USGS Groundwater Information: Branch of Geophysics
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C.J. Powers, and F.P. Haeni
U.S. Geological Survey, 11 Sherman Place U-5015, Storrs, CT 06269
Massachusetts Military Reservation, 322 East Inner Road, Box 41 Otis Air National Guard, MA 02542-4673
Continuous seismic-reflection profiling (CSP) and ground-penetrating radar (GPR) sur- veys were conducted by the U.S. Geological Survey in April 1998 over the northern part of Johnís Pond, a glacial kettle pond southeast of Otis Air National Guard Base, Cape Cod, Mas- sachusetts. The surveys were conducted to delineate the types and thickness of sedimentary units that may control the infiltration of contaminated groundwater into Johnís Pond.
Sand-and-gravel deposits, collapse features and recent organic sediments were imaged with the CSP and GPR methods. Hummocky to chaotic reflections were interpreted as sand- and-gravel deposits. Slightly wavy, parallel reflections located in depressions in the sand-and- gravel deposits were interpreted as filled collapse features. Lower amplitude, horizontal, lami- nar reflections were interpreted as organic sediments. Entrapped methane gas within some of the organic sediments created a reflection zone that obscured deeper reflections in the CSP records.
The CSP and GPR methods provide complementary information over most of the sur- veyed part of the pond. The methods detect similar interfaces, but a particular interface may produce a stronger reflection in one record than in the other. For example, regions of the pond containing organic sediments with entrapped methane gas, which prevent penetration of the acoustic signal, were penetrated and imaged by GPR. Conversely, regions of the pond contain- ing electrically conductive sediments or deep water, which attenuate the GPR signal, were im- aged using CSP. The CSP and GPR data were interpreted to generate a bathymetric map and a map of sediment type and thickness beneath Johnís Pond.
Final copy as submitted to Symposium on the Application of Geophysics to Engineering and Environmental Problems for publication as: Powers, C.J., Haeni, F.P., and Smith, S., 1999, Integrated use of continuous seismic-reflection profiling andground-penetrating radar methods at John's Pond, Cape Cod, Massachusetts, in Powers, M.H., Cramer, Lynn, and Bell, R.S., eds., Symposium on the Application of Geophysics to Engineering and Environmental Problems, Oakland, California, March14-18, 1999, Proceedings: Wheat Ridge, Colo., Environmental and Engineering Geophysical Society, p. 359-368.
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