Kansas Geological Survey, Open-file Report 2005-11
by
J.M. Healey1, G.P. Tsoflias2, D.W. Steeples2,
P. Vincent2, S.D. Sloan2, J. Blair2, and C.D. McElwee2
1 The University of Kansas, Kansas Geological Survey, 1930 Constant Ave., Lawrence, KS 66047
2 The University of Kansas, Department of Geology, 1475 Jayhawk Blvd., Lawrence, KS 66045
KGS Open File Report 2005-11
April 2005
In north-central Kansas the Republican River and its associated alluvial sediments are important regional surface and groundwater sources. A test site adjacent to the Republican River (near Clay Center, KS), has been established within the porous alluvial sediments to study stream-aquifer interaction and aquifer heterogeneity. The site is monitored with seven observation wells oriented along a line perpendicular to the river channel and centered around a productive irrigation well. Geophysical techniques, including direct-push electrical conductivity (EC), ground penetrating radar (GPR), and shallow seismic reflection, are used to investigate the hydrologic properties of the site.
Electrical conductivity profiling is commonly used for gross lithologic definition of the subsurface. Recently, EC has been used to extract additional information about subsurface characteristics based on the three main parameters that control the electrical properties of soils: lithology, water content, and water chemistry. At the Clay Center test site EC profiles were obtained at seven locations, approximately 33 meters apart. These closely spaced conductivity profiles provide a general description of the vertical and lateral variation of the subsurface lithology. On the EC profiles the water table is indicated by an abrupt change in electrical conductivity. This indicator was observed during undisturbed hydrologic conditions and during a pumping test.
GPR reflection data were acquired in line with the observation wells at the Clay Center test site and were integrated with the EC profiles. Radar data collected during undisturbed hydrologic conditions imaged shallow lithologic alterations, but did not image as deep as the water table. Variations in reflection character and attenuation of the GPR signal demonstrate close agreement with subsurface electrical conductivity variations and provide the means to extend the EC data laterally, between observation wells.
High-resolution shallow seismic reflection data sets were collected to image the top of the saturated zone during and after the pumping test. Differences as well as similarities in the arrival times and amplitudes of P-wave reflections are evident in both data sets. Preliminary data analysis identifies a water table reflection both during and after the pumping test.
The geophysical techniques employed provide complementary information about the hydrologic properties of the subsurface. Integration of electrical conductivity profiles, GPR reflection data, and shallow seismic reflection data offer the potential for improved subsurface characterization.
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Kansas Geological Survey, Geohydrology
Placed online May 2, 2005
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