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I I07 November 2002 ' AGE-NC Protect No 96-0263 Page 5 of 6 ' MTBE was detected in monitoring well samples MW2 and MW4 through MW8 at concentrations ranging from 11 gg/l(MWS)to 21,000 gg/1(MW7) TBA was detected in the sample collected from MW7 at a concentration of 2,100 gg/1 No other fuel additives were detected in the ground water samples collected from the site I The current and past ground water sample analytical results are summarized on Table 3 Copies of the laboratory report(CTEL Lab I D No 0207-009-1 and 0207-009-11),QA/QC report and chain-cf- custody form are in Appendix E 4.0. SUMMARY AND CONCLUSIONS lBased on the results of this investigation, AGE concludes that ' Depth to ground water ranged from 6 80 feet to 7 90 feet below the well casing tops The prevailing ground water flow direction in June 2002 was inferred to be towards the north-northwest at an average hydraulic gradient of 0 005 feet/feet ' Benzene and MTBE concentrations in ground water samples MW2 and MW4 through MW7 exceeds the DHS' Maximum Contaminant Level of 1 0 µg/1 and 13 gg/1, respectively, in drinking water • The TBA concentration of 2,100 gg/1 in ground water sample MW7 exceeds the DHS' Action Level of 12 gg/l in drinking water • The dissolved hydrocarbon plume extends northward from the former UST and dispenser areas, but not beyond the two down-gradient monitoring wells (MW9 and MW10) The dissolved phase plume has been defined laterally in all directions Isoconcentration maps illustrating the approximate extent of TPH-g-, benzene- and MTBE-impacted ground water are depicted on Figures 4, 5 and 6 I5.0. RECOMMENDATIONS Based on the findings of this investigation, AGE recommends I • Continued quarterly monitoring of the ground water monntormg wells The next monitoring event should be performed in September 2002 iPerformance of a ground water aquifer pumping test to test the feasibility of ground water iextraction as a remedial alternative at the site i I