U.S. Department of the Interior

U.S. Geological Survey

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
Cover image: Three-dimensional rendering of surficial topography and hydrogeologic layers beneath the 

Lake Michigan Basin. (Image by David Lampe, U.S. Geological Survey.)
Hydrogeologic Framework of Bedrock 

Units and Initial Salinity Distribution for 

a Simulation of Groundwater Flow for the 

Lake Michigan Basin

By David C. Lampe 

National Water Availability and Use Pilot Program

Scientific Investigations Report 2009–5060

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

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.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction ....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................2

Groundwater Model .............................................................................................................................2

Hydrogeologic Setting .........................................................................................................................2

Hydrogeologic Framework of Bedrock Units............................................................................................4

Correlation of Stratigraphy to Hydrogeologic Units........................................................................4

Sources of Lithologic Data..................................................................................................................6

Illinois.............................................................................................................................................6

Wisconsin......................................................................................................................................6

Michigan........................................................................................................................................7

Indiana...........................................................................................................................................7

Ohio.......... ......................................................................................................................................7

Areas Under Lake Michigan ......................................................................................................7

Stratigraphic Framework Interpolation Methods............................................................................7

Initial Salinity Distribution of Groundwater in Bedrock Hydrogeologic Units ..................................24

Sources of Groundwater Salinity Data ...........................................................................................24

Interpolation Methods Used to Develop Initial Salinity Distribution..........................................24

Summary .......................................................................................................................................................46

Acknowledgments.......................................................................................................................................47

References Cited..........................................................................................................................................47

Figures

1. Map showing the location of Lake Michigan Basin, groundwater-model boundary 

and innermost model domain, structural geologic features, and general bedrock 

geology of the study area............................................................................................................3

2. Stratigraphic chart showing time- and rock-stratigraphic framework nomenclature 

for the Lake Michigan Basin region, the U.S. Geological Survey principal aquifers in 

the model area, and the hydrogeologic units used in the model..........................................5

3–17. Maps showing thickness of—

3. Quaternary hydrogeologic unit..........................................................................................9

4. Jurassic hydrogeologic unit ............................................................................................10

5. Upper Pennsylvanian hydrogeologic unit......................................................................11

6. Lower Pennsylvanian hydrogeologic unit .....................................................................12

7. Michigan hydrogeologic unit...........................................................................................13

8. Marshall hydrogeologic unit............................................................................................14

9. Devonian-Mississippian hydrogeologic unit.................................................................15

10. Silurian-Devonian hydrogeologic unit............................................................................16

11. Maquoketa hydrogeologic unit .......................................................................................17

12. Sinnipee hydrogeologic unit............................................................................................18

13. St. Peter hydrogeologic unit ............................................................................................19

14. Prairie du Chien-Franconia hydrogeologic unit ...........................................................20
iv

15. Ironton-Galesville hydrogeologic unit............................................................................21

16. Eau Claire hydrogeologic unit..........................................................................................22

17. Mount Simon hydrogeologic unit....................................................................................23

18. Graph showing groundwater density and total dissolved-solids 

concentrations for data from Gupta (1993)....................................................................25

19–38. Maps showing the initial total dissolved-solids concentration of groundwater in—

19. Quaternary hydrogeologic unit, model layer 1..............................................................26

20. Quaternary hydrogeologic unit, model layer 2..............................................................27

21. Quaternary hydrogeologic unit, model layer 3..............................................................28

22. Jurassic hydrogeologic unit, model layer 4 ..................................................................29

23. Upper Pennsylvanian hydrogeologic unit, model layer 5 ...........................................30

24. Lower Pennsylvanian hydrogeologic unit, model layer 6 ...........................................31

25. Michigan hydrogeologic unit, model layer 7.................................................................32

26. Marshall hydrogeologic unit, model layer 8..................................................................33

27. Devonian-Mississippian hydrogeologic unit, model layer 9 ......................................34

28. Silurian-Devonian hydrogeologic unit, model layer 10 ...............................................35

29. Silurian-Devonian hydrogeologic unit, model layer 11 ...............................................36

30. Silurian-Devonian hydrogeologic unit, model layer 12 ...............................................37

31. Maquoketa hydrogeologic unit, model layer 13 ...........................................................38

32. Sinnipee hydrogeologic unit, model layer 14................................................................39

33. St. Peter hydrogeologic unit, model layer 15 ................................................................40

34. Prairie du Chien-Franconia hydrogeologic unit, model layer 16 ...............................41

35. Ironton-Galesville hydrogeologic unit, model layer 17................................................42

36. Eau Claire hydrogeologic unit, model layer 18..............................................................43

37. Mount Simon hydrogeologic unit, model layer 19........................................................44

38. Mount Simon hydrogeologic unit, model layer 20........................................................45

Tables

1. Sources of lithologic data for each State in the study area..................................................6

2. Maximum thicknesses for each hydrogeologic unit...............................................................8

3. Sources of salinity data for each State in the study area ...................................................25

4. Hydrogeologic units, model layers, data sources, and maximum total dissolvedsolids concentration for the initial salinity concentrations .................................................46
v

Conversion Factors

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2

) 259.0 hectare (ha)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

liter (L) 33.82 ounce, fluid (fl. oz)

liter (L) 2.11 pint (pt)

liter (L) 1.0566 quart (qt)

liter (L) 0.264 gallon (gal)

Density

pound per cubic foot (lb/ft3

) 16.02 kilogram per cubic meter (kg/m3)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance below the vertical datum.

Concentrations of chemical constituents in water are given in milligrams per liter (mg/L).

Abbreviations

ASCII American Standard Code for Information Interchange

DEM Digital Elevation Model

GIS Geographic Information System

GWRP Groundwater Resources Program

IGS Indiana Geological Survey

USGS U.S. Geological Survey

WCR Well construction report
vi
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

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. 

Introduction 

At the request of Congress, the U.S. Geological Survey 

(USGS) Groundwater Resources Program (GWRP) was established to identify, measure, and assess the Nation’s groundwater resources. A pilot phase of the GWRP is the water 

availability and use initiative that focuses on the Great Lakes 

region (U.S. Geological Survey, 2002). The goal of the initiative is to provide information about trends in water availability 

and use and to develop an improved capability to forecast the 

availability of water for future economic and ecological uses. 

The best methods of evaluating the resource must be determined and used with the resulting information delivered in a 

manner that helps citizens, communities, and natura1-resource 

managers gain an improved understanding of the Nation’s 

water resource. 

To aid in forecasting water availability, a variable-density 

groundwater-flow model is being developed for the Lake 

Michigan Basin and surrounding area. The Lake Michigan 

Basin was selected for the study for the following reasons:

1. The entire watershed is in the United States, and many 

datasets already are available within the USGS.

2. Groundwater is withdrawn from bedrock and glacialdeposit aquifers, both of which are important aquifer 

systems throughout the Great Lakes Basin. 

3. Important issues related to groundwater and surface-water 

interaction can be simulated with the model. 

4. Groundwater withdrawals in the Lake Michigan Basin 

may affect the locations of groundwater divides with 

Lakes Superior, Huron, and Erie. 

5. Problems caused by large-scale groundwater withdrawals have been documented in the basin (Grannemann and 

Reeves, 2005). 
2 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

Development of the model is a focused effort to simulate 

flow of groundwater at a regiona1 scale and is a component in understanding the water balance in the basin. The 

model should identify the source of water to wells, define the 

complexities of the drainage basin, and provide a regional 

framework for use in future, smaller scale groundwater-flow 

simulations.

A groundwater-flow model requires multiple datasets that 

define hydrogeologic conditions in the area of study. A fundamental dataset for any groundwater-flow model is information 

on the description and distribution of geologic materials that 

underlie the area to be modeled. Mapping of the distribution of 

important aquifers and confining units is needed to define the 

hydrogeologic framework for a model.

Although the Lake Michigan Basin is the focus of the 

GWRP modeling effort, the model extends into neighboring 

drainage basins, including the Mississippi River Basin and 

other Great Lakes basins. Because of the large size and complexity of the study area, an extensive literature review was 

completed and multiple datasets were compiled to characterize 

the bedrock geology of the study area. Data for hydrogeologic 

units were compiled separately for overlying unconsolidated 

sediments (Arihood, 2008) and for bedrock units.

In most cases, groundwater-flow models are used to estimate the flow of freshwater in aquifers. However, in many geologic structural basins, aquifers may be saturated with naturally 

occurring brines that can affect the movement of fluids through 

geologic formations. Groundwater in many bedrock formations 

within the Lake Michigan Basin is affected by highly saline 

brines from sources within the Michigan Structural Basin. The 

interaction of brines with surrounding freshwater cannot be 

simulated by the standard USGS MODFLOW-2000 code that is 

commonly used for regional groundwater-flow models (Harbaugh and others, 2000). A second code, SEAWAT-2000, was 

developed to include the effects of variable density on groundwater flow (Langevin and others, 2003). 

