This document presents the Remedial Investigation/Feasibility Study (RI/FS) Work Plan for the contaminant characterization efforts to be conducted as part of the Resource Conservation and Recovery Act (RCRA) corrective action involving selected sites (e.g., solid waste management units (SWMUs)) at Yuma Proving Ground (YPG), Arizona. The RCRA corrective action will be conducted under the direction of YPG in coordination with the State of Arizona, Department of Environmental Quality (ADEQ). As directed by the ADEQ, and in agreement with YPG, the investigation and restoration of the selected sites will follow the format established under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and the National Contingency Plan (40 Code of Federal Regulations (CFR) Part 300). A remedial investigation (RI) will be performed and will be followed by a feasibility study (FS) if it is determined that conditions at specific sites warrant additional action (e.g., remediation). The RI/FS will be conducted in compliance with policies and procedures established under the US Army Environmental Center (AEC) Installation Restoration Program (IRP) and related programs.