Oak Ridge National Laboratory

 

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Technique to find mineral treasures helping locate buried waste drums

OAK RIDGE, Tenn., Sep. 12, 1995 — Mineral exploration techniques are helping researchers at Oak Ridge National Laboratory (ORNL) find barrels of low-level radioactive waste buried on the 35,000-acre Department of Energy (DOE) Oak Ridge Reservation.

In what was standard procedure during the 1940s and '50s, workers buried hundreds of the 55-gallon steel drums in trenches typically 20 feet wide, 20 feet deep and sometimes hundreds of feet long. Records show where most of the drums are buried; however, some records showing additional trench locations were destroyed in a 1957 fire.

Fortunately, environmental geophysicists at ORNL can map the reservation with what is essentially a "high-altitude metal detector." Information gained with this technique, used to locate minerals in many parts of the world, is vital to DOE officials who will now know the locations and approximate quantities of buried materials. This information is especially important if a site is to be decommissioned, said ORNL geophysicist Jon Nyquist.

During two sessions, each spanning a few months, researchers gathered data by using a helicopter equipped with sensors that detect iron and steel. The sensors, which detect changes in the magnetic, radioactive and electrical properties of the ground, were attached to the helicopter's base and suspended from a 100-foot cable. The helicopter flew about 200 feet above the ground along north-south flight lines at 150-foot intervals. Sensors transmitted the information to a computer that recorded data from each sensor at 0.1 second intervals, or about every six to 10 feet along the flight path.

The magnetic sensors measure the disturbance in the Earth's magnetic field that is created by buried steel or iron. The electromagnetic system aboard the helicopter broadcasts radio waves to the ground. "This creates electric currents in the ground," Nyquist said. "The more conductive the ground, the stronger the currents. Metal conducts electricity, so you get strong currents. These currents create a radio signal that the receiver coil detects."

Since the aerial survey was done, Nyquist and other ORNL researchers have been evaluating the data for quality and sensitivity, developing tools for rapid display and enhancement of the data and notifying managers who need this information for particular sites.

In addition to its use for this project, geophysicists use this technology for geologic mapping, such as distinguishing shales from limestones. They also use environmental geophysics to detect contaminated groundwater. No system is perfect, however, and Nyquist notes that geophysical screening can be affected by interference from nearby buildings, pipes, power lines and earth-fill from construction. Nevertheless, it provides geophysicists with a valuable mapping tool they use in conjunction with other techniques to obtain accurate results.

Funding for the project was provided by DOE's Environmental Restoration Remote Sensing and Special Surveys Program.

Other ORNL researchers working on the project are Bill Doll, Les Beard and Amy King.

ORNL, one of DOE's multiprogram national research and development facilities, is managed by Lockheed Martin Energy Systems, which also manages the Oak Ridge K-25 Site and the Oak Ridge Y-12 Plant.