HYDRAULIC AND GEOPHYSICAL TOOLS FOR HYDROSTRATIGRAPHIC ANALYSIS OF A BEDROCK AQUIFER

Recent studies done near Madison, Wisconsin, have shown that preferential flow paths may be the source of various major spring complexes in the area. Identifying these flow paths within an aquifer system can be challenging due to the limited access to the subsurface. A study in the Pheasant Branch watershed, on the western edge of the greater Madison metropolitan area, has utilized various field techniques on a deep well near a major spring complex to analyze the hydrostratigraphy and test different conceptual models of spring flow.

Geophysical logging of the deep well provided information about stratigraphy, potential fracture zones, and rock and water characteristics. Dynamic flow meter testing allowed for the identification of particular zones of high flow contribution. Interval slug tests were done in consecutive 3.7' sections up the borehole to analyze for hydraulic conductivity. A municipal pump signature test allowed for analysis of the current hydrologic impact of urban pumping on the groundwater system near the springs.

The Pheasant Branch watershed is a candidate for rapid urbanization and is being researched as part of an integrated study designed to provide the community with several alternative management scenarios for future growth in which the potential impacts on springs and wetlands are considered. Ultimately, the field results from the well tests as well as stratigraphic information from a large area surrounding the watershed will be used to refine a 3-D MODFLOW model of Pheasant Branch. This groundwater flow model will be used estimate the potential impacts of increased municipal pumping, decreased recharge, and contamination caused by urbanization.