Potentiometric Surface of the Ozark Aquifer in 

Northern Arkansas, 2004

Prepared in cooperation with the

ARKANSAS NATURAL RESOURCES COMMISSION

and the ARKANSAS GEOLOGICAL COMMISSION

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U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2005-5208
Potentiometric Surface of the Ozark Aquifer 

in Northern Arkansas, 2004

By T.P. Schrader

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2005-5208

Prepared in cooperation with the

ARKANSAS NATURAL RESOURCES COMMISSION

and the ARKANSAS GEOLOGICAL COMMISSION
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2005

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

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.

Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report.
Contents

 iii

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

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

Aquifer Description .................................................................................................................................................................................. 1

Potentiometric Surface ........................................................................................................................................................................... 5

Summary .................................................................................................................................................................................................... 9

Selected References ............................................................................................................................................................................... 9

Plates

1. Map showing potentiometric surface of the Ozark aquifer in northern Arkansas, 2004 ...................................In pocket

Figures

1. Map showing location of study area ........................................................................................................................................ 2

2. Map showing location of Ozark Plateaus aquifer system. .................................................................................................... 3

Tables

1. Stratigraphic column with descriptions of lithologic and geohydrologic properties of the Ozark aquifer and 

adjacent confining units within Arkansas ............................................................................................................................... 4

2. Information pertaining to measured wells and springs in the Ozark aquifer in northwestern Arkansas and southcentral Missouri, 2004 ................................................................................................................................................................. 6
Potentiometric Surface of the Ozark Aquifer in Northern 

Arkansas, 2004

By T.P. Schrader

Abstract

The Ozark aquifer in northern Arkansas comprises dolomites, limestones, sandstones, and shales of Late Cambrian to 

Middle Devonian age, and ranges in thickness from approximately 1,100 feet to more than 4,000 feet. Hydrologically, the 

aquifer is complex, characterized by discrete and discontinuous 

flow components with large variations in permeability. 

The potentiometric-surface map, based on 59 well and 5 

spring water-level measurements collected in 2004 in Arkansas 

and Missouri, indicates maximum water-level altitudes of about 

1,188 feet in Benton County and minimum water-level altitudes 

of about 116 feet in Randolph County. Regionally, the flow 

within the aquifer is to the south and southeast in the eastern and 

central part of the study area and to the northwest and north in 

the western part of the study area. Comparing the 2004 potentiometric-surface map with a predevelopment potentiometricsurface map indicates general agreement between the two surfaces. Potentiometric-surface differences could be attributed to 

differences in pumping related to changing population from 

1990 to 2000, change in source for public supplies, processes or 

water use outside the study area, or differences in data-collection or map-construction methods.

Introduction

The Ozark aquifer is the largest aquifer, both in area of outcrop and thickness, and the most important source of freshwater 

in the Ozark Plateaus physiographic province, supplying water 

to large areas of northern Arkansas, southern Missouri, northeastern Oklahoma, and southeastern Kansas. Water use from 

the Ozark aquifer in Arkansas was estimated to be 30.8 million 

gallons per day (Mgal/d) in 2000 (Holland, 2004). Water use 

was 32.3 Mgal/d in 1985, 33.3 Mgal/d in 1990, and 35.8 in 1995 

(Holland, 1987: Holland, 1993; Holland, 1999). Water use 

increased about 11 percent from 1985 to 1995, then decreased 

about 14 percent from 1995 to 2000. Water use from the Ozark 

aquifer declined when some public suppliers converted from a 

ground-water to a surface-water source and a decline in domestic ground-water supply when some domestic users connected 

to surface-water source public suppliers (T.W. Holland, written 

commun., U.S. Geological Survey, 2005). A good understanding of changes and trends in water levels is important for continued use, planning, and management of this resource. 

The U.S. Geological Survey (USGS) in cooperation with 

the Arkansas Natural Resources Commission and the Arkansas 

Geological Commission conducted a study of the potentiometric surface of the Ozark aquifer. The study is part of an ongoing 

effort to monitor ground-water levels in Arkansas’ major aquifers. This report presents the potentiometric-surface map of the 

Ozark aquifer within the Ozark Plateaus of northern Arkansas 

(figs. 1 and 2), representing conditions during 2004.

The study area includes Arkansas counties lying completely or partially within the Ozark Plateaus of the Interior 

Highlands major physiographic division (Fenneman, 1938). 

The study area is bounded on the north by Missouri, on the west 

by Oklahoma, on the east by the Mississippi Alluvial Plain, and 

on the south by the Ouachita Province (fig. 1).

