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

J

SOUTH DAKOTA

WVOM/NG

NEW MEXICO

TEXAS

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U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 141,4-A
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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

By DONALD G. JORGENSEN, JOHN O. HELGESEN, DONALD C. SIGNOR, 

ROBERT B. LEONARD, JEFFREY L. IMES, and SCOTT C. CHRISTENSON

REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1 4 1 4 A
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

Any use of trade, product, or firm names in this publication

is for descriptive purposes only and does not imply

endorsement by the U.S. Government.

Library of Congress Cataloging in Publication Data

Jorgensen, Donald G.

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/ by Donald G. Jorgensen...[et. al.].

67 p. cm. (Regional aquifer-system analysis Central Midwest) (U.S. Geological Survey professional paper ; 1414-A) 

Includes bibliographical references (p. 65-67). 

Supt. of Docs. no. I 19.16:1414-A

1. Aquifers Middle West. I. Jorgensen, Donald G. II. Series. Ill Series: U.S. Geological Survey professional paper : 1414-A. 

GB1199.3.M54A63 1996.

553.7'9'0977-dc20 96-27549

CIP 

ISBN 0-607-87032-X

For sale by the U.S. Geological Survey, Branch of Information Services, Box 25286,

Federal Center, Denver, CO 80225.
FOREWORD

THE REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM

The Regional Aquifer-System Analysis (RASA) Program was started 

in 1978 following a congressional mandate to develop quantitative appraisals of the major ground-water systems of the United States. The RASA 

Program represents a systematic effort to study a number of the Nation's 

most important aquifer systems, which in aggregate underlie much of the 

country and which represent an important component of the Nation's total 

water supply. In general, the boundaries of these studies are identified by 

the hydrologic extent of each system and accordingly transcend the political 

subdivisions to which investigations have often arbitrarily been limited in 

the past. The broad objective for each study is to assemble geologic, 

hydrologic, and geochemical information, to analyze and develop an understanding of the system, and to develop predictive capabilities that will 

contribute to the effective management of the system. The use of computer 

simulation is an important element of the RASA studies, both to develop an 

understanding of the natural, undisturbed hydrologic system and the 

changes brought about in it by human activities, and to provide a means of 

predicting the regional effects of future pumping or other stresses.

The final interpretive results of the RASA Program are presented in 

a series of U.S. Geological Survey Professional Papers that describe the 

geology, hydrology, and geochemistry of each regional aquifer system. Each 

study within the RASA Program is assigned a single Professional Paper 

number, and where the volume of interpretive material warrants, separate 

topical chapters that consider the principal elements of the investigation 

may be published. The series of RASA interpretive reports begins with 

Professional Paper 1400 and thereafter will continue in numerical sequence 

as the interpretive products of subsequent studies become available.

Gordon P. Eaton 

Director

CONTENTS

	Page

Abstract..................................................................................... Al

Introduction............................................................................... 2

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

Physical Setting ................................................................... 2

Study Approach ................................................................... 3

Acknowledgments................................................................. 5

Geology and Paleohydrology ...................................................... 8

Geohydrology............................................................................. 18

Plains Subregion................................................................... 19

Western Interior Plains Aquifer System ......................... 19

Geohydrologic Units ............................................. 19

Properties............................................................. 21

Model Analysis and Hydrologic Budget ................ 24

Use and Potential ................................................. 28

Western Interior Plains Confining System ..................... 28

Geologic Definition and Correlation ...................... 28

Properties............................................................. 31

	Pago

Use and Potential ................................................. A32

Great Plains Aquifer System .......................................... 34

Geohydrologic Units ............................................. 34

Properties............................................................. 36

Model Analysis and Hydrologic Budget ................ 37

Use and Potential ................................................. 40

Great Plains Confining System and Related Hydrologic

Units........................................................................ 46

Ozark Subregion................................................................... 47

Ozark Plateaus Aquifer System ...................................... 48

Geohydrologic Units ............................................. 49

Properties............................................................. 53

Model Analysis and Hydrologic Budget ................ 55

Use and Potential ................................................. 56

Geochemistry of Regional Aquifers ............................................ 62

References Cited......................................................................... 65

ILLUSTRATIONS

FIGURES 1-6. Maps showing:

1. Location and extent of study area ................................................................................................................................. A3

2. Regional aquifer-system analyses contiguous to the Central Midwest regional aquifer-system analysis ........................ 4

3. Physiographic subdivisions............................................................................................................................................ 5

4. Climatic characteristics of central United States, 1931-60 ............................................................................................ 6

5. Estimated annual recharge to exposed geohydrologic units of the Central Midwest RASA, 1951-80 ............................ 7

6. Regional geology of central United States ..................................................................................................................... 9

7. Generalized geologic sections across study area .................................................................................................................... 10

8-16. Maps showing:

8. Major faults .................................................................................................................................................................. 11

9. Major structural features .............................................................................................................................................. 12

10. Precambrian and Late Cambrian geographic and geologic conditions ........................................................................... 13

11. Early Devonian geographic and geologic conditions ...................................................................................................... 14

12. Early Mississippian geographic and geologic conditions ................................................................................................ 15

13. Early Permian geographic and geologic conditions ........................................................................................................ 16

14. Late Triassic geographic and geologic conditions .......................................................................................................... 17

15. Early Cretaceous geographic and geologic conditions .................................................................................................... 18

16. Predevelopment equivalent-freshwater head in Cambrian and Ordovician rocks ........................................................... 20

17. Geohydrologic section showing major regional geohydrologic units and regional flow in the Plains and Ozark subregions ... 21 

18-28. Maps showing:

18. Dissolved-solids concentrations in water from lower units in the Western Interior Plains aquifer system

and the Ozark and St. Francois aquifers in the Ozark Plateaus aquifer system ............................................................. 22

19. Extent of major aquifer systems ................................................................................................................................... 23

20. Estimated regional intrinsic permeability of lower units in the Western Interior Plains aquifer system ........................ 25

21. Estimated regional intrinsic permeability of upper unit in the Western Interior Plains aquifer system ........................ 26

22. Model-computed and field hydraulic head for model layer 5 representing lower units in the Western

Interior Plains aquifer system and the Ozark and St. Francois aquifers in the Ozark Plateaus aquifer system ............. 27

23. Lateral flow-velocity vectors for model layer 4 representing upper unit in the Western Interior Plains

aquifer system and the Springfield Plateau aquifer in the Ozark Plateaus aquifer system ............................................. 29

V
VI CONTENTS

Page

FIGURE 24. Lateral flow-velocity vectors for model layer 5 representing lower units in the Western Interior Plains

aquifer system and the combined Ozark aquifer, St. Francois confining unit, and St. Francois aquifer in the

Ozark Plateaus aquifer system ...................................................................................................................................... 30

25. Estimated regional intrinsic permeability of the Western Interior Plains confining system ........................................... 32

26. Thickness of evaporite deposits in the Western Interior Plains confining system .......................................................... 33

27. Dissolved-solids concentrations in water from rocks older than those of the Great Plains aquifer system

at depths less than 500 feet ........................................................................................................................................... 34

28. Potentiometric surface and extent of Great Plains aquifer system in North America .................................................... 35

29. Geohydrologic section showing Maha and Apishapa aquifers, Great Plains aquifer system .................................................. 36

30-36. Maps showing:

30. Predevelopment potentiometric surface of the Maha aquifer, Great Plains aquifer system ........................................... 37

31. Thickness of Great Plains aquifer system ...................................................................................................................... 38

32. Estimated regional intrinsic permeability of the Great Plains aquifer system ............................................................... 39

33. Comparison of field or estimated and simulated predevelopment hydraulic-head distributions for Maha aquifer .......... 41

34. Simulated vertical volumetric flow between Maha aquifer and overlying units ............................................................. 42

35. Simulated vertical volumetric flow between the Great Plains aquifer system and underlying units ............................... 43

36. Inferred hydraulic-head declines in Denver Basin and simulated hydraulic-head declines in response to

development of Great Plains aquifer system .................................................................................................................. 44

37. Graphs showing observed and simulated water-level changes at selected locations in Great Plains aquifer system .............. 45

38. Graph of simulated changes in recharge, discharge, and storage in response to 1940-79 pumpage from

Great Plains aquifer system ................................................................................................................................................. 46

39-48. Maps showing:

39. Geohydrologic units overlying regional aquifer systems in the Plains subregion ............................................................ 47

40. Thickness of Great Plains confining system ................................................................................................................... 48

41. Physiographic features of the Ozark subregion .............................................................................................................. 49

42. Outcrop areas of regional geohydrologic units in and adjacent to the Ozark Plateaus physiographic province .............. 51

43. Predevelopment potentiometric surface of the Ozark aquifer ......................................................................................... 53

44. Thickness of Ozark aquifer ............................................................................................................................................ 54

45. Recharge to water table as estimated by Dugan and Peckenpaugh (1985) and redistributed recharge to

account for water that remains internal to a cell of the Ozark model ............................................................................ 57

46. Distribution of lateral hydraulic conductivity and transmissivity for Ozark model layer 2 ........................................... 58

47. Distribution of lateral hydraulic conductivity and transmissivity for Ozark model layer 3 ........................................... 59

48. Distribution of lateral hydraulic conductivity and transmissivity for Ozark model layer 4 ........................................... 60

49. Sketch showing ground-water budget of the Ozark Plateaus aquifer system based on simulation ......................................... 61

50-52. Maps showing:

50. Chloride concentrations in water from lower units in the Western Interior Plains aquifer system and the

Ozark and St. Francois aquifers in the Ozark Plateaus aquifer system .......................................................................... 63

51. Chloride concentrations in water from upper unit in the Western Interior Plains aquifer system and the

Springfield Plateau aquifer in the Ozark Plateaus aquifer system .................................................................................. 64

52. Dissolved-solids concentrations in water from upper unit in the Western Interior Plains aquifer system

and the Springfield Plateau aquifer in the Ozark Plateaus aquifer system ..................................................................... 66

TABLES

Page

TABLE 1. Generalized correlation of geohydrologic units to stratigraphic units in most of the Plains subregion .................................. A24

2. Water in storage in geohydrologic units in the CMRASA area ............................................................................................. 31

3. Generalized correlation of geohydrologic units to stratigraphic units in most of the Ozark subregion .................................. 50
CONTENTS VII

Page

CONVERSION FACTORS

Multiply

inch (in.)

foot (ft)

square foot (ft2 )

mile (mi)

square mile (mi2 )

acre-foot (acre-ft)

gallon (gal)

million gallons (Mgal)

foot per second (ft/sj

square foot per second (ft 2/s)

cubic foot per second (ft3/s)

gallon per minute ( gal/mm)

gallon per day (gal/d)

By

25.4

0.3048

0.09290

1.609

2.590

1,233

3.785

3,785

0.3048

0.09290

0.02832

0.06309

0.06309

To obtain

millimeter

meter

square meter

kilometer

square kilometer

cubic meter

liter

cubic meter

meter per second

square meter per second

cubic meter per second

liter per second

liter per day

Temperature in degree Fahrenheit (°F) can be converted to degree Celsius (°C) as follows:

SEA LEVEL

In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929) a geodetic datum derived from a 

general adjustment of the first-order level nets of the United States and Canada, formerly called "Sea Level Datum of 1929."

REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

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

By DONALD G. JORGENSEN, JOHN O. HELGESEN, DONALD C. SIGNOR, ROBERT B. LEONARD, 

JEFFREY L. IMES, and SCOTT C. CHRISTENSON

ABSTRACT

Three regional aquifer systems were investigated in a 

370,000-square-mile area extending from the foothills of the Rocky 

Mountains in Colorado to the Mississippi River in eastern Missouri, 

and from South Dakota to mountainous parts of Arkansas and Oklahoma. These aquifer systems and internal confining systems are composed of sedimentary rocks ranging in age from Cambrian through 

Cretaceous. The study area is informally divided into the Plains 

subregion and Ozark subregion.

Along the physiographic boundary between the Plains subregion 

and the Ozark subregion, two regional ground-water flow systems are 

laterally adjacent. In general, regional ground-water flow is outward 

from the uplands in the Ozark Plateaus and eastward from the western part of the Interior Plains. The approximate location of the 

boundary between these two flow systems is a broad physiographic 

low that roughly parallels the Central Lowland province.

The Western Interior Plains aquifer system in the Plains subregion consists of water-bearing dolostone, limestone, and shale. The 

lower units of this aquifer system are composed mostly of dolostone 

and sandstone of Cambrian and Ordovician age, and an upper unit is 

composed mostly of limestone of Mississippian age. The upper unit 

and lower units are separated at most locations by a confining unit of 

very slightly permeable shale. Porosity and permeability in the aquifer system, especially primary porosity, are a function of depth. Secondary porosity is a function of diagenesis, especially fracturing and 

dissolution. Dissolved-solids concentrations in water in the aquifer 

system range from less than 10,000 to more than 300,000 mg/L (milligrams per liter). Most water is a sodium chloride type, with chloride concentrations as large as 190,000 mg/L. A numerical-model 

analysis of flow in the aquifer system indicates that fluid velocities 

are extremely slow, and little flow moves out of a geopressured zone 

in the Anadarko Basin.

The Western Interior Plains confining system restricts flow 

between the Western Interior Plains aquifer system and overlying 

geohydrologic units, principally the Great Plains aquifer system and 

the High Plains aquifer. The confining system is composed of rocks 

ranging in age from Pennsylvanian through Jurassic. The confining 

system consists mostly of very slightly permeable shale beds, which 

are confining units, and sandstones and limestones, which are

aquifers in some areas. In part of the Anadarko Basin, the lower 

sandstone beds in the confining system are geopressured. The 

geopressure is transmitted but attenuated to the subjacent Western 

Interior Plains aquifer system. Formations of Permian age include 

halite and gypsum as well as shale, limestone, and sandstone. These 

evaporite deposits are only slightly permeable and, where present, 

virtually eliminate vertical flow through the system.

The Great Plains aquifer system consists of two regional aquifers 

separated in much of the area by a confining unit. The lower aquifer, 

the Apishapa, is not as areally extensive as the upper aquifer, the 

Maha (which consists mostly of the Dakota Sandstone). Concentrations of dissolved solids in the water in this aquifer system exceed 

5,000 mg/L in most of the interior part of the system; concentrations 

of less than 1,000 mg/L exist in recharge areas. A regional flow 

model indicates that the predevelopment, steady-state flow rate was 

about 342 ft 3/s (cubic feet per second), most of which represented 

leakage to or from vertically adjacent units near the edges of the 

aquifer system rather than lateral flow from or to outcrop areas. The 

aquifer system is recharged mainly at outcrops in southeastern Colorado and northeastern New Mexico. Transient simulations show that 

oil and gas development in the Denver Basin and development of 

freshwater in other areas have resulted in declines in the potentiometric surface. Withdrawals of about 800 ft3/s during 1970-79 were 

derived mostly from induced recharge or intercepted discharge to 

overlying units or to a lesser extent from storage depletion.

The Ozark subregion is an area of highly dissected karstic terrain 

characterized by numerous streams and springs. Nearly all well 

water or spring water in the subregion is from the Ozark Plateaus 

aquifer system. The Ozark Plateaus aquifer system consists of five 

units, which from bottom to top are the St. Francois aquifer, St. 

Francois confining unit, Ozark aquifer, Ozark confining unit, and the 

Springfield Plateau aquifer. Recharge to all the aquifer units is from 

precipitation. Discharge is mostly to the streams of the Ozarks and 

the Missouri, Mississippi, and other rivers along the perimeter of the 

subregion. Water in the aquifer system is a calcium bicarbonate type 

and generally has dissolved-solids concentrations less than 500 mg/L. 

Regional predevelopment flow of 7,091 ft3/s through the

Al
A2 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

aquifer system was simulated. Pumping rates are small compared to 

the large natural rates of recharge and discharge.

INTRODUCTION

The study area of the Central Midwest Regional 

Aquifer-System Analysis (CMRASA) includes about 

370,000 mi 2 (fig. 1). It extends from the foothills of 

the Rocky Mountains in Colorado to the Missouri and 

Mississippi Rivers in eastern Nebraska and Missouri 

and from South Dakota to the Ouachita, Arbuckle, 

and Wichita Mountains in Arkansas and Oklahoma.

Several important regional-aquifer systems containing both fresh and saline water were studied. 

Prior to this study, little was known about the 

regional flow and hydrochemistry of aquifer systems 

in much of the area.

Within the central United States, four other 

regional aquifer-system analyses (RASA) (fig. 2) share 

geographic or hydrologic boundaries with this study. 

These other RASA studies are the High Plains (Weeks 

and others, 1988), the Northern Great Plains 

(Downey and Dinwiddie, 1988), the Northern Midwest (Young, 1992), and the Gulf Coast (Grubb, in 

press).

PURPOSE AND SCOPE

The investigation summarized in this report is one 

of several studies of the U.S. Geological Survey's 

Regional Aquifer-System Analysis (RASA) program, 

which is described in the "Foreword." The background, purpose, scope, objectives, and planned 

approach of this study are described in the projectplanning report (Jorgensen and Signer, 1981). The 

major purpose of the CMRASA study is to describe 

the water resources in the regional aquifers that occur 

in rocks of Cambrian through Cretaceous age. In 

most of the study area, except for the Ozarks of southern Missouri, northwestern Arkansas, southeastern 

Kansas, and northeastern Oklahoma, little is known 

about these water resources. Other purposes of the 

study are to evaluate potential uses of the water considering quantity, current use, water quality, and contamination. The scope of the study does not 

specifically include the High Plains aquifer, although, 

at a few locations, the High Plains aquifer is in direct 

hydraulic connection with aquifer units of the 

CMRASA. The High Plains aquifer is a separate 

regional aquifer that overlies some of the units 

described herein.

The findings of the CMRASA are reported in five 

chapters of U.S. Geological Survey Professional Paper

1414: Chapter A (this report) is the summary chapter, 

which collates the important findings reported in other 

chapters; chapter B describes the geohydrologic 

framework; chapter C describes the modeling analysis 

of the regional aquifer systems; chapter D describes 

the geohydrologic and model analyses of the Ozark 

Plateaus aquifer system; and chapter E describes the 

geohydrologic and model analyses of the Great Plains 

aquifer system.

