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E-mail:

P.M. McMahon, USGS, Denver, Colorado
pmcmahon@usgs.gov

Stopping Contamination in Its Tracks

Because of the application of a new remediation technology by USGS researchers in Colorado, the movement of chlorinated solvents off the Denver Federal Center has literally been stopped in its tracks. Chlorinated solvents are one of the most common contaminants of ground water in the United States.

The remediation technology -- permeable reactive barriers -- destroys the solvents in the ground water. With such a barrier, water passes through, but is chemically altered in the process. The barrier uses zero-valence iron to completely destroy the chlorinated solvents as ground water moves through the iron.

Zero-valence iron being placed in aquifer to form a permeable reactive barrier that will destroy contaminants in water.

The reactive barrier technique has a lot going for it. The technology is maintenance free and less expensive than other remediation technologies. The Federal Highway Administration and the General Services Administration are using the technology at the Denver Federal Center because it is an essentially natural remediation method that is cost effective. The USGS served as an advisor to the U.S. Army Corps of Engineers during design and installation of the barrier. Continued evaluation of the hydraulic and geochemical performance of the reactive barrier by the USGS will provide valuable information for future applications of this technology.

The reactive barrier method is a technology that can be applied across the country in dealing with chlorinated solvents.

Concentrations of selected chlorinated solvents in ground water entering and exiting zero-valence iron at the Denver Federal Center. Numbers in parentheses are the drinking water standards for the indicated compounds.

What Are Chlorinated Solvents?

Chlorinated solvents, such as carbon tetrachloride, chloroform, and ethylene dichloride, were developed after World War II as safe non-flammable cleaning agents. They are used in various industrial processes and replace volatile hydrocarbon-based solvents. By substituting chlorine for hydrogen, industry had a still-efficient solvent that was less volatile. As with many chemical compounds used by industry and agriculture, it was not known at the time of development what their impacts would be to human health or the environment.

Contaminant concentrations entering and leaving zero-valence iron.