GEOHYDROLOGY OF THE 

OZARK PLATEAUS AQUIFER SYSTEM 

IN PARTS OF MISSOURI, ARKANSAS, 

OKLAHOMA, AND KANSAS

U.S, GEOLOGICAL SURVEY PROFESSIONAL PAPER 1414-D
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Geohydrology of the 

Ozark Plateaus Aquifer System 

in Parts of Missouri, Arkansas, 

Oklahoma, and Kansas

By J.L. IMES and L.F. EMMETT

REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1414-D

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Robert M. Hirsch, Acting 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

Imes, Jeffrey L.

Geohydrology of the Ozark Plateaus aquifer system in parts of Missouri, Arkansas, Oklahoma, and Kansas / by J.L. 

Imes and L.F. Emmett.

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

1414-D)

Includes bibliographical references.

1. Aquifers Ozark Mountains. I. Emmett, Leo F. II. Title. III. Series. IV. Series: U.S. Geological Survey 

professional paper ; 1414-D. 

GB1199.3.09I44 1993

551.49'09767'1 dc20 93-37490

CIP

For sale by U.S. Geological Survey, Map Distribution, 

Box 25286, MS 306, 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.

n?.

Robert M. Hirsch 

Acting Director

CONTENTS

Abstract 

Introduction 

j, ^|1Y*f\/\QA LU£/UDw C11J.U QTlfl fitf*nt"l^ O\*U^^C .... . ____...... . .

Description of study area 

Previous investigations 

Physiography and geology of the Ozark Plateaus province 

and adjacent parts of the Interior Plains and

Physiographic features - 

Tectonic activity and depositional history

Ground-water flow and geohydrologic properties of the

Regional geohydrologic units 

Basement confining unit -

Configuration of the upper surface 

Lithology and permeability 

St. Francois aquifer 

Structural features

Lithology and geohydrologic properties 

Recharge, ground-water flow, and discharge 

Chemical quality of ground water - 

St. Francois confining unit 

Structural features 

Thickness 

Lithology and geohydrologic properties 

Ozark aouifer ____ .. .._. ___ .......... _ ._

Thickness - ____ . ... ___ ..........

Lithology and geohydrologic properties 

Recharge, ground-water flow, and discharge 

Chemical quality of ground water 

Ozark confining unit

Thickness

Page

Dl

1

3

4

4

8

8

8

11

19

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27

27

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32

34

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34

38

38

42

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43

48

51

57

57

57

Ground-water flow and geohydrologic properties of the

Ozark area Continued 

Regional geohydrologic units Continued 

Ozark confining unit Continued

Lithology and geohydrologic properties -- 

Springfield Plateau aquifer 

Structural features 

Lithology and geohydrologic properties 

Recharge, ground-water flow, and discharge 

Chemical quality of ground water 

Western Interior Plains confining system 

Structural features 

Thickness 

Lithology and geohydrologic properties 

Lateral ground-water movement in the nearsurface weathered zone of the Western 

Interior Plains confining system 

Unnamed local geohydrologic units 

Post-Paleozoic deposits 

Interaction of surface and ground water: Recharge to the

regional ground-water flow system 

Estimates of recharge and discharge

Model simulation of predevelopment ground-water flow 

Boundary conditions on lateral ground-water flow 

Boundary conditions and leakage coefficients governing 

vertical ground- water flow 

Boundary conditions associated with recharge and 

discharge of ground water 

Magnitude and distribution of hydraulic properties 

determined by model simulations

Regional ground- water budget 

Availability and use of ground water and well yields 

Summary and conclusions 

Selected references

D60 

63 

63 

63 

63 

67 

69 

74 

74 

74 

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ILLUSTRATIONS

FIGURES 1-10.

11. 

12-15.

Maps showing:

1. Central Midwest Regional Aquifer-System Analysis study area 

2 Location of stjudv 3.1*63. « »« - 

3. Approximate boundary of the Ozark Plateaus aquifer system 

4.

5.

6.

7.

8.

9.

10.

Mean annual precipitation in and adjacent to study area from 1951 to 1980- 

Physiographic subdivisions of the Ozark Plateaus and adjacent areas 

Large rivers and streams within and bordering study area 

Thickness of Paleozoic sedimentary rocks in study area 

Structural features of the midcontinent - 

Distribution and orientation of large faults and fracture systems in study area 

Generalized flow of ground water in deeper units of the Ozark Plateaus aquifer system 

Schematic cross section of regional geohydrologic units in and adjacent to the Ozark Plateaus aquifer systemMaps showing:

12. Outcrop areas of regional geohydrologic units in and adjacent to the Ozark Plateaus province 

13. Areal extent and configuration of top of the Basement confining unit -

14. Depth of the St. Francois aquifer below land surface 

15. Areal extent and configuration of top of the St. Francois aquifer 

D2

5

6

7

10

12

14

18

20

21

24

25

26

29

30
VI CONTENTS

FIGURES 16-50.

51.

52.

53.

54. 

55-61.

62.

63.

64

65.

66-67.

Maps showing:

16. Thickness of the St. Francois aquifer 

17. Predevelopment potentiometric surface of the St. Francois aquiferWater type in the St. Francois aquifer 

Dissolved-solids, chloride, and sulfate concentrations in ground water from the St. Francois aquifer 

Areal extent and configuration of top of the St. Francois confining unit 

Thickness of the St. Francois confining unit 

Shale content of the St. Francois confining unit 

Net shale thickness in the St. Francois confining unit 

Depth of the Ozark aquifer below land surface - - . 

Areal extent and configuration of top of the Ozark aquifer 

Thickness of the Ozark aquifer 

Distribution of hydraulic conductivity of the Ozark aquifer 

Predevelopment potentiometric surface of the Ozark aquifer 

Water type in the Ozark aquifer 

Dissolved-solids concentrations in ground water from the Ozark aquifer 

Chloride concentrations in ground water from the Ozark aquifer 

Sulfate concentrations in ground water from the Ozark aquifer 

Areal extent and configuration of top of the Ozark confining unit 

Thickness of the Ozark confining unit 

Shale content of the Ozark confining unit 

Net shale thickness in the Ozark confining unit 

Depth of the Springfield Plateau aquifer below land surface 

Areal extent and configuration of top of the Springfield Plateau aquifer 

Thickness of the Springfield Plateau aquifer

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

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35.

36.

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40.

41.

42.

43.

44.

45.

46.

47.

48.

49.

50. Altitude of top, thickness, and potentiometric surface of rocks in area C (fig. 48) that are

stratigraphically equivalent to the Springfield Plateau aquifer 

Schematic diagram of surface- and ground-water exchange mechanisms in the Ozark Plateaus province 

Map showing distribution of primary and secondary karst areas in the Ozark Plateaus province 

Graph showing effect of precipitation on water levels in observation well in Phelps County, Missouri 

Graph showing effect of precipitation on water levels in observation well in Howell County, Missouri 

Maps showing:

55. Selected springs of the Ozark Plateaus province 

56 Estim&tftd rGch&Fffft to \vfltGi* t&folf* » «« -« - .- ««««- - »»» » » « »« »» 

57. Area represented by ground-water flow model of the Ozark Plateaus aquifer system, showing

orientation and numbering of finite-difference grid 

Predevelopment potentiometric surface of the Springfield Plateau aquifer 

Water type in the Springfield Plateau aquifer .-- 

Dissolved-solids concentrations in ground water from the Springfield Plateau aquifer 

Chloride concentrations in ground water from the Springfield Plateau aquifer 

Sulfate concentrations in ground water from the Springfield Plateau aquifer 

Altitude of top of the Western Interior Plains confining system 

Thickness of the Western Interior Plains confining system 

Predevelopment potentiometric surface of near-surface weathered zone of the Western Interior Plains

Location of unnamed local geohydrologic units in northeastern part of the Ozark Plateaus province 

Altitude of top, thickness, and potentiometric surface of rocks in area B (fig. 48) that are

stratigraphically equivalent to the Springfield Plateau aquifer 

58.

59.

60.

61.

Model representation of the Western Interior Plains confining system (layer 1) 

Model representation of the Springfield Plateau aquifer and post-Paleozoic sediments (layer 2) - 

Model representation of the Ozark aquifer (layer 3) 

Model representation of the St. Francois aquifer (layer 4) - .

Plan view of hypothetical model cells showing areas of intracell and intercell ground-water flow 

Cross section of two hypothetical model cells showing recharge contributions to ground-water flow within model

CG11S 8.HQ. DcuWcGTl IxlOClGl CG US - - »« ..»». - ..« --«.»»»- »» » »- .»__. __»....... ._____________.....__..».____.._. ._____....

Plan view showing method of distributing regional base flow to model cells 

Graph showing sensitivity of model layers 2 and 3 to selected changes in hydraulic properties 

Maps showing:

66. Recharge to water table as estimated by Dugan and Peckenpaugh (1986) and redistributed recharge to 

account for ground water that remains internal to a model cell 

67. Distribution of vertical hydraulic conductivity and leakage coefficient for model layer 1, representing

leakage through the Western Interior Plains confining system 

D31 

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109
CONTENTS VII

FIGURES 68-72.

73.

74.

Maps showing:

68. Distribution of lateral hydraulic conductivity and transmissivity for model layer 2, representing the

Springfield Plateau aquifer and Cretaceous sands of the Mississippi Embayment 

69. Distribution of vertical hydraulic conductivity and leakage coefficient between the Springfield Plateau 

and Ozark aquifers and between Cretaceous sand and the Ozark aquifer 

70.

71.

72.

Distribution of lateral hydraulic conductivity and transmissivity for model layer 3, representing the

Distribution of vertical hydraulic conductivity and leakage coefficient between the Ozark and 

St. Francois aquifersDistribution of lateral hydraulic conductivity and transmissivity for model layer 4, representing the 

St. Francois aquifer

Diagram showing regional ground-water budget of the Ozark Plateaus aquifer system based on simulation 

Map showing estimated average daily withdrawal of ground water by county from the Ozark Plateaus

aquifer system and the Western Interior Plains confining system during 1970-1979 

Page

DUO

112

113

114

115

116

118

TABLES

TABLE 1. Generalized correlation of Paleozoic stratigraphic units and regional geohydrologic units in study area2. Explanation of symbols used in maps of major chemical constituents 

3. Water budgets for the Ozark Plateaus aquifer system 

D16

36

117

CONVERSION FACTORS AND VERTICAL DATUM

For readers who wish to convert measurements from the inch-pound system of units to the metric system of units, the conversion factors 

are listed below:

Multiply inch-pound units

inch (in)

foot (ft)

mile (mi)

square foot (ft2) 

square mile (mi2)

foot per second (ft/s)

foot per day (ft/d)

foot per mile (ft/mi)

inch per year (in/yr)

square foot per second (ft2/s)

square foot per day (ft2/d)

cubic foot per second (ft3/s)

gallon per minute (gal/min)

gallon per day (gal/d)

gallon per day per foot (gal/d/ft)

billion gallons per day (Bgal/d)

million gallons per day (Mgal/d)

By 

Length

25.4

0.3048

1.609

Area

0.09294

2.59

Flow

0.3048

0.3048

0.1894

25.4

0.0929

0.0929

0.02832

0.06309

0.003785

12.419

43.81

0.04381

To obtain metric units

millimeter (mm) 

meter (m) 

kilometer (km)

square meter (m2) 

square kilometer (km2)

meter per second (m/s) 

meter per day (m/d) 

meter per kilometer (m/km) 

millimeter per year (mm/yr) 

square meter per second (m2/s) 

square meter per day (m2/d) 

cubic meter per second (m3/s) 

liter per second (L/s) 

cubic meter per day (m3/d) 

liters per day per meter (L/d/m) 

cubic meter per second (m3/s) 

cubic meter per second (m3/s)

To convert temperature in °F (degrees Fahrenheit) to °C (degrees Celsius) subtract 32 and multiply by 1.8.

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 leveling nets of both the United States and Canada, formerly called Sea Level Datum of 1929.

REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM 

IN PARTS OF MISSOURI, ARKANSAS, OKLAHOMA, AND KANSAS

By J.L. IMES and L.F. EMMETT

ABSTRACT

The Ozark Plateaus aquifer system consists of Paleozoic sedimentary rocks that overlie Precambrian igneous rocks designated 

the Basement confining unit. Geohydrologic units of the Ozark 

Plateaus aquifer system are designated from the stratigraphically 

lowest to highest: the St. Francois aquifer, the St. Francois confining unit, the Ozark aquifer, the Ozark confining unit, and the 

Springfield Plateau aquifer. The Ozark Plateaus aquifer system is 

stratigraphically equivalent and laterally adjacent to the Western 

Interior Plains aquifer system, which extends west from the study 

area to the Rocky Mountains. The Western Interior Plains confining system confines the Ozark Plateaus aquifer system along the 

western and southern boundaries of the study area and also was 

studied as part of this investigation. Maps are presented depicting 

the areal extent, thickness, and upper surface of each geohydrologic unit and the predevelopment potentiometric surface of the aquifers. Maps also were prepared showing water type and 

concentrations of dissolved solids, chloride, and sulfate in water 

from each aquifer on the basis of available chemical analyses. Potential well yields from each aquifer and lithologic descriptions of 

each geohydrologic unit are presented as indicators of the relative 

permeability of the confining units and the aquifers.

The mainly freshwater Ozark Plateaus aquifer system is almost 

entirely surrounded by and hydraulically isolated from saline 

ground-water flow systems. The northern boundary and discharge 

area for the Ozark Plateaus aquifer system is the Missouri River 

alluvial valley. The eastern boundary is the Mississippi River alluvial valley from its confluence with the Missouri River southward 

to the Mississippi Alluvial Plain, which forms the southeast 

boundary. The southern boundary of the aquifer system is approximately parallel to the Arkansas River valley. The western boundary of the aquifer system is a complex transition zone where 

freshwater flows westward from the Ozark Plateaus and mixes 

with salinewater flowing eastward through the Western Interior 

Plains aquifer system.

A three-dimensional finite-difference model was used to simulate regional ground-water flow in the Ozark Plateaus aquifer system under predevelopment conditions. Local flow, mostly recharge 

that discharges to nearby streams in aquifer outcrop areas, was 

excluded from the simulation. Differentiation between "local" and 

"regional" recharge was based primarily on analysis of base flow of 

streams and topographic factors. Estimated total ground-water recharge to regional and local systems is about 25 percent of precipitation; however, simulated recharge to just the regional flow 

system averages about 22 percent of the total recharge (or 6 percent of precipitation) throughout the modeled area. The simulation 

of predevelopment conditions suggests that inflow to the regional 

ground-water flow system was about 7,000 cubic feet per second. 

Outflow consisted of about 4,000 cubic feet per second discharging 

to streams and springs in the study area and about 3,000 cubic 

feet per second discharging as boundary flow to the Mississippi, 

Neosho, Missouri, and Arkansas Rivers, the aquifers of the Mississippi Embayment, and the water table in the overlying Western 

Interior Plains confining system. Present-day rates of inflow and 

outflow are probably similar inasmuch as current (1987) withdrawals of ground water are comparatively small (about 300 cubic 

feet per second).

The steady-state model calibration yielded estimates of the lateral hydraulic conductivity of the St. Francois, Ozark, and Springfield Plateau aquifers. The lateral hydraulic conductivity of the St. 

Francois aquifer ranges from l.GxlO"4 foot per second near the St. 

Francois Mountains to 8.0xlO~5 foot per second elsewhere. The lateral hydraulic conductivity of the Ozark aquifer ranges from 

1.0xlO~5 foot per second in the south to S.OxlO"4 foot per second in 

the north and east. The lateral hydraulic conductivity of the 

Springfield Plateau aquifer is about 2.5X10"4 foot per second.

Dissolved-solids concentration in the generally calcium magnesium bicarbonate water of the Ozark aquifer and the generally calcium bicarbonate water of the Springfield Plateau aquifer ranges 

from 200 milligrams per liter where the aquifers crop out to greater than 2,000 milligrams per liter near the western boundary of 

the aquifers.

Approximately 200 million gallons per day of ground water are 

withdrawn from the Ozark Plateaus aquifer system by large-yield 

public-supply, industrial, and irrigation wells in the Ozark Plateaus province and adjacent areas.

INTRODUCTION

Regional Aquifer-System Analysis (RASA) programs 

have been developed by the U.S. Geological Survey "to 

provide an understanding of existing ground-water 

flow system and water-quality distributions on a regional scale, to provide predictive capabilities through 

which the consequences of development can be evaluated, again on a regional scale, and to provide a 

framework for more detailed local investigations." 

(Bennett, 1979, p. 42.) Regional aquifer studies are

Dl
D2 REGIONAL AQUIFER-SYSTEM ANALYSIS-CENTRAL MIDWEST

underway or have been completed in five large areas 

within the central United States (Sun, 1986). These 

studies (fig. 1) are the Central Midwest Regional 

Aquifer-System Analysis (CMRASA) as described by 

Jorgensen and Signer (1981), the Northern Midwest 

Regional Aquifer-System Analysis as described by 

Steinhilber and Young (1979), the Gulf Coast Regional 

Aquifer-System Analysis as described by Grubb 

(1984), the Northern Great Plains Regional AquiferSystem Analysis as described by Dinwiddie (1979), 

and the High Plains Regional Aquifer-System Analysis as described by Weeks (1978).

The geohydrology of the Ozark Plateaus province 

(synonymous with the term "Ozarks" in this report) 

and of adjacent parts of the Interior Plains and Arkansas Valley was studied as part of the Central Midwest Regional Aquifer-System Analysis (CMRASA). 

The CMRASA study focused on a regionally significant source of ground water and geohydrologic units 

that confine or otherwise affect the hydrology of the 

regional aquifer system. The Ozark Plateaus aquifer 

system was chosen for a more detailed geohydrologic 

study because it is a predominantly freshwater 

system that is almost entirely surrounded by, but hydraulically isolated from, neighboring saline groundwater flow systems. The mainly carbonate rocks of the 

Ozark Plateaus are the source of freshwater for most 

public water users and for virtually all self-supplied 

domestic water users in the area. The carbonate rocks 

that constitute the aquifer system contain extensive

EXPLANATION

CENTRAL MIDWEST REGIONAL 

AQUIFER-SYSTEM ANALYSIS

NORTHERN MIDWEST REGIONAL 

AQUIFER-SYSTEM ANALYSIS

GULF COAST REGIONAL

AQUIFER-SYSTEM ANALYSIS

NORTHERN GREAT PLAINS REGIONAL 

AQUIFER-SYSTEM ANALYSIS

HIGH PLAINS REGIONAL

AQUIFER-SYSTEM ANALYSIS

I T 

0 200 400 KILOMETERS

FIGURE 1. Central Midwest Regional Aquifer-System Analysis study area and adjacent Regional Aquifer-System Analysis study

areas.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D3

areas of karst, which render the Ozark Plateaus 

aquifer system susceptible to ground-water contamination. Consequently, care needs to be used in construction of wells and in disposal of wastes to protect 

the ground-water resources in the aquifer area.

Because the Ozark area is located within a humid 

climatic zone and contains an extensive region of 

karst terrane and a well-developed network of solution channels, the area contains one of the largest 

concentrations of springs in the United States. Thousands of springs scattered across the Ozarks yield 

from less than a gallon to millions of gallons of water 

per day. The combined flow of the ten largest springs 

is about 2,000 cubic feet per second (1.3 billion gallons per day). Springs, large and small, were important to the early settlement of the Ozarks because 

they served as domestic and stock-water supplies, 

powered grist mills, provided salt (from mineralized 

springs in and around Saline County Missouri), were 

developed into health spas because of their supposed 

medicinal qualities, and were used as a refrigerant 

as evidenced by the many springhouses that still 

exist in the Ozarks. Currently (1987) the springs also 

provide water for trout and bass hatcheries and 

water for recreational use.

Because of the extensive network of solution channels and conduits in the highly karstic carbonate 

rocks, ground water may be easily contaminated in 

this area. Surface contaminants are quickly transported from recharge areas and intercepted by wells 

or concentrated at spring discharge sites. The sources 

of contamination often are unexpected. For example, 

in 1978 a sinkhole collapse occurred in a municipal 

sewage lagoon at West Plains, a small town in the 

south-central Ozarks. Several days later, Mammoth 

Springs, located 36 miles southeast of West Plains, 

began showing evidence of raw-sewage contamination. Before the collapse it was not known that the 

catchment area of Mammoth Springs extended to the 

vicinity of West Plains. In the northeastern part of 

the Ozarks, a liquid-fertilizer pipeline ruptured 13 

miles west of Maramec Spring in the Dry Fork River 

valley (Vandike, 1981). Rare cave fauna and thousands of trout were killed at the spring orifice. These 

events emphasize the susceptibility of the Ozarks 

ground-water system to contamination.

Also of concern is the contamination of ground 

water in the Ozarks on a regional scale by effluent 

from private septic tanks and sewage lagoons, livestock wastes, agricultural pesticides and fertilizers, 

and authorized and unauthorized landfills. Chemical 

analysis of spring waters in upper reaches of the 

White River drainage basin indicates nitrate concentrations 13 times larger than in springs of the Current River basin to the east (Barks, 1978). The larger 

concentrations are attributed to greater densities of 

population and livestock. Ground water beneath 

towns and cities may be contaminated by leakage of 

gasoline and fuel oil from corroded underground storage tanks. Gasoline and other volatile organic compounds already have been discovered in domestic 

wells in and near several cities in Missouri.

These problems, and the potential for more serious 

problems as a growing population places increasing 

demands upon the ground-water system, indicate the 

need for a comprehensive investigation of the invaluable freshwater resources of the Ozark Plateaus. 

This report describes regional factors that control 

ground-water flow in the Ozarks and identifies the 

major geohydrologic units through which the ground 

water moves.

PURPOSE AND SCOPE

The purpose of the Central Midwest RASA is to assess the ground-water resources contained in the regional aquifers of the study area and to provide an 

improved understanding of the flow of water, quality 

of water, and hydraulic properties of rocks in the 

regional aquifer system in order to permit a better 

evaluation of available ground-water resources. To accomplish the purpose of the Central Midwest RASA 

for the Ozark Plateaus aquifer system, several objectives were set and accomplished. The objectives of the 

study described in this report were the following:

1. Identify the major geohydrologic units of the 

Ozarks and describe their lithologic and geologic 

characteristics, especially those characteristics 

that affect the movement of ground water.

2. Describe the flow of water in each of the identified aquifers (including areas of recharge and discharge) and the restriction of ground-water flow 

by the confining units.

3. Describe the background chemical composition of 

water in the Ozark Plateaus aquifer system.

4. Describe the current (1987) use and availability 

of water in the Ozark Plateaus aquifer system.

5. Construct a digital ground-water flow model of 

the Ozark Plateaus aquifer system to analyze 

current concepts about water flow in the aquifer 

system, recharge to the system, relative transmissivity of geohydrologic units in the system, and 

boundary conditions imposed on the system. 

The Ozark Plateaus aquifer system is confined 

along its western and southern border by the Western Interior Plains confining system, a major geohydrologic unit that stretches west to the Rocky
D4 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

Mountains (Jorgensen and others, 1993). Because 

the Western Interior Plains confining system has 

major effects on the Ozark Plateaus aquifer system, 

the confining system is also discussed in this report. 

Similarly, the geohydrologic characteristics of postPaleozoic deposits that blanket the southeast flank 

of the aquifer system are discussed. A more detailed 

description of the geohydrology of the post-Paleozoic 

deposits can be found in Luckey (1985) and Brahana 

and Mesko (1988). Several small, unnamed geohydrologic units that overlie the Ozark Plateaus aquifer system in the northeast part of the Ozark 

Plateaus are briefly discussed.

DESCRIPTION OF STUDY AREA

The Central Midwest RASA study area extends 

from the foothills of the Rocky Mountains in Colorado to the Mississippi River in eastern Missouri and, 

generally, from South Dakota to Texas (fig. 1). This 

report provides a more comprehensive description of 

the Ozark Plateaus aquifer system in the easternmost part of the Central Midwest RASA study area 

(fig. 2). The boundaries of the study area are approximately coincident with the natural flow boundaries of the Ozark Plateaus aquifer system. The 

area of investigation encompasses parts of four 

states: southern Missouri, southeastern Kansas, 

northeastern Oklahoma, and northern Arkansas. 

The study area is approximately 65,500 square 

miles, or about 18 percent of the larger Central 

Midwest RASA area.

The approximate boundary of the Ozark Plateaus 

aquifer system and counties and selected towns within the States that contain the aquifer system are 

shown in figure 3. The study area is bounded by the 

Missouri River to the north, the Arkansas River to 

the south, the Mississippi River to the east, and the 

Neosho River to the southwest.

Geologic strata included in the Ozark Plateaus aquifer system extend beyond the boundaries of the 

study area and constitute geohydrologic units in 

these neighboring regions that are stratigraphically 

equivalent to the Ozark Plateaus aquifer system. 

Some of these units have been or currently (1987) 

are being studied as part of the Northern Midwest 

RASA, the Central Midwest RASA, and the Gulf 

Coast RASA. Refer to Emmett and Imes (1984) and 

Imes (1985) for studies of those units north of the 

Ozarks, Jorgensen and others (1993) for studies of 

those units west and south of the Ozarks, and Brahana and Mesko (1988) for studies of those units southeast of the Ozarks.

Rainfall in the study area normally is abundant 

and fairly well distributed throughout the year; mean 

monthly precipitation ranges from about 2 inches in 

January to about 4 inches in June. However, extended periods of no rain and periods of flooding are not 

unusual. Mean annual precipitation in the Ozarks 

(Hedman and others, 1987) generally increases to the 

southeast and varies from 36 inches per year in the 

north, near the Missouri River, to 50 inches per year 

in the extreme south, where the Arkansas River 

flows out of the study area (fig. 4). Precipitation during the cool season (October to April) replenishes soil 

moisture lost during the warm season (May to September) when consumptive water requirements are 

largest. Excess soil moisture and, consequently, 

ground-water recharge are most likely to occur during the cool season.

PREVIOUS INVESTIGATIONS

Information about well construction, water levels, 

and chemical quality of water from wells drilled in 

the study area in the late 19th and early 20th centuries has been published in U.S. Geological Survey 

Water-Supply Papers (Barton, 1905; Shepard, 1904, 

1907). Additional data about the occurrence, availability, use, and chemical quality of ground water in 

the study area have been published in various State 

and Federal publications. These studies were made 

by various State agencies, often in cooperation with 

the U.S. Geological Survey, and generally encompassed one or more counties in a State. For example, Reed and others (1955), in a study of the 

groundwater resources of Ottawa County, Oklahoma, documented a 200- to 300-foot decline in water 

levels in wells open to Lower Ordovician rocks (Roubidoux Formation and Gasconade Dolomite). Water 

levels declined more than 400 feet in the vicinity of 

Miami, Oklahoma (fig. 3), from 1900 to 1950. When 

wells first tapped the Lower Ordovician rocks in 

Oklahoma in about 1900, the artesian pressure was 

sufficient to make them flow (Heed and others, 1955, 

p. 10). Three aquifer tests were made in 1944 on 

deep wells (1,055 ft to 1,235 ft) open to the Roubidoux Formation. Analysis of the data gave an average transmissivity of 5,080 feet squared per day 

(38,100 gallons per day per foot) and an average coefficient of storage of 8xlO~5 (Reed and others, 1955, 

p. 104). Stramel (1957) documented a decline in 

water level from 1882 to 1954 of about 110 feet in 

the Pittsburg, Kansas, well field. Use of water from 

the well field averaged 1.4 million gallons per day 

during that period.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D5

Feder and others (1969) appraised the water resources in the Joplin, Missouri, area. They defined 

two geohydrologic units: a shallow aquifer principally 

composed of limestone of Mississippian age and a 

deep aquifer principally composed of dolomite and 

small quantities of sandstone of Ordovician and 

Cambrian age. The two aquifers are separated by a 

leaky confining unit consisting of Lower Mississippian and Upper Devonian silty limestone and shale. 

They noted that in the eastern part of the area, the 

potentiometric surface of the deep aquifer is 50 to 

100 feet below the potentiometric surface of the shallow aquifer, and in the west the head difference increases to as much as 180 feet.

Saline County, Missouri (fig. 3), straddles the transition between the fresh ground water of the Ozarks

and the saline ground water of northwestern Missouri. A study of the ground-water resources of Saline County (Miller, 1971) noted that salinewater 

(dissolved-solids concentration greater than 1,000 

mg/L) occurs in the troughs between anticlinal structures, and freshwater (dissolved-solids concentration 

less than 1,000 mg/L) occurs along the crests and 

flanks of these structures. Miller described the saline ground water in Saline County as a connate 

water that probably had its origin either by entrapment of seawater in marine sediments or by shale 

membrane filtration of more dilute waters.

Lamonds (1972) provided information on the occurrence, availability, and chemical quality of surface 

water and ground water for the Ozark Plateaus province in northern Arkansas. He identified the Gunter

105° 100° 95° 90°

45°

"WYOMING" ~ - -

EXPLANATION

CENTRAL MIDWEST RASA STUDY AREA

AREA OF STUDY DESCRIBED IN THIS REPORT

40°

35°

SOUTH DAKOTA

I .-COLORADO 

' NEWMEXJCO

100 200 MILES 

III I 

Tl I I

100 200 KILOMETERS

FIGURE 2. Location of study area described in this report and larger Central Midwest Regional Aquifer-System Analysis (RASA) study

area.
96° 95° 94° 93° 92° 91' 90°

/ \L

39°38°

L_ \ r~i TV' %

89° 88°

EXPLANATION

APPROXIMATE BOUNDARY 

OF OZARK PLATEAUS AQUIFER SYSTEM AND STUDY AREA

STCLAIR

_! HICKORY ! CAMDEN 

VERNON

\- ~-^BOURBON 1 

, 1- ,_ -J

JCRAWFOR

INEOSHO"/' _ , -f^ ___ PITTSBURG, DADE - J.

CEDAR

.PULASKll pHELps | | ^OENEViEVE)^.^

I ^^\ ,- L_ VIBURNUM ' ST\ / \' I I 44 ; FRANCOISV x / PERRY ; .AS' X v " IRON - - I \ f -i

37'

36°

35°

GOMERY I /LA. ^CHEROKEE 

KANS ' /BETTE LAWRENCE |-__ SPRINGFIELD

I CHRISOf f^WA NEWTON

» BENTON I CARROLL

I STONE INDEPENDENCE^., 

Lt SON.'/

IFRANKLIN! JOHNSON

VANBUREN CLEBURNE

40 60 MILES 

1

20 40 60 KILOMETERS

O

05

FIGURE 3. Approximate boundary of the Ozark Plateaus aquifer system and counties and selected towns within study area.
96° 95

EXPLANATION

40 LINE OF EQUAL MEAN ANNUAL 

PRECIPITATION, IN INCHES 

PER YEAR- Interval is 2 inches

0 20 40 60 KILOMETERS

36°U

35° U

I

I 

I

I

ft)

FIGURE 4. Mean annual precipitation in and adjacent to study area from 1951 to 1980. From National Weather Service National Oceanic and Atmospheric Administration

(NOAA).
D8 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

Sandstone Member of the Van Buren Formation and 

the Roubidoux Formation as the most productive 

water-bearing rocks in northern Arkansas.

Vineyard and Feder (1974) presented data for 585 

Missouri springs, most of which discharge from dolomite rocks on the Salem Plateau. The principal geologic formations from which the springs flow are the 

Gasconade, Eminence, and Potosi Dolomites.

Gann and others (1974, 1976) presented a general 

summary of information about the occurrence, availability, use, and quality of water in Missouri south of 

the Missouri River and exclusive of the Mississippi 

Alluvial Plain. Included in the report on southcentral Missouri is a generalized map of the potentiometric surface in the aquifer consisting of Cambrian 

and Ordovician dolomitic rocks. Also included is a 

summary of ground-water tracer experiments.

Emmett and others (1978) described the water resources in the Springfield area in Missouri. Included 

in the report is a two-dimensional model of groundwater flow in Lower Ordovician and Upper Cambrian 

rocks. Drawdown after 50 years of pumping was predicted on the basis of a projected increased rate of 

withdrawal of 10 million gallons per day from existing wells.

Harvey (1980) presented a generalized summary of 

the hydrology of aquifers composed of Ordovician and 

Cambrian rocks in the Springfield-Salem Plateaus of 

southern Missouri and northern Arkansas. He described ground-water recharge in the Salem Plateau 

as primarily occurring in three ways: through losing 

streams, through sinkholes, and by infiltration in upland areas. Harvey (1980) also states that the rate at 

which ground water is pumped in the SpringfieldSalem Plateaus and contiguous areas (200 ftVs) is 

about 5 percent of the total streamflow at the 80- 

percent point on streamflow-duration curves for 

major streams.

Harvey and others (1983) presented hydrologic information on three basins in south-central Missouri. 

Emphasis was placed on distinguishing losing from 

gaining stream reaches and determining their relation to ground-water movement. The authors evaluated various methods used in defining gaining and 

losing streams. They concluded that the most important controlling factor on the hydrology of Ozark basins is the quantity and type of structural 

deformation imposed on the rocks.

Spruill (1984) evaluated water-resource problems 

related to abandoned lead and zinc mines in Cherokee County, Kansas (fig. 3) and adjacent areas in 

Missouri and Oklahoma. The mines are in rocks of 

Mississippian age, which form the shallow aquifer. 

Pumping from the underlying deep aquifer has lowered the potentiometric surface in the deep aquifer 

and increased the potential for downward movement 

of water from the shallow aquifer. Spruill (1984) believes that drill holes open to both shallow and deep 

aquifers and abandoned wells with corroded or leaky 

casings present the greatest contamination hazard to 

water supplies in the deep aquifer.

Kleeschulte and others (1985) described the 

ground-water resources of a three-county area in 

western Missouri that straddles a freshwater-salinewater transition zone. The transition zone diagonally 

crosses the three counties and separates freshwater 

in the southeast from salinewater in the northwest. 

Kleeschulte and others (1985, p. 55) state that the 

position of the freshwater-salinewater transition zone 

has not substantially moved during recent years, but 

minor fluctuations in water quality occur along the 

zone.

ACKNOWLEDGMENTS

During any large multi-State study, such as the 

CMRASA, cooperation between the district offices of 

the U.S. Geological Survey is essential to the proper 

and efficient completion of the project. The authors 

thank district personnel in adjacent states for giving 

the extra effort necessary for the successful completion of this study. We especially thank Christi Hansen of the Kansas district for working with the 

Missouri district on the task of eliminating discrepancies between geohydrologic units at the Kansas 

and Missouri state boundaries. Thanks to Dave Freiwald and Gus Ludwig of the Arkansas district for 

many consultations regarding the conceptualization 

of ground-water flow in the Ozark Plateaus aquifer 

system in northern Arkansas. We thank Dave Freiwald for contributing to the sections of this report on 

physiography and geology, climate, and surface-water 

and ground-water interaction. We thank Scott Christenson and Gregg Adams of the Oklahoma district for 

discussion of concepts regarding the interaction of 

freshwater in the Ozark Plateaus aquifer system 

with salinewater flow systems west of the study area.

PHYSIOGRAPHY AND GEOLOGY OF THE OZARK 

PLATEAUS PROVINCE AND ADJACENT PARTS OF 

THE INTERIOR PLAINS AND ARKANSAS VALLEY

PHYSIOGRAPHIC FEATURES

The Ozark Plateaus province is a geologic uplift, or 

dome, that rises above surrounding lowlands. The
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D9

physiographic province is subdivided into four sections: the Salem Plateau, the Springfield Plateau, the 

St. Francois Mountains, and the Boston Mountains 

(fig. 5; Fenneman, 1938). The topographic axis of the 

broad anticlinal fold that forms the nearly elliptical 

uplift stretches from the extreme northwestern corner of Arkansas to the St. Francois Mountains in 

southeast Missouri. Surface altitudes along the axis 

are highest in Wright and Iron Counties, Missouri 

(fig. 3), where altitudes exceed 1,700 feet, and generally range from 1,500 to 1,700 feet between the counties. The flanks of the province are steeper to the 

east where the plateau terminates abruptly near the 

Mississippi River (400-ft altitude) and less steep to 

the west where land-surface altitudes are about 600 

to 800 feet at the eastern edge of the Interior Plains 

(fig. 5). In northern Arkansas the symmetry of the 

dome is broken by the Boston Mountains, a higher 

plateau that rises abruptly above the rest of the 

province to altitudes exceeding 2,000 feet.

The Salem Plateau generally coincides with that 

part of the Ozarks where Ordovician and Upper 

Cambrian rocks are exposed, and includes some isolated areas where younger rocks that once covered 

the plateau still remain. Along a major topographic 

ridge that parallels the axis of the Ozark uplift and 

extends from northeastern Oklahoma to the St. Francois Mountains in southeastern Missouri, the Salem 

Plateau is a relatively flat upland plain. Stream 

channels are not deeply incised, but solution features 

such as sinkholes indicate the presence of subsurface 

channel development. To the north and south away 

from the divide, the streams increase in size and in 

density and cut deeply into the plain. A welldissected topography is present throughout most of 

the remainder of the plateau except between the 

major river valleys where the flat uplands are remnants of the original plain.

The Springfield Plateau is a crescent-shaped area, 

open to the northeast, that borders the Salem Plateau and generally coincides with the area in which 

Mississippian rocks are exposed. The plateau surface 

is nearly coplanar with the bedding of the Mississippian rocks; however, the plateau is not a structural 

plain, as indicated by the presence of truncated 

structural features in the interior of the plateau. The 

plain is interrupted by isolated, low hills of Pennsylvanian rocks, evidence that the process of peneplanation was not completed. A factor contributing to the 

present-day relief on the plateau surface is dissolution of the soluble limestone that forms the plateau.

The St. Francois Mountains are remnants of more 

resistant Precambrian igneous peaks that were exposed when Cambrian sediments were stripped away.

The approximately 70-square-mile region in southeastern Missouri is characterized by rounded peaks 

that have steep sides and are separated by broad, 

flat valleys. The highest point in the area, Taum 

Sauk Mountain, has an elevation of 1,772 feet. There 

is no general level that can be traced across the 

mountain range to reveal an ancient peneplain surface. The entire region probably was once a part of 

the Salem Plateau peneplain, which has an elevation 

of about 1,500 feet around the St. Francois Mountains. Later periods of uplift and renewed erosion 

have destroyed evidence of the original peneplain 

surface.

The Boston Mountains differ from the St. Francois 

Mountains in that they are composed entirely of the 

remnants of an ancient peneplain (Bretz, 1965). The 

Boston Mountains constitute a higher, east-westoriented plateau on the southern flank of the Ozark 

Plateaus province. The northern boundary of the 

Boston Mountains is an escarpment rising about 700 

feet above the Springfield Plateau. The mountainous 

plateau is capped by a thick, resistant Pennsylvanian 

sandstone. Both the dip of the sandstone strata and 

the slope of the plateau horizon are to the south, but 

the horizon slope is less than the dip of the strata; 

consequently, younger Pennsylvanian rocks form the 

southern boundary of the plateau where it merges 

into hills of the Arkansas Valley.