The potentiometric-surface map presented in this report 

was prepared from ground-water level data collected by the 

USGS during February 2004. Additionally, streambed altitudes 

in areas where the aquifer is unconfined and hydraulically connected to the surface were used as bounding (maximum groundwater level) values. Spring locations were documented in outcrop areas. Water levels from springs in the Ozark aquifer were 

determined as land-surface altitude from topographic maps and 

used as reference points.

Aquifer Description

The Ozark Plateaus aquifer system (fig. 2) in and adjacent 

to the Ozark Plateaus is divided into five hydrogeologic units 

based on relative rock permeability and well yields. These units 

crop out in a concentric pattern centered on and dipping away 

from the St. Francois Mountains of southeastern Missouri. The 

boundaries between these hydrologic units do not always conform to geologic time divisions or formation boundaries, but 

were chosen to delineate groups of rocks having similar hydrologic properties. These geohydrologic units consist of rocks that 

range in age from Cambrian to Mississippian and are the St. 

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

Ozark confining unit, and Springfield Plateau aquifer (Imes and 

Emmett, 1994). The St. Francois aquifer and St. Francois confining unit underlie the Ozark aquifer. The Ozark confining unit 

overlies the Ozark aquifer. The Springfield Plateau aquifer 

overlies the Ozark confining unit (table 1).
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2 Potentiometric Surface of the Ozark Aquifer in Northern Arkansas, 2004

Figure 1. Location of study area.
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 Aquifer Description 3

Figure 2. Location of Ozark Plateaus aquifer system.
Table 1. Stratigraphic column with descriptions of lithologic and geohydrologic properties of the Ozark aquifer and adjacent confining units 

within Arkansas (modified from Lamonds, 1972; Imes, 1990; Imes and Smith, 1990) ERA PERIOD

GEOLOGIC 

UNIT

GEOHYDROLOGIC

UNIT

LITHOLOGY

THICKNESS

(feet)

GEOHYDROLOGY

Paleozoic

Devonian

Chattanooga Shale

Ozark

confining

unit

Shale unit that crops out in a narrow band 

that outlines the Ozark aquifer and is 

missing where the Ozark aquifer is 

exposed at the surface.

0 - 200 Unit is relatively impermeable because of large shale 

content.

Clifty Limestone

Ozark

aquifer

Chert with lenses of limestone, dolomite, 

and cherty sandstone.

0 - 250 The residual cherty rubble, weathered from cherty 

limestone and sandstone of the unit, may yield 2 

Penters Chert to 5 gallons per minute.

Silurian

Lafferty Limestone Limestone, dolomite, sandstone, and 

minor amounts of shale

0 - 2,000 The limestones and dolomites commonly yield 5 to 

10 gallons per minute from solution channels, 

bedding planes, and fractures. Similar yields 

may be obtained from the sandstone where it is 

porous or fractured. These units contain many 

springs. Yields from springs and some wells 

may exceed 50 gallons per minute.

St. Clair Limestone

Brassfield Limestone

Ordovician

Cason Shale

Fernvale Limestone

Kimmswick Limestone

Plattin Limestone

Joachim Dolomite

St. Peter Sandstone

Everton Formation

Smithville Formation Dolomite, dolomitic limestone, and 

minor amounts of sandstone and 

shale.

100 - 1,000 The solution channels and fractures in the dolomite 

and dolomitic limestone commonly yield 5 to 10 

gallons per minute. Wells that tap large solution 

channels may yield more than 50 gallons per 

minute, but large yields are uncommon. These 

units yield water to several large springs.

Powell Dolomite

Cotter Dolomite

Jefferson City Dolomite

Roubidoux Formation

Sandstone and sandy dolomite. Not 

exposed in Arkansas.

100 - 250 Yields of as much as 450 gallons per minute may be 

obtained from some wells, but yields are highly 

variable and generally average less than 150 

gallons per minute.

Gasconade Dolomite Dolomite, sandy dolomite, and sandstone. 

Not exposed in Arkansas.

350 - 650 The most productive water-bearing part of this unit is 

the Van Buren Formation. Wells that tap into the 

Van Buren Formation commonly yield 150 to 

300 gallons per minute and may yield as much 

as 500 gallons per minute.

Van Buren Formation

Cambrian

Eminence Dolomite

Potosi Dolomite

Doe Run Dolomite

St. Francois

confining

unit

Shale and shaley dolomite, siltstone, and 

limestone conglomerate. Shales 

present both as distinct beds and 

disseminated throughout dolomite 

matrix. Not exposed in Arkansas.

0 - 750 Permeability is minimal to moderate. Unit is more 

permeable where transected by fault and 

Derby Dolomite fracture zones.