The use of the variable density SEAWAT-2000 code in 

place of MODFLOW-2000 requires additional information, 

including the distribution of salinity throughout the model 

domain. Salinity is considered either as an initial condition 

subject to evolution through time or, as in the case of the Lake 

Michigan Basin model, as a fixed condition influencing the 

circulation of groundwater. A literature review was performed 

and datasets were compiled to evaluate the distribution of 

salinity in groundwater in the study area. 

Purpose and Scope

This report describes the sources of data and the methods 

used to develop the hydrogeologic framework of bedrock units 

and the sources of data and the methods used to map the salinity of groundwater in the Lake Michigan Basin and surrounding area. The maps of the hydrogeologic framework and the 

salinity data are intended for use as input data for simulation 

of groundwater flow in the Lake Michigan Basin. Bedrock 

lithologic data from approximately 54,000 well records were 

compiled, evaluated for discrepancies, and interpolated in a 

geographic information system (GIS) to develop maps for 

each hydrogeologic unit simulated in the model. These data 

were supplemented by data and maps from previous investigations. Salinity data evaluated for this report included total 

dissolved solids concentrations and density determinations. A 

linear relation between salinity and density was developed to 

infer concentrations where only density data were available. 

Methods to extend interpretations into areas having little or 

no data are described. Results are presented in maps showing 

thickness and concentration of total dissolved solids for each 

hydrogeologic unit and corresponding model layer.

Groundwater Model

The area of study for the Lake Michigan Basin groundwater model is approximately 180,000 mi2

 and incorporates 

the entire drainage basin of the lake (approximately 45,000 

mi2) and adjacent parts of Michigan; Indiana; Illinois; Ohio; 

Wisconsin; and Ontario, Canada (fig. 1). The model simulates 

flow of groundwater in unconsolidated sediments and sedimentary rocks extending below the surface to the crystalline 

rocks of Precambrian age. 

Groundwater-flow models use the mathematical method 

of finite difference to compute approximate solutions to differential equations that describe the flow of groundwater in 

space and time. Models require three-dimensional discretization of the area to be modeled, resulting in a grid network in 

the horizontal dimension and layers in the vertical dimension. 

The intersections of the grid with the layers form model cells 

that are assigned dimensions and hydraulic properties.

The Lake Michigan Basin groundwater model is discretized into a grid of 391 by 261 cells. The model has 20 layers: 3 that simulate the glacial and unconsolidated sediments 

and 17 that simulate the bedrock units. The model provides 

additional detail in the area of greatest interest, in this case, 

the Lake Michigan Basin, by use of smaller grid spacing in the 

innermost model domain (fig. 1) compared with the grid spacing at the model boundaries. The smallest interior grid cells 

are 5,000 by 5,000 ft. At the model boundaries, the size of grid 

cells reaches approximately 68,930 ft (13 mi) from north to 

south by 116,490 ft (22 mi) from east to west.

Hydrogeologic Setting

The study area for the Lake Michigan Basin groundwater-flow model encompasses the entire Michigan Structural 

Basin centered in the Lower Peninsula of Michigan and 

extending into parts of Illinois, Wisconsin, Indiana, Ohio, and 

Ontario, Canada. The Michigan Structural Basin is bounded 

by the Canadian Shield to the north, the Wisconsin Arch to 

the west, the Kankakee Arch to the southwest, the Findlay 

Arch to the southeast, and the Algonquin Arch to the east 

(Olcott, 1992, fig. 9; Lloyd and Lyke, 1995, fig. 6) (fig. 1). 
Introduction 3

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Lake Michigan Basin groundwaterflow model boundaryInnermost model domain

Bedrock Geology

Lower Mesozoic Era (Triassic and Jurassic Period) sedimentary rocksUpper Paleozoic Era (Pennsylvanian and Permian Period) sedimentary rocksMiddle Paleozoic Era (Silurian, Devonian, and Mississippian Period) sedimentary rocksLower Paleozoic Era (Cambrian and Ordovician Period) sedimentary rocksPrecambrian Era sedimentary rocksIgneous and metamorphic rocks

Michigan Basin

Canadian Shield

Wisconsin Arch

Kankakee Arch

Findlay Arch

Algonquin Arch Lake Michigan drainage basin

LAKE MICHIGAN

WISCONSIN

ILLINOIS INDIANA

MICHIGAN

OHIO

LAKE HURON

LAKE ERIE

LAKE SUPERIOR

LAKE WINNEBAGO

Geology from Reed and Bush, 2005 Base from U.S. Geological Survey digital data 1:100,000 1983. Universal Transverse Mercator projection

Zone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

ONTARIOCANADA

Water

MichiganBasin Structural geologic feature 

Illinois Basin

(LOWER PENINSULA)

MICHIGAN

(UPPER PENINSULA)

46°

41°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 1. Location of Lake Michigan Basin, groundwater-model boundary and innermost model domain, structural geologic features, and general bedrock geology of the study area. Land areas in white are in Canada.
4 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

The Kankakee Arch separates the Michigan Structural Basin 

from the Illinois Structural Basin—part of which is included 

in the southwest section of the study area. The Findlay Arch 

separates the Michigan Structural Basin from the Appalachian 

Structural Basin to the southeast (Colton, 1962). Cambrian 

rocks of the Wisconsin Arch make up the western boundary of 

the model.

Within the Michigan Structural Basin, Precambrian 

crystalline rocks and the Precambrian Jacobsville Sandstone 

are overlain by approximately 14,000 ft of younger Paleozoic and Mesozoic Era sedimentary rocks (Cohee and others, 

1951; fig. 2). The Paleozoic Era rocks are made up of Cambrian Period sandstones and dolomites, Ordovician Period 

sandstones and limestones overlain by shale, Silurian and 

Devonian Period limestones and dolomites, and Mississippian Period limestones and shales. The Mesozoic Era rocks 

are made up of Pennsylvanian Period sandstones and shales 

and Jurassic Period sandstones. These rocks are overlain by 

glacial deposits from Wisconsinan age and earlier glaciations 

and unconsolidated sediment of recent age. All of the glacial 

and unconsolidated sediments and sedimentary rocks located 

within the boundary of the study area are included within the 

Lake Michigan Basin model.

Hydrogeologic Framework of Bedrock 

Units

The sedimentary rocks within the boundary of the 

simulation were divided into 14 hydrogeologic units. The 14 

units were then subdivided into a total of 17 model layers for 

use within the simulation (fig. 2). The Silurian-Devonian and 

Mount Simon hydrogeologic units were subdivided into three 

and two model layers, respectively. Both the hydrogeologic 

units and model layers were identified by evaluating the major 

lithology of the geologic formation and its relative importance 

as a water-bearing formation within the simulation area. 

Correlation of Stratigraphy to Hydrogeologic Units

Six aquifers designated by the USGS as “principal 

aquifers” are within the model area (fig. 2; Olcott, 1992). The 

surficial aquifer system is found within the Quaternary hydrogeologic model unit. The Pennsylvanian aquifer is simulated by 

the upper Pennsylvanian hydrogeologic unit. The Mississippian 

aquifer is simulated by the Marshall hydrogeologic unit and 

partially by the Michigan and Devonian-Mississippian hydrogeologic units. The Silurian-Devonian aquifer is simulated by 

the Silurian-Devonian and parts of the Maquoketa hydrogeologic units. The Cambrian-Ordovician aquifer is simulated by 

the Maquoketa, Sinnipee, St. Peter, Prairie du Chien-Franconia, 

Ironton-Galesville, Eau Claire and Mount Simon hydrogeologic units. The Jacobsville aquifer is simulated by parts of the 

Mount Simon hydrogeologic unit.

Figure 2 shows the correlation of units in the model. 

Confining units are shown in red, aquifers in blue, and units 

that act as aquifers in some parts of the model area and confining units in others are shown in light blue. Five of the 15 

hydrogeologic units simulate aquifer materials, 4 of the 15 

units simulate confining unit materials, and 6 of the 15 units 

describe units that have properties of aquifers and confining 

units. The basal confining unit of the Lake Michigan Basin 

groundwater flow model is the Precambrian crystalline rock 

that underlies the entire model area. Overlying the crystalline rock is the Precambrian Jacobsville Sandstone, which is 

located in the Upper Peninsula of Michigan, and a series of 

Cambrian and Ordovician aquifers including the Mount Simon 

Formation, the Ironton and Galesville Sandstones, and the 

St. Peter Sandstone. An upper Ordovician confining unit, the 

Maquoketa Group, primarily consisting of shale, underlies 

a series of Silurian and Devonian limestones and dolomites. 

The Silurian-Devonian hydrogeologic unit was divided into 

three model layers. The uppermost of the three model layers represents a discontinuous eroded surface in parts of the 

model area. The remaining portion of the unit was divided 

into two model layers based upon thickness. Mississippian 

and Devonian shales form a confining unit above the Silurian 

and Devonian limestones and dolomites and are overlain by 

Quaternary glacial deposits in Illinois, Indiana, Ohio and parts 

of Wisconsin. 