The Arkansas Valley, a physiographic section located south of the Ozark Plateaus province (fig. 5), occupies the northern half of the Ouachita province. The 

Arkansas Valley is the southernmost physiographic 

division in the study area. The lowland is characterized by a series of east-west-trending, parallel folds 

created by lateral compression from the northwardmoving Ouachita Mountain thrust front. The closely 

spaced, tight folds along the Ouachita Mountains 

grade to less closely spaced, gentle folds along the 

Ozark Plateaus. Faulting in the Arkansas Valley is 

extensive, and the downthrown sides are commonly 

on the north. Erosion of the folds has produced a series of linear ridges and mesas separated by broad, 

flat valleys.

The northwestern edge of the study area includes 

part of the areally extensive Interior Plains physiographic province (Fenneman, 1938) that borders the 

western edge of the Ozark Plateaus province. The Interior Plains province is a plain of low relief characterized by a series of east-facing escarpments that 

indicate the presence of more resistant strata (usually limestone) in the surficial Pennsylvanian rocks. 

Local relief in the area adjacent to the Ozark Plateaus generally is less than 250 feet, the areas of 

greater relief occurring where major streams cut the
35'

96° 95° 94° 93°

92

\ I 

0 20 40 

FIGURE 5. Physiographic subdivisions of the Ozark Plateaus and adjacent areas. (Physiography from Fenneman, 1938.)
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM Dll

underlying rocks. In southeast Kansas a 25-milewide, distinctive belt of slightly rolling terrane that 

gradually merges into the Springfield Plateau defines 

the outcrop area of a thick, slightly consolidated, 

basal Pennsylvania!! shale.

Much of the study area is bordered by alluvial valleys of the larger rivers of the midcontinental United 

States. The interior of the Ozark region contains 

many spring-fed rivers and large streams. Three continental rivers border parts of the study area (fig. 6): 

the Missouri River to the north, the Mississippi River 

to the east, and the Arkansas River to the south. The 

Neosho River of Kansas and Oklahoma forms a segment of the southwestern border of the study area. A 

major drainage system, the Marais des Cygnes and 

Osage Rivers and their tributaries, directs surface 

water from the Interior Plains in eastern Kansas into 

the Ozark area to discharge into the Missouri River 

along the northern border of the study area. This is 

the only large surface-water system that drains into 

the Ozark area; all other surface waters drain away 

from or around the uplifted Ozark region. The Blackwater River and other smaller streams drain water 

in the northwestern corner of the study area to the 

Missouri River. The Spring, White, Buffalo, and Illinois Rivers and other smaller streams drain the 

southern and southwestern third of the study area 

and discharge into either the Neosho or Arkansas 

Rivers. The eastern one-third to one-half of the study 

area is drained by the Gasconade, Meramec, Big, St. 

Francis, Black, Current, and Eleven Point Rivers and 

other smaller streams that discharge directly into either the Missouri or Mississippi River or discharge 

into rivers in the Mississippi Alluvial Plain.

TECTONIC ACTIVITY AND DEPOSITIONAL HISTORY

Crystalline rocks of Precambrian age form the 

foundation upon which younger sedimentary rocks 

were deposited during periods of submergence of the 

Ozark area. Magmatic activity in late Precambrian 

time resulted in several periods of granitic intrusion 

into middle Precambrian metasedimentary rocks. 

Late Precambrian volcanic activity created a wide 

belt of elevated volcanic rock, part of which supports 

the present-day Ozark Plateaus (Snyder, 1968). The 

predominantly rhyolitic and granitic basement rocks 

of the Ozark uplift are part of an epizonal graniterhyolite complex that extends in a large band from 

western Texas to western Ohio; (Lidiak and others, 

1966; Muehlberger and others, 1966, 1967). This 

complex probably formed the continental divide in 

Late Precambrian time. There is evidence, in the

form of 1,400-million-year-old stromatolitic limestones, of at least one Precambrian marine inundation, but no extensive sedimentary record remains 

(Stinchcomb, 1976). Metamorphic rocks constitute a 

small part of the basement rocks in the Ozark Plateaus and primarily are the result of contact metamorphism between magma intrusions and the host 

rocks.

Precambrian rocks crop out in two areas of the 

Ozark Plateaus: a larger area located in and slightly 

southwest of the St. Francois Mountains (fig. 5) and 

a much smaller area consisting of five small hills in 

Mayes County, Oklahoma (fig. 3). The St. Francois 

Mountains are the surface expression of a broader 

region of volcanic and granitic rocks termed the St. 

Francois terrane (Kisvarsanyi, 1979, 1981). The 

1,500-million-year-old rhyolitic ash-flow tuffs exposed 

in this area are the oldest rocks in the province. Rhyolite also is dominant in a second volcanic province 

at the southwestern edge of the Ozarks in northeastern Oklahoma, but the rocks there are approximately 

200 million years younger than those within the St. 

Francois terrane (Denison, 1981). After the two periods of major extrusive volcanic activity, and before 

the region was inundated by the transgressing Cambrian sea, the Precambrian surface was subjected to 

millions of years of erosion and provided enormous 

quantities of sediments to basins located southeast 

and northwest of the Ozarks. Structural and geochemical investigations of the St. Francois terrane 

indicate that it was once a major volcanic feature 

and that thousands of feet of volcanic rock were eroded from the Precambrian surface. Southwest of the 

St. Francois terrane, in the central part of the Ozark 

Plateaus, volcanic rocks were completely removed by 

erosion, exposing the underlying granitic rocks. The 

resulting rugged topography of the buried Precambrian surface along the ancient continental divide is evident wherever the density of drillholes that penetrate 

the Precambrian is sufficient to detect abrupt variations in altitude within short distances. Away from 

the narrow divide the Precambrian surface is more 

rolling; occasional hills rise a few hundred feet above 

the plain (Snyder, 1968).

Tectonic activity and erosion of large quantities of 

overburden during periods when the Ozark land 

mass was lifted above sea level created faults and 

fractures in the Precambrian basement. A major rift 

(New Madrid rift zone) along the southeastern edge 

of the Ozark Plateau beneath what is now the Mississippi Alluvial Plain also contributed to regional 

faulting and fracturing. The numerous faults and 

fractures exhibit preferential orientation to the 

northwest-southeast and northeast-southwest, and
96° 95° 94° 93° 92° 91 C 90° 89° 88°

39°38°

37°

36°

35°

EXPLANATION

BOUNDARY OF STUDY AREA

20 40 60 MILES 

_]_____I I

I I I 

20 40 60 KILOMETERS

Oh-1

to

O

i

FIGURE 6. Large rivers and streams within and bordering study area.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D13

they provide avenues for movement of ground water 

through otherwise virtually impermeable rock. Many 

of the faults and fracture zones in younger consolidated Paleozoic rocks in the eastern part of the 

Ozarks are the result of repeated differential movement across weak zones associated with faults in the 

underlying basement rocks.

Where they are exposed today, Precambrian rocks 

usually are weathered to a distinctive dark red soil. 

Another characteristic weathering product is the 

"black sand" found in small creeks and streams 

throughout the St. Francois Mountains. Subsurface 

evidence of the erosional history is provided by the 

presence of an arkose conglomerate at the base of 

Cambrian rocks.

Overlying the Precambrian basement complex beneath the study area is a sequence of Paleozoic sedimentary rocks, ranging in thickness from near 0 to 

more than 6,000 feet (fig. 7). Generally, these rocks 

are thin to absent in the vicinity of the St. Francois 

Mountains and northeastern Oklahoma; they are 

much thicker where the flanks of the Ozark uplift dip 

into adjacent basins. A stratigraphic column identifying the sequence of geologic formations that constitute the Paleozoic rocks in parts of the four-State 

area is shown in table 1. General descriptions of the 

stratigraphic relations among these formations and 

the areal distribution, thickness, lithology, and paleontology of the formations are available in Caplan 

(1954 and 1957), Huffman (1958), Koenig (1961), and 

Zeller (1968).

Stratigraphic nomenclature varies to some degree 

primarily because geologic nomenclature has developed somewhat independently for each of the major 

geologic basins that surround the Ozark uplift. Many 

of the geologic formations, especially those composed 

of Silurian and younger rocks, are thick units in the 

adjoining basins but are thin and of limited areal extent, or missing, in the study area. Because units 

and their names vary within the study area, the 

stratigraphic nomenclature chart (table 1) has been 

divided into five columns, each representing a part of 

the study area (southeastern Missouri, southwestern 

Missouri, southeastern Kansas, northeastern Oklahoma, and northern Arkansas).

There are unresolved problems in the geologic history of certain formations in this region. The geologic 

history and formation boundaries of the deepest Cambrian rocks in the tristate area of Missouri, Kansas, 

and Oklahoma still are somewhat obscure, resulting 

in conflicting stratigraphic terminology for certain 

Cambrian rocks along the western and southwestern 

flanks of the Ozarks. For this report, the geologic history and nomenclature of the Cambrian strata in the

tristate area as proposed by Kurtz and others (1975) 

has been used. There also is some question about the 

age assignment of certain Upper Devonian and Lower 

Mississippian formations (Koenig, 1961).

Seas advancing westward in Late Cambrian time 

transgressed the Ozarks as the entire study area 

slowly subsided. In early Late Cambrian time, a 

large land mass in the shallow Cambrian sea 

stretched north and south less than 100 miles west 

of the Kansas-Missouri and Oklahoma-Arkansas 

state lines. Large islands were present in the St. 

Francois Mountains region of southeastern Missouri 

and in northeastern Oklahoma and northwestern 

Arkansas. The Lamotte Sandstone, formed from the 

first Cambrian sediments to be deposited upon the 

Precambrian surface, originated as permeable wellsorted sands that probably were derived from the 

Precambrian land mass in southeastern Missouri. 

The clean quartzose sandstone, deposited in a 

shallow-water shelf environment, contains a basal 

arkosic conglomerate composed of weathered and 

broken Precambrian rock.

Deposition of sand that forms the Lamotte Sandstone was followed by deposition of sediments that 

now constitute the Bonneterre Dolomite, Davis Formation, and Derby and Doe Run Dolomites. The Bonneterre Dolomite, initially deposited as a calcareous 

mud, contains large reef and back-reef facies that encircle at least three sides of the St. Francois Mountains (Gerdemann and Myers, 1972). The sediments 

were later lithified as the sea regressed, and the 

near-reef facies underwent subsequent dolomitization 

in the mixing zone where depositional seawater was 

flushed from the limestone by freshwater of meteoric 

origin. The offshore facies have retained, their limestone composition. The reefs are evidence that the 

Precambrian volcanic rocks of the St. Francois Mountains were islands in the Late Cambrian sea. The 

permeable reef facies are the site of one of the 

world's largest lead-zinc-copper districts. The metals 

are reported to have been transported to the area by 

hot sodium-calcium-chloride brines and precipitated 

as sulfides by biogenically reduced sulfur (Gerdemann and Myers, 1972).

Less permeable clay, silt, and sand were more 

prevalent during the later stages of deposition of sediments that formed the Bonneterre Dolomite and the 

overlying Davis Formation. The shale content of the 

Davis Formation is considerably larger than that of 

the other Cambrian formations and probably indicates cyclic deposition of calcareous mud and clay 

during a period in which the Cambrian sea was shallow over much of the Ozarks. A major facies transition zone that trends approximately north and south
96° 95° 94° 93° 92° 91' 90° 89°

39°38°

37°

36°

35°

EXPLANATION

AREA WHERE PALEOZOIC ROCKS 

ARE MISSING AND UNDERLYING PRECAMBRIAN ROCKS ARE EXPOSED

 500 - LINE OF EQUAL THICKNESS Interval, 

in feet, is variable

- - - - BOUNDARY OF STUDY AREA

0 20 40 60 MILES

I I I

I I T

0 20 40 60 KILOMETERS

FIGURE 7. Thickness of Paleozoic sedimentary rocks in study area.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D15

through western Missouri and Arkansas separates 

the Lamotte Sandstone, Bonneterre Dolomite, and 

Davis Formation in the east from a related, timetransgressive, near-shore fades, the Reagan Sandstone (Kurtz and others, 1975), in the west.

As the sea again transgressed upon the Ozark 

area, calcareous mud with some clay and silt, now 

represented by the Derby and Doe Run Dolomites, 

was deposited offshore. The Derby and Doe Run Dolomites are regarded as transition units between underlying rocks that contain a large fraction of clastic 

material and overlying rocks that contain only small 

quantities of clastic material. Continued inundation 

of the area was accompanied by thick deposits of calcareous mud. At the close of Late Cambrian time, the 

entire area was uplifted and the lithified calcareous 

mud was diagenetically altered to dolostone as an expanding zone of freshwater moved through the rocks. 

The deposits are now represented by the Potosi and 

Eminence Dolomites, the uppermost Cambrian formations in the study area. Both the Potosi and the 

Eminence Dolomites can be characterized as massively bedded, medium-grained dolostones.

The Ozark uplift and other major arches and 

basins of the midcontinent began to develop near the 

end of Late Cambrian time and throughout Early Ordovician time (fig. 8). At first, the structural features 

resulted more from subsidence of surrounding basins 

than from uplift of the Ozark domal mass. The Ozark 

dome generally remained below water, but sedimentation atop the dome was thinner than in the basins. 

An unconformity between Cambrian and Ordovician 

rocks marks emergence of the Ozark landmass. Renewed submergence of the area in Early Ordovician 

time initiated an interval in which thick deposits of 

mainly calcareous sediments were deposited. These 

sediments were subsequently lithified and extensively dolomitized and are now represented by the Van 

Buren Formation, Gasconade Dolomite, Roubidoux 

Formation, Jefferson City Dolomite, Cotter Dolomite, 

Powell Dolomite, and Smithville Formation. The only 

notable exceptions to the dominance of dolostone in 

these formations are the Gunter Sandstone member 

of the Van Buren Formation (used as a marker in 

both field surveys and subsurface mapping) and variable quantities of sandstone in the Roubidoux Formation (ranging from as little as 10 percent to nearly 

100 percent). A major unconformity marks the end of 

this depositional period and signals a change in the 

tectonic activity of the Ozark Plateaus. Uplift of the 

Ozark area resulted in considerable fracturing and 

faulting of the competent carbonate rocks. Dolomitization occurred as freshwater flushed formational 

seawater from the rocks. Erosion of the dome was

deep and widespread and resulted in the development of an extensive paleokarst. The unconformity 

marks the beginning of a series of major and minor 

regressions and transgressions of the sea across the 

Ozarks.

Sedimentation in the advancing seas at the beginning of Middle Ordovician time began with permeable sands that are represented by the Burgen 

Sandstone at the extreme southwestern edge of the 

Ozark Plateaus (Huffman, 1958). It continued with 

the more widespread sand deposits that formed the 

St. Peter Sandstone. A sequence of mainly limestone 

and dolostone formations, beginning with the Dutchtown Formation (Koenig, 1961) and Joachim Dolomite and ending with the Kimmswick Limestone 

(equivalent to the Viola Limestone of Oklahoma), 

constitutes the remaining sedimentary rocks attributed to this period of inundation. Sediments of the 

carbonate sequence were not limited to calcareous 

mud; sand, clay, and silt also were deposited in significant quantities. The formations deposited during 

this transgression are generally thinner and have 

smaller area! distribution than those deposited during the Early Ordovician transgression.

Deposits of Late Ordovician age are not well represented in the Ozark Plateaus. Relatively thin deposits 

of calcareous mud, clay, sand, and silt are characteristic of the shallow-marine environment of Late Ordovician time. Rock sequences that currently (1987) 

represent the lithified and diagenetically altered sediments generally are thin or absent throughout most of 

the Ozarks. The Fernvale Limestone, Sylvan Shale, 

and Cason Shale are confined to the Arkansas Valley 

and the southwestern and southern flanks of the 

Ozark Plateaus. Likewise, the Cape Limestone 

(Koenig, 1961), Maquoketa Shale, Thebes Sandstone, 

Orchard Creek Shale, and Girardeau Limestone are 

confined to a small area along the eastern boundary of 

the Ozark Plateaus. Each of the formations stratigraphically bounded by the top of the Kimmswick 

(Viola) Limestone and the base of the Thebes Sandstone are unconformable with overlying and underlying rocks, indicating that the sediments from which 

these rocks formed were deposited during a series of 

relatively rapid regressions and transgressions of the 

Late Ordovician sea. It is possible that much of the 

Ozark highlands remained exposed throughout the 

Late Ordovician and that most or all of these sediments were not deposited in the interior of the 

Ozarks. The permeability of the exposed carbonate 

rocks increased throughout the Late Ordovician.

Silurian and Devonian sediments also are represented only along the flanks of the Ozark uplift. 

These two geologic periods are characterized by short
Table 1. Generalized correlation of Paleozoic stratigraphic units and regional geohydrologic units in study area

[Blue lines mark boundaries between geohydrologic units]

oI-4 

Ci

Erathem System Southeastern Missouri Southwestern Missouri Southeastern Kansas Northeastern Oklahoma Northern Arkansas

Aquifers and confining 

units described in this 

report

Geohydrologic unit Geohydro- logic system

POST-PALEOZOIC SEDIMENTS

PALEOZOIC

PENNSYLVANIAN

MISSISSIPPIAN

DEVONIAN

Pleasanton Formation 1 

Marmaton Group 1 

Cherokee Shale1

Vienna Limestone1 

Tar Springs 

Sandstone 1 

Glen Dean Limestone1 Hardinsburg 

Sandstone 1 

Golconda Formation1 

Cypress Formation1 Paint Creek 

Formation 1 

Yankeetown 

Sandstone 1 

Renault Formation 1 

Aux Vases Sandstone 1

Ste. Genevieve 

Limestone3 

St. Louis Limestone3 Salem Limestone3 

Warsaw Limestone3 

Keokuk Limestone 3 

Burlington Limestone3

Fern Glen Limestone3Chouteau Limestone Hannibal Shale 

Bachelor Formation4Bushberg Sandstone 

Glen Park Limestone Chattanooga Shale

Kansas City Group 

Pleasanton Formation 

Marmaton Group 

Cherokee Shale

Fayetteville Shale 

Batesville Sandstone

Hindsville Limestone 

Carterville FormationSt. Louis Limestone Salem Limestone 

Warsaw Limestone 

Keokuk Limestone 

Burlington Limestone 

Elsey Formation Reeds Spring 

Formation 

Pierson Formation

Northview Shale Sedalia Limestone 

Compton LimestoneChattanooga Shale

Kansas City Group 

Pleasanton Group 

Marmaton Group 

Cherokee Group

St. Louis Limestone Salem Limestone 

Warsaw Limestone 

Keokuk Limestone 

Burlington Limestone

Fern Glen Limestone

Chouteau Limestone

Chattanooga Shale

Marmaton Group 

Cabiniss Group Krebs Group 

Atoka Formation Bloyd Shale 

Hale FormationPitkin LimestoneFayetteville Shale 

Batesville Sandstone 

Hindsville Limestone

Moorefield Formation 

Keokuk Limestone

Boone Formation 

Reeds Spring Member St. Joe Limestone 

Member

Northview Equivalent 

Compton Equivalent

Woodford Chert 

Chattanooga Shale

McAlester Formation 

Hartshorne Sandstone 

Atoka Formation Bloyd Shale 

Hale Formation

Pitkin LimestoneFayetteville Shale 

Batesville Sandstone

Moorefield Formation

Boone Formation 

Reeds Spring Member 

St. Joe Limestone 

Member

Chattanooga Shale

SPRINGFIELD PLATEAU 

AQUIFER

OZARK CONFINING UNIT

WESTERN INTERIOR PLAINS CONFINING SYSTEM 2OZARK PLATEAUS AQUIFER SYSTEM
u1 1

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St. Laurent LimestoneGrand Tower

Limestone

Clear Creek Chert

Little Saline Limestone

Bailey Limestone

Bainbridge Limestone

Sexton Creek

Limestone4

Girardeau LimestoneOrchard Creek Shale

Thebes Sandstone

_ Maquoketa Shale _ 

_ Cape Limestone4

Kimmswick LimestoneDecorah Formation

Plattin LimestoneRock Levee Formation4

Joachim Dolomite

Dutchtown Formation4

St. Peter SandstoneEverton FormationSmithville Formation

Powell Dolomite

Cotter Dolomite

Jefferson City Dolomite

Roubidoux Formation

Gasconade Dolomite

Van Buren Formation

Gunter Sandstone

Member

Eminence DolomitePotosi DolomiteDoe Run DolomiteDerby DolomiteDavis FormationBonneterre DolomiteReagan Sandstone

Lamotte Sandstone

Callaway Formation

Fortune Formation 4

Kimmswick LimestonePlattin Limestone

Joachim Dolomite

St. Peter SandstoneEverton FormationSmithville Formation

Powell Dolomite

Cotter Dolomite

Jefferson City Dolomite

Roubidoux Formation

Gasconade Dolomite

Gunter Sandstone

Member

Eminence Dolomite

Potosi Dolomite

Doe Run DolomiteDerby DolomiteDavis Formation

Bonneterre Dolomite

Reagan SandstoneLamotte Sandstone

Cotter Dolomite

Jefferson City Dolomite

Roubidoux Formation

Gasconade Dolomite

Van Buren Formation

Gunter Sandstone

Member

Eminence DolomitePotosi Dolomite

Doe Run DolomiteDerby DolomiteDavis Formation

Bonneterre Equivalent

Reagan Sandstone

Lamotte Sandstone

Salisaw FormationFrisco LimestoneSt. Clair Limestone

Sylvan ShaleFernvale Limestone

Viola Limestone

Fite Limestone

Tyner FormationBurgen Sandstone

Smithville Equivalent

Powell DolomiteCotter Dolomite

Jefferson City Dolomite

Roubidoux Formation

Gasconade Dolomite

Van Buren Formation

Gunter Sandstone

Member

Eminence Dolomite

Potosi Dolomite

Doe Run DolomiteDerby DolomiteDavis Formation

Bonneterre Equivalent

Reagan SandstoneLamotte Sandstone

Clifty Limestone

Penters ChertLafferty Limestone

St. Clair Limestone

Brassfield Limestone

Cason Shale

Fernvale Limestone

Kimmswick Limestone

Plattin Limestone

Joachim Dolomite

St. Peter SandstoneEverton FormationSmithville Formation

Powell Dolomite

Cotter Dolomite

Jefferson City Dolomite

Roubidoux Formation

Gasconade Dolomite

Van Buren Formation

Gunter Sandstone

Member

Eminence Dolomite

Potosi Dolomite

Doe Run DolomiteDerby DolomiteDavis Formation

Bonneterre Dolomite

Reagan SandstoneLamotte Sandstone

PRECAMBRIAN IGNEOUS AND METAMORPHIC ROCKS

tfWe9u2

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ST.

FRANCOIS 

CONFINING

UNIT

ST.

FRANCOIS

AQUIFER

BASEMENT

CONFINING

UNIT

1Geologic unit in southeastern Missouri that is stratigraphically equivalent to geologic units in the Western Interior Plains confining system, but not part of the confining system. 

2The Western Interior Plains confining system also includes younger sediments west of the study area.3Geologic unit in southeastern Missouri that is stratigraphically equivalent to geologic units in the Springfield Plateau aquifer, but not part of the aquifer. 

Unit follows usage of the Missouri Division of Geology and Land Survey.
D18 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

episodes of submergence and emergence of the 

Ozarks as represented by unconformable geologic 

contacts. Sediments during Silurian time were mainly calcareous mud. By the latter part of Devonian 

time, less permeable clay and silt had become the 

dominant sediments. Rocks assigned to these periods 

of deposition generally are thin, but thick (up to 

1,000 ft) deposits, primarily composed of limestone 

and dolostone, cover the extreme eastern flank of the 

Ozarks, and a smaller thickness of Silurian and Devonian rocks remain beneath the Arkansas Valley. 

The Chattanooga Shale (Late Devonian) represents 

one of the more extensive and hydrologically important geologic formations lithified from the clay parent 

material. Major erosional events of the Ozarks in 

Missouri mark the close of both Silurian and Devonian time. Regional freshwater aquifers were developed, and the permeability of underlying Ordovician 

and Cambrian rocks was greatly enhanced.

The Ozark Plateaus have undergone two major cycles of submergence and uplift since Devonian time. 

At the end of Devonian time and the beginning of the 

first depositional cycle, Mississippian sediments, 

mainly calcareous mud and less permeable clay, were 

deposited in the advancing sea. These deposits have 

lithified to form the thin, relatively impermeable 

limestone and shaly limestone formations (Compton 

Limestone, Sedalia Limestone, Hannibal Shale, and 

Northview Shale) that are present in the Springfield 

Plateau and along the northern and western flanks 

of the Ozarks. These sediments were covered by 

much thicker deposits of calcareous mud that now 

are represented by massive, permeable limestone formations, such as the Boone Formation and equivalents and the Burlington and Keokuk Limestones. 

The limestone formations also contain large quantities of chert. Chert is less common in the thinner and 

less permeable overlying rocks of the Warsaw Lime1030 ior 99° 97° 95° 93° 91 C 87° 85°

43C

41 <

39C

37C

35C

 y-a*^

FIGURE 8. Structural features of the midcontinent (modified from Jorgensen and others, 1993). Dashed lines indicate approximate

location.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D19

stone, Salem Limestone, St. Louis Limestone (Moorefield Formation), and Ste. Genevieve Limestone. The 

top of the Ste. Genevieve Limestone is marked by a 

significant erosional surface formed during a period 

of emergence of the Ozark landmass from the Mississippian sea.

Several hundred feet of Upper Mississippian rock 

a stratigraphic sequence from the Aux Vases Sandstone to the Vienna Limestone is limited to the extreme eastern flank of the Ozarks and may never 

have covered the remainder of the Ozark Plateaus. 

Sand that lithified to form the Aux Vases Sandstone 

probably was derived from the exposed Ozark highland. The Aux Vases Sandstone locally is cemented 

with silica, which reduces the permeability of these 

rocks. Other geologic formations in this sequence 

generally contain significant quantities of shale interbedded with lesser quantities of limestone and sandstone. The composition of these low-permeability 

rocks indicates that the parent material was deposited in a low-energy environment. These formations 

have not yet been correlated with Upper Mississippian rocks of the southwestern and southern parts of 

the study area as represented by the Carterville Formation, Hindsville Limestone, Batesville Sandstone, 

and Fayetteville Shale. Erosion at the end of the 

Mississippian Period removed Mississippian strata 

from the St. Francois Mountain region and perhaps 

much of the present Salem Plateau.

The second cycle of deposition began in Early 

Pennsylvanian time when the sea again transgressed 

over most, if not all, of the Ozark uplift. Large quantities of clay, sand, and calcareous mud were deposited atop Mississippian rocks around the circumference 

of the Ozarks and directly on Ordovician rocks in the 

center of the Salem Plateau. Renewed uplift of the 

Ozarks in Middle Pennsylvanian time ended the sedimentation. The lithified sediments formed thick layers of Pennsylvanian shale, sandstone, and limestone 

across much of the Ozarks. Widespread and deep erosion occurred after Pennsylvanian seas receded and 

continues to present time; it has removed all but a 

few remnants of the Pennsylvanian deposits from the 

Ozark Plateaus.

Remnants of Pennsylvanian rock can be found in a 

few scattered areas about 100 miles northwest of the 

St. Francois Mountains. These rocks are in direct 

contact with the Jefferson City Dolomite of Ordovician age, this juxtaposition providing evidence of the 

effectiveness of the post-Mississippian erosion. The 

thickness of Pennsylvanian rocks increases west and 

south of the Ozark Plateaus. Removal of this thick 

layer of rock from the Ozark uplift released stress 

previously developed in the underlying Mississippian

and Ordovician rocks, resulting in faults and large 

fractures that approximately parallel the major and 

minor axes of the uplift (fig. 9). One set of faults and 

fractures is aligned approximately 55 degrees west of 

north, and the other approximately 35 degrees east 

of north. Lineament studies of Landsat imagery show 

evidence for many more deep-seated faults and fractures (Kisvarsanyi and Martin, 1977). The deep lineaments indicate tectonic activities that resulted in 

extensive breaks in the crustal rocks and associated 

block movements. These deep-seated faults and fractures are seen in the surface or shallow subsurface 

as slip-strike features as well as faults with vertical 

movement.

The southeastern flank of the Ozark uplift was 

submerged in early Mesozoic time as a result of renewed tectonic activity along the New Madrid rift 

zone (Schwalb, 1982). Submergence was followed by 

deposition of hundreds of feet of sand and clay of 

Cretaceous, Tertiary, and Quaternary age in the Mississippi Embayment (fig. 8). These post-Paleozoic deposits are in direct contact with Early Ordovician 

carbonate rocks, the latter being a buried southeast 

extension of the present-day Salem Plateau (fig. 5). 

The boundary between the Ozark Plateaus and the 

more recent sediments of the Mississippi Alluvial 

Plain, termed the "Fall Line," is a well-defined, almost linear transition from the rugged topography of 

the Ozarks to the nearly flat alluvial plain. Currently, the Ozark uplift is tectonically stable.

GROUND-WATER FLOW AND GEOHYDROLOGIC 

PROPERTIES OF THE OZARK AREA

The boundaries of the Ozark Plateaus aquifer system are determined by a combination of geologic and 

hydrologic conditions near the flanks of the Ozark 

Plateaus province. The northern boundary of the aquifer system generally is defined by the Missouri 

River valley, a major discharge area (fig. 10). Similarly, the Mississippi River valley is a discharge area 

from its confluence with the Missouri River valley to 

the Mississippi Alluvial Plain, and this stretch is considered the northeastern boundary of the aquifer system. There is some ambiguity about this boundary: 

The lowermost geohydrologic units dip so steeply and 

are so deeply buried along the eastern margin of the 

Ozarks that few data are available to verify that the 

Mississippi River valley is a discharge area for these 

deeply buried units. However, data on ground-water 

chemistry of the deep aquifers at the north and south 

ends of this reach of the Mississippi River indicate 

highly mineralized water is present along the eastern
96°

39°

38°

37°

36°

35°

95° 94° 93° 92° 91' 90° 89°

T

EXPLA

FAULT OR 

- - - - BOUNDARY 

0 20 

I I.

I r\ 

0 20 40 

FIGUKE 9. Distribution and orientation of large faults and fracture systems in study area.
I I 

EXPLANATION

REGIONAL GROUND-WATER DIVIDE

GENERALIZED DIRECTION OF

REGIONAL GROUND-WATER FLOW

£^; . :-;r^ 35° U

3

1*1 

H » 

03

FIGURE 10. Generalized flow of ground water in deeper units of the Ozark Plateaus aquifer system. O to
D22 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

flanks of the Ozarks. This finding suggests that 

freshwater from the Ozarks probably discharges upward into shallower geohydrologic units and does not 

flow eastward beneath the Mississippi River.

The Mississippi Alluvial Plain approximately 

marks the southeastern boundary of the Ozark Plateaus aquifer system. Most of the ground water that 

flows through Paleozoic rocks toward the Mississippi 

Alluvial Plain discharges upward into overlying Cretaceous, Tertiary, and Quaternary sediments near 

the Ozark Escarpment, or "Fall Line," the line of 

bluffs that marks the surface contact between Paleozoic rocks and alluvium (figs. 5, 10). A small part of 

the southeastward-flowing freshwater flows a greater 

distance beneath the post-Paleozoic sands and clays 

of the alluvial plain. The maximum distance that 

freshwater moves to the southeast beneath the alluvium is not known.

The southern boundary of the aquifer system is 

thought to be approximately parallel to the Arkansas 

River valley. Ground water in the Ozark Plateaus 

aquifer system is saline only in the region between 

the Boston Mountains and the Arkansas River.

A complex mixing zone is present along the west 

edge of the aquifer system where freshwater moving 

westward from its source in the Ozark highlands 

meets salinewater moving eastward through the 

Western Interior Plains aquifer system (Jorgensen 

and others, 1993). The western boundary of the 

Ozark Plateaus aquifer system is located in a broad, 

topographically low area. Ground-water quality along 

the boundary is characterized by the transition between nearly stagnant salinewater in the Western 

Interior Plains aquifer system and freshwater in the 

Ozark Plateaus aquifer system. At this broad, topographically low area the freshwater either discharges 

into shallower aquifers or mixes with the salinewater and discharges as base flow into the Osage and 

Neosho Rivers and their tributaries or into the Missouri and Blackwater Rivers and their tributaries.

Recharge to the Ozark Plateaus aquifer system is 

almost entirely from direct infiltration of precipitation. Precipitation that is not returned to the atmosphere as evapotranspiration or routed to streams by 

overland flow may infiltrate the unsaturated zone 

rather quickly, because soil and subsoil in the 

Ozarks is thin, near-surface faults and fracture systems are common, and dissolution of the predominating carbonate rocks is widespread.

An important control on ground-water flow in the 

Ozark Plateaus aquifer system is a regional groundwater divide that parallels a major topographic 

ridge extending across the Ozarks from the tristate 

area of Kansas-Oklahoma-Missouri to the Mississippi River east of the St. Francois Mountains (fig. 10). 

The divide separates the physiographic province into 

two approximately equal-area ground-water provinces. North of the divide, ground water moves from 

the uplands and discharges into the Missouri, Mississippi, Meramec, Osage, and Gasconade Rivers 

and their tributaries. South of the divide, ground 

water discharges into the Neosho and Spring Rivers 

to the southwest and the White River to the south. 

Generally, water flowing in the deeper part of the 

aquifer system discharges only to the largest rivers, 

whereas water moving through the upper part of 

the aquifer system forms local flow patterns that 

terminate at the smaller streams. To the southeast, 

deep-flowing ground water discharges into the Mississippi Alluvial Plain, but shallower ground water 

is intercepted by southeast-flowing rivers such as 

the Eleven Point, Current, and St. Francis Rivers 

and their tributaries.

A second ground-water divide trends east and 

west across the Boston Mountains of northern Arkansas. Ground water north of the divide flows toward the White, Buffalo, and Illinois Rivers. Ground 

water south of the divide flows toward the Arkansas 

River. Because several thousand feet of Pennsylvanian shale separates the aquifer system from the 

Arkansas River, it is possible that much of the 

southward-flowing ground water does not discharge 

to the Arkansas River, but instead turns southeast 

to discharge upward into more permeable postPaleozoic sediments of the Mississippi Alluvial 

Plain. Streamflow measurements on northern tributaries of the Arkansas River under low-flow conditions do not indicate a source of water from the 

deeper geohydrologic units. Saline springs rising 

from Paleozoic rocks beneath the Mississippi Alluvial Plain may be evidence of the discharge of water 

into the alluvium after the water has traveled beneath the Peimsylvanian shale (Augustine Ludwig, 

U.S. Geological Survey, oral commun., 1985). There 

are no hydraulic-head data from the deeper aquifers 

to support the discussed flow pattern south of the 

Boston Mountains.

The flow pattern in the Ozark Plateaus aquifer 

system is mainly topographically controlled, but local 

perturbations are produced by major faults and their 

associated fracture systems. The large fracture systems in the Ozark Plateaus are oriented in two nearly orthogonal patterns (fig. 9). Many regions having 

extensive fractures and faults are characterized by 

increased or decreased permeability in the plane of 

the fractures. The effect of fractures on the movement of ground water in the Ozarks region is most 

apparent on a local scale. Regionally, it is more diffi-
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D23

cult to detect the effects of particular fractures on 

ground-water flow, especially where the flow is 

strongly influenced by topography.

REGIONAL GEOHYDROLOGIC UNITS

The geohydrologic units of the Ozark area are classified on the basis of two characteristics: (1) the general hydraulic properties of the rock unit and (2) the 

hydrologic relation of that unit to adjacent units. The 

geohydrologic unit boundaries are not constrained by 

geologic age boundaries or stratigraphic unit boundaries (Jorgensen and Rosenshein, 1987). Because 

regional fades changes can spatially alter the hydraulic characteristics of a rock unit, the same geologic formation can be assigned to different geohydrologic units in different parts of the study area. Where 

possible, regional aquifer units of the Ozark Plateaus 

aquifer system are named after the physiographic 

region in which they generally are the main source of 

ground water, and regional confining units are 

named after the aquifers they confine.

The relative stratigraphic position of the regional 

geohydrologic units in and adjacent to the Ozark Plateaus aquifer system is shown in figure 11. The basal 

unit, composed primarily of igneous rocks of Precambrian age, is the Basement confining unit. Overlying 

the Basement confining unit is the Ozark Plateaus 

aquifer system, a group of Paleozoic rocks subdivided 

into a sequence of three aquifers and two confining 

units. From stratigraphically lowest to highest, these 

geohydrologic units are the St. Francois aquifer, the 

St. Francois confining unit, the Ozark aquifer, the 

Ozark confining unit, and the Springfield Plateau aquifer. The Ozark Plateaus aquifer system is bounded 

on the west by the laterally adjacent and stratigraphically equivalent salinewater-bearing rocks of 

the Western Interior Plains aquifer system. It is 

overlain along the western and southern edges by the 

Western Interior Plains confining system. The latter 

two geohydrologic units are major units that stretch 

from the Rocky Mountains to the Ozark Plateaus. 

The southeastern edge of the Ozark Plateaus aquifer 

system subcrops beneath post-Paleozoic sediments 

(fig. 11) of the Mississippi Alluvial Plain. Generally, 

the oldest units are exposed nearest the core of the 

Ozark uplift at the St. Francois Mountains, producing the characteristic concentric outcrop pattern 

shown on geologic bedrock maps of the Ozark Plateaus province (fig. 12; Imes, 1990a). Generally, the 

eight geohydrologic units located within the Ozark 

study area (the Western Interior Plains aquifer system is not present in the study area) are continuous

in the subsurface from their areas of outcrop to the 

boundary of the study area. Some exceptions occur 

locally where the rocks of the units are missing because of nondeposition or postdepositional erosion.

Three areas in the northeastern part of the 

Ozarks located in and near the Missouri counties of 

St. Louis, Ste. Genevieve, and Gasconade (fig. 3) are 

blanketed with Mississippian or Pennsylvanian consolidated deposits that are stratigraphically equivalent, but hydrologically unrelated, to the Springfield 

Plateau aquifer and Western Interior Plains confining system. These unnamed geohydrologic units are 

not important on a regional scale, but are important 

locally and are included in this discussion of the geohydrology of the Ozarks.

