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IP-RZ, GAVIN NEWSOM GOVERNOR C0.LI i0 R LI I• NFELD SECRETARRY FOR Water Boards ENVIRONMENTAL PROTECTION Central Valley Regional Water Quality Control Board 10 March 2021 Andrew Richle Water Plant Superintendent City of Lodi 2001 W. Turner Road Lodi, CA 95242 CONCURRENCE WITH CPSA GWET AND SVE SYSTEMS DECOMMISSIONING ACTIVITIES WORK PLAN, CITY OF LODI CENTRAL PLUME SOURCE AREA, LODI, SAN JOAQUIN COUNTY Central Valley Water Board staff has reviewed the 4 March 2021 CSPA GWET and SVE Systems Decommissioning Activities Work Plan (work plan) prepared by Civil Hydro Tech (CHT) on behalf of the City of Lodi (City) for the Lodi Central Plume Source Area (CSPA) in Lodi. The work plan provides a plan for performing the closure activities associated with the decommissioning of the CPSA Groundwater Extraction and Treatment (GWET) and Soil Vapor Extraction (SVE) systems. The work plan was submitted in accordance with the 18 May 2020 letter from Central Valley Water Board staff that generally concurred with the recommendations in the 12 May 2020 Central Plume Source Area Groundwater Extraction and Soil Vapor Extraction Systems Closure Report. That letter also summarized the rationale for the decommissioning of the remediation system that operated from 2011 to 2019. In the work plan, CHT proposes to remove all remediation equipment and to abandon all GWET and SVE wells in accordance with the methods provided in the work plan. A limited soil excavation will also be conducted to remove residual tetrachloroethene (PCE) soil contamination along the sewer line in an alleyway where the PCE leakage occurred. The residual PCE in this area has been delineated by several soil vapor samples that show PCE in soil vapor up to 153,000 micrograms per cubic meter. The locations of the GWET wells, SVE wells, equipment (TS-1), piping, and the proposed soil excavation are shown on Figures 2 and 3 of the work plan. The soil excavation will be approximately 100 feet by 6 feet to a depth of 5 feet with a volume of approximately 115 cubic yards. Following excavation, sidewall samples will be collected from the perimeter of the excavation at lineal intervals of approximately 20 feet and bottom samples every 500 square feet of excavation bottom. Excavated soil will be stockpiled, sampled, and covered. Based on the results of soil profiling, the soil will be transported to an appropriate landfill for disposal. Following completion of KARL E. LONGLEY SCD, P.E., CHAIR I PATRICK PULUPA, ESQ., EXECUTIVE OFFICER 11020 Sun Center Drive#200, Rancho Cordova, CA 95670 1 www.waterboards.ca.gov/centralvallay