Iowa State’s Robert Ewing discovered why past theories attempting to predict how long it takes for a contaminated site to be freed of contamination are far too optimistic.

Scientists trying to predict how long contaminated soils and rocks will stay polluted have been using wrong formulas in the process, according to an ISU study. The rates actually vary according to how porous and connected the rocks are.

Ewing, assistant scientist of agronomy, has been working with soil around the Department of Energy’s Pacific Northwest National Laboratory near Richland, Wash., which was used during the Cold War by the United States to try to produce plutonium.

Large quantities of uranium stored in the tanks at the site leaked into the surrounding soil. Scientists have overestimated how quickly the contaminated soil will move into the Columbia River and free the area of soil and rock pollution, Ewing said.

Ewing said the pollutions gets in the pores inside the rocks, so in order to free the area of contamination it must first leave the pores.

“Once you remove the source of the [polluted uranium], the contaminant moves back out of the rock slowly,” Ewing said. “The problem is, how do you describe that slow release?”

Ewing said depending on how porous the rocks are and how connected the pores are, the diffusion rate can be predictable. As contaminants inside a rock begin to leach back out, they can take a long journey through the pores like a maze which makes them susceptible to hitting dead ends in the rocks.

“Something trying to diffuse out could take decades running into a dead end, down another dead end, another and so forth,” he said.

Environmentalists before Ewing’s research had a skewed view at how to predict when the contamination would leave.

“Before this research, we were getting results that weren’t making sense. We’ve been scratching our heads about this for 30 or 40 years,” Ewing said. “This is an enormous step forward.”

Ewing hopes that future estimates on how long contaminated sites will be free of pollution will be more accurate.