Unconsolidated deposits of Quaternary alluvial material fill the major river and stream valleys of the 

Ozarks, especially along the Missouri and Mississippi 

River valleys. Thick deposits of unconsolidated Cretaceous, Tertiary, and Quaternary sediments onlap part 

of the Ozark Plateaus aquifer system in southeast 

Missouri and northeast Arkansas (fig. 12). These unconsolidated sediments, which are grouped under the 

general term "post-Paleozoic sediments," can yield 

abundant supplies of ground water. However, a detailed study of these sediments is beyond the scope of 

this investigation. Hydrologic and lithologic characteristics of the post-Paleozoic sediments are described 

in this report only to the extent that they affect 

ground-water flow in the underlying Ozark Plateaus 

aquifer system.

The geohydrologic units in the study area that underlie, compose, and overlie the Ozark Plateaus aquifer system, from the stratigraphically oldest to 

youngest unit, are discussed in the following sections 

of the report.

BASEMENT CONFINING UNIT

The Basement confining unit is considered the base 

of the Ozark Plateaus aquifer system in the Ozarks 

because no known aquifers are present beneath the 

unit. The confining unit is not limited to the Ozark 

area, but forms the base of regional ground-water 

flow systems throughout the Central Midwest RASA 

study area. The Basement confining unit is primarily 

composed of igneous rocks of Precambrian age, which 

are part of a series of extensive rhyolite-granite complexes that stretch across the midcontinent. The crystalline rocks are nearly impermeable, and wells that 

tap these rocks yield no significant amount of water. 

However, in outcrop areas where the rocks are 

weathered, fractured, or faulted, yield of wells may
D24 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

range from near 0 to 70 gallons per minute, but rarely exceeds 10 gallons per minute.

CONFIGURATION OF THE UPPER SURFACE

The Basement confining unit is exposed at three 

general locations in the Ozark Plateaus: a large area 

in and southwest of the St. Francois Mountains of 

southeastern Missouri, a much smaller area limited to

five low hills in Mayes County (fig. 3) in northeastern 

Oklahoma, and an isolated exposure in Camden 

County, Missouri, named the Decatureville structure 

(McCracken, 1971). The St. Francois Mountains of 

southeast Missouri correspond to both a structural 

and topographic high on the surface of the Basement 

confining unit (fig. 13; Imes, 1989). Because many exploration wells have been drilled to locate and define 

commercial iron deposits in the Precambrian rocks 

and lead and zinc deposits in overlying sediments, the

WEST

	EXPLANATION

A WESTERN INTERIOR PLAINS CONFINING SYSTEM

B WESTERN INTERIOR PLAINS AQUIFER SYSTEM

a, STRATIGRAPHICALLY EQUIVALENT TO OZARK CONFINING UNIT

B2 STRATIGRAPHICALLY EQUIVALENT TO ST. FRANCOIS CONFINING UNIT

	OZARK PLATEAUS AQUIFER SYSTEM 

C SPRINGFIELD PLATEAU AQUIFER 

D OZARK CONFINING UNIT 

E OZARK AQUIFER 

F ST. FRANCOIS CONFINING UNIT 

G ST. FRANCOIS AQUIFER 

H BASEMENT CONFINING UNIT 

I POST- PALEOZOIC SEDIMENTS

FIGURE 11. Schematic cross section of regional geohydrologic units in and adjacent to the Ozark Plateaus aquifer system.
96° 95° 94° 93° 92° 91' 90°

39 C

38°37°

36°

35 C

.V, - !: : ;! : - 89° KXPLANATION BASEMENT CONFINING UNIT ST. FRANCOIS AQUIFER ST. FRANCOIS CONFINING UNIT OZARK AQL'IFER OXARK CONFINING UNIT SPRINGFIELD PLATEAU AQUIFER WESTERN INTERIOR PLAINS CONFINING SYSTEM POST-PALEOZOIC SEDIMENTS ---- BOUNDARY OF STUDY AREA

0 20 40 60 MILES

I I 

1 I T 

0 20 40 60 KILOMETERS

i 

o

§ s

§

X

I

FIGURE 12. Outcrop areas of regional geohydrologic units in and adjacent to the Ozark Plateaus province. White areas within boundary of study area are local geohydrologic 

units that are stratigraphically equivalent to regional geohydrologic units. See section "Unnamed Local Geohydrologic Units." O

ISOen
96° 95° 94° 93° 92° 91 C 90°

89°__________8JT_______ I I

EXPLANATION

OUTCROP AREA OF CONFINING UNITAREAL EXTENT OF CONFINING UNIT IN 

SUBSURFACE WITHIN THE STUDY AREA

- - - - BOUNDARY OF STUDY AREA

 500 LINE OF EQUAL ALTITUDE Shows altitude of 

top of confining unit. Interval, in feet, is variable. 

Datum is mean sea level

FAULT U, upthrown side; D, downthrown side

36° - 35° - 20

I

40 60 MILES

_|____I II I 

0 20 40 60 KILOMETERS

OtoOi

1

I

9

FIGURE 13. Area! extent and configuration of top of the Basement confining unit.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D27

density of test-hole data in the vicinity of the St. 

Francois Mountains is large (Kisvarsanyi, 1975). Consequently, the surface of the Basement confining unit 

can be mapped fairly accurately in this area. The surface is rugged and broken by numerous faults. The 

altitude of the surface of the basement confining unit 

can vary by as much as 1,000 feet within a few miles. 

The generally rugged topographic features exhibited 

by the confining unit evolved as thousands of feet of 

volcanic rocks were eroded from structural highs 

during the several hundred million years of late Precambrian and Early Cambrian time before the submergence of the area by Late Cambrian seas.

Beyond the St. Francois Mountains, the surface of 

this confining unit dips steeply to the north, east, 

and south, where the flanks of the Ozark uplift dip 

into adjacent basins. To the west the surface dips 

more gently toward a subsurface plateau that ranges 

in altitude from about 400 to 1,000 feet below sea 

level. The subsurface plateau encompasses most of 

southwestern Missouri and extreme northeastern 

Oklahoma and northwestern Arkansas; it generally 

corresponds to the Ozark Plateaus physiographic 

province. Structure contours in figure 13 have been 

extended southward beyond the limit of well-log data 

in western Arkansas; this extension was made on the 

basis of seismic reflection data presented by Lillie 

and others (1983).

LlTHOLOGYAND PERMEABILITY

Most of the exposed Basement confining unit consists of rhyolitic volcanic rocks (Kisvarsanyi, 1981). 

Granitic rocks were emplaced as dikes and sills beneath the rhyolitic cover in several stages. Porosity 

can occur in rhyolitic rocks by development of columnar jointing at the base of ash-flow tuffs and by expansion of trapped gas bubbles in lava flows 

(Hyndman, 1972). However, rhyolitic rocks in the 

vicinity of the St. Francois Mountains have little porosity and, more importantly, the pores are not interconnected. Thus, even in the more porous igneous 

rocks of this region, permeability is extremely small.

Secondary permeability has developed in the Precambrian basement but is mainly confined to fracture 

systems and faults. Fault displacements generally 

are on the order of tens of feet but can be as large as 

1,200 feet. The faults usually are nearly vertical and 

are characterized by a lack of brecciation (Anderson, 

1970). The extensive network of fracture and fault 

zones in the block-faulted Ozark uplift probably is 

not confined to the volcanic terrane of the St. Francois Mountains where this evidence is visible. Aeromagnetic surveys (Allingham, 1960; Denison, 1981; 

Kisvarsanyi, 1981) and correlation of major lineaments on Landsat imagery with physiographic features and known fault zones (Kisvarsanyi and 

Martin, 1977) indicate that the Precambrian surface 

is more fractured than suggested by well-log data.

ST. FRANCOIS AQUIFER

The St. Francois aquifer, the lowermost geohydrologic unit of the Ozark Plateaus aquifer system, is 

composed of permeable sandstone and dolostone overlying the Basement confining unit. Three Upper 

Cambrian formations are included in the aquifer: the 

Lamotte Sandstone, the Reagan Sandstone, and the 

Bonneterre Dolomite (table 1). The St. Francois aquifer is named for the geographic region, the St. Francois Mountains, where the aquifer is exposed and is 

used as a source of water for domestic and public 

supply. Wells tapping this aquifer may yield from 100 

to 500 gallons per minute. However, this aquifer is 

rarely used beyond the outcrop area because the 

overlying Ozark aquifer yields more water at a shallower depth.

The geologic formations that constitute the St. 

Francois aquifer extend beyond the boundary of the 

Ozark Plateaus aquifer system. Few hydrologic data 

are available to verify that the boundary of the 

Ozark Plateaus aquifer system also represents the 

limit of lateral ground-water flow in the St. Francois 

aquifer. The boundary of the aquifer is largely delineated from potentiometric-head and dissolved-solids 

concentration data from the overlying Ozark and 

Springfield Plateau aquifers. In other words, the 

boundary of the St. Francois aquifer is assumed to be 

approximately coincident with the boundary of the 

overlying aquifers. There is some evidence that suggests this assumption is correct. Water levels measured during construction of a deep test well near the 

boundary of the Ozark Plateaus aquifer system in St. 

Louis County, Missouri (fig. 3), indicate that potentiometric head increases with depth. Although the St. 

Francois aquifer is buried to a depth exceeding 2,500 

feet, the head in this aquifer is higher than heads in 

shallower aquifers. Thus, the Missouri and Mississippi River valleys probably are discharge areas for this 

aquifer. Deep wells located in Pettis and Jasper 

Counties, Missouri, near the western edge of the 

Ozark Plateaus aquifer system, yield freshwater from 

the St. Francois aquifer. The relatively large leakance of the overlying St. Francois confining unit, 

which hydraulically separates the St. Francois aquifer from the Ozark aquifer, probably ensures that the
D28 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

limit of lateral ground-water flow in the St. Francois 

aquifer nearly coincides with the limit of the Ozark 

aquifer. However, this assumption cannot be verified 

because of the lack of well data.

STRUCTURAL FEATURES

The St. Francois aquifer crops out in the St. Francois Mountains in broad valleys between more resistant, exposed peaks of the Basement confining unit 

(fig. 12). The largest unbroken outcrop area is located 

at the northeast edge of the St. Francois Mountains 

where the Basement confining unit is uplifted to within a few hundred feet of land surface. The total outcrop area is only about 590 square miles. Beyond the 

relatively small outcrop area, the aquifer dips into the 

subsurface and is buried beneath younger water-yielding rocks. The dip is steepest to the northeast and 

east toward the Illinois Basin and to the southeast 

toward the Mississippi Alluvial Plain, where the aquifer is buried to a depth of about 3,550 to 10,000 feet 

(fig. 14). About 60 miles west of the St. Francois 

Mountains, the aquifer dips less steeply into the subsurface and the unit forms a relatively flat subsurface 

area beneath the western half of the Salem Plateau, 

the Springfield Plateau, and that part of the Interior 

Plains within the study area. The depth of burial of 

the aquifer is generally between 800 and 1,500 feet in 

this region. The aquifer is more deeply buried in the 

southern part of the study area. The aquifer dips 

steeply into the subsurface southeast of a line extending from the extreme western tip of the Boston Mountains to the southeastern edge of the St. Francois 

Mountains. Burial depth exceeds 10,000 feet in the 

extreme southern part of the study area.

The altitude of the top of the St. Francois aquifer 

generally is greater than 500 feet above sea level in 

and near the St. Francois Mountains (fig. 15; Imes, 

1990b). The altitude of the top is below sea level in 

the remainder of the study area except along the 

common border between Camden County and Laclede County, Missouri (fig. 3), where a small outcrop 

of igneous rocks form the core of the Decatureville 

structure (McCracken, 1971). The top of the aquifer 

generally is more than 1,000 feet below sea level 

along the western edge of the study area and 

throughout most of northern Arkansas.

THICKNESS

Thickness of the St. Francois aquifer varies considerably and seems to reflect the rugged topography of

the underlying Precambrian surface (Basement confining unit). Variation of the thickness is apparent in 

the vicinity of the St. Francois Mountains and in 

northeastern Oklahoma (fig. 16; Imes, 1990b) but is 

not as apparent elsewhere in the study area because 

insufficient well-log data are available to define the 

thickness changes. The aquifer is missing in the center of the St. Francois Mountains of southern Missouri where the Basement confining unit crops out. 

The aquifer extends from the St. Francois Mountains 

to the boundary of the study area but locally is missing where peaks in the Basement confining unit 

breach the aquifer. The larger areas where the aquifer is not present in the subsurface are located in 

northeastern Oklahoma.

The thickness of the aquifer generally ranges from 

about 300 to 700 feet in southern Missouri, except 

near locations where the aquifer is breached. The aquifer is thickest (greater than 1,000 ft) beneath the 

Mississippi Alluvial Plain near the southeastern part 

of the Ozark Plateaus province. The aquifer generally 

ranges from about 100 to 300 feet thick in northern 

Arkansas. The aquifer is thinner in the western and 

southwestern part of the study area where the Lamotte Sandstone and Bonneterre Dolomite are not 

present.

LlTHOLOGYAND GEOHYDROLOGIC PROPERTIES

The Lamotte Sandstone and the Bonneterre Dolomite form the rock matrix of the St. Francois aquifer 

in the eastern three-quarters of the study area. Much 

of the lithologic data on the Lamotte Sandstone is 

based on drill cuttings from wells located near the 

St. Francois Mountains where the formation is not so 

deeply buried. In this location the Lamotte generally 

is a well-sorted, medium-grained, quartzose sandstone containing locally derived arkosic material at 

or near its base. Because the sandstone is well sorted 

and relatively clean, the permeability of the sandstone at this location is high. The sandstone contains 

possible fluvial, aeolian, and beach-environment components as well as shallow-marine deposits. Less is 

known about this sandstone away from the vicinity 

of the St. Francois Mountains. In 1984, several deep 

test wells were drilled to the Precambrian basement 

in western Missouri as part of an assessment of strategic minerals in the midcontinent. Information from 

these strategic-mineral and other test wells in southcentral Missouri indicate that the lithology, and probably the permeability, of the Lamotte Sandstone in 

this area differs little from the lithology and permeability farther east. The sandstone is described by
96° 95° 94° 93° 92° 91 C 90° 89° 88°

39°38°

37°

36°

35°

 :.: -'.-'. ' . :'. '. ' . ' / "~T~ ,. j _...

EXPLANATION

OUTCROP AREA OF AQUIFER

AREAL EXTENT OF AQUIFER IN 

SUBSURFACE

AREA WHERE AQUIFER (OR 

EQUIVALENT UNIT) IS MISSING IN SUBSURFACE

---- BOUNDARY OF STUDY AREA

- 500- LINE OF EQUAL DEPTH Interval, 

in feet, is variable

0 20 40 60 MILES

I I I

I I T

0 20 40 60 KILOMETERS

FIGURE 14. Depth of the St. Francois aquifer below land surface. Information outside of study area is from stratigraphically equivalent unit.

§§

^ 

ffi

8

cc

1

ato

CD
96° 95° 94° 93° 92° 91 C

39°38 C

37°

36 C

35°

90° 89°__________88°_______

I

EXPLANATION

OUTCROP AREA OF AQUIFER

AREAL EXTENT OF AQUIFER IN 

SUBSURFACE

AREA WHERE AQUIFER (OR 

EQUIVALENT UNIT) IS 

MISSING IN SUBSURFACE

- - - - BOUNDARY OF STUDY AREA

-500- LINE OF EQUAL ALTITUDE 

Shows altitude of top of aquifer. Interval, in feet, is variable. Datum is sea level

*£ U * -/ g FAULT u, upthrown side; D, down-

> thrown side

0 20 40 60 MILES

I I I

I I T

0 20 40 60 KILOMETERS

OCOo

FIGURE 15. Areal extent and configuration of top of the St. Francois aquifer. Information outside of study area is from stratigraphically equivalent unit.
96° 95° 94° 93° 92° 91 c 90° 89J 88°

39°38°

37°

36°

35°

EXPLANATION

OUTCROP AREA OF AQUIFER

- - - - BOUNDARY OF STUDY AREA

-500- LINE OF EQUAL THICKNESS 

Interval, in feel, is variable

0 20 40 60 MILES

I I I

I I I

0 20 40 60 KILOMETERS

.Is

I i

FIGURE 16. Thickness of the St. Francois aquifer. Information outside of study area is from stratigraphically equivalent unit.

I

§

soO co
D32 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

Caplan (1960), on the basis of samples from six wells 

in northwestern Arkansas, as a loosely cemented, 

subangular to rounded quartz sandstone that occasionally is dolomitic. Fragments of feldspar from the 

underlying Precambrian rocks are encased in the 

sandstone at its base. It is probable that the permeability of the Lamotte Sandstone is lower south of 

the Boston Mountains where the unit is buried beneath thousands of feet of younger sediments (fig. 

14).

Near the St. Francois Mountains, the overlying 

Bonneterre Dolomite is predominantly a coarsegrained dolostone containing numerous small cavities 

and resting on a sandy dolostone basal unit. The lithology of the Bonneterre in this area is indicative of 

a barrier-reef facies that developed in shallow water 

offshore from islands of Precambrian rock that rose 

above the Cambrian sea. The offshore facies of the 

Bonneterre Dolomite predominantly was a finegrained limestone with some clastic material, mainly 

shale (Gerdemann and Myers, 1972). The Bonneterre 

Dolomite probably is more permeable in the reef and 

back-reef facies adjacent to the St. Francois Mountains than in the offshore facies where the unit is 

finer grained and contains a larger fraction of shale.

The western one-quarter of the aquifer is composed 

of the Reagan Sandstone, a near-shore facies of the 

Lamotte Sandstone, Bonneterre Dolomite, and Davis 

Formation (Kurtz and others, 1975). The Reagan 

Sandstone generally is a poorly sorted sandstone containing small quantities of silt and shale. Little is 

known about the geohydrologic properties of this 

sandstone because few water-supply wells are drilled 

deep enough to penetrate the sandstone. However, information from a well drilled in Jasper County, Missouri (fig. 3), indicates that the Reagan Sandstone 

probably is hydrologically similar to the moderately 

permeable Lamotte Sandstone.

Estimates of the hydraulic conductivity of the St. 

Francois aquifer were made using specific-capacity 

data. The method that was used to estimate the hydraulic conductivity can be divided into two procedures. First, because most wells do not penetrate the 

entire thickness of an aquifer, it is necessary to use a 

correction factor to determine the specific capacity of 

each well as if it penetrated the entire thickness of 

the aquifer. The specific-capacity data from partially 

penetrating wells were corrected to values one would 

expect from fully penetrating wells using a derivation 

presented by Todd (1959). Second, the corrected specific-capacity data were used with the steady-state 

Thiem equation or the Jacob approximation to the 

Theis equation (Lohman, 1979) to estimate the aquifer transmissivity. Transmissivity values were converted to hydraulic conductivity by dividing by the 

aquifer thickness.

The estimated hydraulic conductivity of the St. 

Francois aquifer in the immediate vicinity of the St. 

Francois Mountains ranges from as great as 1x10 

foot per second to less than lxlO~6 foot per second. 

The hydraulic conductivity is greater in the St. Francois Mountains and decreases radially away from the 

mountains. Data are insufficient to estimate the distribution of hydraulic conductivity beyond the vicinity of the St. Francois Mountains, primarily because 

wells away from the St. Francois Mountains that 

penetrate the confined aquifer are also open to other 

aquifers.

Warner and others (1974), using water-level data 

from observation wells and the Jacob modified nonequilibrium formula (Lohman, 1979), estimated the 

transmissivity of the combined Lamotte Sandstone 

and Bonneterre Dolomite at three mines near the 

eastern edge of the St. Francois Mountains as 

1.8xlO~3, 5.4xlO~3, and 3.0xlO~4 foot squared per 

second. Corresponding values of estimated storage 

coefficients were 0.0085, 0.0043, and 0.0026 (dimensionless). Using estimated thicknesses of the St. 

Francois aquifer at these mine locations, we estimated hydraulic conductivities of the aquifer to be 

6.2xlO~6, 1.4xlO~5, and 4.5xlO~7 foot per second, respectively. The corresponding projections of the probable hydraulic conductivity at these mine sites, as 

determined from contoured specific-capacity data, are 

IxlO"4, 7xlO~6, and 2xlO~6 foot per second. The differences in the estimates are not so large as they appear when one considers the sparsity of the specificcapacity data for the aquifer and the differences in 

the techniques used for these estimates.

RECHARGE, GROUND-WATER FLOW, AND DISCHARGE

Ground-water levels in the vicinity where the St. 

Francois aquifer crops out are mainly controlled by 

topographic features (fig. 17). The altitude of the potentiometric surface varies from more than 1,100 feet 

above sea level in the upland areas to less than 600 

feet above sea level in the major river valleys. Depth 

to water in the outcrop area ranges from a few feet 

in the valleys to as much as 150 feet in the highlands. Ground water discharges to the St. Francois 

and Black Rivers to the south and the Big River to 

the north. The head data indicate that ground water 

discharges toward these rivers even in the region immediately surrounding the outcrop area, where the 

aquifer is confined (Imes, 1990b). In this region the 

leakance of the overlying confining unit is large
96° 95° 94° 93° 92° 91 c 90°

39C38 C

37°

36 C

35C

89°__________8JT_____ ~~l I

EXPLANATION

OUTCROP AREA OF AQUIFERAREAL EXTENT OF AQUIFER IN 

SUBSURFACE

---- BOUNDARY OF STUDY AREA

-500- POTENTIOMETRIC CONTOUR 

Shows altitude at which water levels would have stood in tightly cased wells. Contour interval is 100 feet. 

Datum is sea level

0 20 40 60 MILES 

II I

\ T 

0 20 40 60 KILOMETERS

1

O3

FIGURE 17. Predevelopment potentiometric surface of the St. Francois aquifer. Information outside of study area is from stratigraphically equivalent unit. Rivers shown only in

part; see figure 6 for their full extent. O 

wCO
D34 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

enough so that heads in the St. Francois aquifer are 

affected by topographic relief.

Few wells are open to the St. Francois aquifer beyond the vicinity of the St. Francois Mountains, and 

the wells that do penetrate the St. Francois aquifer 

also are open to the overlying Ozark aquifer. Therefore, heads observed in these wells are composite 

heads, and little is known about heads in the St. 

Francois aquifer beyond the vicinity of the St. Francois Mountains. Because the St. Francois aquifer is 

seldom used for withdrawals of large quantities of 

ground water, the present-day potentiometric surface 

of the aquifer probably varies little from the predevelopment potentiometric surface. An exception to 

this statement occurs along the Viburnum Trend lead 

ore deposits on the western flank of the St. Francois 

Mountains. Pumpage to dewater lead-mine shafts 

has caused large drawdowns in the vicinity of the 

mining area.

CHEMICAL QUALITY OF GROUND WATER

Bicarbonate is the dominant anion in samples of 

ground water from wells near the outcrop area of the 

aquifer (fig. 18; table 2; Imes and Davis, 1990a). Calcium and magnesium are the dominant cations; in 

most of this area the concentration of the dominant 

cation does not exceed 50 percent. Locally, the water 

type can be calcium bicarbonate or magnesium bicarbonate. The water type in wells located a few miles 

northwest and southwest of the outcrop area is sodium bicarbonate or bicarbonate with sodium as the 

dominant cation.

Near the St. Francois Mountains the dissolved-solids content of ground water in the aquifer varies 

from less than 100 to more than 400 milligrams per 

liter (fig. 19; Imes and Davis, 1990a). In general, 

areas of larger concentration seem to be located 

southwest and northwest of the mountains. Elsewhere, the dissolved-solids concentration ranges from 

about 200 to 400 milligrams per liter except at the 

easternmost well location, where the measured dissolved-solids concentration was less than 100 milligrams per liter. Dissolved-solids concentrations in 

water from the few wells that are open to the aquifer 

and overlying geohydrologic units in Phelps, Pettis, 

and Jasper Counties, Missouri (fig. 3), are not large, 

but the actual concentrations in water from the St. 

Francois aquifer cannot be determined.

The concentration of chloride ions in water from 

the St. Francois aquifer in the vicinity of the St. 

Francois Mountains varies from less than 5 milligrams per liter to more than 60 milligrams per liter

(fig. 19). Water samples containing the larger concentrations were obtained from wells located northwest 

and southwest of the mountains. Ground water to 

the northeast of the mountains generally contains 

chloride concentrations of less than 10 milligrams 

per liter, but a small area in southwest St. Francois 

County (fig. 3) contains more than 10 milligrams per 

liter.

The sulfate concentrations in ground water vary in 

a pattern similar to that shown by the chloride ions 

(fig. 19). The wells that contain larger sulfate concentrations are located northwest (38 mg/L) and southwest (60 mg/L) of the St. Francois Mountains and in 

southwest St. Francois County (150 mg/L).

The concentrations of dissolved solids, chloride, 

and sulfate reported above and mapped in figure 19 

are based on water samples from a few wells located 

in a small area in and near the outcrop area of the 

aquifer. They probably do not reflect ion concentrations far from the St. Francois Mountains where the 

aquifer is confined and deeply buried.

ST. FRANCOIS CONFINING UNIT

The St. Francois confining unit, the lower confining 

unit in the Ozark Plateaus aquifer system, retards 

the flow of ground water between the more permeable St. Francois aquifer and the overlying Ozark aquifer. The confining unit is composed of shale, 

siltstone, dolostone, and limestone. It is missing in 

the St. Francois Mountains but is nearly continuous 

in the subsurface from its outcrop area around the 

St. Francois Mountains to the boundaries of the 

study area. Three Upper Cambrian geologic formations, the Davis Formation and the Derby and Doe 

Run Dolomites (table 1), form the confining unit.

STRUCTURAL FEATURES

Erosion of the Ozark dome has exposed the St. 

Francois confining unit at land surface in a thin, 

nearly circular band around the St. Francois Mountains (fig. 12). The total outcrop area is about 400 

square miles and surrounds a central core of older 

rocks where the unit is missing. Northeast, east, and 

southeast of the outcrop area, the confining unit dips 

steeply into the subsurface (fig. 20; Imes, 1990c). The 

dip is greatest to the east, where it can exceed 150 

feet per mile. From an altitude of 1,000 feet above 

sea level in the outcrop area at the eastern edge of 

the St. Francois Mountains, the confining unit plunges into the subsurface to an altitude of more than
96° 95° 94° 93° 92° 91' 90° 89° 88°

39°

38°

37°

36°

35°

X .tiiiiiiiinm..i.r «» yuan lmmiiiiiiiiiiiiiiiiiiii\

 ~ \

EXPLANATION

OUTCROP AREA OF AQUIFER

AREAL EXTENT OF AQUIFER IN 

SUBSURFACE

AREA WHERE AQUIFER (OR 

EQUIVALENT UNIT) IS 

MISSING IN SUBSURFACE

- - - - BOUNDARY OF STUDY AREA

BOUNDARY BETWEEN AREAS OF 

DIFFERENT MAJOR CHEMICAL 

CONSTITUENTS Dotted where inferred

XAM MAJOR CHEMICAL CONSTITUENTS 

See table 2 for explanation of symbols

0 20 40 60 MILES

I I I

H I I

0 20 40 60 KILOMETERS

§

1

FIGURE 18. Water type in the St. Francois aquifer. Information outside of study area is from stratigraphically equivalent unit. O

CO
D36 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

TABLE 2. Explanation of symbols used in maps of major chemical constituents

[Two-letter code is used to designate the cation and anion present in concentrations larger than 49.99 

percent. If a cation or anion is not present in a concentration larger than 49.99 percent, the species 

is designated by X and the cation or anion existing in the largest concentration is listed as a third 

symbol. Thus, XAN indicates a bicarbonate water with no cation present in a concentration larger 

than 49.99 percent, but with sodium present in the largest concentration of the three cations]

Anion

Cation

Calcium

Magnesium

Sodium

Mixed cation

Bicarbonate

CA

MA

NA

XA (C, M, N)

Chloride

CC

MC

NC

XC (C, M, N)

Sulfate

CS

MS

NS

XS (C, M, N)

Mixed anion

CX (A, C, S)

MX (A, C, S)

NX (A, C, S)

XX

91° 90° 89° 91 c 90° 89° 91 C 90° 89°

DISSOLVED SOLIDS

39°

38°

37°

CHLORIDE SULFATE

0 20 40 60 MILES

I .1.1 I

I \~\ I

0 20 40 60 KILOMETERS

EXPLANATION

OUTCROP AREA OF AQUIFER

AREAL EXTENT OF AQUIFER IN SUBSURFACE

AREA WHERE AQUIFER IS MISSING IN SUBSURFACE

- - - - BOUNDARY OF STUDY AREA

- 300 - LINE OF EQUAL CONCENTRATION Dissolved solids 

interval is 100 milligrams per liter. Interval for chloride 

and sulfate, in milligrams per liter, is variable

FIGURE 19. Dissolved-solids, chloride, and sulfate concentrations in ground water from the St. Francois aquifer.
96° 95° 94° 93° 92° 91' 90°

'EXPLANATION1

OUTCROP AREA OF CONFINING UNIT

AREAL EXTENT OF CONFINING UNIT 

IN SUBSURFACE

i/V;:';:Y' AREA WHERE CONFINING UNIT (OR ' ' ' '' ' "' EQUIVALENT UNIT) IS MISSING IN 

SUBSURFACE

- - - - BOUNDARY OF STUDY AREA

400 - LINE OF EQUAL ALTITUDE Shows

altitude of top of confining unit. Interval, 

in feet, is variable. Datum is sea level in feet, i

-g FAULT U, upthrown side; D, downthrown 

side

40 60 MILES 

i i

-n U ^-- I

__________,_________?> ^ ^

FIGURE 20. Areal extent and configuration of top of the St. Francois confining unit.

l~l T

20 40 60 KILOMETERS

i 'S '"'-: H i ? ^ hy i________i________

;. Information outside of study area is from stratigraphically equivalent unit.

9

I 

£

OCO
D38 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

3,000 feet below sea level at the eastern edge of the 

Ozark Plateaus province. West of the St. Francois 

Mountains, the unit dips less steeply into the subsurface, and the top of the unit forms a broad, gently 

sloping subsurface plateau, broken by several small 

depressions and hills. The altitude of the top of the 

unit is lower than 7,000 feet below sea level beneath 

the Arkansas River at the southern boundary of the 

Ozark Plateaus aquifer system.

The confining unit is -missing in the subsurface 

from several small isolated areas in western Missouri, northeastern Oklahoma, and northwestern Arkansas (fig. 20). The altitude of the top of the unit 

generally increases near areas where the unit is 

missing in northeastern Oklahoma. The increase is 

consistent with the existence of uplifted Precambrian 

knobs. In contrast, the altitude of the top of the unit 

in western Missouri and northwestern Arkansas 

changes little near areas where the unit is missing. 

These latter areas may, therefore, represent areas of 

nondeposition. Most of the areas where the confining 

unit is missing coincide with areas where the underlying St. Francois aquifer is absent (fig. 14).

THICKNESS

The St. Francois confining unit, as determined 

from well-log data, ranges from 0 to 730 feet thick 

(fig. 21; Imes, 1990c). This semipermeable rock unit 

thins against the flanks of the St. Francois Mountains in southeastern Missouri and near the local 

areas where it is missing in the southwestern and 

western parts of the study area. Beyond its outcrop 

area the thickness of the confining unit ranges from 

200 to 400 feet throughout much of the Salem Plateau. The thickness of the unit exceeds 600 feet beneath the northwest edge of the Mississippi Alluvial 

Plain. West of the Salem Plateau the unit gradually 

decreases in thickness until stratigraphically equivalent geohydrologic units pinch out a few miles west of 

the Ozark Plateaus aquifer system in eastern Kansas 

and northeastern Oklahoma (Kurtz and others, 

1975). In the southwestern part of the study area the 

unit is, for the most part, less than 100 feet thick. In 

northern Arkansas the unit generally varies between 

100 and 400 feet thick, but is 730 feet thick in Madison County, Arkansas (fig. 3). This area of increased 

thickness coincides with a deep depression in the 

Precambrian surface.

The Davis Formation is absent from the St. Francois confining unit at isolated locations in Saline and 

Douglas Counties, Missouri (fig. 3), but it is part of 

the unit elsewhere. The Davis thins to the southwest

because lower sediments of the Davis become more 

clastic and grade into Reagan Sandstone (Thacker, 

1974), a formation included in the underlying St. 

Francois aquifer. The Derby and Doe Run Dolomites 

are uniform in thickness and are part of the confining unit throughout the study area.

LlTHOLOGY AND GEOHYDROLOGIC PROPERTIES

The Davis Formation generally contains a large 

percentage of clastic rocks and has the most continuous shale unit in the entire sequence of Cambrian 

strata. Clastic rocks usually are more prevalent near 

the base of the Davis Formation, and carbonate rocks 

are more predominant near the top. The lithology of 

the Davis Formation has been defined in more detail 

in the vicinity of the St. Francois Mountains where 

numerous mineral test holes have penetrated the formation. In this area, the lower part of the Davis formation is a coarse-grained, massively bedded 

dolostone with a significant shale content and a welldefined zone of conglomerate cemented with dolomite 

(Fletcher, 1974). The upper part of the Davis Formation generally is not so thickly bedded, is more fine 

grained, and does not contain as much shale. A massive, coarse-grained dolostone tops the upper part. 

Locally, the Davis Formation may contain large 

quantities of sand and silt. The distribution of shale 

is not uniform, and in some areas sand may be the 

dominant clastic component. It is expected that the 

effectiveness of the Davis Formation as a confining 

unit may be impaired in these sand-rich areas. In the 

southwest part of the Ozark Plateaus, the sand-toshale ratio of the Davis Formation increases and the 

lower part of the formation becomes the Reagan 

Sandstone.

The Derby and Doe Run Dolomites generally have 

a smaller shale content than the Davis Formation; 

however, locally they may contain nearly as much 

shale and silt as the Davis Formation. The Derby 

and Doe Run Dolomites are regarded as a transition 

unit, dividing Cambrian sedimentary rocks with a 

large clastic content below from sedimentary rocks 

that contain only small quantities of clastic material 

above.

The shale content of a geohydrologic unit commonly is used as a measure of the effectiveness of the 

unit in restricting leakage. Therefore, maps of the 

shale content (in percent of total thickness) and net 

shale thickness of the St. Francois confining unit are 

presented in figures 22 and 23. However, it must be 

emphasized that the presence or absence of shale is 

not the only determining factor in assessing the
96° 95° 94° 93° 92° 91 90° 89°

39°

38°

37°36°

35C

EXPLANATION

OUTCROP AREA OF CONFINING UNIT

AREAL EXTENT OF CONFINING UNIT 

IN SUBSURFACE

AREA WHERE CONFINING UNIT 

(OR EQUIVALENT UNIT) IS MISSING IN SUBSURFACE

-- - - BOUNDARY OF STUDY AREA

- 500- LINE OF EQUAL THICKNESS Interval, 

in feet, is variable

0 20 40 60 MILES

I .1.1 II \~~\ I

0 20 40 60 KILOMETERS

FIGURE 21. ^Thickness of the St. Francois confining unit. Information outside of study area is from stratigraphically equivalent unit.

oM 

O

1

»O 

coCO
96° 95° 94° 93° 92° 91 90° 89° 88°

39°

38°

-^

37°

36°

35°

EXPLANATION

OUTCROP AREA OF CONFINING UNITAREAL EXTENT OF CONFINING UNIT 

IN SUBSURFACE

AREA WHERE CONFINING UNIT (OR 

EQUIVALENT UNIT) IS MISSING IN 

SUBSURFACE

AREA OF ZERO SHALE CONTENT

- - - - BOUNDARY OF STUDY AREA

V 10 LINE OF EQUAL SHALE CONTENT 

Interval, in percent, is variable

\ 

/>>

/^ / -0J:J

0 20 40 60 MILES

I I I

0 20 40 60 KILOMETERS

G rf^ 

o

OI I

o2

1

1

FIGURE 22. Shale content of the St. Francois confining unit. Information outside of study area is from stratigraphically equivalent unit.
96° 95° 94° 93° 92° 91 C 90° 89° 88°

39°38°37°

36°

35C

EXPLANATION

OUTCROP AREA OF CONFINING UNITAREAL EXTENT OF CONFINING UNIT 

IN SUBSURFACE

AREA WHERE CONFINING UNIT (OR 

EQUIVALENT UNIT) IS MISSING IN SUBSURFACE

AREA OF ZERO SHALE CONTENT 

- - - - BOUNDARY OF STUDY AREA

40 LINE OF EQUAL NET THICKNESS OF 

SHALE Interval is 20 feet

0 20 40 60 MILES 

I I I n^ i i

0 20 40 60 KILOMETERS

O

ffi

s9

,O

FIGURE 23. Net shale thickness in the St. Francois confining unit. Information outside of study area is from stratigraphically equivalent unit.
D42 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

effectiveness of a carbonate and clastic geohydrologic 

unit as a confining unit. Other factors include the 

primary and secondary permeability of the carbonate 

and the presence or absence of fractures.

The shale content of the St. Francois confining unit 

ranges from 0 to about 40 percent (fig. 22; Imes, 

1990c). In the northern half of the study area, the 

shale content of the unit is less than 10 percent 

along a band extending west from the northern edge 

of the St. Francois Mountains. To either side of this 

band, the shale content increases to more than 20 

percent. Shale content locally exceeds 30 percent in 

an area southwest of the St. Francois Mountains. In 

the southwestern part of the study area, the shale 

content ranges from less than 10 percent to more 

than 20 percent. A small area in northeastern Oklahoma is devoid of shale. Also, no shale is present 

throughout a large area that parallels the western 

boundary of the study area. No lithologic data are 

available for this unit in the southernmost parts of 

the study area.

Most of the shale in the St. Francois confining unit 

forms thick beds, but it also is common throughout 

the limestone and dolostone matrix as shale partings 

less than a few inches thick. The net shale thickness 

map (fig. 23) shows the effective shale thickness of 

the unit as if the shale existed in a single bed instead of being distributed throughout the unit. Generally, the net shale thickness is greater in the east 

where the confining unit is thicker. The net shale 

thickness is least, less than 20 feet, along a band 

stretching west from the northern edge of the St. 

Francois Mountains; it is greater north and south of 

this band. To the north the net shale thickness increases to about 100 feet near the Missouri River in 

the north-central part of the Salem Plateau. South of 

the band the net shale thickness increases to more 

than 100 feet locally in a region extending from 

Texas County, Missouri (fig. 3), to the west flank of 

the St. Francois Mountains. Throughout the western 

half of the Ozark study area, the net shale thickness 

generally remains less than 40 feet, except in one 

small locality in northwestern Arkansas where it exceeds 60 feet. In northeastern Oklahoma, the thickness generally is less than 20 feet.

