Scientists at Pacific Northwest National Laboratory believe a research project using 35 newly drilled wells will help explain the baffling behavior of uranium contamination at Hanford.
A decade ago, Hanford officials believed uranium contamination at the nuclear reservation just north of Richland along the Columbia River was a problem that time would solve.
After the most contaminated soil was dug up and hauled to a landfill for low-level radioactive waste in central Hanford, they expected the uranium-contaminated ground water below it to naturally dissipate.
Instead, levels of contamination remain at up to three times the drinking water standard in the ground water.
"The plume here has been far more persistent than expected," said John Zachara, PNNL chief scientist who is leading a team of experts in underground geochemistry, hydrology and microbiology on the research project.
They're hoping that with the array of new wells equipped with sophisticated monitoring devices they will be able to get to the bottom of the mystery of how uranium behaves deep underground.
"We're looking at some very aggressive technology," said Mike Thompson, Department of Energy hydrogeologist.
With the $13 million research project, scientists believe they will learn more about how, where and when uranium binds to the soil, moves with the ground water, then binds with the soil again, with some of it eventually reaching the Columbia River.
Among the key issues are the daily and seasonal fluctuations in the level of the Columbia River, creating what Thompson describes as a washing-machine action in the uranium contamination.
Scientists want to know more about how the different chemistry of the river water and ground water from various sources affects the uranium contamination, how the ground water moves and how thin layers of sediment in the soil bind and release the uranium.
"Sites like these are complicated scientifically and the action is below ground where you can't look at it," Zachara said.
During World War II and the Cold War when plutonium was made at Hanford for the nation's nuclear weapons program, the 300 Area just north of Richland was used to make uranium into fuel for reactors. As a byproduct of the process, 60 tons of dissolved uranium was released into the ground in disposal ponds and trenches in the 300 Area.
The vast majority of uranium contamination was in the top 15 feet of soil, which has been dug up, Thompson said. But the lighter contamination deeper in the soil appears to be acting as a persistent and long-term source to keep recontaminating the ground water near the Columbia River.
This summer the national lab research project began with the drilling of 35 wells 60 feet deep that form a triangle centered on the location of the first disposal pond used for the release of uranium-contaminated water. Each side of the triangular array of wells is about 65 yards long.
They're equipped with sensors that can detect temperature and measure electrical resistivity. That allows an in-depth look at information such as the consistency of underground soil and the underground movement of water from different sources -- rain, ground water and river water.
The first use of the wells calls for injecting tracers of salt and varying temperatures into the ground to follow their movement.
Later tests are proposed to include reinjecting contaminated ground water from the uranium plume to observe the behavior of the uranium.
DOE's goal is to understand enough about the properties of the 96 acres of ground water contaminated with uranium at the 300 Area to find ways to restore it to drinking water quality.
Although the uranium enters the river just upstream from the Richland city water uptake, the river almost immediately dilutes the contamination to easily meet standards for drinking water.
The research project is planned to be completed in five years. It's being paid for with a competitive grant the national lab won in DOE's Field-Scale Subsurface Research Challenge.