PLANT

CSI analysis is cleaning up groundwater


May 13, 2009
by Corinne Lynds, Senior Editor

Barbara Sherwood Lollar, who initiated the concept and goals for the EPA report and is one of the five international authors, in her University of Toronto research laboratory.

Photo: Noelle Stapinsky

A technique developed at the University of Toronto (U of T) is helping industry remove dangerous contaminants found in groundwater. Compound specific isotope analysis (CSIA), outlined in a report released by the US Environmental Protection Agency (EAP) in January, offers a new way to monitor and improve clean-up efforts.

Getting rid of organic chemicals, such as dry-cleaning fluids, solvents and petroleum hydrocarbons found in groundwater is typically accomplished by using microbes to biodegrade the contaminants into harmless end products. U of T’s Stable Isotope Laboratory, which has been pioneering carbon isotope research since the early 1990s, has found that CSIA does the same thing, but it’s faster and improves the results.

“The elements of carbon that form the basis for the hydrocarbon contaminants actually come in two types of isotopes,” explains U of T geochemist Barbara Sherwood Lollar, the scientist who initiated the concept and goals for the EPA report and is one of the five international authors. “When microbes degrade contaminants, they prefer the lighter isotope carbon 12 over the heavier isotope carbon 13. The resulting change in the ratio of these isotopes in the contaminant is a dramatic and definitive indicator of biodegration.”

According to the report, A Guide for Assessing Biodegration and Source Identification of Organic Ground Water Contaminants Using Compound Isotope Analysis, the traditional monitoring approach at sites often provides less than compelling evidence the contaminants are actually being degraded. When that’s the only data available, it’s difficult to exclude the possibility that a reduction in concentrations is caused by some other process such as dilution or dispersion, or that the monitoring wells failed to adequately sample the plume of contaminated ground water. Stable isotope analyses provides unequivocal documentation that biodegradation or abiotic transformation processes actually destroyed the contaminant.

When organic contaminants are degraded in the environment, the ratio of stable isotopes will often change, and the extent of degradation is recognized and predicted from the change.

What makes the information in this new report different from other scientific and professional journals is that it speaks directly to industry. “[It’s] written specifically for the practitioners in accessible language with clear procedural information and decision making strategies,” explains Sherwood Lollar who describes the repair as a milestone. It’s intended as a best practice manual that regulators and site managers (who are not geochemists) can use to tackle pollution issues.