GROUNDWATER FOR THE FUTURE Brackish Groundwater and its Potential to Augment Freshwater Supplies By Jennifer S. Stanton and Kevin F. Dennehy

Secure, reliable, and sustainable resources are fundamental to the Nation’s production, independence, and ecological and human health and -being. Indications are that at any given time, are under stress in selected parts of the country. The large-scale development of groundwater resources has caused declines in the amount of groundwater in storage and declines in discharges to bodies (Reilly and others, 2008). in some regions, particularly in arid and semiarid regions, is not adequate to meet demand, and severe intensifies the stresses affecting water resources (National Drought Mitigation Center, the U.S. Department of , and the National Oceanic and Atmospheric Association, 2015). If these drought conditions continue, water shortages could adversely affect the human condition and threaten environmental flows necessary to maintain ecosystem health. In support of the national census of water resources, the U.S. Geological Survey (USGS) completed the national brack- ish groundwater assessment to provide updated information about brackish groundwater as a potential to augment or replace freshwater supplies (Stanton and others, 2017). Study objectives were to consolidate available data into a comprehen- sive database of brackish groundwater resources in the United States and to produce a summary report highlighting the distri- bution, physical and chemical characteristics, and use of brackish groundwater resources. This assessment was authorized by section 9507 of the Omnibus Public Management Act of 2009 (42 U.S.C. 10367), passed by Congress in March 2009. Before this assessment, the last national brackish groundwater compilation was completed in the mid-1960s (Feth, 1965). Since that time, substantially more hydrologic and geochemical data have been collected and now can be used to improve the understanding of the Nation’s brackish groundwater resources.

What is Brackish Groundwater? consumption. Water that is high in Where is Brackish Groundwater? dissolved solids may taste bitter, salty, All water naturally contains dis- The national brackish groundwa- or metallic; smell unpleasant; or may solved solids that, if present in sufficient ter assessment focused on defining the be toxic. Water with higher dissolved- concentration, can make a surface-water occurrence of brackish groundwater at solids concentrations can be used for a or groundwater resource “brackish”. depths less than 3,000 feet (ft) below land variety of purposes other than drinking In general, brackish groundwater is surface because few data were readily water. For the national brackish ground- groundwater that has a dissolved-solids available below that depth. Groundwater- water assessment, brackish groundwater content greater than freshwater but not as chemistry data for about 380,000 was quantitatively defined as having a much as seawater; however, a variety of groundwater samples were compiled from dissolved-solids concentration between classification schemes have been used to 33 sources (Qi and Harris, 2017) for this 1,000 and 10,000 mg/L. Saline ground- quantitatively describe that have assessment. Those data were summarized water commonly refers to any waters different dissolved-solids concentrations. with a coarse, three-dimensional grid that having dissolved-solids concentrations Dissolved solids (also referred to as total indicated occurrences of brackish ground- of at least 1,000 mg/L and includes the dissolved solids) is a measure of the water at some depth within 3,000 ft below brackish concentration range and higher concentration of all organic and inorganic land surface in every State except New water. For comparison, seawater dissolved substances (like , met- Hampshire and Rhode Island (fig. 1). has a dissolved-solids concentration of als, and salts) present in a water sample. Most of the known brackish groundwater 35,000 mg/L (table 1). The U.S. Environmental Protection is within in the Western Midcontinent Agency secondary maximum contami- Table 1. Water categories based on region. Other significant occurrences of nant level, a nonmandatory standard that dissolved-solids concentration. brackish groundwater generally are in only applies to public water systems, the Coastal Plains, Eastern Midcontinent, Dissolved-solids Categories of advises a level of 500 milligrams per concentration, and Southwestern Basins regions (fig. 1). water1 liter (mg/L) for dissolved solids (U.S. in milligrams per liter States along the Atlantic coast have the Environmental Protection Agency, 2015), largest number of observations; how- Fresh Less than 1,000 although numerous water supplies exceed ever, the groundwater in these States is this level. Water with dissolved-solids Brackish 1,000 to 10,000 generally freshwater with little brackish levels exceeding 1,000 mg/L is gener- Highly saline Greater than 10,000 groundwater occurrence except along ally considered undesirable for human 1Seawater contains about 35,000 milligrams per liter. the coastline. In general, dissolved-solids

