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Proposal for of Site Cleanup Confirmation May 5, 1992 <br /> Southland, 7-El even No 20680, 9110 Thornton Road, Stockton, CA 5 <br /> ■ Nondetectable to low BTEX (8 ppm) and TPH-as-gasoline (100 ppm) concentrations <br /> In sod samples collected at 35, 40, and 45 feet below ground surface dunng the <br /> installation of well MW-17A, which is located adjacent to the former underground <br /> storage tanks <br /> Since the March 1991 report was issued, additional sod data has been collected indicating that sod <br /> remediation may be complete On September 17, 1991, a total of sex sod samples were collected <br /> from the tank pit which had contained the three underground storage tanks The analytical results <br /> were below detection limits for all samples for BTEX and TPH-as-gasoline compounds Additionally, <br /> two sod samples were collected from the trench which heldp'pinq associated with the underground <br /> tanks �_sample contained low levels of detectable BTEX compounds, although TPH-as-gasolmei7 <br /> `was billow method detection limits The second sample had an elevated TPH-as-gasolin-b <br /> �anceftratilon, reported at 2,100 ppm, which is believed to be a localized hot spot )Results for <br /> ethylene dibromide (EDB) and lead were below detection limits for all tank pit and piping trench soil <br />' samples ' <br /> On September 18, 1991, sod samples were collected at depths of 4 5, 20 5, 36, and 41 5 feet below <br /> grade during drilling for the on-site well MW-207 Analysis of these samples reported BTEX <br /> compounds below detection limits One soil sample (from 415 feet) contained detectable) <br /> Concentrations of TPH-as-gasoline, reported at 9 parts per million (ppm) <br /> 3.0 PROPOSED SCOPE OF WORK AND APPROACH <br /> Groundwater Technology proposes the following scope of work to confirm that site cleanup has <br /> been achieved The first focus of the confirmation program will be on the vadose zone sods beneath <br /> the site Hydrocarbon concentrations in these sods are critical in confirming site cleanup, as the <br /> presence of residual gasoline compounds in the sods could be a source for future groundwater <br /> degradation if groundwater levels increase <br /> I <br /> Sod samples will be collected from the vadose zone soils and analyzed for gasoline hydrocarbons to <br /> Iconfirm that cleanup of the site sods has been achieved Once the sod data is collected, <br /> adjustments to the frequency of monitoring well and domestic well sampling will be made Decisions <br /> to abandon existing monitoring wells can be made after the sod data is collected <br /> 'GROUNDWATER <br /> v 'TECHNOLOGY, INL <br /> I <br />