U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2014–5149

Prepared in cooperation with the Arkansas Natural Resources Commission

Aquifers of Arkansas—Protection, Management, and 

Hydrologic and Geochemical Characteristics of Groundwater 

Resources in Arkansas
Cover.

1. Photograph courtesty of Dr. J. Van Brahana, University of Arkansas at Fayetteville

2. Illustration by Clay Baker courtesy of Dr. J. Van Brahana, University of Arkansas at Fayetteville

3. U.S. Geological Survey photograph by Ralf Montanus

4. Photograph courtesy of Jeffrey B. Connelly, University of Arkansas at Little Rock

5. Photograph courtesy of Bill Martin, Texas Historical Commission

6. U.S. Geological Survey photograph by Timothy M. Kresse

7. U.S. Geological Survey photograph by Joshua M. Blackstock

8. Photograph courtesy of Lon & Kathryn Stucker, Jot ‘Em Down Store and Museum

9. Photograph courtesty of D. Todd Fugitt, Arkansas Natural Resources Commission

10. U.S. Geological Survey photograph by Joshua M. Blackstock

11. Modified from Daniel S. Yeats, USGS Factsheet 2004–3086

12. U.S. Geological Survey photograph by Timothy M. Kresse

Background Image

U.S. Geological Survey photograph by Joshua M. Blackstock
Aquifers of Arkansas—Protection, 

Management, and Hydrologic and 

Geochemical Characteristics of 

Groundwater Resources in Arkansas

By Timothy M. Kresse, Phillip D. Hays, Katherine R. Merriman, 

Jonathan A. Gillip, D. Todd Fugitt, Jane L. Spellman, Anna M. Nottmeier, 

Drew A. Westerman, Joshua M. Blackstock, and James L. Battreal

Prepared in cooperation with the Arkansas Natural Resources Commission

Scientific Investigations Report 2014–5149

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: 2014

Suggested citation:

Kresse, T.M., Hays, P.D., Merriman, K.R., Gillip, J.A., Fugitt, D.T., Spellman, J.L., Nottmeier, A.M., Westerman, D.A., 

Blackstock, J.M., and Battreal, J.L., 2014, Aquifers of Arkansas—Protection, management, and hydrologic and 

geochemical characteristics of groundwater resources in Arkansas: U.S. Geological Survey Scientific Investigations 

Report 2014–5149, 334 p., http://dx.doi.org/10.3133/sir20145149. 

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

ISSN 2328-031X (print)

ISSN 2328-0328 (online)

ISBN 978 1 4113 3858 6
iii

Acknowledgments 

The authors would like to extend their gratitude to numerous persons who contributed valuable 

time assisting in various phases of data gathering, interpretation of data, providing invaluable 

references and publications, reviewing pertinent sections of the report, and other tasks. Without 

their assistance, important information inevitably would have been lost from such a large and 

comprehensive publication.

Terry Holland, U.S. Geological Survey (USGS), contributed large tracts of time in providing data 

and in numerous conversations on the history of water use, information on types of use, and 

details on important water users throughout Arkansas. The water-use section for all of the 

aquifers was greatly improved by his constant input throughout the project. 

Lyle Godfrey, Darcia Routh, and Evelyn Kort with the Arkansas Department of Health provided 

data on public supply sources in Arkansas and were available throughout the project for 

consultation, review of pertinent sections, and verbal discussions on the historical development 

and changes in use of groundwater as an important source of public water supply. Amy Wilson, 

Beaver Water District, provided information specifically related to the history of public-supply 

water use in northwestern Arkansas.

Paul Barlow and Stan Leake, USGS, were involved in several conference calls, in addition to 

serving as technical reviewers, for sections of the report dealing with stream/groundwater 

interaction in the Mississippi River Valley alluvial aquifer along the extent of the Arkansas 

River. The authors appreciate these gentlemen sharing their extensive experience in the area of 

streamflow depletion and other issues related to stream/groundwater interaction.

Tony Schrader, USGS, provided information related to water levels and especially the history of 

the water levels and water use of the Sparta aquifer in Union County and the successful reversal 

of declining water levels in the Sparta aquifer from implementation of conjunctive water-use 

strategies in Union County. 

Roger Miller, Arkansas Department of Environmental Quality, compiled and provided 

groundwater-quality data from approximately 1,000 well (and spring) sites from the 

Department’s ambient groundwater monitoring program and special short-term groundwater 

investigations. Roger additionally was available for answering numerous questions related to 

descriptive metadata associated with many of the groundwater sites.

Jason Robertson, Arkansas Plant Board, provided pesticide data collected by the agency 

in the Mississippi embayment of eastern Arkansas and additionally presented a history of 

pesticide sample collection in Arkansas. Ken Steele and Brian Haggard, University of Arkansas 

at Fayetteville, assisted in researching historical publications related to groundwater studies 

throughout northwestern Arkansas by various staff and students at the University of Arkansas. 

Brian Clark, U.S. Geological Survey, provided short descriptions of numerous groundwater flow 

models for various aquifers in addition to frequent consultation on various issues related to 

aquifers of the Mississippi embayment.

Although normally recognized as routine duties on the part of various USGS personnel, several 

persons spent an inordinate amount of time in reviewing and editing the entire report. Jim 

Petersen, USGS Arkansas Water Science Center, served as report specialist and peer reviewer. 
iv

In total, Jim probably read through the entire report, including figures and tables, on three 

different occasions. Although considering multiple reviewers for reviewing various sections 

of the report to reduce the burden on any one person, the authors decided for purpose of 

consistency that the report would benefit by the use of one outside peer review. Geoffrey Delin, 

regional Groundwater Specialist in Denver, Colorado, with extensive experience in groundwater 

studies, agreed to act as sole outside peer review for the report. Although busy with travel and 

other duties, Geoff used every free moment over a 5-month period to carefully review the text, 

tables, and figures and to provide valuable insight and thoughtful comments. Finally, our thanks 

to Keith Lucey for his thorough and insightful edits of the final draft report.
v

Contents

Acknowledgments .......................................................................................................................................iii

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

Introduction ....................................................................................................................................................2

Purpose and Scope .............................................................................................................................3

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

Groundwater Protection and Management Programs ...........................................................................5

Groundwater Quality Protection and Restoration ..........................................................................5

Groundwater Contamination Prevention Programs .......................................................................5

Wellhead Protection ...................................................................................................................6

Water Well Construction ...........................................................................................................6

Pesticide Management ..............................................................................................................6

State Nonpoint Source Program ..............................................................................................6

Oversight of Public Water-Supply Systems ............................................................................7

National Environmental Policy Act ..........................................................................................7

Permit Programs .........................................................................................................................7

Underground Injection Control ........................................................................................7

Hazardous Waste ...............................................................................................................8

Solid Waste .........................................................................................................................8

Waste Utilization ................................................................................................................8

Onsite Sewage Disposal Systems ..................................................................................8

Mining ..................................................................................................................................9

Oil and Gas Production .....................................................................................................9

Stormwater .........................................................................................................................9

Groundwater Remediation and Restoration .........................................................................10

Groundwater Remediation Level Interim Policy .........................................................10

Federal and State Programs for Hazardous Waste Sites .........................................10

Brownfields Program ......................................................................................................10

Elective Site Cleanup Program ......................................................................................10

Abandoned Mine Lands ..................................................................................................10

Underground Storage Tanks ..........................................................................................11

Groundwater Quantity and Use .......................................................................................................11

Reasonable Use/Correlative Rights Doctrine ......................................................................11

Statutory Water Laws and Policy ...........................................................................................11

Critical Groundwater Area Designation ................................................................................12

Groundwater and Climate Variation ......................................................................................14

Monitoring and Assessment of Groundwater ...............................................................................15

Arkansas Department of Health .............................................................................................16

Arkansas Department of Environmental Quality .................................................................16

Arkansas State Plant Board ....................................................................................................16

Arkansas Natural Resources Commission ...........................................................................18

U.S. Geological Survey ............................................................................................................18

Overview of Aquifers of Arkansas ...........................................................................................................18

Geologic Setting .................................................................................................................................22

Groundwater Use in Arkansas ........................................................................................................26
vi

Reporting and Registration .....................................................................................................26

Categories of Water Use .........................................................................................................26

Statewide Groundwater Use ..................................................................................................28

Irrigation ............................................................................................................................29

Public Supply ....................................................................................................................29

Domestic (Self-Supplied) ................................................................................................36

Commercial .......................................................................................................................38

Industrial ............................................................................................................................42

Mining ................................................................................................................................45

Aquaculture (Fish and Minnow Farming) ....................................................................46

Duck Hunting (Wildlife Impoundments) .......................................................................48

Livestock ............................................................................................................................48

Electric ...............................................................................................................................52

Groundwater Discharge to Surface-Water Bodies .....................................................................52

Aquifers of the Coastal Plain ....................................................................................................................54

Quaternary Alluvial Aquifers ............................................................................................................54

Mississippi River Valley Alluvial Aquifer ...............................................................................54

Geologic Setting ...............................................................................................................55

Hydrologic Characteristics ............................................................................................58

Sources of Recharge ......................................................................................................60

Groundwater Flow ...........................................................................................................60

Water Use .........................................................................................................................62

Agriculture and Irrigation Use ..............................................................................62

Aquaculture Use .....................................................................................................72

Duck Hunting Use ...................................................................................................73

Public-Supply Use ..................................................................................................73

Domestic Use ..........................................................................................................74

Industrial Use ..........................................................................................................74

Water Level Trends ..........................................................................................................74

Grand Prairie ...........................................................................................................75

Grand Prairie Area Demonstration Project and Bayou Meto Project ...........82

West of Crowleys Ridge .........................................................................................83

East of Crowleys Ridge ..........................................................................................84

Southeastern Arkansas .........................................................................................85

Deductive Analyses, Projections of Aquifer Conditions, and Sustainable 

Use ........................................................................................................................86

Results of Groundwater-Flow Simulation Models .............................................87

Optimization and Sustainable Yield ......................................................................93

Mississippi Embayment Regional Aquifer Study ...............................................95

Water Quality ....................................................................................................................96

General Geochemistry and Water Type ..............................................................98

Source of Elevated Trace Metals ......................................................................100

Occurrence, Distribution, and Sources of Elevated Chloride 

Concentrations ........................................................................................103

Temporal Trends in Chloride Concentrations ...................................................110

Occurrence of Pesticides ....................................................................................110
vii

Minor Alluvial Aquifers in Coastal Plain .............................................................................112

Red River Alluvial Aquifer .............................................................................................112

Hydrogeologic Setting .........................................................................................112

Water Use ..............................................................................................................112

Water Quality .........................................................................................................113

Ouachita-Saline Rivers Alluvial Aquifer .....................................................................113

Hydrogeologic Setting .........................................................................................113

Water Quality .........................................................................................................113

Jackson Group ................................................................................................................................114

Hydrogeologic Setting ...........................................................................................................114

Water Use ................................................................................................................................115

Water Quality ...........................................................................................................................116

General Geochemistry and Water Type .....................................................................116

Nitrate ..............................................................................................................................118

Iron ...................................................................................................................................118

Sulfate ..............................................................................................................................120

Chloride ............................................................................................................................120

Cockfield Aquifer ..............................................................................................................................120

Geologic Setting ......................................................................................................................121

Hydrologic Characteristics ...................................................................................................121

Water Use ................................................................................................................................122

Water Levels ............................................................................................................................129

Water Quality ...........................................................................................................................131

General Geochemistry and Water Type .....................................................................131

Iron ...................................................................................................................................134

Nitrate ..............................................................................................................................134

Sulfate ..............................................................................................................................135

Chloride ............................................................................................................................135

Sparta Aquifer ..................................................................................................................................136

Geologic Setting ......................................................................................................................137

Hydrologic Characteristics ...................................................................................................138

Water Use ................................................................................................................................138

Domestic and Public Supply ........................................................................................144

Irrigation ..........................................................................................................................147

Industrial Use .................................................................................................................147

Water Levels ............................................................................................................................149

Northeastern Arkansas ................................................................................................156

Grand Prairie and Jefferson County ...........................................................................157

Southern Arkansas ........................................................................................................158

Deductive Analyses, Projections of Aquifer Conditions, and Sustainable Use ...........161

Water Quality ...........................................................................................................................167

General Geochemistry and Water Type .....................................................................168

Nitrate ..............................................................................................................................171

Iron ...................................................................................................................................172

Sulfate ..............................................................................................................................173

Chloride ............................................................................................................................173
viii

Cane River Aquifer ...........................................................................................................................175

Geologic Setting ......................................................................................................................175

Hydrologic Characteristics ...................................................................................................176

Water Use ................................................................................................................................176

Water Quality ...........................................................................................................................181

General Geochemistry and Water Type .....................................................................181

Nitrate ..............................................................................................................................184

Iron ...................................................................................................................................184

Silica .................................................................................................................................184

Sulfate ..............................................................................................................................184

Chloride ...........................................................................................................................184

Carrizo Aquifer ..................................................................................................................................184

Geologic Setting ......................................................................................................................185

Hydrologic Characteristics ...................................................................................................185

Water Use ................................................................................................................................186

Water Quality ...........................................................................................................................186

General Geochemistry and Water Type .....................................................................186

Nitrate ..............................................................................................................................188

Iron ...................................................................................................................................188

Sulfate ..............................................................................................................................189

Chloride and Dissolved Solids .....................................................................................189

Wilcox Aquifer ..................................................................................................................................190

Geology .....................................................................................................................................190

Hydrologic Characteristics ...................................................................................................192

Water Use ................................................................................................................................192

Water Levels ............................................................................................................................197

Water Quality ...........................................................................................................................200

General Geochemistry and Water Type .....................................................................201

Nitrate ..............................................................................................................................203

Iron ...................................................................................................................................204

Sulfate ..............................................................................................................................205

Chloride and Dissolved Solids .....................................................................................205

Nacatoch Aquifer .............................................................................................................................205

Geology .....................................................................................................................................205

Hydrologic Characteristics ...................................................................................................206

Water Use ................................................................................................................................207

Public Supply ..................................................................................................................213

Industry ............................................................................................................................213

Water Levels ............................................................................................................................213

Water Quality ...........................................................................................................................217

General Geochemistry and Water Type .....................................................................217

Nitrate ..............................................................................................................................219

Iron ...................................................................................................................................219

Sulfate ..............................................................................................................................221

Chloride ............................................................................................................................221
ix

Ozan Aquifer .....................................................................................................................................221

Hydrogeologic Setting ...........................................................................................................222

Hydrologic Characteristics ...................................................................................................222

Water Use ................................................................................................................................222

Water Quality ...........................................................................................................................222

General Geochemistry and Water Type .....................................................................223

Nitrate ..............................................................................................................................223

Iron ...................................................................................................................................225

Sulfate ..............................................................................................................................225

Chloride ...........................................................................................................................225

Conceptual Model of Groundwater Geochemical Evolution ..................................226

Tokio Aquifer .....................................................................................................................................227

Geology .....................................................................................................................................227

Hydrologic Characteristics ...................................................................................................228

Water Use ................................................................................................................................228

Water Levels ............................................................................................................................233

Water Quality ...........................................................................................................................233

General Geochemistry and Water Type .....................................................................235

Nitrate ..............................................................................................................................237

Iron ...................................................................................................................................237

Sulfate ..............................................................................................................................238

Chloride ...........................................................................................................................240

Trinity Aquifer ...................................................................................................................................240

Geologic Setting ......................................................................................................................240

Hydrologic Characteristics ...................................................................................................241

Water Use ................................................................................................................................241

Water Levels ............................................................................................................................243

Water Quality ...........................................................................................................................243

General Geochemistry and Water Type .....................................................................246

Nitrate ..............................................................................................................................248

Iron ...................................................................................................................................248

Sulfate ..............................................................................................................................248

Chloride ............................................................................................................................249

Aquifers of the Interior Highlands ..........................................................................................................250

Arkansas River Valley Alluvial Aquifer .........................................................................................250

Geologic Setting ......................................................................................................................250

Hydrologic Characteristics ...................................................................................................251

Groundwater-Flow Simulation Models ...............................................................................251

Water Use ................................................................................................................................253

Water Quality ...........................................................................................................................253

General Geochemistry and Water Quality .................................................................253

Nitrate ..............................................................................................................................254

Iron and Arsenic ............................................................................................................256

Sulfate ..............................................................................................................................257

Chloride ............................................................................................................................258
x

Ouachita Mountains Aquifer ..........................................................................................................259

Geology .....................................................................................................................................259

Hydrologic Characteristics ...................................................................................................259

Water Use ................................................................................................................................261

Water Quality ...........................................................................................................................261

General Geochemistry and Water Type .....................................................................261

Nitrate ..............................................................................................................................263

Iron ...................................................................................................................................264

Sulfate ..............................................................................................................................265

Chloride ............................................................................................................................267

Western Interior Plains Confining System ...................................................................................267

Geologic Setting ......................................................................................................................267

Hydrologic Characteristics ...................................................................................................267

Water Use ................................................................................................................................268

Water Quality ...........................................................................................................................268

General Geochemistry and Water Type .....................................................................269

Nitrate ..............................................................................................................................272

Iron ...................................................................................................................................272

Sulfate ..............................................................................................................................274

Chloride ............................................................................................................................274

Conceptual Model of Groundwater Geochemical Evolution ..................................274

Springfield Plateau Aquifer ............................................................................................................277

Geologic Setting ......................................................................................................................277

Hydrologic Characteristics ...................................................................................................278

Water Levels ............................................................................................................................280

Water Use ................................................................................................................................281

Water Quality ...........................................................................................................................281

General Geochemistry and Water Quality .................................................................282

Nitrate ..............................................................................................................................285

Bacteria ...........................................................................................................................288

Sediment .........................................................................................................................289

Pesticides ........................................................................................................................289

Iron ...................................................................................................................................289

Chloride ............................................................................................................................290

Sulfate ..............................................................................................................................290

Ozark Aquifer ....................................................................................................................................291

Geologic Setting ......................................................................................................................291

Hydrologic Characteristics ...................................................................................................293

Water Levels ............................................................................................................................294

Deductive Analysis and Projections of Groundwater Movement ..................................297

Water Use ................................................................................................................................298

Water Quality ...........................................................................................................................300

General Geochemistry and Water Type .....................................................................300

Nitrate ..............................................................................................................................305

Pesticides ........................................................................................................................307
xi

Radium .............................................................................................................................307

Iron ...................................................................................................................................307

Sulfate ..............................................................................................................................309

Chloride ............................................................................................................................309

Summary .....................................................................................................................................................309

References .................................................................................................................................................311

Figures

1. Map showing location of critical groundwater areas in eastern Arkansas and 

counties referenced in this report ..........................................................................................13

2. Map showing location of ambient groundwater-quality monitoring sites in 

Arkansas .....................................................................................................................................17

3. Map showing combined outcrop, subcrop areas, and physiographic regions for 

the 16 aquifers serving as major and minor sources of groundwater supplies 

throughout Arkansas .................................................................................................................20

4. Graph showing total and irrigation use from groundwater and surface-water 

sources in Arkansas from 1925 to 2010 ..................................................................................28

5. Map showing location of Arkansas cities and major rivers referenced in this 

report ............................................................................................................................................32

6. Graph showing surface-water and groundwater use for domestic and public 

supply and population of Arkansas from 1950 to 2010 .........................................................33

7. Maps showing population, in thousands, by water source and water use, in 

million of gallons per day, by water source in Arkansas, 2010 ..........................................37

8. Map showing extent of the Mississippi embayment with location of Quaternary 

aquifers ........................................................................................................................................56

9. Map showing surface geology of the West Gulf Coastal Plain and Mississippi 

Alluvial Plain in southern and eastern Arkansas .................................................................57

10. Map showing wells with reported water use from the alluvial aquifers in the 

Coastal Plain in Arkansas, 2010 ...............................................................................................63

11. Maps showing water use from alluvial aquifers in Arkansas from 1965 to 2010 ............64

12. Map showing change in percentage of water use from the alluvial aquifers in 

the Coastal Plain alluvial aquifer system in Arkansas from 1965 to 2010 .........................68

13. Graph showing rice acreage and corresponding irrigation water use from 

Mississippi River Valley alluvial aquifer in the Grand Prairie region of Arkansas, 

1905–57 ........................................................................................................................................69

14. Graph showing acres of rice harvested and groundwater use for irrigation of 

rice in Arkansas .........................................................................................................................70

15. Graph showing acres harvested of irrigated and nonirrigated soybeans for 

Arkansas .....................................................................................................................................71

16. Graph showing acres harvested of irrigated and nonirrigated cotton for 

Arkansas .....................................................................................................................................72

17. Maps showing selected potentiometric contours of water levels for selected 

time periods in the Mississippi River Valley alluvial aquifer in Arkansas ........................76

18. Hydrograph of water levels in wells completed in Mississippi River Valley 

alluvial aquifer in the Grand Prairie region of Arkansas .....................................................83

19. Hydrographs of water levels in wells completed in the Mississippi River Valley 

alluvial aquifer west of Crowleys Ridge in northeastern Arkansas ..................................85
xii

20. Hydrographs of water levels in wells completed in the Mississippi River Valley 

alluvial aquifer east of Crowleys Ridge in northeastern Arkansas ...................................86

21. Hydrographs of water levels in wells completed in the Mississippi River Valley 

alluvial aquifer in southeastern Arkansas .............................................................................87

22. Map showing areal extents for all groundwater flow-simulation models 

conducted in the Mississippi River Valley alluvial aquifer in eastern Arkansas ............88

23. Map showing spatial extent of the Mississippi Embayment Regional AquiferSystem Analysis study including the Mississippi River Valley alluvial aquifer 

study area ...................................................................................................................................91

24. Map showing percentage of recent average annual pumping from the 

Mississippi River Valley alluvial aquifer with reductions for surface-water 

diversions simulated in scenario 3 of Clark and others ......................................................97

25. Box plots showing the interquartile range of selected chemical constituents in 

groundwater from alluvial deposits in the Coastal Plain of southern and eastern 

Arkansas .....................................................................................................................................99

26. Maps showing spatial distribution of selected chemical constituents in 

groundwater from alluvial deposits in the Coastal Plain of southern and eastern 

Arkansas ...................................................................................................................................101

27. Box plots for selected chemical constituents in groundwater from alluvial 

deposits as related to geomorphological units in the Mississippi Alluvial Plain 

of eastern Arkansas ................................................................................................................102

28. Map showing distribution of chloride concentrations in groundwater from 

alluvial deposits of the Coastal Plain in Arkansas .............................................................104

29. Map showing distribution of chloride concentrations in groundwater from the 

Mississippi River Valley alluvial aquifer in Bayou Bartholomew watershed of 

southeastern Arkansas ...........................................................................................................106

30. Map showing distribution of chloride concentrations in groundwater from the 

Mississippi River Valley alluvial aquifer overlain onto a map of Quaternary 

geomorphological landforms .................................................................................................107

31. Map showing distribution of arsenic concentrations in groundwater from the 

Mississippi River Valley alluvial aquifer overlain onto a map of Quaternary 

geomorphological landforms .................................................................................................109

32. Graphs showing relation of A, specific conductance and pH; B, well depth and 

nitrate; C, specific conductance and iron; and D, specific conductance and 

sulfate in groundwater from Jackson Group in southeastern Arkansas .......................117

33. Box plots showing the interquartile range for selected chemical constituents in 

groundwater from the Jackson Group in southeastern Arkansas ..................................118

34. Maps showing spatial distribution of selected chemical constituents in 

groundwater from the Jackson Group in southeastern Arkansas ..................................119

35. Map showing wells with reported water use from the Cockfield aquifer in 

Arkansas, 2010 .........................................................................................................................123

36. Map showing water-use rates for the Cockfield aquifer in southeastern 

Arkansas from 1965 to 2010 ....................................................................................................125

37. Map showing change in percentage of water use from the Cockfield aquifer in 

southeastern Arkansas from 1965 to 2010 ...........................................................................127

38. Map showing potentiometric surface of the Cockfield aquifer in Arkansas, 2009 .......130

39. Hydrographs of water levels in wells completed in the Cockfield aquifer in 

southeastern Arkansas ...........................................................................................................131

40. Maps showing spatial distribution of selected chemical constituents for 

groundwater from the Cockfield aquifer in southeastern Arkansas ...............................133
xiii

41. Box plots showing interquartile range of selected chemical constituents in 

groundwater from the Cockfield aquifer in southeastern Arkansas ...............................134

42. Graphs showing relation of concentrations of dissolved solids to A, bicarbonate 

and B, chloride in groundwater from the Cockfield aquifer in southeastern 

Arkansas ...................................................................................................................................136

43. Map showing wells with reported water use from the Sparta aquifer in 

Arkansas, 2010 .........................................................................................................................139

44. Maps showing water-use rates for the Sparta aquifer in Arkansas from 1965 

to 2010 ........................................................................................................................................141

45. Map showing change in percentage of water use from the Sparta aquifer in 

Arkansas from 1965 to 2010 ....................................................................................................145

46. Hydrograph showing water use in the Sparta aquifer from the city of El Dorado 

and Union County and water levels in the Monsanto well in the Sparta aquifer 

near El Dorado, Union County, Arkansas .............................................................................146

47. Hydrograph showing water use and water levels in well E in the Sparta 

aquifer in Columbia County, Arkansas .................................................................................148

48. Maps showing A, change in water levels for the Sparta aquifer in Arkansas 

from predevelopment to 2011; B, change in water levels for the Sparta aquifer 

in Union County from 2003 to 2011 ........................................................................................150

49. Maps showing selected potentiometric contours of water levels in the Sparta 

aquifer in Arkansas .................................................................................................................151

50. Hydrographs showing water levels in wells A and B in the Sparta aquifer and 

water levels in a well in the Mississippi River Valley alluvial aquifer in Poinsett 

County, Arkansas .....................................................................................................................156

51. Hydrographs showing water use and water levels in wells C and D in the 

Sparta aquifer in Arkansas and Jefferson Counties, Arkansas .......................................157

52. Map showing location of water-level and water-quality monitoring wells in the 

Sparta aquifer of southern Arkansas and northern Louisiana .........................................160

53. Hydrographs showing effects of change in industrial groundwater use on water 

levels in wells completed in the Sparta aquifer in southern Arkansas ..........................161

54. Map showing extent of area for historical groundwater flow-simulation models 

constructed for regional analysis of the Sparta aquifer in the Mississippi 

embayment of the southern United States ..........................................................................163

55. Maps showing spatial distribution of selected chemical constituents for 

groundwater from the Sparta aquifer in Arkansas ............................................................169

56. Graphs showing relation between A, well depth and nitrate; B, iron and sulfate; 

C, dissolved solids and bicarbonate; and D, dissolved solids and chloride for 

groundwater from the Sparta aquifer in Arkansas ............................................................171

57. Box plots showing interquartile range of selected chemical constituents for 

groundwater from the Sparta aquifer in Arkansas ............................................................172

58. Map showing wells with reported water use from the Cane River aquifer in 

Arkansas, 2010 .........................................................................................................................177

59. Maps showing water-use rates for the Cane River aquifer in Arkansas from 

1965 to 2010 ...............................................................................................................................179

60. Box plots showing interquartile range of selected chemical constituents for 

groundwater from the Cane River aquifer in Arkansas .....................................................182

61. Maps showing spatial distribution of selected chemical constituents for 

groundwater from the Cane River aquifer in Arkansas .....................................................183
xiv

62. Map showing spatial distribution of selected chemical constituents for 

groundwater from the Carrizo aquifer in Arkansas ...........................................................187

63. Box plots showing interquartile range of selected chemical constituents for 

groundwater from the Carrizo aquifer in Arkansas ...........................................................189

64. Map showing wells with reported water use from the Wilcox aquifer in 

Arkansas, 2010 .........................................................................................................................191

65. Maps showing water-use rates for the Wilcox aquifer in Arkansas from 1965 

to 2010 ........................................................................................................................................194

66. Map showing change in percentage of water use from the Wilcox aquifer in 

Arkansas from 1965 to 2010 ....................................................................................................196

67. Maps showing potentiometric surface of the Wilcox aquifer in Arkansas, 2009 .........198

68. Hydrographs of water levels in wells completed in the Wilcox aquifer in 

Arkansas ...................................................................................................................................200

69. Maps showing spatial distribution of selected chemical constituents in 

groundwater from the Wilcox aquifer in Arkansas ............................................................202

70. Graph showing relation of well depth and nitrate in groundwater from the 

Wilcox aquifer in Arkansas ....................................................................................................203

71. Box plots showing interquartile range of selected chemical constituents in 

groundwater from the Wilcox aquifer in Arkansas ............................................................204

72. Map showing wells with reported water use from the Nacatoch aquifer in 

Arkansas, 2010 .........................................................................................................................208

73. Maps showing water-use rates for the Nacatoch aquifer in Arkansas from 1965 

to 2010 ........................................................................................................................................210

74. Map showing change in percentage of water use from the Nacatoch aquifer in 

Arkansas from 1965 to 2010 ....................................................................................................212

75. Hydrographs of water levels in wells completed in the Nacatoch aquifer in 

Arkansas ...................................................................................................................................214

76. Maps showing potentiometric surface of the Nacatoch aquifer in Arkansas, 

February–March 2011 .............................................................................................................215

77. Maps showing spatial distribution of selected chemical constituents for 

groundwater from the Nacatoch aquifer in Arkansas ......................................................218

78. Graph showing relation of well depth and nitrate concentrations in groundwater 

from the Nacatoch aquifer in Arkansas ...............................................................................220

79. Box plots showing interquartile range of selected chemical constituents in 

groundwater from the Nacatoch aquifer in Arkansas ......................................................220

80. Maps showing spatial distribution of selected chemical constituents in 

groundwater from the Ozan aquifer in southwestern Arkansas .....................................224

81. Box plots showing interquartile range of selected chemical constituents in 

groundwater from the Ozan aquifer in southwestern Arkansas ......................................225

82. Graphs showing relation of A, bicarbonate and sulfate; relation of specific 

conductance and B, chloride; C, percent bicarbonate; and D, percent sulfate in 

groundwater from the Ozan aquifer in southwestern Arkansas .....................................226

83. Map showing wells with reported water use for the Tokio aquifer in Arkansas, 

2010 ............................................................................................................................................229

84. Maps showing water-use rates for the Tokio aquifer in Arkansas from 1965 

to 2010 ........................................................................................................................................231

85. Map showing potentiometric surface of the Tokio aquifer in Arkansas, spring 

2011 ............................................................................................................................................234
xv

86. Hydrographs of water levels in wells completed in the Tokio aquifer in 

Arkansas ...................................................................................................................................235

87. Maps showing spatial distribution of selected chemical constituents in 

groundwater from the Tokio aquifer in Arkansas ...............................................................236

88. Box plots showing interquartile range for selected chemical constituents in 

groundwater from the Tokio aquifer in Arkansas ...............................................................238

89. Graphs showing relation of A, specific conductance and dissolved solids; 

B, sulfate and bicarbonate; C, specific conductance and sulfate; and 

D, specific conductance and chloride in groundwater from the Tokio aquifer 

in Arkansas ...............................................................................................................................239

90. Map showing wells with reported groundwater use for the Trinity aquifer in 

Arkansas, 2010 .........................................................................................................................242

91. Maps showing water-use rates for the Trinity aquifer in Arkansas from 1965 

to 2010 ........................................................................................................................................244

92. Maps showing spatial distribution of selected chemical constituents in 

groundwater from the Trinity aquifer in Arkansas .............................................................247

93. Box plots showing interquartile range of selected chemical constituents in 

groundwater from the Trinity aquifer in Arkansas .............................................................249

94. Map showing percent sand calculated from lithologic logs for the Arkansas 

River Valley alluvium in west-central Arkansas .................................................................252

95. Maps showing spatial distribution of selected chemical constituents in 

groundwater from the Arkansas River Valley alluvial aquifer in western 

Arkansas ...................................................................................................................................255

96. Box plots showing interquartile range of selected chemical constituents in 

groundwater from the Arkansas River Valley alluvial aquifer in western 

Arkansas ...................................................................................................................................256

97. Graph showing relation of iron and sulfate concentrations in groundwater 

from the Arkansas River Valley alluvial aquifer in western Arkansas ............................257

98. Graph showing relation of chloride and bromide concentrations in 

groundwater samples from the Arkansas River Valley alluvial aquifer near 

Dardanelle, Arkansas ..............................................................................................................258

99. Maps showing spatial distribution of selected chemical constituents in 

groundwater from the Ouachita Mountains aquifer in western Arkansas ....................262

100. Box plots showing interquartile range of selected chemical constituents in 

groundwater from the Ouachita Mountains aquifer in western Arkansas ....................264

101. Graphs showing relation of concentrations for A, nitrate and iron; B, nitrate 

and sulfate; C, sulfate and iron; D, nitrate and dissolved solids; E, iron and 

dissolved solids; and F, sulfate and dissolved solids in groundwater from 

the Ouachita Mountains aquifer in western Arkansas .....................................................266

102. Box plots showing interquartile range of selected chemical constituents in 

groundwater from the Western Interior Plains confining system in northern 

Arkansas ...................................................................................................................................270

103. Graphs showing relation of A, dissolved solids and bicarbonate; B, bicarbonate 

and pH; C, dissolved solids and pH; D, calcium plus magnesium/bicarbonate 

and sodium/chloride; E, dissolved solids and sulfate; and F, dissolved solids 

and chloride in groundwater from the Western Interior Plains confining 

system in northern Arkansas .................................................................................................271

104. Maps showing spatial distribution of selected chemical constituents in 

groundwater from the Western Interior Plains confining system in northern 

Arkansas ...................................................................................................................................273
xvi

105. Graph showing relation between dissolved-solids concentrations and pH 

values with a depiction of the evolution of chemical water types for groundwater 

from the Western Interior Plains confining system in northern Arkansas ....................275

106. Graphs showing relation between dissolved-solids concentrations and A, iron 

and B, arsenic concentrations in groundwater from the Western Interior Plains 

confining system in northern Arkansas ...............................................................................276

107. Diagram showing conceptual model of karst hydrogeologic setting for the 

Springfield Plateau aquifer in northern Arkansas ..............................................................279

108. Hydrograph of water levels in a well completed in the Springfield Plateau 

aquifer in northern Arkansas .................................................................................................281

109. Map showing spatial distribution of calcium/magnesium ratios in groundwater 

from the Springfield Plateau aquifer in northern Arkansas ..............................................283

110. Graphs showing relation of bicarbonate to A, calcium and B, calcium plus 

magnesium in groundwater from the Springfield Plateau aquifer in northern 

Arkansas ...................................................................................................................................284

111. Bar graphs showing the relation of agricultural land use in percent of total 

land use to mean nitrate concentrations in groundwater from A, wells and 

springs and B, springs in the Ozark Plateaus aquifer system in northwest 

Arkansas ...................................................................................................................................287

112. Graph showing analysis of covariance for nitrate concentrations and 

agricultural land use for Group I and Group II springs ......................................................288

113. Box plots showing interquartile range of selected chemical constituents in 

groundwater from the Springfield Plateau aquifer of northern Arkansas .....................290

114. Hydrographs of water levels in wells completed in the upper and lower Ozark 

aquifer of northern Arkansas .................................................................................................295

115. Map showing potentiometric surface of the Ozark aquifer in northern 

Arkansas, 2010 .........................................................................................................................296

116. Map showing wells with reported groundwater use from the Ozark aquifer in 

northern Arkansas, 2010 .........................................................................................................299

117. Maps showing spatial distribution of selected chemical constituents in 

groundwater from the Ozark aquifer in northern Arkansas .............................................302

118. Graphs showing relation of pH to A, well depth and B, dissolved solids in the 

upper Ozark aquifer and to C, well depth and D, dissolved solids in the lower 

Ozark aquifer; and relation of bicarbonate to dissolved solids in E, the upper 

Ozark aquifer and F, the lower Ozark aquifer ......................................................................304

119. Bar graphs showing nitrate concentrations and agricultural land use for 

groundwater from A, the Ozark aquifer in northeastern Arkansas and B, from 

the Springfield Plateau aquifer in northwestern Arkansas ..............................................306

120. Box plots showing interquartile range of selected chemical constituents in 

groundwater from the upper Ozark aquifer in northern Arkansas ..................................308

121. Box plots showing interquartile range of selected chemical constituents in 

groundwater from the lower Ozark aquifer in northern Arkansas ..................................308
xvii

Tables

1. Primary and secondary drinking water regulations for selected constituents and 

characteristics .............................................................................................................................4

2. Nomenclature, geologic age, use, and number of sites with groundwater-quality 

data for the 16 major and minor aquifers in Arkansas ........................................................21

3. Stratigraphic column and correlated geohydrologic units of the Coastal Plain 

Province in southern and eastern Arkansas .........................................................................22

4. Stratigraphic column and correlated geohydrologic units of the Ouachita 

Mountains Region, Arkansas ...................................................................................................23

5. Stratigraphic column and correlated geohydrologic units of the Ozark Plateaus 

Province in northern Arkansas ................................................................................................25

6. Groundwater use by category for Arkansas from published reports ...............................27

7. Groundwater use for irrigation supply by counties and years in Arkansas ....................30

8. Groundwater use for public supply by counties and years in Arkansas .........................34

9. Groundwater use for domestic supply by counties and years in Arkansas ....................39

10. Groundwater use for commercial supply by counties and years in Arkansas ...............41

11. Groundwater use for industrial supply by counties and years in Arkansas ....................43

12. Groundwater use for mining supply by counties and years in Arkansas ........................45

13. Groundwater use for aquaculture supply by counties and years in Arkansas ..............46

14. Groundwater use for wildlife impoundments (1965–80) and duck hunting 

(2005–10) supply by counties and years in Arkansas ..........................................................49

15. Groundwater use for livestock supply by counties and years in Arkansas ....................50

16. Groundwater use for electric supply by counties and years in Arkansas .......................52

17. Water use from alluvial aquifers in Arkansas, 1965–2010 ...................................................66

18. Range, mean, and median of annual rise-decline in water level by county for 

wells in the Mississippi River Valley alluvial aquifer............................................................80

19. Descriptive statistics for selected chemical constituents in groundwater from 

alluvial deposits in the Coastal Plain Province of southern and eastern Arkansas .......99

20. Water use from the Jackson Group in southeastern Arkansas, 1965–80 ......................116

21. Descriptive statistics for selected chemical constituents in groundwater from 

the Jackson Group in southeastern Arkansas ...................................................................117

22. Water use from the Cockfield aquifer in southeastern Arkansas, 1965–2010 ...............128

23. Descriptive statistics for selected chemical constituents in groundwater from 

the Cockfield aquifer in southeastern Arkansas ................................................................132

24. Water use from the Sparta aquifer in Arkansas, 1965–2010 ............................................143

25. Descriptive statistics for selected chemical constituents in groundwater from 

the Sparta aquifer in Arkansas ..............................................................................................170

26. Water use from the Cane River aquifer in Arkansas, 1965–2010 .....................................178

27. Descriptive statistics for selected chemical constituents in groundwater from 

the Cane River aquifer in Arkansas ......................................................................................182

28. Water use from the Carrizo aquifer in Arkansas, 1965–80 ................................................186

29. Descriptive statistics for selected chemical constituents in groundwater from 

the Carrizo aquifer in Arkansas .............................................................................................188

30. Water use from the Wilcox aquifer in Arkansas, 1965–2010 ............................................193

31. Descriptive statistics for selected chemical constituents in groundwater from 

the Wilcox aquifer in Arkansas .............................................................................................203
xviii

32. Water use from the Nacatoch aquifer in Arkansas, 1965–2010 .......................................209

33. Descriptive statistics for selected chemical constituents in groundwater from 

the Nacatoch aquifer in Arkansas ........................................................................................219

34. Water use from the Ozan aquifer in southwestern Arkansas, 1965–80 ..........................222

35. Descriptive statistics for selected chemical constituents in groundwater from 

the Ozan aquifer in southwestern Arkansas .......................................................................223

36. Water use from the Tokio aquifer in Arkansas, 1965–2010 ...............................................230

37. Descriptive statistics for selected chemical constituents in groundwater from 

the Tokio aquifer in Arkansas ................................................................................................237

38. Water use from the Trinity aquifer in Arkansas, 1965–2010 ..............................................246

39. Descriptive statistics for selected chemical constituents in groundwater from 

the Trinity aquifer in Arkansas ...............................................................................................248

40. Descriptive statistics for selected chemical constituents in groundwater from 

the Arkansas River Valley alluvial aquifer in western Arkansas .....................................254

41. Descriptive statistics for selected chemical constituents in groundwater from 

the Ouachita Moutains aquifer in western Arkansas ........................................................263

42. Descriptive statistics for selected chemical constituents in groundwater from 

the Western Interior Plains confining system in northern Arkansas ..............................270

43. Descriptive statistics for selected chemical constituents in groundwater from 

the Springfield Plateau aquifer in northern Arkansas .......................................................284

44. Descriptive statistics for selected chemical constituents in groundwater from 

the upper Ozark aquifer in northern Arkansas ...................................................................303

45. Descriptive statistics for selected chemical constituents in groundwater from 

the lower Ozark aquifer in northern Arkansas ....................................................................303
xix

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2

)

acre 0.4047 hectare (ha)

acre 0.4047 square hectometer (hm2

) 

acre 0.004047 square kilometer (km2

)

square mile (mi2

) 259.0 hectare (ha)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

million gallons (Mgal) 3,785 cubic meter (m3)

acre-foot (acre-ft) 1,233 cubic meter (m3)

acre-foot (acre-ft) 0.001233 cubic hectometer (hm3

) 

Flow rate

acre-foot per year (acre-ft/yr) 1,233 cubic meter per year (m3

/yr)

acre-foot per year (acre-ft/yr) 0.001233 cubic hectometer per year (hm3

/yr)

foot per second (ft/s) 0.3048 meter per second (m/s)

foot per day (ft/d) 0.3048 meter per day (m/d)

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

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

cubic foot per second per square 

mile [(ft3

/s)/mi2]

 0.01093 cubic meter per second per square 

kilometer [(m3/s)/km2]

cubic foot per day (ft3

/d) 0.02832 cubic meter per day (m3/d)

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)

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

/s)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

ton, short (2,000 lb) 0.9072 megagram (Mg) 

Radioactivity

picocurie per liter (pCi/L) 0.037 becquerel per liter (Bq/L) 

Specific capacity

gallon per minute per foot 

[(gal/min)/ft]

 0.2070 liter per second per meter 

[(L/s)/m]

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Transmissivity*

foot squared per day (ft2

/d) 0.09290 meter squared per day (m2/d) 
xx

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

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

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

(NGVD 29)

Altitude, as used in this report, refers to distance above the vertical datum.

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times 

foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25°C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).
xxi

Acronyms

ADEQ Arkansas Department of Environmental Quality 

ADH Arkansas Department of Health

AGS Arkansas Geological Survey

AML Abandoned Mine Land

ANRC Arkansas Natural Resources Commission

AOGC Arkansas Oil and Gas Commission

APCEC Arkansas Pollution Control and Ecology Commission

ARWUDBS Arkansas Water-Use Data Base System

ASPB Arkansas State Plant Board

AWRC Arkansas Water Resources Center

AWWCC Arkansas Water Well Construction Commission

BMP Best management practice

CERCLA Comprehensive Environmental Response Compensation and Liability Act

CFR Code of Federal Regulations

CWA Clean Water Act

EARCS Eastern Arkansas Region Comprehensive Study

EPA U.S. Environmental Protection Agency

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act

GPS Global Positioning System

GPWUA Grand Prairie Water Users Association

HWD Hazardous Waste Division

Koc Organic carbon partition coefficient

MCL Maximum contaminant level

NEPA National Environmental Policy Act

NPDES National Pollutant Discharge Elimination System

NPL National Priority List

NPS Nonpoint source

NRCS Natural Resources Conservation Service

NWIS National Water Information System

RASA Regional Aquifer-System Analysis

RATFA Remedial Action Trust Fund Act

RCRA Resource Conservation and Recovery Act

SDWA Safe Drinking Water Act

SMCRA Surface Mining Control and Reclamation Act

SMRD Surface Mining and Reclamation Division

SWAP Source Water Assessment Programs

SWMD Solid Waste Management Division

UCWCB Union County Water Conservation Board

UIC Underground injection control

USACE U.S. Army Corps of Engineers

USDA U.S. Department of Agriculture

USGS U.S. Geological Survey

UST Underground storage tanks

WHPP Wellhead Protection Program

Aquifers of Arkansas—Protection, Management, 

and Hydrologic and Geochemical Characteristics of 

Groundwater Resources in Arkansas

By Timothy M. Kresse1, Phillip D. Hays1, Katherine R. Merriman1, Jonathan A. Gillip1, D. Todd Fugitt2, 

Jane L. Spellman3

, Anna M. Nottmeier1, Drew A. Westerman1, Joshua M. Blackstock1, and James L. Battreal2

Abstract

Sixteen aquifers in Arkansas that currently serve or have 

served as sources of water supply are described with respect to 

existing groundwater protection and management programs, 

geology, hydrologic characteristics, water use, water levels, 

deductive analysis, projections of hydrologic conditions, and 

water quality. State and Federal protection and management 

programs are described according to regulatory oversight, 

management strategies, and ambient groundwater-monitoring 

programs that currently (2013) are in place for assessing and 

protecting groundwater resources throughout the State.

Physical attributes, groundwater geochemistry, and 

groundwater quality are described for each of the 16 aquifers 

of the State. Information in regard to the hydrology and 

geochemistry of each of the aquifers is summarized from 

about 550 historical and recent publications. Additionally, 

more than 8,000 sites with groundwater-quality data were 

obtained from the U.S. Geological Survey National Water 

Information System and the Arkansas Department of 

Environmental Quality databases and entered into a spatial 

database to investigate distribution and trends in chemical 

constituents for each of the aquifers.

The 16 aquifers of the State were divided into two 

major physiographic regions of the State: the Coastal Plain 

Province (referred to as Coastal Plain) of eastern and southern 

Arkansas, which includes 11 of the 16 aquifers, and the 

Interior Highlands Division (referred to as Interior Highlands) 

of western Arkansas, which includes the remaining 5 aquifers. 

The 11 aquifers in the Coastal Plain consist of various 

geologic units that are Cenozoic in age and consist primarily 

of Cretaceous, Tertiary, and Quaternary sands, gravels, silts, 

and clays. Groundwater in the Coastal Plain represents one 

of the most valuable natural resources in the State, driving 

the economic engines of agriculture, while also supplying 

abundant water for commercial, industrial, and public-supply 

use. In terms of age from youngest to oldest, the aquifers 

of the Coastal Plain include Quaternary alluvial aquifers, 

including the Mississippi River Valley alluvial aquifer (the 

most important aquifer in Arkansas in terms of volume of 

use and economic benefits), the Jackson Group (a regional 

confining unit that served for decades as an important source 

of domestic supply), and the Cockfield, Sparta, Cane River, 

Carrizo, Wilcox, Nacatoch, Ozan, Tokio, and Trinity aquifers. 

The Mississippi River Valley alluvial aquifer accounts for 

approximately 94 percent of all groundwater used in the State, 

and the aquifer is used primarily for irrigation purposes. The 

Sparta aquifer is the second most important aquifer in terms 

of use, and the aquifer was used in the past dominantly as a 

source of public and industrial supply, although increasing 

irrigation use is occurring because of critically declining water 

levels in the Mississippi River Valley alluvial aquifer. Other 

aquifers of the Coastal Plain generally are used as important 

local sources of domestic, industrial, and public supply, in 

addition to other minor uses. Water quality generally is good 

for all aquifers of the Coastal Plain, except for elevated iron 

concentrations and localized areas of high salinity. The high 

salinity results from intrusion from underlying formations, 

evapotranspiration processes in areas of low recharge, 

and inadequate flushing in downgradient areas of residual 

salinity from deposition in marine environments. Trends in 

the spatial distribution of individual chemical constituents 

are related to position along the flow path for most aquifers 

of the Coastal Plain. These trends include elevated iron and 

nitrate concentrations with lower pH values and dissolved 

solids in groundwater from the outcrop areas, transitioning to 

lower iron and nitrate (related to changes in redox) and higher 

pH and dissolved solids (dominantly from the dissolution 

of carbonate minerals) in groundwater downgradient from 

outcrop areas. Groundwater generally trended from a calciumto a sodium-bicarbonate water type with increasing cation 

exchange along the flow path.

The Interior Highlands of western Arkansas has less 

reported groundwater use than other areas of the State, 

reflecting a combination of factors. These factors include 

prevalent and increasing use of surface water, less intensive 

agricultural uses, lower population and industry densities, 

1

U.S. Geological Survey.

2

Arkansas Natural Resources Commission.

3

FTN Associates, Ltd.
2 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

lesser potential yield of the resource, and lack of detailed 

reporting. The overall low yields of aquifers of the Interior 

Highlands result in domestic supply as the dominant use, 

with minor industrial, public, and commercial-supply use. 

Where greater volumes are required for growth of population 

and industry, surface water is the greatest supplier of water 

needs in the Interior Highlands. The various aquifers of the 

Interior Highlands generally occur in shallow, fractured, wellindurated, structurally modified bedrock of this mountainous 

region of the State, as compared to the relatively flat-lying, 

unconsolidated sediments of the Coastal Plain. In terms 

of age from youngest to oldest, the aquifers of the Interior 

Highlands include: the Arkansas River Valley alluvial aquifer, 

the Ouachita Mountains aquifer, the Western Interior Plains 

confining system, the Springfield Plateau aquifer, and the 

Ozark aquifer. Spatial trends in groundwater geochemistry 

in the Interior Highlands differ greatly from trends noted 

for aquifers of the Coastal Plain. In the Coastal Plain, the 

prevalence of long regional flow paths results in regionally 

predictable and mappable geochemical changes along the 

flow paths. In the Interior Highlands, short, topographically 

controlled flow paths (from hilltops to valleys) within 

small watersheds represent the predominant groundwaterflow system. As such, dense data coverage from numerous 

wells would be required to effectively characterize these 

groundwater basins and define small-scale geochemical 

changes along any given flow path for aquifers of the 

Interior Highlands. Changes in geochemistry generally were 

related to rock type and residence time along individual flow 

paths. Dominant changes in geochemistry for the Ouachita 

Mountains aquifer and the Western Interior Plains confining 

system are attributed to rock/water interaction and changes 

in redox zonation along the flow path. In these areas, 

groundwater evolves along flow paths from a calcium- to 

a sodium-bicarbonate water type with increasing reducing 

conditions resulting in denitrification, elevated iron and 

manganese concentrations, and production of methane in 

the more geochemically evolved and strongest reducing 

conditions. In the Ozark and Springfield Plateau aquifers, 

rapid influx of surface-derived contaminants, especially 

nitrogen, coupled with few to no attenuation processes was 

attributed to the karst landscape developed on Mississippianand Ordovician-age carbonate rocks of the Ozark Plateaus. 

Increasing nitrate concentrations are related to increasing 

agricultural land use, and areas of mature karst development 

result in higher nitrate concentrations than areas with less karst 

features.

Introduction

Groundwater is vitally important to the State of 

Arkansas. A total of approximately 11,450 million gallons 

per day (Mgal/d) of water was used in Arkansas in 2010, 

and approximately 7,873 Mgal/d (69 percent) was from a 

groundwater source. Irrigation water use accounts for the 

largest groundwater withdrawals, resulting in 94 percent of 

the total groundwater used in Arkansas. Total groundwater 

use has increased from approximately 892 Mgal/d in 1960 

(Stephens and Halberg, 1961) to approximately 7,873 Mgal/d 

in 2010, an increase of 774 percent. Of 2010 groundwater use, 

about 94 percent is from the Mississippi River Valley alluvial 

aquifer. Recent scenarios of sustainable water levels for the 

Mississippi River Valley alluvial aquifer indicate that only 45 

to 50 percent of current (2013) withdrawals from this aquifer 

are sustainable (Clark and others, 2013). These estimates of 

sustainable yield compare closely with earlier optimization 

models (Czarnecki and others, 2003a), which indicated that 

the sustainable yield from the Mississippi River Valley alluvial 

aquifer was equal to the amount of water withdrawn during 

the late 1970s and early 1980s, although use has continued to 

grow since this earlier time period. Similarly, model scenarios 

using water levels and pumping rates from the Sparta aquifer 

indicate that less than 60 percent of withdrawals from the 

Sparta aquifer are sustainable (McKee and others, 2004). 

These increasingly large withdrawals of groundwater have 

caused substantial declines in water levels in areas of greatest 

pumping. Such withdrawals can adversely affect aquifers and 

water users, with reliance on alternate water sources becoming 

an increasing necessity. 

The Arkansas Natural Resources Commission (ANRC) 

received statutory authority and was charged by the State 

of Arkansas to develop the Arkansas Water Plan in 1969 

(Ark. Code Ann. Sec. 15–22–503). The plan provides a 

comprehensive planning process for the conservation, 

development, and protection of the State’s water resources, 

with a goal of long-term sustainable use for the health, wellbeing, environmental, and economic benefit to the State of 

Arkansas. This plan was to be used by all State agencies, 

commissions, and political subdivisions in all matters 

pertaining to the discharge of their respective duties and 

responsibilities as they may affect the State’s water resources. 

The first Arkansas Water Plan was published in 1975. In 

1985, the Arkansas General Assembly enacted Ark. Code 

Ann. Sec. 15–22–301, which broadened the powers of the 

ANRC’s planning responsibilities to include (1) an inventory 

of the State’s water resources; (2) the determination of the 

current needs and the projection of future needs of all water 

uses in the State; and (3) the determination of whether excess 

surface water existed that might be put to beneficial use. From 

this statute, an updated State Water Plan was required, which 

resulted in the 1990 update. These plans were instrumental 

in shaping Arkansas’ water policy and providing needed 

guidance with respect to developing and protecting the State’s 

water resources. 

The 1990 plan contained eight basin reports with an 

executive summary document (http://anrc.ark.org/divisions/

water-resources-management/arkansas-water-plan). An 

important outcome of the 1990 plan was the motivation 

behind the development of Act 154 of 1991, the Arkansas 
Methods 3

Groundwater Protection and Management Act. This Act 

outlined the State’s role in groundwater planning, provided 

authority to the ANRC to delineate critical groundwater 

areas, and gave the ANRC limited authority to allocate 

groundwater within those areas under specific conditions. 

Though the authority to limit groundwater use was extremely 

restricted, it represented the first such authority in the State. 

The State Water Plan and associated legal authority have 

provided valuable assistance to the State with respect to the 

conservation and protection of groundwater in Arkansas. It has 

been successful in promoting conservation, education, and a 

conjunctive use strategy relying on sustainable groundwater 

use and excess surface water. This policy is helping the State 

move towards conjunctive and sustainable water use. A 

major outcome from the 1990 State Water Plan and resulting 

Arkansas Groundwater Protection and Management Act was 

the implementation of use of excess surface water by major 

industrial users in Union County, Ark. Industries in this area 

of the State previously had used groundwater from the Sparta 

aquifer, which had shown severe water-level declines and was 

designated as a critical groundwater area. Since the switch 

to surface-water use in this area, water levels in the Sparta 

aquifer have increased more than 80 ft (T.P. Schrader, U.S. 

Geological Survey, oral commun., 2013).

In 2011, the ANRC recognized the need to update 

the Arkansas Water Plan. With more than two decades 

passing since the publication of the 1990 State Water Plan, 

groundwater use has shifted by various demands, total 

groundwater use has increased, new data and information 

have been developed, and new water issues have emerged. 

The ANRC recognized the need for a detailed groundwater 

summary that would be independent of past summaries 

included in individual basin reports. Suggested changes 

included documenting changes over time in groundwater 

use and water levels, in addition to documenting spatial and 

temporal trends in groundwater quality for all the State’s 

aquifers. The purpose of the comprehensive groundwater 

report was to (1) establish a clear identification of all Federal, 

State, and local entities with water resources authority; 

(2) identify stakeholders and critical groundwater issues and 

needs of the State; (3) collect all existing water-use and waterlevel data and document changes over time; (4) identify shifts 

in groundwater use related to changes in population, changes 

in land use, changes in water needs, and other criteria; and 

(5) collect all available groundwater-quality data to identify 

areas with poor water quality and define spatial and temporal 

changes as affected by natural and anthropogenic sources.

Water managers, planners, regulators, and groundwater 

users, as well as the institutions charged with the protection 

and management or with a vital interest in groundwater 

in Arkansas, have long recognized the importance of 

groundwater as a resource supporting life, health, and the 

economy in the State. These entities have expended great 

effort in collecting data, characterizing, and understanding 

this important resource. Abundant data, data reports, 

and interpretive reports are available from these efforts; 

however, no comprehensive synthesis and intellectual 

resource compendium has been compiled in regard to the 

State’s aquifers. The current large-scale task of updating the 

Arkansas State Water Plan has highlighted the need for such a 

compendium and has provided the framework to address this 

need.

Various meetings between the ANRC, U.S. Geological 

Survey (USGS), and other stakeholders established the need 

for a comprehensive source of groundwater information by 

State and local authorities, water-resources managers and 

planners, and the public. Therefore, the USGS, in cooperation 

with the ANRC, compiled a compendium to aid in addressing 

these concerns and to cover all aspects of the groundwater 

resources of Arkansas including status and changes in water 

law and policy, water rights, water use, water quality, water 

quantity, water levels, and stream-aquifer interaction. 

Purpose and Scope

The purpose of this report is to provide a compilation 

of geologic, hydrologic, and water-quality data for all major 

and minor aquifers in the State and to describe the geologic 

framework, overall use by category, current and past waterlevel information, and general water quality associated with 

each aquifer. The purpose also is to provide a comprehensive 

reference of the collective studies of groundwater in Arkansas 

and to develop an intellectual resource compendium on 

groundwater. Review of available data and interpretive studies 

was performed for each aquifer identified as currently being 

or having been used as sources of water supply, resulting in 

the identification and summary descriptions of 16 aquifers 

within the State of Arkansas. This report provides a general 

encyclopedic reference of the state of knowledge on aquifers 

in Arkansas to support water management, planning, 

development, academic, and legislative needs. The geographic 

scope for this study and level of data collection were confined 

to the boundaries of the State of Arkansas, though some 

discussion extends to adjacent States for aquifer systems that 

are of regional importance and cross State boundaries.

Methods

Water-use data referenced in this report were derived 

from numerous historical reports, the 5-year USGS wateruse reports, and the Arkansas Water-Use Data Base System 

(ARWUDBS). The water-use data from the 5-year water-use 

reports (1960–2005) (Stephens and Halberg, 1961; Halberg 

and Stephens, 1966; Halberg, 1972, 1977; Holland, 1981, 

1987, 1993, 1999, 2004, 2007) were compiled into a Microsoft 

Access database. The 2010 water-use report was not published 

at the time of this writing (2013), and the 2010 water-use 

data were compiled from the ARWUDBS and placed into 
4 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

the Microsoft Access database. This allowed querying by 

county, year, or use category. On occasion, conflicting wateruse values were found between ARWUDBS, the 5-year 

water-use reports, and the historical reports. When there was 

conflict between the historical reports and the 5-year wateruse reports, the values were taken from the 5-year water-use 

report. ARWUDBS was assumed to be more up-to-date than 

the 5-year water-use reports, and values from ARWUDBS 

were used when a conflict between ARWUDBS and the 5-year 

water-use report occurred; any changes from the 5-year wateruse reports were footnoted in the appropriate water-use table. 

Inventories of public-water supplies, municipal websites, and 

oral or written communication with the Arkansas Department 

of Health (ADH) were used to determine the public-supply 

source or duration of groundwater use by municipalities. 

Potentiometric-surface maps and water-level data were 

provided by the USGS. 

Groundwater-quality data from approximately 8,000 sites 

in Arkansas were used to produce statistical analyses and 

spatial-distribution maps for selected chemical constituents 

associated with 16 aquifers. Approximately 7,000 waterquality data were extracted from the USGS National Water 

Information System (NWIS) database (U.S. Geological 

Survey, 2013b). Data were extracted irrespective of collection 

date and included field data (pH, specific conductance), major 

ions (calcium, magnesium, sodium, potassium, chloride, 

sulfate, and bicarbonate), select trace metals (iron, manganese, 

and arsenic), hardness, and dissolved solids. Approximately 

1,000 sites with groundwater-quality data were extracted 

from the Arkansas Department of Environmental Quality 

(ADEQ) database (Roger Miller, Arkansas Department of 

Environmental Quality, written commun., 2012). The ADEQ 

operates a water-quality laboratory; groundwater samples 

collected by the ADEQ Water Division are analyzed by 

U.S. Environmental Protection Agency (EPA) approved 

methods with data stored in an internal database at their Little 

Rock office. The ADEQ additionally has participated in the 

USGS Standard Reference Sample project (http://bqs.usgs.

gov/) for numerous years, which evaluates and improves 

the performance of participating laboratories. Multiple State 

and Federal agencies, university libraries, and archives 

additionally were searched for relevant data and interpretive 

reports; about 550 publications are referenced herein with 

summaries of important data, results, and interpretations 

included in this report.

Water type was determined by converting all majorion weight concentrations to equivalent concentrations 

(milligrams per liter [mg/L] to milliequivalent per liter 

[meq/L]). In this manner, each cation or anion was calculated 

as a percent of the total cations and anions, respectively. Major 

cations and anions are those comprising more than 50 percent 

of the total cations and anions in milliequivalents per liter, 

respectively. Where no one cation or anion constitutes more 

than 50 percent of the total cations and anions, respectively, 

then a mixed water type was assigned using the dominant 

(ions with the highest percentage of the total cations and 

anions in milliequivalents per liter) cations and anions.

Water-quality requirements by various users can vary 

widely depending on the intended use (industrial, public 

supply, irrigation or other uses). In assessing general water 

quality for this report, water-quality data were compared to the 

EPA Federal drinking-water standards (U.S. Environmental 

Protection Agency, 2009). These standards address a wide 

array of inorganic and organic constituents. Because only 

inorganic constituents serving as important indicators of 

general water quality were reviewed for this report, drinkingwater standards were only discussed for these constituents. 

The Federal drinking-water standards are threefold and include 

mandatory and recommended standards. Federal maximum 

contaminant levels (MCLs) are enforceable (for public and 

community supply systems) and are based on adverse health 

effects. Federal lifetime health advisories are nonregulatory 

estimates of acceptable drinking-water levels for a chemical 

substance based on health effects information (often leads to 

development of MCLs). Federal secondary drinking-water 

regulations are nonenforceable guidelines regarding cosmetic 

effects (such as tooth or skin discoloration) or aesthetic 

effects (such as taste, odor, or color) of drinking water (U.S. 

Environmental Protection Agency, 2009). MCLs, lifetime 

health advisories, and secondary drinking-water regulations 

for the constituents reviewed in this report are found in table 1. 

Detailed information for all primary and secondary drinkingwater standards can be found at http://water.epa.gov/drink/

contaminants/index.cfm.

Table 1. Primary and secondary drinking water regulations for 

selected constituents and characteristics.

[NA, not applicable; mg/L, milligrams per liter; mg/d, milligrams per day]

Constituents and 

characteristics

Maximum 

contaminant 

levels

Lifetime 

health 

advisories

Secondary 

regulations

pH NA NA 6.5–8.5

Dissolved solids NA NA 500 mg/L

Sodium1 NA NA 30–60 mg/L

Chloride NA NA 250 mg/L

Sulfate NA NA 250 mg/L

Iron NA NA 0.3 mg/L

Manganese NA 0.3 mg/L2 0.05

Arsenic 0.01 mg/L 0.002 mg/L3 NA

1

Health-based drinking water advisory of 20 mg/L for individuals on a 500 

mg/d restricted sodium diet.

2

Dietary manganese. The lifetime health advisory includes a threefold 

modifying factor for increased bioavailability from drinking water.

3

Based at 10-4 cancer risk.
Groundwater Protection and Management Programs 5

Groundwater Protection and 

Management Programs

There are three main components of groundwater 

protection and management: (1) ensuring the available 

quantity necessary for the various uses, (2) protecting and 

restoring groundwater quality, and (3) ambient monitoring 

of groundwater quality on a continuous basis. State waterresources protection authority is generally divided among 

various State agencies. The ADEQ has primary waterquality protection authority, and the ADH has authority over 

public drinking-water-supply programs. The ANRC has 

comprehensive planning and water-quantity authority and is 

responsible for protection of diminishing groundwater supplies 

in areas where agricultural, public, and industrial needs have 

placed unsustainable demands on production capacities of 

certain aquifers. The broad scope of groundwater protection 

and management activities requires a multiagency approach to 

address groundwater quantity and quality issues. This section 

presents a summary of water law, policy, and regulatory 

programs that have evolved and the role that various Federal 

and State agencies have taken to address groundwater 

protection and management in the State of Arkansas.

