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WELL INSTALLATION AND INTERIM REMEDIAL ACTION REPORT <br />www.arcadis.com <br />FINAL_Forward CHCF (CDCR) Well Installation Report_10182024 <br /> <br />10 <br />5 Geological and Hydraulic Assessment <br />This section presents the drilling and hydraulic testing results from tests conducted on extraction wells CDCR- <br />EW-3 and CDCR-EW-4. The hydraulic tests were used to assess the extraction well production capacities and <br />aquifer response to extraction, establish aquifer hydraulic parameters , and calculate the capture zone of each <br />extraction well. The results of these individual assessments were then combined with previous hydraulic testing <br />results for extraction well CDCR-EW-2 (Appendix F; Arcadis 2023b) to assess the predicted combined <br />groundwater extraction system capture of the VOC plume mass with total VOC (TVOC) concentrations of greater <br />than 25 µg/L, beneath the CDCR property. <br />The current approach to groundwater capture at the CDCR property with wells screened in the intermediate and <br />portions of the shallow zone, rather than just the shallow zone, was developed in response to hydraulic testing of <br />groundwater extraction well CDCR-EW-1 (Arcadis 2023b) and downgradient groundwater quality testing. <br />Hydraulic testing from CDCR-EW-1 indicated that the extraction capability from the shallow zone was poor, with a <br />sustainable yield of less than 1 gpm, and minimal radius of influence (drawdown was not detected in wells located <br />several feet away) and therefore minimal groundwater capture of the shallow plume. Subsequent installation and <br />hydraulic testing of intermediate screened groundwater extraction well CDCR-EW-2 indicated a greater <br />sustainable extraction rate (sustainable yield of 50 gpm), with hydraulic response noted in both the shallow and <br />intermediate groundwater zones more than 380 feet from the extraction well, thereby indicating effective <br />groundwater capture. <br />Capture of groundwater from the intermediate zone was also indicated to be required due to vertical migration of <br />the shallow VOC plume into the intermediate groundwater zone within a few hundred feet downgradient of the <br />highest detected shallow VOC concentrations. This was based on individual constituent presence and migration <br />(carbon tetrachloride) and change in chemical ratios (PCE and TCE) in the intermediate zone across the CDCR <br />facility (Arcadis 2023b). Groundwater extraction wells CDCR-EW-3 and CDCR-EW-4 were installed to enable <br />capture of the TVOC plume with concentrations greater than 25 µg/L at the CDCR property. <br />5.1 CDCR Geology and Hydrogeology <br />The uppermost sedimentary deposits in the area, the Victor Formation, are known to be heterogeneous and <br />laterally and vertically discontinuous, indicative of a fluvial depositional environment. Boreholes advanced in the <br />central portion of the CDCR property reflected this heterogeneity, where within the distance of only tens of feet <br />significant changes in thickness of permeable materials (i.e., sands and gravels) have been observed. <br />The lithological investigation data to date indicate that the thickness of permeable materials thins in both the <br />shallow and intermediate WBZs with movement eastwards in the remedial portion of the CDCR assessment area. <br />Thicker permeable materials, as a paleo-channel feature, appear to be orientated from the southwest to <br />northeast, with the highest total thicknesses of permeable materials indicated near borehole CDCR-SV-01 and <br />extraction well CDCR-EW-3. <br />Groundwater flow is regionally orientated from the southwest towards the northeast as indicated by quarterly <br />groundwater monitoring from the groundwater investigation and regional monitoring well dataset (Arcadis 2023c, <br />2024a, 2024b, 2024c). However, localized groundwater flow at the CDCR property will likely preferentially migrate <br />along the zone of thickest permeable materials, which was indicated from groundwater levels collected in spring <br />2024 as part of the hydraulic testing activities. Ongoing groundwater monitoring of the expanded well network in <br />this area will be used to confirm this interpretation on a seasonal basis.