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Mr. Alan Buehler, P.G., RWQCB May 18, 2018 Work Plan for Additional Site Investigation Project No. 2092-2057-01 2057 South El Dorado Street, Stockton, CA Page 3 recent years have likely resulted in decreased ability to remove fuel contaminants in the vapor phase by SVE. A groundwater extraction and treatment (GET) system has been installed at the Site, replacing the SVE remedial approach. The GET system has operated on a limited basis, however, due to high influent groundwater contaminant concentrations that resulted in TBA breakthrough into the effluent groundwater. Initially, groundwater treatment was completed solely through use of granular activated carbon (GAC) vessels. In late 2016, the system was retrofitted to use 35% concentrated hydrogen peroxide to pre-treat the wastewater, prior to GAC treatment. Use of the equipment was subsequently discontinued due to persistent issues with TBA breakthrough. A service station formerly operated at 2070 South El Dorado Street, immediately east of this Site. Fuel storage USTs, which should have been removed by 1999, still remain in the ground at this property (see Figure 3 for approximate location). No assessment for potential fuel contaminants at 2070 South El Dorado Street appear to have been completed. The RWQCB requested historical records regarding USTs at this property in the March 2018 letter, and Stratus is currently working to obtain these records from the San Joaquin County Environmental Health Department (SJCEHD). These records will be provided to the RWQCB at a later date, once they are received. WORK PLAN FOR ADDITIONAL SITE INVESTIGATION Scope of Work The objectives of the proposed scope of work are to: Further investigate the lateral and vertical extent of fuel contaminant impact to groundwater east of the Site. Additionally evaluate subsurface lithologic/geologic conditions. Assess the shallow soil adjacent to the in-place UST at 2070 South El Dorado Street for possible petroleum hydrocarbon impact. To accomplish the objectives listed above, Stratus is proposing the following activities: Advance four CPT borings (CPT-5 through CPT-8) to a depth of approximately 120 feet bgs offsite. Collect groundwater samples from sampling boreholes advanced immediately adjacent to the CPT-5 through CPT-8 boring locations. Groundwater sampling depths adjacent to CPT-5 through CPT-8 are expected to be similar to sampling depths at CPT-1 through CPT-4. KAQuick N Save #2 \Work Plans \Q-N-S#2-WP-2018.doc STRATUS