NGWA.org Ground Water Monitoring & Remediation 1

© 2012, The Author(s)Ground Water Monitoring & Remediation

© 2012, National Ground Water Association.doi: 10.1111/j1745–6592.2012.01399.x

Building the Wall

Permeable Treatment Wall Removes Sr-90 and Earns AMEC an NGWA Outstanding Groundwater Remediation Award

BY REBECCA VANDERMEULEN

The Western New York Nuclear Services Center opened in 1961 about 30 miles south of Buffalo,

New York. The 3300-acre site was used for the reprocessing of spent nuclear fuel and disposal of nuclear waste. A total of 640 metric tons of spent fuel was processed there between 1966 and 1972, when the plant was shut down so its capacity could be increased.

After the facility closed, however, new federal regulations were issued for places like the Western New York Nuclear Services Center. Rather than design the plant to fit these require-ments, the company that operated it decided to get out of the nuclear fuel processing business altogether.

A subsequent decision from the U.S. Department of Energy was made to decommission the plant and turn the land over to New York State. Removing the nuclear waste that remained on the site—the land has been renamed the West Valley Demonstration Project—proved to be a decades-long challenge that is not expected to be complete until about 2020.

A single pass trencher is in action as it helps build a permeable treatment wall at the West Valley Demonstration Project site in New York. The wall was designed by the engineering firm AMEC. The wall is designed to remove Sr-90 from a 1000-ft plume.

2 R. VanderMeulen/ Ground Water Monitoring & Remediation NGWA.org

successfully reduced discharge of the isotope to water on the surface, but the contaminated groundwater continued to flow.

Another solution was in order.Biedermann’s firm built a 35-ft

wall in 1999 to test how well a per-meable treatment wall would work. Biedermann, who was the project manager, says the idea was to assess whether a zeolite would sufficiently remove Sr-90 from the groundwater. The pilot wall used a zeolite called clinoptilolite, which was largely effec-tive. However, the wall exposed other design flaws.

For one, the design included a retaining wall made of steel sheet pil-ing. The metal was driven into clay-like soil that created areas where the zeolite was impermeable. That, along with its short length, lowered its effectiveness. “The groundwater had an opportu-nity to go around the wall rather than through it,” Biedermann says.

After this pilot project, his com-pany contacted AMEC in 2007 and asked the firm to design a new wall. Frappa had been involved with West Valley since the mid-1990s, when he worked for another engineering firm and had studied alternative methods of addressing the groundwater plume.

“We wanted to put in a system that was passive,” Biedermann says. “We wanted a system that would sit in the wall and work by itself, and all we would have to do is monitor it.”

Frappa turned to Rabideau, a pro-fessor at his alma mater who had been studying zeolites since the 1990s.

The project required a zeolite that will remove strontium in the presence of high levels of calcium and magne-sium, which naturally compete for the zeolite surface. In addition, it would need to resist crumbling and allow the West Valley groundwater to easily pass through the wall.

Over the next two years Rabideau and Shannon Seneca, a student in his doctoral program, evaluated two zeolites—one from a mine in Idaho and one from an Oregon mine—and assessed how well they filtered Sr-90. Some of their tests involved ground-water from the West Valley site.

These tests demonstrated that a zeolite from the Bear River Zeolite mine in southeastern Idaho, containing

“As the groundwater flows through the wall, it removes the strontium,” Frappa explains. “The strontium levels inside the wall are very low, if detect-able at all, so it’s showing that the zeolite is removing the strontium from the water.”

Alan Rabideau, Ph.D., PE, a professor in the Civil, Structural, and Environmental Engineering Department at the University at Buffalo, conducted research on the most effective zeolite to use for the treatment wall. The wall’s design for continuous in situ treatment was the first one like it in the world, and Rabideau knows of only one similar system that now exists elsewhere.

Frappa says working with state and federal officials, along with the various private stakeholders involved, was one of the project’s challenges. Finding a solution that met the needs of all was satisfying.

“Once we had buy-in, I think everyone was looking forward to see-ing how this technology would work,” Frappa says.

