Since the 1940's, defense related nuclear waste has been stored in single-shell tanks (SST) on the Hanford Site. The radioactive components on the waste are regulated in accordance with the Atomic Energy Act. The hazardous components are regulated in accordance with the Resource Conservation and Recovery Act as implemented by the Washington State Dangerous Waste Regulations. This report provides a background of the SST waste and a description of the initial studies underway to characterize the material to provide information to support performance assessment studies and regulatory compliance while minimizing unnecessary radiation doses to workers.