending on the selection of the final remedy the larger size of the Groundwater Treatment System could impact the amount of filter media used to complete the cleanup operations. It also could result in.potentially new Air Resources Control Board (ARCB) permit requirements if an air stripper is proposed. As described in the 1994 EIR,these impacts would be significant and mitigable with adoption of the following measure. Miti ation K.3: (a)The extraction wells developed as part of the CAP shall be maintained and monitored during Phases V and VI,to be employed as needed for the extraction of any residual contamination by leachate. e Impact K.4: 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 landfill (Phases V and VI). Since none of the proposed vertical expansion of the landfill has occurred since the 1994 EIR,and there are no new relevant regulatory requirements regarding potential impacts from groundwater contamination due to settlement-related failures,there would be no changes in the impacts or mitigation measures. As described in the 1994 EIR,these impacts would be significant and mitigable with adoption of the following measure. GRASSETTI ENVIRONMENTAL CONSULTING