Groundwater Quality Protection and Restoration

There are numerous potential and actual sources of 

groundwater contamination in the State, both natural and 

manmade. Arkansas Department of Environmental Quality 

(2012) identified the 10 major sources of contamination 

in Arkansas to be animal feedlots, fertilizers, pesticides, 

underground storage tanks, surface impoundments, landfills, 

septic systems, hazardous wastes sites, saltwater intrusion, 

and spills. It is difficult to define which sources have the 

greatest effect on groundwater quality because each source 

varies in areal extent and degree of alteration of groundwater 

quality. For example, a point source, such as a landfill, may 

result in severe impact to groundwater with numerous organic 

chemicals exceeding safe drinking-water standards, but the 

areal extent of the plume may be limited with no offsite 

migration and no known groundwater users at risk. On the 

other hand, contamination from nonpoint sources, such as 

agricultural activities, may be areally extensive with minimal 

effect on the use of the groundwater for drinking-water 

supply or other purposes. Point-source prevention programs 

are almost entirely established as regulatory programs and 

are administered primarily by ADEQ. Most nonpoint sources 

are related to agriculture and other land-use activities and 

commonly are addressed by joint efforts of several agencies, 

with lead oversight relegated to the ANRC. 

Despite the threat to groundwater resources, no Federal 

or State statute comprehensively addresses groundwater 

protection. There are currently only patchworks of law at the 

Federal and State levels that address groundwater protection. 

The EPA has been designated by Congress to be the primary 

Federal agency responsible for groundwater protection; 

however, there is no comprehensive Federal groundwater 

law comparable to the legislation addressing surface-water 

pollution. Instead, the EPA enforces requirements of a myriad 

of Federal laws having provisions that protect groundwater 

quality. These laws include among others: the Safe Drinking 

Water Act (SDWA) of 1974 (42 USC §300f et seq.[and the 

following]) and amendments; the Resource Conservation and 

Recovery Act (RCRA) of 1976 (42 USC §6901 et seq.); and 

the Comprehensive Environmental Response Compensation 

and Liability Act (CERCLA) of 1980 (42 USC §9601 et 

seq.) and amendments. The Clean Water Act (CWA) of 1972 

(33 USC §1251 et seq.), including the 1977 amendments, 

is the primary Federal law in the United States that governs 

the discharge of pollutants into the Nation’s waters. The 

CWA’s primary regulatory mechanism is the National 

Pollutant Discharge Elimination System (NPDES), which 

requires permits to be issued for discharges of any pollutant 

or combination of pollutants into navigable waters. Certain 

sections specifically address groundwater, but it is unclear 

whether the CWA’s pollution-control provisions apply to 

groundwater. Some provisions of the CWA clearly apply to 

groundwater. For example, Section 106 provides for regional 

monitoring of surface water and groundwater; and Section 304 

provides for development of specific water-quality criteria, 

which would include groundwater quality (Quatrochi, 1996). 

Act 472 of 1949, the Arkansas Water and Air Pollution 

Control Act, codified as Arkansas Code Annotated (ACA 

§8–4–101 et seq.), defines groundwater as a part of “waters 

of the state” that are subject to protection. This act is the 

primary statute providing authority to State agencies for the 

regulation of various programs that protect human health and 

the environment; however, Act 472 of 1949 does not contain 

reporting requirements for groundwater contamination nor 

does it contain numerical standards or other guidance for 

monitoring or remediating groundwater contamination. ADEQ 

is the State’s delegated authority responsible for implementing 

various EPA programs and enforces environmental policies set 

by the Arkansas Pollution Control and Ecology Commission 

(APCEC); however, other State agencies also have authority 

to enact rules and regulations that address groundwater 

protection. Restoring aquifers to beneficial use and minimizing 

human exposure to contaminants can be very costly when 

protection mechanisms have failed or were not in place. Most 

remedial activities are the responsibility of ADEQ.

Groundwater Contamination Prevention 

Programs

There are a number of potential threats to groundwater 

drinking-water supplies from point and nonpoint sources of 

contamination. This section describes various State programs 

initiated with the intended purpose of preventing potential 

contamination of drinking water and its sources. 
6 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Wellhead Protection

Originally, the Federal SDWA focused primarily on 

treatment as the means of providing safe drinking water at 

the tap. The law was amended in 1986 and 1996 and required 

many actions to protect drinking water and its sources. The 

amendments of 1986 specified that certain program activities, 

such as delineation, contaminant-source inventory, and 

source-management plans, be incorporated into state Wellhead 

Protection Programs (WHPP). Implementation of Arkansas’ 

WHPP began in the early 1990s. The WHPP is a voluntary 

program that is maintained by the public water systems and 

local communities with technical assistance and guidance 

provided by the ADH. The goal of the program is to develop 

strategies and methods for managing a wellhead protection 

area for groundwater sources of public supply. 

The 1996 amendments greatly enhanced the existing law 

by recognizing source-water protection of all public drinkingwater supplies (surface and groundwater). States were asked 

to develop and implement Source Water Assessment Programs 

(SWAPs) to evaluate the vulnerability of public drinking-water 

systems to possible sources of contamination throughout the 

State and use this information as a management tool for the 

benefit and protection of public water systems. In Arkansas, 

the WHPP is now part of the SWAP. Arkansas’ SWAP includes 

delineating the source-water assessment areas, conducting 

contaminant source inventories, determining the susceptibility 

of each public water supply source to contamination from 

the inventoried sources, and releasing the results of the 

assessments to the public (Arkansas Department of Health, 

2009). Those systems that are considered vulnerable are 

advised to take action through community education programs 

or by passing city ordinances to protect water sources.

Water Well Construction

The Arkansas Water Well Construction Commission 

(AWWCC) regulates the development of groundwater supplies 

to provide safe water for public consumption, and Act 855 of 

2003 (ACA §17–50–401 et seq.) provides a means of holding 

persons who violate Arkansas law regarding water-well 

construction accountable for their actions. AWWCC licenses 

water-well contractors and registers drillers, pump installers, 

and their apprentices. 

The rules and regulations of the Arkansas Water Well 

Construction Commission (2011) provide minimum standards 

for the construction and abandonment of water wells (that is, 

water supply, geothermal, and monitoring) so that groundwater 

is protected from contamination. Water-well contractors must 

file a well-completion report for each well. Well-completion 

data are maintained in an ANRC database that is linked to the 

USGS water-use database (http://water.usgs.gov/watuse/). 

Water-well records also may be obtained from Arkansas 

Geological Survey (AGS), which has over 145,000 water-well 

construction records on file by county and township/range that 

date from the early 1970s.

Administrative and investigative functions are carried 

out by ANRC. ANRC responds to complaints from the public 

about water-well construction, as well as inspecting wells 

for violations of the rules and regulations. ANRC also works 

closely with ADH and its Environmental Health Specialist 

in each county and conducts well inspections in each county. 

These inspections are to ensure the protection of groundwater 

through compliance with the rules and regulations established 

by the ANRC.

Pesticide Management

The Arkansas State Plant Board (ASPB) is the lead 

agency for implementing the Federal Insecticide, Fungicide, 

and Rodenticide Act (FIFRA) of 1996 (7 USC §136 et seq.). 

The ASPB has been monitoring groundwater since 2004 using 

an EPA-approved Pesticide Management Plan that allows the 

agency to work with ADH to determine actions to be taken 

in the event pesticide contamination is confirmed (Arkansas 

State Plant Board, 2013). ASPB also developed the Arkansas 

Agricultural Abandoned Pesticide Program as a way for 

farmers to safely and properly dispose of unused pesticides. 

This program is conducted in cooperation with ASPB, the 

University of Arkansas Cooperative Extension Service, the 

Arkansas Farm Bureau, ANRC, and ADEQ. Representatives 

from these agencies comprise the Abandoned Pesticide 

Advisory Board. The Abandoned Pesticide Advisory Board 

selects counties for collection events and has a goal of holding 

at least one collection event in every county in Arkansas. 

The Advisory Board uses priority watersheds as a guiding 

principle when selecting counties for pesticide collections. 

The pesticide collections began in 2005 in northeastern 

Arkansas; by the spring of 2009, at least one collection had 

been held in each county in eastern Arkansas. By the spring 

of 2011, the Abandoned Pesticide Program had collected 

over 744,000 pounds of unwanted pesticides from Arkansas 

farmers in 55 different counties (Arkansas State Plant Board, 

2013). The pesticide collections are paid for by the pesticide 

manufacturers through a fee added to the registration of each 

agricultural pesticide used in Arkansas. There is no cost to the 

farmer, and participation in the program is anonymous.

State Nonpoint Source Program

Potential sources of nonpoint source (NPS) pollution in 

groundwater include excess fertilizers, chemicals, and animal 

wastes from row-crop agriculture, residential and urban areas, 

pastures, and concentrated animal feeding operations. ANRC 

is responsible for developing and implementing the State’s 

NPS program (Arkansas Natural Resources Commission, 

1999). This program is a cooperative effort of many local, 

State, and Federal agencies; regional and local entities; 

nonprofit organizations; and watershed groups. The program 

promotes voluntary action to improve water quality. Projects 

may include implementation of best management programs 
Groundwater Protection and Management Programs 7

(BMPs), demonstrations of effective techniques, technical 

assistance, education, and monitoring. ANRC’s NPS program 

is supported by grant funds under Section 319 of the CWA.

Oversight of Public Water-Supply Systems

The SDWA was passed by Congress in 1974 to protect 

public health by regulating the Nation’s drinking-water 

supply. The SDWA authorizes the EPA to set national healthbased standards that protect against naturally occurring and 

manmade contaminants in drinking water. The EPA, States, 

and public water systems work together to ensure that these 

standards are met.

The ADH has primary enforcement responsibility and 

provides oversight of public water systems throughout the 

State. ADH reviews new water-system facility construction, 

inspects water-system facilities, troubleshoots water-treatment 

and distribution problems, investigates complaints, and 

collects and analyzes samples to determine water quality. 

ADH enacts rules to ensure that public water systems adhere 

to EPA regulations (Arkansas State Board of Health, 2012b) 

enacted under the authority of Act 96 of 1913 as amended 

(ACA §20–7–109). These rules and regulations incorporate the 

Federal National Primary Drinking Water Regulations found 

in Title 40 of the Code of Federal Regulations (40 CFR) parts 

141, 142, and 143 (U.S. Environmental Protection Agency, 

2001).

Monitoring the quality of drinking water is a joint 

responsibility of ADH and the State’s public water-supply 

systems. According to ADH (Bradley Jones, Arkansas 

Department of Health, oral commun., 2013), Arkansas has 

over 1,190 individual groundwater wells used for public 

drinking-water supply. Statewide, there are about 710 

community public drinking-water systems, of which about 

690 use groundwater as their only water source. These 

groundwater systems serve more than 870,000 residents. 

Additionally, there are about 35 facilities defined by the 

SDWA as noncommunity, nontransient public water systems 

that rely on groundwater. These smaller facilities include 

schools, daycare centers, and businesses. There are also 

about 375 transient noncommunity public systems such as 

restaurants, churches, community centers, and campgrounds 

that use groundwater.

National Environmental Policy Act

The National Environmental Policy Act (NEPA) of 1969 

(42 USC §4321 et seq.) and amendments require that all 

actions sponsored, funded, permitted, or approved by Federal 

agencies undergo planning to ensure that environmental 

considerations (including impacts to groundwater) are given 

due weight in project decision making. NEPA has procedural 

requirements for all Federal government agencies to prepare 

environmental assessments (EAS) and environmental impact 

statements (EISs). 

Permit Programs

Protecting groundwater is accomplished through issuance 

of permits, inspections, as well as continuous monitoring 

and enforcement of the regulations. ADEQ and other State 

agencies issue many types of permits for activities that can 

have a negative effect on groundwater quality. Permits can 

establish limits for specific chemicals or groups of pollutants 

or can require BMPs designed to reduce release of pollutants 

to surface and groundwater resources.

Underground Injection Control

Part C of the SDWA of 1977 required the EPA to 

establish regulations for the disposal of wastewaters in 

underground reservoirs. The Underground Injection Control 

(UIC) program is responsible for regulating the construction, 

operation, permitting, and closure of injection wells 

constructed for underground storage or disposal of wastewater. 

Arkansas was given primary enforcement authority to 

administer the UIC program in 1982. There are three classes 

of underground injection wells in Arkansas—Class I, Class 

II, and Class V (U.S. Environmental Protection Agency, 

1984). ADEQ has the authority to regulate Class I and V 

wells (excluding bromine-related, spent-brine disposal wells). 

The Arkansas Oil and Gas Commission (AOGC) has State 

primacy to regulate Class II wells and shares enforcement 

authority with ADEQ of the Class V bromine-disposal wells 

as recognized in a Memorandum of Understanding between 

ADEQ, AOGC, and EPA. Corresponding Federal regulations 

found in 40 CFR parts 144, 145, and 146 provide performance 

standards for location, design, installation, construction, and 

maintenance of permitted facilities. ADEQ issues UIC permits 

pursuant to APCEC Regulation 17 (Arkansas Pollution 

Control and Ecology Commission, 2005). AOGC issues Class 

II well permits under General Rule H, General Rules and 

Regulations (Arkansas Oil and Gas Commission, 2013). 

Class I wells inject hazardous and nonhazardous wastes 

into saline formations found at depths between 2,500 and 

8,700 ft below ground surface. Class I requirements stipulate 

that a facility be able to demonstrate that injected waste will 

not impact groundwater (or surface water) for 10,000 years. 

There are 14 operating Class I wells in Arkansas: 4 hazardous 

and 10 nonhazardous wells (Linda Hanson, Arkansas 

Department of Environmental Quality, oral commun., 2013). 

Four of the wells are “shut-in,” meaning the wells are not 

currently injecting fluids. 

Class II wells are the primary means of disposal for 

energy and production wastes and include enhanced oilrecovery injection wells and saltwater disposal wells. Most of 

the injected fluid is saltwater (brine), which is brought to the 

surface in the process of producing oil and gas. In addition, 

brine and other fluids, like diesel fuel, are injected to enhance 

oil and gas production. There are approximately 28 Class 

II commercial disposal wells and over 500 noncommercial, 

producer-owned Class II disposal wells in Arkansas (State 
8 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Review of Oil and Natural Gas Environmental Regulations, 

2012).

Class V wells are shallow, subsurface treatment and 

disposal systems such as air conditioning return-flow wells, 

cooling water return-flow wells, drainage wells for stormwater 

runoff, dry wells, recharge wells, saltwater intrusion barrier 

wells, septic systems for multiple dwellings, subsidencecontrol wells, geothermal wells, solution-mining wells, 

spent-brine, return-flow wells, in-situ recovery, motor-vehicle 

waste disposal, and wells used in experimental technology. 

Large-capacity cesspools are also Class V wells, but they 

are banned in Arkansas under authority of the ADH. There 

are approximately 136 Class V wells that are permitted by 

ADEQ and 74 bromine wells permitted by AOGC (Linda 

Hanson, Arkansas Department of Environmental Quality, 

oral commun., 2013; Rex Robertson, Arkansas Oil and Gas 

Commission, oral commun., 2013).

Hazardous Waste

The ADEQ’s Hazardous Waste Division (HWD) 

implements Arkansas’ RCRA Subtitle C waste-management 

program governing the management and disposition of 

hazardous wastes, used oils, and universal wastes and 

administers the State’s hazardous waste program under 

authority of the Arkansas Hazardous Waste Management 

Act 406 of 1979, as amended (ACA §8–7–02 et seq.) The 

HWD received delegation of the Federal RCRA hazardous 

waste-management program from the EPA. State and Federal 

hazardous waste-management regulations and requirements 

are merged into a single reference document, APCEC 

Regulation 23 (Arkansas Pollution Control and Ecology 

Commission, 2012a). 

The HWD relies on record keeping to maintain a “cradleto-grave” tracking system for all generated hazardous wastes. 

Proper management and pollution-prevention techniques are 

designed to ensure against contamination of groundwater. 

If there is improper management of hazardous wastes, the 

program requires that actions be taken to remedy the situation 

and to restore, to the extent possible, quality of the affected 

groundwater. A strong oversight and enforcement effort are 

maintained to provide high visibility as a deterrent against 

future violations. Certain permitted facilities that are used to 

manage hazardous wastes have specific construction criteria 

designed to protect groundwater quality. Permit conditions 

for these facilities include the requirement for groundwater 

monitoring that meets the requirements of APCEC 

Regulation 23. 

Solid Waste

Nonhazardous landfills are subject to Federal regulation 

under Subtitle D of RCRA, 40 CFR, parts 258 and 257. 

ADEQ’s Solid Waste Management Division (SWMD) 

regulates the management and disposal of nonhazardous 

wastes through adoption of Subtitle D and by implementing 

rules and regulations in APCEC Regulation 22 (Arkansas 

Pollution Control and Ecology Commission, 2008), which 

came into effect in 1993 and was adopted pursuant to the 

Arkansas Solid Waste Management Act.

Permits are required for various classes of landfills. Class 

1 landfills include all municipal solid waste landfill units. 

These landfills can accept household wastes, commercial 

wastes, and approved industrial wastes. Class 3 landfills accept 

commercial, industrial, and special solid wastes, and Class 4 

landfills accept construction and demolition debris and other 

nonputrescible wastes. The solid waste program permitting 

requirements for facilities accepting wastes are directed at 

protecting groundwater and surface water, while assuring 

the safe management and disposal of wastes. Permitting 

requirements for Class I landfills and most Class 3 landfills 

include liners and leachate-collection/treatment systems, 

groundwater-monitoring systems, and other environmental 

protection systems that protect groundwater. At a minimum, 

semiannual reports are submitted by facilities required 

to monitor groundwater. If constituents in groundwater 

around the landfill exceed the EPA MCLs for drinking-water 

supplies, corrective action is required to bring the facility into 

compliance. A Post-Closure Trust Fund pays for corrective 

action needed after closure of landfills. The SWMD currently 

(2013) evaluates environmental monitoring data for one closed 

landfill.

Waste Utilization

Pursuant to Act 472 of 1949, as amended, ADEQ has the 

power to issue permits “to prevent, control or abate pollution.” 

Therefore, any waste-disposal system that does not discharge 

directly into the waters of the State must be operated under 

the terms and conditions of a no-discharge water permit. An 

example of a no-discharge permit is a UIC well permit. Other 

no-discharge permits are required for land application, land 

farming, and subsurface disposal of water-treatment-plant 

residuals, and industrial and animal wastes.

Permit procedures for liquid animal waste-management 

systems are described in APCEC Regulation 5 enacted in May 

2012 (Arkansas Pollution Control and Ecology Commission, 

2012b). An objective of the regulation is to control nutrients 

from confined animal operations with such systems. 

Obtaining a permit requires, among other conditions, an 

approved waste-management plan that is prepared by Natural 

Resource Conservation Service (NRCS), the University of 

Arkansas Cooperative Extension Service, a Certified Nutrient 

Management Planner, a water-quality technician from ANRC, 

or a professional engineer. By limiting the amount of nutrients 

applied to those actually required by crops, excess amounts of 

nutrients can be controlled and surface water and groundwater 

protected.

Onsite Sewage Disposal Systems

The ADH administers the Arkansas State Board of 

Health Rules and Regulations pertaining to onsite wastewater 

systems (Arkansas State Board of Health, 2012a). These 
Groundwater Protection and Management Programs 9

regulations were enacted under the authority of Act 402 of 

1977 and established minimum standards for the design and 

construction of individual sewage disposal systems, including 

alternate and experimental sewage system applications and 

subdivision systems. Onsite wastewater-system permits are 

required for operation, and the systems must be installed by 

licensed contractors. These systems typically are designed 

by ADH Designated Representatives and approved by 

local health units. There are approximately 400,000 onsite 

wastewater systems in Arkansas (Renae Mites, Arkansas 

Department of Health, oral commun., 2013). 

Mining

The Surface Mining and Reclamation Division (SMRD) 

of ADEQ regulates surface mining and reclamation, which 

includes the coal program and the noncoal program. The 

Surface Mining Control and Reclamation Act of 1977 

(SMCRA) established performance standards for coal mining 

operations for the express purpose of protecting society and 

the environment from the adverse effects of surface coal 

mining operations and to ensure reclamation of mine sites. 

States were charged with submitting a State program covering 

surface coal mining and reclamation operations. As such, the 

Arkansas Surface Coal Mining and Reclamation Act, Act 134 

of 1979, authorized the State to develop, adopt, issue, and 

amend rules and regulations pertaining to surface coal mining 

and reclamation operations. Active coal mines must comply 

with APCEC Regulation 20 (Arkansas Pollution Control and 

Ecology Commission, 2002). Regulation 20 has a groundwater 

protection clause requiring mine operators to control or 

prevent the discharge of acid mine drainage into groundwater 

systems. 

Act 827 of 1991, as amended, deals with the reclamation 

of land affected by the mining of noncoal minerals, such as 

bauxite, clay, and sand and gravel, using open-cut mining 

methods. A 1999 amendment authorized the regulation of 

soil and shale pits with some exemptions based on the size 

of the pit and the distance from adjacent property lines. 

APCEC Regulation 15, the Arkansas Open Cut Mining and 

Land Reclamation (Arkansas Pollution Control and Ecology 

Commission, 2012c), set performance standards that must be 

followed during mining and the process of reclaiming land 

to a beneficial use. Act 1166 of 1997 provided a regulatory 

framework for the operation, reclamation, and safe closure 

of new stone quarries and any land purchased or leased for a 

quarry. 

Oil and Gas Production

Arkansas has a long history of oil and gas production 

beginning in the early 1900s. In 2012, there were about 

7,000 oil-production wells in southern Arkansas and about 

4,000 gas-production wells in northern Arkansas; however, 

since 2004, the majority of gas production has occurred 

in north-central Arkansas, where gas-production is being 

developed at a rate of about 700–900 wells per year (State 

Review of Oil and Natural Gas Environmental Regulations, 

2012) through the use of horizontal drilling and hydraulic 

fracturing. 

Oil and gas exploration and production, as well as 

hydraulic fracturing, is regulated by the AOGC. This authority 

was given to AOGC in Subtitle 6, Title 15 of the Arkansas 

Code. Regulations describing requirements for oil and gas 

well development activities, including hydraulic fracturing 

and use of Class II UIC wells, have been adopted under 

the authority of these statutes. Storage of saltwater prior to 

injection in Class II UIC wells is regulated by ADEQ under 

APCEC Regulation 1 (Arkansas Pollution Control and 

Ecology Commission, 1993). 

Concerns by local citizens and citizen groups on the 

potential environmental effects of gas production resulted in 

more stringent State regulations. For example, AOGC General 

Rule B–19 was among the first rules in the Nation to require 

public disclosure of the chemicals used in hydraulic fracturing 

operations; AOGC General Rule B–26 governs the siting, 

construction, and operation of pits and tanks used for the 

holding or storage of well fluids; AOGC General Rules B–17, 

B–26, and B–34 address spill prevention and cleanup; and 

AOGC General Rule–19 has production casing requirements 

specific to the Fayetteville Shale that are the first line of 

defense in protecting groundwater during hydraulic fracturing 

operations (Arkansas Oil and Gas Commission, 2013). 

Responsibilities for water use and disposal related to 

hydraulic fracturing for gas production are through various 

State programs. The use of surface water for makeup water 

is governed by regulations administered by ANRC. The 

AOGC and ADEQ respond to complaints of water-well 

contamination, and AOGC has adopted joint standards with 

ADEQ. The inclusion of multiuse reserve pits in the rules 

(General Rule B–17 [Arkansas Oil and Gas Commission, 

2013] and APCEC Regulation 34 [Arkansas Pollution Control 

and Ecology Commission, 2011a]) encourages reuse and 

recycling of return flow waters from gas-production operations 

for hydraulic fracturing purposes. The ADH regulates sources 

of ionizing radiation including naturally occurring radioactive 

materials (NORM). A produced water or effluent concentration 

of greater than or equal to 60 picocuries per liter (pCi/L) for 

combined radium-226 and radium-228 would be subject to 

ADH regulations. Owners/operators would be required to 

notify the ADH as part of the ADH’s NORM General Licensee 

registration process. Regulatory efforts are coordinated with 

the Arkansas Department of Environmental Quality and the 

Arkansas Oil and Gas Commission (Bevill Bernard, Arkansas 

Department of Health, written commun., 2014).

Stormwater

Urban stormwater discharges are generated by runoff 

from paved surfaces including streets, parking lots, and other 

impervious areas (for example, buildings) during rainfall 

and snow events, which often contain pollutants in quantities 

that could adversely affect water quality. Most urban and 

industrial stormwater discharges are considered point 

sources and therefore require coverage by a NPDES permit 
10 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

under APCEC Regulation 2 (Arkansas Pollution Control 

and Ecology Commission, 2011b). The primary method to 

control stormwater discharges is through use of BMPs. There 

are a variety of traditional and low-impact BMPs, including 

retention and detention ponds, biofilters, grassed filter strips, 

porous pavement, wetlands, and others. BMPs are especially 

important in northern Arkansas because stormwater can 

discharge directly through karst features into aquifers. 

Groundwater Remediation and Restoration

Remediation of groundwater contaminated by 

anthropogenic sources often is required to restore groundwater 

to its previous uses. Numerous sites in Arkansas have been 

investigated or remediated under voluntary actions, through 

enforcement, or under hazardous waste permits. Most 

cleanups are overseen by ADEQ, but if radiological materials 

are involved, ADH will lead the cleanup effort. This section 

describes some of the programs through which groundwater 

remediation is managed in Arkansas.

Groundwater Remediation Level Interim Policy

The goal of groundwater remediation in Arkansas is 

to protect, enhance, and restore, to the extent technically 

and economically feasible, groundwater conditions to the 

maximum beneficial use, while maintaining conditions 

that are protective of human health and the environment 

(Ellen Carpenter, Arkansas Department of Environmental 

Quality, oral commun., 2005). It is the policy of ADEQ 

that until final regulations are enacted by APCEC specific 

to the establishment of groundwater cleanup standards, 

cleanup levels or goals will be established on a case-bycase basis in a consistent manner. The process includes full 

characterization of the contaminant plume, source-control 

measures, BMPs to control migration of the plume, and a 

groundwater cleanup strategy. Preliminary remediation goals 

are established after an evaluation of risks to human health 

and the environment; consideration is given to the current and 

reasonably anticipated future land use, including groundwater 

usage. Because many citizens drink groundwater and use it 

in their homes, ADEQ currently classifies all groundwater 

in Arkansas as a potential source of drinking water. It is not 

necessary for groundwater to be defined as an aquifer (that is, 

a saturated permeable geologic formation that can produce a 

significant quantity of water) in order to be protected. Thus, 

final groundwater remediation levels are the existing Federal 

MCLs. Institutional controls, such as deed restrictions or city 

ordinances, are used with source controls to minimize the 

potential for human exposure to contamination by limiting 

groundwater use. 

Federal and State Programs for Hazardous Waste Sites

The Federal “Superfund” program, authorized by 

CERCLA, was established to identify, prioritize, and clean 

up hazardous wastes sites posing threats to human health and 

the environment. Sites identified under the Superfund program 

are placed on the National Priority List (NPL). In 2013, there 

were 14 NPL sites in Arkansas (U.S. Environmental Protection 

Agency, 2013). ADEQ HWD ensures that State requirements 

are met during investigation and cleanup of sites designated 

under this Federal “Superfund” program. ADEQ’s HWD 

administers a similar cleanup program for abandoned hazardous 

wastes sites under authority of the Remedial Action Trust Fund 

Act (RATFA) of 1985. The Arkansas RATFA State Priority 

List identifies those hazardous substance sites for which 

expenditures to investigate and remediate are authorized. 

Brownfields Program

Arkansas Voluntary Cleanup Act (Act 1042 of 1997, as 

amended) established the Brownfields Program and provides 

a streamlined process for the remediation and redevelopment 

of abandoned industrial or commercial properties that are 

contaminated or are perceived to be contaminated with 

hazardous constituents. ADEQ hopes to encourage the 

development of Brownfields as a sustainable land-use policy as 

an alternative to new development of Greenfields, or pristine 

properties, in the State of Arkansas. In December 2000, the 

EPA and ADEQ entered into a Memorandum of Agreement

to support ADEQ’s Brownfields Program and define the roles 

and responsibilities of EPA Region 6 and ADEQ. The rules and 

requirements of the program are outlined in APCEC Regulation 

No. 29 (Arkansas Pollution Control and Ecology Commission, 

2006). Upon successful completion of the Brownfields 

Program, participants are provided limitations on liability for 

the eligible property. 

Elective Site Cleanup Program

The ADEQ administers an Elective Site Cleanup Program, 

which allows responsible parties to enter into an agreement 

with ADEQ for cleanup of sites. The Elective Site Cleanup 

Program does not offer a release of liability but does offer 

participants a means to address historic contamination on their 

site without penalty and with known objectives. ADEQ is 

working to promote the Elective Site Cleanup Program in order 

to maximize cleanups of sites within the State. There is also a 

number of sites undergoing voluntary cleanup through Consent 

Administrative Orders.

Abandoned Mine Lands

The SMCRA created an Abandoned Mine Land (AML) 

fund to pay for the cleanup of mine lands abandoned before the 

passage of the statute in 1977. The law was amended in 1990 to 

allow funds to be spent on the reclamation of mines abandoned 

after 1977. The trust fund is financed by a fee assessed on every 

ton of coal mined in the country. A portion of AML fees are 

distributed to States with an approved reclamation program to 

fund reclamation activities. The SMRD currently uses stateof-the-art surveying and computer-aided design systems to 

perform the functions necessary to produce reclamation plans 

for the AML sites in Arkansas. 
Groundwater Protection and Management Programs 11

Underground Storage Tanks

The ADEQ Regulated Storage Tank Division drafts, 

administers, and enforces State regulations pertaining to 

underground storage tanks (USTs) as prescribed by 40 CFR 

280, as well as aboveground petroleum storage tanks. There 

are approximately 13,000 regulated storage tanks located 

at over 5,600 active facilities across the State (Arkansas 

Department of Environmental Quality, 2012). These tanks are 

located primarily at retail gasoline and diesel sales facilities 

but may also include bulk petroleum storage facilities, 

private fleet-fueling facilities, and emergency generating 

stations. Prior to the mid-1980s, USTs had been regulated 

in a fragmented fashion by the Federal government through 

various environmental statutes. When studies revealed 

growing problems with a large number of tank systems, 

along with an alarming potential for future problems, the 

U.S. Congress mandated changes that were initiated by the 

States (U.S. Environmental Protection Agency, 1988). These 

standards focused on new tank system installation standards 

(for example, secondary containment), existing tank upgrades, 

registration requirements, closure requirements, and corrective 

action requirements. The controlling regulation for regulated 

storage tanks in Arkansas is the APCEC Regulation 12 

(Arkansas Pollution Control and Ecology Commission, 2009).

The number of confirmed releases in Arkansas peaked 

in 2001 and has slowly declined since that time (Arkansas 

Department of Environmental Quality, 2012). Releases 

from USTs are required to be investigated, and those with 

groundwater impacts are required to have owners define the 

vertical and horizontal extent of contamination. Once defined, 

a Corrective Action Plan is implemented to mitigate the 

impact of contamination. The effectiveness of remediation 

normally is evaluated through groundwater monitoring. 

Groundwater Quantity and Use

Water law traditionally has been concerned with 

the quantity of water available for all shared uses. The 

development and management of groundwater resources in 

Arkansas takes place within a framework of common law, 

legislative law, and administrative policy. Arkansas is a 

water-rich State with a mean annual precipitation of 48 inches 

in the north and 56 inches in the south (Kleiss and others, 

2000; Pugh and Westerman, 2014). However, long-term 

unsustainable water use for industry, public supply, and the 

agricultural economy of eastern Arkansas has resulted in 

groundwater depletion issues, and groundwater policy has 

emerged in response to these events.

Reasonable Use/Correlative Rights Doctrine

A water right, as defined by law, is not legal title to the 

water but the legal right to use it in a manner dictated by State 

law. In Arkansas, groundwater is generally subject to the same 

treatment given to surface water in case law as early as 1882 

and conforms to the riparian doctrine, or rights system, which 

is recognized in Eastern States. This concept holds that the 

riparian owner, that is, the property owner of land overlying a 

groundwater source of water, has the right to withdraw and use 

beneficially the water and shares this right equally with other 

riparian owners. Additionally, water withdrawals are limited 

to what is determined to be reasonable in comparison with 

other riparian owners. All riparian owners have equal right 

to use reasonable amounts of groundwater, but this right may 

vary with time and is subject to modification; for example, 

as new users exert their rights to the water (Arkansas Natural 

Resources Commission, 2011).

Disputes over groundwater generally have been resolved 

according to a reasonable use test. There were two early cases 

in Arkansas that dealt with the question of the right to use 

groundwater:

1. In 1957, the Arkansas Supreme Court applied the riparian 

rights concept of reasonable use to groundwater use in 

Jones v. Oz-Ark-Val Poultry Co. (Looney, 1990; Arkansas 

Natural Resources Commission, 2011). This case was 

a conflict between industrial use and domestic use of 

groundwater. The court recognized that under State law 

domestic use is given the highest priority, and the right 

to use groundwater is a correlative right among property 

owners in which each has the right to a reasonable amount 

up to the full extent of the water use need, if the supply is 

sufficient such that other users are not adversely impacted. 

Thus, groundwater is subject to the reasonable use/

correlative rights doctrine, which includes the concept of 

shared reductions in time of allocation.

2. In 1975, the court again addressed the reasonable 

use doctrine and the right to use groundwater when 

it dealt with the right to transfer water away from a 

“riparian land” in groundwater cases. In Lingo v. City of 

Jacksonville (Looney, 1990; Arkansas Natural Resources 

Commission, 2011), the court indicated that it would be 

permissible for a riparian owner to remove groundwater 

and either use it or sell it away from the tract of land 

from which it was pumped, if this use did not injure the 

common supply of the riparian owners.

Statutory Water Laws and Policy

One of the first documented water-resources reports 

was published in 1939 by the Arkansas State Planning Board 

(Arkansas State Planning Board, 1939). This report is one 

of the first documents to identify a groundwater depletion 

problem in the Grand Prairie and to suggest a study of 

augmenting groundwater in the rice producing area with a 

diversion and importation of surface water. Importantly, the 

report called for the establishment of a permanent Water 

Resources Commission. In 1957, Arkansas began to move 

away from traditional case-by-case adjudication of water 
12 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

rights, and the General Assembly passed legislation creating a 

State agency with the responsibility to resolve water conflicts. 

Specifically, this agency, a predecessor to ANRC, had the 

authority to allocate available stream water during periods 

of shortage (Act 81 of 1957, ACA §15–22–201 et seq.), but 

Act 81 excluded any control over groundwater (Mack, 1963). 

Prior to 1957, bills had been introduced to the legislature to 

“facilitate the conservation of groundwater” by encouraging 

surface-water developments and to make the filing of waterwell logs mandatory, but these bills did not pass or were 

withdrawn (Mack, 1963; McGuiness, 1951).

The ANRC serves as the State’s primary water-resources 

planning and management agency with authority to develop 

the State Water Plan and other appropriate policy documents. 

The agency’s groundwater policy has evolved over the 

past few years in response to substantial groundwater-level 

declines observed in eastern and southern parts of the State. 

In general, the policy, as outlined by the 1975 and 1990 water 

plans, is to provide for the unmet water demand through the 

practices of conservation, education, and the use of excess 

surface water in a conjunctive-use pumping strategy to 

protect groundwater resources. Although implementation of 

the policy, especially with respect to use of excess surface 

water, has progressed slowly and groundwater levels 

continue to decline throughout much of the State, regulation 

of groundwater withdrawals has been reserved as a last 

resort for groundwater resource protection (D. Todd Fugitt, 

Arkansas Natural Resources Commission, oral commun., 

2013). However, various pieces of legislation were passed to 

establish a comprehensive groundwater-protection program 

as outlined in ANRC’s Rules and Regulations, Title IV, 

“Rules for the Protection and Management of Groundwater” 

(Arkansas Natural Resources Commission, 2005) that 

encourages the conservation of groundwater while protecting 

the beneficial use of aquifers for future generations. Key 

legislation includes:

1. Act 1051 of 1985 (ACA §15–22–301 et seq.) requires 

all groundwater users to report water usage to ANRC. 

As ANRC is charged with the duty to make various 

determinations concerning water supply and demand, 

it is important that the agency has some mechanism 

for receiving water-use information. Domestic uses of 

groundwater having a potential flow rate of less than 

50,000 gallons per day are exempt from reporting. The 

quantity, location, type of use, and name of the user must 

be registered on an annual basis with the Commission. 

The quantity used must be reported by March 1 of the 

following year. In 2009, there were approximately 

49,558 registered wells reported in the State. Of this total, 

48,599 (98.1 percent) were agricultural wells, most of 

which were used for irrigation and were located primarily 

in eastern Arkansas. The remaining 959 reported wells 

were used predominately for commercial, industrial, 

and public water supply purposes (Arkansas Natural 

Resources Commission, 2012a).

2. Act 154 of 1991, the Arkansas Ground Water Protection 

and Management Act, was an outcome of the 1990 

Arkansas Water Plan, which attempted to address 

some of the deficiencies in the law with regard to 

groundwater, especially groundwater depletion. The 

act provided ANRC with authority to designate critical 

groundwater areas and provided a process for initiation 

of regulation limiting groundwater withdrawals in these 

areas. The legislation also authorized ANRC to develop 

a groundwater-classification system and groundwaterquality standards, set groundwater rights, establish 

water-use registration fees, and establish a mechanism 

for local groundwater management, but little guidance 

is provided as to what may be included in a regulatory 

program (Looney, 1995). The law mandated that ANRC 

evaluate the condition of the State’s aquifers on a biennial 

basis and make recommendations concerning safe yields 

and critical groundwater areas. The ANRC works with 

the USGS, the U.S. Department of Agriculture (USDA)-

NRCS, and the AGS to monitor water levels and water 

quality in a network of over 1,200 wells statewide to 

evaluate the State’s groundwater resources.

3. Act 1426 of 2001 (ACA §15–22–903 et seq.), an 

amendment to the Arkansas Ground Water Protection and 

Management Act, requires individuals with nondomestic 

water wells in certain aquifers to install meters to 

accurately compute water usage.

Critical Groundwater Area Designation

Pumping from the most productive aquifers in 

Arkansas—the Mississippi River Valley alluvial and Sparta 

aquifers—has led to declining water levels, reduced well 

yields, and the deterioration of the water quality in areas 

throughout the Coastal Plain of eastern and southern 

Arkansas. These aquifers are the principal sources of water 

for irrigation, industrial, and public drinking-water supplies 

in this region. Since enactment of the Arkansas Ground Water 

Protection and Management Act, ANRC has designated three 

critical groundwater areas (fig. 1) in Arkansas.

The South Arkansas critical groundwater area is 

composed of the Sparta aquifer in Bradley, Calhoun, 

Columbia, Ouachita, and Union Counties. Since the 1996 

designation, education, conservation, and development and 

usage of excess surface water have caused water levels 

within the areas to stabilize or rise (Arkansas Natural 

Resources Commission, 2013a) in the Sparta aquifer. 

The Grand Prairie critical groundwater area, 

designated in 1998, includes the Mississippi River Valley 

alluvial and Sparta aquifers within Arkansas, Jefferson, and 

Prairie Counties as well as parts of Lonoke, Pulaski, and 

White Counties. Water-level data from this area continue to 

show declines (Arkansas Natural Resources Commission, 

2013a).
Critical groundwater aArkansas Natural Reso

Base from U.S. Geological Survey digital data, 1:2,000,000

YELL

LEE

UNION

WHITE

POLK

POPE

DREW

PIKE

SCOTT

CLARK

CLAY

ASHLEY

DESHA

BENTON

LOGAN

SALINE

IZARD

PULASKI LONOKE

ARKANSAS

NEWTON

GRANT

CHICOT

MADISON

STONE

MILLER

SHARP

CROSS

DALLAS

PRAIRIE

BOONE

PHILLIPS

PERRY

SEARCY

MARION

FULTON

SEVIER

MISSISSIPPI

JEFFERSON

NEVADA

POINSETT

GARLAND

COLUMBIA

BAXTER

OUACHITA

BRADLEY

JOHNSON

WASHINGTON

MONROE

GREENE

JACKSON

CARROLL

HOWARD

LINCOLN

CALHOUN

CONWAY FAULKNER

VAN BUREN FRANKLIN

CRAIGHEAD

HEMPSTEAD

RANDOLPH

CLEBURNE

MONTGOMERY

LAWRENCE

ST. FRANCIS

CRAWFORD

CLEVELAND

HOT SPRING

INDEPENDENCE

LITTLE

RIVER

WOODRUFF CRITTENDEN

LAFAYETTE

SEBASTIAN

94° 92° 91° 93°

90°

36°

35°

34°

EXPLANAT

Crowleys R

Cache, 20

South Ar

Grand Pr

Eastern Ark

concer

Critical gro

and yea

0 15 30 0 30 

15

45

Figure 1. Location of critical groundwater areas in eastern Arkansas and counties referenced in this report. 
14 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

The Cache critical groundwater area, designated in 2009, 

includes the Mississippi River Valley alluvial and Sparta 

aquifers within parts of Clay, Craighead, Cross, Greene, Lee, 

Poinsett, and St. Francis Counties lying west of Crowleys 

Ridge. Water-level data from this area continue to show 

declines (Arkansas Natural Resources Commission, 2013a).

Specific criteria used in designating a critical 

groundwater area include water levels declining at a rate of 1 

foot per year (ft/yr) or more, water levels declining below the 

top of a confined aquifer or below the 50-percent saturated 

thickness for an unconfined aquifer, and groundwater-quality 

degradation. Water-level data collected by the ANRC, the 

USGS, and the USDA-NRCS suggest that there are additional 

areas throughout the State experiencing substantial waterlevel declines that may qualify for future critical groundwater 

area designation (Arkansas Natural Resources Commission, 

2012a).

The designation of a critical groundwater area allows 

Federal, State, and local groups to work together in providing 

a managed and protected resource for current and future water 

users by focusing on conservation and education. Critical 

area designation also allows Federal and State agencies to 

focus cost-share and tax incentives for conservation projects 

within those areas. Critical area designation does not involve 

regulation of water use or well drilling but is a proactive 

process, which focuses on the prevention and mitigation of 

problems associated with groundwater-level declines and 

groundwater-quality degradation. The most effective tools 

in use by the State are education programs, conservation tax 

incentives, and the development of alternative surface-water 

supplies and a conjunctive-use strategy.

The Arkansas Groundwater Protection and Management 

Act also provides a process for the initiation of a regulation 

limiting groundwater withdrawals in critical groundwater 

areas. ANRC must determine if implementation of a 

regulatory program is necessary and, if determined, follow 

administrative procedures, which include public hearings in 

the affected counties. Once ANRC has made a declaration of 

necessity, a regulatory program may be implemented through 

a system based on the issuance of water rights. Groundwater 

rights would be prioritized by the type of usage: sustaining 

life, maintaining health, and increasing wealth. To date, ANRC 

has not sought regulatory authority in any of the designated 

areas (Arkansas Natural Resources Commission, 2011).

An important goal of Arkansas water users, water 

planners, and water-policy managers is achieving longterm, effective, fair, and equitable uses of the State’s limited 

groundwater resources. Water-resources policies and programs 

focus on conjunctive use of the State’s groundwater and 

surface-water resources at optimized levels that are sustainable 

while providing the maximum amount of water possible to 

support life, health, and commerce. This sustainable yield 

conjunctive-use strategy is supported using water budget 

and groundwater model approaches. ANRC and other State 

water planners advocate sustainable-yield groundwater 

protection as a means of achieving the specific goals of 

preventing broad, long-term groundwater-level declines, 

assuring long-term viability of aquifers to provide necessary 

yields, preventing litigation, providing groundwater supplies 

for drought, preventing groundwater-quality degradation, 

protecting riparian rights, and providing courts with an 

objective means for determining reasonable and unreasonable 

uses. While the definition of sustainable yield can be subject 

to interpretation, Arkansas water policy has tended to follow 

a deferred perennial yield strategy, which accepts that 

current groundwater levels or levels defined by the critical 

groundwater area designation are reasonable or are at least 

acceptable. Groundwater-level monitoring data, groundwaterbudget studies, and groundwater-modeling efforts show that 

for broad areas of several important aquifers in the State, 

rates of groundwater usage are not sustainable (Arkansas 

Natural Resources Commission, 2013a), and collaborative 

conservation efforts by ANRC, industry, municipalities, and 

local community networks are the primary tools in developing 

solutions in these areas.

Groundwater and Climate Variation

Numerous factors affect changes in groundwater levels 

and the volume of stored water in Arkansas’ aquifers. Prior 

to extensive mining of groundwater to meet the increasing 

water-supply demands from industrial, commercial, public, 

irrigation, and other uses, groundwater levels and volume of 

water stored in the State’s aquifers were primarily dependent 

on precipitation patterns and stream stage coupled with 

recharge characteristics of surficial sediments in the aquifer 

outcrop and subcrop (any area where an aquifer is covered 

by unconsolidated deposits) areas. Because of these relations, 

long-term changes in climate controlling spatiotemporal 

patterns in precipitation, drought, and evapotranspiration 

can have a substantial influence on groundwater discharge 

and recharge (Hanson and others, 2004). To understand and 

define the long-term changes, research needs to address 

the effects of natural climate patterns on interannual to 

multidecadal timescales; a lack of understanding of climate 

patterns on these timescales is a major obstacle to the reliable 

characterization of global climate trends resulting from human 

activities (Ghil, 2002). State water planners and managers 

must understand the nature and potential magnitude of 

changes in climate—whether natural or human-induced—

and evolving water needs and prepare for any contingency 

resulting from varying weather patterns to ensure the health 

of people and the viability of State commerce. Although 

difficulties can arise in establishing Arkansas policy because 

of the uncertainty in predicting long-term trends in climate 

patterns in the State, various studies have been conducted to 

establish historical patterns of the effects of precipitation on 

groundwater levels and to predict potential effects of longterm climate trends on available groundwater resources in 

the State. As such, ANRC and other State water planners and 
Groundwater Protection and Management Programs 15

managers are aware of potential effects on water resources 

from varying climate trends and are conducting studies for 

improving the understanding of these effects on aquifers in 

Arkansas.

Various studies have documented the effects of shortterm climate trends on groundwater levels in the State. 

Czarnecki and Schrader (2013) compared groundwater-level 

fluctuations in wells completed in the Mississippi River Valley 

alluvial aquifer to variability in annual precipitation from 2004 

through 2010, which included some of the wettest and driest 

years on record for Arkansas. The wettest year on record for 

Arkansas occurred in 2009 with 81.79 inches of precipitation 

compared to an average precipitation (2004 through 2010) 

of 47.1 in/yr. In contrast, 2005 and 2010 were the 7th and 

14th driest years on record (1878 to 2010) with 34.55 and 

36.52 in/yr, respectively. Drier conditions between 2004 

and 2008 led to an average decline in groundwater levels of 

1.62 ft, whereas wetter conditions between 2006 and 2010 led 

to an average rise in groundwater levels of 1.36 ft (Czarnecki 

and Schrader, 2013).

Kresse and Huetter (1999) compared precipitation 

amounts to water levels from six wells completed in the 

Mississippi River Valley alluvial aquifer in Jefferson County 

for the period between 1955 and 1994. Average precipitation 

in Jefferson County for this period was 48.5 inches, which 

compares closely with the average of 47.1 from Czarnecki 

and Schrader (2013). Several years of lesser and greater 

(relative to the average) precipitation resulted in decreases 

and increases, respectively, in groundwater levels for the six 

wells. Two of the six wells were within a well-defined cone 

of depression in the Grand Prairie region, whereas four wells 

were outside this cone of depression; the four wells outside 

the cone of depression showed the greatest variation in water 

levels. For example, from 1976 through 1978, precipitation 

ranged from approximately 6 to 10 inches below average, 

during which time water levels in the four wells outside the 

cone of depression had water-level decreases ranging from 

approximately 5.5 to 7.0 inches. The year 1980 had an annual 

precipitation amount approximately 20 inches above average, 

and the same four wells exhibited water-level increases 

ranging from approximately 1.0 to 4.0 inches despite steadily 

increasing irrigation use in the area. The two wells within 

the cone of depression showed a minor water-level increase 

of approximately 0.5 inch in one well and only a diminution 

of a long-term decreasing water-level trend in the other well 

in 1980. These studies demonstrate a strong influence on 

water levels from changes in annual precipitation within 

short temporal scales, an important indicator of the effects of 

climate variability. Inspection of these data also shows that 

climate has considerably lesser control on water levels in areas 

where stress on the aquifer is great, and most of the water is 

being removed from storage.

Long-term climate trends can affect the hydrologic 

cycle in many ways. Components of the hydrologic cycle that 

may be affected include atmospheric water vapor content, 

precipitation and evapotranspiration patterns, snow cover and 

melting of ice and glaciers, soil temperature and moisture, 

and surface runoff and streamflow (Bates and others, 2008). 

Potential hydrologic effects of long-term climate trends 

have been well documented, although relatively little 

research has been conducted on effects of climate trends on 

groundwater (Holman, 2006). Anthropogenic factors, such 

as reduction in streamflow, lowering of the water table, and 

removal of water from storage through groundwater pumping 

complicates quantification of the effects of changing climate 

on groundwater (Kundzewicz and others, 2007). Clark and 

others (2013) used a frequency analysis of hydroclimate data 

and global climate model results to improve understanding of 

aquifer hydrologic response in the Mississippi embayment. 

Although temperatures in the Mississippi embayment are 

projected to increase slightly (1–1.5 degrees Celsius [°C]) and 

precipitation to decrease slightly (approximately 5 percent) 

over the next two decades, model simulations from Clark 

and others (2013) showed little difference between drier 

climate or wetter climate model scenarios in terms of percent 

groundwater-level change. The lack of difference in the two 

scenarios was attributed to the fact that the greatest change in 

the overall groundwater budget in the Mississippi embayment 

was primarily the result of the magnitude of groundwater 

removed from storage, with changes in net recharge having 

negligible effects. It should be noted, however, that such 

models evaluate groundwater flow on large regional scales 

and do not provide robust evaluation of groundwater flow and 

water levels at local scales caused by small-scale variation 

in recharge and pumping. The studies by Kresse and Huetter 

(1999) and Clark and others (2013) suggest that reduced 

recharge from changing climate trends may show little effect 

on water levels in wells within cones of depression or in areas 

where pumping is removing large quantities of water from 

storage but will affect more strongly water levels in wells 

outside of these areas that show large water-level responses to 

local precipitation on short time scales.

Monitoring and Assessment of Groundwater

Monitoring of groundwater is conducted by numerous 

Federal and State agencies and universities in Arkansas. 

Groundwater monitoring includes mandated monitoring at 

regulated sites, which has been previously discussed, shortterm research-oriented monitoring, and ambient monitoring. 

Mandated monitoring by regulatory agencies (for example, 

ADEQ) is a valuable resource but often is limited by a 

reduced number of constituents. Additionally, this monitoring 

often is associated with contaminated sites and cannot be 

used to describe natural or background groundwater 

geochemistry. 

A substantial amount of groundwater research has been 

conducted by the University of Arkansas in Fayetteville. 

Although this research has resulted in scientific data and 

information that can be used to understand, manage, 
16 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

and protect water resources within Arkansas, most of the 

resulting data and reports are not available online. Hardcopy 

reports, theses, and journal articles are available at the 

Arkansas Water Resources Center (AWRC) technical library, 

which can be accessed at http://www.uark.edu/depts/awrc/

index.html.

There are numerous ambient monitoring programs 

as well as site-specific studies related to assessment of 

groundwater quantity and quality issues. Many of the studies 

involve cooperative efforts by the USGS, ANRC, ADEQ, and 

other Federal and State agencies. Groundwater monitoring is 

not limited to water quality, as there is a substantial ongoing 

effort in the State to monitor and evaluate water levels, 

especially in critical groundwater areas. Data collection sites 

primarily include existing irrigation and domestic wells and a 

few public water-supply wells. Some monitoring wells have 

been installed by ANRC and USGS to serve as data-collection 

points in specific aquifers. Groundwater-quality monitoring 

activities in Arkansas are funded in large part by EPA grants 

under Sections 106 and 319 of the Clean Water Act. Funding 

for some conservation-monitoring programs has been made 

through the NRCS. The following subsections document some 

of the ongoing groundwater-monitoring programs in Arkansas.

Arkansas Department of Health

The ADH currently (2013) maintains a database of 

approximately 1,300 wells that are sampled every 3 years for 

inorganic, organic (for example, pesticides, herbicides, volatile 

organic compounds, and semi-volatile organic compounds), 

and radiological contaminants. However, treated water 

predominantly is sampled, which does not necessarily reflect 

the natural chemistry of groundwater (Arkansas Department 

of Health, 2013). Nitrate is monitored on at least an annual 

basis, total coliform sampling is conducted monthly, and 

trihalomethanes and byproducts of disinfection are monitored 

on a quarterly or annual basis depending on the source and the 

population served by the system. Additionally, raw water from 

groundwater wells that may be directly influenced by surface 

waters is sampled weekly for bacteriological testing and other 

parameters as required by the SDWA. 

Arkansas Department of Environmental Quality

The ADEQ has developed an ambient groundwatermonitoring program to help assess the quality of groundwater 

in various aquifers throughout the State (fig. 2). The 

program, begun in 1986 as part of ADEQ’s responsibilities 

in administering its Groundwater Protection Strategy 

(Arkansas Department of Environmental Quality, 1996), 

currently (2013) includes 11 areas selected for monitoring, 

with sampling conducted from multiple wells in each area 

on a 3-year rotational basis. These areas were chosen as high 

risk localities on the basis of local contamination threats 

and aquifer vulnerabilities. These data are used to document 

trends and changes in water quality over time. The monitoring 

program currently (2013) consists of approximately 250 well 

and spring sites. Samples are analyzed for a full suite of 

inorganic constituents, including major cations, anions, and 

trace metals; in addition, semivolatile and volatile organic 

analyses are performed on samples in areas where industry, 

landfills, and other facilities store, manufacture, or dispose 

of organic chemicals. In areas with row-crop agriculture, 

samples commonly are analyzed for pesticides. Published 

reports for each area of the State are produced following each 

sampling event (Arkansas Department of Environmental 

Quality, 2013d). Data are accessible through various ADEQ 

publications and in the EPA’s STORET database. Summaries 

of monitoring results are presented in the State 305(b) report, 

which is published in accordance with Section 106(e) of the 

Clean Water Act (Arkansas Department of Environmental 

Quality, 2012). 

Arkansas State Plant Board

The goal of ASPB’s groundwater monitoring program 

is to prevent the State’s groundwater from being polluted 

by agricultural chemicals and to respond appropriately 

if pollution is found. ASPB recognizes that preserving 

groundwater quality is less costly and more ecologically 

sound than restoring groundwater to its natural state, a 

process that may not be technically or economically viable 

(Arkansas State Plant Board, 2013). The groundwater 

monitoring program is a voluntary program that offers 

laboratory testing of groundwater samples from agricultural 

wells to help ensure that producers and applicators are using 

pesticides in accordance with label directions to protect 

and preserve groundwater. ASPB monitors groundwater 

in areas that may be considered vulnerable to agricultural 

pesticide contamination based on area use patterns and the 

concentration of agricultural production land in the vicinity. 

Since inception of the groundwater-sampling program in 

2004, ASPB has sampled 271 wells in 30 counties. Results are 

summarized in annual reports. These reports and all sample 

results can be found on the ASPB Web site (Arkansas State 

Plant Board, 2013).
YELL

LEE

UNION

WHITE

POLK

POPE

DREW

PIKE

SCOTT

CLARK

CLAY

ASHLEY

DESHA

BENTON

LOGAN

SALINE

IZARD

PULASKI LONOKE

ARKANSAS

NEWTON

GRANT

CHICOT

MADISON

STONE

MILLER

SHARP

CROSS

DALLAS

PRAIRIE

BOONE

PHILLIPS

PERRY

SEARCY

MARION

FULTON

SEVIER

MISSISSIPPI

JEFFERSON

NEVADA

POINSETT

GARLAND

COLUMBIA

BAXTER

OUACHITA

BRADLEY

JOHNSON

WASHINGTON

MONROE

GREENE

JACKSON

CARROLL

HOWARD

LINCOLN

CALHOUN

CONWAY FAULKNER

VAN BUREN FRANKLIN

CRAIGHEAD

HEMPSTEAD

RANDOLPH

CLEBURNE

MONTGOMERY

LAWRENCE

ST. FRANCIS

CRAWFORD

CLEVELAND

HOT SPRING

INDEPENDENCE

LITTLE

RIVER

WOODRUFF CRITTENDEN

LAFAYETTE

SEBASTIAN

Base from U.S. Geological Survey digital data, 1:2,000,000

94° 92° 91° 93°

90°

36°

35°

34°

EXPLANATION

Monitoring wells, by age

ANRC, Arkansas NaturaUSGS, U.S. Geological SADEQ, Arkansas Depart

0 15 30 0 30 60 KIL

15

4

45

Figure 2. Location of ambient groundwater-quality monitoring sites in Arkansas.
18 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Arkansas Natural Resources Commission

The ANRC sponsors groundwater monitoring in six 

groundwater study areas within the State. Water-level 

monitoring is a cooperative program with ANRC, USGS, 

NRCS, and local water-resources agencies. Each spring 

approximately 700 wells are monitored in the Mississippi 

River Valley alluvial aquifer resulting in the largest 

number of water-level measurements for an aquifer in the 

State. This number varies from year to year depending on 

available resources. There are approximately 300 wells 

that are monitored for water levels in the Sparta aquifer. A 

monitoring schedule has been established to obtain data from 

the Mississippi River Valley alluvial aquifer and the Sparta 

aquifer on an annual basis. These measurements are made 

each spring to minimize the effects of seasonal pumping 

for irrigation. The drawdown that results from seasonal 

pumping is determined by the NRCS and ANRC by taking 

measurements of the alluvial aquifer in the spring and fall. 

Additionally, hydrogeologic data are collected statewide; 

however, resources are focused on study areas where waterlevel declines and water-quality degradation have been 

observed historically. Results of assessments are published 

annually by ANRC in the Arkansas Groundwater Protection 

and Management Report (Arkansas Natural Resources 

Commission, 2012a). Long-term water-level data collected 

over a 25-year period indicate that there are areas of the State 

experiencing groundwater withdrawals of such magnitude that 

demand on the aquifer exceeds the sustainable yield, resulting 

in consistently falling groundwater levels and the development 

of depressions in the potentiometric surfaces of the Mississippi 

River Valley alluvial and Sparta aquifers (Arkansas Natural 

Resources Commission, 2013a). 

U.S. Geological Survey

The USGS, in cooperation with State, Federal, and 

other local governmental agencies, collects a large amount 

of data each year pertaining to the groundwater resources 

of Arkansas. The USGS samples 24 wells (or springs) in 

14 aquifers (fig. 2) on a 5-year rotational basis for a variety 

of constituents including nutrients, metals, radioactivity, 

organics, and selected primary and secondary drinking-water 

constituents. USGS also participates in a cooperative program 

to measure groundwater levels for seven aquifers in Arkansas 

on a rotating basis with water levels from over 600 available 

Mississippi River Valley alluvial and Sparta aquifer wells 

being measured on a 2-year rotation (Arkansas Natural 

Resources Commission, 2011). USGS also measures specific 

conductance and groundwater levels continuously at 23 (as 

of 2013) real-time stations (fig. 2). These data, accumulated 

since 1969, constitute a part of the USGS’ National Water 

Information System (NWIS), a database for developing an 

improved understanding of the water resources of the State. 

The NWISWeb database provides access to groundwater 

levels and water-quality data at sites throughout the State. 

This Web service provides methods for retrieving daily 

data, such as water levels and other real-time data (U.S. 

Geological Survey, 2013b). The wells monitored by USGS 

are in a constant state of flux depending on cooperator needs 

and funding and are not differentiated on figure 2, which 

only depicts total wells monitored by the USGS in 2013. For 

a current list of water-quality and continuous water-level 

monitoring sites see http://ar.water.usgs.gov/. 

Overview of Aquifers of Arkansas

Prior to any discussion of aquifers, defining the 

frequently used terms is useful and important to the reader. 

Groundwater generally is defined as any water under the 

surface of the ground (Freeze and Cherry, 1979; Fetter, 1988), 

which creates little confusion on the part of the scientific 

community, regulators, and the general public. The term 

“aquifer,” however, is not such a simple term, is often hotly 

debated, and can lead to problems in applying regulations 

pertaining to required monitoring and remediation of impacted 

aquifers (Skinner, 1984). Various definitions are found for 

the term “aquifer.” Fetter (1988) defines an aquifer as “... a 

geologic unit that can store and transmit water at rates fast 

enough to supply reasonable amounts to wells.” Freeze and 

Cherry (1979) define an aquifer as “... a saturated permeable 

geologic unit that can transmit significant quantities of water 

under ordinary hydraulic gradients.” Freeze and Cherry 

(1979) also provide an alternative definition widely used in 

the water-well industry “... is permeable enough to yield 

economic quantities of water to wells.” The above definitions 

all have qualitative descriptors, such as “reasonable amounts,” 

“significant quantities,” and “economic quantities,” which 

only serve to create further confusion. 

Less permeable geologic units that restrict the vertical 

movement of groundwater between aquifers are referred to 

as “confining units.” Fetter (1988) defines a confining unit 

as “A body of material of low hydraulic conductivity that is 

stratigraphically adjacent to one or more aquifers. It may lie 

above or below the aquifer.” Where a stratigraphic unit of 

regional extent restricts the vertical movement of groundwater 

from underlying or overlying aquifers, these units often are 

assigned a formal name of “confining unit.”

A problem that arises from strict application of these 

terms is that local use may be at variance with regional 

hydrologic perception and designations for various 

hydrogeologic units. An example that highlights the 

importance of the discussion of “aquifers” and “confining 

units” is found in the nomenclature associated with the 

correlation of stratigraphic geologic units and regional 

hydrologeologic units in the Ozark Plateaus in northern 

Arkansas. The Springfield Plateau aquifer is a regional 

aquifer across parts of Arkansas, Oklahoma, Kansas, and 

Missouri and is confined by less permeable shale and 

sandstone rocks of upper Mississippian to Pennsylvanian 

age, collectively referred to as the Western Interior Plains 
Overview of Aquifers of Arkansas 19

confining system (Imes and Emmett, 1994). Although 

regionally serving as an upper confining system for the 

underlying more porous and permeable Springfield Plateau 

aquifer, the formations constituting this confining system 

are important local sources of domestic supply. The aquifer 

typically yields less than 10 gallons per minute (gal/min) 

and upwards to 20–50 gal/min and often serves as the only 

source of water across large areas of the Boston Mountains 

in Arkansas (fig. 3). Regionally, however, the relatively low 

permeability of these strata impedes vertical flow of water into 

the underlying and more hydrologically productive formations 

of the Springfield Plateau aquifer. 

For this report, although the regional hydrogeologic 

nomenclature often is applied for the hydrogeologic 

formations of importance to the State, the designation of 

aquifer is implied for any formation or group of formations 

that have served or currently serve as important local or 

regional water supplies for any use. A review of the history of 

groundwater use in Arkansas identified 16 distinct formations 

or groups of formations that historically and currently serve 

as aquifers (fig. 3). For this report, aquifers are grouped into 

the Coastal Plain Province and the Interior Highlands Division 

physiographic regions of the State (referred to as Coastal 

Plain and Interior Highlands, respectively, in the remainder 

of this report). Aquifers of the Coastal Plain generally are 

characterized by unconsolidated sediments with higher 

porosity and greater yields compared to aquifers in the Interior 

Highlands, which generally are characterized by fractured 

bedrock with low secondary porosity and lesser yields 

(see “Geologic Setting” in the next section for additional 

information on the differing geology in these two regions of 

the State). These 16 aquifers, the formation(s) hosting the 

aquifers, and the number of sites with available groundwaterquality data are listed in table 2.

