Chemical oxidant candles used to clean up groundwater contamination
January 17, 2011
LINCOLN, Neb. – A University of Nebraska-Lincoln soil environmental chemist and several of his students have developed an apparently effective and low-cost solution to groundwater contamination at a former central Nebraska landfill.
For the past year and a half, Institute of Agriculture and Natural Resources soil environmental chemist Steve Comfort and several of his Environmental Restoration Science graduate and undergraduate students have been working at an abandoned landfill near Cozad to clean up groundwater contaminated with toxic trichloroethylene, a once commonly used solvent and degreaser.
“There are lots of contamination sites like this one across the country, which is a legacy of widespread TCE use and improper disposal through the 1980s,” Comfort said. “The challenge is finding low-cost, low-tech methods cash-strapped communities can use to remediate this known threat to human health.”
Trouble is, proven clean-up methods aren’t always one size fits all.
At Cozad, TCE-containing chemicals were disposed in the landfill by various industries, including a company that once produced automobile shock absorbers. Heavy clay soils and tightly confined groundwater aquifers at the scene of the contamination plume don’t lend themselves to injections of liquid-based permanganate, a chemical compound that oxidizes TCE, turning it into harmless chloride and carbon dioxide.
UNL graduate student Mark Christianson of North Platte solved the problem by hand making hundreds of three-foot chemical oxidant candles, which are a mix of simple paraffin wax and granular permanganate that dissolve and mix with the TCE over time.
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“The candles were placed into the contaminated groundwater by installing some designated wells and inserting the candles directly into holes made by our direct-push probing machine. The original idea of slow-release oxidants was developed at The Ohio State University, but to our knowledge, this is the first attempt at a field trial,” Comfort said.
“The candles were just put in a few weeks ago, so we are now waiting to see the full extent of their effectiveness,” Christianson said this summer. “So far, it’s looking very, very good.”
The former U.S. Navy nuclear submariner and 2009 UNL water science graduate hand-melts and mixes the paraffin-permanganate concoction and pours it into cardboard tubes about three feet long and of a diameter to fit the bore holes. The cardboard tube is removed before candles are placed down the holes. Hundreds of these candles have been placed in and around the Cozad site.
To find out exactly where the plume of contamination was and where to place the candles, Comfort and his students used electrical resistivity imaging equipment to get two-dimensional images of the groundwater at and near the now-closed landfill.
“We then used those images to sample the groundwater and determine that the contamination plume was confined to one region, which told us where we needed to concentrate our efforts,” Comfort said.
Back at their IANR laboratory, Comfort and his students then conducted “treatability studies” to come up with the best and most cost-effective method for removing TCE from the site, which resulted in the hand-made candles.
“Before we got involved, the City of Cozad was having to use an environmental consultant and sample wells every year at substantial cost. This hasn’t really solved the problem and they have been dealing with this landfill contamination since the 1980s,” Comfort said. “With the help and creativity of our graduate students, I think what we’re trying will work and will do so very inexpensively.”
The research is partially funded by the U.S. Environmental Protection Agency and IANR’s Agricultural Research Division.
Comfort began coordinating UNL’s environmental restoration science major, within UNL’s School of Natural Resources, about four years ago. More information on this undergraduate program of study can be found at http://snr.unl.edu/undergrad/programs/envressci.asp.