Bedrock units that are younger than the DevonianMississippian confining unit are not present within the model 

area outside the state of Michigan (fig. 2). Within Michigan, 

the Marshall Sandstone is overlain by the Michigan Formation confining unit. The Bayport Limestone, Parma Sandstone, 

and the shale portion of the Saginaw Formation make up the 

Lower Pennsylvanian hydrogeologic unit. The remainder of 

the Saginaw Formation and Grand River Formations make up 

the upper Pennsylvanian hydrogeologic unit and are partially 

overlain by the Jurassic Ionia Formation. Quaternary glacial 

deposits completely cover the bedrock within the modeled 

area, except for parts of the bedrock in the Upper Peninsula of 

Michigan. 

Some hydrogeologic units in the Lake Michigan Basin 

groundwater-flow model act as aquifers in some parts of the 

model area and confining units in other areas of the model 

(fig. 2). The Eau Claire hydrogeologic unit acts as an aquifer 

where it is a coarse grained sandstone in Michigan’s Upper 

Peninsula and northeastern Wisconsin, but it acts as a confining unit where it becomes finer grained in southeastern 

Wisconsin. In northeastern Illinois, the Eau Claire hydrogeologic unit is a siltstone and acts as a confining unit. The Prairie 

du Chien-Franconia hydrogeologic unit can be an aquifer 

where karstic dolomite is present or where the sandstone units 

dominate; but, often, where no karst is present and the clastic 

sedimentary rocks are siltstones, this unit can act as a confining unit. The Sinnipee hydrogeologic unit, when overlain by 

the Maquoketa hydrogeologic unit, is unweathered and acts as 

a confining unit. Weathered portions of the unit are aquifers. 
Hydrogeologic Framework of Bedrock Units 5

Time-stratigraphic

unit

System Series

References

Quaternary

Jurassic

Pennsylvanian

Mississippian

Devonian

Silurian

Ordovician

Cambrian

Precambrian

Upper

Glacial deposits Glacial deposits Glacial deposits Glacial deposits Glacial deposits

Wisconsin Illinois Indiana Ohio Michigan

Ionia Fm

Upper

Lower

Upper

Middle

Lower

Upper

Middle

Lower

Grand River Fm

Saginaw Fm

Parma Sandstone

Bayport Ls

Michigan Fm

Marshall Sandstone

Coldwater Shale

Sunbury Shale

Ellsworth Shale

Antrim Shale

Traverse Group

Detroit River Group

Bass Islands Group 

Salina Group

Niagara Group

Manistique Group

Burnt Bluff Group

Cataract Group

Upper Richmond Group

Middle

Trenton Fm

Black River Fm

Glenwood Fm

St. Peter Sandstone

Prairie du Chien Gr

Trempealeau Fm

Lower

Franconia Fm

Galesville

Sandstone

Eau Claire Fm

Mount Simon

Sandstone

Middle

Upper

Lower Absent

Catacosinos

and others, 2001

Gray and others,

1985

Jacobsville Sandstone

Crystalline Basement

Complex

Coldwater Shale

Sunbury Shale

Ellsworth Shale

Antrim Shale

Muscatatuck

Group

Salina Group

Salamonie Dolomite

Brassfield Limestone

Absent

Maquoketa Group

Trenton Limestone

Black River Limestone

Ancell Group

Prairie du Chien Gr

Potosi Dolomite

Franconia Sandstone

Ironton Sandstone

Galesville Sandstone

Eau Claire Sandstone

Mount Simon

Sandstone of 

Dresbach Group

Crystalline Basement

Complex

Absent

Coldwater Shale

Sunbury Shale

Bedford Shale

Antrim Shale

Traverse Group

Dundee Formation

Detroit River Group

Absent

Salina Group

Lockport Group

Cataract Group

Rochester Shale

Dayton Formation

Cincinnati group

Trenton Limestone

Black River Group

Wells Creek Fm

Absent

Knox Dolomite

Kerbel Fm

Eau Claire Fm

Mount Simon

Sandstone

Crystalline Basement

Complex

Hull, 1990

Antrim Shale

Milwaukee Fm

Thiensville Fm

Absent

Waubakee Fm

Racine Fm

Manistique Fm

Hendricks Fm

Byron Fm

Mayville Fm

Neda Fm

Maquoketa Fm

Sinnipee Group

Prairie du Chien Gr

Glenwood Fm

St. Peter Fm

Trempealeau Group

Tunnel City Group

Eau Claire Fm

Mount Simon

Formation

Wonewoc Fm

Absent

Keweenawan

Supergroup

Wisconsin 

Geological

and Natural History

Survey, 2006

Buschbach, 1964

Kolata and Graese, 1983

Kolata, 1990

Mikulic and others, 1985

Willman and others, 1975

Young and Siegel, 1992

Maquoketa Group

Galena Group

Platteville Group

Ancell Group

Prairie du Chien Gr

Potosi Dolomite

Franconia Fm

Ironton Sandstone

Galesville Sandstone

Eau Claire Fm

Mount Simon

Sandstone

Crystalline Basement

Complex

New Albany Shale

Group

Cedar Valley Limestone

Wapsipinicon Limestone

Racine Dolomite

Sugar Run Dolomite

Joliet Dolomite

Kankakee Dolomite

Wilhelmi Fm

Absent

Mississippian System

(Undifferentiated)

Absent

Hydrogeologic unit

(model layer)

Quaternary

(1-3)

Jurassic (4)

Upper

Pennsylvanian

(5)

Lower

Pennsylvanian

(6)

Michigan (7)

Marshall (8)

DevonianMississippian

(9)

Silurian-Devonian

(11-12)

Maquoketa (13)

Sinnipee

(14)

St. Peter

(15)

Prairie du ChienFranconia

(16)

IrontonGalesville

(17)

Eau Claire (18)

Mount Simon 

(19-20)

EXPLANATION

Absent

Pennsylvanian System

(Undifferentiated)

USGS 

principal 

aquifer

Surficial aquifer

system

Pennsylvanian

Mississippian

SilurianDevonian

CambrianOrdovician

Silurian-Devonian

(10)

1

1Rocks of the Pennsylvanian System were grouped with 

the Mississippian-Devonian hydrogeologic unit for Illinois

Saginaw Fm (Shale)

Jacobsville

Aquifer

Aquifer/confining unit

Confining unit

Erosional surface

Depositional surface Gr, Group

Fm, Formation

Ls, Limestone

Figure 2. Stratigraphic chart showing time- and rock-stratigraphic framework nomenclature for the Lake Michigan Basin region, the 

U.S. Geological Survey principal aquifers in the model area, and the hydrogeologic units used in the model.
6 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

Model layers 11 and 12 of the Silurian-Devonian hydrogeologic unit are aquifers in Wisconsin and Illinois, but the layers 

act as a confining unit in Michigan due to changes in lithology. 

The Lower Pennsylvanian hydrogeologic unit is dominated 

by the Parma Sandstone and Bayport Limestone, which act as 

aquifers in south central Michigan. In other areas, the unit is 

made up of shale of the Saginaw Formation, thus making it a 

confining unit. 

Sources of Lithologic Data

Several studies have gathered data on bedrock stratigraphy for parts of the Lake Michigan Basin model study area. 

Prior to 2006, few data sources describe the bedrock geology 

beneath Lake Michigan. Kontis and Mandle (1980) developed 

a computerized database system to facilitate the collection, 

evaluation, and manipulation of large quantities of hydrogeologic information used during the development of the stratigraphic framework of the northern Midwest Regional AquiferSystem Analysis for parts of Illinois, Wisconsin, Michigan and 

Indiana. Feinstein and others (2005) described the geologic 

framework for a regional model for southeastern Wisconsin. 

Bricker and others (1983) compiled sources of CambrianOrdovician bedrock formations and developed maps showing 

the structure and thickness of the formations for the state of 

Michigan. S.C. Meyer and others (Illinois State Water Survey, 

written commun., 2008) described the geologic framework for 

a regional model of northeastern Illinois. 

Lithologic data from well records and from prior investigations were compiled to map the distribution of hydrogeologic units within the Lake Michigan Basin model study area. 

The sources of this information are listed for each State in 

table 1.

Illinois

A recent study centered on northeastern Illinois (S.C. 

Meyer and others, Illinois State Water Survey, written 

commun., 2008) established a detailed hydrostratigraphic 

framework that included part of the Lake Michigan Basin 

groundwater-flow model that is in Illinois. This framework 

is similar in conception to the hydrostratigraphic layering 

developed in previous studies (Feinstein and others, 2005) for 

adjacent areas of Wisconsin. 

Wisconsin

Lithologic information for parts of the study area in 

Wisconsin was retrieved from 6,813 well drillers’ logs from 

the wiscLITH lithologic and stratigraphic database (Wisconsin 

Geologic and Natural History Survey, 2004). Well construction reports (WCR) were used to supplement the wiscLITH 

data (Wisconsin Department of Natural Resources, 2006). 

Information about depth to the top of the bedrock surface 

was provided from 15,179 WCRs and 6,625 WCRs provided 

additional information on the depth to crystalline Precambrian 

bedrock within the state. 

