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SEcorz --- _ - --- - _ -- 7-Eleven Store #14117 Corrective Action Plan October 12, 2007 Page 3 Groundwater. A report, Results of Oxygen Injection Feasibility Pilot Study, summarizing the results of the test was submitted to the CRWQCB on May 9, 2006. CONTAMINANT DISTRIBUTION IN GROUNDWATER Initial remedial action was requested by the SJCEHD in January 2004 based on increasing levels of tert-butyl alcohol (TBA) in wells located at the 7-Eleven site and immediately east on the adjacent property. However, since January 2004, TBA concentrations at the site have decreased significantly. Referring to the TBA isoconcentration maps for the first quarter 2004 through the first quarter 2007 (Figures 3 through 6), TBA concentrations have declined in concentration and lateral extent on the 7-Eleven site. As summarized in the Additional Site Assessment and Site Conceptual Model submitted to the SJCEHD in September 2005, the lateral limits of shallow contamination in soil and groundwater have been defined to the north, west and southwest of the site. Additional groundwater analytical data collected by the City of Stockton in September 2003 along the southern side of Country Club Boulevard provide lateral definition of BTEX, TAME, MtBE and TBA to the southeast of the 7-Eleven site (Groundwater Investigation Report, Condor Earth Technologies, Inc., October 2003). Based on the assessments noted above and upon review of historical groundwater data for the 7-Eleven and adjacent USA Gasoline sites (Table 3 and Attachment B), the lateral extents of the petroleum hydrocarbon plume dissolved in groundwater are defined. Additionally, the elevated concentrations of TBA, which prompted the initial request for remedial action, are no longer the primary constituent of concern. Current constituents of concern at the 7-Eleven site include TPHg and BTEX in wells MW-2, MW-3 and MW-4 (Table 3). Therefore, this CAP has been generated to address TPHg and BTEX concentrations dissolved in groundwater in the vicinity of wells MW-2, MW-3 and MW-4. GEOLOGY Based on the description of the soil samples collected from historical soil boring data and presented in the Additional Site Assessment and Site Conceptual Model submitted to the SJCEHD in September 2005, the lithology underlying the site consists primarily of clay and silt from grade to approximately 15 feet below ground surface (bgs). From 15 feet bgs to total depth (110 feet bgs) of investigation, the lithology consists primarily of alternating layers of fine-grained sand, silt and clayey silt. A well defined and continuous sand unit is located throughout the site at approximately 20-25 feet bgs. Historical depth to water has generally ranged from 7 to 9 feet bgs. Copies of the cross sections submitted with the Additional Site Assessment and Site Conceptual Model submitted to the SJCEHD in September 2005 are included in Attachment C. 14117 CAP 10-12-07.doc SECOR International, Inc.