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WELL INSTALLATION AND INTERIM REMEDIAL ACTION REPORT www.arcadis.com FINAL_Forward CHCF (CDCR) Well Installation Report_10182024 1 1 Introduction On behalf of Forward, Inc. (Forward), Arcadis U.S., Inc. (Arcadis) has prepared this Well Installation and Interim Remedial Action Report (Report) for the installation of additional groundwater monitoring points and remedial wells as part of the interim remedial action (IRA) associated with the California Department of Corrections and Rehabilitation (CDCR) property located on South Austin Road in Stockton, California. The monitoring points and remedial wells discussed in this Report were installed at the California Health Care Facility (CHCF) and at the Northern California Youth Correctional Center (NCYCC), both of which are within the CDCR property boundary. The CDCR property is approximately 1,500 feet to the north of the Forward Landfill, which is located at 9999 South Austin Road in Manteca, California (Forward Landfill). This Report presents a summary of the methods and results from the May 2024 installation of one extraction well (CDCR-EW-4) and two monitoring wells (AMW-60S and AMW-60M) at the CHCF, and the July/August 2024 installation of one extraction well (CDCR-EW-3) and two groundwater monitoring wells (AMW-61S and AMW- 61M) at the NCYCC facility. The wells were installed and hydraulically tested as part of the remedial scope which requires an IRA to address the volatile organic compound (VOC) plume mass in groundwater beneath the CDCR property. The data collected during the effort described in this report was used to design a treatment system to address the remediation scope in Item 3c, which requires the hydraulic capture of the 25 ug/L or greater total VOC plume. The field activities were performed in general accordance with the CDCR Site Investigation Remedial Design Work Plan Second Addendum (Work Plan; Arcadis 2023a), which was conditionally approved by the Central Valley Regional Water Quality Control Board (RWQCB) on March 27, 2023 (RWQCB 2023). 2 Background This section describes the objective of the extraction and monitoring well installations, provides an overview of the well locations and installations, and provides a brief site description. 2.1 Objective and Well Installation Overview Arcadis proposed installing the two groundwater extraction wells (CDCR-EW-3 and CDCR-EW-4) and four groundwater monitoring wells (AMW-60S, AMW-60M, AMW-61S, and AMW-61M), as shown on Figures 1 and 2, as part of the remedial scope to address the requirement in CAO R5-2017-0703 (RWQCB 2017) for an IRA to address the VOC plume mass in groundwater beneath the CDCR property. Arcadis installed one new extraction well (CDCR-EW-4) and one separate co-located monitoring well pair (AMW- 60S/AMW-60M) in May 2024. As described in the Work Plan (Arcadis 2023a), a second extraction well (CDCR- EW-3) was planned for installation near monitoring well pair AMW-60S/AMW-60M; however, grain size analysis results from the pilot test borehole indicated that low-permeability soils were prevalent at the proposed well location in the northeast portion of the VOC plume beneath the CDCR property. In an email sent to the RWQCB on May 17, 2024, Arcadis on behalf of Forward requested approval to relocate the proposed extraction well closer to former cone penetration test (CPT) location CDCR-SB-01 (Arcadis 2023b), approximately 300 feet west of the originally proposed extraction well CDCR-EW-3 location (near monitoring well pair AMW-60S/AMW-60M). Former CPT boring CDCR-SB-01 (Figure 2) indicated the presence of a greater total