PHYSICAL SETTING

Much of the study area is bounded laterally by 

major geologic structural features (Rocky Mountain 

Uplift on the west, the Sioux Uplift on the northeast, 

and a series of uplifts on the south), or by major rivers 

(Mississippi, Missouri, and Arkansas Rivers) and 

includes parts of two major physiographic divisions 

(Interior Plains and Interior Highlands). The Interior 

Plains includes the Great Plains and the Central Lowland, and the Interior Highlands includes the Ozark 

Plateaus and the Ouachita Province (fig. 3). The Ouachita Province includes the Arkansas Valley, which is 

between the Boston Mountains of the Ozark Plateaus, 

and the Ouachita Mountains south of the study area.

Land-surface altitude ranges from less than 500 ft 

along the Fall Line on the Mississippi Alluvial Plain 

and the Arkansas Valley to about 6,000 ft in the 

extreme western part of the area adjacent to the 

Rocky Mountains. Topography of the Ozark Plateaus 

is hilly to rugged and is mostly covered with hardwood forest, whereas most of the Interior Plains area 

is characterized by a relatively flat land surface and 

vegetation cover is mostly grass and rowcrops.

Characteristics related to climate, including runoff 

and potential evapotranspiration, are shown in 

figure 4. Precipitation for 1931-60, which included 

two major droughts (1933-37 and 1952-57), ranged 

from more than 40 in. in the Ozark Plateaus to 12 in. 

in eastern Colorado (Eagleman, 1976, fig. 3). Potential evapotranspiration greatly exceeds precipitation 

(fig. 4). Another regional study (Dugan and Peckenpaugh, 1985) determined that the amount of water 

passing the root zone and recharging the water table 

during 1951-80 ranged from more than 15 in. annually 

in part of the Ozarks to less than 1 in. annually in 

Colorado (fig. 5). The southeastern part of the study 

area has abundant water resources, especially surface 

water. Annual surface-water runoff ranged from more 

than 25 in. in the Ozark Plateaus to 1 in. or less in 

western Kansas and eastern Colorado during 1931-60. 

Annual runoff exceeded 27 in. during 1951-80 in the 

Ozarks (Hedman and others, 1987). Most of the
REGIONAL AQUIFERS SUMMARY A3

105

Ouachita 

Arbuckle Mountains

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

FIGURE 1. Location and extent of study area.

western part of the study area is deficient in surface 

water but has substantial ground-water resources, 

mainly the High Plains aquifer, which overlies some of 

the aquifers described in this report.

STUDY APPROACH

Large quantities of hydrologic, geologic, and 

water-quality data were collected, evaluated for accuracy and adequacy, and collated into data files (Helgesen and Hansen, 1989). In general, these data are 

available in the District offices of the U.S. Geological 

Survey in each state. Much of the data are available 

in publications, including data reports, and as computer-stored data. On the basis of data and other general information, a conceptual model of the hydrologic 

system was developed. Computer models of the

aquifer were constructed to test the conceptualization 

of hydrologic-system operation. The computer models 

required extensive information on numerous aquifer 

properties and hydrologic relations. Data for various 

models were not always available; in these cases, special studies were conducted to obtain the additional 

data or information. Also, special techniques to estimate the information needed for the models were 

developed to supplement available information. The 

computer models also were used to improve estimates 

of hydrologic data.

Water-chemistry data were evaluated for accuracy 

and plotted or otherwise displayed. The resulting 

maps and displays were interpreted in reference to 

geochemical processes that could produce observed 

geochemical conditions. The geochemical processes 

were, in turn, evaluated to determine whether they
A4 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

10°

35

EXPLANATION

CENTRAL MIDWEST REGIONAL AQUIFER-SYSTEM ANALYSIS

HIGH PLAINS REGIONAL AQUIFER-SYSTEM ANALYSIS - 

Partly overlies Central Midwest RASA study area

NORTHERN GREAT PLAINS REGIONAL AQUIFER-SYSTEM ANALYSIS 

NORTHERN MIDWEST REGIONAL AQUIFER-SYSTEM ANALYSIS 

GULF COAST REGIONAL AQUIFER-SYSTEM ANALYSIS

FIGURE 2. Regional aquifer-system analyses contiguous to the Central Midwest regional aquifer-system

analysis (RASA).

were consistent with flow processes simulated by the 

computer models.

Finally, the information and results of the modeling and geochemical analyses were interpreted in reference to potential use of the water resources. The 

study was diverse and wide in scope and required a 

multidiscipline team approach.

Many supplementary studies were conducted as 

part of the larger study. An extensive study to determine the quantity of flow to the water table was conducted by Dugan and Peckenpaugh (1985) and by 

Dugan (1986). Several detailed surface-water analyses were made to investigate ground-water and surface-water interchange: Hedman and others (1987) 

investigated the low-flow characteristics of streams in

the Ozark subregion; Hedman and Engel (1989) investigated the low-flow characteristics of the Plains subregion; and Hedman and Jorgensen (1990) 

investigated hydrologic relations between the Missouri 

River, the Missouri River alluvial valley, and the 

regional aquifers in a reach of the Missouri River 

between Yankton, South Dakota, and St. Louis, Missouri. Special techniques were developed for the study 

including (1) log analyses to estimate permeability 

(Jorgensen, 1989), (2) ground-water and surface-water 

interaction (Jorgensen and others, 1989a and b), (3) 

simulation of oil and gas withdrawals in a 

ground-water model, and (4) a method for determining direction of flow in an aquifer containing water of 

variable density (Jorgensen and others, 1982).
REGIONAL AQUIFERS SUMMARY A5

105

SOUTH DAKOTA

Boundary of stud

Springfield - j 

Salem Plateaus

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

^mmmmm PHYSIOGRAPHIC-DIVISION BOUNDARY Dashed where approximate

 PHYSIOGRAPHIC-PROVINCE BOUNDARY Dashed where approximate

- PHYSIOGRAPHIC-SECTION BOUNDARY

FIGURE 3. Physiographic subdivisions (modified from Fenneman, 1946).

ACKNOWLEDGMENTS

The plan for this investigation was developed with 

the assistance of the Arkansas Geological Commission, 

the Colorado Geological Survey, the Kansas Geological Survey, the Missouri Division of Geology and 

Land Survey, the Nebraska Conservation and Survey 

Division, the South Dakota Geological Survey, and 

the Oklahoma Geological Survey.

The study was greatly aided by a Liaison Committee between State agencies and the U.S. Geological 

Survey. The Liaison Committee not only disseminated information concerning the study to State agencies but also helped identify sources of data, defined 

areas of concern, and made valuable suggestions that 

aided the study. Committee members included: 

Orville Wise, Arkansas Geological Survey Commission; Robert Longenbaugh, Office of Colorado State 

Engineer; William Hambleton, Kansas Geological Survey; Donald Miller, Missouri Division of Geology and 

Land Survey; Verlon Vrana, Nebraska Natural 

Resources Commission; and Robert Arndt, Oklahoma 

Geological Survey.
A6 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

J FMAMJJASOND 

MONTH 200 MILES

200 KILOMETERS

EXPLANATION

CLIMATIC CHARACTERISTICS GRAPHS 

Moisture deficit

Moisture surplus

Potential evapotranspiration

Precipitation

Actual evapotranspiration

LINE OF EQUAL ANNUAL RUNOFF Interval, in inches, is variable 

LINE OF EQUAL ANNUAL PRECIPITATION Interval 12 inches 

LINE OF EQUAL ANNUAL POTENTIAL EVAPOTRANSPIRATION Interval 10 inches

FIGURE 4. Climatic characteristics of central United States, 1931-60 (precipitation and evapotranspiration from

Eagleman, 1976; runoff from Busby, 1966).

-10-
REGIONAL AQUIFERS SUMMARY A7

105° 100

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

RANGE OF MEAN ANNUAL RECHARGE Values in inches 

| | Less than 0.1 | | 0.5-1.0 |^^| 5 - 10

| | 0.1 - 0.25 | | 1-2 |^^ 10-15

I I 0.25 - 0.50 Ififij 2-5 HJH More than 15

RECHARGE AREA WHERE CENTRAL MIDWEST REGIONAL 

AQUIFER-SYSTEM ANALYSIS GEOHYDROLOGIC UNITS 

ARE NOT EXPOSED

FIGURE 5. Estimated annual recharge to exposed geohydrologic units of the Central Midwest RASA, 1951-80 (from Dugan and

Peckenpaugh, 1985).

The study also was served by a stratigraphy advisory group that included: Orville Wise, Arkansas 

Geological Commission; Richard Pearl, Colorado Geological Survey; P. Alien Macfarlane, Kansas Geological Survey; Thomas Thompson, Missouri Division of 

Geology and Land Survey; Marvin Carlson, Nebraska

Conservation and Survey Division; and Charles Mankin, Oklahoma Geological Survey. This group, along 

with Claire Davidson of the Geological Names Committee of the U.S. Geological Survey, contributed significantly to the resolution of problems related to 

stratigraphic correlation and nomenclature.
A8 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

GEOLOGY AND PALEOHYDROLOGY

The C MR AS A study area lies within the stable 

interior of the North American continent. The hydrologic boundaries of the area are largely controlled by 

structural features. Since Cambrian time, most of the 

study area has undergone relatively gentle 

deformation involving upwarp and downwarp of the 

Earth's crust over large areas. Structurally, the 

CMRASA area has been dominated by broad basins 

and arches. Accordingly, most folding of sedimentary 

rocks has been subtle, and there are few major fault 

zones of regional significance. However, along the 

south and west margins of the study area, strong 

crustal deformation from mountain-building forces 

resulted in intense folding and faulting. The lateral 

change from simple to complex geologic structure was 

the major factor in defining the southern and western 

boundaries of the study area. The structural change is 

relatively abrupt in most locations, but is transitional 

in others.

The present areal distribution of major timestratigraphic units in the CMRASA study area is 

shown in figure 6. Geologic sections (fig. 7) illustrate 

the general regional continuity of the units; the severest structural deformation is along the south and west 

margins of the study area. Faulting (fig. 8) was substantial in these areas and caused a major offset of 

rock units. Most faults in the interior of the study 

area have much less offset than the offsets of the 

faults along the south and west margins.

Although structural deformation is not severe over 

most of the study area, stratigraphic nomenclature 

still differs markedly among States and structural 

areas (fig. 9; Jorgensen and others, 1993, plate 1). 

Hundreds of recognized geologic names have been 

assigned to rock units within the thick stratigraphic 

interval. The geologic units, either singly or in combination, form the geohydrologic units described in this 

study.

The present hydraulic characteristics and flow systems result from past geologic processes. A brief summary of geologic history is presented with special 

emphasis on the changes and processes that have 

resulted in the present hydraulic characteristics of the 

rocks, chemistry of the water, and distribution of the 

flow systems. Additional information is presented in 

Jorgensen (1993).

Rocks of Precambrian age underlie the stratigraphic section of interest to this study (Jorgensen 

and others, 1993, plate 2); they consist mainly of igneous and metamorphic rocks of various types that 

together form the so-called "basement complex." Deep 

burial of these rocks at most locations has precluded

detailed knowledge of their nature. The geologic configuration of the rocks of Precambrian age over most 

of the study area has been mapped by Sims (1985).

Information concerning faults and fractures in the 

rocks of Precambrian age is of special importance 

because these features mark zones of weakness in the 

rocks that were reactivated at various intervals during 

geologic time. The orientation of fractures, faults, and 

anticlines also indicates something about the tectonic 

stresses on the rocks.

Large faults oriented to the present northwestsoutheast existed in Precambrian time. This alignment is the same as the boundary between metamorphic and igneous rocks of Precambrian age in the 

region (Warner, 1980, p. 14). Warner concludes that 

the central United States was moderately mobile during Precambrian time. Precambrian tectonic activity 

may have started the Transcontinental Arch (fig. 10). 

Lineaments within rocks of Precambrian age mapped 

by Hayes '1962) are aligned North 50° West and 

North 65° East.

The top of the basement surface represents a major 

unconformity (resulting from a long period of erosion 

or nondeposition). Permeable broken or weathered 

rock on the basement surface, sometimes termed 

"granite wash," is included in the rocks studied 

because of its sediment-like character. Faulting and 

fracturing of competent rocks in the basement complex established permeable paths for ground-water 

flow and created anisotropic permeability. The alignment of faults and fractures and other lineaments 

changed somewhat during the Paleozoic Era but kept 

the general trends of approximately North 35° West 

and North 55 ° East.

At the beginning of the Cambrian Period, the 

study area was above sea level, and rocks of Precambrian age were being eroded. Erosion continued 

through Middle Cambrian. However, during Late 

Cambrian, the area was inundated, except for the 

Transcontinental Arch and small islands, by a marine 

sea (fig. 10). The first deposits were nearshore sand, 

parent material of the Lamotte, Sawatch, and Reagan 

Sandstones. Calcareous mud was deposited in some 

areas along with the sand. The thickest sediment was 

deposited in a subsiding basin that extended from central Oklahoma through central Arkansas. The advances of the sea were interrupted by periods of sea recession. During the recessions, sand and calcareous mud 

was lithified to sandstone and limestone. The entire 

study area, except for the center of the present Anadarko and Arkoma Basins, was above water at some 

time. The saline water deposited with the sediment 

probably was flushed from the Cambrian mantle and 

subjacent rocks. Erosion removed overburden load
REGIONAL AQUIFERS SUMMARY A9

200 KILOMETERS

EXPLANATION

QUATERNARY DEPOSITS

TERTIARY DEPOSITS

Mz MESOZOIC ROCKS Cretaceous. Jurassic, and Triassic age 

UPz UPPER PALEOZOIC ROCKS Permian, Pennsylvanian, and Mississippian age 

MPz MIDDLE PALEOZOIC ROCKS Devonian and Silurian age 

LPz LOWER PALEOZOIC ROCKS Ordovician and Cambrian age

PRECAMBRIAN ROCKS

A'

TRACE OF SECTION Shown in figure 7 

CONTACT 

FIGURE 6. Regional geology of central United States (modified from Kinney, 1966).
AID REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

FEET " Zone of 2 

complex o 

.geology U

10,000 1

5.000 

SEA 

LEVEL

5.000 

10,000-

Quaternary and Tertiary deposits 5-^

Mesozoic rocks

B

o< »§

5,000 |

SEA 

LEVEL

5,000 _

10,000 

15,000 

20,000 

25,000 

30,000 

35,000 

Zoneof 

complex 

geology

Quaternary and Tertiary deposits 

Mesozoic rocks

B1

Paleozoic rocks

/ / ' .- OVO

I / 'W~< > -'$^£

]f I ^~ ' /' . . ' ^ I I' ^ ' ' ^ i

- .

' -/ , - Precambrian rocks ''_ ' , > --', " ~

VERTICAL SCALE GREATLY EXAGGERATED

0 100 200 300 MILES

I I I 

0 100 200 300 KILOMETERS

EXPLANATION 

FAULT Arrows show direction of movement

FIGURE 7. Generalized geologic sections across study area; 

location of sections shown in figure 6.

and resulted in extensional fracturing. The fracturing 

created secondary permeability but, more importantly, created paths along which dissolution, especially of calcareous material, occurred. At some 

locations, especially near coastlines, rocks containing

saline water were in contact with fresh ground water 

from the land masses. At these locations, dissolution 

and dolomitization occurred.

During the Ordovician Period, the OklahomaArkansas Basin continued to subside and the Ozark 

Uplift began. Sediment thickness in excess of 6,000 ft 

accumulated. Compaction of the sediment squeezed 

water from the rock as primary porosity was reduced. 

At temperatures normally found at depths of 5,000 ft 

or greater, thermal diagenesis of organic material and 

clay minerals could be expected. Thermal 

diagenesis of organic material results in the production 

of C02 (carbon dioxide), water, and hydrocarbons. 

Thermal diagenesis of clay results in liberation of 

water and the changing of smectite to illite. These 

processes generate pressure and generally create fluids 

rich in C0 2 that, in turn, result in the dissolution of 

selected carbonate and silicious material and selectively increase secondary porosity and permeability. 

Most sediment of Ordovician age was nearshore calcareous mud, largely algal lime. As during Late Cambrian time, the sea was cyclic but generally advancing. 

During periods of sea recession, the calcareous mud 

was lithified to limestone, and dolomitization occurred 

near coastlines. Erosion removed sediment and 

resulted in extensional fracturing, which, in turn, created paths for dissolution of carbonate and other rock 

material by near-surface ground water of meteoric origin. All processes, in general, increased porosity and 

permeability.

Nearly the entire study area, except for southern 

Oklahoma, Arkansas, and the present Salina Basin, 

was uplifted during the Silurian and Devonian Periods 

(fig. 11). The exposed rocks were severely eroded; 

large quantities of pre-Silurian rock were removed, 

resulting in unloading and extensional fracturing. 

Regional flow systems of ground water of meteoric origin developed and flushed the formational waters from 

the rocks of Cambrian and Ordovician age. Near-surface dissolution of carbonate material greatly 

increased the permeability of the exposed rocks. At 

the end of the Devonian, or possibly during very early 

Mississippian time, the transgressing sea is believed to 

have completely submerged the area exclusive of the 

Transcontinental Arch. Sand was deposited nearshore, 

and extensive clay was deposited offshore. The extensive clay of very slight permeability restricted fluid 

flow from the underlying carbonate rocks to the overlying sediment. The dominant positive element during 

Early Mississippian time was the Colorado-Wyoming 

Uplift, and the dominant negative element was the 

subsiding Anadarko Basin (fig. 12). The most important characteristic of the Mississippian Period was the 

active tectonism that initiated large structural
REGIONAL AQUIFERS SUMMARY All

105

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

THRUST FAULT Sawteeth on overthrust side 

NORMAL FAULT Hachures on downthrown side

 CONCEALED FAULT

FIGURE 8. Major faults (modified from King, 1968; Sims, 1985; Krueger and Keller, 1986).

features, which henceforth were to affect geology and 

hydrology. In addition to the Colorado-Wyoming 

Uplift and the Anadarko Basin, the Nemaha Uplift 

(Ridge) and the Arkoma Basin (Ouachita Trough) 

also were forming. Calcareous sediment was deposited 

in the shallow equatorial seas over the clay.

