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f 1 eutpgi at-r"I ks Inc. Page 2 L Soil Vapor Extraction Pilot Test Work Plan Project No. 770.2 September 17,2003 PHS/EHD directed that additional water table wells be placed to.the northwest of MW-5 and r in the location of the former tank excavation. GTI responded to this directive by submitting L: our November 30, 2001 work plan addendum that included provisions for two additional water table wells. The two new deep wells, MW-104 and MW-106, and the two water table r wells, MW-7 and MW-8, were installed on May 8 & 9, 2002. r _ Five consecutive quarters of groundwater monitoring have been completed since the installation of the additional wells.and..the residual diesel.contamination continues to impact L groundwater quality. Non-aqueous phase liquids (NAPL) detected during the installation of well MW-7 suggests that remediation by natural attenuation will not be sufficient to address residual contamination. This pilot test work plan has,been developed to address the residual diesel contamination in soil. GTI proposes to conduct a pilot test utilizing high vacuum soil rvapor extraction. 2.0 SITE CHARACTERISTICS The geology, hydrogeology and contaminant distribution will be discussed in the following sections. 2.1 Geology • The geology of the site consists primarily of alternating layers, lenses and interstratifed beds of clays, silts and sands. Units containing gravels are less frequent. See Figures 3 & 5 - Cross-Sections for more information. Figures 3 & 5 provide a geologic interpretation of the units observed in the borehole drill logs. The locations of the cross r sections are indicated in Figure 2. L • Figure 3: Geologic Cross-Section A-A' illustrates the-subsurface from the southwest to northeast sections of the subject .area. The interpretation incorporates sub-classes such as gravelly clay and silty clay, which are consolidated into the general category of clays. There is little correlation in lithologic units between borings. Boring MW-3 (logged by Wm. Hunter& Associates) contains significantly more clay than the other boreholes. • Figure 5: Geologic Cross-Section B-B' illustrates the subsurface from the northwest to southeast sections of the subject area. There is little correlation in lithologic units between borings as in Cross-Section A — A'. Boring MW-2 (logged by Win. Hunter & LAssociates) contains significantly more clay than the other boreholes. Together with the MW-3 data this suggests that contamination would be.less likely to migrate eastward across the site.