ARCHIVED REPORTS_REMEDIAL INVESTIGATION REPORT 2000

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07 February 2000 AGE-NC Project No. 95-0144 Page 3 of 4 Ground water was within the screened intervals of MW-19A,MW-20A and MW-21A. Ground water elevations in wells MW-19, MW-20 and MW-21 were between 1.49 and 1.80 feet lower in the lower screened intervals beneath the confining clay layer than in the upper screened interval. Data from the upper screened interval, established in first-encountered ground water was used for gradient determination. 3.2. ANALYTICAL RESULTS OF WATER SAMPLES During the November 1999 monitoring,TPH-g was detected in samples from monitoring wells MW- 20A and MW-20B at concentrations of 3,200 parts per billion(ppb,reported as micrograms per liter) and 490 ppb, respectively. BTEX compounds were detected in samples from wells MW-20A and MW-20B at concentrations as high as 280 ppb (benzene, MW-20A). TPH-d was detected in wells MW-19A,MW-20A,MW-21A and MW-20B at concentrations ranging from 110 ppb to 3,900 ppb. TPH-mo was detected in monitoring wells MW-20A and MW-20B at concentrations of 480 ppb and 330 ppb,respectively.A large variation in hydrocarbon concentrations occurred in wells MW-20 and MW-21, relative to the August 1999 sampling event. The reason for this shift is not clear. Of the remaining wells, detected concentrations of hydrocarbons in ground water increased in one well and decreased in four wells since the August 1999 sampling event. MTBE was detected in ground water samples from wells MW-19A and MW-19B at concentrations of 1.3 ppb and 1.5 ppb, respectively. Other oxygenates were not detected at the site during the November 1999 monitoring event. Historically, only low concentrations of MTBE and TBA have been detected intermittently at the site. Analytical results for November 1999 are summarized on Table 2. Analytical results of historical ground water samples are summarized on Tables 3 and 4. The laboratory report (MAI Laboratory I. D. Nos. 25482-25491) and chain-of-custody forms are included in Appendix B. 4.0. SUMMARY/CONCLUSIONS Based upon data collected from the site, AGE concludes: • Ground water elevation decreased approximately one foot at the site during the previous quarter. Ground water remained above the screened interval in four of the shallow wells sampled during the current quarter. Ground water elevations in wells completed beneath the clay layer were lower than in wells completed within first ground water. • Petroleum hydrocarbons were detected in four of the ten wells sampled during the November 1999 monitoring event. Overall, concentrations of hydrocarbons have generally remained Advanced GeoEnvironmental,Inc.