The Natural Attenuation Software (NAS) was developed with funding from the U.S. Navy and in collaboration with U.S. Geological Survey for application to ground water systems. It was designed to help environmental cleanup professionals estimate how far underground plumes of contamination will migrate from a source, such as a solvent spill or underground gasoline storage tank leak, and how long cleanup will take with natural attenuation in various environments with or without use of remediation technologies.

“The ability to return contaminated ground water to a pristine state is limited, so a heavy emphasis is placed on meeting achievable remedial action objectives,” says Mark Widdowson of Blacksburg, professor of civil and environmental engineering at Virginia Tech. “We want to at least limit the damage and to have an objective we can reach, such as to reduce the size of the contamination plume and to take advantage of the natural attenuation capacity of an aquifer.”

Natural attenuation is when, under the right conditions, microbes and minerals in the earth bind to or degrade contaminants into less harmful compounds. “But all things are not equal from site to site,” Widdowson says. “For example, contaminants at sites in the U.S. West, where there is less moisture and carbon in the soil, often degrade more slowly than at sites in the East.”

The first step is to define the site, then remediate or remove the source area as much as possible. “A plume is a symptom. We want to reduce the mass in the source and the amount of material that leaves the source. Then we want to take advantage of a sites attenuation capacity,” Widdowson explains.

“Once site data - the type and numbers of contaminants and site characteristics - are entered into NAS, you can decide what level of remediation should be performed to meet the goal and how long it will take to clean up the site,” Widdowson notes.

“The software lets you ask 'what if?' 'What if we remove 50 percent or 80 percent of the mass, how much benefit will there be over what time?' 'What if we remediate the source for 12 months, what will the response be in 10 years, 20 years and 50 years?'” Widdowson says. “The software does not simulate the intricacies of the remediation process, but goes to expense and effort. We think this software will help save hundreds of thousands of dollars at each site and up to a billion dollars over the long haul.”

Tests recently have been completed at eight different sites with funding from the Department of Defense Environmental Security Technology Certification Program.

The eight DOD test sites, located on the U.S. West Coast, Southeast, and Northeast, were diverse in terms of geography, hydrogeologic settings and contamination source, and they were sites with long-term data sets.

The researchers used the information history already had presented to confirm the results the software predicted when site conditions were entered. “We tested how well the software replicated results,” Widdowson says. “Then we did predictions continued or for alternative remediation strategies.”

The researchers also tested the software with incomplete data, “because all the desired information is not necessarily known. It's always a case of how good the data is. In the process, we made the software more flexible for people to use,” Widdowson reveals. The NAS is available free at www.nas.cee.vt.edu.