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' Corrective Action Plan Montgomery Ward Auto Service Center, Stockton, CA 3.0 CHEMICALS OF POTENTIAL CONCERN Gasoline and its related constituents, e g , BTEX and methyl tertiary butyl ether (MTBE) have been detected in ground water beneath the Montgomery Ward Site The chemical of concern is gasoline and its related constituents 3.1 Extent of Contamination Soil Figure 3 shows a summary of the contaminant concentrations detected in soil samples collected from the Montgomery Ward Site These data suggest there are two separate soil plumes at the Montgomery Ward Site (see Figures 4, 5 and 6) The first plume is centered around soil borings B-6 and B-11 (the former USTs location) This plume extends in a northeast to southwest direction covering a surface area of approximately 5,650 square feet The second plume is centered around monitoring well MW-2 (former location of fuel islands) and covers a surface area of approximately 2,700 square feet Ground Water Figures 9 and 10 are TPH-G and benzene isoconcentration maps, respectively, for September 1997, covering the Former Unocal and Montgomery Ward Sites September 1997 data were used because this is the most recent data available for the Former Unocal Site These data show that ® Unocal well MW-10 defines the northern edge of the plume, ® Unocal well MW--16 and Montgomery Ward well MW-6 define the eastern edge of the plume, ■ Montgomery Ward well MW-5 defines the southern edge of the plume, ■ Unocal well MW-17 defines the western edge of the plume south of the Former Unocal Site Note, all Unocal and Montgomery Ward ground water wells are terminated at depths of 70 feet bgs or less The Delta College well in which r petroleum hydrocarbons are present, is located west of Unocal well MW-17, and is known to have perforations at multiple depths ranging from 40 feet bgs to 322 feet bgs The apparent disparity between the analytical data associated with ground water samples collected from Unocal well MW-17 (no petroleum hydrocarbons detected) and the Delta College well (petroleum hydrocarbons present) probably is due to the fact that pumping of the Delta College well has caused vertical migration of the contaminants, and Unocal well MW-17 is not deep enough to encounter the contamination_ The extent of the plume west of Montgomery Ward well MW-4 has not been defined 'n �a +#,v l+o f +nql, t" u,ii camplee at the MnntgntnerV Wnrd S to ("PP Tah1Pg 1 BasoLI Vll Lill. LI�JLLILJ Vl through 7) and ground water data for both the Montgomery Ward and Former Unocal sites (see Table S), it is clear that the ground water contamination located north of the fuel islands on the Montgomery Ward Site and on the Former Unocal Site is sourced by the Project No 1232 - 7 - SAB WORD 1232CAP