A review of table 2 reveals a large variation and a 

disparity in the number of sites with water-quality data 

available, which reflects the attention focused on the 

Mississippi River Valley alluvial aquifer relative to other 

aquifers over the years that often was based on economic 

value or importance as a regional public-supply source. For 

example, the Mississippi River Valley alluvial aquifer in 

the Coastal Plain, used almost solely for irrigation supply, 

accounted for more than 94 percent of all groundwater 

withdrawn in Arkansas and 62 percent of total combined 

groundwater and surface-water withdrawals in the State for 

2010. Therefore, this aquifer is monitored more extensively 

than other aquifers and included 4,061 sites (as of 2013) 

with some form of water-quality data. The Sparta aquifer 

long has been an important source of public-supply water 

and has in recent years become an important source of 

irrigation supply as groundwater levels have declined in 

the Mississippi River Valley alluvial aquifer in certain 

areas of the State. In keeping with this importance, the 

database for the Sparta aquifer includes 1,626 sites with 

associated water-quality data. Although of local importance 

to families relying on groundwater as a source of domestic 

supply, other aquifers are of less importance from a regional 

perspective and have a limited number of sites with waterquality data. An exception to this pattern is the large 

number of water-quality sites associated with the Arkansas 

River Valley alluvial aquifer. A monitoring program by the 

Arkansas Geological Commission (now known as Arkansas 

Geological Survey), the U.S. Army Corps of Engineers, 

and the USGS, between 1957 and 1972, collected abundant 

water-level and limited water-quality data prior to and after 

completion of the lock and dam system in 1969 on the 

Arkansas River. These data were input into the USGS NWIS 

database (U.S. Geological Survey, 2013b).
Springfield-Salem Plateaus Boston Mountains Arkansas Valley Ouachita Mountains West Gulf Coastal Plain Mississippi Alluvial Plain COASTAL PLAIN PROVINCE Interior Highlands Interior Highlands Modified from Fenneman, 1938 Physiographic regions of Arkansas Ca

CoNa

Oz

Tri

OzSp

Sp

Ja

To

W

EXPLA

Undifferen

Coastal Pl

Ca

Interior Hig

Ou

W

Ar

Co

Base from U.S. Geological Survey digital data Universal Transverse Mercator projection, zone 15 North American Datum of 1983 Hydrogeologic data modified from Boswell, 1965; Hosman and others, 1968; Payne, 1968; Hosman, 1982; Petersen and others, 1985; Hosman, 1988; Haley and others, 1993 0 15 

0 30 

15 

94° 92° 91° 93° 90° 36°35° 34° Arkansas River Arkansas River Mississippi River Mississippi River White River Red River Fall line

Figure 3. Combined outcrop, subcrop areas, and physiographic regions for the 16 aquifers serving as major and minor sources of groundwater supp
Overview of Aquifers of Arkansas 21

Table 2. Nomenclature, geologic age, use, and number of sites with groundwater-quality data for the 16 major and minor aquifers in 

Arkansas.

Major 

division Province Section

Formation 

or group of 

formations

Geologic 

age

Hydrogeologic 

unit name Aquifer code Aquifer use1

Waterquality 

sites

Atlantic 

Plain

Coastal 

Plain

Mississippi 

Alluvial Plain 

and West Gulf 

Coastal Plain

Coastal Plain 

Alluvium Quaternary

Mississippi 

River Valley, 

OuachitaSaline, and Red 

River alluvial 

aquifers

110ALVM, 112ALVM

112VLTR, 112TRRC

IR, ps, in 4,061

Jackson Group Tertiary Vicksburg-Jackson 

confining unit

124JCKS D 68

Cockfield 

Formation Tertiary Cockfield aquifer 124CCKF IN, IR, ps 257

Sparta Sand Tertiary Sparta aquifer 12405MP, 124SPRT, 

124MMPS IR, PS, IN 1,626

Cane River 

Formation Tertiary Cane River aquifer 124CRVR, 124CANR PS, d 45

Carrizo Sand Tertiary Carrizo aquifer 124CRRZ D 12

Wilcox Group Tertiary Wilcox aquifer 124WLCX, 124WLCXG PS, ir, in 170

Nacatoch Sand Cretaceous Nacatoch aquifer 211NCTC PS 143

West Gulf 

Coastal Plain

Ozan Formation Cretaceous Ozan aquifer 212OZAN D 14

Tokio Formation Cretaceous Tokio aquifer 212TOKO PS, in 165

Trinity Group Cretaceous Trinity aquifer 218TRNT PS, in 38

Interior 

Highlands

Ouachita 

Province

Arkansas 

Valley

Arkansas 

River Valley 

Alluvium

Quaternary

Arkansas River 

Valley alluvial 

aquifer

110ALVM, 110TRRC

112TRRC PS, IR, d 680

Ouachita 

Mountains

Collier Shale 

through 

Boggy Formation2

Cambrian through 

Pennsylvanian

Ouachita Mountains aquifer

325HRSR, 325MCAL

326ATOK, 328JKFK

330ARKS, 330HSPG

330STNL, 350MSRM

361PKCK, 364BGFK

D 162

Ozark 

Plateaus

Boston 

Mountains

Moorefield 

Formation 

through 

McAlester 

Formation3

Mississippian and 

Pennsylvanian 

Western Interior 

Plains Confining System

325HRSR, 325MCAL

326ATKN, 326ATOK

328BLYD, 328CNHL

328JKFK, 3331BSVL

331MFLD, 331PTKN

D 287

SpringfieldSalem 

Plateaus

Boone Formation Mississippian Springfield Plateau aquifer 330BOON D, ps 95

Van Buren 

Formation 

through 

Clifty Limestone4

Ordovician 

through DevonianOzark aquifer

361FRVL, 364EVRN

364JCHM, 364STPR

367CTJF, 367CTTR

368PWLL, 371POTS

367RBDX, 367GNTR

PS, d 131

1

IR, irrigation; PS, public supply; IN, industrial; D, domestic. Listed in order of highest use by volume. Primary use in capital letters; secondary use in small 

caps.

2

Collier Shale, Crystal Mountain Sandstone, Mazarn Shale, Blakely Sandstone, Womble Shale, Bigfork Chert, Polk Creek Shale, Blaylock Sandstone, Missouri Mountain Shale, Arkansas Novaculite, Hot Springs Sandstone, Stanley Shale, Jackfork Sandstone, Johns Valley Shale, Atoka Formation, Hartshorne 

Sandstone, McAlester Formation, Savanna Formation, and Boggy Formation.

3

Moorefield Formation, Batesville Sandstone, Fayetteville Shale, Pitkin Limestone, Hale Formation, Bloyd Formation, Atoka Formation, Hartshorne Sandstone, and McAlester Formation.

4

Van Buren Formation, Gasconade Formation, Roubidoux Formation, Jefferson City Dolomite, Cotter Dolomite, Powell Dolomite, Smithville Formation, 

Everton Formation, St. Peter Sandstone, Joachim Dolomite, Plattin Limestone, Kimmswick Limestone, Fernvale Limestone, Cason Shale, Brassfield Limestone, 

St. Clair Limestone, Lafferty Limestone, Penters Chert, and Clifty Limestone.
22 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Geologic Setting

The Coastal Plain Province, which includes the 

Mississippi Alluvial Plain and West Gulf Coastal Plain 

physiographic sections (fig. 3), is underlain by Mesozoic and 

Cenozoic sedimentary deposits (table 3) (McFarland, 2004). 

These sedimentary deposits represent the cyclic transgression 

and regression of Mesozoic and Cenozoic seas that followed 

extensive continental inundation by inland seas that extended 

from Central America to New England (Manger, 1983; Arthur 

and Taylor, 1998). The Mississippi River defines the eastern 

border of Arkansas and falls roughly along the axis of the 

Mississippi embayment, a south-plunging, asymmetrical 

geosyncline with the dip of the beds being steeper on the 

western side of the Mississippi embayment in the Coastal 

Plain. The Mississippi embayment is a result of downwarping 

and rifting related to the Ouachita orogeny, which formed a 

deep basin for subsequent sedimentation (Hosman, 1996). 

The Mississippi embayment represents an extension of the 

Coastal Plain into the continental interior (Manger, 1983). 

Table 3. Stratigraphic column and correlated geohydrologic units of the Coastal Plain Province in southern and eastern Arkansas.

Time-stratigraphic unit Group Formation Regional geohydrologic unit Era System Series Cenozoic

Quaternary

Holocene Alluvium Mississippi River Valley, Ouachita-Saline River, and 

Red River alluvial aquifers1 Pleistocene Terrace deposits

Tertiary

Eocene

Jackson Jackson Group Vicksburg-Jackson confining unit1 Claiborne

Cockfield Formation Upper Claiborne aquifer1

Cook Mountain Formation Middle Claiborne confining unit1

Sparta Sand

Memphis 

Sand3

Middle Claiborne aquifer1,2

Cane River Formation Lower Claiborne confining unit1

Carrizo Sand Lower Claiborne aquifer1

Wilcox undifferentiated Upper, middle, and lower Wilcox aquifers1

Paleocene Midway Porters Creek Clay Midway confining unit1 Clayton Formation

Mesozoic

Cretaceous

Upper

Arkadelphi Marl

Nacatoch Sand McNary - Nacatoch aquifer4

Saratoga Chalk

Marlbrook Marl

Annona Chalk

Ozan Formation

Brownstone Marl

Tokio Formation

Tokio - Woodbine aquifer4

Woodbine Formation

Lower

Kiamichi Shale

Goodland Limestone

Trinity

Paluxy Sand

Trinity aquifer4

De Queen Limestone

Holly Creek Formation

Dierks Limestone

Delight Sand

Pike Gravel

1

Modified from Hart and others (2008).

2

North of 35°N latitude, the Lower Claiborne confining unit and Lower Claiborne aquifer are undifferentiated and referred to regionally as the middle Claiborne aquifer (Hart and others, 2008).

3

North of 35°N latitude, the Sparta Sand, Cane River Formation, and Carrizo Sand are undifferentiated and refered to regionally as the Memphis Sand 

(Counts, 1957; Hosman and others, 1968; Payne, 1972; Petersen and others, 1985; Hart and others, 2008).

4

Modified from Renken (1998).
Overview of Aquifers of Arkansas 23

Downwarping and downfaulting proceeded further as a 

response to the weight of sediment accumulation enabling 

further accommodation of a very thick sequence of Mesozoic 

through modern sediments (Hosman, 1996). 

While the oldest sediments exposed at the surface in the 

Coastal Plain are Cretaceous in age, Jurassic-age sediments 

have been encountered in the subsurface (Manger, 1983; Clark 

and Hart, 2009). Strata of Mesozoic and Cenozoic ages rest 

on an erosional surface developed on underlying Paleozoic 

rocks (Manger, 1983). The Cretaceous sedimentary deposits 

exposed in the West Gulf Coastal Plain of southwestern 

Arkansas represent shallow and often restricted (hypersaline) 

marine environments (McFarland, 2004). Toward the axis of 

the Mississippi embayment, these deposits were covered by 

Cenozoic deposits consisting of Tertiary marginal marine and 

continental deposits with a veneer of Quaternary terrace and 

alluvial deposits. The veneer of Quaternary terrace and alluvial 

deposits dominate eastern Arkansas with minor exposures 

of Tertiary units (Hosman and others, 1968; Hosman, 1982, 

1996; Manger, 1983; McFarland, 2004; Clark and others, 

2011b). The Cenozoic deposits constitute the main waterbearing units of importance within the Mississippi embayment 

(Clark and others, 2011b) 

The strata of Mesozoic and Cenozoic age found at the 

surface in Arkansas are poorly cemented and indurated and 

therefore are soft and easily eroded, resulting in a relatively 

flat terrain with some low hills. The Mississippi River has 

eroded a broad valley into the Tertiary deposits filling the 

Mississippi embayment and leaving Crowleys Ridge as a 

prominent erosional remnant. Crowleys Ridge comprises 

Tertiary deposits capped by Quaternary loess (Manger, 1983; 

McFarland, 2004). 

Sedimentary Paleozoic-age rocks are exposed over 

most of western Arkansas. This area is part of the Interior 

Highlands, which is subdivided into two provinces: the 

Ouachita Province and Ozark Plateaus Province. The 

sedimentary rocks of the Ouachita Mountains physiographic 

section consist of a thick sequence of shale, chert, sandstone, 

conglomerates, novaculite, and volcanic tuff deposited during 

the Paleozoic Era (table 4) within an elongate, subsiding 

Table 4. Stratigraphic column and correlated geohydrologic units of the Ouachita Mountains Region, Arkansas.

Time-stratigraphic unit Series Formation Regional geohydrologic unit1

Era System

Cenozoic Quaternary

Holocene Alluvium

Pleistocene Terrace Deposits

Paleozoic

Pennsylvanian

Des Moinesian

Boggy Formation

Ouachita Mountains aquifer

Savanna Formation

McAlester Formation

Hartshorne Sandstone

Atokan Atoka Formatioin

Morrowan

Johns Valley Shale

Jackfork Sandstone

Stanley Shale

Mississippian Hot Springs Sandstone

Arkansas Novaculite

Devonian Middle and Upper

Sillurian

Missouri Mountain Shale

Blaylock Sandstone

Ordovician

Upper Polk Creek Shale

Middle Bigfork Chert

Lower

Womble Shale

Blakely Sandstone

Mazarn Shale

Crystal Mountain Sandstone

Cambrian Collier Shale

1

Modified from Renken (1998).
24 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

trough (Renken, 1998). Deposition from the Ordovician 

through the early Mississippian times represents “starved 

basin” conditions in which deposition was extremely slow. 

These sediments are overlain by late-Mississippian and 

early-Pennsylvanian sediments that were a result of very 

rapid deposition into a subsiding trough (Manger, 1983). The 

Ouachita Mountains are true geosynclinal mountains formed 

from strata deposited in deep water settings and uplifted 

and deformed by the compressional events associated with 

continental collision. The general structure of the Ouachita 

Mountains is a broad uplift with complex folds and numerous 

complex faults (Manger, 1983; McFarland, 2004). Sediments 

of the Ouachita Mountains are well indurated and generally 

well cemented as a result of deep burial, intense compression, 

and complex diagenetic history (Renken, 1998). The Arkansas 

Valley physiographic section comprises Quaternary-age 

alluvial deposits that filled a synclinorium generally lying 

between dipping rocks of the Boston Mountains to the north 

and the highly folded rocks of the Ouachita Mountains to the 

south, although these deposits are assigned to the Ouachita 

Province by Renken (1998). 

The Ozark Plateaus consist of sedimentary strata that 

dip radially away from the core of the Ozark dome, which is 

located in southeastern Missouri (Manger, 1983). The Ozark 

Plateaus (table 5) are divided two physiographic sections: 

the Boston Mountains and the Springfield-Salem Plateaus 

(fig. 3). The Salem Plateau is characterized by outcropping 

Ordovician-age sedimentary rocks, which constitute the 

Ozark aquifer (table 5). These rocks crop out over much of 

north-central and northeastern Arkansas and consist mainly 

of karsted limestones and dolostones with some sandstone 

and shale. The Springfield Plateau is characterized by the 

outcrop of the Mississippian-age Boone Formation, which 

comprises karsted limestone interbedded with chert. The 

Boone Formation constitutes the Springfield Plateau aquifer 

(table 5). The Springfield Plateau aquifer is separated from the 

underlying Ozark aquifer by the Chattanooga Shale, which 

is the primary unit of the Ozark confining unit. Locally, the 

Ozark confining unit is absent and the Springfield Plateau 

aquifer rests unconformably on rocks of the Ozark aquifer. 

The Boston Mountains are characterized by outcropping 

Pennsylvanian-age sedimentary rocks that constitute the 

Western Interior Plains confining system, which overlies the 

Springfield Plateau aquifer (table 5). The rocks of the Boston 

Mountains are composed mainly of sandstones and shales, 

with some limestone units occurring near the base. The Ozark 

Plateaus have experienced extensive erosion and have deeply 

dissected stream valleys throughout. Sedimentary rocks of the 

Ozark Plateaus generally are nearly flat lying and dip toward 

the south. Gentle, low-amplitude folds have been observed 

in the Ozark Plateaus. A majority of the faults in the Ozark 

Plateaus are normal, with displacement generally occurring 

downward on the southern side. Rocks of the Ozark Plateaus 

were deposited on a relatively shallow continental shelf that 

was exposed at numerous times during the Paleozoic resulting 

in erosional surfaces throughout the stratigraphic sequence 

(Manger, 1983; Imes and Emmett, 1994; Renken, 1998; 

McFarland, 2004). 
Overview of Aquifers of Arkansas 25

Table 5. Stratigraphic column and correlated geohydrologic units of the Ozark Plateaus Province in northern Arkansas.

Time-stratigraphic unit Formation Regional geohydologic unit1

Era System

Paleozoic

Pennsylvanian

McAlester Formation

Hartshorne Sandstone

Atoka Formation

Bloyd Shale

Hale Formation Western Interior Plains confining 

system

Mississippian

Pitkin Limestone

Fayetteville Shale

Batesville Sandstone

Moorefield Formation

Boone Formation

 St. Joe Limestone Member Springfield Plateau aquifer

Devonian

Chattanooga Shale Ozark confining unit

Clifty Limestone

Penters Chert

Upper Ozark aquifer

Silurian

Lafferty Limestone

St. Clair Limestone

Brassfield Limestone

Ordovician

Cason Shale 

Fernvale Limestone

Kimmswick Limestone

Plattin Limestone

Joachim Dolomite

St. Peter Sandstone

Everton Formation

Smithville Formation

Powell Dolomite

Cotter Dolomite

Jefferson City Dolomite

Roubidoux Formation 

Gasconade Dolomite

 Gunter Sandstone Member

Lower Ozark aquifer Van Buren Formation

Cambrian

Eminence Dolomite

Potosi Dolomite

Doe Run Dolomite

Derby Dolomite

Davis Formation

St. Francois confining unit

Bonneterre Formation

Reagan Sandstone

Lamotte Sandstone

St. Francois aquifer

Precambrian Precambrian Precambrian intrusive and volcanic igneous rocks Basement confining unit

1

Modified from Imes and Emmet (1994).
26 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Groundwater Use in Arkansas

Arkansas traditionally has been considered a waterrich State with a mean annual precipitation of 48 inches 

in the north and 56 inches in the south (Kleiss and others, 

2000; Pugh and Westerman, 2014). This precipitation is 

the primary input for the State’s water budget that includes 

the groundwater and surface-water systems; associated 

ecosystems; interception and uptake by vegetation; runoff 

plus direct input into streams, lakes, and other surface 

water bodies; and infiltration through soil and rock to the 

water table. Evapotranspiration processes redistribute water 

back into the atmosphere to renew this important part of 

the hydrologic cycle. Predevelopment groundwater levels 

reflect equilibrium between the natural filling of groundwater 

reservoirs by infiltration of precipitation and eventual 

discharge of groundwater as base flow to streams or springs. 

Historical and increasing demands on groundwater have 

changed this natural balance, have highlighted the fact that 

the resource is not without limit, and have necessitated the 

review of water use and water-use reporting requirements 

for groundwater throughout the State. Arkansas is the fourth 

largest user of groundwater in the Nation (Kenny and others, 

2009). Groundwater use is extremely important for the State as 

groundwater irrigation is critical to agriculture—the keystone 

in the economy (McGraw and others, 2012). Irrigation 

accounts for the highest percentage of groundwater use in 

Arkansas (Holland, 2007), especially for rice production that 

requires large volumes of water during its growing season. 

Other groundwater uses in Arkansas include public supply, 

domestic rural self supply, commercial, industrial, mining, 

livestock, aquaculture, and duck hunting, as well as its use as 

an important source of base flow to surface-water bodies. 

Reporting and Registration 

Since 1950, the USGS has conducted a water-use 

inventory by State every 5 years. From 1960 to 1985, the 

water-use inventory was conducted at the county level by 

computing aggregated estimates. Data were compiled from 

multiple Federal, State, and local sources. Many estimates of 

water use were based on multipliers of water requirements 

by type of use. Other early methods of data collection used 

surveys sent to known industrial, commercial, and publicsupply entities; completion of the surveys was less than 

complete and not always accurate. 

Data collection first began on a site-specific basis for 

surface-water withdrawals for irrigation in 1969. Surveys in 

1980 and 1984 collected information on the amount of water 

used by industrial facilities (Arkansas Industrial Development 

Commission, 1980; Harrington and Childers, 1985). An 

inventory of public-water suppliers was completed in 1985. 

Beginning in 1987, water-use data-collection forms were 

mailed directly to industrial, commercial, and public-supply 

water users, which resulted in improved reporting (Baker, 

1990). 

 In 1985, ANRC and USGS began collecting annual 

site-specific water-use information for all groundwater wells 

with a potential pumping rate more than 50,000 gal/d or 

surface-water users that withdraw more than 1 acre-foot per 

year (acre-ft/yr) (in accordance with Arkansas Act 1051 of 

1985). Domestic users were exempted from the requirement 

to register their wells. ANRC in conjunction with the 

USGS created the Arkansas Water-Use Data Base System 

(ARWUDBS) to register, store, and conduct queries from 

Arkansas water-use data. Data from this system are available 

from the USGS, Little Rock, Ark. To generate a more 

complete water-use dataset, an annual $10 fee per well or relift 

(pumping from surface water) has been assessed by ANRC. 

Failure to comply with water-use registration requirements 

by ANRC results in a fine for the water user or well owner. 

Failure to comply after 2 years can result in the user’s loss 

of water rights. Metering of the sustaining aquifers (Sparta, 

Cockfield, Cane River, Carrizo, Wilcox, Nacatoch, Roubidoux, 

and Gunter) was required in new wells after September 2001 

and in all wells after September 2006 (Arkansas Natural 

Resources Commission, 2013b).

The 1985 water-use compilation represents the first 

site-specific, water-use data effort for the State. As such, the 

1985 water-use data were likely underestimated, as the many 

thousands of water users needed time to comply with the 

new reporting requirements. The 1985 data possibly were 

underestimated by as much as 50 percent (Baker, 1990). The 

underestimation problems decreased by 1988 as more water 

users moved into compliance. Because agricultural users may 

not know exactly how much water is used in any particular 

year, they also report the type, acreage, and water-application 

rate of various crops. The reported acreage after 1988 was 

more accurate than the estimated acreage used in early wateruse compilations (Baker, 1990). More information on the 

transition to the site-specific database can be found in Baker 

(1990).

Water-use data are reported through several avenues. 

In 2002, an interactive website was established for use in 

the Conservation District offices in 29 counties in eastern 

Arkansas because most irrigation use occurs in these counties. 

Agricultural users can verbally report their water use to trained 

personnel at a County Conservation District office or mail the 

registration form to ANRC. More information on the Arkansas 

water-use database can be found in National Research Council 

(2002).

Categories of Water Use

The USGS water-use reporting program has changed 

its definition of categories through the years. Estimated 

groundwater use for Arkansas by category is shown in table 6. 

In the 1950 and 1955 compilations, only five categories 

were considered at the State level (rural, public, industrial, 

irrigation, and water power). In 1960, county-level estimates 

were reported but did not give water-use values for Jefferson 

and Ouachita Counties. Also in 1960, rural estimates were 
Table 6. Groundwater use by category for Arkansas from published reports. [Units are million gallons per day. Data marked with “--” indicates data were not published for that year and category]

Year Aquaculture1 Commercial2 Domestic3 Duck hunting4 Electric5 Industrial Irrigation Livestock3 Mining2 Public supply6 Total 

1938 -- -- -- -- -- -- -- -- -- -- 320 A

1945 -- -- -- -- -- -- -- -- -- -- 525 B

1950 -- -- 35 -- -- 65 678 -- -- 35 813 M

1952 -- -- 35 -- -- 70 720 -- -- 40 865 B

1955 -- -- 24 -- -- 121 790 -- -- 28 963 M

19607 -- -- 26.08 -- -- 101.75 712.75 18.57 -- 33.15 7892.3 S

1965 103.51 -- 31.32 0.48 5.94 73.88 949.35 12.54 -- 53.71 1,230.73 H

1970 212.18 -- 48.8 0.28 4.14 114.6 1,063.9 16.27 -- 70.85 1,531.16 H

1975 229.65 -- 46.15 1.26 2.45 105.76 2,033.3 28.53 -- 88.91 2,536.01 H

1980 284.88 -- 56.88 5.36 3.06 90.83 3,481.4 22 -- 109.97 4,054.38 H

1981 233 -- 55 -- 2.37 92.7 3,760 23 -- 104 4,300 H

1982 237.52 -- 55.64 -- 5.24 82.99 3,386.6 21.37 -- 99.19 3,890 H

1985 --8 6.03 60.42 -- 1.09 64.01 3,332.7 8241.95 1.03 104.49 3,811.72 H

1990 98.53 14.31 50.61 -- 2.43 98.92 4,296.2 26.43 1.82 118.95 4,708.2 H

1995 228.25 0.39 37.61 -- 5.15 107.95 4,925.7 15.43 0.00 135.11 5,455.59 H

2000 187.35 3.85 31.22 -- 2.92 67.07 6,506.5 15.46 0.21 138.02 6,952.25 H

2005 245.82 3.16 17.83 81.14 0.93 65.75 6,942.2 15.53 0.24 137.69 7,510.29 H2010 181.14 0.95 13.26 80.43 4.28 61.17 7,367.75 27.1 0.18 133.66 7,873.75 u

1Aquaculture was not reported prior to 1965. The 1970 water-use report used the term fish and minnow farms.2Commerical and mining categories were lumped into the industrial category prior to 1985.3In the 1950 and 1955 water-use reports, a“rural” category included both domestic supply and livestock use. For this report, “rural” use is displayed under the domestic catego4Water use for wildlife impoundments was reported from 1965 through 1980 and included water withdrawn for migratory waterfowl. This category was not reported separatel

this type of use continued and, if reported, would have been combined into the irrigation category. Duck hunting was reinstated as a use category in the 2005 water-use report. 

5In 1950, 1955, and 1960 water-use reports, the electric category included nonconsumptive use of hydroelectric power and was removed from this summary.6The 1950 water-use report used the term municipal supply.7Groundwater use was not reported for Jefferson and Ouachita Counties in 1960.8In the 1985 water-use report, aquaculture was combined into the livestock category.
28 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

divided into rural domestic and rural livestock. Beginning 

in 1965, county-level groundwater use was reported by 

aquifer, as well as for wildlife impoundments for migratory 

waterfowl and aquaculture. Additional water-use compilations 

were completed for 1981 and 1982 (Hall and Holland, 1984; 

Holland and Hall, 1986). Mining and commercial use were 

divided into separate categories in 1985 (Holland, 1987). Data 

for aquaculture were combined with the livestock category in 

1985. 

Early reports did not separate water consumed by 

hydroelectric processes from nonconsumptive uses, and the 

amount of water stored behind dams was included in these 

early estimates; therefore, the total amount of water used was 

unrepresentatively high for 1950, 1955, and 1960 and was not 

included in the summary shown in table 6. More information 

on how the categories in the national program have changed 

through the years is found at U.S. Geological Survey (2013a). 

Statewide Groundwater Use

All counties in Arkansas report some groundwater 

use (Terrance W. Holland, U.S. Geological Survey, written 

commun., 2013). The largest groundwater use occurs in 

eastern Arkansas, where row-crop agriculture is prevalent, 

widespread, and the largest user of groundwater. The counties 

with the largest groundwater use since 1960 are Arkansas, 

Lonoke, and Poinsett. Since 2005, the greatest water use has 

been in Poinsett County. Water use has increased steadily 

in Arkansas since the earliest reported estimates (fig. 4; 

table 6). Irrigation is consistently the largest water use in 

the State (94 percent of groundwater use in 2010), and 

groundwater use for irrigation increased more than tenfold 

from 1950 to 2010. The second largest use of groundwater 

has been aquaculture because use has been heavily dependent 

on commercial demand. Duck hunting, a very important 

recreation and tourist industry in central and eastern Arkansas, 

has incomplete records, but groundwater use for flooding of 

fields and woodlands for seasonal habitat has increased over 

the years. Livestock agriculture is important in many counties; 

however, the most change in water use for that category 

can be attributed to differences in reporting requirements. 

Groundwater-use changes in the livestock, industrial, 

commercial, and mining categories are mostly because of the 

changes in reporting. More detailed discussions on reporting 

by category are in the following sections.

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

Water use, in million gallons per day

1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Year

1925

Water used, in million gallons per day

 Groundwater (total)

 Groundwater (irrigation only)

 Surface water (total)

 Surface water (irrigation only)

EXPLANATION

Data from MacKichan (1951, 1957); Baker (1955); Arkansas Water Study Commission (1956); Stephens and Halberg (1961); Halberg and Stephens (1966); 

Halberg (1972, 1977); Holland (1981, 1987,1993, 1999, 2004, 2007). Water use for nonconsumptive use by hydroelectric generation was not included.

Figure 4. Total and irrigation use from groundwater and surface-water sources in Arkansas from 1925 to 2010. 
Overview of Aquifers of Arkansas 29

Irrigation

The irrigation-use category comprises water applied 

for crop or pasture and includes lawns at parks and golf 

courses. Other onfarm applications for this category include 

water used for preirrigation, frost protection, chemical 

application, weed control, field preparation, crop cooling, 

harvesting, dust suppression, leaching of salts from the root 

zone, microirrigation, and sprinkler irrigation. Estimates of 

conveyance loss (leakage from an irrigation ditch, canal, or 

pipe) were included in previous water-use reports but were not 

reported beginning in 2000 (U.S. Geological Survey, 2013a). 

Row-crop agriculture consistently has been the leading 

driver in Arkansas’ economy. One in every six jobs was related 

to agriculture in 2010 (McGraw and others, 2012). Arkansas 

is the Nation’s leading producer of rice and ranks third in the 

Nation in cotton production and ninth in soybean production 

(U.S. Department of Agriculture, 2011; McGraw and others, 

2012). Other important agricultural commodities in Arkansas 

are wheat, grain sorghum, and pecans. 

Irrigation use is dependent on many factors, including 

the types of crops, management practices, climatic conditions, 

market factors, and Congressional controls. Soybeans 

account for the most acreage planted and harvested (U.S. 

Department of Agriculture, 2011), but rice uses the most 

water per acre. Most rice farmers inundate their fields with 

3–6 inches of standing water during the growing season (April 

to September). Every county in Arkansas has reported rice 

acreage, but the lowlands of eastern Arkansas generally have 

been the largest producers (Engler and others, 1963). In 2011, 

22 counties, primarily in eastern Arkansas, grew rice (U.S.

Department of Agriculture, 2012). 

Groundwater use for irrigation by county is shown in 

table 7 for 1960–2010. Use also was calculated at the State 

level for 1950 and 1955. Irrigation has consistently been the 

largest use of groundwater since official USGS inventories 

began in 1950 (table 6). Farmers began to increasingly 

depend upon irrigation in the 1970s for watering other 

traditionally dryland crops such as corn, soybeans, and 

cotton. From 1970 to 1975, groundwater use for irrigation 

increased by 91 percent. Use was fairly steady in the 1980s, 

then again increased 28 percent from 1985 to 1990 and again 

increased another 32 percent from 1995 to 2000 (fig. 4; 

table 7). Statewide irrigation use has increased over 930 

percent from 1960 to 2010. Generally, the counties with 

irrigated rice acreage coincide with the greatest groundwater 

usage. Arkansas County was the largest groundwater user 

for irrigation from 1960 to 1970 and 1990 to 2000. Poinsett 

County was the largest groundwater user and harvested the 

most acres of rice in the State in the 1980s and since 2000 

(Terrance W. Holland, U.S. Geological Survey, written 

commun., 2012). 

The Mississippi River Valley alluvial aquifer is 

the primary source of irrigation water in Arkansas. 

The Mississippi River Valley alluvial aquifer supplied 

approximately 7,050 Mgal/d, 96 percent of irrigation water 

used in 2010 (Terrance W. Holland, U.S. Geological Survey, 

written commun., 2012). In an effort to reduce groundwater 

pumping for irrigation, many farmers initiated waterconservation practices, including tailwater recovery systems, 

polypipe irrigation, precision land grading (land-leveling), 

and planting of less water-intensive crops. Research has 

demonstrated substantial reductions in water use from many 

of these practices (Vories and others, 2005; Smith and others, 

2007). The decline of water use in Arkansas County since 

2000 has been attributed to enactment of these measures 

(Czarnecki and Schrader, 2013). 

Public Supply 

The public-supply water-use category represents water 

withdrawn by municipalities or rural-water associations 

and delivered to domestic, commercial, industrial, and 

thermoelectric power uses. Public or private systems that 

deliver water to a minimum of 25 people or have a minimum 

of 15 service connections are required to report their water-use 

data to ANRC (Holland, 2007). Water used for firefighting, 

street washing, flushing of water lines, and filling of 

swimming pools is included in this category. 

Around the late 1800s, Arkansans obtained drinking 

water from groundwater supplies except for the cities of 

Little Rock and Newport (fig. 5), which were located near 

the Arkansas and White Rivers, respectively (Veatch, 1906). 

Comparison of groundwater use for public supply with 

increasing population through 2010 is illustrated in figure 6. 

Groundwater withdrawals for public supply stabilized at about 

135 Mgal/d from 1995 to 2010 (tables 6 and 8). Surface-water 

use surpassed groundwater use for public supply beginning 

in 1955 (fig. 6). The proportion of surface water used for 

public supply gradually increased to become much more 

than that of groundwater; as of 2010, surface-water use for 

public supply was more than twice that of groundwater. The 

increased use of surface water is attributed to the availability 

of surface water—construction of several reservoirs and 

river intakes occurred throughout the twentieth century and 

other major surface-water diversions are currently (2013) 

in construction—as well as an increasing population in 

northwestern Arkansas, which predominantly uses surface 

water. As of 2012, only 36 percent of Arkansans receive their 

drinking water from public-supplied groundwater sources 

(Terrance W. Holland, U.S. Geological Survey, written 

commun., 2012).
Table 7. Groundwater use for irrigation supply by counties and years in Arkansas.—Continued [Counties shown are only those with published data. Data from Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and Hall (1986); Ho2004, 2007). Units are million gallons per day] County 1960 1965 1970 1975 1980 1982 1985 1990 1995 2000 

Arkansas 108.72 125.97 130.93 153.26 229.88 318.99 214.23 419.02 450.93 616.45 

Ashley 9.83 14.32 17.94 35.15 89.19 75.00 60.61 67.29 69.11 97.84 

Baxter 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.03 0.00 0.00 

Benton 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.12 

Bradley 0.00 0.00 0.00 0.01 0.40 0.58 0.28 0.02 0.00 0.00 

Calhoun 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.00 0.00 

Carroll 0.00 0.00 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Chicot 13.37 11.67 19.98 42.45 63.91 67.86 72.05 106.60 120.77 127.79 

Clark 0.00 0.00 0.00 0.00 0.79 0.89 1.01 0.00 0.00 0.00 

Clay 17.73 19.50 17.89 58.61 148.16 141.76 174.37 195.48 169.76 263.06 

Cleburne 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Cleveland 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.02 0.00 0.00 

Columbia 0.00 0.00 0.00 0.00 0.07 0.04 0.06 0.00 0.00 0.00 

Conway 0.14 0.21 0.40 1.19 3.50 2.82 1.84 0.70 0.67 1.30 

Craighead 28.64 47.26 59.04 138.72 215.17 200.35 196.46 228.97 305.31 337.08 

Crawford 0.00 1.08 1.49 0.71 3.88 2.98 3.68 0.06 0.02 0.10 

Crittenden 10.82 25.29 27.62 35.96 77.91 53.21 110.20 59.10 102.33 119.42 

Cross 53.39 67.00 80.12 164.71 220.35 237.56 255.25 335.35 281.05 408.64 

Dallas 0.00 0.00 0.00 0.00 0.22 0.00 0.00 0.00 0.00 0.00 

Desha 24.36 39.00 69.09 113.53 131.42 103.16 106.45 207.07 216.50 310.95 

Drew 6.32 7.07 14.01 22.66 44.01 43.61 40.13 36.03 54.65 51.42 

Faulkner 0.91 0.00 0.00 0.23 0.43 0.31 0.29 0.63 0.35 0.73 

Franklin 0.00 0.08 0.00 0.00 1.13 0.50 0.32 0.26 0.07 0.00 

Fulton 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Grant 0.03 0.09 0.10 0.00 0.00 0.00 0.00 0.06 0.00 0.00 

Greene 7.87 12.82 11.64 2.33 131.90 79.18 124.25 105.79 147.09 154.89 

Hempstead 0.00 0.00 0.00 0.00 0.74 1.00 1.05 0.00 0.00 0.00 

Hot Spring 0.00 0.00 0.00 0.03 0.27 0.06 0.34 0.00 0.00 0.00 

Howard 0.00 0.00 0.00 0.00 0.09 0.00 0.00 0.00 0.00 0.00 

Independence 1.50 2.05 3.76 6.93 17.34 23.05 31.65 7.59 16.50 33.62 

Izard 0.00 0.00 0.00 0.00 0.04 0.02 0.03 0.00 0.00 0.00 

Jackson 52.55 48.73 50.69 153.59 206.88 211.05 197.66 265.97 275.32 360.55 

Jefferson --1 41.03 45.54 100.94 147.62 123.87 123.56 153.56 282.40 413.34 

Johnson 0.00 0.31 0.93 1.19 2.56 2.18 2.43 0.43 0.30 0.56 

Lafayette 2.45 3.87 3.22 11.31 19.04 16.54 14.67 0.00 20.62 9.12 

Table 7. Groundwater use for irrigation supply by counties and years in Arkansas. [Counties shown are only those with published data. Data from Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and Hall (1986); Ho2004, 2007). Units are million gallons per day]
Table 7. Groundwater use for irrigation supply by counties and years in Arkansas.—Continued [Counties shown are only those with published data. Data from Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and Hall (1986); Ho2004, 2007). Units are million gallons per day]

County 1960 1965 1970 1975 1980 1982 1985 1990 1995 2000 

Lawrence 19.61 15.69 18.75 70.82 150.84 155.83 150.34 212.49 257.44 294.63 

Lee 12.29 24.14 20.42 39.27 117.12 131.94 96.33 163.68 157.63 233.75 

Lincoln 17.19 23.51 51.84 70.76 87.35 90.13 84.62 107.52 128.34 167.34 

Little River 0.58 0.60 0.98 0.30 3.35 2.35 1.04 1.41 0.00 0.00 

Logan 0.04 0.16 0.18 0.18 0.93 1.61 1.51 0.98 0.37 0.23 

Lonoke 92.28 100.69 104.06 158.74 246.85 198.32 201.36 232.75 234.09 334.01 

Miller 1.45 1.50 1.78 0.98 0.81 3.49 17.76 6.86 9.28 6.38 

Mississippi 3.46 3.74 3.70 4.84 29.93 27.81 48.28 98.01 132.05 178.05 

Monroe 31.11 52.28 39.39 74.49 125.55 117.09 114.40 173.59 177.81 233.74 

Nevada 0.00 0.00 0.00 0.00 0.26 0.22 0.49 0.00 0.00 0.00 

Newton 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.01 

Ouachita --1 0.00 0.00 0.00 0.02 0.02 0.22 0.00 0.00 0.00 

Perry 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 

Phillips 13.99 13.33 12.01 15.11 77.28 65.56 71.63 115.20 132.32 198.07 

Pike 0.00 0.00 0.00 0.00 0.58 0.83 0.98 0.00 0.00 0.00 

Poinsett 52.33 85.18 98.12 175.89 303.20 334.86 296.76 394.52 430.98 581.70 

Polk 0.00 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Pope 0.00 0.41 0.51 1.85 2.57 2.03 3.88 2.05 1.09 0.87 

Prairie 51.51 67.52 56.32 119.69 157.32 149.44 147.17 193.56 190.56 226.51 

Pulaski 5.37 5.57 8.16 13.50 23.30 20.68 22.19 17.59 13.52 20.43 

Randolph 3.16 2.97 3.09 17.89 41.88 42.72 41.08 50.67 59.17 85.45 

Saline 0.00 0.00 0.00 0.00 0.07 0.24 0.04 0.34 0.00 0.03 

Sebastian 0.00 0.00 0.01 0.01 0.61 0.53 1.03 0.06 0.00 0.00 

Sevier 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 

Sharp 0.00 0.00 0.00 0.00 0.00 0.00 0.04 0.00 0.00 0.00 

St. Francis 37.45 30.17 46.34 99.30 137.28 131.05 106.97 155.85 181.65 245.51 

Stone 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 

Van Buren 0.00 0.00 0.00 0.00 0.02 0.02 0.02 0.00 0.00 0.00 

Washington 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.05 

White 1.42 1.83 2.10 10.90 49.36 43.92 47.43 39.02 55.81 45.62 

Woodruff 30.64 52.30 41.18 114.34 165.68 157.50 140.68 138.94 249.82 347.09 

Yell 0.24 0.40 0.53 0.96 2.34 1.86 3.62 1.01 0.00 0.00 

Total 712.75 949.35 1,063.91 2,033.33 3,481.41 3,386.61 3,332.74 4,296.15 4,925.70 6,506.46 

1Data not reported from Jefferson and Ouachita Counties in 1960.
YELL LEE UNION WHITE POLK POPE DREW PIKE SCOTT CLARK CLAY ASHLEY DESHA BENTON LOGAN SALINE IZARD LONOKE PULASKI ARKANSAS NEWTON GRANT CHICOT MADISON STONE MILLER SHARP CROSS DALLAS PRAIRIE BOONE PHILLIPS PERRYSEARCY MARION FULTON SEVIER MISSISSIPPI JEFFERSON NEVADA POINSETT GARLAND COLUMBIA BAXTER

OUACHITA

BRADLEY

JOHNSON

WASHINGTON

MONROE

GREENE

JACKSON

CARROLL

HOWARD

LINCOLN

CALHOUN

CONWAY

FAULKNER

FRANKLIN VAN BUREN

CRAIGHEAD

HEMPSTEAD

RANDOLPH

CLEBURNE

MONTGOMERY

LAWRENCE

ST. FRANCIS

CRAWFORD

CLEVELAND

HOT SPRING

INDEPENDENCE

LITTLE RIVER

WOODRUFF

CRITTENDEN

LAFAYETTE

SEBASTIAN

LOUISIANA

TENNESSEE

MISSISSIPPI

TEXAS

MISSOURI

OKLAHOMA

ARKANSAS

Bull Shoals Lake

Beaver

Lake

Lake

Columbia

Arkansas River

Buffalo River

Little Misso uri River

Mississippi River

Saline River

Ouachita River

Arkansa s River

Red River

White River

Black River

Cache River

Little Red River

Greenville

Memphis

Mountain Bentonville Home

Rogers

Paragould

Harrison

Blytheville

Springdale

Siloam

Springs

Jonesboro

Fayetteville

Batesville

Marion

West Memphis

VanBuren

Fort

Smith

Forrest

City

Maumelle Jacksonville

Little

Rock

Hot Springs

Malvern Pine

Bluff

Arkadelphia

Hope

Camden

Texarkana

Magnolia El Dorado

Mammoth Piggott Spring Corning

Rector

Eureka Springs

Holiday Island

Decatur Yellville

Osceola

Mountain View

Grubbs Diaz

Jacksonport Newport Harrisburg

Heber

Springs

Ozark

Wynne Atkins

Dardanelle

Madison

Morrilton

Des Arc

Brinkley

De Valls Bluff Marianna

Hazen

Carlisle

Lonoke

Ulm

Stuttgart

Almyra

DeWitt

Sheridan

Gillett Carthage

Dierks

Rison

Murfreesboro

Okolona DeQueen

Sparkman

Gurdon

Kingsland

Lockesburg

Winchester

Fordyce

Horatio Mineral

 Springs

Prescott

McGehee

Arkansas City

Monticello

Wilmar

Emmet

Warren

Dermott

Foreman

Ashdown Ogden Rosston

Lake Smackover Village

Norphlet

Stamps

Lewisville

Hamburg

Eudora Crossett

Fouke

Bradley

Cherokee

Village

Ben

Lomond Winthrop Ozan

Tokio

Blevins

Helena

Searcy

Cabot

Base from U.S. Geological Survey digital data, 1:100,000Universal Transverse Mercator projection, zone 15North American Datum of 1983

15

0 30 450 15 30 

36°

35°

34°

90°

93° 94° 92° 91°

EXPL

CG

Figure 5. Location of Arkansas cities and major rivers referenced in this report.
Overview of Aquifers of Arkansas 33

Figure 6. Surface-water and groundwater use for domestic and public supply and population of Arkansas from 1950 to 2010. 

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Year

0

50

100

150

200

250

300

350

400

Water use1, in million gallons per day 

0

500

1,000

1,500

2,000

2,500

3,000

3,500

Population of Arkansas2, in thousands

Water used, in million gallons per day

 Public supply from groundwater sources

 Public supply from surface-water sources

 Domestic supply from groundwater sources

Population

EXPLANATION

1

Water use data from MacKichan (1951, 1957); Baker (1955); Stephens and Halberg (1961); Halberg and Stephens (1966); 

 Halberg (1972, 1977); Holland (1981, 1987, 1993, 1999, 2004, 2007). 

2

Annual population for Arkansas from www.census.gov. 
34 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Table 8. Groundwater use for public supply by counties and years in Arkansas.—Continued

[Counties shown are only those with published data. Data from Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and 

Hall (1986); Holland (1981, 1987, 1993, 1999, 2004, 2007). Units are million gallons per day]

County 1960 1965 1970 1975 1980 1982 1985 1990 1995 2000 2005 2010

Arkansas 1.04 1.66 2.14 2.98 4.02 3.43 3.49 4.18 4.74 4.86 6.02 4.83

Ashley 0.82 0.93 1.43 1.65 2.27 2.21 2.09 2.25 2.75 2.18 2.12 1.75

Baxter 0.20 0.34 0.46 0.38 0.55 0.46 0.46 0.53 0.71 0.81 0.53 0.50

Benton 0.89 2.36 2.00 1.78 0.43 0.43 0.43 4.30 0.77 0.88 1.10 4.62

Boone 0.61 0.02 0.05 1.94 1.98 1.67 1.22 0.64 0.50 0.83 0.88 0.90

Bradley 0.40 0.74 0.64 0.69 0.98 0.87 0.99 0.96 1.14 1.11 1.22 1.32

Calhoun 0.11 0.12 0.13 0.20 0.31 0.28 0.28 0.40 0.86 0.32 0.40 0.56

Carroll 0.07 0.55 1.11 1.42 1.46 1.75 1.75 0.46 0.54 0.55 0.90 0.80

Chicot 0.65 0.79 0.73 0.98 1.76 1.75 1.68 1.55 2.28 1.74 1.82 1.81

Clark 0.18 0.20 0.02 0.22 0.48 0.42 0.42 0.31 0.21 0.06 0.07 0.06

Clay 0.49 0.58 0.86 0.97 1.42 1.15 1.09 1.61 1.60 1.83 1.42 1.68

Cleburne 0.00 0.02 0.05 0.05 0.12 0.13 0.13 0.12 0.15 0.06 0.08 0.00

Cleveland 0.06 0.11 0.14 0.15 0.41 0.43 0.43 0.80 1.03 1.33 0.54 1.00

Columbia 1.03 1.48 1.82 1.93 2.66 2.71 3.00 3.12 4.18 0.63 1.38 1.34

Conway 0.53 1.02 1.07 1.29 1.39 1.12 1.12 0.15 0.24 0.00 0.00 0.00

Craighead 1.65 3.08 4.38 5.46 7.44 6.77 6.90 8.70 11.90 13.76 13.52 15.27

Crawford 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Crittenden 1.97 2.16 3.54 4.76 5.79 5.23 6.03 7.70 9.52 16.28 8.47 6.69

Cross 0.51 0.61 1.06 1.39 2.20 2.07 2.02 1.16 2.95 1.79 2.44 2.63

Dallas 0.45 0.50 0.63 0.59 0.76 0.83 0.85 0.92 0.85 0.84 1.34 0.76

Desha 0.65 0.78 0.85 1.38 1.35 1.35 4.22 5.82 2.28 1.88 2.18 1.07

Drew 0.38 1.02 2.06 2.51 2.82 2.67 2.79 2.02 2.04 3.03 2.78 3.14

Faulkner 0.00 0.02 0.09 0.32 0.84 0.82 0.82 1.80 1.30 0.16 0.52 2.74

Franklin 0.15 0.52 1.26 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Fulton 0.08 0.12 0.16 0.29 0.38 0.34 0.34 0.67 0.41 0.03 1.28 1.55

Garland 0.01 0.01 0.01 0.34 0.13 0.13 0.13 0.10 0.13 0.19 0.13 0.00

Grant 0.15 0.31 0.80 1.11 1.30 1.29 1.04 1.33 1.80 1.20 2.03 1.47

Greene 0.84 1.12 1.90 1.87 2.99 2.77 2.33 2.92 3.43 4.17 4.23 4.36

Hempstead 0.83 1.08 1.04 2.25 2.56 2.14 1.91 0.19 1.87 4.01 2.65 2.37

Hot Spring 0.00 0.00 0.00 0.00 0.08 0.09 0.09 0.00 0.00 0.00 0.00 0.03

Howard 0.05 0.35 0.06 0.05 0.12 0.14 0.14 0.42 0.18 0.13 0.01 0.00

Independence 0.04 0.04 0.10 0.59 1.17 1.13 1.13 1.24 1.06 0.82 0.87 0.69

Izard 0.14 0.11 0.17 0.64 1.22 1.13 0.86 0.99 1.86 1.84 1.01 0.93

Jackson 0.81 0.87 0.89 1.16 1.32 1.60 1.66 1.38 1.89 1.96 1.52 1.59

Jefferson --1 5.40 7.83 8.86 11.63 10.93 10.97 10.98 16.54 15.98 14.25 13.14

Johnson 0.00 0.04 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Lafayette 0.33 0.36 0.38 1.04 0.80 0.87 0.96 1.14 0.94 0.85 0.92 0.93

Lawrence 0.39 0.71 0.86 1.20 1.28 1.34 1.43 1.37 1.52 1.94 1.61 1.15

Table 8. Groundwater use for public supply by counties and years in Arkansas. 

[Counties shown are only those with published data. Data from Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and 

Hall (1986); Holland (1981, 1987, 1993, 1999, 2004, 2007). Units are million gallons per day]
Overview of Aquifers of Arkansas 35

Table 8. Groundwater use for public supply by counties and years in Arkansas.—Continued

[Counties shown are only those with published data. Data from Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and 

Hall (1986); Holland (1981, 1987, 1993, 1999, 2004, 2007). Units are million gallons per day]

County 1960 1965 1970 1975 1980 1982 1985 1990 1995 2000 2005 2010

Lee 0.50 0.56 0.59 0.98 1.40 1.38 1.31 1.27 1.96 1.27 0.99 1.73

Lincoln 0.23 0.29 0.42 0.59 0.88 0.85 0.85 0.88 1.30 1.71 1.04 1.48

Little River 0.25 0.31 0.49 0.81 0.89 0.87 0.97 0.89 1.05 0.65 0.61 0.56

Logan 0.00 0.04 0.11 0.15 0.10 0.09 0.09 0.11 0.00 0.00 0.00 0.00

Lonoke 0.69 0.74 1.38 2.10 2.54 2.08 2.34 1.92 3.01 3.14 6.49 7.27

Madison 0.00 0.00 0.00 0.01 0.02 0.02 0.02 0.30 0.31 0.01 0.00 0.00

Marion 0.02 0.08 0.19 0.41 0.56 0.51 0.50 0.45 0.02 0.02 0.03 0.00

Miller 0.00 0.00 0.05 0.10 0.20 0.21 0.21 0.10 0.10 0.22 0.25 0.10

Mississippi 3.02 3.85 4.83 5.38 7.09 4.64 5.05 9.42 9.03 7.49 4.05 7.19

Monroe 0.73 0.74 0.81 0.97 1.25 1.30 1.41 1.64 1.80 1.74 1.49 1.33

Montgomery 0.03 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.30 0.03 0.00

Nevada 0.28 0.32 0.43 0.47 0.63 0.61 0.56 0.07 0.10 0.24 0.15 0.09

Newton 0.00 0.00 0.03 0.08 0.10 0.09 0.09 0.22 0.20 0.27 0.97 0.97

Ouachita --1 0.23 0.52 0.77 0.98 0.91 0.91 0.39 0.53 1.24 0.97 1.16

Perry 0.00 0.03 0.05 0.07 0.10 0.10 0.10 0.09 0.09 0.00 0.01 0.01

Phillips 1.86 2.60 3.12 3.12 3.41 3.41 3.27 3.42 4.53 4.46 3.70 3.17

Pike 0.10 0.36 0.54 0.03 0.06 0.06 0.06 0.07 0.10 0.05 0.05 0.05

Poinsett 0.86 1.29 1.79 3.51 2.83 2.55 2.53 3.52 3.37 2.80 5.12 2.86

Polk 0.00 0.00 0.03 0.11 0.22 0.20 0.20 0.00 0.00 0.01 0.00 0.00

Pope 0.12 0.21 0.45 0.43 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Prairie 0.26 0.33 0.41 0.51 0.87 0.86 0.80 0.79 0.83 0.82 0.79 0.77

Pulaski 2.20 3.17 3.76 4.19 3.38 1.58 1.81 4.18 3.74 4.97 4.56 3.72

Randolph 0.00 0.00 0.06 0.10 0.16 0.21 0.21 0.18 0.19 0.15 0.33 0.11

Saline 0.04 0.07 0.23 0.64 0.75 0.69 1.43 2.01 1.62 1.65 1.63 4.50

Scott 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.69 0.00

Searcy 0.11 0.11 0.17 0.15 0.25 0.23 0.24 0.17 0.17 0.45 0.00 1.31

Sebastian 0.03 0.08 0.10 0.08 0.09 0.13 0.13 0.00 0.00 0.00 0.20 0.00

Sevier 0.30 0.95 0.12 0.16 0.20 0.18 0.18 0.16 0.25 1.30 1.15 0.29

Sharp 0.05 0.09 0.98 1.05 1.42 1.10 1.30 0.75 0.75 0.79 3.80 0.78

St. Francis 0.69 1.42 1.88 2.55 2.93 2.62 3.04 2.96 3.65 4.10 5.18 4.99

Stone 0.05 0.09 0.00 0.00 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.28

Union 2.39 3.79 4.35 5.04 7.88 7.17 7.45 7.85 8.90 8.00 8.44 5.34

Van Buren 0.00 0.00 0.10 0.02 0.04 0.04 0.04 0.03 0.00 0.00 0.00 0.00

Washington 0.92 0.25 0.13 0.31 0.02 0.02 0.02 0.00 0.01 0.00 0.00 0.00

White 0.43 0.33 0.28 0.30 0.55 0.49 0.49 0.78 0.88 0.88 0.75 0.04

Woodruff 0.28 0.48 0.74 0.72 0.80 0.73 0.73 0.81 0.96 1.02 0.96 1.88

Yell 0.20 0.74 0.98 0.56 0.93 0.88 0.93 1.27 1.47 0.20 2.00 0.00

Total 33.15 53.71 70.85 88.91 109.97 99.19 104.49 118.95 135.11 138.02 137.69 133.66

1

Data not reported from Jefferson and Ouachita Counties in 1960.
36 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

The largest population centers served by groundwater 

are in central and northeastern Arkansas (fig. 7). The largest 

population center served by groundwater in 2010 was 

Jonesboro (Craighead County) (Terrance W. Holland, U.S. 

Geological Survey, written commun., 2012). Other large 

groundwater users for public supply are the cities of Stuttgart 

(Arkansas County), Pine Bluff (Jefferson County), and El 

Dorado (Union County), which all withdraw from the Sparta 

aquifer. West Memphis (Crittenden County), Blytheville 

(Mississippi County), and Paragould (Greene County) are the 

largest public-supply users of the Wilcox aquifer. The largest 

withdrawal for public supply from the Cockfield aquifer is the 

town of Crossett (Ashley County). 

Eastern Arkansas relies heavily on groundwater for 

public supply, tapping many aquifers including the Sparta, 

Wilcox, Mississippi River Valley alluvial, Cockfield, and 

Nacatoch aquifers. The Sparta aquifer is the predominant 

source of public supply in southern Arkansas, serving as 

the drinking-water source for over 120 municipalities. The 

second-highest amount of groundwater withdrawn for public 

supply comes from the Wilcox aquifer in the area east of 

Crowleys Ridge and west of the Mississippi River, which 

serves 35 municipalities, whereas west of Crowleys Ridge, 

the Mississippi River Valley alluvial aquifer serves over 

70 municipalities. In southeastern Arkansas, the Cockfield 

aquifer supplies municipalities in Ashley, Bradley, and Chicot 

Counties. In far northeastern Arkansas, the Nacatoch aquifer 

supplies eastern Clay and northeastern Greene Counties 

(fig. 5). 

 Groundwater in central Arkansas primarily was obtained 

from the Arkansas River Valley alluvial aquifer. The city of 

Little Rock obtained groundwater solely from wells prior 

to 1915 and then mixed groundwater with water from the 

Arkansas River until 1926, when groundwater was abandoned 

because of taste and odor problems (University of Arkansas at 

Little Rock Water Study Task Force, 2000). Currently (2013), 

surface water is the primary public-supply source in western 

Arkansas, whereas groundwater is predominantly used in 

eastern Arkansas (fig. 7). 

The Ozark aquifer is the primary high-yield, waterbearing aquifer in the Ozark Plateaus but requires deep drilling 

to median depths of approximately 1,300 ft to reach the 

high-producing deeper formations in the aquifer. Insufficient 

yields from shallower formations limit groundwater use in 

the Ozark Plateaus. Many municipalities have had trouble 

providing water to their populations because of low-yield 

wells, water-quality issues (including the common occurrence 

of radium), uncertainty of obtaining a good producing well, 

and the expense of drilling deep wells (Albin, 1965; Lamonds, 

1972; Imes and Emmet, 1994); therefore, this area relies more 

on surface water for public supply (Brahana and others, 1993). 

Surface-water reservoirs were built in many areas in central 

and western Arkansas in the 1960s and 1970s. Beaver Lake 

in northwestern Arkansas (fig. 5), constructed in the 1960s, 

supplies more water than any other surface-water body in the 

State. The counties of Benton, Boone, Carroll, Madison, and 

Washington are supplied by the lake (Beaver Water District, 

2010), which allowed many municipalities in northwestern 

Arkansas to switch from groundwater to surface-water 

sources. Construction of infrastructure needed to distribute 

water from Bull Shoals Lake to users in Boone, Newton, and 

Searcy Counties also is underway (Ozark Mountain Regional 

Public Water Authority, 2013). 

Southwestern Arkansas traditionally has used 

groundwater from multiple aquifers. The towns of Hope 

(Hempstead County) and Prescott (Nevada County) withdrew 

from the Nacatoch and Tokio aquifers. Hope supplements 

its groundwater supply with surface water, while Prescott 

currently (2013) only uses the Little Missouri River. The 

towns of Ashdown, Foreman (Little River County), and 

Texarkana (Miller County) used the Red River alluvial 

aquifer for public supply; these cities now rely on surface 

water (Southwest Arkansas Water District, 2013). Many cities 

in Lafayette County have public-supply wells completed 

in the Cane River Formation. The Trinity aquifer supplied 

many cities in Sevier County as well as Murfreesboro (Pike 

County) and Mineral Springs (Howard County). Horatio 

and Lockesburg (Sevier County) still use the Trinity aquifer, 

Murfreesboro now uses the Little Missouri River, and Mineral 

Springs uses the Tokio aquifer.

Domestic (Self-Supplied) 

Domestic water use is for household purposes such 

as drinking, food preparation, bathing, washing clothes 

and dishes, flushing toilets, as well as watering lawns and 

gardens. Most water used for domestic purposes is provided 

by public suppliers, yet approximately 1 percent of Arkansas’ 

population supplies their own water (Holland, 2007). The 

domestic-use category is calculated by applying an application 

rate to the rural population not serviced by public-supply 

systems. The rural population not serviced by publicsupply systems is calculated for each county by subtracting 

the population served by public suppliers, which is obtained 

when the supplier reports its water use, from the population 

of the county obtained through census data. In early reports, 

the domestic population was split into populations with 

and without running water. The application rates used to 

estimate domestic use has changed over the reporting periods, 

increasing from 50 gal/d per person in 1965 to 80–97 gal/d 

per person in 2010 (Halberg and Stephens, 1966; Terrance W. 

Holland, U.S. Geological Survey, written commun., 2013).
Public supply groundwater

Population served by

water source

Domestic 

groundwater

WATER

SOURCE

Public supply surface water

Annual water use by

water source

Base from U.S. Geological Survey digital data: 1:2,000,000 0 60 120 MILES 30

0 60 120 KILOMETERS 30

90

90

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

Figure 7. Population, in thousands, by water source (domestic groundwater, public supply groundwater or public supply surface water) and water u

day, by water source in Arkansas, 2010.
38 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Estimated domestic groundwater use in Arkansas 

increased with increasing population prior to 1985 (fig. 6). 

Domestic use increased by 23 percent between 1975 and 

1980 reporting years (table 6) because of a drought in 1980. 

Domestic groundwater use peaked in 1985 and has been 

decreasing ever since. These decreases resulted largely from 

expansion of public-supply systems sourcing from large 

surface-water reservoirs into areas that previously relied on 

groundwater. Domestic use was reported in all 75 Arkansas 

counties from 1960 to 1985 and also in 1995. The number of 

counties reporting domestic use dropped from 71 in 2000 to 

48 in 2010 (table 9). The largest populations with self-supplied 

groundwater sources are in southwestern and northwestern 

Arkansas (fig. 7). Rural residents in Miller County used the 

most domestic groundwater in 2010 (0.75 Mgal/d); Pope 

and Baxter Counties were second in the use of domestic 

groundwater (0.73 Mgal/d).

Almost all aquifers in the State provide some water for 

domestic use. The Mississippi River Valley alluvial aquifer is 

the primary source for domestic supply in eastern Arkansas; 

whereas east of Crowleys Ridge some have tapped the Wilcox 

aquifer. Many of the aquifers used in southern Arkansas for 

public supply are also used for domestic supply: Cane River, 

Carrizo, Cockfield, Red River alluvium, Tokio, and Trinity 

aquifers. The depth required to reach the Sparta aquifer 

results in limited domestic use of that aquifer. Domestic 

users in Clark County often tap the Ozan aquifer. Domestic 

users in parts of eastern Arkansas use groundwater from the 

Jackson Group. Domestic users in northern Arkansas use the 

Springfield Plateau and Ozark aquifers.

Commercial

The commercial (self-supplied) category includes 

consumptive water use by schools, restaurants, grocery stores, 

gas stations, hotels, parks, office buildings, recreation areas, 

and government facilities (including military sites). Prior to 

1985, commercial use was included with the industrial wateruse category. In 1990 and 1995, fish hatcheries were included 

in this category, whereas from 1965 to 1980 and since 2000, 

fish hatcheries were included in the aquaculture category (U.S. 

Geological Survey, 2013a). 

