Savannah River Site workers once relied on toxic solvents to clean machinery at the nuclear weapons complex.
Today, those solvents have contaminated ground water beneath 5 to 10 percent of the 310-square-mile site, according to scientists.
Now they're relying on nature -- aided by bacteria and subterranean steam -- to clean up the problem.
It will take millions of dollars and many years to clean the mess -- but if some SRS scientists are correct, the effort might not take as long as once thought.
"We have a toolbox of technologies," said Christopher Bergren, a deputy project manager for Bechtel Savannah River Inc., which is completing some ground water cleanup for the site's owner, the U.S. Department of Energy.
"Depending upon the conditions, we go to the toolboxes and pull out the appropriate technologies."
One of those methods, bioremediation, uses nature to break down solvents within the soil. Workers pump air, methane and other gases through horizontal wells that extend hundreds of feet beneath an inactive landfill.
Bacteria thrive upon the gases. As the colonies of microbes grow, they produce enzymes that break down the solvents within the soil, said James Kupar, an environmental engineer for Bechtel.
Bioremediation avoids some problems of more traditional cleanup methods, because it destroys the pollutants in place, rather than requiring workers to remove them and dispose of them elsewhere, Mr. Kupar said.
"This is about as simple as it can get for a remediation project," he said. "You're not impacting the environment. You're not removing anything or having to replace anything."
The cleanup at one site -- a former 55-acre landfill -- is expected to take about six years, at a cost of about $500,000 per year, said Ronald Socha, Bechtel's project leader.
By using horizontal wells instead of traditional wells perpendicular to the soil, site officials saved about $1.6 million, he said.
Scientists will deploy another new method in nearby "M-Area," where workers once manufactured nuclear fuel for the site's five nuclear reactors.
The technology, called "dynamic underground stripping," uses steam to remove solvents from the soil.
Workers will inject steam into a polluted area where solvents once were stored, Mr. Kupar said. The steam's pressure should force contaminants to a nearby well where they can be removed, he said. The superheated oxygen within the steam further breaks down the chemicals, he said.
SRS will be only the third site nationwide to use the method, which is expected to take one year, Mr. Kupar said. If workers used older technologies, cleanup would take 30 years, he said.
"It's sort of like taking a sledgehammer to kill a fly," he said. But that "sledgehammer" approach makes the method too expensive for use in many areas, Mr. Kupar said.
The geography in many contaminated areas also is unsuitable for drilling horizontal wells. At most contaminated sites, workers continue to use slower, more traditional methods of cleanup.
The U.S. Department of Energy, which owns SRS, does not have a legal deadline for cleaning the groundwater, said Rick Ford, an Energy Department spokesman at SRS.
The department must only treat water until it meets the standards mandated by the federal Clean Water Act, he said.
Some nuclear-watchdog groups remain displeased with the course of SRS efforts to clean groundwater, saying the U.S. Department of Energy should pursue cleanup more aggressively.
"We're extremely concerned that SRS is pursuing new and ongoing missions when they haven't even cleaned up past contamination," said Rita Kilpatrick of Campaign for a Prosperous Georgia. "The federal government needs to take full responsibility for SRS contamination and ensure cleanup right away."
The site's Citizens Advisory Board has hired a consultant to assess the success rate of cleanup efforts in the site's A- and M-Areas, a board member said.
"What we're concerned about with the plume cleanup is whether or not we're getting our money's worth," said Bill Lawless, co-chairman of the board's environmental restoration and waste management committee. "As citizens, we want to make sure that the money that is being spent is being spent wisely."
For cleanup efforts to be successful, new methods might be needed, Dr. Lawless said. An older method -- which pumped water from the earth, stripped it of solvents, and reinjected it into the soil -- probably has run its course, he said.