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<br /> 30 November 2005
<br /> „AGE-NC Project No 96-0235' �r
<br />' Pagel 10 of 13
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<br /> 'r 3 51 ' SOUTHERN UST AREA
<br /> • A release of petroleum hydrocarbons(TPH-g, TPH-d)and benzene,toluene,ethyl benzene
<br /> and xylene (BT EX)''eompounds'withF low"concentrations of, 1,2'DCAr°occurred from-= - '
<br /> dispenser line releases near the northern excavation(UST No 3 area) The southern UST `f
<br /> removal samples were non-detected for chemicals of concern Additionally, shallow soll"
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<br /> samples collected iim well MW-2,MW-,7 were non-detect for chemicals of concern TPH-g � Lc�
<br /> was reported at a concentration as great as 2,100 mg/kg iri the soil sample collected from the -
<br /> northern UST removal'samples, TPH-g was also reported at 320 mg/kg in a soil sample ,SLr1 A
<br /> collected at 20 feet bsg in boring B 10 The highest TPH-g and BTEX impact to soil in the
<br /> 1 : , upper'vadose zone was removed through excavation t at the UST No' 3 area, it does not
<br /> appear that any residual vadose zone hydrocarbons are present in this area The aerial extent
<br /> of the soli contamination in soil appears defined to the near the former UST, No 3 area _
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<br /> Available data is suggestive of a release was most significant at the northern edge of the
<br /> former UST No 3 area Once the petroleum hydrocarbons were released to the'subsurface,
<br />' the contaminants migrated north under well MW-7 and vertically to a depth of approximately
<br /> ,60 feet bsg near well MW42 The,"deep"migration of hydrocarbons indicates a historically
<br /> depressed water table depth of near 35 feet bsg >o Y
<br /> Based on ten years of ground water monitoring for TPH-g and,BTEX compounds near the
<br /> UST No 3 area,the impacts to ground water appear to be stable in the areas of wells MW-l,
<br /> MW-2, MW-3 and MW-' 5 The groundwater plume appears to be somewhat symetrical,
<br /> extending approximately 80 feet east to west and 80 feet north to south, surrounding UST
<br /> No 3 area "' 4
<br /> • Maximum concentrations detected were in the UST No 3 area are TPH-g at 47,000 µg11, q
<br /> ' TPH-d at,30,000 µg/l, and�benzene at 5,1001 pg/1 (MW-2) Significant concentratlonsW , '
<br /> TPH-g,'TPH'd and BTEX have been consistently reported in samples collected`from well'
<br /> MWS 1', 'located east of the former UST No 3 area The new wells installed(MW-16 through
<br /> s T `MWI 24)to define the vertical extent of dissolved hydrocarbron contamination demonstrated.'
<br /> "liiriited impact at the�southern edge of the,UST No 3 area,at'a depth of 75 feet bsg, and not ;
<br /> greater than 100 feet across the entire UST No r3 area Off-site grab ground water samples _
<br /> were``non-det ce t or hydrocarbon contamination at all`depths sampled A minor release of,-,
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<br />' r 1', -DC_=_7 o y likely occurred with the'TPH, the 1;2-DCA plume appears to be stable in
<br /> samples `collected from the monitoring swell network 'The maximum concentration of -
<br /> ° 1,2-DCA at the site is currently 41 µg/l'(MW-1)'; ,' '
<br /> The lateral and vertical ektent of TPH and BTEX has been defined by the,sample set Trends !
<br /> '> of contamination detected lin selected, wells are depicted in Appendix F The lateral
<br /> ti distribution of hydrocarbon's is depicted iii Figures 4 and 5 as well as by section view in
<br /> Figure 7
<br /> Advanced GeoEnvironmental,Inc
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