Most withdrawals for commercial use have been small 

(less than 0.05 Mgal/d; table 10), and many are seasonal. This 

is especially true for school district wells and recreational 

areas such as Federal, State, local, and private parks that 

primarily use water during peak times in the summer. Most 

commercial withdrawals are from the Mississippi River 

Valley alluvial aquifer, but several other aquifers also provide 

water for this use. Poinsett County had the most commercial 

groundwater use in 2010 (0.48 Mgal/d).
Overview of Aquifers of Arkansas 39

Table 9. Groundwater use for domestic supply by counties and years in Arkansas.—Continued

[Counties shown are only those with published data. Data from Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and 

Hall (1986); Holland (1981, 1987, 1993, 1999, 2004, 2007). Units are million gallons per day]

County 1960 1965 1970 1975 1980 1982 1985 1990 1995 2000 2005 2010

Arkansas 0.32 0.32 0.50 0.26 0.34 0.34 0.29 0.36 0.28 0.17 0.18 0.00

Ashley 0.48 0.53 0.54 0.62 0.66 0.85 0.69 0.44 0.38 0.57 0.18 0.00

Baxter 0.24 0.26 0.72 0.66 1.06 1.14 1.32 1.60 0.85 0.93 0.66 0.73

Benton 0.69 0.81 1.38 1.63 2.32 2.35 2.79 2.21 3.21 0.40 0.51 0.00

Boone 0.32 0.37 0.65 0.68 0.93 1.01 1.13 0.33 0.38 0.58 0.49 0.41

Bradley 0.25 0.26 0.37 0.15 0.20 0.19 0.17 0.28 0.19 0.23 0.05 0.09

Calhoun 0.15 0.16 0.24 0.24 0.22 0.23 0.24 0.11 0.12 0.19 0.10 0.05

Carroll 0.23 0.29 0.48 0.58 0.60 0.63 0.75 0.56 0.49 0.99 0.30 0.57

Chicot 0.29 0.38 0.49 0.38 0.44 0.47 0.44 0.37 0.22 0.00 0.18 0.18

Clark 0.34 0.38 0.48 0.57 0.50 0.47 0.47 0.53 0.29 0.12 0.07 0.32

Clay 0.48 0.53 0.64 0.64 0.78 0.76 0.73 0.09 0.10 0.00 0.00 0.00

Cleburne 0.23 0.26 0.49 0.32 0.22 0.19 0.14 0.44 0.10 0.01 0.09 0.00

Cleveland 0.20 0.21 0.36 0.39 0.43 0.45 0.47 0.11 0.01 0.00 0.07 0.00

Columbia 0.43 0.51 0.74 0.73 0.75 0.80 0.83 0.24 0.24 0.16 0.06 0.07

Conway 0.30 0.37 0.62 0.53 0.69 0.68 0.71 0.47 0.23 0.29 0.18 0.18

Craighead 0.78 0.84 1.31 1.05 0.42 0.22 0.25 1.91 0.60 0.47 0.46 0.44

Crawford 0.40 0.52 0.75 0.68 1.07 1.18 1.44 1.11 0.32 0.03 0.65 0.00

Crittenden 0.79 0.77 1.02 0.47 0.68 0.71 0.77 0.43 0.05 0.07 0.18 0.16

Cross 0.45 0.45 0.72 0.46 0.46 0.49 0.49 0.08 0.01 0.01 0.00 0.00

Dallas 0.20 0.20 0.27 0.19 0.35 0.34 0.34 0.35 0.24 0.27 0.11 0.00

Desha 0.39 0.45 0.50 0.35 0.48 0.48 0.43 0.40 0.08 0.31 0.00 0.00

Drew 0.33 0.39 0.60 0.47 0.68 0.38 0.40 0.01 0.34 0.07 0.07 0.11

Faulkner 0.49 0.61 1.04 1.24 1.69 1.82 2.21 1.88 1.88 0.54 0.47 0.40

Franklin 0.24 0.25 0.44 0.51 0.58 0.60 0.66 0.35 0.32 0.01 0.00 0.00

Fulton 0.17 0.20 0.36 0.45 0.47 0.48 0.52 0.58 0.63 0.69 0.09 0.00

Garland 0.62 0.58 0.74 1.00 1.17 1.22 1.52 2.03 1.28 0.88 0.07 0.00

Grant 0.21 0.23 0.43 0.27 0.25 0.24 0.28 0.11 0.26 0.41 0.12 0.10

Greene 0.49 0.51 0.86 0.98 0.98 1.01 1.08 0.94 1.05 0.05 0.05 0.32

Hempstead 0.35 0.42 0.66 0.67 1.08 1.08 1.08 0.90 0.94 0.90 0.78 0.49

Hot Spring 0.41 0.47 0.93 0.93 0.71 0.78 0.85 0.59 0.30 0.52 0.16 0.30

Howard 0.18 0.18 0.36 0.47 0.55 0.56 0.59 0.53 0.25 0.25 0.05 0.00

Independence 0.44 0.50 0.88 0.18 0.92 1.06 1.13 0.66 0.46 0.51 0.17 0.34

Izard 0.18 0.20 0.33 0.37 0.41 0.42 0.43 0.40 0.32 0.23 0.14 0.16

Jackson 0.48 0.50 0.66 0.66 0.36 0.36 0.33 0.25 0.25 0.28 0.14 0.18

Jefferson --1 1.18 1.19 0.60 0.48 0.47 0.43 0.00 0.04 0.02 0.12 0.03

Johnson 0.25 0.29 0.48 0.59 0.84 0.92 0.99 0.03 0.33 0.51 0.00 0.06

Lafayette 0.21 0.23 0.35 0.28 0.35 0.35 0.34 0.35 0.31 0.25 0.19 0.16

Lawrence 0.38 0.41 0.53 0.56 0.62 0.68 0.67 0.36 0.04 0.01 0.00 0.00

Lee 0.54 0.65 0.88 0.50 0.71 0.44 0.41 0.11 0.10 0.23 0.01 0.00

Table 9. Groundwater use for domestic supply by counties and years in Arkansas. 

[Counties shown are only those with published data. Data from Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and 

Hall (1986); Holland (1981, 1987, 1993, 1999, 2004, 2007). Units are million gallons per day]
40 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Table 9. Groundwater use for domestic supply by counties and years in Arkansas.—Continued

[Counties shown are only those with published data. Data from Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and 

Hall (1986); Holland (1981, 1987, 1993, 1999, 2004, 2007). Units are million gallons per day]

County 1960 1965 1970 1975 1980 1982 1985 1990 1995 2000 2005 2010

Lincoln 0.37 0.44 0.60 0.34 0.15 0.14 0.15 0.12 0.01 0.01 0.00 0.00

Little River 0.19 0.21 0.41 0.34 0.68 0.70 0.73 0.51 0.60 0.59 0.10 0.00

Logan 0.34 0.40 0.55 0.60 0.87 0.91 0.97 1.10 0.73 0.88 0.86 0.00

Lonoke 0.55 0.59 0.90 1.03 1.42 1.50 1.72 1.10 1.55 1.38 0.55 0.00

Madison 0.27 0.33 0.58 0.63 0.76 0.77 0.85 0.54 0.79 1.03 0.60 0.39

Marion 0.17 0.19 0.28 0.44 0.54 0.59 0.65 0.59 0.13 0.02 0.61 0.67

Miller 0.40 0.43 0.52 0.60 0.93 1.02 1.05 1.28 0.01 0.14 0.72 0.75

Mississippi 0.19 1.42 1.13 0.80 0.79 0.69 0.66 0.35 0.01 0.08 0.00 0.11

Monroe 0.32 0.39 0.45 0.40 0.24 0.23 0.18 0.13 0.02 0.04 0.00 0.30

Montgomery 0.15 0.18 0.33 0.37 0.54 0.53 0.57 0.42 0.51 0.47 0.47 0.04

Nevada 0.24 0.23 0.40 0.41 0.55 0.55 0.55 0.38 0.41 0.38 0.25 0.19

Newton 0.20 0.24 0.38 0.46 0.50 0.59 0.64 0.41 0.44 0.49 0.06 0.05

Ouachita --1 0.44 0.77 0.62 0.27 0.08 0.30 0.85 0.28 0.48 0.06 0.00

Perry 0.14 0.16 0.30 0.35 0.40 0.42 0.46 0.38 0.33 0.66 0.32 0.36

Phillips 0.72 0.71 0.67 0.48 0.52 0.51 0.44 0.29 0.11 0.05 0.00 0.00

Pike 0.18 0.20 0.45 0.43 0.56 0.55 0.56 0.51 0.55 0.45 0.23 0.26

Poinsett 0.65 0.75 0.84 0.70 0.32 0.25 0.21 0.29 0.23 0.34 0.16 0.16

Polk 0.28 0.29 0.60 0.65 0.89 0.91 0.94 0.79 0.76 0.74 0.83 0.66

Pope 0.71 0.41 0.94 1.05 1.58 1.61 1.84 1.55 1.77 1.35 0.27 0.73

Prairie 0.25 0.27 0.41 0.30 0.10 0.10 0.09 0.31 0.11 0.13 0.18 0.14

Pulaski 0.14 0.18 2.31 1.80 5.80 3.93 4.67 7.44 0.08 1.11 0.00 0.54

Randolph 0.29 0.32 0.50 0.67 0.73 0.69 0.71 0.76 0.54 0.31 0.49 0.44

Saline 0.60 0.61 1.14 0.94 1.84 1.80 1.99 1.21 2.26 1.59 0.57 0.00

Scott 0.19 0.24 0.42 0.47 0.62 0.62 0.68 0.64 0.70 0.66 0.36 0.36

Searcy 0.22 0.27 0.41 0.44 0.56 0.59 0.59 0.45 0.23 0.16 0.07 0.04

Sebastian 0.02 0.41 0.43 1.97 0.89 0.86 1.10 0.32 0.22 0.10 0.51 0.00

Sevier 0.21 0.22 0.41 0.47 0.63 0.65 0.66 0.57 0.70 0.68 0.27 0.29

Sharp 0.16 0.16 0.17 0.11 0.39 0.40 0.47 0.14 0.08 0.00 0.27 0.26

St. Francis 0.70 0.70 1.01 0.83 0.48 0.49 0.51 0.80 0.31 0.13 0.18 0.03

Stone 0.18 0.18 0.36 0.45 0.57 0.55 0.61 0.67 0.27 0.45 0.00 0.06

Union 0.61 0.65 0.76 0.41 0.35 0.33 0.38 0.26 0.27 0.63 0.66 0.43

Van Buren 0.22 0.26 0.40 0.25 0.52 0.57 0.64 0.77 0.49 0.01 0.04 0.11

Washington 1.10 0.78 1.70 1.95 2.20 2.31 2.67 1.38 2.97 1.40 0.18 0.00

White 0.62 0.74 1.33 1.16 1.22 1.28 1.35 0.52 1.04 1.57 0.73 0.00

Woodruff 0.30 0.34 0.39 0.24 0.30 0.28 0.27 0.24 0.20 0.03 0.08 0.00

Yell 0.27 0.31 0.56 0.68 0.72 0.79 0.75 0.04 0.41 0.52 0.00 0.04

Total 26.08 31.32 48.80 46.15 56.88 55.64 60.42 50.61 37.61 31.23 17.83 13.26

1

Data not reported from Jefferson and Ouachita Counties in 1960.
Overview of Aquifers of Arkansas 41

Table 10. Groundwater use for commercial supply by counties and years in Arkansas. 

[Commercial and mining categories were lumped into the industrial category prior to 1985. Counties shown are only those with published data. Data from 

Holland (1987, 1993, 1999, 2004, 2007). Units are million gallons per day]

County 1985 1990 1995 2000 2005 2010

Arkansas 0.05 0.63 0.00 0.91 0.18 0.00

Baxter 0.31 0.00 0.00 0.07 0.00 0.00

Benton 0.45 0.24 0.00 0.02 0.00 0.00

Boone 0.00 0.00 0.00 0.01 0.00 0.00

Bradley 0.01 0.00 0.00 0.00 0.00 0.00

Carroll 0.00 0.00 0.00 0.07 0.10 0.05

Clark 0.01 0.00 0.00 0.00 0.00 0.00

Clay 0.00 0.14 0.00 0.00 1.97 0.00

Cleburne 0.43 0.00 0.00 0.01 0.00 0.00

Columbia 0.10 0.00 0.00 0.02 0.00 0.00

Conway 0.05 0.02 0.00 0.00 0.00 0.00

Craighead 0.00 0.00 0.00 0.00 0.00 0.06

Crittenden 0.00 0.00 0.00 1.07 0.00 0.00

Cross 0.00 0.00 0.00 0.05 0.00 0.00

Franklin 0.11 0.13 0.00 0.00 0.00 0.00

Fulton 0.00 0.00 0.00 0.02 0.00 0.00

Garland 0.40 0.00 0.01 0.01 0.00 0.00

Greene 0.12 0.00 0.07 0.07 0.14 0.09

Hempstead 0.00 0.00 0.00 0.00 0.01 0.00

Hot Spring 0.18 0.01 0.01 0.01 0.00 0.03

Howard 0.00 0.34 0.00 0.01 0.00 0.00

Independence 0.00 0.00 0.00 0.01 0.00 0.00

Jefferson 0.89 0.94 0.00 0.00 0.00 0.00

Johnson 0.00 0.30 0.00 0.01 0.00 0.00

Lawrence 0.00 0.00 0.00 0.00 0.24 0.00

Lincoln 0.33 0.00 0.00 0.00 0.00 0.00

Little River 0.20 0.00 0.00 0.04 0.06 0.08

Logan 0.03 1.05 0.00 0.00 0.00 0.00

Lonoke 0.01 0.00 0.00 0.30 0.00 0.00

Madison 0.15 0.00 0.00 0.02 0.00 0.00

Marion 0.32 0.00 0.00 0.04 0.00 0.00

Miller 0.00 0.00 0.00 0.00 0.00 0.01

Mississippi 0.65 0.00 0.00 0.00 0.00 0.00

Monroe 0.00 0.00 0.01 0.33 0.00 0.00

Montgomery 0.20 0.00 0.00 0.02 0.00 0.06

Nevada 0.02 0.00 0.00 0.01 0.00 0.00

Newton 0.00 0.00 0.00 0.01 0.00 0.00

Perry 0.15 0.00 0.00 0.00 0.00 0.00

Phillips 0.00 0.00 0.00 0.08 0.00 0.02

Pike 0.18 0.00 0.01 0.00 0.00 0.00

Poinsett 0.02 2.51 0.16 0.51 0.19 0.48

Polk 0.08 0.00 0.00 0.00 0.01 0.01

Pope 0.16 8.00 0.10 0.04 0.10 0.02

Pulaski 0.11 0.00 0.00 0.01 0.12 0.03

Randolph 0.03 0.00 0.00 0.01 0.00 0.00

Scott 0.00 0.00 0.00 0.01 0.00 0.00

Searcy 0.00 0.00 0.00 0.01 0.00 0.00

Stone 0.00 0.00 0.00 0.00 0.01 0.01

Washington 0.08 0.00 0.02 0.03 0.03 0.00

Yell 0.20 0.00 0.00 0.01 0.00 0.00

Total 6.03 14.31 0.39 3.85 3.16 0.95
42 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Industrial

The industrial water-use category includes water used 

for fabrication, processing, washing, and cooling in facilities 

that manufacture products. Prior to 1985, water used in 

commercial and mining operations was included in the 

industrial category. From 1985 to 1995, this category also 

included water provided by public suppliers to industrial 

users. As of the 2000 report, the industrial category refers to 

“self-supplied” industrial water use. Large decreases in water 

use are noted from 1982 to 1985 and from 1995 to 2000 and 

corresponded to the two changes in reporting (table 11). 

Early industrial groundwater users in the State were 

railroads, ice companies, and lumber and paper mills (Veatch, 

1906). Arkansas is home to a diversity of industries including 

pulp and paper mills, food processors, oil refineries, and 

chemical plants. Most industrial groundwater use occurs in 

southern Arkansas. The majority of groundwater use is from 

the Sparta aquifer, with lesser amounts from the Mississippi 

River Valley alluvial, Cockfield, Wilcox, and Nacatoch 

aquifers. For the last decade, paper mills were the largest user 

of groundwater for industrial purposes (Terrance W. Holland, 

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

Jefferson County consistently has reported the most 

industrial groundwater withdrawals in the State. Industrial 

groundwater use in Jefferson County in 2010 was 35.35 

Mgal/d, a 17-percent decrease from 2005 (table 11). In 

Jefferson County, 80 to 95 percent of groundwater comes from 

the Sparta aquifer and the remainder from the Mississippi 

River Valley alluvial aquifer. Industrial growth in Jefferson 

County has been centered in Pine Bluff. 

Union County has several industrial facilities that 

withdraw groundwater from the Sparta aquifer, with 

chemical and oil companies as the larger users. In response 

to decreasing water levels in the Sparta aquifer, multiple 

conservation measures were initiated to reduce reliance 

on groundwater. For example, a nationally recognized 

conservation effort was initiated in Union County involving 

the Union County Water Conservation Board, local industries, 

businesses, community leaders, ANRC, and USGS. As a 

result, Union County decreased its use of groundwater, which 

resulted in rising groundwater levels in the Sparta aquifer (see 

“Sparta Aquifer” section for further information). 

The Cockfield aquifer is the primary source of water for 

pulp and sawmilling industries in Ashley County. The Wilcox 

aquifer is tapped in Mississippi and Greene Counties for 

various industrial processing including plastic, fertilizer, and 

steel production, among others. Smaller withdrawals are made 

from the Ozark, Tokio, Nacatoch, and other aquifers within the 

State for numerous local industries.

Reporting changes were a main factor in the trends in 

use for the industrial category. Industrial groundwater use 

peaked in 1955 (table 6), but use may have been greater in 

1960; Jefferson County, the county with the most industrial 

groundwater use, was not reported (tables 6 and 11). If the 

industrial use for Pine Bluff (Jefferson County) in 1958 that 

was reported by Bedinger and others (1960) as 33.55 Mgal/d 

had been included, then total use for the State would have 

been estimated at 135 Mgal/d. Industrial use decreased by 

about 45 percent from 1960 to 1965 because use in Ashley 

County fell from 28.24 to 7.47 Mgal/d after the construction 

of a lake to supply a paper company with water (Encyclopedia 

of Arkansas, 2013; U.S. Army Corps of Engineers, 2013a). 

Statewide use increased 55 percent from 1965 to 1970 to 

114.6 Mgal/d. After commercial and mining categories were 

separated from the industrial category in 1985, industrial 

use decreased to 64.01 Mgal/d. Use again increased by 

approximately 35–40 Mgal/d in 1990 and 1995 because 

of another change in reporting; public-supply deliveries to 

industry were included in this category from 1985 to 1995. (In 

1985, changes in reporting to ARWUDBS were assumed to 

counteract increases in use because of the additional publicsupply deliveries to industry.) Industrial groundwater use has 

stabilized between 60 and 70 Mgal/d since 2000. 
Overview of Aquifers of Arkansas 43

Table 11. Groundwater use for industrial supply by counties and years in Arkansas.—Continued

[Counties shown are only those with published data. Commercial and mining categories were lumped into the industrial category prior to 1985. Data from 

Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and Hall (1986); Holland (1981, 1987, 1993, 1999, 2004, 2007). 

Units are million gallons per day]

County 1960 1965 1970 1975 1980 1982 1985 1990 1995 2000 2005 2010

Arkansas 8.86 0.00 0.05 0.01 0.09 0.10 0.02 0.00 0.00 0.00 0.00 0.00

Ashley 28.24 7.47 9.21 10.67 10.03 10.04 9.96 3.80 7.50 8.73 6.20 8.40

Baxter 0.01 0.07 0.25 0.28 0.14 0.23 0.08 0.00 0.00 0.00 0.61 0.00

Benton 2.10 0.11 0.30 0.70 0.15 0.08 0.08 0.00 0.00 0.00 0.00 0.06

Boone 0.00 0.01 1.65 0.00 0.05 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Bradley 0.20 0.38 0.53 0.53 0.45 0.44 0.44 0.00 0.00 0.37 0.46 0.52

Calhoun 0.00 0.03 0.00 0.21 0.51 0.37 0.01 0.00 0.00 0.06 0.00 0.01

Carroll 0.01 0.00 0.01 0.01 0.05 0.02 0.00 0.00 0.00 0.00 0.00 0.00

Chicot 0.01 0.02 0.01 0.03 0.45 0.03 0.02 0.00 0.00 0.00 0.00 0.00

Clark 0.00 0.05 0.24 0.12 0.51 0.19 0.05 0.00 0.54 0.23 0.27 0.14

Clay 0.62 0.00 0.00 0.01 0.70 0.04 0.00 0.00 0.00 0.00 0.00 0.00

Cleburne 0.01 0.04 0.12 0.09 0.13 0.22 0.01 0.00 0.00 0.00 0.00 0.00

Cleveland 0.36 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Columbia 0.17 1.12 3.17 3.23 2.87 2.97 3.17 1.63 1.55 2.05 2.08 7.94

Conway 0.22 0.02 5.40 5.02 0.06 0.03 0.01 0.00 0.00 0.00 0.00 0.00

Craighead 0.68 0.19 0.72 0.30 0.46 0.10 0.00 0.00 0.00 0.00 0.00 0.00

Crawford 0.78 0.00 0.01 0.00 0.03 0.03 0.03 0.00 0.00 0.00 0.00 0.00

Crittenden 0.19 0.07 0.05 0.01 0.17 0.02 0.00 0.11 0.20 0.19 0.30 0.24

Cross 1.05 0.00 1.22 1.60 0.30 0.33 0.25 0.00 0.00 0.17 0.40 0.41

Dallas 0.01 0.00 0.00 0.06 0.14 0.14 0.13 0.00 0.00 0.00 0.00 0.00

Desha 1.70 0.00 0.01 0.03 0.97 0.88 1.98 1.69 6.14 2.92 3.19 3.24

Drew 0.23 0.13 0.20 0.01 0.01 0.04 0.00 0.00 0.00 0.00 0.00 0.00

Faulkner 0.10 0.00 0.01 0.00 0.03 0.07 0.00 0.00 0.00 0.00 0.00 0.00

Franklin 0.04 0.00 0.07 0.19 0.19 0.15 0.06 0.00 0.00 0.00 0.00 0.00

Fulton 1.30 0.00 0.00 0.00 0.02 0.01 0.00 0.00 0.00 0.00 0.00 0.00

Garland 0.36 0.34 0.35 0.74 0.51 0.59 0.40 0.25 0.00 0.03 0.06 0.00

Grant 0.42 0.00 0.11 0.10 0.07 0.04 0.07 0.08 0.00 0.23 0.15 0.26

Greene 0.14 0.12 0.15 0.45 0.17 0.13 0.01 0.00 0.37 0.29 0.00 0.11

Hempstead 0.00 0.01 0.04 0.01 0.01 0.02 0.00 0.00 0.00 0.00 0.00 0.00

Hot Spring 0.35 0.08 0.62 0.15 0.22 0.11 0.02 0.21 0.14 0.01 0.00 0.00

Howard 0.00 0.27 0.35 0.72 0.49 0.26 0.00 0.00 0.00 0.00 0.00 0.00

Independence 0.25 0.00 0.03 0.04 0.09 0.13 0.02 0.00 0.00 0.00 0.00 0.00

Izard 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.00

Jackson 1.26 1.01 0.41 2.06 0.79 0.74 0.74 0.00 0.00 0.00 0.00 0.18

Jefferson --1 38.96 51.23 44.83 45.45 39.79 30.09 84.65 75.56 37.13 42.54 35.35

Johnson 0.22 0.01 0.02 0.03 0.10 0.08 0.05 0.00 0.00 0.00 0.00 0.00

Lafayette 2.24 0.56 0.71 0.20 0.19 0.20 0.14 0.00 0.00 0.00 0.00 0.01

Lawrence 1.00 0.00 0.00 0.01 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.00

Lee 0.16 0.02 0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Table 11. Groundwater use for industrial supply by counties and years in Arkansas. 

[Counties shown are only those with published data. Commercial and mining categories were lumped into the industrial category prior to 1985. Data from 

Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and Hall (1986); Holland (1981, 1987, 1993, 1999, 2004, 2007). 

Units are million gallons per day]
44 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Table 11. Groundwater use for industrial supply by counties and years in Arkansas.—Continued

[Counties shown are only those with published data. Commercial and mining categories were lumped into the industrial category prior to 1985. Data from 

Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and Hall (1986); Holland (1981, 1987, 1993, 1999, 2004, 2007). 

Units are million gallons per day]

County 1960 1965 1970 1975 1980 1982 1985 1990 1995 2000 2005 2010

Lincoln 0.61 0.03 0.19 0.34 0.40 0.38 0.00 0.00 0.00 0.00 0.00 0.00

Little River 0.03 0.34 1.41 1.28 0.47 0.25 0.27 0.00 0.00 0.24 0.24 0.00

Logan 0.00 0.01 0.16 0.01 0.04 0.05 0.03 0.00 0.00 0.00 0.00 0.00

Lonoke 5.92 0.00 0.82 0.52 1.28 1.09 1.08 0.00 0.97 0.81 0.59 0.74

Madison 0.00 0.00 0.01 0.00 0.01 0.04 0.01 0.00 0.00 0.00 0.00 0.00

Marion 0.07 0.07 0.04 0.08 0.22 0.19 0.00 0.00 0.00 0.00 0.00 0.00

Miller 0.05 0.08 0.40 0.21 0.23 0.19 0.16 0.00 0.00 0.00 0.00 0.14

Mississippi 0.88 2.88 6.96 7.33 3.80 4.39 1.73 2.75 7.65 2.66 2.16 1.67

Monroe 1.11 0.01 0.00 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Montgomery 0.00 0.05 0.06 0.06 0.10 0.11 0.01 0.00 0.00 0.00 0.00 0.00

Nevada 0.00 0.00 0.39 0.13 0.04 0.04 0.03 0.00 0.00 0.01 0.17 0.00

Newton 0.00 0.00 0.04 0.12 0.17 0.12 0.12 0.00 0.00 0.00 0.00 0.00

Ouachita --1 1.75 5.94 2.84 2.64 2.49 2.26 0.00 0.79 0.81 0.00 0.00

Perry 0.02 0.00 0.03 0.02 0.02 0.09 0.00 0.00 0.00 0.00 0.00 0.00

Phillips 0.13 1.19 5.37 5.07 2.44 2.36 2.36 0.00 0.01 0.00 0.00 0.00

Pike 0.24 0.07 0.12 0.15 0.27 0.12 0.00 0.00 0.00 0.00 0.00 0.00

Poinsett 0.47 0.00 0.29 0.35 0.43 0.21 0.14 0.00 0.00 0.11 0.00 0.00

Polk 0.25 0.33 0.10 0.33 0.03 0.03 0.01 0.00 0.00 0.00 0.00 0.00

Pope 0.52 0.05 0.02 0.04 0.47 0.23 0.04 0.00 0.00 0.00 0.00 0.00

Prairie 1.09 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Pulaski 6.73 0.00 0.00 0.74 0.71 0.99 0.52 0.00 0.00 0.00 0.00 0.00

Randolph 0.00 0.02 0.01 0.01 0.01 0.02 0.01 0.00 0.00 0.00 0.00 0.00

Saline 0.00 0.01 0.01 0.18 0.27 0.07 0.00 0.00 0.00 0.00 0.00 0.00

Scott 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.00

Searcy 0.09 0.00 0.00 0.00 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.00

Sebastian 0.00 0.00 0.05 0.04 0.05 0.05 0.04 0.00 0.00 0.00 0.00 0.00

Sevier 0.22 0.00 0.00 0.00 0.12 0.12 0.05 1.03 0.00 0.00 0.00 0.00

Sharp 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.66 0.00 0.00

St. Francis 0.55 0.68 0.30 0.37 0.31 0.11 0.01 0.00 0.00 0.07 0.00 0.00

Stone 0.00 0.01 0.01 0.03 0.05 0.02 0.01 0.00 0.00 0.00 0.00 0.00

Union 28.62 15.12 14.38 12.47 8.20 9.64 6.02 2.72 6.41 9.23 6.33 1.75

Van Buren 0.01 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Washington 0.00 0.00 0.01 0.02 0.03 0.04 0.07 0.00 0.00 0.00 0.00 0.00

White 0.15 0.04 0.05 0.05 0.04 0.03 0.01 0.00 0.00 0.04 0.00 0.00

Woodruff 0.66 0.02 0.13 0.03 0.02 0.00 0.00 0.00 0.12 0.00 0.00 0.00

Yell 0.04 0.03 0.03 0.46 1.26 0.89 1.14 0.00 0.00 0.02 0.00 0.00

Total 101.75 73.88 114.60 105.76 90.83 82.99 64.01 98.92 107.95 67.07 65.75 61.17

1

Data not reported from Jefferson and Ouachita Counties in 1960.
Overview of Aquifers of Arkansas 45

Mining

Water use in the mining category is defined as water used 

for coal, sand, and gravel operations, and additionally includes 

saline withdrawals from oil and natural gas wells. Water use in 

this category dominantly is for drilling and washing processes 

associated with mining operations. Prior to the development of 

the ARWUDBS in the 1980s, water-use estimates for mining 

operations were obtained from the Arkansas Geological 

Commission (now Arkansas Geological Survey) and were 

included in the industrial category. 

Groundwater use for mining has been minimal in 

Arkansas with maximum use in 1990 of 1.82 Mgal/d 

(table 12); use for any one county has not been more than 

0.5 Mgal/d. Use for this category has averaged 0.21 Mgal/d 

since 2000. Users in Polk County (0.07 Mgal/d) withdrew 

the most groundwater for mining purposes in 2010. Recently, 

Arkansas has seen an increase in natural gas development 

in the Fayetteville Shale; however, most water use for this 

development has been from surface-water sources (Terrance 

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

Table 12. Groundwater use for mining supply by counties and years in Arkansas. 

[Counties shown are only those with published data. Data from Holland (1987, 1993, 1999, 2004, 2007). Units are million gallons per day]

County 1985 1990 1995 2000 2005 2010

Ashley 0.00 0.18 0.00 0.00 0.00 0.00

Benton 0.01 0.00 0.00 0.04 0.00 0.02

Calhoun 0.00 0.18 0.00 0.00 0.00 0.00

Clark 0.01 0.00 0.00 0.00 0.00 0.00

Conway 0.00 0.00 0.00 0.02 0.00 0.00

Craighead 0.00 0.18 0.00 0.06 0.08 0.02

Crittenden 0.02 0.02 0.00 0.00 0.00 0.00

Cross 0.00 0.18 0.00 0.00 0.00 0.00

Desha 0.03 0.00 0.00 0.00 0.00 0.00

Franklin 0.05 0.00 0.00 0.00 0.00 0.00

Garland 0.01 0.00 0.00 0.00 0.00 0.00

Greene 0.00 0.00 0.00 0.02 0.07 0.02

Hempstead 0.02 0.02 0.00 0.00 0.00 0.00

Hot Spring 0.01 0.02 0.00 0.00 0.00 0.00

Howard 0.46 0.00 0.00 0.00 0.00 0.00

Independence 0.02 0.00 0.00 0.00 0.00 0.00

Izard 0.01 0.02 0.00 0.00 0.00 0.00

Jackson 0.00 0.18 0.00 0.00 0.00 0.00

Jefferson 0.00 0.00 0.00 0.00 0.01 0.01

Johnson 0.05 0.00 0.00 0.00 0.00 0.00

Little River 0.25 0.05 0.00 0.00 0.00 0.00

Logan 0.00 0.01 0.00 0.00 0.00 0.00

Lonoke 0.00 0.02 0.00 0.00 0.00 0.00

Miller 0.02 0.18 0.00 0.00 0.00 0.00

Poinsett 0.00 0.18 0.00 0.06 0.08 0.04

Polk 0.00 0.00 0.00 0.00 0.00 0.07

Pope 0.01 0.18 0.00 0.00 0.00 0.00

Randolph 0.00 0.00 0.00 0.01 0.00 0.00

Saline 0.01 0.00 0.00 0.00 0.00 0.00

Sebastian 0.03 0.22 0.00 0.00 0.00 0.00

White 0.01 0.00 0.00 0.00 0.00 0.00

Total 1.03 1.82 0.00 0.21 0.24 0.18
46 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Aquaculture (Fish and Minnow Farming)

The aquaculture category represents water use associated 

with fish hatcheries and the farming of aquatic organisms 

including fish, shellfish, and algae. In reports from 1965 to 

1980, withdrawals in this category were reported as “fish and 

minnow farming.” This included the National Fish Hatcheries 

in Baxter, Clay (now a State hatchery), Cleburne, and Fulton 

Counties. Water use at trout hatcheries was considered 

negligible in 1980 and thus was not reported (tables 6 and 

13). In 1990 and 1995, fish hatcheries were included in the 

commercial category. Fish-hatchery water use has been 

included in the aquaculture category since 2000. From 

1965 to 1985, water-use data for aquaculture were derived 

by multiplying aquaculture acreage by an application rate. 

Application rates were developed by the Arkansas Game and 

Fish Commission, the USDA Soil Conservation Service (now 

the USDA Natural Resources Conservation Service), and 

the U.S. Bureau of Sport Fisheries and Wildlife at Stuttgart 

(Halberg and Stephens, 1966; Halberg, 1972, 1977; Holland, 

1981). Catfish and minnow ponds use an application rate of 

7–8.9 acre-ft, and rough ponds as well as fishing ponds use 

a 3-acre-ft application rate. After 1985, water use for fish 

farming was reported and registered in ARWUDBS.

Aquaculture is an important industry in Arkansas. 

Multiple counties in southeastern Arkansas began aquaculture 

in the 1960s (Broom and Reed, 1973; Kaliba and Engle, 

2006). Goldfish farming reportedly began in Lonoke County 

as early as the 1940s (Engle, 2012). Arkansas leads the 

Nation in the production of baitfish (Kaliba and Engle, 2006; 

Stone and Selden, 2006), and the world’s largest producer of 

baitfish is located in Lonoke County. Other commonly grown 

aquaculture crops are bass, carp, catfish, crayfish, and koi. Fish 

commonly are raised in large ponds surrounded by earthen 

berms filled with groundwater. Approximately 98 percent of 

all withdrawals for aquaculture are from the Mississippi River 

Valley alluvial aquifer (Terrance W. Holland, U.S. Geological 

Survey, written commun., 2013). Some aquaculture wells in 

Chicot County reach the Cockfield aquifer, whereas wells in 

Arkansas and Lonoke County are completed in the Sparta 

aquifer. Historically, trout production was of local importance 

in the Ozark Plateaus of northern Arkansas. Trout require very 

high-quality, low-temperature water. Springs of the Springfield 

Plateau and Ozark aquifers provide an abundant source of 

suitable water, and hundreds of trout farms have operated in 

Arkansas over the years. Lower market prices and problems 

of nutrient enrichment and sediment—associated with poultry 

and livestock production and development (Adamski and 

others, 1995)—have forced many of the trout farms to close. 

Currently (2013), only two large trout farms are known to be 

active, one north of Harrison (Boone County) and one near 

Yellville (Marion County).

Table 13. Groundwater use for aquaculture supply by counties and years in Arkansas.—Continued 

[Counties shown are only those with published data. Data for 1985 were combined with the livestock category and are not shown. Data from Halberg and 

Stephens (1966); Halberg (1972, 1977); Holland and Hall (1986); Holland (1981, 1993, 1999, 2004, 2007). Units are million gallons per day]

County 1965 1970 1975 1980 1982 1990 1995 2000 2005 2010

Arkansas 2.70 3.86 3.81 12.05 10.09 0.76 23.34 8.88 8.26 0.64

Ashley 0.27 6.55 5.46 8.33 6.75 2.75 13.80 0.00 22.91 8.82

Baxter 0.01 0.07 0.05 0.00 0.50 0.00 0.00 0.00 0.00 0.00

Benton 0.77 0.91 5.54 0.61 0.50 0.20 0.36 0.00 0.07 0.00

Boone 0.03 0.05 1.87 0.11 0.09 0.00 0.00 0.00 0.00 0.00

Bradley 0.34 0.21 0.07 0.07 0.07 0.00 0.00 0.00 0.00 0.00

Chicot 0.00 3.48 3.54 4.34 3.56 12.89 32.42 44.67 56.79 46.78

Clark 0.00 0.01 0.00 1.34 1.09 0.00 0.00 0.00 0.00 0.00

Clay 1.94 0.13 0.64 1.37 1.11 0.95 0.77 0.00 1.52 0.92

Cleburne 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Cleveland 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Columbia 0.00 0.29 0.17 1.10 0.89 0.00 0.00 0.00 0.00 0.00

Conway 0.80 1.16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Craighead 0.64 0.75 0.32 0.15 0.13 0.23 0.05 1.23 0.16 0.23

Crawford 0.00 0.15 0.06 0.02 0.02 0.00 0.00 0.00 0.00 0.00

Crittenden 0.30 0.98 1.21 4.13 3.37 0.00 0.00 0.07 1.50 0.82

Cross 0.49 2.51 1.68 3.43 2.80 0.55 0.82 0.00 0.02 0.02

Dallas 0.00 0.19 0.47 0.14 0.12 0.00 0.00 0.00 0.00 0.00

Desha 6.01 11.82 11.26 14.15 11.49 3.30 12.63 12.83 9.67 10.68

Drew 1.14 8.53 9.54 1.11 0.91 0.31 0.79 0.98 0.03 0.29

Faulkner 0.00 1.84 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Table 13. Groundwater use for aquaculture supply by counties and years in Arkansas. 

[Counties shown are only those with published data. Data for 1985 were combined with the livestock category and are not shown. Data from Halberg and 

Stephens (1966); Halberg (1972, 1977); Holland and Hall (1986); Holland (1981, 1993, 1999, 2004, 2007). Units are million gallons per day]
Overview of Aquifers of Arkansas 47

Table 13. Groundwater use for aquaculture supply by counties and years in Arkansas.—Continued 

[Counties shown are only those with published data. Data for 1985 were combined with the livestock category and are not shown. Data from Halberg and 

Stephens (1966); Halberg (1972, 1977); Holland and Hall (1986); Holland (1981, 1993, 1999, 2004, 2007). Units are million gallons per day]

County 1965 1970 1975 1980 1982 1990 1995 2000 2005 2010

Franklin 0.14 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Fulton 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.13 0.00

Garland 0.00 0.33 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Grant 0.06 0.26 0.13 0.17 0.14 0.00 0.00 0.00 0.00 0.00

Greene 2.42 6.48 4.65 7.92 6.42 11.96 0.00 0.02 12.91 12.42

Hempstead 0.21 0.25 0.00 0.02 0.02 0.00 0.00 0.00 0.00 0.00

Hot Spring 0.12 1.84 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Howard 0.00 0.11 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Independence 0.00 0.94 0.15 0.10 0.08 0.00 0.00 0.00 0.00 0.00

Izard 0.00 0.01 0.00 0.05 0.04 0.00 0.00 0.00 0.00 0.00

Jackson 5.72 7.28 7.11 3.40 2.76 1.95 6.61 1.74 3.40 2.20

Jefferson 0.22 5.33 5.33 7.24 6.25 3.00 7.36 4.65 2.03 0.25

Johnson 0.18 0.00 0.00 0.03 0.03 0.00 0.00 0.00 0.00 0.00

Lafayette 0.62 0.92 0.61 0.65 0.53 0.00 1.52 0.02 4.49 3.28

Lawrence 1.03 4.58 4.52 1.30 1.06 0.17 0.06 0.00 0.26 0.00

Lee 0.00 0.37 0.33 0.27 0.27 0.74 4.70 0.14 3.64 3.86

Lincoln 2.19 17.31 13.01 1.22 1.04 2.48 2.92 0.00 3.89 1.07

Little River 0.00 0.06 0.03 0.00 0.00 0.00 0.00 0.01 0.00 0.00

Logan 0.00 0.29 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Lonoke 53.66 70.33 95.15 123.04 102.56 32.31 66.63 57.36 56.60 41.44

Madison 0.21 0.19 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Marion 0.03 0.00 3.46 3.97 3.21 0.00 0.00 0.00 0.00 0.00

Miller 0.00 0.29 0.29 0.40 0.32 0.02 0.45 0.00 0.35 0.00

Mississippi 0.00 1.19 0.94 2.50 2.02 0.00 0.00 0.08 0.98 0.84

Monroe 2.87 6.05 6.70 39.80 33.15 3.96 0.00 0.00 13.38 13.80

Montgomery 0.00 0.09 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Newton 0.03 0.01 1.73 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Ouachita 0.00 0.28 0.10 0.04 0.03 0.00 0.00 0.00 0.00 0.00

Perry 0.00 1.71 0.25 0.00 0.00 0.03 0.00 0.00 0.00 0.00

Phillips 0.41 1.37 0.26 0.04 0.04 0.02 0.00 2.80 0.02 0.05

Pike 0.00 0.08 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00

Poinsett 0.35 1.59 0.96 3.24 2.66 5.59 11.51 0.17 4.72 2.78

Polk 0.21 0.22 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Pope 0.00 0.30 0.00 0.00 0.00 0.05 0.00 0.00 0.00 0.00

Prairie 8.44 21.43 21.14 29.30 24.86 12.83 33.21 42.87 32.89 29.12

Pulaski 0.92 2.76 2.09 1.25 1.05 0.24 0.48 0.17 0.09 0.05

Randolph 0.00 0.48 0.27 0.44 0.35 0.05 0.01 0.00 0.00 0.00

Saline 1.07 0.29 0.08 0.10 0.08 0.00 0.00 0.00 0.00 0.00

Scott 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Sebastian 0.21 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Sevier 0.04 0.07 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Sharp 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

St. Francis 0.42 2.82 1.46 0.45 0.40 0.01 3.47 2.80 2.33 0.57

Stone 0.00 0.01 0.04 0.02 0.02 0.00 0.00 0.00 0.00 0.00

Union 0.00 0.03 0.00 0.10 0.08 0.00 0.00 0.00 0.00 0.00

Washington 0.26 0.17 3.46 3.97 3.21 0.00 0.00 0.00 0.00 0.00

White 1.04 2.56 2.69 0.85 0.76 0.40 1.03 1.19 0.27 0.21

Woodruff 4.94 7.03 7.02 0.55 0.61 0.78 3.31 4.67 2.50 0.00

Yell 0.00 0.91 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Total 103.50 212.18 229.65 284.88 237.54 98.53 228.25 187.35 245.82 181.14
48 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Aquaculture was the second largest category of water use 

in Arkansas in 2010 (table 6). Because data for aquaculture 

were combined with data for livestock for 1985, aquaculture 

groundwater use for the State in 1985 was assumed to be 

approximately 220 Mgal/d. Reports for 1990 and 1995 also 

included fish farming in the livestock category (Holland, 

1993, 1999); data for 1990 and 1995 shown in table 6 were 

extracted from ARWUDBS instead of the published 5-year 

reports (Terrance W. Holland, U.S. Geological Survey, written 

commun., 2012).

Statewide, the peak of groundwater use for aquaculture 

occurred in 1980 at 284.88 Mgal/d. Lonoke or Chicot Counties 

generally have had the greatest withdrawals with 41.44 and 

46.78 Mgal/d, respectively, being used in 2010 (table 13). At 

times, production in the State has been limited because of a 

lack of fish processing facilities; increases in water-use rates 

were seen after the installation of fish processing facilities. In 

Chicot County, increases in water-use rates for aquaculture 

were noted in 1980 and again in 1990 after two catfish 

processing facilities were constructed (Kaliba and Engle, 

2006). Aquaculture production rates, and thus water use, since 

have declined because of foreign imports of catfish and other 

species (Stone and Selden, 1991). 

Duck Hunting (Wildlife Impoundments)

Withdrawals for duck hunting provide habitat for 

migratory waterfowl. Duck hunters, particularly in the 

Grand Prairie region, withdraw water to provide habitat for 

migrating ducks. This category was reported as “Wildlife 

Impoundments” from 1965 to 1980 (table 6). Withdrawals for 

this practice were reported in the irrigation category from 1985 

to 2003, and the “Duck Hunting” category was reinstated for 

the 2005 compilation (Terrance W. Holland, U.S. Geological 

Survey, written commun., 2012). Accounting for this water 

use is extremely important because duck hunting occurs in the 

winter when recharge to the aquifers is the greatest (Holland, 

2007).

The expansion of duck hunting was coincidental with 

increased rice agriculture in eastern and southern Arkansas. 

Reports of the area being good for commercial game hunters 

began around the 1920s. Cleared rice fields provide food, 

water, and a natural wintering habitat for migratory waterfowl 

in an area close to the Mississippi Flyway (a migratory flight 

pattern for birds flying south from Canada and the northern 

States). Duck (hunting) clubs have formed in many areas, and 

fallow cropland is flooded with water from irrigation wells 

to provide habitat to attract ducks. Approximately 22 percent 

of rice fields are flooded for migratory bird habitat following 

the rice harvest (Wilson and Branson, 2002). Arkansas, 

particularly in the Grand Prairie region, is an international 

duck hunting destination, and many farmers supplement 

income from growing crops by leasing land for duck hunting 

(Bowman and Wright, 1999). 

The majority of water used for duck hunting has been 

withdrawn from the Mississippi River Valley alluvial aquifer; 

however, in the Grand Prairie region, groundwater is now 

being removed from the Sparta aquifer to flood fields for 

hunting with 1–2 percent of the water used statewide for duck 

hunting being withdrawn from the Sparta aquifer (Terrance 

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

2013). Groundwater use for this category has increased 

approximately 166 percent from 1965 to 2010 (table 14). Most 

groundwater withdrawn for duck hunting was in the Grand 

Prairie region, and Arkansas County reported the most water 

used for this category in 2005 and 2010. 

Livestock 

The livestock water-use category includes water 

consumed by stock and poultry including feedlots, dairy 

farming, and other needs in the production of animal crops. 

The amount of water used generally falls beneath the reporting 

threshold, so only a small amount of livestock use is reported 

to ARWUDBS. Most use in this category is estimated by 

multiplying the water requirements of a type of animal 

(for example dairy cows, hogs, poultry) by the livestock 

production values from the USDA. More information on this 

calculation can be found in Holland (2007).

In 1985, this category was called Agriculture (nonirrigation). Groundwater use reported for this category was 

erroneously high in 1985 (table 6) because the national 

USGS water-use reporting program combined the categories 

of aquaculture and livestock. Livestock use for 1985 was 

assumed to be similar to that in 1982 and 1990, between 21 

and 26 Mgal/d. The 1990 and 1995 reports also included 

fish farming in the livestock category (Holland, 1993, 1999); 

however, data for 1990 and 1995 shown in table 15 were 

extracted from ARWUDBS (Terrance W. Holland, U.S. 

Geological Survey, written commun., 2012).

All counties have reported groundwater use for livestock 

(table 15). Nationally, Arkansas produced the second most 

broilers (chickens), the fourth most turkeys, and the tenth 

most eggs in 2012 (University of Arkansas Division of 

Agriculture, 2013). The poultry industry primarily is located in 

northwestern Arkansas, the location for many national poultry 

producers. Benton and Washington Counties were the largest 

groundwater users for livestock (excluding data in 1985). 

Groundwater use for livestock has remained relatively stable 

since 1995, at around 15 Mgal/d, until a change in reporting 

in 2010 caused increased usage in Lee, Lonoke, Mississippi, 

Poinsett, and White Counties.
Overview of Aquifers of Arkansas 49

Table 14. Groundwater use for wildlife impoundments (1965–80) and duck hunting (2005–10) supply by counties and years in Arkansas. 

[Counties shown are only those with published data. Data from Halberg and Stephens (1966); Halberg (1972, 1977); Holland (1981, 2007). Units are million 

gallons per day]

County 1965 1970 1975 1980 2005 2010

Arkansas 0.08 0.08 0.04 0.00 24.67 22.84

Baxter 0.05 0.00 0.00 0.00 0.00 0.00

Clay 0.15 0.00 0.00 0.00 0.00 0.00

Crittenden 0.00 0.00 0.00 0.00 0.12 0.84

Cross 0.00 0.00 0.00 0.00 0.00 0.21

Dallas 0.00 0.00 0.25 0.00 0.31 0.00

Desha 0.00 0.00 0.00 0.00 4.91 1.68

Drew 0.00 0.00 0.00 0.00 0.20 0.40

Independence 0.00 0.00 0.00 0.00 0.02 0.00

Jackson 0.00 0.00 0.00 0.00 8.18 3.79

Jefferson 0.00 0.00 0.00 0.00 5.14 4.55

Lafayette 0.00 0.00 0.00 0.00 4.62 2.83

Lawrence 0.00 0.00 0.00 0.00 0.22 0.00

Lee 0.00 0.00 0.00 0.00 7.42 7.90

Lincoln 0.00 0.00 0.00 0.00 0.03 0.00

Little River 0.00 0.00 0.00 0.00 0.00 0.02

Lonoke 0.00 0.00 0.00 0.00 3.65 2.68

Miller 0.00 0.00 0.00 0.00 5.00 2.40

Mississippi 0.01 0.01 0.01 0.00 0.00 0.00

Monroe 0.00 0.00 0.00 0.00 5.54 18.90

Phillips 0.00 0.00 0.00 0.00 0.04 0.02

Poinsett 0.00 0.00 0.00 5.36 0.75 2.86

Pope 0.19 0.19 0.96 0.00 0.00 0.00

Prairie 0.00 0.00 0.00 0.00 1.01 2.35

Pulaski 0.00 0.00 0.00 0.00 0.80 0.43

Randolph 0.00 0.00 0.00 0.00 0.00 0.26

St. Francis 0.00 0.00 0.00 0.00 2.68 4.99

White 0.00 0.00 0.00 0.00 4.88 0.00

Woodruff 0.00 0.00 0.00 0.00 0.95 0.48

Total 0.48 0.28 1.26 5.36 81.14 80.43
50 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Table 15. Groundwater use for livestock supply by counties and years in Arkansas.—Continued

[Counties shown are only those with published data. Data from Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and 

Hall (1986); Holland (1981, 1987, 1993, 1999, 2004, 2007). Units are million gallons per day]

County 1960 1965 1970 1975 1980 1982 1985 1990 1995 2000 2005 2010

Arkansas 0.15 0.11 0.08 0.16 0.08 0.03 3.67 0.01 0.03 0.03 0.02 0.66

Ashley 0.19 0.11 0.10 0.22 0.09 0.05 5.27 0.08 0.04 0.04 0.03 0.03

Baxter 0.14 0.05 0.05 0.26 0.07 0.07 0.14 0.07 0.14 0.14 0.15 0.14

Benton 1.42 1.06 1.38 2.04 2.10 1.82 3.00 2.02 0.98 1.03 1.12 0.98

Boone 0.13 0.11 0.65 0.66 0.16 0.16 0.31 0.22 0.46 0.46 0.54 0.48

Bradley 0.09 0.06 0.37 0.18 0.13 0.14 0.28 0.12 0.05 0.05 0.05 0.05

Calhoun 0.08 0.04 0.06 0.08 0.04 0.04 0.02 0.02 0.04 0.04 0.02 0.01

Carroll 0.38 0.21 0.31 0.69 0.20 0.29 0.32 0.42 0.58 0.58 0.68 0.67

Chicot 0.47 0.18 0.21 0.39 0.12 0.06 3.59 0.07 0.06 0.06 0.04 0.09

Clark 0.20 0.16 0.21 0.34 0.17 0.14 1.15 0.16 0.13 0.13 0.10 0.09

Clay 0.12 0.14 0.20 0.27 0.12 0.09 1.18 0.11 0.04 0.04 0.06 0.09

Cleburne 0.12 0.15 0.24 0.39 0.56 0.54 0.52 0.67 0.95 0.95 0.24 0.24

Cleveland 0.22 0.08 0.12 0.14 0.15 0.14 0.19 0.32 0.10 0.11 0.12 0.16

Columbia 0.19 0.12 0.18 0.39 0.31 0.21 1.14 0.24 0.12 0.12 0.12 0.12

Conway 0.24 0.23 0.24 0.49 0.54 0.51 0.59 0.56 0.33 0.33 0.39 0.46

Craighead 0.28 0.14 0.14 0.17 0.12 0.12 0.21 0.07 0.05 0.05 0.05 0.08

Crawford 0.20 0.18 0.27 0.36 0.46 0.45 0.46 0.45 0.25 0.25 0.24 0.21

Crittenden 0.21 0.10 0.08 0.07 0.06 0.02 3.38 0.02 0.01 0.01 0.00 0.06

Cross 0.21 0.17 0.14 0.16 0.13 0.08 2.89 0.07 0.04 0.04 0.03 0.94

Dallas 0.08 0.05 0.06 0.08 0.04 0.04 0.14 0.04 0.04 0.04 0.02 0.02

Desha 0.37 0.10 0.08 0.23 0.07 0.06 21.62 0.04 0.04 0.04 0.02 0.01

Drew 0.19 0.12 0.12 0.35 0.11 0.10 1.00 0.28 0.08 0.08 0.07 0.13

Faulkner 0.23 0.27 0.29 0.50 0.31 0.38 0.38 0.38 0.37 0.37 0.30 0.24

Franklin 0.22 0.24 0.31 0.54 0.25 0.56 0.54 0.67 0.36 0.36 0.40 0.37

Fulton 0.10 0.06 0.06 0.39 0.11 0.13 0.08 0.15 0.25 0.25 0.33 0.34

Garland 0.16 0.12 0.10 0.13 0.08 0.13 0.08 0.06 0.10 0.10 0.06 0.05

Grant 0.09 0.06 0.07 0.12 0.09 0.08 0.23 0.06 0.08 0.08 0.07 0.13

Greene 0.06 0.18 0.19 0.23 0.27 0.10 7.67 0.12 0.06 0.06 0.06 0.56

Hempstead 0.43 0.33 0.53 0.83 0.77 0.73 0.76 0.99 0.38 0.38 0.58 0.55

Hot Spring 0.17 0.15 0.15 0.19 0.11 0.15 0.11 0.00 0.12 0.12 0.11 0.11

Howard 0.45 0.28 0.40 0.68 0.91 0.80 0.89 0.98 0.34 0.33 0.44 0.54

Independence 0.68 0.21 0.27 0.65 0.21 0.39 0.39 0.37 0.31 0.31 0.35 0.53

Izard 0.15 0.07 0.10 0.29 0.12 0.12 0.15 0.13 0.22 0.22 0.24 0.21

Jackson 0.12 0.10 0.10 0.21 0.14 0.05 2.80 0.06 0.03 0.03 0.02 0.05

Jefferson --1 0.10 0.14 0.24 0.12 0.10 6.33 0.08 0.04 0.04 0.04 0.05

Johnson 0.30 0.17 0.20 0.35 0.34 0.32 0.44 0.55 0.26 0.25 0.29 0.29

Lafayette 0.14 0.12 0.21 0.36 0.31 0.33 0.92 0.51 0.23 0.23 0.26 0.22

Lawrence 0.07 0.05 0.05 0.25 0.06 0.06 1.10 0.22 0.14 0.14 0.17 0.14

Table 15. Groundwater use for livestock supply by counties and years in Arkansas. 

[Counties shown are only those with published data. Data from Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and 

Hall (1986); Holland (1981, 1987, 1993, 1999, 2004, 2007). Units are million gallons per day]
Overview of Aquifers of Arkansas 51

Table 15. Groundwater use for livestock supply by counties and years in Arkansas.—Continued

[Counties shown are only those with published data. Data from Stephens and Halberg (1961); Halberg and Stephens (1966); Halberg (1972, 1977); Holland and 

Hall (1986); Holland (1981, 1987, 1993, 1999, 2004, 2007). Units are million gallons per day]

County 1960 1965 1970 1975 1980 1982 1985 1990 1995 2000 2005 2010

Lee 0.30 0.18 0.13 0.23 0.12 0.06 0.30 0.04 0.02 0.02 0.02 1.21

Lincoln 0.18 0.11 0.12 0.21 0.16 0.15 1.19 0.52 0.11 0.11 0.10 0.22

Little River 0.17 0.16 0.21 0.43 0.24 0.19 0.23 0.24 0.23 0.23 0.23 0.24

Logan 0.39 0.35 0.38 0.69 0.65 0.65 0.63 0.71 0.43 0.43 0.51 0.46

Lonoke 0.25 0.19 0.26 0.51 0.30 0.17 92.36 0.35 0.14 0.14 0.12 1.17

Madison 0.60 0.27 0.38 0.80 0.37 0.44 0.46 0.43 0.52 0.52 0.55 0.54

Marion 0.06 0.06 0.06 0.33 0.09 0.08 3.28 0.06 0.18 0.18 0.19 0.17

Miller 0.22 0.21 0.30 0.59 0.48 0.43 0.88 0.38 0.22 0.22 0.21 0.18

Mississippi 0.20 0.12 0.10 0.08 0.07 0.06 2.05 0.02 0.01 0.01 0.00 1.10

Monroe 0.07 0.03 0.03 0.06 0.02 0.01 8.75 0.01 0.01 0.01 0.01 0.29

Montgomery 0.15 0.12 0.15 0.20 0.29 0.27 0.34 0.33 0.17 0.17 0.20 0.16

Nevada 0.19 0.16 0.26 0.46 0.35 0.45 0.34 0.34 0.14 0.14 0.16 0.15

Newton 0.05 0.04 0.04 0.19 0.06 0.05 0.04 0.00 0.13 0.13 0.14 0.13

Ouachita --1 0.07 0.13 0.16 0.14 0.12 0.13 0.12 0.07 0.07 0.05 0.08

Perry 0.11 0.10 0.12 0.17 0.19 0.18 0.27 0.88 0.15 0.15 0.13 0.12

Phillips 0.30 0.08 0.08 0.14 0.11 0.03 0.07 0.04 0.02 0.02 0.01 0.12

Pike 0.19 0.16 0.25 0.37 0.40 0.39 0.51 0.69 0.20 0.20 0.18 0.34

Poinsett 0.17 0.06 0.06 0.09 0.12 0.09 2.69 0.02 0.02 0.02 0.02 1.53

Polk 0.16 0.16 0.28 0.51 0.70 0.77 0.88 0.84 0.28 0.28 0.33 0.42

Pope 0.56 0.29 0.38 0.58 0.60 0.82 0.80 1.15 0.37 0.37 0.38 0.39

Prairie 0.12 0.09 0.09 0.15 0.08 0.04 41.99 0.09 0.05 0.05 0.03 0.03

Pulaski 0.20 0.17 0.14 0.34 0.11 0.10 1.11 0.03 0.09 0.09 0.06 0.85

Randolph 0.06 0.05 0.06 0.33 0.06 0.08 0.43 0.45 0.19 0.19 0.23 0.22

Saline 0.15 0.10 0.10 0.17 0.09 0.07 0.16 0.07 0.08 0.08 0.07 0.05

Scott 0.16 0.18 0.20 0.35 0.43 0.38 0.54 0.67 0.28 0.28 0.30 0.24

Searcy 0.07 0.06 0.04 0.36 0.10 0.10 0.08 0.11 0.22 0.22 0.22 0.19

Sebastian 0.34 0.21 0.20 0.44 0.34 0.30 0.27 0.36 0.21 0.21 0.23 0.24

Sevier 0.29 0.17 0.24 0.53 0.64 0.66 0.66 1.01 0.37 0.37 0.32 0.37

Sharp 0.08 0.04 0.05 0.24 0.07 0.07 0.08 0.06 0.18 0.18 0.24 0.25

St. Francis 0.25 0.20 0.16 0.16 0.16 0.05 0.34 0.04 0.02 0.02 0.02 0.03

Stone 0.18 0.08 0.10 0.33 0.19 0.17 0.20 0.21 0.21 0.21 0.25 0.26

Union 0.16 0.11 0.11 0.15 0.21 0.34 0.46 0.36 0.12 0.12 0.12 0.12

Van Buren 0.16 0.06 0.12 0.31 0.14 0.11 0.13 0.11 0.22 0.22 0.16 0.14

Washington 1.85 1.15 1.41 2.01 2.52 2.63 2.83 2.67 1.04 1.04 1.14 1.09

White 0.40 0.34 0.52 0.83 0.43 0.48 1.19 0.70 0.45 0.45 0.39 3.37

Woodruff 0.09 0.05 0.05 0.11 0.05 0.02 0.50 0.01 0.02 0.01 0.01 0.12

Yell 0.64 0.38 0.50 0.84 0.89 0.86 0.84 0.92 0.41 0.41 0.37 0.41

Total 18.57 12.54 16.27 28.53 22.00 21.37 241.95 26.43 15.43 15.46 15.53 27.10

1

Data not reported from Jefferson and Ouachita Counties in 1960.
52 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Electric

The electric water-use category includes water consumed 

by thermoelectric power generation from fossil fuels, 

geothermal, nuclear, or thermoelectric power. Most water 

used for this purpose was derived from surface water; less 

than 1 percent of water used in Arkansas for thermoelectric 

power generation was pumped from groundwater sources 

(Holland, 2007). Independence County was the largest user of 

groundwater for electric use with 1.20 Mgal/d used in 2010 

(table 16).

Groundwater Discharge to Surface-Water 

Bodies

In addition to benefits gained from the pumping 

of groundwater for various uses, groundwater naturally 

discharges to surface-water bodies (springs, streams, wetlands, 

lakes, and other water bodies on the land surface), which 

support many processes, activities, and standard uses. Before 

human development of groundwater resources, the terminus 

of all groundwater flow paths was discharge to surfacewater bodies. Groundwater provides a relatively stable 

input of water to surface-water bodies. Conversely, surface 

runoff from precipitation often provides a discontinuous or 

“flashy” source of water to surface-water bodies. Important 

aquatic species and aquatic ecosystems have evolved to 

depend on groundwater discharge to streams, wetlands, and 

lakes, particularly during dry seasons and drought (National 

Wildlife Federation, 2014). Humans rely on the continuity 

of groundwater contribution to stream base flow to maintain 

typical surface-water uses during dry season and drought. 

Discharging groundwater also moderates the temperature 

of surface-water bodies and affects water quality. In recent 

decades, groundwater discharge to streams and wetlands has 

decreased significantly because of groundwater pumping 

(Brahana and Mesko, 1988; Williamson and others, 1990; 

Arthur and Taylor, 1998).

The reduction of groundwater discharge to surface-water 

bodies, particularly during dry periods, has had a strong 

deleterious effect on many important aquatic species and 

aquatic ecosystems. Human water uses, including irrigation, 

industry, public supply, recreational use, fishing, and waterfowl hunting, also have been adversely affected. As such, 

streamflow depletions by groundwater pumping have become 

an important water-resource management issue as a result of 

the negative effects that the reduced flows have on aquatic 

ecosystems, the availability of surface water for drinking and 

other needs, and the quality and aesthetic value of streams 

(Stanton and others, 2010; Barlow and Leake, 2012). Stream 

base flow from groundwater is an important criterion that 

water regulators and planners consider when evaluating 

conjunctive use, water allotment, and sustainable yield needs 

in the State. 

Groundwater contributions to streams, wetlands, 

lakes, and associated ecosystems provide considerable 

benefit, although perhaps difficult to quantify. Historically, 

benefits from natural processes that occur in natural, healthy 

aquatic ecosystems—such as clean water for drinking and 

other uses, decomposition of wastes, and amelioration of 

Table 16. Groundwater use for electric supply by counties and years in Arkansas. 

[Counties shown are only those with published data. Data from Halberg and Stephens (1966); Halberg (1972, 1977); Holland and Hall (1986); Holland (1981, 

1987, 1993, 1999, 2004, 2007). Units are million gallons per day]

County 1965 1970 1975 1980 1982 1985 1990 1995 2000 2005 2010

Craighead 0.31 0.18 0.06 0.05 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Franklin 0.02 0.03 0.04 0.00 0.00 0.00 0.00 0.20 0.02 0.00 0.05

Independence 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.53 0.47 0.00 1.20

Jefferson 0.00 0.00 0.00 0.00 1.87 0.00 0.02 1.74 0.63 0.00 1.12

Lafayette 1.80 1.15 1.09 1.68 1.39 1.06 1.20 1.12 0.90 0.50 0.35

Little River 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.35

Mississippi 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.62

Phillips 0.72 0.72 0.23 0.05 0.12 0.00 1.19 1.51 0.42 0.43 0.34

Pulaski 2.98 1.63 0.76 1.03 1.48 0.03 0.02 0.00 0.00 0.00 0.19

St. Francis 0.11 0.38 0.25 0.03 0.04 0.00 0.00 0.00 0.36 0.00 0.00

Woodruff 0.00 0.05 0.02 0.22 0.32 0.00 0.00 0.05 0.12 0.00 0.06

Total 5.94 4.14 2.45 3.06 5.23 1.09 2.43 5.15 2.92 0.93 4.28
Overview of Aquifers of Arkansas 53

contaminants—were often overlooked and were not assessed 

and quantified in terms of economic benefit. Within the last 

decade, however, the benefits that are supplied by ecosystems

have been recognized and assessed in terms of economic 

benefit. These benefits have been termed “ecosystem 

services,” and defined as any positive benefit that wildlife or 

ecosystems provide to people (National Wildlife Federation, 

2014). Ecosystem services are now a market-oriented 

objective recognized by Federal agencies, including the EPA 

and the USDA, and were included in the Food, Conservation, 

and Energy Act of 2008 (122 Stat. 923). The USDA has set 

policy for agriculture and forestry programs in providing 

environmental offsets and in developing economic accounting 

practices and procedures for quantifying environmental 

goods and services (U.S. Department of Agriculture, 2006). 

The USDA’s goal is to enhance fish and wildlife habitat 

maintenance, pollution protection, surface-water runoff, 

floodwater management, water sustainability, and cultural 

benefits. The advent of practical economic accounting 

procedures to quantify and incorporate groundwater 

remunerative benefits into resource analysis, planning, and 

allocation is a significant advancement of water-resource 

management.

