NATIONAL BRACKISH GROUNDWATER ASSESSMENT

The amount of fresh or potable groundwater in storage has declined for many areas in the United States and has 

led to concerns about the future availability of water for drinking-water, agricultural, industrial, and environmental needs. Use of brackish groundwater could supplement or, in some places, replace the use of freshwater 

sources and enhance our Nation’s water security. However, a better understanding of the location and character of brackish groundwater is needed to expand development of the resource and provide a scientific basis for 

making policy decisions. To address this need, the U.S. Department of Interior’s WaterSMART initiative, through 

the USGS Groundwater Resources Program, is conducting a national assessment of brackish aquifers.

All water naturally contains dissolved solids 

that, if present in sufficient concentration, 

can make a surface-water or groundwater 

resource “brackish,” typically defined as 

distastefully salty. Although quantitative 

definitions of this term vary, it is generally 

understood that brackish groundwater is 

water that has a greater dissolved-solids 

content than occurs in freshwater, but not 

as much as seawater (35,000 milligrams per 

liter). It is considered by many investigators to have dissolved-solids concentration 

between 1,000 and 10,000 milligrams per 

liter (mg/L). The term “saline” commonly 

refers to any water having dissolved-solids 

concentration greater than 1,000 mg/L and 

includes the brackish concentration range.

What is brackish groundwater?

Why study brackish groundwater?

Groundwater in basin-fill aquifers of the Southwest often increases in dissolved-solids content 

as it travels along its flow path as a result of geochemical interactions with the aquifer matrix and 

through evaporative processes. At the end of its flow path, groundwater may be brackish or saline 

and discharges to the surface through springs such as this one in Death Valley. Photo by USGS 

hydrologist David Anning.

In many parts of the country, groundwater withdrawals 

exceed recharge rates and have caused groundwater-level 

declines, reductions to the volume of groundwater in storage, lower streamflow and lake levels, or land subsidence. 

It is expected that the demand for groundwater will continue to increase because of population growth, especially in 

the arid West. Further, surface-water resources are fully appropriated in many parts of the country, creating additional 

groundwater demand. Development of brackish groundwater as an alternative water source can help address concerns 

about the future availability of water and contribute to the 

water security of the Nation.

Brackish groundwater is potentially abundant. Early studies 

indicated that mineralized groundwater underlies most of 

the country (fig. 1). Further, advances in desalination technologies are making treatment and use of brackish groundwater for potable water supply more feasible.

U.S. Department of the Interior

U.S. Geological Survey

Info Sheet

2013

Despite the need for alternative water sources and the 

potential availability of brackish groundwater, the most 

recent national map showing the distribution of mineralized 

groundwater was published in 1965. An updated evaluation 

is needed to take advantage of newer data that have been 

collected over the past 50 years. In addition, consistent information about chemical characteristics (such as major-ion 

concentrations) and hydrogeologic characteristics (such as 

aquifer material, depth, residence time, thickness, flow patterns, recharge rates, and hydraulic properties) of brackish 

groundwater has not been compiled at the national scale. 

Improved characterization is important for understanding 

and predicting occurrences in areas with few data and for 

assessing limitations imposed by different uses and (or) 

treatment options. This information is needed to understand the potential to expand development of the brackish 

groundwater resource and to provide reliable science for 

making policy decisions.
About the Study

The objectives of the study are to identify 

and characterize significant brackish aquifers in the United States. Brackish aquifers are defined for purposes of this study 

as aquifers that have groundwater within 

3,000 ft of land surface, contain dissolvedsolids concentrations between 1,000 and 

10,000 milligrams per liter, and can yield 

usable quantities of water. The study is intended to provide information about brackish aquifers at national and regional scales 

and is not for defining site-specific or 

localized conditions. Study results can be 

used to identify areas where further evaluation of the brackish aquifers will be most 

productive for potential users of the resource.

Salt deposits, such as halite or gypsum, are found in many sedimentary basins in the United States 

and are highly soluble. Other deposits are less soluble but can contribute dissolved solids when in 

contact with groundwater over longer periods of time. Source: Siim Sepp, http://www.sandatlas.org/.

Major components of the study

• Compiling existing information that can be used to 

assess brackish aquifers 

• Describing, to the extent that available data permit, 

dissolved-solids concentrations, other chemical characteristics, horizontal and vertical extents of aquifers 

containing brackish groundwater, ability of the aquifers to yield water, and current brackish groundwater 

use 

• Generating national maps of dissolved-solids concentrations

• Identifying data gaps that limit full characterization 

of brackish aquifers 

Groundwater discharge and rainfall-runoff collect and evaporate from this brackish 

playa lake in Saline Valley, CA. Photo by USGS hydrologist David Anning.

Improvements upon previous work

• An updated national inventory of brackish groundwater: Previous national assessments of the distribution of brackish groundwater used only a limited 

amount of the dissolved-solids data that currently are 

available. A more complete set of information will 

be assembled from a wide variety of sources and will 

include more recently collected data. 

