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CDCR and DGS 5 - 16 September 2025 Required Actions: IT IS HEREBY ORDERED, pursuant to Water Code section 13267, CDCR and DGS (collectively, Discharger) are jointly and severally required to: No later than 1 February 2026, submit a Vadose Zone and Groundwater Plume Investigation Work Plan (Work Plan) containing a proposal to investigate the on-site sources of carbon tetrachloride and chloroform (and any other VOCs) contributing to detections of such contamination at and downgradient of the CDCR Facilities. The Work Plan shall identify sampling locations and intervals (with an explanation providing a technical justification for the selection of such locations and depths) and also contain the following: 1) Vadose Zone: The Work Plan shall propose a detailed sampling methodology, detection limits and protocols for sampling of the individual intervals within the vadose zone for VOCs. The soil vapor samples shall be analyzed for VOCs by utilizing United States Environmental Protection Agency (USEPA) Method TO -15. 2) Saturated Zones: The Work Plan shall propose a detailed sampling methodology, detection limits and protocols for sampling of the individual intervals within the aquifer zones for VOCs to determine the lateral and vertical extent of any VOC contamination caused by one or more sources at the CDCR Facilities. If dedicated pumps will be placed in the wells, please state the depth of the screen interval(s). All samples shall be analyzed for VOCs by United States Environmental Protection Agency (USEPA) Method 8260B and analytes shall be reported. 3) Borehole Logging: Proper description of all stratigraphy is a critical component of updating the hydrogeologic model in this area. The Discharger shall explain in detail how the material from each borehole will be described in compliance with Title 27 (see Title 27 of the California Code of Regulations, Section 20415(e)(2)). Further, a site conceptual model will need to be developed, so continuous coring is expected, such that visual description by an appropriate Registered Professional will occur. 4) Drilling Methodology: The Work Plan shall describe in detail the method of drilling as well as any potential interference it may have on data collection and evaluation. 5) Zones of Highest Hydraulic Conductivity: The Work Plan shall describe how the extent of the zones of hydraulic conductivity, both vertically and laterally, will be defined. Submit a Soil Gas and Groundwater Investigation Report No later than 15 January 2027, submit a Soil Gas and Groundwater Investigation Report that includes a site conceptual model that defines the stratigraphy, the defined