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w Corral Hollow Sanitary Landfill -2- 2011 San Joaquin County Department of Public Works California Department of Transportation 3. Two groundwater zones have been encountered beneath the landfill. The shallow zone is currently monitored by wells SB-1, MW-4, MW-5, and MW-8. Depth to water in the shallow zone ranges between 17 to 79 feet below ground surface ("bgs"). Shallow groundwater beneath the site has only been encountered along the northeast portion of the landfill. A deeper aquifer underlies the landfill site and is monitored by wells MW-6 and MW-7. Depth to groundwater in the deeper zone ranges between 304 and 359 feet bgs. 4. In the past, groundwater flow in the shallow zone appeared to;�mound around well SB-1 and flow northerly and southerly. Currently, shallow groundwater beneath the landfill flows southwesterly at a gradient of 0.0375 feet per foot. Groundwater impacts were detected in the shallow groundwater during the fourth-quarter 1991 and were confirmed in February 1992. Volatile Organic Compounds ("VOCs") were first detected in shallow well MW-5 and also in newly installed well MW-8. Groundwater flow in the deep aquifer is toward the northeast at a gradient of 0.004 feet per foot. VOCs have not been detected in the deep aquifer. 5. The landfill was closed, and a final cover was constructed in the fall of 1995 as a corrective action measure. The cover„;was constructed;under WDR Order 94-259 and was installed over the known footprint ofthe”four,WMUs. 6. In 2001, the County installed a landfill`gas ("LFG'):system t6aabate migrating LFG observed in perimeter probes.and to control VOC'impacts yin groundwater. Thirty nine LFG wells were initial lyl ins"tailed., During 2003; the County investigated the source of increasing inorganics observed in well MV\/, , but the cause of was inconclusive. During 2003, a perimeter"drainage ditch"�along then brthern boundary of the landfill was re- graded to min imizef.ponding and infiltration beneath the ditch. Waste Found Outside the WMUs 7. In:2005, the County:conducted.an investigation to determine whether refuse was found beneath the drainage.ditch, theapcess road, and east of the access road to the boundary of the:landfill. This investgation`encountered refuse in all three areas, all of which are outside of,the landfill boundary. The existing closure cover does not extend to these areas. The County installed an additional five LFG extraction wells along the northeast boundary to capture LFG'from beneath,refuse identified during this investigation. 8. Following this initialjnvestigation, Cal Recycle requested an investigation of the extent of the closure cap beyond the known footprint of the WMUs. The County delineated the refuse not only on County property but within the right of way of the adjacent Caltrans, property during August 2007. Based on the site investigations conducted, the County estimates approximately 1.3 acres of county property and approximately 0.6 acres on the adjacent Caltrans property requires extension of the closure cover.