U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2013–5130

Prepared in cooperation with the Arkansas Natural Resources Commission and 

the Arkansas Geological Survey

Water Levels in the Aquifers of the Nacatoch Sand of 

Southwestern and Northeastern Arkansas and the Tokio 

Formation of Southwestern Arkansas, February–March 2011

36o

35o

34o

94o 93o 92o 91o

90o

Fall

line

West

Gulf

Coastal

Plain

Mississippi

Alluvial

Plain

Ouachita

Mountains

Arkansas Valley

Ozark Plateaus

INTERIOR

HIGHLANDS

COASTAL

PLAIN

SEVIER

HOWARD PIKE

CLARK

HEMPSTEAD LITTLE

RIVER

NEVADA

CLAY

GREENE

MILLER

LAFAYETTE

COLUMBIA TEXAS

LOUISIANA

MISSISSIPPI

TENNESSEE

MISSOURI

OKLAHOMA

Mississippi River
 
Water Levels in the Aquifers of the 

Nacatoch Sand of Southwestern and 

Northeastern Arkansas and the Tokio 

Formation of Southwestern Arkansas, 

February–March 2011

By T.P. Schrader and Kirk D. Rodgers

Prepared in cooperation with the Arkansas Natural Resources Commission and 

the Arkansas Geological Survey

Scientific Investigations Report 2013–5130

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

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

Suggested citation:

Schrader, T.P., and Rodgers, K.D., Water levels in the aquifers of the Nacatoch Sand of southwestern and northeastern 

Arkansas and the Tokio Formation of southwestern Arkansas, February–March 2011: U.S. Geological Survey Scientific 

Investigations Report 2013–5130, 21 p., http://pubs.usgs.gov/sir/2013/5130/. 

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iii

Contents

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

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

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

Water-Level Measurements ..............................................................................................................3

Linear Regression ................................................................................................................................3

Geographic Information System (GIS) Methods ............................................................................3

Nacatoch Sand ..............................................................................................................................................5

Hydrogeologic Setting ........................................................................................................................5

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

Long-Term Water-Level Changes ......................................................................................................6

Tokio Formation ...........................................................................................................................................14

Hydrogeologic Setting ......................................................................................................................14

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

Long-Term Water-Level Changes ....................................................................................................15

Summary .......................................................................................................................................................19

References ...................................................................................................................................................20

Figures

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

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

3. Graph showing estimated withdrawals by county from the Nacatoch aquifer 

for the northeastern study area ................................................................................................6

4. Graph showing estimated withdrawals from the Nacatoch aquifer for the 

southwestern study area ............................................................................................................7

5. Map showing potentiometric surface of the Nacatoch aquifer, northeastern 

Arkansas, February and March 2011 ........................................................................................8

6. Map showing potentiometric surface of the Nacatoch aquifer, southwestern 

Arkansas, February and March 2011 ........................................................................................9

7. Hydrographs showing water levels for selected wells completed in the Nacatoch 

aquifer ..........................................................................................................................................12

8. Graph showing estimated withdrawals by county from the Tokio aquifer for the 

southwestern study area ..........................................................................................................14

9. Map showing potentiometric surface of the Tokio aquifer, southwestern 

Arkansas, February and March 2011 ......................................................................................16

10. Hydrographs showing water level for selected wells completed in the 

Tokio aquifer ...............................................................................................................................19

Tables

1. Water-level data collected during February and March 2011 from wells 

completed in the Nacatoch aquifer ........................................................................................10

2. Water-level data collected during February and March 2011 from wells 

completed in the Tokio aquifer ................................................................................................17
iv

Conversion Factors, Vertical Datums, and Abbreviations

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/min) 0.06309 liter per second (L/s)

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

gallons per foot per day 0.012419 cubic meter per meter per day 

(m3/m/d)

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

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).

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

Altitude, as used in this report, refers to distance above the vertical datum.
Water Levels in the Aquifers of the Nacatoch Sand of 

Southwestern and Northeastern Arkansas and the 

Tokio Formation of Southwestern Arkansas, February–

March 2011

By T.P. Schrader and Kirk D. Rodgers

Abstract

The aquifers in the Nacatoch Sand and Tokio Formation 

in southwestern Arkansas and the Nacatoch Sand in 

northeastern Arkansas are sources of water for industrial, 

public supply, domestic, and agricultural uses. Potentiometricsurface maps were constructed from water-level measurements 

made in 47 wells completed in the Nacatoch Sand and 45 

wells completed in the Tokio Formation during February 

and March 2011. Aquifers in the Nacatoch Sand and Tokio 

Formation are hereafter referred to as the Nacatoch aquifer 

and the Tokio aquifer, respectively. 

The direction of groundwater flow in the Nacatoch 

aquifer in southwestern Arkansas is towards the southeast 

in Hempstead, Little River, and Miller Counties and eastsoutheast in Clark and Nevada Counties. A potentiometric 

high is located within the outcrop area of north-central 

Hempstead County. Two cones of depression exist in the 

Nacatoch aquifer, one at Hope in southeastern Hempstead 

County and one in Clark County. 

The direction of groundwater flow in the Nacatoch 

aquifer in northeastern Arkansas generally is towards the 

southeast. A potentiometric high in the study area is located 

along the north and northwestern boundaries of the area, but 

water levels may be higher outside the study area. 

In northeastern Arkansas, groundwater withdrawals from 

the Nacatoch aquifer increased by 564 percent from 1965 to 

2010. In southwestern Arkansas, groundwater withdrawals 

from the Nacatoch Sand increased by 125 percent from 1965 

to 1980, and withdrawals decreased by 85 percent from 1980 

to 2010. In southwestern Arkansas, groundwater withdrawals 

from the Tokio aquifer increased by 201 percent from 1965 

to 1980, and withdrawals decreased by 81 percent from 1980 

to 2000. Withdrawals from the Tokio aquifer increased by 

291 percent from 2000 to 2005, and withdrawals decreased by 

32 percent from 2005 to 2010.

The direction of groundwater flow in the Tokio aquifer 

in southwestern Arkansas generally is towards the south 

or southeast. The potentiometric high is within the outcrop 

area in the northern part of the area. Artesian flow exists or 

is inferred in southeastern Pike, northeastern Hempstead, 

and northwestern Nevada Counties. One apparent cone of 

depression might exist northwest of Hope in Hempstead 

County. 

Introduction

Groundwater is a renewable resource important for 

economic growth and quality of life. Aquifers in the Nacatoch 

Sand and Tokio Formation in southwestern Arkansas and 

the Nacatoch Sand in northeastern Arkansas are sources of 

water for industrial, public supply, domestic, and agricultural 

uses. Monitoring of groundwater levels and withdrawals 

provides information needed to plan and manage the resource 

effectively. 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 provide potentiometric-surface maps and water-level 

hydrographs associated with aquifers in the Nacatoch Sand 

and Tokio Formation (hereafter referred to as the Nacatoch 

aquifer and Tokio aquifer, respectively) in southwestern 

Arkansas and the Nacatoch aquifer in northeastern Arkansas. 

