COLUMBUS, Ohio -- Geophysicists at Ohio State University have found a new application for ground penetrating radar: detecting subsurface liquid hazardous waste.
By changing the antenna configuration within a standard ground penetrating radar (GPR) device, they were able to detect deposits of creosote buried beneath an EPA cleanup site in Marion, Ohio.
The technique may hold promise for finding other kinds of buried hazardous waste.
Jeffrey Daniels, professor of geological sciences, and his graduate students found several deposits around an abandoned wood treatment facility, including two tanks of creosote that were buried beneath several feet of cement.
They reported their results in a recent issue of the journal Geophysical Research Letters.
"Without this new antenna arrangement, we never would have found those underground tanks," said Daniels. "Nobody would ever have known they were there."
How well GPR detects certain objects depends on the alignment of the sending and receiving antennas within the device, Daniels said. The common arrangement -- the two antennas side by side -- detects smooth objects like buried pipes or flat layers of rock very well, and is often used in bridge or road inspection.
Jagged objects such as broken rocks confuse side-by-side antennas because they scatter the radar signal.
In their latest paper in Geophysical Research Letters, the geophysicists showed that crossing the antennas into a T-shaped formation brings into focus coarse deposits of hazardous waste mixed with rocks and soil.
Erich Guy, geology graduate student, led the investigation of the Marion site. Other graduate students working on the project included Stan Radzevicius and Jennifer Holt.
Between the 1890s and 1960s, the Marion facility used large quantities of creosote, a common wood preservative. It stored the oily, foul-smelling liquid in two aboveground tanks.
The aboveground tanks were long gone by 1999, on the cold February day the Ohio State students inspected the abandoned 100-acre lot.
Both the Ohio EPA and the U.S. EPA had studied the site throughout the 1990s, but hadn't been able to pinpoint exactly how creosote had leaked from the property into the nearby Little Scioto River.
"There was a slight odor of creosote in the air, but it was nothing you'd really notice," said Holt.
The students surveyed a football-field sized portion of the property with a commercially available GPR device, first with the antennas in a side-by-side configuration, and then with the antennas crossed. They used software to create 3-D maps of the subsurface.
The map created by the side-by-side configuration showed a messy jumble of signals. The rocks, soil, and clay on the property obscured the deposits of creosote.
The cross-pole test produced a cleaner signal. Rocks, soil, and clay became invisible to the radar, but glowing bright red on the 3-D maps were several well-defined areas that contained some kind of foreign material -- the creosote.
The geophysicists detected creosote buried in a pit near a former pump house, and in a trench connecting two cement pads that supported the missing storage tanks.
It also detected creosote hiding in a couple of unlikely spots -- beneath the tank pads.
"At first we thought the pads were there just to support the storage tanks," said Daniels. "But the GPR showed that there was definitely something underneath them."
Two months later, the EPA broke through the cement pads and uncovered two buried tanks of creosote that were leaking into the surrounding soil.
Without the GPR data, the EPA probably wouldn't have found the buried tanks.
"The cleanup crew was hesitant to go to all that trouble and expense, until we showed them the data," said Guy.
"Whether the wood treatment company intentionally buried the creosote is a matter for the EPA to decide," Daniels said, "but this discovery confirms the usefulness of GPR for this application."
Daniels and his students will continue to inspect sites for the EPA as part of a cooperative agreement with that agency to further develop the technique.
They also received a grant from the National Science Foundation to improve the image quality of the 3-D maps they produce with GPR.
"As far as we know, we're the only group in the country that is working on this," Daniels said. The geophysicists will pursue this project together with researchers at Ohio State's Electroscience Laboratory.
The above story is based on materials provided by Ohio State University. Note: Materials may be edited for content and length.
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