U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007–5218

Prepared in cooperation with the Arkansas Natural Resources Commission and the 

Arkansas Geological Survey

Potentiometric Surfaces and Water-Level Trends in 

the Cockfield and Wilcox Aquifers of Southern and 

Northeastern Arkansas, 2006

36o

35o

34o

94o 93o 92o 91o

90o

MISSOURI

MISSISSIPPI

TEXAS

OKLAHOMA

TENNESSEE

LOUISIANA

ATLANTIC

West Gulf Coastal Plain

Mississippi

Alluvial

Plain

Ouachita Mountains

Ozark Plateaus

Coastal Plain

INTERIOR

HIGHLANDS

Ouachita

province

Arkansas Valley

PLAIN

CLAY

GREENE

CRAIGHEAD MISSISSIPPI

POINSETT

CROSS

CRITTENDEN

ST. FRANCIS

LEE

ARKANSAS

GRANT JEFFERSON

DALLAS

CLEVELAND LINCOLN

DESHA

DREW

CHICOT

ASHLEY

BRADLEY

CALHOUN

UNION

OUACHITA

COLUMBIA

NEVADA

HEMPSTEAD

CLARK

HOT SPRING

Mississippi River
Potentiometric Surfaces and WaterLevel Trends in the Cockfield and Wilcox 

Aquifers of Southern and Northeastern 

Arkansas, 2006

By T.P. Schrader

In cooperation with the Arkansas Natural Resources Commission and

the Arkansas Geological Survey

Scientific Investigations Report 2007-5218

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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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.

Suggested citation:

Schrader, T.P., 2007, Potentiometric surfaces and water-level trends in the Cockfield and Wilcox aquifers of southern 

and northeastern Arkansas, 2006: U.S. Geological Survey Scientific Investigations Report 2007-5218, 27 p.
iii

Contents

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

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

Methods...........................................................................................................................................................2

Cockfield Formation.......................................................................................................................................4

Hydrogeologic Setting .........................................................................................................................4

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

Water-Level Trends ..............................................................................................................................8

Wilcox Group................................................................................................................................................15

Hydrogeologic Setting .......................................................................................................................15

Potentiometric Surface......................................................................................................................15

Water-Level Trends ............................................................................................................................21

Summary........................................................................................................................................................25

References....................................................................................................................................................27

Figures

1. Map showing location of study areas ..........................................................................................3

2. Diagram showing well-numbering system ..................................................................................4

3. Graphs showing water use from the Cockfield aquifer, 1975-2000..........................................4

4. Map showing potentiometric surface of the Cockfield aquifer in southeastern

Arkansas, 2006 ..............................................................................................................................5

5. Water-level hydrographs for selected wells completed in the Cockfield aquifer in

southeastern Arkansas..............................................................................................................10

6. Graph showing water use from the Wilcox aquifer, 1975-2000 ..............................................15

7. Map showing potentiometric surface of the Wilcox aquifer in southern Arkansas,

2006 ...............................................................................................................................................16

8. Map showing potentiometric surface of the Wilcox aquifer in northeastern

Arkansas, 2006 ............................................................................................................................17

9. Water-level hydrographs for selected wells completed in the Wilcox aquifer in 

 northeastern Arkansas ..............................................................................................................22

Tables

1. Water-level data collected from wells completed in the Cockfield aquifer in

southeastern Arkansas, 2006......................................................................................................6

 2. Range, mean, and median of annual rise/decline in water level by county for wells

in the aquifer, 1986-2006 ..............................................................................................................9

3. Water-level data collected from wells completed in the Wilcox aquifer in southwestern

 Arkansas, 2006 ............................................................................................................................18

4. Water-level data collected from wells completed in the Wilcox aquifer in northeastern

 Arkansas, 2006 ............................................................................................................................19

5. Range, mean, and median of annual rise/decline in water level by county for wells in 

 the Wilcox aquifer in the northeastern study area, 1986-2006............................................21
iv

Conversion Factors and Datums

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Flow rate

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

gallon per minute (gal/m) 0.6308 liter per second (L/s)

million gllons per day (Mgal/d) 0.04381 cubic meter per second (m3

/s)

Temperature in degrees Celsius (  ̊C) may be converted to degrees Fahrenheit ( ̊F) as follows:  ̊F = (1.8 x  ̊C) + 32

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD of 1929).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD of 1983).
Potentiometric Surfaces and Water-Level Trends in 

the Cockfield and Wilcox Aquifers of Southern and 

Northeastern Arkansas, 2006

By T.P. Schrader

0.01 to 0.07 feet per year. Arkansas, Ashley, Bradley, Chicot, 

Columbia, Drew, Lincoln, and Union Counties have mean 

annual declines from 0.4 to 0.55 feet per year. Desha County 

has a mean annual decline of about 1.35 feet per year.

The direction of ground-water flow in the southwestern 

study area of the Wilcox Group generally is south and east. 

The lowest water-level altitude measured in southwestern 

Arkansas was 147 feet above the National Geodetic Vertical 

Datum of 1929 near the Ouachita River in Clark County; the 

highest water-level altitude measured was 397 feet above the 

National Geodetic Vertical Datum of 1929 in the outcrop area 

of Hempstead County. The direction of ground-water flow in 

the northeastern study area of the Wilcox Group generally is 

south and east. The lowest water-level altitude measured in 

northeastern Arkansas was 120 feet above the National Geodetic Vertical Datum of 1929 near West Memphis in Crittenden County; the highest water-level altitude measured was 368 

feet above the National Geodetic Vertical Datum of 1929 on 

Crowleys Ridge in Clay County. Hydrographs from 28 wells 

with historical water levels from 1986 to 2006 were evaluated 

using linear regression to calculate the annual rise or decline. 

All 28 wells showed an annual decline from 1986 to 2006. 

Craighead, Greene, Mississippi, and Poinsett Counties have 

mean annual declines from 0.27 to 1.00 feet per year. Crittenden, Lee, and St. Francis Counties have mean annual declines 

from 1.39 to 1.64 feet per year.

Introduction

The Cockfield Formation of Claiborne Group and the 

Wilcox Group contain aquifers that provide sources of ground 

water in southern and northeastern Arkansas, where in 2000 

about 9.9 million gallons per day (Mgal/d) was withdrawn 

from the Cockfield Formation of Claiborne Group and about 

22.2 Mgal/d was withdrawn from the Wilcox Group (Holland, 

2004). Major withdrawals from the aquifers were for industrial 

and public water supplies, with lesser but locally important 

withdrawals for domestic and livestock uses.

Abstract

The Cockfield Formation of Claiborne Group and the 

Wilcox Group contain aquifers that provide sources of ground 

water in southern and northeastern Arkansas. In 2000, about 

9.9 million gallons per day was withdrawn from the Cockfield 

Formation of Claiborne Group and about 22.2 million gallons per day was withdrawn from the Wilcox Group. Major 

withdrawals from the aquifers were for industrial and public 

water supplies.

A study was conducted by the U.S. Geological Survey in 

cooperation with the Arkansas Natural Resources Commission 

and the Arkansas Geological Survey to determine the water 

level associated with the aquifers in the Cockfield Formation 

of Claiborne Group and the Wilcox Group in southern and 

northeastern Arkansas. During February and March 2006, 56 

water-level measurements were made in wells completed in 

the Cockfield aquifer and 59 water-level measurements were 

made in wells completed in the Wilcox aquifer, 16 in southwestern and 43 in northeastern Arkansas. This report presents 

the results as potentiometric-surface maps and as long-term 

water-level hydrographs. 