The study areas comprise parts of 10 counties in two 

areas of northeastern and southwestern Arkansas. The 

northeastern study area includes most of Clay and Greene 

Counties in the Mississippi Alluvial Plain physiographic 

province (fig. 1). This area is bounded on the north and east by 

the Missouri State line and on the west by the western extent 

of the Nacatoch aquifer. The southern boundary of this area 

was defined by the southern extent of water withdrawals from 

wells screened in the Nacatoch aquifer. The southwestern 

study area includes parts of eight counties (Clark, Hempstead, 

Howard, Little River, Miller, Nevada, Pike, and Sevier) in the 

West Gulf Coastal Plain physiographic province (fig. 1). This 

area is bounded on the north by the Fall Line separating the 
2 Water Levels in the Aquifers of the Nacatoch Sand and the Tokio Formation, Arkansas, February–March 2011

Interior Highlands from the West Gulf Coastal Plain, on the 

west by the extent of use and the availability of wells, and on 

the east by the eastern borders of Clark and Nevada Counties. 

The southwestern study area was limited to the occurrence 

of freshwater where the southern boundary of the area is 

defined by a freshwater/saltwater interface. To the south, the 

groundwater is considered saline (more than 1,000 milligrams 

per liter of dissolved solids) and is not suitable for most uses 

(Boswell and others, 1965; Petersen and others, 1985). 

This report presents the results of water-level 

measurements made in 47 wells completed in the Nacatoch 

aquifer and in 45 wells completed in the Tokio aquifer during 

February and March 2011. These measurements were used to 

construct potentiometric-surface maps. All water-level data are 

stored in the USGS Ground-Water Site Inventory (GWSI) data 

storage system and are available at http://waterdata.usgs.gov. 

Long-term water-level hydrographs were prepared for selected 

wells. Water-level data collected by the USGS from 1965 

to 2010 were used to construct the hydrographs. The Tokio 

Formation is stratigraphically below the Nacatoch Sand and 

separated by five stratigraphic units, listed here in descending 

stratigraphic order: Saratoga Chalk, Marlbrook Marl, Annona 

Chalk, Ozan Formation, and Brownstown Marl. The Saratoga 

Chalk, Marlbrook Marl, and Annona Chalk are nonwaterbearing and the five-unit section can obtain a thickness of 900 

feet (ft) (Petersen and others, 1985). These five units rarely are 

used as water sources and are not discussed in this report.

Cones of depression within a potentiometric surface are 

indicators of where pumping rates are exceeding the local 

recharge rates to the aquifer. As a well is pumped, water levels 

are drawn down, forming a local cone of depression. Water 

levels will recover over time if pumping rates do not continue 

to exceed the recharge rates to the aquifer. Pumping rates that 

exceed recharge rates for an extended period of time will cause 

cones of depression to enlarge. Local cones of depression can 

intersect and coalesce, causing a regional decrease in water 

Figure 1. Location of study areas.

36o

35o

34o

94o 93o 92o 91o

90o

0 20 40 MILES

0 20 40 KILOMETERS

Fall

line

West

Gulf

Coastal

Plain

Mississippi

Alluvial

Plain

Ouachita

Mountains

Arkansas Valley

Ozark Plateaus

INTERIOR

HIGHLANDS

COASTAL

PLAIN

EXPLANATION

Study areas

Boundary of physiographic major division

Boundary of physiographic province

SEVIER

HOWARD PIKE

CLARK

HEMPSTEAD LITTLE

RIVER

NEVADA

CLAY

GREENE

MILLER

LAFAYETTE

COLUMBIA TEXAS

LOUISIANA

MISSISSIPPI

TENNESSEE

MISSOURI

OKLAHOMA

Mississippi River

Physiographic division boundaries 

from Fenneman (1938) Base from U.S. Geological Survey

digital data, 1:100,000
Methods 3

levels within the aquifer. Variations in climatic conditions and 

resulting recharge rates can result in the natural rise or decline 

of water levels and could account for changes shown by longterm hydrographs.

Methods

Water-Level Measurements

Personnel from the USGS measured water levels 

during February and March 2011 in wells screened in 

the Nacatoch or Tokio aquifers. Measurements by USGS 

personnel were made with steel or electric tapes graduated 

in hundredths of a foot. The steel and electric tapes 

were calibrated during January 2011 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 

(Cunningham and Schalk, 2011). 

Well locations were measured using Global Positioning 

System receivers to acquire the horizontal coordinate 

information (latitude and longitude) based on the North 

American Datum of 1983. Land-surface altitude, feet above 

National Geodetic Vertical Datum of 1929 (NGVD 29), was 

determined for each well by superposition of the wells latitude 

and longitude on a USGS 7.5-minute quadrangle topographic 

map and is accurate to about one-half the topographic contour 

interval of 5 to 10 ft. Herein, all water-level and land-surface 

altitudes are referenced to NGVD 29.

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 that indicate, respectively, the 

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

sequence number of the well in the quarter-quarter-quarter 

section. The letters are assigned counterclockwise, beginning 

with “A” in the northeast quarter, quarter-quarter or quarterquarter-quarter section. 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 the quarterquarter-quarter section of section 4 from which data were 

collected. 

Linear Regression

Two methods are used for calculating the annual rise or 

decline of water levels. One method is to take the difference 

between the final and initial water levels and divide by the 

period of time. This method uses two measurements, and 

calculated values are dependent solely on the final and initial 

water levels. A second method uses the linear regression 

of water levels and time of measurement to calculate the 

annual rise or decline of water levels. Linear regression is 

more robust because it 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, β

(equation 1), of the line is the annual rise or decline of water 

levels. The intercept, β0, is the water level in the year 1900, 

the origin for the graph. The predevelopment water level will 

not be discussed as this condition cannot be demonstrated. The 

equation of the regression line or line of best fit, Y = aX + b, 

may be written as:

h = βt + β0 (1)

where

h is water-level altitude, in feet;

β is the slope of the line, in feet per year; 

t is time, in years; and 

β0 is the y-intercept or water-level altitude at 

time equal to 1900, in feet.

Five assumptions are 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).

Geographic Information System (GIS) Methods

Longitude and latitude of wells were obtained from 

the USGS National Water Information System (NWIS) 

and geocoded using ArcGIS (Esri, 2011). The coordinates 

and the measured water levels then were used to construct 

potentiometric maps of the Nacatoch and Tokio aquifers by 

interpolation. This process produces a raster image that assigns 

a range of values to each color in the image. The image then 

is converted to contour polylines using the raster to contour 

tool. Upon conversion, the contour polylines were corrected 

and refined using the PAEK (Polynomial Approximation with 

Exponential Kernel) method of smoothing (Bodansky and 

others, 2002). This method uses a maximum allowable offset 

to smooth lines. 

