Scientists use natural bacteria to help break down solvents in groundwater

Linking research to operations.

Idaho National Engineering and Environmental Laboratory scientists are demonstrating a faster, more effective, less expensive way to clean up groundwater contaminated with hazardous solvents by using microbes.

"We're very excited about it," said Kent Sorenson, principal scientist/engineer on the INEEL's Test Area North groundwater cleanup.

"It's fun to find new solutions to serious contamination problems that are worldwide issues. Any site that has residual solvents contamination is potentially amenable to this approach. "

The INEEL has been proving the effectiveness of bioremediation during the past two years with ongoing cleanup of a two-mile-long, half-mile-wide solvent contaminations plume in groundwater beneath Test Area North. The innovative techniques that are destroying hazardous trichloroethene (TCE) also have great potential to clean up similar pollution that plagues groundwater in many other places worldwide.

Enhanced In Situ Bioremediation

At Test Area North, Sorenson and his INEEL colleagues have developed a way to greatly improve the ability of natural subsurface bacteria to break down the chlorinated solvent. They are doing it by injecting a common food-grade preservative, sodium lactate, into the upstream part of the contaminated plume where pollution concentrations were highest.

It's working. Contaminant concentrations have decreased dramatically since 1998, when INEEL started using the technique.

"I think it's very marketable'" Sorenson said. "Chlorinated solvents are the most common groundwater contaminants at hazardous waste sites and municipal landfills in the United States."

He noted that area communities looking for ways to clean up TCE-polluted groundwater include Pocatello and Boise in Idaho and Bozeman, Montana.

The project is a prime example of how INEEL is integrating science with its environmental restoration mission at Test Area North, said Lance Peterson, technical manager of innovative treatment technologies for the groundwater cleanup. "We did that. It was a huge challenge."

For about 20 years until the mid-1970's workers disposed of waste TCE by injecting it down a well at Test Area North - a common practice at industrial sites in those days.

Data show that the best, fastest, least expensive way to clean up the groundwater is to:

• Use enhanced in situ bioremediation instead of pump-and-treat in groundwater around the old injection well, in what was the most contaminated part of the plume.
• Use pump-and-treat in the part of the plume with medium concentrations of contamination.
• Use a second innovation called monitored natural attenuation in the outer edges of the plume.
  

Monitored Natural Attenuation

With monitored natural attenuation, periodic groundwater samples are gathered at strategically placed monitoring wells to confirm computer models that INEEL scientists have developed. These models predict that TCE in the most polluted part of the plume will break down to harmless byproducts naturally before it will pose a threat to people or the environment - achieving cleanup in that part of the plume for less money than using pump-and-treat would cost.

"This is what INEEL's Subsurface Science Initiative is intended to be - research and development - looking at processed that occur in the subsurface and controlling those processes in a way that beneficially affects contamination problems," Sorenson said.