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Twelve wells and one piezometer have been constructed at the site to monitor the two aquifers, though only nine wells are presently used for groundwater monitoring as a result of decreasing water levels (Table 1 and Figure 2). Table 1 Existing Well Construction Summary Well Date`'' Total Screen/ Name Constructed Depth(ft) Filter Interval(ft) Shallow Zone Wells 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 6-30 MW-9A March 2012 96.3 76.3-96.3 MW-10A March 2012 86.3 66.3-86.3 MW-11A March 2012 51.1 31.1-51.1 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 326 299-326 358-390(l) MW-6 July 2003 477 405-435 450-477 302-333(l) MW-7 July 2003 430 353-385 402-430 (1) Wells MW-6 and-7 are constructed with three sampling intervals. The upper interval is in use at this time As shown above, seven wells and one piezometer have been constructed to intercept the shallow groundwater that is perched within the Corcoran Formation. Five have been constructed to intercept the deeper aquifer, two of which are active. The deep regional aquifer is the uppermost groundwater unit beneath the site in areas where the Corcoran Formation is absent. Historical groundwater equipotential contours provided in quarterly monitoring reports suggest that groundwater in the shallow aquifer flows to the south at a gradient 0.0375 feet per foot (ft/ft). However,the recent EMP field work suggests the presence of a groundwater flow divide near the northeastern edge of the landfill, with groundwater flowing to the south of the divide at a gradient of about 0.05 ft/ft and groundwater flowing to the north/northeast of the divide at a gradient ranging from 0.02 to 0.05 ft/ft (Figure 3). The hydraulic gradient for the shallow aquifer was determined by contouring the January and • March 2012 groundwater elevation data for wells screened in this aquifer. Engineering Feasibility Study Geo-Logic Page ■ 5 Corral Hollow Sanitary Landfill ASSOCIATES January 25,2013