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URS May 20,2011RECEIVED Mr. Ross Atkinson MAY 2 4 2011 Engineering Geologist Regional Water Quality Control Board—Central Valley Region NME H 11020 Sun Center Drive, #200 R f l-iWAVICES Rancho Cordova,California 95670-6114 Subject: Evaluation Status Report World Enterprises Site Stockton, California Dear Mr. Atkinson: URS Corporation(URS)has prepared this letter report on behalf of RadioShack in response to your letter dated April 20,2011,to provide the Regional Water Quality Control Board(RWQCB)—Central Valley Region the evaluation status for the World Enterprises site in Stockton,California(Figure 1). This report is organized in the following sections: Background, Field Activities,Results, Groundwater Goals, Conclusions and Recommendations, and References. BACKGROUND The World Enterprises site is located in Stockton, California. This site was operated as a debris disposal site(debris from demolished buildings, including wood,rubble, concrete, and other fill materials)under San Joaquin Local Health District Use Permits to World Enterprises from 1970 to 1978. On July 17, 2003, during an annual site inspection,the San Joaquin County Environmental Health Department(SJCEHD)staff measured methane gas concentrations up to 30,000 parts per million by volume(ppmV) (3 percent by volume) along the property boundary. As a result of this inspection, SJCEHD required Tandy Corporation(site owner, currently known as RadioShack)to assess whether the methane concentration along the property boundary was greater than 5 percent by volume,and if found to be greater than 5 percent by volume,to implement measures for controlling methane from leaving the site. RadioShack contracted with URS to assess the extent of methane at the World Enterprises site. Since 2004,URS has installed 10 gas-migration monitoring probes, 2 vapor extraction wells, and 3 groundwater monitoring wells at the World Enterprises site (Figure 2). As a result of the field investigations, methane concentrations along a portion of the property boundary were found to be above 5 percent by volume. In September 2006, a passive soil vapor extraction (SVE) trench was installed to control methane from leaving the site under SJCEHD oversight. Prior to the installation of the passive SVE trench,the methane concentrations had historically exceeded 5 percent by volume within VW-4, VW-5S, VW-5D, VW-6S, and VW-6D. Since the passive SVE trench installation, methane concentrations had decreased within these probes to less than 5 percent by volume during the sampling quarter following the installation, and have continued to be less than 5 percent during the subsequent quarters. In December 2005, a vapor extraction pilot test was conducted to evaluate the feasibility of installing a permanent landfill gas extraction system. During this test, vapor samples were collected from the two extraction wells and analyzed for volatile organic compounds (VOCs). Analytical results of these URS Corporation Crown Corporate Center 2870 Gateway Oaks Drive,Suite 150 Sacramento,CA 95833 Tel:916.679.2000 Fax:916.679.2900 H:1Wprocess1255321WorldEnterprise\Closure1052011 doc