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' GEORGE AND MEI•RANISHI • <br /> 1600 Durham Ferry Rd. <br /> Page 2 oto <br /> 7/1/98 Monitoring well MW-107 was installed with a screen interval of 47 <br /> to 49.5 feet bsg. <br /> 7/23-24/01 Impacted soil in and around the former UST pit area was <br /> excavated. Average total depth of excavation was 11 ft. bsg, locally 13.5 feet <br /> bsg. Approximately 500 cubic yards of contaminated soil containing an estimated <br /> 4,900 pounds of TPH-g were removed. At the end of Oct. 2001 , impacted soil <br /> was disposed at Forward Landfill. <br /> Between 5/04/95 and 2/22/02, twenty ground water monitoring events were <br /> conducted. <br /> The results of these investigations have shown: <br /> • Soil is impacted by TPH-g, BTEX compounds and possibly by MTBE to <br /> depths as great as 50 feet bsg northeast of the former UST pit (MW-102). <br /> • Soil left in place at the base of the excavation walls contained as much as <br /> 26,200 mg/kg TPH-g, 7.79 mg/kg benzene, 142 mg/kg toluene, 93.2 <br /> mg/kg ethyl benzene, 476 mg/kg total xylenes, and possibly 38.5 mg/kg <br /> MTBE (unconfirmed by EPA Method 8260). The most intensely impacted <br /> soil appears to be shallower than 15 feet bsg. <br /> • Shallow groundwater is impacted by TPH-g and BTEX compounds in the <br /> area of MW-1, MW-2, MW-4 and MW-5, all located in the general former <br /> UST and dispenser areas; outlying wells MW-3, MW-6, MW-7 and MW-8 <br /> groundwater sample results show only occasional, low concentrations of <br /> contaminants. <br /> • The well monitoring the most intensely impacted ground water is MW-2, <br /> which recently had a ground water sample with 86,600 Itg/I TPH-g, 2,060 <br /> µg/I benzene, 6,010 gg/I toluene, 2,320 µg/I ethyl benzene and 11,300 µg/I <br /> total xylenes. <br /> • Deeper groundwater, monitored by MW-102, MW-202, MW-105 and <br /> MW-107 has not been impacted or has had only occasional low <br /> concentrations of contaminants, thereby delineating the vertical extent of <br /> impacted ground water. <br /> GTI has calculated ground water velocities of 0.103 to 1.04 feet per year in <br /> shallow soil (10 to 20 or 25 feet bsg) and 5.25 to 134 feet per year in deeper soil <br /> (30 to 50 feet bsg). In addition, GTI has determined that predominantly positive <br /> vertical gradients exist at the site that minimizes the potential for downward <br /> migration of dissolved contaminants. <br /> GTI proposed in the 05 February 2002 Work Plan Bio-VentingNapor Extraction <br /> and in the 10 May 2002 Work Plan Addendum for Bio-VentingNapor Extraction <br />