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and tetraethyl lead. Toluene was the only analyte detected in the sample, at a <br /> concentration of 0.0113 mg/kg. The soil sample analytical results are presented <br /> in Table 4 and on Drawing 1. <br /> During the removal of tank F, two soil samples were collected from the bottom <br /> of the excavation and analyzed for BTEX, ethylene dibromide, and tetraethyl <br /> ' lead. Toluene was the only analyte detected in the samples, at concentrations <br /> of 0.0118 mg/kg. The soil sample analytical results are presented in Table 4 <br /> and on Drawing 1 . <br /> 2.4 Ground-water Characterization <br /> ' Ground-water sampling and analysis has been conducted at the site since <br /> January 1987. Following confirmation of ground-water impact, overexcavation <br /> activities were performed in September 1987 (as discussed in preceding <br /> sections of this document) to remove a potential source of ground-water impact. <br /> � Wells MW-1 , MW-2, and MW-3 were installed in January 1987; however, wells <br /> MW-1 and MW-2 were removed in September 1987 during the overexcavation <br /> of the impacted soil near the former tank complex. Wells MW-4 and MW-5 were <br />' installed in September 1987. Since that time, the ground-water elevation has <br /> dropped, and these wells, as well as well MW-3, are now dry. To continue with <br /> ground-water monitoring, deeper wells (MW-9, MW-10, and MW-11) were <br /> installed in March 1990. <br /> Table 1 presents the historical ground-water analytical results. Concentrations <br />' of petroleum hydrocarbons in wells MW-9, MW-10, and iViW-1 have historically <br /> been relatively low or nondefectable. Since March 1990, 14 samples have been <br /> collected from wells MW-9, MW-10, and MW-11 . Nine of the samples did not <br />' contain detectable concentrations of petroleum hydrocarbons. Toluene was not <br /> detected in any of the other five samples; xylenes were detected in one of the <br />' samples; benzene was detected in two samples; and total petroleum <br /> hydrocarbons were detected in three samples. <br />' Based on ground-water flow directions and gradients reported by Elder <br /> Engineering, Inc., the predominant flow direction of first-encountered ground <br /> water is to the northwest with a gradient of 0.0075 foot per foot. Figure 4 is a <br />' diagram presenting monitoring date and flow direction. This information is for <br /> the time period from March 29, 1990, to June 10, 1991 . <br />' Given the ground-water monitoring data reviewed by EMCON Associates, it <br /> appears that the extent of petroleum hydrocarbon impact has been defined <br /> downgradient by MW-11 and laterally to the north by MW-10. To evaluate the <br /> lateral extent to the south, EMCON Associates proposes installing one <br /> additional well at the location shown on Drawing 1 (see Section 3.3). <br /> pjf1f921t920201 a 4 Rev. 0 June 1, 1992 <br /> fEmco 4 Assoc€otos <br />