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05 November 2002 <br /> AGE-NC Project No 96-0235 <br /> Page 3 of 5 - <br /> 3 1 GROUND WATER GRADIENT AND FLOW DIRECTION <br /> 1 <br /> The elevation of ground water in each well was calculated by subtracting the depth to ground water <br /> from the surveyed casing elevations (Table 1) Depths to ground water ranged from 1752 feet to <br /> t20 43 feet below the tops of the well casings, ground water was within the screened intervals of the <br /> shallow-screened wells,but was approximately 11 feet above the screened interval of intermediate- <br /> screened wells MW-3 and EW-2 and between 19 57 and 21 55 feet above the screened intervals of <br /> I the deep-screened wells <br /> Ground water elevations at the site ranged from 12 35 feet (MW-4) to 13 97 feet (MW-2) below <br /> mean sea level The average ground water elevation in the wells decreased by approximately 1 4 feet <br /> since the May 2002 ground water mmirtonng event <br />' Figure 3 illustrates the ground water potentiometric surface based on the shallow-and deep-screened <br /> data sets Near the former UST cluster, the shallow-screened data delineated an inward-radiating <br />' ground water flow pattern,with a net flow towards the southeast, the deep-screened data delineated <br /> a dominant ground water flow direction toward the east Near the former UST No 3 excavation <br /> ground water flow direction at the shallow-screened level was inferred to be towards the east- <br /> southeast,ground water flow direction at the deep-screened level was inferred to be inward-radiating <br /> between south and southwest The inferred ground water gradient in the shallow zone was 0 002 ft/ft <br /> near the former UST cluster and 0 004 ft/ft near the former UST No 3 location,the inferred ground <br /> water gradient in the deep zone was 0 001 ft/ft near the former UST cluster and 0 014 ft/ft near the <br /> former UST No 3 <br /> 32 ANALYTICAL RESULTS OF WATER SAMPLES <br /> TPH-g was detected in the samples collected from MW-1, MW-2, MW-10, MW-11B, EW-1 and <br /> EW-2 at concentrations as high as 50,000 micrograms per liter(µg/1) in the sample collected from <br />' EW-1 TPH-d was detected in samples collected from MW-1, MW-2, MW-9, MW-10, MW-11B, <br /> EW-1 and EW-2 at concentrations as high as 12,000 gg/l (MW-10, EW-1) <br />' BTEX compounds were detected in samples MW-1, MW-2, MW-10, MW-I IB, EW-1 and EW-2 <br /> at maximum concentrations of 1,700 µg/1 benzene, 6,500 µg/1 toluene,2,200 µg/1 ethylbenzene and <br /> s 9,100 µg/1 xylenes, in the sample from. EW-1 <br /> MTBE was detected by EPA Method 8260B in the water samples collected from MW-9,MW-10, <br /> MW-11B, MW-12B, MW-13A, MW-13B and EW-1 at concentrations ranging from 13 µg/1 <br /> ' (MW-13A)to 460 gg/1(EW-1) TBA was detected in the water samples collected from MW-6B and <br />' MW-11B at a concentrations of 14 µg/1 and 8 6 µg11, respectively Water samples analyzed from <br /> Advanced GeoEnvironmental,Inc <br />