PAEK is a smoothing algorithm that sets a tolerance by 

which lines are smoothed. A higher tolerance preserves less 

detail from the original interpolated contour line and a lower 

tolerance preserves more detail. This method allows for the 

preservation of end points. 
4 Water Levels in the Aquifers of the Nacatoch Sand and the Tokio Formation, Arkansas, February–March 2011

Figure 2. Diagram showing well-numbering system.

PRINCIPAL MERIDIAN

BASE LINE

TOWNSHIPS

SOUTH NORTH

WEST EAST RANGES

1E

2E

3E

4E

1W 2W 3W 4W 5W

5E

1N 2N 3N 4N

1S

2S

3S

4S 5S

6S

7S

8S

1

2

3

4

5

6

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 RANGE: 03 West TOWNSHIP: 01 South

D

C

B

A A

B

C

D

A

B

C

D

A

B

C

D

A

B

C

D

A

B

C

D

SECTION: 04

WELL 01S03W04BBD16

N

S

E

W
Nacatoch Sand 5

Nacatoch Sand

Hydrogeologic Setting

The Nacatoch Sand of the Navarro Group of Late 

Cretaceous age is underlain by the Saratoga Chalk and 

overlain by the Arkadelphia Marl. In the northeastern study 

area, the Nacatoch Sand subcrops beneath Quaternary alluvial 

and terrace deposits at its western extent. The altitude of the 

top of the Nacatoch Sand ranges from 50 to 100 ft above 

NGVD 29 along the western extent and dips southeasterly to 

1,200 ft below NGVD 29 at the Mississippi River. Petersen 

and others (1985) found this unit to be approximately 100 

ft in thickness at the subcrop increasing to near 600 ft at the 

downdip extent of the formation. In the northeastern study 

area, the Nacatoch Sand is composed of fine sand, interbedded 

clay and limestone in the lower part, increasing in grade 

upward to loose fine quartz sand in the upper part (Petersen 

and others, 1985). In western Clay and Greene Counties, 

the Nacatoch Sand is recharged by precipitation through the 

overlying alluvial and terrace deposits. 

The Nacatoch Sand in the southwestern study area 

outcrops in a 3- to 8-mile (mi) wide belt from central Clark 

County southwestward towards western Hempstead County. 

Across Little River County, the belt subcrops beneath 

alluvial and terrace deposits (Boswell and others, 1965). The 

highest altitude of the Nacatoch Sand in the southwestern 

study area is approximately 300 ft above NGVD 29 in the 

outcrop and descends southeasterly to about 800 ft below 

NGVD 29 at the southern extent of the area. At the outcrop, 

the Nacatoch Sand is about 100 ft in thickness and has a 

maximum thickness of 600 ft (Petersen and others, 1985). The 

Nacatoch Sand in the southwestern study area is composed 

of three distinct units. The lower unit contains interbedded 

gray clay, sandy clay and marl, dark clayey fine-grained sand, 

and hard irregular concretionary beds with lenses of slightly 

glauconitic calcareous fossiliferous sand (Plebuch and Hines, 

1969). The middle unit is composed of dark-green sand with 

coarse glauconite grains. The unit is fossiliferous where 

it is glauconitic and contains irregular concretionary beds 

(Plebuch and Hines, 1969). The upper unit consists of gray, 

fine-grained, unconsolidated quartz sand that is commonly 

crossbedded. Locally, the Nacatoch Sand has a few hard 

lenses and locally, is massive with beds of fossiliferous, sandy 

limestone. The upper unit is the primary water-bearing unit 

of the Nacatoch Sand (Counts and others, 1955; Plebuch and 

Hines, 1969; Ludwig, 1972). 

Recharge of the Nacatoch aquifer in the southwestern 

area occurs by precipitation in the outcrop areas of Clark, 

Hempstead, and Nevada Counties and through the overlying 

alluvium and terrace deposits in Little River County and 

northeastern Texas. The Nacatoch aquifer supplies water 

to northeastern Clay and Greene Counties, southern Clark 

County, central Hempstead County, southeastern Little River 

County, northern Miller County, and northwestern Nevada 

County. 

In the valleys of Clark and Nevada Counties, artesian 

wells yield 1 to 2 gallons per minute (gal/min). Wells yield 

150 to 300 gal/min in Hempstead and western Nevada 

Counties. In the southwestern area, 2 to 20 miles southeast 

of the outcrop, groundwater can be saline. Groundwater flow 

in the Nacatoch Sand is generally to the southeast. In Clark, 

Miller, and Nevada Counties, well yields are low and may 

contain substantial concentrations of chloride (Counts and 

others, 1955). 

Estimated withdrawals from the northeastern study area 

of the Nacatoch Sand from 1965 to 2010 rose 564 percent 

from 0.25 million gallons per day (Mgal/d) to 1.66 Mgal/d 

with a maximum usage in 1990 of 2.21 Mgal/d (fig. 3). From 

1990 to 2010, withdrawal rates decreased by 25 percent from 

2.21 Mgal/d to 1.66 Mgal/d (Holland, 1993, 1999, 2004, 

2007; Terrance W. Holland, U.S. Geological Survey, written 

commun., 2013).

Withdrawals from the southwestern study area of the 

Nacatoch Sand were estimated to be 2.11 Mgal/d in 1965 

and increased by 125 percent in 1980 to 4.75 Mgal/d (fig. 4). 

From 1980 to 2010, withdrawals decreased by 85 percent. 

This decrease has been attributed to public water supplies 

converting to surface-water sources and relying less on 

groundwater sources (Halberg and Stephens, 1966; Halberg, 

1972, 1977; Holland and Ludwig, 1981; Holland, 1987, 1993, 

1999, 2004, 2007; Terrance W. Holland, U.S. Geological 

Survey, written commun., 2013). 

Potentiometric Surface

Potentiometric-surface maps of the Nacatoch aquifer 

were constructed using measurements from 47 wells collected 

during February and March 2011 (figs. 5 and 6; table 1). 

Water-level altitudes were calculated (table 1) and used to 

map the potentiometric surface, which is represented by 

contour lines showing water-level altitudes of equal value 

(figs. 5 and 6). Groundwater flow, in general, is perpendicular 

to contour lines in the direction of downward hydraulic 

gradient. 

In the northeastern Nacatoch study area (fig. 5), 

groundwater-flow direction is towards the southeast. A 

potentiometric high of 271 ft above NGVD 29 is located 

along the northern border of the study area in Clay County. 

The lowest water-level altitude of 233 ft was measured in 

northeastern Greene County. 

Groundwater-flow direction in the southwestern 

Nacatoch study area (fig. 6) is towards the southeast in 

Hempstead, Little River, and Miller Counties and eastsoutheast in Clark and Nevada Counties. An increase in the 

clay content in the direction of the downdip may affect the 

direction of groundwater flow (Boswell and others, 1965). 

