Shallow Seismic Refraction Survey of Near-Surface Ground Water Flow |
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| Authors: | Keith A Sverdrup |
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| Institution: | Keith A. Sverdrup is an assistant professor of geophysics at the University of Wisconsin-Milwaukee in the Department of Geological and Geophysical Sciences, Milwaukee, WI 53201. He is one member of a group of three geophysicists and two hydrogeologists who form a hydro-geophysics core in the department. His research interests include shallow structure determined by seismic, gravity and magnetic methods, and microseismicity-tectonics problems. |
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| Abstract: | A shallow seismic refraction survey was conducted as part of a geologic and hydrologic investigation of an area adjacent to a proposed coal strip mine in southeastern Illinois. Data obtained from the survey were used to estimate the thickness and geometry of litho-logic units within approximately 40 feet of the surface in unconsolidated material overlying bedrock. Data from a nearby ground water monitoring well and several shallow geologic cores obtained in the survey area indicated the presence of a silt-clay unit roughly 10 feet beneath the surface. This unit strongly inhibits the vertical movement of ground water, resulting in a perched water table.
The refraction survey revealed that the morphology of the top of this silt-clay layer is dominated by a narrow, sinuous channel criss-crossing the survey region with an overall downward trend in elevation from the mine site to a small creek roughly 0.25 miles away. Detailed knowledge of the location of this channel was used to identify optimal sites for shallow ground water monitoring stations. The method proved to be a relatively rapid and cost-efficient means of obtaining detailed information concerning the thickness and geometry of the near-surface unconsolidated materials. |
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