The regional direction of ground-water flow in the 

Cockfield Formation of Claiborne Group generally is towards 

the east and southeast, away from the outcrop, except in areas 

of intense ground-water withdrawals, such as western Drew 

County, southeastern Lincoln County, southwestern Calhoun 

County, and near Crossett in Ashley County. There are three 

cones of depression indicated by relatively low water-level 

altitudes in southeastern Lincoln County, southwestern 

Calhoun County, and near Crossett in Ashley County. The 

lowest water-level altitude measured was 44 feet above the 

National Geodetic Vertical Datum of 1929 in Lincoln County; 

the highest water-level altitude measured was 346 feet above 

the National Geodetic Vertical Datum of 1929 in Columbia 

County at the outcrop area. Hydrographs from 40 wells with 

historical water levels from 1986 to 2006 were evaluated 

using linear regression to calculate the annual rise or decline. 

Calhoun and Cleveland Counties have mean annual rises from 
2 Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers

A study was conducted by the U.S. Geological Survey 

(USGS) in cooperation with the Arkansas Natural Resources 

Commission and the Arkansas Geological Survey to determine 

the water level associated with the aquifers in the Cockfield 

Formation of Claiborne Group and the Wilcox Group (hereafter the respective aquifers are referred to as the Cockfield 

aquifer and the Wilcox aquifer) in southern and northeastern 

Arkansas. During February and March 2006, 56 water-level 

measurements were made in wells completed in the Cockfield 

aquifer and 59 water-level measurements were made in wells 

completed in the Wilcox aquifer, 16 in southwestern and 43 

in northeastern Arkansas. This report presents the results as 

potentiometric-surface maps and as long-term water-level 

hydrographs. 

The study areas of the Cockfield and Wilcox aquifers 

(fig. 1) include much of the West Gulf Coastal Plain and the 

Mississippi Alluvial Plain in Arkansas. The study area of 

the Cockfield aquifer in southeastern Arkansas is bounded 

on the east by the Mississippi River and on the south by the 

Louisiana State line. The western boundary is defined by the 

western extent of the outcrop and subcrop (Hosman, 1982) of 

the Cockfield Formation. The northern boundary is defined by 

the locations of observation wells. The study area boundary of 

the Wilcox aquifer in southwestern Arkansas is defined by the 

outcrop of the Wilcox Group and the locations of observation 

wells in Clark, Hempstead, Hot Spring, Nevada, and Ouachita 

Counties. The study area of the Wilcox aquifer in northeastern Arkansas is bounded on the north by the Missouri State 

line and on the east by the Mississippi River. The western and 

southern boundaries of the study area are defined by the extent 

of the outcrop at or near Crowleys Ridge, and by the location 

of observation wells that penetrate the Wilcox aquifer.

This report is the fourth in a triennial series of reports 

discussing the potentiometric surfaces of the Cockfield and 

Wilcox aquifers. Earlier reports in 2003, 2000, and 1996-1997 

can be referenced through Yeatts (2004), Schrader and Joseph 

(2000), and Joseph (1998), respectively. The potentiometric 

surfaces for 1991 were published in a map report (Westerfield, 

1994). In the report by Yeatts (2004), 55 and 56 wells completed in the Cockfield and Wilcox aquifers, respectively, were 

measured for water levels.

Methods

The well-numbering system used in this report is based 

upon the location of the wells according to the Public Land 

Survey System used in Arkansas. The component parts of a 

well number are the township number, the range number, the 

section number, three letters which indicate, respectively, the 

quarter section, the quarter-quarter section, and the quarterquarter-quarter section in which the well is located, and a 

sequence number. The letters are assigned counterclockwise, 

beginning with “A” in the northeast quarter or quarter-quarter 

or quarter-quarter-quarter section in which the well is located. 

For example, well 01S03W04BBD16 (fig. 2) is located in 

Township 1 South, Range 3 West, and in the southeast quarter 

of the northwest quarter of the northwest quarter of section 4. 

This well is the 16th well in this quarter-quarter-quarter section of section 4 from which data were collected.

The horizontal coordinate information of wells was 

determined using a global positioning system (GPS) referenced to the North American Datum of 1983 (NAD 83), 

with accuracy to about one-tenth of a second of latitude and 

longitude (approximately 10-20 feet). The vertical coordinate 

information was determined with accuracy to about 5 feet (ft) 

from topographic maps referenced to the National Geodetic 

Vertical Datum of 1929 (NGVD of 1929). Herein all altitudes 

are referenced to NGVD of 1929.

Water levels were measured by USGS personnel at public 

water supply, industrial, commercial, domestic, and observation wells open to the Cockfield or Wilcox aquifers. Water levels were measured at least 1 hour after pumping from the well 

had ceased. Measurements were recorded after consecutive 

measurements, with a 5-minute interval, differed by no more 

than 0.02 ft. Measurements were made using steel or electric 

tapes graduated to hundredths of a foot. The steel and electric 

tapes used by USGS personnel were calibrated during January 

2006 prior to collecting measurements from wells. Calibration of steel and electric tapes was performed by comparing 

the field steel or electric tape to a standardized steel tape used 

only for calibration of field tapes.

There are five assumptions associated with linear regression: (1) Y is linearly related to X, (2) data used to fit the 

linear regression are representative of data of interest, (3) variance of the residuals is constant and does not depend on X or 

on anything else, (4) the residuals are independent, and (5) the 

residuals are normally distributed. The assumption of a normal 

distribution is involved only when testing hypotheses, requiring the residuals from the regression equation to be normally 

distributed (Helsel and Hirsch, 1992). 

Linear regression can be used with a hydrograph of water 

level versus time to calculate the annual rise or decline in 

water level. Another method for calculating the annual rise or 

decline is to take the difference between the final and initial 

water levels and divide by the period of time. This method is 

determined from two measurements and calculated values are 

dependent solely on the final and initial water levels. Linear 

regression includes all the measurements to determine the 

trend line, resulting in a value that is dependent on all water 

levels during the period of record. The slope, ß1

, of the line 

is the annual rise or decline in water level. The intercept, ß0, 

would be the water level in the year 1900, the origin for the 

graph. This requires the assumption that the pumping rate 

would be constant throughout the period of pumping. This 

condition is not commonly met or the data are not available to 

demonstrate that this has occurred. The predevelopment water 

level will not be discussed as this condition can not be demonstrated. The R2

 term is used as an indicator of the variability of 

the water-level data. Values of R2 can range from 0.00 to 1.00. 
Methods 3

Figure 1. Location of study areas.

36o

35o

34o

94o 93o 92o 91o

90o

0 20 40 MILES

0 20 40 KILOMETERS

MISSOURI

MISSISSIPPI

TEXAS

OKLAHOMA

TENNESSEE

LOUISIANA

ATLANTIC

West Gulf Coastal Plain

Mississippi

Alluvial

Plain

Ouachita Mountains

Ozark Plateaus

Coastal Plain

INTERIOR

HIGHLANDS

Ouachita

province

Arkansas Valley

PLAIN

CLAY

GREENE

CRAIGHEAD MISSISSIPPI

POINSETT

CROSS

CRITTENDEN

ST. FRANCIS

LEE

ARKANSAS

GRANT JEFFERSON

DALLAS

CLEVELAND LINCOLN

DESHA

DREW

CHICOT

ASHLEY

BRADLEY

CALHOUN

UNION

OUACHITA

COLUMBIA

NEVADA

HEMPSTEAD

CLARK

HOT SPRING

Mississippi River

Physiographic division boundaries 

from Fenneman and Johnson (1946)

Base from U.S. Geological Survey

digital data, 1:100,000

Study areas

 Cockfield aquifer in southeastern Arkansas

 Wilcox aquifer in southwestern Arkansas

 Wilcox aquifer in northeastern Arkansas

EXPLANATION

Crowley Ridge

Physiographic division boundary

 Major Division

 Province

 Section
4 Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers

A high value of R2 can indicate a linear change in water level. 

A low value of R2 can indicate sporadic change in water level.

