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PHASE V11 SUBSURFACE INVESTIGATION San Joaquin County Montgomery Ward Auto Service Center Public Health Services Department 5400 Pacific Avenue, Stockton,CA Site Code 2163 Further assessment north of the Montgomery Ward site is not warranted based on the fact that ' Unocal recently installed well MW-16 in the sidewalk immediately north of the Montgomery Ward site The benzene concentration in a water sample collected from well MW-16 in December 1995 was 150 ppb (see Figure 3) ' Hydropunch locations HP-1 and HP-2 were installed east of Montgomery Ward wells MW-5 and MW-6 (see Figure 2) In EAI's opinion, the benzene concentrations detected in hydropunch HP-1 (36 2 ppb) and hydropunch HP-2 (3 ppb) are sufficient to define the easterly ' edge of the dissolved ground water plume Hydropunches HP-3 and HP-4 and well MW-7 were installed south of well MW-5 (see Figure 2) No hydrocarbons were detected in the water samples collected from hydropunches HP-3 and HP-4 nor in the water sample collected from well MW-7 (see Table 7) Based on these testing results, the extent of hydrocarbons In ground water in a southerly direction did not extend to hydropunch HP-4 Therefore, the southerly edge of the dissolved phase ground ' water plume is between well MW-5 and hydropunch HP-4 Well MW-7 is the most southerly boundary well Further assessment west of existing Montgomery Ward well MW-4 was proposed as part of ' the Phase VII activities However, due to subterranean obstructions this work could not be completed Only a low level of benzene (1 3 ppb) was detected in Unocal well MW-17, which 1s located westerly of Montgomery Ward well MW-2 (see Figure 3) 6.2 SOIL It is EAI's opinion that the extent of unsaturated zone soil contamination has been adequately defined at the Montgomery Ward site Figures 5 and 6 are cross-sections which depict the extent of soil contamination, and Figure 4 is a site plan showing the cross-section locations If necessary, a Corrective Action Plan evaluating potential soil remedial options can be prepared for the Montgomery Ward site f i - i tProject No 1232 - 8 - ENVIRONMENTAL AUDIT, INC