The highest water-level altitude of 443 ft was measured in the 

outcrop area of north-central Hempstead County. The lowest 

water-level altitude of 143 ft was found near Hope in southern 

Hempstead County and probably is associated with pumping 

in the area. 
6 Water Levels in the Aquifers of the Nacatoch Sand and the Tokio Formation, Arkansas, February–March 2011

A cone of depression exists in Hempstead County at 

Hope. Historical water levels decreased 40 ft from 185 ft in 

1942 to 145 ft in 1969 (Ludwig, 1972). In January of 2002, 

the water-level altitude was 119 ft (Schrader and Scheiderer, 

2004). This depression alters local groundwater flow from 

the regional direction, with groundwater flowing towards 

Hope from the west, north, and northeast directions (Schrader, 

2007). Another cone of depression exists in Clark County. 

Water levels in the cone of depression have risen from 146 ft 

in 2002 to 152 ft in 2011. Minor variations are seen in the 

water levels in the remaining southwest and northeast study 

areas when compared to those published in previous studies. 

Long-Term Water-Level Changes

Six hydrographs (two in the northeastern study area and 

four in the southwestern study area) from wells completed in 

the Nacatoch Sand with long-term water-level measurements 

(minimum of 20 years) were constructed. Annual decline or 

rise in feet per year (ft/yr) for water levels for each well was 

determined using linear regression. A 20-year minimum period 

reduces the effect of short-term localized pumping rates and 

variations in climate on water levels in a single well. 

Evaluation of long-term data indicates declining 

water levels in the northeastern study area (fig. 7). 

Clay County well 21N06E23DAC1 (Site A) shows an 

average annual decrease of 0.51 ft/yr. Clay County well 

20N08E10ABC1 (Site B) shows an average annual decrease 

of 1.06 ft/yr. This decline could be associated with increased 

withdrawals from 0.25 Mgal/d in 1965 to 1.98 Mgal/d 

in 1990 (Holland, 1993, 1999, 2004, 2007; Terrance W. 

Holland, U.S. Geological Survey, written commun., 2013), 

a 692-percent increase (fig. 3). The withdrawal rate in Clay 

County decreased by 39 percent (fig. 3) from 1.98 Mgal/d 

in 1990 to 1.21 Mgal/d in 2010 (Holland, 1993, 1999, 2004, 

2007; Terrance W. Holland, U.S. Geological Survey, written 

commun., 2013). The decrease in water level shows no 

apparent relation to withdrawals, however, it could be caused 

by water leakage to underlying rock units or from climatic 

variations. 

Hydrographs from four wells having historical waterlevel measurements in the southwestern study area are shown 

in figure 7 (sites C–F).The water-level hydrograph for Clark 

County well 08S19W09ACC1 (Site C, fig. 7) shows an annual 

decrease of 0.18 ft/yr. Water level overall has decreased from 

185.91 ft in 1963 to 177.30 ft in 2011. Estimated withdrawals 

Figure 3. Estimated withdrawals by county from the Nacatoch aquifer for the northeastern study area.

0

1

2

3

1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Withdrawals, in million gallons per day

Clay County

Greene County

Total northeastern area

EXPLANATION

Water use data from Halberg and Stephens, 1966; 

Holland and Ludwig, 1981; and Holland, 1987, 1993, 

1999, 2004, 2007; Terrance W. Holland, U.S. Geological 

Survey, written commun., 2013
Nacatoch Sand 7

from Clark County vary over this time period. Between 

1990 and 1995, withdrawal rates increased slightly from 

0.29 Mgal/d to 0.34 Mgal/d; from 1995 to 2000, the rate of 

withdrawal decreased to 0.02 Mgal/d. This may be associated 

with a decrease in pumping rates. Between 2000 and 2005, 

withdrawal rates increased from 0.02 Mgal/d to 0.43 Mgal/d; 

in 2010, withdrawal rates decreased to 0.14 Mgal/d. (fig. 4; 

Holland, 1993, 1999, 2004, 2007; Terrance W. Holland, U.S. 

Geological Survey, written commun., 2013). 

The water-level hydrograph for Hempstead County well 

13S25W35DDC1 (Site D, fig. 7) shows an annual increase 

of 0.15 ft/yr. From 1975 to 1979, water level decreased from 

187.74 ft to 175.11 ft. During this time period, withdrawals 

increased from 1.44 Mgal/d in 1975 to 1.98 Mgal/d in 1980 

(Halberg, 1977; Holland and Ludwig, 1981). From 1979 to 

1999, the water level increased from 175 ft to 220 ft. From 

1980 to 1985, withdrawal estimates decreased by 92 percent, 

from 1.98 Mgal/d to 0.15 Mgal/d (Holland, 1987). Withdrawal 

estimates increased slightly from 0.15 Mgal/d in 1985 to 

0.32 Mgal/d in 1995 then decreased to 0.27 Mgal/d in 2000. 

Between 2000 and 2005, withdrawal estimates increased 

by 611 percent from 0.27 Mgal/d to 1.92 Mgal/d. Overall 

withdrawal estimates for Hempstead County between 2005 

and 2010 decreased by 1.42 Mgal from 1.92 Mgal/d in 2005 

to 0.50 Mgal/d in 2010 (Holland, 2007; T.W. Holland, U.S. 

Geological Survey, written commun., 2013), a 74-percent 

decrease in withdrawals. 

The water-level hydrograph for Miller County well 

14S28W13CCB1 (Site E, fig. 7) shows an annual increase 

of 0.07 ft/yr from 1966 to 2011. Water levels have remained 

relatively stable since 1966. Withdrawal estimates from Miller 

County have not changed since 2005 (Holland, 2007; Terrance 

W. Holland, U.S. Geological Survey, written commun., 2013). 

The water-level hydrograph for Nevada County well 

11S22W08DAC2 (Site F, fig. 7) shows that between 1985 and 

1988, water levels increased 88.84 ft. Water use decreased 

from 1.11 Mgal/d to 0.44 Mgal/d between 1985 and 1990 

(Holland, 1987, 1993). The increase in water level may be 

associated with decreased pumping rates. Water level has not 

changed appreciably since 1990. Although water levels in 

these six wells may be associated with changes in water use, 

they also may be affected by climatic variations or changes 

in leakage to and from overlying and underlying rock units 

(Schrader, 2007).

Figure 4. Estimated withdrawals from the Nacatoch aquifer for the southwestern study area. 

