Cleaning Underground Aquifers: Unique Two-Part Process Helps Remove Sources of Contaminants

The patent-pending technique, which uses a macroemulsion composed of alcohol and food-grade surfactants, simultaneously reduces the density of the pollutant - to keep it from sinking farther into the groundwater - and helps separate it from soil particles so it can be flushed out. Known as "density modified displacement," the approach could cut the cost of environmental remediation by reducing both the time required for clean up and the amount of contaminated effluent that must be treated.

The technique was reported in the September 15 issue of the journal Environmental Science and Technology. Researchers from the Georgia Institute of Technology, the University of Michigan and the University of Oklahoma participated in the research, which was sponsored by the U.S. Environmental Protection Agency (EPA), Great Lakes Mid-Atlantic Center for Hazardous Substance Research.

"We're trying to make remediation of contaminated groundwater more efficient, because it is now largely driven by economics," said Kurt Pennell, an associate professor in Georgia Tech's School of Civil and Environmental Engineering. "The idea is to make this process so efficient that the cost of cleaning up a site is less expensive than traditional approaches which rely on groundwater extraction and long-term monitoring."

The technique offers a new approach to removing dense nonaqueous phase liquids (DNAPLs), including tetrachloroethane (PCE), trichloroethene (TCE) and chlorobenzene (CB). Relatively stable chemicals that don't readily degrade, their concentrations in groundwater must be kept to a few parts-per-billion (ppb) to meet environmental standards.

"A single 55-gallon drum of one of the compounds can contaminate hundreds of thousands of gallons of groundwater," Pennell noted.

Established remediation techniques (pump and treat) often rely on pumping large amounts of contaminated water out of the ground, flushing the pollutants with it. However, these techniques require large volumes of water and may need to be operated for decades. The cost of treating the contaminated water and the time required make this approach very expensive -- and serves only to contain the contaminated groundwater.

The approach developed by the Georgia Tech team could allow remediation engineers to directly address pollution mass removal, with recovery rates exceeding 90 percent.

"Our approach is to aggressively treat the source zone where the actual spill occurred and remove the compound, then separate and treat or recycle it above ground," Pennell explained. "We are trying to remove the long-term source of groundwater contamination in a manner that will produce the most results for the least cost. It's generally not economically feasible to treat an entire aquifer."