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Geosynteccl <br /> consultants <br /> • In 2024, one new monitoring well (W-345)was installed between Site 49 Central Area <br /> OU and UST 817B Central Area OU to address data gaps. <br /> 1.4 Data Gaps For RI/FS <br /> In 2024 the groundwater data from the last 40 years at RRI was evaluated to determine if there <br /> were remaining data gaps that would need to be addressed to move forward with the RDFS for <br /> each proposed groundwater operable unit. Some data gaps identified were addressed as part of the <br /> 2024 annual groundwater monitoring event(Geosyntec 2025). The following data gaps remain for <br /> the RI/FS and are still being addressed: <br /> • Site 4: <br /> ■ A background metals evaluation is being completed to confirm that concentrations <br /> of barium (which currently exceed drinking water screening levels) are naturally <br /> occurring. <br /> • Site 49 Central Area: <br /> ■ A background metals evaluation is being completed to confirm that concentrations <br /> of barium (which currently exceed drinking water screening levels) are naturally <br /> occurring. <br /> • UST 817B Central Area: <br /> ■ The extent of petroleum hydrocarbons in groundwater west of the former UST is <br /> being evaluated. <br /> ■ The extent of the secondary source remaining in soil, which was investigated per <br /> the Final 2022 Limited Soil and Groundwater Investigation: UST 817E(Geosyntec <br /> 2024a), is being evaluated. <br /> ■ The extent of petroleum hydrocarbons in soil vapor,which was investigated per the <br /> Final 2022 Limited Soil and Groundwater Investigation: UST 817E (Geosyntec <br /> 2024a), is being evaluated. <br /> • Landfill Area: <br /> ■ Installation and sampling of new groundwater monitoring wells in the Stockton <br /> Soda Ash Port, LLC RRI Terminal (previously referred to as "Stockton Soda Ash <br /> Terminal") rail line construction area are planned to be completed following the <br /> construction activities. <br /> ■ A background metals evaluation is planned to be completed to determine whether <br /> metals concentrations above drinking water screening levels are naturally occurring <br /> or are associated with a waste cell. <br /> ■ The extent of PFAS in groundwater is being evaluated by the Navy;per the ESCA, <br /> this is a Navy-retained responsibility. <br /> • Site 3: <br /> RRI 2025 Groundwater Monitoring Work Plan 6 May 2025 <br />