U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2014–3024

April 2014

In partnership with the NAWQA 

Program, we collected a significant 

amount of groundwater-quality 

data that neither agency could have 

obtained individually. The data 

provide an important snapshot of the 

overall health of groundwater –the 

region’s primary source of drinking 

water. The information generated 

through this partnership will help 

our region formulate more effective 

groundwater management strategies 

in the future.

 Michael P. Ekberg, 

 Miami Conservancy District

Sampling a public-supply well in 

San Bruno, CA. Photograph by Cathy 

Munday, U.S. Geological Survey

National Water-Quality Assessment (NAWQA) Program 

Groundwater Studies: Principal Aquifer Surveys

The NAWQA Program

In 1991, the U.S. Congress 

established the National Water-Quality 

Assessment (NAWQA) program within 

the U.S. Geological Survey (USGS) to 

develop nationally consistent long-term 

datasets and provide information about 

the quality of the Nation’s streams and 

groundwater. The USGS uses objective 

and reliable data, water-quality models, 

and systematic scientific studies to 

assess current water-quality conditions, 

to identify changes in water quality 

over time, and to determine how natural 

factors and human activities affect the 

quality of streams and groundwater. 

NAWQA is the only non-regulatory 

Federal program to perform these types 

of studies; participation is voluntary.

In the third decade (Cycle 3) of 

the NAWQA program (2013–2023), 

the USGS will evaluate the quality 

and availability of groundwater 

for drinking supply, improve our 

understanding of where and why water 

quality is degraded, and assess how 

groundwater quality could respond to 

changes in climate and land use. These 

goals will be addressed through the 

implementation of a new monitoring 

component in Cycle 3: Principal Aquifer 

Surveys.

What will Participants Gain from the NAWQA Principal Aquifer Survey?

The survey will provide water utilities and resource managers with 

information about the following:

• Regulated and unregulated constituents from natural or human sources.

• Pesticides, pharmaceuticals, hormones, and other constituents of concern for human health.

• Baseline groundwater quality for comparison with future conditions.

• Regional and national statistics on water quality, as context for individual wells.

• A comparison of water quality in the shallow and deep parts of aquifer systems.

• Environmental tracers that 

can be used to understand 

sources and sustainability of 

groundwater supplies. 

• Improving understanding of 

local, regional, and national 

hydrogeology. 

NAWQA Principal Aquifer Survey

Principal aquifers are regionally 

extensive aquifers that can be used as 

a source of drinking water. Principal 

Aquifer Surveys (PAS) will assess the 

quality of groundwater used for public 

supply and will use newly collected data 

along with existing water-quality data.

Previously, the NAWQA program 

focused on the quality of groundwater 

in shallow monitoring wells and in 

domestic-supply wells and evaluated the 

distribution of contaminants in shallow 

groundwater (fig. 1). The PAS studies 

will focus on public-supply wells that 

tap deeper groundwater than typical 

domestic-supply wells. The PAS studies 

will be carried out over entire principal 

aquifers, rather than targeting smaller 

areas. The USGS will use the PAS data 

to develop contaminant distribution maps 

for deeper groundwater, thus completing a 

three-dimensional picture of groundwater 

quality and complementing previous 

NAWQA studies. 

NAWQA Principal Aquifer Survey 

Study Design

The USGS has identified 68 principal 

aquifers across the Nation. Groundwater 

pumped from these aquifers provides 45 

percent of the Nation’s drinking-water 

supply. During these Cycle 3 studies, 

NAWQA will sample groundwater used 

for public supply in 20 of the 68 principal 

aquifers (fig. 2). These 20 principal 

aquifers account for 76 percent of the 

Nation’s groundwater pumped for public 

supply and 85 percent of the groundwater 

pumped for domestic supply. 

Samples collected by the USGS for 

the PAS assessments will be analyzed 

for a large suite of regulated and 

unregulated constituents. The methods 

used by the NAWQA program will include 
For more information 

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

NAWQA reports and data can be obtained 

here:

NAWQA Groundwater Project Chief

U.S. Geological Survey

12201 Sunrise Valley Drive, MS 413

Reston, VA 20192-0002

Telephone: (703) 648-5716

Figure 2. Principal 

aquifers in the United 

States selected 

for monitoring 

in the Principal 

Aquifer Surveys 

(PAS) and for 

additional intensive 

study (which are 

identified), as well as 

important principal 

aquifer systems not 

included in this 

Cycle 3 assessment. 

Printed on recycled paper

By Karen R. Burow

and Kenneth Belitz

more constituents, detected at lower 

concentrations, than other programs. 

These constituents include trace elements, 

radioactivity, nutrients, salinity, pesticides, 

and volatile organic compounds. The 

NAWQA program will also include 

sampling for pharmaceuticals, hormones, 

and microbial indicators. The PAS studies 

are focused on untreated groundwater 

collected from public-supply wells, rather 

than treated drinking water delivered 

to consumers. The PAS studies are 

designed to assess groundwater quality 

at the regional scale and to complement 

regulatory monitoring programs. Findings 

will assist water-utility managers and 

regulators in making decisions about 

future monitoring needs and drinkingwater issues. 

 Reporting Results

The NAWQA PAS will provide 

new water-quality data and assessment 

of water resources to participants. 

Results of the sampling will be provided 

to well owners at no cost. Well-owner 

information will be kept confidential. Data 

summaries and interpretive reports will 

be made publically available on NAWQA 

websites and through USGS databases and 

publications.

References

Nolan, B.T., and Hitt, K.J., 2006, 

Vulnerability of shallow groundwater 

and drinking-water wells to nitrate in the 

United States: Environmental Science and 

Technology, v. 40, no. 24, p. 7834–7840.

Figure 1. Statistical model 

for groundwater from 

domestic wells sampled 

during 1991–2003 (Nolan 

and Hitt, 2006). ≤, less than 

or equal to; >, greater than

Predicted nitrate concentration,

in milligrams per liter as nitrogen

≤1

> 1–5

>5–10

EXPLANATION

>10

Missing data

Central

Valley 

aquifer 

system

Glacial aquifer system

North Atlantic

Coastal Plain

aquifer system

Mississippi Embayment, 

Coastal Lowlands, Texas Coastal

Uplands aquifer systems

Selected principal aquifers

Other principal aquifers

PAS monitoring and

additional intensive studies

PAS monitoring

Important, not selected

ISSN 2327-6932 (print) 

ISSN 2327-6916 (online)

http://cx.doi.org/10.3133/fs20143024