U.S. Department of the Interior

U.S. Geological Survey

Water-Resources Investigations Report 00–4008

The Importance of Ground Water

in the Great Lakes Region

Sandstone, carbonate, 

and shale aquifer

Rocks that are generally 

poorly permeable

(mostly shale)

Carbonate aquifer

Carbonate and sandstone aquifer

Sandstone aquifer

Granite and gneiss

(moderate to poor aquifer)

Great Lakes Basin boundary

Bedrock aquifers of the Great Lakes Basin

0 50 100 MILES

0 50 100 KILOMETERS

L a k e S u p e r i o r

L

a

k

e

M i c h i g a n

Lake

Huron

Georgian

Bay

L a k e Eri e

Lake Ontario
I

The Importance of Ground Water in the

Great Lakes Region

By N.G. Grannemann, R.J. Hunt, J.R. Nicholas, T.E. Reilly, and T.C. Winter

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 00–4008

Lansing, Michigan

2000
II

U.S. DEPARTMENT OF THE INTERIOR

Bruce Babbitt, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

For additional information Copies of this report can be

write to: purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

Water Resources Division Federal Center

6520 Mercantile Way, Suite 5 Box 25286

Lansing, MI 48911 Denver, CO 80225-0286
III

Why do we need to know more about ground-water conditions in the Great Lakes Region? ............................................... 1

What are the major ground-water issues in the Great Lakes Region? ................................................................................... 1

Geology establishes the framework for aquifers .................................................................................................................... 3

How does ground water move in the Great Lakes Region? ................................................................................................... 3

Most ground water moves in local flow systems ..................................................................................................... 3

Most ground water for municipal supply comes from regional ground-water flow systems .................................. 4

How is ground water replenished? ......................................................................................................................................... 5

How much ground water is pumped in the Great Lakes Region? .......................................................................................... 6

Some areas where the effects of ground-water pumping have been evaluated ...................................................................... 6

Chicago-Milwaukee Area ........................................................................................................................................ 7

Green Bay-Fox River Area ...................................................................................................................................... 8

Toledo, Ohio Area .................................................................................................................................................... 8

Irrigation throughout the Great Lakes watershed .................................................................................................... 9

Ground-water and surface-water interactions ...................................................................................................................... 10

Ground-water flow into the Great Lakes .............................................................................................................................. 10

A relatively small amount of ground water flows directly to the Great Lakes ...................................................... 11

Ground water keeps streams flowing during periods of low surface runoff .......................................................... 11

Ground water, wetlands, and stream ecology ....................................................................................................................... 11

Ground water and wetlands .................................................................................................................................... 11

Ground water provides refuge for aquatic organisms ............................................................................................ 12

Summary and conclusions .................................................................................................................................................... 12

Issues related to the amount of ground water ........................................................................................................ 12

Issues related to the interaction of ground water and surface water ...................................................................... 12

Issues related to changes in ground-water quality as development expands ......................................................... 13

Issues related to ecosystem health and quantity and quality of ground water ....................................................... 13

References ............................................................................................................................................................................ 13

1. Map showing surficial geology of the Great Lakes Basin .............................................................................................. 1

2. Maps showing

A. Bedrock aquifers of the Great Lakes Basin ........................................................................................................ 2

B. Approximate extent of the freshwater bearing carbonate aquifer in Ohio,

 Indiana, Illinois, and parts of Michigan and Wisconsin .................................................................................. 2

C. Approximate extent of the sandstone aquifer west of Lake Michigan ............................................................... 2

3. Geologic section showing generalized local and regional ground-water flow

 systems in the Great Lakes Region ............................................................................................................................. 3

4. Map showing estimated ground-water withdrawal rates for some major U.S. metropolitan areas ................................ 4

5. Diagram showing generalized ground-water flow

A. Under natural conditions .................................................................................................................................... 5

B. Affected by pumping .......................................................................................................................................... 5

CONTENTS

FIGURES
IV

6. Map showing decline in water levels in the sandstone confined aquifer, Chicago and

 Milwaukee areas, 1864–1980 ....................................................................................................................................... 6

7. Generalized section showing aquifers, confining unit, and direction of ground-water flow near

 Green Bay, Wisconsin .................................................................................................................................................. 7

8. Maps showing simulated potentiometric surfaces in the sandstone aquifer, northeastern

 Wisconsin

A. In 1957................................................................................................................................................................ 8

B. In 1990 ................................................................................................................................................................ 8

9. Map showing potentiometric surface for the carbonate aquifer near Toledo, Ohio, July 1986 ...................................... 9

10. Schematic diagram showing approximate average water budget for Lake Michigan .................................................... 9

11. Map showing average ground-water and surface-runoff components of

 selected watersheds in the U.S. portion of the Great Lakes Basin ............................................................................ 10

CONVERSION FACTORS AND VERTICAL DATUM

 Multiply By To obtain

cubic foot per second (ft3/s) 0.02832 cubic meter per second

million gallons per day (Mgal/d) 0.04381 cubic meter per second

cubic mile per year (mi3/yr) 4.16832 cubic kilometers per year

Sea level: In this report “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)—a geodetic

datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called

Sea Level datum of 1929.
1

The Importance of Ground Water in the Great Lakes Region

Figure 1. Surficial geology of the

Great Lakes Basin.

“Governments should immediately take steps to enhance groundwater research in order to better understand the role of groundwater in the Great Lakes Basin.“

—Interim International Joint Commission (IJC) Report, 1999,

Recommendation IV, Page 30

Although more than 1,000 mi3 of ground water are stored

in the basin—a volume of water that is approximately equal

to that of Lake Michigan—development of the groundwater resource must be carefully planned. Development of

the ground-water resource removes water from storage and

alters the paths of ground-water flow. Ground water that

normally discharges to streams, lakes, and wetlands can be

captured by pumping (the most common form of development), which may deplete or reduce inflows to the Great

Lakes.

Ground water is important to ecosystems in the Great

Lakes Region because it is, in effect, a large, subsurface

reservoir from which water is released slowly to provide a

reliable minimum level of water flow to streams, lakes, and

wetlands. Ground-water discharge to streams generally

provides good quality water that, in turn, promotes habitat

for aquatic animals and sustains aquatic plants during

periods of low precipitation. Because of the slow movement of ground water, the effects of surface activities on

ground-water flow and quality can take years to manifest

themselves. As a result, issues relative to ground water are

often seemingly less dire than issues related to surface water

alone.

Ground water is a major natural resource in the Great

Lakes Region that helps link the Great Lakes and their

watershed. This linkage needs to be more fully understood

and quantified before society can address some of the

important water-resources issues in the region.

