Potentiometric Surface

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3313

Sheet 1 of 2

Potentiometric Surface, 2012, and Water-Level Differences, 2005–12,

of the Sparta Aquifer in North-Central Louisiana

By

Benton D. McGee and Jeffrey A. Brantly

2015

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government

For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, 

Denver, CO 80225, 1–888–ASK–USGS

Digital files available at http://dx.doi.org/10.3133/sim3313

Suggested citation: McGee, B.D., and Brantly, J.A., 2015, Potentiometric surface, 2012, and

water-level differences, 2005–12, of the Sparta Aquifer in north-central Louisiana: U.S. Geological 

Survey Scientific Investigations Map 3313, 2 sheets, http://dx.doi.org/10.3133/sim3313.

Printed on recycled paper

Prepared in cooperation with the

Louisiana Department of Transportation and Development

The Sparta aquifer, of Eocene age, is within the Mississippi embayment, a 

geosyncline plunging gently to the south whose axis approximately follows the present 

course of the Mississippi River (Cushing and others, 1970). A sequence of alternating 

sand and clay beds make up the Sparta aquifer, which is situated between and confined 

by the massive clay layers of the overlying Cook Mountain and underlying Cane River 

confining units (fig. 2).

The Sparta aquifer outcrops in northwestern Louisiana (fig. 1) and generally dips 

toward the east and southeast except along the northern border of the State where the 

dip is northeasterly. The aquifer ranges in thickness from 50 to 500 ft in north-central 

and northwestern Louisiana (McWreath and others, 1991). The regional dip is 25–50 ft 

per mile to the east and southeast (Payne, 1968).

The lithology of the Sparta aquifer is highly variable both laterally and vertically. 

Beds in the lower half of the aquifer generally consist of fine to medium sand; the beds 

in the upper half of the aquifer generally consist of sand, clay, and lignite. The existing 

pattern of lineations of sand concentrations in the aquifer has been attributed to the 

depositional processes of a system of braiding, constantly shifting stream channels, 

interlacing lakes, marshes, and swamps of a large deltaic-fluvial plain (Payne, 1968). 

The sand bodies may act locally and, for short periods, as separate hydraulic units, but 

over longer periods and larger areas, these units act as an integral part of the unified 

Sparta aquifer (Payne, 1968).

The Sparta aquifer is recharged by direct infiltration of rainfall in the outcrop 

area (fig. 1) and by leakage from alluvium and adjacent aquifers. Discharge is by 

withdrawal from wells and leakage through adjacent confining beds (Payne, 1968). 

Prior to development of the aquifer in Louisiana, which began in the early 1900s 

(McWreath and others, 1991), water levels were above the top of the aquifer in most 

areas, and water generally flowed in a southeasterly direction from the outcrop area 

toward areas of discharge in the southeast (Ryals, 1980). By 1965, development 

around the aquifer had resulted in local and regional water-level declines, and the 

general direction of flow in much of the aquifer was radially toward a large regional 

cone of depression centered over West Monroe.

The Sparta aquifer contains only saltwater in areas east and south of the downdip limit of freshwater shown on figure 1. Saltwater extends several miles west of the 

down-dip limit of freshwater into the freshwater extent of the aquifer as a low-angle 

wedge along the base of the aquifer (Brantly and others, 2002). Regional waterlevel declines have altered the direction of flow and created gradients favorable for 

encroachment as lateral movement into freshwater areas or as upconing from the base 

of the aquifer toward pumping wells.

