Groundwater Resources Program

Hydrogeology, Distribution, and Volume of Saline 

Groundwater in the Southern Midcontinent and Adjacent 

Areas of the United States

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2013–5017

ALABAMA

ARKANSAS

COLORADO

FLORIDA

IOWA

ILLINOIS

INDIANA

KANSAS

KENTUCKY

LOUISIANA

MICHIGAN

MINNESOTA

MISSOURI

MISSISSIPPI

MONTANA

NEBRASKA

NEW

MEXICO

OKLAHOMA

SOUTH

DAKOTA

TENNESSEE

TEXAS

WISCONSIN

WYOMING

UNITED STATES

MEXICO

GULF OF

MEXICO

LAKE MICHIGAN
 
Hydrogeology, Distribution, and Volume 

of Saline Groundwater in the Southern 

Midcontinent and Adjacent Areas of the 

United States

By Noël I. Osborn, S. Jerrod Smith, and Christian H. Seger

Groundwater Resources Program

Scientific Investigations Report 2013–5017

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

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Suggested citation:

Osborn, N.I., Smith, S.J., and Seger, C.H., 2013, Hydrogeology, distribution, and volume of saline 

groundwater in the southern midcontinent and adjacent areas of the United States: U.S. Geological Survey 

Scientific Investigations Report 2013–5017, 58 p., http://dx.doi.org/10.3133/sir20135017. 
iii

Contents

Abstract ..........................................................................................................................................................1

Introduction ....................................................................................................................................................1

Purpose and Scope .............................................................................................................................2

Approach ...............................................................................................................................................2

Methods .................................................................................................................................................3

Limitations and Assumptions .............................................................................................................3

Hydrogeology, Distribution, and Volume of Saline Groundwater .........................................................5

High Plains Regional Aquifer System ...............................................................................................6

Gulf Coast Regional Aquifer System .................................................................................................8

Aquifer Systems of the Gulf Coast Regional Aquifer System ..............................................8

Coastal Lowlands Aquifer System ................................................................................12

Mississippi Embayment and Texas Coastal Uplands Aquifer Systems ..................18

Groundwater Chemistry of the Gulf Coast Regional Aquifer System ...............................26

Saline-Water Volume of the Gulf Coast Regional Aquifer System ...................................26

Edwards-Trinity Regional Aquifer System .....................................................................................28

Central Midwest Regional Aquifer System ...................................................................................31

Great Plains Confining System ...............................................................................................35

Great Plains Aquifer System ...................................................................................................35

Western Interior Plains Confining System ............................................................................39

Western Interior Plains Aquifer System ...............................................................................39

Ozark Plateaus Aquifer System ..............................................................................................42

Saline-Water Volume of the Central Midwest Regional Aquifer System ........................42

Northern Midwest Regional Aquifer System in Northern Missouri ..........................................44

Mississippian Aquifer ...............................................................................................................44

Cambrian-Ordovician Aquifer .................................................................................................44

Summary of Saline Groundwater in the Southern Midcontinent ..............................................49

Summary .......................................................................................................................................................54

References Cited .........................................................................................................................................55

Figures

1. Map showing regional aquifer systems in the southern midcontinent and adjacent 

areas, as defined in the U.S. Geological Survey Regional Aquifer-System Analysis 

Program .........................................................................................................................................4

2. Map showing dissolved-solids concentrations and 1996–97 saturated thickness 

in the aquifer-assessment area of the High Plains regional aquifer system .....................7

3. Map showing aquifer systems in the Gulf Coast regional aquifer system ........................9

4. Generalized section from the western boundary of the Gulf Coast regional aquifer 

system in Texas to the Continental Slope showing relation of hydrogeologic units 

of the Texas coastal uplands aquifer system, the coastal lowlands aquifer system, 

and the geopressured zone .....................................................................................................11

5. Map showing dissolved-solids concentrations and thickness in the aquiferassessment area of permeable zone A in the coastal lowlands aquifer system, 

Gulf Coast regional aquifer system .........................................................................................13
iv

6. Map showing dissolved-solids concentrations and thickness in the aquifer-

assessment area of permeable zone B in the coastal lowlands aquifer system, 

Gulf Coast regional aquifer system .........................................................................................14

7. Map showing dissolved-solids concentrations and thickness in the aquifer-

assessment area of permeable zone C in the coastal lowlands aquifer system, 

Gulf Coast regional aquifer system .........................................................................................15

8. Map showing dissolved-solids concentrations and thickness in the aquifer-

assessment area of permeable zone D in the coastal lowlands aquifer system, 

Gulf Coast regional aquifer system .........................................................................................16

9. Map showing dissolved-solids concentrations and thickness in the aquifer-

assessment area of permeable zone E in the coastal lowlands aquifer system, 

Gulf Coast regional aquifer system .........................................................................................17

10. Map showing dissolved-solids concentrations and thickness in the aquifer-

assessment area of the Mississippi River Valley alluvial aquifer in the 

Mississippi embayment and Texas coastal uplands aquifer systems, Gulf Coast 

regional aquifer system ............................................................................................................19

11. Map showing dissolved-solids concentrations and thickness in the aquifer-

assessment area of the upper Claiborne aquifer in the Mississippi embayment 

and Texas coastal uplands aquifer systems, Gulf Coast regional aquifer system .........20

12. Map showing dissolved-solids concentrations and thickness in the aquifer-

assessment area of the middle Claiborne aquifer in the Mississippi embayment 

and Texas coastal uplands aquifer systems, Gulf Coast regional aquifer system .........21

13. Map showing dissolved-solids concentrations and thickness in the aquifer-

assessment area of the lower Claiborne-upper Wilcox aquifer in the Mississippi 

embayment and Texas coastal uplands aquifer systems, Gulf Coast regional 

aquifer system ............................................................................................................................22

14. Map showing dissolved-solids concentrations and thickness in the aquifer-

assessment area of the middle Wilcox aquifer in the Mississippi embayment and 

Texas coastal uplands aquifer systems, Gulf Coast regional aquifer system .................23

15. Map showing dissolved-solids concentrations and thickness in the aquifer-

assessment area of the lower Wilcox aquifer in the Mississippi embayment and 

Texas coastal uplands aquifer systems, Gulf Coast regional aquifer system .................24

16. Map showing dissolved-solids concentrations and thickness in the aquifer-

assessment area of the McNairy-Nacatoch aquifer of the Mississippi embayment 

and Texas coastal uplands aquifer systems, Gulf Coast regional aquifer system .........25

17. Map showing dissolved-solids concentrations and thickness in the aquifer-

assessment area of the Edwards aquifer, Edwards-Trinity regional aquifer system .....29

18. Map showing aquifer systems in the Central Midwest regional aquifer system ...........32

19. Generalized section from central Colorado to eastern Missouri showing 

hydrogeologic units and direction of groundwater flow in the Central Midwest 

regional aquifer system ............................................................................................................33

20. Map showing dissolved-solids concentrations and thickness in the aquifer-

assessment area of the Maha aquifer in the Great Plains aquifer system, Central 

Midwest regional aquifer system ...........................................................................................36

21. Map showing dissolved-solids concentrations and thickness in the aquifer-

assessment area of the Apishapa aquifer in the Great Plains aquifer system, 

Central Midwest regional aquifer system .............................................................................37

22. Map showing major structural features of the Central Midwest regional 

aquifer system and adjacent areas ........................................................................................38
v

23. Map showing dissolved-solids concentrations and thickness in the aquiferassessment area of the upper aquifer unit in the Western Interior Plains aquifer 

system and the Springfield Plateau aquifer in the Ozark Plateaus aquifer system, 

Central Midwest regional aquifer system .............................................................................40

24. Map showing dissolved-solids concentrations and thickness in the aquiferassessment area of the lower aquifer units in the Western Interior Plains aquifer 

system and the Ozark aquifer in the Ozark Plateaus aquifer system, Central 

Midwest regional aquifer system ...........................................................................................41

25. Map showing dissolved-solids concentrations and thickness in the aquiferassessment area of the Mississippian aquifer in northern Missouri, Northern 

Midwest regional aquifer system ...........................................................................................45

26. Map showing dissolved-solids concentrations and thickness in the aquiferassessment area of the Cambrian-Ordovician aquifer in northern Missouri, 

Northern Midwest regional aquifer system ..........................................................................46

27. Map showing extent of slightly to moderately saline groundwater in aquiferassessment areas of the High Plains, Gulf Coast, Edwards-Trinity, Central 

Midwest, and Northern Midwest regional aquifer systems ...............................................50

28. Map showing extent of very saline groundwater in aquifer-assessment areas 

of the High Plains, Gulf Coast, Edwards-Trinity, Central Midwest, and Northern 

Midwest regional aquifer systems .........................................................................................51

29. Map showing extent of saline groundwater in aquifer-assessment areas of the 

High Plains, Gulf Coast, Edwards-Trinity, Central Midwest, and Northern Midwest 

regional aquifer systems ..........................................................................................................52

30. Graph showing volume of saline water in aquifer-assessment areas of aquifer 

systems in the southern midcontinent and adjacent areas ...............................................54

Tables

1. Classification of groundwater based on dissolved-solids concentration .........................2

2. Regional aquifer systems, aquifer systems, and aquifers in the southern 

midcontinent and adjacent areas as defined in the U.S. Geological Survey 

Regional Aquifer-System Analysis Program ...........................................................................5

3. Time-stratigraphic, rock-stratigraphic, and hydrogeologic units of the High 

Plains regional aquifer system ..................................................................................................6

4. Estimated water volume of salinity zones in the aquifer-assessment area of the 

High Plains aquifer, High Plains regional aquifer system .....................................................8

5. Time-stratigraphic, rock-stratigraphic, and hydrogeologic units of the Gulf Coast 

regional aquifer system ............................................................................................................10

6. Estimated water volume of salinity zones in aquifer-assessment areas of the 

coastal lowlands aquifer system, Gulf Coast regional aquifer system .............................27

7. Estimated water volume of salinity zones in aquifer-assessment areas of the 

Mississippi embayment and Texas coastal uplands aquifer systems, Gulf Coast 

regional aquifer system ............................................................................................................27

8. Time-stratigraphic, rock-stratigraphic, and hydrogeologic units of the Edwards 

aquifer, Edwards-Trinity regional aquifer system .................................................................30

9. Estimated water volume of salinity zones in the aquifer-assessment area of the 

Edwards aquifer, Edwards-Trinity regional aquifer system ................................................30

10. Time-stratigraphic, rock-stratigraphic, and hydrogeologic units of the Plains 

subregion, Central Midwest regional aquifer system .........................................................34
vi

11. Time-stratigraphic, rock-stratigraphic, and hydrogeologic units of the Ozark 

subregion, Central Midwest regional aquifer system .........................................................34

12. Estimated water volume of salinity zones in the aquifer-assessment areas of the 

Maha and Apishapa aquifers in the Great Plains aquifer system, Central Midwest 

regional aquifer system ............................................................................................................43

13. Estimated water volume of salinity zones in aquifer-assessment areas of the 

Western Interior Plains and Ozark Plateaus aquifer systems, Central Midwest 

regional aquifer system ............................................................................................................43

14. Time-stratigraphic, rock-stratigraphic, and hydrogeologic units of the Northern 

Midwest regional aquifer system in northern Missouri ......................................................47

15. Estimated water volume of salinity zones in the aquifer-assessment areas of the 

Mississippian and Cambrian-Ordovician aquifers in northern Missouri, Northern 

Midwest regional aquifer system ...........................................................................................48

16. Summary of estimated water volume of salinity zones in aquifer-assessment 

areas of aquifer systems and aquifers in the southern midcontinent and 

adjacent areas ...........................................................................................................................53

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

kilometer (km) 0.6214 mile (mi)

Area

acre 4,047 square meter (m2

)

acre 0.004047 square kilometer (km2

)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

acre-foot (acre-ft) 1,233 cubic meter (m3

)

Flow rate

foot per year (ft/yr) 0.3048 meter per year (m/yr)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L) 

or micrograms per liter (μg/L).
Hydrogeology, Distribution, and Volume of Saline 

Groundwater in the Southern Midcontinent and Adjacent 

Areas of the United States

By Noël I. Osborn, S. Jerrod Smith, and Christian H. Seger 

Abstract 

The hydrogeology, distribution, and volume of saline 

water in 22 aquifers in the southern midcontinent of the 

United States were evaluated to provide information about 

saline groundwater resources that may be used to reduce 

dependency on freshwater resources. Those aquifers underlie 

six States in the southern midcontinent—Arkansas, Kansas, 

Louisiana, Missouri, Oklahoma, and Texas—and adjacent 

areas including all or parts of Alabama, Colorado, Florida, 

Illinois, Kentucky, Mississippi, Nebraska, New Mexico, South 

Dakota, Tennessee, and Wyoming and some offshore areas 

of the Gulf of Mexico. Saline waters of the aquifers were 

evaluated by defining salinity zones; digitizing data, primarily 

from the Regional Aquifer-System Analysis Program of the 

U.S. Geological Survey; and computing the volume of saline 

water in storage.

The distribution of saline groundwater in the southern 

midcontinent is substantially affected by the hydrogeology 

and groundwater-flow systems of the aquifers. Many of 

the aquifers in the southern midcontinent are underlain 

by one or more aquifers, resulting in vertically stacked 

aquifers containing groundwaters of varying salinity. Saline 

groundwater is affected by past and present hydrogeologic 

conditions. Spatial variation of groundwater salinity in the 

southern midcontinent is controlled primarily by locations 

of recharge and discharge areas, groundwater-flow paths and 

residence time, mixing of freshwater and saline water, and 

interactions with aquifer rocks and sediments.

The volume calculations made for the evaluated aquifers 

in the southern midcontinent indicate that about 39,900 

million acre-feet (acre-ft) of saline water is in storage. About 

21,600 million acre-ft of the water in storage is slightly to 

moderately saline (1,000–10,000 milligrams per liter [mg/L] 

dissolved solids), and about 18,300 million acre-ft is very 

saline (10,000–35,000 mg/L dissolved solids). The largest 

volumes of saline water are in the coastal lowlands (about 

16,300 million acre-ft), Mississippi embayment and Texas 

coastal uplands (about 12,000 million acre-ft), and Great 

Plains (about 8,170 million acre-ft) aquifer systems. Of the 

22 aquifers evaluated in this report, the Maha aquifer in the 

Great Plains aquifer system contains both the largest total 

volume of saline water (about 6,280 million acre-ft) and the 

largest volume of slightly to moderately saline water (about 

5,150 million acre-ft).

Introduction

Freshwater resources are under increasing stress from 

growing water-use demands and changes in climate (Federal 

Interagency Panel on Climate Change and Water Data and 

Information, 2011). In the southern midcontinent, the volume 

of fresh groundwater in storage is decreasing in response to 

groundwater withdrawals in many aquifer systems, such as 

the High Plains, the Mississippi River Valley alluvium, the 

coastal lowlands, and the Mississippi embayment aquifer 

systems (Reilly and others, 2008). Climate change and 

variability can affect water availability through changes 

in precipitation amount, intensity, and timing and changes 

in evapotranspiration (Brekke and others, 2009). These 

changes in precipitation and evaporation may affect surfacewater runoff, streamflow, and reservoirs and may also affect 

groundwater recharge, discharge, and storage in aquifers 

(Gurdak and others, 2009). Advances in technology such 

as membrane filtration and reverse osmosis are reducing 

the cost of desalination (Anderson and Woosley, 2005). 

Because of increasing demand for freshwater supplies and 

decreasing costs of desalination, saline groundwater is being 

considered a source of water that could reduce dependency 

on freshwater resources (Alley, 2003; Galloway and others, 

2003; Anderson and Woosley, 2005). The 2012 Texas State 

Water Plan recommends brackish groundwater desalination 

as a water-management strategy to meet at least some of the 

State’s projected water needs; currently (2013), 34 municipal 

desalination facilities in Texas use brackish groundwater as a 

raw water source (Texas Water Development Board, 2013).

The term “saline groundwater,” as used in this report, 

includes groundwater with dissolved-solids concentrations 

between 1,000 and 35,000 milligrams per liter (mg/L). 

Saline groundwater is considered slightly saline, moderately 

saline, or very saline if the groundwater has dissolved-solids 

concentrations of 1,000–3,000; greater than 3,000–10,000; 

and greater than 10,000–35,000 mg/L, respectively (table 1) 
2

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

(Winslow and Kister, 1956). Groundwater with dissolvedsolids concentrations greater than 35,000 mg/L (the 

average concentration of seawater) is referred to as “brine”; 

groundwater with dissolved-solids concentrations less than 

1,000 mg/L is referred to as “fresh.” 

Saline groundwater is known to be present in the southern 

midcontinent of the United States (Krieger and others, 1957; 

Feth and others, 1965), but more information about the 

distribution and volume of saline aquifers is necessary to 

evaluate and develop saline-groundwater resources. The study 

described in this report was conducted as a pilot study through 

the U.S. Geological Survey (USGS) Groundwater Resources 

Program with the purpose of assessing and mapping saline 

aquifers in the southern midcontinent as potential water 

sources. Results of the study will help the USGS address 

the goals of the SECURE Water Act, Section 9507 (2009), 

to describe significant brackish aquifers located throughout 

the United States. (The SECURE Water Act does not define 

“brackish aquifers,” but the term “brackish” commonly refers 

to water with dissolved-solids concentrations between 1,000 

and 10,000 mg/L [Freeze and Cherry, 1979; LBG-Guyton 

Associates and NRS Consulting Engineers, 2003], which 

fall within the saline-water classifications used herein). 

Information and maps in this report can be used in conjunction 

with geologic, hydrologic, chemical, climatic, and other types 

of information for regional planning activities. The regionalscale information provided in this report provides a framework 

for a systematic comparison of the saline-groundwater 

resources across the southern midcontinent region.

Early large-scale inventories of saline-groundwater 

resources of the United States include those of Krieger and 

others (1957) and Feth and others (1965). Surveys of saline 

groundwater in the southern midcontinent include those by 

Winslow and Kister (1956), who identified aquifers containing 

saline groundwater in Texas, and Winslow and others (1968), 

who presented information on the distribution, potential 

yield, aggregate sand thickness, and chemical analysis of 

saline groundwater in Louisiana. Core Laboratories, Inc. 

(1972), described a broad survey of principal saline aquifers 

in Texas; that survey includes a descriptive inventory of 

principal saline aquifers and their characteristics; geologic 

maps and sections, which illustrate aquifer location, thickness, 

structure, and salinity; and tables of supporting data. LBGGuyton Associates and NRS Consulting Engineers (2003) 

evaluated the distribution and volume of groundwater 

containing between 1,000 and 10,000 mg/L of dissolved-solids 

concentrations in each major and minor aquifer in Texas. 

Purpose and Scope

This report describes the hydrogeology, distribution, 

and volume of saline-groundwater resources in the southern 

midcontinent of the United States. Maps showing the thickness 

and dissolved-solids concentrations of saline water in 22 

aquifers and tables listing the volume of saline water in each 

aquifer are provided. Methods used to compute the volume 

of saline water in each aquifer are described. The distribution 

and volume of saline groundwater are substantially affected 

by the hydrogeology and groundwater flow of the aquifers; 

therefore, the hydrogeology and groundwater-flow system of 

each aquifer are described in context with the occurrence of 

saline groundwater.

Approach

This study focused on regional aquifer systems studied 

by the USGS Regional Aquifer-System Analysis (RASA) 

Program between 1978 and 1995. The RASA Program 

defined regional hydrogeology and established a framework 

of background information of geology, hydrology, and 

geochemistry of the Nation’s important aquifer systems 

that could be used for regional assessment of groundwater 

resources and in support of detailed local studies (Sun and 

others, 1997). Reports from the RASA studies are well-suited 

for regional assessment of saline groundwater in the southern 

midcontinent because the RASA Program (1) assembled 

data from numerous local studies into regional databases 

and provided consistent and integrated information across 

political boundaries (such as States, municipalities, and special 

water-management districts); (2) provided comprehensive 

descriptions of the geologic, hydrologic, and geochemical 

characteristics of aquifer systems that are necessary for 

understanding the occurrence of saline groundwater; 

(3) produced regional maps including aquifer structure, 

thickness, sand percentage, hydrologic properties (such as 

porosity and transmissivity), and water chemistry; (4) used 

groundwater-flow and geochemical models to provide a 

quantitative understanding of regional flow in the aquifer 

systems; and (5) studied the largest aquifers in the southern 

midcontinent. 

Several types of available geologic and hydrologic data 

were collected and compiled as part of the RASA Program. 

Data such as lithologic and geophysical logs, hydraulic heads, 

water chemistry, and aquifer properties were obtained from 

Federal, State, and private sources. The completeness, quality, 

Table 1. Classification of groundwater based on dissolved-solids 

concentration.

