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Open-File Report 2006–1216

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In cooperation with the Office of Environmental Protection of the Fort Peck Tribes

Helicopter Electromagnetic and Magnetic Survey Maps and Data, East Poplar Oil Field Area, August 2004, Fort Peck Indian Reservation, Northeastern Montana

By Bruce D. Smith, Joanna N. Thamke, Michael J. Cain, Christa Tyrrell, and Patricia L. Hill

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This report is a data release for a helicopter electromagnetic and magnetic survey that was conducted during August 2004 in a 275-square-kilometer area that includes the East Poplar oil field on the Fort Peck Indian Reservation. The electromagnetic equipment consisted of six different coil-pair orientations that measured resistivity at separate frequencies from about 400 hertz to about 140,000 hertz. The electromagnetic resistivity data were converted to six electrical conductivity grids, each representing different approximate depths of investigation. The range of subsurface investigation is comparable to the depth of shallow aquifers. Areas of high conductivity in shallow aquifers in the East Poplar oil field area are being delineated by the U.S. Geological Survey, in cooperation with the Fort Peck Assiniboine and Sioux Tribes, in order to map areas of saline-water plumes. Ground electromagnetic methods were first used during the early 1990s to delineate more than 31 square kilometers of high conductivity saline-water plumes in a portion of the East Poplar oil field area. In the 10 years since the first delineation, the quality of water from some wells completed in the shallow aquifers in the East Poplar oil field changed markedly. The extent of saline-water plumes in 2004 likely differs from that delineated in the early 1990s. The geophysical and hydrologic information from U.S. Geological Survey studies is being used by resource managers to develop ground-water resource plans for the area.

Version 1.0

Posted August 2006

Digital data and other information are provided in six directories with a “readme.txt” file that describes the contents of the directory.

Geographic information such as topographic map.
Grids of the electromagnetic and magnetic field data for the horizontal coplanar coil pairs.
Flight-line data in a Geosoft OASIS MONTAJ database.
Geotiff (UTM13N. NAD27 projected “.tif” files) of the grids.
This report and appendix 1 as “.pdf” files.
The programs needed to read GEOSOFT and ERMAPPER images and data.

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