Radioactive Waste Contamination of Soil and Groundwater at the Hanford Site Laura A. Hanson University of Idaho Principles of Environmental Toxicology November 2000 Abstract The Hanford Site in southeastern Washington State is the location of the largest nuclear waste storage area in the United States. Since plutonium production facilities at Hanford were shut down in 1987,cleaning up the leftover waste at the Hanford Site has become one of the largest environmental cleanup projects in history. Legal, political, technical, and social aspects of the cleanup contribute to the overall complexity of the situation. There is, however, a sense of urgency surrounding the cleanup efforts. Of the 177 underground nuclear waste storage tanks on the Hanford Site 67 are known to be leaking currently and a large proportion of the tanks are at or approaching the end of their design lives. Cleanup efforts are presently focused on removing the waste from the storage tanks and immobilizing it for long-term storage. While it remains a primary concern, it is currently unknown what the long-term ecological consequences of the leaked nuclear wastes will be.2 1. Introduction 1.1 The Hanford Site In June 1942 the Manhattan Engineer District of the Army Corps of Engineers was instructed to locate a site where industrial facilities for a secret weapons project would be built. The Hanford Nuclear Reservation, which encompasses 560 square miles in southeastern Washington State, was established as the location for the plutonium production site in March 1943. The site was separated into several regions where different activities would take place (Figure 1). Within two years, nuclear reactors, processing facilities, support facilities, underground waste storage tanks, and nuclear fuel fabrication facilities had been constructed and were in operation to produce plutonium fuel for military defense (Gephart and Lundgren, 1998). Between its establishment in 1943 and deactivation in 1987, approximately 110,000 tons of nuclear fuel were processed at the Hanford Site (Wald, 1998; Gephart and Lundgren, 1998). Hanford produced more than 73 tons of nuclear weapon- and reactor fuel-grade plutonium during its years of operation (Gephart and Lundgren, 1998). The production of plutonium fuel generated millions of gallons of highly radioactive waste, as well as non-radioactive hazardous waste and mixed waste. The U.S. Department of Energy (DOE) currently manages the Hanford Site, and is responsible for cleaning up the now-defunct plutonium processing facility.3 Figure 1. Map of the Hanford Site in southeastern Washington State (from USDOE: Hanford). The 100 Area of the Hanford Site housed nuclear reactors, the 200-East and –West Areas were home to fuel reprocessing facilities and waste storage areas, and the 300 Area was dedicated to nuclear fuel fabrication and research. 1.2 Occurrence of Waste in and around the Hanford Site On a volume basis, Hanford contains over two-thirds of the DOE’s highly radioactive waste (Gephart and Lundgren, 1998). About 50%, or 54 million gallons, of the radioactive waste at the Hanford Site is contained in 177 underground storage tanks, many of which are leaking. During operation, the primary consideration when making decisions regarding waste management was nuclear materials production. As a result, the methods by which Hanford’s waste was managed are unacceptable by today’s standards. For example, prior to 1970 solid low-level and transuranic waste4was frequently disposed of in cardboard boxes in unlined trenches (Wald, 1998). In 1989 the DOE began a comprehensive environmental cleanup effort at the Hanford Site at a cost of more than $1 billion per year (Zorpette, 1996). Cleaning up radioactive waste is a complex process because it cannot be degraded the way organic substances can. James D. Werner, director of strategic planning and analysis in the Office of Environmental Management of the DOE summarizes the complexity of cleaning up radioactive waste: “The stuff we’re dealing with can’t go away until it decays. You can containerize it, solidify it, immobilize it and move it, but you can’t make it go away” (Zorpette, 1996). In 1996 the total radioactivity at the Hanford Site was estimated at approximately 437 million curies (Ci, see Appendix A), distributed as follows (Gephart and Lundgren, 1998):  Underground waste tanks = approximately 215 million Ci  Cesium and strontium capsules = 150 million Ci  Stored irradiated fuel = 50 million Ci  Facilities = 18 million Ci (in pipes, filters, etc.)  Solid waste = 2.5 million Ci  Soil and groundwater contamination = 1.5 million Ci Several different types of waste were generated by plutonium processing at the Hanford Site, including high-level and low-level radioactive waste, transuranic waste, hazardous waste, and mixed waste. High-level waste (HLW) is generally defined as the waste generated during the chemical separation of uranium and plutonium from undesirable radioactive elements. Most of the radioactive elements discharged to the underground waste storage tanks were contained in HLW. Low-level waste (LLW) is any radioactive waste that is not spent fuel, high-level, or transuranic waste. The LLW is a general category and can include liquid waste, contaminated clothing, tools, and equipment. Transuranic waste is radioactive waste containing greater than 100 nanocuries per gram of alpha-emitting isotopes with atomic numbers higher than 92. Transuranic waste is generated primarily during nuclear fuel reprocessing and the manufacture of plutonium weapons. Hazardous wastes are non-radioactive wastes, such as metals or chemical compounds that are known to pose environmental or human health risks. Mixed waste is hazardous waste combined with radioactive material.5Approximately 99% of the total radioactivity contained in the underground waste storage tanks at the Hanford Site is due to cesium-137 (137Cs) and strontium-90 (90Sr). Cesium-137 is the most abundant of all radioactive isotopes present in the tank waste (Gephart and Lundgren 1998). The objective of this study is to examine the potential for widespread environmental contamination by the 137Cs contained in the underground waste storage tanks at the Hanford Site. 2. Background Information 2.1 Radiation Radiation is a form of energy that is transmitted by electromagnetic waves or by streams of subatomic