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R I 1 I WORK PLAN FOR DESTRUCTION OF SOIL VAPOR EXTRACTION AND SPARGE WELLS Former Ranch Market 23569 S. Santa Fe Road Riverbank,CA 95367 1.0 INTRODUCTION This Work Plan for Destruction of Soil vapor Extraction and Sparge 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 soil vapor extraction and sparge wells that were used to remediate soil and groundwater 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 in Appendix A. In a letter dated May 15, 2018, Mr. Alan Buehler, P.G., of the Central Valley Regional Water Quality Control Board(Central Valley Water Board)requested the submittal of a work plan which includes: • A proposal to destroy remaining Site remedial wells; • A proposal to assess soil and groundwater in the vicinity of the suspected downgradient former underground storage tanks(UST); • A proposal to assess groundwater downgradient of MW-7; • Well construction details and historical groundwater data for DW-I R,DW-2R, DW-3,and DW-4. This Work Plan does not include a proposed scope of work to assess soil and groundwater in the vicinity of the suspected downgradient USTs or to assess groundwater downgradient of MW-7. The Work Plan does,however, include documented evidence of the suspected downgradient USTs. Condor and Mr. Obaid maintain that ample evidence confirms the past existence of the downgradient USTs and investigation of such is not the responsibility of Mr. Obaid. 2.0 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. 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. 3.0 SUBSURFACE CONDITIONS Based upon previous investigations, soil beneath the Site consists of silt and clay from the ground surface to approximately 8/10 feet bgs, silty/clayey sand to poorly graded sand from 8/10 feet to approximately 17/20 feet bgs, silt to clay from approximately 17/20 feet to approximately 30/35 feet bgs, predominantly ,,4 t00% CONDOR