[Modified from Winslow and Kister, 1956, p. 5; mg/L, milligrams per liter]

Class Description

Dissolved-solids 

concentration 

(mg/L)

Fresh Less than 1,000

Saline Slightly saline 1,000–3,000

Moderately saline Greater than 3,000–10,000

Very saline Greater than 10,000–35,000

Brine Greater than 35,000
Introduction

3

and distribution of those data vary considerably. For example, 

subsurface data of water chemistry and hydrology typically are 

restricted to near-surface, freshwater aquifers and to deeper 

areas with oil and gas development. Although the distribution 

of data varied considerably, data were selected to represent the 

regional scope of the studies (Sun and Johnston, 1994). 

Aquifers described in this report are in five regional 

aquifer systems defined by the RASA Program: the High 

Plains, Gulf Coast, Edwards-Trinity, Central Midwest, 

and Northern Midwest. The aquifers underlie six States in 

the southern midcontinent—Arkansas, Kansas, Louisiana, 

Missouri, Oklahoma, and Texas—and adjacent areas 

including all or parts of Alabama, Colorado, Florida, Illinois, 

Kentucky, Mississippi, Nebraska, New Mexico, South Dakota, 

Tennessee, and Wyoming and some offshore areas of the Gulf 

of Mexico (fig. 1). 

Hydrogeologic features described in this report include 

22 aquifers, permeable zones, and units (termed aquifers in 

this report) that are in 10 aquifer systems (table 2). An aquifer 

is defined as a geologic formation, group of formations, or 

part of a formation that contains sufficient saturated permeable 

material to yield substantial quantities of water to wells and 

springs (Lohman and others, 1972) and may consist of fresh, 

saline, or brine water. An aquifer system is a grouping of 

aquifers and confining units that generally function together as 

an individual flow system (Miller and Appel, 1997).

Methods

Described in this section are the methods used to 

(1) define salinity zones used in the saline-groundwater 

assessment; (2) digitize data for dissolved-solids 

concentration, aquifer thickness, elevation, sand percentage, 

and porosity from published map reports; and (3) compute the 

volume of saline water in storage. 

For the purpose of assessing the distribution and volume 

of saline groundwater, four salinity zones were defined by 

dissolved-solids concentrations of 1,000–3,000 mg/L; greater 

than 3,000–10,000 mg/L; greater than 10,000–20,000 mg/L; 

and greater than 20,000–35,000 mg/L. The salinity zones 

are comparable to the three saline-water classes defined by 

Winslow and Kister (1956) (table 1) except that the “very 

saline” class (greater than 10,000–35,000 mg/L dissolvedsolids concentration) was divided into two zones (greater 

than 10,000–20,000 and greater than 20,000–35,000 mg/L 

dissolved-solids concentration) in this report to provide a more 

detailed assessment of very saline waters.

Contours representing dissolved-solids concentration, 

aquifer thickness, elevation, sand percentage, and porosity 

were digitized from published map reports. Control points 

and faults also were digitized when available. Digitization 

included large-format scanning of each map, registration 

of each map into geographic space, and manual tracing of 

point and line features into a geodatabase at a scale greater 

(finer) than the scale stated on each map. Aquifer-thickness 

maps were not available for two aquifers evaluated in this 

report (the lower aquifer units and upper aquifer unit in the 

Western Interior Plains aquifer system). For these aquifers, 

elevation contours representing the altitudes of the top and 

the base of each aquifer were digitized, and thickness was 

computed by subtracting continuous surfaces interpolated 

from digitized elevation contours. Each contour dataset was 

interpolated to a continuous surface (raster) at 1-kilometer 

resolution (cell size) by using the Topo to Raster tool (Esri, 

2012a). If available, the control-point dataset was used as an 

additional input to the tool to guide interpolation between 

contours. The dissolved-solids-concentration raster was used 

as the input to the Contour List tool (Esri, 2012b) to generate 

selected additional contours needed to define the four salinity 

zones. The additional dissolved-solids concentration contours 

were then merged with the original mapped dissolvedsolids-concentration contours. The merged dissolved-solidsconcentration contours were converted to polygons (zones) 

by using the Feature to Polygon tool (Esri, 2012c) and were 

clipped to the aquifer-assessment areas, which were defined 

by the intersection of aquifer-thickness data coverage and 

dissolved-solids-concentration data coverage (areas where 

both thickness and dissolved-solids-concentration data were 

available). The resulting salinity zones were used to calculate 

rasters of mean aquifer thickness, mean sand percentage, and 

mean porosity by using the Zonal Statistics as Table tool (Esri, 

2012d). 

The volume of saline water in storage was computed 

for each salinity zone in each aquifer-assessment area by 

multiplying the salinity zone area, mean aquifer thickness or 

saturated thickness, mean porosity or specific-yield fraction, 

and mean sand-fraction values where available. Most of 

the saline groundwater described in this report flows under 

confined conditions, and the thickness used in the volumetric 

calculations for the confined salinity zones was calculated as 

the mean total aquifer thickness. Groundwater in the High 

Plains aquifer flows under unconfined conditions, and the 

mean 1996–97 saturated thickness of the High Plains aquifer 

was used in the volumetric calculations instead of the mean 

total aquifer thickness. Porosity data were not available for 

some aquifers, and for these aquifers, specific yield was used 

instead of porosity. In aquifers for which mapped data were 

available, mean thickness, porosity, and sand percentage were 

determined from interpolated raster files. In aquifers for which 

mapped data were not available, average values were obtained 

from the literature.

Limitations and Assumptions

Because of the regional scope of this study, only 

aquifers in regional aquifer systems (many of which underlie 

several States) were evaluated. A limitation of this study is 

that it does not include many of the smaller aquifers in the 

southern midcontinent. Additionally, only those aquifers 

with sufficient information on the distribution of dissolvedsolids concentrations of saline water were evaluated for this 

study. 
4

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Figure 1. Regional aquifer systems in the southern midcontinent and adjacent areas, as defined in the U.S. Geological Survey Regional 

Aquifer-System Analysis Program.

ALABAMA

ARKANSAS

COLORADO

FLORIDA

IOWA

ILLINOIS

INDIANA

KANSAS

KENTUCKY

LOUISIANA

MICHIGAN

MINNESOTA

MISSOURI

MISSISSIPPI

MONTANA

NEBRASKA

NEW

MEXICO

OKLAHOMA

SOUTH

DAKOTA

TENNESSEE

TEXAS

WISCONSIN

WYOMING

UNITED STATES

MEXICO

42°

38°

34°

30°

26°

110° 105° 100° 95° 90° 85°

Base from National Atlas digital data

Lambert Conformal Conic projection

Modified from Sun and others, 1997, fig. 1

EXPLANATION

Edwards aquifer

 freshwater zone

Regional aquifer systems

 High Plains (partly overlies

 Central Midwest regional

 aquifer system)

Not included in saline

 water assesssment

 Gulf Coast

 Edwards-Trinity

 Central Midwest

 Northern Midwest

0 150 300 MILES

0 150 300 KILOMETERS

GULF OF

MEXICO

LAKE MICHIGAN

LA

KS

AR

MO

TX

OK

Six southern

midcontinent States

Area

enlarged
Hydrogeology, Distribution, and Volume of Saline Groundwater

5

The aquifer-assessment areas, which were determined 

on the basis of availability of both aquifer thickness and 

dissolved-solids-concentration data in the saline parts of 

the aquifers, usually are smaller than the actual extent of 

the aquifers. Although some of the maps in this report show 

dissolved-solids concentrations and thickness of parts of an 

aquifer containing freshwater (dissolved-solids concentrations 

less than 1,000 mg/L) or brine (dissolved-solids concentrations 

more than 35,000 mg/L), the maps in this report do not 

necessarily represent entire aquifers.

The regional-scale information provided in this report 

provides a framework for a systematic comparison of the 

saline-groundwater resources across the southern midcontinent 

region; however, this report does not provide detailed 

information on saline aquifers at a local level. Furthermore, to 

develop saline-groundwater resources, types of information 

not provided in this report (such as aquifer depth, well yields, 

water chemistry, and potential effects on freshwater aquifers) 

would be needed.

An assumption used in this study is that the volume of 

groundwater in storage does not change with time. In fact, 

the volume of groundwater in storage changes in response 

to both naturally occurring mechanisms, such as aquifer 

recharge and discharge to streams, and human-induced 

mechanisms such as groundwater withdrawals, deep-well 

injection, agricultural irrigation, and artificial recharge of 

water (Freeze and Cherry, 1979). Many of these mechanisms 

also have the potential to alter water chemistry. For example, 

groundwater withdrawals can induce the movement of saline 

water from underlying aquifers and from seawater into parts 

of aquifers that previously contained freshwater (Alley and 

others, 1999). In the southern midcontinent, activities by the 

petroleum industry have the potential to change the volume 

of water in storage and to alter water chemistry; for example, 

the petroleum industry withdraws large quantities of brine and 

saline water with production of oil and gas that are disposed of 

by injection into geologic units of Ordovician and Cambrian 

age (Jorgensen and Signor, 1981). Another common practice 

of the petroleum industry is waterflooding, a technique to 

recover hydrocarbons in old oil fields by injecting saline water 

into wells (Jorgensen and Signor, 1981).

Hydrogeology, Distribution, and 

Volume of Saline Groundwater

Several processes and factors affect the distribution and 

volume of saline-groundwater resources. The areal extent of 

an aquifer is controlled by hydrogeologic factors such as the 

types of rocks and sediments through which groundwater flow 

takes place, hydraulic properties, and the geologic history 

of those rocks and sediments. The volume of saline water 

in storage is by definition controlled by the areal extent, 

thickness, and porosity of an aquifer.

The chemical composition of groundwater is primarily 

determined by the mineralogy of rocks and sediments 

that compose an aquifer and by the length of time water 

is in contact with the minerals (Renken, 1998). Meteoric 

water, which enters groundwater-flow systems primarily as 

precipitation from rainfall, contains few dissolved solids 

(Renken, 1998). As meteoric water moves from recharge 

areas down the hydraulic gradient in aquifers, dissolvedsolids concentrations generally increase as the residence 

time of groundwater increases and water-rock interactions 

(such as mineral dissolution, mineral precipitation, and ion 

Table 2. Regional aquifer systems, aquifer systems, and aquifers 

in the southern midcontinent and adjacent areas as defined in 

the U.S. Geological Survey Regional Aquifer-System Analysis 

Program. 

Regional 

aquifer system

Aquifer 

system Aquifer

High Plains High Plains High Plains

Gulf Coast

Coastal lowlands

Permeable zone A

Permeable zone B

Permeable zone C

Permeable zone D

Permeable zone E

Mississippi 

embayment 

and 

Texas coastal 

uplands1

Mississippi River 

Valley alluvial

Upper Claiborne

Middle Claiborne

Lower Claiborne-Upper 

Wilcox

Middle Wilcox

Lower Wilcox

McNairy-Nacatoch

Edwards-Trinity Edwards-Trinity Edwards

Central Midwest

Great Plains

Maha

Apishapa

Western Interior Plains 

and 

Ozark Plateaus2

Upper aquifer unit and 

Springfield Plateau

Lower aquifer units and 

Ozark

Northern 

Midwest

Mississippian Mississippian

Cambrian-Ordovician Cambrian-Ordovician

1

Mississippi embayment and Texas coastal uplands aquifer systems are 

mapped together in this report.

2

Western Interior Plains and Ozark Plateaus aquifer systems are mapped 

together in this report.
6

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

exchange) progress (Hem, 1985; Siegel, 1989). Mixing 

of freshwater with saline water can occur by upward flow 

of saline groundwater from underlying geologic units, 

downward leakage through overlying units, and mixing of 

groundwater with surface water (Hem, 1985; Pettijohn, 1996; 

McMahon and others, 2007). Thus, the spatial variation of 

groundwater salinity is affected by factors and processes such 

as recharge sources, locations of recharge and discharge areas, 

groundwater residence time, water interactions with aquifer 

rock and sediments, and mixing of freshwater with saline 

water.

The following sections include a brief summary of 

the hydrogeology, groundwater-flow system, salinity, and 

processes that affect the water chemistry of each regional 

aquifer system. The sections also include maps showing 

the aquifer thickness and dissolved-solids concentrations of 

saline water of each aquifer-assessment area and the estimated 

volume of saline water in storage for each salinity zone.

High Plains Regional Aquifer System

The High Plains regional aquifer system, consisting 

of the High Plains aquifer, underlies 174,000 square miles 

(mi2) in parts of Colorado, Kansas, Nebraska, New Mexico, 

Oklahoma, South Dakota, Texas, and Wyoming (fig. 1). One 

of the largest aquifers in the Nation, the High Plains aquifer is 

the primary water supply for about 2.3 million people and also 

sustains more than one-quarter of the Nation’s agricultural 

production (Gurdak and others, 2009). The High Plains 

aquifer is an unconfined aquifer that consists mainly of 

near-surface sand and gravel deposits of late Tertiary and 

Quaternary age. The principal rock-stratigraphic unit forming 

the High Plains aquifer is the Ogallala Formation of late 

Tertiary age (table 3), which consists of clays, silts, sands, and 

gravels deposited by streams that flowed eastward from the 

Rocky Mountains (Gutentag and others, 1984). Underlying the 

High Plains aquifer is bedrock of Permian to Cretaceous age 

that is in hydraulic connection with the High Plains aquifer in 

places (Ryder, 1996). The 1996–97 saturated thickness of the 

High Plains aquifer ranged from 0 feet to approximately 1,000 

ft and averaged approximately 200 ft (Fischer and others, 

2000) (fig. 2). The specific yield of the aquifer ranges from 

3 to 35 percent and averages 15 percent (Weeks and others, 

1988).

Recharge to the High Plains aquifer is by diffuse 

infiltration of precipitation, infiltration of irrigation water, 

focused infiltration of storm and irrigation water runoff 

through streambeds and other topographic depressions (such 

as playas), and upward flow of water from underlying aquifers 

(Gurdak and others, 2009). Groundwater in the High Plains 

aquifer flows regionally from west to east and discharges to 

streams and springs. Groundwater also is discharged by well 

withdrawals (Gutentag and others, 1984; Weeks and others, 

1988; Gurdak and others, 2009). 

Most water in the High Plains aquifer has dissolvedsolids concentrations less than 500 mg/L, but dissolved-solids 

concentrations exceed 1,000 mg/L in the southern part of the 

aquifer in Texas and in small areas throughout the aquifer 

(fig. 2) (Weeks and others, 1988). In most areas of the High 

Plains aquifer, elevated dissolved-solids concentrations 

are caused by natural upward flow of saline groundwater 

from underlying geologic units and by pumping of highcapacity wells, which can induce or enhance upward flow 

of saline water from underlying geologic units (Weeks and 

others, 1988; Gurdak and others, 2009). The concentration 

of dissolved solids in groundwater exceeds 1,000 mg/L 

along parts of rivers connected to this aquifer because of 

irrigation practices. In stream valleys where the water table 

is near land surface, salts that accumulate in the soil owing to 

evapotranspiration are dissolved and flushed with irrigation 

water and transported to the aquifer (Weeks and others, 1988). 

An estimated 34.5 million acre-feet (acre-ft) of slightly saline 

water is stored in the aquifer-assessment area of the High 

Plains aquifer (table 4).

Table 3. Time-stratigraphic, rock-stratigraphic, and 

hydrogeologic units of the High Plains regional aquifer system.

[Modified from Gutentag and others, 1984, table 1; Fm, Formation; Gp, 

Group]

Time-stratigraphic unit Rock-stratigraphic 

unit

Hydrogeologic 

unit

System Series

Quaternary

Holocene and 

Pleistocene

Valley-fill deposits

High Plains 

regional 

aquifer 

system

Dune sand

Loess

Pleistocene Unconsolidated 

alluvial deposits

Tertiary

Miocene

Ogallala Fm

Arikaree Gp

Oligocene White River 

Gp

Brule 

Fm

Cretaceous

Upper and 

Lower 

Cretaceous

Undifferentiated 

rocks

Jurassic

Upper and 

Middle 

Jurassic

Undifferentiated 

rocks

Triassic Upper 

Triassic Dockum Gp

Permian

Upper and 

Lower 

Permian

Undifferentiated 

rocks
Hydrogeology, Distribution, and Volume of Saline Groundwater

7

Figure 2. Dissolved-solids concentrations and 1996–97 saturated thickness in the aquifer-assessment area of the High Plains regional 

aquifer system.

100

200

100

100

400

600

200

600

200

400

200

100

100

100

8001,000

200

100

400

200

200

100

100

100

100

200

400

100

200

200

100

200

100

100 100

100

100

100

200

100

100

100

100 200

400

200

200

100

200

100

400

600

400

600

1,000

ARKANSAS

COLORADO

IOWA

KANSAS

LOUISIANA

MINNESOTA

MISSOURI

NEBRASKA

NEW

MEXICO

OKLAHOMA

SOUTH

DAKOTA

TEXAS

WYOMING

High Plains

regional

aquifer system

Six southern

midcontinent

States

Area enlarged

104° 100° 96°

42°

39°

36°

33°

Base from National Atlas digital data

Lambert Conformal Conic Projection

Dissolved-solids data modified from Krothe and others, 1982, sheet 1

Saturated-thickness data from Fischer and others, 2000

EXPLANATION

Dissolved solids, in milligrams per liter

 < 1,000

 1,000 to 3,000

Line of equal saturated thickness—

 Intervals 100 and 200 feet

100

0 50 100 150 200 MILES

0 50 100 150 200 KILOMETERS
8

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Gulf Coast Regional Aquifer System

Aquifer Systems of the Gulf Coast Regional 

Aquifer System

The Gulf Coast regional aquifer system underlies an area 

of about 230,000 mi2 onshore in parts of Alabama, Arkansas, 

Florida, Illinois, Kentucky, Louisiana, Mississippi, Missouri, 

Tennessee, and Texas and an additional 60,000 mi2 offshore 

(fig. 3) (Grubb, 1998). The Gulf Coast regional aquifer system 

consists of three aquifer systems: (1) the coastal lowlands, 

(2) the Mississippi embayment, and (3) the Texas coastal 

uplands. These three aquifer systems were further divided into 

seven aquifers, five permeable zones, and six confining units 

(table 5). 

Sediments composing the Gulf Coast regional aquifer 

systems were deposited mostly during Quaternary and 

Tertiary times. Deposition of these sediments was in fluvial, 

deltaic, or shallow marine environments, resulting in an 

interbedded sequence of sand, silt, and clay with some gravel, 

lignite, and limestone (Williamson and Grubb, 1997). The 

sediments that compose these aquifers and confining units 

generally dip toward the Gulf of Mexico and become thicker 

and less permeable downdip (Grubb, 1998). Excess fluid 

pressure (termed “geopressure”) developed as sediments 

were buried more rapidly than fluids could be expelled 

from compacting sediments (Grubb, 1998). Gulf Coast 

sediments thin over uplifted structural features, such as 

the Sabine uplift, and thicken in depressions, such as the 

Mississippi embayment (Grubb, 1998). The relation of 

hydrogeologic units of the Texas coastal uplands aquifer 

system and the coastal lowlands aquifer system is illustrated in 

figure 4. 

Simulation of groundwater flow in the aquifer systems 

indicates that regional groundwater flow prior to withdrawal 

of groundwater (predevelopment) generally was from areas 

of high water-level altitude toward major rivers or broad 

extensive areas at low land-surface elevation (Grubb, 1998); 

however, large-scale groundwater withdrawals throughout the 

Gulf Coast regional aquifer systems have lowered hydraulic 

heads, which has caused changes in recharge and discharge, 

flow velocity, flow direction and magnitude, and land-surface 

subsidence (Williamson and Grubb, 1997). Large-scale 

development of groundwater resources in the freshwater 

part of the aquifer system has changed flow patterns in the 

saline part and induced flow updip toward pumping centers 

(Williamson and Grubb, 1997).

Table 4. Estimated water volume of salinity zones in the aquifer-assessment area of the High Plains aquifer, High Plains regional 

aquifer system.

[mg/L, milligrams per liter; values may not sum to totals because of independent rounding]

Salinity zone, dissolvedsolids concentration 

(mg/L)1

Area 

(million acres)

Mean 1996–97 

saturated thickness

(feet)2

Mean specific 

yield fraction3

Water volume

(million acre-feet)

1,000–3,000 3.71 66.5 0.14 34.5

1

Determined from dissolved-solids-concentration map (modified from Krothe and others, 1982, sheet 1).

2

Computed from saturated thickness map (modified from Fischer and others, 2000).

3

Computed from specific yield map (modified from Cederstrand and Becker, 1998).
Hydrogeology, Distribution, and Volume of Saline Groundwater

9

Figure 3. Aquifer systems in the Gulf Coast regional aquifer system.

