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Pre-Tank Relining Site Assessment Report 3 The Southland Corporation 4501 North Pershing Avenue Stockton California February 28, 1997 8020/modified 8015. If MTBE was detected by EPA method 8020, an additional analysis by EPA method 8260 was used to confirm its presence. Groundwater.was not.encountered in borings GP1, GP2, GP5, and GP6. F Following collection of soil and groundwater samples, each soil boring was grouted back to surface grade with neat cement. 3.0 RESULTS OF SOIL AND GROUNDWATER SAMPLE ANALYSES . 3.1 Site Geology Based on review of the SJCPHS files three sites adjacent to the subject site have had reported releases of gasoline-range petroleum hydrocarbons: Cardlock Gasoline Station,4555',,N. Pershing Ave., located 100 feet west of subject site Shell Service Station,4445 N. Pershing Ave.,..on southeast corner of Pershing and Rosemarie Lane Exxon Service Station,4444 N. Pershing Ave., on. southwest corner of Pershing and Rosemarie Lane Groundwater monitoring and sampling has been ongoing at the Exxon site since 1987 and conducted at the Cardlock and Shell sites since 1992. In 1988, Exxon installed a 30-foot-deep groundwater monitoring well, MW-9, approximately 10 feet east and 10 feet south of Southland's tank pit(Figure 2). The depth to groundwater in MW-9 has ranged from 30 feet BGS in 1990 to 20 feet BGS in April 1996. Seasonal water table fluctuations average 2 to 3 feet. Historical groundwater flow direction at the three sites has been northeast, and the gradient at the Exxon site_on August 8, 1996 was 0.006 foot per foot. The materials encountered during recent drilling at the site consisted predominately of a silty clay, near surface grade, overlying clayey silt and silty very fine sand to total depth of the borings (Appendix A). Groundwater was encountered approximately 17 to 18 feet BGS during drilling. Static groundwater levels in the three borings(GP3, GP4, GP7) in which groundwater was encountered ranged from 14.3 to 17.7 feet BGS. 3.2 Results of Soil Sample Analyses Table 1 summarizes the laboratory analytical results for eight soil samples collected from the seven soil borings drilled February 20, 1997. Benzene was detected in one sample, GP4 at 17 feet BGS, at a concentration of 0.0095 milligrams per kilogram(mg/kg). MTBE was detected in four of the seven samples at concentrations ranging from 0.76 mg/kg to 0.068 mg/kg. The presence of MTBE was confirmed in sample GP1-15'at a concentration of 0.91 mg/kg using EPA method 8260. TPH-G was•not detected in 0472ASMT.RPT(Sthl.56) - FLUOR DANIEL GTI