Geophysicist develops method for finding underground contaminants

When a property is suspected of having contaminated soil or groundwater, it is usually a lengthy and costly process to confirm the presence of pollutants and to delineate the extent of the contamination. Soon that process may be simplified considerably.

University of Rhode Island geophysicist Reinhard Frohlich, an associate professor of geosciences, has devised a cost-effective, new method for finding underground contaminants that will reduce drilling and digging beneath the surface. By inserting two metal spikes in the ground at various distances and connecting them to an electric current, Frohlich can measure the voltage between the spikes and determine the resistivity of the soil, which tells him if the soil is polluted.

“My initial objective was to do an experiment at the surface that would explain what was going on beneath the surface,” said Frohlich, whose research was funded by a $55,000 grant from the U.S. Environmental Protection Agency.

Resistivity measurements, which calculate a material’s opposition to the flow of electric current, are widely used to track contaminated salts dissolved in groundwater because they are good conductors of electricity. But Frohlich’s experiments focused on finding organic compounds like toluene, benzene, xylene, ethylbenzene, phenol and other cancer-causing substances that do not conduct electricity.

“Our system seems to work very well on all organic compounds. Resistivity increases significantly in areas where the aquifer is polluted compared to clean areas,” he said. “We should be able to use this as the first step in the remediation process because it’s quicker and allows us to drill fewer borings into the aquifer.” Frohlich tested his system at the Picillo Pig Farm in West Coventry, a Superfund site where illegal dumping of chemical waste was discovered following an explosion in 1978. The R.I. Department of Environmental Management and the EPA have been monitoring and cleaning the site for more than 20 years.

“The Picillo Farm is a suitable site for our experiments because the results can be compared with the many monitoring wells and other analyses that have been conducted there over the years,” Frohlich said. In addition to field tests at the Picillo Farm, Frohlich conducted controlled laboratory tests comparing clean soil with contaminated soil of known composition.

His study will next attempt to quantify the amount of contaminants at a given location. “It’s one thing to identify a clean or contaminated site, but we want to also get a quantitative value for the contaminants,” said Frohlich. “That’s something that the EPA would really like to be able to do.”