A

B

A

C

D

C

D

B

A

B

A

C

D

C

D

C

D

B

A

B

C A DB

6

3

2

1

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

R-3-W

T-1-S

SECTION 4

WELL 01S03W04BBD16

4S 3S 2S 1S

5W 4W 3W 2W 1W 1E 2E 3E 4E

PRINCIPAL MERIDIAN

BASELINE

WEST

RANGES

EAST SOUTH

TOWNSHIPS NORTH

Figure 2. Well-numbering system.

Cockfield Formation

Hydrogeologic Setting

The Cockfield Formation of Claiborne Group (hereafter 

referred to as the Cockfield Formation) is Eocene age and 

generally consists of discontinuous fine- to medium-grained 

sand units interbedded with silt, clay, and lignite, all of 

nonmarine origin, in southeastern Arkansas. Most of the sand 

beds constitute the Cockfield aquifer and are found near the 

base of the Cockfield Formation. The Cockfield Formation 

generally ranges from 100 to 400 ft thick near the outcrop 

area and thickens downdip of the outcrop area reaching 625 

ft thick in northeastern Chicot County (Onellion and Criner, 

1955). Total sand thickness in the Cockfield Formation generally ranges from 20 to 150 ft. The Cockfield Formation is 

underlain throughout the study area by calcareous and sandy 

marl, limestone, and carbonaceous clay of the Cook Mountain 

Formation of Claiborne Group. The Cockfield Formation is 

overlain by silty clays of the Jackson Group throughout much 

of southeastern Arkansas. In the confined part of the aquifer, 

the potentiometric surface can be near or above land surface. 

Sand beds at the base of the overlying Jackson Group in parts 

of southeastern Arkansas may be in hydraulic connection with 

the Cockfield aquifer (Ackerman, 1987). The Cockfield aquifer comprises the water-yielding strata within the Cockfield 

Formation.

The Cockfield Formation outcrops in Grant, Dallas, 

Cleveland, Calhoun, Bradley, Columbia, and Union Counties 

and dips southeastward. In the subcrop area, the Cockfield 

Formation is overlain by terrace deposits and alluvium of 

Quaternary age. The terrace deposits may attain a thickness of 

40 ft, and as much as 60 ft of alluvium overlies the Cockfield 

Formation in some of the larger river valleys. 

Most recharge to the Cockfield aquifer occurs by infiltration of rainfall on the upland outcrop areas and by inflow from 

the overlying alluvium; most discharge is to rivers in outcrop 

areas, to vertically adjacent units where the Cockfield aquifer is confined, and to wells (Ackerman, 1987). Well depths 

are shallow and yields of most wells in the outcrop areas are 

small, less than 30 gallons per minute (gal/min), but in other 

areas downdip of the outcrop, wells screened the full thickness of the aquifer often yield 100 to 500 gal/min (Westerfield, 

1994).

Withdrawals from the Cockfield aquifer in the study area 

during 2000 totaled about 9.9 Mgal/d (Holland, 2004) (fig. 3). 

Withdrawals from the Cockfield aquifer generally increased 

from 1975 to 2000, the exception being a decrease in 1985, 

producing 5.2 Mgal/d in 1975, 7.2 Mgal/d in 1980, 5.0 Mgal/d 

in 1985, 8.1 Mgal/d in 1990, and 9.8 Mgal/d in 1995 (Halberg, 1977; Holland and Ludwig, 1981; Holland, 1987, 1993, 

1999, 2004). Most wells completed in the Cockfield aquifer 

study area provide small volumes of water for domestic and 

livestock use. In some locations, the Cockfield aquifer yields 

volumes large enough to supply industrial and public supply 

systems.

5.2

7.2

5.0

8.1

9.8 9.9

0

2

4

6

8

10

12

1975 1980 1985 1990 1995 2000

WATER USE, IN MILLION GALLONS PER DAY

Data compiled from Halberg, 1977; 

Holland and Ludwig, 1981;

Holland 1987, 1993, 1999, 2004

Figure 3. Water use from the Cockfield aquifer, 1975-2000.
Cockfield Formation 5

Adjacent to Arkansas, the State of Mississippi pumped 

about 27 Mgal/d from the Cockfield aquifer in 1999 (D.E. 

Burt, U.S. Geological Survey, written commun., 2003). Immediately across the Arkansas/Mississippi State line, the city of 

Greenville, Mississippi, pumped about 11 Mgal/d from the 

Cockfield aquifer in 1999 (D.E. Burt, U.S. Geological Survey, 

written commun., 2003), or about 11 percent more than all of 

Arkansas pumped from the Cockfield aquifer in 2000. The 

large amount of withdrawal from Greenville probably contributes to lower water levels in Arkansas (Ackerman, 1987; 

Joseph, 1998; Schrader and Joseph, 2000). 

Potentiometric Surface

The potentiometric-surface map shows the altitude of the 

water surface in 56 tightly cased wells in the Cockfield aquifer 

(fig. 4) during February and March 2006, in southeastern 

Arkansas (table 1). The potentiometric surface was constructed by determining the water-level altitude at wells, and 

constructing contour lines along points of equal water-level 

altitude. The direction of ground-water flow is perpendicular 

to the contours in the direction of decreasing water level. 

UNION

DREW

ASHLEY

CHICOT

DESHA

ARKANSAS

GRANT

DALLAS

JEFFERSON

COLUMBIA

OUACHITA

BRADLEY

LINCOLN

CALHOUN

CLEVELAND

320

280

280

300

300

240

220

200

120

160

240

240

220

140

140

120

100

160

100

80

80

220

260

180

200

160

140

120

100

80

80

60

160

200

280

260

Ouachita

River

Saline

River

Greenville,

Mississippi

Crossett

346

291

262

252 310

232

261

158 154 200

229 174

189

69

70

97 114

131 108

106 112

176 134

125 92

103

86

257 233

72 194

209

161

265

101

95

105

86

87

92

70 63

83

87

66

80

83

99

44

73

160

89

86

82

89

83

A

B

C

D

F

H

I

E

G

J

ARKANSAS

Study area

0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

G 66

Outcrop of Cockfield Formation (modified from Hosman, 1988)

Potentiometric contour–Shows altitude at which water

 level would have stood in tightly cased wells. Hachures

 indicate depression. Dashed where approximately located. 

 Contour interval 20 feet. Datum is National Geodetic Vertical 

 Datum of 1929

Well completed in the Cockfield aquifer—Number is

 water-level altitude. Letter, where present, corresponds

 to hydrograph in figure 5

EXPLANATION

180

34°

33°30'

91°30'

92°30'

92°

Figure 4. Potentiometric surface of the Cockfield aquifer in southeastern Arkansas, 2006.
6 Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers

Table 1. Water-level data collected from wells completed in the Cockfield aquifer in southeastern Arkansas, 2006.—Continued

[Horizontal datum is NAD of 1983; NGVD of 1929, National Geodetic Vertical Datum of 1929—a geodetic datum derived from a general 

adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929; --, missing data]

Station Name

Latitude

(degrees,

minutes,

seconds)

Longitude

(degrees,

minutes,

seconds)

Water-level

altitude

(feet above

NGVD of 1929)

Depth to

water

(feet below

land-surface

datum)

Land-surface

datum

(feet above

NGVD of 1929)

Well depth

(feet)

