Engineers Find Volcanic Mineral’s Affinity For Strontium-90 Makes It Ideal Choice For West Valley Cleanup

WEST VALLEY, N.Y. -- Starting this month, the same material cat-lovers use to sanitize their pets' litter boxes will be used to remove strontium-90 from groundwater in a pilot project at the West Valley Demonstration Project that is based on successful testing of the technology at the University at Buffalo.

The site is the first in the U.S. to use an underground barrier constructed of clinoptilolite (the technical term for this type of cat litter, which is actually a zeolite mineral) for groundwater remediation. The project is being watched closely by operators of other Department of Energy sites.

If the project proves successful -- and extensive lab testing and mathematical modeling at UB strongly suggest that it will be -- it will provide nuclear sites with what UB engineers say is a rare commodity: a cost-effective remediation alternative to pump and treat.

"We are delighted that UB's engineers are putting to use such an enormously cost-effective method for cleaning contaminated groundwater," said UB President William R. Greiner. "The innovative work of Professor Rabideau and his team has great potential, not only for West Valley, but for other U.S. Department of Energy nuclear sites as well. It's a classic win-win situation: matching the expertise of UB's researchers with a community need. Everyone benefits."

Added Mark Karwan, dean of the UB School of Engineering and Applied Sciences: "This is another excellent example of UB's partnership with government and industry to help provide technical solutions to issues of importance to society. Dr. Alan Rabideau and his colleagues have helped provide the scientific basis on which this important project can proceed."

The West Valley Demonstration Project, managed by West Valley Nuclear Services for the U.S. Department of Energy and New York State, has been an innovator in demonstrating cost-effective environmental technologies. For example, since 1996, the Western New York facility has been successfully turning high-level nuclear waste into glass cannisters through a process termed "vitrification."

This month, construction will begin on an underground trench measuring 30 feet deep, 28 feet long and 6 feet wide that will contain a permeable treatment wall. Once the trench has been dug, it will be filled with zeolite, a natural volcanic material used for applications ranging from cat-litter boxes, horse stalls and turf grasses to waste-disposal projects. The clinoptilolite selected by West Valley has a particularly strong preference for strontium over other ions.

How did cat litter turn into the substance of choice for remediating contaminated groundwater?

According to the UB engineers, the zeolite's honeycomb structure provides significant internal surface area, allowing for a "high cation exchange capacity," meaning that dissolved ions in the groundwater -- such as strontium -- easily can replace the naturally occurring ions attached to the zeolite.

The same characteristics make clinoptilolite suitable for cat litter: the hollow structure of its particles helps with the removal of moisture and odor.

"It turns out that clinoptilolite has a strong preference for strontium over the other substances dissolved in groundwater," said Alan Rabideau, Ph.D., UB associate professor of civil, structural and environmental engineering who led the research that verified the performance of the zeolite for this application.

"It's somewhat analogous to a water filter that you might use in your kitchen," he said, noting that the zeolite "filters out" the strontium-90, leaving the groundwater free of contamination.

As an alternative to pump and treat, a process now under way in an adjacent area of the groundwater plume at West Valley, Rabideau said that the zeolite technology has two major advantages: cost and overall effectiveness.

"It has cost West Valley up to $1 million per year to operate a pump-and-treat system for a portion of the groundwater plume," explained Rabideau. "Pump-and-treat has kept the front end of the plume from significantly moving, but the extracted water must be treated and disposed of, and very little of the total strontium is actually removed from the soil. On the other hand, the treatment wall will cost about $1 million to put in place, and, according to our models, should remain effective for over 25 years."

He added that since it takes strontium-90 about 28 years to naturally decay, it is possible that construction of another treatment wall with the zeolites will be unnecessary.

"It's a no-brainer," Rabideau said. "Here, we have a project that may have a one-time cost of $1 million versus one that may have a yearly cost of $1 million, with no clear end in sight."

According to West Valley officials, the design of the treatment wall at West Valley provides for the passive treatment of groundwater; that is, the water will not have to be collected, diverted, channeled or pumped during operation. Groundwater simply will flow through the permeable treatment wall, where it will be cleaned by the zeolite; samples will be taken regularly to assess how the treatment wall is performing.

Rabideau pointed out that a field-scale, zeolite treatment wall has been attempted only once before, at the Chalk River Nuclear Laboratories, a facility run by the Atomic Energy of Canada, Ltd. in Ontario, Canada. However, he said, the Chalk River project differs significantly from the West Valley installation because it uses active pumping to direct the groundwater through the wall prior to discharging it to a nearby stream.

The application at West Valley is the first time the technology will be tested in the field as the exclusive cleanup method for a particular problem area.

West Valley officials and UB engineers noted that since the contaminated groundwater plume is not expected to reach drinking water sources, it is not a threat to public health.

"However, the idea that the water has some measurable level of radioactivity in it is uncomfortable for all parties involved," explained Rabideau, "and that's why it is being cleaned up."

Bob Campbell, president of Westinghouse/West Valley Nuclear Services, said, "This cleanup is one of many complex tasks that we have to carry out in order to complete the project. We're happy to have the expertise that the engineers at UB continue to provide."

Rabideau's co-principal investigator on the project is John VanBenschoten, Ph.D., associate professor in the UB Department of Civil, Structural and Environmental Engineering. Others that worked on the project include former doctoral student Chih Huang, Ph.D.; Todd Snyder, instructional support specialist; Chandra Ganguly, UB doctoral candidate, and Amita Patel, Amy Chang, Yongrong Zhgang and Mohamed Bagha, all master's students.

West Valley scientists working on the UB component of the project include Beth Fallon, project manager; Mark Hemann, senior hydrologist; Craig L. Repp, manager of environmental projects, and Bob Steiner, senior environmental engineer.

A subsidiary of Westinghouse, West Valley Nuclear Services manages the West Valley Demonstration Project under contract with the Department of Energy and in cooperation with the New York State Energy Research and Development Authority.