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' Corrective Action Plan Montgomery Ward Auto Service Center, Stockton, CA ' Monitoring data presently available indicate that the change in ground water flow direction is caused by the pumping of a San Joaquin Delta College irrigation well located westerly of the Montgomery Ward Site and southwesterly of the Former Unocal Site (see Figures 1 and 3) (see Section 2 3) 2.2 Former Unocal Site The property located at 5606 Pacific Avenue was developed as a gasoline station in or about 1955 (see Figure 1) 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 , benzene, toluene, ethylbenzene and xylenes (BTEX) 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 Fortner Unocal Site had been adequately addressed and that Unocal should now focus its efforts on ground water contamination (see Kaprealian, 1991) A bank is currently located on the Former Unocal Site To the best of EAI's knowledge, as of the date of this CAP, no ground water remediation activities have been initiated at the Former Unocal Site nor has the County directed Unocal to complete ground water remediation Montgomery Ward and Unocal have been coordinating ground water monitoring activities to occur on the same date for the past several years The Former Unocal Site is currently only completing ground water monitoring activities once per year The most recent monitoring data available for the Former Unocal Site (September 1997) shows that the most downgradient on-site Unocal well (MW-11) had a TPH-G concentration of 50,000 parts per billion (ppb), a benzene concentration of 15,000 ppb and an MTBE concentration of 2,400 ppb (see Table 8) 1 The benzene concentration in Unocal well MW-11 was 150 ppb in June 1992 and 15,000 ppb in September 1997 (see Table 8) Between June. 1992 and September 1997, Unocal well MW-11 has been sampled 19 times The average benzene concentration in well MW- 11 between this time period is approximately 11,534 ppb These data indicate that the soil remediation measures implemented at the Former Unocal Site did not completely address impacted soil, and that a residual source of soil contamination remains beneath the Former Unocal Site which has and will continue to impact ground water 2.3 San Joaquin Delta College Irrigation Well eSan Joaquin Delta College owns an irrigation .yell located southwest of the intersection of Robinhood Drive and Pacific Avenue (see Figures 1 and 3) This well is located approximately 135 feet west of the western boundary of the Montgomery Ward Site This ' well was installed in or about 1950 This well is reported to be 322 feet deep with perforations in multiple zones as follows 4 -SABProject No 1232 - 4 - SAB WORD 1232CAP