UNITED STATES

MEXICO

ALABAMA

ARKANSAS

FLORIDA

ILLINOIS

KANSAS KENTUCKY

LOUISIANA

MISSOURI

MISSISSIPPI

OKLAHOMA

TENNESSEE

TEXAS

100° 95° 90°

34°

30°

26°

Sabine

uplift

Base from National Atlas digital data

Lambert Conformal Conic projection

Modified from Hosman and Weiss, 1991, fig. 2

Sabine uplift from Grubb, 1998, fig. 5

0 60 120 180 240 MILES

0 60 120 180 240 KILOMETERS

MIssissippi River

GULF OF

MEXICO

EXPLANATION

Coastal lowlands aquifer system

Mississippi embayment aquifer system

Texas coastal uplands aquifer system

Gulf Coast

regional

aquifer system

Six southern

midcontinent

States

Area

enlarged
10

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Table 5. Time-stratigraphic, rock-stratigraphic, and hydrogeologic units of the Gulf Coast regional aquifer system. 

[Modified from Grubb, 1998, table 1]

Coastal lowlands aquifer system

Time-stratigraphic unit Rockstratigraphic unit Hydrogeologic unit

System Series

Quaternary

Holocene

Permeable zone A

Coastal lowlands aquifer system

Pleistocene 

Permeable zone B

Tertiary

Pliocene

Permeable zone C

Miocene

Zone D confining unit

Permeable zone D

Zone E confining unit

Permeable zone E

Oligocene and 

Eocene

Vicksburg and Jackson 

Groups Vicksburg-Jackson confining unit

Mississippi embayment aquifer system Texas coastal uplands aquifer system

Time-stratigraphic unit Rockstratigraphic unit Hydrogeologic unit Hydrogeologic unit

System Series

Quaternary Holocene and 

Pleistocene Alluvium Mississippi River Valley alluvial aquifer

Mississippi embayment aquifer system

Not present

Oligocene and 

Eocene

Vicksburg and 

Jackson Groups

Vicksburg-Jackson confining 

unit Vicksburg-Jackson confining unit

Tertiary

Eocene

Claiborne Group

Upper Claiborne aquifer Upper Claiborne aquifer

Texas coastal uplands aquifer 

system

Middle Claiborne confining unit Middle Claiborne confining unit

Middle Claiborne aquifer Middle Claiborne aquifer

Lower Claiborne confining unit Lower Claiborne confining unit

Lower Claiborne-upper Wilcox 

aquifer

Lower Claiborne-upper Wilcox 

aquifer

Wilcox Group Middle Wilcox aquifer Middle Wilcox aquifer

Paleocene

Lower Wilcox aquifer Not present

Midway Group Midway confining unit1 Midway confining unit

Cretaceous Upper Cretaceous McNairy-Nacatoch aquifer1

1

Included in the Mississippi embayment aquifer system by Grubb (1984), Hosman and Weis (1991), and Renken (1998).
Hydrogeology, Distribution, and Volume of Saline Groundwater

11

Figure 4. Generalized section from the western boundary of the Gulf Coast regional aquifer system in Texas to the Continental Slope 

showing relation of hydrogeologic units of the Texas coastal uplands aquifer system, the coastal lowlands aquifer system, and the 

geopressured zone.

NORTHWEST SOUTHEAST

Modified from Grubb, 1998, fig. 9

VERTICAL SCALE GREATLY EXAGGERATED

0

0 20 40 60 80 KILOMETERS

20 40 60 80 MILES

Vicksburg-Jackson confining unit

Coastal lowlands aquifer system Edge of

Continental

Shelf

Texas coastal uplands

aquifer system

Midway confining unit

Top of geopressured zone Top of geopressured zone

2,000

FEET

NAVD 88

4,000

2,000

6,000

8,000

10,000

12,000

Continental Slope

12

3

4

13

5

6

14

15 16

7

8

9

17

10

11

NAVD 88, North American Vertical Datum of 1988

Gulf Coast

regional

aquifer system

Six southern

midcontinent

States

Approximate

line of section

EXPLANATION

Hydrogeologic units of the coastal lowlands aquifer system Hydrogeologic units of the Texas coastal uplands aquifer system

Permeable zone A (Holocene-upper

 Pleistocene deposits)

Permeable zone B (Lower Pleistocene-

 upper Pliocene deposits)

Permeable zone C (Lower Pliocene-

 upper Miocene deposits

Zone D confining unit

Permeable zone D (middle Miocene

 deposits)

Zone E confining unit

Permeable zone E (lower Miocene-

 upper Oligocene deposits)

Upper Claiborne aquifer

Middle Claiborne confining unit

Middle Claiborne aquifer

Lower Claiborne confining unit

Lower Claiborne-upper Wilcox aquifer

Middle Wilcox aquifer

Midway confining unit—Base of Texas coastal

 uplands aquifer system

Contact—Dashed where approximately located; 

 Queried where uncertain

Vicksburg-Jackson confining unit—Base of the

 coastal lowlands aquifer system

11

10

9

17

8

16

7

15

6

14

5

13

4

3

12

?

? ?
12

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Coastal Lowlands Aquifer System

The coastal lowlands aquifer system underlies an area of 

about 160,000 mi2, including both onshore and offshore areas 

(fig. 3). This aquifer system consists mostly of interbedded 

sands and clays of Oligocene age and younger (Weiss, 1992). 

The average thickness of these sediments is approximately 

6,000 ft, with a maximum thickness of more than 18,000 ft 

offshore from southern Louisiana (Weiss, 1992). Because the 

interbedded sand and clay beds of the coastal lowlands aquifer 

system are not regionally extensive, these sediments were 

divided vertically into five aquifers (termed “permeable zones 

A, B, C, D, and E”) and two confining units on the 

basis of distinct changes in vertical hydraulic head gradients 

and local lithology (Weiss, 1992) (figs. 5–9, table 5). 

The coastal lowlands aquifer system overlies the Tertiary 

hydrogeologic units of the Mississippi embayment and 

the Texas coastal uplands aquifer systems and is separated 

from these hydrogeologic units by the regionally extensive 

Vicksburg-Jackson confining unit (Weiss, 1992). The 

Vicksburg-Jackson confining unit is the base of the coastal 

lowlands aquifer system except where the geopressured 

zone is present, and in those areas, the geopressured zone 

is considered to be the base of the coastal lowlands aquifer 

system (Grubb, 1998) (fig. 4).

Water in the coastal lowlands aquifer system is 

unconfined in outcrop areas, but most of the aquifer 

system is confined (Ryder, 1996). The aquifer system is 

recharged primarily by infiltration of precipitation that falls 

on topographically high aquifer-outcrop areas. Additional 

recharge occurs in areas where groundwater withdrawals have 

reversed the groundwater-flow direction, causing water to 

flow from streams into the aquifers. Natural discharge occurs 

by evapotranspiration, flow into streams, and upward flow 

to shallow aquifers in coastal areas or in the Gulf of Mexico 

(Ryder, 1996). Model simulations by Grubb (1998) indicated 

that regional predevelopment groundwater flow in the coastal 

lowlands aquifer system generally was from areas of high 

water-level altitudes between the major rivers and adjacent to 

the outcrop band of the Vicksburg-Jackson confining unit to 

the major rivers and to regional discharge areas parallel to the 

shoreline. 
Figure 5. Dissolved-solids concentrations and thickness in the aquifer-assessment area of permeable zone A in the coastal lowlands aquifer system

aquifer system. 1,100

1,000800

200

1,100

900

700

700

200

600

400

200

400

600

400 600

800

1,200

1,000

700 200

200

900

TEXAS

MISSISSIPPI

LOUISIANA

F

ALABA

MEXICO UNITED STATES

99° 96° 93° 90° 

32°30°28°26°

Mississippi River

GULF OF

MEXICO

Base from National Atlas digital dataLambert Conformal Conic projection

Dissolved-solids data modified from Pettijohn and others

Thickness data modified from We

0 60 120 180 240 MILES0 60 120 180 240 KILOMETERS

EXPLANATION

Dissolved solids, in mill per liter < 1,000 1,000 to 3,000 > 3,000 to 10,000 > 10,000 to 20,000 > 20,000 to 35,000 > 35,000Line of equal thickness— Interval 100 and 200 fe

700

Coastal

lowlands

aquifer

system

Permeable zone A

aquifer-assessment

area boundary

Six southern

midcontinent

States

Area enlarged
Figure 6. Dissolved-solids concentrations and thickness in the aquifer-assessment area of permeable zone B in the coastal lowlands aquifer system

aquifer system.

5,000

4,000

3,000

2,000

1,500

1,000

500

3,000

5,0004,000 5,000

MISSISSIPPI

LOUISIANA

F

ALABA

TEXAS

MEXICO UNITED STATES

99° 96° 93° 90° 

32°30°28°26°

Mississippi River

GULF OF

MEXICO

Base from National Atlas digital dataLambert Conformal Conic projection

Dissolved-solids data modified from Pettijohn and others

Thickness data modified from We

0 60 120 180 240 MILES0 60 120 180 240 KILOMETERS

EXPLANATION

Dissolved solids, in mill per liter < 1,000 1,000 to 3,000 > 3,000 to 10,000 > 10,000 to 20,000 > 20,000 to 35,000 > 35,000Line of equal thickness— Intervals 500 and 1,000 

500

Coastal

lowlands

aquifer

system

Permeable zone B

aquifer-assessment

area boundary

Six southern

midcontinent

States

Area enlarged
Figure 7. Dissolved-solids concentrations and thickness in the aquifer-assessment area of permeable zone C in the coastal lowlands aquifer system

system. 6,000

5,000

4,000

3,000 1,500

500

3,000

1,000

500

1,500

4,000

2,000

3,000

1,000

500

1,500

2,000

1,000

2,000

1,500 1,000

500

2,000

2,000

3,000

4,000

500

500

1,000

1,500

TEXAS

MISSISSIPPI

LOUISIANA

F

ALABA

MEXICO UNITED STATES

99° 96° 93° 90° 

32°30°28°26°

Mississippi River

GULF OF

MEXICO

Base from National Atlas digital dataLambert Conformal Conic projection

Dissolved-solids data modified from Pettijohn and others

Thickness data modified from We

0 60 120 180 240 MILES0 60 120 180 240 KILOMETERS

EXPLANATION

Dissolved solids, in mill per liter < 1,000 1,000 to 3,000 > 3,000 to 10,000 > 10,000 to 20,000 > 20,000 to 35,000 > 35,000Line of equal thickness— Intervals 500 and 1,000 

500

Permeable zone C

aquifer-assessment

area boundary

Coastal

lowlands

aquifer

system

Six southern

midcontinent

States

Area enlarged
Figure 8. Dissolved-solids concentrations and thickness in the aquifer-assessment area of permeable zone D in the coastal lowlands aquifer system

aquifer system.

7,000

5,000

3,000

2,000 1,500

1,000

500

3,000 2,000

4,000 2,000

5,000

4,000

4,000

500 2,000 1,500

1,500

1,000500

6,000

4,000

3,000

5,000

1,000

5,000 6,000

TEXAS

MISSISSIPPI

LOUISIANA

F

ALABA

MEXICO UNITED STATES

99° 96° 93° 90° 

32°30°28°26°

Mississippi River

GULF OF

MEXICO

Base from National Atlas digital dataLambert Conformal Conic projection

Dissolved-solids data modified from Pettijohn and others

Thickness data modified from We

0 60 120 180 0 60 120 180 240 KILOMETERS

EXPLANATION

Dissolved solids, in mill per liter < 1,000 1,000 to 3,000 > 3,000 to 10,000 > 10,000 to 20,000 > 20,000 to 35,000 > 35,000Line of equal thickness— Interval 500 and 1,000 

500

Coastal

lowlands

aquifer

system

Permeable zone D

aquifer-assessment

area boundary

Six southern

midcontinent

States

Area enlarged
Figure 9. Dissolved-solids concentrations and thickness in the aquifer-assessment area of permeable zone E in the coastal lowlands aquifer system

system. 4,000 3,000 2,000

500

3,000

2,000

1,500

1,000

1,000

3,000 1,500 500

500 1,000 1,500 1,000 2,000

1,000

500

500

1,500

500

2,000

1,000

TEXAS

MISSISSIPPI

LOUISIANA

F

ALABA

MEXICO UNITED STATES

99° 96° 93° 90° 

32°30°28°26°

Mississippi River

GULF OF

MEXICO

Base from National Atlas digital dataLambert Conformal Conic projection

Dissolved-solids data modified from Pettijohn and others

0 60 120 180 240 MILES Thickness data modified from Wei0 60 120 180 240 KILOMETERS

EXPLANATION

Dissolved solids, in milli per liter < 1,000 1,000 to 3,000 > 3,000 to 10,000 > 10,000 to 20,000 > 20,000 to 35,000 > 35,000Line of equal thickness— Interval 500 and 1,000 f

500

Coastal

lowlands

aquifer

system

Permeable zone E

aquifer assessment

area boundary

Six southern

midcontinent

States

Area enlarged
18

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Mississippi Embayment and Texas Coastal Uplands 

Aquifer Systems

The Mississippi embayment and Texas coastal uplands 

aquifer systems underlie about 188,000 mi2 in parts of 

Alabama, Arkansas, Florida, Illinois, Kentucky, Louisiana, 

Mississippi, Missouri, Tennessee, and Texas (fig. 3). The 

Mississippi embayment and Texas coastal uplands aquifer 

systems consist of thick sequences of Cenozoic deposits. The 

maximum thickness of the Mississippi embayment aquifer 

system is approximately 6,000 ft, and the maximum thickness 

of the Texas coastal uplands aquifer system is approximately 

7,000 ft (Ackerman, 1996). The Mississippi embayment and 

Texas coastal uplands aquifer systems are contiguous and 

share many of the same hydrogeologic units. Furthermore, the 

saline-groundwater flow systems of the two aquifer systems 

are interconnected. For these reasons, the saline groundwaters 

in both aquifer systems are mapped and evaluated together in 

this report. 

The aquifers in the Mississippi embayment and laterally 

equivalent Texas coastal uplands aquifer systems typically 

consist of one or more massive sand beds and are separated 

by confining units of regionally extensive clay beds (Grubb, 

1998). The aquifers in the Texas coastal uplands aquifer 

system typically are thicker and contain more sand than 

equivalent aquifers in the Mississippi embayment aquifer 

system (Grubb, 1998). The regional hydrogeologic units in the 

combined Mississippi embayment and Texas coastal uplands 

aquifer systems, from youngest to oldest, are (1) Mississippi 

River Valley alluvial aquifer, (2) Vicksburg-Jackson confining 

unit, (3) upper Claiborne aquifer, (4) middle Claiborne 

confining unit, (5) middle Claiborne aquifer, (6) lower 

Claiborne confining unit, (7) lower Claiborne-upper Wilcox 

aquifer, (8) middle Wilcox aquifer, (9) lower Wilcox aquifer, 

(10) Midway confining unit, and (11) McNairy-Nacatoch 

aquifer (table 5). The Mississippi embayment aquifer system 

contains all of these hydrogeologic units; the Texas coastal 

uplands aquifer system contains all of the hydrogeologic units 

except the Mississippi River Valley alluvial aquifer, the lower 

Wilcox aquifer, and the McNairy-Nacatoch aquifer. Maps of 

dissolved-solids concentrations and thickness of aquifers in 

the Mississippi embayment and Texas coastal uplands aquifer 

systems are shown in figures 10–16.

The Mississippi River Valley alluvial aquifer consists 

of alluvial and terrace deposits of Quaternary age and is age 

equivalent with permeable zone A in the coastal lowlands 

aquifer system (Hosman and Weiss, 1991) but is separated 

from the coastal lowlands aquifer by the Vicksburg-Jackson 

confining unit (Ackerman, 1996). The Mississippi River 

Valley alluvial aquifer overlies aquifers and confining units of 

Tertiary age (table 5) and consists of deposits of gravel, sand, 

and clay, which commonly grade upward from gravel and 

coarse sand at the base to fine sand overlain by silt and clay at 

the surface (Pettijohn, 1996).

The Mississippi River Valley alluvial aquifer is exposed 

at land surface throughout its areal extent. Regionally, the 

alluvial aquifer is unconfined, but locally it is confined under 

a layer of silt, clay, and fine-grained sand (Ackerman, 1996). 

The alluvial aquifer is absent on Crowleys Ridge (fig. 10), an 

erosional remnant of Tertiary strata, which acts as a barrier to 

regional groundwater flow (Ackerman, 1996). In areas where 

the Mississippi River Valley alluvial aquifer overlies or is 

incised into the underlying Tertiary aquifers, there is upward 

flow of groundwater from the underlying aquifers (Pettijohn, 

1996). 

The Vicksburg-Jackson confining unit, consisting of 

massive clay beds, separates the Mississippi River Valley 

alluvial aquifer and aquifers and confining units in the 

underlying Claiborne Group (table 5). The Claiborne Group 

contains a thick sequence of massive sand beds separated 

by thick, extensive marine clay beds (Hosman and Weiss, 

1991). The upper Claiborne aquifer consists of interbedded 

fine sand, silt, and clay. The aquifer is as thick as 2,400 ft 

in southeastern Texas and generally less than 300 ft thick in 

the Mississippi embayment. The middle Claiborne aquifer 

underlies the middle Claiborne confining unit and consists 

primarily of the Sparta Sand. The middle Claiborne aquifer 

has a large sand content in the Mississippi embayment, where 

the aquifer generally contains more than 60 percent sand. The 

lower Claiborne confining unit hydraulically separates the 

underlying lower Claiborne-upper Wilcox aquifer from the 

middle Claiborne aquifer. The lower Claiborne-upper Wilcox 

aquifer consists primarily of the Carrizo Sand or its equivalent 

Meridian Sand Member of the Tallahatta Formation, which 

is a massive and extensive sand (Hosman and Weiss, 1991). 

In the central part of the Mississippi embayment, the lower 

Claiborne-upper Wilcox aquifer merges with the middle 

Claiborne aquifer where the clay of the lower Claiborne 

confining unit changes to sand facies. The middle Claiborne 

and lower Claiborne-upper Wilcox aquifers are not present 

over the Sabine uplift, in an area of about 7,000–9,000 mi2

centered on the Texas-Louisiana State boundary (figs. 12–13), 

owing to lack of deposition or erosion (Grubb, 1998).

The middle Wilcox aquifer generally consists of thin 

interbedded sand, silt, and clay, but in the northern part of the 

Mississippi embayment, the middle Wilcox aquifer contains 

massive sand beds (Hosman and Weiss, 1991; Grubb, 1998). 

The aquifer is more than 80 percent sand throughout most of 

the northern part of the Mississippi embayment, but the sand 

content gradually decreases to the southeast where it is less 

than 40 percent throughout a large part of southern Mississippi 

(Grubb, 1998). The lower Wilcox aquifer occurs in only the 

Mississippi embayment aquifer system (table 5). The aquifer is 

generally less than 400 ft thick but thickens southward to more 

than 1,200 ft in central Mississippi (Hosman and Weiss, 1991). 

The Midway confining unit is the basal confining unit of most 

of the Mississippi embayment and Texas coastal uplands 

aquifer systems (fig. 4, table 5) (Grubb, 1998; Hosman and 

Weiss, 1991).
Hydrogeology, Distribution, and Volume of Saline Groundwater

19

Figure 10. Dissolved-solids concentrations and thickness in the aquifer-assessment area of the Mississippi River Valley alluvial 

aquifer in the Mississippi embayment and Texas coastal uplands aquifer systems, Gulf Coast regional aquifer system.

ALABAMA

ARKANSAS

ILLINOIS

KENTUCKY

LOUISIANA

MISSOURI

MISSISSIPPI

TENNESSEE

250

200

150

200

150

150

100

150

100

100

100

150

100

CROWLEYS

RIDGE

93° 90° 87°

36°

34°

32°

Mississippi River

Base from National Atlas digital data

Lambert Conformal Conic projection

Dissolved-solids data modified from Pettijohn and others, 1988, sheet 5

Thickness data modified from Hosman and Weiss, 1991, pl. 9

0 30 60 90 120 MILES

0 30 60 90 120 KILOMETERS EXPLANATION

Dissolved solids, in milligrams

 per liter

 < 1,000

 1,000 to 3,000

Line of equal thickness—

 Interval 50 feet

150

Mississippi embayment

and Texas coastal uplands

aquifer systems

Six southern

midcontinent

States Mississippi River Valley alluvial

aquifer-assessment area boundary

Area enlarged
20

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Figure 11. Dissolved-solids concentrations and thickness in the aquifer-assessment area of the upper Claiborne aquifer in the 

Mississippi embayment and Texas coastal uplands aquifer systems, Gulf Coast regional aquifer system.