Davis Formation

4 Potentiometric Surface of the Ozark Aquifer in Northern Arkansas, 2004
Potentiometric Surface 5

The Ozark aquifer in Arkansas is composed of dolomites, 

limestones, sandstones, and shales of Upper Cambrian to Middle Devonian age (table 1) and ranges in thickness from approximately 1,100 feet (ft) in the northwestern corner of the State to 

more than 4,000 ft in the west-central portion of the State (Imes, 

1990). Most wells completed in the aquifer yield between 50 

and 100 gallons per minute (gal/min) although some wells may 

yield as much as 600 gal/min (Imes and Emmett, 1994; Adamski and others, 1995). 

The Ozark aquifer is underlain by the St. Francois confining unit (the uppermost geologic unit of which is the Doe Run 

Dolomite; table 1). The Ozark aquifer is exposed in much of 

southern and central Missouri and north-central Arkansas (fig. 

2) where uplift of the Ozark dome and erosion of younger rocks 

has formed a deeply dissected, rugged topography that is the 

primary recharge area of the aquifer. The aquifer is overlain by 

the Ozark confining unit mainly in the southern and western 

part of the study area (table 1). Within the Mississippi Alluvial 

Plain, east and southeast of the outcrop area (figs. 1 and 2), thick 

deposits of Cretaceous-, Tertiary-, and Quaternary-age sediments unconformably overlay the Ordovician-age rocks of the 

Ozark aquifer. Within this part of the Mississippi Alluvial Plain, 

major rivers receive substantial discharge from the adjacent 

Ozark aquifer (Mesko and Imes, 1995).

The geohydrology of the Ozark aquifer is complex, consisting of a combination of discrete and discontinuous flow 

components resulting from spatial variations in regolith thickness, faults, the presence of chert nodules, lithology, and 

cementation. Primary porosity and permeability are low for 

most rock units of the aquifer, although secondary permeability 

resulting from fracturing, bedding planes, and dissolution of the 

carbonate rocks is spatially variable and ranges from moderate 

to large (Adamski, 1996). Hydraulic conductivity ranges from 

1x10-8 feet per second (ft/s) to more than 1x10-3 ft/s (Imes and 

Emmett, 1994). The principal recharge area for the aquifer is in 

central and south-central Missouri and north-central Arkansas, 

where the aquifer is hydraulically connected to the surface and 

the potentiometric surface mimics the land-surface topography. 

Beneath the Mississippi Alluvial Plain (fig. 1), the rocks 

composing the Ozark aquifer dip at about 45 feet per mile (ft/

mi) to the southeast. In the northern part of the study area, the 

regional dip is about 26 ft/mi southward, increasing to 175 ft/mi 

or more at the southern boundary of the Ozark Plateaus (Imes, 

1990). The depth of the Ozark aquifer increases to more than 

4,000 ft below land surface in the southern part of the study 

area. In this area, water quality is affected by increasing 

amounts of dissolved solids, fluoride, sulfide, and radium as 

water moves downdip, away from recharge areas (Imes and 

Emmett, 1994). The combination of greater depth and poorer 

water quality limits the viability of the Ozark aquifer as an economic source of water in the southernmost part of the study 

area.

Potentiometric Surface

The potentiometric-surface map (plate 1) indicates the altitude to which water levels would rise in wells completed in the 

Ozark aquifer. Water levels were measured during February 

2004, to the nearest 0.01 ft from a measuring point of known 

altitude using a graduated steel tape or electric water-level indicator. The altitude of the land surface was determined by first 

locating the wells and springs using a global positioning system 

instrument to read the latitude and longitude. The location then 

was plotted using a computer plotting program along with the 

altitude of land surface from digital 7.5-minute USGS topographic quadrangle maps. The potentiometric surface was contoured using the measured water-level data (table 2) from 59 

wells and 5 springs. Additional bounding values were used 

where the Ozark aquifer is exposed at the surface. Land-surface 

contours and stream altitudes from a 1:500,000 scale topographic map of Arkansas (U.S. Geological Survey, 1990) were 

considered in the construction of the potentiometric-surface 

map (plate 1) to prevent contours from crossing streams at inappropriate locations, and to reflect the general land-surface 

topography where appropriate.

The Ozark aquifer covers a large area in Arkansas and has 

variable thickness and hydrologic properties. Data point distribution is sparse in some areas. The potentiometric-surface map 

is intended to show the general configuration of the potentiometric surface and should not be used to estimate exact waterlevel altitude or depth to water at any given location. 

The extent of the potentiometric-surface map presented on 

plate 1 covers approximately half the area of the Ozark Plateaus 

in Arkansas (fig. 1). The Ozark aquifer in the southern part of 

the study area is not a viable source of water because of the 

greater depths and poorer water quality. Few wells have been 

constructed in that area and data are not available for contouring 

purposes.