Other datasets that describe specific areas of Wisconsin 

were used to supplement the wiscLITH database and WCRs. 

The southeastern portion of the state was described by the 

hydrologic framework developed for a groundwater model in 

southeast Wisconsin (Feinstein and others, 2005; Eaton and others, 1999). The hydrologic framework for a groundwater-flow 

model of a part of south-central Wisconsin by Krohelski and 

others (2000) was also included. Additional information on the 

top of bedrock was taken from (1) a lithologic database of parts 

of northeastern Wisconsin (B.A. Brown, Wisconsin Geological 

and Natural History Survey, written commun., 2005), (2) figures 

describing the thickness of glacial deposits in a part of northcentral Wisconsin (Batten, 1987), and (3) maps describing the 

elevation of the bedrock surface and the depth to Precambrian 

crystalline rock in an area south of Lake Winnebago (Batten, 

2004; W.G. Batten, Wisconsin Geological and Natural History 

Survey, written commun., 2006). Additional information on the 

depth to Precambrian crystalline rock was obtained from R.D. 

Cotter (U.S. Geological Survey, unpublished data, 1986), Olcott 

(1966) and W.G. Batten (Wisconsin Geological and Natural 

History Survey, unpublished data, 1979). 

Table 1. Sources of lithologic data for each State in the study area.

State Sources

Illinois S.C. Meyer and others, Illinois State Water Survey, written commun., 2008

Wisconsin Batten (1987, 2004), Eaton and others (1999), Feinstein and others (2005), Krohelski and others (2000), 

Olcott (1966), Wisconsin Department of Natural Resources (2006), Wisconsin Geological and Natural 

History Survey (2004)

Michigan Bricker and others (1983), Michigan Department of Environmental Quality (2008)

Indiana Gray (2003), Indiana Geological Survey (2005)

Ohio Ohio Division of Geological Survey (2005), Wickstrom and others (1992)
Hydrogeologic Framework of Bedrock Units 7

Michigan

Hydrogeologic unit surfaces within Michigan were interpreted primarily by use of 22,586 well logs from the Michigan 

Department of Environmental Quality’s Wellogic database 

(Michigan Department of Environmental Quality, 2008). 

Additional logs from wells in Quaternary deposits were also 

used to characterize the top of bedrock surface within Michigan (D.P. Lusch, Michigan State University, written commun., 

2006). Isopach and structure maps from the Michigan Geological Survey also were used to define the St. Peter and lower 

hydrogeologic units where well log information was sparse 

(Bricker and others, 1983). Updated information from Nadon 

and others (2000) was used to characterize the extent of the St. 

Peter Sandstone in the Lower Peninsula of Michigan. 

Indiana

Hydrogeologic unit surfaces within Indiana were interpreted by use of 2,753 oil and gas well logs from the Indiana 

Geological Survey’s (IGS) Petroleum Database Management 

System, which contains oil and gas well logs for the state of 

Indiana (Indiana Geological Survey, 2005). Contours of the 

top of bedrock surface were used to characterize the bottom of 

the Quaternary hydrogeologic unit surface (Gray, 2003). 

Ohio

Hydrogeologic unit surfaces within Ohio were interpreted 

by use of 749 well logs from Wickstrom and others (1992). 

Contours of the top of bedrock were used to characterize the 

bottom of the Quaternary hydrogeologic unit surface (Ohio 

Division of Geological Survey, 2005).

Areas Under Lake Michigan

Little information was found describing the bedrock units 

beneath Lake Michigan. The base altitude of the Antrim Shale 

was characterized by use of information from C.S. Swezey 

(U.S. Geological Survey, written commun., 2008). 

Stratigraphic Framework Interpolation Methods

A hydrogeologic framework for a groundwater-flow 

model of northeastern Illinois, which includes the entire area 

of Illinois in the Lake Michigan Basin groundwater-flow 

model, was used as the sole data source for the state of Illinois 

(S.C. Meyer and others, Illinois State Water Survey, written 

commun., 2008). The hydrogeologic framework used for the 

northeastern Illinois groundwater-flow model corresponds to 

the framework used with the Lake Michigan Basin model, 

except for Pennsylvanian bedrock. The Illinois model grouped 

the Pennsylvanian Period bedrock with the Devonian-Mississippian Period bedrock because they have similar lithologies 

and physical properties. The Illinois Pennsylvanian bedrock 

units were therefore included with the Devonian-Mississippian 

hydrogeologic unit in the Lake Michigan Basin groundwaterflow model. The nodal data from the northeastern Illlinois 

groundwater-flow model were converted into ARC-INFO GIS 

point coverages (Environmental Systems Research Institute, 

2003) for each hydrogeologic unit in Illinois. 

The well log data for Wisconsin, Michigan, Indiana, and 

Ohio initially were assigned to multiple hydrogeologic units 

based on the lithologic log associated with each well. Landsurface altitude information reported for the well log was compared to the land-surface altitude interpreted from the digital 

elevation model (DEM) data for the study area. If the difference between the reported altitude of the well and the land surface DEM was greater than 10 ft, the reported altitude of the 

well log was investigated. If the source of the difference was 

not apparent, the well log was not used in the development of 

the hydrogeologic units. Each lithologic unit described in the 

well logs was assigned to a hydrogeologic unit (fig. 2). The 

lithologic log for a well included depth information for each 

lithologic unit. The depth information associated with the bottom of each hydrogeologic unit in the model was subtracted 

from the reported land-surface altitude of the well to obtain an 

altitude of the bottom of the unit. This process was repeated 

for each hydrogeologic unit described in the well log. Data 

points for each separate hydrogeologic unit in Michigan, 

Indiana and Ohio were grouped and then converted into an 

ARC-INFO point coverage (Environmental Systems Research 

Institute, 2003). Available contour data describing the elevation of the bedrock surface (bottom of hydrogeologic unit 1, 

fig. 2) within the state of Indiana also were interpolated using 

the TOPOGRID command in ARC-INFO and then converted 

into ARC-INFO point coverages.

The hydrologic framework developed for a groundwater 

model in southeast Wisconsin (Feinstein and others, 2005; 

Eaton and others, 1999) has the same layering configuration as 

the Lake Michigan Basin groundwater-flow model. Nodal data 

from both the southeast Wisconsin model and a groundwaterflow model by Krohelski and others (2000) were converted 

into ARC-INFO point coverages (Environmental Systems 

Research Institute, 2003). All sources of data for Wisconsin 

were interpolated using the Surfer software package (Golden 

Software Inc., 2002). Contours of the interpolated Wisconsin 

data were visually inspected and evaluated for data inaccuracies within the Surfer software package. Files in ASCII format 

were then exported from the software and then converted into 

ARC-INFO point coverages.

Within Michigan, the Wellogic database included sparse 

information for the deeper hydrogeologic units in the Lower 

Peninsula. Isopach and structural contour maps (Bricker and 

others, 1983) were used to supplement the Wellogic data for 

the St. Peter through the Mount Simon hydrogeologic units 

(fig. 2). The contours were digitized and elevation surfaces 

were generated using the TOPOGRID command in ARCINFO, version 8.3 (Environmental Systems Research Institute, 2003). Structural contours of the top of the Glenwood 
8 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

Formation were used as the bottom of the Sinnipee hydrogeologic unit. Isopach data of the underlying formations were 

then subtracted from the bottom of the next youngest hydrogeologic unit, thus creating the surface altitude for the rest of 

the underlying units. These interpolated surfaces were then 

converted into ARC-INFO point coverages for each hydrogeologic unit. 

The geologic logs for many of the wells used to define 

the hydrogeologic layering in the Michigan Structural Basin 

include the St. Peter Sandstone with underlying rock associated with the Prairie du Chien Formation. To separate the two 

hydrogeologic units, the bottom surface of the St. Peter was 

revised by use of contour information from a recent interpretation of its stratigraphy by Nadon and others (2000). 

Point coverages for each hydrogeologic unit were 

grouped across states and then interpolated to create a topof-hydrogeologic-unit altitude surface using a kriging interpolator available in ARC-INFO, version 8.3 (Environmental 

Systems Research Institute, 2003). Within Michigan, interpolations were restricted to areas within the subcrop boundaries 

of each hydrogeologic unit, which were determined by use of 

the bedrock geology map of Michigan (Michigan Department 

of Environmental Quality, 1987). Because the USGS MODFLOW-2000 code requires continuous hydrogeologic units 

and model layers throughout the area of the model, areas outside of the subcrop boundaries were assigned an altitude equal 

to 0.2 ft less than the overlying hydrogeologic unit to maintain 

the layer throughout the modeled area.

The interpolated surfaces were evaluated to determine if 

areas existed where surfaces crossed, indicating the absence of 

one or more hydrogeologic units. The lower, or older, surface 

was subtracted from the upper, or younger, surface to identify 

areas that had an apparent negative unit thickness. If the areas 

with apparent negative thickness were also mapped as areas 

where the unit is absent, the thickness of the hydrogeologic 

unit within that area was assigned an arbitrary value of 0.2 ft. 