Significant secondary porosity and permeability 

have not developed in the limestone and dolostone of 

the Davis Formation or in the Derby and Doe Run 

Dolomites. The relatively fine grained nature of the 

dolostones suggests that the rocks are relatively impermeable, even in areas containing little or no 

shale. However, there is evidence from bore-hole 

cores that the upper part of the Derby and Doe Run 

Dolomites is more permeable along a northwesttrending reef zone passing through Wright and Douglas Counties, Missouri (fig. 3). The location of the 

reef zone corresponds to the transition between the 

greater net shale content of the eastern half of the 

study area and the lesser net shale content of the 

western half (fig. 23). Because the shaly Davis Formation is absent in part of the reef, it is possible that 

interchange of water between the St. Francois aquifer and the overlying Ozark aquifer occurs more 

readily in the vicinity of the reef zone.

The authors are unaware of any quantitative measurements of the hydraulic conductivity of the St. 

Francois confining unit. Fletcher (1974) reports that 

the withdrawal of large quantities of water from the 

St. Francois aquifer by lead mining companies in the 

Viburnum Trend near the western flank of the St. 

Francois Mountains did not seem to significantly affect water levels in the overlying Ozark aquifer. He 

concluded that the Davis Formation forms an effective confining unit in the study area. However, he 

also concluded that ground-water levels were affected 

more severely near the major fracture zones that 

penetrate the confining unit. It seems, therefore, that 

the permeability of the St. Francois confining unit is 

increased near fracture zones, at least in the vicinity 

of the St. Francois Mountains. Also, potentiometrichead data from the underlying St. Francois aquifer 

indicate that water levels in the aquifer are affected 

by local topographic relief at distances of at least 15 

miles from its outcrop area, where the aquifer is buried 300 to 800 feet deep. Thus, the permeability of 

the confining unit in that area is large enough to 

allow topographic relief to affect heads in the underlying St. Francois aquifer.

OZARK AQUIFER

The Ozark aquifer is a thick sequence of waterbearing rock, mainly dolostone, limestone, and sandstone formations, ranging in age from Late Cambrian 

to Middle Devonian. The water-yielding capacity of 

the individual formations varies, but collectively they 

act as a regional aquifer. Stratigraphically, the basal 

formation of the aquifer is the Cambrian Potosi Dolomite (table 1). In the northeastern part of the study 

area, the upper boundary of the aquifer coincides 

with the base of the Upper Ordovician Maquoketa 

Shale. Generally, this shale formation disconformably 

overlies the Kimmswick Formation, but locally it 

may overlie the Cape Limestone (Koenig, 1961). 

Many of the younger formations within the aquifer 

are not present in the Salem Plateau, where the aquifer crops out and is deeply eroded. West and south
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D43

of the Salem Plateau, the Maquoketa Shale is absent, and younger, Devonian rocks are included as 

part of the aquifer. In this area the upper boundary 

of the aquifer is represented stratigraphically by the 

base of the Upper Devonian Chattanooga Shale.

STRUCTURAL FEATURES

The outcrop area of the Ozark aquifer is approximately coincident with the Salem Plateau (see figs. 5, 

25). The Cambrian rocks that constitute the basal 

formations of the aquifer crop out around the core of 

the St. Francois Mountains and along river valleys in 

the Salem Plateau, most notably the Osage, Meramec, and Current Rivers (fig. 6). The rocks that 

form the Ozark aquifer have been removed entirely 

from the core of the St. Francois Mountains. Ordovician rocks, primarily the Gasconade Dolomite, the 

Roubidoux Formation, and the Jefferson City Dolomite, make up the largest part of the aquifer's roughly circular outcrop area, which is circumscribed by a 

thin ring of less permeable rocks (part of the Ozark 

confining unit) along much of the perimeter of the 

Salem Plateau (fig. 12). Surface drainage systems on 

the aquifer's carbonate rocks have formed severely 

dissected, rugged topographic features. The aquifer is 

broken by numerous faults and fracture systems (fig. 

9; McCracken, 1971).

In the north-central part of the Salem Plateau (in 

and near Gasconade, Maries, and Osage Counties, 

Missouri, fig. 3) the aquifer is buried beneath as 

much as 200 feet of relatively impermeable Pennsylvanian shale. In the extreme northeastern part of the 

Ozark Plateaus province the aquifer dips beneath 

overlying geohydrologic units to a depth of 1,000 feet 

below land surface at the confluence of the Missouri 

and Mississippi River valleys (fig. 24). Along the 

northwest edge of the Mississippi Alluvial Plain from 

Jackson County, Arkansas, to Scott County, Missouri, 

the aquifer is covered by thick deposits of Cretaceous, Tertiary, and Quaternary sediments. More resistant rocks of the Ozark aquifer crop out as a series 

of isolated hills surrounded by alluvial deposits along 

the northwest edge of the Mississippi Alluvial Plain. 

In Kansas and western Missouri the aquifer dips 

gently into the subsurface to the west. The top of the 

aquifer is less than 500 feet below land surface in 

most of the Springfield Plateau, but is 1,000 feet 

deep near the western boundary of the study area. 

Southward from the Boston Mountains the aquifer is 

buried beneath thick deposits of younger rocks.

Near the western boundary of the study area the 

aquifer dips to the west at about 14 feet per mile (fig.

25; Imes, 1990d). The Ozark aquifer is exposed at 

land surface in a series of island-like outcrops (figs. 

12, 24) extending from Barry County, Missouri, to Sequoyah County, Oklahoma (fig 3). The outcrops coincide with an area in northeast Oklahoma where 

rocks that constitute the St. Francois confining unit 

and St. Francois aquifer are absent in the subsurface 

along a southwest extension of the Ozark uplift (figs. 

14, 20). The altitude of the top of the aquifer exceeds 

1,000 feet above sea level along the northern edge of 

the Boston Mountains, but decreases to lower than 

6,000 feet below sea level beneath the Arkansas Valley (fig. 25).

THICKNESS

The Ozark aquifer is the thickest aquifer in the 

study area. The aquifer rapidly thickens to the northeast, east, and south of the St. Francois Mountains 

and is more than 3,000 feet thick within 19 miles of 

its eroded area (fig. 26; Imes, 1990d). The rate of 

thickening radially from the mountains is much less 

to the northwest, where rocks that constitute the aquifer were uplifted and eroded along a northwest extension of the Ozark uplift. The aquifer thickness 

varies from about 800 to about 1,000 feet in this 

area.

In southwestern Missouri, southeastern Kansas, 

and northeastern Oklahoma, the aquifer thickness 

varies from 800 to 1,500 feet, generally increasing 

from northwest to southeast. The thickness is highly 

variable over short distances in Oklahoma, where 

more of the older rocks of the aquifer are present in 

the valleys between Precambrian hills. At one location in eastern Craig County, Oklahoma (fig. 3), 

where a prominent peak in the Basement confining 

unit rises above the subsurface plateau (fig. 13), the 

Ozark aquifer is only 270 feet thick.

In northern Arkansas, the aquifer becomes thicker 

to the south, with the exception of a small northeastsouthwest-trending area in and adjacent to Madison 

County (fig. 3), where it thins locally. The unit is 

about 1,500 feet thick near the Missouri-Arkansas 

border and increases to about 5,000 feet thick beneath the Arkansas River. It is less than 1,500 feet 

thick in the vicinity of Madison County.

LlTHOLOGYAND GEOHYDROLOGIC PROPERTIES

The Ozark aquifer contains formations that encompass a wide range of lithologies with varying permeability and porosity. The rocks that constitute the
96° 95° 94° 93° 92° 91 c 90° 89° 88°

39°

38°

37°

36°

35°

__________ I I

EXPLANATION

OUTCROP AREA OF AQUIFER

AREAL EXTENT OF AQUIFER IN 

SUBSURFACE

- - - - BOUNDARY OF STUDY AREA

500 - LINE OF EQUAL DEPTH Dashed where 

approximately located. Interval, in feet, 

is variable

0 20 40 60 MILES

I I I

\ I I 

0 20 40 60 KILOMETERS

r1

goP-H

I

I

FIGURE 24. Depth of the Ozark aquifer below land surface. Information outside of study area is from stratigraphically equivalent unit.
96° 95° 94° 93° 92° 90° 89° 

I

88°

39°38°37°36°

35°

EXPLANATION

OUTCROP AREA OF AQUIFERAREAL EXTENT OF AQUIFER IN 

SUBSURFACE

---- BOUNDARY OF STUDY AREA

500- LINE OF EQUAL ALTITUDE Shows altitude 

of top of aquifer. Interval, in feet, is variable. 

Datum is sea level

FAULT u, upthrown side; D, downthrown side _ 20 40 60 MILES 

I I I

\ \ \ 

0 20 40 60 KILOMETERS

t

§ 3

I 

1

1

hH *3

H

FIGURE 25. Areal extent and configuration of top of the Ozark aquifer. Information outside of study area is from stratigraphically equivalent unit. a ^

en
96° 95° 94° 93° 92° 90° 89° 88°

39°38°

37°

36°

35°

EXPLANATION

OUTCROP AREA OF AQUIFERAREAL EXTENT OF AQUIFER IN 

SUBSURFACE

- - - - BOUNDARY OF STUDY AREA

600 - LINE OF EQUAL THICKNESS Interval, 

in feet, is variable

20 40 60 MILES 

I_____I I

I I I 

0 20 40 60 KILOMETERS

H

i

1jg

S? 53£

CO

FIGURE 26. Thickness of the Ozark aquifer. Information outside of study area is from stratigraphically equivalent unit.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D47

aquifer are dolostone, limestone, sandstone, chert, 

and shale. Dolostone is the predominant rock type in 

the Ozark aquifer. Dissolution of the carbonate rocks 

along fractures and bedding planes, including karst 

development, is the main process by which secondary 

permeability has developed in the aquifer. Sandstone 

is present as massive, clean, well-sorted bodies in 

some formations and, therefore, is relatively permeable where it is not cemented.

The rocks that collectively form the Ozark aquifer 

are grouped into five unnamed zones according to 

their regional geohydrologic properties and the relative hydraulic conductivity of adjacent zones. A significant lithologic boundary that separates the lower 

three zones from the upper two zones is stratigraphically coincident with the base of the Ordovician Sylvan and Cason Shales (table 1). The lithology of the 

rocks that form the lower three zones is predominantly dolostone and sandstone, whereas the upper 

two zones are predominantly limestone and shale.

The lowermost of the five zones is represented stratigraphically by rocks in the interval between the base 

of the Potosi Dolomite and top of the Smithville Formation (table 1). This zone contains the most permeable and porous rocks in the Ozark aquifer, is the 

thickest of the zones, and is present everywhere in the 

study area except in the St. Francois Mountains. The 

Potosi and Eminence Dolomites are the basal rocks of 

the Ozark aquifer. The Potosi Dolomite probably is, on 

a regional basis, the most permeable geologic unit 

within the aquifer and the most reliable source of 

water for large-capacity wells in the Ozarks. In the 

northern half of the study area, the coarsely crystalline, massive dolostone formation contains large 

quantities of druse (cavities encrusted with finely 

crystalline quartz) and is vuggy. Because the vugs are 

interconnected and solution channels are well developed in the soluble carbonate rock, the formation is 

very permeable. The overlying Eminence Dolomite is 

similar lithologically, but has less secondary porosity 

and permeability. In the southern and southeastern 

parts of the study area, the Potosi and Eminence Dolomites generally are undifferentiated (Caplan, 1960; 

McCracken, 1964). The characteristic quartz druse 

recognizable in the Potosi Dolomite to the north is 

missing or present only in small concentrations in the 

south. The permeability of these formations is less to 

the south where they are more deeply buried and solution channels are not well developed.

The Gasconade Dolomite and Roubidoux Formation 

are two of the more important water-bearing units in 

the area; they are especially important as sources of 

water in northwestern Arkansas and northeastern 

Oklahoma, where the Potosi Dolomite is thinner and

less permeable (Lamonds, 1972; Melton, 1976). Thus, 

their increased importance as a source of water in the 

southwest is due more to their increased thickness 

and permeability compared to other formations of the 

Ozark aquifer than to an increase in their absolute 

permeability. The Gasconade Dolomite contains a 

well-defined, permeable, basal sandstone member, 

called the Gunter Sandstone Member. The Gunter 

Sandstone Member is composed of loosely cemented 

sandstone along a line that extends from Cooper 

County, Missouri, south into Boone County, Arkansas 

(fig. 3). The sandstone content of the member decreases and the unit becomes more dolomitic east and west 

of this line (Fuller and others, 1967, p. 290). The Roubidoux Formation is a loosely to well-cemented sandstone or a sandy to cherty dolostone containing 

several distinct sandstone bodies. The stratigraphic 

sequence from the Jefferson City Dolomite to the 

Smithville Formation consists predominantly of dolostone with small quantities of shale, chert, and sandstone; it is less permeable regionally than the 

stratigraphically lower rocks of the Ozark aquifer.

The second zone, in ascending order, is composed of 

rocks stratigraphically bounded by the base of the 

Everton Formation and the top of the Decorah Formation (table 1). This sequence of rock units is missing from the Salem Plateau region of the Ozarks (fig. 

5). The St. Peter Sandstone probably is the most permeable and most significant water-yielding unit of 

this zone. It generally is a clean, round-grained, 

quartzose sandstone with little indication of bedding 

in the eastern part of the study area, but it becomes 

shaly, and presumably less permeable, in the western 

part of the study area. The underlying Everton Formation is a sandy dolostone interbedded with sandstone, limestone, and chert. Where the Everton 

Formation is sandstone, it is difficult to distinguish 

from the St. Peter Sandstone. In northwestern Arkansas, the St. Peter Sandstone and the Everton 

Formation are well cemented and have only slight 

permeability. There is evidence that the St. Peter 

Sandstone changes facies in the extreme southeast 

and becomes a sandy limestone. Dolomite and limestone beds are present in the St. Peter Sandstone in 

the south. The Burgen Sandstone of northeastern 

Oklahoma is lithologically similar to, and correlative 

with, the St. Peter Sandstone (Huffman, 1958) and, 

like the St. Peter Sandstone, is permeable. Of remaining formations in this zone, the Joachim Dolomite and Plattin Limestone are moderately 

permeable dolostone and limestone with small quantities of shale and sandstone. The Decorah Formation, limited to extreme eastern Missouri, primarily 

is shale and is not permeable.
D48 REGIONAL AQUIFER-SYSTEM ANALYSIS-CENTRAL MIDWEST

The third zone is represented by rocks in the stratigraphic sequence from the base of the Kimmswick 

Limestone to the top of the Cape Limestone (table 1; 

Koenig, 1961). These rocks are limited to the extreme 

northeastern and western parts of the study area. 

The rocks of this zone are predominantly limestone. 

Significant secondary porosity and permeability have 

not developed.

The fourth and fifth zones include the sequence of 

formations in the stratigraphic interval bounded by 

the base of the Sylvan and Cason Shales and the base 

of the Chattanooga Shale (table 1), which is the stratigraphic top of the Ozark aquifer. The formations in 

these zones are not present in the northeastern part 

of the study area. The fourth zone contains the nearly 

impermeable Sylvan Shale of Oklahoma and the 

Cason Shale of Arkansas. These formations are distinct shale units that contain only small quantities of 

dolomitic sandstone. The fifth zone includes Silurian 

and Devonian limestone and chert formations that are 

limited to the northwestern and southern parts of the 

study area. Rocks of the fifth zone are more permeable 

than rocks of the fourth zone but are relatively impermeable in comparison with the three lower zones. The 

generally small permeability of the fifth zone reflects 

a lack of secondary permeability, such as solutionchannel development. The Penters Chert is the thickest and probably most permeable of these rocks in 

Arkansas. The dense chert formation is fractured and 

brecciated throughout northern Arkansas (Wise and 

Caplan, 1979).

The Ozark aquifer is used in most of the study area 

as a source of water for both public and domestic consumption. Consequently, many wells have been constructed in the aquifer, and there is a considerable 

quantity of specific-capacity data available for the aquifer. The hydraulic conductivity of the Ozark aquifer 

was estimated from these specific-capacity data. Most 

of the wells that penetrate the aquifer are open to 

several zones. The hydraulic-conductivity estimates 

are treated as if they were valid for the entire thickness of the aquifer. No attempt has been made to determine the hydraulic conductivity of the individual 

zones. However, it is possible to make some general 

statements concerning the hydraulic properties of the 

zones estimated on the basis of specific-capacity data. 

Generally, specific-capacity data in the Salem Plateau 

reflect the hydraulic properties of the thick lowermost 

zone. In the southwest and south (Boston Mountains), 

the data are most representative of the Gasconade 

Dolomite and Roubidoux Formation of the lowermost 

zone. Data in the extreme northeastern part of the 

study area are mainly derived from wells that penetrate the second and third zones.

The estimated hydraulic conductivity of the Ozark 

aquifer varies from more than l.OxlO"3 foot per second to less than l.OxlO"8 foot per second (fig. 27). 

The hydraulic conductivity north of the northernmost 

regional ground-water divide (line of dots on fig. 27) 

varies from about l.OxlO"5 foot per second to about 

l.OxlO"3 foot per second. The areas of greatest hydraulic conductivity are concentrated along an eastwest line from Vernon County, Missouri, to the northern edge of the St. Francois Mountains, and along 

the Missouri River from Moniteau County to St. 

Louis County, Missouri (fig. 3). The Missouri River 

alluvium is in contact with the Ozark aquifer along 

this reach. The hydraulic conductivity generally decreases south of the ground-water divide. Near the 

southern boundary of the study area, the hydraulic 

conductivity decreases to less than l.OxlO"8 foot per 

second.

RECHARGE, GROUND-WATER FLOW, AND DISCHARGE

Mapping the potentiometric surface of an aquifer 

requires the assumption that the hydraulic head does 

not vary with depth. This assumption is not valid in 

an aquifer as thick and lithologically complex as the 

Ozark aquifer. Vertical head differences in the aquifer tend to be masked by the fact that most head 

data are measured in wells that are open to at least 

several hundred feet of the aquifer. Thus, the measured heads are a weighted average of the heads in 

the various lithologic units that are open to the well. 

The variation of head with depth in the Ozark aquifer generally is not large in comparison to the variation of head laterally in the aquifer, so the 

potentiometric surface map constructed for the Ozark 

aquifer (fig. 28) probably is a good representation of 

the lateral head distribution in the aquifer.

Ground water in the Ozark aquifer is unconfined in 

the Salem Plateau (fig. 12), and the potentiometric 

surface of the aquifer is strongly influenced by the 

major topographic features of the plateau. The altitude of the potentiometric surface along the northernmost regional ground-water divide (fig. 10) generally 

ranges from 1,200 to 1,400 feet (fig. 28; Imes, 1990d). 

Many divides of lesser regional importance parallel 

the highland areas between the major river valleys of 

the Salem Plateau (fig. 6). The altitude of the potentiometric surface in these upland areas varies considerably but generally ranges between 1,000 and 600 feet. 

Ground-water movement in the Salem Plateau is from 

the upland areas between major rivers and streams 

toward the valleys where the water discharges as 

stream base flow. Regional ground-water movement
96° 95° 94° 93° 92° 91 c 90° 89° 

I

88°

39°38°

37°

36°

35°

/ '___\MO(

EXPLANATION

OUTCROP AREA OF AQUIFERAREAL EXTENT OF AQUIFER IN 

SUBSURFACE

- - - - BOUNDARY OF STUDY AREA

- REGIONAL GROUND-WATER DIVIDE

- 100- LINE OF EQUAL HYDRAULIC

CONDUCTIVITY Interval, in units of 

10-6 foot per second, is variable

20 40 60 MILES

I I I

n i i

0 20 40 60 KILOMETERS

FIGURE 27. Distribution of hydraulic conductivity of the Ozark aquifer. Information outside of study area is from stratigraphically equivalent unit.

CD
D50 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

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1

 S

2 

fa
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D51

through the aquifer in this area generally is controlled 

by the larger rivers and regional topographic features, 

whereas local ground-water movement in the uppermost part of the aquifer also is controlled by the 

smaller streams and local topographic features. Along 

the northern and eastern boundaries of the Salem 

Plateau, the aquifer is incised by the Missouri and 

Mississippi Rivers. The rivers are major discharge 

areas for ground water moving north and east from 

the Salem Plateau.

At the northwestern boundary of the study area, 

ground water in the Ozark aquifer moves northward 

beneath the overlying Ozark confining unit and 

Springfield Plateau aquifer (fig. 12), then discharges 

upward into the Missouri River valley at the northern edge of Saline, Cooper, and Moniteau Counties 

(fig. 3). The discharge area also is a mixing zone of 

freshwater and salinewater. Saline ground water 

moving eastward toward the study area emerges 

from beneath the Western Interior Plains confining 

system, and discharges into the same reach of the 

Missouri River valley. Along the western edge of the 

Ozark study area, westward-flowing freshwater in 

the Ozark aquifer mixes with eastward-flowing 

saline-water of the Western Interior Plains aquifer 

system. The mixed water converges toward the South 

Grand, Marais des Cygnes, and Osage River valleys 

(fig. 10) and discharges through overlying confining 

units into the river systems. The discharge area coincides with the area in which the overlying Ozark confining unit is devoid of shale and consists only of 

limestone (see section "Ozark Confining Unit").

In southwestern Missouri, the aquifer is recharged 

by leakage through the overlying confining unit, and 

water in the aquifer flows to the west and northwest 

into southeastern Kansas. The boundary of the aquifer is not well defined in this area because of the 

broad freshwater-salinewater mixing zone and the 

lack of a well-defined discharge area. Although 

water-level data are sparse, evidence indicates that 

the more northerly flowing ground water in this area 

turns northeastward and discharges into the Marais 

des Cygnes and Osage Rivers, whereas the more 

westerly flowing ground water turns southward and 

discharges through overlying deposits into the 

Neosho River valley in northeastern Oklahoma (fig. 

10).

The direction of ground-water flow in northern Arkansas is difficult to accurately determine because 

data are sparse south of the northernmost tier of 

counties (Lamonds, 1972). The probable direction of 

ground-water flow in this area can be inferred from 

regional topography and geology, the altitude of 

major rivers, and available water-quality and

hydraulic-conductivity data. A regional ground-water 

divide (fig. 10) parallels the crest of the Boston 

Mountains in northern Arkansas and separates the 

region into two distinct ground-water provinces. The 

divide approximately parallels the northern limit of 

the Western Interior Plains confining system (fig. 

12). North of the divide, the Ozark aquifer is recharged by leakage through the overlying units and 

by infiltration of precipitation on the outcrop area of 

the aquifer. The mainly fresh ground water flows to 

the White and Buffalo Rivers and their tributaries 

(fig. 10). South of the divide, water in the aquifer 

flows toward the Arkansas River valley. Because of 

the large thickness of shale in the Western Interior 

Plains confining system near the Arkansas River, it 

is unlikely that any significant quantity of water in 

the Ozark aquifer discharges through the confining 

system into the Arkansas River. Instead, the water 

probably moves eastward to the Mississippi Embayment. The presence of saline springs along the edge 

of the Mississippi Alluvial Plain near the southeastern border of the study area lends support for this 

concept of ground-water flow.

Water in the Ozark aquifer that flows southeast beneath the Mississippi Alluvial Plain encounters saline ground water in adjacent aquifers of the 

Mississippi Embayment (fig. 8). Because the Ozark 

aquifer dips so steeply into the subsurface beneath 

the post-Paleozoic overburden (fig. 25), and because 

hydrologic data on the Ozark aquifer is sparse in this 

area, it is difficult to determine the distance that 

freshwater travels beneath the alluvium. However, 

much, if not most, of the freshwater discharges directly into the overlying alluvial sediments, or percolates upward through Cretaceous sand deposits to 

discharge into the alluvial sediments, within a few 

miles of the Ozark Escarpment. Then it discharges 

into the Black and White Rivers (fig. 10) that flow on 

the alluvial sediments. This abrupt discharge of 

ground water occurs within a 5- to 10-mile-wide band 

along the southeast edge of the Ozark Escarpment 

where permeable post-Paleozoic deposits are in direct 

hydraulic contact with the Ozark aquifer. Beyond 

this band, a confining unit of slightly permeable Cretaceous clay separates the Ozark aquifer from the 

permeable alluvial material.

CHEMICAL QUALITY OF GROUND WATER

The chemical composition of ground water in the 

Ozark aquifer is a product of dissolution of the dolostone and limestone that form the bulk of the aquifer. The most common water type in the Ozark
D52 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

aquifer is calcium bicarbonate or bicarbonate with 

calcium as the most prevalent cation (fig. 29; table 2; 

Imes and Davis, 1991). A large area in the northcentral part of the Salem Plateau contains mainly 

magnesium bicarbonate water. Water that is of a 

mixed cation bicarbonate type, with either magnesium or calcium dominating, forms a transition zone 

between many of the areas that contain calcium bicarbonate or magnesium bicarbonate water. There 

are small areas near the western and southwestern 

boundaries of the study area in which the water type 

is sodium bicarbonate or bicarbonate with sodium as 

the dominant cation. These areas indicate the transition between the predominantly bicarbonate water of 

the Ozark Plateaus aquifer system and the predominantly sodium chloride water that encircles the plateau to the west, south, and east.

The dissolved-solids content of ground water in the 

Ozark aquifer reflects the movement of water from 

the regional ground-water divides toward the surrounding basins. The dissolved-solids content is least 

along the two major ground-water divides shown in 

figure 10, generally ranging from less than 200 to 

about 300 milligrams per liter (fig. 30; Imes and 

Davis, 1991). Away from the two divides the 

dissolved-solids content increases to greater than 400 

milligrams per liter. In the north-central part of the 

Salem Plateau, a small area containing dissolvedsolids concentrations greater than 500 milligrams per 

liter is associated with the recharge of ground water 

through overlying deposits of Pennsylvanian clay, 

shale, and sandstone. At the edges of the study area, 

the dissolved-solids content of ground water in the 

Ozark aquifer reaches much higher values.

At the extreme northeastern edge of the Ozark 

study area, the dissolved-solids content of the water 

increases to the northeast and exceeds 5,000 milligrams per liter where freshwater from the Ozark aquifer mixes with salinewater from other regional 

aquifers that border the eastern Ozarks outside the 

study area. Dissolved-solids concentrations increase 

to as much as 10,000 milligrams per liter in the mixing zone along the western boundary of the aquifer. 

Figure 30 clearly indicates where salinewater discharges at the northwestern edge of the study area 

in Saline and Cooper Counties, and, to a lesser degree, where salinewater mixes with freshwater and 

discharges in Bates and Henry Counties, Missouri 

(fig. 3).

Southeast of the St. Francois Mountains, the dissolved-solids content increases as freshwater in the 

Ozark aquifer moves beneath the Mississippi Alluvial 

Plain and mixes with saline ground water. Few 

water-quality data are available for the area south of

the Boston Mountains; however, dissolved-solids concentrations of water in this area are believed to be 

quite large (exceeding 1,000 mg/L) because water entering the deeply buried Ozark aquifer must pass 

through thick Pennsylvanian shales, resulting in 

water having large concentrations of minerals and 

salts.

The chloride concentration in the Ozark aquifer 

generally is less than 10 milligrams per liter in the 

Salem Plateau, where the Ozark aquifer crops out, 

and in the Springfield Plateau, where the aquifer is 

overlain by the Ozark confining unit and Springfield 

Plateau aquifer (figs. 5, 12, 31; Imes and Davis, 

1991). Two areas, one in the Salem Plateau in northeastern Arkansas and the other in the Springfield 

Plateau in northeastern Oklahoma, have chloride 

concentrations that locally range from 10 to more 

than 100 milligrams per liter. The chloride concentration does not seem to increase appreciably in the 

north-central part of the Salem Plateau where Pennsylvanian shale and sandstone cover the Ozark aquifer between the Gasconade and Meramec River 

valleys (fig. 6). Chloride concentrations increase significantly away from the Ozark Plateaus province. In 

the extreme northeastern and southeastern part and 

along the western boundary of the study area, where 

the Ozark aquifer is in contact with regional salinewater, the chloride concentrations exceed 1,000 milligrams per liter. Analysis of water from one well that 

penetrates the Ozark aquifer beneath the Mississippi 

Alluvial Plain in Jackson County, Arkansas (fig. 3), 

indicated a chloride concentration of 17,000 milligrams per liter.

Sulfate concentrations in the Ozark aquifer generally are less than 10 milligrams per liter in the 

Salem Plateau (fig. 32; Imes and Davis, 1991). An exception occurs in the north-central part of the plateau where the aquifer is capped by Pennsylvanian 

shale and sandstone. In this area sulfate concentrations may exceed 140 milligrams per liter locally. The 

origin of the sulfates probably is pyrite that has concentrated in sinkholes on the paleokarst surface of 

the aquifer beneath the Pennsylvanian rocks. Sulfate 

concentrations exceed 100 milligrams per liter in a 

small area and 300 milligrams per liter in one well 

in Jefferson County, Missouri (fig. 3). The source of 

the sulfate ions in this area is not known but may be 

related to the mining of surficial lead and zinc sulfide 

deposits. Filled sinkholes also are present in the surface of the Ozark aquifer in this area, but any Pennsylvanian overburden that may' have once covered 

the area has been removed by erosion. Sulfate concentrations generally are less than 20 milligrams per 

liter in the Springfield Plateau where the Ozark
96° 95° 94° 93° 92° 91 C 90° 89° 88°

39°38°

37°

36°

35°

\ \

EXPLANATION

OUTCROP AREA OF AQUIFER

AREAL EXTENT OF AQUIFER IN 

SUBSURFACE

- BOUNDARY OF STUDY AREA

REGIONAL GROUND-WATER DIVIDE

BOUNDARY BETWEEN AREAS OF 

DIFFERENT MAJOR CHEMICAL 

CONSTITUENTS Dashed where inferred

MAJOR CHEMICAL CONSTITUENTS 

See table 2 for explanation of symbols

20 40 60 MILES

I I I

\ \ \ 

0 20 40 60 KILOMETERS

§

I

FIGURE 29. Water type in the Ozark aquifer. 0

C71CO
96° 95° 94° 93° 92° 90°

39 C38° - 36°

35'

V

§1^£ _[/ OKlJA ^ n

rH-

_T

I I 

EXPLANATION

OUTCROP AREA OF AQUIFERAREAL EXTENT OF AQUIFER IN 

SUBSURFACE

- - - - BOUNDARY OF STUDY AREA

REGIONAL GROUND- WATER DIVIDE

 200 LINE OF EQUAL DISSOLVED-SOLIDS 

CONCENTRATION Interval, in 

milligrams per liter, is variable

0 20 40 60 MILES

I II II I I I

0 20 40 60 KILOMETERS

o

en

I

FIGURE 30. Dissolved-solids concentrations in ground water from the Ozark aquifer. Information outside of study area is from stratigraphically equivalent unit.
96° 95° 94° 93° 92° 91' 90° 89° 88°

39 C38 C37C36C

35 C

EXPLANATION

OUTCROP AREA OF AQUIFERAREAL EXTENT OF AQUIFER IN 

SUBSURFACE

- - - - BOUNDARY OF STUDY AREA

REGIONAL GROUND-WATER DIVIDE

100 LINE OF EQUAL CHLORIDE

CONCENTRATION Interval, in 

milligrams per liter, is variable

0 20 40 60 MILES

I I I

~~l I I

0 20 40 60 KILOMETERS

FIGURE 31. Chloride concentrations in ground water from the Ozark aquifer. Information outside of study area is from stratigraphically equivalent unit.

1i

s

s

O

or or
96° 95° 94° 93° 92° 91 c 90° 89° 88°

39°

38°

37°

36°

35°

EXPLANATION

OUTCROP AREA OF AQUIFERAREAL EXTENT OF AQUIFER IN 

SUBSURFACE

- - - - BOUNDARY OF STUDY AREA

REGIONAL GROUND-WATER DIVIDE

100 LINE OF EQUAL SULFATE

CONCENTRATION Interval, in milligrams per liter, is variable

,<_r

rr1 - VT--M K<-^ J" x _>, rV1 ' ' ,H i«v /r - i u ^-^ i 0 20 40 60 MILES I I I I I I 0 20 40 60 KILOMETERS h- £ r >

o

en

1

1

- 

o

a

FIGURE 32. Sulfate concentrations in ground water from the Ozark aquifer. Information outside of study area is from stratigraphically equivalent unit.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D57

aquifer is confined. Along the northwest edge of the 

Ozark Plateaus province and beyond its boundaries 

(fig. 5), the concentrations of sulfate exceed 20 milligrams per liter.

Naturally occurring radioactivity in ground water 

in excess of U.S. Environmental Protection Agency 

(USEPA) drinking-water regulations (U.S. Environmental Protection Agency, 1979) has been detected in 

the Ozark aquifer where freshwater comes into contact with more mineralized water of the transition 

zone in the tristate region of Kansas, Missouri, and 

Oklahoma. Radium-226 activity ranged from 0.5 to 

11 picoCuries per liter in 58 public water-supply or 

industrial wells open to the Ozark aquifer (Macfarlane, 1981). Ten of the samples exceeded the USEPA 

maximum contaminant level of 5 picoCuries per liter. 

The Missouri Department of Natural Resources 

(written commun., 1983) listed 31 public water supplies exceeding maximum contaminant levels in 

1983. Eighteen of the 31 sites are in or immediately 

adjacent to the study area. The combined radium-226 

and radium-228 activity ranged from 5.1 to 13.9 picoCuries per liter.

OZARK CONFINING UNIT

The Ozark confining unit restricts flow between the 

Ozark aquifer and the overlying Springfield Plateau 

aquifer. The confining unit, composed predominantly 

of slightly permeable shale and limestone, is the uppermost confining unit in the Ozark Plateaus aquifer 

system. The confining unit is missing from the Salem 

Plateau (figs. 5, 12), an area that includes approximately the eastern two-thirds of the study area. In 

the western and southern one-third of the study 

area, the unit extends continuously from its outcrop 

area to the boundary of the Ozark Plateaus aquifer 

system, except for local areas in northern Arkansas 

where rocks that form the unit are missing.

The geologic formations in the confining unit are 

not all present everywhere in the study area. Along 

the extreme northeastern flank of the Ozarks, the 

confining unit is composed of a sequence of formations that include the stratigraphic interval from the 

base of the Upper Ordovician Maquoketa Shale to 

the top of the Lower Mississippian Chouteau Limestone (table 1). Probably some of the formations in 

this thick, predominantly limestone sequence are important water-bearing units for the area east of the 

Ozark Plateaus. Because of the relatively small areal 

extent of these formations, they have not been subdivided into aquifers and confining units in this study. 

In the western and southern part of the study area,

the confining unit is much thinner and composed 

mainly of Upper Devonian shales and Lower Mississippian shales and limestones.

STRUCTURAL FEATURES

The Ozark confining unit crops out in a thin strip 

that surrounds the outcrop area of the underlying 

Ozark aquifer (fig. 12). It dips gently to the west in 

western Missouri and eastern Kansas at about 14 

feet per mile. The top of the confining unit is at 

about sea level at the boundary of the Ozark Plateaus aquifer system in southeastern Kansas (fig. 33; 

Imes, 1990e). In northeastern Oklahoma, atop a 

southwestern extension of the Ozark uplift, the altitude of the top of the unit varies from about 700 to 

1,000 feet. The altitude of the unit decreases abruptly along the western and southern flanks of the extension. In northern Arkansas the altitude of the top 

of the confining unit decreases from about 1,000 feet 

in Carroll County (fig. 3) to lower than 5,000 feet 

below sea level beneath the Arkansas Valley (fig. 5). 

The dip increases from about 30 feet per mile in the 

northern part to about 250 feet per mile in the southern part of northern Arkansas.

THICKNESS

Well logs indicate that the thickness of the Ozark 

confining unit generally ranges from near 0 to more 

than 1,000 feet in the Ozark Plateaus province. The 

unit is thickest in one small area at the extreme 

eastern edge of Perry County, Missouri (figs. 3, 34; 

Imes, 1990e). In northeastern St. Louis County, Missouri, the unit is more than 200 feet thick. However, 

the confining unit generally is less than 100 feet 

thick and is, therefore, relatively thin in comparison 

to the other geohydrologic units. The confining unit is 

less than 10 feet thick along a narrow belt from 

Christian County, Missouri, to Montgomery County, 

Kansas. This belt is nearly coincident with the Bourbon arch, which extends from southwestern Missouri 

into southeastern Kansas and separates the Forest 

City and Cherokee basins (fig. 8).

North and south of this belt, the confining unit 

thickens to about 80 feet. In northern Arkansas, the 

thickness of the confining unit generally increases 

southward from the Salem Plateau to about 50 feet 

in the Arkansas Valley. Rocks that form the confining 

unit are missing in the subsurface from small areas 

in Kansas and Oklahoma (not shown in fig. 34) and 

from larger areas in northern Arkansas. The unit
96° 95° 94° 93° 92° 91 C 90°

39°

38°

37°

36°

35°

/V. ;' _. _J i \ ^ v>x 1 i \ ' ' ' '' , ] ^

:-./ / ' ____ __I ' :/ < ^ - \ _/

89°__________88^________ I 

EXPLANATION

OUTCROP AREA OF CONFINING UNIT

AREAL EXTENT OF CONFINING UNIT 

IN SUBSURFACE

AREA WHERE CONFINING UNIT IS 

MISSING IN SUBSURFACE

- - - - BOUNDARY OF STUDY AREA

 500 LINE OF EQUAL ALTITUDE Shows

altitude of top of confining unit. Interval, in feet, is variable. Datum is sea level.

FAULT u, upthrown side; D, downihrown 

side

cn oo

20 40 60 MILES 

I I I

\ \ 

0 20 40 60 KILOMETERS

2i i% 

I

01

FIGURE 33. Areal extent and configuration of top of the Ozark confining unit. Information outside of study area is from stratigraphically equivalent unit.
96° 95° 94° 93° 92° 91 c 90° 89° 88°

39°38°

37°36°

35°

I I 

EXPLANATION

OUTCROP AREA OF CONFINING UNIT

AREAL EXTENT OF CONFINING UNIT 

IN SUBSURFACE

AREA WHERE CONFINING UNIT IS 

MISSING IN SUBSURFACE

- - - - BOUNDARY OF STUDY AREA

20 LINE OF EQUAL THICKNESS 

Interval, in feet, is variable

0 20 40 60 MILES 

II I

\ T 

0 20 40 60 KILOMETERS

l_,

I I I \ r L_ ^

f- ^ l| /

FIGURE 34. Thickness of the Ozark confining unit. Information outside of study area is from stratigraphically equivalent unit.

O W

§

I

OJ

O 

en CO
D60 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

also is absent in the subsurface from a large area in 

the northern part of the Ozark Plateaus province 

(Gasconade County, Missouri (fig. 3), and vicinity) 

where Pennsylvanian rocks are in direct contact with 

the underlying Ozark aquifer. In addition, it is missing from a large area southeast of the Ozark Plateaus province where the Ozark Plateaus aquifer 

system is blanketed by unconsolidated sediments of 

the Mississippi Alluvial Plain.

LlTHOLOGYAND GEOHYDROLOGIC PROPERTIES

The leakance of the Ozark confining unit varies because of local lithologic and structural differences. 

