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Additional Soil Vapor Assessment Work Plan Page 4 CPSA,Lodi,California March 22,2024 The PSG samples indicated the presence of residual PCE in SV at concentrations of 14,500 µg/m3 (northwest sample)and 67,900 µg/m3(northeast sample),which exceeded the PCE residential ESL of 150 µg/m3. TCE concentrations in SV were also detected at 147 and 155 µg/m3. Based on the results of the 2023 soil vapor assessment activities, the City proposed performing additional sub-slab and depth discrete soil vapor assessment to define the extent of the residual PCE plume beneath and outside of the 212 and 210 W. Pine St.buildings. This Work Plan outlines the proposed scope of work for performing the additional assessment activities. SCOPE OF WORK Based on the results of the 2023 SVA activities and the comments from the Water Board in their February 9, 2024 Review of Soil Vapor Assessment Report, City of Lodi Central Plume Source Area letter, the City proposes to perform the following additional assessment activities— • Discrete depth SV sampling to determine the extent of residual PCE in soil and soil vapor behind the 212 West Pine Street building and the intersection of the sewer lateral emanating from the building and the main sewer lateral; • Sub-slab SV sampling with paired passive indoor air sampling at 212 West Pine Street and at Guild Cleaners Inc (Guild), located at 17 South Church Street; and, • Sub-slab soil vapor sampling at 210 West Pine Street. The Water Board had also requested the City to perform the following additional activities as part of our proposed Work Plan in their letter— • Additional delineation to define the extent of residual PCE in soil vapor near the 18 S. Pleasant Ave. residence; and, • An evaluation of remedial alternatives at, and adjacent to the building at 212 W Pine St. • An additional round of sub-slab sampling from the existing sub-slab vapor probes installed beneath the 212 West Pine Street building The City proposes to do the first two activities as part of our feasibility evaluation of alternatives study following completion of the ASVA activities suggested in this Work Plan. The City proposes to do an additional round of SS sampling in August/September 2024 after completion of interim remedial measures at the 212 W. Pine St. building. Additionally, the August IA data will provide us a seasonal data point that is different from the one collected in March 2023. In addition, the Water Board in their March 19 2024 Meeting for Vapor Mitigation Discussion of Sentinel Building, which summarized the March 7 2024 meeting discussion between the City, Water Board staff, CHT, and the owners of the Sentinel Building at 212 West Pine Street, Lodi (Sentinel Building), requested that the City should include active indoor air sampling procedures during building occupancy hours instead of passive indoor air sampling so as to mitigate the effects of the HVAC system non-operation during non-business hours. 581 MONTEGO TERRACE,SUNNYVALE,CA 94089 TEL:415-424-3009