Blacksburg, VA -- The contamination of ground water due to leaking storage tanks and pipelines has occurred for decades, and the effects of the pollution remain at hundreds of thousands of sites throughout the world. To combat this problem, experts are using in situ bioremediation, a developing technology that now accounts for nearly $870 billion in worldwide annual expenditures. A computer model for assisting engineers in cleaning up the polluted ground waters has been developed by Mark Widdowson, a Virginia Tech civil engineer.
Widdowson's began his research as a doctoral student at Auburn University. His thesis was on a computer modeling project for simulating the biodegradation of contaminants in groundwater. Now 12 years later, he has an improved Sequential Electron Acceptor Model, 3 Dimensional (SEAM3D)and the software has been accepted as the preferred bioremediation code by the Waterways Experiment Station (WES) of Vicksburg, Miss. The U.S. Department of Defense placed WES in charge of the national Groundwater Modeling System (GMS).
"The SEAM3D software is designed to model the distribution of contamination over space and time, including biological reactions," Widdowson explains. "It's a Fate and Transport Model."
For example, the software will indicate how widespread and how fast a contaminated body of underground water will spread. This knowledge might be particularly important if the contaminated ground water was nearing a wetland, a stream, or a reservoir.
"Most plumes of contaminants in ground water never exceed a certain size because they become stable over time. However, the key word is attenuation, brought about by the presence of microorganisms in the adjacent soil and/or water. We learned in the 1990s that these microorganisms are a major player in reducing the strength of the contaminated areas," Widdowson explains.
At many sites, the Environmental Protection Agency (EPA) favors monitored natural attenuation of sites, letting nature take care of the problem. However, it learned that engineering the bioremediation through the addition of oxygen and other nutrients to a contaminated site would stimulate the bacteria to speed up their work.
The SEAM3D computer model developed by Widdowson is the tool now used to determine how well microorganisms will respond to contaminated ground water at each site and whether or not nature can handle the problem alone.
Widdowson's model is able to track each individual contaminant, such as benzene, toluene, ethylbenzene, xylene, and the recently banned MTBE. It might show that one pollutant will biodegrade, but that the presence of the remaining ones will not, thus calling for the appropriate additional treatment.
An expert in hydrosystems and geoenvironmental engineering, Widdowson explains GMS is similar to a Windows software program for computers. "GMS serves as an interface for about a half a dozen codes for solving various ground water problems," he says.
He has partnered with the U.S. Navy to use SEAM3D to predict the spread of chlorinated solvents at its Little Creek Naval Amphibious Base in Virginia Beach. He is also using the software to simulate a controlled release of jet fuel at an Air Force base in Mississippi. And his model simulations of a gasoline-contaminated site near Beaufort, S.C. were instrumental in explaining why natural attenuation was ineffective.
The various projects he has conducted to date illustrate that microorganisms can help clean up some sites at a faster rate than others.