TEXAS

TENNESSEE

OKLAHOMA

MISSISSIPPI

MISSOURI

LOUISIANA

KANSAS KENTUCKY

ILLINOIS

FLORIDA

ARKANSAS

ALABAMA

MEXICO

UNITED STATES

Sabine

uplift

2,400

100

1,400

1,200

400

400

200100

100

800

600

2,000

1,500

1,000

100

100

600

1,000

1,000

200

100

400

200

1,500

600

100° 95° 90°

34°

30°

26°

1,400

GULF OF

MEXICO

Mississippi River

Base from National Atlas digital data

Lambert Conformal Conic projection

Dissolved-solids data modified from Pettijohn and others, 1988, sheet 3

Thickness data modified from Hosman and Weiss, 1991, pl. 11

0 60 120 180 240 MILES

0 60 120 180 240 KILOMETERS

EXPLANATION

Dissolved solids, in milligrams

 per liter

 < 1,000

 1,000 to 3,000

 > 3,000 to 10,000

 > 10,000 to 20,000

 > 20,000 to 35,000

 > 35,000

Line of equal thickness—

 Intervals 100, 200, and 500 feet

200

Mississippi embayment

and Texas coastal uplands

aquifer systems

Six southern

midcontinent

States Upper Claiborne

aquifer-assessment area boundary

Area enlarged
Hydrogeology, Distribution, and Volume of Saline Groundwater

21

Figure 12. Dissolved-solids concentrations and thickness in the aquifer-assessment area of the middle Claiborne aquifer in the 

Mississippi embayment and Texas coastal uplands aquifer systems, Gulf Coast regional aquifer system.

TEXAS

TENNESSEE

OKLAHOMA

MISSISSIPPI

MISSOURI

LOUISIANA

KANSAS KENTUCKY

ILLINOIS

FLORIDA

ARKANSAS

ALABAMA

MEXICO

UNITED STATES

200

600

400

200

400

1,000

1,600

800

400

600

800

400

800

200

1,000

600

200

800

200

200

600

400

600

400

1,000

2,400

200

1,200

1,200

2,000

Sabine uplift

100° 95° 90°

34°

30°

26°

GULF OF

MEXICO

Mississippi River

Base from National Atlas digital data

Lambert Conformal Conic projection

Dissolved-solids data modified from Pettijohn and others, 1988, sheet 2

Thickness data modified from Hosman and Weiss, 1991, pl. 13

0 60 120 180 240 MILES

0 60 120 180 240 KILOMETERS

EXPLANATION

Dissolved solids, in milligrams

 per liter

 < 1,000

 1,000 to 3,000

 > 3,000 to 10,000

 > 10,000 to 20,000

 > 20,000 to 35,000

 > 35,000

Line of equal thickness—

 Intervals 200 and 400 feet

400

Mississippi embayment

and Texas coastal uplands

aquifer systems

Six southern

midcontinent

States Middle Claiborne

aquifer-assessment area boundary

Area enlarged
22

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Figure 13. Dissolved-solids concentrations and thickness in the aquifer-assessment area of the lower Claiborne-upper Wilcox aquifer 

in the Mississippi embayment and Texas coastal uplands aquifer systems, Gulf Coast regional aquifer system.

TEXAS

TENNESSEE

OKLAHOMA

MISSISSIPPI

MISSOURI

LOUISIANA

KANSAS KENTUCKY

ILLINOIS

FLORIDA

ARKANSAS

ALABAMA

MEXICO

UNITED STATES

Sabine uplift

1,200

300

500

100

400

200

300

600

200

300

100

100

600

300

300

700

100

50

500

300

400

200

300

200

100

200

100

200

300

900

700

600

900

1,000

100° 95° 90°

34°

30°

26°

GULF OF

MEXICO

Mississippi River

Base from National Atlas digital data

Lambert Conformal Conic projection

Dissolved-solids data modified from Pettijohn and others, 1988, sheet 2

Thickness data modified from Hosman and Weiss, 1991, pl. 15

0 60 120 180 240 MILES

0 60 120 180 240 KILOMETERS

EXPLANATION

Dissolved solids, in milligrams

 per liter

 < 1,000

 1,000 to 3,000

 > 3,000 to 10,000

 > 10,000 to 20,000

 > 20,000 to 35,000

 > 35,000

Line of equal thickness—

 Intervals 50 and 100 feet

500

Mississippi embayment

and Texas coastal uplands

aquifer systems

Six southern

midcontinent

States Lower Claiborne-upper Wilcox

aquifer-assessment area boundary

Area enlarged
Hydrogeology, Distribution, and Volume of Saline Groundwater

23

Figure 14. Dissolved-solids concentrations and thickness in the aquifer-assessment area of the middle Wilcox aquifer in the 

Mississippi embayment and Texas coastal uplands aquifer systems, Gulf Coast regional aquifer system.

TEXAS

TENNESSEE

OKLAHOMA

MISSISSIPPI

MISSOURI

LOUISIANA

KANSAS KENTUCKY

ILLINOIS

FLORIDA

ARKANSAS

ALABAMA

MEXICO

UNITED STATES

5,000

4,000

3,500

3,000

2,500

500

1,500

2,000

4,500

1,500

1,000

500

100

200

1,500

4,500

2,000

100

200

300

400

1,000

500

500

1,500

2,000

2,500

3,000

1,500

3,000

100° 95° 90°

34°

30°

26°

GULF OF

MEXICO

Mississippi River

Base from National Atlas digital data

Lambert Conformal Conic projection

Dissolved-solids data modified from Pettijohn and others, 1988, sheet 1

Thickness data modified from Hosman and Weiss, 1991, pl. 16

0 60 120 180 240 MILES

0 60 120 180 240 KILOMETERS

EXPLANATION

Dissolved solids, in milligrams

 per liter

 < 1,000

 1,000 to 3,000

 > 3,000 to 10,000

 > 10,000 to 20,000

 > 20,000 to 35,000

 > 35,000

Line of equal thickness—

 Intervals 100 and 500 feet

500

Mississippi embayment

and Texas coastal uplands

aquifer systems

Six southern

midcontinent

States Middle Wilcox

aquifer-assessment area boundary

Area enlarged
24

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Figure 15. Dissolved-solids concentrations and thickness in the aquifer-assessment area of the lower Wilcox aquifer in the Mississippi 

embayment and Texas coastal uplands aquifer systems, Gulf Coast regional aquifer system.

ALABAMA

ARKANSAS

FLORIDA

ILLINOIS

KENTUCKY

LOUISIANA

MISSOURI

MISSISSIPPI

TENNESSEE

TEXAS

93° 90° 87°

36°

34°

32°

600

300

100

800

600

400

1,000

900

800

400

100

300

400

500

800

700 600

300

400

500

200

300

100

100

200

300

200

1,100

1,200

900

1,000

900

GULF OF

MEXICO

Mississippi River

Base from National Atlas digital data

Lambert Conformal Conic projection

Dissolved-solids data modified from Pettijohn and others, 1988, sheet 1

Thickness data modified from Hosman and Weiss, 1991, pl. 17

0 40 80 120 160 MILES

0 40 80 120 160 KILOMETERS

EXPLANATION

Dissolved solids, in milligrams

 per liter

 < 1,000

 1,000 to 3,000

 > 3,000 to 10,000

 > 10,000 to 20,000

 > 20,000 to 35,000

 > 35,000

Line of equal thickness—

 Interval 100 feet

500

Mississippi embayment

and Texas coastal uplands

aquifer systems

Six southern

midcontinent

States Lower Wilcox aquifer-assessment

area boundary

Area enlarged
Hydrogeology, Distribution, and Volume of Saline Groundwater

25

Figure 16. Dissolved-solids concentrations and thickness in the aquifer-assessment area of the McNairy-Nacatoch aquifer of the 

Mississippi embayment and Texas coastal uplands aquifer systems, Gulf Coast regional aquifer system.

ALABAMA

ARKANSAS

ILLINOIS

KENTUCKY

MISSOURI

MISSISSIPPI

TENNESSEE

450

400

350

250

150

50

300

200

50

100

100

50

50

100

350

250

150

200

300

400

91° 90° 89° 88°

37°

36°

35°

34°

Mississippi River

Base from National Atlas digital data

Lambert Conformal Conic projection

Dissolved-solids data modified from Renken, 1998, fig. 81

Thickness data modified from Hosman and Weiss, 1991, pl. 19

0 20 40 60 80 MILES

0 20 40 60 80 KILOMETERS

EXPLANATION

Dissolved solids, in milligrams

 per liter

 < 1,000

 1,000 to 3,000

 > 3,000 to 10,000

Line of equal thickness—

 Interval 50 feet

150

Mississippi embayment

and Texas coastal uplands

aquifer systems

Six southern

midcontinent

States

McNairy-Nacatoch aquifer-assessment

area boundary

Area enlarged
26

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

The McNairy-Nacatoch aquifer, of Upper Cretaceous age, 

is the lowermost hydrogeologic unit in the Gulf Coast regional 

aquifer system (table 5). This aquifer consists of sand, minor 

gravel, and clay deposited in a deltaic environment (Renken, 

1998), which by way of a facies change, grades downdip to 

clay, marl, and limestone (Brahana and Mesko, 1988). 

Aquifers in the Mississippi embayment aquifer system 

are recharged by infiltration of precipitation on aquifer-outcrop 

areas, which are generally along the perimeter of the aquifer 

system. Groundwater discharge is to pumping wells, to incised 

rivers and streams, and as upward leakage to shallower 

aquifers (Renken, 1998). Regional groundwater flow is 

downdip toward the axis of the Mississippi embayment and 

then southward toward the Gulf of Mexico (Pettijohn, 1996). 

Groundwater flow is generally toward the streams; however, 

high streamflow or sustained pumping can locally reverse the 

hydraulic gradients and induce recharge from the streams to 

the aquifer, especially near the Mississippi River (Hosman 

and Weiss, 1991). Aquifers in the Texas coastal upland 

aquifer system are recharged by infiltration of precipitation 

on topographically high aquifer-outcrop areas. Groundwater 

discharge is to pumping wells, to evapotranspiration, to 

streams in outcrop areas, and as upward leakage to shallower 

aquifers in downdip areas (Ryder, 1996).

Groundwater Chemistry of the Gulf Coast 

Regional Aquifer System

Groundwater in the Gulf Coast regional aquifer system 

is generally fresh in and near outcrop areas of the aquifers and 

permeable zones. Dissolved-solids concentrations generally 

increase downdip toward the Gulf of Mexico and toward 

principal discharge areas. The deeper parts of the aquifers 

and permeable zones contain brine with dissolved-solids 

concentrations that can exceed 100,000 mg/L (Grubb, 1998) 

(figs. 5–16).

The major chemical and physical processes that affect 

water chemistry of the aquifers in the Gulf Coast regional 

aquifer system are water-rock interactions (leaching of 

soluble salts from the unsaturated zone, alteration of albite 

and other silicate minerals, cation exchange, and dissolution 

of evaporites) and mixing of freshwater with upward flow 

of saline water from underlying units (Pettijohn, 1996). 

The primary water type in aquifer outcrop areas and updip 

areas near the outcrops, where median dissolved-solids 

concentrations are less than 1,000 mg/L, typically is calcium 

bicarbonate or a mixture of calcium bicarbonate and sodium 

bicarbonate (Pettijohn, 1996). The major processes controlling 

the water chemistry in these outcrop and updip areas are 

leaching of soluble salts from the unsaturated zone and 

alteration of silicates (Pettijohn, 1996). In middip areas, 

where the median concentration of dissolved solids ranges 

from 1,000 mg/L to 3,000 mg/L, the primary water types are 

either sodium bicarbonate or a mixture of sodium bicarbonate 

and calcium bicarbonate, and the major processes controlling 

water chemistry are upward flow from underlying deposits, 

dissolution of residual evaporite crystals, and alteration of 

silicates (Pettijohn, 1996). In middip to downdip areas, where 

the median concentration of dissolved solids ranges from 

3,000 mg/L to 10,000 mg/L, the primary water types are either 

sodium bicarbonate or sodium chloride, or a mixture of the 

two, and the major processes are dissolution of evaporites 

and alteration of silicates (Pettijohn, 1996). In downdip areas, 

where the concentration of dissolved solids exceeds 10,000 

mg/L, the primary water type is sodium chloride, and the 

major processes controlling water chemistry are dissolution 

of halite in salt domes and upward flow from underlying 

deposits (Pettijohn, 1996). The major process controlling 

chemistry of the brine, with dissolved-solids concentrations 

greater than 35,000 mg/L, is dissolution of halite in salt domes 

(Williamson and Grubb, 1997). Dissolution of halite occurs in 

areas where salt domes penetrate a permeable zone or aquifer 

at depths greater than approximately 4,000 ft. At depths less 

than approximately 4,000 ft, salt domes commonly are sealed 

by relatively impervious cap rocks, and thus dissolution of 

halite is minimal (Pettijohn, 1996).

Mixing of water by upward flow from underlying units 

is the most likely process causing slightly saline water in 

the Mississippi River Valley alluvial aquifer in a few small 

areas in northeast Louisiana and southeast Arkansas (fig. 10) 

(Pettijohn, 1996). Slightly saline water in the McNairyNacatoch aquifer in a small area in southeastern Missouri, 

southwestern Kentucky, and northwestern Tennessee (fig. 16) 

is the result of upward flow of water from the underlying 

Ozark Plateaus aquifer system (Renken, 1998). In local 

areas near the Gulf Coast, groundwater withdrawals have 

caused lowering of water levels in and near pumping 

centers and have induced the movement of seawater into 

parts of aquifers that previously contained freshwater (Grubb, 

1998).

Saline-Water Volume of the Gulf Coast Regional 

Aquifer System

About 28,300 million acre-ft of saline water is estimated 

to be in the aquifer-assessment areas of the Gulf Coast 

regional aquifer system. The coastal lowlands aquifer system 

contains about 16,300 million acre-ft of saline water (table 6), 

and the Mississippi embayment and Texas coastal upland 

aquifer systems contain about 12,000 million acre-ft of saline 

water (table 7). Gulf Coast aquifers with the largest estimated 

volumes of saline water are permeable zone B (5,040 million 

acre-ft) and the middle Wilcox aquifer (4,700 million acre-ft) 

(tables 6 and 7).
Hydrogeology, Distribution, and Volume of Saline Groundwater

27

Table 6. Estimated water volume of salinity zones in aquiferassessment areas of the coastal lowlands aquifer system, Gulf 

Coast regional aquifer system.

[mg/L, milligrams per liter; values may not sum to totals because of 

independent rounding]

Salinity zone, 

dissolvedsolids 

concentration 

(mg/L)1

Area 

(million 

acres)

Mean 

thickness 

(feet)2

Mean 

sand 

fraction3

Mean 

porosity 

fraction4

Water 

volume 

(million 

acre-feet)

Permeable zone A

1,000–3,000 9.88 685 0.53 0.28 1,000

3,000–10,000 9.17 865 0.47 0.28 1,040

10,000–20,000 13.8 862 0.32 0.28 1,070

20,000–35,000 9.09 798 0.31 0.28 630

TOTAL 3,740

Permeable zone B

1,000–3,000 7.33 725 0.56 0.28 833

3,000–10,000 5.03 1,010 0.45 0.28 640

10,000–20,000 6.4 1,320 0.35 0.28 828

20,000–35,000 15.0 2,420 0.27 0.28 2,740

TOTAL 5,040

Permeable zone C

1,000–3,000 5.61 836 0.43 0.28 565

3,000–10,000 4.38 1,180 0.37 0.28 535

10,000–20,000 4.03 1,460 0.34 0.28 560

20,000–35,000 4.80 1,720 0.39 0.28 902

TOTAL 2,560

Permeable zone D

1,000–3,000 5.30 905 0.45 0.28 604

3,000–10,000 7.82 1,420 0.36 0.28 1,120

10,000–20,000 3.00 1,600 0.39 0.28 524

20,000–35,000 3.62 1,850 0.41 0.28 769

TOTAL 3,020

Permeable zone E

1,000–3,000 3.00 909 0.35 0.28 267

3,000–10,000 5.06 1,160 0.34 0.28 559

10,000–20,000 3.64 1,370 0.33 0.28 461

20,000–35,000 4.46 1,590 0.34 0.28 675

TOTAL 1,960

TOTAL Coastal lowlands aquifer system 16,300

1

Determined from dissolved-solids-concentration maps (modified from 

Pettijohn and others, 1988).

2

Computed from thickness maps (modified from Weiss, 1992).

3

Computed from sand-percentage maps (modified from Weiss, 1992).

4

Computed from average porosities compiled by Core Laboratories, Inc. 

(1972).

Table 7. Estimated water volume of salinity zones in aquiferassessment areas of the Mississippi embayment and Texas 

coastal uplands aquifer systems, Gulf Coast regional aquifer 

system. 

[mg/L, milligrams per liter; values may not sum to totals because of 

independent rounding; NA, data not available]

Salinity zone, 

dissolved-solids 

concentration 

(mg/L)1

Area 

(million 

acres)

Mean 

thickness 

(feet)2

Mean 

sand 

fraction3

Mean 

porosity 

fraction4

Water 

volume 

(million 

acre-feet)

Mississippi River Valley alluvial aquifer

1,000–3,000 0.506 91 NA 5

0.28 12.9

TOTAL 12.9

Upper Claiborne aquifer

1,000–3,000 4.04 615 0.47 0.30 345

3,000–10,000 7.51 722 0.47 0.30 767

10,000–20,000 5.53 942 0.51 0.30 794

20,000–35,000 5.09 852 0.44 0.30 578

TOTAL 2,480

Middle Claiborne aquifer 

1,000–3,000 7.95 629 0.58 0.30 860

3,000–10,000 7.97 664 0.46 0.30 728

10,000–20,000 8.36 838 0.41 0.30 870

20,000–35,000 5.08 498 0.37 0.30 283

TOTAL 2,740

Lower Claiborne-upper Wilcox aquifer

1,000–3,000 8.07 337 0.69 0.24 451

3,000–10,000 10.30 206 0.68 0.24 344

10,000–20,000 2.94 183 0.67 0.24 86.1

20,000–35,000 2.35 176 0.66 0.24 65.1

TOTAL 946

Middle Wilcox aquifer

1,000–3,000 7.47 1,190 0.44 0.24 934

3,000–10,000 10.6 1,010 0.40 0.24 1,040

10,000–20,000 5.10 1,640 0.43 0.24 868

20,000–35,000 11.8 1,730 0.38 0.24 1,860

TOTAL 4,700

Lower Wilcox aquifer

1,000–3,000 6.24 197 0.67 0.24 198

3,000–10,000 6.02 213 0.63 0.24 194

10,000–20,000 8.53 251 0.65 0.24 334

20,000–35,000 5.50 423 0.56 0.24 313

TOTAL 1,040

McNairy-Nacatoch aquifer

1,000–3,000 2.35 126 0.81 6

0.25 60.0

3,000–10,000 1.38 53 0.81 6

0.25 14.8

TOTAL 74.8

TOTAL Mississippi embayment and Texas

 coastal uplands aquifer systems

12,000

1

Determined from dissolved-solids-concentration maps (modified from 

Pettijohn and others, 1988; Renken, 1998).

2

Computed from thickness maps (modified from Hosman and Weiss, 1991).

3

Computed from sand-percentage maps (modified from Hosman and Weiss, 

1991).

4

Computed from average porosities compiled by Core Laboratories, Inc. 

(1972).

5

Specific yield from Ackerman (1996).

6

Average porosity from Emmons (1921).
28

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Edwards-Trinity Regional Aquifer System 

The Edwards-Trinity regional aquifer system underlies 

a 77,000-mi2 area that extends from western Texas into 

southeastern Oklahoma and southwestern Arkansas (fig. 1). 

This regional aquifer system consists of three major aquifers: 

the Edwards, Trinity, and Edwards-Trinity aquifers (Ryder, 

1996), but there only was sufficient information to map the 

distribution of saline groundwater in the Edwards aquifer in 

south-central Texas (fig. 17).

Extensively faulted, fractured, and cavernous carbonate 

rocks of Cretaceous age make up the Edwards aquifer (Ryder, 

1996). The aquifer is composed of limestone and dolostone 

of the Georgetown Formation and Edwards Group (table 8) 

(Ryder, 1996). The Trinity aquifer, composed of the less 

permeable and clay-rich Glen Rose Limestone (table 8), 

underlies and is adjacent to the Edwards aquifer to the north 

(Barker and Ardis, 1996). The arc-shaped Edwards aquifer is 

generally coincident with a region of northeastward-trending 

faults known as the Balcones fault zone (fig. 17) (Ryder, 

1996). Thickness of the Edwards aquifer ranges from less than 

300 ft in the northeast to about 800 ft in the southwest and 

averages about 550 ft. The effective porosity of the Edwards 

aquifer generally ranges from 2 to 14 percent and averages 

approximately 6 percent (Maclay, 1995). 

Recharge to the Edwards aquifer is primarily from losses 

from streams that cross the aquifer outcrop (recharge zone), by 

infiltration of precipitation in the recharge zone, and by inflow 

from the adjacent Trinity aquifer (Maclay, 1995; Barker and 

Ardis, 1996; Lambert and others, 2010). Groundwater flows 

from the recharge zone in a downdip direction to the south and 

southeast into the confined parts of the aquifer. The freshwater 

flow is subsequently diverted by northeastward-trending 

faults to the east and northeast through solutionally enlarged 

fractures and is discharged from springs and pumping wells 

(Maclay and Land, 1988; Maclay, 1995; Barker and Ardis, 

1996; Lambert and others, 2010). 