0

1

2

3

4

5

1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Withdrawals, in million gallons per day

Clark County

Hempstead County

Howard County

Little River County

Miller County

Nevada County

Total southwestern area

EXPLANATION

Water use data from Halberg and Stephens, 1966: 

Holland and Ludwig, 1981; and Holland, 1987, 1993, 

1999, 2004, 2007; Terrance W. Holland, U.S. Geological 

Survey, written commun., 2013
270 260250 240 240 250 271 265 256 235 258 263 242 243 250 238 233 90°40' 90°20' 36°20' 36°00' Base from U.S. Geological Survey digtal data 1:24,000 Projection Universal Transverse Mercator, North American Datum of 1983, Zone 15 North

0 5 10 KILOMETERS

0 5 10 MILES

Missouri

Missouri

A

B

CLAY

GREENE

EXPLANATION

Northeastern study area

Approximate western limit o

250 Potentiometric contour - Sho

level would have stood in tigwhere approximately locatedDatum is National Geodetic V(NGVD 29)

A 271 Control point - Letter, where 

hydrograph in figure 7. Numbabove NGVD 29

Figure 5. Potentiometric surface of the Nacatoch aquifer, northeastern Arkansas, February and March 2011.
Figure 6. Potentiometric surface of the Nacatoch aquifer, southwestern Arkansas, February and March 2011. 

"

;

; ;

Hope

197 177

260

280

200

300

220

320

180

340 360 380

160

260

220

200

220

300 340

180

200

360 400

280

240

260

260

240

280

300 320

220

217

217

216

227

312

162

238

298

244

238

257

185

234

185

364

248

283

416

289

332

318

443

152

178

240 166 166

183

191

177

248

94°00' 93°30'

34°00'

33°30'

F

E D

Base from U.S. Geological Survey digital data 1:24,000Projection Universal Transverse Mercator,North American Datum of 1983, Zone 15 North

0 10 20 KILOMETERS

0 10 20 MILES

LITTLE RIVER

SEVIER

HOWARD

PIKE

HEMPSTEAD

MILLER

LAFAYETTE

COLUMBIA

NEVADA

CLARK

Texas

Outcro

Approx

250 Potent

level wwhere Datum (NGVD 

D 185 Control 

hydrogabove N

C

;177 Flowing 

above N

93°00'

Southw

268

218
10 Water Levels in the Aquifers of the Nacatoch Sand and the Tokio Formation, Arkansas, February–March 2011

Table 1. Water-level data collected during February and March 2011 from wells completed in the Nacatoch aquifer.—Continued

[NGVD 29, National Geodetic Vertical Datum of 1929; horizontal datum is North American Datum of 1983]

Station 

name

Latitude 

(degrees, 

minutes, 

seconds)

Longitude 

(degrees, 

minutes, 

seconds)

Water-level altitude

(feet above NGVD 29)

Depth to water 

(feet below 

land surface)

Land-surface datum

(feet above NGVD 29)

Date of 

measurement

Clark County

08S19W06DCB1 340359 930433 191 79.21 270 03/04/2011

08S19W09ACC1 340323 930228 177 -0.30 177 03/04/2011

08S20W34DAB1 335954 930744 183 17.24 200 03/03/2011

09S20W16DBD1 335708 930847 166 74.84 241 03/03/2011

09S20W16DDC1 335657 930845 166 66.78 233 03/03/2011

09S21W21DAD1 335625 931453 240 105.39 345 03/03/2011

10S20W22DCB1 335054 930757 178 81.54 260 03/02/2011

10S21W12BAB1 335321 931225 152 68.53 221 03/02/2011

Clay County

19N04E01BDB1 361910 903560 263 16.93 280 03/07/2011

19N07E23BAC1 361602 901748 242 80.43 322 03/08/2011

19N07E23DBC1 361549 901730 243 40.24 283 03/08/2011

19N07E26AAA1 361532 901703 250 26.18 276 03/08/2011

20N04E36DCC1 361929 903542 258 21.35 279 03/07/2011

20N08E10ABC1 362313 901202 256 84.24 340 03/08/2011

20N08E15BAA1 362224 901208 235 145.90 381 03/07/2011

21N06E23DAC1 362619 902329 271 28.61 300 03/07/2011

21N07E25AAC1 362550 901607 265 76.77 342 03/07/2011

Greene County

18N06E24ABB2 361112 902256 238 32.06 270 03/08/2011

18N06E24BDA1 361058 902300 233 42.74 276 03/08/2011

Hempstead County

11S24W08BDB1 334837 933619 443 26.95 470 03/01/2011

11S24W21ADD1 334641 933449 318 52.34 370 03/01/2011

11S24W22ADD1 334647 933343 332 33.29 365 03/01/2011

11S24W34CBC1 334444 933438 289 31.50 320 03/01/2011

11S26W27BDD1 334611 934645 416 13.74 430 03/01/2011

12S24W28CDC1 334012 933536 143 209.53 353 03/01/2011

12S25W15DBC1 334214 934036 283 27.52 311 02/28/2011

12S25W34BAC1 334002 934055 248 71.86 320 02/28/2011

12S26W21AAC1 334158 934739 364 33.57 398 02/24/2011

13S25W18AAB1 333740 934332 218 64.74 283 02/25/2011

13S25W35DDC1 333406 933931 185 188.17 373 03/01/2011

13S26W17DDB1 333705 934845 234 57.49 291 02/28/2011

14S25W04DDD1 333317 934132 185 75.34 260 03/01/2011

Little River County

13S28W31BCC1 333509 940251 257 53.51 311 02/22/2011

14S30W01DAA1 333426 940904 248 33.70 282 02/22/2011

Table 1. Water-level data collected during February and March 2011 from wells completed in the Nacatoch aquifer.

[NGVD 29, National Geodetic Vertical Datum of 1929; horizontal datum is North American Datum of 1983]
Nacatoch Sand 11

Table 1. Water-level data collected during February and March 2011 from wells completed in the Nacatoch aquifer.—Continued

[NGVD 29, National Geodetic Vertical Datum of 1929; horizontal datum is North American Datum of 1983]

Station 

name

Latitude 

(degrees, 

minutes, 

seconds)

Longitude 

(degrees, 

minutes, 

seconds)

Water-level altitude

(feet above NGVD 29)

Depth to water 

(feet below 

land surface)

Land-surface datum

(feet above NGVD 29)

Date of 

measurement

Miller County

14S28W13CCB1 333158 935727 238 28.41 266 02/23/2011

14S28W17BBC1 333240 940134 244 26.38 270 02/22/2011

14S28W34CDC1 332919 935920 298 6.60 298 02/23/2011

Nevada County

10S22W23DCB1 335105 931935 238 4.47 242 03/01/2011

11S20W15CDC1 334622 930905 162 13.06 175 03/01/2011

11S20W22AAA1 334624 930926 177 -2.05 175 03/01/2011

11S21W14CAB1 334652 931434 197 -1.10 196 03/01/2011

11S22W08DAC2 334760 932314 268 37.75 306 03/02/2011

11S23W12ABB1 334837 932541 312 69.01 381 03/02/2011

12S22W09CDD1 334230 932250 227 2.27 229 03/01/2011

12S22W22ACD1 334108 932135 216 126.07 342 03/01/2011

12S22W23CBA1 334102 932057 217 112.43 329 03/02/2011

13S22W07BDC1 333744 932514 217 126.32 343 03/02/2011
12 Water Levels in the Aquifers of the Nacatoch Sand and the Tokio Formation, Arkansas, February–March 2011

Figure 7. Water levels for selected wells completed in the Nacatoch aquifer.

