Of all the troubling images evoked by the Hanford Nuclear Reservation, the nation’s most contaminated nuclear site, the plume of uranium-tainted groundwater seeping into the Columbia River comes near the top of the list. Millions of gallons of radioactive waste were processed at the site and, starting in the ’40s, government scientists detected it in the area’s groundwater.
One site, called the 300 Area, has a plume of several million gallons affecting a 3,000-foot stretch of the Columbia River shoreline. Monitoring wells and riverbank springs have had uranium levels in excess of drinking-water standards set by the Environmental Protection Agency.
The river provides drinking water to nearly a dozen water systems, including Richland, but so far, levels in the river itself have been negligible. Still, federal Superfund law requires that groundwater be returned to its “beneficial use.” In other words, it needs to be drinkable again.
For a while, government scientists, cleanup contractors, and regulators envisioned a scenario where that would happen on its own. They removed and disposed of the top-most layers of contaminated soil in the mid-’90s and figured fluctuating groundwater levels would in effect wash away the remaining uranium, carrying it to the river at low enough levels over the course of a decade or so.
That has not happened. Kenton Rod (’12 PhD) looked closely—very closely—at the soil beneath the 300 Area and found it has a way of holding on to uranium, slowing its release into the environment.
“Nothing is going to happen fast here,” he says.
Just why that is gets at the curious nature of soil, which Rod notes is “one of the most complex mediums that a scientist can investigate.”
Sitting in a common area of the WSU Tri-Cities campus, he explains how soil has a mix of physical, biological, and chemical properties, while at the same time serving as an interface of solid, liquid, and gas.
“You try and pick those elements apart and it’s not an easy task,” he says.
In the case of the 300 Area’s uranium waste, a byproduct of the process that made plutonium for the Nagasaki-bound atom bomb “Fat Boy” and the Cold War arms race, Rod saw something very small—the chemistry and structure of individual soil particles—having an inordinate effect on the area’s 300-plus acres.
The soil, says Rod, wants to hold on to a certain amount of uranium all the time and will resist efforts to be rinsed clean. There is also a limit to how much uranium the water will want to pick up, just as there is only so much sugar you can put in your coffee before it’s saturated.
But having a far greater effect, Rod found, are cracks in the soil particles. They are nanometers thin, which is to say they are measured in millionths of a millimeter. And once uranium enters, the crack is like a bottle in a dishwasher: water has a hard time getting it out.
“Add all those up and that’s what helping these uranium plumes persist in the groundwater,” says Rod. “But it’s letting enough go, that it’s keeping the groundwater above EPA standards. It is letting it go, just very slowly. It’s a very slow process. It’s going to be a while. People are keeping their eyes on it.”
Indeed, in 2011 the Department of Energy released a draft proposed plan for remediating the 300 Area and noted that scientists were not seeing an expected decline in groundwater uranium levels.
“There’s a continuing source,” says Mike Thompson, a department hydrogeologist working on the area. The department is now proposing to put phosphates in the groundwater and soil above it. The phosphates will attach to the uranium, says Thompson, converting it into a more stable, less mobile, and otherwise insoluble mineral.
