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GEOMATnix Three groundwater monitoring wells were installed at the locations shown on Figure 2 in April and May 1991 by RESNA (formerly Water Work Corporation). The depth to groundwater beneath this site was about bl feet bgs in 1991; the depth to water in February 1995 was about 55 feet bgs. Groundwater monitoring has been performed in these wells since May 1991. TPH-G, total petroleum hydrocarbons ' as diesel (TPH-D), and BTEX have been reported sporadically in groundwater samples collected from some of the wells at concentrations near the detection limits. Analytical results for groundwater monitoring performed from May 1991 through February 1995 are summarized in Table 2. During the ' February 1995 round, TPH-G and BTEX were not detected and TPH-D was detected at a concentration of 51 micrograms per liter(µg/e); however, the laboratory that performed the analysis indicated that the material did not match the diesel standard. Subsequent groundwater sampling performed by Geomatrix in May 1995 indicated that non-petroleum hydrocarbon by-products of biodegradation present in the groundwater were resulting in overstated or false-positive results for TPH-D(Geomatrix, 1995) In a 1 August 1995 meeting with CREMCO and Geomatrix, SJCEHD staff stated that residual concen- trations of lead and BTEX in soil are no longer of concern at this site and that criteria presented in the "California Water Resource Control Board's Leaking Underground Fuel Tank Field Manual" (LUFT ' Manual) should be used for evaluating site closure. The SJCEHD also concurred with Geomatrix's recommendation that further groundwater monitoring at this site did not appear warranted. However, the SJCEHD indicated the site could not be closed at this time because of the TPH-G reported at a concentration of 300 mg/kg in the soil sample collected in 1989 from 15 feet bgs in soil boring SBI. This concentration exceeds the maximum allowable level of 100 mg/kg for TPH-G in soil as presented in the LUFT Manual. California Water Service Company(CWSC) provides drinking water obtained from groundwater for the ' portion of the City of Stockton in the vicinity of the site. The water supply well located closest to the site (Station 53) is cross-gradient and approximately 325 feet west/southwest of the former underground storage tanks located at the site. The well at Station 53 is screened from 250 to 530 feet bgs. CWSC has no wells in the vicinity screened shallower than 200 feet bgs 3.0 OBJECTIVES AND SCOPE OF WORK The objective of the additional soil and groundwater assessment performed by Geomatrix was to obtain ' data to seek closure at this site, if warranted, or to further characterize the extent of petroleum hydrocar- bons in soil at the site and develop a soil remediation plan, if needed. The work plan described a two- step approach to meet the objective. Step 1 consisted of drilling a confirmation soil boring adjacent to -� boring SB I. If the concentrations of TPH-G in soil samples coilected from this boring were less than 100 mg/kg, then no additional soil assessment would be required and groundwater monitoring would be performed in the existing groundwater monitoring wells. Step 2 consisted of performing additional soil assessment if the concentration of TPH-G in soil samples collected from the confirmation soil boring were greater than 100 mg/kg; installing one additional downgradient groundwater monitoring well; and 2