The freshwater zone of the Edwards aquifer (fig. 1) is 

bounded to the south and southeast by a zone of transition 

from freshwater to saline water containing groundwater with 

dissolved-solids concentrations ranging from 1,000 mg/L to 

10,000 mg/L. Fresh groundwater enters the freshwater/salinewater transition zone from the freshwater zone in the western 

part of the Edwards aquifer. Relatively low-permeability rocks 

in the freshwater/saline-water transition zone allow small 

flows toward the northeast, where groundwater discharges to 

the freshwater zone in the eastern part of the aquifer (Lambert 

and others, 2010). The freshwater/saline-water transition zone 

is separated downdip from a saline-water zone, with dissolvedsolids concentration greater than 10,000 mg/L, by faults that 

offset permeable layers of the aquifer and restrict groundwater 

flows across them. Dissolved-solids concentrations in the 

saline-water zone rapidly increase downdip toward the Gulf 

of Mexico from 10,000 mg/L to more than 250,000 mg/L 

(Maclay and Land, 1988).

Water chemistry of the Edwards aquifer is controlled 

primarily by geologic processes that occurred in late Tertiary 

time, when the deeply buried aquifer, saturated with brine, 

was uplifted and faulted. Large volumes of freshwater began 

to infiltrate the aquifer in the fault zone that previously had 

been isolated from meteoric conditions, allowing freshwater 

to mix with older brine and saline water (Maclay, 1995). 

Groundwater flow from the adjacent Trinity aquifer also 

may mix with water in the freshwater/saline-water transition 

zone, a hypothesis supported by helium-isotope data (Hunt 

and others, 2010). Isotope and geochemical data from wells 

indicate that water in the freshwater/saline-water transition 

zone is mostly meteoric water that likely has been recharged 

from the freshwater zone in the recent geologic past (less 

than tens of thousands of years) in a hydraulically active flow 

system (Groschen and Buszka, 1997). Isotope data from deep 

wells in the saline-water zone indicate that the older water has 

been thermally altered in reactions with carbonate rocks and is 

in a hydraulically stagnant flow system (Groschen and Buszka, 

1997). 

Only the slightly and moderately saline waters of the 

freshwater/saline-water transition zone were mapped in the 

Edwards aquifer assessment area (fig. 17) because insufficient 

water chemistry data were available to map saline water with 

dissolved-solids concentrations greater than 10,000 mg/L. An 

estimated 49.1 million acre-ft of slightly to moderately saline 

water is stored in the Edwards aquifer (table 9).
Hydrogeology, Distribution, and Volume of Saline Groundwater

29

Figure 17. Dissolved-solids concentrations and thickness in the aquifer-assessment area of the Edwards aquifer, Edwards-Trinity 

regional aquifer system.

KINNEY

MEDINA

HAYS

TRAVIS

UVALDE

BEXAR

ZAVALA ATASCOSA

WILLIAMSON

MAVERICK

GUADALUPE

FRIO

CALDWELL

WILSON

COMAL

BELL

UNITED STATES

MEXICO

290

240

250

270

310

280

290300

450

400

350

430

450

260

320

100° 99° 98°

31°

30°

29°

BALCONES FAULT ZONE (APPROXIMATE)

Base from National Atlas digital data

Lambert Conformal Conic projection

Dissolved-solids data modified from Lambert and others, 2009, fig. 1

 and Winslow and Kister, 1956, pl. 1

Thickness data modified from Flores, 1990, fig. 4

0 20 40 60 80 MILES

0 20 40 60 80 KILOMETERS

EXPLANATION

Dissolved solids, in milligrams

 per liter

 > 1,000 to 3,000

 > 3,000 to 10,000

Line of equal thickness—

 Interval 10 feet

250

Edwards-Trinity

regional

aquifer system

Six southern

midcontinent

States

Edwards aquifer-assessment area boundary

Area enlarged
30

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Table 8. Time-stratigraphic, rock-stratigraphic, and 

hydrogeologic units of the Edwards aquifer, Edwards-Trinity 

regional aquifer system. 

[From Maclay and Land, 1988, fig. 3; Ls, Limestone; Fm, Formation; 

Gp, Group]

Time-stratigraphic unit Rockstratigraphic unitHydrogeologic 

System Stage unit

Cretaceous

Washitan Stage

Buda Ls

Confining 

Del Rio unit

Clay

Georgetown 

Fm

Edwards 

aquifer Fredericksburgian 

Stage

Edwards 

Gp

Pearson Fm

Kainer Fm

Trinitian Stage

Glen 

Rose 

Ls

Upper Glen 

Rose

Confining 

unit

Lower Glen 

Rose

Trinity 

aquifer

Table 9. Estimated water volume of salinity zones in the aquifer-assessment area of the Edwards aquifer, Edwards-Trinity regional 

aquifer system.

[Only saline waters with dissolved-solids concentrations of 1,000–10,000 mg/L were evaluated; mg/L, milligrams per liter; values may not sum to totals because 

of independent rounding]

Salinity zone, dissolvedsolids concentration 

(mg/L)1

Area 

(million acres)

Mean thickness 

(feet)2

Mean porosity 

fraction3

Water volume 

(million acre-feet)

1,000–3,000 0.644 443 0.06 17.1

3,000–10,000 0.952 561 0.06 32.0

TOTAL 49.1

1

Determined from dissolved-solids-concentration maps (modified from Flores, 1990; Lambert and others, 2009) and well data (modified from Groschen and 

Buszka, 1997).

2

Computed from thickness map (modified from Flores, 1990).

3

Maclay, 1995.
Hydrogeology, Distribution, and Volume of Saline Groundwater

31

Central Midwest Regional Aquifer System

The Central Midwest regional aquifer system underlies 

a 370,000-mi2 area in all of Kansas and Nebraska and parts of 

Arkansas, Colorado, Missouri, New Mexico, Oklahoma, South 

Dakota, Texas, and Wyoming (fig. 1). The regional aquifer 

system consists of three aquifer systems: Great Plains, Western 

Interior Plains, and Ozark Plateaus (fig. 18) (Jorgensen and 

others, 1996). The regional aquifer system is divided into two 

subregions based on groundwater-flow systems: the Plains 

subregion, consisting of the Great Plains aquifer system, the 

Western Interior Plains confining system, and the Western 

Interior Plains aquifer system; and the Ozark subregion, 

consisting of the Ozark Plateaus aquifer system (fig. 18) 

(Jorgensen and others, 1996). The Great Plains confining 

system and the High Plains regional aquifer system (fig. 1) 

overlie most of the Great Plains aquifer system (fig. 19). The 

High Plains regional aquifer system is described in the section 

“High Plains Regional Aquifer System.”

The rock-stratigraphic units of the Western Interior Plains 

aquifer system in the Plains subregion are approximately age 

equivalent to those of the Ozark Plateaus aquifer system in 

the Ozark subregion. Rocks of the upper aquifer unit in the 

Western Interior Plains aquifer system are age equivalent to 

the Mississippian rocks of the Springfield Plateau aquifer, 

and rocks of the lower aquifer units in the Western Interior 

Plains aquifer system are age equivalent to rocks of the Ozark 

aquifer, the St. Francois confining unit, and the St. Francois 

aquifer in the Ozark Plateaus aquifer system (tables 10 and 11) 

(Jorgensen and others, 1996). 

Although the Western Interior Plains and Ozark Plateaus 

aquifer systems consist of age-equivalent rock-stratigraphic 

units, the two aquifer systems have separate groundwater-flow 

systems (Jorgensen and others, 1996). Regional groundwater 

flow in the Western Interior Plains aquifer system is generally 

eastward, and a large component of groundwater flow in 

the Ozark Plateaus aquifer system is westward. Eastwardflowing saline groundwater from the Western Interior Plains 

aquifer system converges with the westward-flowing fresh 

groundwater from the Ozark Plateaus aquifer system in a 

broad, topographically low area that extends from northeastern 

Oklahoma into central Missouri and then flows vertically 

upward to streams or to overlying rock units (fig. 19) 

(Jorgensen and others, 1996). The shared boundary between 

the two flow systems is a transition zone between freshwater 

and saline water. Because the Western Interior Plains and 

Ozark Plateaus aquifer systems share the transition zone 

between freshwater and saline water, saline groundwaters 

in both systems are mapped and evaluated together in this 

report.
Figure 18. Aquifer systems in the Central Midwest regional aquifer system.

Ozark subregion

Plains subregion

ARKANSAS

COLORADO

IOWA

ILLINO

KANSAS

MINNESOTA

MISSOURI

MISSIS

NEBRASKA

NEW

MEXICO

OKLAHOMA

SOUTH DAKOTA

TEN

TEXAS

WISCONSIN WYOMING

105° 100° 95° 90°

42°39°36°

River

Mississippi

Missouri River

Base from National Atlas digital dataLambert Conformal Conic projection

Modified from Jorgensen and others, 1

0 100 200 0 100 200 300 KILOMETERS

Aquifer systems in the Central Midwest regional aquifer system

Plains subregion

 Great Plains aquifer system Western Interior Plains aquifer system Ozark subregion  Ozark Plateaus aquifer systemApproximate boundary between Plains and Ozark subregions

EXPLANATION

Central Midwest

aquifer system

Six southern

midcontinent

States

Area enlarged
Hydrogeology, Distribution, and Volume of Saline Groundwater

33

Figure 19. Generalized section from central Colorado to eastern Missouri showing hydrogeologic units and direction of groundwater 

flow in the Central Midwest regional aquifer system. COLORADO KANSAS

KANSAS

MISSOURI

Zone of complex geology. Geohydrologic

relations have not been defined with 

certainty and thus are not shown

High Plains aquifer

Great Plains confining system

Great Plains aquifer system

Western Interior Plains confining system

Western Interior Plains aquifer system

Basement confining unit

Ozark Plateaus aquifer system

Transition zone between

flow systems

NOT TO SCALE

PLAINS SUBREGION

OZARK SUBREGION

Front Range

WEST EAST St. Francois Mountains

EXPLANATION

Direction of groundwater flow

Modified from Jorgensen and others, 1996, fig. 17

Central Midwest

aquifer system

Six southern

midcontinent

States

Approximate

line of section
34

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Table 10. Time-stratigraphic, rock-stratigraphic, and hydrogeologic units of the Plains subregion, Central Midwest regional aquifer 

system.

[Modified from Jorgensen and others, 1996, table 1; Fm, Formation; Sh, Shale; Ls, limestone; Ss, Sandstone; ss, sandstone; Dol, Dolomite; Gp, Group]

Time-stratigraphic unit Rock- and time-stratigraphic units Hydrogeologic unit

Quaternary and Tertiary Ogallala Fm and unconsolidated deposits High Plains aquifer

Upper Cretaceous Pierre Sh, Niobrara Fm, Carlile Sh, Greenhorn 

Ls, Graneros Sh Great Plains confining system

Lower Cretaceous

Dakota Ss, “D” ss, “J” ss, and equivalent of 

Newcastle Ss Maha aquifer

Kiowa Sh and equivalent of Skull Creek Sh Apishapa confining unit Great Plains aquifer system

Cheyenne Ss and equivalent of Fall River Ss and 

Lakota Ss Apishapa aquifer

Jurassic through 

Upper Mississippian 

(Chesterian)

Morrison Fm, Sundance Fm, Entrada Ss, 

Dockum Fm, Elk City Ss, Doxey Sh, Big 

Basin Ss, Cloud Chief Fm, Day Creek Dol, 

Whitehorse Ss, Nippewalla Gp, Sumner Gp, 

Cedar Hills Ss, Garber Ss, Wellington Fm, 

Chase Gp, Council Grove Gp, Admire Gp, 

Wabaunsee Gp, Shawnee Gp, Douglas Gp, 

Lansing Gp, Kansas City Gp, Pleasanton Gp, 

Marmaton Gp, Cherokee Gp, Atokan rocks, 

Morrowan rocks, and Springer Gp

Western Interior Plains confining system

Upper Mississippian through 

Upper Cambrian

Meramecian, Osagean, and Kinderhookian rocks Upper aquifer unit

Western Interior Plains 

aquifer system

Chattanooga Sh and Woodford Sh Confining unit

Hunton Gp, Sylvan Sh, equivalent of Galena 

Dol, Viola Ls, Simpson Gp, Arbuckle Gp, and 

Reagan Ss

Lower aquifer units

Cambrian and Precambrian Mostly igneous and metamorphic rocks Basement confining unit

Table 11. Time-stratigraphic, rock-stratigraphic, and hydrogeologic units of the Ozark subregion, Central Midwest regional aquifer 

system. 

[Modified from Jorgensen and others, 1996, table 3; Gp, Group; Sh, Shale; Fm, Formation; Ls, Limestone; Ss, Sandstone; Dol, Dolomite] 

Time-stratigraphic unit Rock- and time-stratigraphic units Hydrogeologic unit

Middle Pennsylvanian through 

Upper Mississippian 

(Chesterian)

Marmaton Gp, Cherokee Gp, Atokan rocks, Bloyd Sh, Hale 

Fm, Morrowan rocks, Pitkin Ls, Fayetteville Sh, and 

Batesville Ss

Western Interior Plains confining 

system

Mississippian

Moorefield Fm, St. Louis Ls, Salem Ls, Warsaw Ls, Boone 

Fm, St. Joe Ls Member of Boone Fm, Keokuk Ls, 

Burlington Ls, and Fern Glen Ls

Springfield Plateau aquifer

Ozark Plateaus aquifer system

Lower Mississippian and Upper 

Devonian

Chouteau Gp, Chattanooga Sh, Northview Sh, and Hannibal 

Sh Ozark confining unit

Middle Devonian through Upper 

Cambrian

Clifty Ls, Penters Chert, Lafferty Ls, St. Clair Ls, Brassfield 

Ls, Cason Sh, Fernvale Ls, Kimmswick Ls, Plattin Ls, 

Joachim Dol, St. Peter Ss, Everton Fm, Smithville Fm, 

Powell Dol, Cotter Dol, Jefferson City Dol, Roubidoux 

Fm, Gasconade Dol, Gunter Ss Member of Gasconade Dol, 

Eminence Dol, and Potosi Fm

Ozark aquifer

Upper Cambrian Elvins Gp, Derby and Doe Run Dols, Davis Fm St. Francois confining unit

Bonneterre Dol, Lamotte Ss, and Reagan Ss St. Francois aquifer

Precambrian Mostly igneous and metamorphic rocks Basement confining unit
Hydrogeology, Distribution, and Volume of Saline Groundwater

35

Great Plains Confining System

The Great Plains confining system overlies the Great 

Plains aquifer system in most places (fig. 19) and restricts flow 

to and from the Great Plains aquifer system and the overlying 

High Plains aquifer. The confining system consists mostly of 

very slightly permeable Cretaceous shale and is as thick as 

8,000 ft in the Denver Basin (Jorgensen and others, 1993).

Great Plains Aquifer System

The Great Plains aquifer system encompasses an area of 

about 170,000 mi2 in the northern part of the Plains subregion 

(fig. 18). The Great Plains aquifer system is divided into the 

Maha aquifer (consisting mostly of the Dakota Sandstone), 

the Apishapa confining unit (consisting mostly of the Kiowa 

Shale), and the Apishapa aquifer (consisting mostly of the 

Cheyenne Sandstone) of Early Cretaceous age (table 10) 

(Jorgensen and others, 1996). Both the Maha aquifer and 

Apishapa aquifer consist primarily of permeable, loosely 

cemented, medium- to fine-grained sandstones (Helgesen and 

others, 1993; Jorgensen and others, 1996). The Maha aquifer 

is the thickest and most areally extensive unit of the Great 

Plains aquifer system, ranging in thickness from less than 100 

ft in eastern Colorado to more than 900 ft in central Nebraska 

(fig. 20); thickness of the Apishapa aquifer is generally less 

than 400 ft (fig. 21) (Helgesen and others, 1993). Porosity of 

both aquifers ranges from approximately 10 to 30 percent, 

generally being smallest in the deeper basins (Helgesen and 

others, 1993).

Strata of the Great Plains aquifer system were deposited 

during Early Cretaceous time in an environment that fluctuated 

between marine shoreline and nonmarine (Jorgensen and 

others, 1996). The Laramide orogeny of Late Cretaceous 

and early Tertiary time uplifted the Rocky Mountains (Front 

Range uplift) and formed the adjacent Denver and Raton 

Basins (fig. 22). In late Tertiary time, broad uplift and regional 

tilting to the east led to development of the modern westto-east hydraulic gradient in the Great Plains aquifer system 

(Jorgensen and others, 1996). Erosion has exposed the rocks of 

the Great Plains aquifer system along the eastern and southern 

margins of the aquifer system. In areas where the Great Plains 

confining system is absent, the High Plains aquifer directly 

overlies the Great Plains aquifer system along the southern 

and eastern margins of the aquifer system, and Quaternary-age 

deposits directly overlie the aquifer system (Jorgensen and 

others, 1993).

Recharge by direct infiltration in outcrop areas of the 

Great Plains aquifer system occurs in southeastern Colorado, 

northeastern New Mexico, and the Black Hills uplift in 

southwestern South Dakota (fig. 22) (Helgesen and others, 

1993). Local recharge occurs near the southern and eastern 

extents of the aquifer system, where the aquifers are close 

to land surface. Most recharge to the system, however, is 

by downward leakage through overlying hydrogeologic 

units, such as the High Plains aquifer and the Missouri 

River alluvium (Helgesen and others, 1993; Jorgensen and 

others, 1996). Most discharge from the Great Plains aquifer 

system is by upward flow into overlying geologic units, but 

some discharge is to streams in aquifer outcrop areas along 

the Missouri River Valley and along the eastern edge of the 

aquifer system (Helgesen and others, 1993; Miller and Appel, 

1997).

Flow of groundwater through the Great Plains aquifer 

system is primarily from southwest to east-northeast toward 

the eastern edge of the aquifer system in Kansas and eastern 

Nebraska (Helgesen and others, 1993). Deep burial by several 

thousand feet of younger sediments and faulting along the 

western margin of the Denver and Raton Basins have isolated 

much of the aquifer system hydraulically from freshwater at 

or near land surface (Helgesen and others, 1993). As a result, 

groundwater moves very slowly (calculated velocities from 

0.01 to 10 feet per year) through most areas of the Great Plains 

aquifer system (Helgesen and others, 1993). 

Concentrations of dissolved solids in water from the 

Great Plains aquifer system generally are less than 1,000 

mg/L in areas where the aquifer system is at or near land 

surface, primarily near the southern and eastern margins of 

the aquifer system, and in a small area in northwest Nebraska 

(Helgesen and others, 1993) (figs. 20 and 21). Water in these 

areas is primarily a calcium-bicarbonate type, formed where 

meteoric water entering the aquifers resulted in dissolution of 

carbonate cement (Helgesen and others, 1993). Small areas of 

calcium-sulfate-type and sodium-chloride-type water are near 

the eastern boundary of the system, where regionally flowing 

water from the west becomes diluted by freshwater recharge 

(Helgesen and others, 1993). 

In areas where the Great Plains aquifer system is overlain 

by the Great Plains confining system, dissolved-solids 

concentrations generally exceed 1,000 mg/L, and groundwater 

is mostly a sodium-bicarbonate or sodium-chloride type 

(Helgesen and others, 1993). Water containing 1,000–10,000 

mg/L dissolved solids is characteristic of much of the Great 

Plains aquifer system (Helgesen and others, 1993). The nearshore depositional environment of sediments composing this 

aquifer system probably included original formation water 

that was fresh to moderately saline. Deep burial by several 

thousand feet of younger sediments and faulting along the 

western margin of the aquifer system restricted freshwater 

flow and prevented complete flushing of original formation 

water from much of the slow-moving groundwater in this 

aquifer system (Helgesen and others, 1993).

Dissolved-solids concentrations of 10,000–20,000 

mg/L are common in the central and east-central parts of this 

aquifer system and probably are related to a combination of 

incomplete flushing of formation water and upward flow of 

saline water from adjacent salt-bearing strata (Helgesen and 

others, 1993). In central Kansas, saline water in this aquifer 

system is related to upward flow from the underlying Permian 

Cedar Hills Sandstone, which contains brine from underlying 

evaporite deposits (Helgesen and others, 1993). Groundwater 

containing more than 100,000 mg/L dissolved solids in the 

Nebraska Panhandle probably is caused by upward flow 

of brine along faults or fractures from underlying Permian 

evaporite deposits (Russell, 1961; Helgesen and others, 1993). 
36

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Figure 20. Dissolved-solids concentrations and thickness in the aquifer-assessment area of the Maha aquifer in the Great Plains 

aquifer system, Central Midwest regional aquifer system.

