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' 26 June 2000 • AGE-NC Pi oject No 96-0263 ' Page 3 of 4 ' MW-7 and MW-8 at concentrations i anging from 78 micrograms per liter (µg/1) to MW-8 to 6,800 gg/l in MW-5 BTE&X compounds were detected in the water samples collected from monitoring wells MW-2, MW-4, MW-5, MW-7 and MW-8 Benzene concentrations 1 anged from 3 µg/l in MW-8 to 980 µg/l ' in MW-2 Toluene, ethylbenzene and xylenes were also detected in these wells at concentrations ranging fiom 0 68 [g/l of xylenes in MW-8 to 560 gg/l of toluene in MW-7 MTBE was detected by EPA method 8020 in monitoring wells MW-2, MW-4, MW-5, MW-7 and MW-8 at concenti ations ianging fiom 31 µg/l in MW-8 to 27,000 µg/1 in MW-7 MTBE was i econfr ped by EPA method 8260m and was detected in the same wells as well as MW-6 at concenti ations I anging fi om 4 7 µg/l in MW-6 to 30,000 gg/l In MW-7 No other oxygenates were detected in the ground water samples The cui I ent and past gi ound watel sample analytical results aI a summarized on Table 2 The laboratory teport (MAI Sample ID Nos 35846-35853), QA/QC report and chain-of-custody form I . are Included in Appendix C Figures 4 and 5 depicts the appy oximate at eal distribution of Impacted gi ound water containing benzene and MTBE, 1 espectively, foi the Api Il 2000 gi ound water monitor Ing event 4 0. SUMMARY AND CONCLUSIONS The following conclusions wei e drawn fi om the t esults of this Investigation • Depth to ground water i anged from 6 88 feet to 7 70 feet below the well casing tops The prevailing gi ound water flow dit ection to April 2000 is towai ds the north-northwest The hydraulic gi adient (0 005 feet/feet) Indicates that the gi ound watei table is nearly flat M * The dissolved hydi ocaibon plume extends northwai d fi om the formei UST and dispenser areas and beyond the two down-gradient monitor Ing wells (MW-5 and MW-8) The plume is defined to the south and west by monitoring wells MW-1 and MW-3, respectively The lateral distirbution of dissolved benzene and MTBE was approximated and is depicted on Figur es 4 and 5, respectively I0 Excluding MW-2, the hydrocarbon and MTBE concepti ations have decreased since the last monitoring event in January 2000 Slight incl eases of benzene, ethylbenzene and MTBE concentrations occurred in MW-2 between the January 2000 and April 2000 monitoring events Advanced Ge0E11vironnlental,Inc