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ri <br /> t , <br /> 15 October 2000 <br /> AGE-NC Project No 96-0232 <br /> Page13of15 <br /> I If S t <br />' - —from-EW-1 at 140µg/l - <br /> "` MTBE increased from 260,ug/l to 1,600µg/l in EW-I grab samples collected between 19 <br />' July and 11 August 2000, however, significant MTBE decreases were reported over the last <br /> i four consecutive sampling events <br /> a <br />' The results from the ground water monitoring and sampling events performed in August 2000 are <br /> ' � r <br /> as follows <br />' r Generally, depth to ground water at the site varied between 13 and 17 feet big <br /> • Fust Zone ground water flow direction at the site appeared to be oriented generally between <br />' west-northwest and west-southwest at a general gradient between 0 003 and 0 004 (Figure <br /> 5), Second Zone ground water flow direction appeared to be oriented west-northwest to west- <br /> southwest at an average gradient of 0 007 ft/ft (Figure 6), Secondary Aquifer Zone ground <br /> water flow direction appeared to oriented west-northwest to west-southwest at an average <br /> gradient of 0 006 ft/ft (Figure 7), Primary Aquifer Zone ground water flow direction <br /> . appeared to onented'west-northwest at an average gradient of 0 006 ft/ft (Figure 8) <br /> • Due to the law ground water gradient at the site, slight variations in ground water <br /> " measurements or changes of recharge/discharge of the local ground water could greatly <br /> modify ground water flow direction ' <br /> 15 <br /> • The greatest concentrations of on-site dissolved MTBE were detected in MW-1 at <br />' „ r concentrations as high as`3,900 µgd, lesser concentrations of MTBE were detected on-site <br /> from MW4 and MW-9A <br /> • ,The greatest concentrations of off-site dissolved MTBE were detected in MW-7, MW-11B <br /> (screened 65 to 75 feet bsg)and from MW-13A(screened 10 to 20 feet bsg) at concentrations <br /> { ;, as high as 2601µg/l, lesser concentrations of MTBE were detected off-site from MW-6B <br /> " (screened 43 to 481feet bsg),MW-1IA(screened 40 to 50 feet big) and:MW-12A (screened <br />' 10 to 20 feet bsg) at concentrations as high as 5 5 µgn <br /> I „I <br /> w • The estimated extent of First Zone Aquifer and Second Zone Aquifer dissolved MTBE are <br />' depicted in Figures 9 and 10 <br /> • The greatest concentration of dissolved TPH-d is detected off-site in MW-11B (screened 65 <br />' to 75 feet bsg),at a concentration of 2,000 4g/1 Lesser concentrations of dissolved TPH-d <br /> were encountered in MW-9C (screened 130 to 150 feet bsg), MW-12A(screened 10 to 20 <br /> feet bsg) and MW-13A, B, C and D (screened between 10 and 150 feet bsg) <br />' Low concentrations of TBA and 1,2-DCA were detected in the water samples collected from <br /> MW-1OC and MW-I3A and MW-13D <br /> I <br /> Advanced GeoEnvironmental,Inc- <br />