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0 . Pre-Tank Relining Site Assessment Report 3 The Southland Corporation 4627 Da Vinci Drive Stockton California March 3 1997 3 0 RESULTS OF SOIL AND GROUNDWATER SAMPLE ANALYSES 3 1 Site Geology The materials encountered during recent drilling at the site consisted of silty clay from grade to 9 feet BGS underlain by clayey silt with some silty very fine sand to total depth of exploration at 15 feet BGS (Appendix A) Groundwater was encountered approximately 7 to 12 feet BGS during drilling Static groundwater levels in six borings (GP-1 GP-5 GP-7, GP-8 GP-9 and GP-10) were approximately 7 feet BGS 3 2 Results of Soil Sample Analyses Table 1 summarizes the laboratory analytical results for 18 soil samples collected from the ten soil borings drilled February 21, 1997 Benzene was detected in samples GP-3 and GP-5 at 5 feet BGS at concentrations of 0 44 and 0 11 milligrams per kilogram (mg/kg) respectively and in GP-7 at 10 feet BGS at a concentration of 0 42 mg/kg MTBE was detected in six of the 18 samples at concentrations ranging from 0 11 mg/kg to 12 mg/kg TPH-G concentrations of 150 mg/kg, 7 9 mg/kg and 10 mg/kg were detected in samples GP-3 and GP-5 at 5 feet BGS, and GP-7 at 10 feet BGS respectively Copies of laboratory analyses reports and chain-of-custody manifests are included in Appendix C 3 3 Results of Groundwater Sample Analyses Table 2 summarizes the laboratory analytical results of groundwater samples collected from six soil borings GP-1, GP-5, GP-7, GP-8, GP-9 and GP-10 on February 21 1997 Elevated concentrations of BTEX, TPH-G, and MTBE were reported in groundwater samples GP-1 GP-5 and GP-7 Groundwater sample GP-1 contained the highest concentrations of benzene MTBE and TPH-G of all samples at 390 ug/L, 16,000 ug/L, and 16,000 ug/L, respectively The concentration of 1 600 ug/L MTBE reported in GP-8 using EPA method 8020 was confirmed using EPA method 8260 at a concentration of 870 ug/L Copies of laboratory analyses reports and chain-of-custody manifests are included in Appendix C 4 0 SUMMARY and CONCLUSION A total of 10 geoprobe points were drilled at the subject site six angled borings to vertical depths of 15 feet under the three USTs and four vertical borings to a depth of 15 feet BGS surrounding the UST pit (Figure 2) A total of 18 soil samples and six groundwater samples were collected for analysis Analytical results indicate the soil and groundwater contain BTEX TPH-G and MTBE The highest concentrations of BTEX, MTBE and TPH-G were found beneath the southern end of the UST pit and trend in a southerly direction away from the tank pit toward GP-7 and GP-8 (Table 1) 0470ASMT RPT(Sth 59) r•� FLUOR DANIEL GTI