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Final Remedial Plan - Geweke <br />' 2 January 1992 <br /> Page 3 of 15 <br /> and subsequently converted these borings to ground water <br /> monitoring wells (MW-1 through MW--4) . The impact of the <br />' unauthorized release was apparent in the ground water. <br /> Moderate levels of hydrocarbon contamination were encountered <br /> in soil samples at several isolated depths. <br />' A subsequent investigation was performed by Brown and Caldwell <br /> q g <br /> Consultants (BCC) . Five soil borings were drilled (GL-1 through GL- <br /> 5) in February 1986 followed by the installation of an additional <br /> monitoring well .(MW-5) in July of the:. same year. Of the soil <br /> borings, two of them (GL-2 and GL-3) were drilled on the location <br /> of the former tanks. Only moderate levels of hydrocarbon <br /> contaminants were detected in samples from these borings . A re- <br /> sampling of the wells indicated that the highest concentration of <br /> hydrocarbon contamination occurred in MW-4 (BCC report dated July <br />' 1990) . <br /> Four additional ground water wells (MW--6 through MW-9) were <br /> installed by BCC in July 1990 to further define the extent of the <br /> dissolved hydrocarbon plume. Soil samples from 40 to 50 feet below <br /> ground surface from some of the pilot borings contained moderate <br /> levels of contamination, which was attributed to the lateral <br />' migration of contaminants along the capillary fringe. Again, the <br /> levels of hydrocarbon contaminants in MW-4 was the highest. The <br /> dissolved contamination plume appeared to have migrated off-site <br />' (BCC report dated July 1990) . <br /> The most recent investigations were conducted by PES. Four ground <br />' water monitoring wells (MW-10 through MW-13) and one extraction <br /> well (EW-1) were installed by PES in May 1991. A full delineation <br /> of the extent of the dissolved contamination plume was established, <br />' confirming the off--site migration ; of hydrocarbon contaminants. <br /> Similar to the previous investigations, the highest level of <br /> contamination was encountered in MW-4 . PES also conducted an <br /> aquifer test on the extraction well EW-1. An extraction rate of 2 <br /> gallons per minute was estimated (PES Problem Assessment Report, <br /> dated 31 July 1991) . <br />' 1.4 . ASSUMPTIONS <br /> The extent of the vadose zone contamination was not fully <br /> addressed. -Actually,- none of the soil borings drilled indicated the <br /> presence of any. "real" vadose" zone contamination. ' Several soil <br /> samples showing detected levels of hydrocarbon contamination were <br />