Late Mississippian time was characterized by a 

cyclic but generally receding sea and, by the end of 

the Mississippian, only the deeper parts of the Anadarko and Arkoma Basins were submerged. Thermal 

diagenesis of organic material continued in these

basins. Elsewhere lithification, erosion, fracturing, 

and dissolution occurred.

During Pennsylvanian time, large compressive 

stresses developed primarily north to south. The 

stresses probably were related to the collision of the 

African, South American, and North American plates. 

These stresses were relieved by downwarp and uplift. 

The uplift occurred in a wide arcuate belt along the 

west and southern boundaries of the study area, 

whereas the east-central part of the study area 

remained stable at or above sea level. The uplifts 

included the Front Range, Apishapa, Criner,
A12 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

105° 100 95°

[ Boundary of stud

r'St,jFrancbis 

Mountains

Hugoton 

Embayment

Wet Mountain 

UpNft 

Sangr 

de CristoX Raton Sedgwick /S/ Cherokee

Amarilfo UpHft 

TEXAS

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

FIGURE 9. Major structural features (modified from Carlson, 1963; Merriam, 1963; Oetking and others, 1966,1967; Bennison

and Chenoweth, 1984; Renfro, no date).

Amarillo, Wichita, Arbuckle, Ouachita, Ozark, Nemaha, and the Cambridge-Central Kansas Uplifts; subsidence was mostly in the Anadarko and Arkoma 

Basins.

Most sediment of Pennsylvanian age was clay, 

sand, calcareous mud and, in the eastern part of the 

area, organic material. Rapid deposition of clay and 

sand in the Anadarko Basin may have trapped water, 

creating a geopressured zone in the sediments of Morrowan age. Pre-Pennsylvanian rocks were buried to 

depths of nearly 20,000 ft, and thermal diagenesis of 

organic material was rapid and nearly complete. The 

deep burial reduced primary porosity, but secondary 

porosity and permeability were increased in selected 

strata. Adjacent to the Front Range and the Amarillo-Wichita Uplifts (fig. 9), permeable arkosic sediment was deposited in a band a few tens of miles in

width. Fresh ground water from the adjacent uplifts 

moved through the arkosic deposits.

Permian time was a period of reduced tectonic 

activity compared to the Pennsylvanian. However, 

the effects of major activity during the Pennsylvanian 

were still being felt. The Early Permian sea, similar 

to the Late Pennsylvanian sea, was cyclic with alternate recessions and transgressions. During Leonardian 

time (Early Permian) and earlier, the seaway to the 

east through the Ozark area was closed as regional 

upward tilting occurred to the east. The closing of the 

seaway restricted circulation, increased salinity, and 

resulted in extensive evaporite deposition over nearly 

the entire CMRASA area (fig. 13). In addition to the 

regional tilting, uplift of the Ozarks continued. Major 

fracturing of the pre-Pennsylvanian carbonate rocks in 

the Ozark area occurred as a result of uplift stresses
REGIONAL AQUIFERS SUMMARY A13

Shallow sea 

(low Precambrian islandsP

\ ' Littorgl zone 

J (shallowicyclic sea; . 

sand and calcareous mud)

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

t

LAND AREA 

WATER AREA 

SUBSIDENCE

-h -J- -»-?-»-?-+ PRECAMBRIAN RIFT Queried where uncertain 

FIGURE 10. Precambrian and Late Cambrian geographic and geologic conditions.

and, later, of the reduction in stress caused by unloading (erosion). Rocks in the Ouachita Uplift were eroding or subsiding rapidly and, by the end of the Early 

Permian, little relief remained.

Tectonic activity in Colorado continued from the 

Pennsylvanian into the Permian. Arkosic sediment 

continued to be deposited along the Front Range, 

Apishapa, and Sierra Grande Uplifts. In Oklahoma, 

the Anadarko Basin continued to subside, and the

Wichita Uplift continued to rise. Detritus from the 

Wichita Uplift was a dominant source of sediment.

The sea retreated to the west during Late Permian 

time as the study area continued to be tilted upward 

to the east. At the end of the Permian, more than 

20,000 ft of Pennsylvanian-Permian sediment had 

been deposited in the Anadarko Basin. Most rocks of 

Permian age are shale, sandstone, limestone, and 

evaporite deposits. The sandstone and limestone are 

relatively permeable in comparison to evaporite and
A14 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

105'

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

LAND AREA 

WATER AREA 

FIGURE 11. Early Devonian geographic and geologic conditions.

shale. The extensive layers of shale and evaporite 

severely restricted flow to and from the subjacent 

rocks of pre-Pennsylvanian age.

At the end of Permian time, the rocks of Pennsylvanian age and, if present, Permian rocks around the 

St. Francois Mountains were being eroded. A regional 

flow system developed in the highly fractured, permeable rocks of Cambrian and Ordovician age. The 

extent of the regional flow system outward from the 

St. Francois Mountains (fig. 13) was controlled by 

topography and the extent of overlying confining 

shale.

Deposition during Early Triassic time occurred 

only in northwestern Colorado and western Nebraska. 

Red clay, calcareous mud, and dolomite were deposited in the sea with restricted circulation. During the 

Late Triassic, uplifts in central Colorado were being 

eroded rapidly, and the sediment was being deposited 

in a freshwater lake in the Dockum Basin (fig. 14).

In general during the Triassic, land masses within 

the CMRASA area had little relief and were not major 

sources of sediment. The erosion and removal of 

low-permeability rocks of Pennsylvanian and Permian 

age in the Ozark Uplift increased the extent of the
REGIONAL AQUIFERS SUMMARY A15

Shallow marine

sediment \

NEBRASKA

^ \ StTallpwtTiarine.

sedimeqt

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

LAND AREA I UPLIFT

WATER AREA r SUBSIDENCE 

FIGURE 12. Early Mississippian geographic and geologic conditions (modified from Craig and Varnes, 1979).

Ozark flow system. Permeability of the then-exposed 

carbonate rocks increased largely as a result of weathering and near-surface dissolution.

Most of the CMRASA area was above sea level 

during Jurassic time; however, a sea in which clay and 

sand were being deposited existed in the western part 

of the area. Subsidence along the present Mississippi 

Embayment was such that the Jurassic sea encroached 

into the new lowland. The Ozark ground-water flow 

system continued to expand as during the Triassic. At

the end of the Jurassic, the sea receded, and the entire 

CMRASA area was above sea level.

At the beginning of the Early Cretaceous Epoch, 

nearly the entire CMRASA area was above sea level, 

and the rocks were being eroded. This was ended by a 

transgression of the Cretaceous sea from the north and 

south. Moderately permeable fine-grained sand and 

intercalated clay were deposited on alluvial plains or 

in nearshore estuaries by the advancing sea. As the sea 

advanced, offshore clay replaced nearshore sand as the 

dominant sediment. This very slightly permeable
A16 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

ent\3(f Ozark groundwater flow system

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

LAND AREA 

WATER AREA

EVAPORITE DEPOSITS 

DOLOMITE

I I I I PRESENT EXTENT OF LEONARDIAN ROCKS Hachures 

point toward Leonardian-age rocks

AXIS OF UPLIFT

FIGURE 13. Early Permian (Wolfcampian-Leonardian) geographic and geologic conditions (modified from McKee and

others, 1967).

clay, which today forms the Kiowa Shale and equivalents, restricted vertical flow to the aquifer material 

below. The maximum extent of the Kiowa sea is 

unknown; however, it its likely that the sea covered 

the entire C MR ASA area with the exception of part of 

the Siouxan Arch and the Ozark Uplift (fig. 15). Clay 

deposition was ended by a recession of the sea, which 

was partly the result of regional uplift of the eastern

part of the study area. The Pascola Uplift in the 

bootheel area of southeastern Missouri may have been 

contemporaneous with this regional uplift.

A period of erosion ensued until it was interrupted 

by a second advance of the Early Cretaceous sea. 

During this second advance, permeable nearshore sand 

(parent material of the Dakota Sandstone) was deposited initially followed by clay. The maximum extent of
REGIONAL AQUIFERS SUMMARY A17

Base modified from U.S. Geological Survey 

1:7,600,000. National Atlas, 1970

EXPLANATION

LAND AREA 

WATER AREA

PRESENT AREA OF LATE TRIASSIC ROCKS 

? - SUBSIDENCE Queried where uncertain

FIGURE 14. Late Triassic (maximum sea) geographic and geologic conditions (modified from McKee and others, 1959).

the sea is not known exactly, except that it covered 

more than the present area of the Dakota Sandstone 

and may have covered most of the western part of the 

CMRASA area (fig. 15).

During Late Cretaceous time, clay was the dominant sediment, and maximum sedimentation was in 

the Denver Basin. Burial in the basin ranged from 

about 3,000 to 8,000 ft, and compaction reduced primary porosity and permeability. Thermal diagenesis

may have increased permeability locally in the buried 

sandstone of Early Cretaceous age. Near the end of 

the Cretaceous, many areas, such as the Front Range, 

were uplifted rapidly during the early part of the 

Laramide orogeny, and the sea receded northward as 

the western part of the area was again tilted upward.

The Laramide orogeny continued into Tertiary 

time as evidenced by mountain building in central 

Colorado and Wyoming. Extensive erosion of the
A18 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

105° 100'

j --r-marine clay 

COLORADO

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

LAND AREA 

WATER AREA 

- SUBSIDENCE r

FIGURE 15. Early Cretaceous (maximum sea) geographic and geologic conditions.

uplifted areas and widespread deposition of permeable 

alluvium on the plains followed. Regional 

ground-water flow from west to east in the Lower 

Cretaceous sandstone and in the underlying rocks of 

Cambrian to Mississippian age was established.

In the eastern part of the area, erosion continued 

to remove Pennsylvanian and Permian rocks from the 

Ozark area, and the Ozark flow system continued to 

develop in rocks of Cambrian to Mississippian age.

GEOHYDROLOGY

A hydraulic system delineated regionally can have 

more than one aquifer or confining unit and may 

include several formations and rock types. From a 

regional point of view, an aquifer also can contain a 

series of discontinuous confining units; however, the 

size of the discontinuous confining units is much 

smaller than the size of the delineated aquifer. On the
REGIONAL AQUIFERS SUMMARY A19

other hand, a confining unit also can contain discontinuous zones that are permeable. Again, the size of 

the permeable zones is much smaller than the size of 

the confining unit.

In a hydrologic analysis of large regions that contain many geohydrologic units, it is useful to employ 

the terms aquifer system and confining system. An 

aquifer system consists of two or more aquifers in the 

same hydraulic system that are separated at most 

locations by one or more confining units that impede 

ground-water movement but do not greatly affect the 

regional hydraulic continuity of the system. A confining system contains two or more confining units separated by one or more aquifers that are not in the same 

hydraulic system. A confining system acts collectively 

to restrict flow to and from external aquifers that are 

not in the same hydraulic system.

Geohydrologic units within the study area were 

defined by hydrologic relations and hydraulic properties of the sedimentary rocks. The relation of the 

geohydrologic unit to ground-water flow is essential in 

conceptualization of regional-aquifer systems. The 

flow within most regional aquifers is controlled by the 

altitudes of major recharge areas, major discharge 

areas, and major structural features. Thus, topography is a major control on ground-water flow in 

regional aquifer systems.

Geohydrologic units in the CMRASA area, except 

adjacent to major structural uplifts, such as the 

Rocky Mountains, the Amarillo, Wichita, Arbuckle, 

and Ouachita Uplifts, and other areas of complex 

stratigraphic relations, coincide or correlate to a considerable degree with regional stratigraphic units. 

Along the physiographic boundary between the Interior Plains and the Interior Highlands (fig. 3) two 

regional ground-water flow systems are laterally adjacent. Regional flow westward in the Ozark Plateaus 

aquifer system merges with eastward flow in the Western Interior Plains along the physiographic boundary. 

The approximate location of the boundary between 

these two flow systems (figs. 16 and 17) is marked by 

a low in the equivalent freshwater-head surface, which 

is nearly coincidental with a topographic low in eastern Kansas and northeastern Oklahoma. The extent of 

the flow systems in most areas also is apparent from 

the map of dissolved-solids concentration (fig. 18). 

Flow systems in the Interior Highlands, except south 

of the Boston Mountains, contain water with less than 

1,000 mg/L (milligrams per liter) dissolved solids.

The boundary between the flow systems also 

roughly parallels the physiographic boundary of the 

Central Lowland province in the western part of the 

Interior Plains and the Ozark Plateaus Province and 

Ouachita Province of the Interior Highlands north of

the Arkansas River. For convenience, the CMRASA 

area is divided into two subregions, referred to as simply the "Plains 1 ' subregion and the "Ozark" subregion. 

The geohydrologic units in the two subregions are 

described separately. The areal extents of the regional 

aquifer systems studied are shown in figure 19.

The lowermost confining unit in both the Plains 

and Ozark subregions is the basement confining unit. 

The basement confining unit is composed mostly of 

Precambrian-age crystalline rocks. The rocks may be 

fractured and water yielding at many locations, such 

as in the Denver Basin and in southeastern South 

Dakota, but on a regional basis they are assumed to 

form the base of the regional flow system. The top of 

the basement unit ranges from more than 34,000 ft 

below sea level in central Oklahoma to more than 

1,000 ft above sea level in the St. Francois Mountains 

of the Ozarks, and from more than 7,000 ft below sea 

level in the Denver Basin along the Rocky Mountains 

in east-central Colorado to about 500 ft above sea 

level in southeastern South Dakota (Jorgensen and 

others, 1993, plate 3).

PLAINS SUBREGION

The Plains subregion is by far the larger of the two 

subregions in areal extent (fig. 19). As concerns the 

CMRASA study, the subregion is underlain by rocks 

that range in age from Precambrian to Late Cretaceous and comprise five geohydrologic units. From 

oldest to youngest, these units are the basement confining unit, the Western Interior Plains aquifer system, the Western Interior Plains confining system, the 

Great Plains aquifer system, and the Great Plains 

confining system (fig. 17).

WESTERN INTERIOR PLAINS AQUIFER SYSTEM

GEOHYDROLOGIC UNITS

The Western Interior Plains aquifer system consists of water-bearing dolostone, limestone, and shale 

that directly overlie the basement confining unit in 

the western part of the Interior Plains physiographic 

division. The major stratigraphic units included in the 

system are listed in table 1. Not all stratigraphic units 

listed are aquifers; some form confining units. A geologic formation may be an aquifer in one part of the 

area and a confining unit elsewhere. The Western 

Interior Plains aquifer system includes the lower 

units, a confining unit, and an upper unit (table 1). 

Equivalent freshwater-head and water-chemistry 

data indicate that the lower units and the upper unit,
A20 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

 600 LINE OF EQUIVALENT-FRESHWATER HEAD Shows approximate 

altitude of equivalent-freshwater head. Interval, in feet, is variable. 

Datum is sea level

i i i i i i EXTENT OF CAMBRIAN AND ORDOVICIAN ROCKS 

FIGURE 16. Predevelopment equivalent-freshwater head in Cambrian and Ordovician rocks.

which are water bearing, are within a reasonably distinctive hydraulic system.

The lower units, at most locations, consist of aquifers in dolostone, limestone, and sandstone of Cambrian and Ordovician age separated by confining units 

of very slightly permeable material, such as shale or 

limestone. The lower units of the aquifer system are 

separated at most locations from the overlying upper 

unit by a relatively thin confining unit. The confining 

unit is composed mostly of the slightly permeable 

Chattanooga and Woodford Shales. The upper unit of

the aquifer system is an aquifer composed of permeable limestone that is mostly Mississippian in age.

Ground-water flow in the aquifer system is regionally (but not necessarily locally) southeastward from 

north-central Nebraska and otherwise from west to 

east toward a broad potentiometric low in eastern 

Kansas and Oklahoma (fig. 16). Discharge in the 

broad low area generally is vertically upward to 

streams or to the near-surface water table.

At many locations along the western and southern 

boundaries of the study area and near uplifts, such as
REGIONAL AQUIFERS SUMMARY A21

WEST

EAST

Zone of complex geology. Geohydrologic 

relations have not been defined with 

certainty and thus are not shown

Great Plains confining system

Transition zone between 

flow systems

NOT TO SCALE

EXPLANATION

 > DIRECTION OF GROUND-WATER FLOW

FIGURE 17. Major regional geohydrologic units and regional flow in the Plains and Ozark subregions. 

Section extends from central Colorado to St. Francois Mountains in southeastern Missouri.

the Front Range, Amarillo, Wichita, and Ouachita, 

complex faulting has disrupted the strata. At these 

locations, the hydraulic relations between specific 

strata are complex and generally unknown, and the 

aquifers cannot be described in terms of a few geologic 

formations. However, the hydraulic continuity of the 

geohydrologic system is implied by the continuous distribution of equivalent freshwater head (fig. 16).

PROPERTIES

The altitudes of the tops of the lower units, the 

shale confining unit that separates the upper unit from 

the lower units, and the upper unit of the Western 

Interior Plains aquifer system are shown in Jorgensen 

and others (1993, plates 4-6). All units of the system 

generally slope away from the Missouri River and the 

Ozark Uplift toward the Denver, Anadarko, and 

Arkoma Basins except along the Rocky Mountains. 

The thickest sections of the aquifer system (exceeding 

5,000 ft) are in west-central Oklahoma and 

west-central Arkansas in the Anadarko and Arkoma 

Basins (Jorgensen and others, 1993, plate 7) in which 

maximum deposition occurred. Additionally, these 

rocks have been protected, for the most part, from 

erosion since their deposition. Thus, diagenetic

processes, which generally are associated with uplift 

and erosion and which result in large increases in permeability, have not acted on these rocks. Accordingly, the stratigraphic units in the deep basins that 

did not undergo uplift diagenesis are considerably less 

permeable than the same stratigraphic units elsewhere 

that did undergo uplift diagenesis. For example, the 

dolostone and limestone in and adjacent to the Ozark 

Uplift and the Cambridge-Central Kansas Uplift and 

the Nemaha Uplift in southeastern Nebraska and 

northeastern Kansas are fractured, solutioned, and 

very permeable because they have undergone uplift 

diagenesis and surficial weathering during several 

extensive periods.

