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GEOMA-MIX SOIL AND GROUNDWATER ASSESSMENT 540 North Aurora/969 East Fremont Streets Stockton, California 1.0 INTRODUCTION ' This report describes the results of an additional soil and groundwater assessment performed by Geo- matrix Consultants, Inc. (Geomatrix) on behalf of Chevron Real Estate Management Company (CREMCO) at 540 North Aurora/969 East Fremont Streets (the site) in Stockton, California as shown on Figure 1. The work performed was described in the Geomatrix 12 October 1995"Site Closure Work ' Plan, 540 North Aurora/969 East Fremont Street, Stockton, California" (work plan). 2.0 BACKGROUND Thr w the site in January 1987. The locations of the Three underground fuel storage tanks were removed from ary ' former tanks are shown on Figure 2. Two of the tanks (3,500 and 4,000 gallons) were used to store leaded gasoline, and the third tank (3,500 gallons) was used to store diesel fuel. Soil samples were collected beneath each of the tanks from the base of the tank excavation and analyzed by Canonie Environmental. Soil samples collected from beneath the diesel tank were reported not to contain detectable petroleum hydrocarbons. Soil samples collected from beneath the two leaded gasoline tanks ' (tanks 2 and 3) were reported to contain volatile petroleum hydrocarbons at concentrations of 130 milligrams per kilogram (mg/kg) beneath tank 2 and 160 mg/kg beneath tank 3. In addition, lead was reported at concentrations of 17 mg/kg in soil samples collected from beneath tank 2 and 20 mg/kg in soil samples from beneath tank 3. Based on the results of the laboratory analytical analyses con- ducted during the initial investigation, the San Joaquin County Environmental Health Division (SJCEHD) approved closure of the site and indicated that no further remedial action was required. However, because of a change in the regulations and the promulgation of lower allowable lead concen- trations in soil, SJCEHD reopened the case in 1989 and requested additional characterization. In December 1989, five soil borings were drilled at the locations shown on Figure 2 by Water Work ' Corporation. Laboratory analytical results for soil samples collected from the borings indicated that lead was not present at concentrations greater than the method detection limit of 0.0005 mg/kg. Low concentrations of benzene,toluene, ethylbenzene, and xylenes (BTEX) were detected in several samples collected from two of the five soil borings (SB I and S132). The results of the soil samples analyzed during the previous investigations conducted at the site by Water Work Corporation and Canonie Environmental are summarized in Table 1. Total petroleum hydrocarbons as gasoline (TPH-G) was reported at a concentration of 300 mg/kg in the sample collected from boring SB I at a depth of 15 feet below ground surface (bgs). 1