COLORADO

IOWA

KANSAS

MINNESOTA

NEBRASKA

NEW

MEXICO

OKLAHOMA

TEXAS

WYOMING

SOUTH

DAKOTA

105° 102° 99° 96°

44°

42°

40°

38°

36°

200

200

800

100

100

300

300

200

300

100

300

200

300

100

300

300

900

100

200

400

200

200

200

400

100

100

100

200

200

200

100

300

100

200

200

100

100

200

400

700

100

600

100

200

200

500

400

300

400

500

600

500

700

100

100

300

200

200

100

400

200

100

800

500 400

400

900 600

600

200

100 200

200

100

200

100

300

U

D

U

D

U

D

U

D

U

D U

D

Base from National Atlas digital data

Lambert Conformal Conic projection

Dissolved-solids data modified from Helgesen and others, 1993, pl. 6

Thickness data modified from Helgesen and others, 1993, pl. 3

0 50 100 150

0 50 100 150 200 KILOMETERS

200 MILES

EXPLANATION

Dissolved solids, in milligrams

 per liter

 < 1,000

 1,000 to 3,000

 > 3,000 to 10,000

 > 10,000 to 20,000

 > 20,000 to 35,000

 > 35,000

Line of equal thickness—

 Interval 100 feet

Fault showing relative

 displacement—U, upthrown;

 D, downthrown

500

U

D

Great Plains

aquifer system

Maha aquifer-assessment

area boundary

Six southern

midcontinent

States

Area enlarged
Hydrogeology, Distribution, and Volume of Saline Groundwater

37

Figure 21. Dissolved-solids concentrations and thickness in the aquifer-assessment area of the Apishapa aquifer in the Great Plains 

aquifer system, Central Midwest regional aquifer system.

COLORADO

IOWA

KANSAS

MINNESOTA

NEBRASKA

NEW

MEXICO

OKLAHOMA

TEXAS

WYOMING

SOUTH

DAKOTA

300

200

100

400

200

200

100

200

100

300

100

100

300

400

300

200

100

200

300

200

100

200

100

100

100

200

100

100

100

300

200

200

100

100

100

100

100

100

100

100

100

200

U

D

U

D

U

D

U

D

U

D

U

D

105° 102° 99° 96°

44°

42°

40°

38°

36°

100 100

300

100

200

100

400

200

200

300

200

300

Base from National Atlas digital data

Lambert Conformal Conic projection

Dissolved-solids data modified from Helgesen and others, 1993, pl. 6

Thickness data modified from Helgesen and others, 1993, pl. 1

0 50 100 150

0 50 100 150 200 KILOMETERS

200 MILES

EXPLANATION

Dissolved solids, in milligrams

 per liter

 < 1,000

 1,000 to 3,000

 > 3,000 to 10,000

 > 10,000 to 20,000

 > 20,000 to 35,000

 > 35,000

Line of equal thickness—

 Interval 100 feet

Fault showing relative

 displacement—U, upthrown;

 D, downthrown

200

U

D

Great Plains

aquifer system

Six southern

midcontinent

States Apishapa aquifer-assessment

area boundary

Area enlarged
38

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Figure 22. Major structural features of the Central Midwest regional aquifer system and adjacent areas.

ARKANSAS

COLORADO

IOWA

ILLINOIS

KANSAS

MINNESOTA

MISSOURI

MISSISSIPPI

NEBRASKA

NEW

MEXICO

OKLAHOMA

SOUTH DAKOTA

TENNESSEE

TEXAS

WISCONSIN WYOMING

105° 100° 95° 90°

42°

39°

36°

Arkoma basin

Dalhart

basin

Cherokee

basin

Raton

basin

St. Francois

Mountains

Forest

City basin

Denver

basin

Kennedy

basin

Central Nebraska

(Salina) basin

Siouxana arch

Chadron arch

Cambridge arch

Las Animas arch

Central Kansas

uplift

Wet Mountains

uplift

Sangre de

Cristo uplift

Sierra Grande

arch

Front Range

uplift

Hartville uplift

Amarillo uplift

Wichita uplift

Anadarko

basin

Hugoton

embayment

Sedgwick

basin

Arbuckle

uplift

Ozark

uplift

Bourbon arch

Nemaha uplift

Seminole

arch

Ouachita

uplift

Mississippi

embayment

Cimarron uplift

Black Hills

uplift

River

Mississippi

Missouri River

Base from National Atlas digital data

Lambert Conformal Conic projection

Modified from Jorgensen and others, 1996, fig. 9

0 100 200 300 MILES

0 100 200 300 KILOMETERS

EXPLANATION

Major structural feature Central Midwest

aquifer system

Six southern

midcontinent

States

Area enlarged
Hydrogeology, Distribution, and Volume of Saline Groundwater

39

Western Interior Plains Confining System

The Western Interior Plains confining system is present in 

both the Plains and Ozark subregions. The confining system, 

consisting of mostly shale, limestone, sandstone, and evaporite 

deposits of Pennsylvanian and Permian age, restricts flow 

between the High Plains and Great Plains aquifer systems 

and the underlying Western Interior Plains aquifer system 

(table 10). Thickness of the confining system ranges from 0 ft 

in northeastern Nebraska and in the Ozark subregion to more 

than 20,000 ft in the Anadarko Basin (Jorgensen and others, 

1993). 

Although the Western Interior Plains confining system 

functions as a regional confining unit, permeable limestone 

and sandstone formations in the system are locally water 

bearing (Baker and Leonard, 1995). Water from the system at 

depths of 500 ft or more below land surface generally contains 

large concentrations of dissolved solids, locally as large as 

300,000 mg/L; however, the concentrations of dissolved solids 

in water from depths of less than 500 ft vary greatly (Baker 

and Leonard, 1995). In eastern Kansas and parts of Oklahoma, 

some of the permeable sandstone units are locally important 

aquifers that provide freshwater for municipal supply, 

agriculture, and other uses (Ryder, 1996). Little is known 

about saline waters in these aquifers, and those waters are not 

described in this report.

Western Interior Plains Aquifer System

The Western Interior Plains aquifer system in the Plains 

subregion (fig. 18) is divided into an upper aquifer unit, a 

confining unit, and lower aquifer units (table 10). The upper 

aquifer unit consists primarily of limestone of Mississippian 

age, and the lower aquifer units consist of dolostone, 

limestone, and sandstone of Cambrian to Devonian age. The 

upper aquifer unit and lower aquifer units are separated at 

most locations by a shale confining unit (Jorgensen and others, 

1996). 

All rock-stratigraphic units of the Western Interior 

Plains aquifer system dip away from the Missouri River 

and the Ozark uplift toward the Denver, Anadarko, and 

Arkoma Basins, except along the Front Range uplift (fig. 22). 

The upper aquifer unit was removed from large parts of 

the Western Interior Plains aquifer system by erosion in 

Mississippian time (Jorgensen and others, 1996), and as a 

result, the thickness of the upper aquifer unit is generally less 

than 1,000 ft (fig. 23). Thickness of the lower aquifer units 

exceeds 10,000 ft in the Anadarko Basin in south-central 

Oklahoma (fig. 24) (Signor and others, 1996). 

Rocks of the Western Interior Plains aquifer system 

are deeply buried beneath the thick Western Interior Plains 

confining system in most of the Plains subregion. Deeply 

buried geologic units are less permeable and less porous than 

the same units in shallower areas that have been exposed to 

subaerial weathering (Baker and Leonard, 1995). Regional 

porosity of the upper and lower aquifer units is small (about 1 

percent) in deep basins but increases to 10–15 percent near the 

Central Kansas, Nemaha, and Ozark uplifts (fig. 22) (Signor 

and others, 1996). 

Groundwater flow in the Western Interior Plains 

aquifer system is regionally southeastward from northcentral Nebraska and otherwise eastward toward a broad 

topographic and potentiometric low area in eastern Kansas 

and northeastern Oklahoma. Discharge in the broad, 

topographically low area is vertically upward to streams or 

to the near-surface water-table aquifers (fig. 19) (Jorgensen 

and others, 1996). Minimal recharge to the aquifer system 

occurs from vertical leakage through the overlying confining 

system (Signor and others, 1996). Groundwater in the Western 

Interior Plains aquifer system moves very slowly, with 

modeled velocities as slow as 40 ft per million years in deeply 

buried rock-stratigraphic units, because in most of the area 

both intrinsic permeability and hydraulic gradient are small 

(Signor and others, 1996). 

Most water in the Western Interior Plains aquifer system 

is saline or brine and is a sodium-chloride type (Jorgensen 

and others, 1996). Dissolved-solids concentrations of water 

in the upper aquifer unit range from less than 10,000 mg/L 

in the transition zone to the freshwater-flow system of the 

Ozark Plateaus aquifer system and in southeastern Nebraska 

(fig. 23) to more than 250,000 mg/L in small areas of northcentral Oklahoma and south-central Kansas (Jorgensen and 

others, 1996). The dissolved-solids concentrations of water 

in the lower aquifer units range from less than 3,000 mg/L in 

the transition zone to the freshwater-flow system of the Ozark 

Plateaus aquifer system and in areas of northern and eastern 

Nebraska (fig. 24) to more than 300,000 mg/L in southwestern 

Oklahoma. Dissolved-solids concentrations range from 10,000 

to 35,000 mg/L in parts of eastern Nebraska, along the Las 

Animas arch in eastern Colorado, along the Nemaha uplift in 

northeastern Kansas, and along the Arbuckle uplift in southcentral Oklahoma (fig. 24), where the lower aquifer units are 

close to land surface and receive some recharge (Baker and 

Leonard, 1995). The large dissolved-solids concentrations in 

the Western Interior Plains aquifer system are attributed to 

a paleomarine evaporative brine, slow-moving groundwater 

and long residence time, and minimal recharge through the 

overlying confining system (Jorgensen and others, 1996). 
Figure 23. Dissolved-solids concentrations and thickness in the aquifer-assessment area of the upper aquifer unit in the Western Interior Plains aqu

Springfield Plateau aquifer in the Ozark Plateaus aquifer system, Central Midwest regional aquifer system.

ARKANSAS

COLORADO

IOWA

KANSAS

MISSOURI

NEBRASKA

OKLAHOMA

TEXAS

102° 99° 96° 93°

40°38°36°

2,800

1,800

600

200

400

200

600400

200

200

2,400

600 400

200 400

600

800 200

200

1,000

400

200

400

200

200

200 200

800

800 1,000

400

200

200400

200

600

200

200

400

1,000

800 200

400

200

400

800

1,200

200

400

200

1,000

2,400

1,000

1,000

600 1,000

800

600

2,200

400

200

200

400

400

600

600

400

Base from National Atlas digital dataLambert Conformal Conic projection

Dissolved-solids data modified from Signor and others, 1996, fig. 26; and Imes and E

Thickness data modified from Jorgensen and others, 19

0 60 120 180 

0 60 120 180 240 KILOMETERS

EXPLANATION

Dissolved solids, in milligrams per liter < 1,000 1,000 to 3,000

 > 3,000 to 10,000 > 10,000 to 20,000

 > 20,000 to 35,000 > 35,000

Line of equal thickness— Intervals 200 and 400 feetBoundary between aquifer systems 

400

Aquifer-assessment area boundary of the

upper unit of the Western Interior Plains

aquifer system and the Springfield Plateau

aquifer of the Ozark Plateaus aquifer system

Ozark

Plateaus

aquifer 

system

Western Interior

Plains aquifer 

system

Six southern

midcontinent

States

Area enlarged
Figure 24. Dissolved-solids concentrations and thickness in the aquifer-assessment area of the lower aquifer units in the Western Interior Plains aq

aquifer in the Ozark Plateaus aquifer system, Central Midwest regional aquifer system.

WYOMING

ARKANSA

COLORADO

IOWA

KANSAS

MISSO

NEBRASKA

OKLAHOMA

SOUTH

DAKOTA

TEXAS

NEW MEXICO

Missouri River

13,000

7,000

5,000

2,500

2,000 1,500

500

0

1,500

1,500

1,000

500

0

500

500

500

500

1,000

500

500

1,000

0

0

0

0

3,000

0

1,500

0

1,000

1,000

3,000

1,000

0

0

0

2

500

500

500 500

1,000

0

500

0

0

0

0

0

1,000

500

1,000

500

1,500

2,000

1,000

1,000 5,000

1,000

500 2,500

0

0

0

0

0

0

0

0

1,000

1,500

1,500

0 1,000

1,000

500

1,000 1,500

1,500

5,000

1,000

1,500

1,000

1,000

1,000

1,000

1,000 1,000

500

1,000

2,000

500

500

1,500

500

5,000 2,5002,000

9,000 11,000

7,000

1,500 1,000

2,500

500

1,500

Base from National Atlas digital dataLambert Conformal Conic projection

Dissolved-solids data modified from Signor and others, 1996, fig. 24; Imes and Dav

Thickness data modified from Jorgensen and others, 1993

0 60 120 180 240 MILES0 60 120 180 240 KILOMETERS

EXPLANATI

Dissolved so milligram < 1,000 1,000 to 3,0 > 3,000 to 1 > 10,000 to  > 20,000 to  > 35,000Line of equa Intervals  2,000, and Boundary be aquifer sy

500

Aquifer-assessment area boundary of the

lower unit of the Western Interior Plains

aquifer system and the Ozark aquifer

of the Ozark Plateaus aquifer system

Ozark

Plateaus

aquifer 

system

Western Interior

Plains aquifer 

system

Six southern midcontinent

States

Area enlarged

108° 105° 102° 99° 96° 93°

42°40°38°36°34°
42

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Ozark Plateaus Aquifer System

The Ozark Plateaus aquifer system in the Ozark 

subregion (fig. 18) is divided into the Springfield Plateau 

aquifer, Ozark confining unit, Ozark aquifer, St. Francois 

confining unit, and St. Francois aquifer (table 11) (Signor 

and others, 1996). The Springfield Plateau aquifer consists 

of fractured, permeable Mississippian limestone (Jorgensen 

and others, 1993). The Ozark confining unit underlies the 

Springfield Plateau aquifer, where it restricts flow between the 

Springfield Plateau aquifer and the Ozark aquifer (Imes and 

Emmett, 1994). The Ozark aquifer consists of highly fractured 

and moderately faulted rocks of Late Cambrian to Middle 

Devonian age. Lithologies of this aquifer include dolostone, 

limestone, sandstone, chert, and shale, with dolostone being 

the dominant rock type. Thickness of the Ozark aquifer 

generally ranges from about 800 to 1,500 ft (Signor and 

others, 1996). Underlying the Ozark aquifer is the St. Francois 

confining unit, which restricts flow between the Ozark aquifer 

and the St. Francois aquifer at most locations (Jorgensen and 

others, 1993). The confining unit consists of very slightly 

permeable shale, siltstone, dolostone, and limestone and 

ranges in thickness from 0 to 730 ft (Jorgensen and others, 

1993). The St. Francois aquifer consists of Upper Cambrian 

sandstone and dolostone and is generally 200 to 500 ft thick 

(Jorgensen and others, 1993). 

The Springfield Plateau aquifer crops out at the land 

surface over part of the Ozark subregion and dips into the 

subsurface along the western and southern boundaries of 

the subregion, where the aquifer is overlain by the Western 

Interior Plains confining system (Jorgensen and others, 1993). 

Recharge to the Ozark Plateaus aquifer system is primarily by 

infiltration of precipitation that falls on the topographically 

high aquifer-outcrop areas near the center of the Ozark 

subregion. Regional groundwater flow is radially outward 

from the recharge area (Baker and Leonard, 1995). 

Concentrations of dissolved solids in the Ozark Plateaus 

aquifer system generally are less than 500 mg/L but exceed 

1,000 mg/L in the transition zone to the saline-water-flow 

system of the Western Interior Plains aquifer system (figs. 23 

and 24) (Baker and Leonard, 1995). Water from the Ozark 

and St. Francois aquifers is generally a calcium-magnesiumbicarbonate type, caused by dissolution of the predominately 

dolostone rocks of the Ozark and St. Francois aquifers, and 

water from the Springfield Plateau aquifer is generally a 

calcium-bicarbonate type, similar to the composition of the 

predominately limestone rocks of the Springfield Plateau 

aquifer (Baker and Leonard, 1995). 

Saline-Water Volume of the Central Midwest 

Regional Aquifer System

Estimated water volume of salinity zones in aquiferassessment areas of the Great Plains aquifer system is about 

8,170 million acre-ft of saline water, of which 6,280 million 

acre-ft is in the assessment area of the Maha aquifer, and 

1,890 million acre-ft is in the assessment area of the Apishapa 

aquifer (table 12). Estimated water volume of salinity zones 

in the combined aquifer-assessment areas of the Western 

Interior Plains and Ozark Plateaus aquifer systems is about 

2,660 million acre-ft of saline water, of which 497 million 

acre-ft is in the assessment area of the upper aquifer unit 

and the Springfield Plateau aquifer, and 2,160 acre-ft is in 

the assessment area of the lower aquifer units and the Ozark 

aquifer (table 13). 
Hydrogeology, Distribution, and Volume of Saline Groundwater

43

Table 12. Estimated water volume of salinity zones in the aquifer-assessment areas of the Maha and Apishapa aquifers in the Great 

Plains aquifer system, Central Midwest regional aquifer system.

[mg/L, milligrams per liter; values may not sum to totals because of independent rounding] 

Salinity zone, dissolvedsolids concentration 

(mg/L)1

Area 

(million acres)

Mean 

thickness 

(feet)2

Mean 

porosity 

fraction3

Water volume

(million acre-feet)

Maha aquifer

1,000–3,000 27 278 0.26 1,950

3,000–10,000 37.6 351 0.24 3,200

10,000–20,000 14.3 329 0.24 1,110

20,000–35,000 1.02 137 0.15 21

TOTAL 6,280

Apishapa aquifer

1,000–3,000 17.1 143 0.21 514

3,000–10,000 27.8 175 0.22 1,070

10,000–20,000 8.29 180 0.19 284

20,000–35,000 1.04 149 0.15 23.2

TOTAL 1,890

TOTAL Great Plains aquifer system 8,170

1

Determined from dissolved-solids-concentration map (modified from Helgesen and others, 1993, pl. 6).

2

Computed from thickness maps (modified from Helgesen and others, 1993, pls. 1 and 3).

3

Computed from porosity map (modified from Signor and others, 1996, fig. 35).

Table 13. Estimated water volume of salinity zones in aquifer-assessment areas of the Western Interior Plains and Ozark Plateaus 

aquifer systems, Central Midwest regional aquifer system.

[mg/L, milligrams per liter; values may not sum to totals because of independent rounding]

Salinity zone, dissolvedsolids concentration 

(mg/L)1

Area 

(million acres)

Mean 

thickness 

(feet)2

Mean 

porosity 

fraction3

Water volume 

(million acre-feet)

Upper aquifer unit and Springfield Plateau aquifer

1,000–3,000 4.77 238 0.08 90.9

3,000–10,000 5.10 190 0.09 87.2

10,000–20,000 6.56 403 0.05 132

20,000–35,000 3.68 725 0.07 187

TOTAL 497

Lower aquifer units and Ozark aquifer

1,000–3,000 4.44 753 0.07 234

3,000–10,000 17.5 630 0.06 662

10,000–20,000 18.9 768 0.05 726

20,000–35,000 15.2 702 0.05 534

TOTAL 2,160

TOTAL Western Interior Plains and Ozark Plateaus aquifer systems 2,660

1

Determined from dissolved-solids-concentration maps (modified from Imes and Davis, 1991; Imes and Emmett, 1994; Signor and others, 1996).

2

Thickness of the upper and lower aquifer units were computed by taking the difference between the elevation maps of the aquifers’ surfaces (modified from 

Jorgensen and others, 1993); thickness of the Springfield Plateau and Ozark aquifers were computed from thickness maps (modified from Jorgensen and others, 

1996).

3

Computed from porosity maps (modified from Signor and others, 1996, figs. 23 and 25).
44

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Northern Midwest Regional Aquifer System in 

Northern Missouri

The Northern Midwest regional aquifer system underlies 

about 161,000 mi2 in parts of Illinois, Indiana, Iowa, Minnesota, 

Missouri, and Wisconsin (Sun and others, 1997), but only the 

part in northern Missouri was evaluated for this study (fig. 

1). The Mississippian aquifer and the Cambrian-Ordovician 

aquifer, the two major aquifers in the northern Missouri part 

of the Northern Midwest regional aquifer system, are bounded 

to the south by the Missouri River and to the east by the 

Mississippi River (figs. 25–26). 

Mississippian Aquifer

The Mississippian aquifer in northern Missouri consists 

of carbonate rocks of Mississippian age that are approximately 

age equivalent to those of the Springfield Plateau aquifer 

in the Ozark Plateaus aquifer system (tables 11 and 14); 

however, these aquifers are hydraulically separated by the 

Missouri River (Miller and Appel, 1997). The Keokuk and 

Burlington Limestones are the primary water-yielding rocks 

in the Mississippian aquifer (table 14). Both of these rockstratigraphic units consist of crystalline limestone containing 

chert nodules (Imes, 1985). Miller and Vandike (1997) estimate 

the specific yield of the Mississippian aquifer to be 5 percent.