“The Great Lakes aquatic ecosystem is made up not only

of the lakes themselves, but also of the complex network

of tributaries and groundwater on which the lakes depend.”

—Interim IJC Report, Page 25

By N.G. Grannemann, R.J. Hunt, J.R. Nicholas, T.E. Reilly, and T.C. Winter

Why do we need to know more about ground-water

conditions in the Great Lakes Region?

Ground water is a major natural resource in the Great

Lakes Region that helps link the Great Lakes and their

watershed. This linkage needs to be more fully understood and quantified before society can address some

of the important water-resources issues in the Great

Lakes.

The Great Lakes constitute the largest concentration of

unfrozen fresh surface water in the western hemisphere—

about 5,440 mi3

. Because the quantity of water in the lakes

is so large, ground water in the Great Lakes Basin is often

overlooked when evaluating the hydrology of the region.

Ground water, however, is more important to the hydrology

of the Great Lakes and to the health of ecosystems in the

watershed than is generally recognized.

The major ground-water resources issues in the Great

Lakes Region revolve around 1) the quantity of ground

water, 2) ground-water and surface-water interaction,

3) changes in ground-water quality as development

expands, and 4) ecosystem health in relation to quantity

and quality of water.

What are the major ground-water issues in the

Great Lakes Region?

Silt and clay (glacial lake deposits)

Sand and gravel (outwash, alluvial 

and ice contact deposits)

Unstratified Drift

Stratified Drift

Till (ground and end moraines)

Bedrock areas where the glacial cover is absent 

(e.g. parts of Canadian Shield) are not distinguished.

EXPLANATION

Lake Superior

Lake Michigan

Lake Huron Lake Erie

Lake Ontario

from The Great Lakes: An Environmental Atlas and Resource Book, 1995
2

Figure 2. (A) Bedrock aquifers of the Great Lakes Basin (modified from Great Lakes Commission,

1975); (B) Approximate extent of the freshwater bearing carbonate aquifer in Ohio, Indiana, Illinois,

and parts of Michigan and Wisconsin (modified from Casey, 1996, figure 14); (C) Approximate extent

of the sandstone aquifer west of Lake Michigan (modified from Young, 1992, figure 16).

A

B

C

A major attraction of the Great Lakes Region is the

abundant water supply on which manufacturing, power

generation, transportation, agricultural, and recreational

sectors have historically relied. Most large public water

supplies are obtained from the lakes themselves, but ground

water is the source of drinking water for about 8.2 million

people within the watershed. Although most residents of

Chicago use water from Lake Michigan, many people in the

Chicago suburbs who live outside of the watershed, but are

close to it, use ground water as a source of supply. As the

suburban areas near the watershed boundary expand, more

and more people depend on ground water to supply household water needs. Small manufacturing companies in suburban locations also are increasing their ground-water use.

As communities encroach upon agricultural areas, conflicts

between agricultural and other ground-water users will

increase (Alley and others, 1999). Therefore, ground-water

resources need to be characterized according to their occurrence, availability, quality, and use to develop a sustainable

supply for all uses.

Pumping ground water can capture water from or intercept flow to streams and alter the area that contributes

ground water to the Great Lakes. Thus, ground-water withdrawals can divert ground water that would normally discharge to the Great Lakes system.

“Water quantity and water quality are inextricably linked.

For most uses, quantity alone does not satisfy the

demand.”

—Interim IJC Report, Page 26

In addition to water quantity issues in the Great Lakes

Region, water quality also can be of concern. As development increases, activities that could threaten the quality of

ground water also increase. Human health needs to be

safeguarded, as does the health of many other organisms

that rely on clean water. Thus, the major ground-water

resource issues in the Great Lakes Region revolve around

1) the quantity of ground water, 2) the interaction of ground

water and surface water, 3) changes in ground-water quality as development expands, and 4) ecosystem health in

relation to quantity and quality of water. In summary,

ground water is an essential part of the Great Lakes Region

water-supply system. It is a critical resource for maintaining human health and healthy ecosystems.

Sandstone, carbonate, 

and shale aquifer

Rocks that are generally 

poorly permeable

(mostly shale)

Carbonate aquifer

Carbonate and sandstone 

aquifer

Sandstone aquifer

Granite and gneiss

(moderate to poor aquifer)

Great Lakes Basin boundary

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

L a k e S u p e r i o r

L a k e M i c h i g a n

Lake

Huron

Georgian

Bay

Lake E r i e

Lake Ontario

Lake

Michigan

Lake Erie

ILLINOIS

WIS.

MICHIGAN

INDIANA

KENTUCKY

OHIO

EXPLANATION

Aquifer boundary—aquifer extends 

beyond edge of map

IOWA

MINNESOTA

WISCONSIN

ILLINOIS

MISSOURI

MICHIGAN

INDIANA

NEBRASKA SOUTH DAKOTA

L a k e M i c h i g a n

EXPLANATION

Aquifer boundary—dashed where uncertain

Areas of aquifer where water is generally 

too saline for most uses

[No data beneath most of Lake Michigan]
3

Figure 3. Generalized local and regional ground-water flow systems in the Great Lakes Region.

Geology establishes the framework for aquifers

Ground water is present throughout the Great Lakes

Basin, but the quantity that can be withdrawn varies depending on the characteristics of the water-bearing rocks

and sediments (aquifers). Unconsolidated material that was

deposited at or near the land surface as a result of large-scale

glacial ice advances and retreats during the last 2 million

years make up the most productive aquifers. These deposits

are as much as 1,200 feet thick in parts of Michigan and are

several hundred feet thick in buried bedrock valleys in

Illinois, Wisconsin, and New York. The deposits are thin or

nonexistent in areas where bedrock that was not easily

eroded by glacial ice is exposed at land surface. Most glacial

deposits are composed of mixtures of sand and gravel, and

silt and clay (fig. 1). Sand and gravel deposits (outwash and

ice-contact deposits) are the most productive aquifers because they have greater permeability and effective porosity

than do the finer grained deposits. Some areas with silt and

clay at the surface (till or glacial lake deposits) contain more

permeable deposits at depth and are able to yield moderate

to large amounts of water to wells. In general, however, the

silt and clay deposits are not aquifers.