Regional permeability values for the lower units 

and the upper unit of the Western Interior Plains 

aquifer system are shown in figures 20 and 21. Estimates of permeability were calculated because nearly 

all the measured values available are from drill-stem 

tests that tested sections of oil- and gas-reservoir 

rocks. These measured values are mostly from tests of 

only thin intervals of rock (a few feet) and are site 

specific. The estimates of permeability range from 

IxlO'11 ft 2 in eastern Kansas to less than IxlO'17 ft 2 

in the Anadarko Basin and IxlO"18 ft 2 in the Denver 

and Arkoma Basins. The very slight permeability in
A22 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

PLAINS 

NEBRA^KASUBREGtON

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

 20.000 LINE OF EQUAL DISSOLVED-SOLIDS CONCENTRATION 

IN WATER MOSTLY FROM MIDDLE ORDOVICIAN, 

UPPER ORDOVICIAN, SILURIAN, AND DEVONIAN 

ROCKS Dashed where approximately located. Interval, 

in milligrams per liter, is variable

 20.000- LINE OF EQUAL DISSOLVED-SOLIDS CONCENTRATION 

IN WATER MOSTLY FROM UPPER CAMBRIAN AND 

LOWER ORDOVICIAN ROCKS Dashed where approximately 

located. Interval, in milligrams per liter, is variable

LIMIT OF LOWER UNITS IN THE WESTERN INTERIOR 

PLAINS AND OZARK PLATEAUS AQUIFER SYSTEMS

APPROXIMATE BOUNDARY BETWEEN PLAINS AND 

OZARK SUBREGIONS

-*- APPARENT DIRECTION OF LATERAL FLOW Based 

on pressure and density near the center line of the 

geohydrologic unit

FIGURE 18. Dissolved-solids concentrations in water from lower units in the Western Interior Plains aquifer system and the 

Ozark and St. Francois aquifers in the Ozark Plateaus aquifer system.
REGIONAL AQUIFERS SUMMARY A23

105° 100

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

APPROXIMATE EXTENT OF MAJOR AQUIFER SYSTEMS 

I ///\ Great Plains aquifer system

Western Interior Plains aquifer system 

__ Ozark Plateaus aquifer system

 APPROXIMATE BOUNDARY BETWEEN PLAINS AND OZARK 

SUBREGIONS

FIGURE 19. Extent of major aquifer systems.

the Anadarko Basin is in part evidenced by the large 

equivalent- freshwater head in west-central Oklahoma 

shown in figure 16. Pressure from the overlying 

geopressure zone in the Morrowan sediment is attenuated downward into the aquifer system. However, 

because permeability is so slight, the pressure is not 

dissipated in the aquifer system by lateral flow. Permeability values are affected by depth as is indicated 

by the small permeability values in the Arkoma,

Anadarko, and Denver Basins. In general, values of 

permeability less than 1x10 ~ 15 ft 2 are considered typical of confining material, not of aquifer material. 

However, the aquifer system is regionally distinct 

from the overlying confining system and the underlying basement confining unit.

Leakance through the confining unit that separates 

the lower units from the upper unit of the Western 

Interior Plains aquifer system varies directly with the
A24 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

TABLE 1. Generalized correlation of geohydrologic units to stratigraphic units in most of the Plains subregion

[From Jorgensen and others, 1993]

Geohydrologic unit

High Plains aquifer

Great Plains confining system

Great 

Plains 

aquifer 

system

Maha aquifer

Apishapa 

confining unit

Apishapa 

aquifer

Western 

Interior 

Plains 

confining 

system

Western 

Interior 

Plains 

aquifer 

system

Upper aquifer 

unit

Confining unit

Lower aquifer 

units

Basement confining unit

Principal rock-stratigraphic unil(s)

Ogallala Formation and 

unconsolidated deposits

Pierre Shale, Niobrara Formation, 

Carlile Shale, Greenhorn Limestone, 

Graneros Shale

Dakota Sandstone, "D" sandstone, 

"J" sandstone, and equivalent of 

Newcastle Sandstone

Kiowa Shale and equivalent of 

Skull Creek Shale

Cheyenne Sandstone and equivalent of Fall 

River Sandstone and 

Lakota Sandstone

Morrison Formation, Sundance Formation, 

Entrada Sandstone, Dockum Formation, 

Elk City Sandstone, Doxey Shale, Big 

Basin Sandstone, Cloud Chief Formation, 

Day Creek Dolomite, Whitehorse 

Sandstone, Nippewalla Group, Sumner 

Group, Chase Group, Council Grove 

Group, Admire Group, Wabaunsee Group, 

Shawnee Group, Douglas Group, Lansing 

Group, Kansas City Group, Pleasanton 

Group, Marmaton Group, Cherokee Group, 

Atokan rocks, Morrowan rocks, and 

Springer Group

Meramecian, Osagean, and 

Kinderhookian rocks

Chattanooga Shale and Woodford Shale

Hunton Group, Sylvan Shale, 

Galena Dolomite, equivalent of Viola 

Limestone, Simpson Group, Arbuckle 

Group, and Reagan Group

Mostly igneous and metamorphic rocks

Time- stratigraphic unit

Quaternary- and 

Tertiary

Upper Cretaceous

Lower 

Cretaceous

Jurassic 

through 

Upper 

Mississippian 

(Chesterian)

Upper 

Mississippian 

through 

Upper 

Cambrian

Cambrian and 

Precambrian

vertical hydraulic conductivity and inversely with 

thickness. No measurements of vertical hydraulic 

conductivity are available; the thickness generally 

ranges from 0 to 300 ft.

MODEL ANALYSIS AND HYDROLOGIC BUDGET

A numerical ground-water flow model was developed and used to test conceptualization of flow in the 

regional aquifer systems of the study area (Signer and 

others, in press). In addition, two other numerical 

models were developed to simulate flow in more detail 

in the Great Plains and Ozark Plateaus aquifer systems as described in Helgesen and others (1993) and 

Imes and Emmett (1994). The regional model simulated the Western Interior Plains aquifer system, the 

Western Interior Plains confining system, the Great 

Plains aquifer system, and the Ozark Plateaus aquifer

system. However, only the results for the regional 

model in simulating flow in the Western Interior 

Plains aquifer system will be described in this section.

The numerical model selected was a modular 

three-dimensional, finite-difference, ground-water 

flow model developed by McDonald and Harbaugh 

(1984). It is designed to simulate two- and 

three-dimensional movement of ground water of constant density through porous material. The model 

consists basically of a grid superimposed on each of 

the major geohydrologic units. The grid has 28 rows, 

33 columns, and uniform cell size of 28 mi x 28 mi. 

The model row orientation was set to coincide with 

the principal directions of lineaments, North 35° West 

and North 55 ° East, which facilitated consideration of 

anisotropic hydraulic conductivity. Major geohydro-
REGIONAL AQUIFERS SUMMARY A25

105'

I / SOUTH DAKOTA ;

Base modified from U.S. Geological Survey 

1:7,500.000, National Atlas, 1970

EXPLANATION

-70 LINE OF EQUAL ESTIMATED REGIONAL PERMEABILITY Value is the

thickness-weighted mean horizontal intrinsic permeability. Interval, in feet 

squared, is variable

EXTENT OF LOWER UNITS IN WESTERN INTERIOR PLAINS AQUIFER 

SYSTEM

APPROXIMATE BOUNDARY BETWEEN PLAINS 

AND OZARK SUBREGIONS

FIGURE 20. Estimated regional intrinsic permeability of lower units in the Western Interior Plains aquifer system.

logic units in the study area are represented as layers 

in the model. From top to bottom the layers are:

Layer 1 The surficial unit, which consists of the 

High Plains aquifer and the Great Plains confining 

system.

Layer 2 The Great Plains aquifer system.

Layer 3 The Western Interior Plains confining 

system.

Layer 4 The upper unit of the Western Interior 

Plains aquifer system in the Plains subregion and the 

Springfield Plateau aquifer in the Ozark subregion.

Layer 5 The lower units of the Western Interior 

Plains aquifer system in the Plains subregion and the 

combined Ozark aquifer, St. Francois confining unit, 

and the St. Francois aquifer in the Ozark Plateaus 

aquifer system in the Ozark subregion.
A26 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

SOUTH DAKOTA 

Boundary of

PLAINS 

SUBREGION

NEBRASKA^

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

 10- LINE OF EQUAL ESTIMATED REGIONAL PERMEABILITY Value is the

thickness-weighted mean horizontal intrinsic permeability. Interval, in feet 

squared, is variable

I I I I I i EXTENT OF UPPER UNIT IN WESTERN INTERIOR PLAINS AQUIFER SYSTEM

 APPROXIMATE BOUNDARY BETWEEN PLAINS 

AND OZARK SUBREGIONS

FIGURE 21. Estimated regional intrinsic permeability of upper unit in the Western Interior Plains aquifer system.

In general, data needed for simulation of 

ground-water flow in the model are water levels; altitude of geohydrologic units modeled; thicknesses, 

which can be determined by difference in altitudes of 

individual layers; intrinsic permeability (or hydraulic 

conductivity); and vertical leakance between centerlines of two vertically adjacent aquifer units or across 

confining-unit boundary conditions and source terms 

(vertical leakance is the effective vertical permeability 

divided by the thickness of the confining unit or

distance between centerlines of two vertically adjacent 

model layers).

Boundary conditions for the model are no-flow, 

general-head, constant-head (specified head), and 

head-dependent boundaries (stream simulation). 

Source terms are water withdrawn or injected per 

model cell.

The model-calculated hydraulic head for layer 5 is 

shown in figure 22. In general, a comparison of modelcalculated value correlates well with equivalent-
REGIONAL AQUIFERS-SUMMARY A27

105° 100° 95° 90°

40'

35'

I I 0 100 200 KILOMETERS

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

/\/\

EXPLANATION

MODEL-LAYER BOUNDARY

 .000 MODEL-COMPUTED HYDRAULIC-HEAD 

CONTOUR Interval, in feet, is variable. 

Datum is sea level

 zOOO FIELD HYDRAULIC-HEAD CONTOUR 

Interval, in feet, is variable. Datum is 

sea level

 APPROXIMATE BOUNDARY BETWEEN THE 

PLAINS AND OZARK SUBREGIONS

FIGURE 22. Model-computed and field hydraulic head for model layer 5 representing lower units in the Western Interior Plains 

aquifer system and the Ozark and St. Francois aquifers in the Ozark Plateaus aquifer system.
A28 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

freshwater head, especially considering the variability 

of the results of drill-stem tests on which the 

equivalent-freshwater-head map was based. The Western Interior Plains aquifer system contains water of 

variable density and, thus, a direct comparison in all 

respects between model-calculated hydraulic head and 

equivalent head is not possible.

The velocity vectors of flow as calculated by the 

model for model layers 4 and 5 are shown in figures 23 

and 24. The lengths of the arrow shafts in the figures 

are scaled logarithmically as to rate of movement. The 

arrowhead shows direction. Figures 23 and 24 show 

the extremely slow velocity of flow in the Western 

Interior Plains aquifer system. Both figures show flow 

outward from the geopressured zone in west-central 

Oklahoma. However, the velocities are extremely 

slow, confirming the slight permeability of the hydrologic units in that area. Accordingly, the quantity of 

flow outward from the geopressure zone is small. The 

transition zone between the Western Interior Plains 

and Ozark Plateaus aquifer systems is shown by the 

difference in direction of flow at the zone. Flow velocities in the Ozark Plateaus aquifer system are about 

five orders of magnitude greater than in the Western 

Interior Plains aquifer system.

USE AND POTENTIAL

Most of the water in the Western Interior Plains 

aquifer system is saline and could not be used as a 

potable water supply without treatment. However, 

the aquifer system contains a large quantity of water 

as listed in table 2. The accuracy of table 2 is based on 

assumptions stated later in the text. Oil and gas are 

produced from some zones within the aquifer system. 

Also, at some locations large quantities of brine produced with oil and gas from rocks above the aquifer 

system are being injected into the aquifer system.

Results of the flow simulation indicated that fluid 

velocities are very slow in the deeply buried units and 

that the aquifer system is nearly isolated from the 

overlying Great Plains aquifer system, especially in 

the area where halite and gypsum are present in the 

intervening confining system. Because of the degree of 

isolation, the slow velocity of flow, and the ambient 

water chemistry, the aquifer system has potential for 

material storage or waste disposal. For example, 

model results indicated that the velocity of water 

moving through pore spaces in the aquifer system in 

western Kansas is about 4x10"5 ft per year or about 40 

ft in a million years. Even for a fluid velocity three 

orders of magnitude greater, the movement would be 

only about 7.6 mi in a million years. These rates 

assume that the integrity of the overlying confining

system is maintained. Excess pore pressure, intensive 

drilling, or tectonic activity could result in loss of the 

integrity of the confining system. Evaluation of areas 

having pressure either greater than hydrostatic or less 

than hydrostatic would be useful in any evaluation of 

potential for storage or disposal of wastes. At some 

locations, such as near the uplifts that mark the 

boundaries of the CMRASA area, there has been considerable tectonic activity in the geologic past.

WESTERN INTERIOR PLAINS CONFINING SYSTEM

GEOLOGIC DEFINITION AND CORRELATION

The Western Interior Plains confining system consists of confining units separated by aquifers that are 

not in close hydraulic connection. That is, the aquifers are not in the same hydraulic system. Collectively, the confining units and the included aquifers 

restrict flow to and from the underlying Western Interior Plains aquifer system. The Western Interior 

Plains confining system is at land surface in much of 

the eastern part of the Plains subregion and in a significant part of the Ozark subregion. At some locations, the confining system is overlain directly by the 

High Plains aquifer system or, in small areas of eastern Nebraska and northeastern Kansas, by glacial till 

and loess. However, in much of the Plains subregion, 

the confining system is overlain by the Great Plains 

aquifer system.

Large pore pressures exist in a geopressured zone 

near the base of the confining system in the Anadarko 

Basin in Oklahoma. At this location, equivalentfreshwater hydraulic head exceeds 6,000 ft in sand and 

shale of Morrowan age. The pressure is transferred, 

but attenuated, into the underlying dolostone and 

limestone strata of the Western Interior Plains aquifer 

system (fig. 16) where equivalent-freshwater head 

exceeds 4,000 ft in the very slightly permeable rocks 

at the same location.

Formations of Pennsylvanian age form a major 

part of the confining system (Jorgensen and others, 

1993, plate 2); they consist mostly of shale with limestone, sandstone, and some coal. In the deeper part of 

the Anadarko and Arkoma Basins, the ratio of limestone to sandstone decreases. In the shallower areas, 

the ratio of limestone to sandstone exceeds one. Adjacent to the Amarillo Uplift and Sierra Grande Arch 

(fig. 9), thick sections of permeable arkoses of Pennsylvanian and Permian age are present. These rocks 

are thought to have been derived from erosion of granitic rocks on the uplifts and to extend only a few tens 

of miles from the uplifts. The arkosic gravel, therefore, is not considered to be an important regional 

aquifer.
REGIONAL AQUIFERS^SUMMARY A29

35

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

x y

EXPLANATION

 LATERAL FLOW VECTOR Length of shaft 

indicates relative magnitude

 APPROXIMATE BOUNDARY BETWEEN THE 

PLAINS AND OZARK SUBREGIONS

FIGURE 23. Lateral flow-velocity vectors for model layer 4 representing upper unit in the Western Interior Plains aquifer 

system and the Springfield Plateau aquifer in the Ozark Plateaus aquifer system.
A30 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

105

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

 - LATERAL FLOW VECTOR Length of shaft 

indicates relative magnitude

 APPROXIMATE BOUNDARY BETWEEN THE 

PLAINS AND OZARK SUBREGIONS

FIGURE 24. Lateral flow-velocity vectors for model layer 5 representing lower units in the Western Interior Plains aquifer 

system and the combined Ozark aquifer, St. Francois confining unit, and St. Francois aquifer in the Ozark Plateaus aquifer 

system.
REGIONAL AQUIFERS SUMMARY A31

TABLE 2. Water in storage in geohydrologic units in the CMRASA area

[Data in millions of acre-feet; , no data. Total ground water in storage. Drainable water would be less if nonyielding 

clay layers and specific yield of permeable units are taken into consideration]

Geohydrologic unit

Western Interior Plains aquifer system

Slate

Arkansas

Colorado

Kansas

Missouri

Nebraska

New Mexico

South Dakota

Oklahoma

Texas

Wyoming

Total

State

Arkansas4 

Arkansas5

Kansas

Missouri

Oklahoma

Total

Great Plains aquifer sy!

_

1,553

2,717

7,035

54

190

9

244

11,802

Springfield aquifer 1

30 

50

25

118

45

268

stem Upper unit

Plains subregion

188

818

29

174

8

625

137

51

2,030

Geohydrologic unit

Ozark aquifer St. Francois aquifer

Ozark subregion3

1,775 51 

1,113 39

127 7

3,329 544

445 8

6,789 649

Lower units

71

223

1,631

121

766

9

8

2,099

215

-

5,143

Combined 

St. FrancoisOzark aquifer 2

1,825 

1,152

134

3,873

454

7,438

Regional model layer 4. 2 Regional model layer 5.

3Leo F. Emmett, U.S. Geological Survey, written commun., 1987.

4Freshwater. 5Saline water.

Permian-age formations in the Western Interior 

Plains confining system consist mostly of shale with 

evaporite deposits, sandstone, and limestone. Formations of Triassic and Jurassic age are mostly shale, 

sandstone, and limestone.

PROPERTIES

The areal extent and altitude of the top of the confining system are shown in Jorgensen and others 

(1993, plate 8). The altitude ranges from more than 

6,000 ft above sea level in northeastern New Mexico 

to more than 3,000 ft below sea level in the Denver 

Basin. In general, the top of the exposed confining 

system slopes west to east toward a broad physiographic low near the outcrop area adjacent to the 

western perimeter of the Ozark subregion. The thickness of the confining system (Jorgensen and others, 

1993, plate 9) ranges from more than 20,000 ft in the 

Anadarko Basin to 0 ft in northeastern Nebraska and 

in the Ozark subregion.

The estimated mean horizontal intrinsic permeability (weighted by thickness of different lithologies) of 

the confining system ranges from less than 1x10 ~16 to 

about 5xlO'13 ft 2 (fig. 25). The aquifer units in the 

Western Interior Plains confining system in the deep 

basins are, in general, more permeable than aquifer 

units in the underlying Western Interior Plains aquifer system because permeability and porosity generally decrease with depth. However, leakage through 

the confining system at most locations is very small 

because the system includes thick layers of shale and 

extensive layers of nearly impermeable salt and other 

evaporite deposits that form effective confining units. 

