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Geosyntec consultants evaluation of COCs and identification of source locations will be conducted over the next three months concurrently with the third quarter 2018 groundwater monitoring well sampling event. If potential COCs in groundwater are identified as part of the COC evaluation that were not sampled for during the third quarter 2018 groundwater monitoring event, then sampling for additional COCs may be conducted as part of the GMWP data gaps investigation. A separate COC evaluation report will be provided to DTSC and the RWQCB for review and approval. The third quarter 2018 groundwater monitoring program is based on the previous evaluations of media specific COCs at RRI, which identified VOCs, TPH and metals as the COCs in groundwater at RRI (Tetra Tech, 2002, Environmental Risk Services Corporation [ERS], 2012a, ERS 2012b, ERS 2012c, ERS 2012d). VOCs, in particular chlorinated solvents, are the primary COCs detected in groundwater at RRI (Tetra Tech, 2002,ERS 2015b).TPH in groundwater is generally detected in the same locations as the VOC benzene (ERS 2015b). During the most recent sampling event conducted in 2015 arsenic, mercury and cobalt were the only metals detected in groundwater at RRI at concentrations above drinking water criteria(ERS 2015b). Arsenic in groundwater at RRI has been demonstrated to be naturally occurring and therefore is not included in this GMWP (ERS 2016a). Mercury was detected above DTSC tapwater screening level in the southern landfill area at W- 069, W-064, W-223 and W273. Cobalt was detected above United States Environmental Protection Agency(EPA)tapwater screening level in the southern landfill area at W-173, W-225 and W-230. PFAS have been detected in groundwater at Site 3 and a technical memorandum of the PFAS results was submitted to DTSC and the RWQCB on 14 March 2018 (Geosyntec, 2018). The Port plans to discuss the detection of PFAS with the Navy,and PFAS are not addressed in this GMWP. Cis-1,2-dichloroethene (cis-1,2-DCE) and vinyl chloride (VC) are currently the most prevalently detected VOCs in groundwater and serve as a proxy for the chlorinated solvent groundwater plume. Figure 3 displays isoconcentration contours of cis-1,2 DCE and VC in groundwater with concentrations above their respective Maximum Contaminant Levels(MCLs) based on the most recent sample collected from each well. RRI Groundwater Monitoring Work flan 5 1 June 2018