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Site Investigation Work Plan Deuel Vocational Institution(DVI), Tracy, California Introduction 23 feet below ground surface(bgs),to promote enhanced reductive dechlorination of chlorinated solvents in site groundwater. After the EOS injections were completed,the injection points were abandoned using bentonite slurry. Details of the EOS pilot test are presented in the Baseline Sampling Results, Pilot Test Activities, and Second Quarter 2011 Groundwater Monitoring Report(URS 2011). In February 2015, a soil vapor survey indicated the presence of a localized volatile organic compound (VOC)plume in the vicinity of MW-15 (URS 2015). In November 2015,URS installed MW-26-BP to evaluate groundwater conditions near the areas with the highest soil vapor VOC concentrations. Initial sampling results indicated that the highest VOC concentrations in MW-26-BP were cis-1,2-dichloroethene (cis-1,2-DCE) (1,000 micrograms per liter[gg/L]),PCE (280 gg/L), and TCE (59 gg/L). Details of the well installation,the initial sampling results, and the proposed remedial action were presented in the MW-26-BP Well Installation Report and Work Plan for Additional In Situ Remediation, Deuel Vocational Institution Burn Pit(In Situ Remediation Work Plan) (URS 2016a). On April 22,2015,the CVWB issued draft Monitoring and Reporting Plan Order No. R5-2015-0808 (MRP),which reduced the number of MWs for sampling and the frequency of sampling from quarterly to semi-annually. The draft MRP, implemented for the first time in the second quarter of 2015 (2Q15), also removed the requirement for an analysis of dissolved metals. In addition,the MRP added sampling of MW-1-MB through MW-5-MB,which originally were installed to monitor groundwater quality in the maintenance area south of the burn pit. These wells were sampled previously from 2003 through 2010, with analyte concentrations below maximum contaminant levels (MCLS) for several years before the submittal of a request for site closure in 2010.All five wells were sampled in 4Q15. MW-3-MB and MW-5-MB,the two wells that historically had the highest concentrations, also were sampled in 2Q15 and 2Q 16.None of the chemicals analyzed in these samples exceeded their respective MCLS. URS requested that these wells be removed from the Monitoring and Reporting Program. In April 2016,URS submitted a work plan proposing additional in situ remediation in the general vicinity of the burn pit,where residual contamination by chlorinated volatile organic compounds(CVOCs)was present at concentrations greater than 500 gg/L. URS proposed the use of an amendment that could induce both biotic and abiotic reduction of the CVOCs. Specifically,URS proposed using EHC®Liquid (EHC-L), a concentrated microemulsion of controlled-release, food-grade organic carbon,nutrients, and iron(ELS' emulsion), designed for on-site dilution with cold water. A microbial consortium containing Dehalococcoides (DHC) and other anaerobic bacterial strains also was to be injected,to ensure that reductive dechlorination would progress until the CVOCs are reduced to nontoxic ethene. The CVWB approved the work plan on July 21,2016. Details of the proposed remediation are provided in the In Situ Remediation Work Plan. This report includes a summary of the proposed injection work and the baseline data collected before injections began in December 2017. In May 2016, CVWB requested that perfluorooctanoic acid(PFOA)and perfluoro octane sulfonic acid (PFOS)analyses be incorporated into the 4Q16 sampling event.URS submitted a work plan in which selected wells(MW-6-BP,MW-24-BP, and MW-25-BP)would be evaluated for these compounds. Analytical sampling results showed that PFOA and PFOS compounds were not detected at concentrations greater than the laboratory reporting limits. Additional sampling for these compounds was not recommended. Details of the sampling protocol are presented in PFOA Sampling in Selected Wells (URS 2016b). For reasons not readily explainable,PCE detections in groundwater samples that have been collected from MW-9-13P have fluctuated widely since September 2012. PCE concentrations have fluctuated from 83 gg/L in January 2020 to as high as 1,100 gg/L in November 2019. The source of the PCE is unknown 1-3