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Scientific Investigations Report 2009–5060

National Water Availability and Use Pilot Program

Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution for a Simulation of Groundwater Flow for the Lake Michigan Basin

By David C. Lampe

ABSTRACT

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The U.S. Geological Survey is assessing groundwater availability in the Lake Michigan Basin. As part of the assessment, a variable-density groundwater-flow model is being developed to simulate the effects of groundwater use on water availability throughout the basin. The hydrogeologic framework for the Lake Michigan Basin model was developed by grouping the bedrock geology of the study area into hydrogeologic units on the basis of the functioning of each unit as an aquifer or confining layer within the basin. Available data were evaluated based on the areal extent of coverage within the study area, and procedures were established to characterize areas with sparse data coverage. Top and bottom altitudes for each hydrogeologic unit were interpolated in a geographic information system for input to the model and compared with existing maps of subsurface formations. Fourteen bedrock hydrogeologic units, making up 17 bedrock model layers, were defined, and they range in age from the Jurassic Period red beds of central Michigan to the Cambrian Period Mount Simon Sandstone.

Information on groundwater salinity in the Lake Michigan Basin was compiled to create an input dataset for the variable-density groundwater-flow simulation. Data presented in this report are referred to as “salinity data” and are reported in terms of total dissolved solids. Salinity data were not available for each hydrogeologic unit. Available datasets were assigned to a hydrogeologic unit, entered into a spatial database, and data quality was visually evaluated. A geographic information system was used to interpolate salinity distributions for each hydrogeologic unit with available data. Hydrogeologic units with no available data either were set equal to neighboring units or were vertically interpolated by use of values from units above and below.

First posted May 15, 2009

For additional information contact:
Howard W. Reeves, Project Chief National Water Availability and Use Pilot Program, U.S. Geological Survey, 6520 Mercantile Way
Lansing, MI  48911

Great Lakes Pilot

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Suggested citation:

Lampe, D.C., 2009, Hydrogeologic framework of bedrock units and initial salinity distribution for a simulation of groundwater flow for the Lake Michigan Basin: U.S. Geological Survey Scientific Investigations Report 2009–5060, 49 p.



Contents

Abstract

Introduction

Purpose and Scope

Groundwater Model

Hydrogeologic Setting

Hydrogeologic Framework of Bedrock Units

Correlation of Stratigraphy to Hydrogeologic Units

Sources of Lithologic Data

Illinois

Wisconsin

Michigan

Indiana

Ohio

Areas Under Lake Michigan

Stratigraphic Framework Interpolation Methods

Initial Salinity Distribution of Groundwater in Bedrock Hydrogeologic Units

Sources of Groundwater Salinity Data

Interpolation Methods Used to Develop Initial Salinity Distribution

Summary

Acknowledgments

References Cited



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