220

240

260

280

300

320

340

1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 1995 1999 2003 2007 2011

Water level, in feet aboveNGVD 29

A. CLAY COUNTY, WELL 20N08E10ABC1

NODATA

220

240

260

280

300

320

340

1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 1995 1999 2003 2007 2011

Water level, in feet aboveNGVD 29

B. CLAY COUNTY, WELL 21N06E23DAC1

NO DATA

120

140

160

180

200

220

240

1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 1995 1999 2003 2007 2011

Water level, in feet aboveNGVD 29

C. CLARK COUNTY, WELL 08S19W09ACC1

NO DATA
Nacatoch Sand 13

Figure 7. Water levels for selected wells completed in the Nacatoch aquifer.—Continued

160

180

200

220

240

260

280

1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 1995 1999 2003 2007 2011

Water level, in feet above NGVD 29

F. NEVADA COUNTY, WELL 11S22W08DAC2

140

160

180

200

220

240

260

1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 1995 1999 2003 2007 2011

Water level, in feet abvoveNGVD 29

D. HEMPSTEAD COUNTY, WELL 13S25W35DDC1

180

200

220

240

260

280

300

1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 1995 1999 2003 2007 2011

Water level, in feet aboveNGVD 29

E. MILLER COUNTY, WELL 14S28W13CCB1

NO DATA
14 Water Levels in the Aquifers of the Nacatoch Sand and the Tokio Formation, Arkansas, February–March 2011

Tokio Formation

Hydrogeologic Setting

The Tokio Formation of Cretaceous age underlies 

the Brownstown Marl and overlies consolidated rocks 

of Mississippian and Pennsylvanian age in Clark and 

northeastern Nevada Counties (Plebuch and Hines, 1969); 

the Trinity Group of Early Cretaceous age in Pike, Nevada, 

Miller, and most of Hempstead Counties (Petersen and others, 

1985); and the Woodbine Formation of Late Cretaceous age 

in Little River, Sevier, Howard, and northwestern Hempstead 

Counties (Boswell and others, 1965). The Tokio Formation 

outcrops in a southwest-to-northeast trending band from east 

Sevier County to west-central Clark County. The outcrop 

attains a maximum width of about 10 mi in Howard County 

and extends approximately 8 mi to the southwest into Sevier 

County. In this area, the Tokio Formation is overlain in several 

places by terrace deposits of Quaternary alluvium. The unit 

also outcrops in northwestern Little River County, west of the 

southwestern area. The unit ranges in thickness from about 

50 ft to more than 300 ft, dips towards the southeast, and is 

composed of discontinuous, interbedded gray clay and poorly 

sorted, cross-bedded quartz sands, lignite, and a prevalent 

basal gravel (Counts and others, 1955; Boswell and others, 

1965; Plebuch and Hines, 1969; Petersen and others; 1985). 

The Tokio Formation does not occur in the northeastern study 

area.

The Tokio aquifer receives recharge from precipitation 

where it outcrops or is overlain by permeable alluvial and 

terrace deposits. Salinity increases downdip to the southsoutheast. The Tokio aquifer becomes slightly to moderately 

saline downdip (southeast) from near Prescott across Nevada 

County (Petersen and others, 1985). 

The Tokio aquifer yields potable water to wells in eastern 

Little River County, southeastern Sevier County, southern 

Howard and Pike Counties, western Clark County, northern 

and central Hempstead County, and northwestern Nevada 

County. Wells penetrating the Tokio aquifer range in depth 

from a few feet in the outcrop area to about 1,200 ft at Hope 

and Prescott (Ludwig, 1972). Wells in central Hempstead 

County yield up to 300 gal/min. Artesian wells producing as 

much as 90 gal/min occur in the bottom-land areas adjacent to 

streams (Counts and others, 1955). Historic records indicate 

that water levels in the aquifer did not decline appreciably 

from 1950 to 1968, and that water levels had not been greatly 

affected by withdrawal of water at Hope and Prescott during 

this period (Ludwig, 1972). Estimates of water withdrawn 

from the Tokio aquifer increased by 201 percent from 

2.00 Mgal/d in 1965 to 6.02 Mgal/d in 1980 (fig. 8). Water 

withdrawn from the Tokio aquifer was estimated to be 

Water use data from Halberg and Stephens, 1966: 

Holland and Ludwig, 1981; and Holland, 1987, 1993, 

1999, 2004, 2007; Terrance W. Holland, U.S. Geological 

Survey, written commun., 2013

0

1

2

3

4

5

6

7

1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Withdrawals, in million gallons per day

Clark County

Hempstead County

Howard County

Nevada County

Pike County

Sevier County

Total Tokio aquifer

EXPLANATION

Figure 8. Estimated withdrawals by county from the Tokio aquifer for the southwestern study area.
Tokio Formation 15

1.17 Mgal/d in 2000, a decrease of 81 percent from 1980. 

Water withdrawn from the Tokio aquifer was estimated to 

be 4.58 Mgal/d in 2005, an increase of 291 percent from 

2000. Water withdrawn from the Tokio aquifer was estimated 

to be 3.13 Mgal/d in 2010, a decrease of 32 percent from 

2005 (Halberg and Stephens, 1966; Holland and Ludwig, 

1981; Holland, 1999, 2004, 2007; Terrance W. Holland, U.S. 

Geological Survey, written commun., 2013).

Potentiometric Surface

Potentiometric-surface maps of the Tokio aquifer were 

constructed using measurements from 45 wells collected 

during February and March 2011 (fig. 9; table 2). Waterlevel altitudes were calculated (table 2) and used to map 

the potentiometric surface, which is represented by contour 

lines showing water-level altitudes of equal value (fig. 9). 

Groundwater flow, in general, is perpendicular to contour lines 

in the direction of downward hydraulic gradient.

In the southwestern area, the direction of groundwater 

flow in the Tokio aquifer generally is towards the south or 

southeast. The potentiometric high is within the outcrop area 

in the northwestern part of the southwestern area. The highest 

water-level altitude measured was 491 ft above NGVD 29 in 

Howard County. The lowest water-level altitude measured 

was 124 ft above NGVD 29 about 5 mi northwest of Hope 

in Hempstead County. An area of artesian flow exists or is 

inferred in southeastern Pike, northeastern Hempstead, and 

northwestern Nevada Counties as evidenced by eight flowing 

artesian wells. 

A cone of depression may exist about 5 mi northwest 

of Hope. The northern one-half of this apparent cone of 

depression is shown on figure 9. Water-level data in the 

Tokio aquifer were not available south of Hope. There is 

a cone of depression in southern Howard County. This is 

the first documentation of a cone of depression in this area. 

A comparison of the 2011 map with the 2002 and 1999 

potentiometric-surface maps for the Tokio aquifer shows one 

substantial change; the 300-ft contour is positioned further 

north in Howard County. The change in this contour is because 

of the measurement at well 10S27W02ACD1, which had not 

been measured prior to 2005. 

