Desalination of Ground Water: Earth Science Perspectives

GROUND-WATER RESOURCES FOR THE FUTURE Desalination of Ground Water: Earth Science Perspectives

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 water- treatment 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 contrib- �� ute significantly to ensuring a safe, Less than 500 sustainable, affordable, and adequate 500 to 1,000 More than 1,000 water supply for our nation.” � �� Inadequate information � �� Guiding vision for Desalination and Water Purification Technology Roadmap prepared Figure 1. Depth to saline ground water in the United States (generalized from Feth and others, by the U.S. Bureau of Reclamation and 1965) Sandia National Laboratories (2003). in milligrams of solids per liter (mg/L). parts that contain freshwater, because Desalination presents the possibility Water with a TDS concentration greater the need to utilize saline ground water of providing freshwater not only from than 1,000 mg/L commonly is considered has been limited. Most ground-water the ocean, but also from saline ground saline. This somewhat arbitrary upper resource evaluations have been devoted water. The potential importance of limit of freshwater is based on the suit- to establishing the extent and properties desalination is exemplified, for example, ability of water for human consumption. of freshwater aquifers, whereas evalua- by New Mexico where approximately Although water with TDS greater than tions of saline water-bearing units have 75 percent of ground water is too saline 1,000 mg/L is used for domestic sup- been mostly devoted to determining the for most uses without treatment (Reyn- ply in areas where water of lower TDS effects on freshwater movement. olds, 1962, p. 91). Earth-science issues content is not available, water containing Much of the work to characterize related to desalination of ground water more than 3,000 mg/L is generally too saline ground-water resources in the include the distribution of saline ground- salty to drink. The U.S. Environmental United States was done in the 1950s, water resources, the chemical charac- Protection Agency has established a 1960s, and 1970s. Surveys of saline teristics and suitability of ground water guideline (secondary maximum contami- water resources of several States (for for desalination, effects of extraction of nant level) of 500 mg/L for dissolved example, Winslow and Kister, 1956), saline ground water on connected fresh- solids. Ground water with salinity greater and of selected areas within States (for water resources, and disposal of residual than seawater (about 35,000 mg/L) is example, Hood, 1963), were published in products. These issues are discussed by referred to as brine. the late 1950s and early 1960s. Krieger posing a series of basic questions. and others (1957) undertook a prelimi- Where is saline ground water nary survey of the saline water resources What is saline ground water? located? of the United States during this period. Later, Feth and others (1965) prepared Salinity is a term used to describe the Little is known about the hydro- a generalized map of the depth to saline amount of salt in a given water sample. geology of the parts of most aquifers ground water for the conterminous It usually is referred to in terms of total that contain saline water compared to the United States (fig. 1). This map provides dissolved solids (TDS) and is measured

U.S. Department of the Interior Fact Sheet 075–03 U.S. Geological Survey Printed on recycled paper October 2003 a preliminary perspective on the loca- the USGS developed quantitative assess- that might be of interest for saline-water tion of saline ground-water resources, ments of 25 of the Nation’s most impor- development. Thus, surface and subsur- but provides limited information about tant regional aquifer systems, as part of face geophysical techniques to supple- critical factors required to understand the the Regional Aquifer-System Analysis ment information from wells may prove development potential of the resources (RASA) Program (USGS Professional useful tools for saline water-resource such as aquifer hydraulic conductivity Paper Series 1400−1425). Reports on the evaluation. and well yields. geochemistry of some of these aquifer Reports published in U.S. Geological systems and the Ground-Water Atlas of How do we characterize the Survey (USGS) Professional Paper Series the United States (Miller, 2000) produced chemistry of saline ground water 813 in the 1970s present very general- as a part of the RASA Program contain with respect to suitability for ized analyses of ground-water resources maps and data about dissolved-solids and within each of the 21 Water Resources specific ion concentrations for selected desalination? Regions of the United States. Many areas (fig. 2). The dissolved-solids concentration of of these reports contain a short sum- Subsurface data on water chemistry saline ground waters typically is less than mary statement about the saline water and hydrology typically are restricted that of seawater. Saline ground water, resources of a region, including use of to near-surface, freshwater aquifers and however, has a greater tendency than sea- saline aquifers as a source of treatable to sediments containing deeper, com- water to precipitate sulfate (for example, water, place to store freshwater, or place monly highly saline, oil-field water. Few gypsum), carbonate (for example, to dispose of liquid waste. Subsequently, wells are located in intermediate areas 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 ��° 0 to 1,000 little research has been undertaken on the ��° 1,000 to 3,000 chemical suitability of water from various 3,000 to 10,000 aquifers as sources for desalination.

