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L. McMahan June 15, 2018 Page 2of3 Hydrocarbons (TPH) were the only chemicals of concern (COC). HERO also recommended selecting monitoring wells based on any detections of constituents of potential concern (COPC) from the most recent monitoring event. The GMWP proposed to only sample wells with detections of VOCs that exceeded maximum contaminant levels (MCL) or total petroleum hydrocarbons (TPH) that exceeded 100 pg/L. The RTC states that a media-specific evaluation of COCs and identification of source locations will be conducted concurrently with the third quarter 2018 groundwater sampling event. The RTC indicates the COG evaluation will be submitted separately for regulatory review and approval. The RTC also states if the COG evaluation identifies chemicals that were missing from this GMWP, then additional groundwater samples may be collected as part of a GMWP data gaps investigation. The RTCs also indicate a review, in response to DTSC comments, identified mercury and cobalt as COCs at select locations. HERO's comments were not adequately addressed by the Port of Stockton. In addition, HERO is concerned that the COG evaluation has not been completed prior to finalizing the GMWP. According to the GMWP Introduction, the GMWP is meant to comprehensively address data gaps in the RRI groundwater monitoring network. However, based on the Port's response, the COG evaluation will identify the COCs and data gaps. HERO reiterates our original comments and recommends selecting monitoring wells based on any detections of COPCs. 2. Response to HERO's May 1, 2018 General Comments #4a (metals) — HERO recommended expanding the analytical suite to include metals. The Port of Stockton's response stated that mercury and cobalt would be added to the analytical suite since recent detections of these metals were above drinking water criteria (tapwater screening levels). HERO does not agree with screening out COPCs based on comparisons to screening criteria. HERO reiterates our previous comment and recommends sampling for all metals. This will be important in the future risk assessments which will present both total and site-related cancer risks and non-cancer hazard estimates. 3. Response to HERO's May 1, 2018 General Comments #4b (PFAS) and #5 (Site 3) -- HERO recommended adding PFAS to the analytical suite for grab groundwater samples collected at Site 3 and adding investigation findings from the "Final Site 3 PFAS Work Plan" (Geosyntec, 2017). The Port of Stockton's response states that PFAS will not be added to the i GMWP analytical suite because the Port considers the PFAS detection to be a previously unidentified environmental condition.