The Hanford Site, situated on a roughly 560 square mile area in the Columbia River Valley, in south-central Washington, is owned by the Federal government and is managed by the US Department of Energy (DOE). For more than 40 years facilities at the Hanford Site produced plutonium for the nation's nuclear weapons defense program. The legacy of this program is environmental contamination on a massive scale. The Hanford Site today contains an estimated 5 billion cubic yards of solid and dilute radioactive and hazardous chemical wastes. Approximately 440 billion gallons of liquid wastes have entered the soil, and over 200 square miles of groundwater below Hanford have been contaminated (GAO, 1989). This case focuses on a statistical evaluation plan for only a fraction of the total wastes at Hanford: the underground storage containers and the toxic wastes buried therein.
Built between 1943 and 1964, there are 149 single-shell underground storage tanks (SSTs) at the Hanford Site with capacities ranging from 55,000 to 1 million gallons of waste. The DOE estimates that the SSTs contained up to 77 million gallons of liquid and solid waste in 1966, but by 1988 this volume was reduced to about 37 million gallons, including 8 million gallons of liquid (GAO, 1989). Nearly 1 million gallons are suspected or known to have leaked from 67 of the SSTs into the surrounding soil. Pumpable interstitial liquid and supernatant wastes are being removed from SSTs and transferred to safer, double-shell tanks (DST). These DSTs are a tank-in-tank design and were placed into service beginning in 1971. To date, none of the 28 DSTs placed in operation are known to have leaked. No new wastes have been added to the tanks since November 1980.
The year is 1989, and the Washington State Department of Ecology is reviewing aWaste Characterization Plan for the Hanford Single-Shell Tanks. Sampling and analysis of the waste in the single-shell tanks will be conducted by the US Department of Energy and Westinghouse Hanford Company in accordance with this plan. The first phase of the plan consists of a reference sampling plan which will be used to determine the magnitude of various uncertainties involved in single-shell tank (SST) waste characterization. The costs involved in this characterization are immense. Results of the reference sampling phase will shape the design of sampling and analysis procedures for the remainder of the SST waste characterization effort, scheduled to continue well beyond the year 2000.
Contractor assistance is requested to assist with the Department of Ecology's review of the SST Waste Characterization Plan. Specifically, asistance is needed to review the section dealing with a statistical evaluation of data requirements for the reference sampling plan. This section identifies several sources of uncertainty in the tank sampling and analysis procedures, and presents a statistical approach for determining the appropriate number of samples for analysis. Your task is (rather than to produce a technical memorandum assessing the sampling plan as the original contractor did) to be prepared to discuss the reference sampling plan on May 12 (no written report is needed for this case). Among the items to think about are:
The Hanford home page is maintained by the Department of Energy.
There are some problems with the tank cleaning project (Seattle Daily Journal of Commerce, April 18, 1996). And here is the result of a search on the Seattle Times homepage fornews on Hanford.