Bedrock What are the effects of using saline ground waters on fresh-

��° water resources and the environ- ment? ��° Although one might at first consider saline ground water as a “new” source

��° of water, the parts of aquifers containing saline water commonly are con-

�� nected 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 develop- � �� ment in three dimensions and with time. Variable density numerical models have Figure 2. Dissolved-solids concentrations in basin-fill aquifers in Arizona and New Mexico are been used successfully to simulate the typically less than 1,000 mg/L, but can be much higher. Areas of higher concentrations include low subsurface occurrence and movement parts of some basins where dissolved solids are concentrated by evapotranspiration from shallow of saltwater in coastal environments in ground water, basins with smaller fluxes of water naturally circulating through the ground-water many locations. The use of these models system, near deposits of saline minerals, and in some areas of salt buildup from intensive irriga- to quantify the movement of inland saline tion. (modified from Kister, 1973; Robson and Banta, 1995) water resources would aid in understand- ing the impacts of utilizing saline water mations have associated water that is only resources for desalination. slightly saline (less than 10,000 mg/L), �� Disposal of the volumes of brine notably in the intermountain basins of the �� produced as a residual product of desali- western United States. Coal-bed methane �� nation is a primary environmental issue water in the Powder River Basin of Wyo- �� associated with desalination. Residual ming is generally less than 3,000 mg/L �� products from desalination of seawater TDS. The likely presence of organic �� are pumped to the sea. The expense of compounds in this water complicates

�� geologic disposal of residual products treatment. from inland saline ground water is �� a major factor that affects the cost- Summary Remarks �� effectiveness of ground-water desalination. Disposal of residual products of Desalinated ground water potentially

�� desalination requires careful consider- represents an increasing component of �� the Nation’s water supply; however, �� ation of their chemical composition. For example, disposal in deeper (higher tem- relatively little is known about saline Figure 3. Normative analysis (Bodine and perature) saline aquifers may lead to pre- ground-water resources. An improved Jones, 1986) can be useful in characterizing cipitation of minerals, including calcite knowledge base is needed to better define the chemical composition of saline water. and gypsum that have lower solubility at their distribution and physical and chemi- Calculated simple salt norms demonstrate the higher temperatures (Kharaka and others, cal characteristics; to predict the effects preferred association of cations and anions 1997). Underground injection of saline of saline-water extraction on the envi- based on relative solubility of evaporite miner- water currently is done in the United ronment; and to support proper disposal als. These are derived from the equilibrium States to dispose of oil-field brines. of waste products. This information is salt assemblages obtained on complete needed to support economic develop- evaporation of a water sample under ambi- ent conditions. The resulting cation-anion Are there other sources of treatment of the resources, and to provide a associations (simple salts) readily show the able ground water? scientific basis for regulatory and policy relative abundance of principal scale-forming issues. mineral phases. This is illustrated graphically Other sources of ground water may be by comparison of simple salt mineral percent- amenable to desalination. These pos- References Cited ages calculated from analyses of brackish sibilities, for which research continues, ground water, seawater, and subsurface brine include treating water co-produced with Bodine, M.W., Jr., and Jones, B.F., 1986, (data from Wood and Jones, 1990). In this oil and conventional natural gas (Kharaka The salt norm: A quantitative chemi- way, a quick evaluation can be made of the and others, 1999) and water co-produced cal-mineralogical characterization of magnitude and type of potential scaling prob- with coal-bed methane (Rice and Nuccio, natural water: U.S. Geological Survey lems for a given saline water resource. 2000). Many oil- and gas-producing for- 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 shal- lowest ground water containing more than 1,000 parts per million dissolved solids: U.S. Geological Survey Hydro- logic Investigations Atlas HA−199. Galloway, D.L., Alley, W.M., Barlow, P.M., Reilly, T.E., and Tucci, P., 2003, (Left photograph) A desalination plant for the City of Cape May, New Jersey, was built inside Evolving issues and practices in man- the brick building of the former Cape May Water Works. (Right photograph) The automated aging ground-water resources—Case desalination plant can produce from 750,000 to 2 million gallons of water per day. studies on the role of science: U.S. (Photos: Jennifer Kopp, courtesy of CapeMay.com) Geological Survey Circular 1247, 73 p.

