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<br /> Oxygenates
<br /> Meth 1 tert-Bu 1 Ether(MTBE), tert-Butanol (TBA), Di-isopropyl ether(DIPS), Eth 1
<br /> Cert-
<br /> butyl ether(ETBE),and tert-Amyl Methyl ether(TAME) were not detected in any of the
<br /> wells during this monitoring event,except MW-DIS-1. TBA was detected in the original
<br /> sample collected from MW-DIS-1 on March 28,2000 at a concentration of 90 gg/L. TBA was
<br /> not detected in MW-DIS-1 in the subsequent sampling event on May 5,2000. All oxygenates
<br /> were analyzed by EPA Method 8260 during this sampling event.
<br /> There have been no confirmed detections of the MTBE, D1PE,ETBE, and TAME at this site.
<br /> TBA has been detected once,in five different wells,and twice in MW-DIS-1.
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<br /> Other Additives
<br /> All upgradient wells were sampled and analyzed for oxygenates, 1,2-DCA and EDB during
<br /> this sampling event. These compounds are known as lead scavengers and were a common
<br /> gasoline additive.
<br /> i EDB was detected in MW-DIS-1,NP-1-90',NP-1-80',NP-1-70',and SVE-South at
<br /> concentrations of 27 and 29, 110, 1,600, 170,and 500 gg/L,respectively. EDB was not
<br /> detected in MW-DIS-1 during the previous sampling event. 1,2-DCA was detected in
<br /> MW-DIS-1, NP-1-90',NP-1-80',NP-1-70',and SVE-South at concentrations of 74 and 71, 140,
<br /> 2,600, 180,and 990 gg/L respectively.
<br /> Conclusions
<br /> Since 1991,groundwater levels have risen approximately 33 feet(from 77 ft bgs to 44 ft bgs),
<br /> and the direction of groundwater flow has changed directions by almost 180 degrees.
<br /> Between 1991 and July 1994, the groundwater flow direction was predominantly towards
<br /> the northwest at an average groundwater flow direction and magnitude of 312°and
<br /> 0.0006 ft/ft. From October 1995, through today, the groundwater flow direction has been
<br /> consistently towards the southeast,at an average direction and magnitude of 143°and
<br /> 0.0008 ft/ft. The groundwater flow direction has been toward the southeast for the past 14
<br /> sampling events,indicating a stable flow regime. Due to the switch in flow directions,
<br /> previous downgradient wells are now upgradient wells.
<br /> Prior to the switch in groundwater flow directions, the extent of the plume was defined
<br /> horizontally by monitoring wells MW-DIS-3, MW-DIS-BS,MW-DIS-9,and MW-DIS-10.The
<br /> vertical extent downgradient of the source area was defined by monitoring well
<br /> MW-DIS-BD. Recently, the downgradient extent of the TPH-gas and BTEX plume was
<br /> delineated with CPT grab groundwater samples during the Additional Characterization
<br /> Investigation.
<br /> Analytical results from all wells at the site have been extremely consistent,with the
<br /> exception of monitoring wells MW-DIS-1 and-2,which have had significant reductions in
<br /> concentrations of petroleum hydrocarbons.
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<br /> There have been no confirmed detections of oxygenates at this site with the exception of
<br /> TBA. TBA is a former gasoline additive, and was used as an octane booster prior to the
<br /> advent of oxygenated gas. TBA was detected in monitoring wells NP-1-70',NP-1-90',and
<br /> SVE-North on December 23, 1997,in MW-DIS-1,and SVE-South on May 21, 1998, and in
<br /> MW-DIS-1 during this event.
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