The potentiometric-surface map depicts the general direction of ground-water flow within the Ozark aquifer, with 

ground-water movement perpendicular to the contours in the 

direction of the hydraulic gradient. The direction of regional 

ground-water flow generally is to the south and southeast in the 

eastern and central part of the study area and to the northwest 

and north in the western part of the study area, but has greater 

variability in areas where the unconfined part of the aquifer is 

hydraulically connected to the surface. In these areas, the flow 

direction is affected more by local topography (flowing from 

high altitudes toward stream valleys).

The potentiometric-surface map indicates the highest 

water-level altitude of about 1,188 feet above NGVD of 1929 in 

Benton County. The water-level altitudes in this area are reflective of the influence of the land-surface topography and not the 

regional flow pattern of the aquifer. Water-level altitudes of less 

than 400 ft above NGVD of 1929 are mapped along the eastern 

and southeastern part of the study area in Lawrence, Randolph, 

and Sharp Counties. The lowest water level of 116 feet above 

NGVD of 1929 was measured in eastern Randolph County.
6 Potentiometric Surface of the Ozark Aquifer in Northern Arkansas, 2004

Table 2. Information pertaining to measured wells and springs in the Ozark aquifer in northwestern Arkansas and south-central Missouri,

2004.

[NA, not applicable,--, not available; Aquifer code designations are: 357BFLD, Brassfield Limestone; 364STPR, St. Peter Sandstone; 364EVRN, Everton

Formations; 368PWLL, Powell Dolomite; 367CTTR, Cotter Dolomite; 367CRJF, Cotter-Jefferson City Dolomite; 368JFRC, Jefferson City Dolomite; 367RBDX, 

Roubidoux Formation, 367GNTR, Gunter Sandstone member of Van Buren Formation; 367POTS, Potosi Dolomite; Vertical datum is NGVD of 1929. Horizontal 

datum is NAD of 1983]

Latitude

(degrees,

minutes,

seconds)

Longitude

(degrees,

minutes,

seconds) Station name

Land

surface

altitude

(feet above

NGVD of

1929)

Well

depth

(feet 

below 

landsurface

datum)

Aquifer

code of

formation

at depth

of well

Water

level

altitude

(feet above

NGVD of

1929)

Depth to

water

(feet)

Date of

measurement

State of Arkansas

Baxter County wells

361610 921143 19N11W31DAA1 640 193 367CTTR 555 84.97 2/11/2004

361714 923026 19N14W29DBC1 720 1,625 367GNTR 664 56.27 2/11/2004

362114 921423 20N11W35CCA1 600 295 367CTTR 565 35.44 2/11/2004

362309 921419 20N12W23CBA1 600 550 367RBDX 547 52.53 2/11/2004

362431 921912 20N13W13ABD1 620 209 367CTTR 548 72.02 2/11/2004

362435 922026 20N13W14ABC1 580 493 367CTTR 546 34.39 2/11/2004

362700 921558 21N12W33ACB1 610 500 367RBDX 567 42.93 2/11/2004

Benton County Wells

362004 935553 19N28W11BAD1 1,260 1,030 367RBDX 1,188 71.88 2/18/2004

361954 940618 19N29W07DAA1 1,210 1,659 367GNTR 1,065 144.68 2/18/2004

362456 942723 20N33W14ACD1 1,185 1,600 367GNTR 755 430.44 2/18/2004

362512 942720 20N33W14DBC1 1,230 1,614 367GNTR 803 426.78 2/18/2004

362417 943607 20N34W21ABD1 1,022 380 364EVRN 992 30.48 2/18/2004

362636 940138 21N29W35DDB2 1,405 1,769 367GNTR 1,063 342.15 2/18/2004

Boone County Wells

361150 930258 18N19W19BCC1 1,150 1,649 367GNTR 925 224.66 2/12/2004

361022 930050 18N19W33BBB1 1,300 2,055 367GNTR 718 582.36 2/12/2004

362703 925503 21N18W20CCD1 880 1,415 371POTS 643 237.24 2/11/2004

Carroll County Wells

362022 932604 19N23W04BAC1 1,365 1,587 367RBDX 1,164 200.96 2/17/2004

361918 932633 19N23W08ADD1 1,355 2,300 367GNTR 1,101 253.8 2/17/2004

362340 934458 20N26W16DCA1 1,198 1,332 367GNTR 1,062 136.4 2/17/2004

362313 934253 20N26W23ACA1 1,335 1,713 371POTS 1,048 287.1 2/17/2004

362939 934412 21N26W10CDC1 1,090 1,122 367GNTR 993 97.3 2/17/2004

362921 934641 21N26W17BCC1 1,010 1,058 367RBDX 968 41.76 2/17/2004
 Potentiometric Surface 7