The effectiveness of the hydraulic connection between 

the overlying Springfield Plateau aquifer and the underlying Ozark aquifer, therefore, can vary considerably from one location to another.

Along the northeast boundary of the study area, 

the Ozark confining unit is lithologically more complex than elsewhere, primarily because it is composed of more formations. Limestone predominates 

the rock strata, but shale is well represented, and 

sandstone also is present in small quantities. The 

thickness of the major shale formations the Maquoketa Shale, Orchard Creek Shale, Chattanooga 

Shale, and Hannibal Shale (table 1) may total as 

much as 100 feet. Many of the limestone rocks contain a significant fraction of argillaceous material in 

the form of shale partings that are distributed in the 

carbonate matrix. The small quantities of sandstone 

are confined mostly to scattered occurrences in the 

Grand Tower Limestone and St. Laurent Limestone 

and to the thin Bushberg Sandstone. In the northwest part of the study area, the lithology of this confining unit changes locally depending on the presence 

or absence of one or more of three Lower Mississippian formations: the Compton Limestone, the Sedalia 

Limestone, and the Northview Shale. In northeastern 

Oklahoma and northern Arkansas, the confining unit 

is represented by the Chattanooga Shale, a predominantly shale unit containing small and areally limited quantities of sandstone. The Chattanooga Shale 

extends throughout the southwestern and southern 

parts of the study area and is the most important 

formation in the confining unit.

The shale content and equivalent shale thickness 

of the Ozark confining unit provide one indication of 

its effectiveness as a confining unit. Shale in the 

Ozark confining unit exists as distinct beds, shale 

partings, and as distributed shale in a limestone and 

dolostone matrix. Shale beds and partings can form 

effective barriers to the vertical leakage of ground

water across the unit. They also can allow the free 

passage of water if they contain a significant density 

of fissures or fractures. Distributed shale can block 

the passage of ground water through the pore spaces 

in a carbonate rock matrix and reduce the vertical 

hydraulic conductivity of the rock.

The shale content of the Ozark confining unit as a 

percentage of the total thickness of the unit ranges 

from 0 to 100 percent (fig. 35; Imes, 1990e). Generally, shale constitutes a smaller percentage of rock type 

in the north and becomes more predominant in the 

south. The Chattanooga Shale is absent in the north, 

and the Northview Shale is the primary source of 

shale there. Several isolated areas along the north 

and northwest edge of the study area are devoid of 

shale because of the discontinuous area! distribution 

of the Northview Shale. In southwestern Missouri 

and southeastern Kansas the percentage of shale in 

the confining unit varies abruptly within short distances from less than 20 to 100 percent. In the 

southwestern and southern part of the study area, 

the confining unit is represented almost exclusively 

by the Chattanooga Shale. In much of this area, 

shale constitutes 100 percent of the confining unit.

The shale content map cannot be used alone to 

evaluate probable spatial variations in the vertical 

hydraulic conductivity of the confining unit because 

the net shale content of a thin unit having a large 

percentage of shale can be considerably less than the 

net shale content of a thick unit having a small percentage of shale. The net thickness of shale in the 

confining unit can be calculated using the shale content and thickness maps of the unit. The net shale 

thickness map (fig. 36) shows the total thickness of 

shale as if it were consolidated into one distinct bed 

instead of being distributed throughout the unit.

In the extreme northeastern part of the study area, 

the net shale thickness increases to the northeast to 

more than 120 feet. The net shale thickness in this 

area reflects both an increasing thickness and an increasing shale content. There is no shale in the confining unit in several areas along the northwest edge 

of the study area. The lack of shale in these isolated 

locations does not necessarily indicate the Ozark confining unit is permeable. The limestones that constitute the confining unit are thick in this area 

(approximately 50 to 100 ft) and have not developed 

a significant secondary permeability. Thus, the limestones can form an effective barrier to the vertical 

leakage of ground water if their primary permeability is sufficiently small and their thickness sufficiently large. However, there are data that indicate the 

vertical hydraulic conductivity of the confining unit 

in this area is greater than the conductivity of the
96° 95° 94° 93° 92° 90° 89° 88°

39°

38°

37°36°

35°

EXPLANATION

OUTCROP AREA OF CONFINING UNITAREA WHERE CONFINING UNIT IS 

MISSING IN SUBSURFACE

AREA OF ZERO SI IALE CONTENT

---- BOUNDARY OF STUDY AREA

60 LINE OF EQUAL SHALE CONTENT 

Interval, in percent, is variable

0 20 40 60 MILES 

I I I

\ \ I 

0 20 40 60 KILOMETERS

I

dCO

£

CO.

FIGURE 35. Shale content of the Ozark confining unit. Information outside of study area is from stratigraphically equivalent unit.
96° 95° 94° 93° 92° 91 C 90° 89° 88°

EXPLANATION

OUTCROP AREA OF CONFINING UNIT

AREAL EXTENT OF CONFINING UNIT 

IN SUBSURFACE

AREA WHERE CONFINING UNIT IS 

MISSING IN SUBSURFACE

AREA OF ZERO SHALE CONTENT

- - - - BOUNDARY OF STUDY AREA

60 LINE OF EQUAL NET THICKNESS OF 

SHALE Interval, in feet, is variable

36° - 35° - 0 20 40 60 MILES 

I_____I I

\ I I 

0 20 40 60 KILOMETERS

O 

O5 to

FIGURE 36. Net shale thickness in the Ozark confining unit. Information outside of study area is from stratigraphically equivalent unit.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D63

unit farther south. The difference in head between 

the underlying Ozark aquifer and the overlying 

Springfield Plateau aquifer ranges from 10 to 50 feet 

in the areas where shale is missing. In southwestern 

Missouri and southeastern Kansas, where the net 

shale thickness of the thinner confining unit ranges 

from less than 10 to more than 40 feet, the head difference usually is more than 50 feet. In northeastern 

Oklahoma and northern Arkansas the net shale 

thickness of the unit generally increases to the south 

and varies from less than 10 feet to more than 80 

feet. The areas of greater net shale are located along 

the southwest extension of the Ozark uplift into 

northeastern Oklahoma.

SPRINGFIELD PLATEAU AQUIFER

The Springfield Plateau aquifer is a sequence of 

water-bearing Mississippian limestone and chert that 

forms the uppermost geohydrologic unit in the Ozark 

Plateaus aquifer system. Geologic formations that 

are stratigraphically equivalent, but hydrologically 

unrelated, to those that constitute the Springfield 

Plateau aquifer are present in the extreme northeastern part of the study area. These formations are 

not considered to be part of the Springfield Plateau 

aquifer. In the western part of the study area, the 

aquifer is composed of the limestone formations between the base of the Pierson Formation and the top 

of the St. Louis Limestone (table 1). In northeastern 

Oklahoma the Springfield Plateau aquifer is represented by three geologic formations: the Boone Formation, the Keokuk Limestone, and the Moorefield 

Formation. Because the permeability of the Moorefield Formation is smaller in northern Arkansas, 

where the shale content of the formation is larger, 

this formation is not included as part of the Springfield Plateau aquifer in Arkansas, and the aquifer is 

represented there only by the Boone Formation.

STRUCTURAL FEATURES

The Springfield Plateau aquifer crops out on the 

Springfield Plateau, which constitutes about onethird of the Ozark Plateaus province (figs. 5, 12). In 

the northwestern part of the study area, the aquifer 

dips to the northwest at about 11 feet per mile. West 

of the Springfield Plateau, the aquifer is buried beneath nearly impermeable rocks of the Western Interior Plains confining system to a maximum depth of 

about 250 feet in the more northerly areas and about 

500 feet in southeastern Kansas (fig. 37). The western boundary of the aquifer in northeastern Oklahoma is approximately coincident with the western 

edge of the outcrop area of the aquifer. However, 

near the southern reach of that boundary the aquifer 

dips abruptly into the subsurface and is overlain by 

as much as 4,000 feet of the Western Interior Plains 

confining system. The aquifer is missing in the subsurface beneath the Arkansas River along the southern boundary of the aquifer in Oklahoma. In 

northern Arkansas, where the southward dip of the 

aquifer can exceed 200 feet per mile, the depth of 

burial by the confining system exceeds 5,000 feet.

The altitude of the top of the aquifer in the northwestern part of the study area ranges from about 800 

feet above sea level near the western boundary of the 

Salem Plateau to about 500 feet or less at the western edge of the aquifer (fig. 38; Imes, 1990f). The altitude of the aquifer top in the outcrop area generally 

is greater than 1,000 feet and locally can exceed 

1,500 feet. Near its southern boundary, the top of the 

aquifer can be lower than 5,000 feet below sea level. 

The Springfield Plateau aquifer has been eroded from 

the part of the study area that extends southeast 

into the Mississippi Alluvial Plain.

THICKNESS

Northwest of the Salem Plateau the thickness of 

the Springfield Plateau aquifer is less than 200 feet 

(fig. 39; Imes, 1990f). The thickness of the aquifer 

generally increases to the northwest from near zero 

along the boundary of the Salem Plateau. Rocks that 

constitute the aquifer are missing in the subsurface 

from two relatively small areas in and near Henry 

County, Missouri (fig. 3). The aquifer generally is 

thicker in southwestern Missouri, southeastern Kansas, and northeastern Oklahoma, ranging from 200 

to 400 feet thick throughout most of the area. In 

northeastern Oklahoma, the aquifer is thinner near 

the small areas where the aquifer is missing and 

older rocks are exposed. The thickness of the aquifer 

can exceed 300 feet in areas between outcrops of the 

older rocks. The thickness of the aquifer in northern 

Arkansas generally is less than 400 feet. Unlike the 

thickness of geohydrologic units above and below the 

Springfield Plateau aquifer, the thickness of the aquifer does not greatly increase in the southern part of 

the study area.

LlTHOLOGYAND GEOHYDROLOGIC PROPERTIES

The Springfield Plateau aquifer primarily consists 

of coarsely crystalline limestones of Mississippian 

age that commonly contain a large percentage of
D64 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

 a

-

g 

1 

I

2 "3

o
96

39° - AREAL EXTENT OF AQUIFER IN 

SUBSURFACE

AREA WHERE AQUIFER (OR

EQUIVALENT UNIT) IS MISSING IN SUBSURFACE

---- BOUNDARY OF STUDY AREA

 250- LINE OF EQUAL ALTITUDE Shows 

altitude of top of aquifer. Interval, in feet, is variable. Datum is sea level

FAULT u, upthrown side; D, downthrown

I I I 

0 20 40 60 KILOMETERS

O 

&§

3

Hcc

ES

FIGURE 38. Areal extent and configuration of top of the Springfield Plateau aquifer. Information outside of study area is from stratigraphically equivalent unit.

en
96° 95° 94° 93° 92° 91 C 90° 89° 88°

37'

EXPLANATION

OUTCROP AREA OF AQUIFER

AREAL EXTENT OF AQUIFER IN 

SUBSURFACE

AREA WHERE AQUIFER (OR EQUIVALENT 

UNIT) IS MISSING IN SUBSURFACE

BOUNDARY OF STUDY AREA

LINE OF EQUAL THICKNESS Interval, in 

feet, is variable

36° - 35° - 0 20 40 60 MILES

I I.I II \~\ I

0 20 40 60 KILOMETERS

a

O> 052i

1 i

FIGURE 39. Thickness of the Springfield Plateau aquifer. Information outside of study area is from stratigraphically equivalent unit.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D67

chert. In western Missouri and southeastern Kansas 

the more important geologic formations in the aquifer are the thicker and more permeable Burlington 

and Keokuk Limestones (table 1). These two formations have similar lithologies: medium-crystalline to 

coarsely crystalline bedded limestone containing 

abundant quantities of gray chert, mainly in the 

form of nodules. The upper 100 to 200 feet of the extremely soluble limestone is a well-developed karst 

terrane with an extensive network of solution channels. Most of the solution channels are oriented along 

joints and bedding planes. In many areas these solution channels have enlarged to the point where the 

rock matrix has collapsed, producing caves and other 

large karst features and significantly increasing the 

rock permeability. The underlying Fern Glen Limestone and Pierson Formation are not as thick as the 

Burlington and Keokuk Limestones and do not contain an extensive network of solution channels 

(Frick, 1980); however, these formations are permeable. Formations that overlie the Burlington and 

Keokuk Limestones are not thick or areally extensive 

in this area, and where they are present, the lack of 

solution-channel development and presence of interbedded shale usually makes them much less permeable than the underlying rocks of the aquifer.

In northeastern Oklahoma, the Burlington Limestone is not present, and the Springfield Plateau aquifer is composed of the Boone Formation, the 

Keokuk Limestone, and the Moorefield Formation 

(table 1). The Boone Formation and Keokuk Limestone are lithologically and hydrologically similar to 

the Burlington and Keokuk Limestones of southwestern Missouri, but they are not as permeable because 

the karst terrane is not as well developed. The upper 

part of the Boone Formation generally contains significant quantities of chert. Generally, the chert is 

fractured, and the formation is permeable. Chert is 

much less common in the St. Joe Limestone Member, 

the basal member of the Boone Formation. The 

Reeds Spring Member of the Boone Formation and 

the overlying Keokuk Limestone have similar lithologies in this area. Both formations consist of dense, 

fine-grained limestone and massive gray chert. The 

chert content of the Keokuk Limestone is greater 

than that of the Reed Springs Member. Chert in the 

Keokuk Limestone of northeastern Oklahoma is fractured, and the formation is permeable. The Moorefield Formation, which grades from argillaceous 

limestone to siltstone and shale, probably is not very 

permeable.

In northern Arkansas, the aquifer is represented 

by the Boone Formation. The chert content of the 

Boone Formation increases from west to east, but the

formation remains permeable because of dissolution 

of limestone along fractures and bedding planes. The 

Boone Formation is the source of many springs 

where the unit crops out in northern Arkansas. The 

Moorefield Formation in northern Arkansas contains 

a significant fraction of shale and for this reason is 

assigned to the Western Interior Plains confining system in the southern part of the study area.

RECHARGE, GROUND-WATER FLOW, AND DISCHARGE

Where the Springfield Plateau aquifer crops out 

and is unconfined, the potentiometric surface generally reflects the local topographic relief. The altitude 

of the potentiometric surface is highest along a line 

from Barry County, Missouri, to Washington County, 

Arkansas (figs. 3, 40; Imes, 1990f), where it exceeds 

1,400 feet. From the areas with the highest waterlevel altitude, ground water discharges downward 

through the underlying Ozark confining unit into the 

Ozark aquifer and then moves east to discharge into 

the White River, or it moves laterally in the Springfield Plateau aquifer to the west and discharges into 

the Spring and Neosho Rivers. Even where the 

Springfield Plateau aquifer is confined beneath several hundred feet of shale, sandstone, and limestone 

along the western perimeter of the study area (fig. 

37), the potentiometric surface of the aquifer is still 

affected by local topographic relief.

In west-central Missouri, ground-water flow in the 

Springfield Plateau aquifer is controlled by topographic relief and by interaction with saline ground 

water in stratigraphically equivalent beds that constitute the Western Interior Plains aquifer system. 

The transition zone between freshwater and salinewater is a few miles west of the eastern limit of the 

overlying Western Interior Plains confining system 

(fig. 12) and coincides with the transition zone 

bounding the underlying Ozark aquifer. The effect of 

topography on the potentiometric surface of the shallower Springfield Plateau aquifer is more apparent in 

the transition zone than the corresponding effect on 

the deeper Ozark aquifer. Most freshwater that enters the Springfield Plateau aquifer in the upland 

areas between the eastward-flowing rivers flows perpendicular to the river valleys and discharges into 

the Blackwater, Marais des Cygnes, and South 

Grand River valleys (fig. 40). Eastward-moving saline 

ground water flows parallel to and beneath these 

major river valleys and, subsequently, mixes with the 

freshwater from the upland areas and discharges 

into the rivers. This is possible because the lower potentiometric heads in the river valleys do not impede
96° 95° 94° 93° 92° 90° 89°

39 C38C

37°

36C

35C

EXPLANATION

OUTCROP AREA OF AQUIFERAREAL EXTENT OF AQUIFER IN 

SUBSURFACE

AREA WHERE AQUIFER (OR EQUIVALENT 

UNIT) IS MISSING IN SUBSURFACE

- - - - BOUNDARY OF STUDY AREA

1200- POTENTIOMETRIC CONTOUR Shows 

altitude al which water levels would have stood in tightly cased wells. Contour interval, in feet, is variable

20 40 60 MILES 

I I I

I I \ 

20 40 60 KILOMETERS

oCi 00

I

1

I

FIGURE 40. Predevelopment potentiometric surface of the Springfield Plateau aquifer. Information outside of study area is from stratigraphically equivalent unit. River

systems shown only in part; see figure 6 for more detail.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D69

the eastward movement of the saline ground water, 

whereas the heads in the upland areas are sufficiently high to prevent the saline ground water from flowing beneath the uplands.

Water-level data for the Springfield Plateau aquifer in northern Arkansas are sparse. The few head 

measurements available in Searcy County, Arkansas (fig. 3), where the aquifer crops out and is a 

source of domestic water supply, are insufficient for 

contouring the water table. The general direction of 

ground-water flow in the Springfield Plateau aquifer in northern Arkansas is assumed to be similar 

to that of the Ozark aquifer because (1) the outcrop 

of the Springfield Plateau aquifer in Arkansas occupies only a narrow band that parallels the outcrop 

area of the Ozark aquifer, and (2) the Springfield 

Plateau aquifer abruptly dips beneath thick deposits of relatively impermeable shale that constitute 

the overlying Western Interior Plains confining system. Because of the high altitude of the water table 

near the Boston Mountains and the low altitude of 

the Arkansas River valley, it is hypothesized that 

ground water in the southern part of the study 

area generally moves south toward the Arkansas 

River valley.

CHEMICAL QUALITY OF GROUND WATER

Water type in the part of the Springfield Plateau 

aquifer that crops out in southwestern Missouri 

and northeastern Oklahoma is calcium bicarbonate 

(fig. 41; table 2; Imes and Davis, 1990b). The water 

type in this area is controlled by the dominance of 

limestone in the aquifer. West of the outcrop area 

in southeastern Kansas is a small area containing 

calcium sulfate water. Northeast of this area, where 

the aquifer is blanketed by up to a few hundred 

feet of shale and silty sandstone, sulfate is the 

dominant anion, but sodium replaces calcium as the 

dominant cation. Sodium chloride water is present 

in the aquifer along most of the northwestern 

boundary of the study area where the aquifer is 

confined by the Western Interior Plains confining 

system. Near Saline County, Missouri (fig. 3), the 

water type is predominantly sodium chloride, but 

calcium bicarbonate water is present in areas of 

local recharge.

At the northwestern edge of the Salem Plateau in 

and near Saline County, Missouri, the dissolvedsolids concentration of water in the Springfield Plateau aquifer ranges from about 500 milligrams per 

liter to about 10,000 milligrams per liter (fig. 42; 

Imes and Davis, 1990b). The high concentrations of

dissolved solids occur where eastward-flowing salinewater mixes with freshwater in the aquifer in 

northern Saline County parallel to the Missouri 

River, in southern Saline County parallel to the 

Blackwater River, and in east-central Saline County 

parallel to Salt Fork (not shown). The dissolvedsolids concentration is less than 1,000 milligrams 

per liter where the aquifer is recharged by freshwater percolating through a thin layer of Pennsylvanian rocks in central Saline County. Large 

meanders in the 500- and 1,000-milligrams-per-liter 

concentration lines in and near Henry County, 

Missouri, indicate where salinewater mixes with 

freshwater in the aquifer and discharges into the 

South Grand, Marais des Cygnes, and Osage Rivers. Dissolved-solids concentrations in areas where 

the aquifer crops out in southwestern Missouri, 

northeastern Oklahoma, and northern Arkansas 

can exceed 400 milligrams per liter locally, but 

more typically they are within the range of 100 to 

300 milligrams per liter. At the western boundary 

of the aquifer in northeastern Oklahoma the concentration of dissolved solids increases abruptly.

In the outcrop area, chloride concentrations in 

ground water from the aquifer generally are less 

than 10 milligrams per liter in southwestern Missouri and northeastern Oklahoma, but can exceed 

100 milligrams per liter locally in northwestern Arkansas (fig. 43; Imes and Davis, 1990b). Where the 

aquifer lies beneath the Western Interior Plains 

confining system in southeastern Kansas and northeastern Oklahoma, the chloride concentration increases to greater than 100 milligrams per liter. In 

and near Saline County, Missouri (fig. 3), chloride 

concentrations in ground water are larger beneath 

the Missouri and Blackwater Rivers than beneath 

the highlands between the rivers (fig. 6). The increase in chloride concentrations is due to mixing of 

salinewater with freshwater in these areas.

Sulfate concentrations in water from the aquifer 

generally are less than 10 milligrams per liter in 

the outcrop area (fig. 44; Imes and Davis, 1990b). 

Concentrations greater than 50 milligrams per liter 

occur near Saline County, Missouri, and along part 

of the western boundary of the aquifer. The areas of 

greatest concentrations are located in the tristate 

(Kansas-Oklahoma-Missouri) lead-zinc mining district. Presumably, the larger concentrations of sulfate in this area are the product of the oxidation of 

sulfide minerals that took place when the mine 

shafts were dewatered. Later refilling of the mine 

shafts with ground water allowed dissolution of the 

sulfate ions, resulting in local larger concentrations 

of sulfate in the water (Spruill, 1984).
96° 95° 94° 93° 92° 91' 90° 89° 88°

39°

38°

37°

36°

35°

EXPLANATION

OUTCROP AREA OF AQUIFER

AREAL EXTENT OF AQUIFER IN 

SUBSURFACE

AREA WHERE AQUIFER (OR EQUIVALENT 

UNIT) IS MISSING IN SUBSURFACE

- - - - BOUNDARY OF STUDY AREA

BOUNDARY BETWEEN AREAS OF 

DIFFERENT MAJOR CHEMICAL CONSTITUENTS Dotted where inferred _ CA MAJOR CHEMICAL CONSTITUENTS See 

V _^ table 2 for explanation of symbols

40 60 MILES 

I I

\ I I 

0 20 40 60 KILOMETERS

o-J

o

FIGURE 41. Water type in the Springfield Plateau aquifer. Information outside of study area is from stratigraphically equivalent unit.
96° 95° 94° 93° 92° 91 C 90° 89°

39 C38C

37°

36°

35C

- - - - BOUNDARY OF STUDY AREA

 '.;... 200- LINE OF EQUAL DISSOLVED-SOLIDS 

'"" CONCENTRATION Interval, in milligrams 

per liter, is variable

20 40 60 MILES

I I I

\ \ 

0 20 40 60 KILOMETERS

£a

d03

£

FIGURE 42. Dissolved-solids concentrations in ground water from the Springfield Plateau aquifer. Information outside of study area is from stratigraphically equivalent unit.

River systems shown only in part; see figure 6 for more detail. O-3
96° 95° 94° 93° 92° 91

39°38C37°

36C

35C

m®Jh .r^vi

90° ______ 89° ___________ 88° _______ 

I I

EXPLANATION

OUTCROP AREA OF AQUIFER

AREAL EXTENT OF AQUIFER IN 

SUBSURFACE

AREA WHERE AQUIFER (OR EQUIVALENT 

UNIT) IS MISSING IN SUBSURFACE

/' - - - - BOUNDARY OF STUDY AREA

 250- LINE OF EQUAL CHLORIDE CONCENTRATIONInterval, in milligrams per liter, is variable - tSD

20 40 60 MILES

I I I

I I I 

0 20 40 60 KILOMETERS

2i

gq

FIGURE 43. Chloride concentrations in ground water from the Springfield Plateau aquifer. Information outside of study area is from stratigraphically equivalent unit.
96° 95° 94° 93° 92° 91 C

39°

38°37°36°

35°

T \ \ 10 LINE OF EC 

I ^ *~^\ ** *>. Interval,!

\ / X \^y ?

90° _____89^__________88^_______ I I

EXPLANATION

OUTCROP AREA OF AQUIFERAREAL EXTENT OF AQUIFER IN 

SUBSURFACE

AREA WHERE AQUIFER (OR EQUIVALENT 

UNIT) IS MISSING IN SUBSURFACE

/ _ _ _ _ BOUNDARY OF STUDY AREA

LINE OF EQUAL SULFATE CONCENTRATIONin milligrams per liter, is variable

0 20 40 60 MILES

I I I

I I T

0 20 40 60 KILOMETERS

./

FIGURE 44. Sulfate concentrations in ground water from the Springfield Plateau aquifer. Information outside of study area is from stratigraphically equivalent unit.

1

i

o<I

CO
D74 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

WESTERN INTERIOR PLAINS CONFINING SYSTEM

The Western Interior Plains confining system is a 

thick (as much as 20,000 ft) and areally extensive 

geohydrologic unit that extends from the Rocky 

Mountains to western Missouri and northern Arkansas (Jorgensen and others, 1993). This confining 

system overlies and effectively confines the extensive Western Interior Plains aquifer system (Jorgensen and others, 1993) west of the Ozark area. 

This confining system also confines the western and 

southern edges of the Ozark Plateaus aquifer system (figs. 11, 12).

Within the larger region encompassed by the 

study of the Central Midwest Regional AquiferSystem Analysis, this confining system includes 

rocks that range from Late Mississippian to Jurassic age, but along the western and southern flanks 

of the Ozarks, where the system confines the Ozark 

Plateaus aquifer system, it contains only Upper 

Mississippian and Pennsylvanian rocks. Within the 

study area, the Western Interior Plains confining 

system is represented by a sequence of rocks ranging from the Carterville Formation of Mississippian 

age to the Kansas City Group of Pennsylvanian age 

(table 1). Geologic formations that are stratigraphically equivalent to those that constitute the Western Interior Plains confining system are present in 

the north-central Salem Plateau and in the extreme 

northeastern part of the study area. Although these 

units have quite similar geohydrologic characteristics and significantly affect the hydrology of local 

areas in which they are present, they are not hydraulically continuous with the equivalent units in 

the western and southern parts of the study area 

and are, therefore, not designated as part of the 

Western Interior Plains confining system. In southwestern Missouri the Western Interior Plains 

confining system includes four Mississippian formations (the Carterville Formation, Hindsville Limestone, Batesville Sandstone, and Fayetteville Shale) 

and a sequence of Pennsylvanian formations from 

the stratigraphically lower Cherokee Shale to the 

Kansas City Group. Mississippian rocks are only a 

small part of the total thickness of the confining 

system. Only the Pennsylvanian formations are 

present in southeastern Kansas. In northeastern 

Oklahoma the confining system includes the stratigraphic sequence from the base of the Mississippian 

Hindsville Limestone to the Pennsylvanian Marmaton Group. In the Boston Mountains of northern 

Arkansas, the confining system extends from 

the basal Moorefield Formation to the McAlester 

Formation.

STRUCTURAL FEATURES

The Western Interior Plains confining system is 

stratigraphically the uppermost geohydrologic unit in 

the study area, excluding unconsolidated alluvium 

along streams and rivers and post-Paleozoic deposits 

of the Mississippi Alluvial Plain. Along the western 

boundary of the study area, the topography of the 

surface of the unit is characterized by gently rolling 

hills and broad alluvial valleys. The altitude of the 

top of the confining system ranges from less than 800 

feet in the river valleys to more than 1,000 feet in 

the upland areas (fig. 45; Imes, 1990g). At the southern edge of the Ozark Plateaus, the surface of the 

confining system reflects the rugged topography of 

the Boston Mountains. It is common for the altitude 

of the top of the confining system to change by more 

than 1,500 feet within a few miles in the Boston 

Mountains. The altitude of the confining system 

ranges from less than 400 feet in the lowlands of the 

Arkansas Valley to more than 2,000 feet on highland 

ridges in the Boston Mountains. The confining system has been removed by erosion from the Mississippi Alluvial Plain in southeastern Missouri and 

northeastern Arkansas.

THICKNESS

Generally, the thickness of the Western Interior 

Plains confining system increases away from the 

Ozark Plateaus province. The unit thickens at a 

greater rate to the south than to the west. In the 

western part of the study area the confining system 

thickens at a fairly uniform rate of about 12 feet per 

mile to the northwest and is about 400 feet thick 

along the western edge of the Ozark Plateau aquifer 

system (fig. 46; Imes, 1990g). Irregularities in the 

thickness of the Western Interior Plains confining 

system near the western flank of the Springfield Plateau do not seem to conform to the surface drainage 

pattern and probably are an expression of erosional 

features on top of the underlying Springfield Plateau 

aquifer.

Near the Kansas-Oklahoma border, the confining 

system thickens at a rate of about 25 feet per mile to 

the west, and near the southwest edge of the study 

area the rate is about 80 feet per mile to the southwest. Only a narrow band of the Western Interior 

Plains confining unit is within the boundaries of the 

study area in northeastern Oklahoma. The rate of 

thickening of the unit away from the Ozark Plateaus 

is greater south of the Boston Mountains. In this 

area the confining system thickens at a rate of about
96° 95° 94° 93° 92° 91 c 90° 89r 

I

88°

36° - 35° rEXPLANATION OUTCROP AREA OF CONFINING SYSTEM AREA WHERE CONFINING SYSTEM IS MISSING IN SUBSURFACE - - - - BOUNDARY OF STUDY AREA / 800 LINE OF EQUAL ALTITUDE Shows altitude of top of confining system. Interval, in feet, is variable. y Datum is sea level \ 0 20 40 60 MILES

I I I

I I I

0 20 40 60 KILOMETERS

FIGURE 45. Altitude of top of the Western Interior Plains confining system.

I

ffi

9

I

1

a <j Ot
96° 95° 94° 93° 92° 91°

/ \L 

1 "\

_T

90°

39° - | x .

v.y r ( /" } - - - - BOUNDARY OF STUDY AREA

/ - 38° - 37 C

36C

35° - 89° EXPLANATION OUTCROP AREA OF CONFINING SYSTEM AREA WHERE CONFINING SYSTEM IS MISSING IN SUBSURFACE 500 LINE OF EQUAL THICKNESS Interval, in feet, is variable 20 40 60 MILES

I I I

\ \ \ 

0 20 40 60 KILOMETERS

i

1

i

FIGURE 46. Thickness of the Western Interior Plains confining system.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D77

180 feet per mile to the south and is thicker than 

6,000 feet beneath the Arkansas Valley.

LlTHOLOGYAND GEOHYDROLOGIC PROPERTIES

The Western Interior Plains confining system consists of alternating sequences of low-permeability 

shale and low-permeability to relatively permeable 

limestone, sandstone, and coal. The less permeable 

rocks dominate the system and restrict vertical leakage and lateral movement of ground water. The more 

permeable rocks in the confining system do not form 

distinct aquifers regionally. Thus, the rocks that form 

the confining system collectively impede the flow of 

water to and from the underlying Ozark Plateaus 

aquifer system. It is plausible for a thick and 

complex geohydrologic unit, such as the Western Interior Plains confining system, to include local waterbearing aquifers and permeable zones. The designation "Western Interior Plains confining system" indicates that, on a regional scale, the rocks composing 

the unit impede the vertical flow of water and confine 

the underlying aquifers.

In Arkansas the stratigraphically lowest formation 

assigned to this confining system is the Moorefield 

Formation (table 1), because of its large shale content and low permeability. However, the shale content of this formation decreases to the west, and the 

formation is permeable enough to assign it to the 

Springfield Plateau aquifer in Oklahoma. The stratigraphically higher Batesville Sandstone, a calcareous 

sandstone containing some shale, is only slightly permeable because the sand grains are tightly cemented. 

Of the remaining Mississippian formations in the 

confining system, the Hindsville Limestone, Fayetteville Shale, and Pitkin Limestone are thickest 

and the most extensive. The Hindsville Limestone 

and Pitkin Limestone probably have a larger permeability than the other Mississippian rocks of the confining system and are not as effective in impeding 

the vertical flow of ground water. On the other hand, 

throughout northern Arkansas and northeastern 

Oklahoma the Fayetteville Shale is thick and contains a large fraction of shale (Caplan, 1954; Huffman, 1958). Thus, this shale restricts vertical 

ground-water flow in these two areas.

Pennsylvanian rocks constitute the greater part of 

the Western Interior Plains confining system, both in 

thickness and area! extent. The lithology of these 

rocks is predominantly shale; sandstone and limestone also are well represented. The leakance of this 

thick sequence of rocks is governed by significant 

quantities of slightly permeable shale. The rocks restrict the movement of ground water between land 

surface and the underlying Springfield Plateau aquifer. Some of the larger sandstone formations, mostly 

those of the Cherokee Shale (table 1), are more 

permeable than other formations in the confining 

system. The near-surface weathered zone of the confining system has somewhat different hydraulic properties than the deeper, unweathered parts. Because 

the near-surface shale layers are fractured and 

slightly permeable, secondary permeability has developed in the near-surface limestone formations, and 

local ground-water flow systems are present in the 

upper 300 feet of the weathered confining system. 

This permeable layer contrasts with the consolidated 

and compacted lower part of the confining system.

Hydraulic heads in the Western Interior Plains 

confining system probably have changed little from 

their predevelopment levels. Even if the heads in a 

more permeable zone within the confining system 

were lowered by pumping of domestic wells, this 

head decrease would not necessarily reflect the hydraulic heads in other permeable zones in the confining system, because of the poor hydraulic connection 

among the zones. The head distribution within the 

confining system varies both vertically and laterally. 

Water-level measurements from wells that are open 

to most or all of the water-yielding layers of the confining system represent a weighted-average water 

level of the more permeable zones of the confining 

system. No single head value can represent hydraulic 

heads in the confining system because hydraulic gradients usually are nearly vertical in the low-permeability zones and nearly horizontal in the higher 

permeability zones.

LATERAL GROUND-WATER MOVEMENT IN THE NEAR-SURFACE WEATHERED 

ZONE OF THE WESTERN INTERIOR PLAINS CONFINING SYSTEM

Heads in the near-surface weathered zone of the 

Western Interior Plains confining system are greatly 

affected by topographic features. Generally, groundwater supplies are replenished by precipitation that 

infiltrates the ground in upland areas and percolates 

to the water table. The ground water then flows 

downgradient toward lowland areas where it discharges into perennial streams. Ground-water levels 

in the upland areas tend to be as much as 100 feet 

lower than the average land-surface altitude. Near 

the northwestern boundary of the study area, ground 

water in the near-surface weathered zone of the 

Western Interior Plains confining system primarily 

moves towards the major valleys associated with the 

Blackwater, Marais des Cygnes, and South Grand
D78 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

Rivers (fig. 6). Heads in the river valleys generally 

are less than 800 feet above sea level. A groundwater divide that extends northwest from Barton 

County, Missouri (fig. 3), separates the ground-water 

flow in the northwestern part of the study area from 

the ground-water flow in a larger area to the southwest and south. In the latter area the ground water 

moves into the Neosho River in southeastern Kansas 

and northeastern Oklahoma and into the Arkansas 

River in northeastern Oklahoma and northern Arkansas (fig. 47). Water levels along the divide range 

from 800 to 1,000 feet above sea level, whereas water 

levels in the Arkansas River valley are less than 600 

feet above sea level. In the Boston Mountains of 

northern Arkansas, heads in the weathered zone of 

the confining system vary markedly over relatively 

short distances. The altitude of ground-water levels 

exceeds 2,000 feet in the uplands of the Boston 

Mountains and decreases to less than 300 feet in the 

lower reaches of the Arkansas River valley.

The predevelopment head map shown here (fig. 47; 

Imes, 1990g) represents the head distribution in the 

near-surface weathered zone of the confining system 

and, therefore, indicates the approximate lateral 

movement of ground water in this zone. It does not 

represent the movement of ground water in the deeper layers of the confining system. Water-level measurements used in the construction of figure 47 

generally are from wells that are open only to the 

upper 100 to 300 feet of the weathered zone of the 

confining system. The head data also reflect measurements at various times throughout this century, and 

thus the head distribution is only an approximation.

UNNAMED LOCAL GEOHYDROLOGIC UNITS

Mississippian and Pennsylvanian rocks stratigraphically equivalent to geohydrologic units previously defined and described, but not considered part 

of the regional geohydrologic units, are located in 

three areas in the northeastern part of the Ozark 

Plateaus province (fig. 48). These areas are labeled A 

(located in the north-central Salem Plateau), B (located in St. Louis and Jefferson Counties, Missouri (fig. 

3)), and C (located in Ste. Genevieve and Perry Counties, Missouri). These rocks do not have a direct hydrologic relation with stratigraphically equivalent 

units in the western part of the Ozark Plateaus province. However, they have hydraulic properties that 

are similar to those of the regional geohydrologic 

units because they are composed of the same geological formations. Although some of these units are important as sources of domestic water supply in the

northeastern part of the study area, the units are not 

extensive enough to be classified as one of the regional geohydrologic units.

Permeable Mississippian geologic formations, most 

of which are stratigraphically equivalent to those of 

the Springfield Plateau aquifer, crop out in areas B 

and C (fig. 48) in eastern Missouri along the Missouri 

and Mississippi Rivers. They dip into the subsurface 

to the east. The formations, mainly composed of limestone, include those from the base of the Fern Glen 

Limestone to the top of the Ste. Genevieve Limestone 

(table 1). In area B, the altitude of the top of the 

sequence generally decreases from nearly 700 feet 

where it feathers out against the Ozark confining 

unit to the southwest (fig. 12) to less than 400 feet 

along the Mississippi River and where it is confined 

by Pennsylvanian rocks in the northeast (fig. 49; 

Imes, 1990f). The unit thickens northeastward from 

its terminus at the outcrop of older rocks and is more 

than 900 feet thick at the center of a nearly circular 

depression in the northeast corner of the area. The 

unit yields water to domestic wells, especially in the 

southwestern half of the area where the dissolvedsolids concentration of the water is less than 1,000 

milligrams per liter (Gleason, 1935). The distribution 

of water levels in the unit is affected by the topographic relief of the area, even where the unit is confined beneath Pennsylvanian rocks (fig. 49; Imes, 

1990f). Water levels in the unit are greater (about 

600 ft) in the southwest near the outcrop area of 

older rocks, and decrease to about 400 feet along the 

Missouri and Mississippi Rivers. Generally water levels are about 50 to 100 feet below land surface in the 

upland areas and at land surface along the major 

river valleys. In the southwestern part of the area, 

ground water from the unit recharges the Ozark aquifer, whereas in the northeastern part of the area, 

ground water in the Ozark aquifer discharges into 

this local unit.

Rocks in area C, which are stratigraphically equivalent to those of the Springfield Plateau aquifer, crop 

out in a narrow band along the Mississippi River. 

