Kansas Geological Survey, Open-file Report 2011-2
Carl D. McElwee, Brett R. Engard, Brian J. Wachter, Shane A. Lyle, John Healey, and J. F. Devlin
University of Kansas
KGS Open File Report 2011-2
Considerable research has shown that the major control on the transport and fate of a pollutant as it moves through an aquifer is the spatial distribution of hydraulic conductivity. Although chemical and microbial processes play important roles, their influence cannot be understood without a detailed knowledge of the subsurface variations in hydraulic conductivity at a site. Many theories have been developed to quantify, in a generic sense, the influence of these variations using stochastic processes or fractal representations. It is increasingly apparent, however, that site-specific features of the hydraulic conductivity distribution (such as high conductivity zones) need to be quantified to reliably predict contaminant movement. Conventional hydraulic field techniques only provide information of a highly averaged nature or information restricted to the immediate vicinity of the test well. Therefore, development of new innovative methods to delineate the detailed hydraulic conductivity distribution at a given site should be a high priority. The research proposed here is directed at addressing this problem by developing techniques to map 3-D hydraulic conductivity distributions.
Since spatial changes in hydraulic conductivity are a major factor governing the transport and fate of a pollutant as it moves through an aquifer, we focus on the development of new innovative methods to delineate these spatial changes. The objective of the research proposed here is to build on our previous work to develop and improve field techniques for better definition of the three-dimensional spatial distribution of hydraulic conductivity by using hydraulic tomography coupled with high-resolution slug testing.
We have worked for many years to quantify hydraulic conductivity fields in heterogeneous aquifers. One promising method we have worked on extensively is high- resolution slug testing. This method allows the delineation of the vertical distribution of hydraulic conductivity near an observation well. We propose to combine this method with another innovative method for investigating the hydraulic conductivity distribution between wells, called hydraulic tomography. We will use an oscillating signal and measure its phase and amplitude through space in order to estimate the hydraulic conductivity distribution of the material through which it has traveled. Our preliminary work shows that the phase and amplitude of the received signal can be measured over reasonable distances. The high-resolution slug testing results will be used as an initial condition and will provide conditioning for the tomographic inverse procedure, to help with any non-uniqueness problems. Slug test data are most accurate near the tested well and should probably not be extrapolated blindly between wells. Together, slug testing and hydraulic tomography should be more powerful than either one used alone and should give the best opportunity to characterize the hydraulic conductivity in-situ by a direct measure of water flow, as an alternative to indirect methods using geophysical techniques.
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Kansas Geological Survey, Geohydrology
Placed online Dec. 15, 2011
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