U.S. Department of the Interior

U.S. Geological Survey

USGS Scientific Investigations Report 2005-5223

Revised May 2006

Framework for Regional Synthesis of Water-Quality Data 

for the Glacial Aquifer System in the United States

By Kelly L. Warner and Terri L. Arnold

Introduction

The glacial aquifer system is the largest principal 

aquifer in aerial extent and ground-water use for public supply in the United States. A principal aquifer is 

defined as a regionally extensive aquifer or aquifer 

system that has the potential to be used as a source of 

potable water (U.S. Geological Survey, 2003). Multiple 

aquifers often are grouped into large, extensive aquifer 

systems such as the glacial aquifer system.

The glacial aquifer system is considered here to 

include all unconsolidated aquifers above bedrock north 

of the line of continental glaciation throughout the country (fig. 1). Total withdrawals from the glacial aquifer 

system were 3,560 million gallons per day in 2000, 

which constitutes almost 5 percent of total withdrawals from all aquifers in the United States (Maupin and 

Barber, 2005). Approximately 41 million people relied 

on the glacial aquifer for public supply and domestic use 

in 2000. 

The U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program began assessing 

the glacial aquifer system in 1991. The assessment 

of water-quality data on a regional scale, such as the 

glacial aquifer system, is coincident with the regional 

framework established by the Regional Aquifer-System Analysis Program (RASA) (Sun and others, 1997). 

From 1978 to 1995, the RASA Program systematically 

evaluated 25 of the Nation’s most important groundwater systems including studies in the glacial aquifer 

system in the northeast, Midwest, and northern Midwest 

United States. The NAWQA Program is building on the 

work of the RASA Program to study the water quality of 

16 of the most important ground-water systems (Lapham 

and others, 2005). Over 1,700 water-quality samples 

have been collected by the NAWQA Program from 1991 

to 2004 to assess the glacial aquifer system. This large 

data set is unique in that the samples have been collected using a consistent sampling protocol, and multiple 

nested samples. The nested samples address the recently 

recharged shallow ground water, deeper water from principal aquifers often used for domestic supply, and source 

water used for public supplies within the glacial aquifer 

system. Information concerning the NAWQA Program 

including study unit boundaries is shown in figure 1 

(Lapham and others, 2005).

A framework for comparison of water quality across 

the glacial aquifer system has been developed based on 

two primary characteristics: intrinsic susceptibility and 

vulnerability. Intrinsic susceptibility, which is a measure 

of the ease at which water enters and moves through 

aquifer material, is a characteristic of the aquifer and 

overlying material and of the hydrologic conditions. 

Intrinsic susceptibility is independent of the chemical characteristics of the contaminant and its sources. 

In this way, intrinsic susceptibility assessments do 

not target specific natural or anthropogenic sources of 

contamination but instead consider only the physical 

factors affecting the flow of water to, and through the 

ground-water resource (Focazio and others, 2002). On 

a regional scale, intrinsic susceptibility is represented by 

the spatial distribution of fine- or coarse-grained material 

at the land surface, and the physical setting of the aquifer 

system. Vulnerability, which is a function of both intrinsic susceptibility and the proximity and characteristics of 

contaminant sources, includes consideration of features 

related to anthropogenic sources of contaminants, such 

as the character of the upgradient land use (for example, 

urban, agricultural, undeveloped, and others); as well 

as features related to natural sources of contaminants, 

such as the mineralogy of the aquifer material or the 

geochemical conditions within the aquifer system. The 


framework helps categorize this large region into areas 

of similar hydrogeologic characteristics for which water 

quality can be compared. The purpose of this report is 

to describe this framework and how it will be used for 

regional synthesis of water-quality data for the glacial 

aquifer system.

Regional Framework

The regional framework (fig. 1b) consists of two primary characteristics: (1) intrinsic susceptibility that is an 

indication of how easily water moves through the aquifer 

system, and (2) vulnerability that refers to the tendency 

or likelihood of contaminants to reach the groundwater system (Focazio and others, 2002). The regional 

framework for the glacial aquifer system focuses on 

the vulnerability from contaminants of natural sources. 

Land use can be overlain on this regional framework 

as an indication of vulnerability from anthropogenic 

sources. Likewise, many other indicators of natural and 

anthropogenic sources can be overlain on this framework 

for making a comparative assessment of ground-water 

quality. 

Intrinsic Susceptibility

The glaciated area was divided for analysis of water 

quality into two types of surficial deposits—coarseor fine-grained (fig. 1b). The purpose of dividing the 

glacial aquifer system based on surficial deposits is to 

incorporate intrinsic susceptibility into the framework. 