If the areas with apparent negative thickness were not mapped 

as areas where the unit is absent, which was common in areas 

of sparse data coverage, artificial data points were used to 

control the results of the interpolation procedure. Points with 

values similar to existing well log data were included to produce a consistent surface across the area in question.

Because very few data were available for the geology 

beneath Lake Michigan, elevations for each hydrogeologic 

unit were linearly interpolated across the lake from data 

points in Wisconsin to points directly east in Michigan. This 

produced a decrease in elevation and a gradual thickening 

of the units from Wisconsin eastward into Michigan and the 

Michigan Structural Basin. The bottom of the Devonian-Mississippian hydrogeologic unit surface was adjusted to reduce 

the extent of the unit, thus making it similar to the unit extent 

interpreted by C.S. Swezey (U.S. Geological Survey, written 

commun., 2008) and J.A. East (U.S. Geological Survey, written commun., 2008) under Lake Michigan. 

The interpolated surfaces were evaluated for accuracy 

within the Upper Peninsula of Michigan in areas with sparse 

data coverage (C.J. Hoard, U.S. Geological Survey, written 

commun., 2005). Additional data points were added to define 

thicknesses for the Prairie du Chien through Mount Simon 

hydrogeologic units in these areas.

Interpolated surfaces for each hydrogeologic unit were 

then converted to ASCII format text files that listed the elevations of each hydrogeologic unit in each cell of the groundwater-flow model. These altitude values for the hydrogeologic 

units were then imported into the Lake Michigan Basin 

groundwater-flow model. 

Figures 3–17 display the unit thickness values for each 

hydrogeologic unit. The shaded elongated areas around the 

borders of the figures represent the larger cells at the boundary of the model. The uncharacteristic appearance of the 

Devonian-Mississippian hydrogeologic unit beneath Lake 

Michigan (fig. 9) is due to small amounts of Devonian-Mississippian materials found in eastern Wisconsin. Isolated blocks 

like those found near the Lake Michigan shore in Wisconsin 

(see figs. 10–14) represent areas where small amounts of data 

were present in a model cell outside of the innermost model 

domain. The maximum thicknesses for each hydrogeologic 

unit are listed in table 2. The Jurassic, Lower Pennsylvanian, 

Marshall and Ironton-Galesville hydrogeologic units have 

thicknesses less than 550 ft. The Silurian-Devonian hydrogeologic unit has thicknesses less than about 7,550 ft. 

Table 2. Maximum thicknesses for each hydrogeologic unit.

Hydrogeologic unit Maximum thickness 

(feet)

Quaternary 1,107

Jurassic 195

Upper Pennsylvanian 601

Lower Pennsylvanian 527

Michigan 720

Marshall 493

Devonian-Mississippian 2,260

Silurian-Devonian 7,538

Maquoketa 2,162

Sinnipee 1,632

St. Peter 1,364

Prairie du Chien-Franconia 2,060

Ironton-Galesville 543

Eau Claire 1,566

Mount Simon 3,014
Hydrogeologic Framework of Bedrock Units

9

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feetLess than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 3. Thickness of the Quaternary hydrogeologic unit.
10 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feet10 feet

Areas where the thickness of the hydrogeologic unit is less than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 4. Thickness of the Jurassic hydrogeologic unit.
Hydrogeologic Framework of Bedrock Units

11

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feet10 feet

Areas where the thickness of the hydrogeologic unit is less than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 5. Thickness of the Upper Pennsylvanian hydrogeologic unit.
12 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feet10 feet

Areas where the thickness of the hydrogeologic unit is less than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 6. Thickness of the Lower Pennsylvanian hydrogeologic unit.
Hydrogeologic Framework of Bedrock Units

13

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feet10 feet

Areas where the thickness of the hydrogeologic unit is less than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 7. Thickness of the Michigan hydrogeologic unit.
14 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feet10 feet

Areas where the thickness of the hydrogeologic unit is less than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 8. Thickness of the Marshall hydrogeologic unit.
Hydrogeologic Framework of Bedrock Units

15

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feet10 feet

Areas where the thickness of the hydrogeologic unit is less than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 9. Thickness of the Devonian-Mississippian hydrogeologic unit.
16 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feet10 feet

Areas where the thickness of the hydrogeologic unit is less than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 10. Thickness of the Silurian-Devonian hydrogeologic unit.
Hydrogeologic Framework of Bedrock Units

17

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feet10 feet

Areas where the thickness of the hydrogeologic unit is less than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 11. Thickness of the Maquoketa hydrogeologic unit.
18 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feet10 feet

Areas where the thickness of the hydrogeologic unit is less than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 12. Thickness of the Sinnipee hydrogeologic unit.
Hydrogeologic Framework of Bedrock Units

19

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feet10 feet

Areas where the thickness of the hydrogeologic unit is less than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 13. Thickness of the St. Peter hydrogeologic unit.
20 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feet10 feet

Areas where the thickness of the hydrogeologic unit is less than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 14. Thickness of the Prairie du Chien-Franconia hydrogeologic unit.
Hydrogeologic Framework of Bedrock Units

21Figure 15. Thickness of the Ironton-Galesville hydrogeologic unit.

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feet10 feet

Areas where the thickness of the hydrogeologic unit is less than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°
22 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

Figure 16. Thickness of the Eau Claire hydrogeologic unit.

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feet10 feet

Areas where the thickness of the hydrogeologic unit is less than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°
Hydrogeologic Framework of Bedrock Units

23

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Unit Thickness

10,000 feet1,000 feet100 feet10 feet

Areas where the thickness of the hydrogeologic unit is less than 10 feet

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 17. Thickness of the Mount Simon hydrogeologic unit.
24 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

Initial Salinity Distribution 

of Groundwater in Bedrock 

Hydrogeologic Units 

The use of the variable-density SEAWAT-2000 code in 

place of MODFLOW-2000 requires additional data including 

an initial or fixed distribution of salinity throughout the modeled area to account for its effect on hydraulic gradients and 

hydraulic conductivity. This section describes the data sources 

and procedures used to evaluate the initial salinity of groundwater within the Lake Michigan Basin model study area. Only 

data that originated from water samples or geophysical methods were used in developing the distributions. Data presented 

in this report are referred to as “salinity data” and are reported 

in terms of the concentration of total dissolved solids, which 

is an expression for the combined content of all inorganic 

and organic substances contained in a volume of water (Hem, 

1985, p. 157). 

Sources of Groundwater Salinity Data

Several studies have gathered data on the salinity of 

groundwater for parts of the Lake Michigan Basin model study 

area. Kammerer (1998) investigated the geology, groundwater 

flow, and total dissolved-solids concentrations within Wisconsin aquifers. Gupta (1993) compiled an extensive dataset of 

the total dissolved-solids concentrations and fluid densities for 

areas of Indiana, Michigan, Illinois, and Ohio. Schnoebelen 

and others (1995) delineated the approximate location of the 

10,000-mg/L total dissolved-solids boundary in Devonian and 

Silurian carbonate aquifers in northern Indiana. Ryling (1961) 

investigated the distribution of saline water in bedrock aquifers within Wisconsin. Nicholas and others (1987) described 

the salinity of multiple formations at a test well in northeastern 

Illinois. Bond (1972) described the density of groundwater in 

the Mount Simon Formation in northeast Illinois and northwest Indiana. Ging and others (1996) describe the salinity 

of the Marshall aquifer in the Lower Peninsula of Michigan. 

Meissner and others (1996) describe the salinity of the Saginaw aquifer in the Lower Peninsula of Michigan. Wahrer and 

others (1996) describe the salinity of the glaciofluvial aquifer 

system in the Lower Peninsula of Michigan. 

Salinity data were available for only some of the hydrogeologic units within the area of the groundwater-flow model. 

No data were available for the Jurassic, Lower Pennsylvanian, 

Michigan, Devonian-Mississippian, Maquoketa, St. Peter, 

Ironton-Galesville, or Eau Claire hydrogeologic units. Sources 

used in each State are listed in table 3. 

Interpolation Methods Used to Develop Initial 

Salinity Distribution

Data from Gupta (1993) were reported as both the density 

and total dissolved-solids concentration of groundwater; 

however, for the state of Michigan, data were reported only 

in terms of density. The data points reported in both density 

and concentration were used to create a linear regression of 

the relation between the two terms (fig. 18). This regression 

model was used to calculate the missing concentration values 

based on reported density values. Concentration values of total 

dissolved-solids were interpolated spatially by use of a kriging 

interpolator available in ARC-INFO, version 8.3 (Environmental Systems Research Institute, 2003). Contours of total 

dissolved-solids concentration were manually drawn from the 

interpolated surfaces to create the initial distribution of salinity 

for each hydrogeologic unit with available data. 

Salinity data for groundwater in the two Mount Simon 

model layers were created by use of total dissolved-solids 

concentration contours from Bond (1972) in the Illinois region 

of the model. Bond reports seven different distributions of 

concentration that vary with depth. Two distributions were 

selected based on the approximate depths of the two model 

layers that represent the Mount Simon hydrogeologic unit. 