Bedrock aquifers are generally widespread throughout

the region and are more continuous than the aquifers in

glacial deposits. Some bedrock aquifers in the region extend far beyond the watershed boundaries. The relations

between ground water in these aquifers and water in the

Great Lakes is complicated because ground-water divides

and watershed boundaries may not coincide. Carbonate

rocks (limestone and dolomite) are the most common

bedrock aquifers in the region (fig. 2A). Natural processes

may increase permeability by dissolving carbonate minerals in these aquifers, but this increased permeability makes

the aquifers more vulnerable to contamination. The most

extensive carbonate aquifer in the region consists of a series

of limestones and dolomites that underlie a large part of the

upper Midwest (fig. 2B). Sandstone aquifers are the next

most common bedrock aquifer. An extensive sandstone

aquifer underlies much of the northern Midwest and even

extends under Lake Michigan (fig. 2C). In general, shale,

and igneous and metamorphic bedrock have limited wateryielding capacity, and they are not considered regional

aquifers.

How does ground water move in the Great Lakes

Region?

Aquifers and confining units (relatively impermeable

rocks and sediments) make up the ground-water system in

the Great Lakes watershed. This system stores water and

acts as a conduit for water to move from recharge areas to

discharge areas (fig. 3). Recharge takes place between

streams in areas that occupy most of the land surface.

Ground water moves in both local and regional flow systems.

Most ground water moves in local flow systems

To improve our understanding of the importance of unconsolidated aquifers in the Great Lakes watershed,

new geologic maps that show the extent, thickness, and

boundaries of these aquifers are needed.

Ground water in local flow systems commonly travels

relatively short distances underground before discharging

1

2

Local ground-water system

Regional ground-water system

Water table

Great Lake

Sediment

Highly permeable aquifer

Poorly permeable confining unit

Very poorly permeable bedrock

Direction of ground-water flow,

local ground-water system

Direction of ground-water flow,

regional ground-water system

EXPLANATION

Unsaturated zone

Surface-water body

1

1

2

2

2

2

2

1
4

Figure 4. Estimated ground-water withdrawal rates for some major U.S. metropolitan areas (data not available for Canadian areas).

to a stream, lake, or wetland. The Great Lakes Region has

an abundance of small streams, and most ground-water

flow takes place in these shallow systems. The amount of

ground water moving through these systems is not well

quantified, however, because most water-supply studies

have focused on deeper regional flow systems. The most

productive shallow aquifers are composed of sand and

gravel (fig. 1). The extent of these deposits near the land

surface is commonly known and illustrated on maps, but the

thickness and capability to transmit water often is not well

known. To improve our understanding of the importance of

ground-water flow in unconsolidated aquifers in the Great

Lakes watershed, new geologic maps that show the extent,

thickness, and boundaries of these aquifers are needed

(Central Great Lakes Geologic Mapping Coalition, 1999).

Most ground water for municipal supply comes from

regional ground-water flow systems

More work needs to be done to define and quantify the

interactions between regional ground-water flow and

ground-water discharge to the Great Lakes.

Regional ground-water flow systems are usually deeper

below land surface and have longer flow paths than local

flow systems (fig. 3). Confining units that restrict flow of

water between the systems commonly separate local from

regional flow, but thick, unconfined aquifers may have

regional scale ground-water flow. In the Great Lakes Region, regional ground-water flow occurs in both glacial

deposits and bedrock aquifers, depending on the hydraulic

properties of the aquifers and confining units, and the

topographic relief.

Glacial deposits usually consist of a complex assemblage

of sediments (fig. 3). In some parts of the region, glacial

deposits are as much as 1,200 feet in thickness. As thickness

increases, the complexity of the sediment assemblage usually increases. These sediments need to be mapped using

established three-dimensional mapping techniques to understand their geological framework (Bhagwat and Berg,

1991). Hydraulic characteristics of the sediments also need

to be determined for the aquifers that are increasingly being

tapped for water supply. Armed with this hydrogeologic

characterization, water managers will be able to make better

determinations of sustainable withdrawal rates from the

region’s aquifers.

The extent, thickness, hydraulic properties, and general

directions of flow in the most used bedrock aquifers have

been described by regional aquifer studies conducted by the

USGS (Sun and others, 1997) and by State and local

agencies (Bleuer and others, 1991; Batten and Bradbury,

1996; and Passero and others, 1981). Although these studies provide a baseline of hydrologic and geologic information, more work needs to be done to define and quantify the

interactions between regional ground-water flow and

ground-water discharge to the Great Lakes. Divides that are

transient barriers to ground-water movement are estab200

90

78 78

82

63

27

93 15

39

30

11

27 36

10

7

12 15

33

L a k e S u p e r i o r

Lake

Huron

Lake

Erie

Lake Ontario

Parry Sound

Sudbury

Sault Ste. Marie

Sault Ste. Marie

Petoskey

Traverse City

Bay City

Saginaw

Grand Rapids Flint

Detroit

Toledo

Milwaukee

Green Bay

Marquette

Toronto

Hamilton

Trenton

Kingston

Duluth

Thunder Bay

Marathon

Owen Sound

London Sarnia

Erie

Buffalo

Niagara Falls

Cleveland/Akron

Chicago

Rochester Syracuse

Oswego

Massena

Cornwall

Montréal

Trois Rivières CANADA

U.S.A.

L a k e S u p e r i o r

L a k

e

M i c

h i g a n

Lake

Huron

Lake

Erie

Lake Ontario

Georgian

Bay

Great Lakes Drainage Basin

U.S.A./Canada border

Cities/towns

EXPLANATION

Windsor

Ground-water withdrawal

rate, in millions of gallons per day

Lansing

Kalamazoo Battle Creek/

Jackson

Portage/Michigan City

South Bend/Mishawaka

Elkhart/Goshen

Fort Wayne

0 50 100 MILES

0 50 100 KILOMETERS

Source map: Environment Canada
5

lished by a combination of natural and human-induced

stresses on the aquifers. In some areas, bedrock aquifers

may discharge large quantities of water to the lakes, but the

data needed to quantify the amount of flow have not been

collected. In addition, the effects on the Great Lakes of

pumping from regional aquifers are unknown. Many groundwater issues take time to be recognized, but, because of the

large volumes and resulting long travel times for water in

regional flow systems, the time lags expected are usually

much longer than for local flow systems. Thus, adverse

effects of withdrawals may take years to manifest themselves.

How is ground water replenished?

Ground-water recharge rates estimated in previous studies represent the approximate range of recharge to the

water table in the entire Great Lakes Region. A comprehensive study for the entire watershed is needed to

more completely determine the importance of ground

water in the hydrologic budget of the Great Lakes.

Recharge is the term that is commonly used to describe

the process of adding water to the ground-water system.

Although it is difficult to directly measure the amount of

recharge, it is important to estimate recharge rates to understand the effects of ground water on other hydrologic

processes in the basin and to assess how activities at the land

surface may change the recharge rates. The amount of

recharge can vary considerably throughout the basin depending on soil type, precipitation (rates, types, timing, and

amounts), and other factors, including the extent of impervious surfaces (roofed and paved areas) and storm sewers.