Fulton County Wells

361707 913831 19N06W20DCA1 824.6 158 367CTTR 752 72.55 2/10/2004

361728 913503 19N06W23AAD1 680 1,630 367GNTR 453 226.67 2/10/2004

361647 913816 19N06W29AAD1 770 128 367CTTR 738 32.37 2/10/2004

362128 913631 20N06W27DBC1 550 165 368JFRC 485 64.77 2/10/2004

362210 914923 20N08W27ABD1 662 1,282 367GNTR 650 12.14 2/10/2004

362402 915904 20N09W18BAD1 875 950 367RBDX 758 116.85 2/10/2004

Fulton County Springs

361908 913431 19N06W12BDAA1SP 400 NA 367CTTR 400 0 2/10/2004

Independence County Springs

354949 913959 14N06W29BCC1SP 340 NA 367CTTR 340 0 2/10/2004

Izard County Wells

360753 920626 17N11W13AAD1 538 1,729 367RBDX 498 39.79 2/10/2004

361323 915549 18N09W15BCB1 742 600 367CTTR 591 150.98 2/10/2004

Marion County Wells

361300 922940 18N14W08BCC1 700 198 367CTTR 586 114.27 2/12/2004

361748 923222 19N15W14BAA2 640 -- 367CTTR 499 141.17 2/12/2004

361634 923527 19N15W20ACC1 684 900 367RBDX 517 166.81 2/12/2004

361442 924124 19N16W33CCB1 841 753 367RBDX 554 287.39 2/12/2004

361512 925050 19N18W36BDC1 755 1,392 367RBDX 720 35.43 2/12/2004

362452 923951 20N16W03BAB2 895 600 368JFRC 766 129.04 2/11/2004

362225 924919 20N17W19ABC2 860 180 367CTTR 835 25.32 2/11/2004

Newton County Wells

360014 931130 16N21W34ABC1 870 190 364EVRN 804 65.79 2/12/2004

Randolph County Wells

361350 910944 18N02W02CAC1 361 128 367CRJF 309 52.38 2/9/2004

362440 905351 20N02E06AAC1 485 900 367RBDX 116 368.81 2/9/2004

362249 910959 20N02W15DAD1 440 170 367CTTR 415 25.31 2/9/2004

Table 2. Information pertaining to measured wells and springs in the Ozark aquifer in northwestern Arkansas and south-central Missouri,

2004.—Continued

[NA, not applicable,--, not available; Aquifer code designations are: 357BFLD, Brassfield Limestone; 364STPR, St. Peter Sandstone; 364EVRN, Everton

Formations; 368PWLL, Powell Dolomite; 367CTTR, Cotter Dolomite; 367CRJF, Cotter-Jefferson City Dolomite; 368JFRC, Jefferson City Dolomite; 367RBDX, 

Roubidoux Formation, 367GNTR, Gunter Sandstone member of Van Buren Formation; 367POTS, Potosi Dolomite; Vertical datum is NGVD of 1929. Horizontal 

datum is NAD of 1983]

Latitude

(degrees,

minutes,

seconds)

Longitude

(degrees,

minutes,

seconds) Station name

Land

surface

altitude

(feet above

NGVD of

1929)

Well

depth

(feet 

below 

landsurface

datum)

Aquifer

code of

formation

at depth

of well

Water

level

altitude

(feet above

NGVD of

1929)

Depth to

water

(feet)

Date of

measurement
8 Potentiometric Surface of the Ozark Aquifer in Northern Arkansas, 2004