Total dissolved-solids concentrations for groundwater in 

the bedrock hydrogeologic units present in Wisconsin were 

defined by use of data from cross sections included in Kammerer (1998), and the distributions of total dissolved-solids 

concentrations were then compared with those reported by 

Ryling (1961) for similarities. Both datasets have similar distributions of groundwater salinity along the western shoreline 

of Lake Michigan and areas around Lake Winnebago. Much of 

the salinity in the Wisconsin part of the study area is less than 

1,000 mg/L for all of the model layers. Concentrations greater 

than 1,000 mg/L were digitized and included in the salinity 

dataset.

Contour datasets of groundwater salinity for each 

hydrogeologic unit with available data were combined by 

use of the ARC-INFO GIS and spatially interpolated using 

the kriging interpolator (Environmental Systems Research 

Institute, 2003). These distributions were then assigned to the 

model layers corresponding to the hydrogeologic unit (fig. 2). 

Because the vertical distribution of salinity is inconsistent, it 

was necessary to either interpolate data between model layers 

with reported salinity and those without, or assign salinity 

values from a layer with similar hydrogeologic properties. 

Table 4 shows where data were available and how data were 

assigned or interpolated vertically from known to unknown 

locations. Although the distributions for model layers 2 and 3 

were taken from model layer 1, the maximum total dissolvedsolids concentrations vary due to the extent of the model 

layers. The distributions for each model layer were converted 

into ASCII format text files that list the total dissolved-solids 
Initial Salinity Distribution of Groundwater in Bedrock Hydrogeologic Units 25

concentration of each cell in the specific model layer of the 

groundwater-flow model. These values were then imported 

into the groundwater flow model. 

Figures 19–38 display the total dissolved-solids concentration values for each layer of the model. Because the distribution of total dissolved-solids values vary by several orders 

of magnitude, the scales present on the figures vary. Model 

layers in the Quaternary, Jurassic, Upper Pennsylvanian, Lower 

Pennsylvanian, and Michigan hydrogeologic units have total 

dissolved-solids concentrations less than 100,000 mg/L. Model 

layers in the Silurian-Devonian, Sinnipee, St. Peter, Prairie du 

Chien-Franconia, and Ironton-Galesville hydrogeologic units 

have total dissolved-solids concentrations greater than 

400,000 mg/L. 

Table 3. Sources of salinity data for each State in the study area.

State Sources

Illinois Bond (1972), Visocky and others (1985), Young (1992)

Indiana Eberts and George (2000), Gupta (1993), Schnoebelen and others (1998)

Michigan Ging and others (1996), Gupta (1993), Meissner and others (1996), Wahrer and others (1996)

Ohio Gupta (1993)

Wisconsin Kammerer (1998), Ryling (1961), Young (1992)

1.0 1.1 1.2 1.3

Fluid Density

0

100000

200000

300000

400000 TDS

1.0 1.1 1.2 1.3

GROUNDWATER DENSITY, IN KILOGRAMS PER CUBIC METER

400,000

300,000

200,000

100,000

0

TOTAL DISSOVLED-SOLIDS CONCENTRATION, IN MILLIGRAMS PER LITER

y = 1.3794E6x – 1.3778E6

R = 0.96 2

500,000

Figure 18. Groundwater density and total dissolved-solids concentrations for data from Gupta (1993). 

The equation of the best fit line was used to determine the concentration of total dissolved solids for the 

data where only groundwater density was reported. 
26 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0006,0004,0002,0001,000

Hydrogeologic unit not present

8,000

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 19. Initial total dissolved-solids concentration of groundwater in the Quaternary hydrogeologic unit, model layer 1.
Initial Salinity Distribution of Groundwater in Bedrock Hydrogeologic Units 

27

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0006,0004,0002,0001,000

Hydrogeologic unit not present

8,000

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 20. Initial total dissolved-solids concentration of groundwater in the Quaternary hydrogeologic unit, model layer 2.
28 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0006,0004,0002,0001,000

Hydrogeologic unit not present

8,000

Area not colored if less than 1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 21. Initial total dissolved-solids concentration of groundwater in the Quaternary hydrogeologic unit, model layer 3.
Initial Salinity Distribution of Groundwater in Bedrock Hydrogeologic Units 

29

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0006,0004,0002,0001,000

Hydrogeologic unit not present

8,000

Area not colored if less than 1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 22. Initial total dissolved-solids concentration of groundwater in the Jurassic hydrogeologic unit, model layer 4.
30 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0006,0004,0002,0001,000

Hydrogeologic unit not present

8,000

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 23. Initial total dissolved-solids concentration of groundwater in the Upper Pennsylvanian hydrogeologic unit, model layer 5. 
Initial Salinity Distribution of Groundwater in Bedrock Hydrogeologic Units 

31

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0006,0004,0002,0001,000

Model layer not present

8,000

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

Figure 24. Initial total dissolved-solids concentration of groundwater in the Lower Pennsylvanian hydrogeologic unit, model layer 6.
32 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0001,000

Hydrogeologic unit not present

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

100,000

Figure 25. Initial total dissolved-solids concentration of groundwater in the Michigan hydrogeologic unit, model layer 7.
Initial Salinity Distribution of Groundwater in Bedrock Hydrogeologic Units 

33

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0001,000

Hydrogeologic unit not present

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

1,000,000100,000

Figure 26. Initial total dissolved-solids concentration of groundwater in the Marshall hydrogeologic unit, model layer 8.
34 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0001,000

Hydrogeologic unit not present

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

1,000,000100,000

Figure 27. Initial total dissolved-solids concentration of groundwater in the Devonian-Mississippian hydrogeologic unit, model layer 9.
Initial Salinity Distribution of Groundwater in Bedrock Hydrogeologic Units 

35

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0001,000

Hydrogeologic unit not present

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

1,000,000100,000

Figure 28. Initial total dissolved-solids concentration of groundwater in the Silurian-Devonian hydrogeologic unit, model layer 10.
36 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0001,000

Hydrogeologic unit not present

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

1,000,000100,000

Figure 29. Initial total dissolved-solids concentration of groundwater in the Silurian-Devonian hydrogeologic unit, model layer 11.
Initial Salinity Distribution of Groundwater in Bedrock Hydrogeologic Units 

37

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0001,000

Hydrogeologic unit not present

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

1,000,000100,000

Figure 30. Initial total dissolved-solids concentration of groundwater in the Silurian-Devonian hydrogeologic unit, model layer 12.
38 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0001,000

Hydrogeologic unit not present

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

1,000,000100,000

Figure 31. Initial total dissolved-solids concentration of groundwater in the Maquoketa hydrogeologic unit, model layer 13. 
Initial Salinity Distribution of Groundwater in Bedrock Hydrogeologic Units 

39

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0001,000

Hydrogeologic unit not present

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

1,000,000100,000

Figure 32. Initial total dissolved-solids concentration of groundwater in the Sinnipee hydrogeologic unit, model layer 14.
40 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0001,000

Hydrogeologic unit not present

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

1,000,000100,000

Figure 33. Initial total dissolved-solids concentration of groundwater in the St. Peter hydrogeologic unit, model layer 15.
Initial Salinity Distribution of Groundwater in Bedrock Hydrogeologic Units 

41

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0001,000

Hydrogeologic unit not present

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

1,000,000100,000

Figure 34. Initial total dissolved-solids concentration of groundwater in the Prairie du Chien-Franconia hydrogeologic unit, model layer 16. 
42 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0001,000

Hydrogeologic unit not present

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

1,000,000100,000

Figure 35. Initial total dissolved-solids concentration of groundwater in the Ironton-Galesville hydrogeologic unit, model layer 17.
Initial Salinity Distribution of Groundwater in Bedrock Hydrogeologic Units 

43

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0001,000

Hydrogeologic unit not present

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

1,000,000100,000

Figure 36. Initial total dissolved-solids concentration of groundwater in the Eau Claire hydrogeologic unit, model layer 18.
44 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0001,000

Hydrogeologic unit not present

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

1,000,000100,000

Figure 37. Initial total dissolved-solids concentration of groundwater in the Mount Simon hydrogeologic unit, model layer 19.
Initial Salinity Distribution of Groundwater in Bedrock Hydrogeologic Units 

45Figure 38. Initial total dissolved-solids concentration of groundwater in the Mount Simon hydrogeologic unit, model layer 20.

