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Page 2 June 27,2023 Brusca File No. 260-004 Workplan for Additional Plume Definition PLANNED INVESTIGATIVE ACTIVITIES General The planned additional investigative work at the subject property is intended to satisfy the requirements of the referenced June 22, 2023 CVRWQCB letter and to develop additional information to compare site conditions to Low-Threat Closure Policy (LTCP) criteria. The planned work will include additional drilling and sampling at step-out locations to the north, west, and south of the former UST to evaluate the lateral extent of petroleum hydrocarbon impacts to soil and groundwater and to further define the extent of the contamination plume. Additionally, a soil gas sample will be collected for analysis from location SG3 where sampling was unsuccessfully attempted in May 2023 (the sampling equipment for that location provided by the laboratory was faulty). All work will be overseen by a Professional Geologist from our office and sampling will be conducted in accord with standard environmental protocol. The analytical testing will be performed by a State-certified laboratory. Permitting and Utility Clearance Prior to the planned additional borings at the site, the necessary drilling permit will be obtained from the San Joaquin County Environmental Health Department(SJCEHD). Prior to drilling, the boring locations will be marked, and Underground Service Alert will be contacted to clear the locations of underground utilities. In addition, a private utility contractor will be retained to further clear the drilling locations. Additional Drilling and Sampling/Testing To further evaluate the extent of subsurface petroleum hydrocarbon impacts and the limits of the groundwater contamination plume, we have selected three locations to the north, west, and south of the former UST for additional borings for soil and groundwater sampling; the planned boring locations are shown on Plate 3. The borings will be performed with a truck-mounted drill rig using hollow stem augers by a C57-licensed drilling contractor. Each boring will extend to groundwater (expected to occur at a depth on the order of 70 feet). The conditions encountered in the exploratory borings will be observed and documented by a Professional Geologist from our office. Photoionization detector (PID) screening of soils will be performed generally at ten- foot depth intervals. Soil samples from ten-foot depth intervals in each boring will be selected for laboratory analysis; the soil samples will be retrieved in stainless steel sleeves and sealed with Teflon tape and plastic end caps. A temporary PVC well will be installed within each borehole for groundwater sampling. Prior to groundwater sampling, an interface probe will be used to check for free product. Thereafter, a grab groundwater sample will be collected from each borehole via dedicated/disposal bailer; the collected groundwater samples will be quickly transferred to appropriate sample containers(VOAs) obtained from the analytical laboratory. Soil cuttings and decontamination water generated during the planned drilling will be containerized in 55-gallon steel drums and stored onsite pending proper offsite disposal. Following the sampling activities, all borings will be backfilled with neat-cement grout. The soil and groundwater samples collected from the borings will be placed on ice and transported under chain-of-custody documentation a State-certified laboratory for analysis. The soil and