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REPORT ON ADDITIONAL SITE ASSESSMENT AND RECOMMENDATIONS 2 7-Eleven Store No 14117,2725 Country Club Blvd,Stockton CA December 12,2001 Additional site assessment consisting of the installation of 17 soil borings and collection of sod and groundwater samples was completed between September 29 and October 2, 1998 (Fluor Daniel ' GTI, 1998) The borings were installed both at the 7-Eleven site and on adjacent residential property located to the north Concentrations were non-detectable for benzene, toluene, ' ethylbenzene, and total xylenes(BTEX) as measured using EPA Method 8020 Concentrations were also non-detectable for TPH-G as measured using EPA Method 8015, and for MTBE, TAME, ' diisopropyl ether(DIPS), tert-butanol (TBA), and ethyl-tert-butyl ether(ETRE) as measured by EPA Method 8260 Four groundwater monitoring wells were installed in May, 1999 (IT Corporation, 1999) to depths of up to 30 feet below grade in borings drilled to depths of up to 51 feet below grade Well MW-1 is constructed to 30 feet below grade, perforated from 10 feet below grade to total depth Well MW-2 ' is constructed to 25 feet below grade, perforated from 5 feet below grade to total depth The total depth of well MW-3 is 25 feet below grade, and it is perforated to 10 feet below grade Well MW-4 IPis constructed to 25 feet below grade, and is perforated from 10 feet below grade to total depth Well locations are shown on Figure 2 Soil samples collected during well installation contained up to 2 89 mg/kg benzene, 429 mg/kg ' TPH-G, and 0 119 mg/kg MTBE, with highest concentrations at 15 feet below grade Selected halocarbons (analyzed at the request of the SJCPHS) indicating possible dry-cleaner plume ' contributions were also detected in samples from well MW-3 The base of the MTBE plume in soil was identified at less than 25 feet below grade Groundwater monitoring well data indicate the highest MTBE concentrations are consistently found ' in well MW-2, installed in the new tank pit area through one of the conductor casings As of the third quarter 2001, dissolved concentrations ranged up to 650 ug/L benzene (well MW-4), 5,100 ' ug/L TPH-G (well MW-3), and 36,000 ug/L MTBE (well MW-2)