Hanford workers have finished cleaning up much of the chromium in soil along the Columbia River, removing an estimated 129 tons of concentrated chromium before it contaminated groundwater that moves toward the river.
“Removing the chromium contamination keeps it from being driven into the groundwater by rain and snow and is a major success for protecting the river and groundwater from future contamination,” said Rob Cantwell, director of closure operations for Washington Closure Hanford, in a statement.
The form of chromium in the soil at the Hanford nuclear reservation can cause cancer in humans and is particularly toxic to fish and other aquatic life, including salmon fry from salmon spawning areas near the D and H reactors.
Sodium dichromate, which was added as a corrosion inhibitor to river water used to cool Hanford reactors, was brought in by rail car in large quantities and then diluted for use in the reactors. It leaked from pipes or spilled to contaminate the soil.
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Workers dug massive holes down at least to groundwater 85 feet deep in multiple places in two reactor areas to excavate contaminated soil. Because of their size, the dig sites near C Reactor, which is close to B Reactor, and the D and DR reactors were engineered like open pit mines.
One of the three holes dug near Hanford’s D and DR reactors covered the area of more than seven and a half football fields at the ground surface and about one football field at the bottom.
The hole was designed with gently sloped sides at the top to prevent cave ins, giving way to steeper slopes about halfway down its 85-feet-plus depth. It was built in layers of 15 to 18 feet, each with a safety shelf to catch any falling rocks.
The “mother lode” of chromium was found near the D and DR reactors, Hanford officials have said. The contamination was at the highest concentration there, staining the soil a yellow-green color.
Workers went about 10 feet deeper after hitting groundwater because of the high level of contamination. They were digging up wet sand and rocks.
Last year officials saw the level of contamination in the groundwater near the D and DR reactors start to drop.
“Removing chromium while it is in the soil will significantly reduce the amount of time that our groundwater pump-and-treat facilities are operated,” said Mark French, the Department of Energy project director for Hanford along the Columbia River, in a statement.
The groundwater cleanup facilities pump contaminated water out of the ground, remove the chromium and then return the cleaned water to the ground.
Groundwater in the the area near the D and DR reactors and the nearby H Reactor at the horn of the Columbia River as it flows through Hanford is expected to meet standards to protect fish in the next 10 years, said Dennis Faulk, Hanford program manager for the Environmental Protection Agency. Standards to protect fish from contamination are more stringent than those for humans.
Faulk is cautiously optimistic that because of the chromium dug up near the C and B reactors that a pump and treat system will not be needed for groundwater there.
Chromium cleanup also was done near the F and H reactors, which were among nine reactors that produced plutonium for weapons use during World War II or the Cold War.
Not much contamination was found near F Reactor, possibly because large amounts of water poured into the soil there when it was operating and may have moved flushed the contamination out of the soil.
At H Reactor, concentrations declined as workers dug down, Faulk said. Workers dug to about 40 feet deep at the H and F reactors, stopping when they reached groundwater.
N Reactor, Hanford’s most modern, had a different design and used a closed-loop cooling system.
Chromium near the K West and K East reactors still may need to be addressed. Work there is focused now on getting containers of radioactive sludge out of the K West Basin and moving it to central Hanford. It eventually will be treated for disposal.
There is a probability of finding chromium in the soil there based on what is known about the groundwater, Faulk said.
The approximately 2 million tons of contaminated soil dug up has been hauled to the Environmental Restoration Disposal Facility, a lined landfill in central Hanford. The most heavily contaminated soil is mixed with cement to contain the chromium before it is added to the landfill.
The excavated areas have been backfilled with clean soil and some native vegetation already has been planted. In November planting will be finished near the F, H. D and DR reactors as part of 280 acres total of excavated waste sites ready for vegetation.
With the exception of the area near the K East and West reactors, the soil cleanup of the other reactor areas along the river at Hanford is “very, very close” to being finished, Faulk said. “We just have to pick up a few straggler sites,” he said.