Saltwater contamination has forced the closure of water-supply wells for the City of Cape May, Hood, J.W., 1963, Saline ground water in New Jersey, and caused concerns about the future sustainability of ground water. Long-term the Roswell Basin, Chaves and Eddy monitoring of the resource and a numerical ground-water model of the aquifer system of the Counties, New Mexico, 1958-59: U.S. Cape May Peninsula were key elements to help engineers design an approach to combine Geological Survey Water-Supply Paper desalination of brackish ground water at some wells and reduce pumping at others to stabilize 1539−M, 46 p. the saltwater front (Lacombe and Carleton, 2002; Galloway and others, 2003). Kharaka, Y.K., Ambats, G., Thordsen, Lacombe, P.J., and Carleton, G.B., 2002, Sandia National Laboratories, 2002, J.J., and Evans, W.C., 1997, Deep-well Hydrogeologic framework, avail- Tularosa basin national desalination injections of brine from Paradox Val- ability of water supplies, and salt- research facility study: U.S. Bureau of ley, Colorado: Potential major precipi- water intrusion, Cape May County, Reclamation Report to Congress, 34 p. tation problems remediated by nanofil- New Jersey: U.S. Geological Survey tration: Water Resources Research, Water-Resources Investigations Report U.S. Bureau of Reclamation and Sandia v. 33, p. 1013−1020. 01−4246, 151 p. National Laboratories, 2003, Desalina- tion and water purification technology Kharaka, Y.K., Leong, L.Y.C., Doran, G., Miller, J.A., 2000, Ground-water atlas roadmap: U.S. Bureau of Reclamation, and Breit, G.N., 1999, Can produced of the United States: U.S. Geological Desalination and Water Purification water be reclaimed?: Experience with Survey, 13 chapters. Available on the Research and Development Report the Placerita oil field, California, in Internet at http://capp.water.usgs.gov/ #95, Denver, Colorado, 61 p. Sublette, K.L., ed., Environmental gwa/. Issues in Petroleum Exploration, Pro- Winslow, A.G., and Kister, L.R., 1956, duction and Refining: Proceedings 5th Reynolds, S.E., 1962, Twenty-fifth Saline-water resources of Texas: U.S. IPEC meeting, October, 1998, biennial report of the State Engineer of Geological Survey Water-Supply Paper CD−ROM format. New Mexico: The Valliant Company, 1365, 105 p. Albuquerque, New Mexico, 193 p. Kister, L.R., 1973, Quality of ground Wood, W.W., and Jones, B.F., 1990, water in the lower Colorado River Rice, C.A., and Nuccio, V., 2000, Water Origin of solutes in saline lakes and region, Arizona, Nevada, New Mexico, produced with coal-bed methane: springs on the southern High Plains of and Utah: U.S. Geological Survey U.S. Geological Survey Fact Sheet Texas and New Mexico: In T.C. Gus- Hydrologic Investigations Atlas FS−156−00, 2 p. tavson, ed., Geologic framework and HA−478, 2 sheets. regional hydrology: Upper Cenozoic Robson, S.G., and Banta, E.R., 1995, Blackwater Draw and Ogallala Forma- Krieger, R.A., Hatchett, J.L., and Poole, Ground-water atlas of the United tions, Great Plains: The University of J.L., 1957, Preliminary survey of the States, segment 2, Arizona, Colorado, Texas at Austin, Bureau of Economic saline-resources of the United States: New Mexico, and Utah: U.S. Geologi- Geology Report, p. 193−208. U.S. Geological Survey Water-Supply cal Survey Hydrologic Investigations Paper 1374, 172 p. Atlas HA−730C, 32 p.

William M. Alley

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http://water.usgs.gov/ogw Filtration Membrane Element