Searcy County Wells

355126 923401 14N15W15AAC1 1,060 3,534 367GNTR 719 340.83 2/13/2004

355520 923718 15N15W19CDD1 1,100 550 364EVRN 754 346.45 2/12/2004

355750 924133 15N16W09BBA1 925 950 368PWLL 790 135.43 2/12/2004

355416 924025 15N16W34BAD1 1,000 485 364PLTN 815 184.67 2/12/2004

355819 924450 15N17W01CBA1 986 1,320 368PWLL 736 250.02 2/12/2004

360014 923603 16N15W29ACB1 1,090 640 364EVRN 949 141.2 2/12/2004

Sharp County Wells

355812 913318 15N05W06DDD1 645 482 364EVRN 542 103.32 2/10/2004

360233 913338 16N05W06DCC1 450 1,110 367RBDX 409 40.85 2/10/2004

360023 913654 16N06W27ACC1 650 1,000 367CTTR 555 94.87 2/10/2004

360818 912804 17N05W12BDC1 417 425 367CTTR 359 58.42 2/10/2004

360604 913854 17N06W29ABC1 525 900 367CTTR 443 82.13 2/10/2004

361325 913638 18N06W10CBC1 625 1,525 367GNTR 479 146.16 2/9/2004

361813 912337 19N04W15BAA1 584 611 367RBDX 528 55.65 2/9/2004

Sharp County Springs

360228 913211 16N05W17AABA1SP 495 NA 364STPR 495 0 2/10/2004

360325 913631 16N06W10AAA1SP 435 NA 364EVRN 435 0 2/10/2004

360325 913648 16N06W10ABBA1SP 455 NA 364EVRN 455 0 2/10/2004

Washington County Wells

355903 941807 15N31W17BBD1 1,195 2,097 367GNTR 1,151 44.07 2/18/2004

355652 941858 15N31W30CAD1 1,165 2,485 367GNTR 1,150 15.02 2/18/2004

360509 942242 16N32W09ABD1 1,135 1,815 367GNTR 992 142.61 2/18/2004

State of Missouri

Ozark County Wells

363206 923609 21N15W03BAB1 805 550 367GSCD 659 145.58 2/11/2004

363128 923719 21N15W04CCA1 722 505 367GSCD 653 69.03 2/11/2004

Table 2. Information pertaining to measured wells and springs in the Ozark aquifer in northwestern Arkansas and south-central Missouri,

2004.—Continued

[NA, not applicable,--, not available; Aquifer code designations are: 357BFLD, Brassfield Limestone; 364STPR, St. Peter Sandstone; 364EVRN, Everton

Formations; 368PWLL, Powell Dolomite; 367CTTR, Cotter Dolomite; 367CRJF, Cotter-Jefferson City Dolomite; 368JFRC, Jefferson City Dolomite; 367RBDX, 

Roubidoux Formation, 367GNTR, Gunter Sandstone member of Van Buren Formation; 367POTS, Potosi Dolomite; Vertical datum is NGVD of 1929. Horizontal 

datum is NAD of 1983]

Latitude

(degrees,

minutes,

seconds)

Longitude

(degrees,

minutes,

seconds) Station name

Land

surface

altitude

(feet above

NGVD of

1929)

Well

depth

(feet 

below 

landsurface

datum)

Aquifer

code of

formation

at depth

of well

Water

level

altitude

(feet above

NGVD of

1929)

Depth to

water

(feet)

Date of

measurement
Summary 9

In most of the study area the general level and shape of the 

potentiometric surface has changed little since predevelopment, 

1995, or 2001. A comparison of the predevelopment potentiometric surface (Imes, 1990) and the 2004 potentiometric surface 

indicates general agreement between the two surfaces with the 

exception of parts of Benton, Carroll, and Washington Counties. In northwestern Benton County water levels have declined 

and the direction of flow has changed from westward in the predevelopment potentiometric surface to northwestward in the 

2004 potentiometric surface. In northeastern Benton and northwestern Carroll Counties water levels have declined. In northwestern Washington County water levels have declined and the 

direction of flow is northwestward, the same direction as in the 

predevelopment potentiometric surface. The potentiometric 

surface in 2004 is similar to the potentiometric surface in 1995 

(Pugh, 1998) and 2001 (Schrader, 2001). Potentiometric-surface differences could be attributed to differences in hydrologic 

stresses (pumping related to changing population, differences in 

pumping for agricultural uses, or pumping conditions just prior 

to a water-level measurement) or data-collection and map-construction methods (time of year or different numbers and locations of water-level measurements used for constructing maps 

representing different years). 

The Benton, Carroll, and Washington Counties area has 

been experiencing rapid growth in population and agricultural 

use since 1990. Population in these three counties has increased 

36 to 57 percent from 1990 to 2000 (GIS Applications Laboratory, University of Arkansas at Little Rock, 2001). Water use, 

for the entire study area, from the Ozark aquifer has declined by 

14 percent from 1995 to 2000. Water use from the Ozark aquifer 

in Benton, Carroll, and Washington Counties peaked in 1999 

and 1998 at about 8 million gallons per day. In 2003 water use 

from the Ozark aquifer in these three counties declined to about 

3.8 million gallons per day (Terrance W. Holland, U.S. Geological Survey, written commun., 2005). A decrease in water use 

would be expected to cause a rise in water levels. Water levels 

in Benton, Carroll, and Washington Counties in 1998, 2001, 

and 2004 are similar or have declined. Processes other than 

water use in these three counties are having a greater effect on 

water levels in the Ozark aquifer in Benton, Carroll, and Washington Counties. Changes in precipitation, flow in the aquifer 

because of dissolution in a karst environment, or water use outside the study area may affect water levels. The decline in water 

levels in this part of the study area may be caused by the effects 

of processes or water use outside the study area.

