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%1 GAVIN NEWSOM GOVERNOR JARED BLUMENFELD SECRETARY FOR Water Boards ENVIRONMENTAL PROTECTION Central Valley Regional Water Quality Control Board 21 December 2020 RECEIVED Joe Niland JAN 0 5 2021 Lincoln Center Environmental Remediation Trust 3043 Gold Canal Drive, Suite 201 ENVIRONMENTAL HEALTH Rancho Cordova, CA 95670 PFR,%IIT/SE RVICES CONCURRENCE WITH SOIL VAPOR INESTIGATION WORK PLAN, LINCOLN VILLAGE SHOPPING CENTER, STOCKTON, SAN JOAQUIN COUNTY Central Valley Water Board staff has reviewed the December 2020 Soil Vapor Investigation Work Plan (work plan) prepared by Geosyntec on behalf of the Lincoln Center Environmental Remediation Trust for the Lincoln Village Shopping Center in Stockton (Site). The work plan was submitted due to relatively high concentrations of tetrachloroethene (PCE) being detected in shallow soil vapor in an area that had been previously remediated using soil vapor extraction. The vapors were found during the vapor intrusion pilot study that was approved earlier this year. The additional sampling proposed in the work plan is needed to delineate the extent of the PCE in soil vapors near that location which is in the parking lot of the Lincoln Village Shopping Center, but not near any occupied structures. During the vapor intrusion pilot study work, PCE was detected in boring SG-100 at a concentration of 22,000 micrograms per cubic meter (ug/m3) at a depth of 6.5 feet below ground surface (bgs). Concentrations were significantly lower in the deeper intervals sampled in the boring at 620 ug/m3 and 710 ug/m3 at 13 feet and 25 feet bgs, respectively. To investigate this, Geosyntec proposes to install approximately six temporary multi-depth soil vapor probes (TSG-001 through TSG-006) around the SG-100 location at the locations shown on Figure 2 of the work plan. The temporary soil vapor probes will initially be installed at approximately 6.5 and 13 feet bgs, pending subsurface conditions, consistent with the depths of SG-100 where elevated concentrations of PCE were reported. If elevated impacts are observed in the 15-foot soil vapor probe, a third depth (approximately 25 feet bgs) may be sampled. Following the construction of the initial temporary soil vapor probes, a HAPSITEO portable gas chromatograph will be used to screen soil vapor samples and obtain real- time quantitative data with a reporting limit of 1.4 pg/m3 for PCE. The results from the HAPSITEO will be used to select step-out locations for additional temporary soil vapor probes as necessary, to evaluate the extent of elevated PCE concentrations in shallow soil vapor in the vicinity of SG-100 and along the sanitary sewer lateral. Results from KAHL E. LONGLEY ScD, P.E., CHAIR I PATRICK PULUPA, ESO., EXECUTIVE OFFICER 11020 Sun Center Drive#200, Rancho Cordova,CA 95670 1 www.waterboards.ca.gov/centialvallev