Numerous studies have been done on glacial sediments 

to determine differences in susceptibility based on matrix 

composition and texture (Hitt and Nolan, 2005; Arnold 

and Friedel, 2000; Berg and others, 1984). Varying 

horizontal and vertical hydraulic conductivities may 

be present for a range of textures. Information on the 

three-dimensional texture of materials is not available 

on a regional scale, so the coarse- or fine-grained sediment texture at the land surface is a surrogate for intrinsic susceptibility. The spatial distribution of fine- and 

coarse-grained deposits is derived from the digital data 

set by Soller and Packard (1998). Coarse-grained deposits, defined by Soller and Packard (1998) for the glacial 

materials, consist of layered sand and gravel, with less 

common silt and clay beds, deposited in fluvial, glaciofluvial, deltaic, and outwash-plain settings. Fine-grained 

deposits within the regional glacial aquifer system 

framework include fine-grained stratified sediments and 

till. The fine-grained stratified sediments are generally 

clay, silt, and very fine sand, but include lesser amounts 

of coarser material, commonly as interbeds. Till consists of poorly sorted sediments that are unstratified and 

composed of particles ranging in size from clay to large 

boulders. Although there is a wide range of till hydraulic 

conductivity, till is grouped with fine-grained deposits 

in this study. Intrinsic susceptibility considers physical 

factors affecting the flow of water to and through the 

ground-water resource. One of these factors is the physical setting of the aquifer system.

Physical Setting

The glaciated area was classified into two general 

patterns of aquifer geometry—valley-fill deposits, and 

layers or lenses (fig. 1b). The purpose of classifying the 

glacial aquifer system by aquifer geometry is to incorporate the physical setting of the aquifer into the regional 

framework. The valley-fill deposits are glacial deposits 

that fill a bedrock valley (although some deep valleys 

in glacial till are present in the western part of the study 

area), and may be in hydraulic connection to the land 

surface or buried. The layers or lenses are lenticular or 

continuous sand deposits that may be in physical connection to the land surface or buried. The aquifer geometry 

is an indication of the distribution and connectivity of 

aquifer material (potential lateral and vertical hydraulic 

connection). An understanding of the three-dimensional 

configuration of the aquifer and the aquifer boundaries 

is a prerequisite to development and protection of the 

aquifers. Randall (2001) summarizes the need to know 

aquifer geometry in conjunction with surficial material 

because the distribution of the glacial aquifer system is 

not coincident with the surficial distribution of coarsegrained deposits. For example, some coarse deposits 

constitute productive aquifers but are buried beneath 

fine-grained deposits and, thus, are not depicted on surficial geology or soils maps; other deposits are surficial 

but can not be considered aquifers because they rest on 

shallow bedrock and are thinly or variably saturated. The 

interpretation of site-specific information depends as 

much on the patterns of aquifer geometry the investigator expects or recognizes, as it does on the site-specific 

information.

Aquifer geometry is difficult to determine in layers and lenses, but the boundaries of an aquifer within 

a bedrock valley are more easily defined. Aquifers in 

a bedrock valley may be buried, in which case there is 

no surface topographic relief associated with this bed-


rock valley. Alternatively, a bedrock valley with surface 

topographic relief may have a thick sequence of glacial 

deposits in the bottom of the valley. Most of the glacial 

aquifer system located in bedrock valleys in the northeastern United States (East area, fig. 1a) is composed of 

deposits (called stratified drift in the northeastern United 

States) that are present to the land surface and bounded 

by bedrock with topographic relief. Although not common, some of the glacial aquifer system in bedrock valleys in the northeastern United States contains surficial 

confining units. The glacial aquifer system in valleys in 

the Central area (fig. 1a) often contains a thick sequence 

of fine-grained till and is bounded by carbonate bedrock 

(for example, the Mahomet aquifer in Illinois and buried 

valley aquifer near Dayton, Ohio (Rowe and others, 

1999)), but there are many aquifers in valleys near rivers 

that have some topographic relief and are present to the 

land surface. A map of the spatial distribution of buried 

valleys is not available. For this study, the glacial aquifer 

system near river valleys was determined by buffering a 

digital data set of streams by approximately 3 miles and 

overlaying the resulting buffered areas on the surficial 

materials data set (Soller and Packard, 1998). The glacial 

aquifer system in valleys was defined where the buffered stream and coarse-grained sediments intersected. 

