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Focused Groundwater Investigation Work Plan Deuel Vocational Institution(DVI), Tracy, California Introduction 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 VOC plume in the vicinity of MW-15 (URS 2015). In November 2015,URS installed MW-26-BP to evaluate GW 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, Central Valley Regional Water Quality Control Board(CVWB) issued draft Monitoring and Reporting Plan(MRP)Order No. R5-2015-0808,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 GW quality in the maintenance area south of the burn pit. These wells were sampled previously from 2003 through 2010,with analyte concentrations below MCLS for several years before the submittal of a request for site closure in 2010. All five wells were sampled in the fourth quarter of 2015 (4Q 15). MW-3-MB and MW-5-MB,the two wells that historically had the highest concentrations, also were sampled in 2Q15 and the second quarter of 2016 (2Q16).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. 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 fourth quarter of 2016(4Q16) sampling event. URS submitted a work plan in which selected wells(MW-6-BP,MW-24-13P, and MW-25-13P)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 GW samples that have been collected from MW-9- BP have fluctuated widely since September 2012. Detected 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 at this time.URS recommended an investigation to identify the PCE source near MW-9-BP in the Fourth Quarter 2016 Groundwater Monitoring Report, Deuel Vocational Institution Burn Pit(URS 2016c). 1-3