Hydrogeology

Approximate down-dip limit of freshwater

0

80

60

40

120

20

100

140

180

160

-40

-20

-60

-80

-80

200

220

-100

-120

-140

-160

240

40

180

200

220

Mo-5

L-68

L-26

Ja-3

Cl-9

W-223

W-212

W-179

W-172

W-171 W-165W-160

W-156

W-114

Un-86

Un-84 Un-83 Un-82

Un-79

Un-26

Ou-80

Mo-86

Mo-84

L-219

L-208 L-186

L-163

L-152

L-137

L-120

L-119

L-117

L-113

Ja-91 Ja-49

Cl-91

Cl-58

Ca-51

Ca-27

Bi-76

Wb-516

Wb-498

Wb-492

Wb-475

Wb-430

Wb-424

Wb-423

Wb-399

Wb-355

Wb-331

Wb-326

Wb-285

Wb-271

Wb-241

Wb-219

Wb-182

W-144B

Un-238

Un-237

Un-223 Un-206

Un-142

Un-138

Un-136

Sa-389

Sa-356

Ou-445

Ou-444

Ou-404

Ou-402

Ou-163

Na-562

Na-534

Na-519

Mo-423

Mo-350

Mo-347

Ja-356

Ja-154

Ja-149

Ja-148

Ja-147

Ja-115

Cl-224

Cl-154 Cl-151

Cl-150

Cl-149

Cl-148

Cl-136

Cl-116

Cl-111

Ca-86B

Bo-501

Bo-488

Bo-456

Bo-446

Bo-430

Bi-253 Bi-284 Bi-246

Bi-216

Bi-144

Bi-112

Ou-401A

Wb-6694Z

Cl-5717Z

W-28

L-32

Un-80

Wb-467

Wb-274

Un-209

Un-193

Ja-182

L-5868Z

Ou-443

Ou-444

Ruston

Minden

Hodge

West Monroe

Monroe

Farmerville

Winnfield

WINN

SABINE

UNION

CADDO

DE SOTO

BOSSIER

NATCHITOCHES

BIENVILLE

CLAIBORNE

WEBSTER

JACKSON

MOREHOUSE

OUACHITA

RICHLAND

LINCOLN

CALDWELL RED RIVER

Bastrop

Freshwater extent of the Sparta aquifer (Smoot and Seanor, 1991)

Approximate outcrop of the Sparta aquifer (Smoot and Seanor, 1991)

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 the National Geodetic Vertical Datum of 1929

Direction of groundwater flow

Control point and well number

Well with hydrograph (see figs. 3–6)

EXPLANATION

Un-26

 100 

94° 93° 92°

33°

32°

0 4 8 16 MILES

0 4 8 16 KILOMETERS

ARKANSAS

Study area

MISSISSIPPI

LOUISIANA

El Dorado

Figure 1. Potentiometric surface of the Sparta aquifer in north-central Louisiana, March–April 2012.

ISBN 978-1-4113-3905-7

9 7 8141 1 3390 5 7

ISSN 2329-1311 (print)

ISSN 2329-132X (online)

http://dx.doi.org/10.3133/sim3313

The potentiometric surface of the Sparta aquifer during March–April 2012 was 

constructed by using water levels from 117 wells completed in the aquifer (fig. 1). 

Altitudes of water levels ranged from more than 248 ft above the National Geodetic 

Vertical Datum of 1929 (NGVD 29) at well Bo-446 in the outcrop area of northern 

Bossier Parish to more than 203 ft below NGVD 29 at well Ou-80 in Ouachita Parish 

(table 1). Water levels were measured by using steel or electric tapes marked with 

0.01-ft graduations; the wells were not being pumped at the time of the measurements.

Water levels are lowest in areas affected by major pumping centers (cones of 

depression). Flow lines show that movement of groundwater in much of the Sparta 

aquifer is generally eastward or northeastward from areas of recharge toward areas of 

discharge. Flow in much of the eastern half of the aquifer is radially toward a large 

regional cone of depression over the West Monroe area, where the withdrawal rate was 

about 13.49 Mgal/d in 2010 (Sargent, 2011). Flow is locally influenced by small cones 

of depression near pumping centers that include Farmerville (1.57 Mgal/d), Minden 

(2.15 Mgal/d), Ruston (4.18 Mgal/d), Hodge (2.45 Mgal/d), and Winnfield (1.21 

Mgal/d) (withdrawal rates from Sargent, 2011).

Water levels at well Wb-399 (fig. 3), located near the outcrop area of the Sparta 

aquifer in Webster Parish, show seasonal fluctuations of about 0.8 ft but show no longterm trends since 1978. This seasonal fluctuation is typical of wells located in or near 

the outcrop area of the Sparta aquifer. Water levels at wells L-26 (fig. 4) in Lincoln 

Parish and Ou-444 (fig. 5) in Ouachita Parish show long-term declines with little 

seasonal fluctuation, typical of wells located in areas that are minimally influenced 

by local withdrawals, but are heavily influenced by long-term regional declines. 