Long-Term Water-Level Changes

Two hydrographs from wells completed in the Tokio 

aquifer have long-term (minimum of 20 years) water-level 

altitudes (fig. 10). The two wells are located in Hempstead 

County (sites G and H; fig. 9). The minimum 20-year period 

is used to decrease the effect of short-term variations in 

climate and localized pumping rates on water levels in a 

single well. 

Water-level trends vary in different parts of Hempstead 

County. In well 09S23W33CDA1 (site G, figs. 9 and 10), 

in northern Hempstead County, water levels generally 

declined about 0.26 ft/yr from 1958 to 2008. Water levels 

in well 12S24W06DAD1 (site H, figs. 9 and 10), in central 

Hempstead County, fluctuated through a range of about 275.60 

to about 123.80 ft over a 39-year period, although water-level 

rises are seen from 1979 to 1989 and 1999 to 2002. The annual 

decline in water levels at well 12S24W06DAD1 from 1971 

to 2011 was 3.70 ft/yr. The decline and rise in water levels in 

well 12S24W06DAD1 may be associated with the fluctuating 

withdrawals from the Tokio aquifer in Hempstead County, 

while water levels in well 09S23W33CDA1 do not appear 

to have a similar association. Although water levels in these 

two wells may be associated with changes in water use, other 

factors may affect water levels such as climatic variations or 

changes in leakage to and from overlying and underlying rock 

units.
Figure 9. Potentiometric surface of the Tokio aquifer, southwestern Arkansas, February and March 2011.

!

!!

! ;

;

; ! ;!

!

! !

!

!

!

!

!

! !

!!

!

!!

!

!

! !

! !

!

!

;

;

!

; ;

!

!

!

"

"

Hope

Prescott

G

H

320300

280

340

240 260 220200

380 400

180

440

160

460

140

480 240

360

240

220

280

323 293

286 280

432

258

351

214

213

318 306

339

292

399

397

413 414

491

198

279

284 131 124

250

302

360

303

292

399

436 420

437

283 299

269

271

219

207

215

225

279 250

94°00'

93°30'

93°00'

34°00'

33°30'

Base from U.S. Geological Survey digtal data 1:24,000Projection Universal Transverse Mercator,North American Datum of 1983, Zone 15 North

0 10 20 KILOMETERS0 10 20 MILES

LITTLERIVER

SEVIER

HOWARD

PIKE

CLARK

HEMPSTEAD

MILLER

LAFAYETTE

COLUMBIA

NEVADA

Southwestern 

Approximate n

250 Potentiometri

level would hawhere approxDatum is Natio

185 D Control point - 

hydrograph in above NGVD 2

; 271 Flowing artesia

above NGVD 29

Outcrop of Tok

Approximate a
Tokio Formation 17

Table 2. Water-level data collected during February and March 2011 from wells completed in the Tokio aquifer.—Continued

[NGVD 29, National Geodetic Vertical Datum of 1929; Horizontal Datum is North American Datum of 1983; a negative or zero depth to water indicates a flowing artesian well]

Station name

Latitude 

(degrees, 

minutes, 

seconds)

Longitude 

(degrees, 

minutes, 

seconds)

Water-level altitude

(feet above NGVD 29)

Depth to water 

(feet below 

land surface)

Land-surface datum

(feet above NGVD 29) 

Date of 

measurement

Clark County

08S22W15ABB2 340313 932018 225 100.00 325 03/03/2011

09S22W05BBB1 335951 932259 215 97.00 312 03/03/2011

09S22W05BCA1 335936 932257 207 28.00 235 03/03/2011

09S22W10DBA1 335832 932022 260 102.00 362 03/03/2011

09S22W16ACA1 335754 932120 219 14.00 233 03/03/2011

Hempstead County

09S23W20BDA1 335710 932859 250 0.00 250 02/24/2011

09S23W33CDA1 335457 932802 271 -0.92 270 02/24/2011

09S24W25BBB1 335633 933132 269 -0.50 268 02/24/2011

09S24W28ACC1 335617 933415 279 -2.11 277 02/24/2011

09S24W30DCC1 335556 933607 299 91.13 390 02/24/2011

09S24W33ADC1 335526 933356 283 46.06 329 02/24/2011

09S26W08ADA2 335920 934717 437 0.94 438 02/25/2011

09S26W08ADD1 335918 934717 436 0.80 437 02/25/2011

09S26W09CDC1 335846 934656 420 5.08 425 02/25/2011

09S26W18CBB1 335815 934921 399 25.73 425 02/25/2011

10S25W09CDB1 335329 934052 292 69.17 361 02/24/2011

10S25W30CCD1 335048 934310 303 85.27 388 03/01/2011

10S26W03BBA1 335507 934612 360 7.29 367 03/01/2011

11S26W08BBB1 334909 934903 302 69.70 372 03/01/2011

11S26W23BBB1 334720 934602 250 169.09 419 03/01/2011

12S24W06DAD1 334360 933701 124 231.22 355 03/01/2011

12S25W02DDD1 334341 933902 131 235.68 367 03/01/2011

12S27W04BBC1 334450 935358 284 151.38 435 03/01/2011

12S27W05AAC1 334449 935421 279 156.16 435 03/01/2011

12S27W36DBC1 333958 935024 198 62.94 261 02/24/2011

Howard County

09S27W03DBD1 340000 935153 491 70.60 562 02/23/2011

09S27W10BCB1 335930 935232 414 120.09 534 02/23/2011

09S27W18ADB1 335840 935453 413 78.59 492 02/23/2011

09S27W32BDB1 335606 935424 397 54.47 451 02/23/2011

09S27W32BDB2 335606 935424 399 50.96 450 02/23/2011

10S27W02ACD1 335454 935056 292 65.73 358 02/23/2011

10S27W04BBD1 335512 935330 339 53.00 392 02/23/2011

10S27W12CAB1 335356 935021 306 77.15 383 02/23/2011

10S27W18BAC1 335336 935535 318 103.86 422 02/23/2011

11S27W21CDA1 334603 935418 213 67.02 280 02/23/2011

Table 2. Water-level data collected during February and March 2011 from wells completed in the Tokio aquifer.