For example, the amount of water that infiltrates into a

sandy soil is usually greater than that into clayey soil.

Recharge rates in Michigan’s Lower Peninsula range from

nearly 0 to about 23 inches per year (Holtschlag, 1997).

Ground-water recharge rates estimated in previous studies

represent the approximate range of recharge to the water

table in the entire Great Lakes Region. A comprehensive

study for the entire watershed is needed to more completely

determine the importance of ground water in the hydrologic

budget of the Great Lakes.

Urban development may reduce recharge amounts because impervious surfaces (such as roads, buildings, and

paved areas) often drain to storm sewers, a situation that

increases surface runoff and reduces infiltration. These

processes may significantly alter ground-water conditions

in many urban settings by “short-circuiting” to streams and

Figure 5. Generalized ground-water flow (A) under natural conditions and (B) affected by pumping (Note that surface- and

ground-water divides are coincident in A but not in B).

Water table

Surface-water

divide

Ground-water divide

Surface-water

divide

Stream

Lake

Natural

conditions

A

Confining unit

Ground-water flow direction

Stream

Lake

High-capacity

pumping well

Affected by

pumping

B

Confining unit

Water table

Ground-water divide

Ground-water flow direction
6

Figure 6. Decline in water levels in the sandstone confined aquifer,

Chicago and Milwaukee areas, 1864–1980. (Modified from Avery,

1995.)

lakes water that would have infiltrated to the water table.

They also may increase flood potential. Currently, only 7

percent of the Great Lakes watershed is classified as urban;

therefore, the effects of urbanization on ground-water recharge are likely to be localized and the effects on the

watershed as a whole may be minimal. Because urban areas

are rapidly expanding, however, it is important to continue

to monitor the effects of urbanization on ground-water

recharge rates. Other activities associated with urban expansion, such as increased ground-water pumping, along

with reduced recharge rates may increase the drawdown of

water levels caused by pumping.

Recharge to bedrock aquifers is less well understood

than that to unconsolidated aquifers because infiltrating

water may need to move through several layers of geologic

material before reaching the bedrock aquifer. Direct measurement of recharge rates to bedrock aquifers is difficult.

Estimates of these rates have been made in the USGS

Regional Aquifer-System Analysis studies (Sun and others,

1997) mostly by simulating regional ground-water flow

with digital models. These rates vary considerably from

place to place, but generally are much lower than the

estimates of recharge to the water table, especially for nonpumping conditions.

How much ground water is pumped in the Great

Lakes Region?

Total ground-water withdrawal in the Great Lakes Region is estimated to be about 1,510 Mgal/d or 2,336 ft3

/s

(Solley and others, 1998). An additional 200 Mgal/d or 309

ft3

/s is withdrawn from outside the basin but near Lake

Michigan in the Chicago area to supply commercial, industrial, domestic, and public-supply customers. For comparison, the average discharge of the St. Clair River at Port

Huron is about 120,850 Mgal/d or 187,000 ft3

/s. On a

basinwide scale, ground-water withdrawal is a small part of

the overall hydrologic budget and only about 5 percent of

this water is consumed. The remainder is returned mostly as

surface water effluent. Nevertheless, ground water is the

source of drinking water for more than 8 million people on

the U.S. side of the border in the basin (about one third of

the total number of residents) and continues to be a concern

in both the U.S. and Canada. The areas where large quantities of ground water are pumped on the U.S. side of the

Great Lakes watershed are shown in figure 4. The largest

withdrawal takes place in an eight-county area near Chicago, where an unknown amount of the return flow is

discharged outside the Great Lakes watershed. At the same

time, it should be noted that much of the regional groundwater flow in this area also originates outside of the watershed. An analysis of the amount of ground water pumped

from wells in areas just outside the Great Lakes watershed

would help identify the magnitude of this diversion.

Some areas where the effects of ground-water

pumping have been evaluated

The effects of ground-water withdrawals have been

quantified at only a few locations.

Pumping water from aquifers results in lower groundwater levels (fig. 5) and creates a cone of depression around

a well. Because water must converge on the well from all

directions and because the cross-sectional area through

which the flow occurs decreases toward the well, the hy-

“Issues of diversion and consumptive use of Great

Lakes waters (need) to be addressed more comprehensively ...“

—Interim IJC Report, Page 1

Milwaukee

OZAUKEE

FOND DU LAC SHEBOYGAN GREEN

LAKE

MARQUETTE

COLUMBIA

WASHINGTON

MILWAUKEE

DODGE

KENOSHA

RACINE

WAUKESHA

WALWORTH

DANE

ROCK

BOONE

WINNEBAGO

OGLE

LEE

BUREAU

McHENRY

KANE

DE KALB

DU PAGE

LAKE

COOK

LAKE

PORTER

JASPER

KANKAKEE

WILL

KENDALL

PUTNAM

LA SALLE GRUNDY

IROQUOIS

NEWTON

WISCONSIN

ILLINOIS

INDIANA

ILLINOIS

GREEN STEPHENSON

Rock

JEFFERSON

River

Des

Fox

River

River

River

Plaines

0

Base from U.S. Geological Survey 1:2,000,000 Digital Data

Albers Equal-area Conic projection

Standard parallels 33° and 45°, central meridian –89°

25 50 KILOMETERS

25

41°

42°

43°

89° 88° 87°

0 50 MILES

EXPLANATION

Line of equal water-level decline, 1864–1980—Dashed

 where approximate. Interval, in feet, is variable

Major ground-water divide (1980)

Pre-development ground-water divide (about 1864)

LAKE MICHIGAN

Kankakee

700

800

600

700

800

500

300

100

200

200

400

350

375

300

100

50

50

50

100

500

600

300

400

500

200

50

100

100

100

100

Chicago
7

Figure 7. Aquifers, confining unit, and direction of ground-water flow near Green Bay, Wisconsin.

draulic gradient must get steeper toward the well (Heath,

1983). Cones of depression caused by large withdrawals

from extensive confined aquifers can affect very large areas

(Heath, 1983). Any water withdrawn from the groundwater system will divert part of the water that eventually

would have discharged to a stream, lake, or wetland, or been

transpired by vegetation. Even ground water withdrawn at

some distance from the Great Lakes will reduce flow to the

lakes depending on how much of that ground water is

returned to streams as wastewater effluent. If the amount of

water-level decline is sufficient, ground water that would

normally discharge to the Great Lakes may cease and the

ground-water divide may be altered (fig. 5). In some cases,

water may be drawn from streams or the Great Lakes into

the ground-water system. Measurable effects of groundwater withdrawal have been documented at a few locations

near the Great Lakes. In order to understand the effect of

pumping on the water budget, detailed analyses of groundwater systems near the Great Lakes will be required.

