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' `07 February 2003 �. AGE-NC Project No. 98-0468. tPage 3 of 4 ; ' 3.2. ANALYTICAL RESULTS OF GROUND WATER SAMPLES Laboratory analytical results ofgroundwater samples from monitoring wells MW-3 through MW-10 ' are provided for the fourth quarter.2002 monitoring events. Benzene was detected in ground water sample from MW-4 at a concentration of 2.5 micrograms per ' liter (µg11). The remaining BTEX compounds were not detected in other ground water samples analyzed. '. MTBE was detected in five samples analyzed during the monitoring event. MTBE was detected in water-table-well samples MW-3,MW-4 and MW-6 at concentrations 1.8 µg11, 91 gg/l and 75 µg11, respectively. MTBE was also detected in deep-screened-well samples MW-9 and MW-10 for the. ' first time'at concentrations of 66µg11 and 8.6µg/l,respectively.MTBE was not detected in the down . gradient wells MW-7 and MW-8 or cross gradient well MW-5. Laboratory results of ground water-samples analyzed for petroleum hydrocarbons and fuel additives . are summarized in Table 2.The laboratory reports(MAY Laboratory ID: 0212434-01 to'08),quality assurance and quality control (QA/QC)reports and chains-of-custody are included in Appendix B: 4.0. SUMMARYICONCLUSIONS The following summary points and conclusions were drawn from the results of the site investigatiion:, ' Groundwater elevations in the five surveyed wells(MW-1 through MW-5)ranged between 3.44 and 4.58 feet below MSL. Ground water elevation decreased in all the wells except ' MW-3 by as much as 0.23-feet since the previous monitoring event; well MW-3 increased .. by 0.05 feet. . • Ground water flow was inferred to be toward the northeast at a gradient of 0.022;in general, ' the- ground water flow direction and gradient for this monitoring event appear to be consistent with results of previous monitoring events. ' • MTBE was detected in the ground water.samples collected from wells MW-4, MW-6, MW-7,-MW-9 and MW-10 by EPA Method 8260. The down-gradient'extent of MTBE- impacted ground water has been delineated in the first water table; however, the MTBE impact to deep ground water,detected at depths of between 60 and 75 feet in deep-screened wells MW-9 and MW-10, has not been defined below the concentrations of 8.6 µg11. Advanced GeoEnvironmental,Inc.