[NGVD 29, National Geodetic Vertical Datum of 1929; Horizontal Datum is North American Datum of 1983; a negative or zero depth to water indicates a flowing artesian well]
18 Water Levels in the Aquifers of the Nacatoch Sand and the Tokio Formation, Arkansas, February–March 2011

Table 2. Water-level data collected during February and March 2011 from wells completed in the Tokio aquifer.—Continued

[NGVD 29, National Geodetic Vertical Datum of 1929; Horizontal Datum is North American Datum of 1983; a negative or zero depth to water indicates a flowing artesian well]

Station name

Latitude 

(degrees, 

minutes, 

seconds)

Longitude 

(degrees, 

minutes, 

seconds)

Water-level altitude

(feet above NGVD 29)

Depth to water 

(feet below 

land surface)

Land-surface datum

(feet above NGVD 29) 

Date of 

measurement

Nevada County

11S22W08DAC8 334757 932312 214 91.37 305 03/02/2011

12S21W28ADA1 334015 931559 260 5.46 265 03/02/2011

Pike County

08S23W19ADC1 340213 932931 351 -0.81 350 02/23/2011

08S23W35DCA1 340004 932530 258 -1.15 257 02/23/2011

08S24W14AAC1 340324 933134 432 90.98 523 02/24/2011

09S23W17BBC2 335804 932925 280 -0.20 280 02/24/2011

09S24W14AAD1 335810 933139 286 -1.20 285 02/24/2011

Sevier County

10S28W31DCC1 335026 940145 293 36.85 330 02/22/2011

11S29W08DBB1 334907 940704 323 141.90 465 02/22/2011

11S29W13CCD1 334750 940317 280 80.45 360 02/22/2011
Summary 19

Summary

Aquifers in the Nacatoch Sand and Tokio Formation in 

southwestern Arkansas and the Nacatoch Sand in northeastern 

Arkansas are sources of water for industrial, public supply, 

domestic, and agricultural uses. A study was conducted by 

the U.S. Geological Survey in 2011 in cooperation with the 

Arkansas Natural Resources Commission and the Arkansas 

Geological Survey to provide potentiometric-surface maps 

and water-level hydrographs associated with aquifers in the 

Nacatoch Sand and Tokio Formation (hereafter referred to 

as the Nacatoch aquifer and Tokio aquifer, respectively) 

in southwestern Arkansas and the Nacatoch aquifer in 

northeastern Arkansas. 

Potentiometric-surface maps were constructed from 

water-level measurements made in 47 wells completed in 

the Nacatoch aquifer and in 45 wells completed in the Tokio 

aquifer during February and March 2011. In northeastern 

Figure 10. Water level for selected wells completed in the Tokio aquifer.

220

240

260

280

1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 1995 1999 2003 2007 2011

300

320

340

Watet level, in feet above NGVD 29

G. HEMPSTEAD COUNTY, WELL 09S23W33CDA1

NO DATA

120

140

160

180

200

220

240

260

280

1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 1995 1999 2003 2007 2011

Water level, in feet aboveNGVD 29

H. HEMPSTEAD COUNTY, WELL 12S24W06DAD1

NO DATA
20 Water Levels in the Aquifers of the Nacatoch Sand and the Tokio Formation, Arkansas, February–March 2011

Arkansas, groundwater withdrawals from the Nacatoch aquifer 

increased by 564 percent from 1965 to 2010. In southwestern 

Arkansas, groundwater withdrawals from the Nacatoch aquifer 

increased by 125 percent from 1965 to 1980. From 1980 to 

2010, withdrawals decreased by 85 percent. In southwestern 

Arkansas, groundwater withdrawals from the Tokio aquifer 

increased by 201 percent from 1965 to 1980. From 1980 to 

2000, withdrawals decreased by 81 percent. From 2000 to 

2005, withdrawals from the Tokio aquifer increased by 291 

percent. From 2005 to 2010, withdrawals from the Tokio 

aquifer decreased by 32 percent.

In the northeastern Nacatoch study area, groundwaterflow direction is towards the southeast. A potentiometric high 

of 271 feet (ft) above the National Geodetic Vertical Datum of 

1929 (NGVD 29) is located along the northern border of Clay 

County. The lowest water-level altitude (233 ft above NGVD 

29) was measured in northeastern Greene County. 

Groundwater-flow direction in the southwestern Nacatoch 

study area is towards the southeast in Hempstead, Little 

River, and Miller Counties and towards the east-southeast in 

Clark and Nevada Counties. An increase in the clay content 

in the direction of the downdip may affect the direction of 

groundwater flow. The highest water-level altitude (443 ft 

above NGVD 29) was measured in the outcrop area of northcentral Hempstead County. The lowest water-level altitude 

(143 ft above NGVD 29) was measured near Hope in southern 

Hempstead County. 

Two cones of depression exist in the southwestern 

Nacatoch aquifer study area—in Hempstead County at Hope 

(143 ft above NGVD 29) and in Clark County (152 ft above 

NGVD 29). The depression at Hope alters local groundwaterflow directions from the regional direction, with groundwater 

flowing towards Hope from the west, north, and northeast 

directions. 

Six hydrographs (two in the northeastern study area and 

four in the southwestern study area) from wells completed 

in the Nacatoch aquifer displaying long-term water-level 

measurements (minimum of 20 years) were constructed. The 

hydrographs for Clay County wells 20N08E10ABC1 and 

21N06E23DAC1 show an average annual decrease of 1.06 

and 0.51 feet per year (ft/yr), respectively. The water-level 

hydrograph for Clark County well 08S19W09ACC1 has 

remained relatively stable over the 20-year period with an 

annual decrease of 0.18 ft/yr. The hydrograph for Hempstead 

County well 13S25W35DDC1 shows an annual increase of 

0.15 ft/yr. The water-level hydrograph for Miller County well 

14S28W13CCB1 has remained essentially unchanged over 

the minimum 20-year period. The water-level hydrograph for 

Nevada County well 11S22W08DAC2 shows that between 

1985 and 1988, water levels increased 88.84 ft. Although 

water levels in these six wells may be associated with changes 

in water use, they also may be affected by climatic variations 

or changes in leakage to and from overlying and underlying 

rock units.

In the southwestern area, the direction of groundwater 

flow in the Tokio aquifer generally is towards the south or 

southeast. The potentiometric high is within the outcrop area 

in the northwestern part of the southwestern area. The highest 

water-level altitude measured was 491 ft above NGVD 29 in 

Howard County. The lowest water-level altitude measured 

was 124 ft above NGVD 29 about 5 miles northwest of Hope 

in Hempstead County. An area of artesian flow exists or is 

inferred in southeastern Pike, northeastern Hempstead, and 

northwestern Nevada Counties as evidenced by eight flowing 

artesian wells.

Two hydrographs from wells completed in the Tokio 

aquifer have long-term (minimum of 20 years) water-level 

altitudes. The two wells are located in Hempstead County, and 

the hydrographs show differences between water-level trends 

over long periods. In well 09S23W33CDA1, water levels 

generally declined about 0.26 ft/yr from 1958 to 2008. Water 

levels in well 12S24W06DAD1 fluctuated from a range of 

about 276 to about 132 ft over a 39-year period. Water levels 

generally declined from 1971 to 1979, generally rose from 

1979 to 1989, then declined from 1989 to 1999. The annual 

decline in water level at well 12S24W06DAD1 from 1971 

to 2011 was 3.70 ft/yr. The decline and rise in water levels in 

well 12S24W06DAD1 may be associated with the fluctuating 

withdrawals from the Tokio aquifer in Hempstead County, 

while water levels in well 09S23W33CDA1 do not appear to 

have a similar association.

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