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High-Resolution Airborne Geophysics at Hazardous Waste Disposal Sites
Environmental and Engineering Geophysical Society (EEGS), 1995 Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP) proceedings.
L.P. Beard, J.E. Nyquist, and W.E. Doll, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, U.S.A.
M. Chong Foo, T. Jeffrey Gamey, Aerodat, Inc., Mississauga, Ontario, Canada
Expanded Abstract – [pdf] ENV_SAGEEP_AirGeop_HazWaste_LPB_1995
In 1994, a high resolution helicopter survey was conducted over portions of the Oak Ridge Reservation, Tennessee. The 1800 line kilometer survey included multi-frequency electromagnetic and magnetic sensors. The areas covered by the high resolution portion of the survey were selected on the basis of their importance to the environmental restoration effort and on data obtained from the reconnaissance phase of the airborne survey in which electromagnetic, magnetic, and radiometric data were collected over the entire Oak Ridge Reservation in 1992-93. The high resolution phase had lower sensor heights, more and higher EM frequencies, and tighter line spacings than did the reconnaissance survey. When flying over exceptionally clear areas, the high resolution bird came within a few meters of the ground surface. Unfortunately, even sparse trees and power or phone lines could prevent the bird from being towed safely at low altitudes, and over such areas it was more usual for it to be flown at about the same altitude as the bird in the reconnaissance survey, about 30m. Even so, the magnetometers used in the high resolution phase were 20m closer to the ground than in the reconnaissance phase because they were mounted on the tail of the bird rather than on the tow cable above the bird.
The EM frequencies used in the high resolution survey ranged from 74OOHz to 67OOOHz. Only the horizontal coplanar loop configuration was used in the high resolution flyovers Flight line spacings in the high resolution flyover ranged from 46m over large treecovered areas to about 1Om in cleared waste burial grounds. A comparison with ground conductivity and magnetic data from the WAG 11 area shows that the ground survey provides much more detail than the high resolution aerial data, however the aerial survey of WAG 11 detected the major anomalous areas–buried processing equipment, buried drums, and an area of scattered debris. Better resolution could have been obtained had the area been clear enough for the sensor to drop below treetop level. Geologic structures and contacts appear to be as accurately mapped using a coil frequency of 7400Hz. Apparent resistivity maps at the highest frequency–660OOHz–do not correspond well with bedrock geology, but may be correlated with soil variations and the presence of buried metal.