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GAVIN NEwsOM <br /> GOVERNOR <br /> �f <br /> C A O N N • \� .1ARED 13LUMENFELD <br /> D ]y ECRETARY EOR <br /> Water Boards IRONMV-1 PROTECTION <br /> Central Valley Regional Water Quality Control Board <br /> 7 April 2020 <br /> Joe Niland <br /> Lincoln Center Environmental Remediation Trust <br /> 3043 Gold Canal Drive, Suite 201 <br /> Rancho Cordova, CA 95670 <br /> CONCURRENCE WITH VAPOR INTRUSION PILOT STUDY WORK PLAN, LINCOLN <br /> VILLAGE SHOPPING CENTER, STOCKTON, SAN JOAQUIN COUNTY <br /> Central Valley Water Board staff has reviewed the April 2020 Vapor Intrusion Pilot <br /> Study Work Plan (work plan) prepared by Geosyntec on behalf of the Lincoln Center <br /> Environmental Remediation Trust for the Lincoln Village Shopping Center in Stockton <br /> (Site). The work plan was submitted as discussed during our 5 August 2019 meeting <br /> with you regarding remaining volatile organic compounds (VOCs) in groundwater in the <br /> on-Site source area which consist of the dry-cleaning solvent tetrachloroethene (PCE) <br /> and its breakdown products. The work plan was requested to assess vapor intrusion <br /> threat for VOCs off-gassing from groundwater due to pending changes in vapor <br /> intrusion guidance and attenuation factors used for initial screening. Data collected <br /> during this assessment can then be used to develop a site-specific model for both <br /> on-Site and off-Site areas where VOCs are present in the A-zone groundwater. <br /> Geosyntec proposes to conduct a pilot study to assess vapor intrusion in accordance <br /> with the draft Supplemental Guidance for Screening and Evaluation of Vapor Intrusion <br /> currently in a public comment period. Geosyntec proposes to assess vapor intrusion for <br /> two on-Site buildings that include a vacant suite at 858 West Benjamin Holt Drive and <br /> an occupied suite at 240 Lincoln Center at the locations shown on Figure 2 of the work <br /> plan. Groundwater samples will be collected from monitoring well PT-11 near the <br /> unoccupied suite and MW-007A near the occupied suite. The most recent <br /> concentration of PCE in groundwater in these wells was 570 micrograms per liter (ug/L) <br /> for PT-11 and 50 ug/L for MW-007A. In order to assess VOC concentrations in soil <br /> vapor, Geosyntec will also install multi-depth soil vapor probes SG-100 and SG-101 <br /> near the two monitoring wells at the locations shown on Figure 2 of the work plan. The <br /> probes will be screened at five feet below ground surface (bgs), and at ten-foot intervals <br /> below that (15, 25, 35 feet bgs until groundwater is encountered). Soil vapor samples <br /> will be collected from each interval. <br /> For each of the two building suites, Geosyntec will install three sub-slab monitoring <br /> points and collect sub-slab vapor samples. Three indoor air samples will also be <br /> KAKI E. LONGLEY ScD, P.E., CHAIR I PATRICK PULUPA, ESO., EXECUTIVE OFFICER <br /> 11020 Sun Center Drive#200. Rancho Cordova, CA 95670 1 www.waterboards.ca.gov/centralvalley <br />