• Publication of digital datasets: The national inventory and selected results will be published as digital datasets so that other scientists can conduct assessments 

tailored to their specific needs. Published digital data 

relating to brackish groundwater currently are limited 

to a small number of state and regional studies. 

• Enhanced characterization: The updated dissolvedsolids inventory will be used to characterize brackish 

aquifers at a higher spatial resolution than previous 

national work. In addition to dissolved-solids distribution, other chemical characteristics (such as major-ion 

concentrations) and hydrogeologic characteristics 

(such as aquifer material, depth, residence time, 

thickness, flow patterns, recharge rates, and hydraulic properties) will be assessed to determine brackish 

groundwater availability. Improved characterization 

is important for understanding and predicting occurrences in areas with few data, and also for assessing 

limitations imposed by different uses and (or) treatment options. 

• Consistent approach: Although several detailed assessments of brackish aquifers have been conducted at 

state and regional scales, the methods differed among 

the studies. This work will describe brackish aquifers 

using consistent data analysis and assessment methods 

across the country.
Previous Work

A national compilation of data on mineralized (brackish) groundwater was completed in the 1960s (Feth and 

others, 1965). That study provided maps showing depth to 

the shallowest groundwater containing more than 1,000 

mg/L of dissolved solids and chemical types of groundwater, serving as the primary source of information for 

subsequent assessments of the national distribution 

of brackish groundwater. Feth (1965b) also compiled a 

reference list of approximately 500 reports documenting saline groundwater conditions that “is by no means 

exhaustive, but it is representative of the types of information available and will serve to lead the reader into 

the literature.” In addition, Feth (1981) and Richter and 

Kreitler (1991) summarized various models and mechanisms used to explain the spatial and temporal variability 

of dissolved solids in groundwater. Feth (1981) provided 

a national synthesis of chloride in natural waters, noting that the ratio of various other anions to chloride can 

be used to identify the source of brackish groundwater. 

Richter and Kreitler (1991) supplemented work by Feth 

and others (1965) with a map by Dunrud and Nevins 

(1981) showing the approximate extent of halite (sodium 

chloride salt) deposits, 

mapped locations of 

oil fields, estimates 

of the extent of seawater intrusion to 

coastal aquifers, and 

mapped saline springs 

and seeps to identify 

areas where brackish 

groundwater naturally 

occurs. Richter and 

Kreitler (1991) also 

provided a state-bystate summary of the 

occurrence of each 

source of groundwater 

salinization.

USGS Regional Aquifer-System Analysis (RASA) studies were conducted between 1978 and 1995 to define the regional geohydrology 

of the Nation’s important aquifer systems. Maps showing 

dissolved-solids concentrations were published for many 

of these aquifer systems and compiled for the USGS 

Ground Water Atlas of the United States (U.S. Geological Survey, 2000). In some cases, regional RASA studies 

included geochemical characterization and modeling, 

which assisted with understanding, interpolating, and 

extrapolating brackish-water occurrence (for example, 

Busby and others, 1995).

More recently, Androwski and others (2011) used previously published USGS reports to conduct a national 

assessment of the total volume of the saline (dissolvedsolids concentration between 1,000 and 35,000 mg/L) 

component of the principal aquifers of the conterminous 

United States that could be available for desalination. 

The primary sources of dissolved-solids and aquiferdimension information for that study were digital maps 

from the USGS Ground Water Atlas of the United States 

(U.S. Geological Survey, 2000). No recently collected 

dissolved-solids data were used for the study, and depths 

to saline groundwater were estimated using simplistic 

assumptions and methods.

Examples of Regional Assessments of Brackish 

Aquifers

• The USGS, through the Groundwater Resources 

Program, is completing three pilot studies that use geochemical, geophysical, and geostatistical methods and 

previously published work to describe saline aquifers 

for the southern midcontinent, Mississippi embayment, 

and the southeastern United States. These “Challenge 

Area” studies were conducted from 2010 through 2012 

to supplement the 

Groundwater Resources 

Program’s freshwater 

regional groundwater 

availability assessments 

already underway in 

order to achieve a more 

complete picture of the 

Nation’s groundwater 

availability.

• Sandia National Laboratories is assessing the 

relative availability and 

cost of using shallow 

(less than 2,500 feet (ft) 

below land surface) 

brackish groundwater 

as a water source for 

thermoelectric power 

generation in 17 western 

states (Vince Tidwell, Sandia National Laboratories, written commun., 2013). Sources of information for estimating the availability of brackish groundwater include 

volumetric estimates of brackish groundwater in Texas 

and Arizona, USGS water-use information (Kenny and 

others, 2009), and data for wells in the USGS National 

Water Information System (NWIS) that contain brackish 

groundwater.

• The Texas Water Development board is conducting 

the Brackish Resources Aquifer Characterization System 

(BRACS) study to provide a detailed characterization of 

brackish aquifers in Texas using geophysical bore-hole 

logs and available aquifer data (Meyer and others, 2011).

