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12. Groundwater Monitoring Well Network According to the conditions specified in the permit,the groundwater monitoring network was to consist of a minimum of ten wells forthe measurement of water levels and a minimum of five wells for water quality testing. The wells for water quality testing were to be located such that two wells were upgradient from the Vernalis plant site, one on site, and two downgradient. To select the network wells, a preliminary groundwater investigation was conducted by LSCE in 1991 and 1992 (LSCE, 1992),which indicated that the depth to groundwater ranged between$0 feet beneath the valley'floor to the northeast and 250 feet beneath the mountain flanks to the southwest. In addition, a confining clay was identified beginning at an approximate depth of 250 feet beneath the Lone Tree I Mining phase that appeared to divide the underlying aquifer into shallow and deep zones. This clay is most likely the Corcoran Clay Member of the Tulare Formation,which has been reported to extend beneath much of the San Joaquin' Valley, including the present monitoring network area(Hotchkiss, 1972). Further,the investigation indicated that the direction of groundwater flow in the shallow zone was to the southeast. The established monitoring network presently consists of fourteen network wells (see Figure 1). At each well in the original monitoring network,the elevations of the ground surface and wellhead were surveyed by LSCE in November and December, 1994. Ground surface and wellhead elevations were referenced to several local bench marks (DWR,USBR, and San Joaquin County)relative to the USGS datum. The survey was conducted so that measured groundwater depths could be equated to groundwater elevations that, in turn, could be used to determine groundwater flow directions beneath the area. The South Tracy#3 well was installed more recently, and presently,the ground surface elevation estimated from the USGS topographic map for the area(Solyo Quadrangle, 7.5 Minute Series) is utilized to equate depth to water measurements to groundwater elevations. Similarly estimated ground surface elevations are presently utilized to equate depth to water measurements to groundwater elevations at the newly added wells Granite#3 and Granite#4. Depth-to-water measurements are retrieved in seven shallow wells(Hall, Faulkner,Rustan, Thoming, Koster, 4S/6E-5A1,and 4S/6E-6A1), four deep wells(South Tracy#1, South Tracy#3,Brown's#1,and Brown's New), one composite well (the Petz irrigation well), and two newly added wells of unknown well completion intervals(Granite#3 and Granite#4). The South Tracy#3 well(previously referred to as South Tracy#2)has been utilized since 2001 in place of the Ponderosa well,which has a broken airline. The current water quality network includes two wells upgradient from the Vernalis plant(Hall and Faulkner domestic wells),two wells onsite(South Tracy#1 and South Tracy#3 production wells), and one downgradient well(Granite#3 production well). The South Tracy#3 production well was added to the water quality network in 2004 in lieu of the Brown's New well,which became inoperable in 2001 (due to the removal of the pump). Since early 2005, the Brown's#1 well has been inoperable due to vandalism. With the help of Teichert's neighbor to the south, Granite Construction, a replacement well (Granite#3), was established a few hundred feet north of the Brown's#I well. From 1994 to 1997, the Koster irrigation well was sampled periodically(depending on the availability of a tractor engine for the pump). According to the permit requirements,depth-to-water measurements and groundwater quality sampling occurs on a quarterly schedule. Samples from the water quality network wells are analyzed for general minerals,including a selection of metals, and nitrate, all meeting Title 22 requirements. Samples from the 2 ©LUHOORFF & SCALMANINI CONSULTING ENGINEERS