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Well Name Date Total Constructed Depth (ft) Shallow Zone Wells Screen/ Filter Interval (ft) MW -4 April 1988 26.5 14-26.5 MW -5 April 1988 86.5 60-86.5 MW -8 December 2007 85 62-85 SB -1 April 1988 46.5 31-46.5 PZ-1(dry) July 2003 30 1 6-30 Deep Zone Wells MW -1 (dry) October 1987 275 240-275 MW -2 (dry) May 1988 330 298.5-330 MW -3 (dry) May 1988 326 299-326 MW -6 July 2003 477 358-390(1) 405-435 450-477 MW -7 July 2003 430 302-333(l) 353-385 402-430 (1) Wells MW -6 and -7 are constructed with three sampling intervals. The upper interval is in use at this time As shown above, five wells were constructed to intercept the shallow groundwater that is perched within the Corcoran Formation, and five were constructed to intercept the deeper aquifer. The deep aquifer is the uppermost groundwater unit beneath the site in areas where the Corcoran Formation is absent. Wells MW -1, MW -2, and MW -3 and piezometer PZ -1 have gone dry since construction. Historical groundwater equipotential contours provided in quarterly monitoring reports suggest that groundwater in the shallow perched aquifer flows to the south at a gradient 0.0375 feet per foot (ft/ft). The available data suggest that recharge occurs near well SB -1; however, infiltration from a sand and gravel quarry or leakage from the Delta -Mendota Canal and/or California aqueduct to the northeast of the site may also affect the groundwater flow direction and gradient in the shallow aquifer. Historical groundwater equipotential data suggest that groundwater in the deeper aquifer flows to the northeast at a gradient of about 0.004 ft/ft, generally parallel to the regional topographic gradient toward the floor of the Central Valley. 3.4 GROUNDWATER CHEMISTRY Groundwater monitoring at the site began in 1988 with the construction of monitoring wells as part of the Solid Waste Assessment Test (SWAT) program, and as outlined in Section 3.3, while nine wells and one piezometer have been installed at the site, seven monitoring wells comprise the current groundwater monitoring network. Groundwater is sampled on a quarterly basis and reported semiannually. Groundwater in the shallow aquifer has been impacted by VOCs; whereas no VOCs have been identified in the deeper aquifer. VOC impacts to the shallow aquifer were first EMP Report — Phase 1 0 Page ■ 4 VeOI� Corral Hollow Sanitary Landfill ZS February 1, 2012