Over 60 years dating back to World War II, Hanford workers buried an estimated 16 million cubic feet of waste in central Hanford.
Now the Department of Energy is working to solve the riddle of just what was buried in trenches, particularly in the earliest decades, and what potential harm it might pose to people and the environment.
DOE is expecting to find waste ranging from motor vehicles to debris contaminated with plutonium and wrapped in burlap.
The information will be used by DOE to make a proposed decision in 2016 on how to clean up the burial grounds, which combined cover 545 acres or 0.85 square mile. By then most cleanup of burial grounds and other contaminated sites near the Columbia River should be completed, and the cleanup focus will be on central Hanford.
DOE and its regulator, the Washington state Department of Ecology, are providing information to the public now about central Hanford burial grounds because of public interest. Concerns about the buried waste in central Hanford, and how aggressive cleanup should be have been raised in recent years at public meetings and in response to environmental cleanup documents released for public comments.
"There's interest in how we know what is in there and how we find out," said Matt McCormick, manager of the DOE Hanford Richland Operations Office.
"I definitely agree that it's the unknown," said Deborah Singleton, project manager for the Ecology department. "A lot of people speculate, but the onus is on us to determine what is in there."
The Hanford Advisory Board attended a daylong workshop in Richland earlier this month to learn about the issue, and evening meetings for the public were held in Portland and Hood River, Ore., last week. The third and final regional public meeting will be in Seattle on Tuesday.
No evening public meeting is planned in the Tri-Cities on the burial grounds because the daylong Hanford Advisory Board meeting was open to the public and because of the typically low attendance at Tri-City meetings on Hanford, according to DOE.
The decision was made by DOE and its regulators with input from board members, who include representatives of Tri-City interests.
Under proposed changes to the Tri-Party Agreement, DOE would be required to have an updated work plan prepared in late 2011 that will describe how information will be collected on the sites to prepare for the proposed cleanup decision in 2016.
That could include steps such as excavating the waste and disposing of it in a modern landfill, building a cap over waste to prevent water from driving contamination deeper underground or treating it in place with methods such as in-ground grouting.
The ground water in the area already is contaminated from past dumping of contaminated liquid into the soil and from leaks from Hanford's underground tanks holding radioactive waste. Monitoring of the waste sites has not shown that they are contributing to ground water contamination now, according to DOE and the state Department of Ecology.
The waste ranges from construction debris that should not have been contaminated to waste feared to have enough radioactive contamination that it was buried as a precaution in caissons, underground boxes with slanted chutes into which waste was dropped down from the surface of the ground.
It also includes waste with plutonium contamination buried before 1970, when Congress determined that debris contaminated with certain levels of plutonium should be sent to a national geologic repository. Now such waste, classified as transuranic, is sent to the Waste Isolation Pilot Plant in New Mexico.
The central Hanford burial grounds include an estimated 800 pounds of plutonium buried before 1970.
Some of the waste that now would be considered transuranic may have been wrapped in paper or burlap, packaged in fiberboard or wooden boxes, or left uncovered when it was buried. The waste ranges from contaminated rags to motor vehicles.
The most recent waste in the burial grounds is well documented, but historical records are limited for waste buried from the mid '40s to mid '60s. The trenches were used for waste disposal of low-level radioactive waste as recently as 2004.
DOE has used ground-penetrating radar to determine the location of trenches with waste buried before the 1970s. The plan being developed could call for more work with ground-penetrating radar or sampling of underground waste.
The waste is buried in about 360 trenches, most of which are 15 to 25 feet deep. Some of the trenches are more than 1,000 feet long. As trenches filled, workers would design and build new ones.
* More Hanford news at hanfordnews.com.