Definition of potentiometric surface: a surface that represents the height above a datum (usually sea level) at

which the water level stands in tightly cased wells that

penetrate the aquifer. In some wells, the water level

rises above the land surface.

Chicago-Milwaukee Area

The effects of ground-water pumping in the ChicagoMilwaukee metropolitan area where, in 1980, about 300

Mgal/d was withdrawn from a very productive sandstone

aquifer system (fig. 2C), are documented in Young (1992).

Prior to large-scale withdrawal of ground water, recharge

and discharge for the aquifer were in balance at about 350

Mgal/d. When wells were first drilled into the sandstone

aquifer along Lake Michigan, the initial ground-water level

at Milwaukee was reported to be 186 feet above the surface

of Lake Michigan; in Chicago, it was reported to be 130 feet

above the lake surface. By 1980, large-scale pumping had

caused the water levels in wells to decline as much as 375

feet in Milwaukee and 900 feet in Chicago. At some

locations, the quality of ground water was altered when

water levels were drawn below the layer that confines the

aquifer. Ground-water levels below the confining layer will

allow parts of the sandstone aquifer to be exposed to oxygen

in the air, which can trigger some chemical reactions that do

not take place in the absence of oxygen. By 1994, groundwater withdrawals in Chicago for public supply decreased

to about 67 Mgal/d and total ground-water withdrawals

decreased to about 200 Mgal/d. These withdrawals were

concentrated west and southwest of the earlier pumping

centers. As a result, ground-water levels in some parts of the

Chicago area have risen by as much as 250 feet, although

EXPLANATION

Water table

Potentiometric surface in the sandstone aquifer

General direction of ground-water flow

Modified from Batten and Bradbury, 1996

FEET

WEST EAST

FEET

Vertical scale greatly exaggerated

Upper aquifer

Maquoketa-Sinnipee

 confining unit

Sandstone aquifer

Crystalline rocks (base 

 of ground-water flow

 system)

Lake Michigan

River

River

Domestic well

River

High-capacity well

Regional ground-water divide

Water-table divide

1,000

600

200

-200

-600

-1000

-1400

-1800

sea

level

1,000

600

200

-200

-600

-1000

-1400

-1800

sea

level

0 5 10 MILES

0 5 10 KILOMETERS
8

Figure 8. Simulated potentiometric surface in the sandstone aquifer, northeastern Wisconsin, (A) in 1957; and (B) in 1990 (from Conlon, 1998).

levels continue to decline in the southwestern Chicago

(Visocky, 1997) and the Milwaukee metropolitan areas.

Computer simulations of the sandstone aquifer system

indicate that, for 1980 pumping conditions, depressed water levels in the system have caused additional recharge and

have resulted in a reduction of natural discharge (Young,

1992). To keep withdrawals in balance with recharge and

discharge, for 1980 pumping rates, water was withdrawn

from storage in the aquifer system thus accounting for lower

ground-water levels. As a result, in 1980, the ground-water

divide in the aquifer system was displaced, in some places,

about 50 miles west of its original (pre-pumping) position

(fig. 6). The rates of recharge, discharge and removal from

storage will vary depending on pumping rates, hydraulic

properties of the aquifer and confining units, and sources of

water. The hydrologic system is further complicated by the

fact that most effluent from ground-water withdrawals in

the Chicago area is discharged to the Mississippi River

Basin via the Chicago Ship and Sanitary Canal—one of the

few places where water is diverted from the Great Lakes

Basin. However, the amount of ground-water diverted from

the Great Lakes Basin by pumping is unknown because

some of the water captured by pumping is recharged to the

aquifer or removed from storage in the aquifer west of the

surface-water divide. These sources of water need to be

more accurately quantified in order to assess whether, on a

net basis, water is being diverted from the Great Lakes by

ground-water withdrawals.

Green Bay-Fox River Area

The sandstone aquifer also is used as a water-supply

source in the Green Bay-Fox River area of Wisconsin. A

depiction of the potentiometric surface for the aquifer

indicates that water-level declines of as much as 300 feet

have occurred (fig. 7). The depressed water levels were

deep enough in 1957 (fig. 8A) that the city of Green Bay

began pumping water from Lake Michigan to supplement

ground-water sources. Withdrawals of ground water were

reduced, so that by 1990, ground-water levels had risen by

about 100 feet in Green Bay (fig. 8B); levels decreased to

the south, however, because of increases in ground-water

withdrawals by outlying communities.

800

800

700

700

700 700

500

900

600

600

600

800

88 ̊

89 ̊

44 ̊

45 ̊

Sandstone

aquifer

absent

800

Fox

River

Wolf

River

Fox River

800

800

800

700

700

700

700

500

900

900

600

600

800

88 ̊

89 ̊

44 ̊

45 ̊

Sandstone

aquifer

absent

20 MILES 

20 KILOMETERS 

0 10

0 10

800 Potentiometric contour—

Shows line of equal simulated

water-level altitude. Interval is

100 feet. Datum is sea level

EXPLANATION

Ground-water divide

Base composited from USGS digital line 

graphs and other digitized information.

Fox

River

Wolf

River

Fox River

600

Green Bay

Green Bay

A. B.

400

Toledo, Ohio Area

The Toledo, Ohio metropolitan area obtains ground

water from wells open to the carbonate aquifer and from

quarry dewatering near Lake Erie. Pumping has lowered
9

Figure 9. Potentiometric surface for the carbonate aquifer near Toledo, Ohio, July 1986.

Figure 10. Approximate average water

budget for Lake Michigan.

water levels in wells as much as 35 feet below the average

level of Lake Erie (fig. 9). In addition, pumping has induced

water from Lake Erie into the ground-water system and

intercepted water that would have discharged from the

ground-water system to Lake Erie (Breen, 1989; Eberts and

George, in press; and Eberts, 1999). Although water-level

data indicate that these interactions are taking place, the

amounts of water being induced from the lake and intercepted by the pumping have not been quantified.

Irrigation throughout the Great Lakes watershed

Irrigation is the largest consumptive use of water in the

Great Lakes watershed, and ground-water sources contribute about half of the water used for irrigation. In areas

where surface-water sources are not readily available, it is

likely that ground water will be the water source if new

irrigation systems are installed.