Date of 

measurement

Arkansas County

08S02W04ACA1 340139 911406 73 91.62 165 453 3/10/2006

Ashley County

15S04W26CBC1 332144 912932 86 41.88 128 409 3/02/2006

17S04W10BCD2 331417 913030 87 38.18 125 340 3/02/2006

17S04W10CBA1 331406 913033 92 33.30 125 360 3/02/2006

17S06W07ADA1 331442 914510 101 72.85 174 426 3/02/2006

18S04W19DAA2 330710 913247 89 26.89 116 356 3/02/2006

18S08W04BBC1 331038 915627 69 80.30 149 314 3/02/2006

18S08W29DDD2 330630 915629 70 69.80 140 -- 3/02/2006

19S05W12CAC1 330336 913425 86 29.38 115 320 3/02/2006

Bradley County

12S10W10BCA1 334108 920807 103 124.15 227 425 3/01/2006

14S10W01BAD1 333139 920522 86 144.55 231 540 3/01/2006

14S10W31DBA1 332658 921025 97 96.47 193 349 3/01/2006

14S11W35CAB1 332656 921251 114 75.89 190 320 3/01/2006

14S11W35DAC1 332650 921233 108 65.68 174 345 3/01/2006

15S12W11CAB1 332536 921858 131 23.94 155 225 3/01/2006

16S10W11DCB1 331951 920619 106 45.51 152 152 3/02/2006

16S11W11ACA1 332027 921223 112 29.36 141 140 3/02/2006

Calhoun County

11S13W15BBC1 334560 922534 257 53.18 310 70 3/01/2006

13S13W09CBD1 333555 922638 194 38.03 232 147 3/01/2006

13S13W15DBA1 333517 922520 209 23.40 232 122 3/01/2006

14S13W11CAC1 333045 922451 176 28.55 205 105 3/01/2006

14S13W29ADA1 332829 922722 134 26.02 160 81 3/01/2006

14S13W29DAC1 332815 922729 125 14.24 139 -- 3/01/2006

14S14W21ACB1 332931 923249 92 40.27 132 160 3/01/2006
Cockfield Formation 7

Table 1. Water-level data collected from wells completed in the Cockfield aquifer in southeastern Arkansas, 2006.—Continued

[Horizontal datum is NAD of 1983; NGVD of 1929, National Geodetic Vertical Datum of 1929—a geodetic datum derived from a general 

adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929; --, missing data]

Station Name

Latitude

(degrees,

minutes,

seconds)

Longitude

(degrees,

minutes,

seconds)

Water-level

altitude

(feet above

NGVD of 1929)

Depth to

water

(feet below

land-surface

datum)

Land-surface

datum

(feet above

NGVD of 1929)

Well depth

(feet)

Date of 

measurement

Chicot County

13S03W26BBB1 333247 912301 70 69.34 139 422 3/02/2006

14S03W05BBA1 333106 912602 63 75.69 139 510 3/02/2006

15S03W21ABA1 332314 912438 83 38.91 122 400 3/02/2006

16S02W04BAC1 332027 911857 87 38.07 125 330 3/02/2006

18S02W24CDB1 330652 911547 82 47.07 129 364 3/02/2006

18S02W25ABB3 330640 911541 89 46.27 135 332 3/02/2006

18S03W14CCC1 330731 912319 83 14.86 98 320 3/02/2006

Cleveland County

08S13W34BDA1 335902 922444 161 87.02 248 181 3/06/2006

09S10W17CDD1 335534 920942 265 4.73 270 361 3/06/2006

11S11W23BBD1 334449 921258 233 42.03 275 148 3/06/2006

Columbia County

17S20W35BBD1 331313 930914 346 14.91 361 -- 2/28/2006

19S20W34ADC1 330233 930958 291 22.37 313 39.8 2/28/2006

19S21W17CBB1 330520 931857 262 44.12 306 54.8 2/28/2006

19S21W35ADC1 330247 931513 252 3.54 256 30.1 2/28/2006

19S22W36DBB1 330245 932034 310 41.15 351 68.6 2/28/2006

Desha County

12S01W32DCA1 333628 911245 66 69.87 136 495 3/06/2006

12S03W30ADC1 333747 912611 80 72.99 153 280 3/06/2006

13S02W08CAA1 333504 911921 83 64.48 147 515 3/06/2006

Drew County

11S05W35DDB1 334216 913438 99 81.08 180 500 3/03/2006

12S08W33AAB1 333750 915551 72 101.02 173 543 3/03/2006

14S06W21BDC1 332846 914339 95 120.62 216 -- 3/03/2006

14S07W26BAB1 332754 914744 105 125.04 230 440 3/03/2006
8 Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers

Table 1. Water-level data collected from wells completed in the Cockfield aquifer in southeastern Arkansas, 2006.—Continued

[Horizontal datum is NAD of 1983; NGVD of 1929, National Geodetic Vertical Datum of 1929—a geodetic datum derived from a general 

adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929; --, missing data]

Station Name

Latitude

(degrees,

minutes,

seconds)

Longitude

(degrees,

minutes,

seconds)

Water-level

altitude

(feet above

NGVD of 1929)

Depth to

water

(feet below

land-surface

datum)

Land-surface

datum

(feet above

NGVD of 1929)

Well depth

(feet)

Date of 

measurement

Lincoln County

07S06W14BBC1 340709 914026 160 22.22 182 483 3/06/2006

10S05W06CAC1 335204 913918 44 126.30 170 550 3/06/2006

Union County

16S18W22DCD1 331913 925704 232 14.71 247 36 2/28/2006

17S12W27DCA1 331219 921929 158 11.91 170 24 3/01/2006

17S13W17DDC1 331402 922746 154 38.67 193 156 2/28/2006

17S15W31DCA2 331144 924116 200 52.99 253 110 3/01/2006

17S16W33BBA2 331229 924601 229 25.54 255 31 2/28/2006

17S18W15CDA1 331453 925723 261 28.82 290 35 2/28/2006

18S15W21DAC1 330824 923909 174 26.13 200 40 3/01/2006

19S12W28CBA1 330207 922109 189 10.73 200 25 3/01/2006

The regional direction of ground-water flow generally is 

towards the east and southeast, away from the outcrop, except 

in areas of intense ground-water withdrawals, such as western 

Drew County, southeastern Lincoln County, southwestern Calhoun County, and near Crossett in Ashley County (Schrader 

and Joseph, 2000). There are three cones of depression 

indicated by relatively low water-level altitudes in southeastern Lincoln County, southwestern Calhoun County, and near 

Crossett in Ashley County. The cones of depression in southeastern Lincoln and southwestern Calhoun Counties were not 

evident in the 2003 potentiometric-surface map (Yeatts, 2004) 

but more data or different wells were available for 2006. Some 

local ground-water flow in the outcrop area is toward rivers 

that have eroded into the Cockfield Formation and deposited 

alluvium in southern Bradley and Calhoun Counties (Ouachita 

River), and in north Dallas County (Saline River). The lowest 

water-level altitude measured was 44 ft in Lincoln County; the 

highest water-level altitude measured was 346 ft in Columbia 

County at the outcrop area.

Water-Level Trends

Water-level trends in the Cockfield aquifer are illustrated 

by plotting the water levels in hydrographs, and evaluating the 

change in water level over a period of time. Hydrographs from 

41 wells with historical water levels from 1986 to 2006 were 

evaluated using linear regression to calculate the annual rise or 

decline, in feet per year, for each well and grouped by county 

(table 2). Table 2 shows the number of wells with a minimum 

20 years of record, the range of annual rise or decline, and the 

mean and median annual rise or decline by county. Arkansas, 

Desha, Drew, and Lincoln Counties only had one well with a 

minimum 20 years of record. Calhoun and Cleveland Counties have mean annual rises from 0.01 to 0.07 ft/yr. Arkansas, 

Ashley, Bradley, Chicot, Columbia, Drew, Lincoln, and Union 

Counties have mean annual declines from 0.04 to 0.55 ft/yr. 

Desha County has a mean annual decline of about 1.35 ft/yr. 

