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Additional SAe Assessment Report 6 The Southland Cor ration Store#17334 4501 North Pershing Avenue Stockton CA January 15 1998 6 0 SUMMARY Based on the reported concentrations of BTEX,TPH-G, and MTBE in the soil samples collected during the Installation of the five groundwater monitoring wells on September 23 and 24, and November 26, 1997, and the geoprobe soil bonngs drilled on February 20, 1997,the lateral and vertical limits of BTEX,TPH-G, and MTBE have been defined Soil containing low hydrocarbon concentrations appears restricted to a limited area surrounding the tank pit and underlying the fuel dispensers The highest dissolved BTEX, MTBE, and TPH-G concentrations from the groundwater grab samples collected from the geoprobe borings February 20, 1997, and the groundwater samples collected from the monitoring wells on December 19, 1997,were reported in boring GP-4 and monitoring well MW-1, located on the east side of the tank pit Dissolved BTEX,MTBE, and TPH-G were also reported in monitoring well MW 1A,which is screen approximately 19 feet beneath the existing groundwater table, and downgradient well MWS, located on the east side of Pershing Avenue Downgradient from the hydrocarbon source area, BTEX,MTBE, and TPH-G concentrations decline significantly,indicating adequate delineation at this time Further decline in dissolved hydrocarbon concentrations can be expected after removal of underground storage tanks(USTs) at the site 7.0 CLOSURE ABSTRACT The three 10,000-gallon USTs and associated dispensers and product piping at the site are scheduled to be replaced later this year,effectively removing the source of hydrocarbons at the site Dunng the UST removal, a limited (cost-effective) amount of hydrocarbon-impacted soil beneath the tanks will be excavated to further remove the sod hydrocarbon source of the dissolved hydrocarbon plume A well search will also be conducted to Identify any public supply wells within a 2,000 foot radius of the site Information for the well search will be reviewed at the Department of Water Resources(DWR)in Sacramento, CA No-further-action status will be proposed for the site following removal of the USTs pending verification of the following conditions _ 1)Declining BTEX, MTBE,and TPH-G concentrations In wells MWA and MW-1A(located near the hydrocarbon source) and downgradient well MW-4 after completion of source removal 2) Results of the well search showing no public supply wells within 2,000 feet downgradient of the site, or that wells within 2,000 feet of the site are not in hydraulic communication with shallow groundwater containing dissolved hydrocarbons from the Southland site irmsor rpt FLUOR DANIEL GTI