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December 16, 1992 ����� <br /> Unocal Service Station No 6981, Stockton, California Working To Restore Nature <br /> Vapor-Extraction Well installation <br /> our va or-extraction wells (VW-1 through VW-4) were installed in Four borings near toe <br /> 6ank co`rnplex-and-disp-em? islands(Plate 2) These wells were used to conduct a vapor- <br /> extraction test (discussed in Vapor-Extraction Test section) Details on the construction of <br /> the vapor-extraction wells are summarized in Table 2 and are shown on the Logs of Borings <br /> (Appendix B) <br /> Assessment of Ground Water <br /> Ground-Water Monitoring Well Construction <br /> '_o delineate the extent of dissolved hydrocarbons UTI ground water. eight gr_outid-water� <br /> • ( monftot-ing wells (MW-1 through MW 8) were installed onsite and five ground-water, <br /> Tnitoring wells were installed offsite (MW-9 through MW-13) One onsite boring was 7 <br /> (converted to a pumping test well (PTW-1)1) Monitoring wells MW-1 through MW-5 were <br /> Installed in January and February 1990 MW-6 through MW-8 were installed in March 1992 <br /> and MW-9 through MW-13 and PTW-1 were installed in August 1992 Details on the <br /> construction of the wells are summarized in Table 2 and are shown on the Logs of Borings <br /> (Appendix B) <br /> Before ground-water monitoring wells MW-10, MW-11, and MW-12 were installed, the <br /> borings were drilled to dust above ground water and a Hydropunch sampling device was <br /> driven into the saturated sediments Groundwater samples were collected with the <br /> Hydropunch and analyzed for hydrocarbons prior to the completion of the wells Because <br /> dissolved hydrocarbon concentrations were below the laboratory's limits of detection for all <br /> petroleum analytes.the borings were completed as monitoring wells to establish a"zero-line" <br /> for the dissolved hydrocarbon plume <br /> • <br /> 38032-lo 6 <br />