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• Ile 17 March 1996 AGE-NC Project No 95-0128 Page 6 of 8 1 ' the surveyed casing elevation The depth of ground water, casing elevations and ground elevations are depicted on Table 2 - Ground Water Elevations The hydraulic gradient was determined by contouring the ground water elevation in each well Ground water gradient on 10 September 1996 was calculated to be 0 0029 ft/ft (15 5 feet per tile) directed N 34° E The ground water elevation at the site is illustrated in Figure 3 - Ground Water Elevation (September 1996) Ground water gradient on 03 February 1997 was calculated to be 0 007 ft/ft (36 4 feet per 11-iile) directed S 760 E The ground water elevation at the site is illustrated in Figure 4 - Ground Water Elevation (February 1997) 44 ANALYTICAL RESULTS OF GROUND WATER SAMPLES TPH-g and TPH-d were detected in the grab water sample collected from boiing B10 at concentrations of 93,000 and 8,700 kzgll (micrograms per liter or parts per billion ppb), respectively BTE&X and MTBE were also detected in the grab ground water sample at concentrations up to 16,000 ppb Analytical results of the grab water sample are included in Table 3 The laboratory teport (MAI Laboratory ID 73343) QA/QC report and chain-of-custody are in Appendix F Duttng the September 1996 and February 1997 sampling events, the highest concentrations of hydrocarbons were detected in vapor well VW-1, located down-gradient (north) of the former UST r excavation Overall, concentrations of petroleum hydrocarbons detected in samples collected from 1 VW-1 increased between March and September 1996, however, concentrations decreased between September 1996 and February 1997 I TPH- and TPH-d were Q - - g e detected tit monitoring welts MW 4 through MW 7 at concentrations as great as 9,200 ppb (TPH-g, MW-4) MTBE and BTE&X were also detected in each monitoilng well at concentrations up to 1,600 ppb (benzene, MW-4) Analytical results of ground water samples are summarized on Table 3 - Analytical Results of Gf ou,rd rV U / Surnpies The laboratory report tivud Laboratory ID 66629 trtrougn 666-12), QAJQ(- report and chain-of-custody for the September 1996 sampling are included as Appendix H The laboratory report(MAI Laboratory ID 73441 through 73445), QA/QC report and chain-of-custody for the February 1997 sampling are included as Appendix I