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i <br /> Groundwater elevations measured in the deep wells MW-DIS-7D and MW-DIS-8D are not <br /> used to interpret the horizontal groundwater gradient because those wells are screened in <br /> { different stratigraphic intervals from the shallow wells.However, these wells are used to <br /> calculate vertical gradients using the MW-DIS-7S/7D, and MW-DIS-8S/-8D well pairs. The <br /> calculated vertical gradients for each of these well pairs are presented on Table 3. <br /> As shown on Table 1, the groundwater levels have risen about 30 feet at this site since <br /> measurements began in September 1991. Groundwater flow directions were west to <br /> northwest between 1991 and 1994. Groundwater flow directions were not calculated during <br /> 1995 due to SVE system operation (Flow directions were determined in October 1995 when <br /> the system was temporarily turned off). The groundwater flow direction has been <br /> consistently towards the southeast at a magnitude of approximately 0.001 ft/ft since <br /> October 1995. <br /> Analytical Results <br /> Data from the February 1999 sampling event indicate that the groundwater beneath the <br /> 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 February 10 and 11, 1999.The results were typical <br /> of previous sampling events,except TPH as gasoline was detected in monitoring wells <br /> MW-DIS-5,-7S,and-7D. These three wells have typically been non-detect for petroleum <br /> hydrocarbons. BSK laboratory confirmed that these samples were cross-contaminated from <br /> their lab equipment(please see letter from BSK labs to Del Tech Geotechnical Services, <br /> located in the Laboratory Data Sheet section of this report).These wells and MW-DIS-2 were <br /> re-sampled on March 19, 1999. TPH as gasoline was not detected in monitoring wells <br /> MW-DIS-5,-7S,or-71)in the re-sampling event. The results for MW-DIS-2 are discussed <br /> below. <br /> �. Upgradient Wells-MW-DIS-5, -6,-7S,-71),-8S,and-8D. <br /> TPH as gasoline and BTEX compounds were not detected in groundwater samples collected <br /> from upgradient wells MW-DIS-5,-6,-7S,-7D, -8S,and-8D. <br /> Petroleum hydrocarbons have never been detected in wells MW-DIS-5,and -6. <br /> Benzene and toluene were detected one time in MW-DIS-7S in March 1995 at concentrations <br /> just above the detection limit,and have not been detected the last 5 sampling events. <br /> Petroleum hydrocarbons were detected in MW-DIS-7D during the two sampling events <br /> following installation of the well (September 1991 and June 1992),and in April 1994. <br />` Petroleum hydrocarbons have not been detected in MW-DIS-71)the last 8 sampling events. <br /> Petroleum hydrocarbons were detected in MW-DIS-8S one time in December 1996,and have <br /> not been detected in the last 7 sampling events. <br /> 2 <br /> l <br />