SITE INFORMATION AND CORRESPONDENCE

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1117 Lone Palm Avenue,Suite 201 � ATC �.•// Modesto,California 95351 209-579-2221 Fax:209-579-2225 Shaping the Future �1 groundwater remedial option selected and the likelihood of a significant permit process involving multiple regulatory agencies. V ATC submitted the Feasibility Study Addendum, dated January 9, 2009, in which ozone infusion was recommended as a remedial alternative the site. The San Joaquin County Environmental Health Department (SJCEHD) agreed with the recommendation and requested that groundwater samples from the site be analyzed for metals and the results evaluated and compared with nearby contaminated UST sites that were using,or conducting bench scale tests for ozone infusion. In correspondence dated April 20, 2009, the SJCEHD approved switching all site monitoring wells to a semi-annual monitoring schedule except for monitoring well MW-11, to which an annual schedule was prescribed. This monitoring schedule was prescribed until such time as more frequent sampling may be needed for monitoring remedial progress. This semiannual sampling regime is consistent with the State Water Resources Control Board (SWRCB) Directive 2009-0042 that required semiannual monitoring replace quarterly monitoring at petroleum UST sites under its jurisdiction in California except if otherwise justified. ATC submitted the Site Geology Comparison,dated September 24,2009,that summarized data from four contaminated UST sites located within one mile of the subject property that had either conducted ozone infusion bench scale testing, were in the process. of conducting ozone infusion for remediation, or had completed preliminary analysis of soil and groundwater for metals evaluation. This report also contained published industry research on behavior and reactions of metals in the subsurface and compared this information with similar information from the Eggiman site. ATC recommended an insitu pilot test, conducted with monitoring and contingency plans in place,to provide site-specific data for evaluation of the applicability of using ozone infusion to remediate the petroleum hydrocarbon contamination at the site. In correspondence dated October 29, 2009, the SJCEHD agreed with the recommendation in the Site Geology Comparison and directed the submittal of a work plan for conducting an in-situ ozone infusion pilot test. Between May 24 and May 26, 2010, seven injection wells (OSIS, OSId, OS2s, OS2d, OS3, OS4, and OS5) were installed in five borings on site (Figure 2A). On July 27 and 28, 2010 narrow trenches were excavated to a depth of approximately six inches and '/2"stainless steel piping was installed to connect the injection wells to the compound location on the south face of the garage building on site. Details of these activities are summarized in ATC's Remediation Well Installation Report,dated October 25,2010. On March 24,2011, a cabinet-mounted ozone generator was delivered to the site and installed adjacent to the on-site building. Ozone injection into OWls, OWld, OW2s, OW2d, and OW3 was initiated on April 1, 2011. Connections to OW4 and OW5 were completed on April 4, 2011 and the injection cycle was expanded to cover all seven points. Reduced petroleum hydrocarbon concentrations were reported in the groundwater samples collected from the injection wells and most of the monitoring wells at the end of the pilot test on June 14, 2011, while increased petroleum hydrocarbon concentrations were reported in the ~ groundwater samples collected from MW1. The reduced petroleum hydrocarbon concentrations associated with the groundwater sample collected from the injection wells at the end of the pilot test suggest ozone injection was effective in reducing petroleum hydrocarbon concentrations at these S:Enviromental\224931Reports\Eggiman Closure Report.doc 3 v F. V