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Geosyntec° <br /> consultants <br /> 5. GROUNDWATER MONITORING PROGRAM <br /> The updated hydrogeologic CSM, EVS® model, and MAROS concentration trend <br /> evaluation was used to develop a proposed groundwater monitoring program for RRI. <br /> The proposed monitoring program consists of the following components, which are <br /> discussed in more detail below: <br /> • Evaluate the condition of the wells and piezometers at RRI; <br /> • Measure depth to groundwater and total depth in the piezometers and wells at RRI <br /> that can be located and are in good condition; <br /> • Evaluate the condition of historic stream gauges at RRI and measure the surface <br /> water elevations at stream gauges that can be located and are in good condition; <br /> • Sample wells that monitor the lateral and vertical extent of COCs in groundwater <br /> at RRI. <br /> 5.1 Frequency of Monitorine <br /> Groundwater monitoring at RRI is proposed to be conducted during the dry season(third <br /> quarter)2018.The selection of the monitoring frequency will be re-evaluated pending the <br /> results of the third quarter 2018 monitoring event and COC evaluation. COC <br /> concentrations are stable to decreasing at 94% of the wells at RRI, and higher <br /> concentrations of COCs are generally observed during the dry season when there is less <br /> recharge to groundwater(Appendix E). <br /> 5.2 Field Inspection and Depth to Water <br /> Groundwater and surface water levels at RRI will be gauged to evaluate groundwater <br /> flow directions, gradients, and groundwater and surface water interactions. <br /> Field staff will inspect the condition of the 309 wells and 40 piezometers at RRI for which <br /> the condition was last documented as good or unknown (Table 7). At RRI, 24 wells and <br /> 33 piezometers have been documented as decommissioned or destroyed, and 22 wells <br /> and 16 piezometers have been documented as damaged, buried, or unable to be located. <br /> If the wells and piezometers proposed to be inspected can be located and are in good <br /> condition, the depth to water and total well depth will be measured using a water level <br /> RRI Groundwater Monitoring Work Plan 22 1 June 2018 <br />