The rocks dip abruptly to the east. The altitude of 

the top of the unit ranges from greater than 400 feet 

in the west to below sea level in the east (fig. 50; 

Imes, 1990f) where the unit is covered by alluvial deposits of the Mississippi River. In the same short distance, the thickness of the unit increases from near 0 

to more than 1,500 feet (fig. 50; Imes, 1990f). The 

direction of the hydraulic gradient in this local geohydrologic unit is approximately northeast toward 

the Mississippi River valley where ground water discharges to the alluvium from the rocks (fig. 50; Imes, 

1990f). The rocks probably receive ground water from
96° 95° 94° 93° 92° 91 C 90° 89° 88°

39°

38C

37°

36°

35C

EXPLANATION

OUTCROP AREA OF CONFINING SYSTEMAREA WHERE CONFINING SYSTEM IS MISSING 

IN SUBSURFACE

---- BOUNDARY OF STUDY AREA

/ 800 POTENTIOMETRIC CONTOUR Shows altitude at 

which water levels would have stood in tightly cased wells. Contour interval, in feet, is variable. Datum is sea level

40 60 MILES

I____I

20 40 60 KILOMETERS

§

1

FIGURE 47. Predevelopment potentiometric surface of near-surface weathered zone of the Western Interior Plains confining system. River systems shown only in part;

see figure 6 for more detail. d <J

CO
96° 95° 94° 93° 92° 91 c 90° 89° 88°

EXPLANATION

EXTENT OF LOCAL GEOHYDROLOGIC 

UNITS THAT ARE STRATIGRAPHICALLY EQUIVALENT TO REGIONAL 

GEOHYDROLOGIC UNITS

AREA DISCUSSED IN TEXT 

BOUNDARY OF STUDY AREA

37

36° - 35° - 0 20 40 60 MILES 

I I I

I I I 

0 20 40 60 KILOMETERS

O 00

o

2

I

FIGURE 48. Location of unnamed local geohydrologic units in northeastern part of Ozark Plateaus province.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D81

the underlying Ozark aquifer in all but the westernmost part of this area.

Geologic formations that are stratigraphically 

equivalent to the Western Interior Plains confining 

system occur in the areas of higher elevation between river valleys in the north-central part of the 

Salem plateau (area A) and are in direct contact with 

the Ozark aquifer. These undifferentiated Pennsylvanian rocks are the shallowest formations in the area 

and collectively confine the underlying Ozark aquifer. 

The top of these undifferentiated Pennsylvanian 

rocks reflects the gently rolling topography of the uplands. The altitude of the top generally ranges from 

800 to 1,100 feet. The thickness of these rocks in this 

area rarely is more than 200 feet and usually is less 

than 100 feet. In the past, shallow wells (less than 

25 ft deep) were dug into these rocks to provide domestic water. Today these rocks are seldom used as a 

source of water because well yields are small, water 

quality has become degraded, and deeper wells provide high yields of better quality water.

Geologic formations that are stratigraphically 

equivalent to the Western Interior Plains confining

system also are present to a limited extent in areas 

B and C. The rocks, which form the surficial geohydrologic unit in this area, generally are not used as a 

source of water. Pennsylvanian rocks (the Cherokee 

Shale, Marmaton Group, and Pleasanton Formation 

(table 1)) form a large, nearly circular confining system in the northeastern part of area B. The lensshaped system is about 250 feet thick at its center. 

The altitude of the top of these rocks ranges from 

about 450 feet near the Missouri and Mississippi Rivers to about 600 feet near the center of the lens 

(Imes, 1990g). In area C, rocks that are stratigraphically equivalent to the Western Interior Plains confining system crop out in a narrow band along the 

Mississippi River. In this small area the unit consists 

of a thick sequence of Upper Mississippian rocks 

from the Aux Vases Sandstone to the Vienna Limestone (table 1). The altitude of the top of the unit 

decreases from more than 400 feet adjacent to the 

outcrop of the Ozark Plateaus aquifer system to the 

west to less than 200 feet beneath the Mississippi 

River. The thickness of the unit increases eastward 

from 0 to more than 300 feet (Imes, 1990g).

91 c 90° 91 90° 91 c

38° -

20 40 60 MILES

I______I______I

I I I I

0 20 40 60 KILOMETERS

EXPLANATION

OUTCROP AREA OF UNIT

AREAL EXTENT OF UNIT IN 

SUBSURFACE

-400 LINE OF EQUAL ALTITUDE Shows 

altitude of top of unit. Interval is 100 

feet. Datum is sea level

EXPLANATION

OUTCROP AREA OF UNIT

AREAL EXTENT OF UNIT IN 

SUBSURFACE

 200 LINE OF EQUAL THICKNESS 

Interval is 200 feet

FIGURE 49. Altitude of top, thickness, and potentiometric surface of rocks in area B (fig

Springfield Plateau aquifer.

EXPLANATION

OUTCROP AREA OF UNIT

AREAL EXTENT OF UNIT IN 

SUBSURFACE

 400 POTENTIOMETRIC CONTOUR 

Shows altitude at which water 

levels would have stood in tightly 

cased wells. Contour interval is 100 

feet. Datum is sea level

48) that are stratigraphically equivalent to the
D82 REGIONAL AQUIFER-SYSTEM ANALYSIS-CENTRAL MIDWEST

POST-PALEOZOIC DEPOSITS

Unconsolidated, post-Paleozoic deposits, especially 

alluvial sand and gravel along the major river reaches that border much of the study area, are a valuable 

source of large quantities of ground water in the 

area. Although an investigation of the alluvial aquifers is not part of this study, the alluvial aquifers are 

briefly described here because of their hydrologic relation to the Ozark Plateaus aquifer system. In this 

section, the alluvial deposits of each river reach are 

treated as if the entire width of the alluvial valley, 

except the Mississippi Alluvial Plain physiographic 

section, were within the boundaries of the study 

area. More detailed information about these aquifers 

may be found in published literature, some of which 

is cited in the following paragraphs.

Alluvial deposits associated with many small 

streams and rivers in the interior of the study area 

generally are narrow to absent. Water in these alluvial deposits is used for public supply by small towns 

and, principally, as a source for domestic use. Along 

the boundary of the study area, three large rivers

and their alluvial deposits supply large quantities of 

water to municipal, industrial, and domestic users. 

Along the northern boundary the Missouri River alluvium varies from about 1.5 to 6 miles in width and 

averages about 90 feet in thickness. Sand and gravel 

deposits are predominant in the lower part of the alluvium, and sand and clay are predominant in the 

upper part. Yields as large as 3,000 gallons per 

minute have been reported for wells penetrating the 

more permeable gravel beds (Emmett and Jeffery, 

1968, 1969). The Mississippi River alluvium along 

the eastern boundary is hydrologically similar to the 

alluvium of the Missouri River. The Arkansas River 

valley coincides with the southern boundary and part 

of the southwestern boundary of the study area. The 

sand, gravel, silt, and clay deposits along this reach 

of the Arkansas River range from about 40 feet thick 

at the Oklahoma-Arkansas border to about 80 feet 

thick where the river intersects the Mississippi Alluvial Plain. Eight aquifer tests at various locations in 

the alluvium of the Arkansas River valley indicate 

that the transmissivity ranges from 0.06 to 0.25 foot 

squared per second (Bedinger and others, 1963).

39°

91 C 90°

20 40 60 MILES

T~ TI ______|

0 20 40 60 KILOMETERS

EXPLANATION

OUTCROP AREA OF UNIT

AREAL EXTENT OF UNIT IN 

SUBSURFACE

-400 LINE OF EQUAL ALTITUDE Shows 

altitude of top of unit. Interval is 400 

feet. Datum is sea level

EXPLANATION

OUTCROP AREA OF UNIT

AREAL EXTENT OF UNIT IN 

SUBSURFACE

 4oo LINE OF EQUAL THICKNESS 

Interval, in feet, is variable

EXPLANATION

OUTCROP AREA OF UNIT

AREAL EXTENT OF UNIT IN 

SUBSURFACE

 400 POTENTIOMETRIC CONTOUR 

Shows altitude at which water 

levels would have stood in tightly 

cased wells. Contour interval is 100 

feet. Datum is sea level

FIGURE 50. Altitude of top, thickness, and potentiometric surface of rocks in area C (fig. 48) that are stratigraphically equivalent to the

Springfield Plateau aquifer.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D83

The thick unconsolidated sediments of the Mississippi Alluvial Plain along the southeastern boundary 

of the study area provide large quantities of water 

for public water supply and agricultural use. The 

Cretaceous, Tertiary, and Quaternary sediments of 

the alluvial plain thicken to the southeast. Yields 

from wells open to the alluvial aquifer commonly 

range from 1,000 to 2,000 gallons per minute and 

may exceed 4,000 gallons per minute locally Analyses of aquifer tests at nine locations in the alluvial 

aquifer in Missouri indicate the transmissivity of the 

aquifer ranges from 0.17 to 0.63 foot squared per second (Luckey, 1985). The geology and hydrology of the 

alluvial aquifer and the underlying unconsolidated 

post-Paleozoic sediments have been studied extensively (Gushing and others, 1964; Luckey and Fuller, 

1980; Luckey, 1985; and Petersen and others, 1985). 

The area currently is being investigated in detail as 

part of the Gulf Coast Regional Aquifer-System Analysis (Grubb, 1984).

INTERACTION OF SURFACE AND GROUND WATER: 

RECHARGE TO THE REGIONAL 

GROUND-WATER FLOW SYSTEM

The exchange of surface water and ground water is 

a function of the relative altitude of land surface and 

the water table. Generally, recharge occurs by infiltration of precipitation where the water table is 

lower than the land surface; discharge occurs by surface flow where the water table intersects the land 

surface or by evapotranspiration where the water 

table is near the land surface. Because of seasonal 

variations in precipitation, the altitude of the water 

table can fluctuate as much as several tens of feet. A 

schematic diagram that represents the exchange 

mechanisms that are important in the Ozark Plateaus province is shown in figure 51.

Most of the water that percolates to the saturated 

zone moves laterally through shallow, local flow systems; it then discharges into streams as base flow or 

issues through small springs. Of importance to this 

study is the smaller quantity of water that moves 

vertically downward to the deeper, regional groundwater flow system. To estimate the quantity of water 

that percolates to the deep, regional flow system, it is 

necessary to estimate some of the flow components in 

the shallow aquifer system. In practice it is difficult, 

if not impossible, to estimate these flow components, 

especially where the thickness of the aquifer system 

is large and the structure and lithology of the geologic formations composing the aquifer system are complex. Fracture systems and large faults can provide

hydraulic connections between shallow and deep flow 

systems and thus can further complicate their interaction.

In the Interior Plains, Boston Mountains, and Arkansas Valley (fig. 5), surficial geologic materials of 

the uppermost Western Interior Plains confining system are predominantly slightly permeable shale and 

permeable sandstone with some permeable limestone. Weathering processes in the near-surface zone 

of the confining system have reduced permeability 

contrasts between different rocks. The more uniform 

hydraulic properties and generally small hydraulic 

conductivity of the rocks in the confining system create a geohydrologic condition that supports a welldefined, near-surface water table controlled by the 

local topographic features of the area. Contours on 

the water table (Imes and Smith, 1990) tend to parallel rivers and streams and reflect the infiltration of 

precipitation in the uplands, movement of shallow 

ground water from the uplands to adjacent valleys, 

and discharge of the ground water into streams by 

seepage.

The Springfield Plateau is characterized by a deeply weathered cherty limestone that contains a welldeveloped, near-surface karst. The water table generally is easy to define in this area, with water-level 

contours usually trending parallel to the local surface 

topography (Imes and Smith, 1990). Most streams in 

the area gain water by ground-water discharge from 

the Springfield Plateau aquifer. However, there are 

stream reaches that lose water to adjacent aquifers. 

The lost water typically resurfaces downstream in 

the same channel.

An extensive karst system has developed in the 

Ozark aquifer where it crops out in the Salem Plateau (figs. 5, 12, 52). The large thickness of carbonate 

rock and extensive network of solution-enlarged fractures, vertical joints, and bedding planes enables surface water to rapidly infiltrate the Ozark aquifer. 

Major conduit systems, many of which are several 

feet wide and hundreds of feet long, occupy the upper 

few hundred feet of the aquifer. Caverns and large 

springs abound in this part of the Ozarks (Vineyard 

and Feder, 1974). Harvey (1980) identified areas in 

southern Missouri and northern Arkansas where the 

Ozark aquifer contains large concentrations of sinkholes. The well-developed (primary) karst areas are 

defined as having more than 10 sinkholes per 100 

square miles, whereas areas of lesser developed (secondary) karst are defined as having 1 to 10 sinkholes 

per 100 square miles (fig. 52). Solution of limestones 

and dolostones can produce complex and irregular 

surface and shallow-subsurface drainage patterns. 

Consequently, in many areas of the Salem Plateau
D84 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

where the karst is well developed, the water table 

may not reflect the local topography. The geometry of 

the water table in carbonate rocks that contain a 

well-developed system of solution channels or karst 

terrane can be difficult to determine. Because of the 

abrupt changes in permeability, ground water can be 

perched above a less permeable zone. The presence of 

large areas of perched water can create two or more 

near-surface ground-water flow systems within the 

same area, with ground water in each perched area 

flowing in different directions along different conduit 

networks. An example of this phenomenon is shown 

by dye-trace data from the southernmost parts of the 

Salem Plateau (Harvey, 1980). The areally limited, 

possibly temporary, perched ground-water flow cannot be easily differentiated from the deeper, continuous regional flow.

On the other hand, the degree of karst development can enhance the interaction between surface 

and ground waters. This is illustrated in figures 53 

and 54. Figure 53 depicts the effects of precipitation 

on the water level in an observation well located in 

Phelps County, Missouri, in the north-central part of

the Salem Plateau (fig. 52). This well is 650 feet deep 

and cased to a depth of 420 feet in the Ozark aquifer. 

The aquifer in this area contains some solution channels, but the karst terrane is not well developed. The 

seasonal response to precipitation is about 20 to 25 

feet. There is little evidence of any immediate response to individual precipitation events. In contrast, 

the response of the water levels shown in figure 54 is 

immediate and large. This well is located in welldeveloped karst in Howell County, Missouri, in the 

south-central part of the Salem Plateau (fig 52). It is 

1,305 feet deep and cased to a depth of 800 feet of 

the Ozark aquifer. The mean annual precipitation at 

both wells is about 42 inches per year. Variations in 

the water level of the Howell County well can exceed 

170 feet within a few days after a large rainfall. The 

well-developed karst of this area allows surface and 

ground water to interact rapidly to great depths.

The Ozark Plateaus province contains one of the 

largest concentrations of springs in the United 

States (fig. 55). Thousands of springs yield from 

less than a gallon of water per day to millions of 

gallons per day. Few of the springs are monitored

FIGURE 51. Schematic diagram of surface- and ground-water exchange mechanisms in Ozark Plateaus province.
96° 95° 94° 93° 92° 91 C 90° 89° 88°

39C

38° \-37C

36° U

35° U

EXPLANATION

PRIMARY KARST AREASECONDARY KARST AREA 

---- BOUNDARY OF STUDY AREA

A OBSERVATION WELL, PHELPS 

COUNTY, MISSOURI

OBSERVATION WELL, HOWELL 

COUNTY, MISSOURI

0 20 40 60 MILES

I I I

I I I

0 20 40 60 KILOMETERS

s

FIGURE 52. Distribution of primary and secondary karst areas in Ozark Plateaus province. 8

en
D86 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

continuously; therefore, much of the available 

springflow data is a composite of (1) average flow 

over the period of record at springs where continuous measurements were made for some specific 

time interval and (2) instantaneous flow at those 

springs where continuous measurements have not 

been made. The combined flow of the ten largest 

springs in the Ozarks is about 2,000 cubic feet per 

second (1.3 billion gallons per day). Nine springs in 

the Ozarks are first-order springs, that is, they 

have an average discharge greater than or equal to 

100 cubic feet per second (Meinzer, 1923). Many of 

the largest springs rise from nearly tubular conduits several feet wide that descend several hundred feet beneath land surface and connect the rise 

pool of the spring to deep-seated solution-channel 

networks. With few exceptions, the springs are confined to physiographic regions where carbonate 

rocks are the dominant surficial material.

The catchment areas of many large springs cover 

tens of square miles and do not necessarily coincide 

with surface-water drainage boundaries. In many 

cases the presence of a spring catchment area is indicated by sinkholes and losing streams. Although not 

as striking or as apparent as sinkholes, losing 

streams are common throughout the Salem and 

Springfield Plateaus (Imes and Smith, 1990). Losing 

streams are defined by the Missouri Department of 

Natural Resources (1985) as those streams or stream 

reaches that lose 30 percent or more of their flow 

through natural processes such as leakage through a 

permeable soil or bedrock. This definition is proposed 

as part of regulations concerning the movement of 

sewage effluent. Many streams lose smaller percentages of their flow to underlying aquifers or permeable material. The areas having the greatest 

concentrations and longest reaches of losing streams 

are located in the central part of the Salem Plateau. 

Not surprisingly, this area also contains some of the 

best developed karst in the Ozark aquifer. Because of 

the large hydraulic conductivity of the solution-channel networks that connect sinkholes and losing 

streams to springs, the response of springflow to precipitation in the catchment area can be rapid. During 

periods of dry weather, springflow in the larger 

springs is maintained by base flow from the aquifers.

2 _

a: 0 i

1980 1981 1982 1983 1984

130

150

170 J5

I 

190 O

230

FIGURE 53. Effect of precipitation on water levels in observation well in Phelps County, Missouri. Dashed segments in depth curve indicate

periods during which no data were collected. See figure 52 for location of well.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D87

The largest springs issue from the Ozark aquifer. 

Most of the larger springs issue from the Potosi, Eminence, and Gasconade Dolomites (table 1). The 

springs, generally located in or near major river valleys (fig. 55), are points of discharge of both local and 

regional flow in the Ozark aquifer. The large discharge of many of the springs reflects the depth and 

areal extent of the karst terrane. Water-quality analyses of samples from springs in and near Saline 

County, Missouri (fig. 3), indicate that the spring 

water there flows from the underlying confined 

Ozark aquifer. Most of these springs are characterized by a large mineral content. Springs that receive 

most or all of their water from the uppermost part of 

the aquifer generally are less mineralized. Springs 

that flow from the Springfield Plateau aquifer are 

numerous, but not as large as those that flow from 

the Ozark aquifer.

The small number of springs that issue from the 

Ozark confining unit probably receive their water 

from the underlying Ozark aquifer. Some small 

springs are located in the Western Interior Plains 

confining system. These springs issue mineralized 

water because the water has been in contact with

shale and coal. The ground water in the confining 

system moves to the springs through small fractures 

and along bedding planes and shale partings of the 

near-surface weathered zone of the confining system.

ESTIMATES OF RECHARGE AND DISCHARGE

An estimate of the amount of water that percolates 

through the unsaturated zone to the water table in 

the Central Midwest region has been made by Dugan 

and Peckenpaugh (1986). This estimate was made on 

the basis of climate, soil type, slope, land use, and 

consumptive water use by crops and vegetation. The 

estimate showed that mean annual ground-water recharge under preagricultural land-use conditions 

(that is, in woodland and grassland) ranged from 

about 7 to 15 inches per year in the Ozark area, and 

recharge generally increased from the northwest to 

the southeast (fig. 56). Today's mean annual groundwater recharge varies little from that estimated for 

preagricultural times, the largest change being about 

a 10-percent decrease in recharge in southwestern 

Missouri and northwestern Arkansas. The estimate

FIGURE 54. Effect of precipitation on water levels in observation well in Howell County, Missouri. See figure 52 for location of well.
96° 95° 94° 93° 92° 91 C 90°

I I

EXPLANATION

- - - - BOUNDARY OF STUDY AREA

SPRING

# FIRST ORDER SPRING Average 

discharge greater than or equal to 

100 cubic feel per second

37

35° U 0 20 40 60 MILES

I I I

I I I

0 20 40 60 KILOMETERS

a0000

2i i

ES 3

FIGURE 55. Selected springs of Ozark Plateaus province (Vineyard and Feder, 1974).
96° 95° 94° 93° 92° 91 C

39°

38°

37°

36°

35°

90° 89° 

EXPLA

10 LINE OF EQ

THE WA

is 5 inche

 - - BOUNDARY 

0 20 

I 

I I 

0 20 40 

FIGURE 56. Estimated recharge to water table. Modified from Dugan and Peckenpaugh (1986).
D90 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

made by Dugan and Peckenpaugh does not attempt 

to distinguish the recharge to the water table and 

the recharge to the deep aquifers.

Measurements of flow in perennial springs and 

streams when overland flow is minimal provide an 

estimate of the amount of ground-water discharged 

as base flow. Hedman and others (1987) investigated 

the low-flow characteristics of Ozark streams and 

springs to determine the distribution of ground-water 

discharge in small basins. Several types of surfacewater-flow records were available for their analysis. 

Flow-duration curves were developed for the 177 basins in the Ozark area where continuous-record 

springflow- and streamflow-gaging stations provided 

values of mean daily flow; low-flow frequency data 

also were derived for these basins. Partial-record 

springflow and streamflow data and miscellaneous 

measurements were analyzed for another 161 basins. 

The partial-record flow data were correlated graphically with discharge records at nearby continuousrecord stations to estimate flow at recurrence intervals that represent the low-flow at the partial-record 

stations. Seepage-run measurements were made to 

estimate flow at different recurrence intervals at ungaged sites within some of the gaged basins. A significant conclusion reached by Hedman and others 

(1987) is that mean annual water loss (the difference 

between annual precipitation and annual runoff) in 

the Ozark Plateaus is relatively constant at 29 to 30 

inches per year despite the large variation in annual 

precipitation (38 to 50 inches per year) across the 

Ozarks. This generally constant mean annual water 

loss probably is due to deep and extensive karst in 

the area. Exceptions to the constant mean occur in 

areas where a large amount of ground water moves 

between two or more surface-water drainage basins.

Although low-flow estimates were made by investigators for many small basins in the Ozarks, a large 

number of basins still are lacking such measurements. A statistical technique was developed by E.R. 

Hedman (U.S. Geological Survey, 1985, written commun.) to estimate the net ground-water discharge 

and recharge for the remaining basins. Hedman analyzed flow-duration curves to obtain a population of 

Ozark basins not having excessive ground-water 

gains or losses. He excluded those basins with unusually steep flow-duration curves (indicating a lack 

of regional base flow and loss of potential local base 

flow through the permeable karstic surficial aquifer) 

and those with flattened curves (indicating a regional 

base-flow component). Thus he identified a population of 100 basins that, he concluded, do not receive 

significant regional base flow and do not contribute 

to interbasin exchange of ground water, but are primarily characterized by local base flow. Low-flow frequency data from these basins were used to develop 

an empirical relation between combined overland 

runoff and local base flow (as defined by measured 

total runoff for the 100 basins) and precipitation for 

the Ozark Plateaus. Empirical linear, semilogarithmic, and logarithmic relations were also developed 

for several low-flow frequency characteristics such as 

recurrence data (7-day Q2» 7-day QIQ) and duration 

data (Q7o, QQQ, and QQQ). The linear mathematical relation using 7-day Q2 as tne low-flow characteristic 

had the highest correlation coefficient (0.75). The regression equation is shown below.

= 0.924 P-27.1, (1)

where

Q0 is annual overland runoff in inches,

Qlf is the annual local component of base flow in 

inches, and

P is annual precipitation in inches.

Precipitation is the only independent variable in 

the above equation; other basin parameters, such as 

slope, are not involved in the equation. This fact may 

not limit the use of the equation because precipitation is the dominant factor that causes variations in 

overland runoff and base flow in a basin, and because the topography and bedrock lithology of the basins are similar. The empirical equation may be used 

to estimate the combined overland runoff and local 

base flow for all basins in the study area. Estimates 

of net ground-water recharge or discharge in any 

Ozark basin having characteristics similar to those of 

the 100 reference basins can be made by comparing 

the measured total runoff of the basin to the empirically derived estimate of combined overland runoff 

and local base flow. A net ground-water discharge is 

indicated for basins where the measured total runoff 

is greater than the calculated overland flow plus 

local base flow (a component of regional base flow is 

present). A net ground-water recharge is indicated 

for basins where the measured total runoff is less 

than the calculated overland flow plus local base flow 

(potential base flow is lost through the permeable 

karst surficial aquifer).

MODEL SIMULATION OF PREDEVELOPMENT 

GROUND-WATER FLOW

A finite-difference digital model of ground-water 

flow in the Ozark Plateaus aquifer system was constructed and calibrated for steady-state, predevelopment conditions. The model was used to (1) study the
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D91

hydrologic budget of the aquifer system, (2) estimate 

the relative transmissive properties of the aquifers 

and confining units, and (3) evaluate concepts regarding boundary conditions imposed upon the simulated aquifer system. Specific yield and storage 

coefficient were not estimated because the model simulates steady-state conditions.

A three-dimensional modular ground-water flow 

model developed by McDonald and Harbaugh (1984) 

was used. The model contains 616 grid cells, each 

representing a volume of porous material in which 

the hydraulic properties are assumed to be constant. 

The cells are arranged in an evenly spaced rectangular array consisting of 22 rows by 28 columns (fig. 

57). The relatively large area represented by each 

grid cell (195.3 mi2) dictates that the model only simulates regional aspects of the ground-water flow system. Cells are inactive where an aquifer is missing or 

not present. Potentiometric heads are not simulated 

at the inactive nodes. The axes of the grid network 

are oriented approximately northwest and northeast; 

their alignment is the same as that of the model grid 

used to simulate ground-water flow in the regional 

model of the Central Midwest area. These axes 

roughly coincide with the prevailing directions of 

fracture systems and faults (fig. 9), an alignment 

that facilitates the consideration of anisotropic hydraulic conductivity in the model.

The three-dimensional model contains four active 

layers that represent the following: (1) the Western 

Interior Plains confining system, (2) the Springfield 

Plateau aquifer, (3) the Ozark aquifer, and (4) the 

St. Francois aquifer. Potentiometric heads were 

simulated only for the three aquifers that are part 

of the Ozark Plateaus aquifer system. The intervening confining units (Ozark and St. Francois) were 

not simulated as active layers; instead, the hydraulic properties of these two confining units were used 

to calculate vertical leakage coefficients between 

the aquifers. The leakage coefficients were used in 

the model to simulate the vertical flow between the 

aquifers.

Transient simulations were not made because no 

long-term change in head or flow has been documented. Currently (1987) there is little regional drawdown 

in the three aquifers. Cones of depression associated 

with municipal pumping tend to be localized because 

ground-water withdrawals in most of the aquifers are 

small compared with the available quantity of water. 

Also, large-capacity wells are not concentrated in any 

one area. In addition, many of the large-capacity 

wells pump water from unconfined parts of the aquifers where storage properties and nearby recharge 

inhibit the development of large cones of depression.

A transient simulation of the Ozark Plateaus aquifer 

system probably would yield little additional information concerning the hydraulic properties or hydrologic relations of the aquifers in the system.

Large drawdowns have occurred in the tristate 

lead-zinc mining district located in the vicinity of the 

Missouri-Kansas-Oklahoma borders. In this area, 

large-capacity pumps were used to dewater the 

Springfield Plateau aquifer for mining activities 

during the early part of this century. The mining 

pumping, combined with municipal pumping by cities, lowered water levels several hundred feet 

throughout the mining district and surrounding area. 

However, many of the mines have been closed since 

World War II, and water levels have recovered their 

predevelopment altitudes, except where municipal 

pumping, most notably in Ottawa County, Oklahoma 

(fig. 3), is continuing. There are few records of waterlevel measurements during the period of intense 

pumping before 1930, and even fewer records of 

pumping rates are available. Drawdown created by 

mining and municipal pumping in the tristate district, although by far the largest in the Ozark Plateaus, was nevertheless a local condition relative to 

water levels in the remainder of the Ozark Plateaus 

aquifer system. Because of the magnitude of pumping in the tristate mining district and the close proximity of the district to the western boundary of the 

Ozark Plateaus aquifer system, it is probable that 

the effect of the pumping extended into the adjacent 

Western Interior Plains aquifer system.

In the mid-1960's, farmers in a three-county area 

of Missouri north of the tristate mining district 

began to pump water for irrigation. The irrigation 

wells and nearby municipal-supply wells caused 

ground-water levels to decline as much as 80 feet in 

some parts of the area (Kleeschulte and others, 

1985). These wells, which are open to the confined 

part of the Springfield Plateau aquifer and Ozark aquifer, are adjacent to the salinewater-freshwater mixing zone. The effect of pumping from the irrigation 

wells probably also extends into the adjacent Western Interior Plains aquifer system.

BOUNDARY CONDITIONS ON LATERAL GROUND-WATER FLOW

Three types of boundary conditions were used in 

the model for simulation of ground-water flow in the 

Springfield Plateau aquifer, Ozark aquifer, and St. 

Francois aquifer. Each type was selected to best represent the ground-water flow conditions near the 

boundary of the aquifers. A brief description of these 

boundary conditions follows.
96°

39°

38°

37°

36°

35°

95° 94° 93° 92° 91 C 90°

&r

89° 

i 

EX

- - - - BOUN

..

r\ 

0 20 40 

FIGURE 57. Area represented by ground-water flow model of the Ozark Plateaus aquifer system, showing orientation and numbering of finit
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D93

No-flow boundary: This boundary condition does 

not allow water to move beyond the limit of active 

nodes in the modeled area. It is inherent in the design of the model that unless an alternate boundary 

condition is specified at an active node adjacent to 

the inactive nodes, a no-flow boundary will be 

present. The most obvious location where this boundary can be appropriately used is at the interface of 

an aquifer and an impermeable barrier. The boundary condition is probably most often used to delineate 

a boundary that coincides with a stable ground-water 

divide or the axis of a potentiometric trough.

Specified-head boundary: The specified-head boundary condition is perhaps the simplest and most convenient to use in the active area of the model. It 

consists of assigning a fixed potentiometric head at a 

model node. The movement of ground water to or 

from a specified-head node depends upon the relative 

altitude of the potentiometric head at the specifiedhead node and the potentiometric heads at adjacent 

active nodes. This boundary condition commonly is 

used to simulate water moving to and from rivers or 

to and from the water table. To properly use the 

boundary condition to simulate the effect of a river 

on the aquifer, good hydraulic connection between 

the river and aquifer is necessary; that is, the river 

stage must be nearly identical with the water level in 

the aquifer cut by the river. If this condition is not 

met, it may be more appropriate to consider the presence of a hydraulic impedance between the aquifer 

and the river. Specified heads may be used in the 

outcrop area of an aquifer instead of using a specified 

recharge rate; however, this procedure eliminates the 

possibility of deriving information about the aquifer's 

hydraulic parameters in the outcrop area.

Specified-flux boundary: The specified-flux boundary condition is similar to the specified-head boundary condition except that the quantity of water per 

unit area moving to or from a node is specified directly instead of being calculated from the hydraulic gradient between nodes. Thus, water is always entering 

or exiting the cell at a fixed rate. Specified-flux 

boundaries can be used where ground water must 

enter or leave the area of active model cells at a 

known rate, such as where a surficial aquifer is_,recharged by precipitation.

The boundary conditions for each model layer are 

different. Because the Western Interior Plains confining system (layer 1) is not part of the Ozark Plateaus 

aquifer system and is not well represented in the 

study area, layer 1 is treated as a passive layer that 

simulates the vertical movement of water between 

the Ozark Plateaus aquifer system and land surface. 

Potentiometric heads are not simulated for layer 1.

The alternative would be to simulate layer 1 as an 

active layer, which would require estimates of specified flow or specified hydraulic gradient along the 

western and southern model boundary, and estimates 

of lateral hydraulic conductivity.

Model nodes that represent the Western Interior 

Plains confining system are assigned specified heads 

equal to the average hydraulic head of the weathered 

zone within each grid cell; they are designated by the 

letter "S" in figure 58. Local geohydrologic units, 

which are stratigraphically equivalent to the Western 

Interior Plains confining system and are located in 

the north-central part of the Salem Plateau, are not 

simulated because the units are small and consist of 

many isolated pieces rather than a single continuous 

unit. Local units along the eastern boundary of the 

modeled area are also represented by specified-head 

CS") cells (fig. 58).

The area where the Springfield Plateau aquifer 

crops out (fig. 12) is simulated in layer 2 by specifiedflux recharge cells ("O" in figure 59). Specified heads 

("S" in fig. 59) are assigned to cells in three areas: (1) 

where the Missouri River deeply incises the Springfield Plateau aquifer at the northern edge of the 

modeled area, (2) where the Mississippi River cuts 

into rocks stratigraphically equivalent to the aquifer 

near the northeastern boundary of the Ozarks, and 

(3) along the Neosho River in Oklahoma (fig. 6).

The boundary between the Springfield Plateau aquifer and the stratigraphically equivalent upper unit 

of the Western Interior Plains aquifer system west of 

the Ozarks is modeled as a no-flow boundary. In 

Arkansas, the Arkansas River alluvial valley is 

simulated as a no-flow boundary. The alluvial valley 

coincides with a major ground-water valley that separates ground-water flow in the Ozark area from flow 

originating south of the river.

A special condition is simulated where cells in 

layer 2 represent the part of the study area that is 

located within the Mississippi Alluvial Plain. In this 

area, the Springfield Plateau aquifer is not present, 

and the specified-head nodes in layer 2 represent the 

potentiometric heads in Cretaceous sand that overlies the Ozark aquifer. Because the Ozark confining 

unit is not present in this area, the vertical hydraulic 

gradient between layer 2 (Cretaceous sand) and layer 

3 (Ozark aquifer) and leakage coefficients for the respective layers determine the rate at which ground 

water discharges upward from the Ozark Plateaus 

aquifer system. These cells are marked "P" in figure 

59.

The large outcrop area of the Ozark aquifer (fig. 

12) is modeled in layer 3 by specified-flux recharge 

cells, designated "O" in figure 60. Along the northern
96° 95° 94° 93° 92° 91 C 90° 89° 

E

20 

I 

I I 

0 20 40 

FIGURE 58. Model representation of the Western Interior Plains confining system (layer 1).
96° 95° 94° 93° 92

MISSISSIPPI ALLUVIA

I I 

0 20 40 

37°

36°

35° -

FIGURE 59. Model representation of the Springfield Plateau aquifer and post-Paleozoic sediments (layer 2).
96° 95° 94° 93° 92° 91° 90° 89° _

A

U

S

R

0 20 

I T 

0 20 40 

FIGURE 60. Model representation of the Ozark aquifer (layer 3).
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D97

and eastern edge of the Salem Plateau where the 

Missouri and Mississippi River floodplains contact 

the aquifer, specified-head boundary cells ("S" in fig. 

60) are assigned head values equal to the average 

stage of the rivers. A previous ground-water flow 

model for Cambrian and Ordovician rocks (equivalent 

to the Ozark aquifer) north of the Missouri River 

(Imes, 1985) showed that there was no advantage to 

simulating the interaction between the river and the 

aquifer using a streambed leakage coefficient and 

head differences between the river and aquifer. Two 

cells that represent part of the Osage River (fig. 6) 

are specified-head cells ("S" in fig. 60).

The salinewater-freshwater mixing zone in the 

west and southwest and part of the modeled boundary that parallels the Mississippi River to the east 

are treated as no-flow boundaries. Although some salinewater flows into the study area beneath the Marais des Cygnes, Osage, and South Grand Rivers, the 

quantity is believed to be small.

At the southern limit of the modeled area a no-flow 

boundary has been used to represent the trough in 

the potentiometric surface associated with the Arkansas River valley. A no-flow boundary has been 

placed along the southeast boundary of layer 3 at the 

approximate limit of freshwater in the Ozark aquifer.

The four cells that represent the outcrop area of 

the St. Francois aquifer (fig. 12) are represented in 

layer 4 by specified-flux recharge cells ("O" in fig. 61). 

These four cells also include outcrops of the Basement confining unit. At these locations the Basement 

confining unit is fractured and allows some lateral 

flow into the adjacent St. Francois aquifer. Thus, for 

modeling purposes the four cells contain permeable 

rock and receive recharge. Lateral boundary conditions in the lowermost St. Francois aquifer are difficult to determine because few data are available 

beyond the outcrop area. Because the Missouri and 

Mississippi River flood plains are believed to be discharge areas for water in the St. Francois aquifer, 

no-flow boundaries are placed along or in the vicinity 

of the Missouri and Mississippi Rivers (fig. 61). The 

limit of freshwater flow to the west in the St. Francois aquifer is assumed to coincide with that of the 

Ozark aquifer, and a no-flow boundary is assigned 

along the transition zone and the associated regional 

topographic low. In the south, for lack of data to 

prove otherwise, a no-flow boundary is assigned to 

the St. Francois aquifer at the same cells that are 

assigned as no-flow cells representing the Ozark aquifer (layer 3). Freshwater in the St. Francois aquifer 

probably discharges as it passes beneath the Ozark 

Escarpment and enters the Mississippi Embayment. 

A similar situation occurs along the eastern boundary where eastward-flowing ground water in the St. 

Francois aquifer discharges through overlying geohydrologic units into the Mississippi River valley. 

Therefore, no-flow boundaries for the St. Francois aquifer are appropriate along the southeastern and 

eastern boundary of the study area.

BOUNDARY CONDITIONS AND LEAKAGE COEFFICIENTS 

GOVERNING VERTICAL GROUND-WATER FLOW

The Basement confining unit is assigned a zero 

permeability at all nodes except the four cells that 

represent the St. Francois Mountains area; in these 

cells some water movement is allowed into the adjacent St. Francois aquifer. The Basement confining 

unit is treated as an impermeable barrier to the 

downward movement of water out of the Ozark Plateaus aquifer system. Ground-water movement 

through the Ozark and St. Francois confining units 

is assumed to be vertical. Neuman and Witherspoon 

(1969, p. 127) showed that where the hydraulic conductivity of a confining unit is considerably less 

than that of the adjacent aquifers, the direction of 

ground-water flow through the confining unit is 

nearly vertical and the rate of flow is proportional 

to the hydraulic gradient across the unit. This condition allows the use of a simplified flow equation to 

describe the volumetric leakage rate (Qi) through 

the confining unit:

QL = (K'/b) A (AH) when K'«K1 and K2, (2)

where

QL is the flow rate (in units of length cubed divided by time, or L3!^1),

K' is the vertical hydraulic conductivity (LT"1), 

b is the confining unit thickness (L), 

A is the cross-sectional area of flow (L2) or cell

area, 

AH is the difference in hydraulic head across the

confining unit (L), and

KI, K<2 are the hydraulic conductivities of the aquifers overlying and underlying the confining unit (LT"1 ).

