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15 April 2004 <br /> AGE-NC Project No 99-0559 <br /> Page 3 of 13 <br /> from surrounding bodies of rock or sediment(Sanders, 1998), or a part of a body of rock that forms <br /> a distinct hydrologic unit with respect to the flow of ground water(Maxey, 1964) <br /> HUl was Impacted by TPH-g,benzene and MTBE In the former UST area and only by MTBE south <br /> and west of the former UST area HU4, a thick poorly graded sand to silty sand layer encountered <br /> at approximately 92 to 105 feet bsg which was a significant unit of concern,was Impacted by TPH-g, <br /> benzene and MTBE In the former UST area and toward the west and was slightly Impacted by <br /> MTBE(<5 0 µg/1) south of the former UST area The upper HUS (130 feet bsg)was Impacted In the <br /> former UST area by TPH-g, benzene and MTBE, but was less Impacted south of the former UST <br /> area (TPH-g <100 µg/1), and not Impacted west and down-gradient of the former UST area The <br /> lower HUS, at 150 feet, was significantly impacted by TPH-g, benzene and MTBE in the former <br /> UST area,yet was not Impacted by TPH-g and BTEX south or west of the former UST HU5 at 150 <br /> feet was slightly Impacted by MTBE (<5 0 µg11) south of the former UST area <br /> The vertical extent of dissolved TPH-g and benzene does not extend to 130 feet bsg In the area of <br /> CPT-1 or to 60 feet bsg In the area of CPT-3 The vertical extent of dissolved TPH-g and benzene <br /> has not been determined In the area of CPT-2, adjacent to the former UST area and extends to the <br /> lower HU5 at 150 feet bsg Dissolved MTBE does not extend vertically to 130 feet bsg In the area <br /> of CPT-1 The vertical extent of dissolved MTBE has not been detennlned In the areas of borings <br /> CPT-2 and CPT-3 The concentrations of dissolved MTBE detected In the former UST area Increases <br /> with depth, and highest MTBE detection In boring CPT2, the former UST area, was In the sample <br /> collected from HU5 at 150 feet The highest concentration of MTBE detected at the site was from <br /> bonng CPT3, In HU1 TPH-g,benzene and MTBE were detected in the three soil samples collected <br /> from CPT-2 at depths of 80 feet(HU3), 110 feet(upper HU5) and 135 feet bsg (middle HU5) The <br /> vertical extent of Impacted soil has not been defined In the source area, however, adsorbed <br /> concentrations decreased significantly with depth (135 feet bsg) and the 135-foot sample may be <br /> Inferred to be near the lower margin of Impacted soil <br /> On 27 September and 01 through 03 October 2001, four Continuous Multichannel Tubing(CMT) <br /> ground water monitoring wells (MW-5 through MW-8) were Installed Based on analytical results <br /> of grab ground water samples and Interpreted soil profiles from CPT data,the CMT monitoring wells <br /> were designed and constructed utilizing five separate filter pack Intervals, from 45-65 feet bsg, <br /> 87-100 feet bsg, 125-135 feet bsg, 148-160 feet bsg and 174-185 feet bsg, to characterize ground <br /> water gradient,potential contaminant migration pathways and to assess the lateral and vertical extent <br /> of Impacted ground water west and east of the former UST release <br /> Advanced GeoEnvironmental,Inc <br />