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<br /> Analytical Results
<br /> Data from the November 1999 sampling event indicate that the groundwater beneath the
<br /> i Disco site contains detectable levels of total petroleum hydrocarbons (TPH) as gasoline and
<br /> BTEX compounds (benzene,toluene,ethyl benzene and total xylenes). Analytical results are
<br /> presented in Tables 4 and 5. Table 4 presents groundwater sample analysis for TPH-gasoline
<br /> and benzene,toluene,ethyl benzene,and xylenes (BTEX). Table 5 presents analytical results
<br /> for MTBE and other oxygenate compounds. The results are summarized below,dependent
<br /> upon the location of the well in relation to the plume: upgradient,cross-gradient,or within
<br /> the plume.
<br /> The original sampling event occurred on November 8, 1999.The results were typical of
<br /> previous sampling events.
<br /> Upgradient Wells-MW-DIS-5, -6,-7S,-71),-8S, and-813.
<br /> Based on the decision tree(see Figure 4),sampling was not recommended for upgradient
<br /> wells for this monitoring event.
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<br /> Cross-gradient Wells- MW-DIS-3, -9,and-10.
<br /> Based on the decision tree(see Figure 4),sampling was not recommended for cross-gradient
<br /> wells for this monitoring event.
<br /> Wells Within the Plume- MW-DIS-1, MW-DIS-2, NP-1.70', NP-1-80', NP-1.90',SVE-South and
<br /> SVE-North
<br /> 'I'PH as gasoline and BTEX compounds were detected in groundwater samples collected
<br /> from monitoring wells MW-DIS-1, MW-DIS-2,NP-1-70',NP-1-80',NP-1-90',SVE-South and
<br /> SVE-North. The concentrations detected in wells NP-1-70',NP-1-80',NP-1-90',SVE-South
<br /> and SVE-North are consistent with previous sampling events(see Table 4).
<br /> Concentrations detected in MW-DIS-1 during this monitoring event were higher than those
<br /> in July 1999. TPH as gasoline was detected in MW-DIS-1 at a concentration of 17,000µg/L
<br /> and benzene, toluene,ethylbenzene,and total xylenes were detected concentrations of 1,600,
<br /> 1,300,530,and 2,500 jig/L,respectively.
<br /> Oxygenates
<br /> Methyl-tert-Butyl Ether (MTBE), tert-Butanol (TBA),Di-isopropyl ether(DIPE),Ethyl-tert-
<br /> butyl ether(ETBE), and tert-Amyl Methyl ether(TAME)were not detected in any of the
<br /> j wells during this monitoring event. All oxygenates were analyzed by EPA Method 8260
<br /> during this sampling event.
<br /> There have been no confirmed detections of the MTBE,DIPE,ETBE,and TAME at this site.
<br /> TBA has been detected once,in five different wells,but has not been detected twice in any
<br /> well,and has not been detected in any well in five or more consecutive sampling events.
<br /> Other Additives
<br /> Although not requested,the laboratory analyzed and reported 1,2-Dibromoethane,also
<br /> known as ethylene dibromide (EDB),and 1,2-Dichloroethane (1,2-DCA) during this
<br /> sampling event. These compounds are frequently reported with the oxygenates listed above
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