Historical water-level data from ten wells (wells A-J, fig. 4) in 

the Cockfield aquifer were plotted to illustrate the water-level 

trend in selected areas of southeastern Arkansas (fig. 5). The 

hydrographs were selected with an annual rise or decline near 

the mean annual rise or decline for the respective county.
Cockfield Formation 9

Table 2. Range, mean, and median of annual rise/decline in water level by county for wells in the aquifer, 1986-2006.

[Annual rise or decline in water level for each well is calculated using linear regression]

County

Number of

wells

Range or value

of annual

rise/decline (-) 

in water level

(feet/year)

Mean annual

rise/decline (-)

in water level

(feet/year)

Median annual

rise/decline (-)

in water level

(feet/year)

Range of R2

values for

trend line

Arkansas1 1 -0.55 -0.55 -0.55 0.33

Ashley 6 -0.55 to 0.00 -0.33 -0.33 0.01 to 0.87

Bradley 5 -0.55 to 0.22 -0.24 -0.29 0.07 to 0.94

Calhoun 5 -0.22 to 0.18 0.01 0.15 0.01 to 0.76

Chicot 5 -0.84 to -0.11 -0.42 -0.29 0.14 to 0.84

Cleveland 2 -0.11 to 0.26 0.07 0.07 0.42 to 0.47

Columbia 5 -0.40 to 0.29 -0.04 -0.01 0.01 to 0.49

Desha1 1 -1.35 -1.35 -1.35 0.94

Drew1 1 -0.47 -0.47 -0.47 0.97

Lincoln1 1 -0.33 -0.33 -0.33 0.10

Union 9 -0.80 to 0.55 -0.13 -0.15 0.06 to 0.92

1

County produced one hydrograph of 20 years or more.
10 Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers

A. ARKANSAS COUNTY, WELL 08S02W04ACA1

70

80

90

100

110

120

130

1965 1970 1975 1980 1985 1990 1995 2000 2005

WATER LEVEL, IN FEET ABOVE NGVD OF 1929

B. ASHLEY COUNTY, WELL 19S05W12CAC1

70

80

90

100

110

120

1965 1970 1975 1980 1985 1990 1995 2000 2005

No data

Figure 5. Water-level hydrographs for selected wells completed in the Cockfield aquifer in southeastern Arkansas.
Cockfield Formation 11

C. BRADLEY COUNTY, WELL 14S10W31DBA1

80

90

100

110

120

130

1965 1970 1975 1980 1985 1990 1995 2000 2005

D. CALHOUN COUNTY, WELL 14S13W29ADA1

100

110

120

130

140

150

1965 1970 1975 1980 1985 1990 1995 2000 2005

WATER LEVEL, IN FEET ABOVE NGVD OF 1929

No data

Figure 5. Water-level hydrographs for selected wells completed in the Cockfield aquifer in southeastern Arkansas.—Continued
12 Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers

E. CHICOT COUNTY, WELL 14S03W05BBA1

50

60

70

80

90

100

1965 1970 1975 1980 1985 1990 1995 2000 2005

F. CLEVELAND COUNTY, WELL 11S11W23BBD1

210

220

230

240

250

260

1965 1970 1975 1980 1985 1990 1995 2000 2005

WATER LEVEL, IN FEET ABOVE NGVD OF 1929

Figure 5. Water-level hydrographs for selected wells completed in the Cockfield aquifer in southeastern Arkansas.—Continued
Cockfield Formation 13

G. DESHA COUNTY, WELL 12S01W32DCA1

50

60

70

80

90

100

1965 1970 1975 1980 1985 1990 1995 2000 2005

H. DREW COUNTY, WELL 14S07W26BAB1

90

100

110

120

130

140

1965 1970 1975 1980 1985 1990 1995 2000 2005

WATER LEVEL, IN FEET ABOVE NGVD OF 1929

Figure 5. Water-level hydrographs for selected wells completed in the Cockfield aquifer in southeastern Arkansas.—Continued
14 Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers

I. LINCOLN COUNTY, WELL 10S05W06CAC1

40

50

60

70

80

90

100

1965 1970 1975 1980 1985 1990 1995 2000 2005

J. UNION COUNTY, WELL 17S13W17DDC1

120

130

140

150

160

170

1965 1970 1975 1980 1985 1990 1995 2000 2005

WATER LEVEL, IN FEET ABOVE NGVD OF 1929

Figure 5. Water-level hydrographs for selected wells completed in the Cockfield aquifer in southeastern Arkansas.—Continued
Wilcox Group 15

Wilcox Group

Hydrogeologic Setting

The Wilcox Group of Eocene and Paleocene age is 

located throughout most of southern and eastern Arkansas. 

The Wilcox aquifer comprises water-yielding strata within 

the Wilcox Group in two study areas in the southwestern and 

northeastern portions of Arkansas. The Wilcox aquifer in central Arkansas is not extensively used, and water-level data are 

insufficient to determine the potentiometric surface.

The Wilcox Group in the southwestern study area 

consists of interbedded layers of clay, sandy clay, sand, and 

lignite. Formations in the southwestern study area are undifferentiated. Sand beds generally are thin and are not continuous 

over large areas. In most of the southwestern study area, the 

Wilcox Group overlies the Midway Group and is overlain by 

terrace deposits and alluvium of Quaternary age or crops out 

in discontinuous bands that are 1 to 3 miles wide. The Wilcox 

Group becomes progressively thicker downslope from the 

outcrop, ranging in thickness from a few feet in the outcrop to 

about 750 ft in northeastern Bradley County (Albin, 1964).

Recharge to the southwestern study area occurs by 

infiltration of rainfall in the outcrop areas and by inflow from 

overlying terrace and alluvial deposits; discharge flows to 

streams in the outcrop, to overlying formations where the 

aquifer is confined, and to wells (Westerfield, 1994). Well 

depths are shallow and well yields range from 10 to 100 gal/

min (Schrader and Joseph, 2000).

The Wilcox Group in most of the northeastern study area 

consists of thin interbedded layers of lignitic sand and clays. 

The Wilcox Group outcrops at or near Crowleys Ridge in 

Clay, Greene, and Craighead Counties (Broom and Lyford, 

1981). East of Crowleys Ridge, the middle to lower part of the 

Wilcox Group contains a sand bed of 200 ft or more in thickness (Petersen and others, 1985) referred to as the “1,400-foot 

sand” (Ryling, 1960; Plebuch, 1961) or the “lower Wilcox 

aquifer” (Hosman and others, 1968). The Wilcox aquifer in 

the northeastern study area is confined above by a clay bed of 

the Wilcox Group and underlain below by a clay bed of the 

Wilcox Group or the Midway Group.

Recharge to the northeastern study area occurs by infiltration of rainfall in the outcrop areas along the western side 

of Crowleys Ridge; discharge occurs by wells and by flow 

beneath the Mississippi River into Mississippi (Westerfield, 

1994). Well depths range from 157 ft on Crowleys Ridge in 

Clay County to 1,885 ft in Lee County. Well yields range from 

100 to 2,000 gal/min (Schrader and Joseph, 2000).

Withdrawals from the Wilcox aquifer in the study areas 

totaled about 22.2 Mgal/d during 2000, most of which came 

from the northeastern study area (Holland, 2004) (fig. 6). 

Withdrawals from the Wilcox aquifer generally increased from 

1975 to 1995, the exception being a decrease in 1985, producing 24.3 Mgal/d in 1975, 25.7 Mgal/d in 1980, 21.0 Mgal/d in 

1985, 30.9 Mgal/d in 1990, and 41.0 Mgal/d in 1995 (Halberg, 

1977; Holland and Ludwig, 1981; Holland, 1987, 1993, 1999). 

In the southern study area, the primary use of water from the 

aquifer was for domestic supplies, usually from wells on or 

near the outcrop areas. In the northeastern study area, the 

primary use of water from the aquifer was for public supplies, 

but the aquifer is also a source of water for some commercial, 

domestic, and industrial users.

