COMPLIANCE INFO_EW-5 INSTALL PERMIT PACKAGE 2/14/25

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WELL INSTALLATION AND INTERIM REMEDIAL ACTION REPORT www.arcadis.com FINAL_Forward CHCF (CDCR) Well Installation Report_10182024 14 5.2.3 Hydraulic Interpretation Summary The geological and hydrogeological interpretation of the CDCR investigation area indicates a fluvial depositional environment, which was reflected with significant heterogeneity in the deposits encountered at each drilling location. Permeable materials are present in variable thicknesses, with a paleo-channel feature appearing to be orientated from the southwest to northeast in the CDCR investigation area, with the permeable thickness thinning towards the east in the proximity of monitoring wells AMW-60S and AMW-60M (Figure 2). Groundwater flow appears to be locally, at least partly, controlled by the presence, or absence, of the permeable materials, and is orientated towards the north-northeast near extraction wells CDCR-EW-2 and CDCR-EW-4 and re-orientates more towards the northeast near extraction well CDCR-EW-3 and monitoring wells AMW-50S and AMW-50M (Figures 1 and 2). Groundwater extraction wells CDCR-EW-3 and CDCR-EW-4 were indicated by step testing to be able to sustainably produce maximum production rates of 30 and 20 gpm, respectively (Tables 2 and 3, Figures 3 and 4). This is comparable to extraction well CDCR-EW-2, which was indicated to be able to sustainably produce a maximum production rate of 35 gpm (Appendix F; Arcadis 2023b). Aquifer hydraulic conductivity calculated using monitoring well data from hydraulic testing indicated average rates of 228 and 250 ft/day, for CDCR-EW-3 and CDCR-EW-4, respectively (Tables 7 and 10). These hydraulic conductivity rates were relatively comparable to CDCR-EW-2, which indicated 105 ft/day for monitoring wells (Appendix F; Arcadis 2023b). The variation is likely caused by differing localized permeable thickness, but a bulk groundwater flow estimate of approximately 250 ft/day appears reasonable and conservative. Aquifer transmissivity calculated using monitoring well data from hydraulic testing indicated average rates of 6,844 and 7,505 ft2/day for extraction wells CDCR-EW-3 and CDCR-EW-4, respectively (Tables 7 and 10). These aquifer transmissivity rates were comparable to extraction well CDCR-EW-2, which indicated 6,286 ft2/day for when only monitoring wells3 are considered (Appendix F; Arcadis 2023b). 5.3 Groundwater Plume Distribution The CDCR groundwater plume with TVOC concentrations of 25 micrograms per liter (µg/L) or greater (TVOC plume) is presented on Figure 5. TVOCs are calculated by adding together all detected VOC concentrations. The plume geometry has been established by using soil boring and groundwater grab samples (Arcadis 2023b), groundwater monitoring well sample results, and extraction well baseline water quality sample results (Table 12). The most recent analytical data used to define the current TVOC plume distribution (Figures 5 through 7) are from the third quarter 2024 routine sampling event. These data will be presented in the forthcoming Third Quarter 2024 Monitoring Report. The TVOC plume is indicated to originate near soil boring location CDCR-SB-7, for which a shallow groundwater sample (72 to 77 feet bgs) was indicated to contain a concentration of 227 µg/L TVOCs. The TVOC plume extends towards the north/northeast and is orientated with the groundwater flow direction, with the core of the plume following a zone of higher permeable materials. The plume appears to gradually alter direction from north- northeast towards northeast, as it appears to follow the zone of permeable materials and corresponding groundwater flow. 3 Average transmissivity calculated from monitoring well AQTESOLV™ transmissivity estimates from piezometers PZ-1, PZ-2, and PZ-3, and monitoring wells AMW-22, AMW-22S and AMW-50M.