ARCHIVED REPORTS XR0009035 - Laserfiche WebLink

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4.4 Extent of Groundwater Contamination A total of six groundwater samples have been collected and analyzed (Table 3) Gasoline and diesel were detected at concentrations of 800 and 8,500 µgfl (parts per billion) in the hydropunch sample from TT-HP-1, toluene, ethylbenzene, and xylene were detected at concentrations of 16, 14, and 110 ppb in this sample Gasoline and diesel were detected at concentrations of 340 and 130,000 ppb in the sample from the domestic well, but xylene (2 7 ppb) was the only volatile aromatic detected in this well No free-phase hydrocarbons were detected in this well with the oil-water interface probe during monitoring on February 20, and the laboratory results confirm that concentrations are below those that would indicate the presence of free product None of the other water samples contained any detectable hydrocarbons Because none of the water samples represent locations that are directly downgradient from DM-1, it would be premature to attempt to delineate the groundwater plume at this time Therefore, Figure 8 shows only the hydrocarbon concentrations without any attempt to contour the values or locate the zero line Based on the present laboratory data, is is probable that contaminated groundwater is present as far east as OE-2 However, contaminated groundwater does not extend as far east as TT-2 or as far south as TT-1 5.0 CONCLUSIONS AND RECOMMENDATIONS Several conclusions can be drawn from the data collected at this site 1) The three underground storage tanks that were removed from this site can be ruled out as potential sources of soil and groundwater contamination All three tanks were in reasonably good condition when removed, and none of the soil samples collected from beneath them contained detectable concentrations of hydrocarbons A monitoring well has been installed within 15 feet of the excavation, and samples collected from the well exhibited no contamination 2) Hydrocarbon contamination, primarily in the diesel range, was present in soil beneath the dispenser island to a depth of 25 or 28 feet Most of this soil has been removed, was largely segregated from clean soil that had been removed from the tank excavation, and remains stockpiled south of the tank excavation The relatively clean soil has been replaced into the dispenser excavation to create a drilling location and to diminish the potential for downward percolation of any residual soil contamination 3) Diesel contamination is also present to a limited extent in groundwater beneath the dispenser island The predominance of mid-range hydrocarbons and the absence or low concentrations of aromatic hydrocarbons indicate either that the petroleum release occurred some considerable time,m i - 7