Paper No. 48-13
Presentation Time: 5:05 PM

PREFERENTIAL FLOW PATHS IN GLACIAL LAKE OSHKOSH SEDIMENT, OUTAGAMIE COUNTY, WI


DUNKLE, Kallina M., Department of Geosciences, Austin Peay State University, PO Box 4418, Clarksville, TN 37044, dunklek@apsu.edu, HART, David J., Wisconsin Geological and Natural History Survey, University of Wisconsin-Extension, 3817 Mineral Point Rd, Madison, WI 53705, and ANDERSON, Mary P., Geoscience, University of Wisconsin-Madison, 1215 W Dayton St, Madison, WI 53706-1692
Preferential flow paths are continuous fractures or connected units of high hydraulic conductivity (K), e.g. sand bodies within a clay matrix. They are important to groundwater flow and contaminant transport because they allow for faster movement of fluids than the surrounding matrix, but are difficult to detect, especially in heterogeneous glacially-deposited aquitards. Several techniques were used to infer preferential flow paths occurring through connected high K zones in a study site in Outagamie County, Wisconsin. Here, glacio-lacustrine sediments form a regional aquitard comprised of very low conductivity lacustrine clays with embedded sand and gravel bodies. Analysis of well construction reports and information on the known outlets of glacial Lake Oshkosh indicated the sand and gravel are most likely beach and underflow deposits, making up to 20% by volume of the total sediments.

A combination of hard and soft data was used to create 300 three-dimensional hydrostratigraphic models of the site using multiple-point geostatistics. All 300 models had at least one connected high K zone in the horizontal and vertical directions. A representative set of six hydrostratigraphic models was selected based on analyses of statistics of connectivity, imported into groundwater flow models, and calibrated to head data. Finally, particle tracking was performed and compared to statistics of connectivity.

Particle tracking results indicated preferential flow is likely occurring, since every model had examples of individual particles traced through high K units in faster time than nearby particles moving through low K units. Comparisons to connectivity statistics indicated that a hydrostratigraphic model with fewer, longer pathways or one with many shorter pathways can create preferential flow paths and that preferential flow can occur in a glacially-deposited aquitard through connected sand bodies without the presence of fractures.