Staff Reports
WC Monitor
11/20/2015
Washington Closure Hanford has completed digging up most of the chromium contamination near the Columbia River at the Hanford Site, excavating down to more than 85 feet in some places and removing more than 2 million tons of tainted soil. Any remaining work, which could be required near the K East and K West reactors, would be done by another contractor after Washington Closure’s contract expires next fall. “Removing 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, Washington Closure director of closure operations, in a statement.
Washington Closure found “the mother lode” of chromium contamination near the D and DR reactors, Hanford officials have said. The heaviest concentration of the contaminant was found there, staining the soil a yellow-green color. Three huge holes were dug near the D and DR reactors to chase chromium down to groundwater 85 feet deep; workers then dug another 10 feet into wet sand and rock because of the heavy contamination there. Last year, Hanford officials saw the level of contamination in groundwater there start to drop. “Removing the source of contamination is a critical step in protecting groundwater, and 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, Department of Energy project director for the river corridor.
The D and DR reactors and H Reactor, where chromium also was cleaned up, are at the horn of the Columbia River as it passes through Hanford and are near salmon spawning beds. The level of contamination there could be cleaned to standards protective to aquatic life, which are more stringent than for humans, in the next decade now that more contamination has been largely stopped from reaching the groundwater, said Dennis Faulk, Hanford program manager for the Environmental Protection Agency. The type of chromium contamination at Hanford is particularly toxic to fish.
The largest hole near the D and DR reactors was the size of seven and a half football fields at the surface of the ground and one football field at the bottom, according to DOE. It and other excavations down to groundwater near the C Reactor were so large that they were engineered like open-pit mines. Holes were designed with gently sloped sides at the top to prevent cave-ins, giving way to steeper slopes about halfway down. They were built in layers, with a safety shelf every 15 to 18 feet to catch any falling rocks, at the D and DR reactor area.
Chromium also was excavated near the F and H reactors down to groundwater about 40 feet deep. Not much contamination was found near F Reactor, and contamination diminished as workers dug deeper near the H Reactor, Faulk said. Sodium dichromate, which was added as a corrosion inhibitor to river water used to cool the reactors, was brought to the reactors in railcars in large quantities and then diluted for use in the plants. It leaked from piping systems near the reactors or spilled to contaminate the soil. Chromium contamination was not an issue at Hanford’s most modern reactor, N Reactor, which had a different design and used a closed-loop cooling system. The soil near the K East and K West reactors could be contaminated, but efforts there now are focused on removing radioactive sludge from the K West Basin.
The excavated areas near the reactors have been backfilled with clean soil, and some areas already have been planted with native vegetation. Planting will be finished soon near the F, H, D and DR reactors as part of 280 acres total of excavated waste sites near the Columbia River ready for revegetation. With the exception of contamination near the K East and K West reactors, Washington Closure workers are down to a few last soil waste sites to be remediated near the Columbia River, Faulk said. “We take a lot of pride in knowing we are protecting the environment and the contamination is no longer a threat to the Columbia River,” Cantwell said.
