Identification Of Dolines And Karst Recharge Points Using Geophysical Techniques, Oak Ridge, Tennessee

Surface water and contaminants often enter karst systems through a doline, or sinkhole.<br>In this study ground penetrating radar (GPR) and other geophysical methods were applied<br>to identify filled dolines on a colluvium-covered hillslope overlying cavernous limestone<br>at the Y-12 Plant, Oak Ridge Reservation, Tennessee. Although 25 and 50 MHz GPR<br>signals did not penetrate deep enough to reveal mud-filled cavities in the bedrock, dipping<br>radar reflections were obtained over the flanks of a known doline and another filled doline<br>may have been discovered near monitoring well GW734. A troughlike pattern of radar<br>diffractions at least 120 ft (37 m) across and 12 ft (3.7 m) deep was recorded at this<br>location by several GPR profiles. Electromagnetic, resistivity, seismic refraction and<br>gravity surveys suggest this doline structure is filled with relatively dense, resistive<br>residuum or colluvium, and floored by silt or clay. This structure also lies almost directly<br>above a large hydraulically active bedrock cavity (intercepted by monitoring well GW734)<br>for which it may be a recharge point. Further detailed investigation of this doline structure<br>should be undertaken, based on the results of the geophysical surveys and its proximity to<br>the cavity.<br>Note: The submitted manuscript has been authored by a contractor of the U.S.<br>Government under contract No. DE-ACW840R21400. Accordingly, the U.S.<br>Government retains a nonexclusive, royalty-free license to publish or reproduce the<br>published form of this contributioq or allows others to do so, for U.S. Government<br>purposes.