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' PHASE VI SUBSURFACE INVESTIGATION Site Code 2163 Montgomery Ward Auto Service Center 5400 Pacific Avenue, Stockton, CA and 1,1,1-trichloroethane (1,1,1-TCA) (see Table 5) The source of these chlorinated ' hydrocarbons is unknown (see EAI, 1993) TPH-G, BTEX and 1,2-dichloroethane (1,2-DCA) were detected in the ground water samples ' collected from Wells MW-1 and MW-2 (see Table 6) Table 6 also contains the results of quarterly sampling completed at the Montgomery Ward site through February 1995 (see EAI, 199513) 2.2 FORMER UNOCAL SITE The property located at 5606 Pacific Avenue was developed as a gasoline station in or about ' 1955 In or about 1985, the station was closed and the USTs (gasoline and waste oil) were removed Several subsurface investigations of the Former Unocal site were conducted which revealed the presence of elevated concentrations of gasoline related constituents, e g , TPH, ' BTEX and 1,2-DCA, in soil and ground water (see Kleinfelder, 1987) Soil remediation efforts at the Former Unocal site reportedly principally consisted of the ' excavation and off-site disposal of unsaturated zone impacted soils In or about February 1991, a meeting was held between representatives of Unocal and the County wherein the County reportedly agreed that soil contamination at the Former Unocal site had been adequately addressed and that Unocal should now focus its efforts on ground water contamination (see Kaprealian, 1991) To the best of EAFs knowledge, as of the date of this report, no ground water remedia-Lion—act-tvAiesirave-been-lintiated at the Fo,1111erl, Figure 2 shows the location of wells (MW-10 through MW-15) currently associated with the Former Unocal site Table 7 lists the analytical testing results available to EAI for ground water samples collected from wells MW-10 through MW-15 between June 1992 and December 1994 ' (see MPDS, 1995) The direction of ground water flow at the Former Unocal site and Montgomery Ward site, based on information presently available, varies between southerly and easterly (see MPDS, 1995 and ' EAI, 1995B) This indicates that the Montgomery Ward site is down-gradient of the Former Unocal site (see Figure 2) Analytical data for ground water samples collected from the most down-gradient well (well MW-1 1) located on the Former Unocal site clearly show that the ' extent of ground water contamination in the down-gradient direction has not b ned (see Figure 3 and Table 7) Analytical data forte last three quarters show that the benzene concentration in ground water samples collected from well MW-11 has ranged from 14 to 17 ppm Additional investigation activities are needed to define the extent of ground water ' contamination associated with the Former Unocal site Further, these data suggest that it is highly probable that the Montgorriery Ward site has been in12acted y the_ c.ontarnw,a Q1L associated with the Former Unocal site 3.0 FIELD WORK 3 1 DRILLING AND SOIL SAMPLING Between January 23 and 24, 1995, four borings (MW-3 through MW-6) were drilled and sampled on the site as approximately shown on Figure 2 The borings were drilled by V & W Drilling Inc of Rio Vista, California (State License C57# 658786), under supervision of EAI 1 ' Project No 1232 4 ENVIRONMENTAL AUDIT, INC