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Mr. Alan Buehler, P.G., RWQCB May 16,2017 Work Plan for Additional Site Investigation Project No. 2092-2057-01 2057 South El Dorado Street, Stockton, CA Page 3 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. At the time that this Work Plan was prepared, GET was being performed intermittently. However, we intend to operate the GET system as continuously as possible through the remainder of 2017 once all maintenance issues are resolved. A service station formerly operated at 2043 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 2043 South El Dorado Street appear to have been completed. 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. Collect soil analytical data required near the former waste oil tank in order to complete an eventual 'low threat closure policy' evaluation. Retain a shallow soil sample to establish background metals concentrations. Evaluate changes in fuel contaminant concentrations over time in deeper water bearing strata at the Site. To accomplish the objectives listed above, Stratus is proposing the following activities: Advance two CPT borings (CPT-3 and CPT-4) to a depth of approximately 120 feet bgs offsite, on a vacant lot immediately east of 043 South El Dorado Street. Collect groundwater samples from sampl g boreholes advanced immediately adjacent to the CPT-3 and CPT-4 boring 1 cations. Sampling depths adjacent to CPT-3 and CPT-4 will be similar to hist rical onsite CPT sampling locations if geological lithologies are laterally similar. (110A co glO t A C\ , ( A '( ("iTh T \R1A TC'Ut S CtectO a5ittht alAv.-51A s,f1. SAk 10Quick N Save #21Work Plans \Q-N-S#2 work plan 2017.doc