The Mississippian aquifer is unconfined in the eastern and 

southeastern parts of the aquifer, where the aquifer is exposed 

at the surface or is overlain by glacial-drift aquifers. The aquifer 

becomes confined to the northwest, where it is overlain by 

Pennsylvanian shale and sandstone (Imes, 1985). Recharge 

to the aquifer is mostly from infiltration of precipitation 

on the unconfined part of the aquifer. Some recharge is 

from downward leakage from overlying Pennsylvanian and 

Mississippian strata and from upward flow from the underlying 

Cambrian-Ordovician aquifer (Imes, 1985). Regionally, 

groundwater from the northwest flows either eastward toward 

the Mississippi River or southwestward toward the Missouri 

River (Imes, 1985). In the south and southeast, groundwater 

flows from topographically high recharge areas and discharges 

to the Mississippi and Missouri Rivers. 

Dissolved-solids concentrations are smallest (less than 

1,000 mg/L) where the Mississippian aquifer is unconfined in 

the eastern and southeastern parts of the aquifer (fig. 25) (Imes, 

1985). Dissolved-solids concentrations are largest (10,000–

20,000 mg/L) in the south-central part of the aquifer (fig. 25) 

because of upward flow of saline water from the CambrianOrdovician aquifer (Imes, 1985).

Cambrian-Ordovician Aquifer

The Cambrian-Ordovician aquifer in northern Missouri 

consists of several water-yielding sandstones and dolostones 

(table 14). Some of the rock-stratigraphic units in the aquifer are 

equivalent to parts of the Ozark aquifer in the Ozark Plateaus 

aquifer system, but the Missouri River hydraulically separates 

the aquifers in some places (Miller and Appel, 1997). The 

Cambrian-Ordovician aquifer extends across northern Missouri, 

but only the saline waters in the eastern part of the aquifer were 

evaluated for this report (fig. 26) because the mapped thickness 

of the aquifer (Miller and Appel, 1997) was available for only 

the eastern part.

Primary water-bearing rock-stratigraphic units in the 

Cambrian-Ordovician aquifer are the Roubidoux Formation 

and the Gasconade, Eminence, and Potosi Dolomites (table 14). 

Both the Roubidoux Formation and Gasconade Dolomite 

contain permeable dolostones and sandstones (Imes, 1985). 

The Eminence and Potosi Dolomites consist of porous and 

permeable coarse-grained dolostone with solution channels 

(Imes, 1985). The Cambrian-Ordovician aquifer crops out near 

the Missouri and Mississippi Rivers in northeastern Missouri 

(Imes, 1985). The aquifer dips away from the Ozark uplift, to 

the north and west, where the aquifer becomes confined by 

younger rocks (Imes, 1985; Young, 1992). 

Two groundwater-flow systems are in the CambrianOrdovician aquifer: a regional saline-water- flow system and 

a local freshwater-flow system (Imes, 1985). Groundwater 

flow in the regional saline-water-flow system is from Iowa 

into Missouri (Imes, 1985). Some of the saline water flows 

eastward and passes under the Mississippi River into Illinois, 

and some of the saline water flows southward to discharge into 

the Missouri River (Imes, 1985). A local freshwater-flow system 

in the southeastern part of the aquifer is recharged by infiltration 

of precipitation where the aquifer crops out along its southern 

margin and by downward flow of groundwater from overlying 

Mississippian strata (Imes, 1985).

Dissolved-solids concentrations in the CambrianOrdovician aquifer range from about 350 to 750 mg/L in the 

freshwater-flow system, and the water is a calcium-magnesiumbicarbonate type (Siegel, 1989). Dissolved-solids concentrations 

exceed 10,000 mg/L in the saline-water-flow system in areas 

along the Mississippi and Missouri Rivers because of discharge 

of regional slow-moving groundwater (Young and Siegel, 

1992). In most of the saline-water-flow system in northern 

Missouri, dissolved-solids concentrations are between 1,000 

and 10,000 mg/L, and the water is a sodium-mixed anion 

(no dominant anion) type (Young, 1992). This slightly to 

moderately saline water is isotopically depleted in oxygen-18 

and deuterium isotopes with respect to modern precipitation, an 

indication that the source of the groundwater was precipitation 

in a colder climate. The primary source of recharge to this 

aquifer is thought to have been subglacial meltwater from 

Pleistocene-age glaciation in north-central Iowa (Siegel, 1989; 

Young and Siegel, 1992).

The Mississippian and Cambrian-Ordovician aquifers 

in the Northern Midwest regional aquifer system in northern 

Missouri contain an estimated 656 million acre-ft of saline 

water with dissolved-solids concentrations less than 20,000 

mg/L (table 15). The assessment area of the Mississippian 

aquifer contains about 101 million acre-ft of saline groundwater, 

and the assessment area of the Cambrian-Ordovician aquifer 

contains about 555 million acre-ft (table 15).
Hydrogeology, Distribution, and Volume of Saline Groundwater

45

Figure 25. Dissolved-solids concentrations and thickness in the aquifer-assessment area of the Mississippian aquifer in northern 

Missouri, Northern Midwest regional aquifer system.

IOWA

ILLINOIS

MISSOURI

KANSAS

NEBRASKA

300

200

200

100

300

100

300

200

200

100

100

200

200

100

200

100

100

200

200

200

200

200

200

400

100

300

96° 93° 90°

42°

40°

38°

Mississippi River

Missouri River

Base from National Atlas digital data

Lambert Conformal Conic projection

Dissolved-solids data modified from Miller and Appel, 1997, fig. 117; and Imes, 1985, fig. 18

Thickness data modified from Miller and Appel, 1997, fig. 115

0 20 40 60 80 MILES

0 20 40 60 80 KILOMETERS

EXPLANATION

Dissolved solids, in milligrams

 per liter

 < 1,000

 1,000 to 3,000

 > 3,000 to 10,000

 > 10,000 to 20,000

Line of equal thickness—

 Interval 100 feet

300

Northern Midwest

aquifer system

Southernmidcontinent states

Mississippian

aquifer-assessment

area boundary

Area enlarged
46

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Figure 26. Dissolved-solids concentrations and thickness in the aquifer-assessment area of the Cambrian-Ordovician aquifer in 

northern Missouri, Northern Midwest regional aquifer system.

IOWA

ILLINOIS

MISSOURI

KANSAS

NEBRASKA

96° 93° 90°

42°

40°

38°

1,000

1,500

1,500

1,000

2,000

1,000

1,500

Insufficient data

for analysis

Mississippi River

Missouri River

Base from National Atlas digital data

Lambert Conformal Conic projection

Dissolved solids data modified from Young and Siegel, 1992, fig. 31

Thickness data modified from Miller and Appel, 1997, fig. 106

0 20 40 60 80 MILES

0 20 40 60 80 KILOMETERS

EXPLANATION

Dissolved solids, in milligrams

 per liter

 < 1,000

 1,000 to 3,000

 > 3,000 to 10,000

 > 10,000 to 20,000

Line of equal thickness—

 Interval 500 feet

1,500

Northern Midwest

aquifer system

Six States in

the southern 

midcontinent

Cambrian-Ordovician

aquifer-assessment

area boundary

Area enlarged
Hydrogeology, Distribution, and Volume of Saline Groundwater

47

Table 14. Time-stratigraphic, rock-stratigraphic, and hydrogeologic units of the Northern Midwest regional aquifer system in northern 

Missouri.

[Modified from Young, 1992, table 1; Ls, Limestone; Fm, Formation; Ss, Sandstone; Dol, Dolomite] 

Time-stratigraphic unit

Rock-stratigraphic unit Hydrogeologic unit

System Series

Quaternary

Holocene Alluvium Alluvial aquifer

Pleistocene Glacial drift Drift aquifer

Pennsylvanian

Virgilian

Missourian

Desmoinesian

Atokan

Morrowan

Undifferentiated

Confining unit

Mississippian

Chesterian Undifferentiated

Meramecian Ste. Genevieve Ls, St. Louis Ls, Salem Ls, 

Warsaw Ls

Osagean Keokuk Ls, Burlington Ls Mississippian aquifer

Kinderhookian Undifferentiated

Confining unit

Devonian

Upper

Middle

Lower

Undifferentiated

Silurian

Cayugan

Niagaran

Alexandrian

Undifferentiated

Ordovician

Cincinnatian Maquoketa Shale

Mohawkian Kimmswick Fm, Decorah Fm, Plattin Fm, 

Joachim Dol

Cambrian-Ordovician aquifer

Chazyan St. Peter Ss, Everton Dol

Canadian Roubidoux Fm, Gasconade Dol

Cambrian Croixan

Eminence Dol, Potosi Dol, Derby-Doe 

Run Dol

Davis Fm Confining unit

Bonneterre Fm (little information)

Lamotte Ss (probable aquifer)

Precambrian Undifferentiated Confining unit
48

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Table 15. Estimated water volume of salinity zones in the aquifer-assessment areas of the Mississippian and Cambrian-Ordovician 

aquifers in northern Missouri, Northern Midwest regional aquifer system.

[mg/L, milligrams per liter; values may not sum to totals because of independent rounding]

Salinity zone, dissolvedsolids concentration 

(mg/L)1

Area 

(million acres)

Mean thickness 

(feet)2

Mean porosity 

fraction3

Water volume 

(million acre-feet)

Mississippian aquifer

1,000–3,000 2.28 201 0.05 22.9

3,000–10,000 7.30 202 0.05 73.7

10,000–20,000 0.486 192 0.05 4.67

TOTAL 101

Cambrian-Ordovician aquifer

1,000–3,000 0.815 1,360 0.07 77.6

3,000–10,000 4.9 1,460 0.06 429

10,000–20,000 0.688 1,420 0.05 48.8

TOTAL 555

TOTAL Northern Midwest regional aquifer system in northern Missouri 656

1

Salinity zones for the Mississippian aquifer were determined from dissolved-solids-concentration maps (modified from Imes, 1985; Miller and Appel, 1997); 

salinity zones for the Cambrian-Ordovician aquifer were determined from dissolved-solids-concentration maps (modified from Young and Siegel, 1992).

2

Mean thickness of the Mississippian aquifer was computed from thickness maps (modified from Imes, 1985); mean thickness of the Cambrian-Ordovician 

aquifer was computed from thickness maps (modified from Miller and Appel, 1997).

3

Mean porosity of the Mississippian aquifer was based on estimated specific yield (Miller and Vandike, 1997); mean porosity of the Cambrian-Ordovician 

aquifer was estimated from mapped porosities in the lower aquifer units of the Western Interior Plains aquifer system (Signor and others, 1996).
Hydrogeology, Distribution, and Volume of Saline Groundwater

49

Summary of Saline Groundwater in the Southern 

Midcontinent

Many of the aquifers in the southern midcontinent are 

underlain by one or more aquifers, resulting in vertically 

stacked aquifers. For example, in parts of Kansas and 

Nebraska, the High Plains regional aquifer system overlies 

the Great Plains aquifer system, which in turn overlies the 

Western Interior Plains aquifer system (fig. 19). Another 

example of stacked aquifers is in parts of Texas, Louisiana, 

and Mississippi, where permeable zones of the coastal 

lowlands aquifer system are vertically stacked (fig. 4). Thus, 

it follows that, in areas with vertically stacked aquifers, 

groundwaters of varying salinity are also stacked atop each 

other. The combined extents of slightly to moderately saline 

waters (dissolved-solids concentrations of 1,000–10,000 

mg/L), very saline waters (dissolved-solids concentrations 

of 10,000–35,000 mg/L), and all saline waters (dissolvedsolids concentrations of 1,000–35,000 mg/L) of the aquifers 

evaluated in this report are shown in figures 27, 28, and 29, 

respectively. These two-dimensional maps provide a 

visual representation of the three-dimensional (areal and 

vertical) distribution of saline groundwater in the southern 

midcontinent.

The aquifers evaluated in this study contain an estimated 

39,900 million acre-ft of saline water, of which about 21,600 

million acre-ft is slightly to moderately saline (1,000–10,000 

mg/L dissolved solids) and about 18,300 million acre-ft is 

very saline (10,000–35,000 mg/L dissolved solids) (table 16). 

The aquifer systems containing the largest volumes of saline 

water are the coastal lowlands (about 16,300 million acre-ft), 

Mississippi embayment and Texas coastal uplands (about 

12,000 million acre-ft), and Great Plains (about 8,170 million 

acre-ft) aquifer systems (fig. 30, table 16). Of the 22 aquifers 

evaluated in this study, the Maha aquifer in the Great Plains 

aquifer system contains both the largest estimated volume 

of saline water (about 6,280 million acre-ft) and the largest 

estimated volume of slightly to moderately saline water (about 

5,150 million acre-ft) (fig. 30, table 16).
50

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Figure 27. Extent of slightly to moderately saline groundwater (dissolved-solids concentrations of 1,000–10,000 milligrams per liter) 

in aquifer-assessment areas of the High Plains, Gulf Coast, Edwards-Trinity, Central Midwest, and Northern Midwest regional aquifer 

systems.

ALABAMA

ARKANSAS

COLORADO

FLORIDA

IOWA

ILLINOIS

INDIANA

KANSAS

KENTUCKY

LOUISIANA

MICHIGAN

MINNESOTA

MISSOURI

MISSISSIPPI

MONTANA

NEBRASKA

NEW

MEXICO

OKLAHOMA

SOUTH

DAKOTA

TENNESSEE

TEXAS

WISCONSIN

WYOMING

UNITED STATES

MEXICO

42°

38°

34°

30°

26°

110° 105° 100° 95° 90° 85°

Base from National Atlas digital data

Lambert Conformal Conic projection

Dissolved solids, in milligrams

 per liter

 1,000 to 10,000

EXPLANATION 0 150 300 MILES

0 150 300 KILOMETERS

GULF OF

MEXICO

LAKE MICHIGAN
Hydrogeology, Distribution, and Volume of Saline Groundwater

51

Figure 28. Extent of very saline groundwater (dissolved-solids concentrations of 10,000–35,000 milligrams per liter) in aquiferassessment areas of the High Plains, Gulf Coast, Edwards-Trinity, Central Midwest, and Northern Midwest regional aquifer systems.

ALABAMA

ARKANSAS

COLORADO

FLORIDA

IOWA

ILLINOIS

INDIANA

KANSAS

KENTUCKY

LOUISIANA

MICHIGAN

MINNESOTA

MISSOURI

MISSISSIPPI

MONTANA

NEBRASKA

NEW

MEXICO

OKLAHOMA

SOUTH

DAKOTA

TENNESSEE

TEXAS

WISCONSIN

WYOMING

UNITED STATES

MEXICO

42°

38°

34°

30°

26°

110° 105° 100° 95° 90° 85°

Base from National Atlas digital data

Lambert Conformal Conic projection EXPLANATION

Dissolved solids, in milligrams

 per liter

 10,000 to 35,000

0 150 300 MILES

0 150 300 KILOMETERS

GULF OF

MEXICO

LAKE MICHIGAN
52

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Figure 29. Extent of saline groundwater (dissolved-solids concentrations of 1,000–35,000 milligrams per liter) in aquifer-assessment 

areas of the High Plains, Gulf Coast, Edwards-Trinity, Central Midwest, and Northern Midwest regional aquifer systems.

ALABAMA

ARKANSAS

COLORADO

FLORIDA

IOWA

ILLINOIS

INDIANA

KANSAS

KENTUCKY

LOUISIANA

MICHIGAN

MINNESOTA

MISSOURI

MISSISSIPPI

MONTANA

NEBRASKA

NEW

MEXICO

OKLAHOMA

SOUTH

DAKOTA

TENNESSEE

TEXAS

WISCONSIN

WYOMING

UNITED STATES

MEXICO

42°

38°

34°

30°

26°

110° 105° 100° 95° 90° 85°

Base from National Atlas digital data

Lambert Conformal Conic projection EXPLANATION

Dissolved solids, in milligrams

 per liter

 1,000 to 10,000

 10,000 to 35,000

0 150 300 MILES

0 150 300 KILOMETERS

GULF OF

MEXICO

LAKE MICHIGAN
Hydrogeology, Distribution, and Volume of Saline Groundwater

53

Table 16. Summary of estimated water volume of salinity zones in aquifer-assessment areas of aquifer systems and aquifers in the 

southern midcontinent and adjacent areas.

[mg/L, milligrams per liter; values may not sum to totals because of independent rounding]

Aquifer system Aquifer

Water volume (million acre-feet) by salinity zone, 

dissolved-solids concentration 

(mg/L)

Total saline water volume 

(million acre-feet)

1,000–3,000 3,000–10,000 10,000–20,000 20,000–35,000 Aquifer Aquifer 

system

High Plains High Plains 34.5 0 0 0 34.5 34.5

Coastal lowlands

Permeable zone A 1,000 1,040 1,070 630 3,740

16,300

Permeable zone B 833 640 828 2,740 5,040

Permeable zone C 565 535 560 902 2,560

Permeable zone D 604 1,120 524 769 3,020

Permeable zone E 267 559 461 675 1,960

Mississippi 

embayment and 

Texas coastal 

uplands

Mississippi River 

Valley alluvial 12.9 0 0 0 12.9

12,000

Upper Claiborne 345 767 794 578 2,480

Middle Claiborne 860 728 870 283 2,740

Lower ClaiborneUpper Wilcox 451 344 86.1 65.1 946

Middle Wilcox 934 1,040 868 1,860 4,700

Lower Wilcox 198 194 334 313 1,040

McNairy-Nacatoch 60 14.8 0 0 74.8

Edwards-Trinity Edwards 17.1 32.0 0 0 49.1 49.1

Great Plains

Maha 1,950 3,200 1,110 21 6,280

8,170

Apishapa 514 1,070 284 23.2 1,890

Western Interior 

Plains and 

Ozark Plateaus

Upper aquifer unit 

and Springfield 

Plateau

90.9 87.2 132 187 497

2,660

Lower aquifer units 

and Ozark 234 662 726 534 2,160

Mississippian 

and CambrianOrdovician

Mississippian 22.9 73.7 4.67 0 101

656 CambrianOrdovician 77.6 429 48.8 0 555

TOTAL SALINE WATER VOLUME 9,070 12,500 8,700 9,610 39,900 39,900

TOTAL SALINE WATER VOLUME 

BY SALINE CLASSIFICATION

21,600 

Slightly to moderately saline

18,300 

Very saline

39,900 

Saline
54

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Summary

Because of increasing demand for freshwater supplies 

and decreasing costs of desalination, saline groundwater 

is being considered a source of water that could reduce 

dependency on freshwater resources. Saline groundwater 

is known to be present in the southern midcontinent of the 

United States, but more information about the distribution and 

volume of saline aquifers is necessary to evaluate and develop 

saline groundwater resources. The U.S. Geological Survey 

(USGS) evaluated 22 aquifers in the southern midcontinent to 

map the distribution of saline groundwater and to compute the 

volume of saline water in storage.

Saline waters of the 22 aquifers were evaluated by 

defining salinity zones; digitizing data, primarily from the 

Regional Aquifer-System Analysis (RASA) Program of the 

USGS; and computing the volume of saline water in storage. 

Maps and information from five regional aquifer systems 

defined by the RASA Program (the High Plains, Gulf Coast, 

Edwards-Trinity, Central Midwest, and Northern Midwest 

regional aquifer systems) were used in this report. Twentytwo aquifers containing saline water had sufficient data to be 

included in this study. These aquifers underlie six States in 

the southern midcontinent—Arkansas, Kansas, Louisiana, 

Missouri, Oklahoma, and Texas—and adjacent areas 

including all or parts of Alabama, Colorado, Florida, Illinois, 

Kentucky, Mississippi, Nebraska, New Mexico, South Dakota, 

Tennessee, and Wyoming and some offshore areas of the Gulf 

of Mexico.

The distribution of saline groundwater in the southern 

midcontinent is substantially affected by the hydrogeology 

and groundwater-flow systems of the aquifers. Many of the 

aquifers in the southern midcontinent are underlain by one 

or more aquifers, resulting in vertically stacked aquifers 

containing waters of varying salinity. Saline groundwater is 

affected by past and present hydrogeologic conditions. Spatial 

variation of groundwater salinity in the southern midcontinent 

primarily is controlled by locations of recharge and discharge 

areas, groundwater-flow paths and residence time, mixing of 

freshwater and saline water, and interactions with aquifer rock 

and sediments. 

The High Plains aquifer of the High Plains regional 

aquifer system and the Mississippi River Valley alluvial 

aquifer of the Gulf Coast regional aquifer system crop out 

at land surface throughout the extents of these aquifers and 

thus consist primarily of freshwater. In both of these aquifers, 

small areas of slightly saline water (1,000–3,000 milligrams 

per liter [mg/L] dissolved-solids concentrations) are caused by 

natural upward flow of saline groundwater from underlying 

geologic units and by pumping of high-capacity wells, which 

can induce or enhance upward flow of saline water from 

underlying geologic units.