U.S. Department of the Interior Fact Sheet 2017–3054 U.S. Geological Survey Printed on recycled paper July 2017 130° 120° 110° 100° 90° 80° 70° Western Mountain Ranges astern Mountains and Uplands

orthwestern olcanics

40°

Southwestern Basins Western Midcontinent PACIFIC astern Midcontinent

30° ATLANTIC Coastal OCEAN Plains HAWAII

PAATI Minimum depth to brackish or highly saline groundwater, in feet below land surface <50 50 to <500 ALASKA U.S. TERRITORIES 500 to <1,500 20° 1,500 to 3,000 Base map modified from Esri and U.S. Geological Survey digital data, 1:2,000,000 and other scales, variously dated. Brackish or highly saline groundwater 0 250 500 MILES Base map image is the intellectual property of Esri and is used herein under license. Copyright © 2014 Esri and its licensors. All rights reserved. not observed Albers Equal-Area Conic projection, standard parallels 29°30’ N. and 45°30’ N., central meridian 96°00’ W., latitude of origin 23°00’ N. 0 250 500 KILOMETERS North American Datum of 1983

Figure 1. Observed minimum depth to brackish or highly saline groundwater between 0 and 3,000 feet below land surface. concentrations are higher and brackish groundwater is more For example, can exceed the U.S. Environmental Protec- frequently detected with increasing depths below the land tion Agency primary drinking-water standard of 10 micrograms surface. Across the United States, for example, about 70 percent per liter for (fig. 2). Other chemical characteris- of sampled between 1,500 and 3,000 ft below land surface tics also can limit brackish water use; for example, scal- produced brackish or highly saline groundwater; whereas, less ing can impede conveyance, storage, and treatment of brackish than 20 percent of sampled wells between 0 and 50 ft below groundwater. land surface had brackish or highly saline groundwater. Simi- Mineral scaling refers to the deposition or larly, the median dissolved-solids concentration observed across of minerals on a surface or membrane that stores, transmits, or the United States is 334 mg/L for all wells between 0 and 50 ft filters water and can impede flow. For example, scaling can pre- below land surface and 3,692 mg/L for all wells between 1,500 cipitate minerals along the walls of pipes, reducing the interior and 3,000 ft below land surface. diameter of the supply lines. Corrosion, which is less common with brackish groundwater, can cause deterioration of metal What Chemical Factors Affect the Usability of surfaces. is commonly necessary to remove con- Brackish Groundwater? stituents that are related to scaling or that exceed health bench- marks. is the most common form of desalina- In addition to limitations caused by high dissolved-solids tion treatment in the United States. Reverse osmosis systems concentrations, other chemical constituents can be present include a thin, semipermeable barrier that transmits water under that affect the usefulness of brackish groundwater. The chemi- pressure, while excluding solutes. Without proper treatment of cal composition of brackish groundwater is spatially variable source water to reduce scaling potential, reverse osmosis systems because it depends in part on local geologic, hydrologic, and can fail; therefore, information about the minerals that are pres- climatic conditions. Chemical variations in brackish ground- ent and their concentrations will enable a cost/benefit analysis of water are important because they can have implications for the the resource and a given treatment technology. feasibility, treatability, and associated cost of using brackish Detailed information about brackish groundwater chemi- groundwater (McMahon and others, 2015). Specific chemical cal characteristics and scaling potentials was derived from constituents in brackish groundwater can exceed standards for (Parkhurst and Appelo, 1999) and other a particular use, and identifying the constituents is important approaches. For example, the Langelier saturation index is an to determine if brackish groundwater must undergo specialized indicator of the degree of saturation of water with respect to treatment beyond what is required to reduce overall salt content. calcite and is commonly used by the water-supply industry to determine potential for corrosion or scaling (Langelier, 1936). A What Physical Factors Affect the Usability of negative Langelier saturation index value indicates the water is Brackish Groundwater? not likely to precipitate calcite and, thus, could lead to corrosion; When evaluating brackish groundwater as a potential whereas, a positive index value will indicate the water is likely resource, understanding the ability of brackish groundwater- to deposit calcite in the distribution or treatment system. Only bearing to store and transmit usable amounts of water 4 percent of the evaluated groundwater samples (n=14,380) is important. This ability is controlled by the physical properties with a dissolved-solids concentration of 1,000 mg/L or more of the sediments, such as , storage exceeded a Langelier saturation index value of 1 (increased scal- coefficient, specific yield, and porosity. Information about these ing potential), and only 2 percent of samples had an index value properties is limited for most brackish zones; therefore, well- less than -1 (increased corrosion potential) (fig. 3). Some miner- yield data (available for about 16 percent of wells) were used to als identified as potential scaling components include calcite, determine some measure of the ability of wells producing brack- barite, and chalcedony, depending on the source of the water. ish groundwater to provide usable amounts of water. 120° 110° 100° 90° 80° 70° Although compaction and cementation of deeper sediments could limit development of brack- ish groundwater resources in some areas, reported well yields indicate that shallow and deep wells could

