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Geosyntec° consultants • In August 2018, the Port re-surveyed the wells at RRI that were able to be located to obtain updated top of casing elevations and well coordinates. • In April and May 2019, the Port sampled groundwater from wells for dioxins and furans in areas where dioxins and furans were identified as COPCs based on historical site use. • In April and May 2019, the Port collected grab-groundwater samples at three locations at Site 3, seven locations at Site 4, four locations in the Central Area, and 10 locations in the Landfill Area for analysis of VOCs to evaluate the extent of the VOCs plumes. • In July 2020, the Port collected grab-groundwater samples at two locations at Site 3 and four locations in the Central Area to evaluate the extent of the VOC plumes. • In July 2020, the Port installed three new monitoring wells at Site 3 (W-337, W-338, and W-339), four new monitoring wells at Site 4 (W-331, W-332, W-333, and W-334), and four new monitoring wells in the Central Area(W-335, W-336, W-340, and W-341) to monitor the groundwater plumes. • In February 2021, the Port conducted well locating activities using a surveyor to mark historical well coordinates and use hand tools to unearth wells that had been buried. Of the 162 wells previously unable to be located based on visual inspection during the 2018 to 2020 groundwater monitoring events, 124 wells were located(Geosyntec, 2021 a). • In November and December 2022, the Port installed one new monitoring well at Site 3 (W-344R), one new monitoring well at Site 4 (W-342), and one new monitoring well in the Central Area(W-343) to fill in data gaps (Geosyntec, 2023a). • In 2023 monitoring well protection and repair activities were conducted including marking wells with steel fence posts, confirming the presence of signage, confirming the presence of railroad ties to restrict vehicle access, replacing missing vault box lid bolts, re-tapping the threads on well boxes, replacing missing or damaged well caps, replacing damaged well vault boxes,painting well box lids white, and removing sediment that had accumulated in wells. • In 2023 a total of 11 monitoring wells and piezometers that had been damaged below 4 feet below ground surface (bgs) and therefore were not repairable were destroyed. 1.5 Data Gaps For RI/FS The groundwater data from the last 40 years at RRI was evaluated to determine if there were remaining data gaps that would need to be addressed to move forward with the RI/FS for each proposed groundwater operable unit. The following data gaps for the RUFS were identified: • Site 4 o Completion of the background metals evaluation to confirm that barium exceedances of drinking water screening levels are naturally occurring. RRI 2024 Groundwater Monitoring Work Plan 5 June 13,2024