The extent and thickness of the evaporite deposits is 

shown in figure 26.

The pressure of pore water in permeable units of 

the confining system is variable both vertically and 

horizontally because the units are not contained in a 

reasonably distinct hydraulic system. Large pore pressures exist in the previously described geopressured
A32 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

105

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

 10 LINE OF EQUAL ESTIMATED PERMEABILITY Value is the thicknessweighted mean horizontal intrinsic permeability. Interval, in feet squared, 

is variable

i i i i i i EXTENT OF WESTERN INTERIOR PLAINS CONFINING SYSTEM

 APPROXIMATE BOUNDARY BETWEEN PLAINS AND OZARK 

SUBREGIONS

FIGURE 25. Estimated regional intrinsic permeability of the Western Interior Plains confining system.

zone near the base of the confining system. However, 

pore pressure measured in drill-stem tests near the 

centerline of the confining system is below hydrostatic 

pressure in large areas, including the area over the 

geopressured zone. This occurrence of both overpressured and underpressured units reflects the confining 

nature of the system.

USE AND POTENTIAL

At some locations where the aquifer units crop out 

and, in general, at depths less than 500 ft, water from 

aquifer units in the Western Interior Plains confining 

system is fresh and suitable for domestic and other 

uses (fig. 27). However at other locations large quantities of oil and gas are produced from these same rocks,
REGIONAL AQUIFERS SUMMARY A33

105'

/\\v\

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

-700 LINE OF EQUAL THICKNESS OF EVAPORITE 

DEPOSITS IN THE WESTERN INTERIOR 

PLAINS CONFINING SYSTEM Dashed where 

approximate. Interval, in feet, is variable

 i i i i i i i i LIMIT OF PENNSYLVANIAN ROCKS

 APPROXIMATE BOUNDARY BETWEEN PLAINS 

AND OZARK SUBREGIONS

FIGURE 26. Thickness of evaporite deposits in the Western Interior Plains confining system.

such as in the Hugoton gas field. Halite beds are a 

salt resource, and manmade cavities within them are 

used for storage of natural gas and petroleum products. Because the confining system is thick and the 

permeability is small, confining units are candidates 

for storage of wastes or natural gas, petroleum and 

petroleum products, and saline or freshwater. 

However, many technical factors would have to be

considered in evaluating the potential for storage or 

for disposal, including whether the candidate units are 

in a tectonically active area or if the area is adjacent 

to an area of abnormal pore pressures. There is potential for movement of fluids if the rocks are disturbed 

by natural causes, such as tectonics, or manmade 

causes, such as drilling and pressure injection of fluids.
A34 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

100 95°

.- SOUTH DAKOTA l>

j - -~~" - - ^~Y r

Boundary

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

 1.000 LINE OF EQUAL DISSOLVED-SOLIDS CONCENTRATION FROM 

DEPTHS LESS THAN 500 FEET-Dashcd where approximate. 

Interval, in milligrams per liter, is variable

FIGURE 27. Dissolved-solids concentrations in water from rocks older than those of the Great Plains aquifer system at depths

less than 500 feet.

GREAT PLAINS AQUIFER SYSTEM

The Great Plains aquifer system consists of two 

regional aquifers in the same hydraulic system separated in much of the area by a regional confining unit. 

The aquifers are found in regional water-bearing sandstone and other rocks, nearly all of which are of Early 

Cretaceous age. The Great Plains aquifer system is 

one of the most widespread in North America (Helgesen and others, 1982), extending from near the Arctic 

Circle in Canada to New Mexico (fig. 28).

The term Great Plains was chosen because, generally, the aquifer system is present at most locations in 

the Great Plains of North America. The Great Plains 

aquifer system includes the Apishapa (lower aquifer), 

the Maha (upper aquifer), and the intervening 

Apishapa confining unit (fig. 29). The altitude of the 

top of the Great Plains aquifer system (Helgesen and 

others, 1993, plate 4) ranges from more than 6,000 ft 

above sea level in northeastern New Mexico, a 

recharge area, to less than 1,000 ft above sea level in 

southeastern South Dakota, a discharge area, and to 

more than 4,000 ft below sea level in the Denver 

Basin.
REGIONAL AQUIFERS SUMMARY A35

50,

140° 130° 120° 110° 100° 90° 80° 70° 60°

Base from Central Intelligence Agency. 

North America. 1'38.700.000.1992 

Lambert Conformal Conic projection 

Standard parallels 37° and 65°

0 250 750 MILES

I i H r1 '

0 250 500 750 KILOMETERS

Contours modified from Hitchon (1969). 

Lobmeyer (1980), and others

EXPLANATION

 3000 POTENTIOMETRIC CONTOUR Shows altitude of potentiometric surface of the 

Great Plains aquifer system. Hachures indicate depression. Contour interval is 

500, 1000, and 2000 feet. Datum is sea level

----- LIMIT OF GREAT PLAINS AQUIFER SYSTEM

FIGURE 28. Potentiometric surface and extent of the Great Plains aquifer system in 

North America (modified from Helgesen and others, 1982).

The correlation of aquifers to principal formations 

is shown in table 1. The two aquifers have been 

termed the "Dakota aquifer" or the "Dakota aquifer 

system" by various investigators. Others have 

restricted the term "Dakota aquifer" to either the 

upper (Maha) aquifer or the lower (Apishapa) aquifer. 

The name Dakota also has been used as a name for 

lithostratigraphic units as the Dakota Sandstone, the 

Dakota Formation, and the Dakota Group. The controversy as to correlation and terminology has been 

termed aptly the "Dakota controversy." Nearly all 

the items of the controversy relate to correlation of 

lithologic units and not to hydrology. The correlation

of stratigraphic units and their correspondence with 

geohydrologic units is shown in Helgesen and others 

(1993, fig. 11).

The potentiometric surface of the Maha aquifer 

(fig. 30) probably is related closely to heads in the 

Apishapa aquifer because of leakage through the 

Apishapa confining unit. However, there may be considerable head difference in some areas. For example, 

in central South Dakota, just north of the CMRASA 

study area, a significant head difference exists between 

the two aquifers. The major recharge to the aquifer 

system in the study area is in southeastern Colorado 

and northeastern New Mexico (fig. 30). Most ground
A36 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

WEST EAST

Great Plains confining system

(Upper Cretaceous rocks)

.S»'^

-ve and equivalents)- Maha

andstone)

^uivaients) >. Apishapa aquifer

Western iemInterior mieiiui Plains ridmbconfining uumiiimy system b^ini .X5/^?-"''>','>'' (Cambrian through 

(Pennsylvanian through Jurassic rocks) viV,-V- '''/ViV-'- ' ' Mississippian rocks)

confining unitiV-'^'

NOT TO SCALE

EXPLANATION

 > DIRECTION OF GROUND - WATER FLOW

FIGURE 29. Maha and Apishapa aquifers, Great Plains aquifer system. Section extends across

Nebraska from the intersection of North Platte River and Wyoming-Nebraska boundary on the west 

to Missouri River at northernmost extent of Nebraska-Iowa boundary on the east.

water flows from the major recharge area east-northeast toward the eastern edge of the aquifer system in 

Kansas and eastern Nebraska. Near the southern and 

eastern extent of the aquifer system, the aquifers are 

close to land surface, and local recharge occurs 

(fig. 29).

At most locations, the Apishapa aquifer is composed of permeable, partially cemented, medium- to 

very fine-grained sandstone of the Cheyenne Sandstone and equivalents, such as the Fall River and 

Lakota Sandstones. The name Apishapa refers to 

water-bearing sandstones that crop out in the major 

recharge area in the vicinity of the Apishapa River 

and adjacent areas in southeastern Colorado, northeastern New Mexico, and southwestern Kansas.

The Apishapa confining unit separates and restricts 

water flow between the Apishapa aquifer and the overlying Maha aquifer at most locations. The confining 

unit is composed of slightly permeable shale layers, 

which at most locations consist of the Kiowa Shale 

and the equivalent Skull Creek Shale.

The Maha aquifer, which is the upper regional 

aquifer unit of the Great Plains aquifer system, is 

more extensive areally than the underlying Apishapa 

aquifer (fig. 29). The Maha aquifer at most locations 

consists of water-bearing, permeable, partially 

cemented, medium- to fine-grained sandstone of the 

Dakota Sandstone and equivalents, such as the Newcastle Sandstone and the "D" and "J" sandstone of 

informal usage. The aquifer was named from exposures of the water-yielding sandstone along bluffs of

the Missouri River between Blair and Ponca, 

Nebraska. This is the location of the Maha (Omaha) 

Indians as reported by Lewis and Clark.

PROPERTIES

The altitude of the top of the Great Plains aquifer 

system is shown in Helgesen and others (1993, 

plate 4). The aquifer system is 200 to 800 ft thick 

throughout most of the area (fig. 31 j. The Apishapa 

aquifer is typically between 100 and 200 ft thick 

(Helgesen and others, 1993, plate 1). The Apishapa 

confining unit is generally less than 100 ft thick (Helgesen and others 1993, plate 2) and, similar to the 

Apishapa aquifer, is not as extensive as the overlying 

Maha aquifer. The Maha aquifer is the thickest and 

most areally extensive unit of the Great Plains aquifer 

system. Thickness of the Maha ranges from less than 

100 ft in eastern Colorado to about 600 ft in northeastern Nebraska (Helgesen and others, plate 3). The 

maximum thickness exceeds 900 ft in two small areas 

in central Nebraska.

Permeability of both aquifers is mostly primary, 

except possibly in the Denver Basin, because the aquifers consist mostly of slightly cemented sandstone. 

Figure 32 shows the estimated thickness-weighted 

mean horizontal intrinsic permeability of the Great 

Plains aquifer system. Permeability generally 

decreases with depth, being greatest (10~10 ft2 ) in the 

eastern part of the aquifer system and least (10~13 ft2 ) 

in the Denver Basin.
REGIONAL AQUIFERS SUMMARY A37

105

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas. 1970

EXPLANATION

-3000 POTENTIOMETRIC CONTOUR Shows altitude at which water would have 

stood in tightly cased wells. Contour interval, in feet, is variable. Datum is 

sea level

i i i i i i LIMIT OF GREAT PLAINS AQUIFER SYSTEM

FIGURE 30. Predevelopment potentiometric surface of the Maha aquifer, Great Plains aquifer system.

MODKL ANALYSIS AND HYDROLOG1C BUDGET

A computer model was used to test the conceptualization of flow in the Great Plains aquifer system, to 

improve definition of the hydrologic budget of the 

aquifer system, and to evaluate the aquifer system for 

potential use. The finite-difference ground-water flow 

model of McDonald and Harbaugh (1984) was chosen 

as being applicable to the Great Plains aquifer system 

with minor qualifications.

Horizontally, discretization is in the form of a uniform grid consisting of 46 rows and 35 columns

(Helgesen and others, 1993). Each cell is 14 mi x 14 

mi horizontally, for a grid density four times that of 

the regional CMRASA model. The model-grid orientation was North 35 ° West and North 55 ° East. This 

orientation approximately parallels the major bedrock 

joint patterns in the midcontinent region, and the orientation coincides with that of the regional model 

used for the entire CMRASA study area.

The system is discretized vertically into four model 

layers that generally correspond to the principal geohydrologic units. Layer 1 represents the Great Plains 

confining system in most places, or where it is not
A38

106°

REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

104° 102° 100° 98° 96°

36°

^^^^^"^

NEW MEXICO . /^ 

1 1

j'__ _ . - - . - - - OKLAHOMA

;;l 'TEXAS | 

i V i i i

100 200 MILES

100 200 KILOMETERS

EXPLANATION 

 ^ AQUIFER SYSTEM ABSENT

 400 LINE OF EQUAL THICKNESS OF GREAT PLAINS 

AQUIFER SYSTEM Interval 200 feet

FAULT U, upthrown side; D, downthrown side

FIGURE 31. Thickness of Great Plains aquifer system.

present, the layer represents the High Plains aquifer 

or unnamed Quaternary deposits, whichever directly 

overlies the Maha aquifer. Layers 2 and 3 represent 

the Maha and Apishapa aquifers, respectively. (The 

Apishapa confining unit, which separates the two 

aquifers, is not represented by a model layer.) Layer 4 

represents the next 150 ft of strata beneath the Great 

Plains aquifer system, which is equivalent to the top

part of the Western Interior Plains confining system 

in most of the area. In the northeastern part of the 

CMRASA study area, the Western Interior Plains 

confining system is absent, and layer 4 there represents the Western Interior Plains aquifer system. 

Farther northeast, the basement confining unit forms 

the lower boundary of the Great Plains aquifer 

system.
REGIONAL AQUIFERS SUMMARY A39

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

-10- LINE OF EQUAL ESTIMATED PERMEABILITY Value is the thicknessweighted mean horizontal intrinsic permeability. Interval, in feet squared, 

is variable

i i i i i LIMIT OF GREAT PLAINS AQUIFER SYSTEM

FIGURE 32. Estimated regional intrinsic permeability of the Great Plains aquifer system.

Thickness values used in model calculations were 

based on the maps shown in Helgesen and others 

(1993, plates 1-3). Permeability values for layers 1 

and 4 were assigned as fractions of the permeability of 

layer 2 (fig. 32). These fractions were applied 

uniformly within layers 1 and 4. Because the permeability of layer 2 is a function of depth, the permeability of layers 1 and 4 also were simulated as functions 

of depth.

Leakance values (effective vertical hydraulic conductivity divided by thickness) were determined by 

making effective vertical hydraulic conductivity a

function of depth and a ratio of horizontal-to-vertical 

hydraulic conductivity. Where confined conditions 

prevail, storage coefficient was set equal to the product of estimated specific storage times thickness. To 

represent unconfined conditions, storage coefficient 

(specific yield) was set equal to 0.15.

Calibration of the model primarily entailed an 

effort to satisfactorily simulate flow in the aquifer system under natural predevelopment conditions. 

Inadequate information exists, however, to accurately 

define predevelopment conditions. Therefore, these
A40 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

conditions were surmised from field or estimated head 

data.

Calibration of the model to predevelopment conditions resulted in a steady-state head distribution that 

is in general agreement with the field or estimated predevelopment head distribution (fig. 33). Regionally, 

deviations in head were mostly within a contour interval of the predevelopment-head map. Areas of positive 

and negative deviations from field or estimated heads 

were somewhat irregularly distributed regionally.

The predevelopment, steady-state flow rate 

through the aquifer system was simulated as 

342 ft3/s, most of which is vertical leakage to or from 

adjacent units rather than lateral flow from or to outcrop areas. The distribution of rates of vertical interchange per grid cell between the Maha aquifer and the 

overlying units (fig. 34), shows a decrease of several 

orders of magnitude westward into the Denver Basin. 

Direction of the simulated vertical flow is everywhere 

downward into the aquifer system except along the 

eastern and southern edges. Vertical interchange at 

locations where the Great Plains aquifer system 

directly underlies the High Plains aquifer or the Missouri River alluvium constitutes about 60 percent of 

the simulated water budget. If recharge or discharge 

at outcrop areas is considered also, that proportion 

increases to more than 70 percent. Rates of simulated 

downward or upward flow at some individual grid cells 

(196 mi 2 ) exceeded 10 ft 3/s where direct connection 

with the High Plains aquifer or Missouri River alluvium exists. Simulated vertical interchange rates in 

the deepest part of the Denver Basin were less than 

0.001 ft 3/s per grid cell.

Simulated vertical interchange between the Great 

Plains aquifer system and underlying units (fig. 35) 

was very small over most of the area, exceeding 

0.1 ft3/s per grid cell only along the eastern and southern edges. A general westward decrease in vertical 

flow rate per cell is again evident. Direction of the 

simulated vertical interchange is of interest and 

appears to be reasonable hydrologically. The predominantly upward flow along the Missouri River Valley is 

reasonable as simulated. Upward leakage has been 

cited by Schoon (1971) to explain calcium sulfate 

water in the aquifer system in southeastern South 

Dakota. Significant upward flow to the aquifer system 

is simulated in central Kansas. This upward flow 

occurs just west of the evaporite subcrop area, where 

flow may be diverted upward by these rocks of very 

slight permeability.

A simulation of transient conditions in the system 

was made for 1940-79 by adding fluid withdrawals to 

the predevelopment conditions defined by the model. 

Simulated withdrawal rates, by county and decade,

were used to assign rates to cells corresponding with 

areas of development. All pumpage of oil, gas, and 

saline water, which is largely in the Denver Basin, was 

assigned to the Maha aquifer. Freshwater pumpage, 

which is largely near the outcrop in southwestern 

Kansas and associated with irrigation, was assigned to 

the Maha or Apishapa aquifers as appropriate. The 

simulation consisted of four 10-year periods with output recorded at the end of each period.

Simulated response to withdrawals of oil, gas, and 

saline water indicated cumulative head declines of 

500 ft or more in the area of most intense development by the end of the 40-year period (fig. 36). Magnitude and extent of the simulated head declines 

generally resemble the differences between inferred 

predevelopment heads and current heads. Simulated 

head declines in response to freshwater pumpage are 

tens of feet, and exceed 100 ft locally, in parts of 

southern Colorado, southwestern Kansas, eastern 

Nebraska, and southeastern South Dakota (fig. 36). 

The observed and simulated water-level declines at 

selected locations are shown in figure 37.

Sensitivity of the model to changes in several variables was tested for the Great Plains aquifer-system 

model. Simulated hydraulic-head differences were 

most sensitive to changes in hydraulic conductivity 

and direct recharge to the aquifer in outcrop areas. 

Simulated discharge to streams was most sensitive to 

changes in hydraulic conductivity.

The diverse character of the Great Plains aquifer 

system makes it suitable for a wide range of uses. 

Resources of the aquifer system that have been developed are (1) oil and natural gas; (2) freshwater for 

irrigation, municipal, industrial, domestic, stock, or 

other purposes; and (3) saline water produced mainly 

in association with oil, much of which is reinjected to 

maintain reservoir pressure (secondary-recovery procedures).

Assessment of the oil and gas resources is not 

within the scope of this study. Other uses are 

addressed herein based on the current understanding 

of the regional hydrology. This assessment cannot 

incorporate the local variations in geohydrologic conditions that need to be considered.

