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Er/ <br />the aquifer's hydraulic conductivity. Hydraulic conductivities calculated from these CPT data <br />ranged from 4.15 x 10-6 cm/s to 1.04 x 10-5 cm/s (PSC, 2003). <br />In June 1991, Anderson Consulting Group performed a 24-hour pumping test. Groundwater <br />was extracted from well MW -1 at an average rate of 6.7 gpm (ACG, 1991). <br />The depth to groundwater has ranged from approximately 40 to 60 feet bgs. The lowest depth <br />to groundwater was reportedly measured at 60 feet bgs, by PSC in December 1992. In April <br />2006, the depth to groundwater was approximately 41 feet bgs. Recent data indicate that the <br />overall groundwater flow direction is generally to ;the east beneath the site at a gradient of <br />approximately 0.003 foot per foot (Figure 3). <br />2.4 TOPOGRAPHY AND SURFACE WATER <br />The land surface slopes toward the west in the vicinity of the subject site at approximately 0.12 <br />foot per 100 feet. The elevation of the subject site is approximately 17 feet above mean sea <br />level (USGS, 1987). The Eastern San Joaquin Subbasin is drained by the San Joaquin River <br />and several of its major tributaries namely, the Stanislaus, Calaveras, and Mokelumne rivers. <br />The San Joaquin River flows northward into the Sacramento and San Joaquin Delta and <br />discharges into San Francisco Bay (DWR, 2003). <br />A storm water drainage ditch (approximately 1,000 feet long and less than five feet deep) <br />extends westerly_ from the southwestern side of the; facility towards a south -flowing drainage <br />canal. This canal drains into the ephemeral Duck Creek, which is located about 900 feet south <br />of the plant. Duck Creek extends westward to Walker Slough, which in turn flows westward <br />into the San Joaquin River. <br />2.5 UST HISTORY <br />The facility historically operated five UST systems The locations of the five former UST <br />systems are shown on Figure 2A. The following sections summarize information pertaining to <br />each UST system, their removal, and subsequent investigation, remediation, and monitoring <br />activities. <br />2.5.1 Removal of UST Systems <br />The .following subsections summarize information pertaining to each UST system and their <br />removal. Analytical data for soil samples collected during tank removal activities are included <br />in Table 1. <br />4 <br />