40° produce brackish groundwater at sufficient rates for many uses. In the regions with the most brackish groundwater, many of the sampled wells that produce brackish ground-

ATLANTIC water have reported well yields that OCEAN PACIFIC are at least 10 gallons per minute. OCEAN In the Southwestern Basins region 30° (fig. 1), a large part of the sampled wells producing brackish groundwa- PAATI ter can provide yields of at least 100 Arsenic concentration in brackish groundwater, in micrograms per liter n ,427 or 1,000 gallons per minute (fig. 4). ≤10 >10 These results probably represent minimum values because data are Base map modified from Esri and U.S. Geological Survey digital data, 1:2,000,000 and other scales, variously dated. 0 250 500 MILES Base map image is the intellectual property of Esri and is used herein under license. Copyright © 2014 Esri and its licensors. All rights reserved. from reported pumping rates and do Albers Equal-Area Conic projection, standard parallels 29°30’ N. and 45°30’ N., central meridian 96°00’ W., latitude of origin 23°00’ N. 0 250 500 KILOMETERS North American Datum of 1983 not represent maximum potential Figure 2. Concentrations of arsenic in brackish groundwater in the conterminous United States well yields. However, high yields (modified from McMahon and others, 2015). do not guarantee sustained produc-

130° 120° 110° 100° 90° 80° 70° tion or production without adverse consequences. Information about additional physical features of the hydrologic system, such as areas of recharge and discharge and the connection between

40° brackish groundwater and fresh groundwater or surface water, also is needed to evaluate the sustainability of developing brackish groundwater. An understanding of these character- istics provides the ability to assess the ATLANTIC PACIFIC OCEAN potential for extraction of brackish OCEAN groundwater to cause (1) enhanced 30° PAATI movement of more mineralized water angelier saturation inde into freshwater zones, and vice versa; HAWAII ≤–1 >0 to 1 (2) substantial groundwater-level >–1 to 0 >1 declines and land ; and (3) cascading effects on ALASKA and other surface water bodies as the Base map modified from Esri and U.S. Geological Survey digital data, 1:2,000,000 and other scales, variously dated. 0 250 500 MILES hydrologic system attempts to adjust Base map image is the intellectual property of Esri and is used herein under license. Copyright © 2014 Esri and its licensors. All rights reserved. Albers Equal-Area Conic projection, standard parallels 29°30’ N. and 45°30’ N., central meridian 96°00’ W., latitude of origin 23°00’ N. 0 250 500 KILOMETERS to these new withdrawals. North American Datum of 1983 Figure 3. Distribution of Langelier saturation index values in brackish groundwater. on adjacentwater resources. ment, includingtheeffects ofbrackishgroundwater withdrawals needed forevaluatingsustainable brackishgroundwaterdevelop information forspecificbrackish groundwateraquifersthatis development ofbrackishgroundwater istoacquiredetailed ment oftheresource. The nextchallenge withregardtopossible future researchinlocationsthatcouldbehelpfulforthedevelop istics ofbrackishaquifersandcreatesafoundationforfocusing updated basicinformationabouttheoccurrenceandcharacter stretch theirlimitedfreshwatersupplies. quality foravarietyofusescouldhelpwater-stressed regions of brackishgroundwatertoproducenewsuppliesdiffering recreational activities. The strategicdevelopmentandtreatment freshwater resourcescommonlyusedfordrinking,business, and areas, theuseofbrackishgroundwatercouldreduceeffects on the potentialtoenhanceNation’s watersecurity. Insome ter, especiallyinareaswithlimitedfreshwaterresources,has resource. Identificationofnewsourcesbrackishgroundwa support efficientandsustainableeconomicdevelopmentofthe and chemicalcharacteristicsofbrackishgroundwaterwillhelp environment. composition, use,treatmentrequirements,andeffects onthe brackish groundwaterdistribution,accessibility, yield,chemical has beenhamperedbythelackofbasicknowledgeconcerning . The useofbrackishgroundwater, however, oil andgasindustrysuchasdrilling,enhancedrecovery, and generation, ,aquacultureandavarietyofusesinthe for otherwateruses,whichincludecoolingpower augment orreplacetheuseoffreshwaterfordrinkingand Alternative toFreshwaterResources? Can BrackishGroundwaterbeUsedasan does not imply endorsement bytheU.S.Government. Any useoftrade,firm, orproductnamesisfordescriptive purposesonlyand 1,000 gallonsperminute. from wellsthatmeetorexceedreportedwellyieldsof10,100,and Figure 4. Percentage of brackish groundwater samples 100 20 40 60 80 The nationalbrackishgroundwaterassessmenthasprovided A betterunderstandingofthedistributionandphysical Water providersareturningtobrackishgroundwater 0