The total amount of water stored in the Great 

Plains aquifer system is nearly 12 billion acre-ft 

(table 2). However, about half of that amount is 

stored in confining-unit material. Assuming specific 

yield is half of porosity, approximately 3 billion 

acre-ft is in drainable storage. More than half of the 

water in storage is in Nebraska.
REGIONAL AQUIFERS SUMMARY A41

44C

106° 104° 102° 100° 98° 96°

I -I I i I

ISCJUTH- DAKOTA

I

r 

- » ji

100 200 MILES

100 200 KILOMETERS

EXPLANATION

 7800 POTENTIOMETRIC CONTOUR Shows altitude of

approximate predevelopment potentiornetric surface, 

based on field or estimated data. Interval, in feet of 

head, is variable. Datum is sea level

- - 7800- - SIMULATED POTENTIOMETRIC CONTOUR -Shows

model-calculated altitude of predevelopment potentiornetric 

surface. Interval, in feet of head, is variable. Datum 

is sea level

LIMIT OF MAHA AQUIFER WITHIN STUDY AREA 

Screened toward aquifer

FIGURE 33. Comparison of field or estimated and simulated predevelopment hydraulic-head distributions

for Maha aquifer.
A42 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

106° 104'

36°

NEW MEXICO 

I

^ 70 i -'//'- - _ , ___ ___ 

 ' 0X^ TEXAS i rfl

OKLAHOMA 

1 I

100 200 MILES

100 200 KILOMETERS

EXPLANATION

AREA OF SIMULATED UPWARD DISCHARGE 

OUTCROP AREA OF MAHA AQUIFER

 0. 7 LINE OF EQUAL SIMULATED VERTICAL VOLUMETRIC 

FLOW PER MODEL CELL TO OR FROM OVERLYING 

LAYER Negative value denotes upward discharge. 

Interval, in cubic feet per second, is variable

LIMIT OF MAHA AQUIFER WITHIN STUDY AREA 

Screened toward aquifer

FIGURE 34. Simulated vertical volumetric flow between Maha aquifer and overlying units.
REGIONAL AQUIFERS SUMMARY A43

106° 104'

100 200 MILES

100 200 KILOMETERS

EXPLANATION

AREA OF SIMULATED UPWARD FROM UNDERLYING 

ROCK UNIT TO GREAT PLAINS AQUIFER SYSTEM

AREA OF ZERO SIMULATED VERTICAL VOLUMETRIC 

FLOW In areas where the Great Plains aquifer system is 

directly underlain by basement confining unit (in northeastern 

part of the study area) or by evaporite deposits (in central 

Kansas)

LINE OF EQUAL SIMULATED VERTICAL VOLUMETRIC FLOW 

PER MODEL CELL TO OR FROM OVERLYING LAYER 

Negative value indicates upward flow from underlying layer. Interval, 

in cubic feet per second, is variable

LIMIT OF AQUIFER SYSTEM WITHIN STUDY AREA Screened 

toward aquifer

FIGURE 35. Simulated vertical volumetric flow between the Great Plains aquifer system and

underlying units.

0.7-
A44 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

106

100 200 MILES

100 200 KILOMETERS

EXPLANATION

 700 LINE OF EQUAL SIMULATED HEAD DECLINE, 

1940-79 Interval, in feet of head, is variable

- - 700 - - LINE OF EQUAL HEAD DECLINE IN DENVER 

BASIN, AS ESTIMATED FROM INFERRED 

PREDEVELOPMENT CONDITIONS Interval, 

in feet of head, is variable

u i."i.L"'»miii LIMIT OF MAHA AQUIFER WITHIN STUDY AREA 

Screened toward aquifer

FIGURE 36. Inferred hydraulic-head declines in Denver Basin and simulated hydraulic-head declines in 

response to development of Great Plains aquifer system.

Long-term water-yielding capability relates to the 

response of the system and to what degree it can 

adjust to sustain newly imposed rates of withdrawal.

Withdrawals imposed on the natural system affect the 

system's storage, recharge, and discharge, depending 

on rates and location of the withdrawals.
REGIONAL AQUIFERS SUMMARY A45

20

40

20

< 40 

< > 20

I I I I I I I I I

A. Bent County, Colorado

I I I I I I I i i i i i 1 i

i i r

i i

i i i i i i i i i i r

B. Finney County, Kansas

I I I I I I I I I I I I I I I I

20

40

20

I I

C. Russell County, Kansas

I I I I I I I I I I I I

40

D. Charles Mix County, South Dakota

I I I I I I I I I I I I I I I I

EXPLANATION

OBSERVED WATER-LEVEL 

CHANGE

SIMULATED WATER-LEVEL 

CHANGE

Wyo.

D \ /Boundary of 

Nebr. l\ study area

INDEX MAP

FIGURE 37. Observed and simulated water-level changes at selected locations in Great Plains

aquifer system.

Considering only the Great Plains aquifer system 

itself, withdrawals from the system may do one or 

more of the following:

1. Intercept water that would have discharged upward 

to overlying units;

2. Intercept water that would have discharged downward to underlying units;

3. Intercept water that would have discharged to 

streams or to evapotranspiration in aquifer-system 

outcrop areas;

4. Remove water from aquifer-system storage.

Withdrawals also may induce flow from sources of 

water in hydraulic connection with the aquifer system. 

These sources are (1) the High Plains aquifer, (2) 

other adjacent units, and (3) streams in aquifer- system outcrop areas.

Evaluation of the water budget and its changes 

through the simulation of 1940-79 conditions allows 

quantification of effects on the recharge, discharge, 

and storage components of the budget (fig. 38). (Oil 

and gas withdrawals are a very small part of total
A46 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

900

800

700

I- 600

LU 

LU 

Li.

O

CD

O

- 500

<

cc

_J

<

ir 400 

Q

I

300

Q

200

100

SIMULATED SOURCE OF PUMPED FLUIDS 

Net storage depletion

Intercepted discharge to streams

Intercepted discharge to underlying 

units

Induced recharge from or intercepted discharge to overlying 

units

1940 1950 1960 1970 1980

FIGURE 38. Simulated changes in recharge, discharge, and 

storage in response to 1940-79 pumpage from Great Plains 

aquifer system.

withdrawals). Note that the 1970-79 rate of withdrawal was about 800 ft 3/s, which greatly exceeded the 

predevelopment recharge rate of 340 ft 3/s. The simulated source of pumped fluids was mostly induced 

recharge from or intercepted discharge to overlying 

units. Nearly one-third of the withdrawal is derived 

from storage depletion. Large-scale withdrawals from 

the Great Plains aquifer system would be accompanied by severe depletion of storage because of the limited natural recharge (Helgesen and others, 1993).

Some parts of the Great Plains aquifer system possess hydrologic characteristics potentially favorable 

for accepting liquid wastes. Successful and safe 

subsurface disposal of liquid wastes requires an aquifer with porosity and hydraulic conductivity sufficient 

to accept the wastes, and hydrogeologic conditions 

that would prevent movement of the wastes into areas 

where water quality is suitable for development.

Capability for accepting wastes as affected by 

hydraulic properties generally decreases with increases 

in depth of burial. As shown by extensive injection of 

oil-field brine, the strata commonly are capable of 

accepting waste, despite relatively large depths of 

burial. Garbarini and Veal (1968) identified the 

southern flank of the Denver Basin as potentially suitable for waste disposal at depths exceeding 1,000 ft. 

As discussed earlier, flow approaches stagnation in 

most of the Denver Basin, a favorable characteristic 

for waste disposal. Presuming that flow of solutes 

would be principally advective (that is, with the flow 

of water), flow velocities of the waste would be 

equally slow. The overlying confining system would 

restrict flow upward from the aquifer system, 

although its integrity may be reduced by improperly 

abandoned wells. A large downward hydraulic-head 

gradient prevails in most of the area, which creates 

favorable potential to keep the injected wastes in the 

aquifer system in the Denver Basin.

GREAT PLAINS CONFINING SYSTEM AND RELATED 

HYDROLOGIC UNITS

The Great Plains aquifer system is directly overlain by the Great Plains confining system in most 

places (fig. 39). The Great Plains confining system is 

as much as 8,000 ft thick (fig. 40). The confining 

units within this system are composed of shale, which 

include the Upper Cretaceous Graneros, Carlile, and 

Pierre Shales, and slightly permeable Tertiary clay 

and silt. The confining system also includes two 

extensive but minor aquifers. These aquifers are in 

the Greenhorn Limestone and the Niobrara Chalk. 

The confining system, at most locations, effectively 

restricts flow to and from the Great Plains aquifer system and the surficial High Plains aquifer if present, or 

to and from the water table in the soil zone.

The High Plains aquifer (fig. 2) mainly consists of 

permeable sand and gravel deposits of Tertiary and 

Quaternary age (Gutentag and others, 1984). Where 

present, its character permits hydraulic connection 

with adjacent units.

The glacial drift, which is mostly a till, consists of 

heterogeneous clay, silt, sand, and gravel and has a
REGIONAL AQUIFERS SUMMARY A47

105° 100 95°

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

WESTERN INTERIOR PLAINS CONFINING SYSTEM 

GREAT PLAINS CONFINING SYSTEM 

HIGH PLAINS AQUIFER 

GLACIAL DRIFT AND LOESS

 APPROXIMATE BOUNDARY BETWEEN PLAINS AND OZARK 

SUBREGIONS

FIGURE 39. Geohydrologic units overlying regional aquifer systems in the Plains subregion.

variable hydraulic character. Loess, which consists of 

uniform silt-size material, overlies the Great Plains 

aquifer system and the Western Interior Plains confining system at different locations and has moderate 

vertical permeability. The glacial drift and loess 

probably are a leaky confining system for the underlying aquifer units (fig. 39).

OZARK SUBREGION

The Ozark subregion (fig. 41) corresponds to the 

Ozark Plateaus physiographic province and the Ouachita physiographic province north of the Arkansas 

River. The subregion is bounded by the Missouri 

River, the Mississippi River, the Mississippi Alluvial 

Plain, the Arkansas River, and the broad and very
A48 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

105° 100° 95° 90°

WYOMING

y" v ? 

SOUTH DAKOTA

 '" "'" "-- . ,*~TT

40'

35'

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

 2000 LINE OF EQUAL THICKNESS OF GREAT PLAINS CONFINING SYSTEM 

Interval, in feet, is variable

i i i i i i LIMIT OF GREAT PLAINS CONFINING SYSTEM

FIGURE 40. Thickness of Great Plains confining system.

gentle regional topographic low extending from northeastern Oklahoma to the Missouri River in central 

Missouri.

Ground-water flow is, in general, regionally outward from a topographic high along an axis from the 

St. Francois Mountains in southeastern Missouri to 

the tristate corner of Missouri, Arkansas, and 

Oklahoma. Locally, flow generally is toward the deep 

stream valleys. Flow in the three regional aquifers of 

the Ozark Plateaus aquifer system (table 3) also is 

outward from a topographic ridge of the Boston 

Mountains in northwestern Arkansas towards the 

Arkansas Valley. The Ozark Plateaus aquifer system

is underlain by the basement confining unit that is 

composed mostly of igneous and metamorphic crystalline rocks. The basement rocks are fractured and 

locally water bearing, such as in the St. Francois 

Mountains (fig. 41), but on a regional basis they are 

assumed to form the base of the regional flow system.

OZARK PLATEAUS AQUIFER SYSTEM

Nearly all ground water used in the Ozark subregion, either well water or spring water, is from three 

regional aquifers that are within a distinct hydraulic 

system. These three aquifers and two intervening con-
REGIONAL AQUIFERS-SUMMARY A49

KANSAS MISSOURI

OKLAHOMA

60 MILES

0 30 60 KILOMETERS

EXPLANATION

 LIMIT OF OZARK SUBREGION

BOUNDARY OF PHYSIOGRAPHIC PROVINCES

- BOUNDARY OF PHYSIOGRAPHIC SUBDIVISIONS 

FIGURE 41. Physiographic features of the Ozark subregion.

fining units are termed the Ozark Plateaus aquifer system because of their widespread occurrence in the 

Ozark Plateaus physiographic province. The aquifer 

system overlies the basement confining unit and has 

an extensive outcrop area. The aquifer system is overlain by the Western Interior Plains confining system 

in a band that extends along the western and southern 

boundaries of the subregion and by similar rocks along 

the eastern boundary.

GEOHYDROLOGIC UNITS

The Ozark Plateaus aquifer system consists of five 

units, which, from lower to upper, are the St. Francois

aquifer, St. Francois confining unit, Ozark aquifer, 

Ozark confining unit, and Springfield Plateau aquifer.

The geohydrologic units of the Ozark Plateaus 

aquifer system are composed of sedimentary rocks 

that range in age from Cambrian through 

Mississippian (table 3). Boundaries between the geohydrologic units do not always conform to geologictime divisions or to formation boundaries, but delineate groups of rocks having similar hydrologic 

properties. All of the geohydrologic units that comprise the Ozark Plateaus aquifer system crop out in 

the Ozark Plateaus (fig. 42).

The lateral boundaries of each of the three regional 

aquifers generally are the same as those of the Ozark
A50 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

TABLE 3. Generalized correlation of geohydrologic units to stratigraphic units in most of the Ozark subregion

[From Jorgensen and others, 1993]

Geohydrologic uuit

Western Interior Plains

confining system

Ozark

Plateaus

aquifer

system

Springfield

Plateau

aquifer

Ozark confining

unit

Ozark

aquifer

St. Francois

confining unit

St. Francois

aquifer

Basement confining unit

Principal rock-straligraphic uuit(s)

Marmaton Group, Cherokee Group,

Atokan rocks, Bloyd Shale, Hale

Formation, Morrowan rocks, Pitkin

Limestone, Fayetteville Shale, and

Batesville Sandstone

Moorefield Formation, St. Louis Limestone,

Salem Limestone, Warsaw Limestone,

Boone Formation, St. Joe Limestone

Member of Boone Formation, Keokuk

Limestone, Burlington Limestone, and

Fern Glen Limestone

Chouteau Group 1 and

Chattanooga Shale, Northview Shale,

and Hannibal Shale

Clifty Limestone, Penters Chert, Lafferty

Limestone, St. Glair Limestone, Brassfield

Limestone, Cason Shale, Fernvale

Limestone, Kimmswick Limestone, Plattin

Limestone, Joachim Dolomite, St. Peter

Sandstone, Everton Formation, Smithville

Formation, Powell Dolomite, Cotter

Dolomite, Jefferson City Dolomite,

Roubidoux Formation, Gasconade

Dolomite, Gunter Sandstone Member of

Gasconade Dolomite, Eminence Dolomite,

and Potosi Formation

Elvins Group, Derby and Doe Run

Dolomite, Davis Formation

Bonneterre Dolomite,

Lamotte Sandstone,

and Reagan Sandstone

Mostly igneous and metamorphic rocks

Time- stratigraphic unit

Middle

Pennsylvania!!

through Upper

Mississippian

(Chesterian)

Mississippian

Lower Mississippian

and Upper Devonian

Middle

Devonian

through

uppermost

Cambrian

Upper

Cambrian

Precambrian

Designated Chouteau Limestone by U.S. Geological Survey.

subregion. The extent of the ground-water flow along 

the western boundary of the Ozark Plateaus aquifer 

system also is controlled by the thickness and permeability of the Western Interior Plains confining 

system. In general ground water flowing westward 

moves laterally down the hydraulic gradient and 

downdip in the aquifer below the land surface and 

confining system to below the broad topographic low 

that extends from northeastern Oklahoma into central 

Missouri, and then leaks upward (fig. 17). The downdip flow extends to a depth of about 500 ft. The 

Western Interior Plains aquifer system is laterally 

adjacent to the western boundary of the Ozark 

Plateaus aquifer system. In general, both aquifer systems discharge water vertically upward through the 

thin (and therefore leaky) confining system to the

streams or water table in the area of the broad topographic low. The flow system extends to about the 

Fall Line of northeastern Arkansas and the bootheel 

of southeastern Missouri. In general, flow across the 

Fall Line is intercepted by streams, marshes, and 

drainage canals in the Mississippi Alluvial Plain.

The St. Francois aquifer, the lowermost geohydrologic unit of the Ozark Plateaus aquifer system, consists of water-bearing sandstone and dolomite that 

rests on the basement confining unit. The aquifer 

crops out around the St. Francois Mountains (fig. 42) 

for which it is named and is overlain by the St. Francois confining unit.

The hydraulic head of the St. Francois aquifer is 

mostly topographically controlled. The aquifer is 

recharged by infiltration of precipitation through the
96° 95° 94° 93° 90°

39°38°

37°

36°

35°

EXPLANATION 

BASEMENT CONFINING UNIT ST. FRANCOIS AQUIFER 

ST. FRANCOIS CONFINING UNIT 

OZARK AQUIFER 

OZARK CONFINING UNIT

SPRINGFIELD PLATEAU 

AQUIFER

WESTERN INTERIOR PLAINS 

CONFINING SYSTEM

POST-PALEOZOIC SEDIMENTS

- - - - LIMIT OF OZARK SUBREGION

20 40 60 MILES 

J____I I

\ \ \

0 20 40 60 KILOMETERS

FIGURE 42. Outcrop areas of regional geohydrologic units in and adjacent to the Ozark Plateaus physiographic province.
A52 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

soil zone at the outcrops. The aquifer also is recharged 

by flow from the fractured Precambrian rocks of the 

basement confining unit near the outcrop area. 

Beyond the outcrop area, ground-water movement is 

restricted by the overlying confining unit. The aquifer 

discharges upward through the confining unit to overlying aquifers in areas downdip from the outcrop. 

However, exact areas of this discharge are not known 

because the hydraulic head in the aquifer is known 

only in the outcrop area.

The St. Francois confining unit, the lower of the 

two confining units in the Ozark Plateaus aquifer system, restricts flow between the St. Francois aquifer 

and the overlying Ozark aquifer at most locations. 

The leaky confining unit is composed of very slightly 

permeable shale, and slightly permeable siltstone, 

dolostone, and limestone. The rocks are part of three 

Upper Cambrian geologic units the Davis 

Formation, the Derby Dolomite, and the Doe Run 

Dolomite (table 3).

The Ozark aquifer is composed mostly of waterbearing dolostone and is the most permeable and the 

most extensively used aquifer in the Ozark subregion. 