610

600

590

580

570

560

550

540

550 540

530

550

550

540

540

560

570

580

590

570

580

590

610

600

620

630

640

600

580

640

620

600

580

640

Potentiometric contour—Shows 

altitude at which water would stand 

in tightly-cased wells; dashed where 

approximate. Interval is 10 and 20 

feet. Datum is sea level.

Quarry—Shows location of carbonate 

rock quarry.

Well

[Average lake level approximately 572 

feet above sea level]

EXPLANATION

590

0 24

024

MILES

KILOMETERS

TOLEDO

Source: Breen, 1989

Lake Erie

83°45'

83°30'

41°37'30"

Lake Michigan (values in cubic feet per second)

53,000Precipitation on lake

Direct surface-water runoff

8,800

Ground-water discharge to streams entering the lake

32,000

Direct ground-water discharge to the lake

2,700

Diversions into Lake Michigan

50

Return flows from water users

6,000a

Evaporation from the lake

41,000

Outflow to Lake Huron

52,000

Surface-water withdrawals from the lake

7,500b

Ground-water withdrawals from within the basin

2,100

a Return flow is reduced by 3,200 ft3/s that is diverted

 out of the basin at Chicago, Ill.

b Withdrawals for power plant cooling not included
10

Figure 11. Average ground-water and surface-runoff components of selected watersheds in the U.S. portion of the Great Lakes Basin (from

Holtschlag and Nicholas, 1998).

Ground-water and surface-water interactions

“Surface water commonly is hydraulically connected to

ground water, but the interactions are difficult to observe and measure and commonly have been ignored in

water management considerations and policies. Many

natural processes and human activities affect the interactions of ground water and surface water.”

—Winter and others, 1998

Streams interact with ground water in three basic ways:

they gain water from inflow of ground water through the

streambed, they lose water to ground water by outflow

through the streambed, and they do both, gaining in some

reaches and losing in others (Winter and others, 1998). For

ground water to discharge into a stream channel, the

altitude of the water table in the vicinity of the stream must

be higher than the altitude of the stream-water surface.

Conversely, for water in a stream or lake to flow into the

ground, the altitude of the water table in the vicinity of the

stream must be lower than the altitude of the stream-water

surface. The complexity of these interactions may vary

from stream to stream as well as over time.

“In recognition of the frequent and pervasive interaction

between groundwater and surface water and the virtual

impossibility of distinguishing between them in some

instances, the governments of Canada and the United

States should apply the precautionary principle with

respect to removals and consumptive use of groundwater in the Basin.”

—Interim IJC Report Recommendation V

Ground-water flow into the Great Lakes

L a k e S u p e r i o r

L a k e M i c

h i g a n

Lake

Huron

Lake

Erie

Georgian

Bay

Average ground-water component of 

streamflow, (in percent)

EXPLANATION

20 to 39

40 to 59

60 to 79

80 to 99

Ground water

Surface runoff

65 35

Lake

Superior

Lake

Huron

Lake 

Ontario

Lake

Michigan

Lake

Erie

21

79

75

25

72

28

65 35

52 48

Average ground-water and surface-runoff 

components of streamflow, in percent 

Lake Ontario

“Groundwater is important to the Great Lakes ecosystem...”

—Interim IJC Report, Page 5

An approximate water budget for Lake Michigan helps

place the role of ground water in perspective. This water

budget quantifies the flow of water into and out of Lake

Michigan (fig. 10). Inflow of water to Lake Michigan

consists of precipitation on the lake (about 53,000 ft3/s);

direct surface runoff into the lake (about 8,800 ft3/s);

indirect ground-water discharge to the lake (about 32,000

ft3/s); direct ground-water discharge to the lake (about

2,700 ft3

/s); diversions into the lake (about 50 ft3/s); and
11

return flows into the lake from water users (about 6,000 ft3/

s). Outflow of water from Lake Michigan consists of

evaporation from the lake surface (about 41,000 ft3/s);

outflow from Lake Michigan to Lake Huron (about 52,000

ft3

/s); surface-water withdrawals from the lake (about 7,500

ft3

/s); and ground-water withdrawals in the watershed (about

2,100 ft3

/s) (Croley and Hunter, 1994; written commun.,

Great Lakes Commission; Holtschlag and Nicholas, 1998;

and Grannemann and Weaver, 1999). Although small in

comparison to the amount of water in storage in the Great

Lakes, ground water directly and indirectly contributes

about 80 percent of the water flowing from the watershed

into Lake Michigan. On the basis of these data, it is evident

that ground water is an important component of the hydrologic budget for the Great Lakes Region.

A relatively small amount of ground water flows directly

to the Great Lakes

The Great Lakes are in topographically low settings that,

under natural flow conditions, causes them to function as

discharge areas or “sinks” for the ground-water-flow system. Most ground water that discharges directly into the

lakes is believed to take place near the shore (Grannemann

and Weaver, 1999). Of all the Great Lakes, Lake Michigan

has the largest amount of direct ground-water discharge

(2,700 ft3

/s) because it has more sand and gravel aquifers

near the shore than any of the other Great Lakes (Grannemann and Weaver, 1999). Although this is a relatively low

inflow compared to the total streamflow into the lake from

land areas (41,200 ft3/s) (Croley and Hunter, 1994), it is

nearly equal to the amount of water diverted from Lake

Michigan through the Chicago Ship and Sanitary Canal

(Oberg and Schmidt, 1996).

Ground water keeps streams flowing during periods of

low surface runoff

In most instances, the flow of a stream includes both a

surface-water runoff component and a ground-water inflow

component. The fraction of total streamflow that originated

from ground water must be known to analyze and understand the interaction between surface water and ground

water in the stream. Holtschlag and Nicholas (1998) used a

method called “hydrograph separation” to estimate the

amount of ground water in the total streamflow that discharges to the Great Lakes. They call this quantity of water

“indirect ground-water discharge” to the lakes. Prior to this

study, indirect ground-water discharge was not explicitly

considered in estimates of Great Lakes Basin water supply.

Instead, it was incorporated into the streamflow component

of the supply. Surface runoff is a short-term component of

flow that results from precipitation moving overland to a

stream without percolating into an aquifer. Ground-water

discharge is a long-term, persistent component that results

from that part of precipitation that infiltrates into the soil,

percolates into an aquifer, and then flows to a stream.

Although Holtschlag and Nicholas (1998) used data from

195 streamgaging stations in the watershed for their analysis, the combined drainage areas to these stations covered

only 13.6 percent of the total drainage area of the Great

Lakes Basin. These results were extended to the entire basin

by assuming that the average ground-water component of

streamflow estimated for the ungaged streams is about the

same as that estimated for gaged streams in the basin. Using

this approach Holtschlag and Nicholas estimated that the

average ground-water component of streamflow ranges

from 48 percent for Lake Erie to 79 percent for Lake

Michigan (fig. 11).

