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1 . ARCADiSGERAGHTY&MILLER ' Previous Work The two 10,000-gallon gasoline and one 280-gallon waste oil USTs,associated product piping, hydraulic lifts, and oil/water separator were removed and the station facilities demolished in January, 1992 Petroleum hydrocarbons were not detected in soil samples collected beneath the USTs, hydraulic lifts, or oil/water separator. Total ' petroleum hydrocarbons as gasoline (TPHg) and benzene were detected in one soil sample collected from the product piping trench between the dispenser islands at concentrations of 150 and 0 81 parts per million (mg/Kg), respectively This trench ' area was over-excavated, and a confirming soil sample collected from the base of the excavation Petroleum hydrocarbons were not detected in this soil sample ' A second 130-gallon waste oil UST, that was discovered on March 2, 1992, was removed from the eastern portion of the property in May 1992 Petroleum hydrocarbons were not detected in the soil sample collected from beneath this UST. ' Data pertaining to the UST removal were presented in GeoStrategies (GSI) Report No 7827 01-1, Tank Removal Observation Report, dated September 11, 1992 GSI reported that the data collected during the investigation indicated that no M hydrocarbons, benzene (B), toluene (I'), ethylbenzene (E), xylenes (X), or ethylene dibromide (EDB) were detected in the soils beneath the UST pit of the 1992 tanks south of the station building,the excavation pit of the 1992 waste oil UST, beneath the location of the former oil-water separator, or beneath the location of the former hydraulic lifts Two out of four samples collected from the bottom of the piping trenches were nondetect for total petroleum hydrocarbons as gasoline (TPHg), BTEX, ' and EDB The third sample was nondetect for benzene The fourth sample indicated 81 milligrams per kilograms (mg/Kg) benzene In the two samples with TPHg detections toluene ranged from 070 to 14 mg/Kg, ethylbenzene ranged from 017 to ' 5 4 mg/Kg, xylenes ranged from 087 to 32 mg/Kg After further excavation of the trench area with the highest petroleum hydrocarbon concentrations, an additional sample taken at the bottom of the excavation was nondetect for TPHg, BTEX, and ' EDB In October 1993, GSI drilled eight on-site exploratory soil borings (U-A through U-H) in the locations of both the 1967 and the 1992 USTs,the former product dispenser islands, and the former hydraulic lifts, m anticipation of site closure (Exploratory Soil Boring Report (No 782702-3), GSI, December 15, 1993) During ' this investigation, TPHg were detected in soil samples collected at 16 5 feet (2400 mg(Kg) and 31.5 feet (2300 mg/Kg) below ground surface (bgs) from boring U-C, drilled within the former 1967 gasoline UST pit in the southeastern corner of the site, ' and from boring U-D (2900 mg/Kg at 16.5 feet bgs, 1600 mg(Kg at 315 feet bgs), drilled adjacent to former dispenser island D4 While benzene was not detected m