SITE INFORMATION AND CORRESPONDENCE

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DRAFT 28 to 30 feet.2 Soil samples collected from the bottom and sidewall of the excavation indicated TPH-g and benzene concentrations ranged from 3 to 18 ppm and less than 0.05 to 1.7 ppm, respectively. In August 1989, two additional groundwater monitor wells were constructed off-site rn approximately 100 feet east and northeasterly of the former pump island where high constituent S DL4 3 concentrations had previously been detected in groundwater. Analyses of groundwater samples i o e�AY,//", from these wells revealed low concentrations of TPH-g (150 and 240 ppb), xylene (1.4 and n L, , &11- M 1.9 ppb), and ethylbenzene (less than 0.5 and 8.1 ppb); benzene and toluene were not detected. �5a T° " fi In February 1992, three vapor extraction wells and two more groundwater monitor well r+ nI 1 z were installed. Two of the vapor extraction wells were located where the easterly pump island had been while the third well was positioned at the former location of the site's second, westerly pump island. One of the new groundwater monitor wells was constructed about 300 feet down-<— !v�-L gradient of the site while the other was positioned on-site and up-gradient, about 60 feet N southwest of the pair of vapor extraction wells. Analyses of soil samples collected during the drilling of these wells indicated an absence of gasoline constituents in the vicinity of the westerly pump island and at the locations of the two newly installed groundwater monitor wells. However, in the vicinity of the easterly pump island, TPH-g and benzene were detected at concentrations as high as 7,300 ppm and 3.4 ppm, respectively, at a depth of 26 feet; the data indicated that concentrations diminished to 120 ppm and 0.083 ppm,respectively, at a depth of 51 feet. In July 1994, two more groundwater monitor wells were installed southeast and southwest of the site to complete definition of the plume. Water quality data from the array of nine groundwater monitor wells showed that the dissolved phase benzene plume, centered at the location of the easterly pump island, extended down-gradient about 120 feet, no more than 50 to 60 feet off-site. In January 1996, recovery of residual petroleum hydrocarbons in the vadose zone was initiated using Soil Vapor Extraction (SVE) technology. The SVE system was operational through November 1996 and recovered an estimated 400 gallons of TPH-g, including about two gallons of benzene. Z The volume of soil excavated is a point of contention. Petitioner indicates in its Site Closure Summary report that an estimated 1,100 cubic yards of soil were excavated while the County contends that only 350 cubic yards are documented to have been excavated. However,in a March 12, 1991 letter to petitioner,the County states that;`...approximately 1300-1400 cubic yards of contaminated soil..."were excavated. Based on the reported dimensions of the excavation,we have estimated 850 cubic yards. 5