ARCHIVED REPORTS XR0000956 - Laserfiche WebLink

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IfINIGIf-ILURNER Mr. Charles Leubner 23 September 1997 Page 5 Based on these results, the soil in the southeast corner of the excavation that was found during the removal of the tank to contain diesel product appears to be limited both laterally and vertically. tRemote Fill Piping Diesel hydrocarbons were not detected above reporting limits in the sample collected from the soil boring located over the site of the original piping trench sample location (SB-10), or from the three soil borings drilled around the trench site (SB-7,-$,and 9). Although it is not evident from the boring log because of the nature of the soil used for backfilling, SB-10 is believed to be located within the former piping trench. Due to their distance from SB-10, the other borings are probably located outside of the original trenches. The sampling depths of 5 and 10 feet below ground surface for SB-10 were below the 3-foot depth where the sample collected from the bottom of the trench at the time the piping was removed (was found to contain diesel product). Based on the results of these soil borings, the diesel product in the piping trench is believed to be localized in lateral and Ivertical extent. CONCLUSIONS AND RECOMMENDATIONS Gasoline Tank When the gasoline tank was removed in 1990, total petroleum hydrocarbons as gasoline was detected at 290 mg/Kg in the soil sample collected from the bottom of the tank excavation which was 7.5 feet below the ground surface. By a depth of 10 feet below the ground surface, the concentration of total petroleum hydrocarbons as gasoline in soil had attenuated to below reporting limits. Hence, further excavation of the site is not warranted. Because of the concentrations of total petroleum hydrocarbons as gasoline, benzene, toluene, ethylbenzene, and xylenes that were detected in the groundwater sample collected from SB-1, groundwater monitoring is recommended at the former tank site (either over the excavation or adjacent to the tank excavation in the downgradient direction) to confirm the presence of the constituents. If gasoline hydrocarbons are detected in groundwater collected from the monitoring well, we recommend that a risk-based exposure assessment be conducted to evaluate the need for further remediation. The assessment should evaluate potential impacts to downgradient groundwater supply wells located within 2,000 feet of the site. The assessment should also consider potential threats posed to human health by the upward migration of vapors released to soil by the remaining contamination in soil and groundwater.