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2007 Ground Water Summit |
Monday, April 30, 2007 : 2:20 p.m.
Combined Use of Two-Dimensional Surface NMR and TDEM for Hydrogeological Investigations
Joint 2-D surface NMR and TDEM measurements were obtained at several sites in Nebraska, Iowa and Minnesota, with the aim of developing an improved understanding of the hydrogeology at each site. 2-D surface NMR is a large-scale form of magnetic resonance imaging (MRI). Surface NMR measurements and inversions produce 1-D, 2-D and/or 3-D images of the unbound groundwater porosity, and the NMR time decay parameters T1 and T2*, which are empirically linked to hydraulic conductivity. TDEM measurements and inversions produce electrical conductivity profiles, which shed light on the lithology of a site, and in some cases indicate the presence of groundwater. Joint analysis of 2-D surface NMR and TDEM measurements indicates that the two methods yield complimentary information on the hydrogeology at the site scale, and increases the confidence in hydrogeological models developed from surface geophysical measurements. Case studies are presented from field tests over an alluvial aquifer system in Western Nebraska, a Karst system in Southern Minnesota, and a mixed alluvial/bedrock aquifer system in Central Iowa.