Figure 1. Depth to groundwater with total dissolved-solids concentration greater than 1,000 

milligrams per liter in the United States (modified from Feth and others, 1965).
Brackish groundwater is directly used for purposes such 

as cooling water for power generation, aquaculture, and 

for a variety of uses in the oil and gas industry such as 

drilling, enhancing recovery, and hydraulic fracturing.

For purposes requiring lower dissolved-solids content, 

especially drinking water, brackish water is treated 

through reverse osmosis or other desalination processes. In 2010, there were 649 active desalination plants 

in the United States with a capacity to treat 402 million gallons per day (Shea, 2010). Of the desalination 

plant capacity in the United States, 67 percent was for 

municipal purposes, 18 percent for industry, 9 percent 

for power, and the remaining 6 percent for other uses 

(Mickley, 2010). A total of 314 desalination facilities 

are used for municipal purposes, 49 percent of which 

were in Florida, 16 percent in California, 12 percent in 

Texas, and the remaining 23 percent dispersed among 

other states. More than 95 percent of the desalination facilities in the United States are inland (Mickley, 

2010), and most facilities are designed to treat groundwater with dissolved-solids concentrations in the brackish range (Shea, 2010). Recent advances in technology have reduced the cost and energy requirements of 

desalination, making treatment of brackish groundwater 

a more viable option for drinking-water supplies (National Research Council, 2008). 

How is Brackish Groundwater Being Used?

Androwski, James, Springer, Abraham, Acker, Thomas, and Manone, Mark, 2011, Wind-Powered Desalination: An Estimate of 

Saline Groundwater in the United States: Journal of the American 

Water Resources Association, v. 47, no. 1, p. 93-102.

Busby, J.F., Kimball, B.A., Downey, J.S., and Peter, K.D., 1995, 

Geochemistry of water in aquifers and confining units of the 

Northern Great Plains in parts of Montana, North Dakota, South 

Dakota, and Wyoming: U.S. Geological Survey Professional 

Paper 1402-F, 146 p.

Dunrud, C.R., and Nevins, B.B., 1981, Solution mining and 

subsidence in evaporite rocks in the United States: U.S. Geological Survey Miscellaneous Investigations Series Map 1298, scale 

1:5,000,000.

Feth, J. H., and others, 1965, Preliminary map of the conterminous United States showing depth to and quality of shallowest 

ground water containing more than 1,000 parts per million dissolved solids: U.S. Geological Survey Hydrologic Investigations 

Atlas, HA-199, 31 p., 2 plates, scale 1:3,000,000.

Feth, J. H., 1965b, Selected references on saline ground-water 

resources of the United States; U.S. Geological Survey Circular 

499, 30 p.

Feth, J. H., 1981, Chloride in Natural Continental Water-A Review: U.S. Geological Survey Water-Supply Paper 2176, 30 p. 

Kenny, J.F., Barber, N.L., Hutson, S.S., Linsey, K.S., Lovelace, 

J.K., and Maupin, M.A., 2009, Estimated use of water in the 

United States in 2005: U.S. Geological Survey Circular 1344, 52 

p.

Meyer, J.E., Wise, M.R., Kalaswad, Sanjeev, 2011, Pecos Valley 

Aquifer, West Texas—Structure and Brackish Groundwater: 

Texas Water Development Board Report, 85 p. (PDF) 

Mickley, Mike, 2010, Inland desalination—Current status and 

challenges, in Annual WateReuse Symposium, 25th, Washington, 

D.C., 2010, Conference Presentations: Alexandria, Va., WateReuse Assoc., 31 p., accessed September 5, 2012, at http://www.

watereuse.org/information-resources/about-desalination/presentations.

National Research Council, 2008, Desalination—a national 

perspective: Washington D.C., The National Academies Press., 

316 p.

Richter, B.C., and Kreitler, C.W., 1993, Identification of sources 

of groundwater salinization using geochemical techniques: Ada, 

Okla., U.S. Environmental Protection Agency Report EPA/600/2-

91/064, 272 p.

Shea, A.L., 2010, Status and challenges for desalination in the 

United States, in Reuse & Desalination—Water Scarcity Solutions for the 21st Century Conference, Sydney, Australia, 2010, 

Conference Presentations: Alexandria, Va., WateReuse Assoc., 

36 p., accessed September 5, 2012, at http://www.watereuse.org/

information-resources/about-desalination/presentations.

U.S. Geological Survey, 2000, Ground-water atlas of the United 

States: U.S. Geological Survey Hydrologic Investigations Atlas, 

HA-730, 13 chapters, scale 1:1,000,000.

References

Top: Nuclear power plant cooled 

with brackish groundwater. 

Source: U.S. Nuclear Regulatory 

Commission. Right: Brackish 

water desalination facility in 

Harlingen, Texas. The plant was 

built in 2007 and has a capacity 

of 2.25 million gallons per day. 

Source: North Cameron Regional 

Water Supply Corporation.