The scale of interchange of water between the surface 

and subsurface environments is considerable for every 

aquifer system in Arkansas where these environments are 

hydraulically connected. The degree of connectivity is shown 

by direct observation, hydraulic-head distributions, waterquality conditions, water-balance analyses, groundwater-flow 

model results, and other approaches (for example, Hines, 

1975; Ludwig, 1992). Data in many of the surface-water 

hydrology and groundwater hydrology studies in the State 

corroborate the importance of surface-water/groundwater 

interaction by way of physical and chemical hydrology 

results. Several studies in the State have been conducted 

with objectives specifically addressing characterization of 

surface-water/groundwater interaction. Mesko and Imes 

(1995) conducted regional groundwater-flow simulations 

linking simulations of two regional-scale models—the Ozark 

Plateaus aquifer-system model (Imes and Emmett, 1994) and 

the Mississippi embayment aquifer system model (Brahana 

and Mesko, 1988). They noted that historical hydrogeological 

data indicated the potential for groundwater to move from 

the Ozark Plateaus aquifer system beneath the Fall Line 

(escarpment between the Interior Highlands and the Coastal 

Plain; fig. 3) and discharge to overlying embayment aquifers 

or directly to streams. The quantity of water moving under 

the Fall Line was estimated using simulations from the Ozark 

Plateaus aquifer system and the Mississippi embayment 

aquifer system models. Simulation results indicated that 

the rate of groundwater movement from the Ozark Plateaus 

aquifer system under the Fall Line was 650–800 cubic feet per 

second (ft3

/s) more than rate of recharge on the embayment 

side of the Fall Line. The results indicated that the most 

likely alternative discharge for this water was determined 

to be discharge to embayment streams. To determine if 

these differences in simulated groundwater flow could be 

explained by discharge as base flow to streams, low-flow 

seepage measurements were made on the Black River and 

its major tributaries in 1987. The seepage data indicated that 

groundwater did contribute substantial flow to the streams, 

indicating a total groundwater contribution of more than 

1,500 ft3/s, a total stream loss of about 500 ft3/s, and a net 

gain of approximately 1,000 ft3/s, which is an average gain 

of 2.6 cubic foot per second per mile (ft3/s/mi) for measured 

streams. The hydrologic measurement results were in 

agreement with model results and illustrated the scale and 

importance of groundwater contribution to streamflow. 

Freiwald (1987) conducted extensive groundwater 

discharge gain and loss measurements on eight streams and 

their tributaries representative of streams across the Ozark 

Plateaus in northern Arkansas. Study results illustrated 

the importance of groundwater contribution to streams in 

maintaining flow and affecting water quality. The study was 

designed to identify the relative importance of gaining and 

losing sections of typical Ozark streams and to characterize 

the degree of surface-water/groundwater interaction in 

this karst area. Three streams were shown to be gaining—

receiving groundwater—throughout their reaches; the 

remaining five streams were shown to be gaining streams 

through the majority of their reaches. Groundwater contributed 

measurable and substantial streamflow in 51 of 61 measured 

reaches. Losing sections—where water moves from a stream 

into groundwater—tended to be relatively short in length. 

Results indicated that lithology and the presence of faults 

were strong controls on the degree of interchange between the 

groundwater and surface-water environments. Stream reaches 

that received larger inputs of groundwater tended to lie in or 

near Mississippian-age, carbonate-rock outcrop areas; stream 

reaches where water moved into the groundwater environment 

were typically associated with fault zones. Groundwater also 

had a substantial influence on stream-water quality causing 

a notable increase in specific conductance and affecting 

moderation of stream temperature. 

Grosz and others (1988) quantified the degree of 

surface-water/groundwater interaction on the Little Red 

River by conducting detailed monitoring of stream discharge 

at multiple stations from Searcy to the confluence with the 

White River. They also conducted detailed monitoring of 

groundwater levels near the river at 19 piezometers. The 

study was conducted to obtain information needed for 

streamflow allocation planning. Comparison of surface and 

groundwater levels indicated that the Little Red River gained 

groundwater during summer and fall dry periods and lost 

flow to groundwater during periods of high flow. Minimum 

groundwater contribution to the Little Red River was 

estimated at 200–300 ft3

/s during low-flow periods. This 

base-flow component was noted to be a critical resource 

locally for supporting agricultural irrigation during summer 

months. 
54 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

The studies by Freiwald (1987) and Grosz and others 

(1988) highlight the importance of groundwater base flow in 

providing streamflow during times of limited surface-water 

availability, which can affect ecosystem viability. The benefits 

of groundwater contributions to surface water often have been 

overlooked; however, surface-water/groundwater interaction 

is recognized as an important part of ecosystem services, 

which not only defines the critical influence and benefits 

of groundwater, but provides an accounting mechanism for 

quantifying economic impact. 

Aquifers of the Coastal Plain

Groundwater in the Coastal Plain of Arkansas represents 

one of the most valuable natural resources in the State, driving 

the economic engines of agriculture, while also supplying 

abundant water for commercial, industrial, and public-water 

supply. Aquifers in the Coastal Plain consist of various 

geologic units that are Cenozoic and Mesozoic in age and 

consist primarily of Cretaceous, Tertiary, and Quaternary 

sands, gravels, silts, and clays (table 3). Depositional 

processes resulted in a stratigraphy represented by alternating 

accumulations of fine-grained materials, which impede flow 

and serve as confining units, and coarse-grained sands and 

gravels serving as aquifers. Decades of surface and subsurface 

mapping combined with careful geologic interpretation using 

a myriad of methods (age-dating, laboratory analysis, grainsorting, geophysical analysis) categorized and described 

various formations, their inherent hydrologic characteristics, 

and importance as groundwater resources. 

Results of these activities were documented in county 

or multicounty investigations describing the extent and 

importance of these groundwater resources on local and 

regional scales. The reader should refer to figure 5 for 

locations of cities and counties discussed in this section. 

The following sections list and discuss 11 aquifers that have 

served or are currently in use as important sources of water 

supply throughout the Coastal Plain of southern and eastern 

Arkansas. Each of these aquifers is described with respect 

to the depositional history of the formation, hydrologic 

characteristics, water use, water levels and water-level 

declines where significant, applied management tools for 

predicting flow patterns and sustainable use of aquifers, and 

local and regional water quality. Many of the aquifers are 

widely recognized, have long regional flow paths, serve as 

sources of water supply for multiple uses, have boundaries 

extending throughout neighboring States, and have water-use 

values in the millions of gallons per day. Other aquifers have a 

limited extent, serve solely as local sources of water, and often 

lack hydrologic and geochemical data but are nonetheless 

important sources of water to local entities in Arkansas that 

otherwise would have no other source of water.

In terms of age from youngest to oldest, the aquifers 

of the Coastal Plain are discussed in the following 

order: Quaternary alluvial aquifers, which include the 

Mississippi River Valley alluvial aquifer (the most 

important aquifer in Arkansas in terms of volume of use and 

economic benefits) and minor alluvial aquifers, Jackson Group 

(a regional confining unit that served for years as an important 

source of domestic supply), Cockfield, Sparta, Cane River, 

Carrizo, Wilcox, Nacatoch, Ozan, Tokio, and Trinity aquifers. 

Quaternary Alluvial Aquifers

Mississippi River Valley Alluvial Aquifer

Although all of Arkansas’ aquifers are important as 

water-supply sources locally or regionally, in terms of the 

volume of use, economic importance to the State, support 

of ecosystems, as well as abundant use for public, domestic, 

commercial, and industrial supply, the Mississippi River 

Valley alluvial aquifer must be considered the most important 

aquifer and one of the more important natural resources in 

Arkansas. The fertile soils overlying the Mississippi River 

Valley alluvial aquifer had long been recognized by explorers 

into eastern Arkansas. According to an early report by Nuttall 

(1821), “...rice has been tried on a small scale and found to 

answer every expectation. Under the influence of a climate 

mild as the South of Europe, and a soil equal to that of 

Kentucky, wealth will ere long flow, no doubt, to the banks 

of the Arkansa.” Also, President Theodore Roosevelt was 

quoted by The New York Times (1907) while on a tour of 

the Mississippi River Valley area: “The Mississippi Valley 

is a magnificent empire in size and fertility... In wealth of 

natural resources, no kingdom of Europe can compare with the 

Mississippi Valley... [It] is politically and commercially more 

important than any other valley on the face of the globe.” 

The potential for this projected wealth from an 

agricultural perspective only was realized with the advent of 

irrigation, and the Mississippi River Valley alluvial aquifer 

ultimately proved to be the most important source of irrigation 

water in the Mississippi embayment. The Mississippi 

River Valley alluvial aquifer has long been cited as the 

most important water-bearing formation from an economic 

standpoint for northeastern Arkansas (Stephenson and Crider, 

1916). With the expansion of irrigation for agriculture over 

the years, together with the advent of many municipalities and 

industries drilling deeper to obtain better-quality water, the 

Mississippi River Valley alluvial aquifer (commonly referred 

to by most Arkansans as simply the “alluvial aquifer”) has 

transitioned to primarily being a source of irrigation supply. 

The following sections provide an overview of the geologic 

setting, groundwater use, water-level trends, planning and 

management tools, and water quality for the Mississippi River 

Valley alluvial aquifer of eastern Arkansas.
Aquifers of the Coastal Plain 55

Geologic Setting

The Mississippi River Valley alluvial aquifer is the 

uppermost aquifer in eastern Arkansas and comprises 

unconsolidated clastic sediments—sand, gravel, silt, and 

clay—deposited in river and river-proximal environments. 

The aquifer is a part of and contained within the Mississippi 

embayment (fig. 8). The Mississippi embayment lies within a 

syncline that plunges south toward the Gulf of Mexico with 

the axis roughly along the present day Mississippi River (Hart 

and others, 2008). This structural feature was formed through 

extension of the North American continental plate and began 

infilling with sediment beginning during the Jurassic period. 

In a large part of eastern Arkansas, the Mississippi embayment 

was blanketed with alluvial sediment during the Quaternary 

period, resulting in formation of the aptly named Quaternary 

alluvium. The Mississippi embayment extends across parts of 

Alabama, Arkansas, Illinois, Kentucky, Louisiana, Mississippi, 

Missouri, and Tennessee, covering an area of approximately 

160,000 square miles (mi2) (Cushing and others, 1964; 

Williamson and others, 1990; Arthur and Taylor, 1998). The 

Mississippi River Valley alluvial aquifer covers an area of 

approximately 32,000 mi2 within the Mississippi embayment, 

and approximately 54 percent of this aquifer is located in 

eastern Arkansas (Pugh and others, 1997). 

The Mississippi River Valley alluvial aquifer is composed 

of unconsolidated materials ranging from clay and silt in the 

upper part and grading downward to coarse sand and gravel at 

the base (Hosman and Weiss, 1991). The aquifer effectively 

can be divided into two distinct units based on lithologies: 

a lower unit that contains the primary aquifer consisting of 

coarse sands and gravels derived from alluvial and terrace 

deposits that coarsen downward (herein referred to as the 

“Mississippi River Valley alluvial aquifer”), and an upper 

unit that consists of fine sand, silt, and clay that serves as a 

confining unit of varying competency (herein referred to as the 

“Mississippi River Valley confining unit”), which is of local 

importance as a lower-yield aquifer primarily for domestic 

use. 

The importance of the Mississippi River Valley alluvial 

aquifer is reflected in the long-term interest in its geology. 

Veatch (1906) and Stephenson and Crider (1916) reported 

on Quaternary deposits of southern Arkansas and northern 

Louisiana. Fisk (1944) described alluvial sediments as part 

of geologic investigations along the Mississippi River Valley 

by the U.S. Army Corps of Engineers. Krinitzsky and Wire 

(1964) added to the work of Fisk with additional information 

on groundwater conditions. Cushing and others (1964) gave 

a basic description of Quaternary aquifers, with Boswell and 

others (1968) providing greater detail and applying the name 

“Mississippi River Valley alluvial aquifer” to the sediments 

underlying the alluvial plain. Ackerman (1989a) applied the 

term “Mississippi River Valley confining unit” to the finegrained materials that overlie the coarser lower unit of the 

Mississippi River Valley alluvial aquifer.

Virtually all of the landforms and associated sediments 

within the Mississippi River Valley are the direct result of 

fluvial processes. The dominant controls influencing the 

fluvial processes and resulting surface geology of the Lower 

Mississippi Valley were glaciation, climate, relative sea level, 

tectonism, and subsidence (Saucier, 1994). The resulting 

landforms that occupy the area and influence the hydrology 

of the Mississippi River Valley alluvial aquifer for the present 

investigation are valley-train, meanderbelt, and backswamp 

deposits.

Because of the consistency of sediment supply, the 

low-relief character of the area, and the wandering nature of 

streams shifting their positions across the landscape through 

time, the geology of the Mississippi River Valley alluvial 

aquifer at the regional scale is relatively consistent throughout 

its range. For a thorough review of the geography, regional 

geologic framework, and stratigraphy and lithology within 

the Lower Mississippi Valley, the reader is directed to Saucier 

(1994); additional detail is provided in the smaller-scale 

studies and is summarized in the discussion below.

The Mississippi River Valley alluvium is the uppermost, 

surficial formation extending across a large area of the 

Mississippi embayment and unconformably overlies, in 

various areas, the Jackson Group, the Cockfield Formation, 

the Cook Mountain Formation, the Sparta Sand, the Cane 

River Formation, the Carizzo Sand, the Wilcox Group, 

the Midway Group, the Arkadelphia Marl, the Nacatoch 

Sand, and older Paleozoic units (Cushing and others, 1964; 

Boswell and others, 1968; Hosman and others, 1968; Broom 

and Reed, 1973; Ackerman, 1996). The lateral boundary of 

the Mississippi River Valley alluvial aquifer is seen at the 

peripheral areas of the embayment where the contact of the 

base of the alluvial aquifer with older, underlying units is 

exposed. To the west, this boundary closely parallels the “Fall 

Line,” the boundary with the Interior Highlands defined by 

greater topographic relief and outcrop of Paleozoic rock in 

the Interior Highlands (fig. 9). The Fall Line has been cited as 

“one of the most strongly marked physiographic and cultural 

lines on the surface of the globe” (McGee, 1888). The term 

“Fall Line” originally referred to the “fall line of rivers,” and 

was defined as the upper limit of navigation and the lower 

limit of water power, and often marked by waterfalls or points 

where rivers changed from rapid and turbulent to becoming 

broad and slow moving (Hill, 1888). The importance of 

the Fall Line from a hydrological standpoint is that this 

transitional zone between the Interior Highlands and the 

Coastal Plain has been noted as an area of upwelling of deepsourced, high salinity groundwater from Paleozoic rocks of the 

Interior Highlands (see “Occurrence, Distribution, and Sources 

of Elevated Chloride Concentrations” section). Crowleys 

Ridge, a structural high and erosional remnant of Tertiary-age 

units, physically divides the Mississippi River Valley alluvial 

aquifer in the northern part of eastern Arkansas (fig. 8). No 

deposition of Quaternary alluvium occurred on Crowleys 

Ridge (Ackerman, 1996).
56 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Crowleys

Ridge

ARKANSAS

MISSISSIPPI

LOUISIANA

ALABAMA

TENNESSEE

KENTUCKY

TEXAS

ILLINOIS

MISSOURI

Base map from U.S. Geological Survey digital data, 1:2,000,000

EXPLANATION

Loess, silt, sand, and gravel deposits

Quaternary aquifers

Mississippi River Valley alluvial aquifer

Ouachita-Saline River alluvial aquifer

Red River alluvial aquifer

Older formations

Hydrogeologic and geologic units

Boundary of Mississippi embayment

Syncline 

Geology modified from Hosman, 1988

0 30 60 90 120 MILES

0 30 60 90 120 KILOMETERS

37°

36°

35°

34°

33°

32°

31°

94° 93° 92° 91° 90° 89° 88° 87°

Axis of 

Desha 

Basin

Figure 8. Extent of the Mississippi embayment with location of Quaternary aquifers.
Base map from U.S. Geological Survey digital data, 1:2,000,000 Geology map modified from Haley and others, 1993

West Gulf Coastal Plain

Mississippi Alluvial Plain

Fall lineFall line

36°

35°

34°

90°

94° 92° 91° 93°

0 15 30 45 60 

0 30 60 KILOMETERS 15 45

Qsg Ple

Ql Ple

Qss Ple

Qds Ple

Qt Ple

Qso Ho

Qcm Ho

Tc Eo

Tj Eo

Tm Pa

Tw Eo

Mississ

Missi

Water b

*

*

*

M

West Gulf Coastal Pl

K

Kd

K

K

Kt

K

Ko Upper Cretaceous Ozan 

Formation

Ka Upper Cretaceous Annona Chalk

Km Upper Cretaceous Marlbrook 

Marl

Ks Upper Cretaceous Saratoga 

Chalk

Kn Upper Cretaceous Nacatoch Sand

Kad Upper Cretaceous Arkadelphia Marl

Ki Cretaceous Igneous rocks

Tc Eocene Claiborne Group

Tj Eocene Jackson Group

Tm Paleocene Midway Group

Tw Eocene Wilcox Group

Qt Pleistocene terrace deposits on one o

Qal Holocene alluvial deposits of present 

Minor alluvial formations

Other formations

EXPLA

Other 

Figure 9. Surface geology of the West Gulf Coastal Plain and Mississippi Alluvial Plain in southern and eastern Arkansas.
58 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

The lower unit of the Mississippi River Valley alluvial 

aquifer comprises alluvium and terrace deposits consisting 

of a coarse-sand matrix with varying amounts of gravel; the 

base of the aquifer is predominately gravel in some areas. 

The gravels generally coarsen northward and with depth; the 

maximum grain size can be as large as 8 inches to the north 

and 3 inches to the south (Fisk, 1947; Ackerman, 1996). The 

gravel is mostly chert, but other lithologies including quartz, 

sandstone, and igneous rock also are present as a result of 

diverse sediment origin (Cushing and others, 1964; Boswell 

and others, 1968; Broom and Reed, 1973; Stanton and Clark, 

2003). The basal coarse sand and gravel are overlain by finegrained sand and lenses of clay, silt, or sandy silt (Ackerman, 

1996). The basal gravel may be absent in some areas, notably 

in the immediate vicinity of the Fall Line, and clay layers 

occur locally in the lower unit of the aquifer (Halberg and 

Reed, 1964). The lower unit of the Mississippi River Valley 

alluvial aquifer generally ranges in thickness between 0 and 

140 ft with an average thickness of 100 ft and decreases in 

thickness to the south (Ackerman, 1996; Pugh and others, 

1997). Thicker sequences as much as 160 ft occur at two 

locations in Poinsett County on opposite sides of Crowleys 

Ridge, in western Clay County, and in Greene County (Pugh 

and others, 1997). The large range in thickness is a result of 

the deposition on an irregular erosional surface underlying the 

Mississippi River Valley alluvial aquifer (Broom and Reed, 

1973; Broom and Lyford, 1981; Ackerman, 1996). The basal 

gravel typically is thicker where the total thickness of the 

alluvium is the greatest (Sumner and Wasson, 1990).

The environments of deposition for the Mississippi 

River Valley alluvium controlled the spatial distribution of the 

varying hydraulic characteristics of the aquifer. As the glacial 

periods of the Pleistocene waned and sea level rose, regional 

stream gradients decreased and aggradation of sediments 

occurred. The depositional processes were complex, with 

alluvium being deposited, eroded, dissected, reworked, and 

redeposited into terraces as flow conditions changed and 

local gradients changed with sediment aggradation (Boswell 

and others, 1968). The sediment was deposited by braided 

stream, meander belt, backswamp, and valley outwash plain 

depositional processes (Fisk, 1944, 1947; Krinitzsky and 

Wire, 1964; Ackerman, 1996). Deposition of the Mississippi 

River Valley confining unit occurred predominantly under 

lower hydrodynamic energy deposition conditions of the 

backswamp and channel-fill environments, resulting in a 

mantling deposition of fines that reduced the relief of the land 

surface (Gonthier and Mahon, 1993). The coarser-grained, 

high-yield lower unit of the Mississippi River Valley alluvial 

aquifer is characterized by valley-train (or braided-stream) 

deposits originating from high-discharge streams carrying 

coarse-grained glacial outwash fed by meltwater of receding 

glaciers. Valley-train deposits are represented as wide, 

frequently branching channels separating irregular braid bars 

and interfluve areas. 

With the onset of the Holocene, depositional processes 

switched from bedload-dominated braided streams to 

suspended-load dominated meandering streams that remain 

today. Meander-belt deposits include natural levees and point 

bars, both of which are very permeable and provide favorable 

recharge pathways into the Mississippi River Valley alluvial 

aquifer (Bedinger and Reed, 1961; Bedinger and Jeffery, 

1964). Backswamps are meander-belt proximal environments 

characterized by low-relief, shallow, and poorly drained areas 

associated with overbank flooding that generally includes 

massive sequences of fine-grained silts and clays (Saucier, 

1994). Channel-fill deposits are abandoned channels, such as 

oxbow lakes, that typically fill with fine-grained sediments. 

Backswamp and channel-fill deposits are characterized by 

materials of low permeability that are poor avenues for 

aquifer recharge (Bedinger and Reed, 1961; Bedinger and 

Jeffery, 1964). Backswamp deposits occupy parts of Jefferson, 

Lincoln, and large parts of Desha Counties; these deposits 

are a major influence on groundwater flow and geochemical 

evolution in the study area (Kresse and Clark, 2008).

The Mississippi River Valley confining unit generally 

thickens from north to south; however, the thickness of the 

confining unit varies greatly and is absent in many areas. 

Where present, the confining unit ranges up to 150 ft in 

thickness; however, areas of absent and thin zones are 

common across the extent of the confining unit. Trends in 

thickness were controlled by depositional processes, and areas 

of equal thickness tend to parallel major stream channels. The 

Mississippi River Valley confining unit is relatively thick, 

consistently more than 50 ft, in the Grand Prairie region, 

which is bounded by two major rivers. The confining unit is 

absent in areas of Craighead and Poinsett Counties. “Clay 

plugs,” local anomalously thicker clay deposits, occur and 

may be 50–100 ft thicker than the adjacent areas. In other 

areas, the confining unit is present as infilled oxbow lakes 

or meander channels and is therefore much thicker locally 

(Broom and Lyford, 1981; Ackerman, 1989a, 1996; Gonthier 

and Mahon, 1993). In some areas, modern rivers have 

reworked the upper part of the alluvial fill materials. Stanton 

and Clark (2003) showed a confining-unit thickness ranging 

from 0 to 60 ft south of the Arkansas River. 

Hydrologic Characteristics

During predevelopment time, the Mississippi River 

Valley alluvial aquifer was confined where the upper confining 

clay layer was present; in these areas, the potentiometric 

surface was at or above the top of the aquifer (Ackerman, 

1996). As groundwater development increased, widespread 

pumping caused regional declines in water levels to below the 

clay layer across much of the aquifer’s extent, converting the 

aquifer to an unconfined condition. Dewatering the aquifer can 

lead to subsidence and a permanent loss of storage (Konikow, 

2013). Clays present in the aquifer and the confining layer 
Aquifers of the Coastal Plain 59

average approximately 50 percent smectite (Scott and others, 

2000), a type of clay that is highly susceptible to compaction. 

Dewatering of the alluvial aquifer and overlying clay layer 

can lead to irreversible compaction and subsidence, reducing 

the water-yielding capacity of more clay-rich layers and 

reducing the ability of precipitation to move through the clay 

layer and recharge the aquifer. Aquifers and confining units 

containing substantial amounts of fine-grained materials, as 

the Mississippi River Valley alluvial aquifer does, are most 

susceptible to compaction. Marshall (2005) used highprecision static and kinematic Global Positioning System 

(GPS) to document land subsidence of 0.67 in/yr near the 

area of the largest observed water-level declines in the Grand 

Prairie. 

The Mississippi River Valley alluvial aquifer in some 

areas is hydraulically connected to underlying Tertiary 

aquifers. The degree of hydraulic connection is dependent 

on the grain size and permeability of the aquifers, the 

composition of sediments near the contact of the aquifers, and 

the head differences between aquifers (Hosman and Weiss, 

1991). Even where the Mississippi River Valley alluvial 

aquifer is in contact with underlying aquifers, the permeability 

contrast between the higher hydraulic conductivity alluvial 

aquifer and the lower hydraulic conductivity of underlying 

aquifers allows the aquifers to be differentiated (Ackerman, 

1996). 

Aquifer-test data for the Mississippi River Valley alluvial 

aquifer are found in numerous countywide reports dating 

back to the mid-1950s. Ranges in yields and other hydrologic 

characteristics are controlled by the thickness, sediment size 

and distribution, and other physical characteristics of the 

producing zone. Reported yields throughout the Mississippi 

River Valley alluvial aquifer in eastern Arkansas ranged from 

400 to 3,000 gal/min (Onellion and Criner, 1955; Counts, 

1957; Lamonds and others, 1969; Hines and others, 1972; 

Broom and Reed, 1973). Boswell and others (1968) reported 

yields throughout the Mississippi embayment by State, with 

a maximum yield of 5,000 gal/min for Arkansas. Yields of 

2,000 gal/min were cited as common, which was the most 

commonly reported yield cited in the earlier countywide 

reports. 

Hydraulic conductivity values for the Mississippi 

River Valley alluvial aquifer ranged from 60 to 390 feet per 

day (ft/d) (Halberg and Reed, 1964; Boswell and others, 

1968; Broom and Lyford, 1981). Ackerman (1996) listed 

hydraulic conductivity values ranging from 120 to 390 ft/d 

with a geometric mean of 210 ft/d. Krinitzsky and Wire 

(1964), reporting on the Mississippi River Valley alluvial 

aquifer in the lower Mississippi Valley, listed hydraulic 

conductivity values from 38 tests ranging from 120 to 390 

ft/d with a geometric mean of 210 ft/d. Although data from 

Ackerman (1996) and Krinitzsky and Wire (1964) included 

values from other States, the similar range in hydraulic 

conductivity values reflects the uniform geologic character of 

the aquifer throughout the lower Mississippi Valley. Multiple 

investigations have observed that the hydraulic conductivity 

is larger at the base of the aquifer and decreases upward as 

average sediment size decreases (Broom and Lyford, 1981; 

Ackerman, 1989a, 1989b, 1990; Mahon and Ludwig, 1990; 

Mahon and Poynter, 1993).

Transmissivity values ranged from 5,200 to 64,900 foot 

squared per day (ft2

/d) for the Mississippi River Valley alluvial 

aquifer in Arkansas (Halberg and Reed, 1964; Boswell and 

others, 1968; Lamonds and others, 1969; Broom and Reed, 

1973; Broom and Lyford, 1981). Storage coefficients—

dimensionless values describing the volume of water released 

per area of aquifer and depth of drawdown—ranged from 

0.0004 to 0.08 (Halberg and Reed, 1964; Boswell and others, 

1968; Lamonds and others, 1969; Broom and Reed, 1973; 

Broom and Lyford, 1981), which reflects unconfined and 

confined conditions in the aquifer. A review of 75 reported 

storage coefficients (Ackerman, 1996) for the Mississippi 

embayment, mostly from Arkansas, revealed a range from 

0.15 to 0.0009, with 16 values between 0.05 and 0.15, 

34 between 0.001 and 0.01, and 25 values between 0.0001 

and 0.0009. Specific capacities ranged from 18 to 90 gallons 

per minute per foot [(gal/min)/ft] of drawdown (Boswell and 

others, 1968; Lamonds and others, 1969).

A summary of aquifer-test data in Arkansas, which 

included aquifer-test data collected since 1995, and data 

separated for the Mississippi River Valley alluvial aquifer 

by Holocene-age alluvium and Pleistocene-age terrace 

deposits were presented by Pugh (2008a). Pugh also 

reported transmissivity values that ranged from 450 to 

160,000 ft2/d (median of 24,000 ft2/d) and specific-capacity 

values that ranged from 0.06 to 3,200 (gal/min)/ft (median 

of 171 (gal/min)/ft) for the Holocene alluvium. For wells 

completed in Pleistocene terrace deposits, Pugh (2008a) 

reported transmissivity values that ranged from 325 to 

43,000 ft2/d (median of 18,200 ft2/d) and specific-capacity 

values that ranged from 2.02 to 723 (gal/min)/ft (median of 

160 (gal/min)/ft).

Little research has focused on the hydrologic 

characteristics of the Mississippi River Valley confining unit. 

Ackerman (1996) conducted laboratory analyses of samples 

taken from the confining unit; these samples were found to be 

in the clay to silty sand texture range and exhibited hydraulic 

conductivity values ranging from 0.0001 to 0.5 ft/d (values 

consistent with those reported for that range of grain sizes of 

samples by Freeze and Cherry [1979]). Yields for domestic 

wells completed in the Mississippi River Valley confining unit 

ranged from less than 5 to 100 gal/min or more, depending 

upon grain size and depth of wells.
60 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Sources of Recharge

Determining and quantifying sources of recharge is 

important to managing the valuable resource provided by 

the Mississippi River Valley alluvial aquifer, especially for 

accurately modeling flow and predicting sustainable pumping 

rates from continued irrigation use. The principal source 

of recharge to the Mississippi River Valley alluvial aquifer 

is precipitation. The Mississippi embayment experiences a 

mean annual precipitation of 48 and 56 inches in the northern 

and southern parts of the State, respectively (Kleiss and 

others, 2000; Pugh and Westerman, 2014). While no study 

has been conducted to quantify actual recharge rates across 

the aquifer, calibrated Mississippi River Valley alluvial 

aquifer groundwater models constrain recharge values and 

use recharge rates of 0.8–2.6 in/yr (about 1.5–5 percent of 

total precipitation) to simulate recharge from precipitation 

(Mahon and Poynter, 1993; Ackerman, 1996; Arthur, 2001; 

Stanton and Clark, 2003). These models, however, integrated 

locally low and high values of recharge and represented 

average recharge rates across large regional areas of the 

Mississippi River Valley alluvial aquifer. Kresse and Clark 

(2008) applied a chloride mass balance method using chloride 

concentrations in precipitation and groundwater to show 

recharge values from about 0.07 in/yr to 7.8 in/yr in areas of 

Mississippi River Valley backswamp and channel deposits, 

respectively, south of the Arkansas River. 

The Mississippi River Valley alluvial aquifer receives 

abundant recharge where the impermeable clay layer is 

very thin or absent; where the clay layer is present, vertical 

infiltration from the surface is impeded, and recharge by 

lateral flow from adjacent areas is more important (Onellion, 

1956; Bedinger and Reed, 1961; Bedinger and Jeffery, 1964; 

Boswell and others, 1968; Whitfield, 1975). Recharge rates 

are related to grain size and the hydraulic characteristics of 

sediment present at the surface; the type of sediment is, in 

turn, controlled by the environment of deposition. Point-bar, 

channel, and natural-levee deposits are composed of coarser 

sediments that are highly permeable and support higher 

recharge rates. Overbank and backswamp deposits are finegrained sediments deposited in low-energy environments 

removed from main river channels, are less permeable, and 

impede recharge (Bedinger and Reed, 1961; Kresse and 

Clark, 2008). The complex depositional history of the alluvial 

aquifer has resulted in highly variable surface geology and 

therefore highly variable zones of recharge. 

Recharge to the Mississippi River Valley alluvial 

aquifer also may occur through streambeds, as suggested 

by hydraulic gradients near the rivers (Bedinger and Reed, 

1961). However, the pervasive presence of low-permeable 

fine sediments in some lowland river bottoms can reduce 

effectiveness of river-derived recharge. A recent study using 

groundwater chemistry from alluvial wells south of the 

Arkansas River suggests that an important component of 

the recharge to the Mississippi River Valley alluvial aquifer 

may be infiltration of precipitation through coarse channel 

deposits near the river rather than from the river itself (Kresse 

and Clark, 2008). Therefore, the high hydraulic gradients 

near rivers may be more strongly affected by precipitationinduced, higher water levels in the coarser deposits next 

to the river. Upward flow from underlying aquifers can 

contribute to recharge; however, the recharge would likely not 

be substantial because of the higher hydraulic conductivity of 

the lower part of the alluvial aquifer in contrast to the lower 

hydraulic conductivity of underlying aquifers and associated 

confining units (Ackerman, 1996). 

Groundwater Flow

The Mississippi River Valley alluvial aquifer contains 

regional and local flow systems. Regionally, groundwater 

flow tends to follow the topographic gradient (albeit very 

low) with movement generally from the topographically 

higher areas in the northern and western parts of the 

Mississippi embayment to the topographically lower areas 

in the southern and eastern parts of the embayment. This 

regional pattern is locally inflected near streams acting 

as drains to the aquifer and in areas of high withdrawals 

(Schrader, 2006a). Groundwater flow paths can range from 

tens to hundreds of miles before intersecting major rivers 

such as the Mississippi, Arkansas, or White Rivers.

Crowleys Ridge is a barrier to groundwater movement 

(Boswell and others, 1968) in the northeastern part of the 

State. Potentiometric-surface maps (Joseph, 1999; Reed, 

2004; Schrader, 2001b, 2006a, 2008a, 2010) in this area 

reveal a head difference of 20–30 ft on opposite sides of 

Crowleys Ridge, which indicates that even in areas where 

groundwater throughflow would be most likely, Crowleys 

Ridge serves as a hydraulic barrier. Water levels from wells 

on the ridge generally are higher than those of the alluvial 

aquifer, indicating that the ridge is not part of the alluvial 

aquifer flow system (Reed, 2003; Gillip and Czarnecki, 

2009). For more information about the effects of Crowleys 

Ridge on potentiometric surfaces, see the section titled 

“Water Level Trends.” 

The Mississippi River Valley alluvial aquifer is in 

hydraulic connection with numerous rivers that are incised 

into the alluvium. Many rivers may have been gaining flow 

from the aquifer prior to development, but as groundwater 

levels declined regionally in response to withdrawals from 

the aquifer, the head differences were reversed, and the 

more common condition is for the rivers to lose water to 

the aquifer (Ackerman, 1989a). Hunrichs (1983) noted that 

water levels were below some rivers in southeastern 

Arkansas, and some of these rivers were no longer perennial 

streams for parts of their length. The degree of hydraulic 

connection between streams and the Mississippi River Valley 

alluvial aquifer in Arkansas is dependent on the hydraulic 

conductivity of the riverbed materials, the hydraulic gradient 

between the two water bodies, and the extent to which the 

river is incised into the aquifer (Ackerman, 1996; Barlow and 

Leake, 2012).
Aquifers of the Coastal Plain 61

The Mississippi River serves as a hydrologic flow 

boundary for the Mississippi River Valley alluvial aquifer 

at the eastern extent of the aquifer in Arkansas. The river 

is incised through the entire thickness of the aquifer along 

many reaches (Whitfield, 1975; Ackerman, 1989a) and 

recharges the alluvial aquifer for most of the year. The stage 

of the river controls groundwater levels and flow in an 

area adjacent to the river. The Arkansas and White Rivers 

incise a part of the alluvial aquifer, serve as hydrologic flow 

boundaries, and appear to be hydraulically well connected as 

shown by a strong correlation between river stage and local 

potentiometric heads (Freiwald and Grosz, 1988; Ackerman, 

1996). 

Rivers in the Mississippi Alluvial Plain were 

considered primary groundwater-discharge locations during 

predevelopment time. Many of these rivers transitioned to 

important sources of recharge to the Mississippi River Valley 

alluvial aquifer as groundwater levels decreased, reversing 

the river-aquifer head relation at the scale of groundwaterlevel mapping activities. As a result, several numerical 

models in the past two decades were developed using 

river-package simulations; results indicated that rivers are 

volumetrically important sources of recharge to the aquifer 

(Mahon and Ludwig, 1990; Mahon and Poynter, 1993; 

Reed, 2003; McKee and Clark, 2003; Stanton and Clark, 

2003). Reed (2003) depicted flow from model cells along 

the Arkansas River into the Mississippi River Valley alluvial 

aquifer throughout much of Jefferson County in southeastern 

Arkansas. Stanton and Clark (2003) also depicted river model 

cells in southeastern Arkansas as a primary source of recharge 

to the aquifer. From a standpoint of logical analysis, the 

large volume of available water in the river, the hydrologic 

boundary created by the river, and groundwater-level data 

showing gradients of flow away from the river strongly 

suggested that flow was moving from the river into the 

aquifer. 

Prior to the installation of the lock and dam system 

in 1967, the Arkansas River acted as a drain for excess 

groundwater flow for most of the year (Bedinger and Reed, 

1961). Previous publications identified a groundwater divide 

between the water moving into the river and water moving 

away from the river. Although wells near the river exhibited 

higher water levels during high river stage, this effect was 

diminished exponentially away from the river and was small 

beyond a distance of approximately 2 miles (mi) (Bedinger 

and Reed, 1961; Bedinger and Jeffery, 1964; Krinitzsky and 

Wire, 1964; Freiwald and Grosz, 1988; Ackerman, 1996). 

Bedinger and Jeffery (1964) stated that correlations of 

stage and water levels for wells greater than 2 mi from the 

river were “... probably more apparent than real, is caused 

by local recharge from precipitation coincident with riverstage changes.” As such, earlier analysis of the connectivity 

between the Arkansas River and the Mississippi River Valley 

alluvial aquifer recognized the effects of bank storage and the 

limited effects of river-water infiltration into the aquifer at 

distances greater than 1–2 mi. 

While very strong corollary evidence supported the 

concept of the hydraulic connectivity of rivers and the 

alluvial aquifer, questions regarding the volume and rate of 

water leaking from rivers have yet to be answered. The earlier 

interpretation of bank storage and the degree of hydraulic 

connection between the Arkansas River and the Mississippi 

River Valley alluvial aquifer changed with construction of 

lock and dam channelization along the river in the 1960s. 

Resulting higher river stage and higher groundwater gradients 

near the river implied continual direct flow from the river to 

the aquifer. The available data led to definitive statements 

that the Arkansas River contributed appreciable water to 

the aquifer under observed head conditions. The difficult, 

unaddressed, and long-standing debate in hydrogeology has 

centered on the question of how much water passes through 

streambeds in systems that carry an abundant load of finegrained material. Although many streams are in hydraulic 

connection with an aquifer, flow rates are impeded by fine 

stream-bottom sediments and by migration of clay and silt 

into the aquifer matrix. Barlow and Leake (2012) noted 

that thick, silty streambeds (such as that of the Arkansas 

River) will tend to reduce the rate of flow between a stream 

and aquifer, while simultaneously increasing the hydraulic 

gradient between the two water bodies. Additionally, the 

clay-rich Mississippi River Valley confining unit ranges up 

to 100 ft in thickness, whereas the Arkansas River typically 

has channel depths of less than 30 ft, further restricting the 

hydraulic connection between the river and the aquifer in 

many places. 

Kresse and Clark (2008) conducted a study to determine 

the source of elevated chloride concentrations in the 

Mississippi River Valley alluvial aquifer in southeastern 

Arkansas (see “Occurrence, Distribution, and Sources of 

Elevated Chloride Concentrations” section). Their study used 

maps of chloride concentrations, bromide-chloride ratios, 

and other methods to show a correlation of elevated chloride 

concentrations in backswamp areas at greater distances from 

river channels, which suggested that evaporation in these 

areas accounted for the elevated chloride concentrations. 

Additionally, higher chloride concentrations in the Arkansas 

River relative to low concentrations in channel deposits 

proximal to the river suggested that influx of water from the 

Arkansas River may be relatively small, and that infiltration 

of precipitation through coarse-grained channel and naturallevee deposits proximal to the river may be the primary 

avenue for recharge to the Mississippi River Valley alluvial 

aquifer (Kresse and Clark, 2008). While these findings may 

seem to contradict river-package modeling studies (referenced 

above) conducted in the Mississippi River Valley alluvial 

aquifer, this certainly is not the case. The discretization and 
62 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

resolution of these models simply support the statement that 

a certain amount of water moves into the aquifer near a given 

river. While models are effective at estimating the amount of 

water entering the aquifer near the river, the models do not 

necessarily differentiate between direct leakage from rivers 

and infiltration of precipitation into deposits that are proximal 

to and intimately associated with the current river channel. 

Geochemical data provide a valuable aid in determining 

the source and volumetric relation of recharge water into 

the Mississippi River Valley alluvial aquifer. Determination 

of an accurate rate of flow from a river into the aquifer 

requires labor- and cost-intensive methods, including a dense 

network of observation wells or streambed piezometers, 

seepage meters, direct measurement of streamflow at various 

locations, measurements of temperature in the stream and 

streambed, analysis of geochemical tracers, physical aquifer 

and river-bottom hydraulic characteristics, and geophysical 

studies of the stream-aquifer system (Barlow and Leake, 

2012). Alternatively, the very different chemistries of river 

water and rainfall make the exercise of distinguishing 

these sources possible using a less demanding approach. 

A geochemical approach provides strong evidence of the 

dominant recharge source and the relative contribution of 

direct channel recharge compared with infiltration of rainfall 

through permeable, river-proximal channel deposits.

Water Use

The Mississippi River Valley alluvial aquifer is 

extremely important in terms of total water use in Arkansas. 

The State ranks fourth nationally in groundwater use (Kenny 

and others, 2009); in 2010, 94 percent of all groundwater 

use in Arkansas was from the Mississippi River Valley 

alluvial aquifer. Over 47,000 wells reported approximately 

7,400 Mgal/d of use from the Mississippi River Valley 

alluvial aquifer as of 2010 (fig. 10). The economy of eastern 

Arkansas is heavily reliant on agriculture, and water from the 

Mississippi River Valley alluvial aquifer drives agricultural 

production. Locally, industry depends on the aquifer, and 

a recent trend of increasing water use is the flooding of 

agricultural fields to provide duck habitat to improve hunting. 

Water-use rates for the Mississippi River Valley alluvial 

aquifer have increased steadily from 1965 to 2010 (fig. 11). 

The majority of the increase is attributed to irrigation, 

which has increased consistently over time for all reported 

water-use data (fig. 4). In 1965, the average water use by 

county from the Mississippi River Valley alluvial aquifer 

was 22.69 Mgal/d; by 2010, the average use had increased 

to 148.64 Mgal/d per county. Data from 2010 show 21 

counties where reported water-use rates were less than 5 

Mgal/d (but above 0), highlighting the fact that water-use 

increases have been focused within specific counties—areas 

where agricultural use is important (table 17). Since 1965, 

the greatest increase in use from the Mississippi River Valley 

alluvial aquifer was observed in Mississippi County (fig. 12; 

table 17).

Counties in the intensively farmed area of the Grand 

Prairie (Arkansas, Lonoke, and Prairie) historically had 

the highest groundwater use rates until 1985 (fig. 11), 

when water use began to substantially increase in counties 

in northeastern Arkansas. Lonoke County had the most 

withdrawals from 1965 to 1985, with rice irrigation being 

the primary use of the water. From 1990 to 2010, Poinsett 

County was the largest user, primarily for rice irrigation (98 

percent). Jefferson County had the largest water withdrawals 

for industrial purposes (5.94 Mgal/d) in 2010 (Terrance W. 

Holland, U.S. Geological Survey, written commun., 2012).

The following sections focus on the categories of 

water use from the Mississippi River Valley alluvial aquifer. 

The section “Overview of Aquifers of Arkansas” gives 

details on the inclusion of particular withdrawals and the 

definition of the water-use categories. For more information 

on the categories of water use, refer to “Groundwater Use 

in Arkansas” in the “Overview of Aquifers of Arkansas” 

section.

Agriculture and Irrigation Use

Arkansas is the Nation’s leading rice producer (McGraw 

and others, 2012). Rice is a water-intensive crop, and 

traditional rice farming, as practiced in Arkansas, requires 

flooded paddies. Supplemental irrigation application rates 

for rice in Arkansas were estimated at 1.6 to 2.0 acre-ft 

during the growing season, which typically lasts from April 

to September (Engler and others, 1945, 1963; Bedinger and 

Reed, 1961). Current estimates place irrigation application 

rates as much as 3.3 acre-ft during a dry year, with average 

rates of 2.5 acre-ft depending on soil type, water-application 

methods, and degree of management (Henry and others, 

2013). With expansion of rice agriculture, farmers also 

began to irrigate other crops, thus increasing groundwater 

use. Arkansas’ economy greatly benefits from irrigation and 

the Mississippi River Valley alluvial aquifer is the greatest 

source of irrigation water supply.
YELL

LEE

UNION

WHITE

POLK

POPE

DREW

PIKE

SCOTT

CLARK

CLAY

ASHLEY

DESHA

BENTON

LOGAN

SALINE

IZARD

PULASKI LONOKE

ARKANSAS

NEWTON

GRANT

CHICOT

MADISON

STONE

MILLER

SHARP

CROSS

DALLAS

PRAIRIE

BOONE

PHILLIPS

PERRY

SEARCY

MARION

FULTON

SEVIER

MISSISSIPPI

JEFFERSON

NEVADA

POINSETT

GARLAND

COLUMBIA

BAXTER

OUACHITA

BRADLEY

JOHNSON

WASHINGTON

MONROE

GREENE

JACKSON

CARROLL

HOWARD

LINCOLN

CALHOUN

CONWAY FAULKNER

VAN BUREN FRANKLIN

CRAIGHEAD

HEMPSTEAD

RANDOLPH

CLEBURNE

MONTGOMERY

LAWRENCE

ST. FRANCIS

CRAWFORD

CLEVELAND

HOT SPRING

INDEPENDENCE

LITTLE

RIVER

WOODRUFF CRITTENDEN

LAFAYETTE

SEBASTIAN

94° 92° 91° 93°

90°

Base from U.S. Geological Survey digital data, 1:2,000,000

0 15 0 30 

15

EX

CommeDucksElectricIndustriIrrigatioMiningPublic S

Crowleys Well type 

gallonto reprwater-repres

36°

35°

34°

Figure 10. Wells with reported water use from the alluvial aquifers in the Coastal Plain in Arkansas, 2010.
EXPLANA

Annual water withdrawn f

million gallons per day 

0.1 to 50.0 50.1 to 100.0 100.1 to 150.0 150.1 to 200.0 200.1 to 250.0 250.1 to 300.0 300.1 to 350.0 350.1 to 400.0 400.1 to 450.0 No color represents no report

0 60 0 60 120 K

Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977; Holland, 1981, 1987, 1993, 1999, 2004, 2007 Base from U.S. Geological Survey digital data 1:2,000,000 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 

36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 1965 1980 1985 1970 1975

Figure 11. Water use from alluvial aquifers in Arkansas from 1965 to 2010.
EXPLAN

Annual water withdrawn 

million gallons per da

0.1 to 50.050.1 to 100.0100.1 to 150.0150.1 to 200.0200.1 to 250.0250.1 to 300.0300.1 to 350.0350.1 to 400.0400.1 to 450.0

No color represents no repo

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

0 60 0 60 120 

Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977;

 Holland, 1981, 1987, 1993, 1999, 2004, 2007

Base from U.S. Geological Survey digital data 1:2,000,000

19902005 2010

1995 2000

Figure 11. Water use from alluvial aquifers in Arkansas from 1965 to 2010.—Continued
66 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Table 17. Water use from alluvial aquifers in Arkansas, 1965–2010.—Continued

[Data from Halberg and Stephens (1966); Halberg, (1972, 1977); Holland (1981, 1987, 1993, 1999, 2004, 2007). Units are million gallons per day]

County 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Arkansas 113.45 117.38 136.27 209.49 185.07 356.97 402.63 567.33 472.97 496.36

Ashley 22.80 35.38 53.27 109.56 77.43 74.35 90.77 105.78 148.13 128.34

Bradley 0.34 0.00 0.00 0.00 0.56 0.36 0.37 0.00 0.00 0.00

Calhoun 0.00 0.00 0.00 0.00 0.02 0.03 0.04 0.00 0.00 0.00

Chicot 12.19 23.94 46.61 69.19 75.71 116.48 149.52 172.84 247.08 200.76

Clark 0.12 0.09 0.13 0.35 2.17 0.70 0.82 0.00 0.00 0.00

Clay 22.13 19.04 60.33 150.50 175.87 196.40 170.55 260.94 466.06 360.50

Cleburne 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.37

Cleveland 0.04 0.02 0.02 0.03 0.19 0.22 0.06 0.00 0.00 0.00

Columbia 0.00 0.00 0.00 0.00 1.20 0.73 0.85 0.00 0.00 0.04

Conway 2.10 8.06 7.53 5.44 4.19 1.64 1.26 1.94 2.51 1.53

Craighead 48.82 65.87 145.27 222.57 202.84 237.55 314.73 329.12 350.08 355.18

Crawford 1.18 1.71 0.84 2.51 4.15 1.00 0.37 0.38 0.94 0.87

Crittenden 26.37 29.68 38.16 78.98 113.68 62.33 104.26 130.06 151.42 210.75

Cross 67.96 85.37 169.61 226.34 261.00 337.39 284.87 406.53 592.27 508.98

Dallas 0.00 0.00 0.00 0.00 0.27 0.24 0.20 0.00 0.00 0.00

Desha 45.11 81.13 114.04 146.27 128.62 211.71 230.54 324.84 297.34 340.72

Drew 8.51 22.51 32.10 43.60 41.08 35.94 53.85 54.70 74.58 31.34

Faulkner 0.00 1.93 0.36 0.53 0.67 0.78 0.66 0.00 2.22 4.50

Franklin 0.76 1.32 0.27 0.24 0.96 0.71 0.47 0.00 0.39 0.46

Fulton 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01

Grant 0.11 0.11 0.12 0.13 0.23 0.23 0.30 0.00 0.00 3.39

Greene 15.75 18.64 67.93 138.96 131.79 118.15 147.51 152.45 217.60 350.19

Hempstead 0.26 0.00 0.00 0.00 1.81 0.80 1.21 0.00 0.00 0.00

Hot Spring 0.04 0.13 0.14 0.15 0.46 0.22 0.04 0.00 0.00 0.00

Independence 2.17 5.29 7.67 16.85 32.57 7.74 14.71 35.74 41.84 57.58

Jackson 56.87 60.03 164.79 212.89 203.53 269.79 284.10 363.38 382.70 415.50

Jefferson 42.01 51.60 106.79 141.14 133.97 174.73 264.74 377.74 227.36 237.47

Johnson 0.60 0.97 1.25 2.24 2.87 0.90 0.61 1.33 0.32 0.35

Lafayette 4.61 4.37 12.19 18.88 16.62 2.97 23.01 11.00 38.31 23.89

Lawrence 17.72 25.54 77.02 154.11 153.69 212.39 256.61 290.65 222.20 178.65

Lee 25.44 21.80 40.32 116.73 96.60 162.52 161.12 234.23 265.86 305.40

Lincoln 25.88 69.24 83.92 88.74 86.06 110.40 131.35 167.16 181.67 193.96

Little River 1.42 3.52 3.17 5.57 3.22 2.70 1.64 1.76 4.43 4.12

Logan 0.31 0.54 0.29 0.25 0.33 0.20 0.08 1.54 1.65 0.71

Table 17. Water use from alluvial aquifers in Arkansas, 1965–2010.

[Data from Halberg and Stephens (1966); Halberg, (1972, 1977); Holland (1981, 1987, 1993, 1999, 2004, 2007). Units are million gallons per day]
Aquifers of the Coastal Plain 67

Table 17. Water use from alluvial aquifers in Arkansas, 1965–2010.—Continued

[Data from Halberg and Stephens (1966); Halberg, (1972, 1977); Holland (1981, 1987, 1993, 1999, 2004, 2007). Units are million gallons per day]

County 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Lonoke 155.46 177.03 257.15 374.13 293.84 263.65 300.26 373.11 413.08 343.87

Miller 1.71 2.41 1.74 3.86 18.77 8.13 9.26 6.92 16.14 9.08

Mississippi 5.19 7.51 8.48 19.44 50.36 93.68 126.29 185.78 271.19 364.73

Monroe 56.08 45.97 81.80 165.21 124.11 178.60 177.85 235.69 288.33 293.58

Nevada 0.00 0.00 0.00 0.00 0.83 0.33 0.27 0.00 0.00 0.00

Ouachita 0.00 0.00 0.00 0.00 0.36 0.13 0.15 0.00 0.00 0.00

Perry 0.00 1.74 0.28 0.24 0.00 0.00 0.00 0.00 0.46 0.49

Phillips 14.44 14.15 16.85 78.01 71.76 110.89 128.81 204.45 204.37 261.19

Pike 0.42 0.56 0.03 0.06 0.98 0.35 0.24 0.00 0.47 0.64

Poinsett 86.18 100.50 177.68 308.86 299.77 403.22 442.51 583.84 678.17 841.44

Polk 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.03 0.00 0.00

Pope 1.02 1.49 3.25 3.45 6.53 10.59 2.73 2.32 1.55 0.71

Prairie 69.90 70.76 125.79 166.49 469.56 185.00 200.04 242.73 247.57 214.65

Pulaski 12.78 16.80 21.69 33.50 29.54 28.66 18.01 26.35 26.24 15.27

Randolph 3.16 3.98 18.85 42.41 42.05 49.54 57.09 85.88 102.26 111.24

Saline 0.00 0.15 0.12 0.20 0.20 0.20 0.24 0.00 0.98 1.32

Sebastian 0.21 0.12 0.17 0.15 1.07 0.40 0.18 0.00 0.00 0.24

Sevier 0.17 0.03 0.04 0.05 0.04 0.33 0.16 0.00 0.00 0.11

Sharp 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01

St. Francis 32.79 52.26 104.25 140.71 110.90 159.66 189.10 252.22 295.34 345.96

Stone 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.07

Union 0.05 0.00 0.00 0.00 0.46 0.36 0.47 0.01 0.00 0.05

Van Buren 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.41 0.00

Washington 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00

White 3.55 5.42 14.43 47.20 50.50 41.42 59.21 48.32 48.05 34.22

Woodruff 58.00 49.47 22.39 166.97 142.37 140.78 254.48 351.46 265.79 182.48

Yell 0.47 2.52 2.15 3.75 5.96 0.58 0.41 1.16 2.37 0.45

Total 1,066.65 1,308.08 2,227.55 3,716.93 3,859.39 4,375.77 5,061.61 6,592.72 7,252.70 7,433.72
WHITE DREW PIKE ASHLEY DESHA LONOKE ARKANSAS MILLER CROSS PRAIRIE MISSISSIPPI 6,928 JEFFERSON POINSETT MONROE JACKSON LINCOLN CRAIGHEAD LAWRENCE ST. FRANCIS WOODRUFF LITTLE RIVER CRITTENDEN LAFAYETTE 908 631 876628 864 215 649 699 955 424 207 121 335 465 52 649 655 268 462 418 431 190 19 PULASKI LEE CLAY 1,529 GRANT CHICOT PHILLIPSGREENE RANDOLPH 3,420 INDEPENDENCE 2,123 2,573 1,100 1,709 2,982 1,547 UNION SEVIER CLARK BRADLEY CLEVELAND HOT SPRING HEMPSTEAD -100 -35 -100 -100 -100 -100 0 94° 92° 91° 93° 90° 36°35° 34° 0 15 30 

0 30 6

15 45 -100 to 0 1 to 200 201 to 400 401 to 600 601 to 800 801 to 1,000 > 1,000EXP

 Use of the Co

system, bpercent c

No color indicates no 

Base from U.S. Geological Survey digital data, 1:2,000,000

Figure 12. Change in percentage of water use from the alluvial aquifers in the Coastal Plain alluvial aquifer system in Arkansas from 1965 to 2010.
Aquifers of the Coastal Plain 69

The earliest wells completed in eastern Arkansas were 

predominantly in the Mississippi River Valley alluvial aquifer 

and supplied domestic and livestock requirements (Veatch, 

1906). Withdrawal of groundwater from the aquifer for 

agriculture started just before the turn of the 20th century in 

the Grand Prairie for irrigation of rice and, to a lesser extent, 

soybeans. In most areas, the aquifer is high-yielding and 

capable of producing hundreds to thousands of gallons per 

minute and making it very well suited for agricultural supply. 

Rice farming began in 1897 on 3 acres in Lonoke County 

by a single farmer (Stephenson and Crider, 1916). Soils of 

the Grand Prairie did not drain well and were underlain by 

an extensive clay layer, which was perfect for flooding of 

fields. Early rice production efforts were successful, and 

rice agriculture quickly expanded. Commercial rice farming 

began on 70 acres in 1904 in Lonoke County and was present 

throughout the Grand Prairie region by 1910 (Stephenson and 

Crider, 1916; Engler and others, 1945, 1963; Baker, 1955; 

Sniegocki, 1964; Gates, 2005). With the introduction and 

expansion of rice production in the Grand Prairie region, water 

use increased dramatically (fig. 13). Economic rice production 

required irrigation, and farmers in the Grand Prairie relied 

heavily on the Mississippi River Valley alluvial aquifer. The 

entirety of the 1906 rice crop, some 4,000 acres, was reported 

as being irrigated with groundwater (Engler and others, 

1945). By 1916, Arkansas County had more than 250 rice 

irrigation wells (Stephenson and Crider, 1916). Early farmers 

in the Grand Prairie area called the groundwater resources 

“limitless” and “inexhaustible” (Gates, 2005); however, the 

poorly drained soils that provided such optimum conditions 

for rice production also restricted recharge to the aquifer, and 

considerable water-level declines were noted during the early 

history of irrigation as rice production expanded (Engler and 

others, 1945).

Rice cultivation spread quickly to the rest of eastern 

Arkansas because of many factors. Rice commanded high 

Figure 13. Rice acreage and corresponding irrigation water use from Mississippi River Valley alluvial aquifer in the Grand Prairie 

region of Arkansas, 1905–57. 1905 1907 1909 1911 

1913 1915 

1917 

1919 

1921 

1923 1925 1927 

1929 

1931 

1933 1935 1937 1939 

1941 

1943 1945 1947 1949 

1951 

1953 1955 1957 

Year

0 

50 

100 

150 

200 

250 

300 

Irrigated rice acreage, in thousand acres

0 

50 

100 

150 

200 

250 

300 

350 

400 

Groundwater used for irrigation of rice, in million gallons per day 

Groundwater use

Irrigated rice acreage 

Data from Engler and others (1945, 1963). 

EXPLANATION
70 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

market prices nationally with little regional or national 

competition, and drillers offered “water or no pay” discounts 

to farmers looking to make the expensive investment of a 

rice well (Gates, 2005). Farmers saw a use for swampy lands 

and clay-rich soils that were unable to economically produce 

other crops. By 1912, 13 counties grew rice: Arkansas, 

Clay, Craighead, Cross, Jefferson, Lawrence, Lee, Lonoke, 

Monroe, Poinsett, Prairie, St. Francis, and Woodruff. Acreage 

of rice grew rapidly across the State: 189,000 acres were 

documented by 1938 and approximately 600,000 acres in 

1954 (fig. 14).

Natural and economic factors affecting other crops 

influenced the growth of rice agriculture throughout this 

period. Rice production increased through the early part of 

the 20th century (fig. 13). With this boom in rice production 

and resulting irrigation, groundwater withdrawals reached a 

peak in 1920 (Engler and others, 1945, 1963; Rosencrantz, 

1946) but declined the following year as rice acreage 

dropped as a result of market excess. Cotton, a dryland 

crop that conventionally relied on precipitation rather than 

irrigation to meet crop-water requirements, was traditionally 

grown in the Mississippi River Delta; however, the drought of 

1930–31 resulted in a poor cotton harvest causing economic 

hardship for growers. As a result, more farmers turned to rice 

and installed groundwater wells—a controlled and predictable 

water source. 

Government and politics were a large factor affecting 

the increasing acreage of rice and therefore widespread 

and increasing use of the Mississippi River Valley alluvial 

aquifer in Arkansas. Many farmers in the northern Delta 

region switched from dryland cotton to irrigated rice 

production when the Agricultural Adjustment Act of 1933 

placed controls on the amount of cotton produced (Williams, 

2012). However, rice acreage in the Grand Prairie region 

were reduced during the Great Depression years when crop 

prices decreased (Chowdhury, 2002). Rice production and 

groundwater use increased again in the beginning of the 

1940s during World War II, resulting in increased demands on 

domestic food production, and then dropped dramatically in 

the mid-1950s when Congress placed acreage controls on rice 

(fig. 13) (Broom and Reed, 1973; Broom and Lyford, 1981; 

Chowdhury, 2002). 

Figure 14. Acres of rice harvested and groundwater use for irrigation of rice in Arkansas.

Water used for irrigation—Stephens and Halberg (1961);

Halberg and Stephens (1966); Halberg (1972, 1977);

Holland (1981, 1987, 1993, 1999, 2004, 2007)

Harvested rice acreage—U.S. Department of Agriculture

National Agricultural Statistics Service (2012). Irrigation

acreage numbers not available prior to 1972

EXPLANATION

1938 

1940 1942 

1944 

1946 

1948 

1950 1952 

1954 

1956 

1958 

1960 1962 

1964 

1966 1968 1970 1972 

1974 

1976 

1978 

1980 1982 1984 1986 

1988 

1990 1992 1994 1996 

1998 

2000 2002 2004 2006 2008 2010 

Year

0 

200 

400 

600 

800 

1,000 

1,200 

1,400 

1,600 

1,800 

2,000 

Rice harvested, in thousand acres 

0 

1,000 

2,000 

3,000 

4,000 

5,000 

6,000 

Groundwater used for irrigation of rice, in million gallons per day 
Aquifers of the Coastal Plain 71

After World War II, broad availability of affordable farm 

tractors and earth-moving equipment coincided with increased 

rice production and irrigation in southern and eastern 

Arkansas. Previously, much of this area remained undeveloped 

because of high water levels, the prevalence of wetlands and 

swampy soils, and extensive forest. Availability of machinery 

that could clear marsh and forest, ditch and drain wetlands, 

and create farmland changed the economics of farming in 

the area and changed the face of the land (Williams, 2012). 

During this time, rice wells were installed in areas where rice 

previously could not be grown. In Ashley County, irrigation 

wells produced 8 Mgal/d during rice growing season in 1947, 

whereas 5 years earlier, no rice irrigation was reported for 

that county (Hewitt and others, 1949). Similarly, Desha and 

Lincoln Counties had approximately 6 rice wells in 1946 that 

increased to 400 wells with a combined use of 45 Mgal/d 

by 1956 (Bedinger and Reed, 1961). Rice production began 

in Chicot County in 1946; by 1956, 12 Mgal/d was being 

pumped for irrigation (Onellion and Criner, 1955). Rice 

irrigation in Drew County resulted in the withdrawal of 

12 Mgal/d from the aquifer in 1955 (Onellion, 1956). Wells 

in Mississippi County withdrew 2.2 Mgal/d in 1957 for rice 

irrigation (Ryling, 1960). 

Another large and rapid increase in rice acreage and 

irrigation demand occurred when rice acreage controls were 

removed in 1975 with the Rice Production Act of 1975 

(fig. 14). Farmers were allowed to produce in excess of their 

acreage allotment for the first time in 20 years (Chowdhury, 

2002). Reported water use from the Mississippi River Valley 

alluvial aquifer for the irrigation use category approximately 

doubled between 1970 and 1975 (fig. 14; table 17). 

Farmers began to increasingly depend upon irrigation 

in the 1970s for other historically dryland crops such as 

corn, soybeans, and cotton (figs. 15 and 16). Drought in the 

early 1980s increased agricultural demands on groundwater 

and caused dramatic declines in water levels (Mahon and 

Poynter, 1993). Use of groundwater for irrigation increased 

by more than 1,000 Mgal/d from 1975 to 1985 (table 7). 

Irrigation of corn from the Mississippi River Valley alluvial 

aquifer increased from approximately 110 Mgal/d in 2000 to a 

Figure 15. Acres harvested of irrigated and nonirrigated soybeans for Arkansas. 1947 1949 1951 1953 1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 

1985 1987 

1989 

1991 

1993 

1995 1997 

1999 

2001 

2003 

2005 

2007 

2009 

2011 

Year

0 

1 

2 

3 

4 

5 

6 

Soybeans harvested, in million acres

Acres harvested, by crop—U.S. Department of Agriculture

National Agricultural Statistics Service (2012). Irrigation

acreage numbers not available prior to 1972

 Soybeans, total 

 Soybeans, irrigated

 Soybeans, nonirrigated

EXPLANATION
72 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

maximum around 430 Mgal/d in 2007 (Terrance W. Holland, 

U.S. Geological Survey, written commun., 2012). Corn 

irrigation decreased to 300 Mgal/d in 2010. This increase 

of corn agriculture coincided with the increased demand 

of corn for biofuels. Irrigated soybean acreage increased 

from 170,000 acres to 2.6 million acres from 1974 to 2011 

(fig. 15). 

 In 2010, 7,050 Mgal/d was withdrawn in eastern 

Arkansas to irrigate approximately 3.2 million acres 

(Terrance W. Holland, U.S. Geological Survey, written 

commun., 2012). Approximately 1.7 million of those acres 

were planted in rice, a slight increase from 1.6 million acres 

in 2005 (fig. 14). Approximately half of the water used from 

the Mississippi River Valley alluvial aquifer in 2010 was 

for rice irrigation (Terrance W. Holland, U.S. Geological 

Survey, written commun., 2013). Poinsett County reported 

the largest use of the alluvial aquifer for irrigation in 2010 

(data not shown), which accounted for 11 percent of all 

groundwater pumped in the State for irrigation use. 

