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Soil Vapor Assessment Work Plan Page 5 CPSA,Lodi,California January 11,2023 METHODOLOGY Prior to installation of the TSV probes, CHT proposes to install soil borings at SV 1 and SV2 to a depth of 40 feet below ground surface(ft-bgs)using continuous soil coring. The soil cores,which will be collected in acetate liners, will be used to log the soil, and determine the screen intervals for all of the targeted temporary soil vapor probe depths. TSV probes will then be installed near SVI and SV2 in accordance with the DTSC's Advisory- Active Soil Gas Investigations (DTSC, 2012). The TSV probes will be installed using a dual-purpose limited access rig. At each soil vapor sampling location,the drill rig will advance the rods to a total depth of 40 ft-bgs in one boring where the 40 foot TSV probe will be installed, and then drill separate borings for installing the TSV probes at depths of 5, 10, 20, and 30 ft-bgs. The exact depth of the TSV probes will be determined from the soil core samples. Each TSV probe will be constructed with a 1-foot long filter pack in the bottom of the borehole consisting of#2/12 Cemex sack sand. A 0.250-inch outside diameter(0.187-inch inside diameter) polyethylene tube with a HDPE filter at the bottom of the tube will be placed in the center of the borehole during placement of the sand so that the HDPE filter is located in the center of the sand interval. The annular space above the sand will be temporarily sealed using hydrated bentonite slurry that will be pumped down the hole using tremie pipes to a height of 0.5 feet above the top of the sand. This would ensure that representative soil vapor samples are collected for each specified depth. SAMPLING The soil vapor samples will be collected in accordance with the sampling protocols established in the Advisory (DTSC, 2012). Soil vapor samples will be collected in individual certified 1-liter SUMMA® canister where the SUMMA® canister will supply the vacuum to draw soil vapor into the canister for analysis. The TSV probes will be purged and sampled in accordance with Section 4 (Soil Gas Sample Collection) and leak detection will be performed in accordance with Section 4.2.2.1 (Leak Check Compounds [Liquid]) of the Advisory. CHT proposes to use helium as the leak detection compound. Following soil vapor sample collection, a PID will be connected to the polyethylene soil vapor probe tubing to obtain a preliminary field value for the sample collection location. Measurements of vacuums, purging and equilibration time intervals, and PID readings will be recorded on Soil Vapor Sampling Data Sheets. The SUMMA® canister soil vapor samples will be delivered under chain-of-custody protocols to a California-certified laboratory for testing by EPA method TO-15 analysis for chlorinated VOCs. Additionally, the leak detection compound (helium) will be analyzed using Modified ASTM Method D-1946. Upon completion of sampling activities, the TSV probes will be abandoned by removing temporary well points and sealing the borehole with a neat cement grout or by using the appropriate method approved by SJDEH. 649 DISTEL DRIVE,LOS ALTOS,CA 94022 TEL:415-424-3009