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%Moe DRAFT <br /> pump island had been while the third well was positioned at the former location of the <br /> site's second, westerly pump island. One of the new groundwater monitor wells was <br /> constructed about 300 feet down-gradient of the site while the other was positioned on- <br /> site and up-gradient, about 60 feet southwest of the pair of vapor extraction wells. <br /> Analyses of soil samples collected during the drilling of these wells indicated an absence <br /> of gasoline constituents in the vicinity of the westerly pump island and at the locations of <br /> the two newly installed groundwater monitor wells. However, in the vicinity of the <br /> easterly pump island, TPH-g and benzene were detected at concentrations as high as <br /> 7,300 ppm. and 3.4 ppm, respectively, at a depth of 26 feet; the data indicated that <br /> concentrations diminished to 120 ppm and 0.083 ppm, respectively, at a depth of 51 feet. <br /> In July 1994, two more groundwater monitor wells were installed southeast and <br /> southwest of the site to complete definition of the plume. Water quality data from the <br /> array of nine groundwater monitor wells showed that the dissolved phase benzene plume, <br /> centered at the location of the easterly pump island, extended down-gradient about <br /> 120 feet, no more than 50 to 60 feet off-site. <br /> In January 1996, recovery of residual petroleum hydrocarbons in the vadose zone <br /> was initiated using Soil Vapor Extraction(SVE) technology. The SVE system was <br /> operational through November 1996 and recovered an estimated 400 gallons of TPH-g, <br /> including about two gallons of benzene. <br /> Beginning in May 1996, MTBE was analyzed for in quarterly groundwater <br /> samples from site monitor wells. These analyses have not detected MTBE in <br /> groundwater from any site monitor wells. <br /> By letter to petitioner dated January 9, 1997, County staff concluded that "...the <br /> assessment of the lateral extent of groundwater contamination is complete, the assessment <br /> of soil contamination is complete, and the plume appears to be stable." The County <br /> recommended that a feasibility study and corrective action plan (CAP) be submitted, <br /> quarterly groundwater monitoring continue, and data in support of the presence of natural <br /> attenuation be collected. <br /> By letter to the County dated February 7, 1997, petitioner summarized the extent <br /> of remedial activities undertaken at the site and the findings of its investigative efforts. <br /> 6 <br />