Aquaculture Use

Aquaculture—mainly baitfish and catfish production—

is an important industry in Arkansas relying heavily on 

groundwater withdrawal from the Mississippi River Valley 

alluvial aquifer. Arkansas leads the Nation in production of 

baitfish (Kaliba and Engle, 2006; Stone and Selden, 2006). 

In 2010, 97 percent of water used for aquaculture was 

withdrawn from the Mississippi River Valley alluvial aquifer 

(Terrance W. Holland, U.S. Geological Survey, written 

commun., 2013). Substantial groundwater withdrawals were 

from Lonoke and Chicot Counties.

The first aquaculture farms in Arkansas were built 

in Lonoke in the 1940s to raise goldfish (Engle, 2012; 

Arkansas Agriculture Department, 2013). Multiple counties 

in southeastern Arkansas began aquaculture in the 1960s 

(Broom and Reed, 1973; Kaliba and Engle, 2006). Halberg 

and Reed (1964) estimated that 11 Mgal/d were used to 

refill commercial ponds in an area of northeastern Arkansas 

Figure 16. Acres harvested of irrigated and nonirrigated cotton for Arkansas. 

Acres harvested, by crop—U.S. Department of Agriculture

National Agricultural Statistics Service (2012). Irrigation

acreage numbers not available prior to 1972

 Cotton, upland, total

 Cotton, upland, irrigated

 Cotton, upland, nonirrigated

EXPLANATION

0 

0.5 

1 

1.5 

2 

2.5 

3 

Cotton harvested, in million acres

Year

1938 1940 1942 1944 1946 1948 1950 1952 1954 1956 1958 1960 1962 1964 1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 

1994 

1996 1998 2000 2002 2004 2006 2008 2010 
Aquifers of the Coastal Plain 73

including Cross, Lee, Lonoke, Monroe, Prairie, St. Francis, 

and Woodruff Counties. In 1970, there were over 3,000 acres 

of fish farms in Desha and Lincoln Counties (Broom and 

Reed, 1973). 

Aquaculture peaked in the 1980s. Growth and continuity 

of aquaculture in Arkansas has been limited by the lack of 

processing facilities and more recently by competition from 

imported fish. In Chicot County, increases in water-use 

rates for aquaculture were seen in 1980 and again in 1990 

(table 13) after two catfish processing facilities were installed 

(Kaliba and Engle, 2006). Recently, water use and aquaculture 

production rates have declined because of foreign imports of 

catfish and other species (Stone and Selden, 2006; Bell, 2010).

Duck Hunting Use

Arkansas has been an acknowledged duck hunting 

destination since presettlement times (Arkansas Game and 

Fish Commission, 1998). Ducks and geese began using 

land cleared for rice fields as stopping points on their winter 

migration route. As farmers recognized the off-season 

economic potential of leasing land for duck hunting, fields 

were flooded to provide improved stopover habitat. Wateruse reporting did not have a separate category for duck 

hunting until 2005, so determining any trends in water use 

because of duck hunting is difficult with the limited period 

of record. Fields not in production during the off-season are 

flooded using irrigation wells. Many areas where water-level 

declines are an issue, such as the Grand Prairie, continue this 

practice of flooding to create duck habitat. The largest use in 

this category was in Arkansas and Monroe Counties in 2010 

(table 14). 

Public-Supply Use

Until the mid-20th century, all municipalities in eastern 

Arkansas were supplied by groundwater from the Mississippi 

River Valley alluvial aquifer where it was present (Stephenson 

and Crider, 1916; Hale and others, 1947; Engler and others, 

1963). Even where it was not the primary source of water, 

many towns frequently had additional emergency wells 

completed in the Mississippi River Valley alluvial aquifer 

(Stephenson and Crider, 1916; Hale and others, 1947). Waterquality issues related to the Mississippi River Valley alluvial 

aquifer, especially elevated iron concentrations, forced some 

towns to find other sources. 

Declining water levels in the Mississippi River Valley 

alluvial aquifer also forced many municipalities to find other 

water sources, and the Sparta aquifer is currently the primary 

drinking-water source in the Grand Prairie region (fig. 5). 

Three Mississippi River Valley alluvial aquifer wells originally 

were used by the city of Stuttgart (Arkansas County), and 

two Mississippi River Valley alluvial aquifer wells each for 

the cities of Carlisle, Lonoke (both Lonoke County), and 

Hazen (Prairie County) (Stephenson and others, 1916; Engler 

and others, 1945). Stuttgart first tapped the Sparta aquifer 

because of declining water levels in the Mississippi River 

Valley alluvial aquifer and completed its first well into the 

Sparta aquifer by 1947 (Hale and others, 1947; Engler and 

others, 1963). Around the early 1960s, the cities of DeWitt 

and Gillett (Arkansas County) drilled their primary drinkingwater wells deeper into the Sparta aquifer (Engler and others, 

1963). Stuttgart currently has six wells completed in the 

Sparta aquifer; its three Mississippi River Valley alluvial 

aquifer wells are currently (2013) inactive (Lyle Godfrey, 

Arkansas Department of Health, written commun., 2012). 

A combined public-supply use of 1.87 Mgal/d was 

reported in 1960 from the Mississippi River Valley alluvial 

aquifer for Brinkley (Monroe County), DeValls Bluff, Des 

Arc, and Hazen (Prairie County), Forrest City (St. Francis 

County), and Carlisle and Lonoke (Lonoke County) (Halberg 

and Reed, 1964). Currently (2013), Carlisle, DeValls Bluff, 

Forrest City, and Hazen continue to use the Mississippi 

River Valley alluvial aquifer as a sole source. Forrest City 

is the largest public-supply user of the aquifer, pumping 

3.82 Mgal/d in 2010 (Terrance W. Holland, U.S. Geological 

Survey, written commun., 2012). Des Arc still pumps from 

its alluvial wells but added a well completed in the Sparta 

aquifer in 2004. Brinkley and Lonoke now use the Sparta 

aquifer.

Public supply accounted for less than 1 percent of all 

groundwater use in 2010, but the Mississippi River Valley 

alluvial aquifer ranks as the third highest-use aquifer for 

public supply in Arkansas after the Sparta and the Wilcox 

aquifers. More than 50 municipalities use wells completed in 

the Mississippi River Valley alluvial aquifer as their publicsupply source (fig. 10). Lonoke County (primarily the cities 

of Cabot and Jacksonville) used the largest amount of alluvial 

water for public supply from 2000 to 2010. 

Other municipalities using the Mississippi River 

Valley alluvial aquifer are in northeastern Arkansas near 

Crowleys Ridge. All municipalities in Jackson County use the 

Mississippi River Valley alluvial aquifer, which accounted for 

0.81 Mgal/d in 1963 (Albin and others, 1967a) and steadily 

increased to 1.59 Mgal/d by 2010 (Terrance W. Holland, 

U.S. Geological Survey, written commun., 2012). The city of 

Newport originally pumped water from the White River until 

1930, when two wells were drilled into the Mississippi River 

Valley alluvial aquifer (Stephenson and Crider, 1916; Hale, 

1926; Hale and others, 1947). Newport had seven Mississippi 

River Valley alluvial aquifer wells in 2010 and supplied water 

to the cities of Grubbs, Diaz, and Jacksonport (all Jackson 

County). The city of Jonesboro (Craighead County) is another 

major user, withdrawing 2.06 Mgal/d in 2010 (Terrance W. 

Holland, U.S. Geological Survey, written commun., 2012); 

Jonesboro also has wells completed in the Sparta aquifer. 

Although cities east of Crowleys Ridge tap the Wilcox 

aquifer, a few smaller communities use the Mississippi River 

Valley alluvial aquifer.
74 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Domestic Use

Since predevelopment, the Mississippi River Valley 

alluvial aquifer has been the primary source of domestic 

water supply in eastern Arkansas (Stephenson and Crider, 

1916; Onellion and Criner, 1955; Halberg and Reed, 1964; 

Albin and others, 1967a; Lamonds, 1969; Plebuch and Hines, 

1969; Broom and Lyford, 1981). Engler and others (1963) 

noted that all of the estimated 43,000 homes in the Grand 

Prairie relied on wells completed in the Mississippi River 

Valley alluvial aquifer, using about the same amount of water 

as three rice irrigation wells. More recently, domestic supply 

is an important, but lesser in terms of volume, use of the 

Mississippi River Valley alluvial aquifer. Domestic supply 

use has decreased as smaller communities formed rural water 

associations to provide water. Domestic use was less than 

1 percent of total withdrawals from the Mississippi River 

Valley alluvial aquifer in 2010 (Terrance W. Holland, U.S. 

Geological Survey, written commun., 2012). 

Industrial Use

The earliest industrial use of the Mississippi River Valley 

alluvial aquifer was primarily for railroads, ice companies, 

cotton gins, and rice mills (Purdue, 1905; Veatch, 1906; 

Stephenson and Crider, 1916; Engler and others, 1963), but 

predominant industrial use since that time has been for lumber 

and paper industries. Many lumber mills and paper factories 

were present across the State, though somewhat transient in 

the early part of the century, and it was not uncommon for 

withdrawals to occur for only a short time as changes took 

place in operation and production (Mahon and Poynter, 1993). 

Facilities in Pine Bluff (Jefferson County) and in Crossett 

(Ashley County) produce wood and paper products. In Ashley 

County, pumping from the Mississippi River Valley alluvial 

aquifer began around 1900 for sawmills and related paper 

and wood products. Recorded use for wood-products related 

industries in Crossett was 0.2 Mgal/d in 1902, which steadily 

increased over the years: 0.9 Mgal/d in 1920, 2 Mgal/d in 

1925, 10.5 Mgal/d in 1940, 12 Mgal/d in 1946, and 16 Mgal/d 

in 1947 (Hewitt and others, 1949). The Saline River was 

dammed in 1963 to construct a lake and provide a new water 

source for the paper industry in Ashley County (Encyclopedia 

of Arkansas, 2013; U.S. Army Corps of Engineers, 2013a), 

which reduced Ashley County’s industrial consumption of 

groundwater from 28.24 Mgal/d in 1960 to 7.47 Mgal/d in 

1965 (table 11). Records from the ARWUDBS indicate that 

from the mid-1980s to present, all current industrial wells 

in Ashley County tap the Cockfield aquifer (Terrance W. 

Holland, U.S. Geological Survey, written commun., 2012).

 Many wells were drilled in the 1930s and 1940s in 

Jefferson County for ice companies and railroads (Klein and 

others, 1950). Also, the Pine Bluff Arsenal drilled four wells 

into the Mississippi River Valley alluvial aquifer in 1942 

(Klein and others, 1950). These wells were used intermittently, 

depending on production, and pumped a combined 1.1 Mgal/d 

in 1947 but were unused in 1948. Another eight wells in the 

Pine Bluff area were used for industrial purposes with an 

estimated use of 0.3 Mgal/d (Klein and others, 1950). A paperproducts company was the only industrial user in Jefferson 

County in 2010, pumping 6.45 Mgal/d (Terrance W. Holland, 

U.S. Geological Survey, written commun., 2012). Many other 

companies use the Mississippi River Valley alluvial aquifer, 

withdrawing an additional 1.32 Mgal/d in 2010 for a variety of 

manufacturing processes.

Water Level Trends

Prior to widespread agricultural irrigation in the Grand 

Prairie region, the Mississippi River Valley alluvial aquifer 

was confined (Engler and others, 1963). The Mississippi 

River Valley confining unit that overlies the Mississippi River 

Valley alluvial aquifer is a clay-rich unit that is typically 

about 40–100 ft thick and is a primary reason that the region 

is suitable for rice agriculture by holding water to inundate 

the rice plants. However, this clay layer also impedes vertical 

flow, restricts recharge, and in predevelopment time served as 

a confining unit for the underlying Mississippi River Valley 

alluvial aquifer. As groundwater withdrawals increased, 

water levels in many parts of the Mississippi River Valley 

alluvial aquifer declined below the clay layer, and the aquifer 

transitioned to an unconfined condition. In some areas of the 

Grand Prairie, water levels were below the base of the clay 

layer, and withdrawals were recognized as unsustainable, 

with the aquifer being in danger of depletion as early as 1929 

(Engler and others, 1945; Counts and Engler, 1954; Baker, 

1955; Plebuch, 1962; Albin and others, 1967a, b). In extensive 

areas of the Mississippi River Valley alluvial aquifer, declines 

of water levels have resulted in: (1) unconfined conditions 

(that is, the upper section of the aquifer is now unsaturated) 

and (2) reductions in hydraulic pressure, saturated thickness, 

amount of water stored, lateral flow within the aquifer, and 

base flow to streams throughout most of its extent in Arkansas 

(Czarnecki and others, 2012). 

In extensive areas of eastern Arkansas, water was 

withdrawn from the Mississippi River Valley alluvial aquifer 

at rates that exceeded recharge; therefore, those rates could not 

be sustained indefinitely. This water-budget imbalance resulted 

in regional water-level declines, formation of extensive cones 

of depression, reduction of water in storage, and decreases 

in individual well yields. In some areas, water levels have 

declined such that water cannot be pumped at rates needed 

to support demand, particularly for irrigation (Czarnecki 

and Schrader, 2013). In addition, deeper wells were required 

into underlying formations (including the Sparta, Cockfield, 

and Wilcox aquifers) to reach water (Mahon and Poynter, 

1993). Furthermore, excessive dewatering of an aquifer can 

lead to irreversible compaction of the aquifer (subsidence), 

reducing its water-yielding capacity or ability to be recharged 

(Konikow, 2013). 
Aquifers of the Coastal Plain 75

Because of the economic importance of the aquifer 

and concerns regarding depletion, multiple investigations 

focused on water levels in the Mississippi River Valley 

alluvial aquifer in eastern Arkansas (Engler and others, 

1945, 1963; Plebuch, 1962; Albin and others, 1967b; Broom 

and Reed, 1973; Arkansas Geological Commission, 1980; 

Edds and Fitzpatrick, 1984a; Plafcan, 1985, 1986, 1987; 

Plafcan and Edds, 1986; Plafcan and Fugitt, 1987; Ackerman, 

1989b; Plafcan and Remsing, 1989; Westerfield, 1989, 1990; 

Westerfield and Baxter, 1990a, 1990b, 1990c; Westerfield 

and Touschner, 1991, 1992, 1993; Mahon and Poynter, 1993; 

Westerfield and Gonthier, 1993; Westerfield and Poynter, 

1993, 1994; Stanton and others, 1998; Joseph, 1999; Schrader, 

2001b, 2006a, 2008a, 2010; Reed, 2004). Water-level surfaces, 

represented by potentiometric contours from predevelopment 

through 2008, constructed from multiple studies are shown 

in figure 17. Predevelopment-water levels for the Mississippi 

River Valley alluvial aquifer typically were reported as 

near land surface (within 20 ft) and sloped gently from the 

northwest to southeast mirroring topography. As groundwater 

irrigation spread across eastern Arkansas, groundwater 

withdrawals exceeded recharge and water levels declined. 

Changes in water levels were seen as early as 1929, when the 

first water-level map of the area was created from water levels 

measured in the Grand Prairie region (Engler and others, 

1945). Water levels rose slightly in the mid-1960s during a 

period of congressional controls on rice acreage. When the 

controls were removed in 1975, water levels again declined. 

Sustained heavy pumping from wells for extensive 

periods resulted in substantial, long-term, and widespread 

water-level declines in parts of eastern Arkansas; cones of 

depression formed and expanded in many areas. A cone of 

depression appeared early in the pumping history of the Grand 

Prairie region, grew to encompass Arkansas County, and 

continued growing in a northwestern direction into Lonoke 

and Prairie Counties, becoming a major regional depression 

(fig. 17). Another cone of depression developed on the western 

side of Crowleys Ridge (fig. 17). The two cones of depression 

were hypothesized as eventually coalescing if withdrawals 

continued at unsustainable rates as defined by Westerfield 

(1990). On the eastern side of Crowleys Ridge, water 

levels do not reflect declines west of the ridge as a result of 

hypothesized recharge from the Mississippi River. Intermittent 

large industrial withdrawals have caused intermittent 

depressions in Ashley County. For more discussion on recent 

changes in water levels in the Mississippi River Valley alluvial 

aquifer see Schrader (2006a, 2008a, 2010).

Rates of water-level declines by county over an 

approximately 20-year period are included in four reports 

from 2004 through 2010 (Reed, 2004; Schrader, 2006a, 2008a, 

2010). A compilation of these 20-year summary statistics for 

water levels in the Mississippi River Valley alluvial aquifer 

are shown in table 18. Although substantial overlap occurs for 

each approximate 20-year period, in addition to the varying 

number of wells measured in each county, inspection of the 

data provides valuable information on effects of pumping 

over time for each of the counties. Generally, water-level 

declines for each county increased in each reporting period. 

For example, Cross County had mean annual declines in water 

levels about 1 ft or more in all periods. The largest mean 

annual decline, 1.21 ft/yr, was an average of water levels in 

eight wells in Lonoke County from 1984 to 2008. A rise in 

water levels was seen in a single well in Independence County 

for all study periods as well as in wells in White County for a 

couple of time periods (table 18). 

Grand Prairie

In the Grand Prairie, withdrawals for rice irrigation had 

exceeded natural recharge rates as evidenced by considerable 

water-level declines (Engler and others, 1963). Water levels in 

the Mississippi River Valley alluvial aquifer began to decline 

after 1910, although groundwater pumping for irrigation in 

this region only began around 1905 (Thompson, 1936). From 

1910 to 1929, water levels in Grand Prairie wells had a net 

decline ranging from a minimum of 10 ft to more than 35 ft 

(Engler and others, 1945). The largest declines averaged 1.5 ft/

yr. Thompson (1931) noted the development of a cone of 

depression that encompassed a majority of Arkansas County, 

at an estimated 130 ft above National Geodetic Vertical Datum 

of 1929 (NGVD 29) (hereinafter all altitudes refer to feet 

above NGVD 29). The largest declines during this period were 

seen in Arkansas County from southeast of Stuttgart to Almyra 

and in Lonoke County northeast of Ulm to Lonoke (Engler 

and others, 1945, 1963).

With increasing irrigation, water-level declines averaged 

1 ft/yr resulting in many shallow wells going dry by 1930 

(Engler and others, 1963). Water levels in Arkansas County 

continued to decrease, with the cone of depression enlarging 

to the northwest into southern Prairie County by 1938 (Counts 

and Engler, 1945). As shown in the potentiometric surfaces in 

figs. 17B and 17C, the surface at the center of the depression 

in Arkansas dropped 10 ft (to the 120-ft contour) from 1929 

to 1938. The largest declines during this period were between 

Stuttgart and Almyra (Engler and others, 1945) because a 

smaller cone of depression developed at the 110-ft contour 

(fig. 17C).

Declines continued from 1938 to 1953 with water levels 

dropping more than 20 ft between Lonoke to Des Arc and 

south to DeValls Bluff (Counts and Engler, 1954). Water levels 

at Stuttgart dropped an additional 30 ft during this time, for a 

total decline of 60 ft since 1910 (Baker, 1955). From 1953 to 

1961, the depression expanded in a northwesterly direction, 

and water-level declines as much as 9 ft were noted in a line 

from Stuttgart to Lonoke (Plebuch, 1962). Also, the contours 

in central to northern Prairie County and some areas between 

Crowleys Ridge and the White River shifted southward 

(Plebuch, 1962). For example, the 1953 surface shows the 

160-ft contour through northern Prairie County (fig. 17E); the 

160-ft contour is shown in central Prairie County in the 1961 

surface (fig. 17F).
Crowleys Ridge Extent of Mississippi River Valley alluvial aquifer (Clark and Hart, 2009) Grand Prairie region

C

170

EXPLANATION

280

270

260

250

240

230

220

210

200

190

180

170

160

150

140

130

120

110

100

90

80

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 (NGVD 29)Well used for control—Letter indicates hydrograph shown on figures 18 to 21

Pote

 an

Base from U.S. Geological Survey digital data, 1:2,000,000Universal Transverse Mercator projection, zone 15North American Datum of 1983 

80 KILOMETERS

200 40 60 80 MIL

200 40 60

LEE

CLAY

ASHLEY

DESHA

ARKANSAS

LONOKE

CHICOT

PRAIRIE

PHILLIPS

JEFFERSON

MISSISSIPPI

MONROE

LINCOLN

JACKSON

WOODRUFF

CRITTENDEN ST FRANCIS

GREENE

CRAIGHEAD

INDEPENDENCE

LAWRENCE

WHITE

PULASKI

CROSS

DREW

POINSETT

RANDOLPH

35°

34°

36°

94° 93° 92° 91°

90°

Mississippi River

Arkansas River

White River

Mississippi River

Arkansas River

White River

Harrisburg

Wynne

West Memphis Des Arc

Brinkley

De Valls Bluff

Ulm

Stuttgart

Almyra

Lonoke

Hamburg

Crossett

Harrisburg

Wynne

West Memphis Des Arc

Brinkley

De Valls Bluff

Ulm

Stuttgart

Almyra

Lonoke

Hamburg

Crossett

N

M

L

K

J

I

H

G

F

E

D

C

B

A

N

M

L

K

J

I

H

G

F

E

D

C

B

A

35°

34°

36°

92°

91°

90°

270

250

230

230

210

210

210

190

190

190

170

170

150

130

230

110

90

90

270

250

230

230

210

210

210

190

190

190

170

170

150

130

230

110

90

90

250

270

35°

34°

36

92°

210

190

170

1

130

A. Predevelopment 

Figure 17. Selected potentiometric contours of water levels for selected time periods in the Mississippi River Valley alluvial aquifer in Arkansas. 

A, p

C, 1938; 

D, 1944; 

E, 1953 and 1955; 

F, 1961 and 1962; 

G, 1965; 

H, 1972; I, 1980; 

J, 1992; 

K, 1998; L, 2004; 

M, 2006; and 

N, 2008. 
280

270

260

250

240

230

220

210

200

195

190

180

170

160

150

140

130

120

115

110

100

EXPLANATION

Crowleys RidgeExtent of Mississippi  River Valley alluvial aquifer (Clark and Hart, 2009)

170 Potentiometric contour—Shows altitude at which water level would have stood in tightly

 cased wells. Dashed where approximately located. Contour intervals 5, 10, and 15 feet.  Datum is National Geodetic Vertical Datum of 1929 (NGVD 29)

Potentiometric contours modifie

Counts and Engler, 1954; P

Base from U.S. Geological Survey digital data, 1:2,000,000Universal Transverse Mercator projection, zone 15North American Datum of 1983 

80 KILOMETERS

200 40 60 80 MILES

200 40 60

C. 1938 D. 1944 E. 1953 and 1955 

ARKANSAS

Area enlarged

35°

34°

36°

92°

210

210

190

190

130

110

170 

100

35°

34°

36°

92°

91°

90°

270

170

230

270

230

210

210

190

170

170

190

130

250

150 110

210

230

250

190

35°

34°

36°

92°

91°

90°

110

190 170150

115

130

195

150

100

35°

34°

36°

92°

91°

90°

270

230

210

210

190

170

170

190

130

250

150

110

Figure 17. Selected potentiometric contours of water levels for selected time periods in the Mississippi River Valley alluvial aquifer in Arkansas. A, p

C, 1938; D, 1944; E, 1953 and 1955; F, 1961 and 1962; G, 1965; H, 1972; I, 1980; J, 1992; K, 1998; L, 2004; M, 2006; and N, 2008.—Continued
EXPLANATION Crowleys Ridge Extent of Mississippi River Valley alluvial aquifer (Clark and Hart, 2009)

290

280

270

260

250

240

230

220

210

200

190

180

170

160

150

140

130

120

110

100

90

80

70

110 Potentiometric contour—Shows altitude at which water level would have stood in tightly cased

 wells. Dashed where approximately located. Contour intervals 10 and 20 feet. Datum is National Geodetic Vertical Datum of 1929 (NGVD 29)

Potentiometric contours m

Ackerman, 1

Base from U.S. Geological Survey digital data, 1:2,000,000Universal Transverse Mercator projection, zone 15North American Datum of 1983 

80 KILOMETERS

200 40 60 80 MILES

200 40 60

G. 1965 H. 1972 I. 1980 

ARKANSAS

Area enlarged

35°

34°

36°

92°

2

1

150

230

190

170

190

150

130

90

110

210

2

230

210

110

130

90

35°

34°

36°

92°

91°

90°

190

210

150

190

170

170

150

230

210

190

170

170

190

150

130

90

110

210

270

250

230

270

250

290

230

170

210

110

130

190

90

35°

34°

36°

92°

91°

90°

70

130

150

270

270

250

230

210

190

170

190

170

130

90

90

110

150

290

230

250

210

190

110

110

230

210

35°

34°

36°

92°

91°

90°

280

100

240

240

120

140

160

140

120

180

200

220

220

200

180

260

260

200

220

240

220

180

280

Figure 17. Selected potentiometric contours of water levels for selected time periods in the Mississippi River Valley alluvial aquifer in Arkansas. 

A, p

C, 1938; 

D, 1944; 

E, 1953 and 1955; 

F, 1961 and 1962; 

G, 1965; 

H, 1972; I, 1980; 

J, 1992; 

K, 1998; L, 2004; 

M, 2006; and 

N, 2008.—Continued
290

280

270

260

250

240

230

220

210

200

190

180

170

160

150

140

130

120

110

100

90

80

70

EXPLANATION

Crowleys RidgeExtent of Mississippi  River Valley alluvial aquifer (Clark and Hart, 2009)

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 (NGVD 29)

90

Potentiometric c

Base from U.S. Geological Survey digital data, 1:2,000,000Universal Transverse Mercator projection, zone 15North American Datum of 1983 

80 KILOMETERS

200 40 60 80 MILES

200 40 60

K. 1998 L. 2004 M. 2006 

ARKANSAS

Area enlarged

35°

34°

36°

92°

190

170

170

190 150

130

110 130

90

90

130

90

90

110

150

210

210

150

170

35°

34°

36°

92°

91°

90°

270

250 230

210 210

230

190

170

190

170

170

170

190150

130

110 130

90

130

90

90

110

150

150

130

210

210

150

170

130

130

190

130

270

250

150

190

230

210

90

35°

34°

36°

92°

91°

90°

270

250

230

210 210

230

190

170

190

170

170

170 190 150

130

110 130

90

130

90

90

110

150

150

130

210

210

150

170

130

270

250

150

190

290

230 250

35°

34°

36°

92°

91°

90°

270

210 210 230

190

170

190

170

170

170 190

150

130

110 130

90

90 90

110

150

150

130

210

210

130

270

250

150

190

290

230

250

Figure 17. Selected potentiometric contours of water levels for selected time periods in the Mississippi River Valley alluvial aquifer in Arkansas. A, p

C, 1938; D, 1944; E, 1953 and 1955; F, 1961 and 1962; G, 1965; H, 1972; I, 1980; J, 1992; K, 1998; L, 2004; M, 2006; and N, 2008.—Continued
Table 18. Range, mean, and median of annual rise-decline in water level by county for wells in the Mississippi River Valley alluvial aquifer.—Continu[Annual rise or decline in water level for each well is calculated using linear regression; negative value indicates decline; positive value indicates rise; Shaded values indicate thgreater than 1 foot/year; >, greater than] County Number of wells 1977– 20021 Range of annual rise/de- cline in water level (feet/year) 1977–20021 Median annual rise/de- cline in water 1977– 20021 Number of wells 1980– 20042 Range of annual rise/de- cline in water level (feet/year) 1980–20042 Mean annual rise/de- cline in water 1980–20042 Median annual rise/ decline in water 1980– 20042 Number of wells 1982– 20063 Range of annual rise/de- cline in water level (feet/year) 1982–20063 Mean annual rise/de- cline in water 1982– 20063 Median annual rise/ decline in water 1982– 20063 Number of wells 1984– 20084 Ra

a

ris

cl

w

l

(fee

198

Arkansas 27 -0.66 to 0.84 -0.11 28 -0.69 to 0.84 -0.1 -0.13 27 -0.80 to 0.77 -0.12 -0.15 30 -0

Ashley 6 -0.33 to 0.02 -0.18 7 -0.37 to 0.11 -0.14 -0.15 9 -0.33 to 0.11 -0.14 -0.18 10 -4

Chicot 2 -0.47 to -0.07 -0.27 2 -0.47 to -0.11 -0.29 -0.29 3 -0.40 to -0.11 -0.26 -0.26 7 -1

Clay 6 -0.51 to 0.18 -0.16 4 -0.55 to 0.03 -0.29 -0.33 7 -0.55 to -0.01 -0.21 -0.15 7 -0

Craighead 5 -1.1 to -0.01 -0.11 4 -1.05 to -0.02 -0.48 -0.42 5 -0.99 to 0.18 -0.37 -0.18 6 -0

Crittenden 4 -0.51 to -0.04 -0.37 4 -0.55 to -0.11 -0.37 -0.42 6 -0.62 to -0.15 -0.37 -0.35 5 -0

-

Cross 5 -1.13 to -0.29 -0.99 5 -1.1 to -0.33 -0.88 -1.02 5 -1.24 to -0.33 -0.94 -1.02 7 -3

-

Desha 5 -0.8 to -0.04 -0.26 4 -0.77 to -0.26 -0.55 -0.58 5 -0.80 to -0.07 -0.5 -0.62 6 -1

-

Drew 2 -0.11 to -0.02 -0.06 1 -0.151 -0.151 -0.151 4 -0.29 to -0.15 -0.24 -0.26 4 -0

-

Greene 4 -0.8 to -0.01 -0.6 4 -0.77 to -0.03 -0.46 -0.53 5 -0.73 to -0.11 -0.53 -0.66 4 -0

-

Independence 1 0.00 0.00 1 0.04 0.04 0.04 1 0.07 0.07 0.07 1 

Jackson 4 -0.88 to -0.25 -0.66 4 -0.84 to -0.26 -0.65 -0.75 5 -0.84 to -0.29 -0.68 -0.77 5 -0

-

Jefferson 6 -0.69 to -0.07 -0.22 6 -0.69 to -0.11 -0.29 -0.24 6 -0.69 to -0.18 -0.32 -0.24 7 -0

Lee 4 -0.62 to -0.29 -0.55 4 -0.65 to -0.29 -0.51 -0.55 5 -0.58 to -0.26 -0.49 -0.55 5 -0

-

Lincoln 3 -0.37 to 

0.69

-0.15 2 -0.44 to 

-0.18

-0.31 -0.31 3 -0.84 to 

-0.33

-0.57 -0.55 4 -1

-

Table 18. Range, mean, and median of annual rise-decline in water level by county for wells in the Mississippi River Valley alluvial aquifer.[Annual rise or decline in water level for each well is calculated using linear regression; negative value indicates decline; positive value indicates rise; Shaded values indicate thgreater than 1 foot/year; >, greater than]
Table 18. Range, mean, and median of annual rise-decline in water level by county for wells in the Mississippi River Valley alluvial aquifer.—Continu[Annual rise or decline in water level for each well is calculated using linear regression; negative value indicates decline; positive value indicates rise; Shaded values indicate thgreater than 1 foot/year; >, greater than]

County

Number 

of wells 

1977–

20021

Range of 

annual 

rise/decline in 

water 

level 

(feet/year) 

1977–20021

Median 

annual 

rise/decline in 

water 

1977–

20021

Number 

of wells 

1980–

20042

Range of 

annual 

rise/decline in 

water 

level 

(feet/year) 

1980–20042

Mean 

annual 

rise/decline in 

water 

1980–20042

Median 

annual 

rise/

decline 

in water 

1980–

20042

Number 

of wells 

1982– 

20063

Range of 

annual 

rise/decline in 

water 

level 

(feet/year) 

1982–20063

Mean 

annual 

rise/decline in 

water 

1982–

20063

Median 

annual 

rise/

decline 

in water 

1982–

20063

Number 

of wells 

1984–

20084

Ra

a

ris

cl

w

l

(fee

198

Lonoke 6 -1.35 to 

0.44

-0.6 4 -1.21 to 

-0.51

-0.79 -0.73 5 -1.06 to 

-0.51

-0.8 -0.88 8 -2

-

Mississippi 9 -0.11 to 

0.02

-0.07 9 -0.15 to 0 -0.06 -0.07 8 -0.22 to 

0.00

-0.09 -0.09 8 -0

Monroe 8 -0.51 to 

-0.03

-0.26 6 -0.58 to 

-0.03

-0.31 -0.29 8 -0.55 to 

-0.01

-0.28 -0.27 9 -0

-

Phillips 3 -0.26 to 

-0.07

-0.11 3 -0.29 to 

-0.11

-0.19 -0.18 3 -0.29 to 

-0.07

-0.18 -0.18 3 -0

-

Poinsett 5 -1.42 to 

-0.03

-0.33 5 -1.35 to 

-0.02

-0.53 -0.33 5 -1.28 to 

0.03

-0.37 -0.18 5 -1

Prairie 10 -0.84 to 

0.48

-0.18 9 -0.73 to 

0.29

-0.29 -0.29 10 -0.66 to 

0.00

-0.31 -0.29 11 -0

Pulaski 1 -0.26 -0.26 1 -0.33 -0.33 -0.33 1 -

Randolph 1 -0.18 -0.18 2 -0.18 to 

-0.04

-0.11 -0.11 1 -0.26 -0.26 -0.26 2 -0

-

St. Francis 8 -0.91 to 

-0.07

-0.54 7 -0.91 to 

-0.07

-0.56 -0.69 7 -0.95 to 

-0.04

-0.56 -0.62 7 -0

-

White 3 -0.33 to 

0.22

-0.22 4 -0.22 to 

0.22

-0.03 -0.06 3 0.11 to 

0.29

0.19 0.18 6 -0

Woodruff 5 -0.51 to 

>0.00

-0.07 5 -0.55 to 0 -0.17 -0.07 5 -0.58 to 

0.00

-0.19 -0.11 5 -0

1Data from Reed (2004); mean for 1977–2002 not available.2Data from Schrader (2006a).3Data from Schrader (2008a).4Data from Schrader (2010).
82 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Comparison of the 1961 and 1965 potentiometricsurface contours shows water-level gains in some areas 

(figs. 17F and 17G; Plebuch, 1962; Albin and others, 1967b). 

This was attributed to a reduction in groundwater pumping 

because of congressional controls on rice acreage that went 

into effect in 1955 (Chowdhury, 2002; Broom and Lyford, 

1981; Broom and Reed, 1973). Consequently, the cone of the 

depression surrounding the Grand Prairie was not as deep 

in 1965 (120-ft contour) as in 1960 (100-ft contours) (Albin 

and others, 1967b). Potentiometric surfaces for areas east 

of Crowleys Ridge also reflected increases in water levels 

between 1955 and 1962 (Plebuch, 1962).

Water use increased as rice-acreage controls were 

removed in 1975 (fig. 14), and water-level declines continued 

to 2008 (Schrader, 2010). A smaller cone of depression 

appeared on the border of Monroe and St. Francis Counties in 

1972 at the 160-ft contour (fig. 17H) and continued to deepen 

and expand horizontally (Ackerman, 1989b). Two smaller 

cones of depression appeared on the border of Lonoke and 

Prairie Counties around 1980 (fig. 17I; Ackerman, 1989b); 

these enlarged and eventually coalesced with the cone of 

depression in Arkansas County by 1992 (fig. 17J). The cone 

of depression in the Grand Prairie currently (2013) continues 

to extend to the northwest and decline vertically in Arkansas 

and Prairie Counties between the Arkansas and White Rivers 

(T.P. Schrader, U.S. Geological Survey, oral commun., 2013). 

In the 2008 surface, two distinct cones of depression were 

seen at the 70-ft contour in central Arkansas County and at 

the 100-ft contour in eastern Lonoke County (fig. 17N). 

Well hydrographs (fig. 18) provide another valuable tool 

for the evaluation of water-level declines in the Grand Prairie 

area. A well near the Arkansas River (well A; location of well 

shown in fig. 17) shows little to no effects from large-scale 

pumping. Wells B, C, and D (figs. 17 and 18) were located 

inside the depression in Arkansas, Prairie, and Lonoke 

Counties, respectively, and reflect declines associated with 

the combined large-scale withdrawals, low recharge, and an 

expanding cone of depression. The largest declines are noted 

in well B in Arkansas County near the center of the cone of 

depression (figs. 17 and 18). 

Grand Prairie Area Demonstration Project and Bayou Meto 

Project

Public concern about declining water levels in the 

Mississippi River Valley alluvial aquifer has been present 

since the 1920s (Engler and others, 1945, 1964; Sniegocki, 

1964; Gates, 2005). A major drought in the early 1980s 

caused massive crop failures and renewed concerns of 

declining water levels. As a result, numerous groundwater 

studies were instigated (Bryant and others, 1985), and 

water-conservation efforts were introduced to address the 

declines. ANRC designated the Grand Prairie area as a 

critical groundwater area for Sparta and Mississippi River 

Valley alluvial aquifers in 1998 (fig. 1; Arkansas Natural 

Resources Commission, 1996). This designation included 

all of Arkansas, Jefferson, and Prairie Counties with parts of 

Lonoke, Pulaski, and White Counties included in the extent 

of the Sparta aquifer. 

Surface-water diversions currently are planned (2013) 

for the White and Arkansas Rivers to provide irrigation 

water and decrease the dependence on both the Mississippi 

River Valley alluvial and Sparta aquifers in the Grand Prairie 

region. The Grand Prairie Area Demonstration Project will 

supply users in Arkansas and Prairie Counties with water 

from the White River; the Bayou Meto Project will deliver 

surface water from the Arkansas River to farmland in 

Lonoke, Prairie, Jefferson, and Arkansas Counties. These 

projects were initially proposed to the U.S. Army Corps of 

Engineers in 1930 as result of concern over rapidly falling 

water levels and were authorized by the Flood Control 

Act of 1950 (Truman, 1949) but delayed for years because 

of political and environmental concerns, lawsuits, and 

other delays (Tacker and others, 2010). Construction of 

onfarm features (surface-water reservoirs and tail-water 

recovery systems) was initiated in the fall of 2000, with 

over $38 million in contracts administered by the NRCS 

using project funds and non-Federal cost-share funds 

provided by the farmers. Over 250 onfarm reservoirs have 

been completed as a part of the project (Arkansas Natural 

Resources Commission, 2012b). For the Grand Prairie 

Area Demonstration Project, construction of the DeValls 

Bluff pumping station on the White River began in 2005, 

and its completion was expected in late 2013 (Arkansas 

Natural Resources Commission, 2012b; U.S. Army Corps of 

Engineers, 2013b). Completion of two of the four pumping 

stations on the Arkansas River in the Bayou Meto Basin 

also was expected in late 2013 (Arkansas Natural Resources 

Commission, 2012b). The Grand Prairie Area Demonstration 

Project is projected to begin operation in June 2016 (Dennis 

Carmen, National Resources Conservation Service, oral 

commun., 2013).
Aquifers of the Coastal Plain 83

West of Crowleys Ridge

Crowleys Ridge serves as a hydraulic divide for the 

Mississippi River Valley alluvial aquifer in northeastern 

Arkansas; water levels can be dramatically different on each 

side of the ridge. During the 1950s and 1960s, water levels 

rose in areas east of Crowleys Ridge and declined west of 

Crowleys Ridge (Albin and others, 1967b; figs. 17E and 

17F). ANRC established the Mississippi River Valley alluvial 

aquifer west of Crowleys Ridge as a critical groundwater area 

in 2009 (fig. 1; Arkansas Natural Resources Commission, 

2009).

The earliest postdevelopment-potentiometric surface for 

this area was created using 1938 water levels (fig. 17C). The 

majority of the aquifer west of Crowleys Ridge experienced 

declines of 10 ft or less from 1938 to 1953, a time when 

rice acreage tripled (Counts and Engler, 1954; Baker, 1955). 

Some areas in western Craighead, Poinsett, Greene, and 

eastern Lawrence and Jackson Counties showed water-level 

rises over that period attributed to recharge from the Cache 

River (Counts and Engler, 1954). By the 1950s, water-level 

declines were observed in wells in areas west of Crowleys 

Ridge in Craighead, Poinsett, and Cross Counties (Plebuch, 

1962). The average decline rate west of Crowleys Ridge 

was 1 ft/yr; the greatest decline was 16 ft/yr in northwestern 

Cross County. Further to the west in Randolph and Lawrence 

Counties, pumpage did not affect water levels during this time 

period (Lamonds and others, 1969).

Two cones of depression formed at the 180-ft contour 

adjacent to the western side of Crowleys Ridge in Cross and 

Poinsett Counties between 1961 and 1965 (fig. 17F and 17G; 

Albin and others, 1967b); each had closed potentiometric 

contours (indicating cones of depression) in 1965 at the 180-ft 

contour near Harrisburg (Poinsett County) and north of Wynne 

(Cross County), respectively. These two cones of depression 

did not appear on the 1972 or 1980 water-level surface maps 

(figs. 17H and 17I; Ackerman, 1989b). These depressions 

reappeared, having expanded and coalesced in the 1983 and 

later maps (not shown in fig. 17; Edds and Fitzpatrick, 1984; 

Plafcan and Edds, 1986), and the depression had deepened to 

the 160-ft contour in 1983 (Edds and Fitzpatrick, 1984). 

Figure 18. Hydrograph of water levels in wells completed in Mississippi River Valley alluvial aquifer in the Grand Prairie region of 

Arkansas.

Water level, in well completed

in the Mississippi River

Valley alluvial aquifer

 Well A (Arkansas County)

 Well B (Arkansas County)

 Well C (Prairie County)

 Well D (Lonoke County) 

60 

80 

100 

120 

140 

160 

180 

200 

1928 1938 1948 1958 1968 

Year

1978 1988 1998 2008 

Water level, in feet above National Geodetic Vertical Datum of 1929

EXPLANATION
84 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

A cone of depression in the Mississippi River Valley 

alluvial aquifer appeared near Brinkley (northeastern Monroe 

County) in 1972 with closure at the 160-ft contour (fig. 17H; 

Ackerman, 1989b). The depression had expanded to the north 

and east by 1992 (fig. 17J; Westerfield and Poynter, 1993) and 

to the south following the border of Monroe and Lee Counties 

by 1996 (not shown in fig. 17; Stanton and others, 1998). 

Between 2000 and 2002 (both years not shown in fig. 17), the 

150-ft potentiometric contour in western St. Francis County 

expanded to central Monroe and western Lee Counties and 

coalesced with the cone of depression that stretched across 

Cross, Poinsett, and southern Craighead Counties (Schrader 

2001b; Reed, 2004). Closure in the bottom of the original 

depression had dropped to the 140-ft contour by 2002, and 

dual cones at the 130-ft contours were observed by 2006 

(Reed, 2004; Schrader, 2008a). Only one of these cones was 

noted in the 2008 potentiometric surface (Schrader, 2010).

By 1994 (not shown in fig. 17), the closed 160-ft contour 

had expanded to include parts of Craighead, Cross, Lee, 

Monroe, Poinsett, St. Francis, and Woodruff Counties (Stanton 

and others, 1998); most of Cross and Poinsett Counties, west 

of Crowleys Ridge, had water levels at or below the 160-ft 

contour (Stanton and others, 1998). By 2000, water levels 

across most of those two counties had declined to the 150-ft 

contour (Schrader, 2001b). From 1994 to 2004, the sevencounty area of Craighead, Cross, Lee, Monroe, Poinsett, St. 

Francis, and Woodruff experienced water-level declines of 

at least 10 ft, from the 160-ft contour in 1994 to the 150-ft 

contour in 2004 (Schrader, 2006a). As of 2008, each of those 

seven counties had areas with water levels within the 140-ft 

contour (Schrader, 2010). 

In Clay (well L), Craighead (well K), and Jackson 

(well M) Counties, water levels dropped quickly after the 

controls on rice acreage were removed with the Rice Control 

Act of 1975 (fig. 19; location of wells shown in fig. 17). Water 

levels for wells in Cross (J) and St. Francis (well N) Counties 

have steadily decreased since measurements first were 

recorded (fig. 19).

East of Crowleys Ridge

The earliest potentiometric surface for the area east 

of Crowleys Ridge was created using 1955 water-level 

measurements (fig. 17E). Water levels in the Mississippi River 

Valley alluvial aquifer east of Crowleys Ridge reportedly 

have been influenced by the Mississippi River (Ryling, 1960; 

Plebuch, 1961; Albin and others, 1967b). After a drought 

in the 1950s, a rise in water levels east of Crowleys Ridge 

between 1955 and 1962 was attributed to a decrease in 

pumpage (Plebuch, 1962); however, the 200-ft contour shifted 

south of West Memphis (Crittenden County) most likely 

because of pumping by that city for public supply. Water 

levels for a well in Crittenden County (well H) have declined 

steadily since the 1980s, with a total decline of roughly 

20 ft (fig. 20; location of wells shown in fig. 17). Waterlevel declines in a Mississippi County well (well I) are less 

drastic and started later in the 1990s; water levels have fallen 

approximately 8 ft and have since rebounded from a minimum 

in 1998. Water levels in both wells declined after the drought 

of 1980 (fig. 20) (Neely, 1991).

A cone of depression in the Mississippi River Valley 

alluvial aquifer potentiometric surface was first documented 

east of Crowleys Ridge in Greene County in 1972 at the 230-ft 

closure (fig. 17H; Ackerman, 1989b). This depression was 

seen in the 1980 (fig. 17I), 1982, and 1984 surfaces (Edds and 

Fitzpatrick, 1984; Plafcan and Edds, 1986) and was enclosed 

by the 220-ft contour in 1992 (Westerfield and Poytner, 1993). 

The cone expanded horizontally through 2002 (Stanton and 

others, 1998; Joseph, 1999; Schrader, 2001b; Reed, 2004) and 

has since contracted in the surfaces constructed for 2004–8 

(Schrader, 2006a, 2008a, 2010). 

The largest cone of depression east of Crowleys Ridge 

is in eastern St. Francis County. It was originally enclosed 

at the 170-ft contour in 1984 (not shown in fig. 17; Plafcan 

and Edds, 1986). The 1992 surface (fig. 17J) showed this 

depression still at the 170-ft contour and had reached the 

eastern side of Crowleys Ridge. Around 2004 (fig. 17L), 

the cone expanded southward into Lee County below the 

southern point of Crowleys Ridge and coalesced with the cone 

of depression on the western side of Crowleys Ridge. Other 

depressions east of Crowleys Ridge include eastern Clay 

County, seen in 2002 (Reed, 2004), and on the eastern border 

of Craighead and Mississippi Counties, seen in 2006 and 2008 

(figs. 17M and 17N).
Aquifers of the Coastal Plain 85

Southeastern Arkansas

Mapping efforts of the potentiometric surface did not 

include southern Arkansas until 1965. Publications from the 

1950s and 1960s reported declines in water levels in these 

areas because of seasonal agricultural pumpage (Hewitt 

and others, 1949; Onellion and Criner, 1955; Bedinger and 

Reed, 1961). In Drew County, the water level in one well 

had dropped 15 ft from 1939 to 1955 (Onellion, 1956). Even 

though water-level declines were noted in this area, cones of 

depression were not documented until mapping of the 1972 

potentiometric surface indicated a cone of depression in 

Ashley County, south of Crossett (fig. 17H). 

Multiple cones of depressions have developed in 

southeastern Arkansas in the Mississippi River Valley 

alluvial aquifer potentiometric surface: eastern Lincoln and 

northwestern Desha Counties, on the border of Desha and 

Chicot Counties, central Drew County, and on the border of 

Ashley and Chicot Counties (fig. 17). Mapping of the 2000 

potentiometric surface revealed a depression in northeastern 

Lincoln County and on the border of Ashley and Chicot 

Counties (not shown in fig. 17; Schrader, 2001b). Another 

cone of depression, enclosed at the 130-ft contour, was noted 

in central Drew County in the 2002 potentiometric-surface 

map (Reed, 2004). These cones of depression continued to 

expand as shown on the 2008 potentiometric-surface map 

(fig. 17N). 

Depressions in the Mississippi River Valley alluvial 

aquifer potentiometric surface developed in Ashley County 

near industrial paper and forestry operations in the vicinity 

of Crossett (fig. 17). Steady declines were seen from 1925 

to 1947, with a total water-level decline of 26 ft (Hewitt 

and others, 1949). As of 1970, two cones of depression had 

appeared in Ashley County (Broom and Reed, 1973): one 

near a paper factory in Crossett and the other near logging 

and forestry operations northeast of Hamburg. The 1972 

map (fig. 17H) shows these two depressions with closure at 

the 70-ft and 110-ft contours. Only the western depression 

appears again in the 2004 surface (fig. 17L), although wateruse rates of Ashley County increased over 460 percent from 

1965 to 2010 (fig. 12). The effects of the large industrial 

groundwater withdrawals on water levels may not be 

represented accurately because of Crossett being located at 

the edge of the Mississippi River Valley alluvial aquifer’s 

extent. 

Figure 19. Hydrographs of water levels in wells completed in the Mississippi River Valley alluvial aquifer west of Crowleys Ridge in 

northeastern Arkansas.

1928 1933 1938 1943 1948 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 2013

Year

100

120

140

160

180

200

220

240

260

280

Water level, in feet above National Geodetic Vertical Datum of 1929

Water level, in well completed

in the Mississippi River

Valley alluvial aquifer

 Well J (Cross County)

 Well K (Craighead County)

 Well L (Clay County)

 Well M (Jackson County)

 Well N (St. Francis County) 

EXPLANATION
86 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Water levels for three wells in southeastern Arkansas are 

shown in figure 21 (locations of wells shown in fig. 17). Well 

E in Ashley County declined in the 1960s and rose following 

the creation of a surface-water source in the early 1970s. 

Water levels in well G in Ashley County declined after 1975 

in response to increased use; water use increased 178 percent 

from 1975 to 2005 (table 17). Water levels generally 

stabilized in well G from 2000 through 2010 and declined by 

approximately 6 ft from 2010 to 2012. Water levels in well F 

in Desha County steadily declined after 1975 in response to 

increased use; water use increased approximately 200 percent 

from 1975 to 2010 (table 17).

Deductive Analyses, Projections of Aquifer Conditions, 

and Sustainable Use

Groundwater often is overlooked in the scheme of 

water management and protection because of the lack of 

direct observations leading to a limited understanding of 

groundwater behavior. This combined with the expansive 

scale and broadly distributed nature of groundwater flow 

and the fact that groundwater moves very slowly in most 

systems—often on time scales beyond the practical constraints 

of direct human observation and experimentation—

necessitates development and use of secondary approaches 

to understanding groundwater that are somewhat different 

than those applied to surface water. Important questions that 

groundwater managers and groundwater scientists may pose 

include: How accurate and representative are our water-use 

and hydraulic parameter measurements? How much water is 

stored in a given aquifer? At what rate can water be produced? 

Where does groundwater flow, and what are the sources and 

outlets? What is a sustainable long-term yield, or how long 

will the aquifer produce water if that yield rate is exceeded? 

How will aquifer yields and groundwater flow paths be 

affected by natural or human-induced changes? These and 

other more specific questions can be addressed effectively by 

digital simulations of groundwater aquifers—groundwaterflow models. 

Figure 20. Hydrographs of water levels in wells completed in the Mississippi River Valley alluvial aquifer east of Crowleys Ridge in 

northeastern Arkansas.

150 

160 

170 

180 

190 

200 

210 

220 

230 

240 

1955 1960 1965 1970 1975 1980 

Year

1985 1990 1995 2000 2005 2010 

Water level, in feet above National Geodetic Vertical Datum of 1929

Water level, in well completed

in the Mississippi River

Valley alluvial aquifer

 Well H (Crittenden County)

 Well I (Mississippi County) 

EXPLANATION
Aquifers of the Coastal Plain 87

Groundwater-flow models simulate the physical 

processes using the governing equation for groundwater 

flow and the ancillary equations describing conditions at 

system boundaries. The appeal and utility of a groundwaterflow model are derived from the ability of a model to 

take a large and complex dataset describing hydraulic 

characteristics, hydraulic stresses, hydrogeologic framework, 

and boundary conditions and, to the degree possible given 

certain data constraints, accurately represent a complex 

natural groundwater system. A major limitation of any 

model is derived from the absolute necessity to input a large, 

complex, and accurate dataset to achieve usable results. 

Because of this, the construction of a groundwater-flow 

model is time-consuming, labor and data intensive, and 

expensive; however, the importance of groundwater resources, 

effective management of those resources, and the utility of 

groundwater-flow models in understanding and predicting 

groundwater behavior has made the model a tool of great 

value, warranting the investments that water managers 

in Arkansas have made in developing and maintaining 

groundwater models for water management. 

Results of Groundwater-Flow Simulation Models

Griffis (1972) developed one of the first groundwaterflow models in the State—a digital simulation of the 

Mississippi River Valley alluvial aquifer in the Grand Prairie 

(fig. 22). The flow model was used to project future waterlevel declines under then-current pumping rates, to determine 

the reduction in withdrawals necessary to abate water-level 

declines, and to explore the feasibility of artificial-recharge 

scenarios for the alluvial aquifer. The artificial-recharge 

scenarios tested by the model included installation of 

recharge wells and dredging or other modification to improve 

aquifer connectivity with Bayou Meto. Results of the study 

determined that a reduction in pumpage of approximately 

50 percent was necessary to stabilize water levels at the 

target 1959 water-level surface. Artificial recharge at Bayou 

Meto was shown to be ineffective. Recharge wells placed 

in the model at the center of the cone of depression were 

found to moderate declines; however, Griffis (1972) noted 

that economic factors and technical problems involved in 

operating recharge wells would have to be resolved to make 

that approach feasible.

Figure 21. Hydrographs of water levels in wells completed in the Mississippi River Valley alluvial aquifer in southeastern Arkansas.

60

70

80

90

100

110

120

130

140

150

160

1960 1965 1970 1975 1980 1985 

Year

1990 1995 2000 2005 2010 

Water-level altitude, in feet above National Geodetic Vertical Datum of 1929

Water level, in well completed

in the Mississippi River

Valley alluvial aquifer

 Well E (Ashley County)

 Well F (Desha County)

 Well G (Ashley County) 

EXPLANATION
LEE WHITE DREW CLAY ASHLEY DESHA IZARD LONOKE ARKANSAS CHICOT SHARP CROSS PRAIRIE PHILLIPS FULTON MISSISSIPPI JEFFERSON POINSETT MONROE GREENE JACKSON LINCOLN CRAIGHEAD RANDOLPH LAWRENCE ST. FRANCIS CLEVELAND INDEPENDENCE WOODRUFF CRITTENDEN 94° 92° 91° 93° 90° 36°35° 34° Base from U.S. Geological Survey digital data, 1:2,000,000 0 15 30 

0 30 60 

15 

45 EXPLANAT

Mississippi River Valley al

model extent—ModifieMahon and Poynter, 199others, 2003a; CzarneckCzarnecki, 2010 Mississippi River Valley al

model extent—ModifieMahon and Poynter, 199Czarnecki and others, 2

Cache and St. Francis Rive

model extent—Modifie

Grand Prairie alluvial aqui

Griffis, 1972; Peralta and others, 1989 Bayou Bartholomew alluvi

from Broom and Reed, 1

Crowleys Ridge Mississippi River Valley al

Cabot WaterWorks Grand Prairie Water Users 

Pine Bluff White River Cache River Saint Francis River Mississippi River Bayou Meto Arkansas RiverBayou Bartholomew

Figure 22. Areal extents for all groundwater flow-simulation models conducted in the Mississippi River Valley alluvial aquifer in eastern Arkansas.
Aquifers of the Coastal Plain 89

Broom and Reed (1973) conducted a study of the 

Mississippi River Valley alluvial aquifer in the Bayou 

Bartholomew watershed (fig. 22) to project the hydrologic 

responses to stresses from ongoing water development. 

Scenario development stresses included construction of 

flood-control levees on the Arkansas and Mississippi Rivers; 

damming; land-use change; drainage-canal construction; 

and groundwater pumpage for irrigation, fish farming, and 

manufacturing. The study included development of an 

electrical analog model of groundwater flow. Reported results 

of the study included basic hydrogeological characteristics of 

the system used for model parameterization and assessment 

of aquifer recharge. Recharge to the aquifer in the modeled 

area was estimated at 161,000 acre-ft for the year 1970, 

with analog results indicating some 70 percent of recharge 

occurring at or near the stream. In a second phase of the 

Bayou Bartholomew study, Reed and Broom (1979) developed 

linked, unsaturated-zone groundwater and surface-water 

models in a calibrated, numerical simulation of the aquiferriver system using a finite-difference equation approach. The 

model provided projections of water-level changes resulting 

from changes in rate and distribution of groundwater pumpage 

and changes in stream and reservoir stage. 

Broom and Lyford (1981) developed a digital model 

of the Mississippi River Valley alluvial aquifer in the Cache 

and St. Francis River Basins with the goal of estimating the 

capability of the aquifer to provide water for rice irrigation 

through the year 2000 (fig. 22). Model results indicated that by 

1978 the total groundwater pumpage of 1,460,000 acre-ft/yr 

comprised water provided from aquifer storage at the rate of 

540,000 acre-ft/yr, water captured from streamflow at a rate of 

approximately 430,000 acre-ft/yr, and water from recharge to 

the aquifer at a rate of 490,000 acre-ft/yr. The 1978 pumping 

rate of 1,460,000 acre-ft/yr was determined to exceed the 

rates needed to sustain minimum water levels throughout 

Poinsett, Craighead, and Cross Counties west of Crowleys 

Ridge by 110,000 acre-ft/yr. Even a reduced pumping rate of 

1,350,000 acre-ft/yr beginning in 1991 was projected to result 

in an aquifer saturated thickness west of Crowleys Ridge of 

less than 50 ft in most of Poinsett and Craighead Counties 

and a substantial part of Cross County by the end of 2000. 

By 2000, the rate of water removal from aquifer storage 

was projected to approach 490,000 acre-ft/yr, and the rate of 

streamflow capture would be about 860,000 acre-ft/yr. 

Peralta and others (1985) developed a groundwaterflow model for the Mississippi River Valley alluvial 

aquifer in the Grand Prairie of east-central Arkansas with 

approximately the same model area as that used by Griffis 

(1972) and incorporated improvements, including use of the 

MODFLOW modeling package and more comprehensive 

water-use, aquifer-characteristics, and boundary datasets. 

Objectives of the Peralta and others (1985) modeling study 

were to project groundwater levels and aquifer saturated 

thickness through 1993, determine where rice irrigation 

would become infeasible, and determine future effects of 

declining water levels on cost of pumping groundwater. 

Model results projected groundwater-level declines as much 

as 28 ft during 1983–93 and areas where well yields were less 

than 500 gal/min would increase from 54 mi2 to as much as 

171 mi2. 

Mahon and Ludwig (1990) developed a calibrated 

groundwater-flow model of the Mississippi River Valley 

alluvial aquifer covering all or part of 23 counties of eastern 

Arkansas located north of the Arkansas River (fig. 22) as 

part of the Eastern Arkansas Region Comprehensive Study 

(EARCS); a multiagency investigation that began in 1985 with 

the U.S. Army Corps of Engineers (USACE), the NRCS, the 

ANRC, the USGS, and the University of Arkansas. The goals 

of the modeling effort were to evaluate the potential effects of 

developing hydraulic structures for supplying irrigation water 

from surface sources for use in areas of potential groundwater 

deficiency and to aid ANRC in predicting and designating 

critical areas—areas where projected groundwater withdrawals 

would result in rates of groundwater-level decline or decreases 

in aquifer saturated thickness that are designated as requiring 

focused water management. Pumpage projections input into 

the model were based on projected water needs according to 

two scenarios: (1) without conservation measures—continuing 

1990 current withdrawals, and (2) with conservation measures 

that decreased 1990 withdrawals by about 30 percent by the 

year 2040. Model results indicated that without conservation 

measures, saturated thickness would decrease to less than 

20 ft over an area of 3,800 mi2

; whereas with conservations 

measures and reduced withdrawals, saturated thickness would 

decrease to less than 20 ft in a 2,300-mi2 area. Three principal 

areas of concern were determined based on these simulations: 

the Grand Prairie area and areas to the east and to the west of 

Crowleys Ridge. The modeling results highlighted the critical 

nature of water-level declines in the Mississippi River Valley 

alluvial aquifer and supported ANRC in developing the critical 

groundwater area designation (See description of critical 

groundwater area designation in the section on “Groundwater 

Protection and Management Programs” for more information 

on this program.).

Water-level declines in the Mississippi River Valley 

alluvial aquifer through the 1980s called greater attention to 

an important and threatened resource and showed the need to 

better understand the flow system. Mahon and Poynter (1993) 

developed a regional groundwater-flow model using a 1-mi2

cell size that was more finely discretized than any model 

previously constructed for the aquifer (fig. 22). Because of the 

size of the area and computing time constraints, two models 

were developed for the eastern Arkansas study area with the 

Arkansas River dividing the study area into a north model 

area and a south model area. Because pumping distribution 

in time and space is a key element in understanding aquifer 

behavior and response, and the historical pumping database 

was recognized as limited and potentially inaccurate, a 
90 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

primary goal of the modeling effort was estimating historical 

pumping distribution. The north and south models were used 

to investigate three different spatial and temporal pumpage 

scenarios to generate an estimated representative pumping 

distribution. The results of Mahon and Poynter (1993), and 

the primary objective of the modeling effort, highlight the 

importance of ongoing water-use monitoring and maintenance 

of an accurate water-use database in the effective planning, 

management, and protection of groundwater resources. 

An improved understanding of the Mississippi River 

Valley alluvial aquifer in Arkansas was advanced by modeling 

conducted as part of the USGS Gulf Coast Regional AquiferSystem Analysis (RASA) model investigations (Williamson 

and others, 1990), which covered 290,000 mi2 in parts of 

Alabama, Arkansas, Florida, Illinois, Kentucky, Mississippi, 

Missouri, Tennessee, Texas, and all of Louisiana (fig. 23). 

Regionwide model results identified the important factors 

controlling regional flow prior to development as being 

topography, outcrop patterns, and geometry of aquifers and 

confining units; interestingly, geologic structure and variation 

in rainfall patterns, while locally important, were found to 

be minor influences at a regional scale. The databases and 

the modeling framework, as well as programing, served as 

the basis for more detailed analysis of subregions across the 

Gulf Coast regional aquifer system; several of the embayment 

models referenced herein were derived from or benefitted 

in some fashion from the RASA model. Ackerman (1989a, 

1989b, 1990, 1996) added greater detail to the RASA 

databases and model and developed a three-layer regional 

model simulating the Mississippi River Valley alluvial aquifer 

in Arkansas (as well as the aquifer’s extents into Louisiana, 

Mississippi, Tennessee, Missouri, and Kentucky) with the 

goal of understanding regional flow paths, aquifer fluxes, 

and effects of development. Ackerman (1989b) described 

the regional hydrogeology of the Mississippi River Valley 

alluvial aquifer in greater detail than previous studies and 

documented the aquifer properties database development, 

model parameterization, development, and calibration; 

described simulation of predevelopment groundwater 

flow system conditions; and described changes in aquifer 

conditions after onset of development, focusing on the year 

1972. Ackerman (1989b) also summarized predevelopment 

conditions as follows: original unperturbed groundwater levels 

mirrored topography with flow paths moving from high areas 

to low areas with rivers acting as major drains and flow lines 

intersecting river basin axes; recharge was quantified and 

important sources were determined as originating from rainfall 

and leakage from underlying aquifers. Changes in the system 

with onset of groundwater development were as follows: flow 

lines shifted and moved water to regional pumping centers 

with pumpage replacing drainage to rivers as the major water 

sink; recharge from rivers increased with many reaches of 

major rivers becoming losing streams; recharge from rainfall 

moving through the clay layer increased; and discharge to 

underlying aquifers increased as those aquifers were also 

developed. Average recharge to the aquifer was quantified at 

approximately 0.8 in/yr.

Carrying the work further, Ackerman (1996) ran 

scenarios on the model documented in the Ackerman (1989b) 

report and explored the potential for future development in 

terms of flow components; stress on the aquifer because of 

development of large-scale pumpage for agricultural water 

use; direction, distribution, and quantity of flow; and changes 

in saturated thickness. These simulations were carried 

through the year 2022. Simulation results at 1985 pumping 

rates showed widespread water-level declines to less than 

75 ft of saturated thickness across much of the area north 

of the Arkansas River and west of Crowleys Ridge; part 

of this area could not sustain the 1985 pumping rate, with 

saturated thickness decreasing to less than 25 ft. A second 

scenario, exploring the possibility of expanded groundwater 

development, incorporated increased pumping rates of 

1.2 Mgal/d per a 25-mi2 area above 1985 rates and showed a 

severe reduction in saturated thickness to less than 50 ft across 

most of the area between the Arkansas and White Rivers and 

a large part of the area immediately west of Crowleys Ridge. 