This process identified the aquifer geometry in the East 

area and adequately represented the aquifer geometry 

in the West, West-Central, and Central areas with some 

modification. These areas are described in the following 

section on “Vulnerability”. Thickness of deposits was 

not appropriate for developing a map of buried valleys 

because the glacial deposits in Michigan are extremely 

thick (up to 1,000 feet thick in some areas). Information 

about locations of buried valleys was included where 

regional maps of the buried valleys were available.

Vulnerability

The vulnerability of the glacial aquifer system is 

difficult to determine because many factors determine 

the composition of the aquifer matrix and geochemical 

conditions needed to mobilize constituents. Physiography and direction of travel of the glacial lobes are 

large-scale features (tens to hundreds of miles) used to 

group areas that may have similar glacial source materials. The glaciated area in the United States was divided 

into four major glacial areas based on differing glacial 

source material—East, Central, West-Central, and West 

areas (figs. 1a, b). Numerous studies have been done on 

glacial sediments that show distinct geochemical differences in the sediment based on geologic source of glacial 

sediment and sediment size (Randall, 2001; Shilts, 1995; 

Shilts, 1993; Shacklette and Boerngen, 1984). Weathering and leaching can dissolve and mobilize many constituents from the sediments that will affect the natural 

Cordilleran

Ice Sheet

Puget

Sound

Basin

EXPLANATION

GLACIAL AQUIFER SYSTEM EXTENT

NAWQA STUDY-UNIT BOUNDARY AND NAME

GROUND-WATER SAMPLING POINT

PERCENT OF STATE TOTAL GROUND-WATER WITHRAWALS FOR

PUBLIC SUPPLY THAT IS FROM THE GLACIAL AQUIFER SYSTEM

No data shown

Greater than 20 to 40

0 to 20

Greater than 40 to 60

Greater than 80 to 100

Greater than 60 to 80

C

Central Columbia

Plateau and

Yakima River Basin

Pacific Ocean

A

UT

MT

ID

NV

OR

IA

CO KS

WY

IL OH

MO

MN

NE

SD WI

ND ME

VA

IN

NY MI

MI

KY

PA

WV

VT

NJ

NH WA

MA

CA

AK

DE

C A N A D A

CTRI

MD 0 200 MILES

0 200 KILOMETERS

Cordilleran

Ice Sheet

Laurentide Ice Sheet

EXPLANATION

West

GLACIAL FRAMEWORK AREA–

Shown only in the United States

GLACIAL AQUIFER SYSTEM EXTENT

150° 140° 130° 120° 110° 100° 90° 80° 70° 60°

60°

50°

40°

130° 120° 110° 100° 90° 80°

60°

50°

40°

East

Central

West-Central

Pacific Ocean

Atlantic

Ocean

Figure 1. (A) Framework areas, (B) flowchart of framework layers, and (C) groun

system, United States.


ground-water chemistry, but the presence of a chemical 

constituent in the aquifer matrix is not directly related to 

its presence in ground water. Changes in aquifer conditions, such as oxidation-reduction potential (redox), 

may begin to mobilize chemical compounds within 

or adsorbed to the glacial source materials, and, thus, 

continue to alter the natural ground-water chemistry. 