Water levels at well Cl-149 (fig. 6), located in the northeastern corner of Claiborne 

Parish near the Arkansas-Louisiana State line, also show long-term declines between 

1980 and 1999; however, water levels have risen more than 24 ft since about 2000, 

primarily because of reduced withdrawals from the Sparta aquifer in and around El 

Dorado, Ark. (Freiwald and Johnson, 2007).

Water-Level Differences

Differences in water levels at 70 wells in the Sparta aquifer measured during the 

period March–April 2005 to March–May 2012 are shown on figure 7. Water-level 

differences were calculated by subtracting the 2012 water-level altitude measurement 

from the 2005 water-level altitude measurement. Water-level differences do not 

necessarily indicate a water-level trend but are intended to show where water-level 

altitudes declined or increased from 2005 to 2012 (table 1). In general, water levels 

declined between 1 and 10 ft throughout the southern half of the aquifer. The largest 

declines, 21.8 ft at well Bi-284 and 38.3 ft at Bi-246, occurred in northeast Bienville 

Parish (table 1). The large declines at both of these wells were localized and caused 

by withdrawals for industrial and public-supply purposes at or near the measured well 

and do not reflect the magnitude of regional water-level changes as indicated by other 

wells in the general area. Water levels generally increased throughout the northern 

half of the Sparta aquifer in Louisiana, primarily because of reduced withdrawals for 

industrial purposes at Bastrop, La., and near El Dorado, Ark. The largest water-level 

increase, 34.83 ft, occurred at well Mo-5 at Bastrop in Morehouse Parish (table 1). 

Water Levels Below the Top of the Aquifer

Potentiometric-surface altitude of the Sparta aquifer for March–April 2012 was 

compared to the altitude of the top of the Sparta aquifer in Louisiana (Brantly and 

others, 2002), and an area was delineated where water levels were at or below the top 

of the aquifer (fig. 7). Water levels were 

at or below the top of the Sparta aquifer 

in all or part of nine parishes, including 

Bienville, Claiborne, Jackson, Lincoln, 

Natchitoches, Ouachita, Union, Webster, 

and Winn. All of these parishes, except 

Natchitoches Parish, obtain the majority 

of their groundwater from the Sparta 

aquifer. Water levels were farthest, more 

than 150 ft, below the top of the aquifer 

along the Bienville-Jackson Parish line 

northwest of the town of Hodge, where 

withdrawals for industrial purposes have 

caused a local cone of depression.

System Series Stratigraphic unit Aquifer or confining unit Tertiary

Eocene

Claiborne

Grou

p

Cockfield Formation

Cockfield aquifer or surficial confining

unit

Cook Mountain Formation

Cook Mountain aquifer or surficial

confining unit

Sparta Sand ta aquifer or confining unit

Cane River Formation Cane River aquifer or confining unit

Carrizo Sand Wilcox aquifer or surficial

confining unit

Wilcox Group, Undifferentiated

Paleocene Midway confining unit Midway Group, Undiff

Spar

Carrizo

erentiated

?

-

Figure 2. Partial column of stratigraphic and 

hydrogeologic units in north-central Louisiana.

Introduction

The Sparta aquifer is used in 15 parishes in north-central 

Louisiana (fig. 1), primarily for public supply and industrial 

purposes. Of those parishes, eight (Bienville, Claiborne, 

Jackson, Lincoln, Ouachita, Union, Webster, and Winn) rely 

on the Sparta aquifer as their principal source of groundwater. 

In 2010, withdrawals from the Sparta aquifer in Louisiana 

totaled 63.11 million gallons per day (Mgal/d) (Sargent, 2011), a 

reduction of more than 11 percent from 1995, when the highest 

rate of withdrawals (71.32 Mgal/d) from the Sparta aquifer were 

documented (Lovelace and Johnson, 1996). The Sparta aquifer 

provides water for a variety of purposes which include public 

supply (34.61 Mgal/d), industrial (25.60 Mgal/d), rural domestic 

(1.50 Mgal/d), and various agricultural (1.40 Mgal/d) (Sargent, 

2011). Of the 13 major aquifers or aquifer systems in Louisiana, 

the Sparta aquifer is currently (2012) the sixth most heavily 

pumped. The Sparta aquifer is the second most heavily pumped 

aquifer in Arkansas, which borders Louisiana to the north. In 

2005, 170 Mgal/d were withdrawn from the Sparta aquifer in 

eastern and southern Arkansas; of that total, about 15.55 Mgal/d 

were withdrawn from the aquifer in Union County, which 

borders Claiborne and Union Parishes to the north (Holland, 

2007) (fig. 1). By 1997, a large cone of depression (a coneshaped depression in the potentiometric surface caused by and 