The areas with greatest potential for development of additional 

pumpage were outside of Arkansas (northwestern Mississippi 

and southeastern Missouri); only a small area south of the 

Arkansas River exhibited potential for increased withdrawals. 

Stanton and Clark (2003) updated and recalibrated the 

Mahon and Poynter (1993) “south model” (fig. 22) using data 

available through 1998. The goals of the modeling effort were 

to determine potential effects of three different groundwater 

withdrawal management strategies and to simulate water-level 

declines resulting from projected groundwater withdrawals for 

the period 1998–2049. The scenarios entailed (1) continuation 

of 1997 pumping rates, (2) extrapolation of the observed 

trend of increasing water use, and (3) withdrawal reduction 

in an area where USACE was planning surface-water 

diversion to reduce demands on groundwater. Model results 

were evaluated using the ANRC critical groundwater area 

designation criterion for maintaining a 50-percent saturated 

formation thickness. Scenario 1 resulted in substantial waterlevel declines centered in Desha and Ashley Counties with an 

area of 81 mi2

 dropping below 50 percent saturated thickness 

by 2049; Scenario 2 resulted in 92 mi2 of the aquifer being 

depleted in the model (as indicated by dry cells) in Desha, 

Lincoln, and Ashley Counties by 2049; and Scenario 3 

resulted in saturated thickness decreasing below 50 percent 

in an area of 374 mi2, and the aquifer was projected to be 

depleted across an area of 64 mi2 by 2049. Model results 

highlighted the unsustainable nature of withdrawal rates in the 

modeled area and showed the improvements to groundwater 

conditions that would be brought about by importation of 

surface water. 
TEXAS

KANSAS

GEORGIA

MISSOURI

OKLAHOMA

FLORIDA

ARKANSAS

ALABAMA

MISSISSIPPI

LOUISIANA

KENTUCKY

TENNESSEE

ILLINOIS

OHIO

INDIANA

SOUTH

CAROLINA

WEST

VIRGINIA

VIRGINIA

NORTH

CAROLINA

UNITED STATES MEXICO GULF OF MEXICO

Base from U.S. National Park ServiceNatural Earth physical map at 500 meters per pixelWeb Mercator Auxiliary Sphere projection

100° 90° 80°

30°

25°

35°

0 200 400 KILOMETERS

0 200 400 MILES

Region

stuextand 

Missis

Mo198

Missis

StuCla

Missis

stu198

Gulf Co

Ack

Coasta

Mo198

Physiographic p

Figure 23. Spatial extent of the Mississippi Embayment Regional Aquifer-System Analysis study including the Mississippi River Valley alluvial aquife
92 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Reed (2003) updated and recalibrated the Mahon and 

Poynter (1993) “north model” (fig. 22) using data available 

through 1998. The goal of the modeling effort was to simulate 

water-level declines resulting from projected groundwater 

withdrawals through the year 2049. Model simulations 

explored three different groundwater management scenarios: 

(1) continuation of 1997 pumping rates, (2) extrapolation of 

the observed trend of increasing water use, and (3) withdrawal 

reduction in two areas of the Grand Prairie where the USACE 

was planning surface-water diversion to reduce demands on 

groundwater (U.S. Army Corps of Engineers, 2007, 2013b). 

Scenario 3 used a conservative assumption that the USACE 

diversion would provide 12 million cubic feet per day (Mft3/d), 

by 2049; the USACE had stated that the diversion effort 

possibly could provide as much as 76 Mft3/d (U.S. Army Corps 

of Engineers, 2013b). Model results were evaluated using 

the ANRC critical groundwater area designation criterion 

for maintaining a 50-percent saturated formation thickness. 

All three model scenarios projected extreme water-level 

declines—large areas of decreases to less than 50 percent 

saturated thickness and broad areas of aquifer depletion. The 

most seriously affected areas were projected to be in the Grand 

Prairie area between the Arkansas River and White River 

and west of Crowleys Ridge along the Cache River. Those 

areas of the aquifer were projected to have depleted areas of 

approximately 400 mi2 under Scenario 1 by 2049 and depleted 

areas of 1,300 mi2 under Scenario 2. Two diversion projects 

proposed by the USACE in the Scenario 3 simulation reduced 

pumping rates to 90 percent of the observed water-use rates 

in the Grand Prairie; however, model results indicated that the 

reduction in withdrawal would do little to decrease the extreme 

water-level declines and depletion of the aquifer. The depleted 

area of the aquifer in the area supplied by the surface-water 

diversion was reduced by approximately 60 mi2 as compared 

to Scenario 2. Model results indicated that at 1997 withdrawal 

rates, water was being withdrawn from the aquifer at rates more 

than could be sustained for the long term. 

Czarnecki (2006a) conducted model scenarios using the 

Reed (2003) revision of the Mahon and Poynter (1993) alluvial 

aquifer north model (fig. 22) to address the concerns of ANRC 

and the Grand Prairie Water Users Association (GPWUA) 

regarding a planned increase in groundwater withdrawals 

for public supply. The GPWUA proposed an additional well 

that increased pumpage from the aquifer from 576,000 gal/d 

to 2,016,000 gal/d. The ANRC’s broad water-management 

responsibilities required understanding and predicting longterm effects of the proposed increase in withdrawals prior to 

issuing a well permit. Groundwater simulations were conducted 

to determine flow and water-level changes from 2005 through 

2049, with scenarios comparing simulated water levels with 

and without the proposed increase in withdrawals. Pumping 

from wells owned by Cabot WaterWorks, located about 2 

mi from the proposed GPWUA wells, also was added to the 

model. The model simulations showed that pumping the 

additional 2,016,000 gal/d combined with the 2,224,754 gal/d 

pumping from the Cabot WaterWorks wells would result in the 

development of a cone of depression. A simulated maximum 

water-level decline of about 8.5 ft occurred over the 45-year 

model simulation, with about 3.3 ft of the decline attributed 

to the proposed well; however, the additional withdrawal 

was shown not to cause water levels to decline below the 

50-percent aquifer saturation criterion. 

Continuing the work supporting water-management 

planning and municipal growth in Lonoke County, Czarnecki 

(2007) conducted additional model scenarios using the Reed 

(2003) alluvial aquifer north model to address the concerns of 

ANRC and Cabot WaterWorks regarding the planned increase 

in groundwater withdrawals for public supply. The ANRC 

again needed to better understand and project long-term effects 

of the proposed increase in withdrawals prior to issuing a well 

permit. Sixteen groundwater-flow scenarios were conducted 

to determine flow and water-level changes from 2007 through 

2049 for the proposed increase in groundwater withdrawals 

from a 2004 rate of 2.24 Mgal/d to between 4.8 and 

8.0 Mgal/d by 2049. Ten of the 16 scenarios included potential 

pumping from proposed new GPWUA wells that would be 

located about 2 mi from the nearest Cabot WaterWorks wells. 

Eight scenarios addressed reduced pumping rates associated 

with the Grand Prairie Area Demonstration Project (U.S. 

Army Corps of Engineers, 2007, 2013b). Projected waterlevel declines for the baseline pumping rate of 4.8 Mgal/d 

from the Cabot WaterWorks wells ranged from 15 to 25 ft; 

increasing pumping rates to 8.0 Mgal/d resulted in waterlevel declines ranging from about 15 to 40 ft. Model results 

indicated that water-level declines would continue beyond 

2049 with continued pumping. All scenarios with increased 

pumping rates resulted in aquifer depletion as indicated by the 

occurrence of dry cells in the model, even for scenarios where 

the USACE Grand Prairie surface-water diversion decreased 

regional demand on the Mississippi River Valley alluvial 

aquifer. Pumping rates of 8.0 Mgal/d resulted in water levels 

falling below 50 percent of aquifer saturated thickness.

Gillip and Czarnecki (2009) updated the north alluvial 

model (Reed, 2003) using water-level and water-use data from 

1998 through 2005 and conducted two scenarios exploring the 

sustainability of then-current and potential water-use patterns. 

The first scenario incorporated reported 2005 water use 

applied as a constant value through 2049; the second scenario 

incorporated the 2005 water-use rate with an annual 2-percent 

increase through 2049. The first scenario showed that the 

2005 water-use rate resulted in a 779-mi2

 area of aquifer 

depletion by 2049 as indicated by dry cells in the model. 

Water-use increases of 2 percent annually (more than doubling 

groundwater withdrawal in the aquifer by 2049) resulted in 

a 2,910 mi2 area of depletion as indicated by dry cells. Most 

areas of aquifer depletion were in the Grand Prairie and Cache 

River areas. The second scenario also resulted in dry cells 

east of Crowleys Ridge. The model results highlighted the 

unsustainable nature of groundwater withdrawals in the Grand 

Prairie, Cache, and Crowleys Ridge areas. 
Aquifers of the Coastal Plain 93

Long-term monitoring of aquifer conditions by ANRC 

showed decreases in saturated thickness and rates of waterlevel declines in an area west of Crowleys Ridge that included 

western parts of Clay, Greene, Craighead, Poinsett, Cross, 

St. Francis, and Lee Counties, indicating that the future 

viability of groundwater in that area was threatened. The 

need for focused management and protection of groundwater 

led to designation of the Cache critical groundwater area for 

the Mississippi River Valley alluvial and Sparta aquifers in 

2009. To assist ANRC in understanding aquifer conditions 

and behavior and to support improved management of 

groundwater, Czarnecki (2010) applied particle-tracking, 

groundwater-flow vectors, and zone-budget analyses using 

the updated Mississippi River Valley alluvial aquifer model 

of Gillip and Czarnecki (2009), focusing on the Cache critical 

groundwater area (figs. 1 and 22). Three scenarios applying 

differing pumping conditions were simulated to determine 

the effect of pumping in Jackson and Woodruff Counties on 

groundwater levels west of Crowleys Ridge. Scenario 1 was a 

baseline scenario in which the 2005 pumping rate was applied 

through 2050 without change; pumping rates prior to 2005 

were varied according to reported or previously modeled 

water use. Scenario 2 applied a zero pumping rate in Jackson 

and Woodruff Counties from 1998 to 2050—a reduction of 

pumping within the model of about 10 percent; the objective 

was not to test a feasible pumping management strategy but 

to determine the broader effect of pumping concentrated 

in those two counties on the surrounding areas. Scenario 3 

applied a pumping rate of 50 percent of the reported 2005 

pumping rate in Jackson and Woodruff Counties from 1998 

to 2050. Comparison of model scenario results showed that 

the reduction in pumping applied in Scenario 2 resulted in 

nearly a 30-percent reduction in aquifer depletion, as indicated 

by dry model cells, compared to the Scenario 1 baseline. 

Zone-budget analyses showed that reduction of pumping in 

Scenarios 2 and 3 resulted in more groundwater flow into 

the Cache critical groundwater area and more flow to rivers. 

Water-level difference maps based on model results showed 

that decreasing pumping rates in Scenario 1 improved water 

levels by 60–80 ft, mostly in Jackson and Woodruff Counties 

but also over parts of western Cross and Poinsett Counties. 

Water-level difference maps for Scenario 3 showed waterlevel increases of 20–40 ft in Jackson and Woodruff Counties 

as compared to Scenario 1. Model results highlighted the 

wide-scale importance of managing pumping in the intensive 

pumping centers in Jackson and Woodruff Counties. 

Optimization and Sustainable Yield

Optimization modeling is an extension of numerical 

simulation of groundwater flow incorporating (1) specific 

water-management objectives; for example, providing specific 

minimum water supply for prioritized users (generally 

referred to in modeling terminology as the objective function), 

(2) managed withdrawal rates at wells and river locations 

(referred to as decision variables), and (3) maintenance of 

specific aquifer (or surface-water) conditions; for example, 

maintaining defined water levels or percent saturation 

for groundwater or minimum streamflows (referred to as 

constraints)—surface-water flow also may be integrated to 

achieve conjunctive-use analysis. Such modeling can support 

optimized use of water resources and maintain key indexes 

of aquifer and surface-water conditions. These extended 

modeling approaches also can be used to determine long-term, 

sustainable groundwater yields as defined by water managers 

and water policy. Groundwater modeling that focuses on 

optimization of use, conjunctive use, and maintenance of 

constraints necessary for sustainable or safe yield use of 

groundwater has been an important tool for Arkansas water 

users, water managers, and water-policy planners in achieving 

effective, fair, and equitable use of this limited resource. 

Arkansas’ water-resources policy and programs have 

moved forward with the goal of conjunctive use of the State’s 

groundwater and surface-water resources at optimized levels 

that are sustainable. This sustained-yield conjunctive-use 

strategy has been supported by using groundwater models 

developed largely through the ANRC/USGS cooperative 

program. ANRC and other State water planners have 

advocated sustainable yield groundwater protection as a means 

of achieving specific goals such as preventing groundwaterlevel declines, assuring long-term viability of aquifers to 

provide certain yields, preventing litigation, providing 

groundwater supplies for drought, preventing groundwaterquality degradation, protecting riparian rights, and providing 

courts with an objective means for determining reasonable 

and unreasonable use. Arkansas’ water policy has tended to 

follow a deferred perennial yield strategy, which accepts that 

current groundwater levels or levels defined by the critical 

groundwater area designation are reasonable or, at least, 

acceptable. The alternative view of requiring the complete 

recovery of Arkansas’ aquifers to predevelopment levels is 

viewed as being difficult to achieve under increasing water 

requirements for irrigation use. For the Mississippi River 

Valley alluvial aquifer, water users and planners noted early 

in the history of development that rates of usage were not 

sustainable; for example, Klein and others (1950) stated 

that in “... the Grand Prairie region as a whole, the present 

pumpage is roughly twice the rate of recharge.” Once the 

unsustainable nature of withdrawals from the Mississippi 

River Valley alluvial aquifer was recognized in the Grand 

Prairie in the 1920s, hydrologists, geologists, and engineers 

began to estimate the sustainable yield (often referred to as 

safe yield) of the aquifer. One of the earliest estimates of 

safe yield is from a USGS press release by Thompson (1931) 

in which he estimated the sustainable yield for the Grand 

Prairie from the Mississippi River Valley alluvial aquifer at 

less than 177,000 acre-ft/yr, with unmet demand at that time 

of 340,000 acre-ft/yr or more. Engler (1958) documented 

withdrawals from the aquifer of approximately 200,000 

acre-ft/yr and commented that volume exceeded sustainable 

levels by about 50,000 acre-ft/yr.
94 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Mahon and others (1989) and Peralta and others (1992, 

1995) developed groundwater optimization models based 

upon the calibrated Mississippi River Valley alluvial-aquifer 

groundwater-flow model of Mahon and Ludwig (1990) 

with the goal of determining optimal sustained groundwater 

yield and conjunctive water-use strategies for east-central to 

northeastern Arkansas, based on a 50-year projected water 

demand from 1990 to 2039. Simulations were designed to 

maximize total annual allocation of surface-water resources 

and sustainable groundwater yield for a 13,000-mi2 area of 

the Mississippi River Valley alluvial aquifer (fig. 22), using 

a sequential steady-state modeling approach incorporating 

increased potential water demand. Five model scenarios were 

simulated: (1) two incorporating pumpage based on meeting 

growing public and irrigation water use, (2) two incorporating 

decreased pumpage based on the potential of implementing 

conservation measures, and (3) one based on a steady rate of 

groundwater pumping in all cells through time. The model 

results indicated that the groundwater pumping strategies 

employed were sustainable; however, total water demand in 

the area could not be met in any of the model scenarios. The 

authors concluded that “Possibly the most appropriate future 

scenario is the one in which public and industrial demand is 

always satisfied, and farmers must utilize improved water 

conservation measures. Implementation of this scenario 

satisfies Arkansas’ priority of use hierarchy” (Peralta and 

others, 1995). 

Czarnecki and others (2003a, b) conducted conjunctiveuse optimization of the Mississippi River Valley alluvial 

aquifer of northeastern (Czarnecki and others, 2003a) and 

southeastern (Czarnecki and others, 2003b) Arkansas (fig. 22) 

using the groundwater models of Reed (2003) and Stanton 

and Clark (2003) as platforms to estimate sustainable yield 

from the alluvial aquifer and from surface water. The goals 

of these optimization modeling studies were to: (1) estimate 

maximum groundwater withdrawal rates for 1997, (2) estimate 

maximum potential withdrawal rates from stream locations, 

(3) maintain groundwater levels at or above specified levels, 

and (4) maintain streamflow at or above specified rates. For 

the optimization model, groundwater levels were constrained 

above 50 percent of aquifer thickness or 30 ft above the 

bottom of the aquifer, whichever resulted in the higher 

groundwater level. Streamflows for most streams incorporated 

in the model were not allowed to drop below minimum flows 

specified by ANRC; these streamflow constraints generally 

were specified at river cells based on average 7-day low flows 

with 10-year recurrence intervals. Because groundwater 

sustainable yield is dependent upon the pumping limit 

specified for each managed well in the model, multiples of 

100 percent, 150 percent, and 200 percent of individual well 

1997 pumping rates were used to set the upper pumping limit, 

and optimization estimates were determined for each of those 

pumping limits. 

Setting an upper limit on individual well pumping rates 

was important because wells located proximal to recharge 

sources such as rivers are effective in intercepting flow, so 

as the withdrawal rate limit for individual wells is increased, 

wells located a distance from recharge sources receive less 

groundwater and are removed as pumping wells, and the 

total number of wells decreases (although the total amount 

withdrawn increases). The optimization model showed 

that if no limits were placed on groundwater withdrawals, 

all of the withdrawals would come from wells adjacent to 

sources of water within the model (Czarnecki and others, 

2003a). Although overall optimized withdrawal would 

be largest for such a scenario, the distribution of wells 

would be unacceptable from a management and farmowner 

standpoint because nearly all of the water production would 

come from wells that are proximal to rivers. Optimization 

results (Czarnecki and others, 2003a) indicated that the 

sustainable yield from groundwater for the study area, with 

1997 withdrawals rates set as an index and upper limit, 

was 360 Mft3/d, approximately 57 percent of the 1997 

withdrawal rate. For the Bayou Meto irrigation project and 

the Grand Prairie irrigation project areas (U.S. Army Corps 

of Engineers, 2007, 2013b) within the larger alluvial north 

model, the sustainable yields determined by optimization were 

18.1 Mft3/d (35 percent of 1997 withdrawals) for the Bayou 

Meto area and 9.1 Mft3/d (30 percent of 1997 withdrawals) for 

the Grand Prairie area. Groundwater sustainable yield for the 

entire north model area increased to 445 Mft3/d—70 percent of 

the amount withdrawn in 1997—if the upper withdrawal limit 

was increased to 150 percent of the 1997 rate. Groundwater 

sustainable yield increased to 526 Mft3 /d—83 percent of 

the amount withdrawn in 1997—if the upper withdrawal 

limit was increased to 200 percent of the 1997 rate. Using a 

specified upper withdrawal limit of 100 percent of the 1997 

withdrawal rate for individual wells, Czarnecki and others 

(2003b) estimated a groundwater sustainable yield for the 

entire alluvial south model study area of 70.3 Mft3/d—a value 

representing 96 percent of the amount withdrawn in 1997 

(73.5 Mft3/d). Groundwater sustainable yield increased to 

80.6 Mft3/d—110 percent of the amount withdrawn in 1997—

if the upper withdrawal limit was increased to 150 percent 

of the 1997 rate. Groundwater sustainable yield increased 

to 110.2 Mft3/d—150 percent of the amount withdrawn 

in 1997—if the upper withdrawal limit was increased to 

200 percent of the 1997 rate. These optimization studies 

pointed out that the then-current (2003) demand on the alluvial 

aquifer was unsustainable in the alluvial north model area, but 

that some potential addition capacity existed in the alluvial 

south model area. 

Czarnecki (2006b) used the optimization model 

of Czarnecki and others (2003b) to analyze potential 

management effects on the alluvial aquifer of surface-water 

diversions for irrigation proposed for Bayou Meto and the 

White River by USACE (U.S. Army Corps of Engineers, 

2007, 2013b) and for a potential industrial water-supply well 

in the alluvial aquifer for a paper mill in Pine Bluff (Jefferson 

County). The study explored the effects on sustainable yield 

of four water-management alternatives, represented in the 

model by applying different sets of constraints on groundwater 

levels and surface-water withdrawals that were being 

considered by ANRC. Scenario 1 was a baseline scenario 
Aquifers of the Coastal Plain 95

in which surface-water withdrawal was allowed from all 

11 rivers—including the Arkansas and White Rivers—for 

the Bayou Meto and Grand Prairie irrigation project areas 

(U.S. Army Corps of Engineers, 2007), while maintaining 

groundwater levels above the 50-percent saturated thickness 

of the aquifer. Scenario 2 evaluated the effect of lowering the 

water-level constraint to a minimum 30 ft aquifer saturated 

thickness. Scenario 3 evaluated the effect of the USACE 

Bayou Meto or Grand Prairie irrigation projects (U.S. Army 

Corps of Engineers, 2007, 2013b) if water from the White 

River or Bayou Meto was not used to augment the alluvial 

aquifer that is used for irrigation; however, withdrawals 

from other rivers were allowed. Scenario 4 evaluated the 

combination of conditions for Scenarios 2 and 3. Additional 

simulations explored the effects of the potential industrial 

supply well near Pine Bluff. Optimization modeling for the 

baseline scenario, Scenario 1, as compared to the differing 

management alternatives represented by Scenarios 2, 3, 

and 4, showed increases in estimated sustainable yield of 

groundwater of approximately 7 percent, 7 percent, and 

13 percent, respectively. The proposed industrial supply 

well in Pine Bluff was simulated as pumping 30 Mgal/d for 

a period of 50 years. Model results showed development of 

a cone of depression and a maximum water-level decline of 

about 40 ft; however, this degree of decline held water levels 

well above a 50-percent saturated thickness for that location. A 

pumping rate of 38.9 Mgal/d resulted in model cells going dry, 

indicating aquifer depletion. 

Czarnecki (2008) used the optimization model of 

Czarnecki and others (2003a) coupled with the alluvial aquifer 

north model to analyze potential management effects of three 

different water-management alternatives on the sustainable 

yield from the Mississippi River Valley alluvial aquifer. 

The model scenarios to test the management alternatives 

were (1) changing the upper limits of groundwater pumping 

to maintain a degree of sustainable pumping at all model 

cells representing wells that reported pumping during 1997, 

(2) assessing the effects on the alluvial aquifer associated with 

establishing minimum flow rates accommodating average 

spring floods and habitat requirements for select aquatic 

species, and (3) assessing the effects on the alluvial aquifer 

that would occur if the Melinda Head Cut Structure, a floodcontrol structure designed to prevent the White River from 

altering course to flow into the Arkansas River, failed and 

river stage was altered on the lower White River. Scenario 

1 results indicated that as the upper limit of groundwater 

withdrawal was reduced first to 75, then 50, and finally 

25 percent of the 1997 groundwater withdrawal rates, a 

spatial expansion of sustainable pumping sites was observed. 

Sustainable groundwater yield for the model area increased by 

13,864,017 ft3/d over the baseline scenario for a groundwater 

withdrawal rate set at 75 percent of the 1997 withdrawal 

rate. For Scenario 2, a streamflow rate of 5,097,600,000 ft3/d 

was reported to be necessary for protection of paddlefish 

spawning. Scenario 3 results showed that decreasing White 

River stage at the Melinda Head Cut Structure caused declines 

in the sustainable yield of groundwater in the region. Model 

simulations of 20-, 30-, and 40-ft groundwater-level declines 

decreased sustainable yield by approximately 7,000,000 ft3/d, 

11,000,000 ft3/d, and 14,000,000 ft3/d, respectively. The 

study emphasized the finding that the weighting of various 

management constraints changed resultant estimations of 

sustainable yield and no single and unique value of sustainable 

yield from groundwater or surface water existed as those 

constraints were varied. 

Mississippi Embayment Regional Aquifer Study 

The USGS in cooperation with other Federal, State, 

local governments, and the private sector studied regional 

groundwater-flow systems across the conterminous United 

States as part of a national assessment of groundwater 

availability conducted from 2004 to 2012, which continued 

as the WaterSmart Program (Reilly and others, 2008). The 

Mississippi Embayment Regional Aquifer Study (MERAS) 

component of the larger assessment covered the extent of the 

Mississippi embayment including eastern Arkansas (fig. 23). 

A numerical groundwater-flow model was developed to 

explore the effects of human activities and climate variability 

on groundwater levels, changes in aquifer storage, and flow 

between groundwater and surface-water bodies. 

The MERAS model was constructed of 13 hydrogeologic 

layers over 78,000 mi2 representing multiple aquifers, including 

the Mississippi River Valley alluvial aquifer and the Sparta 

aquifer. MERAS simulations showed that groundwaterlevel declines of more than 100 ft occurred across 216 mi2

in the Mississippi River Valley alluvial aquifer from 1870 to 

2007 with the greatest expanse of groundwater-level decline 

occurring in Arkansas. Declines of more than 100 ft in the 

Mississippi River Valley alluvial aquifer are substantial 

because the total thickness of the aquifer rarely exceeds 200 ft. 

Cumulative groundwater withdrawals from 1870 to 2007 

from the Mississippi River Valley alluvial aquifer exceeded 

280 million acre-ft. Cumulative change in storage within all 

the aquifers simulated in the MERAS model showed a drastic 

misbalance between withdrawal and recharge to the aquifers, 

with model results indicating a net depletion of 140 million 

acre-ft. The amount of water removed from storage over the 

history of pumping is about 26 percent of the total amount 

stored in the Mississippi River Valley alluvial aquifer. This 

overdraft of water volume being removed from the aquifer 

system, greatly outweighing what is recharging the aquifers, 

has important consequences for sustainability and long-term 

use and management of the aquifers. The importance of the 

MERAS model lies not only in the published results of Clark 

and Hart (2009) and Clark and others (2011b) but from the 

future utility of the existing model as an evolving tool that 

can be updated to address the new and continuing questions 

and issues arising from changing human activities, changing 

natural conditions, and changing water-policy environment that 

challenge water managers and water stakeholders. The tools 

and databases integral to the MERAS model include a database 

of over 2,600 geophysical logs used in the construction of the 

hydrogeologic framework (Hart and Clark, 2008). 
96 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

The MERAS model represents the current state-of-the-art 

in modeling tools for aquifers of eastern Arkansas. Since the 

initial development of the MERAS model, two revisions were 

implemented in 2013 (Clark and others, 2013) to continually 

improve upon the ability to accurately simulate groundwater 

flow. The MERAS model has been utilized in three States 

to provide scenarios of future conditions or proposed 

conservation measures and continues to provide information 

through adaptive scenario analyses with regard to projected 

groundwater demand. 

Three scenarios have been recently completed that 

evaluate potential future conditions in eastern Arkansas: 

(1) simulation of previously optimized pumping values in 

the Mississippi River Valley alluvial and the Sparta aquifers, 

(2) simulation of long-term effects of pumping at average 

recent rates, and (3) simulation of constraints on drawdown 

for most pumping wells (Clark and others, 2013). The results 

of scenario 1 indicated large drawdowns throughout the area 

of the alluvial aquifer, regardless of the substitution of the 

optimized pumping values from earlier model simulations. 

The results of scenario 2 also indicated large areas of 

water-level decline, to below half the saturated thickness, 

throughout the aquifer. The results of scenario 3 reveal some 

effects from the inclusion of multiple aquifers in a single 

simulation. The initial configuration resulted in water levels 

well below the defined drawdown constraint and some areas 

of aquifer depletion in east-central Arkansas. An additional, 

derivative simulation of scenario 3 was configured to apply 

the same drawdown constraints from the Mississippi River 

Valley alluvial aquifer wells to the Sparta aquifer wells in the 

depleted area. This configuration did not produce depleted 

areas within the Mississippi River Valley alluvial aquifer and 

resulted in some similar patterns of limited pumping from the 

original scenario 3 optimization results (fig. 24). 

These simulations offer vitally important management 

information by indicating that even with limited pumping in 

the Mississippi River Valley alluvial aquifer, water levels may 

continue to decline in some areas as a result of pumping in 

the underlying Sparta aquifer, highlighting the connectivity 

of these important aquifers. These simulations indicate the 

need to further evaluate the groundwater resource as a single, 

fully integrated and connected system because pumping from 

one aquifer may affect water levels in another. Additionally, 

some scenarios pointed to new areas of groundwater-level 

decline that are not currently considered problematic. While 

simulations can provide information only with respect to the 

inputs and generalized assumptions, the results indicate and 

highlight areas of future concern that have only recently begun 

to show declines in water level.

Most large-scale groundwater-flow models discussed 

herein were used in rearward looking or deductive testing and 

determination of basic model parameter inputs—hydraulic 

conductivity, storage, recharge, stream interaction, boundary 

effects, and water use. This effort in estimating and verifying 

these basic data is a strong indication that although Arkansas 

maintains some of the most advanced and comprehensive 

groundwater monitoring and water-use monitoring programs 

in the Nation, these data sometimes are insufficient at needed 

scales to effectively satisfy water management, planning, 

and protection needs. This highlights the importance of 

widescale and long-term groundwater monitoring. For 

some of the modeling projects, such deductive testing was 

an important objective, whereas in the remaining models, 

deductive testing was a necessary phase before conducting 

projections of aquifer conditions. Deductive analyses are an 

important component of modeling, particularly for estimating 

conditions in the model for time periods when monitoring 

was sparse and input datasets based on monitoring data 

were sparse or nonexistent, enabling minimizing of model 

error for projections. Projections using groundwater-flow 

and optimization models are state-of-the-art for forecasting 

future conditions in aquifer systems and providing robust, 

quantitative, and statistically defensible results for guiding 

protection and management of valuable groundwater 

resources. Model results for the analyses that have been 

conducted in Arkansas are consistent in one important facet—

quantifying the difference between desired increased water 

use to support a growing and vibrant population and economy 

and the actuality of the finite resource available in any aquifer. 

These results call attention to the critical importance of 

effective and equitable management and apportionment of this 

shared resource.

Water Quality

The quality of groundwater from the Mississippi River 

Valley alluvial aquifer is generally good compared to the 

EPA primary drinking-water standards (U.S. Environmental 

Protection Agency, 2009). Certain common water-quality 

characteristics of the aquifer limit its use for domestic, 

industrial, and public supply purposes and have resulted in 

irrigation as the dominant use of the aquifer. Concentrations 

of hardness, iron, and manganese frequently exceed secondary 

drinking-water regulations that address problems of staining, 

scale formation, and objectionable taste. Localized areas 

contain elevated concentrations of chloride that can adversely 

affect crops including soybeans and rice. Concentrations of 

arsenic in deeper parts (lower unit) of the Mississippi River 

Valley alluvial aquifer exceed the EPA primary drinking-water 

standards; however, domestic wells are completed in the 

arsenic-free shallower part (upper unit) of the aquifer. Because 

irrigation is the main use of the aquifer, the occurrence of 

arsenic does not present obstacles to use of groundwater for 

this purpose. Localized areas of poor water quality result 

from natural sources including microbial-mediated changes 

in reduction/oxidation (redox) conditions, basic rock/

water interactions, or upwelling of high salinity water from 

underlying formations.
Pe

Boundary of the MississippiRiver Valley alluvial aquifer

Grand Prairie

Cache criticalgroundwater area Crowleys Ridge

Base from U.S. Geological Survey digital data, 1:2,000,000 From Clark and others, 2013

94° 92° 91° 93°

90°

36°

35°

34°

0 0 30 

Figure 24. Percentage of recent average annual pumping from the Mississippi River Valley alluvial aquifer with reductions for surface-water diversi

of Clark and others (2013).
98 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Because row-crop agriculture is the dominant land use in 

eastern Arkansas, use of pesticides and fertilizers is the most 

prevalent and ubiquitous anthropogenic threat to groundwater 

quality in the shallow alluvial aquifer. Local sources of 

contamination exist in urban settings (for example, USTs, 

pesticides and fertilizers, small industry, and other sources); 

however, contaminant plumes normally are present at small 

local scales and do not affect large regional areas. 

General Geochemistry and Water Type

Groundwater from the alluvial deposits of the Coastal 

Plain, which includes the extent of the Mississippi River 

Valley alluvial aquifer, is dominantly a calcium-bicarbonate 

water type; sodium, magnesium, chloride, sulfate, silica, and 

iron comprise the remaining major (by weight) ions in solution 

(fig. 25; table 19). Most of the samples collected from wells 

in the Coastal Plain are predominantly from the Mississippi 

River Valley alluvial aquifer (greater than 90 percent), and 

therefore statistical analyses in table 19 are considered 

representative of the aquifer. Most constituents generally 

show a wide variability in concentration based on residence 

time of groundwater along a flow path—the longer the flow 

path, the more time allowed for mineral dissolution and rock/

water interactions that affect the chemical composition of 

groundwater. Constituent variability also is affected locally 

by anthropogenic sources or upwelling of high-salinity water 

from underlying formations. The following sections provide 

more detailed information related to general water quality and 

a discussion of the occurrence, sources, and distribution of 

constituents that contribute to localized or ubiquitous waterquality concerns throughout the extent of the Mississippi 

River Valley alluvial aquifer in eastern Arkansas. It should 

be noted that in some of the figures, some sites appear to be 

outside of the Coastal Plain. This is a result of the scale for 

the physiographic province boundaries (line representing the 

Fall Line), and the fact that where major streams (for example, 

the White River) enter the Coastal Plain, the line does not 

follow some of the thicker deposits upstream (that is, it is 

difficult to define an exact boundary where deposits from one 

stream extend upstream from those of the Mississippi Alluvial 

Plain deposits). All wells were completed in alluvial deposits 

considered belonging to and assigned to the Coastal Plain 

alluvium.

Groundwater-quality data for the Mississippi River 

Valley alluvial aquifer are available in many publications 

that describe general inorganic groundwater chemistry for 

various locations in the State. Several earlier reports were 

part of a statewide assessment of groundwater resources by 

counties that began in the late 1940s (Hewitt and others, 1949: 

Klein and others, 1950; Onellion and Criner, 1955; Onellion, 

1956; Counts, 1957; Ryling, 1960; Bedinger and Reed, 

1961; Plebuch, 1961; Halberg and Reed, 1964; Sniegocki, 

1964; Albin and others, 1967a; Lamonds and others, 1969; 

Hines and others, 1972; Ludwig, 1973). Other assessments 

focused on groundwater quality in particular areas of concern 

or groundwater resources in major basins within eastern 

Arkansas (Broom and Reed, 1973; Broom and Lyford, 1981; 

Fitzpatrick, 1985; Morris and Bush, 1986; Kilpatrick and 

Ludwig, 1990b; Leidy and Morris, 1990a). A large regional 

groundwater-quality assessment of the Mississippi embayment 

in Mississippi, Louisiana, Arkansas, Missouri, Tennessee, 

and Kentucky was performed as part of the National WaterQuality Assessment (NAWQA) Program, and findings were 

summarized in Kleiss and others (2000) and Gonthier (2003). 

The ADEQ conducts groundwater-quality monitoring on a 

rotating 3-year schedule for several areas in eastern Arkansas 

and has published summary reports of the data (Van Schaik 

and Kresse, 1994, 1995, 1996; Kresse and others, 1997; 

Kresse and Huetter, 1999). Most of these groundwater studies 

typically covered one to three counties. These reports provided 

basic descriptive statistics on chemical constituents including 

major ions, trace metals, and nutrients with little to no 

discussion of processes that affected the occurrence, source, 

and distribution of various chemical constituents. 

The first detailed assessment of processes controlling 

inorganic chemistry of groundwater in the Mississippi 

River Valley alluvial aquifer is found in Kresse and Fazio 

(2002). This study collected groundwater-quality samples 

from 118 wells in southeastern Arkansas and developed 

a conceptual model for the evolution of the groundwater 

geochemistry of the Mississippi River Valley alluvial aquifer. 

Previous reports (listed above) had noted the dominantly 

calcium-bicarbonate water type and the elevated iron 

and manganese concentrations in groundwater from the 

aquifer. Kresse and others (1997) provided evidence for 

cation exchange along a flow path driving the transition of 

a calcium-bicarbonate to a sodium-bicarbonate water type, 

in addition to providing evidence for gypsum dissolution 

contributing calcium and sulfate. Kresse and Fazio (2002) 

added to the work of Kresse and others (1997) and used 

analyses of rainwater, shallow groundwater, and deep 

groundwater to develop a conceptual geochemical model 

that accounted for the varying chemistry and water types. 

They showed that young, shallow groundwater (within the 

upper 10 ft of the vertical-flow dominated saturated zone) 

chemistry was explained as rainwater that was concentrated 

through evapotranspiration, sufficiently elevating magnesium, 

potassium, chloride, sulfate, and nitrogen concentrations. 

Most of the calcium and bicarbonate resulted from carbonate 

mineral dissolution in the unsaturated and upper saturated 

zones. High sodium-chloride ratios were explained by 

calcium-sodium cation exchange increasing groundwater 

sodium concentrations relative to chloride. The clay-rich 

upper unit of the aquifer provides abundant exchange capacity 

(Kresse and Fazio, 2002).
Aquifers of the Coastal Plain 99

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron

Constituent Constituent

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

1,295

0

50

100

150

200

250

300

350

400

450

Concentrations, in milligrams per liter

500

Concentration, in micrograms per liter

7,000

8,000

9,000

10,000

0

1,000

2,000

3,000

4,000

5,000

6,000

1,286

1,278

1,507

1,564

3,319

1,606

1,295

Figure 25. Interquartile range of selected chemical constituents in groundwater from alluvial deposits in the Coastal Plain of southern 

and eastern Arkansas.

Table 19. Descriptive statistics for selected chemical constituents in groundwater from alluvial deposits in the Coastal Plain Province 

of southern and eastern Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 0.1 65 659 47.3 1,286

Magnesium (mg/L) 0.03 16 663 22.8 1,278

Sodium (mg/L) 0.23 22 771 61 1,507

Potassium (mg/L) 0.08 1.8 54 2.8 1,314

Bicarbonate (mg/L) 2.0 276 830 151 1,564

Chloride (mg/L) 0.12 23 7,150 237 3,319

Sulfate (mg/L) 0.1 11 1,200 64 1,606

Silica (mg/L) 1.2 31 667 23 912

Nitrate (mg/L as nitrogen) 0.002 0.09 228 7.9 1,444

Dissolved solids (mg/L) 28 320 3,435 292 1,267

Iron (μg/L) 0.05 1,200 109,000 6,812 1,295

Manganese (μg/L) 0.13 413 25,000 1,010 785

Arsenic (μg/L) 0.03 2.09 80 8.8 527

Hardness (mg/L as calcium carbonate) 1.05 220 4,380 215 1,415

Specific conductance (μS/cm) 7 596 10,200 550 3,789

pH (standard units) 4.2 7.2 9.4 0.6 2,141
100 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Groundwater samples from irrigation wells completed 

in the lower, high-yield basal unit of the Mississippi River 

Valley alluvial aquifer provided a chemical composition 

representative of deeper, older waters. Kresse and Fazio 

(2002) conducted a graphical analysis of various constituents 

along a continuum of increasing residence time in the aquifer, 

represented by increasing dissolved-solids concentrations. 

This analysis was used to delineate evolution of groundwater 

chemistry in the deeper, horizontal-flow dominated part of 

the aquifer. Geochemical trends for individual chemical 

constituents with increasing dissolved-solids concentrations 

revealed two populations. The first population of data 

values, ranging from less than 100 to 350 milligrams per 

liter (mg/L) dissolved solids, evolved toward a strongly 

calcium-bicarbonate water type with calcium and bicarbonate 

comprising over 65 and 95 percent of the total cations and 

anions in milliequivalents per liter, respectively. Values for 

pH simultaneously increased within this population from 

approximately 5.9 to 7.4, reflecting the consumption of 

hydrogen ions with the dissolution of carbonate material. 

For the second population of data values, calcium and 

bicarbonate percentages decreased with increasing dissolvedsolids concentrations. This population was characterized 

by increasing sodium, chloride, and sulfate concentrations, 

and decreasing pH values at dissolved-solids concentrations 

from 350 to 746 mg/L. Calculation of saturation indices 

demonstrated that groundwater in the first population was 

undersaturated with respect to calcite, whereas groundwater 

in the second population was supersaturated with respect 

to calcite. No mechanism was proposed for the evolution 

of higher salinity groundwater represented by the second 

population. A later study (described in greater detail in the 

next section) investigated elevated arsenic concentrations 

in southeastern Arkansas (Kresse and Fazio, 2003). That 

study revealed a predictable spatial distribution for the 

water types and groundwater chemistry trends in the alluvial 

aquifer described by Kresse and Fazio (2002) based on 

geomorphology and stratigraphy in southeastern Arkansas.

Source of Elevated Trace Metals 

Trace metals, particularly iron, manganese, and 

arsenic, occur in elevated concentrations in large areas of 

the Mississippi River Valley alluvial aquifer. Concentrations 

exceeding secondary drinking-water regulations (related 

to taste and staining) for iron (0.3 mg/L or 300 μg/L) and 

manganese (0.05 mg/L or 50 μg/L) (table 1) are common 

throughout the Mississippi River Valley alluvial aquifer and 

present problems to farmers because of fouling of irrigation 

well pumps and screens. Elevated concentrations of these 

metals have been mentioned by nearly every author reporting 

on groundwater quality in the alluvial aquifer; however, the 

large database accumulated for this study, together with spatial 

analysis of individual constituents within a geographical 

information system, revealed a trend in the distribution of 

iron concentrations (fig. 26) that could benefit users requiring 

large amounts of water (for example, public supply) with little 

treatment expense. Large areas of low (less than 300 μg/L) 

iron concentrations are located in the northern part of the 

aquifer, in addition to isolated areas in the southern part of the 

aquifer.

A limited attempt at investigating relations of iron (and 

other constituents) to other spatial attributes (for example, 

soils, geology, geomorphology) for this report revealed a 

general relation with the geomorphology of the Mississippi 

embayment; however, a detailed assessment of sources and 

processes accounting for the spatial distribution of dissolved 

iron concentrations was outside the scope of this report. 

Box plots (fig. 27) of selected constituents were constructed 

using an overlay method within a geographical information 

system to categorize individual sites by percentage of various 

geomorphological units as mapped by Saucier (1994). 

Providing explanations for differences in concentrations of 

various constituents related to geomorphology were outside 

of the scope of this report, especially for areas north of the 

Arkansas River. For areas south of the Arkansas River, 

reports are available that describe the relation of various 

chemical constituents to area geomorphology. These reports, 

discussed in the following paragraphs, illuminate the effects of 

depositional processes forming the resulting geomorphology 

on geochemical evolution of groundwater throughout the 

Mississippi River Valley alluvial aquifer.

Kresse and Fazio (2003) provided the first comprehensive 

study addressing the source and distribution of trace metals 

in the Mississippi River Valley alluvial aquifer, which aided 

in understanding the overall evolution of geochemistry in 

the aquifer. Their study was prompted by a lowering of the 

Federal MCL for arsenic from 50 μg/L to 10 μg/L in 2001 

(U.S. Environmental Protection Agency, 2001). Kresse 

and Fazio (2002) reported that 21 of 118 irrigation wells 

sampled in southeastern Arkansas had arsenic concentrations 

exceeding 10 μg/L. They hypothesized that inorganic arsenic 

was the source of these elevated concentrations based on 

statistically significant differences between groundwater in 

older Pleistocene terrace deposits, with lower concentrations 

of iron, arsenic, barium, and manganese, and younger 

Holocene deposits with elevated concentrations of these 

metals. Gonthier (2003) compared groundwater chemistry 

from 25 wells completed in the Holocene alluvium to 29 wells 

completed in Pleistocene valley train deposits and also noted 

significantly higher concentrations of metals in groundwater 

from the Holocene relative to that from the Pleistocene 

deposits. Kresse and Fazio (2003) further investigated the 

occurrence and source of arsenic in groundwater throughout 

Arkansas and employed regression analyses to show 

correlations between redox-sensitive constituents (ammonia, 

nitrate, iron, manganese, phosphorus, barium, and arsenic) 

and total organic carbon for groundwater from the Mississippi 

River Valley alluvial aquifer.
36°

35°

34°

36°

35°

34°

36°

35°

34°

36°

35°

34°

36°

35°

34°

36°

35°

34°

94° 93° 92° 91°

90°

94° 93° 92° 91°

90°

94° 93° 

94° 93° 

94° 93° 92° 91°

90°

94° 93° 92° 91°

90°

West Gulf Coastal 

Plain

Mississippi  Alluvial  Plain

 COASTAL PLAIN PROVINCE

0 0 

Geomorphology 

Base modified from U.S. Geological Survey digital data, 1:250,000

0 to 2526 to 5051 to 100101 to 250251 to 500501 to 1,200

Sulfate, in milligrams per liter

EXPLANATION

0 to 300301 to 1,0001,001 to 10,00010,001 to 25,00025,001 to 50,00050,001 to 109,000

Iron, in micrograms per liter Iron, in micrograms per liter

EXPLANATION

1 to 56 to 1011 to 2526 to 3536 to 5051 to 667

Silica, in milligrams per 

EXPLANATION

0 to 12 to 56 to 1011 to 2526 to 5051 to 228

Nitrate, in milligrams per liter

EXPLANATION

4.2 to 5.96.0 to 6.66.7 to 7.17.2 to 7.57.6 to 8.08.1 to 9.4

pH, in standard units

EXPLANATION

EXPLANATION

Coastal Plain extentCrowleys Ridge Ha

Hb

Hp

Pd

Pp

Ps

Pt

Pv

Pvl

Geomorphology formations

Undifferentiated fluvial deposits

of Cache River terrace

Early Wisconsin Stage valley trainsLate Wisconsin Stage valley trains Sand dune and eolian deposits on valley trains

Undifferentiated alluvial depositsBackswamp depositsPoint bar deposits

Fluvial, point-bar, and channel

deposits of Deweyville Complex

Fluvial, point-bar, and channel

deposits of Prairie Complex

Figure 26. Spatial distribution of selected chemical constituents in groundwater from alluvial deposits in the Coastal Plain of southern and eastern A
102 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Data point

Number of values (n)

95th percentile (where n > 9 and data plot

 above the 90th percentile)

90th percentile (where n > 9)

75th percentile

50th percentile (median)

25th percentile

10th percentile (where n > 9)

5th percentile (where n > 9 and data plot

 below the 10th percentile)

249 Hb, Backswamp deposits

Hp, Point bar deposits

Pd, Fluvial, point bar, and channel deposits of

 Deweyville Complex

Pp, Fluvial, point bar, and channel deposits of

 Prairie Complex

Ps, Sand dune and eolian deposits on valley trains

Pt, Undifferentiated fluvial deposits of Cache River

 terrace

Pv, Early Wisconsin Stage valley trains

Pvl, Late Wisconsin Stage valley trains

EXPLANATION

Geomorphological unit

Geomorphological units Geomorphological units

Hb Hp Pd Pp Ps Pt Pv Pvl Hb Hp Pd Pp Ps Pt Pv Pvl

Hb Hp Pd Pp Ps Pt Pv Pvl

Hb Hp Pd Pp Ps Pt Pv Pvl

0

5

10

15

20

25

30

0

50

100

150

200

Concentration, in micrograms per liter

0

5,000

10,000

15,000

20,000

25,000 Concentration, in milligrams per liter

0

50

100

150

200 452

531

25

303

4

14

471 142

252

344

12

170

5

6

271

72

259

249

6 137

5

5

241

63

126

170

3

35

0

1

34

7

Chloride Sulfate

Iron Arsenic

Figure 27. Selected chemical constituents in groundwater from alluvial deposits as related to geomorphological units in the 

Mississippi Alluvial Plain of eastern Arkansas. 
Aquifers of the Coastal Plain 103

Numerous correlations by Kresse and Fazio (2003) 

indicated an inorganic source of arsenic rather than past 

use of arsenical pesticides. Inverse relations were noted 

for comparisons of iron, manganese, and arsenic to 

nitrate concentrations. When concentrations of iron and 

manganese exceeded 0.5 mg/L, nitrate concentrations were 

less than 0.5 mg/L as nitrogen (N). Similarly, when nitrate 

concentrations were greater than 0.1 mg/L as N, arsenic 

concentrations were less than 5 μg/L, and when nitrate 

concentrations were less than 0.1 mg/L, arsenic concentrations 

ranged upward to 50 μg/L with 21 samples that exceeded 

10 μg/L. These correlations tended to rule out arsenical 

pesticides as the source of arsenic because iron, manganese, 

and arsenic did not occur in the shallow groundwater with 

low dissolved solids but only occurred in groundwater 

along a deep, longer flow path with higher dissolved-solids 

concentrations. 

Arsenic additionally correlated more closely with 

increases in iron, manganese, barium, total organic carbon, 

and total phosphorus. These correlations indicated reductive 

dissolution of iron oxyhydroxide coatings on sand particles 

as the source of elevated arsenic (and other redox sensitive 

constituents) in the Mississippi River Valley alluvial aquifer, 

as had been described for groundwater in alluvial deposits 

across the globe (Nickson and others, 2000; McArthur and 

others, 2001; Mueller and others, 2001; Hon and others, 

2002). Kresse and Fazio (2003) noted that arsenic and 

iron concentrations were noted to increase simultaneously 

up to iron concentrations of approximately 12,000 μg/L; 

at that point, arsenic concentrations decreased as iron 

concentrations continued to increase. Similar to the two 

groupings noted from Kresse and Fazio (2002), iron and 

arsenic concentrations showed abrupt decreases for dissolvedsolids concentrations greater than 350 mg/L. Because iron and 

arsenic concentrations decreased with concomitant increases 

in sulfate concentrations, formation of arsenic-containing iron 

sulfides under sulfate-reducing conditions was interpreted 

as accounting for the loss of arsenic and iron. Subsequent 

studies in elevated arsenic zones in southeastern Arkansas 

employed five-step sequential extraction of sediments, inverse 

geochemical modeling, surface complexation modeling, X-ray 

diffraction analysis, arsenic speciation, and other investigative 

techniques. These studies confirmed reductive dissolution 

of iron oxyhydroxides as the source of elevated arsenic. 

The studies also confirmed that reduction of sulfate with 

coprecipitation of arsenic and sulfide is an important limiting 

process controlling the concentration of arsenic in solution 

(Sharif and others, 2008a, b, 2011). 

The above studies also identified redox processes as an 

important limiting control for dissolved nitrate concentrations 

in the Mississippi River Valley alluvial aquifer. Despite 

extensive application of nitrogen fertilizers for crops in eastern 

Arkansas, nitrate concentrations in the aquifer are relatively 

low. The median concentration of nitrate was 0.02 mg/L for 

118 irrigation well samples from Kresse and Fazio (2002), 

0.05 mg/L for 77 irrigation well samples from Kresse and 

others (1997), and 0.09 mg/L for 1,444 samples compiled 

for this report (table 19). Steele and others (1994) noted that 

groundwater from shallow alluvial wells (less than 50 ft deep) 

had median nitrate concentrations of 2.94 mg/L, whereas 

deep wells (more than 50 ft deep) had median concentrations 

of 0.13 mg/L. In a redox zonation, nitrate follows oxygen 

as the next most energetic electron acceptor. Virtually all 

dissolved nitrate in deeper sections of the Mississippi River 

Valley alluvial aquifer had been reduced to dinitrogen prior 

to reduction of manganese and iron oxides. Together with the 

inverse correlation of nitrate with iron and arsenic (Kresse 

and Fazio, 2003), abundant evidence is available to indicate 

that iron and other trace metals should be present in low 

concentrations in shallow, young, oxygenated waters and 

more elevated in deeper, older, reduced groundwater in the 

Mississippi River Valley alluvial aquifer. Several historical 

reports cited soft water and low iron concentrations in shallow 

wells completed in the Mississippi River Valley alluvial 

aquifer (Ryling, 1960; Plebuch, 1961; Steele and others, 

1994).

Occurrence, Distribution, and Sources of Elevated Chloride 

Concentrations

High chloride concentrations are a common problem 

limiting use of the Mississippi River Valley alluvial aquifer in 

some areas of Arkansas. The median chloride concentration 

for 3,319 samples compiled for this report was 23 mg/L. The 

distribution of chloride concentrations in groundwater from 

alluvial deposits in the Coastal Plain, including the extent 

of the Mississippi River Valley alluvial aquifer, was plotted 

to investigate areas of high salinity (fig. 28). The Arkansas 

River physically divides the alluvial aquifer into northern 

and southern parts and serves as a hydrologic boundary. This 

boundary also was applied to the north and south alluvial 

aquifer groundwater-flow models (described in section 

“Results of Groundwater-Flow Simulation Models”). For this 

report, areas of high salinity are discussed separately for the 

Mississippi River Valley alluvial aquifer north and south of the 

Arkansas River. Changes in lithostratigraphy, geomorphology, 

and underlying formations north and south of the Arkansas 

River have resulted in differing sources for high-salinity water. 

Various publications have addressed these problems separately 

for site-specific areas.
LEE UNION WHITE DREW PIKE CLARK CLAY ASHLEY DESHA LONOKE PULASKI GRANT ARKANSAS CHICOT MILLER CROSS DALLAS PRAIRIE PHILLIPS SEVIER MISSISSIPPI JEFFERSON NEVADA POINSETT COLUMBIAOUACHITA BRADLEY MONROE GREENE JACKSON HOWARD LINCOLN CALHOUN CRAIGHEAD HEMPSTEAD RANDOLPH LAWRENCE ST. FRANCIS CLEVELAND HOT SPRING INDEPENDENCE LITTLE RIVER WOODRUFF CRITTENDEN LAFAYETTE SALINE West Gulf Coastal Plain Mississippi Alluvial Plain Base from U.S. Geological Survey digital data, 1:2,000,000 0 15 

0 30 

15 

94° 92° 91° 93° 90° 36°35° 34° 

C

C

Figure 28. Distribution of chloride concentrations in groundwater from alluvial deposits of the Coastal Plain in Arkansas.
Aquifers of the Coastal Plain 105

Chloride concentrations often are correlated with greater 

concentrations of dissolved solids. Such a correlation was 

shown by Kresse and Fazio (2002) for the Mississippi River 

Valley alluvial aquifer in southeastern Arkansas as discussed 

in the previous section. The EPA established a secondary 

drinking-water regulation for chloride of 250 mg/L based on 

aesthetic qualities including taste (table 1; U.S. Environmental 

Protection Agency, 2009). Elevated chloride concentrations 

also can affect various crops, thus presenting problems to 

farmers in eastern Arkansas. Problems encountered in the 

use of high-salinity waters for irrigation can be acute, such 

as burning of foliage, and chronic, including a reduction in 

the plant’s ability to uptake water as a result of increased 

soil osmotic pressure (McFarland and others, 1998). 

Additionally, high sodium concentrations (often associated 

with high chloride concentrations) can result in soil structure 

deterioration and reduced water infiltration rates (Cardon and 

Mortvedt, 2001; Gilmour, 2000). Salinity also has been shown 

to suppress nutrient uptake and other metabolic processes, 

limiting growth and crop yields (Pulley and Beyrouty, 

1996), and has affected a substantial amount of rice acreage 

in Arkansas (Wilson and others, 1997). For this reason, 

groundwater that contains chloride concentrations exceeding 

100 mg/L is not recommended for rice production (Tacker 

and others, 1994), although some farmers are able to apply 

novel irrigation management approaches to economically 

produce rice and other crops with water containing higher 

concentrations of chloride. For this report, a practical 

definition of elevated chloride concentration is set at 100 mg/L 

as was established in Kresse and Clark (2008).

Numerous reports describe the occurrence of elevated 

chlorides in southeastern Arkansas. Onellion and Criner 

(1955) showed chloride concentrations as high as 1,490 mg/L 

in southwestern Chicot County. Klein and others (1950), 

Bedinger and Reed (1961), Bedinger and Jeffery (1964), 

and Broom and Reed (1973) reported elevated chloride 

concentrations in Jefferson, Lincoln, and Desha Counties but 

did little to identify the source of elevated chloride except to 

comment on proximity to the Arkansas River, which often 

contained elevated chloride concentrations. Fitzpatrick (1985) 

reported high salinity concentrations in the Mississippi River 

Valley alluvial aquifer of southeastern Arkansas (south of 

the Arkansas River). Elevated chloride concentrations were 

attributed to several possible sources: (1) upward flow from 

underlying, high-salinity Tertiary aquifers; (2) influx of water 

from the Arkansas River (in the area of Desha and Lincoln 

Counties); (3) upward migration of deep reservoir brines 

from abandoned oil and gas wells; and (4) migration of deep 

brine upfaults (in Chicot County), although no direct evidence 

was presented to validate or refute these potential sources. 

Fitzpatrick (1985) showed chloride concentrations as high as 

360 mg/L in Desha and Lincoln Counties, corresponding to the 

area described in Bedinger and Reed (1961), and a maximum 

chloride concentration of 1,360 mg/L in Chicot County. Kresse 

and others (1997) sampled 77 wells in parts of southeastern 

Arkansas, including Jefferson, Lincoln, and Desha Counties, 

and noted that 5 groundwater samples exceeded 100 mg/L 

with a maximum concentration of 184 mg/L. They compared 

chloride concentrations from their study in eastern Arkansas 

to older datasets from Klein and others (1950) for Jefferson 

County and Bedinger and Reed (1961) for Desha and Lincoln 

Counties. Based on isoconcentration maps for all studies and 

comparison of mean chloride concentrations between the 

datasets, Kresse and others (1997) concluded that little change 

had occurred over time in the occurrence, areal distribution, 

and concentration of chloride in groundwater from this 

area. Kresse and Fazio (2002) collected 118 groundwater 

samples from irrigation wells in the Bayou Bartholomew 

watershed in southeastern Arkansas and noted 4 samples that 

exceeded 100 mg/L in Jefferson and Lincoln Counties. They 

hypothesized several potential sources of salinity including 

(1) infiltration from the Arkansas River, (2) low recharge rates 

through overlying clays leading to high residence time and 

minimal flushing, (3) downward percolation of irrigation water 

enriched in salts by evapotranspiration, and (4) upward flow of 

high-salinity water from underlying Tertiary aquifers.

Kresse and Clark (2008) provided the first study 

specifically designed to elucidate the sources of saline (more 

than 1,000 mg/L dissolved solids) water in the Mississippi 

River Valley alluvial aquifer in the Bayou Bartholomew 

watershed of southeastern Arkansas. They defined two 

separate areas that each exhibited elevated chloride 

concentrations derived from distinct sources: Area I, which 

comprised most of Jefferson, Lincoln, and Desha Counties, 

and Area II, which is mostly in Chicot County (fig. 29). 

Previous studies provided numerous explanations for the 

elevated chloride concentrations in Area I, including upwelling 

of poor quality water from underlying Tertiary aquifers 

or influx of high-salinity water from the Arkansas River 

(Bedinger and Reed, 1961; Bedinger and Jeffery, 1964, Broom 

and Reed, 1973; Fitzpatrick, 1985). Kresse and Clark (2008) 

documented low chloride concentrations in the underlying 

Cockfield and Sparta aquifers in Area I to rule out upwelling 

from underlying Tertiary aquifers. Spatial correlations between 

geomorphological landforms and chloride concentrations 

were used to show that a concentration of dissolved solids 

from rainwater through evapotranspiration in areas of lowpermeable, clay-dominated backswamp deposits was the most 

likely source of elevated chloride concentrations in Area I. 

Lower chloride concentrations were consistently noted in 

groundwater from high-permeable, coarse channel deposits of 

the Arkansas River and Bayou Bartholomew. This relation was 

demonstrated best for Desha County, which had the largest 

amounts of data (fig. 30). Interestingly, Kresse and Clark 

(2008) noted that the lowest chloride concentrations were from 

wells near the Arkansas River, providing strong evidence that 

infiltration of river water was not a likely source. 
106 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Mississippi River

Bartholomew

Bayou

River

Arkansas 

0 10 20 MILES

0 10 20 KILOMETERS

DREW

ASHLEY

DESHA

CHICOT

JEFFERSON

LINCOLN

CLEVELAND

ARKANSAS

LOUISIANA

Pine Bluff

Crossett

Dumas

McGehee

Dermott

Hamburg

Monticello

Eudora

Area I

Area II

Lake 

Village

92°00’ 91°30' 91°00’ 34°

30' 

34°

00’ 

33°

30' 

33°

00’ Base modified from U.S. Geological Survey digital data,1:250,000 Modified from Haley, 1976

3 to 50

51 to 100

101 to 350

351 to 750

751 to 1,639

Chloride, in milligrams per liter

EXPLANATION

ARKANSAS

Area enlarged

Bayou Bartholomew

watershed

Figure 29. Distribution of chloride concentrations in groundwater from the Mississippi River Valley alluvial aquifer in Bayou 

Bartholomew watershed of southeastern Arkansas (from Kresse and Clark, 2008).
Aquifers of the Coastal Plain 107

RIVER

MISSISSIPPI

RIVER

ARKANSAS

Bartholomew

Bayou

Abandoned

channel of the

Arkansas River

East fork 

of the 

abandoned

channel

Dumas

McGehee

Dermott

DESHA

DREW

CHICOT

LINCOLN ARKANSAS

Base modified from U.S. Geological Survey digital data, 1:250,000 Geomorphology map modified from Saucier, 1994

91°30'

33°

30'

91°15'

33°

45'

0 2.5 5 MILES

0 2.5 5 KILOMETERS

Unconsolidated alluvium

Point bar deposits of the Mississippi

River meander belts 1 through 6

Abandoned channels of the 

Mississippi River

Point bar deposits of the Arkansas 

River meander belts 1 through 8

Point bar deposits of small streams

Backswamp deposits

Early Wisconsin stage valley train 

levels 1 through 5

Undifferientiated fluvial deposits 

of prairie complex

Hal

Hpm

Hchm

Hpa

Hps

Hb

Pve

Ppu

Chloride, in milligrams per liter

3 to 50

51 to 100

101 to 350

351 to 750

EXPLANATION

Area enlarged

ARKANSAS

Figure 30. Distribution of chloride concentrations in groundwater from the Mississippi River Valley alluvial aquifer overlain onto a map 

of Quaternary geomorphological landforms (from Kresse and Clark, 2008).
108 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

In Area II (fig. 29), Kresse and Clark (2008) ruled out 

upwelling of saline water in Tertiary aquifers and abandoned 

oil and gas wells as a source of the salinity problem. They used 

(1) mixing curves developed from bromide-chloride ratios from 

the Mississippi River Valley alluvial and Tertiary aquifers as 

well as brine water from the Smackover Formation of Jurassic 

age, (2) chloride isoconcentration maps for the Mississippi 

River Valley alluvial and Tertiary aquifers, and (3) dates of 

early oil exploration wells. Evidence, including elongation 

of the zone of elevated chloride concentrations in the alluvial 

aquifer, suggested that the most likely source of chloride was 

brine water from the Smackover Formation moving up the 

intersection of two mapped wrench faults (Zimmerman, 1992) 

in the vicinity of Area II. At least one of the faults was described 

as extending into the Smackover Formation and was listed as 

having been active as late as the Pleistocene or Holocene Periods 

(Zimmerman, 1992). Trend analysis of the data indicated that 

no changes occurred in the concentration or spatial distribution 

of chloride concentrations in Area I or Area II from the earliest 

sampling periods in the early 1950s through 1995. This finding 

is similar to Kresse and others (1997), which concluded that 

little to no change had occurred over time in the occurrence, 

areal distribution, and concentration of chloride in southeastern 

Arkansas.

Kresse and Clark’s (2008) demonstration of the 

lithostratigraphic and geomorphologic control on chloride 

concentration distribution in southeastern Arkansas provided 

additional information on trace metal occurrence and 

distribution, particularly elevated arsenic concentrations. 

Whereas chloride and sulfate concentrations were found to be 

elevated in the backswamp deposits, arsenic concentrations were 

lower in these deposits. Similarly, when chloride and sulfate 

concentrations were lower in the channel deposits, groundwater 

in these deposits contained elevated levels of arsenic (fig. 31). 