Regional variations in the source of glacial sediments 

might be used to predict the reactivity of redox-sensitive 

contaminants in the glacial aquifer system. Combining 

Laurentide Ice Sheet

Red River

of the

North Basin

Upper Mississippi River Basin

Eastern

Iowa

Basins

Lower

Illinois

River

Basin

Upper

Illinois

River

Basin Lake ErieLake St. Clair

Drainage

White River Basin

and Great and Little

Miami River Basins

Long Island and

New Jersey Coastal Drainages

Central

Nebraska

Basin

Western

Lake Michigan

Drainages

Delaware

River

Basin

Hudson

River

Basin

Connecticut,

Housatonic,

and Thames

River Basins

New England Coastal

Basins

High Plains Regional Ground

Water Study

-

N

0 200 MILES

0 200 KILOMETERS

Allegheny and

Monongahela

River Basins

Lake Superior Lake Michigan

Lake Huron

Lake Erie

Lake Ontario

Atlantic Ocean

N

-

ALASKA

0 CANADA

0 100 KILOMETERS

100 MILES

Bering Sea

Pacific Ocean

Arctic Ocean

Cook Inlet Basin

B

Glacial Aquifer System Regional Assessment

Laurentide Ice Sheet

Coarsegrained

surficial

deposits

Aquifer

in

layer

or

lens

Aquifer

in

valleyfill

deposit

Finegrained

surficial

deposits

Aquifer

in

layer

or

lens

Aquifer

in

valleyfill

deposit

Coarsegrained

surficial

deposits

Aquifer

in

layer

or

lens

Aquifer

in

valleyfill

deposit

Finegrained

surficial

deposits

Aquifer

in

layer

or

lens

Aquifer

in

valleyfill

deposit

Coarsegrained

surficial

deposits

Aquifer

in

layer

or

lens

Aquifer

in

valleyfill

deposit

Finegrained

surficial

deposits

Aquifer

in

layer

or

lens

Aquifer

in

valleyfill

deposit

Vulnerability

Intrinsic

susceptibility

Physical

setting

West-Central Area

Interior Plains

Great Plains:

Glacial material from northwestern ice

Central Area

Interior Plains

Central Lowlands and Laurentian

Upland: Glacial material from

Great Lakes Lobes

East Area

Appalachian Highlands

Plateaus, Piedmont, Valley and Ridge,

New England: Glacial material over

crystalline rock and metasediment

Cordilleran Ice Sheet

Coarsegrained

surficial

deposits

Aquifer

in

layer

or

lens

Aquifer

in

valleyfill

deposit

Aquifer

in

layer

or

lens

Aquifer

in

valleyfill

deposit

West Area

Highlands, plateaus, and lowlands:

Glacial material over volcanic and

sedimentary rocks

Finegrained

surficial

deposits

nd-water sampling points and percent of ground-water withdrawals for public supply (modified from Maupin and Barber, 2005) within the glacial aquifer 


the physiography map of Fenneman and Johnson (1946) 

with the boundaries of glacial lobes and sublobes as 

defined by Mickelson and others (1983) is the basis for 

the classification of glacial source material into East, 

Central, West-Central and West areas. These boundaries are a general guide for defining the areas (fig. 1a) in 

which to compare water quality across the glaciated area, 

but local detail on source of glacial material and geochemical conditions may further refine the boundaries of 

these areas.

Water Quality 

The framework for the glacial aquifer system classifies the entire study area into smaller areas of similar 

intrinsic susceptibility and vulnerability from natural 

sources. In addition, water-quality data collected 

by NAWQA are being used to delineate groundwater areas of similar chemistry. Comparing the 

areas of similar chemistry to the regional framework will help corroborate the framework design 

that is based on physical characteristics of the 

aquifer system. 

Areas of similar intrinsic susceptibility in 

the glacial aquifer framework may have differing vulnerability depending on distribution of 

the natural or anthropogenic contaminant source. 

For example, in the East, the coarse-grained 

deposits in a bedrock valley may have high 

intrinsic susceptibility, but the vulnerability may 

vary because there is not a uniform distribution 

of natural contaminant or glacial source material. Even in areas where the source of the glacial 

materials is similar, such as the East, Central, 

West-Central, and West areas (fig. 1a), the natural 

contaminant source materials may not be uniform 

in distribution so the vulnerability may not be 

uniform. The unconsolidated nature of the glacial materials also makes these deposits vulnerable to anthropogenic contamination. 

The glacial aquifer system is used extensively as a source of drinking water for public 

and domestic supply; therefore, water quality is 

an issue for water managers, health officials, and 

private well owners. Many natural contaminants 

are present in the glacial aquifer system because 

the geologic source of the aquifer material is 

from rock types containing a wide variety of minerals that contain arsenic, uranium, radon, and other 

potential contaminants. 

Comparison of water quality within and among areas 

of the regional framework will provide insight on source, 

distribution, fate, and transport of possible contaminants. 

Some common water-quality issues across the glacial 

aquifer system include high nitrate, arsenic, radionuclide, and chloride concentrations, and multiple pesticide 

detections. Statistical analysis of contaminant concentrations and pesticide detections in ground water from 

the glacial aquifer system by framework area is shown in 

figure 2. Some variability in contaminant concentration 

among the framework areas helped identify the issues for 

further investigation. In addition to delineating areas of 

similar water chemistry for corroboration of the glacial 

Figure 2. Boxplots showing contaminant concentrations and pesticide 

detections in ground water from the glacial aquifer system.


aquifer system framework, analyses of five regional 

water-quality issues are planned:

(1) Nutrients and pesticides in ground water supplying domestic wells;

(2) The association of arsenic in ground water with 

depth, redox conditions, and ground-water age in varied 

framework areas; 

(3) Radon and uranium in ground water from the 

glacial aquifer system and underlying bedrock aquifers;

(4) Geochemical comparison of trace elements in the 

glacial aquifer system;

(5) Effects of deicing chemicals on ground- and 

surface-water quality.