0 50 100 25 Miles

0 50 100 25 Kilometers

EXPLANATION

Innermost model domainModel boundary

Base from U.S. Geological Survey digital data1:100,000 1983. Universal Transverse Mercator projectionZone 16, Standard Parallel 0° (Equator), Central Meridian 87° W,North American Datum 1983

Total dissolved-solids concentration,in milligrams per liter

10,0001,000

Hydrogeologic unit not present

Area not colored if less than1,000 milligrams per liter

41°

46°

89° 83° 87° 85°

 45°

44°

43°

42°

1,000,000100,000
46 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

Summary 

The U.S. Geological Survey is assessing the availability and use of our Nation’s water resources to gain a clearer 

understanding of the status those resources. A hydrogeologic 

framework and distribution of total dissolved-solids concentrations were developed for input into a groundwater-flow 

model of the Lake Michigan Basin and surrounding area. The 

geology of the study area was divided into 15 hydrogeologic 

units that describe the glacial and bedrock geology of the 

study area. Five of the 15 hydrogeologic units simulate aquifer 

materials, 4 of the 15 units simulate confining unit materials, 

and 6 of the 15 units describe units that have properties of 

aquifers and confining units. These hydrogeologic units were 

subdivided into 20 layers to be used within the Lake Michigan 

Basin groundwater-flow model. The Jurassic, Lower Pennsylvanian, Marshall and Ironton-Galesville hydrogeologic 

units have thicknesses less than 550 ft. The Silurian-Devonian 

hydrogeologic unit has thicknesses less than about 7,550 ft. 

A related background investigation identified different 

data sources that could be used to characterize the groundwater resources of the study area. Existing models, well log databases, and geologic maps provided data to define the extent 

and depth of each hydrogeologic unit within the study area. 

Well log databases were assigned to multiple hydrogeologic 

units based on the lithologic log associated with each well. 

Data for each hydrogeologic unit were grouped and converted 

into a GIS based database. The hydrologic frameworks for 

Table 4. Hydrogeologic units, model layers, data sources, and maximum total dissolved-solids concentration for the 

initial salinity concentrations.

[Data presented in this report are referred to as salinity data and are reported in terms of total dissolved solids (TDS)]

Hydrogeologic unit Model layer Sources of data

Maximum total 

dissolved-solids 

concentration

(milligrams per liter)

Quaternary

1 Data available 6,549

2 Assigned from model layer 1 2,861

3 Assigned from model layer 1 1,067

Jurassic 4 Interpolated from model layers 1 and 5 2,049

Upper Pennsylvanian 5 Data available 5,034

Lower Pennsylvanian 6 Assigned from model layer 5 5,034

Michigan 7 Interpolated from model layers 5 and 8 66,658

Marshall 8 Data available 131,950

Devonian–Mississippian 9 Interpolated from model layers 8 and 11 249,075

Silurian–Devonian

10 Interpolated from model layers 8 and 11 249,075

11 Data available 401,799

12 Assigned from model layer 11 401,799

Maquoketa 13 Interpolated from model layers 11 and 14 379,760

Sinnipee 14 Data available 402,589

St. Peter 15 Interpolated from model layers 14 and 16 407,106

Prairie du Chien–Franconia 16 Data available 413,623

Ironton–Galesville 17 Assigned from model layer 16 413,623

Eau Claire 18 Interpolated from model layers 17 and 19 399,180

Mount Simon

19 Data available 386,410

20 Data available 386,410
References Cited 47

existing models were converted to nodal data points, assigned 

to a hydrogeologic unit, and converted into a GIS database. 

Isopach and structural contour maps were digitized, and elevation surfaces for each hydrogeologic unit were generated by 

use of a GIS. The interpolated surfaces of each hydrogeologic 

unit were then converted into point GIS databases. These data 

were merged, interpolated by use of a GIS, and then converted 

to ASCII format text files that could be imported into the 

groundwater-flow model.

Data were also compiled to define an initial distribution 

of total dissolved-solids concentrations that would be used 

to simulate the effects of density-driven flow of groundwater 

within the study area. Data presented in this report are referred 

to as “salinity data” and are reported in terms of total dissolved solids. When datasets were reported only in terms of 

density, total dissolved solids concentrations were derived by 

use of a linear regression developed from datasets that report 

both total dissolved solids concentration and density. Individual data points and contours of total dissolved-solids concentration and density for hydrologic units were combined and 

interpolated by use of a kriging interpolator for model layers 

with available data. Those layers without data were assigned 

values based on available data from layers above and below. 

The interpolated distributions for each model layer were then 

converted to ASCII format text files that could be imported 

into the groundwater-flow model. Model layers in the Quaternary, Jurassic, Upper Pennsylvanian, Lower Pennsylvanian, 

and Michigan hydrogeologic units have total dissolved-solids 

concentrations less than 100,000 mg/L. Model layers in the 

Silurian-Devonian, Sinnipee, St. Peter, Prairie du Chien-Franconia, and Ironton-Galesville hydrogeologic units have total 

dissolved-solids concentrations greater than 400,000 mg/L.

Acknowledgments

Thanks are extended to the Illinois State Water Survey, 

Wisconsin Geological and Natural History Survey, Ohio Division of Geological Survey, and the Indiana Geological Survey 

for providing expertise and data used for this project. Neeraj 

Gupta is thanked for providing an extensive salinity dataset for 

the Midwest. Daniel Feinstein and Cheryl Buchwald of the U.S. 

Geological Survey provided valued assistance by compiling the 

sources for bedrock lithologies for Wisconsin. Howard Reeves 

and Chris Hoard of the U.S. Geological Survey provided valued 

assistance by compiling sources for bedrock lithology and salinity within Michigan. 

References Cited

Arihood, L.D., 2008, Processing, analysis, and general evaluation of well-driller records for estimating hydrogeologic 

parameters of the glacial sediments in a ground-water flow 

model of the Lake Michigan Basin: U.S. Geological Survey 

Scientific Investigations Report 2008–5184, 26 p.

Batten, W.G., 2004, Preliminary Paleozoic geologic map of 

Fond du Lac County, Wisconsin: Wisconsin Geological and 

Natural History Survey Open-File Report 2004–23, scale 

1:100,000, 1 pl.

Batten, W.G., 1987, Water resources of Langlade County, Wisconsin: Wisconsin Geological and Natural History Survey 

Information Circular 58, 28 p. 

Bond, D.C., 1972, Hydrodynamics in deep aquifers of the 

Illinois basin: Illinois State Geological Survey Circular 470, 

72 p.

Bricker, D.M., Milstein, R.L., and Reszka, C.R., Jr., 1983, 

Selected studies of Cambro-Ordovician sediments within 

the Michigan Basin: Michigan Geological Survey Report of 

Investigation 26, 54 p.

Buschbach, T.C., 1964, Cambrian and Ordovician strata 

of northeastern Illinois: Illinois State Geological Survey 

Report of Investigation 218, 90 p.

Catacosinos, P.A., Westjohn, D.B., Harrison III, W.B., Wollensak, M.S., and Reynolds, R.F., 2001, Stratigraphic lexicon 

for Michigan: Michigan Department of Environmental 

Quality, Geological Survey Division Bulletin 8, 56 p.

Cohee, G.V., Macha, C., and Holk, M., 1951, Thickness and 

lithology of upper Devonian and Carboniferous rocks in 

Michigan: U.S. Geological Survey Oil and Gas Investigation Chart 41, 5 sheets.

Colton, G.W., 1962, Geologic summary of the Appalachian 

Basin, with reference to the subsurface disposal of radioactive waste solutions: U.S. Geological Survey Open-File 

Report 62–28, 121 p.

Eaton, T.T., Bradbury, K.R., and Evans, T.J., 1999, Characterization of the hydrostratigraphy of the deep sandstone aquifer in southeastern Wisconsin: Wisconsin Geological and 

Natural History Survey Open-File Report 1999–02, 30 p.

Eberts, S.M., and George, L.L., 2000, Regional ground-water 

flow and geochemistry in the Midwest Basins and Arches 

aquifer system in parts of Indiana, Ohio, Michigan and Illinois: U.S. Geological Survey Professional Paper 1423–C, 

103 p.
48 Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin

Environmental Systems Research Institute, 2003, ARC-INFO, 

version 8.3: Redlands, Calif.

Feinstein, D.T., Eaton, T.T., Hart, D.J., Krohelski, J.T., and 

Bradbury, K.R., 2005, A regional aquifer simulation model 

for southeastern Wisconsin, Report 1—Data collection, conceptual model development, numerical model construction, 

and model calibration: Southeastern Wisconsin Regional 

Planning Commission, Technical Report 41, 81 p.

Ging, P.B., Long, D.T., and Lee, R.W., 1996, Selected geochemical characteristics of ground water from the Marshall 

aquifer in the central Lower Peninsula of Michigan: U.S. 

Geological Survey Water-Resources Investigations Report 

94–4220, 19 p.

Golden Software Inc., 2002, Surfer, version 8.00: Golden, 

Colo.

Grannemann, N.G., and Reeves, H.W., 2005, Great Lakes 

Basin water availability and use—A study of the National 

Assessment of Water Availability and Use Program: U.S. 

Geological Survey Fact Sheet 2005–3113, 4 p.

Gray, H.H., 2003, Bedrock topography contours, Indiana: 

Indiana Geological Survey, 1:500,000, Line Shapefile. 

Accessed April 4, 2008, at URL http://igs.indiana.edu/

arcims/statewide/ download.html.

Gray, H.H., Droste, J.B., Patton, J.B., Rexroad, C.B., Shaver, 

R.H., 1985, Correlation chart showing Paleozoic supplement stratigraphic units of Indiana: Indiana Geological 

Survey Miscellaneous Map 48.