Ground water, wetlands, and stream ecology

Ground water and wetlands

“Similar to streams and lakes, wetlands can receive

ground-water inflow, recharge ground water, or do both.”

—Winter and others, 1998

Wetlands, once perceived as worthless land, are now

recognized as a necessary component of a vital landscape

(Hunt, 1996). They are often considered the “kidneys of the

landscape” because of their role in mitigating and filtering

the effects of human activity on water resources in the

watershed. Wetland functions have been shown to include

storm and floodwater retention, shoreline protection, and

water-quality improvement. Wetlands also provide wildlife habitat. More than one-third of endangered species in

the United States are associated with wetlands even though

wetlands comprise less than five percent of the landscape.

Vast areas of wetland acreage —more than 50 percent in the

United States, and more than 95 percent in some states that

border the Great Lakes—have been destroyed, modified, or

converted to other uses since presettlement time. Although

the effects of these losses are beginning to be understood,

more study is needed to improve our knowledge about the

role of these important wetland systems.

Wetland hydrology is widely recognized as the primary

effect on wetland ecology, development, and persistence.

An understanding of the hydrology is essential to identify

and quantify wetland functions and processes. For example, ground-water flow has been shown to be important

for the physical and chemical environment of other aquatic

systems because the amount of dissolved solids carried by

ground water is typically much higher than that carried by

surface water. Thus, ground water can have a profound

effect on the acid susceptibility and nutrient status of the

wetland (Hunt and others, 1997). It is widely recognized

that linkages between water-budget components and wetlands are not well known, due, in large part, to poor

understanding of how ground water flows into and out of

wetlands.
12

though the amount of ground water pumped in the region is

small compared to the total amount of water present, ground

water is an important source of public-water supply as well

as an important source of supply for industrial, agricultural,

and domestic needs. Less clearly understood, however, is

the relation between the amount of streamflow discharging

to the Great Lakes and the large portion of that flow that

originates as ground water. The implications of this understanding for water- and land-use practices and, in turn, their

effects on water quantity and quality, have not been fully

incorporated into a policy framework. To help include

information about the implications of the role that ground

water plays in addressing regional water issues, a comprehensive analysis of indirect ground-water discharge to the

Great Lakes is needed.

Direct ground-water discharge to the Great Lakes is not

a large factor in water-budget analyses for the Great Lakes.

Locally, however, direct ground-water discharge to the

Great Lakes may be important, even though the rates and

places of discharge are not well known. A long-term evaluation of direct ground-water discharge to the Great Lakes

would help place this hydrologic process in proper perspective. Near-shore areas with high rates of direct groundwater discharge may provide valuable habitat for aquatic

organisms.

• Issues related to the interaction of ground water and

surface water

Withdrawal of ground water removes that water from the

watershed when it is consumptively used or when the return

flow is discharged to another drainage basin. Under these

circumstances, pumping ground water constitutes a diversion of Great Lakes water. Alternatively, ground-water

withdrawal could have the opposite effect of diverting

ground-water flow into the watershed by altering the groundwater divides. In particular, as withdrawals associated with

urban expansion increase, more accurate data on the amount

and effects of ground-water use need to be collected. Data

on the amounts of ground water pumped both within the

watershed and outside, but near the watershed boundaries

needs to be collected and evaluated for potential diversion

of water to or from the Great Lakes. It is currently thought

that both irrigation and ground-water withdrawals near the

watershed boundaries constitute relatively small amounts

of water; however, both rapidly changing farming practices

and rapidly expanding urban communities could alter these

amounts in a relatively short timeframe, especially during

drought periods. At present, the effects of ground-water

withdrawals have been quantified in detail at only a few

urban locations.

In addition to quantifying the amount of water pumped

out of aquifers, it is also important to improve our knowledge of the amount of water that is recharging them.

Ground-water recharge rates estimated in earlier studies

While problems associated with ignoring ground water in

water-budget analyses are well known (Winter, 1981),

traditional hydrologic analyses have had limited success in

showing the linkage of ground water to physical and chemical hydrology of wetlands. Previous work on ground water

in wetlands has often relied on methods used in aquiferscale studies, such as widely spaced sample intervals and

aquifer tests. Recently, non-traditional investigations of

wetlands have shown substantial complexity within wetland hydrologic systems (Harvey and Nuttle, 1995; Hunt

and others, 1996). Moreover, this research is showing that

ground water has profound effects on the physical and

chemical environment of a wetland (Hunt and others, 1999).

Ground water provides refuge for aquatic organisms

Ground-water discharge to streams may help provide

important habitat for aquatic organisms, including fish. In

addition, because ground-water temperatures are nearly

constant throughout the year, stream reaches with relatively

large amounts of ground-water discharge can provide refuge to organisms from heat in summer and from cold in

winter. For example, some stream reaches in the region

remain unfrozen even though air temperatures are well

below 32o

 Fahrenheit. Other possible benefits to the survival

of aquatic organisms related to ground-water discharge to

streams include increasing concentrations of dissolved oxygen; adding small amounts of nutrients that are essential to

the health of organisms; providing cold pockets of water in

summer; and maintaining streamflow during dry periods.

Summary and conclusions

Ground water is a major natural resource in the Great

Lakes Region because it indirectly contributes more than 50

percent of the stream discharge to the Great Lakes. In

addition, ground water is the source of drinking water for

millions of people in the region, is an important source of

supply for agriculture and many industries, and provides a

relatively uniform supply of water in some ecologically

sensitive areas to sustain plant and animal species. Therefore, to improve our understanding of water-resources

issues in the Great Lakes Region, it is important to have a

better understanding of the role that ground water plays in

the overall hydrologic system of the lakes.

 The main ground-water resources issues in the Great

Lakes Region are related to the amount of ground water, the

interaction of ground water and surface water, changes in

ground-water quality as development expands, and ecosystem health related to quantity and quality of water.

• Issues related to the amount of ground water

Although the amount of water in the Great Lakes Region

is vast, issues related to relatively small quantities of water

are being raised more and more often. For example, even
13

cover only a small part of the Great Lakes Region. A

comprehensive study of ground-water recharge rates for

the entire watershed is needed to more completely determine the role of ground water in the hydrologic budget of

the Great Lakes.

• Issues related to changes in ground-water quality as

development expands

Ground-water quality is as important as quantity for most

water uses. As ground-water development proceeds, the

possibility of altering the quality of ground water increases.

