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16 October 1996 <br /> AGE-NC Project No. 95-0165 <br /> Page 5 of 6 <br /> 3.7. ANALYTICAL RESULTS OF GROUND WATER SAMPLES <br /> Petroleum hydrocarbons were.not detected in either grab water sample collected. Analytical results <br /> of the water samples are summarized on Table 5. The laboratory reports (MAI Lab ID 61214 and <br /> 6605 1) and chain-of-custody are included in Appendix F. <br /> 4.0. CONCLUSIONS AND RECOMMENDATIONS <br /> 4.1. CONCLUSIONS <br /> Based on the data collected during the current and previous investigations at the site, AGE has the <br /> following conclusions: <br /> • Hydrocarbon-impacted soil was removed to a depth of thirty-one, feet bsg; however, ' <br /> analytical results of soil samples collected from the excavation indicted that hydrocarbon- <br /> impacted soil was still present beneath the floor of the excavation in the area of the former <br /> USTs. <br /> Laboratory analysis of soil samples collected from four soil borings advanced in May 1996 <br /> indicated that the lateral extent of impacted soil is limited to the vicinity of the northern end <br /> of the former UST excavation. <br /> • Hydrocarbon-impacted.soil was encountered at depths as:great as fifty-five feet bsg. <br /> LW •' The volume of impacted soil left in place in the vicinity of the former USTs is estimated to <br /> be 116 cubic yards (See Appendix G--.Mass BalanceAssunnptions and Calculations). <br /> • The maximum concentrations of toluene, ethylbenzene and total xylenes in soil samples <br /> too collected from borings in and around the former UST excavation did not exceed state MCLs <br /> for those compounds in water. <br /> The concentration of benzene in soil was.found to exceed the state MCL for water in only <br /> r <br /> one soil sample, 132-35 feet at 0.009 ppm. <br /> Based on the volume of hydrocarbon-impacted soil left in place and hydrocarbon <br /> concentrations in the soil, an estimated 0.00295 gallons_ of benzene is present at the site (see <br /> Appendix G). <br /> m The analytical results on water samples collected from the on-site domestic well suggest that <br /> ground water has not been impacted by the unauthorized release of petroleum hydrocarbons. <br /> L Based on the depth.to ground water, the low concentration of hydrocarbons in soil and soil <br /> composition, it is unlikely that hydrocarbons in soil on the site can or will migrate to the <br /> ground water and pose a significant threat to groundwater quality in the area. <br />