Gupta, Neeraj, 1993, Geologic and fluid-density controls on 

the hydrodynamics of the Mt. Simon Sandstone and overlying geologic units in Ohio and Surrounding states: Columbus, Ohio, The Ohio State University, Ph.D. dissertation, 

266 p.

Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, 

M.G., 2000, MODFLOW-2000, The U.S. Geological Survey modular ground-water model—User guide to modularization concepts and the ground-water flow process: U.S. 

Geological Survey Open-File Report 00–92, 121 p.

Hem, J.D., 1985, Study and interpretation of the chemical 

characteristics of natural water (3d ed.): U.S. Geological 

Survey Water-Supply Paper 2254, 264 p.

Hull, D.N., 1990 (compiler), revised by Larson, G.E., 2000, 

and Slucher, E.R., 2004, Generalized column of bedrock 

units in Ohio: Ohio Department of Natural Resources, Division of Geological Survey, accessed April 24, 2008, at URL 

http://www.dnr.state.oh.us/Portals/10/pdf/stratcol.pdf.

Indiana Geological Survey, 2005, Petroleum Database Management System: Microsoft SQL Server database for managing petroleum well data in Indiana. Accessed December 

18, 2008, at URL http://igs.indiana.edu/pdms/.

Kammerer, P.A., 1998, Geology, ground-water flow, and 

dissolved-solids concentrations in ground water along 

hydrogeologic sections through Wisconsin aquifers: U.S. 

Geological Survey Hydrologic Atlas 731, 4 sheets.

Kolata, D.R., 1990, Overview of sequences. in Leighton, 

M.W., Kolata, D.R., Oltz, D.F., and Eidel, J.J., eds., Interior 

cratonic basins: Tulsa, Okla., American Association of 

Petroleum Geologists Memoir 51, p. 59–73.

Kolata, D.R., and Graese, A.M., 1983, Lithostratigraphy and 

depositional environments of the Maquoketa Group (Ordovician) in northern Illinois: Illinois State Geological Survey 

Circular 528, 49 p.

Kontis, R.J., and Mandle, A.L., 1980, Data-base system for 

northern Midwest regional aquifer-system analysis: U.S. 

Geological Survey Water-Resources Investigations Report 

80–104, 23 p. 

Krohelski, J.T., Bradbury, K.R., Hunt, R.J., and Swanson, 

S.K., 2000, Numerical simulation of groundwater flow in 

Dane County, Wisconsin: Wisconsin Geological and Natural 

History Survey Bulletin 98, 31 p.

Langevin, C.D., Shoemaker, W.B., and Guo, Weixing, 2003, 

MODFLOW-2000, the U.S. Geological Survey modular 

ground-water model—Documentation of the SEAWAT-2000 

version with the variable-density flow process (VDF) and 

the Integrated MT3DMS transport process (IMT): U.S. 

Geological Survey Open-File Report 03–426, 43 p.

Lloyd, O.B., and Lyke, W.L., 1995, Ground-water atlas of the 

United States—Segment 10, Illinois, Indiana, Kentucky, 

Ohio, and Tennessee: U.S. Geological Survey Hydrologic 

Atlas 730–K, 30 p.

Meissner, B.D., Long, D.T., and Lee, R.W., 1996, Selected 

geochemical characteristics of ground water from the Saginaw aquifer in the central Lower Peninsula of Michigan: 

U.S. Geological Survey Water-Resources Investigations 

Report 93–4220, 19 p.

Michigan Department of Environmental Quality, 1987, 

Bedrock geology, polygon Shapefile, scale 1:63,360. 

Accessed December 18, 2008, at http://www.mcgi.state.

mi.us/mgdl/?rel=thext&action=thmname&cid=2&cat= 

Bedrock+Geology.

Michigan Department of Environmental Quality, 2008, 

Wellogic, Statewide Ground Water Database (SGWD): 

Michigan Department of Environmental Quality (continuously updated). Accessed March 28, 2008, at URL http://

www.mcgi.state.mi.us/mgdl ?rel=thext&action=thmname&

cid=2&cat=Drinking +Water+Wells.
References Cited 49

Mikulic, D.R., Sargent, M.L., Norby, R.D., and Kolata, D.R., 

1985, Silurian geology of the Des Plaines River valley, 

northeastern Illinois: Illinois State Geological Survey 

Guidebook 17, 56 p.

Nadon, G.C., Simo, J.A., Dott, R.H., Jr., and Byers, C.W., 

2000, High-resolution sequence stratigraphic analysis of 

the St. Peter Sandstone and Glenwood Formation (Middle 

Ordovician), Michigan Basin, U.S.A.: American Association of Petroleum Geologists Bulletin, v. 84, p. 975–996.

Nicholas, J.R., Sherrill, M.G., and Young, H.L., 1987, Hydrogeology of the Cambrian-Ordovician aquifer system at a 

test well in northeastern Illinois: U.S. Geological Survey 

Water-Resources Investigations Report 84–4165, 30 p.

Ohio Division of Geological Survey, 2005, Bedrock topography of Ohio: Ohio Division of Geological Survey CD-ROM 

BG–3.

Olcott, P.C., 1966, Geology and water resources of Winnebago 

County, Wisconsin: U.S. Geological Survey Water-Supply 

Paper 1814, 61 p.

Olcott, P.C., 1992, Ground-water atlas of the United States—

Segment 9, Iowa, Michigan, Minnesota, and Wisconsin: 

U.S. Geological Survey Hydrologic Atlas 730–J, 31 p.

Reed, J.C., Jr., and Bush, C.A., 2005, Generalized geologic 

map of the United States, Puerto Rico, and the U.S. Virgin 

Islands, version 2.0: U.S. Geological Survey digital data, 

Accessed January 24, 2008, at URL http://pubs.usgs.gov/

atlas/geologic/.

Ryling, R.W., 1961, A preliminary study of the distribution of 

saline water in the bedrock aquifers of eastern Wisconsin: 

Wisconsin Geological and Natural History Survey Information Circular number 5, 23 p.

Schnoebelen, D.J., Bugliosi, E.F., Hanover, R.H., and Rupp, 

J.A., 1998, Approximate location of the 10,000-milligram-per-liter dissolved-solids boundary in the Silurian 

and Devonian carbonate-rock aquifer, southwestern and 

northern Indiana: U.S. Geological Survey Water-Resources 

Investigations Report 95–4071, 12 p.

Schnoebelen, D.J., Bugliosi, E.F., and Krothe, N.C., 1995, 

Delineation of a saline ground-water boundary from 

borehole geophysical data: Ground Water, v. 33, no. 6, 

p. 965–976.

U.S. Geological Survey, 2002, Concepts for national assessment of water availability and use: U.S. Geological Survey 

Circular 1223, 34 p.

Visocky, A.P., Sherrill, M.G., and Cartwright, Keros, 1985, 

Geology, hydrology, and water quality of the Cambrian and 

Ordovician Systems in northern Illinois: Illinois State Geological Survey Cooperative Groundwater Report 10, 136 p.

Wahrer, M.A., Long, D.T., and Lee, R.W., 1996, Selected geochemical characteristics of ground water from the glaciofluvial aquifer in the central Lower Peninsula of Michigan: 

U.S. Geological Survey Water-Resources Investigations 

Report 94–4017, 21 p.

Wickstrom, L.H., Gray, J.D., and Stieglitz, R.D., 1992, Stratigraphy, structure, and production history of the Trenton 

Limestone (Ordovician) and adjacent strata in northwestern 

Ohio: Ohio Division of Geological Survey Report of Investigations 143, 78 p., 1 pl.

Willman, H.B., Atherton, E., Buschbach, T.C., Collinson, C., 

Frye, J.C., Hopkins, M.E., Lineback, J.A., and Simon, J.A., 

1975, Handbook of Illinois stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p.

Wisconsin Department of Natural Resources, 2006, Water 

well data—Wisconsin well construction reports plus other 

related files: Wisconsin Bureau of Drinking Water and 

Groundwater, created December 6, 2005, CD-ROM.

Wisconsin Geological and Natural History Survey, 2004, 

wiscLITH: A digital lithologic and stratigraphic database of 

Wisconsin geology: Wisconsin Geological and Natural History Survey Open-File Report 2003–05, 39 p.

Wisconsin Geological and Natural History Survey, 2006, Bedrock stratigraphic units in Wisconsin: Wisconsin Geological 

and Natural History Survey Open-File Report 2006–06, 1 p. 

Young, H.L., 1992, Summary of ground-water hydrology of 

the Cambrian-Ordovician aquifer system in the northern 

Midwest, United States: U.S. Geological Survey Professional Paper 1405–A, 55 p.

Young, H.L. and Siegel, D.I., 1992. Hydrogeology of the 

Cambrian-Ordovician aquifer system in the northern Midwest, United States: U.S. Geological Survey Professional 

Paper 1405–B, 99 p.

.
Lampe—Hydrogeologic Framework of Bedrock Units and Initial Salinity Distribution, Lake Michigan Basin—Scientific Investigations Report 2009–5060

Printed on recycled paper