The quality of ground water can be altered when water

levels are drawn below the layer that confines the aquifer or

by inducing water of lesser quality into an aquifer. Many

local studies of these problems have been conducted, but

few regional-scale analyses of changes in ground-water

quality as a result of ground-water development have been

done.

• Issues related to ecosystem health and quantity and

quality of ground water

Ground water is essential to maintain wetlands and to

provide healthy habitat for other aquatic systems. Wetland

hydrology is widely recognized as the primary influence on

wetland ecology, development, and persistence, and information about hydrology is essential to understanding and

quantifying wetland functions and processes. Studies of the

role of ground water in selected wetlands in a range of

physiographic settings throughout the Great Lakes watershed are needed to more fully understand the role of

wetlands in the Great Lakes Region.

Conlon, T.D., 1998, Hydrogeology and simulation of ground-water flow in the

sandstone aquifer, northeastern Wisconsin: U.S. Geological Survey WaterResources Investigations Report 97-4096, p. 30–31.

Croley, T.E., II, and Hunter, T.S., 1994, Great Lakes monthly hydrologic data:

National Oceanic and Atmospheric Administration Technical Report ERL

GLERL-83, 84 p.

Eberts, S.M., 1999, Water levels and ground-water discharge, Regional Aquifer

System of the Midwestern Basins and Arches Region, in parts of Indiana, Ohio,

Illinois, and Michigan: U.S. Geological Survey Hydrologic Atlas HA 725, 3

maps.

Eberts, S.M., and George, L.L., in press, Regional ground-water flow and geochemistry in the Midwestern Basins and Arches Aquifer System in parts of Indiana,

Ohio, Illinois, and Michigan: U.S. Geological Survey Professional Paper 1423-

C.

Government of Canada and U.S. Environmental Protection Agency, 1995, The

Great Lakes—An Environmental Atlas and Resource Book, EPA 905-B-95-

001, 46 p.

Grannemann, N.G., and Weaver, T.L., 1999, An annotated bibliography of selected

references on the estimated rates of direct ground-water discharge to the Great

Lakes: U.S. Geological Survey Water-Resources Investigations Report 98-

4039, 22 p.

Great Lakes Basin Commission, 1975, Great Lakes Basin Framework Study,

Appendix 3, Geology and Ground Water, 152 p.

Harvey, J.W., and Nuttle, K.W., 1995, Fluxes of water and solutes in a coastal

wetland sediment: Journal of Hydrology, vol. 164, p. 109–125.

Heath, R.C., 1983, Basic ground-water hydrology: U.S. Geological Survey WaterSupply Paper 2220, 84 p.

Holtschlag, D.J., 1997, A generalized estimate of ground-water recharge rates in the

Lower Peninsula of Michigan: U.S. Geological Survey Water-Supply Paper

2437, 37 p.

Holtschlag, D.J., and Nicholas, J.R., 1998, Indirect ground-water discharge to the

Great Lakes: U.S. Geological Survey, Open-File Report 98-579, 25 p.

Hunt, R.J., 1996, Do created wetlands replace wetlands that are destroyed?, U.S.

Geological Survey Fact Sheet, FS-246-96, 4 p.

Hunt, R.J., Krabbenhoft, D.P., and Anderson, M.P., 1996, Groundwater inflow

measurements in wetland systems: Water Resources Research, vol. 32,

p. 495–507.

Hunt, R.J., Krabbenhoft, D.P., and Anderson, M.P., 1997, Assessing

hydrogeochemical heterogeneity in natural and constructed wetlands: Biogeochemistry, vol. 39, p. 271–293.

Hunt, R.J., Walker, J.F., and Krabbenhoft, D.P., 1999, Characterizing hydrology

and the importance of ground-water discharge in natural and constructed

wetlands: Wetlands, vol. 19(2), p. 458–472.

International Joint Commission, 1999, Protection of the waters of the Great Lakes,

Interim Report to the Governments of Canada and the United States, 40 p.

Oberg, K.A., and Schmidt, A.R., 1996, Measurement of leakage from Lake

Michigan through three control structures near Chicago, Illinois, April– October

1993: U.S. Geological Survey Water-Resources Investigations Report 94-4112,

48 p.

Passero, R.N., Straw, W.T., and Schmaltz, L.J., 1981, Hydrogeologic atlas of

Michigan: Western Michigan University, College of Arts and Sciences, Department of Geology, 35 plates.

Solley, W.B., Pierce, R.R., and Perlman, H.A., 1998, Estimated use of water in the

United States in 1995: U.S. Geological Survey Circular 1200, 71 p.

Sun, R.J., Weeks, J.B., and Grubb, H.F., 1997, Bibliography of Regional AquiferSystem Analysis Program of the U.S. Geological Survey, 1978–96: U.S.

Geological Survey Water-Resources Investigations Report 97-4074, 63 p.

Visocky, A.P., 1997, Water-level trends and pumpage in the deep bedrock aquifers

in the Chicago region, 1991–1995: Illinois State Water Survey Circular 182, 44

p.

Winter, T.C., 1981, Uncertainties in estimating the water balance of lakes: Water

Resources Bulletin: vol. 17, p. 82–115.

Winter, T.C., Harvey, J.W., Franke, O.L., and Alley, W.M., 1998, Ground water and

surface water a single resource: U.S. Geological Survey Circular 1139,

77 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.

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resources: U.S. Geological Survey Circular 1186, 79 p.

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between the Wolf and Fox Rivers near Green Bay, Wisconsin: Wisconsin

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programs in Illinois: Case study of Boone and Winnebago Counties and its

statewide applicability: Illinois State Geological Survey Circular 549, 40 p.

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of the buried Marion-Mahomet trunk valley (Lafayette bedrock valley system)

of Indiana, in Melhorn, W.N., and Kempton, J.P., eds., Geology and hydrogeology

of the Teays-Mahomet bedrock valley systems: Geological Society of America

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Breen, K.J., 1989, Potentiometric-surface map of the Carbonate Aquifer in Silurian

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14

Information

For more information please contact:

Norman Grannemann

Ground-Water Resources Program Coordinator

USGS, Water Resources Division

6520 Mercantile Way, Suite 5

Lansing, MI 48911

phone: (517) 887-8936

email: nggranne@usgs.gov

http://water.usgs.gov/ogw/GWRP.html

Authors:

Norman G. Grannemann

Randall J. Hunt

James R. Nicholas

Thomas E. Reilly

Thomas C. Winter

Layout and illustrations: Michelle M. Greenwood, Aaron T. Konkol, and Robyn L. Trentham

This report was cooperatively funded by the International Joint Commission and the U.S. Geological Survey.

Printed on recycled paper