U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 2005–3097

November 2005

Ground-Water Resources Program

Although often overlooked, ground water is increasingly 

important to all of our lives. Ground 

water is the primary source of 

drinking water to approximately half 

the Nation’s population (134 million 

people), provides about 40 percent 

of the irrigation water essential for 

the Nation’s agriculture, sustains the 

flow of most streams and rivers, and 

helps maintain a variety of aquatic 

ecosystems. Moreover, the near-term 

trend in ground-water withdrawals 

for public supply and irrigation is 

continuing to rise (Hutson and others, 

2004). As the Nation’s principal reserve 

of freshwater, ground water requires 

periodic inventories and ongoing 

evaluations to ensure the resource 

is sufficient to meet the numerous 

needs of the Nation. This fact sheet 

provides a description of the U.S. 

Geological Survey (USGS) GroundWater Resources Program and presents 

highlights of ongoing science activities.

What is the Ground-Water 

Resources Program?

 The Ground-Water Resources 

Program is the principal USGS 

program for assessing the availability of 

ground-water resources at the regional 

and national scale (fig. 1). The GroundWater Resources Program evolved from 

the Regional Aquifer-System Analysis 

(RASA) Program. RASA studies 

(1987–95) primarily were designed to 

quantify ground-water budgets for the 

Nation’s principal aquifers, including 

depletions within those aquifers. The 

Ground-Water Resources Program 

updates and builds upon the RASA 

studies. Data collection and processoriented ground-water science are used 

to assess the long-term availability 

of ground-water supplies while also 

addressing the environmental effects 

of ground-water development on land 

and surface-water resources. Studies 

currently funded by the GroundWater Resources Program conduct 

regionally integrated ground-water 

assessments that fill the information 

gap between national efforts, such 

as the previous RASA studies, and 

local-scale efforts, conducted by the 

USGS Cooperative Water Program in 

conjunction with local partners. The 

scope and complexity of changing 

ground-water issues along with funding 

realities require integration of efforts 

both within the USGS and with other 

Federal, State, and local governments, 

as well as the private sector. Priorities 

for the Ground-Water Resources 

Program include regional and national 

overviews, scientific assessments of 

critical ground-water issues, field 

methods and model development, 

and improved access to fundamental 

ground-water data.

The Ground-Water Resources Program provides objective scientific information and understanding 

needed to assess and assure the availability of the Nation’s ground-water resources.

Goals

• Identify, describe, and make available 

fundamental information regarding 

ground-water availability in the Nation’s 

major aquifer systems, and evaluate this 

information over time.

• Characterize natural and human 

factors controlling recharge, storage, and 

discharge in the Nation’s major aquifer 

systems, and improve understanding of 

these processes.

• Develop and test new tools and field 

methods for the analysis of ground-water 

flow systems and the interactions these 

systems have with surface water.

Recharge, WA

GW Availability,

Denver Basin

GW Availability,

Central Valley

Southwest GW

Resources

GW Availability, Mississippi

Alluvial & Sparta Aquifers

Karst Hydrology

Initiative GW Availability,

NC & SC

Local-scale investigation

Regional-scale investigation

EXPLANATION

Shenandoah

Valley,

VA & WV

Recharge, NC

Recharge, PA

Recharge, WI Water-Availability and

Use Initiative, Great Lakes Recharge, MN

High Plains

Figure 1.  Locations of Ground-Water Resources Program studies in the United States, 2005.
Highlights of the Ground-Water 

Resources Program

 Over the past decade, groundwater issues have evolved in scope 

and complexity as a result of 

escalating demands for the resource. 

USGS scientists are capable of 

addressing this increasing complexity 

by targeting a variety of information 

needs with a multi-component 

approach. The Program’s mission 

and goals are achieved through the 

implementation of the following 

ground-water science components.

Regional Ground-Water Evaluations

 The Ground-Water Resources 

Program addresses national 

and regional interests in ground 

water by supporting large-scale, 

multidisciplinary studies of groundwater availability. The studies 

commonly encompass multiple states 

and include scientific assessments 

of critical ground-water issues. Over 

time, the results of these individual 

ground-water availability studies can 

be combined to provide a national 

assessment. The following are 

examples of national and regional 

evaluations of the Nation’s groundwater resources currently supported 

by the Ground-Water Resources 

Program.

Ground-Water Availability of Regional 

Aquifers

 A major component of the 

Ground-Water Resources Program 

is regional ground-water availability 

studies that involve computer-based 

ground-water flow models as a tool 

for hydrologic assessments of the 

Nation’s most important regional 

aquifers. Three regional aquifers 

geographically distributed across 

the United States were identified for 

study beginning in 2004: the Atlantic 

Coastal Plain aquifers in North and 

South Carolina, the Denver Basin 

aquifer in Colorado, and the Central 

Valley aquifer in California. In fiscal 

year 2006, a study of the Mississippi 

Alluvial and Sparta aquifers in parts 

of Arkansas, Louisiana, Mississippi, 

and Tennessee will begin (fig. 1). 

