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December 28, 1992 Working To Restore Nature <br /> Former Exxon Station No 7-3330, Stockton, California <br /> hydrocarbons was excavated and removed from the site We understand the soil was <br /> disposed of at Class II and Class III facilities <br /> Quarterly monitoring of ground water began at the site in March 1991 Artesian conducted <br /> the second quarter 1992 monitoring event on June 27, 1992 (Artesian, July 27, 1992) <br /> RESNA conducted the third quarter 1992 monitoring event on September 25, 1992 <br /> (RESNA, November 6, 1992) <br />" FOURTH QUARTER 1992 MONITORING EVENT <br /> A technician from RESNA visited the site on November 16, 1992, to take water-level <br /> measurements, perform subjective analyses of ground water from wells MW-3 through MW- <br /> 6, and collect ground-water samples from the wells for laboratory analyses Our field <br />" methods used are sumarized in an attachment to this report Ground water in the wells <br /> exhibited no sublectiv2evidence of hydrocarbons during this site visit (Table 1) <br /> Ground-Water Flow Direction and Gradient <br /> �k The monitoring wells were previously surveyed to provide the elevation of each wellhead <br /> relative to mean sea level We used the depth-to-water measurements and the surveyed <br /> wellhead elevations obtained from previous reports by Artesian to evaluate the direction of <br /> ground-water flow and gradient beneath the site These data are summarized in Table 1 <br /> The ground-water surface elevations obtained from each well were contoured to construct <br /> Potentiometric Surface Map (Plate 3) The ground-water flow direction was to the <br /> northeast with a gradient of 0 002 The direction of ground-water flow is in general <br /> agreement with the flow direction previously reported The depth to ground water beneath <br /> the site decreased by an average of 0 66 feet since September 1992 <br />" <br /> Laboratofy Analyses and Results <br /> Ground-water samples collected from each well were analyzed for total petroleum <br /> hydrocarbons as gasoline (TPHg) using Environmental Protection Agency (EPA) Method <br /> 8015 (modified) and benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) using <br /> EPA Method 602 These samples were analyzed at PACE Inc in Novato, California, which <br />" is certified by the State of California for the requested analyses (Hazardous Waste Testing <br /> Laboratory Certification No 148) <br /> Results of laboratory analyses indicated the sample from well MW-6 contained TPHg and <br /> benzene at concentrations of 190 and 0 7 parts per billion, respectively Concentrations of <br /> 32a2a-1 2 <br /> 12a9mVe <br /> 1 <br />