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An evaluation of the bedrock aquifer system in northeastern Wisconsin

Water-Resources Investigations Report 85-4199

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Abstract

Groundwater is a major source of water in northeastern Wisconsin. This report evaluates the bedrock aquifer system in northeastern Wisconsin and describes how the flow regimes in the system have been altered due to groundwater withdrawals. A three-dimensional finite-difference groundwater flow model was used to aid in evaluation of the regional flow system. In order to simplify the study of the aquifer system, the geologic units were grouped into eight geohydrologic units consisting of fur aquifers and four confining beds. The aquifers are the more permeable sand and gravel layers in the surficial deposits (aquifer 4), Devonian dolomite-Silurian dolomite (aquifer 3), St. Peter Sandstone-Prairie du Chien Group-Jordan Sandstone Member of the Trempealeau Formation (aquifer 2), and the Galesville Sandstone-Eau Claire Sandstone-Mount Simon Sandstone (aquifer 1). The confining beds are the less permeable silts and clays in the surficial deposits (confining bed 4), Maquoketa Shale-Galena Dolomite-Decorah Shale-Platteville Formation (confining bed 3), St. Lawrence Member of the Trempealeau Formation-Franconia Sandstone (confining bed 1). The following aquifer and confining-bed characteristics were determined to represent the aquifer system of northeastern Wisconsin and were used in the development of the model. Aquifer 4 acts as an upper boundary of the bedrock aquifer system. The hydraulic conductivity of aquifer 3 was 7.9 ft/day and the storage coefficient was estimated to be 0.01. Transmissivity input values to the model for aquifer 2 are based on hydraulic conductivities ranging from 3 to 8 ft/day. The storage coefficient for aquifer 2 was 0.0002. The transmissivity input values to the model for aquifer 1 are based on hydraulic conductivities ranging from 2.5 to 8 ft/day and the storage coefficient was 0.0002. A vertical hydraulic conductivity of 0.007 ft/day was assigned to represent confining bed 4. The vertical hydraulic conductivity of confining bed 3 was assigned values of 0.0001 to 0.000004 ft/day. A value of 0.0001 ft/day was used as the vertical hydraulic conductivity for confining bed 2. Confining bed 1 is a lower boundary of the system and was not modeled. Model simulations indicate that, by 1914, groundwater withdrawals from the aquifer system had already impacted the study area. (Author 's abstract)

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
An evaluation of the bedrock aquifer system in northeastern Wisconsin
Series title:
Water-Resources Investigations Report
Series number:
85-4199
Edition:
-
Year Published:
1987
Language:
ENGLISH
Publisher:
U.S. Geological Survey,
Description:
v, 48 p. :ill., maps ;28 cm.