Electrical resistivity surveys, Vars-Winchester esker aquifer, Ontario / G.A. Oldenborger. : M183-2/8769E-PDF

"This Open File reports on results of electrical resistivity surveys performed over the Vars-Winchester esker aquifer near Embrun, Ontario as part of the Natural Resources Canada Groundwater Geoscience Program. Electrical resistivity and induced polarization data were acquired within boreholes as 1D logs, along the surface as 2D profiles, and from surface-to-borehole in 3D. The data were processed and inverted to recover 1D, 2D and 3D models of electrical resistivity and chargeability. The resulting models clearly indicate a resistive esker feature thickest at the centre and thinning on the flanks. The 2D profiles show a more resistive esker centre consistent with a gravel core under sand cover that is supported by the 1D and 3D models. The base of the esker is not clearly resolved in the resistivity models due to the weak contrast of the esker/basement contact that is below the depth of investigation of the surface surveys, and subject to high uncertainty in the surface-to-borehole surveys. The resistivity models reveal significant and coherent electrical layering within the conductive Champlain Sea sediments surrounding the esker. Electrical resistivity is observed to decrease with depth below the water table in the marine muds. Above the water table, the unsaturated zone exhibits anomalously low resistivity that may result from accumulation of salt and other potential electrolytes in road- and crop-side ditches. Chargeability is measurable at the site for the given experiments. Vertical structure of apparent chargeability is evident in the 1D borehole logs. The gravels and sands appear most chargeable, but the normalized chargeability suggests dominantly electrolytic conduction with largely uniform surface conduction. No meaningful chargeability models can be recovered for the 2D or 3D surveys, presumably due to the small values of chargeability and high noise levels"--Summary, page 1.

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publications.gc.ca/pub?id=9.956494&sl=1

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