U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 075–03

October 2003

Desalination of Ground Water: Earth Science Perspectives

Printed on recycled paper

Desalination is a water-treatment 

process that removes salts from water. 

Concerns about the sustainability of 

freshwater supplies, as well as rapid 

advances in membrane and other watertreatment technologies, are fostering a 

renewed interest in desalination as a 

partial solution to increased water 

demand. It is projected that more than 

70 billion dollars will be spent worldwide 

over the next 20 years to design and build 

new desalination plants and facilities 

(Sandia National Laboratories, 2002).

“By 2020, desalination and water 

purification technologies will contribute significantly to ensuring a safe, 

sustainable, affordable, and adequate 

water supply for our nation.” 

Guiding vision for Desalination and Water 

Purification Technology Roadmap prepared 

by the U.S. Bureau of Reclamation and 

Sandia National Laboratories (2003).

Desalination presents the possibility 

of providing freshwater not only from 

the ocean, but also from saline ground 

water. The potential importance of 

desalination is exemplified, for example, 

by New Mexico where approximately 

75 percent of ground water is too saline 

for most uses without treatment (Reynolds, 1962, p. 91). Earth-science issues 

related to desalination of ground water 

include the distribution of saline groundwater resources, the chemical characteristics and suitability of ground water 

for desalination, effects of extraction of 

saline ground water on connected freshwater resources, and disposal of residual 

products. These issues are discussed by 

posing a series of basic questions. 

What is saline ground water? 

Salinity is a term used to describe the 

amount of salt in a given water sample. 

It usually is referred to in terms of total 

dissolved solids (TDS) and is measured 

parts that contain freshwater, because 

the need to utilize saline ground water 

has been limited. Most ground-water 

resource evaluations have been devoted 

to establishing the extent and properties 

of freshwater aquifers, whereas evaluations of saline water-bearing units have 

been mostly devoted to determining the 

effects on freshwater movement. 

Much of the work to characterize 

saline ground-water resources in the 

United States was done in the 1950s, 

1960s, and 1970s. Surveys of saline 

water resources of several States (for 

example, Winslow and Kister, 1956), 

and of selected areas within States (for 

example, Hood, 1963), were published in 

the late 1950s and early 1960s. Krieger 

and others (1957) undertook a preliminary survey of the saline water resources 

of the United States during this period. 

Later, Feth and others (1965) prepared 

a generalized map of the depth to saline 

ground water for the conterminous 

United States (fig. 1). This map provides 

in milligrams of solids per liter (mg/L). 

Water with a TDS concentration greater 

than 1,000 mg/L commonly is considered 

saline. This somewhat arbitrary upper 

limit of freshwater is based on the suitability of water for human consumption. 

Although water with TDS greater than 

1,000 mg/L is used for domestic supply in areas where water of lower TDS 

content is not available, water containing 

more than 3,000 mg/L is generally too 

salty to drink. The U.S. Environmental 

Protection Agency has established a 

guideline (secondary maximum contaminant level) of 500 mg/L for dissolved 

solids. Ground water with salinity greater 

than seawater (about 35,000 mg/L) is 

referred to as brine. 

Where is saline ground water 

located?

Little is known about the hydrogeology of the parts of most aquifers 

that contain saline water compared to the 

�

�

��� ���������

��� ��������������

Less than 500

500 to 1,000

More than 1,000

Inadequate information

�������������������������������������

�����������

Figure 1. Depth to saline ground water in the United States (generalized from Feth and others, 

1965)

GROUND-WATER RESOURCES FOR THE FUTURE
a preliminary perspective on the location of saline ground-water resources, 

but provides limited information about 

critical factors required to understand the 

development potential of the resources 

such as aquifer hydraulic conductivity 

and well yields. 

Reports published in U.S. Geological 

Survey (USGS) Professional Paper Series 

813 in the 1970s present very generalized analyses of ground-water resources 

within each of the 21 Water Resources 

Regions of the United States. Many 

of these reports contain a short summary statement about the saline water 

resources of a region, including use of 

saline aquifers as a source of treatable 

water, place to store freshwater, or place 

to dispose of liquid waste. Subsequently, 

the USGS developed quantitative assessments of 25 of the Nation’s most important regional aquifer systems, as part of 

the Regional Aquifer-System Analysis 

(RASA) Program (USGS Professional 

Paper Series 1400−1425). Reports on the 

geochemistry of some of these aquifer 

systems and the Ground-Water Atlas of 

the United States (Miller, 2000) produced 

as a part of the RASA Program contain 

maps and data about dissolved-solids and 

specific ion concentrations for selected 

areas (fig. 2). 

Subsurface data on water chemistry 

and hydrology typically are restricted 

to near-surface, freshwater aquifers and 

to sediments containing deeper, commonly highly saline, oil-field water. Few 

wells are located in intermediate areas 

that might be of interest for saline-water 

development. Thus, surface and subsurface geophysical techniques to supplement information from wells may prove 

useful tools for saline water-resource 

evaluation.