The analyses of these five regional water-quality 

issues will begin the process of understanding regional 

differences in water quality in similar framework areas 

and the issues affecting the source and transport of contaminants on a regional scale.

References Cited

Arnold, T.L., and Friedel, M.J., 2000, Effects of land use on 

recharge potential of surficial and shallow bedrock aquifers in 

the Upper Illinois River Basin: U.S. Geological Survey WaterResources Investigations Report 00-4027, 18 p.

Berg, R.C., Kempton, J.P., and Cartwright, Keros, 1984, Potential 

for contamination of shallow aquifers in Illinois: Illinois State 

Geological Survey Circular 532, 30 p.

Fenneman, N.M., and Johnson, D.W., 1946, Physical divisions of 

the United States: U.S. Geological Survey Special USGS map, 

scale 1:7,000,000, accessed on June 15, 2005, at URL: http://

aa179.cr.usgs.gov/metadata/wrdmeta/physio.htm/

Focazio, M.J., Reilly, T.E., Rupert, M.G., and Helsel, D.R., 2002, 

Assessing the ground-water vulnerability to contamination—

providing scientifically defensible information for decision 

makers: U.S. Geological Survey Circular 1224, 33 p.

Hitt, K.J., and Nolan, B.T., 2005, Nitrate in ground water—using 

a model to simulate the probability of nitrate contamination of 

shallow ground water in the conterminous United States: U.S. 

Geological Survey Scientific Investigations Map 2881, 2 p.

Lapham, W.W., Hamilton, P.A., and Myers, D.N., 2005, National 

Water-Quality Assessment Program—Cycle II Regional 

Assessments of Aquifers: U.S. Geological Survey Fact Sheet 

2005-3013, 4 p.

Maupin, M.A., and Barber, N.L., 2005, Estimated withdrawals 

from principal aquifers in the United States—2000: U.S. Geological Survey Circular 1279, 46 p.

Mickelson, D.M., Clayton, L., Fullerton, D.S., and Borns, H.W., 

Jr., 1983, The Late Wisconsin glacial record of the Laurentide 

Ice Sheet in the United States: Late-Quaternary environments 

of the United States, Volume 1, the late Pleistocene, S.C. Porter 

(ed.) University of Minnesota Press, Minneapolis, p. 3-37.

Randall, A.D., 2001, Hydrogeologic framework of stratified-drift 

aquifers in the glaciated northeastern United States: U.S. Geological Survey Professional Paper 1415-B, 179 p.

Rowe, G.L., Shapiro, S.D., and Schlosser, P., 1999, Use of environmental tracers to evaluate groundwater age and water-quality trends in a buried-valley aquifer, Dayton area, southwestern 

Ohio: U.S. Geological Survey Water-Resources Investigations 

Report 99-4113, 81 p.

Shacklette, H.T., and Boerngen, J.G., 1984, Element concentrations in soils and other surficial materials of the conterminous 

United States: U.S. Geological Survey Professional Paper 

1270, 105 p. 

Shilts, W.W., 1995, Geochemical partitioning in till: Ministry of 

Energy, Mines, and Petroleum Resources, British Columbia: 

Geological Survey of Canada publication, Paper 1995-2, p. 

149-163.

Shilts, W.W., 1993, Geological survey of Canada’s contributions 

to understanding the composition of glacial sediments: Canadian Journal of Earth Science, v. 30, p. 333-353.

Soller, D.R., and Packard, P.H., 1998, Digital representation of a 

map showing the thickness and character of Quaternary sediments in the glaciated Untied States east of the Rocky Mountains: U.S. Geological Survey Digital Data Series DDS-38.

Sun, R.J., Weeks, J.B., and Grubb, H.F., 1997, Bibliography 

of Regional Aquifer-System Analysis Program of the U.S. 

Geological Survey, 1978-96: U.S. Geological Survey WaterResources Investigations Report 97-4074, 63 p.

U.S. Geological Survey, 2003, Principal Aquifers: National Atlas 

of the United States of America, map scale 1:5,000,000.

For additional information about regional assessments of 

aquifers, contact:

Wayne Lapham

wlapham@usgs.gov

(703) 648-5805

For online information, reports, and data from the 

NAWQA Program:

Summary reports of assessments conducted during the

first decade in the 51 Study Units:

http://water.usgs.gov/nawqa/nawqa_sumr.html

Information and publications from the National Synthesis

Teams: http://water.usgs.gov/nawqa/natsyn.html