Coastal Plains Percentage ofbrackishgroundwatersamplesthatare 10 or more or 10 Reported wellyieldofsampledwell, Midcontinent Brackish groundwaterregion in gallonsperminute Eastern PAATI 100 or more or 100 Southwestern Basins 1,000 or more or 1,000 Midcontinent Western - - - - National DroughtMitigationCenter, theU.S.Departmentof McMahon, P.B., Böhlke,J.K.,Dahm,K.G.,Parkhurst,D.L., Langelier, W.F., 1936, The analyticalcontrolofanti-corrosion Feth, J.H.,1965,PreliminarymapoftheconterminousUnited References Cited to assesstheNation’s brackishgroundwaterresources. than 30national,regional,state,andlocalsourcesthatwereused ishgw/, whichincludesdownloadabledatacompiledfrommore water assessment,goto For MoreInformation Publishing support provided by: Publishing support providedby: U.S. EnvironmentalProtection Agency, 2015,Secondarydrink Stanton, J.S., Anning. D.W., Brown,C.J.,Moore,R.B., Reilly, T.E., Dennehy, K.F., Alley, W.M., andCunningham, Qi, S.L.,andHarris, A.C., 2017,Geochemicaldatabaseforthe Parkhurst, D.L.,and Appelo, C.A.J.,1999,User’s guideto March 13,2016,at National DroughtMitigationCenter, digitaldata,accessed Association, 2016,U.S.droughtmonitorforJanuary6,2015: Agriculture, andtheNationalOceanic Atmospheric ruary 3,2017,at resources: Groundwater, v. 54,no.4,p.464–475,accessedFeb for anupdatednationalassessmentofbrackishgroundwater Anning, D.W., andStanton,J.S.,2015,Chemical considerations www.jstor.org/stable/41226418 tion, v. 28,no.10,p.1500–1521.[Alsoavailableat water treatment:Journalof American Water Works Associa- er.usgs.gov/publication/ha199 2 plates,scale1:3,000,000.[Alsoavailableat solids: U.S.GeologicalSurveyHydrologic Atlas 199,31p., water containingmorethan1,000partspermilliondissolved States showingdepthtoandqualityofshallowestground Rolla Publishing ServiceCenter drinking-water-standards-guidance-nuisance-chemicals at https://www.epa.gov/dwstandardsregulations/secondary- Environmental Protection Agency, accessedMarch2,2016, ing waterstandards—Guidance fornuisancechemicals:U.S. pp1833. Professional Paper1833,185p., groundwater intheUnitedStates:U.S.GeologicalSurvey hon, P.B., Degnan,J.R.,andBöhlke,J.K.,2017,Brackish McGuire, V.L., Qi,S.L.,Harris, A.C., Dennehy, K.F., McMa- https://pubs.usgs.gov/circ/1323 U.S. GeologicalSurveyCircular1323,70p.[Alsoavailable at W.L., 2008,Ground-wateravailabilityintheUnitedStates: F72F7KK1 Geological Surveydatarelease, brackish groundwaterassessmentoftheUnitedStates:U.S. able at Resources InvestigationsReport99–4259,312p.[Alsoavail geochemical calculations:U.S.GeologicalSurvey Water- tion, batch-reaction,one-dimensionaltransport,andinverse PHREEQC (version2)—A computerprogramforspecia For moreinformationaboutthenationalbrackishground https://pubs.er.usgs.gov/publication/wri994259 . http://dx.doi.org/10.1111/gwat.12367 http://droughtmonitor.unl.edu/ https://water.usgs.gov/ogw/gwrp/brack-

.] /.] .] https://dx.doi.org/10.5066/ https://dx.doi.org/10.3133/ https://doi.org/10.3133/fs20173054 ISSN 2327-6932(online) ISSN 2327-6916(print) https://pubs. . http:// . .] . - - - - -