How do we characterize the 

chemistry of saline ground water 

with respect to suitability for 

desalination?

The dissolved-solids concentration of 

saline ground waters typically is less than 

that of seawater. Saline ground water, 

however, has a greater tendency than seawater to precipitate sulfate (for example, 

gypsum), carbonate (for example, 

calcite), and silicate scales (fig. 3). The 

tendency of saline ground water to form 

scale is important to its suitability for 

use in desalination. Saline ground water 

also may contain some constituents, such 

as arsenic, elevated radioactivity, and 

dissolved organic material, at greater 

concentrations than in seawater. Although 

a relatively large body of information 

exists on the chemical behavior of solutes 

within desalination systems, relatively 

little research has been undertaken on the 

chemical suitability of water from various 

aquifers as sources for desalination. 

What are the effects of using 

saline ground waters on freshwater resources and the environment?

Although one might at first consider 

saline ground water as a “new” source 

of water, the parts of aquifers containing saline water commonly are connected hydraulically to parts of the same 

aquifer or aquifer system that contain 

freshwater. Thus, development of one 

resource affects the other, as well as 

potentially affecting the flow and quality 

of surface-water bodies connected to 

the ground-water system. These effects 

may extend over many years or decades. 

Techniques are needed to predict the 

effects of saline ground-water development in three dimensions and with time. 

Variable density numerical models have 

been used successfully to simulate the 

subsurface occurrence and movement 

of saltwater in coastal environments in 

many locations. The use of these models 

to quantify the movement of inland saline 

water resources would aid in understand-

����������

�������

���

����

0 to 1,000

1,000 to 3,000

3,000 to 10,000

Bedrock

����������������������������������

��������������������������

�����������

���°

���°

���°

��°

��°

� �� ��� �����

� �� ��� ����������

������������������

����������������������

�������������������������������

�������

����������

Figure 2. Dissolved-solids concentrations in basin-fill aquifers in Arizona and New Mexico are 

typically less than 1,000 mg/L, but can be much higher. Areas of higher concentrations include low 

parts of some basins where dissolved solids are concentrated by evapotranspiration from shallow 

ground water, basins with smaller fluxes of water naturally circulating through the ground-water 

system, near deposits of saline minerals, and in some areas of salt buildup from intensive irrigation. (modified from Kister, 1973; Robson and Banta, 1995) 
ing the impacts of utilizing saline water 

resources for desalination.

Disposal of the volumes of brine 

produced as a residual product of desalination is a primary environmental issue 

associated with desalination. Residual 

products from desalination of seawater 

are pumped to the sea. The expense of 

geologic disposal of residual products 

from inland saline ground water is 

a major factor that affects the costeffectiveness of ground-water desalination. Disposal of residual products of 

desalination requires careful consideration of their chemical composition. For 

example, disposal in deeper (higher temperature) saline aquifers may lead to precipitation of minerals, including calcite 

and gypsum that have lower solubility at 

higher temperatures (Kharaka and others, 

1997). Underground injection of saline 

water currently is done in the United 

States to dispose of oil-field brines.

Are there other sources of treatable ground water? 

Other sources of ground water may be 

amenable to desalination. These possibilities, for which research continues, 

include treating water co-produced with 

oil and conventional natural gas (Kharaka 

and others, 1999) and water co-produced 

with coal-bed methane (Rice and Nuccio, 

2000). Many oil- and gas-producing formations have associated water that is only 

slightly saline (less than 10,000 mg/L), 

notably in the intermountain basins of the 

western United States. Coal-bed methane 

water in the Powder River Basin of Wyoming is generally less than 3,000 mg/L 

TDS. The likely presence of organic 

compounds in this water complicates 

treatment. 

Summary Remarks

Desalinated ground water potentially 

represents an increasing component of 

the Nation’s water supply; however, 

relatively little is known about saline 

ground-water resources. An improved 

knowledge base is needed to better define 

their distribution and physical and chemical characteristics; to predict the effects 

of saline-water extraction on the environment; and to support proper disposal 

of waste products. This information is 

needed to support economic development of the resources, and to provide a 

scientific basis for regulatory and policy 

issues. 

References Cited

Bodine, M.W., Jr., and Jones, B.F., 1986, 

The salt norm: A quantitative chemical-mineralogical characterization of 

natural water: U.S. Geological Survey 

Water-Resources Investigations Report 

86−4086, 130 p.

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. 

Galloway, D.L., Alley, W.M., Barlow, 

P.M., Reilly, T.E., and Tucci, P., 2003, 

Evolving issues and practices in managing ground-water resources—Case 

studies on the role of science: U.S. 

Geological Survey Circular 1247, 73 p.

Hood, J.W., 1963, Saline ground water in 

the Roswell Basin, Chaves and Eddy 

Counties, New Mexico, 1958-59: U.S. 

Geological Survey Water-Supply Paper 

1539−M, 46 p.

Figure 3. Normative analysis (Bodine and 

Jones, 1986) can be useful in characterizing 

the chemical composition of saline water. 

