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Corrective Action Plan Montgomery Ward Auto Service Center, Stockton, CA 20 BACKGROUND 1 2.1 Montgomery Ward Site ' Several assessments have been completed to date to attempt to define the extent of soil and ground water contamination associated with the Montgomery Ward Site Appendix A provides a descriptive summary of each assessment, the results obtained and the conclusions made Figure 2 is a Site Plan which depicts the former location of the USTs and fuel islands EAI also performed a soil vapor extraction pilot study at the Montgomery Ward Site (see EAI, 1997A) ' SummaLy of Soil and Ground Water Investigations Tables 1 through 7 present the results of testing soil samples collected in association with ' the Montgomery Ward Site, and Table 8 presents the results of testing ground water samples Table 9 provides a summary of the well and probe construction details ' 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 Figure 4 ) The first plume is centered around soil borings B-6 and B-11 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 and covers a surface area of approximately 2,700 square feet In cross-section (see Figure 4 for location) the first plume below the former gasoline UST excavation extends from approximately 15 feet below ground surface (bgs) to ' approximately 50 feet bgs (see Figure 5) The plume appears to be fairly uniform in its lateral extent at all depths from the surface to the ground water table at depths of about 40 feet bgs However, the plume shows higher concentrations in soil at deeper depths ' The cross section of the second plume (see Figure 4 for location), extends from approximately 15 feet bgs to approximately 50 feet bgs (see Figure 6) In this plume, the maximum contaminant concentrations in soil are found at shallow depths ' Figure 7 is a ground water gradient map for September 1997 which includes data for both the Montgomery Ward and Former Unocal Sites which shows a southwesterly flow direction Figure S is a ground water gradient map for December 1997 which shows an ' easterly flow direction Figure 9 is a dissolved total petroleum hydrocarbons as gasoline (TPH-G) isoconcentratson map for September 1997 and Figure 10 a dissolved benzene isoconcentration map for September 1997 September 1997 data were used because this is the most recent data available for the Former Unocal Site (see Table 8) Summary of Soil VMor Extraction Pilot Stud ' In 1996, EAI performed a soil vapor extraction pilot test at the Montgomery Ward Site (see EAI, 1997A) As part of this test, EAI installed seven wells (four vapor extraction wells and three combination vapor extraction/air sparging/ground wdLer 1110nlLuring weiis) ' and ten soil vapor probes The construction specifications of these wells and probes are summarized on Table 9 Appendix B contains diagrams for each well and probe ' Project No 1232 - 2 - SAB WORD 1232CAP