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rl <br /> ATTACHMENT A (continued) <br /> SUMMARY OF PREVIOUS INVESTIGATIONS <br /> SChevron 9-6171, 6633 Pacific Avenue, Stockton, CA <br /> On August 18, 1993, Sierra installed groundwater monitoring well MW-7 Results of <br /> analysis for a groundwater sample from this well indicated nondetectable levels of TPHg <br /> and BTEX <br /> In April 1995, a Corrective Action Plan (CAP) was prepared by Pacific Environmental <br /> Group (PEG) The CAP recommended quarterly groundwater monitoring due to a <br /> chlorinated solvent plume that had co-mingled with groundwater underlying the Chevron <br /> site PEG concluded that any remedial action to reduce hydrocarbon levels would be <br /> complicated by chlorinated solvents and therefore not recommended <br /> On September 22, 1995, PEG drilled five soil borings to investigate soil conditions in the <br /> vicinity of the current USTs and former product islands Concentrations of TPHg (56 <br /> ppm), toluene (0 042 ppm and 0 013 ppm), ethylbenzene (0 17 ppm), and xylenes (1 6 ppm <br /> and 0 031 ppm) were reported <br /> From December 1997 to January 1998, underground piping, three hoists, and two waste oil <br /> tanks were removed by Wendt Construction During removal activities, a previously <br /> unknown waste oil UST and a 6-inch steel well (designated OW-1) were discovered The <br /> • location of this well, as reported by Gettler-Ryan, is shown on Figure 2 PEG collected <br /> soil samples beneath each of the former facilities The samples collected beneath the <br /> hoists were found to contain oil and grease at a maximum concentration of 2,700 mg/kg <br /> The samples from beneath the waste oil USTs were found to contain TPHg and total <br /> petroleum hydrocarbons calculated as diesel (TPHd) at maximum concentrations of 170 <br /> mg/kg and 5,300 mg/kg, respectively Oil and grease was reported at a maximum of <br /> 25,000 mg/kg PCE was detected at a concentration of 160 ppb Benzene and lead were <br /> not detected in soil from either waste oil tank excavation <br /> Results of quarterly groundwater monitoring events indicate that the groundwater flow <br /> direction at the site has fluctuated between flow to the northeast and flow to the southeast <br />