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Project No 58100-06-11 ' March 29, 1995 Page 2 Previous Groundwater Sampling Results In March 1992, Alton Geosciences constructed three monitoring wells (MW-1 through MW-3) ' near the former USTs to a depth of 79 5 feet below the ground surface (bgs) The approximate locations of the former USTs and wells MW-1 through MW-3 are depicted on the Site Plan, Figure 2 ' The results of groundwater monitoring performed by Alton Geoscfences in April 1992, indicated TPHg concentrations in each well ranging between 2,400 and 4,900 ug/l TPHd was reported at ' concentrations ranging from 73 to 180 ug/I, it was noted by the laboratory, however, that the samples did not appear to contain diesel Benzene was detected at concentrations ranging from 260 to 1,100 ug/l, toluene was detected at concentrations ranging from 9 8 to 360 ug/i and total xylenes were detected at concentrations ranging from 22 to 400 ug/l in each of the three wells ' Ethylbenzene was not detected above the laboratory equipment detection limit for each of the three wells Groundwater was encountered at a depth of approximately 66 feet bgs and the ' gradient was reported to be 0 002 ft/ft to the west The results of laboratory tests reported by Environmental Assessors, Inc in October 1993, indicated TPHg concentrations in each well ranging between 4,500 and 27,000 ug/l Benzene was detected at concentrations ranging from 520 to 11,000 ug/l, toluene was detected at concentrations ranging from 93 to 1,500 ug/l and total xylenes were detected at concentrations ranging from 110 to 1,400 ug/l in each of the three wells Ethylbenzene was reported at concentrations of 25 and 9 0 ug/l in MW-2 and MW-3, respectively Ethylbenzene was not detected above the laboratory equipment detection limit for MW-1 Groundwater was encountered ata depth of approximately 68 feet bgs and the gradient was determined to be 0 0006 ft/ft to the northeast ' The results of laboratory tests reported by Ninyo & Moore in .lune 1994, indicated TPHg concentrations to each well ranging between 588 and 1,500 ug/l TPHd was not detected above ' the laboratory equipment detection limit for each well Benzene was detected at concentrations ranging from 238 to 13,700 ug/l, toluene was detected at concentrations ranging from 151 to 418 ug/l and total xylenes were detected at concentrations ranging from 45 7 to 295 ug/l in each of ' the three wells Ethylbenzene was reported at a concentration of 14 5 ug/1 in MW-1 Ethylbenzene was not detected above the laboratory equipment detection limit for MW-2 and MW-3 Groundwater was encountered at a depth of approximately 66 feet bgs ' A cumulative summary of the groundwater monitoring data for the site is presented on the attached Table I 1