Examination of magnetic resonance soundings in the Central Platter River Basin for ground water model enhancements

In 2007, the USGS in cooperation with the Central Platte Natural Resources District, central Nebraska, initiated a four year study to test the usefulness of magnetic resonance rounding (MRS) to gather information on aquifer characteristics. Magnetic resonance sounding is a ground surface applied tool which has the potential to measure hydraulic conductivity at depth using noninvasive means. This in turn will provide a low cost alternative to traditional aquifer tests. MRS also will allow for collection of large data sets of aquifer properties during short periods of time. The work is under way in Dawson County near Lexington, Nebraska to characterize the hydrogeology of the Quaternary-age alluvial and underlying Tertiary-age Ogallala Group aquifers that occur within the Platte River Valley. This county was selected because it lies in an area of Nebraska that has major groundwater- surface water management issues which have stimulated the development of regional and local groundwater models. Data used to evaluate the MRS during this study were derived from traditional constant discharge aquifer tests, borehole flow meter tests, lithologic descriptions, borehole geophysics, and time-domain electromagnetic soundings. This study presents methods and interpretation of MRS. The MRS-derived hydraulic conductivity data will be compared to hydraulic conductivity data from two separate constant discharge pumping tests of the alluvium and Ogallala Group aquifers at Site 72 The MRS-derived hydraulic conductivity data will also be compared to conductivity estimates based on data from a borehole flow meter test. This information can potentially be incorporated into groundwater models of the area to provide improved data sets of aquifer characteristics. The research will document an integrated MRS, surface geophysical, borehole geophysical, borehole flow meter and aquifer test approach in which the hydrostratigraphy of the Platte River alluvial aquifer and Ogallala aquifer can be described.