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Construction Details of construction are contained in the Waste Discharge Requirements for this site. Module 1 (previously designated "Modules 1 and 2")was constructed in 1991. This module was excavated to an elevation of approximately 88 feet NGVD, which is approximately 30 feet below original grade. This Module is provided with a 60-mil HDPE liner installed over a 6-inch(minimum) thick layer of compacted native soil, but was not designed to meet Title 27 and RCRA Subtitle D criteria. At the time of construction, synthetic liners were not required. Module 3 was constructed in 1995, excavated to an elevation of approximately 60 ft NGVD,which is approximately 60 feet below original grade. This Module is provided with a composite liner comprised of a geocomposite clay layer (GCL)under a 60 mil HDPE membrane. This liner design was approved as an engineered alternative to the prescriptive composite liner of Title 27 and RCRA Subtitle D. The interface between Modules 1 and 3 is composed of an anchor trenchiberm at an elevation of approximately 96 feet NGVD. Module 4 was constructed in 2003, excavated to a depth of approximately 60 ft NGVD, which is approximately 60 feet below original grade. This Module is also provided with a composite liner comprised of a geocomposite clay layer(GCL) under a 60-mil HDPE membrane as an approved engineered alternative to the prescriptive composite liner of Title 27 and RCRA Subtitle D. In addition, a one-foot thick layer of soil with not less than 30%passing 200 sieve, compacted to not less than 90% relative density, was constructed under the composite liner. The interface between Modules 3 and 4 is a lined anchor trench/berm, raised approximately three feet above the surrounding surfaces. COMPLIANCE HISTORY SUMMARY Data from the groundwater wells at the North County Landfill did not indicate impact until three VOCs were confirmed at low concentrations in well G-4 in July 2002. Because G-4 is at the western property boundary, County staff contacted the neighbor immediately to the west,requesting permission to drill temporary groundwater monitoring wells to determine the extent of groundwater impact according to the "step out, step down" approach. That property owner did not grant this request but allowed County staff to sample the water from the well on that property. No contaminants were detected. County staff therefore implemented a phased approach for evaluation monitoring within the landfill property. The first phase was to install and monitor the new groundwater well G-6 and the soil gas wells that were installed in 2003 with Module 4. Under Evaluation Monitoring, groundwater and soil gas were sampled quarterly(the WDRs require semi-annual sampling). The soil gas wells on the landfill property boundary were also used to monitor for off-site migration of combustible gas in accordance with CCR Title 27 Section 20925. Monitoring at new groundwater well G-6 indicated no groundwater impact at that location. At G-4, one is VOC was detected in the January 2003 monitoring event. North County RC&SL Public Works/Solid Waste I"Semester 2012 Groundwater Monitoring 2 County of San Joaquin—July 26,2012