Tree Plantation Helps SRS Steer Contaminants Away From Waterways

AIKEN, S.C. – Scientists in the EM program are using a 62-acre plantation of pine trees and other natural resources to greatly limit radioactively contaminated groundwater from reaching waterways on the Savannah River Site (SRS).

The trees effectively act like a forest of tall hydraulic pumps, each drawing up irrigated water containing the contaminant tritium pumped from a nearby holding pond and harmlessly released into the atmosphere through photosynthesis. SRS produced tritium for use in the manufacture of nuclear weapons from the site's inception in the early 1950s until the end of the Cold War.

“With this project, we learned a lot about harnessing nature to continually move towards passive, low-energy, and sustainable cleanup technology with minimal cost,” said Philip Prater, senior physical scientist with DOE-Savannah River. “And it’s accomplished effectively without the generation of any waste.”

The extensive irrigation system uses piping and sprinkler heads to evenly spread the tritiated water over the forest floor debris. Large-scale evaporation also takes place during this process, releasing additional tritium into the atmosphere.

“We knew that capturing and containing the contaminated groundwater seeping to the surface and into a manmade pond would greatly limit this flow from eventually reaching the Savannah River,” said Jeff Thibault, an engineer with Savannah River Nuclear Solutions (SRNS), the site’s management and operations contractor. “However, the challenge was, how do you keep it from overflowing? We do so through the pine plantations irrigation system, which is extremely effective.”

U.S. Forest Service-Savannah River (USFS-SR) researchers and engineers with the EM program began designing this interim treatment in 1999 with the goal of reducing the amount of tritium reaching a creek known as Four-Mile Branch by 25%.

Since 2001, when the treatment began, approximately 190 million gallons of water — including nearly 7,000 curies of tritium that otherwise would have entered the Savannah River — has been harmlessly sprayed throughout thousands of loblolly pine trees.

“Traditional remediation costs associated with this level of tritium removal would be close to $220 million dollars over a 20-year period,” said Marsue Lloyd, USFS-SR civil engineer. “Our costs over that same span of time for this project are approximately $12 million dollars.”

Costs associated with phytoremediation are lower because only a few operators are needed, and the contaminated groundwater flows naturally to the surface without a need for mechanized pumping. In addition, the process, which includes 51 irrigation zones, is largely computerized for optimal evaporation efficiency.

Sampling and testing demonstrate that nearly 90% of the tritium within the water applied to the pine plantation is evaporated, according to Christina Logan with the Savannah River Ecology Laboratory. Logan collects samples and analyzes tritium levels in the irrigated soil.

Thibault noted that public concerns about managing contaminated water at SRS are understandable.

“However, test results validate the level of tritium found within the plants and animals affected by this process are so low as to be insignificant,” Thibault said. “The fact is, optimal water levels are being maintained in the pond while the evaporated tritium becomes virtually immeasurable beyond the irrigated section of forest, much less at the site boundary.”

Over the past 20 years, SRS has protected nearby waterways safely and cost-effectively, Thibault said.

“This project has been extremely effective and the data supporting this success has been verified by South Carolina Department of Health and Environmental Control officials,” Thibault said. “This project represents what can be accomplished through the partnership of multiple organizations sharing the same vision, building on the unique contribution each provides.”