24.3 25.7

21.0

30.9

41.0

22.2

0

10

20

30

40

50

1975 1980 1985 1990 1995 2000

WATER USE, IN MILLION GALLONS PER DAY

Data compiled from Halberg, 1977; 

Holland and Ludwig, 1981;

Holland 1987, 1993, 1999, 2004

Figure 6. Water use from the Wilcox aquifer, 1975-2000.

Potentiometric Surface

The potentiometric-surface maps show the altitude of the 

water surface in tightly cased wells screened in the Wilcox 

aquifer (figs. 7 and 8). The maps are based upon water-level 

data collected from 59 wells during February and March 

2006, 16 wells in the Wilcox aquifer southwestern study area 

and at 43 wells in the Wilcox aquifer northeastern study area 

(tables 3 and 4). The potentiometric surface was constructed 

by determining the water-level altitude in wells and constructing contour lines along points of equal water-level values. The 

direction of ground-water flow is perpendicular to the contours 

in the direction of decreasing water level.

The direction of ground-water flow in the southwestern 

study area generally is south and east, except in Clark County 

where flow is towards the Ouachita River, which has eroded 

into the Wilcox Group and deposited alluvium. The lowest 

water-level altitude measured in southwestern Arkansas was 

147 ft near the Ouachita River in Clark County; the highest 

water-level altitude measured was 397 ft in the outcrop area of 

Hempstead County. 
16 Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers

Figure 7. Potentiometric surface of the Wilcox aquifer in southern Arkansas, 2006.

34°30'

93°30' 34°

92°30'

340

360

320

300

380

160

180 200

220

240

260

280

300

320

340

360

380

240

260

220

280

345 397

339

329

312

256

242

294

274

147

212

265

255

230

341

391

CLARK

DALLAS

NEVADA

OUACHITA

HEMPSTEAD

HOT SPRING

River

Little

Ouachita

Missouri

River

ARKANSAS

Study area

0 10 20 MILES

0 10 20 KILOMETERS

Outcrop of Wilcox Group (from Hosman, 1988)

Potentiometric contour—Shows altitude at which water level would 

 have stood in tightly cased wells. Dashed where approximately located. 

 Contour interval 20 feet. Datum is National Geodetic Vertical Datum of 1929

Well completed in Wilcox aquifer, southern Arkansas—Number 

 is water-level altitude 329

EXPLANATION

180
Wilcox Group 17

Figure 8. Potentiometric surface of the Wilcox aquifer in northeastern Arkansas, 2006.

Paragould

West

Memphis

210

210

200

190

180

160

180

150

140

170

190

180

140

120

130

368

296

194

191

188

196 196

204

142

138

141

120

154 153

161

169

191

352 181

296

141

145

173

180

185

188

195

192

187

202

212

199

208

181

167

171

177 185

175

175

148

139

186

M

K

K

O

P

L

Q

N

CLAY

CROSS

POINSETT

GREENE

CRAIGHEAD

ST. FRANCIS

LEE

CRITTENDEN

MISSISSIPPI

ARKANSAS

Study

area

0 10 20 MILES

0 10 20 KILOMETERS

35°

36°

90°

91°

Crowleys Ridge (from Hosman, 1988)

Potentiometric contour—Shows altitude at which 

 water level would have stood in tightly cased wells. 

 Dashed where approximately located. Contour interval 

 10 feet. Datum is National Geodetic Vertical Datum 

 of 1929

Well completed in Wilcox aquifer, northeastern 

 Arkansas—Number is water-level altitude. Letter, 

 where present, corresponds to hydrograph in figure 9

196

180

EXPLANATION
18 Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers

Table 3. Water-level data collected from wells completed in the Wilcox aquifer in southwestern Arkansas, 2006.

[Horizontal datum is NAD is NAD of 1983; NGVD of 1929, National Geodetic Vertical Datum of 1929—a geodetic datum derived from a general adjustment 

of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929; --, no data]

Station Name

Latitude

(degrees,

minutes,

seconds)

Longitude

(degrees,

minutes,

seconds)

Water-level

altitude

(feet above

NGVD of 1929)

Depth to water

(feet below

land-surface

datum)

Land-surface

datum

(feet above

NGVD of 1929)

Well depth

(feet)

Date of 

measurement

Clark County

07S18W03BBD1 340917 925604 255 14.72 270 47 2/27/2006

07S18W20ABB2 340652 925757 230 11.63 242 18.5 2/27/2006

09S18W20CBB1 335611 925905 212 18.03 230 25.5 2/27/2006

10S18W10DDB1 335216 925613 147 48.31 195 215 2/27/2006

10S20W01BAC1 335403 930612 265 30.26 295 53 2/27/2006

Hempstead County

13S23W04BDD1 333842 932911 345 4.91 350 14.2 2/28/2006

13S24W02DCA2 333829 933311 397 48.90 446 63 2/28/2006

13S24W29ACC1 333524 933635 339 31.60 371 60.2 2/28/2006

14S24W29BCA1 333017 933704 329 25.68 355 30.5 2/28/2006

Hot Spring County

04S16W20CBB1 342144 924532 341 4.25 345 18.2 2/27/2006

05S17W10AAC1 341836 924853 391 18.85 410 26 2/27/2006

Nevada County

12S22W24CDA1 334046 931941 312 32.01 344 41.2 2/27/2006

13S21W02DCC1 333754 931426 256 59.31 315 240 2/27/2006

13S21W11BDA1 333738 931432 242 26.07 268 -- 2/27/2006

14S22W19AAA1 333105 932443 294 43.28 337 75 2/27/2006

Ouachita County

12S19W11DCD1 334144 930105 274 13.82 288 533 3/1/2006
Wilcox Group 19

Table 4. Water-level data collected from wells completed in the Wilcox aquifer in northeastern Arkansas, 2006.—Continued

[Horizontal datum is NAD is NAD of 1983; NGVD of 1929, National Geodetic Vertical Datum of 1929—a geodetic datum derived from a general adjustment 

of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929]

Station Name

Latitude

(degrees,

minutes,

seconds)

Longitude

(degrees,

minutes,

seconds)

Water-level

altitude

(feet above

NGVD of 1929)

Depth to

water

(feet below

land-surface

datum)

Land-surface

datum

(feet above

NGVD of 1929)

Well depth

(feet)

Date of

measurement

Clay County

20N07E01CBB1 362347 901703 368 92.25 460 200 3/07/2006

21N08E14CBB1 362716 901126 296 83.53 380 157 3/07/2006

Craighead County

13N07E14BBA2 354526 901911 194 26.89 221 1,028 3/08/2006

14N05E25DCB1 354843 903029 191 42.24 233 890 3/08/2006

14N05E34DDD1 354737 903209 188 41.37 229 874 3/08/2006

14N06E27ACB2 354858 902613 196 30.98 227 999 3/08/2006

14N07E17DCB1 355008 902202 196 35.57 232 1,070 3/08/2006

15N07E33BAD1 355315 902107 204 28.00 232 1,034 3/08/2006

Crittenden County

04N07E36ADB1 345449 901828 142 59.09 201 1,638 3/09/2006

05N07E29ACC1 350129 902225 138 61.52 200 1,700 3/09/2006

06N07E01ABB1 350520 901807 141 66.06 207 1,541 3/09/2006

06N09E07CAC1 350907 901042 120 90.44 210 1,470 3/09/2006

07N07E14CCC1 351318 901930 154 68.93 223 1,584 3/09/2006

07N08E24CAB1 351238 901148 153 68.37 221 1,540 3/09/2006

08N06E33CBD1 351614 902752 161 53.96 215 1,750 3/09/2006

09N08E29ADD1 352225 901516 169 56.03 225 1,564 3/09/2006

Greene County

16N05E13BAB1 360123 903026 191 99.32 290 545 3/07/2006

17N04E36BCA1 360348 903658 352 152.52 505 311 3/07/2006

17N06E31DCB1 360328 902902 181 104.00 285 462 3/07/2006

18N06E10DCD1 361209 902520 296 23.77 320 120 3/07/2006

Lee County

01N04E09DCC1 344209 904220 141 62.62 204 1,885 3/09/2006

03N05E01BAB1 345413 903136 145 51.18 196 1,702 3/09/2006
20 Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers

Table 4. Water-level data collected from wells completed in the Wilcox aquifer in northeastern Arkansas, 2006.—Continued

[Horizontal datum is NAD is NAD of 1983; NGVD of 1929, National Geodetic Vertical Datum of 1929—a geodetic datum derived from a general adjustment 

of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929]

Station Name

Latitude

(degrees,

minutes,

seconds)

Longitude

(degrees,

minutes,

seconds)

Water-level

altitude

(feet above

NGVD of 1929)

Depth to

water

(feet below

land-surface

datum)

Land-surface

datum

(feet above

NGVD of 1929)

Well depth

(feet)

Date of

measurement

Mississippi County

10N08E17ADD1 352923 901505 173 52.40 225 1,521 3/08/2006

11N08E10AAC2 353538 901301 180 40.07 220 1,380 3/08/2006

11N09E33AAB1 353214 900739 185 52.29 237 1,560 3/08/2006

11N10E20ADA1 353349 900213 188 47.07 235 1,417 3/08/2006

12N09E11DBB1 354033 900548 195 35.23 230 1,452 3/08/2006

12N11E17CDD1 353917 895618 192 52.79 245 1,500 3/08/2006

13N11E08DDA1 354528 895547 186 59.03 245 1,445 3/08/2006

13N11E31CCCC1354221 895807 187 53.51 241 1,500 3/08/2006

14N11E20CCA1 354859 895626 202 37.88 240 1,518 3/08/2006

15N08E08DBC3 355607 901527 212 25.59 238 1,060 3/08/2006

15N09E31ACD1 355306 900952 199 40.69 240 1,158 3/08/2006

15N10E01ADC1 355712 895806 208 39.93 248 1,350 3/08/2006

15N12E23DBC1 355426 894701 181 56.59 238 1,491 3/08/2006

Poinsett County

10N07E16CBB2 352925 902129 167 51.03 218 1,500 3/07/2006

11N05E06CCD1 353622 903618 171 42.72 214 992 3/07/2006

11N05E36AAA1 353234 903009 177 37.38 214 1,175 3/07/2006

11N06E35CDA3 353152 902520 185 30.48 215 1,301 3/07/2006

11N07E03BDD1 353629 901955 175 41.03 216 1,456 3/07/2006

12N05E13BBB1 354038 903059 175 47.28 222 1,071 3/07/2006

St. Francis County

04N06E16CCB1 345712 902830 148 54.36 202 1,615 3/09/2006

04N06E21BAD2 345649 902815 139 61.81 201 1,740 3/09/2006
Wilcox Group 21

The direction of ground-water flow in the northeastern 

study area generally is south and east. Larger ground-water 

withdrawals may have altered the natural direction of flow 

near the centers of pumping at Paragould and West Memphis 

(Joseph, 1998). The lowest water-level altitude measured in 

northeastern Arkansas was 120 ft near West Memphis in Crittenden County; the highest water-level altitude measured was 

368 ft on Crowleys Ridge in Clay County. Crowleys Ridge 

represents an erosional remnant elevated as high as 200 ft 

above the Mississippi Alluvial Plain. Water levels measured 

in wells on Crowleys Ridge are higher because of the higher 

altitude of the Wilcox Group and influence of direct recharge 

to outcrops and subcrops on the ridge. The water levels on 

Crowleys Ridge were not included in the construction of the 

potentiometric surface because of few control points (only 

four wells).

Water-Level Trends

Water-level trends in the Wilcox aquifer northeastern study area are illustrated by plotting the water levels in 

hydrographs, and evaluating the change in water level over 

a period of time. Hydrographs from 28 wells with historical 

water levels from 1986 to 2006 were evaluated using linear 

regression to calculate the annual rise or decline, in feet per 

year, for each well and grouped by county (table 5). Table 5 

shows the number of wells with a minimum of 20 years of 

record, the range of annual rise or decline, and the mean and 

median annual rise or decline by county. Lee and St. Francis 

Counties only had one well with a minimum of 20 years of 

record. All 28 wells showed an annual decline from 1986 to 

2006. Craighead, Greene, Mississippi, and Poinsett Counties 

have mean annual declines from 0.27 to 1.00 ft/yr. Crittenden, 

Lee, and St Francis Counties have mean annual decline of 

from 1.39 to 1.64 ft/yr. Historical water-level data from seven 

wells (wells K-Q, fig. 8) in the Wilcox aquifer were plotted to 

illustrate the water-level trend in selected areas of northeastern Arkansas (fig. 9). The hydrographs were selected with an 

annual rise or decline near the mean annual rise or decline for 

the respective county. Hydrographs are not shown for wells in 

the southwestern study area, because the wells did not have 20 

years of historical data. 

Table 5. Range, mean, and median of annual rise/decline in water level by county for wells in the Wilcox aquifer in the northeastern 

study area, 1986-2006.

[Annual rise or decline in water level for each well is calculated using linear regression]

County

Number of

wells

Range or value

of annual

decline (-) in

water level

(feet/year)

Mean annual

decline (-) in

water level

(feet/year)

Median annual

decline (-) in

water level

(feet/year)

Craighead 3 -0.84 to -0.69 -0.77 -0.77

Crittenden 8 -1.83 to -0.99 -1.39 -1.39

Greene 2 -0.47 to -0.07 -0.27 -0.27

Lee1 1 -1.64 -1.64 -1.64

Mississippi 9 -1.68 to -0.58 -1.00 -0.84

Poinsett 4 -1.53 to -0.17 -0.82 -0.79

St. Francis1 1 -1.57 -1.57 -1.57

1

County produced one hydrograph of 20 years or more.
22 Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers

K. CRAIGHEAD COUNTY, WELL 14N07E17DCB1

180

190

200

210

220

230

240

250

1965 1970 1975 1980 1985 1990 1995 2000 2005

WATER LEVEL, IN FEET ABOVE NGVD 1929

L. CRITTENDEN COUNTY, WELL 08N06E33CBD1

150

160

170

180

190

200

210

220

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Figure 9. Water-level hydrographs for selected wells completed in the Wilcox aquifer in northeastern Arkansas.
Wilcox Group 23

M. GREENE COUNTY, WELL 17N06E31DCB1

160

170

180

190

200

210

220

230

1965 1970 1975 1980 1985 1990 1995 2000 2005

WATER LEVEL, IN FEET ABOVE NGVD 1929

N. LEE COUNTY, WELL 01N04E09DCC1

130

140

150

160

170

180

190

200

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Figure 9. Water-level hydrographs for selected wells completed in the Wilcox aquifer in northeastern Arkansas.—Continued
24 Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers

O. MISSISSIPPI COUNTY, WELL 15N09E31ACD1

180

190

200

210

220

230

240

250

1965 1970 1975 1980 1985 1990 1995 2000 2005

WATER LEVEL, IN FEET ABOVE NGVD 1929

P. POINSETT COUNTY, WELL 12N05E13BBB1

160

170

180

190

200

210

220

230

1965 1970 1975 1980 1985 1990 1995 2000 2005

Figure 9. Water-level hydrographs for selected wells completed in the Wilcox aquifer in northeastern Arkansas.—Continued
Summary 25

Q. ST FRANCIS COUNTY, WELL 04N06E21BAD2

130

140

150

160

170

180

190

200

1965 1970 1975 1980 1985 1990 1995 2000 2005

WATER LEVEL, IN FEET ABOVE NGVD 1929

Figure 9. Water-level hydrographs for selected wells completed in the Wilcox aquifer in northeastern Arkansas.—Continued

Summary

The Cockfield aquifer and the Wilcox aquifer provide sources of ground water in southern and northeastern 

Arkansas. In 2000 about 9.9 Mgal/d was withdrawn from the 

Cockfield aquifer and about 22.2 Mgal/d was withdrawn from 

the Wilcox aquifer. Major withdrawals from the aquifers were 

for industrial and public water supplies, with lesser but locally 

important withdrawals for domestic and livestock uses.