Calculated simple salt norms demonstrate the 

preferred association of cations and anions 

based on relative solubility of evaporite minerals. These are derived from the equilibrium 

salt assemblages obtained on complete 

evaporation of a water sample under ambient conditions. The resulting cation-anion 

associations (simple salts) readily show the 

relative abundance of principal scale-forming 

mineral phases. This is illustrated graphically 

by comparison of simple salt mineral percentages calculated from analyses of brackish 

ground water, seawater, and subsurface brine 

(data from Wood and Jones, 1990). In this 

way, a quick evaluation can be made of the 

magnitude and type of potential scaling problems for a given saline water resource.

(Left photograph) A desalination plant for the City of Cape May, New Jersey, was built inside 

the brick building of the former Cape May Water Works. (Right photograph) The automated 

desalination plant can produce from 750,000 to 2 million gallons of water per day. 

(Photos: Jennifer Kopp, courtesy of CapeMay.com)

Saltwater contamination has forced the closure of water-supply wells for the City of Cape May, 

New Jersey, and caused concerns about the future sustainability of ground water. Long-term 

monitoring of the resource and a numerical ground-water model of the aquifer system of the 

Cape May Peninsula were key elements to help engineers design an approach to combine 

desalination of brackish ground water at some wells and reduce pumping at others to stabilize 

the saltwater front (Lacombe and Carleton, 2002; Galloway and others, 2003). 

�

��

��

��

��

��

��

��

��

�������

������

������

����������������������������������

�����������������������������

��������

������������

�������� ����������

�����
Kharaka, Y.K., Ambats, G., Thordsen, 

J.J., and Evans, W.C., 1997, Deep-well 

injections of brine from Paradox Valley, Colorado: Potential major precipitation problems remediated by nanofiltration: Water Resources Research, 

v. 33, p. 1013−1020.

Kharaka, Y.K., Leong, L.Y.C., Doran, G., 

and Breit, G.N., 1999, Can produced 

water be reclaimed?: Experience with 

the Placerita oil field, California, in 

Sublette, K.L., ed., Environmental 

Issues in Petroleum Exploration, Production and Refining: Proceedings 5th 

IPEC meeting, October, 1998, 

CD−ROM format.

Kister, L.R., 1973, Quality of ground 

water in the lower Colorado River 

region, Arizona, Nevada, New Mexico, 

and Utah: U.S. Geological Survey 

Hydrologic Investigations Atlas 

HA−478, 2 sheets.

Krieger, R.A., Hatchett, J.L., and Poole, 

J.L., 1957, Preliminary survey of the 

saline-resources of the United States: 

U.S. Geological Survey Water-Supply 

Paper 1374, 172 p.

Lacombe, P.J., and Carleton, G.B., 2002, 

Hydrogeologic framework, availability of water supplies, and saltwater intrusion, Cape May County, 

New Jersey: U.S. Geological Survey 

Water-Resources Investigations Report 

01−4246, 151 p.

Miller, J.A., 2000, Ground-water atlas 

of the United States: U.S. Geological 

Survey, 13 chapters. Available on the 

Internet at http://capp.water.usgs.gov/

gwa/.

Reynolds, S.E., 1962, Twenty-fifth 

biennial report of the State Engineer of 

New Mexico: The Valliant Company, 

Albuquerque, New Mexico, 193 p.

Rice, C.A., and Nuccio, V., 2000, Water 

produced with coal-bed methane: 

U.S. Geological Survey Fact Sheet 

FS−156−00, 2 p.

Robson, S.G., and Banta, E.R., 1995, 

Ground-water atlas of the United 

States, segment 2, Arizona, Colorado, 

New Mexico, and Utah: U.S. Geological Survey Hydrologic Investigations 

Atlas HA−730C, 32 p.

Sandia National Laboratories, 2002, 

Tularosa basin national desalination 

research facility study: U.S. Bureau of 

Reclamation Report to Congress, 34 p.

U.S. Bureau of Reclamation and Sandia 

National Laboratories, 2003, Desalination and water purification technology 

roadmap: U.S. Bureau of Reclamation, 

Desalination and Water Purification 

Research and Development Report 

#95, Denver, Colorado, 61 p.

Winslow, A.G., and Kister, L.R., 1956, 

Saline-water resources of Texas: U.S. 

Geological Survey Water-Supply Paper 

1365, 105 p.

Wood, W.W., and Jones, B.F., 1990, 

Origin of solutes in saline lakes and 

springs on the southern High Plains of 

Texas and New Mexico: In T.C. Gustavson, ed., Geologic framework and 

regional hydrology: Upper Cenozoic 

Blackwater Draw and Ogallala Formations, Great Plains: The University of 

Texas at Austin, Bureau of Economic 

Geology Report, p. 193−208.

William M. Alley

For more information on ground-water 

resource issues, please contact:

Office of Ground Water

U.S. Geological Survey

411 National Center

12201 Sunrise Valley Drive

Reston, VA 20192

(703) 648-5001

http://water.usgs.gov/ogw

Filtration 

 Membrane

 Element