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Work Plan for Destruction of Monitoring and Soil Vapor Wells Former Ranch Market, Riverbank CA Page 2 SUBSURFACE CONDITIONS Based upon previous investigations, soil beneath the Site consists of silt and clay from the ground surface to approximately 8 feet to 10 feet below ground surface (bgs), silty clayey sand to poorly graded sand from 8 feet to 10 feet to approximately 17 feet to 20 feet bgs, silt to clay from approximately 17 feet to 20 feet to approximately 30 feet to 35 feet bgs, predominantly sandy soil from approximately 30 feet to 35 feet to approximately 55 feet bgs, silt and clay from approximately 55 feet to approximately 60 feet bgs, and predominantly sandy soil from approximately 60 feet to 70 feet bgs, the maximum depth explored. The depth to groundwater, as measured in December 2019, ranged from 31.53 feet below the top of the well casing (btoc) to 33.02 feet btoc. Groundwater levels beneath the impacted area of the Site have historically ranged from approximately 25 feet btoc to 34 feet bgs between 1998 and 2019. The direction of groundwater flow beneath the Site has varied from eastward to southward. WELL DESTRUCTION WORK PLAN Condor will oversee the destruction of the Site’s ten (10) monitoring wells (MW-1, MW-2, MW-3, MW-4, MW-5, MW-5d, MW-6, MW-7, MW-8, and MW-9), and two (2) soil vapor wells (SV-1 and SV-2) at the request of the Central Valley Water Board, as indicated in a letter dated April 14, 2021 and follow-up email dated June 7, 2021 (Appendix D). The locations of wells proposed to be destroyed are shown in Figure 3, Appendix A. Well destructions will be completed by V&W Drilling (C57-720904), under the direct supervision of Condor, pursuant to state and local guidelines. Copies of available well construction logs are included in Appendix C. Condor and V&W Drilling will destroy the wells pursuant to California Well Standards Bulletins 74-81 and 74-90 published by the California Department of Water Resources, and under permits issued by the San Joaquin County Environmental Health Department (EHD). 4.1 SITE PREPARATION The proposed monitoring well locations will be marked with white paint and Underground Service Alert (USA) will be notified so that utilities can be located and marked at least 48 hours prior to drilling. Condor will receive all permits from EHD prior to initiating any fieldwork. 4.2 FIELDWORK PREPARATION Prior to commencement of fieldwork, a tailgate safety meeting will be held, and the site-specific Health and Safety Plan (Appendix E) will be reviewed and signed by all field personnel and contractors. Well destruction activities will be performed under the supervision of a Condor geologist in accordance with the provisions of the EHD permits. 4.3 DESTRUCTION OF GROUNDWATER MONITORING WELLS A summary of monitoring well construction details are included in Table 1, below. The Site’s 10 monitoring wells will be destroyed emplacing neat cement grout into the well with the aid of explosives. The well boxes will be removed completely prior to placing explosive charges. The 25-grain detonation cord will be placed within each well column from the bottom of the respective well to the bottom of the sanitary seal. Neat cement grout will be placed in one continuous operation, if possible, and once the grout has been allowed to reach the surface, the charges will be set off, allowing the blast to perforate the well casing from the sanitary seal to the total depth. The volume of neat cement grout will be recorded for each well. Any groundwater displaced from the wells will be collected and contained in Department of Transportation (DOT)-approved drums, sealed, labeled, and characterized for disposal.