Information about these aquifers is 

critically needed to better manage 

the ground-water resources in these 

areas that are experiencing escalating 

demands. These assessments will 

document the effects of human 

activities (ground-water depletions) 

on ground-water levels, ground-water 

storage, and ground-water discharge 

to streams and other surface-water 

bodies. The 

selected studies 

emphasize a 

strong methodsdevelopment 

component that helps quantify 

and improve current understanding of 

the ground-water resources. Emphasis 

also is being placed on partnering, 

where possible, with other interested 

agencies to maximize the utility of 

the resultant products. Finally, the 

adequacy of data networks will be 

evaluated to assess the cumulative 

effects of ground-water withdrawals 

at a regional scale.

Natural Ground-Water Recharge

 The need for mapping spatial 

and temporal variability of recharge 

to aquifers remains a topic of great 

interest. Improved knowledge of this 

variability will help water managers 

assess water availability and protect 

vulnerable aquifers under stress 

from increased demands on water 

resources because of expanding 

urbanization or drought. In response 

to that need, the Ground-Water 

Resources Program began an effort 

in 1999 to estimate regional groundwater recharge in the southwestern 

United States. In 2003, this effort 

was extended to more humid parts of 

the United States. Projects are being 

conducted in the States of Minnesota, 

Figure 2.  The Great Lakes Basin pilot study area.

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Water Availability and Use Initiative

ONTARIO

NEW

YORK

QUEBEC

MINNESOTA

PENNSYLVANIA

INDIANA OHIO

WISCONSIN

ILLINOIS

IOWA

MICHIGAN

Lake

Superior

Lake

Heron

Lake

Michigan

Lake

Ontario

Lake

Erie

Study area

EXPLANATION

90 80

48

44

Base map from ESRI 2003 0 60 120 180 240 MILES

0 80 160 240 320 KILOMETERS

The goals of the USGS Water Availability and 

Use Initiative, commencing in 2005 at the request of 

Congress, are to provide citizens, communities, and 

natural-resource managers with

• A clearer understanding of the status and trends in 

water availability and use of the Nation’s surface- and 

ground-water resources, and

• An improved ability to forecast the availability of 

water for future economic and environmental uses.

The Initiative, which is in a pilot phase, focuses on 

the Great Lakes Basin (fig. 2). Additionally, a second 

pilot study focusing on ground-water depletion in the 

western United States will begin in fiscal year 2006. 

Other major water-resources regions will be added 

in the future as funding permits. Planned activities for 

the Great Lakes Basin pilot study include estimation 

of (1) spatial and temporal trends in streamflow 

characteristics, ground-water recharge, ground-water 

flow, and ground-water storage; (2) ground-water basin 

divides; and (3) water use.
North Carolina, Pennsylvania, 

Washington, and Wisconsin, and in 

cooperation with the National WaterQuality Assessment (NAWQA) 

Program, covering many other 

locations in the eastern United States. 

The objectives of these studies are 

to develop a better understanding of 

recharge processes at the local scale 

and to evaluate techniques to scale 

up site-specific recharge estimates to 

regional aquifers. 

Karst Hydrology Initiative/Fractured-Rock 

Aquifer Studies

 Fractured rock and karst 

environments are collectively termed 

“complex aquifers” in the GroundWater Resources Program. Karst 

and fractured-bedrock aquifers 

cover extensive areas of the United 

States and have unique physical 

characteristics that govern groundwater movement within these 

systems. Karst topography composes 

nearly 15 percent of the continental 

United States and about 40 percent 

of the land area located east of 

the Mississippi River (Davies and 

LeGrand, 1972). Much of the recent 

residential development along the 

Piedmont and in western mountain 

communities has occurred in areas 

underlain by fractured bedrock 

where the demand for new drinkingwater sources cannot be satisfied 

by surface-water supplies (rivers or 

reservoirs). As growth continues, the 

problems of ground-water availability 

and vulnerability to contamination 

in these areas also will increase. In 

spite of the value of these complex 

aquifers as water-supply sources, the 

hydrogeologic characteristics of these 

systems are not as well understood 

as other aquifer 

systems, especially 

at a regional scale. 

Better regional 

characterization and 

understanding of 

the hydrogeology 

of complex aquifers 

as well as improved 

analytical and 

data-management 

tools are needed. 

The Ground-Water 

Resources Program 

is currently involved 

in a regional study 

of the karst aquifers 

in Alabama, Illinois, 

Indiana, Kentucky, and Tennessee 

as a prototype for possible regional 

studies of other karst aquifers. The 

Ground-Water Resources Program 

also is supporting complex aquifer 

studies in the Shenandoah Valley of 

Virginia and West Virginia.

Field Methods and Models

 The Ground-Water Resources 

Program supports many types and 

levels of hydrologic research, from 

basic research conducted by the 

USGS National Research Program 

to development of new field 

techniques, geophysical methods and 

applications, and computer models. 

The Ground-Water Resources 

Program strives to identify more 

efficient methods of evaluating 

ground-water resources at a variety 

of scales. Some examples of these 

activities are described below.

Geophysical Methods and Applications

 The USGS supports the 

development and application of new 

geophysical techniques for watersupply and contamination studies. 