In aquifers of the Gulf Coast regional aquifer system, 

dissolved-solids concentrations generally increase from 

recharge areas along the aquifer outcrops downdip toward 

the Gulf of Mexico and principal discharge areas. The 

Figure 30. Volume of saline water in aquifer-assessment areas 

of aquifer systems in the southern midcontinent and adjacent 

areas.

Aquifer system

Coastal lowlands

Mississippi embayment and 

Texas coastal uplands

Great Plains

Western Interior Plains and 

Ozark Plateaus

Mississippian and

Cambrian-Ordovician

Edwards-Trinity 

(Edwards aquifer)

High Plains

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

Volume of saline water, in millions of acre-feet

> 10,000 to 35,000

1,000 to 10,000

EXPLANATION
References Cited

55

major processes that affect saline-water chemistry of the 

Gulf Coast aquifers are water-rock interactions (leaching of 

soluble salts from the unsaturated zone, alteration of albite 

and other silicate minerals, cation exchange, and dissolution 

of evaporites) and mixing of freshwater by the upward flow 

of saline water from underlying units. Dissolution of halite 

occurs in areas where salt domes penetrate a permeable 

zone or aquifer at depths greater than approximately 4,000 

feet (ft). Dissolution of halite is minimal at depths less than 

approximately 4,000 ft because salt domes commonly are 

sealed by relatively impervious cap rocks.

Water chemistry of the Edwards aquifer is primarily 

controlled by geologic processes that occurred in late Tertiary 

time, when the deeply buried aquifer, saturated with brine, was 

uplifted and faulted. Large volumes of freshwater began to 

infiltrate the aquifer in the fault zone that previously had been 

isolated from meteoric conditions, allowing freshwater to mix 

with older brine and saline water.

Slightly to moderately saline water content of much 

of the Great Plains aquifer system results from incomplete 

flushing of original formation water by slow-moving 

groundwater of this aquifer system. Very saline water in the 

central and east-central parts of the aquifer system results 

from upward flow of saline water from underlying saltbearing strata. Groundwater containing more than 100,000 

mg/L dissolved solids in the Nebraska panhandle probably is 

related to upward flow of brine along faults or fractures from 

underlying Permian evaporite deposits.

Most water in the Western Interior Plains aquifer system 

is saline or brine. Large dissolved-solids concentrations, 

which exceed 300,000 mg/L in southwestern Oklahoma, are 

attributed to a paleomarine evaporative brine, slow-moving 

groundwater and long residence time, and minimal recharge 

through the overlying confining system. Eastward flowing 

brine in the Western Interior Plains aquifer system converges 

with westward flowing freshwater in the Ozark Plateaus 

aquifer system in a broad, topographically low area that 

extends from northeastern Oklahoma into central Missouri and 

flows vertically upward to streams or to overlying rock units. 

Saline water occurs in the shared boundary between the two 

flow systems of these aquifer systems.

Water in the Mississippian aquifer in northern Missouri 

ranges from fresh in the eastern and southeastern parts of 

the aquifer, where the aquifer is unconfined, to very saline in 

the south-central part of the aquifer because of upward flow 

of saline water from the underlying Cambrian-Ordovician 

aquifer. Water in the Cambrian-Ordovician aquifer in 

northern Missouri is fresh along the southeastern margin 

of the aquifer, where the aquifer is unconfined. Dissolvedsolids concentrations exceed 10,000 mg/L in areas along 

the Mississippi and Missouri Rivers because of discharge 

of regional slow-moving groundwater. Most water in the 

Cambrian-Ordovician aquifer in northern Missouri has 

dissolved-solids concentrations of 1,000–10,000 mg/L. The 

source of this slightly to moderately saline water is thought to 

be subglacial meltwater from Pleistocene glaciation in northcentral Iowa.

The volume calculations made for the aquifer-assessment 

areas in the southern midcontinent indicate that about 39,900 

million acre-feet (acre-ft) of saline water is in storage. About 

21,600 million acre-ft of the water in storage is slightly to 

moderately saline (1,000–10,000 mg/L dissolved solids), and 

about 18,300 million acre-ft is very saline (10,000–35,000 

mg/L dissolved solids). The largest volumes of saline water 

are in the coastal lowlands (about 16,300 million acre-ft), 

Mississippi embayment and Texas coastal uplands (about 

12,000 million acre-ft), and Great Plains (about 8,170 million 

acre-ft) aquifer systems. Of the 22 aquifers evaluated in this 

report, the Maha aquifer in the Great Plains aquifer system 

contains both the largest volume of saline water (about 

6,280 million acre-ft) and the largest volume of slightly to 

moderately saline water (about 5,150 million acre-ft).

References Cited

Ackerman, D.J., 1996, Hydrology of the Mississippi River 

Valley alluvial aquifer, south-central United States: U.S. 

Geological Survey Professional Paper 1416–D, 56 p.

Alley, W.M., 2003, Desalination of ground water: Earth 

science perspectives: U.S. Geological Survey Fact Sheet 

075–03, 4 p.

Alley, W.M., Reilly, T.E., and Franke, O.L., 1999, 

Sustainability of ground-water resources: U.S. Geological 

Survey Circular 1186, 79 p.

Anderson, M.T., and Woosley, L.H., Jr., 2005, Water 

availability for the Western United States—Key scientific 

challenges: U.S. Geological Survey Circular 1261, 85 p.

Baker, C.H., and Leonard, R.B., 1995, Hydrochemistry of 

aquifer systems in Cretaceous and older rocks underlying 

Kansas, Nebraska, and parts of Arkansas, Colorado, 

Missouri, New Mexico, Oklahoma, South Dakota, Texas, 

and Wyoming: U.S. Geological Survey Water-Resources 

Investigations Report 94–4144, 53 p.

Barker, R.A., and Ardis, A.F., 1996, Hydrogeologic framework 

of the Edwards-Trinity aquifer system, west-central Texas: 

U.S. Geological Survey Professional Paper 1421–B, 61 p.

Brahana, J.V., and Mesko, T.O., 1988, Hydrogeology and 

preliminary assessment of regional flow in the upper 

Cretaceous and adjacent aquifers in the northern Mississippi 

embayment: U.S. Geological Survey Water-Resources 

Investigations Report, 87–4000, 65 p.

Brekke, L.D., Kiang, J.E., Olsen, J.R., Pulwarty, R.S., Raff, 

D.A., Turnipseed, D.P., Webb, R.S., and White, K.D., 2009, 

Climate change and water resources management—A 

Federal perspective: U.S. Geological Survey Circular 

1331, 65 p. (Also available online at http://pubs.usgs.gov/

circ/1331/.)
56

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Cederstrand, J.R., and Becker, M.F., 1998, Digital map 

of specific yield for the High Plains aquifer in parts of 

Colorado, Kansas, Nebraska, New Mexico, Oklahoma, 

South Dakota, Texas, and Wyoming: U.S. Geological 

Survey Open-File Report 98–414, compact disk. 

Core Laboratories, Inc., 1972, A survey of the subsurface 

saline water of Texas—Aquifer rock properties: Texas 

Water Development Board Report 157, v. 3, 364 p.

Emmons, W.H., 1921, Geology of petroleum: New York, 

McGraw-Hill Book Co., Inc., p. 342.

Esri, 2012a, ArcGIS resource center, Desktop 10—Topo to 

raster (spatial analyst): Esri, accessed March 18, 2013, at 

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.

html#//009z0000006s000000.htm.

Esri, 2012b, ArcGIS resource center, Desktop 10—Contour 

list (spatial analyst): Esri, accessed March 18, 2013, at 

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.

html#//009z000000tt000000.htm.

Esri, 2012c, ArcGIS resource center, Desktop 10—Feature to 

polygon (data management): Esri, accessed March 18, 2013, 

at http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.

html#//00170000003n000000.

Esri, 2012d, ArcGIS resource center, Desktop 10—Zonal 

statistics as table (spatial analyst): Esri, accessed March 18, 

2013, at http://help.arcgis.com/en/arcgisdesktop/10.0/help/

index.html#//009z000000w8000000.htm.

Federal Interagency Panel on Climate Change and Water Data 

and Information, 2011, Report to Congress—Strengthening 

the scientific understanding of climate change impacts on 

freshwater resources of the United States, 49 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 Atlas 199.

Fischer, B.C., Kollasch, K.M., and McGuire, V.L., 2000, 

Digital map of saturated thickness in the High Plains 

aquifer in parts of Colorado, Kansas, Nebraska, New 

Mexico, Oklahoma, South Dakota, Texas, and Wyoming, 

1996 to 1997: U.S. Geological Survey Open-File Report 

2000–300. (Also available at http://water.usgs.gov/lookup/

getspatial?ofr00-300_sattk9697.)

Flores, Robert, 1990, Test well drilling investigation to 

delineate the downdip limits of usable-quality ground water 

in the Edwards aquifer, Texas: Texas Water Development 

Board Report 325, 70 p.

Freeze, R.A., and Cherry, J.A., 1979, Groundwater: 

Englewood Cliffs, N.J., Prentice-Hall, 604 p.

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.

Groschen, G.E., and Buszka, P.M., 1997, Hydrogeologic 

framework and geochemistry of the Edwards aquifer salinewater zone, south-central Texas: U.S. Geological Survey 

Water-Resources Investigations Report 97–4133, 47 p. 

Grubb, H.F., 1984, Planning report for the Gulf Coast 

Regional Aquifer System Analysis in the Gulf of Mexico 

coastal plain, United States: U.S. Geological Survey WaterResources Investigations Report 84–4219, 30 p.

Grubb, H.F., 1998, Summary of hydrology of the regional 

aquifer systems, Gulf Coastal Plain, south-central United 

States: U.S. Geological Survey Professional Paper 1416–A, 

61 p.

Gurdak, J.J., McMahon, P.B., Dennehy, K.F., and Qi, S.L., 

2009, Water quality in the High Plains aquifer, Colorado, 

Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, 

Texas, and Wyoming, 1999–2004: U.S. Geological Survey 

Circular 1337, 63 p. 

Gutentag, E.D., Heimes, F.J., Krothe, N.C., Luckey, R.R., and 

Weeks, J.B., 1984, Geohydrology of the High Plains aquifer 

in parts of Colorado, Kansas, Nebraska, New Mexico, 

Oklahoma, South Dakota, Texas, and Wyoming: U.S. 

Geological Survey Professional Paper 1400–B, 63 p.

Helgesen, J.O., Leonard, R.B., and Wolf, R.J., 1993, 

Hydrology of the Great Plains aquifer system in Nebraska, 

Colorado, Kansas, and adjacent areas: U.S. Geological 

Survey Professional Paper 1414–E, 80 p., 10 pls.

Hem, J.D., 1985, Study and interpretation of the chemical 

characteristics of natural water: U.S. Geological Survey 

Water-Supply Paper 2254, 263 p. 

Hosman, R.L., and Weiss, J.S., 1991, Geohydrologic units 

of the Mississippi embayment and Texas coastal uplands 

aquifer systems, south-central United States: U.S. 

Geological Survey Professional Paper 1416–B, 19 p.

Hunt, A.G., Lambert, R.B., and Fahlquist, Lynne, 2010, 

Sources of groundwater based on helium analyses in 

and near the freshwater/saline-water transition zone of 

the San Antonio segment of the Edwards aquifer, southcentral Texas, 2002–03: U.S. Geological Survey Scientific 

Investigations Report 2010–5030, 15 p.

Imes, J.L., 1985, The ground-water flow system in northern 

Missouri with emphasis on the Cambrian-Ordovician 

aquifer: U.S. Geological Survey Professional Paper 1305, 

61 p., 1 pl. 
References Cited

57

Imes, J.L., and Davis, J.V., 1991, Water type and concentration 

of dissolved solids, chloride, and sulfate in ground water 

from the Ozark aquifer in Missouri, Arkansas, Kansas, 

and Oklahoma: U.S. Geological Survey Hydrologic 

Investigations Atlas 711–K, 4 sheets.

Imes, J.L., and Emmett, L.F., 1994, Geohydrology of the 

Ozark Plateaus aquifer system in parts of Missouri, 

Arkansas, Oklahoma, and Kansas: U.S. Geological Survey 

Professional Paper 1414–D, 127 p.

Jorgensen, D.G., Helgesen, J.O., and Imes, J.L., 1993, 

Regional aquifers in Kansas, Nebraska, and parts of 

Arkansas, Colorado, Missouri, New Mexico, Oklahoma, 

South Dakota, Texas, and Wyoming—Geohydrologic 

framework: U.S. Geological Survey Professional Paper 

1414–B, 72 p.

Jorgensen, D.G., Helgesen, J.O., Signor, D.C., Leonard, 

R.B., Imes, J.L., and Christenson, S.C., 1996, Analysis of 

regional aquifers in the central Midwest of the United States 

in Kansas, Nebraska, and parts of Arkansas, Colorado, 

Missouri, New Mexico, Oklahoma, South Dakota, Texas, 

and Wyoming—Summary: U.S. Geological Survey 

Professional Paper 1414–A, 67 p.

Jorgensen, D.G., and Signor, D.C., 1981, Plan of study for 

the Central Midwest Regional Aquifer System Analysis 

in parts of Arkansas, Colorado, Kansas, Missouri, Nebraska, 

New Mexico, Oklahoma, South Dakota, and Texas: U.S. 

Geological Survey Open-File Report 81–206, 28 p.

Krieger, R.A., Hatchett, J.L., and Poole, J.L., 1957, 

Preliminary survey of the saline water resources of the 

United States: U.S. Geological Survey Water-Supply Paper 

1374, 171 p., 2 pls.

Krothe, N.C., Oliver, J.W., and Weeks, J.B., 1982, Dissolved 

solids and sodium in water from the High Plains aquifer 

in parts of Colorado, Kansas, Nebraska, New Mexico, 

Oklahoma, South Dakota, Texas, and Wyoming: U.S. 

Geological Survey Hydrologic Investigations Atlas 658, 

scale 1:2,500,000, 2 sheets.

LBG-Guyton Associates and NRS Consulting Engineers, 

2003, Brackish groundwater in Texas—A manual for Texas 

regional water planning groups: Prepared for the Texas 

Water Development Board, 188 p.

Lambert, R.B., Hunt, A.G., Stanton, G.P., and Nyman, M.B., 

2009, Water-level, borehole geophysical log, and waterquality data from wells transecting the freshwater/salinewater interface of the San Antonio segment of the Edwards 

aquifer, south-central Texas, 1999–2007: U.S. Geological 

Survey Data Series 403 [variously paged].

Lambert, R.B., Hunt, A.G., Stanton, G.P., and Nyman, M.B., 

2010, Lithologic and physicochemical properties and 

hydraulics of flow in and near the freshwater/saline-water 

transition zone, San Antonio segment of the Edwards 

aquifer, south-central Texas, based on water-level and 

borehole geophysical log data, 1999–2007: U.S. Geological 

Survey Scientific Investigations Report 2010–5122, 69 p.

Lohman, S.W., and others, 1972, Definitions of selected 

ground-water terms—Revisions and conceptual 

refinements: U.S. Geological Survey Water-Supply Paper 

1988, 21 p.

Maclay, R.W., 1995, Geology and hydrology of the Edwards 

aquifer in the San Antonio area, Texas: U.S. Geological 

Survey Water-Resources Investigations Report 95–4186, 

64 p.

Maclay, R.W., and Land, L.F., 1988, Simulation of flow in the 

Edwards aquifer, San Antonio region, Texas, and refinement 

of storage and flow concepts: U.S. Geological Survey 

Water-Supply Paper 2336–A, 48 p.

McMahon, P.B., Dennehy, K.F., Bruce, B.W., Gurdak, J.J., and 

Qi, S.L., 2007, Water-quality assessment of the High Plains 

aquifer, 1999–2004: U.S. Geological Survey Professional 

Paper 1749, 136 p.

Miller, D.E., and Vandike, J.E., 1997, Missouri State Water 

Plan Series Volume II, Groundwater resources of Missouri: 

Missouri Department of Natural Resources Water-Resources 

Report No. 46, 210 p.

Miller, J.A., and Appel, C.L., 1997, Ground water atlas 

of the United States—Segment 3, Kansas, Missouri, 

and Nebraska: U.S. Geological Survey Hydrologic 

Investigations Atlas 730–D. 

Pettijohn, R.A., 1996, Geochemistry of ground water in 

the Gulf Coast regional aquifer systems, south-central 

United States: U.S. Geological Survey Water-Resources 

Investigations Report 96–4107, 158 p.

Pettijohn, R.A., Weiss, J.S., and Williamson, A.K., 1988, 

Distribution of dissolved-solids concentrations and 

temperature in ground water of the Gulf Coast aquifer 

systems, south-central United States: U.S. Geological 

Survey Water-Resources Investigations Report 88–4082, 5 

sheets. 

Reilly, T.E., Dennehy, K.F., Alley, W.M., and Cunningham, 

W.L., 2008, Ground-water availability in the United States: 

U.S. Geological Survey Circular 1323, 70 p. (Also available 

at http://pubs.usgs.gov/circ/1323/.)

Renken, R.A., 1998, Ground water atlas of the United 

States—Segment 5, Arkansas, Louisiana, Mississippi: U.S. 

Geological Survey Hydrologic Investigations Atlas 730–F. 
58

Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas

Russell, W.L., 1961, Reservoir water resistivities and possible 

hydrodynamic flow in Denver basin: American Association 

of Petroleum Geologists Bulletin, v. 45, no 12, p. 1925–

1940.

Ryder, P.D., 1996, Ground water atlas of the United States—

Segment 4, Oklahoma, Texas: U.S. Geological Survey 

Hydrologic Investigations Atlas 730–E.

Siegel, D.I., 1989, Geochemistry of the Cambrian-Ordovician 

aquifer system in the northern Midwest: U.S. Geological 

Survey Professional Paper 1405–D, 76 p.

Signor, D.C., Helgesen, J.O., Jorgensen, D.G., and Leonard, 

R.B., 1996, Geohydrology and simulation of steady-state 

flow conditions in regional aquifer systems in Cretaceous 

and older rocks underlying Kansas, Nebraska, and parts of 

Arkansas, Colorado, Missouri, New Mexico, Oklahoma, 

South Dakota, Texas, and Wyoming: U.S. Geological 

Survey Professional Paper 1414–C, 105 p.

Sun, R.J., and Johnston, R.H., 1994, Regional Aquifer-System 

Analysis Program of the U.S. Geological Survey, 1978–

1992, U.S. Geological Survey Water-Resources Circular 

1099, 126 p.

Sun, R.J., Weeks, J.B., and Grubb, H.F., 1997, Bibliography 

of Regional Aquifer-System Analysis Program of the U.S. 

Geological Survey, 1978–96: U.S. Geological Survey 

Water-Resources Investigations Report 97–4074, 63 p.

Texas Water Development Board, 2013, Water for Texas—

Desalination: Brackish groundwater, accessed June 25, 

2013 at http://www.twdb.state.tx.us/publications/shells/

Desal_Brackish.pdf.

Weeks, J.B., Gutentag, E.D., Heimes, F.J., and Luckey, R.R., 

1988, Summary of the High Plains Regional AquiferSystem Analysis in parts of Colorado, Kansas, Nebraska, 

New Mexico, Oklahoma, South Dakota, Texas, and 

Wyoming: U.S. Geological Survey Professional Paper 

1400–A, 30 p.

Weiss, J.S., 1992, Geohydrologic units of the coastal lowlands 

aquifer system, south-central United States: U.S. Geological 

Survey Professional Paper 1416–C, 32 p.

Williamson, A.K., and Grubb, H.F., 1997, Ground-water flow 

in the Gulf Coast aquifer systems, south- central United 

States: U.S. Geological Survey Professional Paper 1416–F, 

109 p.

Winslow, A.G., and Kister, L.R., 1956, Saline-water resources 

of Texas: U.S. Geological Survey Water-Supply Paper 1365, 

105 p., 9 pls.

Winslow, A.G., Hillier, D.E., and Turcan, A.N., Jr., 1968, 

Saline ground water in Louisiana: U.S. Geological Survey 

Hydrologic Atlas 310, 4 sheets.

Young, H.L., 1992, Summary of ground-water hydrology of 

the Cambrian-Ordovician aquifer system in the northern 

Midwest: U.S. Geological Survey Professional Paper 

1405–A, 55 p. 

Young, H.L., and Siegel, D.I., 1992, Hydrogeology of the 

Cambrian-Ordovician aquifer system in the northern 

Midwest, United States, with a section on ground-water 

quality: U.S. Geological Survey Professional Paper 1405–B, 

97 p. 

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Osborn and others—Hydrogeology, Distribution, and Volume of Saline Groundwater in the Southern Midcontinent and Adjacent Areas—SIR 2013–5017

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http://dx.doi.org/10.3133/sir20135017

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