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20 December 2001 <br /> ' AGE-NC Project No 95-0144 <br /> Page 6 of 7 <br /> ' MTBE was detected in ground water samples from MW-4,MW-19A and MW-19B at concentrations <br /> of 1 2 gg/l, 14 gg/l and 10 gg/l, respectively Historically, only low concentrations of MTBE and <br /> ' TBA have been detected intermittently at the site <br /> Analytical results for the fourth quarter 2001 monitoring event are summarized on Table 2 <br /> ' Analytical results of recent and historical ground water samples are s»mmanzed on Tables 3 and 4 <br /> The laboratory report(MAI Lab IDs 83601 through 83610) and chain-of-custody forms are mcluded <br /> m Appendix B <br /> 5.0. SUMMARY/CONCLUSIONS <br /> ' Based upon data collected during the ground water monitoring event, AGE concludes <br /> ' • Ground water elevation decreased approximately 1 09 feet at the site since the previous <br /> ground water monitoring event Ground water remained above the screened interval in five <br /> of the shallow wells sampled during the fourth quarter of 2001 Ground water elevations in <br /> wells completed beneath the clay layer (approximately 35-45 feet bsg) were between <br /> 1 58 feet to 1 86 feet lower than in wells completed within first ground water <br /> ' • Petroleum hydrocarbons were detected in four of the tenwells sampled during the November <br /> 2001 monitoring event Concentrations of TPH-g, TPH-d and TPH-mo have remained <br /> relatively stable since the August 2001 monitoring event <br /> • TPH-g was detected in wells MW-21A and MW-21B located within the former UST No 8 <br /> pit The plume of ground water impacted by TPH-d is larger than the TPH-g plume, <br /> extending lust south of MW-19 and north of MW-20 <br /> ' • Low concentrations of MTBE were detected in ground water samples collected from <br /> monitoring wells MW-4, MW-19A and MW-19B located north of the former UST No 8 pit <br /> ' Based on its sporadic detections and low concentrations, the impact of MTBE on the site is <br /> believed to be minimal <br /> 6 0. RECOMMENDATIONS <br /> Based upon data obtained during the third quarter of 2001 and previous sampling events, AGE <br /> recommends continued quarterly monitoring of the site The next quarterly monitoring event should <br /> ' be scheduled for February 2002, concurrent with monitoring at the Van Buren site <br /> 1 <br /> Advanced GeaRavironmentA Inc <br /> i <br />