The hydrologic properties of the confining unit that 

determine the rate at which water leaks through the 

unit are expressed in the leakage coefficient (L), 

where L = K'lb. The vertical hydraulic conductivity 

(K') is a function of several factors, including the 

presence of shale (usually a slightly permeable material), the rock's primary permeability, the presence of 

fractures, and postdepositional solution-enhanced 

permeability.
36'

35° -

96° 95° 94° 93° 92°

9V

90°

89° __

AC

UN

RE

\ \

0 20 40 

. Model representation of the St. Francois aquifer (layer 4).
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D99

For this model, the effective leakage coefficient governing vertical flow between the centerlines of adjacent aquifers is calculated by the following equation:

d/K=dl/2Kl+d7K+d2/2K2, (3)

where

d/K is the effective inverse leakage coefficient between midpoints of the upper and lower 

aquifer (T),

di, d'y d2 are the thicknesses of the upper aquifer, 

confining unit, and lower aquifer, respectively (L), and

KI, K', K% are the vertical hydraulic conductivites 

of the upper aquifer, confining unit, and 

lower aquifer, respectively (LT"1). 

A somewhat different situation exists between the 

uppermost two active model layers, those representing the Springfield Plateau aquifer and Western Interior Plains confining unit. There is no confining unit 

between the two layers. However, ground-water flow 

between water table in the near-surface weathered 

zone of the Western Interior Plains confining system 

and the underlying Springfield Plateau aquifer is impeded by the large quantity of slightly permeable 

material in the Western Interior Plains confining system. Therefore, a modified form of equation 3 was 

used to determine vertical leakage coefficients between the Western Interior Plains confining system 

and the Springfield Plateau aquifer:

d/K=dl/Kl+d2/2K2, (4)

where

d/K is the effective inverse leakage coefficient (T), 

di, d2 are the thicknesses of the Western Interior 

Plains confining system and the Springfield 

Plateau aquifer, respectively (L), and 

KI, K2 are the vertical hydraulic conductivites of 

the Western Interior Plains confining system 

and the Springfield Plateau aquifer, respectively (LT-1).

Because almost the entire thickness of the Western 

Interior Plains confining system is effective in impeding the flow of ground water, the total thickness of 

the confining system is used in equation 4.

BOUNDARY CONDITIONS ASSOCIATED WITH RECHARGE AND 

DISCHARGE OF GROUND WATER

Two physical processes pertaining to the interaction of ground water and surface water are important 

to the construction of the ground-water flow model 

for the Ozark Plateaus aquifer system: (1) infiltration

of precipitation to the water table and (2) loss or gain 

of water from and to streams due to ground-water 

discharge or recharge. Because of the complexity of 

near-surface hydrologic processes in the Ozarks and 

the regional aspect of the ground-water flow model, it 

is not correct to simply assign a fraction of the mean 

annual precipitation as recharge to the water table 

during model calibration. A large fraction of the infiltrated precipitation never enters the deeper, regional 

ground-water flow system, but moves rapidly through 

surficial aquifer material and discharges into 

streams within the same model cell the precipitation 

first entered.

A technique commonly used to simulate the loss (or 

gain) of ground water through leaky streambeds is to 

(1) specify combined geometric properties (stream 

length, average width, and streambed thickness) and 

hydraulic properties (average stream stage and 

streambed vertical hydraulic conductivity) for 

streams in a model cell as if they were a single 

stream and (2) calculate the quantity of water per 

unit time exchanged between the streams and aquifer (Q) by the following equation.

(5)

where

K' is the streambed vertical hydraulic conductivity 

(LT-1),

m is the streambed thickness (L),

w is the average stream width (L),

/ is the stream length (L),

#st is the average stream stage (L), and

Haq is the simulated hydraulic head in the aquifer 

cut by the stream (L).

It is not feasible to use this technique in this model 

of ground-water flow in the Ozark Plateaus aquifer 

system for several reasons. Stream stage and the actual potentiometric head of the aquifer can vary by 

hundreds of feet within a model-cell area. Streambed 

vertical hydraulic conductivity, thickness, and width 

can seldom be estimated to any degree of accuracy. 

There may be several large streams within one 

model cell with properties that cannot be combined 

as if they were a single stream. Also, the method assumes all flow is vertical through the streambed, an 

assumption that generally is not valid. Because of 

the many uncertainties, the commonly used method 

does not result in a well-defined simulation.

Because the Ozark Plateaus aquifer system flow 

model is a regional model and each model cell is 

large (195.3 mi2), it is essential to determine the 

large quantity of ground water that cannot be accounted for by model simulation because it enters
D100 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

and exits the surficial aquifer within a single model 

cell. An alternative simulation method was developed 

to account for this ground water.

Consider a model cell that may contain one or 

more hydrologic features, such as ground-water divides, ephemeral or intermittent stream reaches, continuous stream reaches, losing stream reaches, 

springs, and spring catchment areas. In general, 

ground-water divides are parallel to surface-water divides with the possible exception of those divides in 

cells that contain losing streams, springs, and spring 

catchment areas. By observation of topography and 

surface-water drainage basins within each model cell, 

and with knowledge of the locations of losing stream 

reaches (from seepage run data) and spring catchment areas (from dye-trace analyses), it is possible to 

partition the total cell area (Ac) into two fractions 

(fig. 62). One fraction (Ai/Ac) represents that part of 

the cell area in which precipitation that infiltrates to 

the water table appears (on the basis of analysis of 

two-dimensional potentiometric maps and topography) to flow to sinks (rivers, streams, or springs) 

within the same cell without crossing a cell boundary 

(intracell flow). It is important to note that some of 

the infiltrated precipitation (recharge) to area A. is 

likely to flow across a cell boundary, especially a subjacent boundary, to sinks in other model cells. This 

possibility is shown by dashed flow lines in figure 63 

(see cell i, j+1), a diagram of ground-water flow paths 

and their relation to model-cell boundaries. A second 

fraction (A(/AC) represents that part of the cell area 

in which all the precipitation that infiltrates to the 

water table flows across a cell boundary to sinks in 

other model cells (intercell flow).

Intracell flow can be expressed as

M(Ai/Ac)Fu (6)

where F^A^, and fu is the specific recharge flux 

(LT"1) to the water table for the cell area. M is defined as a ratio of (a) the recharge to area Aj that 

discharges to sinks within the cell before crossing the 

cell boundary to (b) the total recharge to area Ar The 

factor M is not explicitly calculated, but is a model 

parameter determined during model calibration. Because most of the water that infiltrates to the water 

table in the vicinity of a gaining stream remains in 

the upper part of the surficial aquifer and discharges 

into the nearby stream, M generally is less than but 

nearly equal to 1.0 for large-cell models that simulate flow in thick surficial aquifers. It typically varies 

from about 0.7 to 1.0 and expresses a relation between the volume of aquifer material represented by 

the model cell and the flow paths in the aquifer system. Generally, as the thickness of the represented 

aquifer decreases, the relative penetration depths of 

streams in the cell increase and the value of M decreases. The decrease in M implies that more water 

flows into the subjacent cell. Although values of M 

may vary from one cell to another as the hydraulic 

properties of the aquifer vary, it is assumed that the 

variation is small and a single value of M is appropriate for the entire modeled area.

Intercell flow has two components. The first component, recharge to area A± that flows across a cell 

boundary (fig. 63), is generally small and can be expressed as

(l-M)(Ai/Ac)Fu. (7)

The second component, flow originating in area A0 

(fig. 63), can be expressed as

(8)

The relative areas, Aj and A0, were determined on 

a cell-by-cell basis using information on hydrologic 

and topographic features in each cell. Where seepage 

run measurements under low-flow conditions were 

not available to identify where streams change from 

ephemeral or intermittent to perennial flow, the flow 

conditions indicated by published hydrologic maps 

were used. The regional distribution of specific recharge flux (fu) to the water table under predevelopment conditions was estimated from preagricultural 

ground-water recharge rates determined by Dugan 

and Peckenpaugh (1986).

The above discussion of intracell and intercell flow 

accounts for discharge to streams in a cell that originates as recharge within the cell. Now consider 

water that flows across cell boundaries and enters or 

leaves a cell through streambeds. This flow of water 

is designated Fs in figure 63. Surface water can enter 

the aquifer system by percolation through the streambed of an ephemeral, intermittent, or losing 

stream (fig. 63, cell (i, j)). Ground water can discharge 

from the aquifer system by upward leakage through 

the streambed of a continuous, or gaining, stream 

(fig. 63, cell (i, j+1)). It was assumed during this 

study that intermittent streams generally recharge 

the underlying aquifers. They only receive groundwater discharge during relatively brief periods of 

higher water-table conditions.

If a cell contains only or mostly losing streams and 

the aquifer receives recharge from the streams, the 

sign of Fs is positive. If a cell contains one or more 

gaining streams and the aquifer discharges a net 

flow to the streams, the sign of Fs is negative. Only
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D101

discharge that flows from an adjacent or subjacent 

cell is symbolized by Fs. The net recharge and discharge at each cell that contributes to or results from 

intercellular flow (Fnc) is calculated by the following 

equation:

Fnc = (A0/AC)FU+(1-M) (Ai/Ac)Fu+Fs. (9)

Note that on a regional upland area of a permeable 

aquifer one would expect to find predominantly intermittent streams. In this case, Fs will generally be

small and positive (the aquifer will be recharged by 

the stream), Aj will be nearly zero, and A0 will approach 1. Thus, Fnc«Fu, and cells representing this 

area will receive a large recharge flux. On the other 

hand, one would expect to find predominantly gaining streams in the regional lowlands. In this case, Fs 

will be negative (the aquifer will discharge to 

streams), A0 will approach zero, and Aj will approach 

1. Thus, Fncm-M)Fu-IFs l, and because (1-M) generally is small, there will be a net loss (discharge) 

from the cell.

j-1

A U"'A \V

EXPLANATION

AREAS OF TYPE AO All recharge to water table crosses a cell 

boundary and flows to sinks in adjacent cells

AREAS OF TYPE Ai Most recharge to water table does not cross 

a cell boundary and flows to sinks within the same cell

LOSING STREAM SEGMENT 

INTERMITTENT OR EPHEMERAL STREAM 

KARST CONDUIT 

MODEL CELL INDEX 

SPRING

 BOUNDARY OF MAJOR SURFACE-WATER SYSTEM = + .

- - BOUNDARY OF SURFACE-WATER SUBBASIN p

 CONTINUOUS STREAM 

FIGURE 62. Plan view of hypothetical model cells showing areas of intracell and intercell ground-water flow.
D102 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

To estimate the quantity of Fs for small surfacewater basins in the Ozark area, we used the relation 

derived by Hedman (written commun., 1985) and 

presented in the section titled "Interaction of Surface 

and Ground Water: Recharge to the Regional 

Ground-Water Flow System." The following equations, which relate overland flow and local base flow 

(Qo+Qlf) to precipitation, were used in conjunction 

with measured total runoff (Qt) to estimate the regional component of base flow (Qrf) in small basins in 

the Ozark area:

Qrf=Qt-(Qo+Qif) do)

=Qt-(0.924P-27.1)(2.64xl(r9)Ab, (11)

where 

Qjf is the regional component of base flow in the

basin in cubic feet per second (L^T"1), 

Qt is the total runoff for the basin in cubic feet per

second (L3^1), 

Q0 is the overland flow component of total runoff in

the basin in cubic feet per second (L3T-1),

A-t

 D T3

/ / / /

Sign 

convention

Flux 

out of 

aquifer

Flux 

into 

aquifer

/ / /////.

/ / I I I I / I

' ' I I I I i I

/ / I I I I I

/ 

/ 

/ 

/ 

I 

1111,1

I I I i I 

/ / / I I ,' ./

,/ ,/ I/ " * *

i \ v

/ i \

/ i N

/ i

EXPLANATION

GENERALIZED GROUND-WATER FLOW DIRECTION Dashed for ground 

water that has exited cell in which it first entered water table

\ r» 

<^

k+1

MAGNITUDE AND DIRECTION OF FLOW COMPONENT (SEE 

DISCUSSION IN TEXT)

(i, j+1 ) INDICES OF MODEL CELL

VERTICAL INDEX CORRESPONDING TO MODEL LAYER

FIGURE 63. Cross section of two hypothetical model cells showing 

recharge contributions to ground-water flow within model cells 

and between model cells. Ac, area of model cell; Aj, area of cell 

in which precipitation entering water table appears to flow to 

sinks in same cell; A0, area of cell in which precipitation entering water table flows across cell boundary to sinks in other model cells; F8, water that flows across cell boundaries and enters or 

leaves a cell through streambeds; Fu, recharge to water table; M, 

recharge to area Aj that discharges to sinks within the cell divided by total recharge to area Aj.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D103

Qlf is the local component of base flow in the basin

in cubic feet per second (L3T~1), 

P is precipitation in inches per year (LT"1), and 

A],, is the basin area in feet squared (L2), and 

2.64xlO~9 is a conversion factor from inches 

per year to feet per second.

The above regression equation (equation 11) is approximately valid for all basins in the Ozark area. 

However, several small basins in the area, located 

primarily along the Missouri and Mississippi Rivers, 

have no measurements of total runoff. For these ungaged basins, the total runoff was estimated by a 

separate regression equation that relates total runoff 

to precipitation and was developed from gaged basins 

in the Ozark area (Hedman and others, 1987). The 

equation is

Qt = (P-29.5)(2.64xl(T9)Ab. (12)

The values of Q^ for these ungaged basins can be 

estimated from equation 11 by substituting the value 

of Qt from equation 12 into equation 11. Regional base 

flow estimated from equation 11 is assumed to be 

equivalent or nearly equivalent to the values of Fs. 

This assumption probably is valid for cells containing 

losing streams as well as those containing gaining 

streams, because equation 11 is a regional estimator 

of the combined flows. A deficiency in the estimated 

regional base flow indicates a regional ground-water 

flow into underlying aquifers in a basin, and an excess 

in the estimated regional base flow indicates a regional ground-water flow discharging from underlying aquifers into streams within a basin.

The net gain or loss of regional base flow in each 

basin was distributed to model cells in such a manner that a greater part of these gains or losses was 

assigned to the cells containing larger streams. 

Model cells containing streams were assigned one of 

three weighting codes (A, B, or C) that were determined on the basis of relative stream sizes (fig. 64). 

Cells containing the largest streams were coded A, 

cells containing intermediate-size streams were coded 

B, and cells containing the smallest streams were 

coded C. The distribution of estimated regional base 

flow (Qrf) into each cell containing streams is determined by the following approach. For basins where 

cells contain the same weighting code (A, B, or C), 

100 percent of the estimated regional base flow is 

distributed among the coded cells according to the 

following equation:

where q^ (ij) is the estimated regional base flow for 

coded celli, j; a^- is the area of alluvial material along 

stream reaches or flood plains in the cell; and A is 

the total area of alluvial material in all the coded 

cells. If two different weighting codes are assigned in 

a basin, then 75 percent of the regional base flow 

(Qrf) is distributed into coded cells containing the 

larger streams and 25 percent into coded cells containing the smaller streams. If three different 

weighting codes are assigned in a basin, the distribution is made using 60 percent, 30 percent, and 10 

percent of the regional base flow into coded cells containing the largest streams, intermediate streams, 

and smallest streams, respectively. This method of 

distributing recharge and discharge in each basin is 

logical, but should be considered an approximation of 

the actual distribution.

MODEL CALIBRATION

The steady-state ground-water flow model was calibrated to the predevelopment potentiometric surface of each of the three aquifers represented by 

model layers 2, 3, and 4. Model calibration is a process whereby the difference between simulated hydraulic heads and flow volumes and measured 

hydraulic heads and flow volumes is minimized by 

adjusting and refining model variables that estimate 

hydraulic properties of the simulated flow system. A 

calibrated model may verify the accuracy of the conceptual model or indicate where the conceptual 

model does not adequately portray the actual flow 

system. Because of the large area of each model cell, 

hydraulic heads vary considerably within each cell, 

especially in areas where the aquifers crop out. 

Therefore, a measurement of head in a single well 

usually does not represent the average water level 

in the cell. For calibration, the average head for 

each model cell was estimated from predevelopment 

potentiometric-surface maps for each aquifer (Imes, 

1990b, 1990d, 1990f). The maps generally contain 

considerable detail within the area represented by a 

cell. To obtain a representative head for each cell, 

the contour maps were digitized at the corners, center, and face centers of each cell, and the nine values were then averaged arithmetically.

The accuracy of the simulations was monitored 

during the calibration process by computing the 

average squared difference (error) between simulated potentiometric heads and averaged potentiometric heads obtained from the potentiometricsurface maps. The best simulations resulted in the 

smallest values of the average squared difference.
D104 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

EXPLANATION

A CELLS CONTAINING LARGE STREAMS H 

g CELLS CONTAINING INTERMEDIATE-SIZE STREAMS 

Q CELLS CONTAINING SMALL PERENNIAL STREAMS 

LARGE STREAMS 

INTERMEDIATE-SIZE STREAMS 

SMALL PERENNIAL STREAMS 

INTERMITTENT OR EPHEMERAL STREAMS 

SURFACE-WATER DRAINAGE BASIN BOUNDARY

j + 1 MODEL CELL INDEX

FIGURE 64. Method of distributing regional base flow to model cells.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D105

The average positive difference and average negative difference between simulated and averaged 

potentiometric heads also were monitored to reduce the potential of a large bias in the head differences (that is, to ensure that the simulated 

heads were scattered fairly uniformly about the 

average heads). The accuracy of the simulation in 

a single layer can be improved slightly as hydrologic variables are changed, but sometimes improvement in one layer comes at the expense of 

accuracy of the simulation in other layers. It is 

not possible to closely calibrate simulated heads 

for all layers over the entire modeled area because 

averaged potentiometric-head data are not available for many cells. Head data for layer 2 (Springfield Plateau aquifer and post-Paleozoic sediments) 

are generally not available for northern Arkansas. 

More head data are available for layer 3 (Ozark 

aquifer) than for any other layer, but there are no 

data for parts of this layer south of the Boston 

Mountains. Sufficient data are available for layer 

4 (St. Francois aquifer) to determine the representative water levels only in the immediate vicinity 

of the St. Francois Mountains.

Layer 2 was calibrated to the heads at 161 of 191 

total active nodes. The average squared difference 

(error) between simulated and averaged heads is 

1,590 feet squared (fig. 65), and the average absolute 

error is 27 feet. Specified-head nodes were placed at 

three locations (row 9, columns 5, 6, and 7) to more 

accurately simulate water levels in extreme southwestern Missouri and northeastern Oklahoma (fig. 

59). The nodes are assigned water levels that approximate the stage of the Neosho River immediately 

downstream of the river's confluence with the Spring 

River (fig. 6); this reach includes a large reservoir, 

the Lake of the Cherokees. The specified-head nodes 

were considered because, in the initial simulations, 

not enough water discharged from the Springfield 

Plateau aquifer to the stream. Without the three 

specified-head boundary nodes, the net ground-water 

discharge to the stream at the nodes is 19 cubic feet 

per second; whereas with the specified heads present, 

the net discharge of ground water is 406 cubic feet 

per second.

A total of 286 nodes of a possible 380 active 

nodes were used to calibrate layer 3. The average 

squared error of the simulated heads for layer 3 is 

3,033 feet squared, somewhat greater than that for 

layer 2. The average absolute error is 41 feet. Specified-head nodes were added at two locations (row 

7, columns 17 and 18) in layer 3 (fig. 60). The 

nodes represent water levels in an extremely convoluted section of the Lake of the Ozarks (fig. 6) in

the northwestern part of the study area. The effect 

of the specified-head nodes is to increase the 

amount of ground water discharging from the aquifer from 16 to 357 cubic feet per second and to generally reduce heads in the aquifer in the vicinity of 

the lake. The greatest errors in simulated heads for 

layer 3 are associated with cells (near row 12, column 11) that represent Table Rock Lake in southwestern Missouri (fig. 6). Simulated heads in the 

aquifer at five nodes near the lake are about 90 to 

130 feet greater than the averaged heads. Specifiedhead nodes were not used to simulate Table Rock 

Lake, even though tests of the effect of placing a 

single specified-head node at row 12, column 11, 

showed considerable improvement to three simulated heads in layer 3 in the immediate vicinity of the 

lake. This specified-head node was not used because 

it increased the error in simulated heads in layer 2 

to the north of the lake. No combination of hydraulic properties was satisfactory in minimizing the errors in both layer 2 and layer 3, although in 

general the simulations with the specified head 

were not greatly inferior to those without it.

The use of specified-head nodes to improve the 

quality of the simulation generally is not desirable. 

The three locations (one in layer 2 and two in layer 

3) in which the simulated heads can be improved by 

the introduction of a few specified heads are all associated with large bodies of surface water. In each 

case, the effect of the specified heads is to simulate 

more ground water discharge from the aquifers to 

the streams than was simulated using estimated recharge to the water table. Recharge estimates yielded unrealistically low discharge values because the 

measurements on which the recharge estimates 

were based (mean annual runoff and stream baseflow measurements for the basins containing the 

large surface-water bodies) were obtained after the 

rivers were regulated. Regulation apparently has affected ground-water flow. For example, the estimated regional base flow for the White River 

downstream of Table Rock Lake (fig. 6) suggests 

that large quantities of ground water are discharging to the White River from the underlying aquifers, 

whereas the estimated flow at the lake suggests 

that the aquifer is being recharged in that area. Referring to the computation of mean annual runoff 

for the drainage basins, Hedman and others (1987) 

state, "For basins with major reservoirs, a common 

period of record was used. For basins with recently 

constructed reservoirs, the record before construction was used. For basins with old reservoirs, the 

period of record after regulation began was used, 

and adjustments were made for evaporation from
D106 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

the reservoirs." The three large surface-water bodies 

mentioned here (Lake of the Cherokees, Lake of the 

Ozarks, and Table Rock Lake) are older reservoirs. 

Consequently, the estimates of regional base flow

probably are too small and are not indicative of the 

predevelopment conditions simulated by the model.

Simulated heads for layer 4 were calibrated at only 

21 nodes out of 379 active nodes of the layer. The

CALIBRATION

RECHARGE FACTOR (M)

CHANGED FROM 88 TO

87 PERCENT

KI (VERTICAL)

INCREASED BY

50 PERCENT

Kz (LATERAL)

INCREASED BY

50 PERCENT

K2 (VERTICAL)

INCREASED BY

400 PERCENT

K3 (LATERAL)

INCREASED BY

20 PERCENT

K3 (VERTICAL)

INCREASED BY

400 PERCENT

K4 (LATERAL)

INCREASED BY

50 PERCENT

K4 (VERTICAL)

INCREASED BY

400 PERCENT

L2.3 INCREASED 

BY 50 PERCENT

la-4 INCREASED 

BY 50 PERCENT

EXPLANATION

LAYER 2 (SPRINGFIELD PLATEAU AQUIFER 

AND POST-PALEOZOIC SEDIMENTS)

LAYER 3 (OZARK AQUIFER) 

HYDRAULIC CONDUCTIVITY 

LEAKAGE COEFFICIENT 

Note: Subscripts refer to model layer

1000 2000 3000 4000

AVERAGE SQUARED DIFFERENCE (ERROR) BETWEEN AVERAGE 

FIELD HEADS AND SIMULATED HEADS, IN FEET SQUARED

FIGURE 65. Sensitivity of model layers 2 and 3 to selected changes in hydraulic properties. Dashed vertical lines mark values of errors 

for layers 2 and 3 generated during calibration of model; they are included to help readers compare those errors to errors produced 

by changing selected variables.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D107

average squared error, 12,760 feet squared, is the 

largest of the three simulated layers. The average 

absolute error between simulated and averaged 

heads, 84 feet, also is large. Differences in simulated 

and averaged heads for layer 4 have a positive bias. 

Because the aquifers represented by model layers 3 

and 4 are both thin and hydrologically are closely 

linked near the St. Francois Mountains (in the area 

represented by the 21 calibration nodes), attempts to 

reduce the bias without adversely affecting simulated 

heads in layer 3 failed. Some of the difficulty in calibrating layer 4 may result from small springs that 

discharge at many locations near the southwest edge 

of the mountains.

The model generally is less sensitive to variables 

that control vertical leakage rates than to variables 

that control lateral flow, with the exception of the 

vertical hydraulic conductivity (K{), which controls 

the movement of ground water from layer 1 to layer 

2. Small changes in the average squared errors for 

layers 2 and 3 occur when the ratios of lateral to vertical hydraulic conductivity for either layer are 

changed from 10 to 50 (a 400-percent increase). Thus 

the model is relatively insensitive to the ratio of lateral to vertical hydraulic conductivity of layers that 

represent the major aquifers. The model also is relatively insensitive to changes in the leakage coefficient 

arrays that represent the impedance of ground-water 

flow between layers 2 and 3 and between layers 3 

and 4 by the intervening confining units (fig. 65). The 

model is slightly more sensitive to the leakage coefficients that link layers 2 and 3 than to the leakage 

coefficients that link layers 3 and 4.

The model is most sensitive to changes in the vertical hydraulic conductivity of layer 1, the lateral hydraulic conductivity of layer 3, and recharge to cells 

representing outcrop areas (fig. 65). Because the 

model is steady-state and layer 3 crops out in most of 

the model area, the lateral hydraulic conductivity of 

layer 3 and the recharge factor (M) are not independent variables. Thus, the model is equally sensitive to 

each of these two variables. Decreasing the recharge 

factor from the calibration value of 88 percent to 87 

percent reduces the average squared difference for 

layer 2 from 1,590 to 1,481 feet squared, but it increases the average squared difference for layer 3 

from 3,033 to 3,861 feet squared. The large increase in 

error for layer 3 suggests that the simulated heads in 

layer 3 are relatively sensitive to the recharge factor.

The effect of redistributing the recharge to the 

water table, as estimated by Dugan and Peckenpaugh 

(1986), to account for intracell flow is shown in figure 

66. Before redistribution, the recharge to water table 

at each cell ranges from less than about 100 cubic feet

per second in the northwest to more than 220 cubic 

feet per second in the southeast and reflects the effect 

of increasing precipitation to the southeast in the 

study area. After redistribution, the effective recharge 

per cell (the part that crosses cell boundaries) ranges 

from 12 to 100 percent of the estimated recharge to 

the water table. The distribution pattern is very complex as is shown in figure 66. Areas of greater recharge per cell roughly correspond to areas of greater 

elevation in the Ozark area. The two areas of greater 

recharge in south-central Missouri (Dent and Howell 

Counties, fig. 3) correspond to catchment areas of two 

first-order springs (average discharge greater than 

100 ft3/s; fig. 55). It was noted that a significant simulation error would result from using a uniformly reduced (scaled) estimated recharge as opposed to using 

the redistributed recharge.

MAGNITUDE AND DISTRIBUTION OF HYDRAULIC PROPERTIES 

DETERMINED BY MODEL SIMULATIONS

The hydraulic conductivities and transmissivities 

determined by the calibrated model are regional values. The actual values may vary greatly over short 

distances within the aquifer. Because layer 1 (representing the Western Interior Plains confining system) 

is not part of the Ozarks Plateaus aquifer system, 

layer 1 was modeled as a specified-head layer. Therefore, no information on lateral hydraulic conductivity 

of the layer is derived from the model. The vertical 

hydraulic conductivity of the layer, however, is an important model variable that controls the amount of 

water flowing downward to the Ozark Plateaus aquifer system through the overlying Western Interior 

Plains confining system. The model distribution of 

vertical hydraulic conductivity for layer 1 (Western 

Interior Plains confining system) is shown in figure 

67. Only two values (1.0xlO~7 and 2.0xlO~8 fVs) are 

assigned to the nodes. The larger values are assigned 

to areas where the Western Interior Plains confining 

system is thinner and contains a larger fraction of 

more permeable sandstone and limestone. The leakage coefficient of layer 1 generally decreases to the 

west and south where the confining system becomes 

thicker (fig. 67).

The lateral hydraulic conductivity of nodes in layer 

2, representing the Springfield Plateau aquifer, is constant at 0.00025 foot per second (fig. 68), and the ratio 

of lateral to vertical hydraulic conductivity for the aquifer is 10. It is probable that the actual hydraulic 

conductivity in the Arkansas River Valley, where the 

aquifer is deeply buried, is less than the value derived 

from simulation. Because no field head data can be
96° 95° 94° 93° 92° 91 ' 90° 89°

EXPLANATION

 --- BOUNDARY OF STUDY 

AREA

 200 LINE OF EQUAL ESTIMATED RECHARGE TO 

WATER TABLE 

Estimated by Dugan and 

Peckenpaugh (1986). Interval, in cubic feet per second 

per cell, is variable

 25 LINE OF EQUAL REDIS- _ 

TRIBUTED 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

Less than 25 cubic feet per 

second per cell25 to 50 cubic feet per second per cell50 to 100 cubic feet per 

second per cell

Greater than 100 cubic feet 

per second per cell

36'

35° - 0 20 40 60 MILES

I II I I rn r

0 20 40 60 KILOMETERS

o

00

to

FIGURE 66. Recharge to water table as estimated by Dugan and Peckenpaugh (1986) and redistributed recharge to account for ground water that remains internal to a model

cell.
96° 95 92° 91 C 90° 89°

39°

38°37°

36°

35C

J

88°

EXPLANATION

AREA WHERE MODEL LAYER I 

IS INACTIVE

ZONE OF EQUAL VERTICAL 

HYDRAULIC CONDUCTIVITY

2.0 x 10"8 foot per second 

1.0 x 10"7 foot per second

1 X W11 LINE OF EQUAL LEAKAGE

COEFFICIENT Interval, in units of per second, is variable

40 60 MILES 

I____I

\ I I 

20 40 60 KILOMETERS

1

CO &

FIGURE 67. Distribution of vertical hydraulic conductivity and leakage coefficient for model layer 1, representing leakage through the Western Interior Plains confining system.
96° 95° 94° 93° 92° 91 C 90° 89°

39C38C

37C

36 C

35C

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"-' foot per second

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

is variable

20 40 60 MILES

I____I

I I I 

20 40 60 KILOMETERS

H

G i-1 i-1 

o

£i

1

1

FIGURE 68. Distribution of lateral hydraulic conductivity and transmissivity for model layer 2, representing the Springfield Plateau aquifer and Cretaceous sand of the

Mississippi Embayment.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM Dill

used to compare with the simulated heads in this 

area, the lateral hydraulic conductivity used for calibration in this area may be incorrect. The transmissivity of the Springfield Plateau aquifer ranges from 

0.02 foot squared per second in the northwest and 

southeast to about 0.1 foot squared per second at 

three locations in the west, southwest, and south, 

where the aquifer is thicker (fig. 68). The lateral hydraulic conductivity, where layer 2 represents Cretaceous sands of the Mississippi Embayment (fig. 68), is 

0.0035 foot per second (TO. Mesko, U.S. Geological 

Survey, written commun., 1985). However, because 

nodes in this part of layer 2 are assigned specifiedhead values equal to the potentiometric heads in the 

Cretaceous sediments and because the thickness of 

the layer is arbitrarily set at 0.0001 foot, the lateral 

hydraulic conductivity of the Cretaceous sediments 

given by Mesko cannot be checked by the model.

The model-calibrated vertical hydraulic conductivity 

between the middle of the Springfield Plateau and the 

Ozark aquifer ranges from l.OxlO"8 foot per second at 

nodes where the Ozark confining unit is 100 percent 

shale, to 5.0xlO~8 foot per second at nodes where the 

Ozark confining unit contains no shale (fig. 35). Between these two extremes, the conductivity is linearly 

scaled among the nodes according to the percentageof-shale content of the Ozark confining unit (fig. 69). 

Generally, the calibrated conductivity is smaller in the 

southwestern part of the study area and increases to 

the northeast. The leakage coefficient generally is 

larger (more than 2.0xlO~9 per second) in southwestern Missouri and southeastern Kansas where the 

Ozark confining unit is thinner, whereas the leakage 

coefficient is smaller (less than 2.0xlO~10 per second) 

in the south where the Ozark confining unit is thicker. 

Because the Ozark confining unit is not present beneath the Mississippi Alluvial Plain, the leakage coefficient between the Cretaceous sands and Ozark 

aquifer is large, ranging from about 2.5xlO~9 to about 

l.OxlO"8 per second.

The lateral hydraulic conductivity of layer 3, representing the Ozark aquifer, ranges from about l.OxlO"5 

foot per second near the southern and southeastern 

boundaries of the study area where the aquifer is 

deeply buried to about S.OxKT4 foot per second in .the 

Salem Plateau where deep karst features conduct 

ground water to discharge to streams and large 

springs (fig. 70). Lateral hydraulic conductivity of the 

aquifer along the western edge of the modeled area 

ranges from about 6.0X10"4 foot per second to about 

T.OxlO"4 foot per second. Values of lateral hydraulic 

conductivity for layer 3 are in general agreement with 

hydraulic conductivity estimates (fig. 27) derived from 

specific-capacity data. A constant ratio of lateral to

vertical hydraulic conductivity of 10 was used for 

layer 3 for the entire model. The transmissivity of the 

aquifer is largest along the White River valley (fig. 6) 

where the hydraulic conductivity of the aquifer is 

large and the thickness of the aquifer begins to increase to the south (fig. 70). The transmissivity decreases abruptly to the extreme south and southeast 

because the conductivity of the aquifer decreases 

more abruptly than its thickness increases.

The simulated vertical hydraulic conductivity between the middle of the Ozark and St. Francois aquifers is constant throughout the modeled area at 

l.OxlO"8 foot per second (fig. 71). The vertical hydraulic conductivity was not scaled by the percentage-ofshale content of the St. Francois confining unit because percentage-of-shale data are not available for 

the entire modeled area and because the model is relatively insensitive to this variable. The leakage coefficient is largest at two locations in the west and 

northwest where it exceeds 2.0xlO~10 per second (fig. 

71). The leakage coefficient decreases to less than 

4.0xlO~u per second in much of the eastern and 

southern part of the model except near the St. Francois Mountains and in the extreme southeast, where it 

is greater than l.OxlO"10 per second.

Layer 4, representing the St. Francois aquifer, was 

assigned a lateral hydraulic conductivity of 1.6x10 

foot per second in the area around the St. Francois 

Mountains where the aquifer is exposed or not deeply 

buried, and 8.0xlO~5 foot per second elsewhere in the 

model (fig. 72). The transmissivity of the aquifer is 

greater than 0.1 foot squared per second near the St. 

Francois Mountains and generally decreases uniformly to less than 0.0025 foot squared per second at the 

western edge of the model (fig. 72).

REGIONAL GROUND-WATER BUDGET

The regional ground-water budget determined by 

simulation data is presented here in conjunction with 

the estimates of recharge to the water table by 

Dugan and Peckenpaugh (1986) and the investigation of surface-water and ground-water relations 

discussed by Hedman and others (1987). A diagrammatic regional ground-water budget as derived from 

the model (fig. 73) shows net flow between model layers and to rivers and lakes modeled as specified-head 

boundaries. One flow quantity of special interest is 

the net flow of 867 cubic feet per second from layer 3 

to nodes in layer 2 that represent Cretaceous sands. 

This discharge corresponds to the net flow of groundwater out of the Ozark Plateaus province into the 

Mississippi Embayment.
D112 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

3

C 

o

B Jl

o

l

s

2"oS

I

a

CQ

II

'§

1

13

! s

i
96°

I ' !

39°

95°_____

N ~l- n ' 94° 93° 92° 91° 90° 89°

fvJ A I f^-^r

38°37°

36°

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 second 7.0 x 10"4 foot per second 8.0 x 10"4 foot per second

0.5- LINE OF EQUAL TRANSMISSIVITV Interval, 

in feet squared per second, is variable

40 60 MILES

0 20 40 60 KILOMETERS

oM§

§sCO

1

SI

%

CO3g

FIGURE 70. Distribution of lateral hydraulic conductivity and transmissivity for model layer 3, representing the Ozark aquifer. O h-i

h-i 

CO
96° 95° 94° 93° 92° 90°

39°

38°

37°

36°

35°

89°

EXPLANATION

AREA WHERE ST. FRANCOIS OR OZARK 

AQUIFER IS MISSING

ZONE OF EQUAL VERTICAL HYDRAULIC 

CONDUCTIVITY OF ST. FRANCOIS 

CONFINING UNIT Vertical hydraulic 

conductivity is 1.0 x 10"° foot per second

4 LINE OF EQUAL EFFECTIVE LEAKAGE 

COEFFICIENT Represents restrictive material between centerline of St. Francois aquifer and centerline of Ozark aquifer. Interval, in 10"' 'per second, is variable

20

I

40 60 MILES 

I____I

1 I I

20 40 60 KILOMETERS

FIGURE 71. Distribution of vertical hydraulic conductivity and leakage coefficient between the Ozark and St. Francois aquifers.
96° 95° 94° 93° 92° 91 C 90° 89°

39°38°

37°36°

35°

EXPLANATION

AREA WHERE MODEL LAYER 4 

IS INACTIVE

ZONE OF EQUAL LATERAL 

HYDRAULIC CONDUCTIVITY

8.0 x 1CT5 foot per second 

1.6 x 10"4 foot per second

0.01- LINE OF EQUAL TRANSMISSIVITYInterval, in feet squared per second, 

is variable

40 60 MILES

I_____I

I I I 

20 40 60 KILOMETERS

FIGURE 72. Distribution of lateral hydraulic conductivity and transmissivity for model layer 4, representing the St. Francois aquifer.

s 3

$

CO

GM M

cn
D116 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

It must be emphasized that the water budget 

presented in figure 73 is a model water budget that 

represents only the components of regional, predevelopment ground-water flow in the three aquifers. The 

model water budget is an approximate water budget 

because (1) the model does not simulate the cells modeled as specified heads, and (2) the model does not 

simulate recharge within a cell, only the redistributed 

recharge for intercell flow. The relation between the 

simulated regional-flow water budget and the water 

budget derived from estimates of recharge to the water 

table and surface-water and ground-water interaction 

is shown in table 3. For example, of the 127,187-cubicfeet-per-second mean annual precipitation that falls 

on the outcrop area of the Ozark Plateaus aquifer system, 95,513 cubic feet per second, or 75 percent, is 

removed as evapotranspiration and overland flow to 

streams. Only 25 percent, or 31,667 cubic feet per second, of the mean annual precipitation recharges the 

aquifer system. Because of the large size of model cells 

in the regional model, 24,577 cubic feet per second of 

the water recharging the aquifer system discharges to 

sinks within the same cell receiving the recharge and

cannot be simulated by the model. Thus, 19 percent of 

the precipitation (or 78 percent of the total recharge) is 

unsimulated flow. Only 6 percent of the precipitation 

(or 22 percent of the total recharge) contributes to the 

simulated deeper flow (7,091 ft3/s). Of this deeper intercell flow, 4,035 cubic feet per second discharges to 

streams and springs inside the study area, and 3,056 

cubic feet per second discharges as boundary flow to 

the Missouri, Neosho, Mississippi, and Arkansas Rivers (fig. 6), aquifers in the Mississippi Embayrnent, 

and the water table in the overlying Western Interior 

Plains confining system. Because of the small pumpage from wells (about 320 ft3/s in 1970-1979) in comparison to the large natural flow, the predevelopment 

regional ground-water budget of the Ozark Plateaus 

aquifer system is probably similar to the present-day 

regional budget.

