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COMPLIANCE HISTORY SUMMARY Groundwater monitoring is in accordance with WDRs issued in 1989, 1994 and 2001. These WDRs required monitoring the shallow and deep aquifer on the east side of the landfill, and the deep aquifer on the west side of the landfill. In 1990, deep aquifer wells MW-1, MW-2 and MW-3 became dry. In the fourth quarter of 1991 VOCs (Trichlorofluoromethane and Tetrachloroethene) were first detected in groundwater samples collected from MW-5 (shallow aquifer). Confirmation samples were collected in February 1992 and the presence of VOCs at monitoring well MW-5 was confirmed. The County believes that the presence of VOCs in MW-5 was due to landfill gas (LFG) influence. In 1995 a corrective action plan (CAP)was implemented which included the closure and final cover construction for the landfill. In 1996 closure was complete, including the installation of LFG migration monitoring wells. Monitoring of these wells indicated combustible gas above the regulatory limit of 5%. In 2001 a LFG control and collection system was installed as a corrective action(source removal) against VOC impacts, as well as to prevent offsite migration of LFG. Effectiveness of the LFG system is indicated by the absence of landfill gas at the perimeter monitoring wells and prevention of further degradation of the groundwater as indicated by a reduction of the number of individual constituent VOC detections (Appendix E, Tabular Summary of Historical Monitoring Data). This system is presently extracting as much LFG as possible, as indicated by the low methane concentration of the gas reaching the LFG flare station. The WDR of 2001 required the installation of additional deep-aquifer monitoring wells because the deep aquifer level had lowered such that the deep aquifer wells originally installed (MW-1, -2, and-3) no longer reached that aquifer. In 2003, deep-aquifer monitoring wells MW-6 and-7 were installed. Knowledge of the direction of the flow in this aquifer by monitoring the three previous deep-aquifer wells allowed the downgradient well (MW-6) and the upgradient well (MW-7) to be located. In 2003 an investigation of off-site contamination and the effect on water quality parameters in MW-4 was initiated due to an increasing trend in Nitrate as Nitrogen and a decreasing trend in pH,. This investigation was inconclusive. In late 2003 the drainage ditch adjacent to the eastern access road was improved to reduce ponding and minimize infiltration along the ditch. In September 2005 a subsequent investigation,based on previous trends at MW-4, was conducted to determine if refuse was present below the drainage ditch, the access road, and east of the road at Corral Hollow Landfill 2 Department of Public Works/Solid Waste 2nd Quarter 2007 Groundwater Monitoring County of San Joaquin—July 31,2007