Summary

During February 2004, ground-water levels from 59 wells 

and 5 springs in the Ozark aquifer in northern Arkansas were 

measured, mapped, and contoured by the U.S. Geological Survey in cooperation with the Arkansas Natural Resources Commission and the Arkansas Geological Commission and a potentiometric-surface map of the Arkansas part of the Ozark aquifer 

was constructed. The Ozark aquifer in northern Arkansas is 

composed of dolomites, limestones, sandstones, and shales of 

Upper Cambrian to Middle Devonian age which dip to the south 

and southeast away from the St. Francois Mountains of Missouri. The aquifer is complex, characterized by discrete hydrologic units with large variations in permeability. The principal 

recharge area for the aquifer is in central and south-central Missouri and north-central Arkansas, where the aquifer is hydraulically connected to the surface. 

A potentiometric-surface map of the Ozark aquifer in 

northern Arkansas for 2004 indicates a maximum water-level 

altitude of about 1,188 ft in Benton County, and a minimum 

altitude of about 116 ft in Randolph County. The direction of 

regional ground-water flow is generally to the south and southeast in the eastern half of the study area and to the northwest and 

north in the western half of the study area except in areas where 

the aquifer is unconfined. In these areas, the potentiometric surface generally mimics the land-surface topography. The 2004 

potentiometric-surface map generally is similar in shape to a 

predevelopment potentiometric-surface map except in three 

northwestern counties. Potentiometric-surface differences 

could be attributed to differences in pumping related to changing population from 1990 to 2000, change in source for public 

supplies, processes or water use outside the study area, or differences in data-collection or map construction methods.

Selected References

Adamski, J.C., 1996, Nutrients and pesticides in ground water 

of the Ozark Plateaus in Arkansas, Kansas, Missouri, and 

Oklahoma: U.S. Geological Survey Water-Resources Investigations Report 96-4313, 28 p.

Adamski, J.C., Petersen, J.C., Freiwald, D.A., and Davis, J.V., 

1995, Environmental and hydrologic setting of the Ozark 

Plateaus study unit, Arkansas, Kansas, Missouri, and Oklahoma: U.S. Geological Survey Water-Resources Investigations Report 94-4022, 69 p.

Brahana, J.V., Gonthier, G.J., and Remsing, L.M., 1991, 

Hydrogeologic data for Boone County, Arkansas: U.S. Geological Survey Open-File Report 91-518, 36 p.

Brahana, J.V., Leidy, V.A., Lindt, J., and Hodge, S.A., 1993, 

Hydrogeologic data for Carroll County, Arkansas: U.S. Geological Survey Open-File Report 93-150, 32 p.

Bryant, C.T., Ludwig, A.H., and Morris, E.E., 1985, Groundwater problems in Arkansas: U.S. Geological Survey WaterResources Investigations Report 85-4010, 24 p.

Bush, W.V., Haley, B.R., Stone, C.G., Holbrook, D.F., and 

McFarland, J.D. III, 1980, A guidebook to the geology of the 

Arkansas Paleozoic area (Ozark Mountains, Arkansas Valley, and Ouachita Mountains): Arkansas Geological Commission Guidebook 77-1, 79 p.

Caplan, W.M., 1957, Subsurface geology of northwestern 

Arkansas: Arkansas Geological and Conservation Commission Information Circular 21, 14 p.
10 Potentiometric Surface of the Ozark Aquifer in Northern Arkansas, 2004

Caplan, W.M., 1960, Subsurface geology of pre-Everton rocks 

in northern Arkansas: Arkansas Geological and Conservation 

Commission Information Circular 21, 17 p.

Fenneman, N.M., 1938, Physiography of eastern United States: 

New York, McGraw-Hill Book Co., Inc., 714 p.

Frezon, E.S., Glick, E.E., 1959, Pre-Atoka rocks of northern 

Arkansas: U.S. Geological Survey Professional Paper 314-H, 

18 p.

GIS Applications Laboratory, University of Arkansas at Little 

Rock, 2001, Percent total population change; Arkansas by 

county: 1990 - 2000: accessed August 10, 2001, at URL http:/

/argis.ualr.edu/00_pop_chg.pdf.

Holland, T.W., 1987, Use of water in Arkansas, 1985: Arkansas 

Geological Commission Water Resources Summary 16, 27 p.

Holland, T.W., 1993, Use of water in Arkansas, 1990: U.S. 

Geological Survey Open-File Report 93-48, 1 sheet.

