ARCHIVED REPORTS XR0000653 - Laserfiche WebLink

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November 6, 1992 Working To Restore Nature Former Exxon Station No 7-3330, Stockton, California hydrocarbons were excavated and removed from the site We understand the soil was disposed of at Class II and Class III facilities Quarterly monitoring of ground water began at the site in March 1991 Artesian conducted the second quarter 1992 monitoring event on June 27, 1992 (Artesian, July 27, 1992) PRESENT QUARTERLY MONITORING EVENT A technician from RESNA visited the site on September 25, 1992, to take water-level measurements and perform subjective analyses of ground water from wells MW-3 through MW-6 and to collect ground-water samples from the wells for laboratory analyses Our field methods used are summarized in an attachment to this report Ground water in the wells exhibited no subjective evidence of hydrocarbons during this site visit (Table 1) Ground-Water Flow Direction and Gradient We used the depth-to-water measurements and the wellhead elevations obtained from the Artesian report (Artesian, July 27, 1992) to evaluate the direction of ground-water flow and gradient beneath the site These data are summarized in Table 1 We contoured the ground-water surface elevations obtained from each well to construct a Potentiometric Surface Map (Plate 3) The ground-water flow direction was to the northeast with a gradient of 4 0015 The direction of ground-water flow is in general agreement with the flow direction reported by Artesian during the previous monitoring event The ground water elevation beneath the site decreased by an average of 113 feet since June 1992 Laboratory Analyses and Results Ground-water samples collected from each well were analyzed for total petroleum hydrocarbons as gasoline (TPHg) using Environmental Protection Agency (EPA) Method 8415 (modified) and benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) using EPA Method 602 These samples were analyzed at PACE Inc in Novato, California, which is certified by the State of California for the requested analyses (Hazardous Waste Testing Laboratory Certification No 148) Results of laboratory analyses indicated the sample from well MW-6 contained TPHg and benzene at concentrations of 68 and 0 8 parts per billion, respectively Concentrations of TPHg and BTEX were below detection limits in water sampled from wells MW-3, MW-4, and MW-5 These results are shown on Table 1 1012mgue 32020-1 2 I