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Discrete Depth Soil&Soil Vapor Assessment Work Plan Page 4 CPSA,Lodi,California March 12,2025 18 SOUTH PLEASANT AVENUE RESIDENCE CHT, on behalf of the City, proposes to perform the following activities to further delineate the vertical extent of the residual PCE plume in soil and soil vapor in the vicinity of the 18 S.Pleasant Ave. residence— • Perform discrete depth soil and soil vapor sampling at two locations outside the 18 S. Pleasant Ave. residence where the highest SS PCE concentrations were observed during PSG sampling — SP-1 located northwest of the residence near PSG-1 and SP-2 located northeast of the residence near PSG-2, and, • Collect one (1) indoor air sample in the residence and one (1) ambient air sample from outside the building wall near the alleyway. DISCRETE DEPTH SOIL & SOIL VAPOR SAMPLING CHT will perform discrete depth soil and soil vapor sampling at locations SP-1 and SP-2 (see Figure 3) to delineate the vertical extent of the PCE and TCE in soil vapor along the sewer lateral emanating from the building. Methodology CHT proposes to install soil borings at SP-1 and SP-2 to a depth of 40 to 45 feet below ground surface (ft-bgs) using a dual-purpose limited access rig that can perform continuous soil coring. The soil cores, which will be collected in acetate liners, will be used to log the soil, determine the targeted depth for collection of soil samples, and the screen intervals for the temporary soil vapor (TSV) probe depths. TSV probes will then be installed near SP-1 and SP-2 and in accordance with the 2012 DTSC's Advisory-Active Soil Gas Investigations (Advisory). At each boring location, the drill rig will advance the rods to a total depth of 40 to 45 ft-bgs where the 40 or 45-foot TSV probe will be installed and then drill separate borings for installing the TSV probes at depths of 5, 10, 15, and 25 ft-bgs. The exact depth of the soil samples and TSV probes will be determined from the soil cores. 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. To ensure that representative soil vapor samples are collected for each specified depth, 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. 581 MONTEGO TERRACE,SUNNYVALE,CA 94089 TEL:415-424-3009