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June 13, 1997 <br /> Page 7 <br />• • A well survey performed at DWR identified a total of wells within a 112-mile <br /> radius of the site All wells were constructed to at least 190 feet bgs, with the <br /> exception of the monitoring wells No wells east(downgradient) of the site were <br /> located within a 112-mile radius of the site <br /> • Groundwater is supplied in combination of municipal wells from CWSC and by <br /> Stockton East Municipal Distract No active municipal wells were located to a 1/2- <br /> mile radius of the site <br /> • TPH-g was reported as non-detect in soil samples collected in all three borings <br /> dnlled in 1990 Very low concentrations of benzene were reported in Boring/Well <br /> MW-3 at 18 5 feet and 34 feet bgs at 0 08 ppm and 0 05 ppm, respectively <br /> • Non-detectable concentrations of TPH-g and BTEX were reported in soil samples <br /> collected from offsite Bormg/Well MW-4 in 1991 Based on results of soil sample <br /> analyses from the onsite and offsite borings, the hydrocarbon plume in soil was <br /> limited to the area of the USTs and product islands <br /> • Groundwater analytical results show a historical decreasing trend in TPH-g and <br /> BTEX concentrations to non-detect in Wells MW-1 through MW-4 Pnor to being <br /> buried, TPH and benzene concentrations in Well MW-I were reported at 82 ppb and <br /> nondetectable, respectively Wells MW-2 through MW-4 report non-detect <br />. concentrations of TPH-g and BTEX for the past five consecutive quarters <br /> monitored The downgradient extent of the residual hydrocarbon plume is defined <br /> by Well MW-4 <br /> o The majority of the impacted soil encountered in the UST, product lines and product <br /> island excavations during the site demobilization activities was reportedly <br /> excavated <br /> The known petroleum hydrocarbon sources have been removed from the site <br /> Petroleum hydrocarbon concentrations in groundwater have declined over time to non- <br /> detect and have remained non-detect for five consecutive quarters of monitoring <br /> Residual hydrocarbons in the soil and groundwater are expected to continue to <br /> biodegrade over time Based on the above data, PACIFIC recommends site closure <br /> 9201030A/CLOSURE DOC <br />