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Geosyntec <br /> consultants <br /> 3. GROUNDWATER MONITORING PROGRAM <br /> This section describes the proposed groundwater monitoring program for 2025 at RRI. Pending <br /> DTSC and CVRWQCB approval of this 2025 GMWP, the groundwater monitoring event will be <br /> conducted in the third quarter when concentrations of VOCs have historically been the highest and <br /> the wells at RRI are generally the most accessible because there is less ponded water and vegetation <br /> (Geosyntec 2018a, 2023, 2024). <br /> 3.1 Field Inspection and Depth to Water <br /> Groundwater levels at RRI will be gauged to evaluate groundwater flow directions and gradients. <br /> The wells and piezometers proposed to be gauged in 2025 are listed in Table 4 and were in good <br /> condition the last time they were inspected. The wells and piezometers proposed to be gauged will <br /> be located and visually inspected and the condition will be recorded on a field data sheet. If the <br /> well or piezometer is in good condition, the depth to water and total well depth will be measured <br /> using a water level meter and recorded on a field data sheet with the date and time the measurement <br /> was taken. The wells and piezometers will be gauged within a period of a few days, with all wells <br /> in any given OU gauged on the same day. <br /> 3.2 Selection of Monitoring Wells for Sampling <br /> Figure 5 shows the wells selected for sampling and the constituents each well is proposed to be <br /> sampled for. The wells were selected to meet the objectives described in Section 1.5. The 2025 <br /> sampling plan is provided in Table 4. <br /> Following the initial phase of remediation in the Landfill Area,as described in the Remedial Action <br /> Plan for Soil,Landfill Area (DTSC and CVRWQCB 2021), construction of the RRI Terminal will <br /> begin, which is currently expected to commence in the second quarter of 2025 and estimated to <br /> continue over approximately two years. Due to ongoing soil remedy and construction efforts in <br /> the Landfill Area, only wells and piezometers that were last indicated to be in good condition and <br /> were accessible in 2024 without significant vegetation removal are included as part of the <br /> upcoming 2025 monitoring program (Table 4). This will prevent disturbances and potential <br /> schedule delays to the soil remedy and RRI Terminal Project construction programs. The excluded <br /> wells in the Landfill Area will be assessed when soil remedy and construction activities are <br /> complete. In general, the wells excluded from the 2025 GMWP in the Landfill area exhibit either <br /> non-detect, stable, or decreasing trends for cis-1,2-dichloroethene and vinyl chloride. <br /> In addition, the installation of the replacement monitoring wells proposed in the Rail Line Area <br /> Well Destruction Work Plan (Geosyntec 202 lb) will be completed after the ongoing remediation <br /> and the RRI Terminal construction which will not be completed in 2025. <br /> Wells included in the 2025 sampling plan (Table 4) found to be inaccessible or damaged to the <br /> extent they cannot be sampled during the 2025 sampling event,if any,will not be sampled in 2025. <br /> If a monitoring well included in the 2025 sampling plan, located outside of the Landfill Area, is <br /> found to be inaccessible or damaged during the 2025 sampling event, then the well will be added <br /> to the 2025 well maintenance activities and located and repaired to the extent feasible in <br /> accordance with the procedures described in Section 2 of this work plan. The 2025 groundwater <br /> RRI 2025 Groundwater Monitoring Work Plan 13 May 2025 <br />