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<br /> '1,30 November 2005 �
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<br /> AGE-NC Project No 196-0235
<br /> Page 11^of 13
<br /> 3'5 2`, NORTHERN UST CLUSTER AREA r'
<br /> s A'release of TPH-g,BTEX and MTBE occurred from dispenser lines at the northern portion -
<br /> ' of the tank area Samples collected from beneath the southernxends of e'ach-tank (upon
<br /> 'removal), were "non-detect" for chemicals of concern TPH-g was reported in a samples, "
<br /> collected from the'north end,of the tank excavation at`988 mg/kg of TPH-g,TPH=g was,
<br />' reported in the 15-foot soil sample collected from boring B9 at 7,000 mg/kg TPH-g
<br /> Chemicals of concern were not detected in shallow soil samples collected near wells MW-2 r
<br /> and MW-7 The,highest TPH-g and BTEX impact to soil in the upper vadoselzone was' "
<br /> removed through excavation in December 2003 Currently, no residual vadose -zone
<br /> _ hydrocarbon contamination is present at the,site The aerial extent of the soil contamination '
<br /> In soil appears defined to the near,the` formdr northern cluster area Available data[Is
<br />' suggestivle of a release was most severe at the northern edge of the former northern cluster '
<br /> 'f f UST area After the release, TPH/BTEX and MTBE migrated only slightly north In the area
<br /> of well EW-1 and vertically to a depth of approximately 35 feet bsg near boring B9, The
<br />' "deep"migration of hydrocarbons Indicates a historically depressed water table depth of near'
<br /> 30 feet bsg
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<br /> to • Based on six-years of ground water monitoring, the Impacted ground water appears stable, Y `
<br /> between'wells MW-10, MW-12, MW-13, MW-14,azld MW-15 The plume appears to be
<br /> ' laterally less than than 40 feet east to west and_ approximately 40 feet north to south, ,
<br /> surrounding the former UST area at well EW-1 The maximum concentrations detected were
<br /> TPH-g at,11,000 pg/l, TPH-d at 110,000 µg/l, and benzene at 640 µg/l (MW-10)
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<br /> Significant concentrations of TPH-g,'TPH-d and BTEX compounds were detected In ground
<br /> water samples collected prior to the excavation of the former northern cluster UST area s`
<br /> r However after removal of soil, well MW 10 has generally been non-detect for chemicals of,
<br /> "concern and ' Have been declining in the newly Installed well EW-1
<br /> • The wells Installed,to define the vertical extent of dissolved hydrocarbon contamination
<br /> - demonstrated limited Impact to the eastern edge'Nof the former UST area at wells MW-11 B
<br /> I' and MW-14B, at depths of 4'S feet and 65 feet bsg, respectively Based upon "deep" grab k
<br /> aground,water samples'atl'bonng CPT-4,'the vertical extent Is not greater than 80 feet'bsg' "
<br /> across'the former UST area t ;
<br /> • MTBE was also released with the TPH-g and migrated vertically to the east and, to a lesser
<br /> extent;north and northeast;as evidenced by detection of contaminants In wells MW-9;MW=
<br /> 11B and MW-14B' Low concentrations of 1,2-DCA`have been detected at the site,however, '
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<br /> coentratroris,appear to be stable throughout the,monitoring well network' The current
<br /> maximum coricentrations bf 1,2�-DCA Is 44 µg11 at MW-I IB
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<br /> 'Advanced GeoEnvironmental,Inc
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