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WORK PLAN FOR DESTRUCTION OF MONITORING AND SOIL VAPOR WELLS Former Ranch Market 23569 S. Santa Fe Road Riverbank, CA 95367 INTRODUCTION This Work Plan for Destruction of Monitoring and Soil Vapor Wells (Work Plan) was prepared by Condor Earth (Condor) at the request of Mr. Munir Obaid to present the proposed scope of work to destroy monitoring and soil vapor wells that were used to monitor the groundwater and soil vapor beneath the former Ranch Market located at 23569 S. Santa Fe Road, Riverbank, San Joaquin County, California (Site). The Site location is shown on Figure 1, Appendix A. A Site map showing Site features and well locations is shown on Figure 2 (Appendix A). The Work Plan is in response to a letter from Mr. Alan Buehler, P.G., of the Central Valley Regional Water Quality Control Board (Central Valley Water Board) dated April 14, 2021 and a follow-up email dated June 7, 2021, both of which are included in Appendix D. This Work Plan proposes to destroy all remaining Site monitoring wells as well as the remaining two soil vapor monitoring wells. A site map showing the locations of wells proposed to be destroyed is included on Figure 3, Appendix A. SITE BACKGROUND In 1991, a gasoline release at the Site impacted the groundwater with elevated concentrations of gasoline hydrocarbon constituents, including benzene and the oxygenated gasoline additive methyl-t-butyl ether (MTBE). The groundwater plume has apparently migrated a short distance off of the Site to the south and impacted two nearby parcels. Over the years, 10 groundwater monitoring wells, 20 ozone sparge wells, 10 vapor extraction wells, and numerous soil borings have been installed and sampled to investigate the extent of soil and groundwater contamination. Past reports suggest the bulk of the contaminant mass in the subsurface has been abated by a combination of ozone sparging, vapor extraction, and natural attenuation. Figure 2 in Appendix A shows key Site features and the locations of Site wells and former Site wells. Groundwater monitoring and sampling was initiated at the site in 1998, but regular sampling ceased in 2008. Semiannual groundwater monitoring and sampling resumed in May 2013. In general, concentrations of dissolved petroleum hydrocarbons beneath the Site have continued to decline since active remediation was discontinued, although contaminant concentration trends in well MW-7 have continued to exhibit minor increasing trends. In a January 7, 2020 letter, the Central Valley Water Board staff concurred with closure of the Former Ranch Market underground storage tank (UST) petroleum release case at the Site and required a 60-day public comment period. During the comment period from April 10 through June 14, 2020, one comment was received from the responsible party (RP) of the Barrera’s Market UST case located south (downgradient) of the Site, requesting that the Central Valley Water Board defer closure of Mr. Obaid’s case until they have a chance to perform their own investigation on the Barrera’s Market property. In a June 30, 2020 letter, Central Valley Water Board staff informed Condor that they agreed to defer closure of the Site until the Barrera’s Market investigation was completed; however, in their letter dated April 14, 2021 letter, the Central Valley Water Board indicated that deferment of closure was no longer reasonable and directed submittal of a work plan to destroy the Site’s remaining wells.