A study was conducted by the U.S. Geological Survey in 

cooperation with the Arkansas Natural Resources Commission 

and the Arkansas Geological Survey to determine the water 

level associated with the Cockfield aquifer and the Wilcox 

aquifer in southern and northeastern Arkansas. During February and March 2006, 56 water-level measurements were made 

in wells completed in the Cockfield aquifer and 59 water-level 

measurements were made in wells completed in the Wilcox 

aquifer, 16 in southwestern and 43 in northeastern Arkansas. 

This report presents the results as potentiometric-surface maps 

and as long-term water-level hydrographs. 

The Cockfield Formation is Eocene age and generally 

consists of discontinuous fine- to medium-grained sand units 

interbedded with silt, clay, and lignite, all of nonmarine origin, 

in southeastern Arkansas. Most of the sand beds constitute 

the Cockfield aquifer and are near the base of the Cockfield 

Formation. The Cockfield Formation generally ranges from 

100 to 400 ft thick near the outcrop area and thickens downdip of the outcrop area reaching 625 ft thick in northeastern 

Chicot County. Total sand thickness in the Cockfield Formation generally ranges from 20 to 150 ft. Withdrawals from the 

Cockfield aquifer in the study area during 2000 totaled about 

9.9 Mgal/d. Withdrawals from the Cockfield aquifer generally 

increased from 1975 to 2000, the exception being a decrease in 

1985, producing 5.2 Mgal/d in 1975, 7.2 Mgal/d in 1980, 5.0 

Mgal/d in 1985, 8.1 Mgal/d in 1990, and 9.8 Mgal/d in 1995. 

Most wells completed in the Cockfield aquifer study area provide small volumes of water for domestic and livestock use.

The potentiometric-surface map shows the altitude of the 

water surface in tightly cased wells screened in the Cockfield 

aquifer. The regional direction of ground-water flow generally is towards the east and southeast, away from the outcrop, 

except in areas of intense ground-water withdrawals, such as 

western Drew County, southeastern Lincoln County, southwestern Calhoun County, and near Crossett in Ashley County. 

There are three cones of depression indicated by relatively 

low water levels in southeastern Lincoln County, southwestern Calhoun County and near Crossett in Ashley County. The 

cones of depression in southeastern Lincoln and southwestern 

Calhoun Counties were not evident in the 2003 potentiometric-surface map. The lowest water-level altitude measured 
26 Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers

was 44 ft in Lincoln County; the highest water-level altitude 

measured was 346 ft in Columbia County, at the outcrop area. 

Hydrographs from 40 wells with historical water levels 

from 1986 to 2006 were evaluated using linear regression to 

calculate the annual rise or decline, in feet per year. Calhoun 

and Cleveland Counties have mean annual rises from 0.01 to 

0.07 ft/yr. Arkansas, Ashley, Bradley, Chicot, Columbia, Drew, 

Lincoln, and Union Counties have mean annual declines from 

0.04 to 0.55 ft/yr. Desha County has a mean annual decline of 

about 1.35 ft/yr. 

The Wilcox Group of Eocene and Paleocene age is 

located throughout most of southern and eastern Arkansas. 

There are two study areas in the southwestern and northeastern portions of Arkansas for which potentiometric surfaces 

of the Wilcox aquifer were made. The Wilcox Group in the 

southwestern study area consists of interbedded layers of clay, 

sandy clay, sand, and lignite. Formations in the southwestern 

study area are undifferentiated. Sand beds generally are thin 

and are not continuous over large areas. In most of the southwestern study area, the Wilcox Group overlies the Midway 

Group and is overlain by terrace deposits and alluvium of 

Quaternary age or crops out in discontinuous bands that are 

1 to 3 miles wide. The Wilcox Group becomes progressively 

thicker downslope from the outcrop, ranging in thickness 

from a few feet in the outcrop to about 750 ft in northeastern 

Bradley County.

The Wilcox Group in most of the northeastern study 

area consists of thin interbedded layers of lignitic sand and 

clays. The Wilcox Group outcrops at or near Crowleys Ridge 

in Clay, Greene, and Craighead Counties. East of Crowleys 

Ridge, the middle to lower part of the Wilcox Group contains 

a sand bed of 200 ft or more in thickness referred to as the 

“1,400-foot sand” or the “lower Wilcox aquifer”. The Wilcox 

aquifer in the northeastern study area is confined above by a 

clay bed of the Wilcox Group and confined below by a clay 

bed of the Wilcox Group or the Midway Group.

Withdrawals from the Wilcox aquifer in the study areas 

totaled about 22.2 Mgal/d during 2000, most of which came 

from the northeastern study area. Withdrawals from the 

Wilcox aquifer generally increased from 1975 to 1995, the 

exception being a decrease in 1985, producing 24.3 Mgal/d in 

1975, 25.7 Mgal/d in 1980, 21.0 Mgal/d in 1985, 30.9 Mgal/d 

in 1990, and 41.0 Mgal/d in 1995. 

The potentiometric-surface maps show the altitude of the 

water surface in tightly cased wells screened in the Wilcox 

aquifer. The direction of ground-water flow in the southwestern study area generally is south and east, except in Clark 

County where flow is towards the Ouachita River that has 

eroded into the Wilcox Group and deposited alluvium. The 

lowest water-level altitude measured in southwestern Arkansas was 147 ft near the Ouachita River in Clark County; the 

highest water-level altitude measured was 397 ft in the outcrop 

area of Hempstead County. 

The direction of ground-water flow in the northeastern 

study area generally is south and east. Ground-water withdrawals may have altered the natural direction of flow near the 

centers of pumping at Paragould and West Memphis. The lowest water-level altitude measured in northeastern Arkansas was 

120 ft near West Memphis in Crittenden County; the highest 

water-level altitude measured was 368 ft on Crowleys Ridge in 

Clay County. 

Hydrographs from 28 wells in the northeastern study area 

with 20 years of historical water levels from 1986 to 2006 

were evaluated using linear regression to calculate the annual 

rise or decline, in feet per year, for each well and grouped by 

county. All 28 wells showed an annual decline from 1986 to 

2006. Craighead, Greene, Mississippi, and Poinsett Counties 

have mean annual declines from 0.27 to 1.00 ft/yr. Crittenden, 

Lee, and St Francis Counties have mean annual declines from 

1.39 to 1.64 ft/yr. The wells in the southwestern study area did 

not have 20 years of historical data.
References 27

References

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of the aquifers in the Cockfield Formation, southeastern 

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1 sheet.

Albin, D.R., 1964, Geology and ground-water resources of 

Bradley, Calhoun, and Ouachita Counties, Arkansas: U.S. 

Geological Survey Water-Supply Paper 1779-G, 32 p.

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For more information concerning the research described

in the report:

U.S. Geological Survey

Arkansas Water Science Center

401 Hardin Road

Little Rock, AR 72211-3528

(501) 228-3600

http://ar.water.usgs.gov

U.S. GOVERNMENT PRINTING OFFICE: 2007 – 734-106/26010
Schrader—Potentiometric Surfaces and Water-Level Trends in the Cockfield and Wilcox Aquifers—Scientific Investigations Report 2007–5218

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