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 5 4.2.1 Drilling and Lithologic Logging All soil boring locations for extraction and monitoring well installation were drilled using a hollow-stem auger drill rig operated by ABC Liovin Drilling (ABC Drilling) of Signal Hill, California, to total depths ranging from approximately 80 to 130 feet bgs. Groundwater was encountered at the CHCF during drilling at depths between approximately 61 feet bgs (AMW-60M and AMW-60S) and 68 feet bgs (CDCR-EW-4). Groundwater at the NCYCC was encountered at depths between 62.5 feet bgs (AMW-61M and AMW-61S) and 65 feet bgs (CDCR- EW-3). Lithologic logging was completed by an Arcadis field team member using the Unified Soil Classification System under direction of a California Professional Geologist. Soil cuttings were screened for VOCs using a photoionization detector and noted on the boring logs provided in Appendix B. 4.2.2 Extraction and Monitoring Well Installations This section describes the well installation activities completed in May 2024 at the CHCF and in July 2024 at the NCYCC. May 2024 Extraction and Monitoring Well Installations (CHCF) Two groundwater monitoring wells (AMW-60S and AMW-60M) and one groundwater extraction well (CDCR-EW- 4) were installed by ABC Drilling on May 6 through 16, 2024, under Arcadis’ direction. Well construction details are presented on the field boring logs (Appendix B) and in Table 1. The monitoring wells were completed with a 2- inch-diameter, Schedule 40 polyvinyl chloride (PVC) casing and 0.010-inch factory-slotted PVC screen. The extraction well was completed with a 6-inch-diameter, Schedule 80 PVC casing and 0.020-inch wire wrapped stainless-steel screen. The total depth and screen interval for each well are provided below: • AMW-60S was drilled to a depth of 80 feet bgs, with the shallow screen extending from 57 to 77 feet bgs (screen elevation -16.11 to -36.11 feet above mean sea level [amsl]). • AMW-60M was drilled to a depth of 130 feet bgs, with the intermediate screen extending from 102 to 112 feet bgs (screen elevation -61.69 to -71.69 feet amsl). • CDCR-EW-4 was drilled to a depth of 125 feet bgs, with an upper screen section (shallow WBZ) extending from 92.5 to 97.5 feet bgs (screen elevation -53.09 to -58.09 feet amsl), a deeper screen section (intermediate WBZ) extending from 102.5 to 117.5 feet bgs (screen elevation -63.09 to -78.09 feet amsl), and a 5-foot sump from 117.5 to 122.5 feet bgs. For the monitoring wells, a clean filter pack of sand consisting of No. 1/20 (nominal sieve size 20/40) silica sand was placed in the annular space around each well from the bottom of the boring to approximately 3 feet above the top of the screen interval. A 5- to 7-foot-thick hydrated bentonite chip or pellet seal was placed above the sand pack. The remainder of the annular space was filled with neat cement grout (AMW-60S) or Portland cement with 5% bentonite (AMW-60M). The surface completions consisted of a protective steel monument with three bollards and a 2- by 2-foot concrete pad sloping away from the well. In accordance with the RWQCB’s conditional approval (RWQCB 2023), the monitoring well screened within the shallow WBZ was installed with the top of the screen above the water table to allow for seasonal water table fluctuation. The design of extraction well CDCR-EW-4 was based on the lithologic interpretation of the borehole (Appendix B) sediments combined with review of grain size results from soil samples collected from potential screen zone(s), the laboratory reports are presented in Appendix C. The well screen zones were designed to target the most