The Hanford Advisory Board is concerned that more research should be done before a cleanup plan for uranium-contaminated groundwater becomes final.
A meeting is scheduled tonight in Richland by the Department of Energy and its regulators to discuss and hear comments on the proposed plan for the 300 Area, which is just north of Richland.
Much of the plan follows usual Hanford procedures for digging up contaminated soil and waste sites, treating the waste as needed and then disposing of much of it in a central Hanford landfill for low-level radioactive waste.
However, choosing a final plan for groundwater near the Columbia River that is contaminated with uranium above drinking water standards over about 125 acres may be more controversial.
The 300 Area was used for fabricating uranium into fuel pieces for the Hanford reactors that produced plutonium for the nation’s nuclear weapons program. It also was used for research, including testing processes for chemically removing plutonium from irradiated uranium fuel.
Process trenches used to dispose of contaminated liquid into the soil were removed in the 1990s, and levels of uranium in the groundwater dropped, said Mike Thompson, DOE hydrogeologist. Hanford officials assumed then that if uranium-contaminated soil was excavated down to about 15 feet — which has been done — the groundwater contamination gradually would dissipate.
But it later became clear that more lightly contaminated soil near the groundwater was continually recontaminating the water. As the river would rise and fall, the level of groundwater also would change, allowing the groundwater to periodically soak the contaminated soil.
Digging up all the contaminated soil is not an option, according to DOE. It would cost more than $1 billion and the soil would fill an area measuring 1,000 feet by 1,000 feet in the 70-foot-deep lined landfill in central Hanford.
The digging also could backfire and increase contamination in the groundwater, according to DOE. Water is used to control dust and prevent airborne contamination during excavation, but the water would filter through the soil and push more uranium into the groundwater.
Instead, DOE proposes adding a binding solution to the soil to reduce the movement of contamination to the groundwater while contamination in the groundwater dissipates over time.
Phosphate would be added, which combines with uranium in a carbonate form to make autunite, a uranium phosphate mineral that’s bright yellow and flaky. It’s a stable mineral that does not readily dissolve when hit by water, keeping it in the soil instead of in the water.
The phosphate would be added into the soil in two ways. First, it would be dripped in from the surface of the ground. Second, it would be injected into wells that do not reach the groundwater. The idea is to reach the contamination in the zone where the soil periodically gets soaked.
The method would not have to be 100 percent effective to give the groundwater some protection and allow enough uranium to dissipate to reach regulatory standards in a matter of decades, Thompson said.
About 330 pounds of uranium per year is released to the Columbia River from the Hanford 300 Area, according to DOE. But three irrigation outlets on the Franklin County side of the river release 3,500 pounds of uranium a year into the river from fertilizer and uranium that’s naturally in the ground. In addition, the Yakima River adds about 8,800 pounds a year.
DOE and its regulators are cleaning up the uranium-contaminated groundwater on the Hanford side of the river to comply with federal Superfund law that requires restoration of the aquifer in a reasonable time.
DOE has tried similar solutions to its proposed method in tests at the 300 Area, but the results have not been optimal. Most recently, the agency tried putting the phosphate on the ground and letting it soak in, but results varied from spot to spot.
The Hanford Advisory Board has recommended a field test to determine the effectiveness of the proposed solution. Then DOE and EPA would be better prepared to make a final decision on whether it’s the best method for cleaning up the uranium, and cleanup could be done in a more timely and cost-effective manner, it said.
“It is important to the board that the 300 Area decisions are dependable, protective, defensible and well supported,” the board said in a June letter to DOE and the U.S. Environmental Protection Agency.
DOE has studied the issue of uranium-contaminated groundwater for more than two decades and no better method is on the horizon, Thompson said.
EPA agrees that adding phosphate to the soil is the best technology available.
Most of the uranium in the soil already has been removed, and the plan addresses a small amount that is left and continues to bleed into the groundwater, said Larry Gadbois, an EPA scientist.