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Geosyntec consultants 5. GROUNDWATER MONITORING PROGRAM This section describes the proposed groundwater monitoring program for 2022 at RRI. Pending DTSC and CVRWQCB approval of this 2022 GMWP, the groundwater monitoring event will be conducted in the third quarter when concentrations of VOCs have historically been the highest (Appendix C; Geosyntec, 2018a). 5.1 Field Inspection and Depth to Water Groundwater levels at RRI will be gauged to evaluate groundwater flow directions and gradients. The wells and piezometers proposed to be gauged in 2022 are listed in Table 3 and were in good condition the last time they were inspected. The wells and piezometers proposed to be gauged will be located and visually inspected and the condition will be recorded on a field data sheet. If the well or piezometer is in good condition, the depth to water and total well depth will be measured using a water level meter and recorded on a field data sheet with the date and time the measurement was taken. The wells and piezometers will be gauged within a period of a few days. 5.2 Selection of Monitoring Wells for Sampling Monitoring wells at RRI were selected to be sampled in the 2022 monitoring program if they meet one or more of the following criteria: • The well is planned to be installed in 2022. • The well defines the lateral or vertical extent of a COC plume in groundwater. • One or more VOCs has had increasing concentration trends at the well. • The well is in a former source area and has had the highest recent concentrations of CDCs in the site area. • The well was sampled for a potential COC three or fewer times since 2018 with inconsistent detections of the COC. Figures 24 to 28 show the wells selected for sampling and the constituents each well is proposed to be sampled for. The 2022 sampling plan is provided in Table 3. The start of construction activities in the Landfill Area has been delayed until mid-August 2022 due to the presence of nesting birds. Therefore, the May and June 2022 installation of the replacement monitoring wells proposed in the Rail Line Area Well Destruction Work Plan has also been delayed, and these wells will not be able to be installed and sampled as part of the 2022 groundwater monitoring program. Wells and piezometers still present in the Landfill Area and last indicated to be in good condition are included as part of the upcoming 2022 monitoring program. If approval of this 2022 GMWP is received from DTSC and CVRWQCB such that the 2022 groundwater monitoring event can begin in August 2022, then the remaining well destructions in the Landfill Area will be conducted after the wells are monitored as part of the third quarter 2022 monitoring event. RRI Groundwater Monitoring Work Plan 18 June 2022