The aquifer, except in the St. Francois Mountains 

area, is at land surface throughout the area that generally is termed the "Ozark area" or the "Ozarks." The 

aquifer accordingly is termed the Ozark aquifer 

because of the close association with the Ozarks. The 

aquifer consists of fractured and solutioned dolostone 

with some limestone, sandstone, chert, and shale. 

Sandstone, where it exists as massive bodies, generally 

is clean, well sorted, and permeable; however, in 

northern Arkansas, it is well cemented, slightly 

fractured, and much less permeable. The aquifer, at 

most locations, is underlain by the St. Francois confining unit and overlain by the Ozark confining unit. The 

aquifer crops out in a large area over the Ozark Uplift 

and is a greatly dissected karst terrain with numerous 

streams and springs.

Water in most of the Ozark aquifer is unconfined, 

and its occurrence and flow are controlled by topographic relief. Throughout the outcrop area, ground 

water moves toward the major rivers and their tributaries (fig. 43), and hundreds of springs have developed. Typically, flow to these springs is local because 

most recharge to the springs is in the upland intervalley areas and is discharged in nearby stream valleys. 

The Mississippi and Missouri River Valleys are major 

discharge areas for regional flow from the Ozark 

aquifer.

The Ozark confining unit, the uppermost confining 

unit of the Ozark Plateaus aquifer system, restricts 

flow between the underlying Ozark aquifer and the 

overlying Springfield Plateau aquifer. The Ozark

confining unit is named for its position relative to the 

underlying Ozark aquifer, which it confines. The leaky 

confining unit is composed mostly of shale, shaley 

limestone, and limestone.

The Springfield Plateau aquifer is composed of 

water-bearing limestone and is exposed at many locations on the Springfield Plateau, from which its name 

is taken, in southwestern Missouri. The aquifer, 

except along the Fall Line, extends outward from the 

outcrop area to the periphery of the Ozark subregion 

and dips into the subsurface along the west and south 

boundaries of the subregion, where it is overlain by 

nearly impermeable shale layers of the Western Interior Plains confining system. The aquifer is the uppermost unit of the Ozark Plateaus aquifer system and, 

at most locations, overlies the Ozark confining unit.

The Springfield Plateau aquifer also is present in 

the subsurface south of the Boston Mountains in 

Arkansas. In that area, water in the aquifer contains 

in excess of 1,000 mg/L dissolved solids, probably 

because near-surface permeability has not been developed, and thus, the slowly moving water probably dissolves minerals as it passes through the overlying 

Western Interior Plains confining system. The aquifer 

south of the Boston Mountains is unused because of 

greater dissolved-solids concentrations and small well 

yields.

Hydraulic-conductivity values for the Springfield 

Plateau aquifer are not available. Estimates of 

hydraulic conductivity based on specific capacity 

generally are not available because nearly all wells of 

sufficient diameter to permit measurement of 

drawdown are open to both the Springfield Plateau 

aquifer and the underlying Ozark aquifer.

The Springfield Plateau aquifer is recharged mostly 

at its outcrop areas. In general, water moves locally 

from high intervalley recharge areas to low discharge 

areas along the streams that dissect the area. Regionally, lateral flow in the Springfield Plateau aquifer is 

believed to be similar to that in the underlying Ozark 

aquifer.

The Springfield Plateau aquifer is overlain along 

the western and southern borders by rock that 

restricts or confines flow to and from the aquifer. The 

overlying confining material is the eastern edge of the 

Western Interior Plains confining system, which is 

composed of layers of very slightly permeable shale 

and of moderately permeable limestone, sandstone, 

and coal. The limestone is slightly fractured and has a 

small permeability, except near land surface where 

dissolution has markedly increased permeability. The 

same geologic formations comprising the Springfield 

Plateau aquifer exist near St. Louis in the northeast 

corner of the subregion near the confluence of the
REGIONAL AQUIFERS SUMMARY A53

OKLAHOMA

30 60 KILOMETERS

EXPLANATION

AQUIFER ABSENT

600- - POTENTIOMETRIC CONTOUR Shows altitude at which water level would 

have stood in tightly cased well. Dashed where approximate. Contour 

interval 200 feet. Datum is sea level

 2000 LINE OF EQUAL DISSOLVED-SOUDS CONCENTRATION 

Interval 1,000 milligrams per liter

"""I* MAJOR DIRECTION OF REGIONAL FLOW IN OZARK AQUIFER

i^^ MAJOR DIRECTION OF FLOW IN WESTERN INTERIOR PLAINS AQUIFER 

SYSTEM

FIGURE 43. Predevelopment potentiometric surface of the Ozark aquifer.

Missouri and Mississippi Rivers. These rocks are not 

in the Springfield Plateau aquifer flow system; they 

form two local and isolated flow systems. The rocks 

have hydraulic characteristics that are similar to the 

Springfield Plateau aquifer. The rocks at this location 

are about 900 ft thick and thicken abruptly to the 

east, attaining a thickness of more than 1,500 ft 

within a few miles.

PROPERTIES

The altitude and thickness of the aquifers and confining units are shown in Imes and Emmett (1994). 

The St. Francois aquifer generally is between 200 and 

500 ft thick. The Ozark aquifer is the thickest (commonly about 1,000 ft) geohydrologic unit in the Ozark 

subregion; its thickness is shown in figure 44. The 

Springfield Plateau aquifer is between 100 and 400 ft 

thick throughout much of the subregion.
96° 95° 94° 93° 92° 90°

39°38°

37°

36°

35°

I I

EXPLANATION 

OUTCROP AREA OF AQUIFER

AREAL EXTENT OF AQUIFER IN 

SUBSURFACE

LINE OF EQUAL THICKNESS Interval, 

in feet, is variable

BOUNDARY OF OZARK SUBREGION

0 20 40 60 MILES 

I I I

I I I 

0 20 40 60 KILOMETERS

Qi iO

FIGURE 44. Thickness of Ozark aquifer.
REGIONAL AQUIFERS SUMMARY A55

Estimated hydraulic conductivity of the St. Francois aquifer, based on specific capacity of wells, ranges 

from IxlO"4 to 1x10 "6 ft/s in outcrop areas near the St. 

Francois Mountains and tends to decrease away from 

the outcrop areas. Little data are available elsewhere 

because the rocks become more deeply buried and 

strata that are more water yielding overlie the St. 

Francois aquifer. The St. Francois confining unit is, of 

course, less permeable than the aquifer. The vertical 

hydraulic conductivity of the confining unit decreases 

with increasing shale content. Percentage of shale 

ranges from 0 to more than 40 percent and generally is 

less than 30 percent.

The hydraulic conductivity of the Ozark aquifer 

has been estimated from specific-capacity data and 

inferred from the density of fractures and the degree 

of development of solution openings. The areas of 

greatest hydraulic conductivity are concentrated along 

an east-west line passing through the St. Francois 

Mountains where the hydraulic conductivity may be 

as much as 1x10 "3 ft/s. In areas where dissolution has 

occurred and springs are numerous, the hydraulic 

conductivity exceeds IxlO'1 ft/s. Hydraulic conductivity of the aquifer decreases to the south to as little as 

IxlO"8 ft/s near the southern boundary of the subregion. The hydraulic conductivity of the Ozark confining unit decreases with increasing shale content. Shale 

content ranges from 0 to 100 percent, and shale contents greater than 50 percent are typical.

Values of hydraulic conductivity of the Springfield 

Plateau aquifer from aquifer or specific-capacity tests 

are not available. Hydraulic conductivity is highly 

variable, being large where karst terrain has developed 

and much smaller in nonkarstic areas and at greater 

depths.

MODEL ANALYSIS AND HYDROLOGIC BUDGET

A finite-difference digital model of the Ozark Plateaus aquifer system was made to analyze flow quantities in the hydrologic system (Imes and Emmett, 

1994). The model was constructed to simulate natural 

flow conditions prior to development of water supplies 

from the aquifer system. An ancillary purpose was to 

evaluate the accuracy of estimates of hydraulic properties. The model of McDonald and Harbaugh (1984) 

was used. The model grid consists of 22 rows and 28 

columns, with uniform cell size of 14 mi x 14 mi. The 

axes of the grid network are aligned North 35° West 

and North 55 ° East, generally coinciding with the prevailing directions of the significant lineaments and 

known fault and fracture traces; it is the same alignment that was used in the regional model.

The three-dimensional model contains four layers 

that are, from top to bottom: the Western Interior 

Plains confining system (layer 1), the Springfield Plateau aquifer (layer 2), the Ozark aquifer (layer 3), and 

the St. Francois aquifer (layer 4). The Western Interior Plains confining system is not part of the Ozark 

Plateaus aquifer system and is incorporated into the 

model only as a passive layer that forms the necessary 

restriction to the exchange of water between the water 

table or streams near land surface and the Springfield 

Plateau aquifer. Potentiometric heads are simulated 

only for the three aquifers that are part of the Ozark 

Plateaus aquifer system. The intervening Ozark confining unit and St. Francois confining unit are not 

treated as model layers.

A transient-state model was not developed for the 

Ozark Plateaus aquifer system because of the insignificant amount of regional drawdown in any of the three 

aquifers that are part of the Ozark Plateaus aquifer 

system. Drawdown cones associated with municipal 

pumpage generally are localized and not interconnected regionally because, historically, ground-water 

use in most of the Ozarks has been small. Many of 

the large-capacity wells withdraw water from unconfined parts of the aquifers where large quantities of 

stored water inhibit development of large drawdown 

cones.

The exception to these general statements occurs in 

the tristate lead-mining district located in the vicinity 

of the Missouri, Kansas, and Oklahoma borders. Here, 

large-capacity pumps were used to dewater large areas 

of the Springfield Plateau aquifer during the early 

part of the 20th century. The mining pumpage along 

with municipal pumpage in the area lowered water 

levels several hundred feet throughout the mining district and surrounding area. Many of the mines have 

been closed since World War II, and water levels have 

recovered to predevelopment altitudes except where 

municipal pumpage, most notably in Ottawa County, 

Oklahoma, is continuing.

Accurate modeling of the boundary condition of 

recharge to the water table and stream-aquifer interchange is extremely important because recharge to the 

aquifer from precipitation is the dominant source of 

water to the aquifer system. Stream-aquifer interaction is the dominant discharge of water from the aquifer system. The quantity of recharge to the water 

table per model cell was estimated from results of an 

investigation by Dugan and Peckenpaugh (1985). 

That investigation considered soil slope, permeability, 

depth to water table, land use, and 30 years of climate 

record. However, it is not possible to use these 

recharge values directly. Due to the coarse grid of the 

finite-difference flow model, all ground-water flow is
A56 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

not simulated. The model only simulates intercell 

(regional) flow; it does not simulate intercell flow that 

results from recharge to and discharge from the same 

cell. The recharge rate specified in the model must be 

adjusted downward to represent only that component 

of recharge that becomes intercell (regional) flow. For 

this purpose, a method proposed by Jorgensen and 

others (1989a, 1989b) was used. The application of 

that method and the design, assumptions, boundary 

conditions, and simulation results of the flow model of 

the Ozark Plateaus aquifer system are described by 

Imes and Emmett (1994). The reduced rate of 

recharge used in the model and the total recharge rate 

(estimated by Dugan and Peckenpaugh, 1985) are 

shown in figure 45.

The independently derived and model-cell adjusted 

values of recharge to the water table and stream-aquifer interchange were used in the model to calculate 

hydraulic heads; during calibration, these heads were 

compared to water levels measured in wells. The 

model was tested for sensitivity to changes in recharge 

to the water table, hydraulic conductivity of layers 2, 

3, and 4 (aquifer layers), and vertical leakance 

between layers 1 and 2, layers 2 and 3, and layers 3 

and 4. The model was found to be sensitive to all 

aquifer properties tested, but it was dominantly sensitive to changes in recharge to the water table.

The hydraulic-conductivity and transmissivity values of layers 2, 3, and 4 (Springfield Plateau, Ozark, 

and St. Francois aquifers) of the calibrated model 

(simulated water levels matched well with predevelopment water levels) are shown in figures 46, 47, and 48. 

These maps show effective values for the entire thickness of each unit and do not show the large variations 

that occur locally within each aquifer. Rocks affected 

by surficial karst or paleokarst possess very large 

hydraulic conductivity.

A water budget for the Ozark Plateaus aquifer system shows that prior to development only 6 percent of 

the mean annual precipitation in the aquifer system 

outcrop area contributed to the deeper regional 

ground-water flow that is simulated. About 25 percent of the 127,187 ft 3/s precipitation on the aquifer 

system outcrop area percolated to the water table. Of 

the water that entered the water table, about 78 percent was intracell flow that discharged into nearby 

streams and springs. This water is not simulated in 

the flow model. The remaining 7,091 ft 3/s (6 percent 

of precipitation) became regional ground-water flow 

and is simulated. Of this regional flow, 4,035 ft 3/s of 

water discharged to regional sinks (large streams and 

lakes) inside the study area, and 3,056 ft 3/s of water 

discharged as boundary flow to the Mississippi, Missouri, and other major rivers, aquifers of the Mississippi Embayment, and the water table in the Western 

Interior Plains confining system (fig. 49). Because 

pumping rates are small compared to the large natural 

rates of recharge and discharge, the regional 

ground-water budget prior to development probably is 

similar to the present-day budget.

USE AND POTENTIAL

About 200 Mgal of ground water is withdrawn 

daily from wells completed in the Ozark Plateaus 

aquifer system for public supply, industrial use, 

domestic and stock supplies, and supplemental irrigation. In addition, large withdrawals for dewatering of 

underground mines were common around the turn of 

the century. The Ozark Plateaus aquifer system 

unquestionably supports the largest yields to wells of 

any of the aquifer systems in the CMRASA study 

area.

Wells completed in the St. Francois aquifer yield 

as much as 500 gal/min in areas where a significant 

thickness of Lamotte Sandstone is penetrated. Yields 

of wells penetrating only the Bonneterre Dolomite 

typically are less. However, withdrawals for dewatering mines in the Bonneterre Dolomite in the "Old 

Lead Belt" in southeastern Missouri reportedly ranged 

from 13 to 17 Mgal per day in the early 1900's (Buckley, 1908). These mines mostly were closed by the 

1960's. Mines in the "New Lead Belt," also in the Bonneterre Dolomite in southeastern Missouri, reportedly 

were dewatered at an average rate of 26 Mgal per day 

in 1971 (Warner and others, 1974). Withdrawals at 

individual mines were as much as 4,900 gal/min. The 

St. Francois aquifer, therefore, obviously has the 

potential to support large withdrawals from wells.

The Ozark aquifer is the primary source of water 

to large-yield public-supply, industrial, and irrigation 

wells throughout the Ozarks and adjacent areas (Imes 

and Emmett, 1994). Wells that penetrate all the 

most-permeable units of the aquifer underlying the 

Salem Plateau (fig. 41) yield as much as 1,000 gal/min 

in places. Formations in the Ozark aquifer that yield 

the largest amounts of water to wells are the St. Peter 

Sandstone, the Roubidoux Formation, the Gunter 

Sandstone Member of the Gasconade Dolomite, and 

the Potosi Dolomite. Individual formations, such as 

the Roubidoux and Gasconade, yield 500 gal/min to 

wells locally. The potentiometric surface of the Ozark 

aquifer was lowered as much as 400 ft by large-scale 

municipal and industrial withdrawals near Miami, 

Oklahoma, 200 ft by industrial withdrawals near 

Springfield, Missouri, and 100 ft by municipal withdrawals for Pittsburg, Kansas. Nevertheless, the 

potential for additional development of water supplies
Less than 25 cubic feet per 

second per cell

25 to 50 cubic feet per 

second per cell

50 to 100 cubic feet per 

second per cell

Greater than 100 cubic feet 

per second per cell

25 LINE OF EQUAL REDISTRIBUTED RECHARGE 

TO WATER TABLE 

Corrected to account for flux~ 

that remains internal to a 

model cell. Interval, in cubic feet per second per cell, is 

variable

0 20 40 60 KILOMETERS

36° - 35° -FIGURE 45. Recharge to water table as estimated by Dugan and Peckenpaugh (1985) and redistributed recharge to account for water that remains internal to a cell of the

Ozark model.
95° 94° 93° 92° 90°

39°38°

37°

36°

35°

EXPLANATION

AREA WHERE MODEL LAYER 2 

IS INACTIVE

ZONE OF EQUAL LATERAL 

HYDRAULIC CONDUCTIVITY

2.5 x 10"4 foot per second 

3.5 x 10"3 foot per second

0.04 LINE OF EQUAL TRANSMISSIVITYInterval, in feet squared per second, 

is variable

I I 1 

0 20 40 60 KILOMETERS

60 MILES 

J

O

I-H

O* >IT1 >

 o

FIGURE 46. Distribution of lateral hydraulic conductivity and transmissivity for Ozark model layer 2.
95° 94° 93° 92° 90°

39°

38°

37°

35°

EXPLANATION

AREA WHERE MODEL 

LAYER 3 IS INACTIVE -

ZONE OF EQUAL LATERAL 

HYDRAULIC CONDUCTIVITY

1.0 x 10 -5 foot per second 

8.0 x 10 ~5 foot per second 

1.3 x 10 " 4 foot per second 

2.5 x 10 '4 foot per second 

4.5 x 10 -4 foot per second 

6.0 x 10 -4 foot per second 

6.5 x 10 ~4 foot per seconcf 

7.0 x 10 -4 foot per second 

8.0 x 10~4 foot per second

0.5- LINE OF EQUAL TRANSMISSIVITY Interval, 

in feet squared per second, is variable

20 40 60 MILES 

I____I

I I I

0 20 40 60 KILOMETERS

 O

FIGURE 47. Distribution of lateral hydraulic conductivity and transmissivity for Ozark model layer 3.
96° 95° 94° 93° 92° 90°

\ I

37° - 36° - EXPLANATION AREA WHERE MODEL LAYER 4 IS INACTIVE ZONE OF EQUAL LATERAL HYDRAULIC CONDUCTIVITY 8.0 x 10 " 5 foot per second 1.6 x 10 "4 foot per second -0.07- LINE OF EQUAL TRANSMISSIVITY- Interval, in feet squared per second, is variable

35° - 40 60 MILES 

J____I \ II 

0 20 40 60 KILOMETERS

 O

oo

f

O

FIGURE 48. Distribution of lateral hydraulic conductivity and transmissivity for Ozark model layer 4.
Net recharge from water 

table to layer 2

1,279

EXPLANATION

CONFINING MATERIAL 

MODEL BOUNDARY Impervious 

1,447 NET FLOW, IN CUBIC FEET PER SECO

r*

8- //

to //

>-| V/,

0* /,

et ofthe Ozar

simulation

£ X

(C / /

8 % 

g //

-0 //

1 ^

'/

S- //

1 ^

°" V

1 ^

d ^/

V

. 