Holland, T.W., 1999, Water use in Arkansas, 1995: U.S. Geological Survey Open-File Report 99-188, 1 sheet.

Holland, T.W., 2004, Estimated water use in Arkansas, 2000: 

U.S. Geological Survey Scientific Investigations Report 

2004-5230, 31 p.

Imes, J.L., 1990, 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, scale 

1:750,000.

Imes, J.L., and Emmett, L.F., 1994, Geohydrology of the Ozark 

Plateaus aquifer system in parts of Missouri, Arkansas, Oklahoma, and Kansas: U.S. Geological Survey Professional 

Paper 1414-D, 127 p.

Imes, J.L., and Smith, B.J., 1990, Areal extent, stratigraphic 

relation, and geohydrologic properties of regional geohydrologic units, Missouri: U.S. Geological Survey Hydrologic 

Investigations Atlas HA-711-I, 3 sheets, scale 1:750,000.

Kilpatrick, J.M., and Ludwig, A.H., 1990, Ground-water 

resources of the upper White River basin in Arkansas: U.S. 

Geological Survey Open-File Report 88-724, 48 p.

Lamonds, A.G., 1972, Water-resources reconnaissance of the 

Ozark Plateaus Province, northern Arkansas: U.S. Geological Survey Hydrologic Investigations Atlas HA-383, 2 

sheets, scale 1:500,000.

Leidy, V.A., and Morris, E.E., 1990, Hydrogeology and quality 

of ground water in the Boone Formation and Cotter Dolomite 

in karst terrain of northwestern Boone County, Arkansas: 

U.S. Geological Survey Water-Resources Investigations 

Report 90-4066, 57 p.

Mesko, T.O., and Imes, J.L., 1995, Discharge of ground water 

along the Ozark Escarpment in southeastern Missouri and 

northeastern Arkansas: U.S. Geological Survey WaterResources Investigations Report 95-4103, 12 p.

Pugh, A.L., 1998, Potentiometric surface of the Ozark aquifer 

in northern Arkansas, 1995: U.S. Geological Survey WaterResources Investigation Report 98-4000, 7 p.

Schrader, T. P., 2001, Potentiometric surface of the Ozark aquifer in northern Arkansas, 2001: U.S. Geological Survey 

Water-Resources Investigation Report 01-4233, 11 p.

U.S. Geological Survey, 1990, State of Arkansas (Topographic): U.S. Geological Survey Map Publication 34092-

E1-ST-500, scale 1:500,000, 1 sheet.

Wise, O.A., and Caplan, W.M., 1979, Silurian and Devonian 

rocks of northern Arkansas: Arkansas Geological Commission Information Circular 25, 14 p.
Schrader, T.P.—POTENTIOMETRIC SURFACE OF THE OZARK AQUIFER IN NORTHERN ARKANSAS, 2004—U.S. Geological Survey Scientific Investigations Report 2005-5208
0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

RANDOLPH

LAWRENCE

SHARP

FULTON

IZARD

STONE

INDEPENDENCE

VAN BUREN CLEBURNE

POPE

JOHNSON

CRAWFORD

FRANKLIN

BENTON

WASHINGTON

MADISON

CARROLL

NEWTON

SEARCY

BOONE

MARION

BAXTER

EXPLANATION

OUTCROP OF OZARK AQUIFER

POTENTIOMETRIC CONTOUR--Shows

 altitude at which water level would have

 stood in tightly cased well. Dashed

 where approximately located. Contour

 interval 100 feet. Datum is National

 Geodetic Vertical Datum of 1929

GENERAL DIRECTION OF GROUND-

 WATER FLOW

OBSERVATION WELL COMPLETED

 IN THE OZARK AQUIFER--Measurement

 made in February 2004. Value is the 

 water-level altitude above the National

 Geodetic Vertical Datum of 1929

SPRING IN THE OZARK AQUIFER--

 Measurement made in February 2004

CONTROL POINT--Intersection of land-

 surface contour and stream within area

 where the Ozark aquifer is unconfined.

 Altitude determined from 1:500,000

 topographic map

500

POTENTIOMETRIC SURFACE OF THE OZARK AQUIFER

IN NORTHERN ARKANSAS, 2004 

T.P. SCHRADER

2005

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

SCIENTIFIC INVESTIGATIONS REPORT 2005-5208

Potentiometric-surface map of the Ozark aquifer-Plate 1

Schrader, T.P., 2005, Potentiometric surface of the Ozark aquifer in northern Arkansas, 2004

Prepared in cooperation with the

ARKANSAS NATURAL RESOURCES COMMISSION

and the

ARKANSAS GEOLOGICAL COMMISSION

94o

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36 30' o

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