centered on a pumping well or wells) in the Sparta aquifer 

centered over Union County had merged with the cone of 

depression at West Monroe (Joseph, 1997). In 2004, the rate of 

withdrawal from the Sparta aquifer in Union County began to 

decline and water levels in the aquifer began to rise in nearby 

areas of Arkansas and Louisiana (Freiwald and Johnson, 2007).

Withdrawals from the Sparta aquifer have caused water-level 

declines throughout much of the aquifer in Louisiana. By 1996, 

water levels in the aquifer underlying West Monroe, La. (fig. 

1), had declined about 300 feet (ft) from prepumping conditions 

(Ryals, 1980; Brantly and others, 2002). Water-level declines 

had also occurred at pumping centers near Minden, Ruston, 

Hodge, and Winnfield (fig. 1) (Ryals, 1980), and by 1997, water 

levels were below the top of the aquifer in several parishes 

in Louisiana (McKee and others, 2004). The decline of water 

levels below the top of the aquifer could result in unsaturated 

conditions, which could possibly lead to aquifer compaction and 

reduced well yields. Although land-surface subsidence can result 

from aquifer compaction, land-surface subsidence has not been 

documented in the Sparta aquifer (McKee and Hays, 2002). The 

water-level declines also have created conditions favorable for 

saltwater1 encroachment into freshwater areas of the aquifer 

(Brantly and others, 2002).

Additional knowledge about water levels and flow directions 

in the Sparta aquifer are needed to assess the current condition 

of the aquifer. In 2011, the U.S. Geological Survey (USGS), in 

1

In this report, saltwater is defined as water containing chloride concentrations greater than 

250 milligrams per liter.

cooperation with the Louisiana Department of Transportation 

and Development, began a study to document current (2012) 

water levels, differences in water levels between 2005 and 

2012, and areas where water levels were at or below the top

of the aquifer.

This report presents data and maps that describe the 

potentiometric surface of the Sparta aquifer during March–April 

2012, hydrographs of water levels from selected wells, waterlevel differences between 2005 and 2012, and areas where 

the water levels were at or below the top of the Sparta aquifer 

during March–April 2012. The potentiometric map can be used 

to determine direction of groundwater flow, hydraulic gradients, 

and effects of withdrawals on water levels. Water-level data 

collected for this study are stored in the USGS National Water 

Information System (http://waterdata.usgs.gov/nwis) and are on 

file at the USGS office in Ruston, La.

Description of Study Area

The study area includes the freshwater extent of the Sparta 

aquifer in north-central Louisiana, which extends across about 

7,000 square miles and includes all or parts of Bienville, 

Bossier, Caddo, Caldwell, Claiborne, Jackson, Lincoln, 

Morehouse, Natchitoches, Ouachita, Richland, Sabine, Union, 

Webster, and Winn Parishes (fig. 1). The climate is generally 

warm and temperate with high humidity and frequent rain. The 

average annual temperature is about 66 degrees Fahrenheit, and 

the average annual rainfall is about 57 inches (National Oceanic 

and Atmospheric Administration, 2013). 

157 

158 

159 

160 

161 

162 

163 

41 164 

42 

43 

44 

45 

46 

47 

48 

1975 1980 1985 1990 1995 2000 2005 2010 2015 

Water level, in feet above National Geodetic Vertical Datum of 1929 (NGVD 29) 

Water level, in feet below land surface 

Year 

Well: Wb-399 

Screen interval: 288–298 feet

 below land surface 

Altitude of land surface: 205 feet

 above NGVD 29 

Figure 3. Water levels in well Wb-399, Webster Parish, Louisiana.