Final Report on Assessment of Geologic Controls on Groundwater Flow and Distribution in Precambrian Bedrock, Central Wisconsin, Using Remote Sensing and Geophysical Analysis

Executive Summary: Although it did not provide a quick and reliable technique for the identification of zones of abundant groundwater in covered Precambrian bedrock, this project has contributed significantly to our understanding of the geologic factors which control groundwater distribution and flow in these rocks. A potentiometric surface map based on bedrock wells by Hutasoit and Davidson (1989) shows that groundwater heads vary from 1600 to 1000 feet in elevation with locally complex subpatterns. For the area of study, which includes Wood, Portage, and Marathon Counties, the potentiometric surface is a subdued version of the bedrock topographic surface and is broadly similar to the water table for all wells (Lippelt and Hennings, 1981; Batten, 1989). The complex bedrock topography suggests that local flow systems in the Precambrian bedrock are considerably smaller (1-5km) and shallower than the broad regional systems common to unconsolidated deposits and sandstone terranes (10-50 km). There appears to be excellent interconnection between bedrock and the overlying unconsolidated materials, despite local development of up to 30 ft or more of weathered clayey residuum at the Precambrian surface. Because of this connectivity the Precambrian bedrock appears to be part of an unconfined regional aquifer system, with considerable local complexity caused by topography, degree of weathering, and structural characteristics of individual rock units.