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t ` 1 1 A A{ 1 M1 24 October 1997 AGE-NC Project No 96-0235 A Page 9 of 11 10 3 2 PETROLEUM HYDROCARBON-IMPACTED GROUND WATER TPH-g was detected in MW-1, MW 2, MW-3 and MW-5 at concentrations ranging from 52 ppb to 17,000 ppb Benzene was detected in the,same wells at concentrations ranging from 2 4 ppb to 1,100 ppb Toluene, ethylbenzene, and xylenes were detected in the same wells at concentrations ranging from 0 71 ppb to 2,200 ppb MTBE was detected in the sample collected from MW-2 at a concentration of 58 ppb Isocontours for TPH-g in ground water are illustrated in Figure 7 - TPH-g Isocontours = I TPH-d was detected in wells MW-1 through MW-4 at concentrations ranging from 56 ppb to 2,000 ppb TPH-mo and oil and grease were not detected in any of the ground water samples Monitoring well MW-2, currently the down-gradient well on the property, was the most intensely impacted well, MW-4 was overall the least impacted monitoring well The analytical results for the ground water samples are summarized in Tables 1 and 2 -Analytical Results of Ground Water Samples The laboratory report(MAI Sample Nos 76955 through 76959), chain-of-custody form and QA/QC are included in Appendix C 110. SUMMARY AND CONCLUSIONS Based on the data developed during the activities recounted above, AGE concludes the following - • Approximately 550 cubic yards of hydrocarbon-impacted soil had previously been removed from the former UST excavation Impacted soil was left in place in the excavation t • The lower 5 feet of the excavation was backfilled with imported soil, the upper portion of _ the excavation was backfilled with aerated soil previously removed from the excavation The aerated soil did not contain detectable concentrations of TPH-g (gasoline) or BTE&X, but did contain TPH-d (diesel) and TRPH _ Highly impacted soil was encountered at 4I feet bsg during installation of MW-2, with a ITPH-g concentration of 1,200 ppm and a benzene concentration of 1 I ppm detected This impacted soil,was probably associated with the capillary fringe zone of the ground water elevation near the time of the hydrocarbon release • Soil samples collected and analyzed during installation of four exploratory borings and two monitoring wells generally lacked detectable concentrations of petroleum hydrocarbons, except for low concentrations detected in boring B7 at 25 feet bsg Soil was not sampled at depths greater than 35 feet bsg or analyzed from depths greater than 30 feet bsg Advanced GeoEniironmental,Inc } L