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Additional Soil Vapor Assessment Work Plan Page 2 CPSA,Lodi,California March 22,2024 The City operated the CPSA groundwater extraction and treatment (GWET) and soil vapor extraction(SVE)systems from 2011 through 2019 in the parking lot behind Guildto treat,remove, and mitigate PCE and related VOCs that were released into the soil and groundwater beneath the CPSA during former historic operations of dry cleaners and a printing press. Operation of the CPSA GWET and SVE systems resulted in a significant reduction in PCE and other VOC concentrations in the subsurface soil, soil vapor, and groundwater beneath the CPSA. Following a closure evaluation of the CPSA GWET and SVE systems, the City recommended decommissioning and removal of the existing CPSA GWET and SVE systems, abandoning/removal of all groundwater extraction, groundwater monitoring, and SVE wells, remediation piping, and excavating soil containing elevated VOCs along the sewer line in the alleyway near the intersection with S. Pleasant Avenue. Additionally, the City also proposed, as part of the post-closure activities, to perform indoor and ambient air monitoring in the residential and commercial properties within the CPSA,and address any increased PCE concentrations during indoor air monitoring activities using targeted remediation. The Water Board approved the City's recommendations for closure in their May 18, 2020 Review of Central Plume Source Area Groundwater Extraction and Soil Vapor Extraction Systems Closure Report concurrence letter to Andrew Richle at the City. CHT, on behalf of the City, then submitted the Central Plume Source Area Groundwater Extraction and Treatment and Soil Vapor Extraction Systems Decommissioning Activities Work Plan, on March 4, 2021 to the Water Board outlining the activities associated with decommissioning of the CPSA GWET and SVE system. The 2021 Work Plan was approved by the Water Board in the March 10, 2021 letter to Andrew Richle with the City. Between April and July 2021, the City decommissioned the CPSA GWET and SVE systems and excavated a portion of the alleyway near Pleasant Avenue, where passive soil gas(PSG) sampling had indicated high concentrations of PCE in soil vapor. As part of the post-closure decommissioning activities, CHT, on behalf of the City, performed indoor and ambient air monitoring at several commercial and residential properties within the CPSA in February and October 2022. The results of the indoor and ambient air monitoring were presented to the Water Board in the August 13, 2022 Semi-Annual Indoor and Ambient Air Investigation Letter Report and the January 9, 2023 Results of the October 22 Semi-Annual Indoor and Ambient Air Investigation Letter Report. The results indicated that PCE concentrations were observed to be above the PCE commercial indoor air Environmental Screening Level (ESL) of 2.0 µg/m3 in one or more samples at the 212 W. Pine St. and 11 S. Church St. properties, and the PCE residential indoor air ESL of 0.46 µg/m3 in the 18 S. Pleasant Ave. residence. 581 MONTEGO TERRACE,SUNNYVALE,CA 94089 TEL:415-424-3009