1,447 91

 

c 

,

Springfield Plateau 

, aquifer (layer 2)

1,526 :

2

i6; '..'. ';

\

water taoie, post-raieozoic sediment (part or layer 

and rivers were simulated as specified head 

Net recharge from water boundary, 

table to layers

107 i

*- Riv 

i

2,227 6/

\

 

Ozark aquifer (layer 3)

2!

i

iO

srs

1,7

i

39

^/

N

O

Net recharge from water 

table to layer 4

923 

Rivers

- ->-

,

T

;

I

'

3

i

3

UJ

?

0.

w

UJ

^

8i

St. Francois aquifer (layer 4)
A62 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

from the Ozark aquifer is large, particularly in areas 

removed from municipal and industrial well fields.

Wells completed in the Springfield Plateau aquifer 

generally have smaller yields than wells in the Ozark 

aquifer. Most wells completed entirely in the Springfield Plateau aquifer are for domestic and stock use 

and yield less than 25 gal/min. Some industrial wells 

in Jasper County, Missouri, however, yield as much as 

400 gal/min from fractured zones in the aquifer. Large 

amounts of water were pumped for dewatering mines 

and processing ore in the tristate lead-zinc mining district of southwest Missouri, southeast Kansas, and 

northeast Oklahoma. The pumpage indicates that 

large yields can be obtained in places. Abernathy 

(1941, p. 234) states that as much as 2 Mgal of water 

were pumped daily to dewater some of the mines.

GEOCHEMISTRY OF REGIONAL 

AQUIFERS

The chemistry of water in each of the aquifer systems in the CMRASA area is distinct and is described 

separately below, starting with the Western Interior 

Plains aquifer system.

The Western Interior Plains aquifer system 

includes water-bearing lower units, a confining unit, 

and a water-bearing upper unit. Water from the lower 

units of the Western Interior Plains aquifer system 

contains less than 10,000 mg/L dissolved solids in only 

a few areas; locally and in the eastern part of the Anadarko Basin in Oklahoma, dissolved-solids 

concentrations exceed 300,000 mg/L (fig. 18). Movement of ground water, as indicated by lateral differences in density and pressure, is highly complex. In 

the western part of the area, flow is toward the southeast, changing to east-southeast along the Central 

Kansas Uplift. In the southern part of the area underlain by lower units, water moves radially outward 

from the Anadarko Basin. Virtually all water from the 

lower units is of the sodium chloride type, with chloride concentrations as large as 190,000 mg/L in the 

Anadarko Basin (fig. 50). Sodium-to-chloride ratios 

generally are similar to those of seawater, and calcium-to-magnesium ratios commonly are about 2.5. 

Chloride-to-sulfate ratios, however, typically are 

much larger than that of seawater, suggesting loss of 

sulfate during concentration of the original connate 

waters (Baker and Leonard, 1995).

The formations that constitute the confining unit 

and the upper aquifer unit in the Western Interior 

Plains aquifer system were removed from large parts 

of the area by erosion in Mississippian time. Groundwater flow patterns in the upper unit generally are

similar to those in the underlying rocks. Where the 

upper unit is present, the water is somewhat fresher 

than water in the lower aquifer units. However, the 

distribution of dissolved-solids concentrations is 

broadly similar to that of the lower units; maximum 

concentrations typically are less than 250,000 mg/L 

(fig. 27). Nearly all the water is a sodium chloride 

type, with chloride concentrations locally as large as 

180,000 mg/L (fig. 51). Sodium-to-chloride ratios in 

the upper unit typically are smaller than ratios in the 

lower units, generally ranging from about 0.65 to 0.8. 

Ratios of calcium to magnesium are larger, reflecting 

the presence of more limestone and less dolomite in 

the upper unit. Chloride-to-sulfate ratios tend to be 

smaller than ratios in water from the lower units, but 

typically much larger than ratios in seawater (Baker 

and Leonard, 1995).

Although the Western Interior Plains confining 

system functions as a regional confining unit, the 

areally extensive limestone and sandstone formations 

in the older part of the section are permeable, especially at shallow depths, and locally are water bearing 

or contain prolific reservoirs of oil. Water from the 

confining system at depths below 500 ft generally contains large concentrations of dissolved solids, locally 

as great as 300,000 mg/L. Dissolved-solids concentrations tend to be very large in rocks above and below 

evaporite deposits in the upper part of the confining 

system. At depths greater than 500 ft, most water 

samples are a sodium chloride type, and chloride 

concentrations of 50,000 mg/L or greater are common 

(Baker and Leonard, 1995).

In the southeastern two-thirds of the study area, 

rocks of the confining system have been exposed to a 

long period of erosion and subaerial weathering. 

Increased permeability of many of these rocks, due to 

weathering and dissolution, together with the incursion of meteoric water, has altered the chemical character of the shallow (less than 500 ft deep) ground 

water, which now bears little resemblance to water in 

the regional flow systems. Concentrations of dissolved 

solids range from a few hundred to more than 

100,000 mg/L and vary widely over short distances 

(Baker and Leonard, 1995), reflecting the variability 

of the rock materials both laterally and vertically. 

The more dilute water generally is a calcium bicarbonate type; water with large concentrations of dissolved 

solids is a sodium chloride or calcium sulfate type and 

generally is associated with the presence of evaporite 

deposits.

In the northwestern part of the study area, the 

Western Interior Plains confining system is overlain 

by rocks of Cretaceous age that contain the Great 

Plains aquifer system. This system consists of two
REGIONAL AQUIFERS SUMMARY A63

0 100 200 KILOMETERS

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

.7.000 LINE OF EQUAL CHLORIDE CONCENTRATION

IN WATER MOSTLY FROM MIDDLE ORDOVICIAN 

UPPER ORDOVICIAN, SILURIAN, AND DEVONIAN 

ROCKS Dashed where approximately located. 

Interval, in milligrams per liter, is variable

-7,000- LINE OF EQUAL CHLORIDE CONCENTRATION 

IN WATER MOSTLY FROM UPPER CAMBRIAN 

AND LOWER ORDVIC1AN ROCKS Dashed 

where approximately located. Interval, in milligrams 

per liter, is variable

i i i i i i nil i LIMIT OF LOWER UNITS IN THE WESTERN 

INTERIOR PLAINS AND OZARK PLATEAUS 

AQUIFER SYSTEMS

 APPROXIMATE BOUNDARY BETWEEN PLAINS 

AND OZARK SUBREGIONS

FIGURE 50. Chloride concentrations in water from lower units in the Western Interior Plains aquifer system and the Ozark and

St. Francois aquifers in the Ozark Plateaus aquifer system.
A64 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

105

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

EXPLANATION

 ,,ooo LINE OF EQUAL CHLORIDE CONCENTRATION 

IN WATER MOSTLY FROM UPPER UNITS IN 

THE WESTERN INTERIOR PLAINS AND OZARK 

PLATEAUS AQUIFER SYSTEMS-Dashed where 

approximately located. Interval, in milligrams per 

liter, is variable

i I i i i in MI LIMIT OF UPPER UNITS IN THE WESTERN

INTERIOR PLAINS AND OZARK PLATEAUS 

AQUIFER SYSTEMS

 APPROXIMATE BOUNDARY BETWEEN PLAINS 

AND OZARK SUBREGIONS

FIGURE 51. Chloride concentrations in water from upper unit in the Western Interior Plains aquifer system and the Springfield

Plateau aquifer in the Ozark Plateaus aquifer system.

aquifer units, both composed primarily of slightly 

cemented water-bearing sandstone deposits, that are 

separated by a thin, discontinuous shale confining unit 

(fig. 29). The direction of ground-water flow and the 

chemistry of the water generally are similar in both 

aquifer units. Water generally moves from west to

east through the system. Concentrations of dissolved 

solids exceed 5,000 mg/L in most water from the interior part of the system and are as large as 

125,000 mg/L locally in western Nebraska (Helgesen 

and others, 1993, plate 6). Outside the Denver Basin, 

very large concentrations of dissolved solids seem to
REGIONAL AQUIFERS SUMMARY A65

be related to evaporite deposits in the underlying 

confining system (figs. 17 and 26). Around the southern and eastern boundaries of the system, the aquifers 

are at or near land surface, and concentrations of dissolved solids less than 1,000 mg/L result from addition 

of meteoric water or freshwater from overlying aquifers (Leonard and others, 1983).

Water types in the Great Plains aquifer system differ greatly. The more concentrated water (more than 

5,000 mg/L) generally is a sodium chloride type, but 

fresher water is a sodium sulfate, sodium bicarbonate, 

or calcium bicarbonate type (Helgesen and others, 

1993, plates 6 and 7). Calcium sulfate water in northeastern Nebraska and in small areas near the eastern 

boundary of the system in Kansas probably are 

related to solution of gypsum or to upward leakage of 

water from the underlying rocks of Permian age. Chloride concentrations in water from most parts of the 

system (Helgesen and others, 1993, plate 8) are 

considerably less than in modern seawater, indicating 

that the sediment was deposited in brackish (rather 

than saline) water or that there has been some flushing and dilution of connate water. Sodium-to-chloride 

ratios in water from most of the system also are less 

than ratios in modern seawater (Helgesen and others, 

1993, plate 9); however, near the outcrop area, 

sodium-to-chloride ratios as great as 10 suggest the 

addition of sodium-rich water. Calcium-to-magnesium ratios in most of the aquifer system range from 

about 0.2 to 3.5 and are associated with a wide variety 

of water types and concentrations (Baker and 

Leonard, 1995). Ratios of chloride to sulfate vary 

widely and, generally, seem to relate to chloride concentrations.

The Ozark Plateaus aquifer system consists of 

three aquifer units separated by two confining units 

(table 3). The lowermost aquifer unit, the St. Francois aquifer, is separated from the overlying Ozark 

aquifer by the St. Francois confining unit. The confining unit generally is leaky and locally is absent, and 

the hydrochemistry of the two aquifer units is similar. 

Water in these aquifers commonly contains less than 

500 mg/L dissolved solids (fig. 18) and is a calcium 

magnesium carbonate type. Sodium, sulfate, and 

chloride concentrations in most samples are only a few 

milligrams per liter. Calcium-to-magnesium ratios 

typically are near 1, consistent with the predominantly dolomitic rocks (Baker and Leonard, 1995). 

Overall, the water chemistry represents meteoric 

water charged with carbon dioxide approaching equilibrium with the carbonate rocks through which it is 

moving.

The upper aquifer unit, the Springfield Plateau 

aquifer, is at or near land surface over most of its

areal extent and generally is unconfined. As in the 

underlying aquifers, the chemical character of the 

water is the result of the solution of aquifer materials 

by meteoric water. Dissolved-solids concentrations 

commonly are less than 300 mg/L (fig. 52), and virtually all water samples are a calcium bicarbonate type. 

Calcium-to-magnesium ratios generally are greater 

than 5, reflecting the preponderance of limestone over 

dolostone in the rocks of this unit (Baker and 

Leonard, 1995).

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and older rocks in Bourbon, Crawford, Cherokee, and Labette 

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A66 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

105'

s,

SOUTH DAKOTA

1 '^ I "S y .^f.y-^A-»<

Base modified from U.S. Geological Survey 

1:7,500,000, National Atlas, 1970

 5,000-

EXPLANATION

LINE OF EQUAL DISSOLVED-SOLIDS CONCENTRATION IN WATER 

FROM UPPER UNITS OF THE WESTERN INTERIOR PLAINS AQUIFER 

SYSTEM AND THE SPRINGFIELD PLATEAU AQUIFER IN THE OZARK 

PLATEAUS AQUIFER SYSTEM Dashed where approximate. Interval, 

in milligrams per liter, is variable

APPARENT DIRECTION OF LATERAL FLOW Based on pressure and 

density near the center line of the geohydrologic unit

LIMIT OF UPPER UNITS OF THE WESTERN INTERIOR PLAINS AQUIFER 

SYSTEM AND OF SPRINGFIELD PLATEAU AQUIFER

APPROXIMATE BOUNDARY BETWEEN PLAINS AND OZARK SUBREGIONS 

FAULT U, upthrown side; D, downthrown side

FIGURE 52. Dissolved-solids concentrations in water from upper unit in the Western Interior Plains aquifer system and the 

Springfield Plateau aquifer in the Ozark Plateaus aquifer system.

Grubb, H.F., in press, Summary of hydrology of the regional aquifer systems, Gulf of Mexico Coastal Plain, south-central 

United States: U.S. Geological Survey Professional Paper 

1416-A.

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.

Hayes, W.C., 1962, Precambrian surface showing major lineaments: 

Missouri Geological Survey map, 1 sheet, scale 1:500,000.
REGIONAL AQUIFERS SUMMARY A67

Hedman, E.R., and Engel, G.B., 1989, Flow characteristics for

selected streams in the Great Plains subregion of Central Midwest regional aquifer system and selected adjacent 

areas Kansas and Nebraska, and parts of Colorado, Iowa, 

Missouri, New Mexico, Oklahoma, South Dakota, Texas, and 

Wyoming: U.S. Geological Survey Hydrologic Investigations 

Atlas HA-708, 3 sheets, scale 1:1,000,000.

Hedman, E.R., and Jorgensen, D.G., 1990, Surface-and

ground-water interaction and hydrologic budget of the Missouri River Valley aquifer between Yankton, South Dakota, 

and St. Louis, Missouri: U.S. Geological Survey Hydrologic 

Investigations Atlas HA-721, 1 sheet, scale 1:1,500,000.

Hedman, E.R., Skelton, John, and Freiwald, D.A., 1987, Flow characteristics for selected springs and streams in the Ozark subregion, Arkansas, Kansas, Missouri, and Oklahoma: 

U.S. Geological Survey Hydrologic Investigations Atlas 

HA-688, 4 sheets, scale 1:750,000.

Helgesen, J.O., and Hansen, C.V., 1989, Description of data files 

compiled for the Central Midwest Regional Aquifer-System 

Analysis: U.S. Geological Survey Open-File Report 89-42, 

37 p.

Helgesen, J.O., Jorgensen, D.G., Leonard, R.B., and Signor, D.C., 

1982, Regional study of the Dakota aquifer (Darton's Dakota 

revisited): Ground Water, v. 20, no. 4, p. 410-414.

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 plates.

Imes, J.L., and Eramett, 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., 1989, Some uses of geophysical logs to estimate 

porosity, water resistivity and intrinsic permeability: U.S. 

Geological Survey Water-Supply Paper 2321, 24 p.

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Geological Survey Bulletin 1989-D, 32 p.

Jorgensen, D.G., Gogel, Tony, and Signor, D.C., 1982, Determination of flow in aquifers containing variable density water: 

Ground Water Monitoring Review, v. 2, no. 2, p. 40-45.

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aquifers in Kansas and 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., 25 plates.

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 

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for intracell flow in models with special emphasis on 

water-table recharge and stream aquifer interaction Part 1, 

problems and concepts: Water Resources Research, v. 25, 

no. 4, p. 669-676.

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on water-table recharge and stream-aquifer interaction 

Part 2, a procedure: Water Resources Research, v. 25, no. 4,

p. 677-684. 

King, P.B., compiler, 1968, Tectonic map of North America, in

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scale 1:7,500,000. 

Kinney, D.M., compiler, 1966, Geologic map of the United States:

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America, p. 74-75, scale 1:7,500,000.

Krueger, J.M., and Keller, G.R., 1986, Interpretation of crustal 

structure from regional gravity anomalies, Ouachita Mountains area and adjacent Gulf Coastal Plain: American Association of Petroleum Geologists Bulletin, v. 70, no. 6, p. 667-689.

Leonard, R.B., Signor, D.C., Jorgensen, D.G., and Helgesen, J.O., 

1983, Geohydrology and hydrochemistry of the Dakota aquifer, central United States: Water Resources Bulletin, v. 19, 

no. 6, p. 903-911.

McDonald, M.G., and Harbaugh, A.W., 1984, A modular

three-dimensional finite-difference ground-water flow model: 

U.S. Geological Survey Open-File Report 83-875, 528 p.

McKee, E.D., and others, 1967, Paleotectonic maps of the Permian 

System: U.S. Geological Survey Miscellaneous Geologic 

Investigations Map 1-450, 164 p.

McKee, E.D., Oriel, S.S., Ketner, K.B., MacLachlan, M.E., Goldsmith, J.W., MacLachlan, J.C., and Mudge, M.R., 1959, 

Paleotectonic maps of the Triassic System: U.S. Geological 

Survey Miscellaneous Geologic Investigations Map 1-300, 

33 p., 9 sheets, scale 1:5,000,000.

Merriam, D.F., 1963, Geologic history of Kansas: Kansas Geological Survey Bulletin 162, 317 p.

Oetking, Philip, Feray, D.E., and Renfro, H.B., compilers, 1966, 

Geological highway map of the mid-continent region, Kansas, 

Missouri, Oklahoma, and Arkansas: American Association of 

Petroleum Geologists Map 1, 1 sheet, scale 1:1,900,800.

 1967, Geological highway map of southern Rocky Mountain 

region, Utah, Colorado, Arizona, and New Mexico: American 

Association of Petroleum Geologists Map 2,1 sheet, 

scale 1:1,900,800.

Renfro, H.B., compiler, (no date), Geological highway map of

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Schoon, R.A., 1971, Geology and hydrology of the Dakota Formation in South Dakota: South Dakota Geological Survey 

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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, 109 p., 2 plates.

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midcontinent, U.S.A.: U.S. Geological Survey Open-File 

Report 85-0604, 16 p., 1 sheet, scale 1:1,000,000.

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analysis in parts of Colorado, Kansas, Nebraska, New Mexico, 

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55 p.

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ISBN 0-t07-fl7D32-X

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