Wash. Closure Removes Chromium Source
WC Monitor
6/6/2014
The largest source of chromium contamination near the Columbia River at Hanford has been removed after workers excavated contaminated soil down to groundwater 85 feet deep. Over the years Hanford officials had talked about finding the mother lode of chromium in the soil that was contaminating groundwater near the D and DR Reactors and then the river, said Mark French, Department of Energy project director for the work. “Once we started digging, it became obvious this was it,” he said. Two new groundwater treatment systems have been built near the horn of the Columbia River as it passes through Hanford, one near the D and DR Reactors and another nearby close to the H Reactor. Together they can treat 50 million gallons of contaminated water a month, replacing a smaller system that began operating in 1997. But the level of contamination was not dropping because the groundwater was being recontaminated with chromium in the soil, said Dwayne Crumpler, a hydrogeologist for the Washington State Department of Ecology. Now some initial tests show promise that the level of contamination in the groundwater is starting to go down, he said. “We’ve got the source,” he said.
Sodium dichromate, which was added as a corrosion inhibitor to river water used to cool Hanford reactors, leaked from pipes or spilled to contaminate the soil. The hexavalent chromium contaminating Hanford groundwater is particularly toxic to fish and other aquatic life, including salmon fry from spawning areas in the river near the D and H reactors. To remove the contaminated soil, a Washington Closure Hanford team dug down to groundwater at three places near the D and DR Reactors. Two of the dig sites would merge into one near the D Reactor, but the other dig site is the largest. Enough soil was excavated there to create a hole covering the area of about seven and a half football fields at the ground’s surface and about one football field at the bottom. Because of its size, the hole had to be engineered like an open pit mine. It was designed with gently sloped sides at the top to prevent cave ins, giving way to steeper slopes about halfway down its 85 foot depth. It was built in lifts or layers of 15 to 18 feet, each with a safety shelf to catch any falling rocks.
This is the second time that Washington Closure has dug up chromium-contaminated soil down to groundwater 85 feet deep near the river. The strategy was used successfully near Hanford’s C Reactor in an excavation completed in 2012. Among the tips picked up from the first deep dig was the value of collecting samples of soil as the excavation was in progress, French said. In some places the chromium contamination is obvious, marked by a bright green-yellow stain, but soil contaminated with lower levels of chromium was not always discolored. Workers also learned to put down thick pads to be linked together to keep truck tires from becoming contaminated. Work was carefully managed, with trucks coming and going up and down ramps into the hole, to complete the project safely, French said.
Backfilling to Begin This Fall
About 785,000 cubic yards of soil was removed at that largest dig site and about half as much was removed from the combined smaller site. About a third of that soil was contaminated and was disposed of at the Environmental Restoration Disposal Facility in central Hanford. The most heavily contaminated soil was treated to contain the chromium before it was added to the landfill. Some of the clean soil removed from the holes was used to backfill a nearby area excavated as part of earlier environmental cleanup work. But the rest of the clean soil has been piled around the holes, said Dean Strom, the Washington Closure project manager overseeing the work.
Digging has stopped, but Hanford officials are waiting for testing of samples to be completed to confirm that chromium contamination is gone. Then work to backfill the holes will begin, likely in October, Strom said. Refilling the holes is expected to take about eight months. Then the surface of the ground will be replanted, likely starting in late 2015. Removing the chromium contamination from the soil was significant, in part, because contamination was already reaching the river, French said. Longer term it will reduce the time that groundwater treatment systems need to be operated, he said.
Iron in Soil May Block Tc-99 Contamination
WC Monitor
6/6/2014
Naturally occurring iron in Hanford soil may help protect the Columbia River from technetium-99, according to research at the Pacific Northwest National Laboratory. Kevin Rosso, the associate director for PNNL’s Physical Sciences Division and other scientists, investigated the ability of iron-rich minerals in Hanford soil to change technetium 99 into a form that sticks in the soil. It is information that Hanford officials might find useful as they make decisions about Hanford cleanup, considering that groundwater may be at higher risk where soil has less iron, Rosso said. Research was funded by the Subsurface Biogeochemical Research program within the Department of Energy’s Office of Biological and Environmental Research.
Technetium-99 has contaminated soil and groundwater in central Hanford, where an estimated 1 million gallons of waste from fuel reprocessing has spilled and leaked into the soil. In addition, more than 450 billion gallons of contaminated liquid was discharged into the soil in central Hanford. The technetium left from reprocessing fuel is water soluble, allowing it to be carried with water from rain or snow melt deeper into the soil toward groundwater. Some technetium is being removed from groundwater in central Hanford at the 200 West Pump and Treat Facility, but removing technetium in soil that is deep underground to prevent it from reaching groundwater is difficult.
Rosso found that in the lab, ferrous iron reacts with the soluble form of technetium found in Hanford soil to convert it to a nonsoluble form. “It gets it off the freeway,” he said. Researchers collected samples from two locations in central Hanford to check for iron-bearing minerals—the open trenches used to dispose of reactor compartments from the U.S. Navy’s nuclear-powered submarines and cruisers and the 70-foot-deep Environmental Restoration Disposal Facility. The locations were picked because researchers could easily gather below-ground samples. The samples contained up to 1 percent of magnetic minerals, and 90 percent of that was magnetite, a small black grain with ferrous iron on the surface that interacts with technetium to make it less mobile in the soil. Research was done at the Environmental Molecular Sciences Laboratory, a national facility on the PNNL campus with advanced microscopy and spectroscopy equipment. Next PNNL researchers plan to look at whether an iron-rich clay mineral layer, which is found about 60 feet deep at Hanford along the Columbia River, also reacts with technetium to make it less mobile.
CHPRC Graduates Protégé Firm
WC Monitor
6/6/2014
CH2M Hill Plateau Remediation Co. at Hanford has graduated Project Services Group from the Department of Energy’s Mentor-Protege Program. Project Services Group, a small, disadvantaged business, provided planning, scheduling, estimating, project controls and work planning services. CH2M Hill mentored the company in business development and provided guidance, technical and senior management support. Since Project Services involvement with CH2M Hill began in 2007, the small company’s sales increase surpassed the 15 percent goal set in the mentor-protege agreement. “We have matured as a business and are now bidding on work as a lead,” said Greg S. White, Project Services Group president. “We’ve also expanded our customer base and reputation to secure larger companies like CH2M Hill to bid in support roles.” Partnerships with small businesses, such as Project Services Group, helps CH2M Hill perform its work and meet or exceed its subcontracting goals, said John Fulton, CH2M Hill president.