The amount of drainable water in the Ozark Plateaus aquifer system is a function of specific yield or 

storage coefficient and thickness of the water-yielding 

units. The estimated specific yields for the St. Francois, Ozark, and Springfield Plateau aquifers in the 

freshwater portion of the flow system are 0.05, 0.10,

Net recharge from water 

table to layer 2

1279

Water table

:: 1447 . .. ;

Net recharge from water 

table to layer 3

1739

: : 976

Springfield Plateau 

aquifer (layer 2)

 :-l 526 .:. ' :- ' :' .' : : 2227 -:-//v;: ' . 626': ' va&vp^ 

EXPLANATION

.'";':'-;;. CONFINING MATERIAL 

rrrrr MODEL BOUNDARY, IMPERVIOUS 

1739 NET FLOW, IN CUBIC FEET PER SECOND

Note: Water table, Cretaceous sand (part of layer 2), 

and rivers were simulated as specified-head 

boundaries

Net recharge from water 

table to layer 4

38

Ozark aquifer (layer 3) 923

'.-' 266 '. / 'v

Rivers

Cretaceous sand 

, (outside of the 

i aquifer system)

882' 

Layer 3

' . .: - ; } : : . . - ':" : .: . :-.- . . ::----.-:'l:'::'-----:

:.:i:X: :' ': 290.v:.:-.-:: ;. ::/: ::/: ;:-;::>:.v::: '.'.':"; .62.-;.-:;

/ 

/ 

/ 

/ 

~/ 

 '/

 . /

;. / 

;:/

 / 

/ / / 

/ 

 /t

 ' ' /

 : /

 /

 . f

'~ /

\

/

St. Francois aquifer (layer 4)

FIGURE 73. Regional ground-water budget of the Ozark Plateaus aquifer system based on simulation.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D117

TABLE 3. Water budgets for the Ozark Plateaus aquifer system

[Abbreviations: Ac, area of model cell; A;, area of cell in which precipitation entering water table appears to flow to rinks in same cell; FB , water that flows across cell boundaries and 

enters or leaves a cell through streambeds; Fu, recharge to water table; M, recharge to area A; that discharges to sinks within the cell divided by total recharge to area Aj; , 

not applicable]

Springfield Plateau aquifer Ozark aquifer St. Francois aquifer Ozark Plateaus aquifer system

Flow component

Flow

(ft3 /s)

Percent

Percent of

of recharge 

precipita- to water 

tion table

Flow

(ft3 /s)

Percent

of 

precipitation

Percent

of

recharge 

to water 

table

Flow

(ft3 /B)

Percent

of 

precipitation

Percent

of

recharge 

to water 

table

Flow

(ft 3 /s)

Percent

of 

precipitation

Percent

of

recharge 

to water 

table

Precipitation on outcrop 

areas 1 34,473 100 90,254 100 2,460 100 127,187 100

Calculated overland flow 

to streams and 

evapotranspiration 26,013

Calculated recharge to

water table2

Unsimulated recharge

(intracell flow),

M (Ai/Ac ) Fu

S mulated recharge

(intercell flow),

Fu -M (Ai/Ac )FU

Calculated discharge to

regional sinks rivers,

streams, and springs3 (Fs)

Net recharge from the

water table (see fig. 73)

8,460

6,800

1,660

381

1,279

75

25

20

5

1

4

100

80

20

5

15

67,630

22,617

17,273

5,345

3,606

1,739

75

25

19

6

4

2

1,870 76

100 590 24

76 504 20

24 86 4

16 48 2

8 38 2

95,513

100 31,667

85 24,577

15 7,091

8 4,035

7 3,056

75

25 100

19 78

6 22

3 13

3 9

From National Weather Service (National Oceanic and Atmospheric Administration, 1951-1980).

From Dugan and Peckenpaugh (1986).

3From Hedman and others (1987).

arid 0.07, respectively. In the Boston Mountains and 

Arkansas Valley of Arkansas the aquifer system contains more than 1,000 milligrams per liter dissolved 

solids. In these areas, the specific yields are estimated 

at one-half of the freshwater values. Estimates of the 

drainable water stored in the study area, in cubic feet, 

are listed below by State and aquifer:

State

M: ssouri.. ....................

Kansas.... ...................

Oklahoma..................

Arkansas (fresh).......

Arkansas (saline)......

St. Francois aquifer

2.37xl013

2.95xlOn

3.61xlOn

2.21xl012

1.69xl012

Ozark aquifer

1.45xl014

5.54xl012

1.94X1013

7.73xl013

4.85xl013

Springfield 

Plateau 

aquifer

5.15xl012

l.OTxlO12

1.95xl012

1.30xl«12

2.18xl012

AVAILABILITY AND USE OF GROUND WATER AND 

WELL YIELDS

It is estimated that approximately 200 million gallons per day of water are withdrawn from wells that

are open to the Ozark Plateaus aquifer system (estimate based on records spanning 1970-1979). An estimate of ground water withdrawn daily in each 

county is shown in figure 74. The water is used for 

public supply, industrial use, domestic and stock use, 

and supplemental irrigation of crops. Large amounts 

of water also have been withdrawn in areas where 

underground mining has occurred. Withdrawal of 

ground water associated with underground mining 

has been limited to the St. Francois aquifer in southeastern Missouri and to the Springfield Plateau aquifer in the tristate mining district.

Although the Basement confining unit is considered to be a regional impermeable base for the Ozark 

Plateaus aquifer system, the unit does yield small 

quantities of water to wells via the extensive network of fracture systems and faults that dissect the 

confining unit. Water wells penetrate the Basement 

confining unit only in the immediate vicinity of the 

St. Francois Mountains where the unit crops out or is 

buried beneath thin overburden. Well yields are 

small and vary greatly within short distances. Of 14 

water wells drilled into the Basement confining unit 

in or near its outcrop area, 70 percent yielded less 

than 10 gallons per minute. Two of these wells were
96° 95° 94° 93° 92 91 C

AVERAGE DAILY GROUNDWATER WITHDRAWAL. _ 

IN MILLION GALLONS PER DAY

BENTON ' | | I § , S

_____I |S,___^ MILLER t J____ ____|

V 1 \ "l MARIES L4 CRAW. \

STCLAIR I J \ 1 ,____11 FORD WASH '\ I ~. ' - '^^ ' INGTON * 

I I LKr^ixi^nv CAMDEN (I I I [ ] ntorxUnY i | I I - S'GENEVIEVE

I ST 

FRANCOISN --/ PERRY

/ LA- CHEROKEE

KAN$ l/^Uli __ i 

OKlJA 7~" 9 CRAIG [ j

|NOWATA!\ j OTTAWA I^EW i ii , '

WARE » BENT°N ! CARR°LL I I WARE ' ' | BOONE

1

, / ' '

^MACK-1 x x CRAIGHEAD

/ NEWTON j SEARCY

i .1 i

SEQUOYAH ', FRANKLIN JOHNSON j

ICRAWFORD7 | f '

35° - 0 M M 00 1co0

FIGURE 74. Estimated average daily withdrawal of ground water by county from the Ozark Plateaus aquifer system and the Western Interior Plains confining system during

1970-1979.
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D119

dry, including one drilled to a depth of 310 feet. The 

most productive of the four wells that yielded more 

than 10 gallons per minute was flowing and yielded 

about 70 gallons per minute.

Where the St. Francois aquifer crops out in and 

around the St. Francois Mountains the aquifer is 

used for domestic supply. Water from the St. Francois aquifer also is used for public supply where the 

overlying Ozark aquifer is thin or absent. For example, municipal wells at Farmington and Bismark in 

the St. Francois Mountains area yield 200 to 250 

gallons per minute. Yields from wells that are open 

only to the Bonneterre Dolomite are somewhat less 

than those from wells also open to the Lamotte 

Sandstone. Wells that penetrate only the Bonneterre 

Dolomite in the outcrop area typically produce less 

than 50 gallons per minute, and the production rate 

may increase with well depth; however, this is not 

always the case. Many 200- to 300-foot-deep wells 

that are open only to the Bonneterre yield only a 

small amount of water (between 1 and 10 gal/min). 

This indicates that in some areas the Bonneterre is 

tightly cemented and does not have well-developed 

secondary permeability. Those wells that are open to 

a significant thickness of Lamotte Sandstone usually 

have yields ranging from 100 to 500 gallons per 

minute.

The large withdrawal rates shown in figure 74 for 

Iron and Reynolds counties in Missouri reflect pumping from the St. Francois aquifer for uses associated 

with mining. Lead has been continuously mined in the 

eastern Ozarks of Missouri since the 1720's. Before 

1869, lead was mined from shallow pits above the 

water table. The introduction of the diamond drill for 

prospecting in 1869 led to new discoveries and extensive development of lead ore in the Bonneterre Dolomite below the water table, thus creating a need for 

mine dewatering. Ground water has been pumped to 

dewater mines, process ore (primarily lead and zinc), 

and supply the miners' domestic water needs. It was 

estimated that mines in the area, now known as the 

"Old Lead Belt," were being dewatered at the rate of 

13 to 17 million gallons per day in the early 1900's 

(Buckley, 1908). Most of the mines in the "Old Lead 

Belt" were closed by the 1960's. Before that time, prospecting by mining companies had resulted in the discovery of a "New Lead Belt," known as the Viburnum 

Trend, that extends from near Viburnum in northwestern Reynolds County, Missouri, southward for 

more than 30 miles. As in the "Old Lead Belt," mineralization is in the Bonneterre Dolomite. Warner and 

others (1974) reported that ground water in the Viburnum Trend area was withdrawn at an average rate of 

26 million gallons per day in 1971 for mine dewatering. Pumping rates at individual mines varied from 

450 to 4,900 gallons per minute.

Mine dewatering has not had any lasting effect on 

water levels, as the mines in the "Old Lead Belt" district have refilled with water. Warner and others 

(1974), reporting on the effect of mine dewatering on 

ground-water levels in the Viburnum Trend, stated 

that no obvious decline in water levels in wells open 

to the shallow aquifer (Ozark aquifer) have been reported. However, they did mention that "a memorandum circulated by the U.S. Forest Service, Rolla, 

Missouri, on November 26, 1974, cited the recent development of a number of sizeable sinkholes in the 

vicinity of the AMAX Mine, which might be linked to 

declines in the shallow-aquifer water table in that 

area. This relationship has not been verified" (Warner and others, 1974, p. 75).

Throughout the Ozarks and adjacent areas, the 

Ozark aquifer is the primary source of water to 

large-yield public-supply, industrial, and irrigation 

wells. Yields from water wells that penetrate the 

Ozark aquifer vary somewhat according to the lithology of geohydrologic units that are open to the wells. 

Deep wells in the Salem Plateau commonly are open 

to the most permeable units of the aquifer and can 

yield more than 1,000 gallons per minute. However, 

shallower domestic wells that penetrate only a few 

hundred feet of the less permeable formations, such 

as the Jefferson City and Cotter Dolomites, may 

yield no more than 25 gallons per minute. In St. 

Louis and northern Jefferson Counties, Missouri, in 

the extreme northeastern part of the study area, well 

yields are, on the average, much smaller (less than 

100 gallons per minute) than those in the Salem and 

Springfield Plateaus. Only formations stratigraphically higher than the Smithville Formation (table 2) 

normally are open to wells in this area because the 

underlying, more permeable zones of the aquifer are 

deeply buried and may locally contain salinewater.

The St. Peter Sandstone, the Roubidoux Formation, 

the Gunter Sandstone Member of the Gasconade Dolomite (also referred to in some areas as the Gunter 

Member of the Van Buren Formation), and the Potosi 

Dolomite are the formations within the Ozark aquifer 

that generally yield the largest amount of water to 

wells. The St. Peter Sandstone is present in the study 

area in eastern Missouri and in the Boston Mountains 

of Arkansas. Water wells open to the St. Peter Sandstone in Jefferson County, Missouri, produce between 

50 and 75 gallons per minute (Fuller and others, 

1967). The formation generally does not yield significant quantities of water in Arkansas. The overlying 

Plattin Limestone and Joachim Dolomite are sufficiently permeable to yield water to domestic wells in
D120 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

St. Louis and Jefferson Counties, Missouri, and in 

northern Arkansas. Silurian and Devonian limestone 

and chert of the upper zone are used locally as sources 

of domestic water in the northwestern and southern 

parts of the study area.

The Roubidoux Formation and Gasconade Dolomite 

of the Ozark aquifer are the principal water-bearing 

formations in northeastern Oklahoma, southeastern 

Kansas, northern Arkansas, and western Missouri. 

Water wells open to the Roubidoux Formation in those 

areas commonly yield 30 to 150 gallons per minute 

and occasionally as much as 600 gallons per minute. 

In southern Missouri where the Roubidoux Formation 

crops out or is present at shallow depth, it often is 

used as a source of water for domestic and farm wells. 

Such wells may yield as much as 20 gallons per 

minute. The Gunter Sandstone Member of the Gasconade Dolomite or the Van Buren Formation is a 

principal aquifer in Missouri, in northern Arkansas 

and in southeast Kansas. Wells open to the Gunter 

Sandstone Member commonly yield 40 to 100 gallons 

per minute and as much as 600 gallons per minute to 

wells in the Springfield, Missouri area (Fuller and 

others, 1967).

Yields from wells open to these and adjacent formations previously discussed can locally exceed 1,000 

gallons per minute in northeastern Oklahoma (Marcher and Bingham, 1971). Melton (1976) attempted to 

assess the relative yields from the Roubidoux Formation and Gasconade Dolomite in the Ozark area. He 

concluded that yields from the Roubidoux Formation 

ranged from 4 to 600 gallons per minute and averaged 

50 to 60 gallons per minute. Yields to wells open to the 

Gasconade Dolomite were reported to range from 4 to 

732 gallons per minute and to average 170 gallons per 

minute. Melton presented some evidence that greater 

well yields in this area are obtained from wells located 

along fracture traces or major lineaments.

The Potosi Dolomite of the Ozark aquifer is one of 

the most reliable aquifers in Missouri for municipal 

and industrial water supply. In wells at Rolla, the 

Potosi at a depth of 1,200 feet is 200 feet thick and the 

yield, which is principally from the Potosi, averages 

500 gallons per minute. At Springfield the Potosi is 

approximately 1,700 feet in depth and averages 50 

feet in thickness. Fuller and others (1967) state that 

the combined production below the casing depth, usually 250 to 400 feet, is more than 1,000 gallons per 

minute.

Concentrated pumping has decreased heads in the 

Ozark aquifer locally at Miami, Oklahoma; Pittsburg, 

Kansas; and Springfield, Missouri. At Miami in Oklahoma, deep wells that flowed at the surface before 

1907 showed a decline in water level of more than 400

feet by 1947. The decline in head was attributed to 

ground-water withdrawals as a result of greatly increased population and increased industrial use (Reed 

and others, 1955). Referring to Pittsburg, Kansas, 

Stramel (1957, p. 175) wrote that it has been "estimated that the use of water between 1882 and 1955 averaged 1.4 Mgal/d. Available records indicate that the 

water level declined about 124 feet in the Pittsburg 

well field during this period of 73 years." At Springfield, industrial pumping from the Ozark aquifer has 

caused a cone of depression to form in the potentiometric surface. Static water levels in wells in the center of the cone have been lowered as much as 200 feet 

from their predevelopment condition.

Springs in the Springfield Plateau aquifer have 

served as a source of water for towns in Delaware, 

Mayes, and Adair Counties in Oklahoma (Dover and 

others, 1968). In Missouri the city of Springfield has 

long incorporated the use of a spring in its watersupply system, along with deep wells, lakes, and 

streams. Yields from wells penetrating the Springfield Plateau aquifer generally are less than yields 

from the thicker, somewhat more permeable Ozark 

aquifer. Wells that are open only to the Springfield 

Plateau aquifer usually are domestic-supply wells. To 

obtain greater yields, municipal wells that are open 

to the Springfield Plateau aquifer also are open to 

the underlying Ozark aquifer. Yields in the Springfield Plateau of southwestern Missouri commonly are 

less than 20 gallons per minute. However, there are 

industrial wells in Jasper County, Missouri, that 

yield 300 to 400 gallons per minute from fractured 

zones in the Springfield Plateau aquifer. The Burlington and Keokuk Limestones of the Springfield 

Plateau aquifer are the main water-yielding formations in this area. In the tristate mining district 

(Missouri-Kansas-Oklahoma), ground water is 

pumped from abandoned lead-zinc mine shafts to 

supply some industries. Yields from the mine shafts 

can exceed 1,000 gallons per minute.

In northeastern Oklahoma, water for domestic use 

is obtained from cherty limestones (Marcher, 1969; 

Marcher and Bingham, 1971) of the Springfield Plateau aquifer. Yields usually are less than 10 gallons 

per minute; however, larger yields are reported in Ottawa County, Oklahoma. In northern Arkansas, wells 

penetrating fractures and solution channels in the 

Boone Formation of the Springfield Plateau aquifer 

are reported to yield more than 25 gallons per 

minute (Lamonds, 1972).

Large amounts of water were pumped from the 

Springfield Plateau aquifer in conjunction with the 

mining and processing of the lead-zinc ore from the 

tristate mining district. The large mining district in-
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D121

eludes parts of southwestern Missouri, southeastern 

Kansas, and northeastern Oklahoma. The ore occurs 

in Mississippian limestone within the Springfield 

Plateau aquifer. Mining in the Missouri part of the 

district lasted from about 1850 to about 1957, peaking about 1916. Mining in the Oklahoma and Kansas 

parts of the district began around 1900, peaked 

about 1926, and ceased in the early 1970's. Mine dewatering indicated that large yields of ground water 

were available in some localities. For example, Abernathy (1941, p. 234) stated that some pumping 

plants at zinc mines pumped as much as 2 million 

gallons per day to dewater the mines.

Mine cavities in the tristate mining district have 

refilled with water since being shut down. It has 

been estimated (Spruill, 1984) that the volume of 

water filling the mines is about 132,000 acre-feet (43 

billion gallons). Unfortunately, the mine water is of 

poor quality for most uses and may present a threat 

of contamination to the underlying Ozark aquifer.

Water-bearing sandstone and limestone zones in 

the Western Interior Plains confining system are in 

rocks of Pennsylvanian age and are present near 

land surface in the western and southern part of the 

study area. The rocks have little permeability, and 

wells finished in these rocks invariably yield small 

quantities of water suitable only for domestic and 

stock use. Well-recovery tests on 14 shallow wells 

that penetrated the Western Interior Plains confining 

unit near the western boundary of the Ozark area in 

southwestern Missouri displayed a range of yields 

from 1 to 40 gallons per minute (Kleeschulte and others, 1985). Generally, well yields tended to increase 

from west to east. This may indicate that the easternmost wells, located where the confining system is 

thinner, were receiving ground water from the underlying Springfield Plateau aquifer through the more 

permeable sandstones at the base of the confining 

system. Similar tests conducted on 16 shallow wells 

that penetrated the Western Interior Plains confining 

unit in southwestern Washington County, Arkansas, 

show that well yields in this area also are small, 

ranging from 2.5 to 19 gallons per minute (Muse, 

1982). Water comes to these wells from water-yielding units such as the Hale Formation and perhaps 

the Pitkin Limestone. Other formations that the 

wells penetrate are likely to have a much larger 

shale fraction and presumably yield less water.

SUMMARY AND CONCLUSIONS

The Ozark area contains eight regional geohydrologic units and several smaller units. Five of the geohydrologic units three aquifers and two confining 

units form the mainly freshwater Ozark Plateaus 

aquifer system. The aquifer system is confined below 

by the Basement confining unit. The western and 

southern edges of the aquifer system are confined 

above by the Western Interior Plains confining system. The aquifers and confining units that constitute 

the Ozark Plateaus aquifer system are, in ascending 

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

unit, and the Springfield Plateau aquifer.

The Missouri River alluvial valley is the northern 

boundary and a discharge area for the Ozark Plateaus aquifer system. On the east the Mississippi 

River alluvial valley is the approximate boundary 

from its confluence with the Missouri River southward to the Mississippi Alluvial Plain. The aquifer 

system extends a short distance beneath the alluvial 

plain to the southeast. The southern boundary is approximately parallel to the Arkansas River valley. 

The western boundary is a complex transition zone 

where freshwater in the Ozark Plateaus aquifer system meets salinewater in the stratigraphically equivalent Western Interior Plains aquifer system.

There are two regional ground-water divides in the 

study area. The northernmost divide parallels a 

prominent topographic ridge that extends through 

the Ozark Plateaus from McDonald to Dent County, 

Missouri (figs. 3, 10). Ground water flowing north 

from the divide discharges to the Missouri River. 

Ground water flowing south from the divide discharges to the White River and its tributaries. The 

southernmost regional ground-water divide parallels 

the crest of the Boston Mountains in northern Arkansas. North of this divide, water in the aquifer 

system flows to the White and Buffalo Rivers and 

their tributaries.

The Basement confining unit is a nearly impermeable barrier to the movement of ground water relative to the overlying aquifers. Primary porosity and 

permeability of the Basement confining unit are virtually nonexistent in the Precambrian rocks that constitute this unit. Secondary permeability has 

developed but mainly is confined to fracture zones 

and faults. The largest exposure of the Basement 

confining unit is in the St. Francois Mountains of 

southeast Missouri. From this area the unit dips 

steeply into the subsurface toward basins that surround the Ozark uplift. Water wells penetrate the 

unit only in the immediate vicinity of its outcrop or 

where the unit is buried beneath thin overburden. 

Well yields are small, vary considerably within short 

distances, and generally yield less than 10 gallons 

per minute.
D122 REGIONAL AQUIFER-SYSTEM ANALYSIS-CENTRAL MIDWEST

Three geologic formations, the Lamotte Sandstone, 

the Bonneterre Dolomite, and in the western part of 

the study area, the Reagan Sandstone, are included 

in the St. Francois aquifer. The water-bearing sandstone, dolostone, and siltstone overlie the Basement 

confining unit. The St. Francois aquifer crops out in 

the St. Francois Mountains of southeastern Missouri. 

Beyond the relatively small outcrop area the aquifer 

dips into the subsurface and is buried beneath 

younger, more permeable rocks. The St. Francois aquifer generally is more than 300 feet thick in southern Missouri. In northern Arkansas, the aquifer 

ranges between 100 and 300 feet thick. In the western and southwestern part of the study area, the aquifer generally is less than 300 feet thick and thins 

toward the west.

Water levels in the St. Francois aquifer are controlled by topographic features in the outcrop area. 

Within the outcrop area, discharge from the aquifer 

is to the major streams. Near the outcrop area, 

where the aquifer is confined but not deeply buried, 

ground water discharges through the overlying confining unit and thence to the major streams. Little is 

known about the potentiometric surface of the St. 

Francois aquifer where it is deeply buried because no 

wells are open to the aquifer.

The few water-quality data available for the St. 

Francois aquifer are from water samples in and near 

its outcrop area, where the water type generally is a 

calcium magnesium bicarbonate. Dissolved-solids 

concentration generally ranges from 200 to 400 milligrams per liter. Chloride concentration generally 

ranges from 5 to 60 milligrams per liter. Sulfate concentration may be as large as 150 milligrams per 

liter but generally is much less.

The St. Francois aquifer is used primarily in and 

near its outcrop area. Wells penetrating only the 

Bonneterre Dolomite generally yield less than 50 gallons per minute. Many 200- to 300-foot-deep wells 

open only to the Bonneterre Dolomite yield less than 

10 gallons per minute. Wells open to a significant 

thickness of Lamotte Sandstone may yield 100 to 500 

gallons per minute.

The St. Francois confining unit is composed of 

Upper Cambrian shale, siltstone, dolostone, and 

limestone. It is represented by the Davis Formation 

and the Derby and Doe Run Dolomites. These slightly permeable rocks retard the flow of ground water 

between the St. Francois and Ozark aquifers. The St. 

Francois confining unit is exposed at land surface in 

a thin, nearly circular band around the St. Francois 

Mountains.

Thickness of the St. Francois confining unit ranges 

from near 0 to 730 feet. Throughout much of the

Salem Plateau, the confining unit has a relatively 

constant thickness between 200 and 400 feet. At the 

northwest edge of the Mississippi Alluvial Plain the 

unit is more than 600 feet thick. In the southwestern 

part of the study area, thickness of the confining unit 

seldom exceeds 100 feet. In northern Arkansas, 

thickness of the confining unit generally ranges between 100 and 400 feet, but is greater than 730 feet 

in Madison County, Arkansas (fig. 3).

The Ozark aquifer includes a sequence of Upper 

Cambrian and Middle Devonian rocks that vary in 

water-yielding capacity but collectively are a regional 

aquifer. The Potosi Dolomite is the basal formation in 

the aquifer. The upper boundary of the aquifer in the 

northeast part of the study area is the base of the 

Maquoketa Shale. To the west and south where the 

Maquoketa Shale is absent, Devonian rocks are included as part of the aquifer, and the upper boundary 

of the aquifer is the base of the Chattanooga Shale. 

The outcrop area of the Ozark aquifer is approximately coincident with the Salem Plateau.

The Ozark aquifer is the thickest aquifer in the 

study area. Northeast, east, and south of the St. 

Francois Mountains, the aquifer is more than 3,000 

feet thick. In southwestern Missouri, southeastern 

Kansas, and northeastern Oklahoma, the aquifer 

ranges from 800 to 1,500 feet thick. The aquifer is 

about 1,500 feet thick near the Missouri-Arkansas 

border and increases in thickness southward.

The aquifer is made up of dolostone, limestone, 

sandstone, chert, and shale; dolostone is the predominant rock in most of the study area. Dissolution of 

the carbonate rock along fractures and bedding 

planes and karst development are the main processes 

that develop permeability in the aquifer. Hydraulic 

conductivity in the northern half of the study area, 

as estimated from specific-capacity data, varies from 

about 10~5 foot per second to about 10~3 foot per second. In the Arkansas Valley the hydraulic conductivity is as little as 10"8 foot per second.

Ground water in the Ozark aquifer in the Salem 

Plateau is unconfined. Water levels in the aquifer are 

strongly influenced by major topographic features of 

the plateau. Ground-water movement in the aquifer 

in the Salem Plateau is from the upland areas between rivers and streams toward the valleys where 

the water discharges as base flow. Beyond the boundaries of the Salem Plateau, the Ozark aquifer is confined and water in the aquifer generally flows away 

from the Ozark Plateaus province toward surrounding areas where the deep aquifers contain saline 

ground water.

Water from the Ozark aquifer generally is a calcium magnesium bicarbonate type. Dissolved-solids
GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D123

concentration ranges from 200 to 300 milligrams per 

liter along the regional ground-water divides and is 

as much as 500 milligrams per liter in the northcentral part of the Salem Plateau where the Ozark 

aquifer is overlain by Pennsylvanian shale and sandstone. Chloride concentration of water from the 

Ozark aquifer generally is less than 10 milligrams 

per liter but increases significantly away from the 

Ozark Plateaus province. Sulfate concentration of 

water from the aquifer generally is less than 10 milligrams per liter in the Salem Plateau and less than 

20 milligrams per liter in the Springfield Plateau. 

However, in the north-central part of the Salem Plateau, sulfate concentration of water in the aquifer is 

as much as 140 milligrams per liter. Several small 

areas of the Ozark aquifer along the western and 

southern flanks of the Ozark Plateaus province contain a sodium bicarbonate or a mixed bicarbonate 

type water. These are areas indicative of the transition between the predominantly bicarbonate water in 

the Ozark Plateaus aquifer system and the predominantly sodium chloride water that encircles the aquifer system to the west, south, and east.

Yields from deep wells in the Salem Plateau open 

to the Ozark aquifer may exceed 1,000 gallons per 

minute. Shallower domestic wells that penetrate only 

a few hundred feet of the less permeable rocks of the 

aquifer may yield less than 25 gallons per minute. 

The Potosi Dolomite is the most permeable geologic 

formation within the aquifer. The Roubidoux Formation and Gasconade Dolomite form the main wateryielding formations of the aquifer in the southwestern and southern parts of the study area.

The Ozark confining unit includes the stratigraphic 

interval from the Upper Ordovician Maquoketa Shale 

to the Lower Mississippian Chouteau Limestone. The 

confining unit is not present in the Salem Plateau 

where the stratigraphically lower Ozark aquifer is exposed at land surface. Thickness of the Ozark confining unit ranges from near 0 to more than 1,500 feet. 

In most of the study area, however, the confining unit 

is less than 100 feet thick. Slightly permeable strata 

of the Ozark confining unit impede the movement of 

ground water between the underlying Ozark aquifer 

and the overlying Springfield Plateau aquifer.

The Springfield Plateau aquifer is a sequence of 

water-bearing Mississippian limestones. In western 

Missouri and southeastern Kansas, the Burlington 

and Keokuk Limestones are the most significant formations in the Springfield Plateau aquifer. In northeastern Oklahoma, rocks of the aquifer are the Boone 

Formation, the Keokuk Limestone, and the Moorefield Formation. In northern Arkansas, the aquifer is 

represented by the Boone Formation.

The Springfield Plateau aquifer crops out over 

about one-third of the Ozark Plateaus province as a 

wide band around the western and southern perimeter of the Salem Plateau. The aquifer is buried beneath Pennsylvanian rocks west of the Springfield 

Plateau to a depth of about 250 feet in the more 

northerly areas and to about 500 feet in southeastern 

Kansas. The aquifer ranges from 200 to 400 feet 

thick throughout most of southwestern Missouri and 

southeastern Kansas. In northeastern Oklahoma, the 

aquifer may exceed 300 feet in thickness. In northern 

Arkansas, the aquifer generally is less than 400 feet 

thick.

Water from the Springfield Plateau aquifer is a calcium bicarbonate type. In the outcrop area, dissolvedsolids concentration of the water generally is less 

than 300 milligrams per liter but may exceed 400 

milligrams per liter. Chloride concentration in water 

from the aquifer generally is less than 10 milligrams 

per liter but in northwest Arkansas can exceed 100 

milligrams per liter. Sulfate concentration in water 

from the aquifer generally is less than 10 milligrams 

per liter but is larger in water from the zinc-lead 

mines in the tristate mining district.

The Springfield Plateau aquifer is used as a source 

of water for farm wells, but the aquifer rarely is used 

for public supply because of small well yields. Yields 

from wells that penetrate the Springfield Plateau aquifer in southwestern Missouri commonly are less 

than 20 gallons per minute. Springs from the aquifer, 

however, have been a source of supply for towns in 

Oklahoma, Missouri, and Arkansas.

Regionally, the Western Interior Plains confining 

system generally impedes the vertical and lateral 

flow of water. However, individual formations that 

constitute the confining system locally may be aquifers or confining units. Wells open to aquifers in the 

confining system generally have small yields and are 

capable of supplying water only for domestic and 

stock uses. The configuration of the water table in 

the near-surface weathered layer of the confining system is affected by topography. Generally, ground 

water infiltrates to the water table in upland areas, 

then moves toward the stream valleys where it discharges.

A three-dimensional finite-difference model was 

constructed to simulate regional ground-water flow in 

the Ozark Plateaus aquifer system under predevelopment conditions. Because of the large area (195.3 

mi2) represented by each model cell, the large topographic relief of the surficial aquifers, and the hydrologic complexity of the karst terrane, a new method 

of estimating the distribution of recharge to the uppermost model cells was developed. The method uses
D124 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

independent estimates of (1) recharge to the water 

table, (2) base flow and hydrologic characteristics of 

springs and streams, and (3) topographic features to 

determine the net flux that contributes to intercell 

flow for each model cell that receives recharge. The 

calculated net flux (or regional ground-water recharge) ranges from 12 to 100 percent of the estimated recharge to the water table, depending on the 

hydrologic conditions at a particular cell. The steadystate model calibration yielded estimates of the lateral hydraulic conductivity of the St. Francois, Ozark, 

and Springfield Plateau aquifers. The lateral hydraulic conductivity of the St. Francois aquifer ranges 

from l.GxlO"4 foot per second near the St. Francois 

Mountains to 8.0xlO~5 foot per second elsewhere. The 

lateral hydraulic conductivity of the Ozark aquifer 

ranges from l.OxlO"5 foot per second in the south to 

S.OxlO"4 foot per second in the north and east. The 

lateral hydraulic conductivity of the Springfield Plateau aquifer is uniform at 2.5X10"4 foot per second.

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 cubic feet per second of 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 cubic feet per second (6 percent of precipitation) became regional ground-water flow and is simulated. Of this regional flow, 4,035 cubic feet per 

second of water discharged to regional sinks (large 

streams and lakes) inside the study area, and 3,056 

cubic feet per second of water discharged as boundary flow to the Mississippi, Missouri, Neosho, and 

Arkansas Rivers, aquifers of the Mississippi Embayment, and the water table in the Western Interior 

Plains confining system. 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.

Approximately 200 million gallons per day of 

ground water are withdrawn from the Ozark Plateaus aquifer system by large-yield public-supply, industrial, and irrigation wells in the Ozarks and 

adjacent areas. The quantity of ground water 

pumped for irrigation varies from year to year depending upon rainfall received during the growing 

season. There does not seem to be any regional lowering of water levels in the aquifer system. However,

concentrated pumping has decreased heads in the 

Ozark aquifer locally at Miami, Oklahoma; Pittsburg, 

Kansas; and Springfield, Missouri. With the exception of mine dewatering, use of water from the St. 

Francois aquifer is limited to its area of outcrop and 

adjacent areas where the overlying Ozark aquifer is 

thin or absent. Pumping from the St. Francois aquifer for the purpose of dewatering lead mines in the 

Viburnum Trend averaged 26 million gallons per day 

in 1971.

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GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D125

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Ozark Plateaus province, Missouri, Arkansas, Kansas, and
D126 REGIONAL AQUIFER-SYSTEM ANALYSIS CENTRAL MIDWEST

Oklahoma Basement confining unit: U.S. Geological Survey 

Hydrologic Investigations Atlas HA-711-B, 1 sheet.

 1990a, Major geohydrologic units in and adjacent to the 

Ozark Plateaus province, Missouri, Arkansas, Kansas, and 

Oklahoma: U.S. Geological Survey Hydrologic Investigations 

Atlas HA-711-A, 1 sheet.

 1990b, Major geohydrologic units in and adjacent to the 

Ozark Plateaus province, Missouri, Arkansas, Kansas, and 

Oklahoma St. Francois aquifer: U.S. Geological Survey Hydrologic Investigations Atlas HA-711-C, 2 sheets.

 1990c, Major geohydrologic units in and adjacent to the 

Ozark Plateaus province, Missouri, Arkansas, Kansas, and 

Oklahoma St. Francois confining unit: U.S. Geological Survey 

Hydrologic Investigations Atlas HA-711-D, 3 sheets.

 1990d, Major geohydrologic units in and adjacent to the 

Ozark Plateaus province, Missouri, Arkansas, Kansas, and 

Oklahoma Ozark aquifer: U.S. Geological Survey Hydrologic 

Investigations Atlas HA-711-E, 3 sheets.

 1990e, Major geohydrologic units in and adjacent to the 

Ozark Plateaus province, Missouri, Arkansas, Kansas, and 

Oklahoma Ozark confining unit: U.S. Geological Survey Hydrologic Investigations Atlas HA-711-F, 3 sheets.

 1990f, Major geohydrologic units in and adjacent to the 

Ozark Plateaus province, Missouri, Arkansas, Kansas, and 

Oklahoma Springfield Plateau aquifer: U.S. Geological Survey Hydrologic Investigations Atlas HA-711-G, 3 sheets. 

-1990g, Major geohydrologic units in and adjacent to the

Ozark Plateaus province, Missouri, Arkansas, Kansas, and 

Oklahoma Western Interior Plains confining system: U.S. 

Geological Survey Hydrologic Investigations Atlas HA-711-H, 

3 sheets.

Imes, J.L., and Davis, J.V., 1990a, Water type and concentration of 

dissolved solids, chloride, and sulfate in ground water from the 

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HA-711-L, 2 sheets. 

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Jorgensen, D.G., Helgesen, J.O., and Imes, J.L., 1993, Regional 

aquifers in Kansas, Nebraska, and parts of Arkansas, Colorado, 

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

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Jorgensen, D.G., and Rosenshein, J.S., 1987, Naming Aquifers: 

EOS, American Geophysical Union, v. 68, no. 15, p. 210-211.

Jorgensen, D.G., and Signer, D.C., 1981, Plan of study for the Central Midwest Regional Aquifer-Systems Analysis in parts of Arkansas, Colorado, Kansas, Missouri, Nebraska, New Mexico, 

Oklahoma, South Dakota, and Texas: U.S. Geological Survey 

Water-Resources Investigations Open-File Report 81-206,28 p.

Kane, M.F., Hildenbrand, T.G., and Hendricks, J.D., 1981, Model 

for the tectonic evolution of the Mississippi Embayment and 

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Kisvarsanyi, E.B., 1975, Data on the Precambrian in drillholes in 

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Missouri Division of Geology and Land Survey Contribution to 

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southeastern Missouri: Rolla, Missouri Division of Geology 

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Rolla, Missouri Division of Geology and Land Survey, v. 40, 

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1975, Traverse in Late Cambrian strata from the St. Francois 

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Lamonds, A.G., 1972, Water-resources reconnaissance of the Ozark 

Plateaus province, northern Arkansas: U.S. Geological Survey 

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in Osage County, Oklahoma, and adjacent areas: Bulletin of 

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GEOHYDROLOGY OF THE OZARK PLATEAUS AQUIFER SYSTEM D127

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1 appendix.

Vineyard, J.D., and Feder, G.L., 1974, Springs of Missouri, with 

sections on fauna and flora by WL. Pflieger and R.G. Lipscomb (reprinted 1982): Rolla, Missouri Division of Geology and 

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 LAKEWOOD, Colorado Federal Center, Bldg. 810

 MENLO PARK, California Bldg. 3, Rm. 3128, 345 Middlefield Rd.

 RESTON, Virginia National Center, Rm. 1C402, 12201 

Sunrise Valley Dr.

 SALT LAKE CITY, Utah Federal Bldg., Rm. 8105, 125 

South State St.

 SPOKANE, Washington U.S. Post Office Bldg., Rm. 135, 

W. 904 Riverside Ave.

 WASHINGTON, D.C. Main Interior Bldg., Rm. 2650, 18th 

and C Sts., NW.

Maps Only

Maps may be purchased over the counter at the U.S. Geological Survey offices:

 FAIRBANKS, Alaska New Federal Building, 101 Twelfth 

Ave.

 ROLLA, Missouri 1400 Independence Rd.

 STENNIS SPACE CENTER, Mississippi Bldg. 3101

u.s. GovBOMorr HOOTING OFFICE: 1994-584-924