Finding the ZeoliteA pump and treat system was

installed in 1995 at the West Valley Demonstration Project in an attempt to remove Sr-90 from the water at the beginning of the plume. The system

One problem was a 1000-ft plume of groundwater flowing from the plant. The plume was contami-nated with strontium-90 (Sr-90), a by-product of nuclear fission that is often found in waste from reactors. The U.S. Environmental Protection Agency says the isotope has been linked to bone cancer and leukemia.

An additional challenge is that the contaminated groundwater was not flowing in just one direction. Rather, it flowed north and branched into three different directions. However, no Sr-90 has been located off-site, says Charles Biedermann of consulting firm CH2M HILL B&W West Valley, which the Department of Energy appointed to run part of the decom-missioning project.

After an unsuccessful attempt at using a pump and treat system to remove the isotope from the ground-water, the Sr-90 now appears to be contained by an 860-ft permeable treatment wall designed in partner-ship with engineering firm AMEC. The $7.1 million project was honored with an Outstanding Groundwater Remediation Award from the National Ground Water Association in 2011.

Rick Frappa, PG, principal hydrogeologist at AMEC’s office in Amherst, New York, explains that the wall is filled with a zeolite specially chosen for its affinity for Sr-90.

Aerial view of the location showing the 860-ft-long permeable treatment wall (PTW). It starts in a tight space between two buildings on the left and is oriented east until it dog-legs to the south. White sacks containing zeolite are also evident in the right side of the photo.

NGWA.org R. VanderMeulen/ Ground Water Monitoring & Remediation 3

However, Biedermann says tests from the 86 on-site monitoring wells are showing that the wall is performing as planned. While it will take time for the flow to settle into a state of equilibrium, so far Sr-90 has not been detected in the wall.

Frappa expects the wall to last for two decades, requiring no care beyond monitoring for performance. After 15 or 20 years, a team will have to reevaluate it to determine what to do next. For example, conditions could dictate that parts of the wall be replaced, the wall be lengthened, or a similar wall constructed downstream of the groundwater.

“The fundamental design of such a barrier depends on the fact that it will have to be replaced,” Rabideau says.

However, he adds that even after 20 years, the wall may be able to remain as is. Since the isotope has a half-life of 28.8 years, it is possible that the Sr-90 at West Valley could remain at a safe level simply through the natural process of decay.

“We had a lot of experts giving us their ideas and their thoughts,” Biedermann says of the wall’s con-struction. “It was quite an impressive sight.”

Rebecca VanderMeulen is a freelance writer living in southeastern Pennsylvania. Her work has also appeared in NGWA’s Water Well Journal.

The way it works is relatively simple: Groundwater flows toward the wall and then through it, with the zeolite in the wall removing the Sr-90 and resulting in water that is not contaminated.

The wall was constructed in the fall of 2010. Since the contractors were working with potentially radio-active material, AMEC decided to use a machine called a one-pass trencher to reduce workers’ contact with the soil. As the soil was excavated, Frappa explains, the zeolite was added in its place.

He admits that at the outset, he was unsure of what to expect out of the wall. In the worst-case scenario, he says, the contaminated groundwa-ter would have been backed up and ended up contaminating water beyond the wall itself.

about 85% clinoptilolite along with a mixture of nonreactive minerals, was cost-effective and had the properties AMEC was looking for. Samples of the zeolite were tested at the mine itself to ensure quality. “A mine will produce material, but some of the qual-ity is different depending on where you are at the mine site,” Frappa says.

Building the WallFrappa and his team designed a

wall that was 860 ft long, 39 in. wide and up to 30 ft deep. All told, it con-tains about 2300 metric tons of zeolite from the Bear River mine. It was built in an area that would catch the plume of groundwater contaminated with Sr-90, but not allow it to advance off the former nuclear fuel site or into surface water.

Diagram indicating the permeable treatment wall location in relation to the site topog-raphy and groundwater plume location.

Award DetailsInformation on the National Ground Water Association’s awards program is available on its Web site. Find out past winners and how to honor indus-try leaders and outstanding projects. Go to www.ngwa.org/About/awards/.