For example, the Ground-Water 

Resources Program supports work 

on a web-enabled, earth­‐resistivity 

tomography monitoring system 

to assess and monitor hydrologic 

processes, including aquifer storage 

and recovery and saltwater intrusion 

into coastal aquifers. Additional 

information on geophysical 

applications for ground-water studies 

is available on the Internet at http://

water.usgs.gov/ogw/bgas/. 

Ground-Water Model Development

 The Ground-Water Resources 

Program continues to support the 

enhancement of MODFLOW with 

updates that help scientists and 

engineers simulate a variety of 

hydrologic processes that occur 

in ground-water systems (fig. 3). 

MODFLOW is one of the most 

popular ground-water flow models in 

the world, and the USGS continues 

to develop this widely used product 

as the science of ground-water 

hydrology advances and user needs 

change. Detailed information on 

MODFLOW enhancements is 

available on the Internet at http://

water.usgs.gov/ogw/MODFLOW_

list_of _reports.html. A high priority 

Rhodomine dye is injected in a stream to trace water movement through a

karst aquifer (photograph by Charles Taylor, USGS).

Field testing and development of a web-enabled,

earth-resistivity tomography monitoring system

(photographs by Kamini Singha, USGS).

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Printed on recycled paper

is being placed on the development 

of a coupled ground-water and 

watershed model. This work expands 

the capabilities of MODFLOW to 

better simulate ground-water and 

surface-water interactions at the basin 

scale by coupling MODFLOW with 

the Precipitation Runoff Modeling 

System (PRMS) watershed model. 

Additional information on these and 

other ground-water model codes is 

available on the Internet at http://

water.usgs.gov/software/ground_

water.html . 

Data Collection and Ground-Water 

Level Monitoring Networks

 Measurements of ground-water 

levels from wells are used to monitor 

changes in ground-water conditions 

resulting from climate variability 

and withdrawals. During drought 

conditions, when ground-water-level 

data are in high demand, real-time 

ground-water levels are measured 

at selected wells and transmitted to 

USGS databases for display on the 

Internet for water managers and the 

public. The Ground-Water Resources 

Program supports the Ground-Water 

Climate-Response Network of about 

140 selected wells to assess the 

changes in ground-water conditions 

(storage and water levels) caused by 

climate stresses, especially drought. 

This network is augmented by 

ground-water-level monitoring 

that is supported by the USGS 

Cooperative Water Program. 

Water-level data can 

be viewed at http://

groundwaterwatch.

usgs.gov/.

 The Ground-Water 

Resources Program also 

supports regional evaluation 

of ground-water conditions 

where ground-water 

resources have been 

intensively developed, as in 

the High Plains aquifer in 

the central United States. 

For example, water withdrawal for 

irrigation 

from the High 

Plains aquifer for 

more than 50 years 

has resulted in 

substantial waterlevel declines in the 

aquifer. To understand 

the widespread effects 

of these long-term 

withdrawals on the 

aquifer, Congress 

has mandated that 

the USGS report 

water-level changes 

biennially. A network 

of more than 7,000 

wells are measured 

annually by numerous 

Federal, State, and 

local agencies to assess 

water-level changes in the aquifer. 

More information on the High Plains 

Water-Level Monitoring Project is 

available on the Internet at http://

ne.water.usgs.gov/html/hpactivities.

htm. 

Summary

 Widespread debate concerning 

the Nation’s ability to meet current 

and future demands for available 

freshwater resources is receiving 

greater attention today than at 

anytime in the past. There is 

increasing recognition that competing 

demands for water by humans 

and environmental uses need to 

be thoroughly evaluated prior to 

determining if sufficient supplies 

exist. An integrated understanding of 

the Nation’s ground-water resources 

is necessary for managers and 

Figure 3.  Application of MODFLOW-2000 to the Central Valley

aquifer in California.

Real-time monitoring well that is part of the USGS Ground-Water

Climate-Response Network in Idaho (photograph by Matthew

Gilbert, USGS).

policymakers when making decisions 

about important national, regional, 

and local water-resource issues. The 

Ground-Water Resources Program 

seeks to provide objective scientific 

information in the areas of resource 

assessments, scientific investigations 

related to critical ground-water 

issues, development of field methods 

and models, and acquisition, 

management, and distribution of 

fundamental ground-water data. 

 Kevin F. Dennehy

References

Davies, W.E., and LeGrand, H.E., 1972, 

Karst of the United States, in Herak, 

M., and Stringfield, V.T., eds., Karst, 

important karst regions of the northern 

hemisphere: Amsterdam, Netherlands, Elsevier Publishing Company, 

p. 467–505.

Hutson, S.S., Barber, N.L., Kenny, J.F., 

Linsey, K.S., Lumia, D.S., and 

Maupin, M.A., 2004, Estimated use 

of water in the United States in 2000: 

U.S. Geological Survey Circular 1268, 

46 p.

For additional information on the 

activities of the USGS Ground-Water 

Resources Program, visit our Web site 

at http://water.usgs.gov/ogw/gwrp/ or 

contact:

U.S. Geological Survey

Ground-Water Resources Program

411 National Center

Reston, VA 20192

Phone: 703-648-5001

Fax: 703-648-6693

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