Inspection of the relation of arsenic to sulfate and chloride 

for data collected for this report revealed inverse correlations 

supporting lack of arsenic in groundwater regimes with elevated 

chloride and sulfate concentrations. Kresse and Fazio (2002, 

2003) noted that elevated concentrations of chloride correlated 

with elevated levels of sulfate. Several studies (Kresse and 

Fazio, 2003; Sharif and others, 2008a, b, 2011) hypothesize that 

reduction of sulfate was a controlling factor for elevated arsenic 

concentrations as a result of coprecipitation of arsenic in ironsulfide minerals. Sharif and others (2008b) noted that clay-layer 

thickness correlated with sulfate concentration and inversely 

correlated with arsenic concentrations. This, together with an 

inspection of the geomorphology of the area, indicates that 

areas of increased confining clay layer thickness are observed in 

backswamp environment areas. Relatively small infiltration rates 

have minimally exceeded evaporation in the backswamp areas 

over thousands of years (Sharif and others, 2008b) that has led to 

increases in concentrations of chloride and sulfate delivered with 

rainwater in these areas and has resulted in a dominantly sulfate 

reduction groundwater system (Sharif and others, 2008b). This 

type of groundwater system controls concentrations of soluble 

arsenic previously liberated by reductive dissolution of iron 

oxyhydroxides.

Areas of high salinity have been documented in areas 

north of the Arkansas River, though no definitive sources 

have been identified to explain their occurrence. An area of 

high salinity groundwater was noted near Brinkley (Monroe 

County; fig. 28) where a well with a chloride concentration 

of 22 mg/L in the late 1940s increased to 800 mg/L by 1982. 

Morris and Bush (1986) described a 56-mi2

 area affected 

by saltwater intrusion that was attributed to upward leakage 

from deeper formations. Based on results of sampling from 

217 wells, Morris and Bush (1986) identified two separate areas 

of high concentrations of chloride: (1) an area about 1.5 mi 

north of Brinkley (centered near the well initially identified 

as problematic in the late 1940s) and exhibiting groundwater 

chloride concentrations as much as 960 mg/L, and (2) an 

area approximately 6 mi southwest of Brinkley with chloride 

concentrations exceeding 400 mg/L. Morris and Bush (1986) 

hypothesized three transport pathways to potentially explain 

upward migration of high salinity water: (1) upward influx of 

high concentrations of chloride water from the Sparta Sand in 

areas where the confining layer is thin, (2) upward migration 

along as yet unmapped faults, or (3) movement of saltwater 

from the Nacatoch Sand upward into the Sparta and Mississippi 

River Valley alluvial aquifers through abandoned oil- and gastest boreholes. Although Morris and Bush (1986) characterized 

the areal distribution of high-chloride concentrations and 

addressed immediate concerns, no followup study has been 

completed to definitively explain the source of the chloride. 

In White County (fig. 28), 30 groundwater samples had 

chloride concentrations exceeding 100 mg/L, and 9 samples 

exceeded 1,000 mg/L, with a maximum concentration of 

3,000 mg/L (Counts, 1957). This area reportedly had a rice 

crop that was killed by the high salinity water during a season 

when little surface water was available for mixing with the 

groundwater. Discussions with local residents revealed that 

several wells completed for domestic supplies yielded water 

so salty that the wells were abandoned (Counts, 1957). Counts 

(1957) conducted field tests for chloride on domestic and stock 

wells in the area and produced a chloride map that showed a 

high-chloride area of approximately 20 mi2

 with concentrations 

exceeding 1,000 mg/L. An anecdotal note best relating the 

degree of salinity is found in Counts (1957), who described the 

use of the shallow, high-salinity groundwater for salt production 

during the Civil War when water from dug wells was boiled to 

evaporation for salt. Saltwater was encountered in the Nacatoch 

Sand and in Paleozoic Formations in the area (Counts, 1957), 

and unmapped faults may exist that allow migration of water 

from these deeper formations into the Mississippi River Valley 

alluvial aquifer. Data compiled for this report revealed elevated 

chloride concentrations at various locations along the western 

extent of the Mississippi Alluvial Plain from Pulaski to Clay 

County (fig. 28). This finding suggests upwelling from highsalinity water at depth (possibly from Paleozoic formations) 

occurs along the transition (the Fall Line) from the Interior 

Highlands into the Coastal Plain, thus adding support to the 

theories proposed by Counts (1957) for elevated salinity in this 

area.
Cypress Cre

Choctaw Bayou

Arkansas River

Castor Bayou

Wa

Bayou Bartholomew

Jacks Bay ou Deep Bayo u

JEFFERSON

LINCOLN

A

92°00' 91°40'

34°15'

34°05'

33°55'

Base modified from U.S. Geological Survey digital data, 1:250,000

Geomorphology 

 from 

0 2 4 MILES

0 2 4 KILOMETERS

Arsenic, in micrograms per liter

0.03 to 2.52.6 to 5.05.1 to 10.010.1 to 25.025.1 to 50.050.1 to 80.0

EXPLANATION

Hb

Hp

Pp

Backswamp deposits

Fluvial, point-bar, and channel

deposits of Deweyville Complex

Point bar deposits 

Holocene Pleistocene

ARKANSAS

Area enlarged

Figure 31. Distribution of arsenic concentrations in groundwater from the Mississippi River Valley alluvial aquifer overlain onto a map of Quaternary 

landforms.
110 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Temporal Trends in Chloride Concentrations

A common concern regarding areas of high salinity in 

the Mississippi River Valley alluvial aquifer is the potential 

for these affected areas to expand under natural conditions or 

in response to pumping. Some of these concerns have been 

addressed in a few studies, which also have documented 

low groundwater velocities of approximately 0.25 ft/d in 

the Mississippi River Valley alluvial aquifer (Counts, 1957; 

Broom and Lyford, 1981; Mahon and Ludwig, 1990; Kresse 

and Van Schaik, 1996). Results of these studies demonstrated 

that consistent and detailed monitoring over time may 

be required to note (1) substantial changes in the spatial 

distribution of high-salinity groundwater in the aquifer and 

(2) zones of higher-velocity movement caused by preferential 

flow associated with faults, fractures, lithofacies changes, and 

focused pumping stress.

Recent studies have indicated little to no change in 

the spatial distribution of high-salinity groundwater in 

southeastern Arkansas. In Jefferson County, groundwater 

collected in 1996 with a mean chloride concentration of 

35 mg/L (Kresse and others, 1997) was similar to the mean 

concentration of 39 mg/L that was documented in 1948–49 

(Klein and others, 1950). In Desha County, a mean chloride 

concentration in 1996 of 62 mg/L (Kresse and others, 1997) 

was only slightly higher than the mean of 56 mg/L in 1952 

(Bedinger and Reed, 1961). A chloride isoconcentration map 

for parts of Lincoln and Desha Counties (Klein and others, 

1950) was similar to the map produced from the 1996 data for 

the same region (Kresse and others, 1997). 

Kresse and Clark (2008) used chloride data collected 

from 1946 to 1959 compared to data collected after 1980 to 

identify spatial differences and temporal trends in Jefferson, 

Lincoln, and Desha Counties. A strong similarity was 

noted between these two time periods with greater chloride 

concentrations observed in backswamp deposits and lower 

concentrations in the active and abandoned channel point-bar 

deposits. Additionally, comparisons of sites in close proximity 

between the two time periods showed little difference in 

chloride concentrations. Kresse and Clark (2008) explained 

the lack of change over time as being controlled by (1) low 

groundwater velocities, (2) relatively consistent water levels 

over time, and (3) no large, regional pumping centers. As a 

result of the low diffusion- and dispersion-driven flux rates 

for groundwater in the Mississippi River Valley alluvial 

aquifer in southeastern Arkansas, any substantial changes in 

the occurrence and distribution of higher salinity groundwater 

likely would be on decadal or larger timescales (Kresse and 

Clark, 2008). In Chicot County, chloride data from 217 sites 

from Kresse and others, (2000), 89 sites from Fitzpatrick 

(1985), and 89 sites from Criner (1955) were very similar in 

shape and extent, based on chloride isoconcentration maps 

(Kresse and Clark, 2008). This analysis showed no major 

changes over time in the occurrence and spatial distribution of 

chloride concentrations in Chicot County.

Groundwater data collected during three sampling 

periods in 1989, 1992, and 1995 for the affected area in 

northeastern Arkansas, as outlined in Morris and Bush (1986), 

was reported by Van Schaik and Kresse (1996). Seventeen 

of the 217 wells sampled by Morris and Bush (1986) were 

resampled by Van Schaik and Kresse (1996), with a stated 

goal of evaluating changes in groundwater quality over time 

and expansion in the area of high salinity. No temporal trend 

was noted for the three sampling events. Several wells showed 

no change, others showed only minor increases in chloride 

concentration, and others showed decreases in chloride 

concentrations. Generally, the two areas identified with the 

highest chloride concentrations by Van Schaik and Kresse 

(1996) were similar to those identified by Morris and Bush 

(1986). The well with the high concentration of 960 mg/L 

(Morris and Bush, 1986) had a chloride concentration 

of 830 mg/L in 1989 (Van Schaik and Kresse, 1996). No 

discernible expansion or contraction was noted for the affected 

area described in Morris and Bush (1986). 

In addition to ongoing monitoring efforts by the ADEQ 

in some high-chloride areas, the USGS, in cooperation with 

the ANRC and the AGS, has an ongoing monitoring program 

that collects and reports values of specific conductance and 

chloride concentrations from selected wells in the Mississippi 

River Valley alluvial aquifer in eastern Arkansas (Stanton 

and others, 1998; Joseph, 1999; Schrader, 2001b, 2006a, 

2008a, 2010; Reed, 2004). Results from the 2008 sampling 

period showed specific conductance values ranging from 

111 microsiemens per centimeter (μS/cm) to 2,020 μS/cm 

for 60 alluvial wells (Schrader, 2010). Maximum specific 

conductance values observed in Arkansas, Chicot, Cross, 

Desha, Greene, and Lincoln Counties equaled or exceeded 

1,000 μS/cm. A comparison of specific conductance 

histograms for 2006 and 2008 showed similarity in 

distribution shape, largest category, and mean values, 

indicating a minimal change in overall water quality. In 

summary, studies from 1946 through 2013 for the Mississippi 

River Valley alluvial aquifer show (1) little to no change in 

salinity trend and (2) stable water-quality conditions. Based 

on inspection of groundwater-quality data from continuously 

monitored wells in eastern Arkansas, new areas have not been 

identified with poor water quality.

Occurrence of Pesticides

The monitoring of pesticides in Arkansas gained 

increased attention in the early 1990s with Federal mandates 

to develop a State Management Plan for pesticide use (U.S. 

Environmental Protection Agency, 1994a, b). The ASPB 

enforces Federal pesticide regulations and maintains a 

groundwater monitoring program for pesticides in Arkansas 

(Arkansas State Plant Board, 2013). Prior to 2005, the AWRC 

conducted annual pesticide monitoring for the ASPB and 

published the results in various reports (Nichols and others, 

1993, 1996; Steele and others, 1993, 1994). These reports 
Aquifers of the Coastal Plain 111

provided pesticide detection location and concentration. 

Kresse and others (1997) sampled 77 irrigation wells in 

eastern Arkansas and conducted the first study in Arkansas 

to systematically isolate potential sources and transport 

pathways based on pesticide use and chemical behavior. Their 

study noted that the occurrence of pesticides in groundwater 

was unrelated to the amount of use on crop acreage; instead, 

pesticide occurrence was strongly correlated to leaching 

potential based on chemical characteristics including water 

solubility, organic carbon partition coefficient (Koc), and field 

half-life. Bentazon, with the highest solubility of any of the 

pesticides used in eastern Arkansas, accounted for the greatest 

percentage of detections (36.8 percent), although only the 

14th most frequently used pesticide, followed by molinate 

(18.4 percent detection rate), and metolachlor (8.0 percent 

detection rate). These results were similar to findings of the 

AWRC (Nichols and others, 1993, 1996; Steele and others, 

1993, 1994) and Gonthier (2003), which listed bentazon as the 

most frequently detected pesticide. All of the most frequently 

detected pesticides had water solubilities greater than 

500 mg/L and Koc values less than 200 milliliters per gram 

(mL/g), indicating a high potential for leaching to groundwater 

(Kresse and others, 1997). 

Kresse and Fazio (2002) sampled 118 irrigation wells 

completed in the Mississippi River Valley alluvial aquifer in 

the Bayou Bartholomew watershed in southeastern Arkansas, 

analyzing for 61 pesticides and pesticide byproducts. 

Pesticides were detected in 28 of the 118 samples (24 percent). 

Bentazon again was the most frequently detected pesticide 

and occurred in 19 of the 28 wells (55.9 percent of the total 

detections), followed by prometryn (8.8 percent), molinate 

(5.9 percent), and metolachlor (5.9 percent). Kresse and 

Fazio (2002) summarized rainfall amount and intensity, 

pesticide management practices, irrigation timing and 

rates, and temperature as factors that affect the migration 

potential for pesticides in the subsurface; however, chemical 

characteristics including adsorption, solubility, photo- and 

microbial degradation, and hydrolysis were cited as being the 

most critical factors in controlling the occurrence and types of 

pesticides detected in groundwater. Pesticide concentrations 

typically were three to five orders of magnitude lower than 

Federal drinking-water standards and health advisory limits 

(U.S. Environmental Protection Agency, 2009).

The ASPB has been collecting and analyzing water 

samples from irrigation wells for pesticides since 2005 

(Arkansas State Plant Board, 2013). Review of these data 

revealed that 32 of the 219 wells (14.6 percent) had pesticide 

detections. This percent detection rate is close to that cited in 

Kresse and others (1997), which listed 47 pesticides detected 

in 335 (14.0 percent) irrigation wells sampled collectively by 

the ADEQ, the AWRC, and the USGS through 1996. In data 

published by the ASPB, 2,4-Dichlorophenoxyacetic acid (2,4-

D) accounted for the largest percentage of pesticide detections 

(17 of 219 samples), bentazon accounted for the second largest 

number (12 of 219 samples), followed by metolachlor and 

quinclorac (each with 2 detections). 2,4-D is an herbicide 

used for control of broadleaf plants, is highly soluble with 

a water solubility of 900 mg/L (Agricultural Research 

Service, 2013), and is used on rice in eastern Arkansas (Jason 

Robertson, Arkansas State Plant Board, oral commun., 2013). 

Kresse and Fazio (2002) noted only one detection of 2,4-D 

in 118 irrigation-well samples; however, these samples were 

taken in counties south of the Arkansas River, where the ASPB 

similarly found no detections of 2,4-D. It is not known if this 

means that (1) 2,4-D is used to a greater degree in counties 

north of the river, (2) detection levels were lower in the ASPB 

study, or (3) the use of 2,4-D has increased since 2005. Such 

an analysis is outside the scope of this report. 

In spite of the heavy use of pesticides on crops in eastern 

Arkansas and an average rate of detection of approximately 

14 percent in sampled wells, pesticide concentrations 

are relatively low in comparison to Federal drinkingwater standards. Kresse and Fazio (2002) listed pesticide 

concentrations ranging from 0.002 to 0.519 μg/L, which 

were approximately three to five orders of magnitude below 

listed MCLs and other health advisory standards (U.S. 

Environmental Protection Agency, 2009). Similarly, the ASPB 

works with the ADH to determine potential health effects for 

pesticides in groundwater. These agencies show an absence of 

any adverse health effects for groundwater from the alluvial 

aquifer sampled by the ASPB since 2005 (Arkansas State Plant 

Board, 2013). In summarizing the occurrence of pesticides 

in groundwater, findings from studies to date indicate that 

(1) chemical and physical characteristics of pesticides far 

exceed pesticide use as the overall controlling factor for 

occurrence of pesticides in groundwater, (2) transport of 

pesticides to groundwater appears to be predominantly the 

result of vertical infiltration through the unsaturated zone 

because of normal application practices, rather than through 

back-siphoning and other point-source related events, and 

(3) pesticide groundwater concentrations are very low 

compared to Federal drinking-water standards.

In summary, water-quality problems in the Mississippi 

River Valley alluvial aquifer generally are related to elevated 

concentrations of iron and manganese concentrations that 

are widespread throughout the aquifer. Salinity problems 

and elevated arsenic concentrations are found in isolated 

parts of the aquifer. Because the primary use of the alluvial 

aquifer is for irrigation, practical issues related to elevated 

iron and manganese concentrations primarily are fouling of 

pumps and well screens. Elevated concentrations of chloride 

potentially can affect crop yields. Arsenic concentrations 

exceeded primary drinking-water regulations in some areas, 

but this problem has only been documented in irrigation wells 

that are completed in the deeper basal zone; domestic wells 

are completed in the arsenic-free shallower part (upper unit) 

of the Mississippi River Valley alluvial aquifer. Pesticide 

monitoring since the early 1990s has resulted in approximately 

a 14-percent pesticide detection rate; however, pesticide 

concentrations typically are low and are three to five orders of 

magnitude lower than published MCLs and health advisory 

standards.
112 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Minor Alluvial Aquifers in Coastal Plain

The Mississippi River Valley alluvial aquifer is limited to 

the eastern one-third of Arkansas. However, smaller deposits 

of Quaternary alluvium from other streams in southern 

Arkansas also contain groundwater that provides an important 

source of water in the Coastal Plain. Within the West Gulf 

Coastal Plain in southern and southwestern Arkansas, the 

Red River and Ouachita River alluvial deposits are important 

sources of water.

The principal source of recharge to these alluvial aquifers 

is precipitation (Boswell and others, 1968). The Red and 

Ouachita Rivers are in hydraulic connection with the alluvium 

(Halberg and others, 1968; Ludwig, 1973); therefore, the 

rivers may act as discharge or recharge points for the aquifer. 

Like the Quaternary alluvium of the Mississippi River 

Valley, the Quaternary alluvium of the Red River and Ouachita 

River Valleys are the result of Pleistocene and Quaternary 

erosion and deposition. As sea level rose, the gradient of the 

streams was reduced and aggradation of sediments began. The 

depositional processes were complex, and the alluvium was 

eroded, dissected, and terraced with changing flow conditions 

(Boswell and others, 1968). The smaller scale drainage of 

these basins is reflected in the thinner nature of the alluvium 

compared to that of the Mississippi River Valley.

Red River Alluvial Aquifer

Hydrogeologic Setting

Groundwater contained in the Red River Valley alluvial 

deposits (hereinafter referred to as the “Red River alluvial 

aquifer”) is an important source of water in southern Arkansas. 

The Red River Valley alluvial and terrace deposits underlie an 

area of about 540 mi2 in southwestern Arkansas (figs. 3 and 8) 

with a maximum thickness of 90 ft. The aquifer is comprised 

of a coarsening downward sequence of clay, silt, sand, and 

gravel, (Counts and others, 1955; Ludwig, 1973; Terry and 

others, 1986). Tait and others (1953) reported that in western 

Columbia County, the alluvial deposits of tributaries to the 

Red River are as thick as 80 ft and are comprised of silt and 

clay with a 5–10-ft thick layer of coarse sand or gravel at the 

base. Ludwig and Terry (1980) reported a thickness for the 

Red River alluvium of 75–200 ft, thickening to the south. 

Various reports provide hydraulic characteristics for the 

Red River alluvial aquifer. Boswell and others (1968) reported 

an average specific yield of the Red River alluvial aquifer of 

0.2. Ludwig (1973) reported on the Red River alluvial aquifer 

in the area of Hempstead, Lafayette, Little River, Miller, and 

Nevada Counties. Aquifer tests in the aquifer in Little River 

County yielded hydraulic conductivity values ranging from 

147 to 201 ft/d, transmissivity values ranging from 3,877 to 

13,369 ft2/d, and storage coefficients ranging from 0.002 to 

0.0002. Irrigation wells completed in the Red River alluvial 

aquifer were reported to yield between 200 and 1,200 gal/min. 

Ludwig (1973) estimated that wells in Little River County 

could yield as much as 750 gal/min, and wells in Miller and 

Lafayette Counties could yield as much as 1,500 gal/min. 

Counts and others (1955) reported well yields as high as 

150 gal/min in Little River County and 400 gal/min in Miller 

County. Ludwig and Terry (1980) noted that the Red River 

and its tributaries do not fully penetrate the alluvial aquifer 

in Louisiana, and the same is likely in Arkansas. In general, 

groundwater flows in the direction of the Red River from the 

southwestern State border with Texas to the southern border 

with Louisiana. The 1968 potentiometric surface is available 

in Ludwig (1973). 

Water Use

While many counties in southern Arkansas have reduced 

groundwater use and rely on surface water as the dominant 

or sole source of water supply, use of the Red River alluvial 

aquifer has increased in southwestern Arkansas. Water use 

from the Red River alluvial aquifer historically is included 

with the Mississippi River Valley alluvial aquifer (fig. 10; 

table 17); historic countywide use totals can be seen in 

figure 11. Increases in use occurred from 1965 to 2010 in 

Little River, Miller, and Lafayette Counties (fig. 12), and 

decreases occurred in Sevier and Hempstead Counties over the 

same period. No use has been recorded for Hempstead County 

since 1995, and only a slight amount of use (0.11 Mgal/d) 

was recorded for Sevier County in 2010 (table 17). Lafayette 

County generally used the greatest amount of water from the 

Red River alluvial aquifer. In 2010, there were over 240 wells 

registered in ARWUDBs, and use of the Red River alluvial 

aquifer was estimated to be about 31 Mgal/d—83 percent of 

which was for use as irrigation supply (Terrance W. Holland, 

U.S. Geological Survey, written commun., 2012).

Most irrigation use of the Red River alluvial aquifer 

occurs in southern Lafayette and northwestern Miller Counties 

(fig. 10). Irrigation pumpage from the aquifer was an estimated 

6.9 Mgal/d in 1965 (Ludwig, 1973), which increased 

277 percent to 26.0 Mgal/d in 2010 (Terrance W. Holland, 

U.S. Geological Survey, written commun., 2012). Counts 

and others (1955) previously recorded 17 wells in Little 

River and Miller Counties, 2 of these were irrigation wells 

in Miller County that have since increased to 40 irrigation 

wells (fig. 10; Terrance W. Holland, U.S. Geological Survey, 

written commun., 2012). Common crops in the area mirror 

crops grown in eastern Arkansas: rice, cotton, soybeans, and 

other minor crops. At one time, rice irrigation used as much 

as 50 percent of the water from the aquifer (Ludwig, 1973), 

but as of 2010, the percentage of irrigation water for rice 

production was about 12 percent (Terrance W. Holland, U.S. 

Geological Survey, written commun., 2012). 

Duck hunting is quite common in southwestern Arkansas. 

Many crop-producing areas also flood fields for duck hunting. 

In 2010, 15 percent of the Red River alluvial aquifer’s 

total use was for duck hunting (Terrance W. Holland, U.S. 

Geological Survey, written commun., 2012).
Aquifers of the Coastal Plain 113

Numerous towns throughout southwestern Arkansas used 

the Red River alluvial aquifer as a source of public supply in 

the late 1880s, but surface-water reservoirs were developed 

for this purpose beginning in the early 1900s (Hale, 1926). In 

2010, only 0.24 Mgal/d was withdrawn for public-supply use 

from the aquifer in Little River and Sevier Counties (Terrance 

W. Holland, U.S. Geological Survey, written commun., 2012). 

The availability of other water sources and water-quality 

issues in groundwater from the aquifer has restricted much 

of the domestic and industrial uses of the Red River alluvial 

aquifer (Ludwig, 1973). Surface water is now the predominant 

source of public-supply water in southwestern Arkansas.

Water Quality

Groundwater-quality data from the Red River alluvial 

aquifer for this report show pH values generally more than 

7.0 and ranging upward to 9.4 (fig. 26). Most samples 

are strongly calcium-bicarbonate except as affected by 

salinity sources in Miller County (discussed below). Iron 

concentrations were mostly less than 1,000 μg/L throughout 

the extent of the aquifer (fig. 26). Nitrate concentrations 

dominantly were less than 1 mg/L except in western Little 

River County, where four wells had concentrations exceeding 

the MCL for nitrate of 10 mg/L.

The Red River alluvial aquifer in Miller County is 

another area of high salinity within the Coastal Plain (fig. 28). 

Several alluvial wells, mainly sampled in the early 1950s 

through the late 1960s, had reported chloride concentrations 

ranging upward to 7,150 mg/L, with seven samples from 

the USGS NWIS database having chloride concentrations 

exceeding 1,000 mg/L. Ludwig (1973) stated that chloride 

concentrations as high as 46,250 mg/L had been reported in 

Miller County; however, the highest chloride concentration 

included in the data from the Ludwig (1972) report was only 

7,150 mg/L, similar to the highest concentration from data 

compiled for this report. The high chloride concentration 

in groundwater in Miller County was attributed to oil-field 

activity and more specifically to seepage from brine-storage 

pits. Approximately 60 million gallons (Mgal) of groundwater 

were estimated to have been contaminated based on the areal 

extent of contamination and the thickness and porosity of the 

aquifer (Ludwig, 1973).

Ouachita-Saline Rivers Alluvial Aquifer

Hydrogeologic Setting

Locally, the alluvium of the Ouachita and Saline Rivers 

(hereinafter referred to as the “Ouachita-Saline Rivers alluvial 

aquifer”) provides readily available groundwater (figs. 3 

and 8). In Grant and Hot Spring Counties, alluvium of the 

Ouachita and Saline Rivers unconformably overlie Tertiaryage deposits. The alluvium is comprised of silt and beds of 

fine- to very fine-grained sand with some clay. Locally, the 

alluvium may contain coarse sand. The alluvium ranges from 

0 to 40 ft in thickness in Grant and Hot Springs Counties 

(Halberg and others, 1968). In the area of Clark, Cleveland, 

and Dallas Counties, the alluvium of the Ouachita River is 

comprised of silt, clay, sand, and gravel that reach a maximum 

thickness of about 40 ft (Plebuch and Hines, 1969). 

Groundwater in the Ouachita-Saline Rivers alluvial 

aquifer is unconfined. Where the sand is coarse, the alluvium 

may be in hydraulic connection with the rivers. Specificcapacity tests indicated an average 1.3 (gal/min)/ft drawdown 

and noted a maximum yield of 25 gal/min in Grant and Hot 

Spring Counties (Halberg and others, 1968).

 Although the aquifer is thin in the area of Clark, 

Cleveland, and Dallas Counties, Plebuch and Hines (1969) 

report that two industrial wells south of Arkadelphia yielded 

240 gal/min, with transmissivities of 1,997 and 1,765 ft2

/d and 

storage coefficients of 0.0032 and 0.0038. A nearby well had a 

transmissivity of 400 ft2/d, which indicates a wide variability 

for aquifer properties in the area. Groundwater in this area is 

under water-table conditions. In most locations, the aquifer is 

in hydraulic connection with Pleistocene-age alluvial deposits, 

and no distinction is made between the groundwater from all 

of these combined alluvial deposits.

Water Quality

Unlike the Red River alluvial aquifer, which is contained 

in alluvial deposits from only the Red River, alluvial deposits 

constituting the Ouachita-Saline Rivers alluvial aquifer are 

thin, restricted in areal extent, and incise older Pleistocene 

terrace deposits of the Mississippi River. Many historical 

reports refer to wells that are within these basins as being 

completed in the Ouachita-Saline Rivers alluvial aquifer, 

which often are actually completed in the older Pleistocene 

terrace deposits. Therefore, for purposes of this section of 

the report, water quality will be reported for groundwater 

within the alluvial deposits of the Ouachita River and Saline 

River Basins as the Ouachita-Saline Rivers alluvial aquifer 

without discriminating between these deposits (figs. 3 and 

8). This situation is similar to the alluvial deposits of the 

Arkansas River between Little Rock and the Mississippi 

River being undistinguishable from, and referenced as part of, 

the Mississippi River Valley alluvial aquifer (see section on 

“Arkansas River Valley Alluvial Aquifer”). 

Kresse and Fazio (2002) compared groundwater-quality 

data from Pleistocene-age terrace and Holocene-age floodplain deposits in southeastern Arkansas and noted significantly 

lower iron, manganese, barium, and arsenic concentrations in 

groundwater from the older Pleistocene-age terrace deposits, 

although mean and median concentrations of dissolved 

solids and pH values were similar for both deposits. Gonthier 

(2003) reported on groundwater quality throughout the 

Mississippi embayment, including Arkansas, and noted that 

barium, potassium, dissolved organic carbon, iron, ammonia, 

phosphorus, and dissolved-solids concentrations were greater 

in groundwater from Holocene alluvium than from Pleistocene 

valley trains. Kresse and Fazio (2003) also reported on the 

occurrence of elevated arsenic in the Mississippi River Valley 
114 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

alluvial aquifer of southeastern Arkansas and similarly found 

significantly lower concentrations of arsenic, barium, iron, 

manganese, boron, ammonia, total phosphorus, and total 

organic carbon in groundwater from the older Pleistoceneage terrace deposits compared to the younger, Holocene-age 

flood-plain deposits. Other researchers (Davies and Exley, 

1992; Bangladesh Agricultural Development Corporation, 

1992; British Geological Survey, 2001; Ravenscroft, 2003) 

attributed geochemical differences in alluvial deposits to 

extensive flushing through time to account for the lack of iron, 

arsenic, and other trace metals in older Pleistocene alluvial 

deposits, which could account for the differences in water 

quality for these deposits in Arkansas. Consequently, the 

geochemistry and general water quality of groundwater from 

the Ouachita-Saline Rivers alluvial aquifer might be expected 

to be similar to groundwater in the Pleistocene-age deposits of 

the Mississippi River Valley alluvial aquifer.

Although only limited trace-metal data were available, 

these data appear to support the discussion of water 

quality in wells completed in Pleistocene alluvial deposits 

in southeastern Arkansas. Arsenic concentrations in the 

Ouachita-Saline Rivers alluvial aquifer were less than 2.0 

μg/L, most iron concentrations were less than 300 μg/L 

(fig. 26), all but four sulfate concentrations were below 25 

mg/L (fig. 26), dissolved-solids concentrations generally 

were less than 250 mg/L, and all but one silica concentrations 

were less than 25 mg/L (fig. 26). Numerous wells completed 

in the Ouachita-Saline Rivers alluvial aquifer had nitrate 

concentrations more than 10 mg/L (fig. 26), particularly 

in Calhoun and Bradley Counties. Because most of the 

wells sampled in this area had well depths less than 30 ft, 

they possibly are shallow domestic wells, which are more 

vulnerable to surface sources of nitrate (for example, septic 

systems). Additionally, shallow groundwater is not under 

reducing conditions that are typical for groundwater from the 

deeper parts of the aquifer (see “Source of Elevated Trace 

Metals” in the section “Mississippi River Valley Alluvial 

Aquifer”).

Jackson Group 

The Jackson Group comprises an upper Tertiary-age 

(Late Eocene) sequence of largely unconsolidated clays with 

rare, interbedded siltstone and sandstone units. Because of 

the predominance of fine-grained sediments and overall low 

hydraulic conductivity, the Jackson Group is designated as a 

regional confining unit, although groundwater in deposits of 

the Jackson Group served in the past as an important source 

of water supply throughout a large part of southeastern 

Arkansas. Because the Jackson Group is composed of 

thick, clayey deposits that impede vertical flow of water, it 

is referred to regionally as part of the Vicksburg-Jackson 

confining unit (Arthur and Taylor, 1990; Hosman and Weiss, 

1991; Renken, 1998). The Jackson Group is included in 

regional hydrogeologic framework models. It is listed as the 

Vicksburg-Jackson confining unit separating the Claiborne 

Group from Quaternary deposits in regional models of Clark 

and Hart (2009) and Arthur and Taylor (1998). The southern 

extent of the subcrop served as the western boundary of the 

Mississippi River Valley alluvial model of Ackerman (1996).

In spite of its designation as a regional confining system, 

groundwater contained in thin sandy sections of the Jackson 

Group served a large number of users through the 1990s, 

primarily as a source of domestic and small farm supply. 

Throughout southeastern Arkansas, this group of deposits 

can be considered a minor aquifer because of poor yields and 

lack of an economical supply for industrial, public, irrigation, 

and other important uses. In concert with low yields of 

groundwater from the Jackson Group, groundwater quality is 

some of the poorest of any aquifer in Arkansas.

Hydrogeologic Setting

The Jackson Formation was named by Conrad (1856) 

for type exposures at Jackson, Miss. The Jackson epoch 

completed the main filling of the Mississippi embayment 

(Veatch, 1906), and the structure of the Jackson and Cockfield 

Formations is framed by basinal downwarp with maximum 

downwarping in Desha and Lincoln Counties (Broom and 

Reed, 1973; Spooner, 1935). The Jackson Group contains 

marine and nonmarine beds (Stephenson and Crider, 1916; 

Wilbert, 1953; Onellion and Criner, 1955). The exposures 

at Crowleys Ridge are of a nearshore marine origin and 

were deposited during the last transgression into Arkansas 

(Guccione and others, 1986). The Jackson Group deposits of 

Late Eocene age occur in the subsurface throughout eastern 

Arkansas (Bedinger and Reed 1961; Saucier, 1994; Kresse and 

Fazio, 2002).

The largest area of outcrop of the Jackson Group in 

Arkansas is located south of the Arkansas River (fig. 3) in 

Jefferson, Lincoln, Cleveland, Drew, and Bradley Counties. 

A very narrow outcrop (not shown at the scale of fig. 3) 

also occurs north of the Arkansas River at the base of 

Crowleys Ridge from northern St. Francis County to the 

termination of the ridge in Phillips County. The Jackson 

Group unconformably overlies the Claiborne Group and is 

unconformably overlain by Mississippi River Valley alluvial 

deposits (Stephenson and Crider, 1916; Fisk, 1944). The 

Jackson Group comprises a series of clays with variable 

abundances of fossils, gypsum, marls, carbonate lenses, and 

lignite (Veatch, 1906; Hosman and Weiss, 1991); sands units 

are a minor but important occurrence (Stephenson and Crider, 

1916). The clays are typically light gray to dark greenish or 

blueish gray and, when oxidized, may be red, pink, yellow, 

and brown. The clays are thinly laminated and, in some 

areas, include cross-bedded, fine- to coarse-grained sand 

(Stephenson and Crider, 1916). Although undifferentiated in 

this report, the Jackson Group can be divided in southeastern 

Arkansas into the marine White Bluff Formation (Dall, 1898) 

comprising marl, sand, and clay, and the nonmarine Redfield 
Aquifers of the Coastal Plain 115

Formation (Wilbert, 1953) containing lignitic sediment. The 

Jackson Group is the uppermost unit in the Tertiary System 

and, when overlain by Quaternary alluvium, is a confining bed 

between the Claiborne Group and the Quaternary alluvium 

(Petersen and others, 1985; Hosman and Weiss, 1991). 

In southeastern Arkansas, the outcropping Jackson Group 

forms a high-altitude zone referred to as the Monticello Ridge. 

Alluvial terraces overlap the Jackson Group and older deposits 

in most of Ashley County. The Jackson Group and clays of 

the upper Cockfield Formation generally function as confining 

strata at the base of the alluvial aquifer in this area. Along the 

Monticello Ridge, the Jackson may exceed 400 ft in thickness. 

In a few places in Chicot County, the Jackson Group is only 

a few feet thick; in some areas of Ashley County, the Jackson 

has been entirely eroded and alluvial deposits rest on the 

Cockfield Formation (Broom and Reed, 1973).

The Jackson Group is often difficult to distinguish 

from underlying formations. Where the underlying upper 

Claiborne Group (Cockfield Formation, Cook Mountain 

Formation) contains clay, these clays often are included as 

part of the Jackson Group (Hosman and Weiss, 1991). In 

Bradley, Calhoun, and Jefferson Counties, the upper part 

of the Cockfield contains substantial clay and is difficult 

to differentiate from clays of the Jackson Group without 

paleontological evaluation (Albin, 1964; Kresse and Huetter, 

1999). In Bradley County, the Jackson Group is about 300 ft 

in thickness and consists mainly of gray, brown, and green 

silty clay and some lignite and was deposited under mostly 

marine conditions (Albin, 1964). The Jackson Group is 

divided into two distinct units in Arkansas: the White Bluff 

and Redfield Formations. In Grant County, the White Bluff 

Formation is composed of very fine clay and silty clay. 

Much of the Jackson Group is fossiliferous with hardened 

ferruginous layers locally. In some areas, very fine-grained 

sand interbedded with silt and silty clay occurs. The Redfield 

Formation in Grant County consists primarily of interbedded 

lignitic silts and clays with minor layers of fine sand (Halberg 

and others, 1968). The Jackson Group, as much as 200 ft 

in thickness, crops out in Cleveland County and consists of 

gray, brown, and green silty clay with some lignite and sand 

(Plebuch and Hines, 1969). In Chicot County, the Jackson 

Group consists of blue to gray clay, sandy clay, and thin beds 

of gray sand. The maximum thickness in Chicot County is 200 

ft, and the Jackson Group serves as a confining bed for the 

Cockfield (Onellion and Criner, 1955).

Along the margins of the southern part of Crowleys 

Ridge, the Jackson Group overlies the Claiborne Group, is 

about 500 ft in thickness, and is composed of sandy clay, 

silt, and glauconitic, fossiliferous sandy clay (Guccione and 

others, 1964). In Monroe County, the undifferentiated Jackson 

Group underlies most of the area with an average thickness of 

about 30 ft and a range of thickness from near zero to about 

50 ft. In this area, the Jackson Group consists of clay, silty 

clay, and minor amounts of silt and very fine-grained sand and 

acts as a confining unit between the Sparta aquifer and the 

Mississippi River Valley alluvial aquifer (Morris and Bush, 

1986). Producing wells have not been identified in this area of 

the State. Discussions of deposits of the Jackson Group as a 

viable aquifer are confined to southeastern Arkansas. 

Yields to hand-dug (less than 50 ft) and drilled wells 

(125–204 ft) in Grand and Hot Spring Counties are reported 

to be very small (Halberg and others, 1968). In parts of 

southeastern Arkansas, the Jackson Group generally does not 

yield water to wells in usable quantities (Broom and Reed, 

1973). Plebuch and Hines (1969) reported small yields to 

domestic wells in Cleveland County with total water use of 

0.04 Mgal/d in 1965 (Halberg and Stephens, 1966), and water 

levels ranged from 6 to 60 ft below land surface. The Jackson 

Group is not considered to be a source of water in Chicot 

County (Onellion and Criner, 1955). 

Water Use

Groundwater use from the Jackson Group was confined 

almost solely to a large area of exposed deposits south of 

the Arkansas River. Because of the extensive clay content of 

sediments constituting the Jackson Group, yields were low and 

thus were sufficient for only domestic and livestock supply. 

Plebuch and Hines (1969) reported that the aquifer “... yields 

only small amounts of water and is utilized only for domestic 

purposes.” Halberg and others (1968) similarly reported low 

yields throughout much of the extent of the Jackson Group 

and stated that where larger supplies were needed, wells would 

have to be drilled into the underlying Cockfield or Sparta 

Sand Formations. Halberg and others (1968) did not provide 

values for the yields, but stated the formation was tapped 

primarily by hand-dug and shallow-drilled wells for domestic 

purposes. Kresse and Fazio (2002) reported that prior to 

1960, a minimum of 90 wells in Drew and Lincoln Counties 

and 6 wells in Jefferson County were in use as sources for 

farm and domestic supply. Until the advent of public supply 

systems in Arkansas, which currently serve numerous large 

and small urban communities in addition to outlying rural 

areas, homeowners often had to rely on available shallow 

groundwater resources as a cost-effective supply of water. 

Public water-supply sources have replaced use of groundwater 

from the Jackson Group. Remaining operational wells located 

in 1999 and 2000 by Kresse and Fazio (2002) were used solely 

for watering gardens and other ancillary domestic purposes. 

Kresse and Fazio (2002) reported that most of the wells 

completed in the Jackson Group were less than 50 ft, with 

many less than 30 ft. Only four wells were found to be deeper 

than 50 ft, ranging upward to 150 ft below land surface.

Water-use data for the Jackson Group from 1965 to 1980 

are shown in table 20. Water-use data were not collected for 

this aquifer after 1980. No well depths were available in the 

USGS NWIS database. The combined effects of poor yields, 

undesirable water quality, and available public supply have 

rendered the Jackson Group effectively obsolete as a viable 

water-supply source at the time of this report (2013).
116 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Water Quality

Several historical reports discuss the poor quality of 

groundwater derived from deposits of the Jackson Group, 

highlighting elevated sulfate, iron, and dissolved solids. Klein 

and others (1950) showed sulfate concentrations exceeding 

100 mg/L in 5 of 18 groundwater samples in Jefferson County 

and ranging upward to 243 mg/L; the groundwater ranged 

from a sodium-bicarbonate to a sodium-sulfate water type. 

Onellion (1956) cited numerous incidences of high sulfate 

concentrations (maximum concentration of 1,256 mg/L), 

frequent occurrence of elevated chloride, and appreciable 

dissolved solids in waters from the Jackson Group in Drew 

County. Bedinger and Reed (1961) discussed variation in 

the water quality (described as poor to fair) in groundwater 

samples from the Jackson Group in Lincoln County and 

stated that the water was high in sulfate, although less 

mineralized than groundwater in Drew County. Their data 

revealed a wide range in sulfate concentrations, with a 

maximum of 2,360 mg/L (Bedinger and Reed, 1961). Halberg 

and others (1968) reported on one groundwater sample 

from Grant County that was a dilute, sodium-sulfate water 

type, slightly acidic, and with high iron concentration—this 

sample additionally contained 1.7 mg/L sulfides as hydrogen 

sulfide. Plebuch and Hines (1969) also noted high sulfate 

concentrations resulting from the presence of gypsum 

throughout the formation and stated that high sulfate was the 

major complaint by domestic users from a list of complaints 

in regard to water quality. Four samples collected from wells 

in Cleveland County showed iron concentrations ranging 

from 0.24 to 37 mg/L, dissolved-solids concentrations 

ranging from 198 to 2,650 mg/L, and sulfate concentrations 

ranging from 37 to 1,030 mg/L (Plebuch and Hines, 1969). 

A well completed in the Jackson Group in the Bayou 

Bartholomew watershed had a sodium concentration of 

243 mg/L (more than three times the maximum concentration 

for 118 Mississippi River Valley alluvial aquifer samples); the 

sulfate concentration in this well was 211 mg/L, and boron 

and zinc also were elevated with respect to all 118 Mississippi 

River Valley alluvial aquifer samples (Kresse and Fazio, 

2002). 

General Geochemistry and Water Type

In spite of the lack of importance of the Jackson Group 

as a regional source of water supply, an inspection of the 

USGS NWIS database revealed 68 samples with associated 

groundwater-quality data. This is in large part a result of the 

earlier, countywide, water-assessment reports, which were 

conducted at a time when the Jackson Group was locally 

important as a source of shallow domestic groundwater. 

Groundwater from the Jackson Group varies by water 

type but dominantly is a sodium- and calcium-sulfate water 

type with other mixed water types occurring in various 

areas of the aquifer. Unique to most aquifers in Arkansas, 

sulfate, rather than bicarbonate, was the dominant anion 

for most of the 51 samples with a complete major anion 

(bicarbonate, chloride, and sulfate) chemical analysis. Sulfate 

was the dominant anion in 27 of 51 samples and greater 

than 50 percent (as much as 94 percent) of the anions in 

20 samples. Chloride was the dominant anion in 13 samples 

(greater than 50 percent in 10 samples). Bicarbonate was the 

dominant anion in 11 samples (greater than 50 percent for 

8 samples). For 37 samples with a complete cation analysis, 

sodium was the dominant cation in 21 samples (greater than 

50 percent in 16 of 37 samples). Calcium was the dominant 

cation in 14 samples (greater than 50 percent in only 4 of 

37 samples). 

Values of pH in 67 samples ranged from 2.9 to 8.0 with 

a median value of 6.5 (table 21). Twenty samples (30 percent) 

had pH values less than 5.0 and 40 (60 percent) had pH values 

less than 7.0, demonstrating the prevalence of strongly to 

slightly acidic water throughout the extent of the aquifer. 

Twelve of the samples with pH values less than 5.0 had 

specific conductance values of 2,000 μS/cm ranging up to 

5,490 μS/cm; thus, the lowest pH values occurred at wells 

with the greatest specific conductance values (corresponding 

to higher dissolved-solids concentrations) (fig. 32A). This 

situation is contrary to most other aquifers in Arkansas 

that commonly show increasing pH values with increasing 

carbonate mineral dissolution and resultant increases in 

bicarbonate and dissolved-solids concentrations. The 

prevalence of low-pH values, high sulfate concentrations, 

and high dissolved-solids concentrations strongly suggests 

oxidation of pyrite as a dominant control on groundwater 

geochemistry in the Jackson Group. Oxidation of pyrite has 

been shown to be a common cause of low-pH, high-sulfate 

water (Nordstrom and others, 2000). 

Table 20. Water use from the Jackson Group in southeastern 

Arkansas, 1965–80. 

[Counties shown are only those with published data. Data from Halberg and 

Stephens (1966); Halberg (1972, 1977); Holland (1981). Units are million 

gallons per day]

County 1965 1970 1975 1980

Bradley 0.01 0.05 0.02 0.02

Cleveland 0.04 0.03 0.06 0.08

Drew 0.12 0.33 0.26 0.48

Grant 0.06 0.02 0.01 0.01

Jefferson 0.21 0.06 0.03 0.04

Lincoln 0.27 0.12 0.07 0.07

Total 0.71 0.61 0.45 0.70
Aquifers of the Coastal Plain 117

Table 21. Descriptive statistics for selected chemical constituents in groundwater from the Jackson Group in southeastern Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; NA, not analyzed; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 1.3 26 500 132 37

Magnesium (mg/L) 0.2 13 333 72.9 37

Sodium (mg/L) 2.3 57 618 140 37

Potassium (mg/L) 0.1 8.2 67 13.9 27

Bicarbonate (mg/L) 1.0 32 302 94 51

Chloride (mg/L) 2.5 35 845 155 67

Sulfate (mg/L) 0.6 110 3,080 717 67

Silica (mg/L) 3.1 37 100 22.6 16

Nitrate (mg/L as nitrogen) 0.01 0.54 38 7.89 63

Dissolved solids (mg/L) 11 443 5,330 1,080 35

Iron (μg/L) 0.05 100 19,000 3,870 61

Manganese (μg/L) 20 65 370 142 4

Arsenic (μg/L) NA NA NA NA NA

Hardness (mg/L as calcium carbonate) 4.0 140 2,600 629 67

Specific conductance (μS/cm) 36 701 5,490 1,340 68

pH (standard units) 2.9 6.5 8.0 1.5 67

0 1,000 2,000 3,000 4,000 5,000 6,000 0 1,000 2,000 3,000 4,000 5,000 6,000

0 50 100 150 200 250 300

0 1,000 2,000 3,000 4,000 5,000 6,000

Specific conductance, in microsiemens per centimeter Specific conductance, in microsiemens per centimeter

Well depth, in feet below land surface

Specific conductance, in microsiemens per centimeter

0

500

1,000

1,500

2,000

2,500

3,000

3,500

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

0

5

10

15

20

25

30

35

40

0

1

2

3

4

5

6

7

8

9

Sulfate, in milligrams per liter

Iron, in micrograms per liter

Nitrate, in milligrams

per liter as nitrogen

pH, in standard units

A B

C

D

Figure 32. Graphs showing relation of A, specific conductance and pH; B, well depth and nitrate; C, specific conductance and iron; 

and D, specific conductance and sulfate in groundwater from Jackson Group in southeastern Arkansas.
118 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Nitrate

Nitrate concentrations for 63 samples ranged from 0.01 to 

38 mg/L with a median concentration of 0.54 mg/L (table 21). 

Twenty-three sites had nitrate concentrations greater than or 

equal to 1.0 mg/L, and 8 of these sites had concentrations 

exceeding the Federal MCL of 10 mg/L (U.S. Environmental 

Protection Agency, 2009). Elevated nitrate concentrations 

generally were found in the more shallow wells. All but one 

well with nitrate concentrations greater than 1.0 mg/L had well 

depths of 40 ft or less below land surface—a strong indication 

of the increased vulnerability of shallow wells to surface 

sources of contamination (fig. 32B).

Iron

Iron concentrations in 61 samples ranged from 0.05 to 

19,000 μg/L with a median concentration of 100 μg/L (fig. 33; 

table 21). All iron concentrations greater than 3,000 μg/L 

occurred where specific conductance values were greater 

than 2,000 μS/cm (fig. 32C). Similarly, sulfate concentrations 

greater than 900 mg/L occurred where specific conductance 

values were greater than 2,000 μS/cm. There was a positive, 

linear relation between sulfate and specific conductance 

for specific conductance values greater than 1,000 μS/cm 

(fig. 32D). These relations, together with the trend of 

decreasing pH beyond a conductance of 2,000 μS/cm, adds 

supporting evidence identifying oxidation of pyrite as a 

principal source of the low-pH, high-sulfate, high-iron content 

found in groundwater in the Jackson Group. The greatest 

density of elevated (more than 1,000 μg/L) iron concentrations 

occurred in Drew County (fig. 34).

0

50

100

150

200

250

300

350

400

450

0

100

200

300

400

500

600

700

800

900

Concentration, in micrograms per liter

1,000

Concentrations, in milligrams per liter

500

61

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

37

37

37

51

67

67

61

Constituent Constituent

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron

Figure 33. Interquartile range for selected chemical constituents in groundwater from the Jackson Group in southeastern Arkansas.
ARKANSAS

DALLAS

CALHOUN

JEFFERSON

DREW

OUACHITA

DESHA

CLEVELAND

LINCOLN

BRADLEY

GRANT

HOT SPRING

ARKANSAS

DALLAS

CALHOUN

JEFFERSON

DREW

OUACHITA

DESHA

CLEVELAND

LINCOLN

BRADLEY

GRANT

HOT SPRING

ARKANSAS

DALLAS

CALHOUN

JEFFERSON

DREW

OUACHITA

DESHA

CLEVELAND

LINCOLN

BRADLEY

GRANT

HOT SPRING

ARKANSAS

DALLAS

CALHOUN

JEFFERSON

DREW

OUACHITA

DESHA

CLEVELAND

LINCOLN

BRADLEY

GRANT

HOT SPRING

93° 92°

34°

33°

30’

34°

30’

93° 92°

34°

33°

30’

34°

30’

93° 92°

34°

33°

30’

34°

30’

93° 92°

34°

33°

30’

34°

30’

0 20 40 MILES

0 20 40 KILOMETERS

Iron, in micrograms 

per liter

0 to 250251 to 500501 to 1,0001,001 to 3,0003,001 to 10,000

10,001 to 19,000

EXPLANATION

Dissolved solids, in 

milligrams per liter

11 to 250251 to 500501 to 1,0001,001 to 2,0002,001 to 3,000

3,001 to 5,330

EXPLANATION

3 to 2526 to 5051 to 100101 to 250251 to 500

501 to 845

Chloride, in milligrams

per liter

EXPLANATION

Sulfate, in milligrams 

per liter

1 to 5051 to 100101 to 250251 to 500501 to 1,500

1,501 to 3,080

EXPLANATION

Base modified from U.S. Geological Survey digital data, 1:250,000 Geology map modified from Haley and others, 1993 Universal Transverse Mercator projection, zone 15

Figure 34. Spatial distribution of selected chemical constituents in groundwater from the Jackson Group in southeastern Arkansas.
120 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Sulfate

Sulfate concentrations, as mentioned above, can be 

elevated in groundwater from the Jackson Group. Sulfate data 

were available for 67 samples; concentrations ranged from 0.6 

to 3,080 mg/L with a median of 110 mg/L (fig. 33; table 21). 

Twelve of the 67 samples had concentrations exceeding 

1,000 mg/L, and 26 samples had concentrations exceeding 

the Federal secondary drinking-water regulation of 250 mg/L 

for sulfate (U.S. Environmental Agency, 2009). A spatial 

distribution of sulfate concentrations shows that the highest 

concentrations generally occurred in Drew County. Five of 

the seven samples with sulfate concentrations exceeding 

1,500 mg/L were from wells in Drew County with the other 

two located in Lincoln County (fig. 34). Although these 

patterns suggest that some of the poorest quality of water is 

in the southern extent of the aquifer system, the fact that low 

sulfate concentrations also occur in this area indicates the 

lack of a clear spatial pattern for Jackson Group groundwater 

geochemistry. Most of the elevated sulfate concentrations, 

as noted above, appear to be the result of oxidation of pyrite. 

The abundance of clayey sediments and occurrence of 

lignite throughout the aquifer provide a setting for reducing 

conditions supporting formation of pyrite. Later infiltration 

of oxygenated water may be the source of redox changes that 

result in oxidation of pyrite and generation of low-pH, highsulfate groundwater.

Chloride 

Chloride concentrations ranged from 2.5 to 845 mg/L 

with a median concentration of 35 mg/L (fig. 33; table 21). 

Nine of 67 samples with chloride data had concentrations 

that exceeded the Federal secondary drinking-water regulation 

of 250 mg/L. All but one chloride concentration were 

below 50 mg/L for specific conductance values of less than 

500 μS/cm. Similar to trends noted for sulfate, chloride 

concentrations generally increased with increasing specific 

conductance. Chloride concentrations greater than 100 mg/L 

occurred almost solely in samples with specific conductance 

values greater than 850 μS/cm. Only 35 of the 67 samples 

had values for dissolved solids; 16 (46 percent) of these had 

concentrations that exceeded the secondary drinking-water 

regulation of 500 mg/L. A spatial distribution of dissolvedsolids and chloride concentrations revealed a slightly greater 

concentration of relatively elevated concentrations in Drew 

County (fig. 34). However, only about half as many sites 

had available dissolved-solids data compared to sulfate and 

chloride (table 21), which resulted in too few analyses for 

making strong statements in regard to spatial trends.

The lack of a well-defined spatial pattern for chloride 

(and for other geochemical constituents) probably is related to 

the scale differences in regional and local groundwater flow 

paths. Many shallow aquifer systems, such as the fractured 

surficial bedrock aquifers of the Interior Highlands, do not 

have well-connected, regional flow paths but rather short, 

isolated flow paths with groundwater traveling locally from 

hilltops to valleys in small watersheds. Geochemical evolution 

for groundwater moving along a flow path within an aquifer 

is dependent on available reactive minerals, flow velocities 

affecting residence time, redox changes, and other rock/water 

interaction processes. The Jackson Group reflects this type 

of aquifer system because it is a shallow aquifer composed 

of clay and interbedded sand units that are not regionally 

extensive and it is not an adequate thickness to serve as 

a large yield aquifer for multiple uses. Hence, local flow 

patterns and local variation in permeability play an important 

role in geochemical evolution on a local scale that cannot be 

discerned from a regional-scale analysis.

In summary, groundwater from the Jackson Group has 

some of the poorest water quality of any aquifer in the State, 

especially in view of its extensive use in the past as a source 

of farm and domestic water supply. Sulfate concentrations 

are especially elevated in the aquifer; concentrations ranged 

upward to a maximum of 3,080 mg/L and 12 of 67 samples 

exceeded 1,000 mg/L. Additionally, most groundwater 

samples were of a calcium- and sodium-sulfate water type. 

Correlations of elevated sulfate concentrations to elevated iron 

concentrations and extremely low-pH groundwater strongly 

suggest that oxidation of pyrite in some regions of the aquifer 

contribute to this water type. Nitrate concentrations revealed 

an inverse correlation with well depth, reflecting increased 

vulnerability to surface sources of contamination. Residents 

previously using groundwater from the Jackson Group are 

now serviced by public-supply sources. The combined effects 

of poor yields, undesirable water quality, and available public 

supply have rendered the Jackson Group effectively obsolete 

as a viable water supply. 

Cockfield Aquifer

The Cockfield aquifer contains groundwater of high 

quality that is used throughout southeastern Arkansas. The 

Cockfield aquifer was described as a distinct and separate 

aquifer in an assessment of water resources of the Mississippi 

embayment by Hosman and others (1968); however, in later 

regional hydrogeologic framework analyses in the Mississippi 

embayment, the Cockfield Formation was included with 

undifferentiated sands of the underlying Cook Mountain 

Formation (middle Claiborne confining unit) and overlying 

Jackson Formation (Vicksburg-Jackson confining unit) as 

part of the upper Claiborne aquifer (Arthur and Taylor, 1990; 

Hosman and Weiss, 1991; Hart and others, 2008; Clark and 

Hart, 2009). Recent reports on groundwater use (Holland, 

2007) and on potentiometric surfaces (Pugh, 2010) in 

Arkansas retain the common usage of “Cockfield aquifer.” 

For purposes of this report, the saturated part of the Cockfield 

Formation will be referred to as the Cockfield aquifer. 
Aquifers of the Coastal Plain 121

Geologic Setting

The name Cockfield was first used by Vaughn (1895) 

to describe Eocene- (Tertiary) age beds in northwestern 

Louisiana (Payne, 1975). The Cockfield Formation is the 

uppermost and youngest formation of the Claiborne Group, 

which includes the Cockfield Formation, Cook Mountain 

Formation, Sparta Sand, Cane River Formation, and Carrizo 

Sand (table 3). The Cockfield Formation conformably overlies 

the Cook Mountain Formation and is unconformably overlain 

by the Jackson Group or Quaternary alluvium in Arkansas 

(Onellion and Criner, 1955; Hosman and others, 1968).

 The Cockfield Formation generally consists of fine- to 

medium-grained sand in the basal part and silt, clay, and 

lignite in the upper part. The beds are discontinuous and 

contain carbonaceous material throughout (Hosman and 

others, 1968). The basal part of the overlying Jackson Group 

may contain beds of fine sand that are in contact with the 

Cockfield in south-central Arkansas. These sands are difficult 

to differentiate from the Cockfield Formation and are likely 

in hydraulic connection (Ackerman, 1987a; Pugh, 2010). The 

sand beds yielding the greatest amount of groundwater are 

located near the base of the formation (Pugh, 2010). Deposits 

of the formation are considered nonmarine in origin (Veatch, 

1906) and were deposited as a result of the action of longshore 

currents and deltaic distributary channels within a nearshore 

marine environment (Lautier, 1981). The lower sand facies 

of the formation represent a delta front (Merrill and others, 

1985), and the upper carbonaceous interbedded shale and sand 

facies represent a delta-plain depositional environment. 

The Cockfield Formation is part of a north-northeast 

trending syncline, the Mississippi embayment, which plunges 

to the south-southwest, approximately centered beneath the 

Mississippi River (Hosman and others, 1968; Pugh, 2010). 

The formation dips southeast and toward the axis of the 

embayment (Hosman and others, 1968; Petersen and others, 

1985). Similar to other Tertiary formations, the dip of the 

formation controls the regional direction of groundwater flow 

in the Cockfield aquifer. The formation crops out extensively 

over south-central Arkansas and is exposed over most of 

Union County as well as parts of Bradley, Cleveland, Dallas, 

Grant, and Saline Counties (Hosman and others, 1968; 

Hosman, 1982; Petersen and others, 1985). The formation has 

not been observed in outcrop or identified in the subsurface 

north of about latitude 35 degrees (Hosman and others, 1968).

Thickness of the Cockfield Formation near the outcrop 

generally ranges from 100 to 400 ft with a maximum thickness 

of approximately 700 ft. Considerable variability is noted in 

unit thickness and grain-size distribution across the outcrop 

area. In the southwestern part of the outcrop in Columbia 

County, the formation is composed of interbedded sand and 

clay with occasional thin beds of lignite with a maximum 

formation thickness of approximately 100 ft. Medium-grained 

sand beds are dominant in the formation and usually are 

thin and lenticular. Individual beds seldom exceed 20 ft in 

thickness (Tait and others, 1953). To the northeast in Union 

County, the formation is composed of interbedded, lenticular 

beds of lignitic sand and clay with a maximum formation 

thickness of 300 ft or more. Locally, the sand beds are as much 

as 100 ft thick and make up 50–75 percent of the formation’s 

thickness (Broom and others, 1984). Further northeast into 

Cleveland County, the formation is as much as 200 ft in 

thickness and consists mainly of silt and lignitic clay with 

interbedded sand. The sand beds generally are relatively thin 

with locally thicker sand beds (Plebuch and Hines, 1969). In 

the northeast extent of the outcrop area in Jefferson County, 

the sand beds are discontinuous, and the formation contains a 

considerable amount of clay (Klein and others, 1950; Kresse 

and Huetter, 1999). The formation thickens considerably in the 

subsurface downdip from the outcrop area. In Chicot County, 

the formation ranges from 300 to 625 ft in thickness and 

consists of largely gray to white fine- to medium-grained sand 

containing some lignite, some gray to brown sandy and silty 

clay, and occasional thin beds of lignite. Sand beds may reach 

a continuous thickness of as much as 300 ft but in most places 

is interbedded with layers of clay (Onellion and Criner, 1955). 

Hydrologic Characteristics

Recharge to the Cockfield aquifer is from precipitation 

on the outcrop and leakage through the overlying Mississippi 

River Valley alluvial aquifer in the subcrop area (fig. 3). 

Surface water in the area of outcrop also is a potential 

recharge source (Hosman and others, 1968; Broom and others, 

1984; Petersen and others, 1985). Discharge of groundwater 

is to rivers in outcrop areas, to vertically adjacent units where 

the Cockfield aquifer is confined, and to wells (Ackerman, 

1987a; Pugh, 2010). In the outcrop area and where overlain 

by Quaternary alluvium, the aquifer is under water-table 

conditions. Where overlain by the Jackson Group, the aquifer 

is under confined conditions. In the confined part of the 

aquifer, the potentiometric surface can be near or above land 

surface (Ackerman, 1987a; Pugh 2010). 

The degree of hydraulic connection between sands 

within the Cockfield aquifer is not known (Hosman and others, 

1968; Broom and others, 1984). In and near the outcrop area, 

well depths generally are shallow (less than 200 ft), and yields 

of most wells are small, less than 30 gal/min. Downdip from 

the outcrop area, well depths can exceed 600 ft, and wells 

screening the full thickness of the aquifer often yield 100–

500 gal/min (Westerfield, 1994; Pugh, 2010). Pugh (2010) 

summarized aquifer test data from the aquifer. Based on 

data from 11 sites, the average specific capacity was 5.36 

(gal/min)/ft with a minimum of 0.15 (gal/min)/ft and a 

maximum of 23.7 (gal/min)/ft. Based on data from four sites, 

the average transmissivity was 3,330 ft2/d with a minimum 

of 325 ft2/d and a maximum of 6,280 ft2/d). Based on data 

from one site, the storage coefficient was 0.00026. Pugh 

(2010) also reported that the aquifer commonly yields less 

than 100 gal/min to wells with a maximum of 750 gal/min. 

An aquifer test in Chicot County yielded a transmissivity of 

approximately 6,800 ft2

/d, a storage coefficient of 0.0008, and 
122 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

a hydraulic conductivity of approximately 110 ft/d (Hosman 

and others, 1965). The maximum reported well yield in Chicot 

County was 410 gal/min (Onellion and Criner, 1955). In 

Columbia County, only domestic wells tap the aquifer (Tait 

and others, 1953). In Jefferson County, the aquifer and the 

Jackson Group are undifferentiated, and the average well yield 

from the combined aquifers is 5 gal/min (Klein and others, 

1950; Kresse, 1999). The aquifer is used mainly as a source 

of domestic water supplies in Dallas and Cleveland Counties; 

however, the town of Kingsland in Cleveland County used 

groundwater from the Cockfield Formation for public supply. 

Well yields more than 300 gal/min are reported in Cleveland 

County (Plebuch and Hines, 1969).

Water Use

The Cockfield aquifer is an important source of 

groundwater throughout eastern Arkansas. There is widespread 

use of the aquifer for domestic purposes, and yields are high 

enough in some areas to supply public and industrial systems 

(Petersen and others, 1985; Joseph, 1998b; Yeatts, 2004). In 

2010, more than 50 percent of use occurred in Ashley County 

for public and industrial supply (Terrance W. Holland, U.S. 

Geological Survey, written commun., 2012). The general 

locations of 70 wells with reported use from the aquifer in 

2010 are shown in figure 35. 

The earliest reports of water use from the Cockfield 

aquifer documented domestic wells scattered across southern 

and eastern Arkansas, including communities in Chicot, 

Cleveland, Dallas, Desha, Drew, Jefferson, Phillips, and 

Union Counties (Veatch, 1906). Many of these communities 

later reported public supply from the aquifer. Municipalities 

in Chicot County primarily drew from the aquifer in the early 

part of the 19th century. Water use was reported in Lake 

Village as early as 1910 and in Eudora in 1916 (Hale, 1927; 

Onellion and Criner, 1955). Both municipalities continue their 

use of the aquifer (Lyle Godfrey, Arkansas Health Department, 

written commun., 2012). 
YELL

LEE

UNION

WHITE

POLK

POPE

DREW

PIKE

SCOTT

CLARK

CLAY

ASHLEY

DESHA

BENTON

LOGAN

SALINE

IZARD

PULASKI LONOKE

ARKANSAS

NEWTON

GRANT

CHICOT

MADISON

STONE

MILLER

SHARP

CROSS

DALLAS

PRAIRIE

BOONE

PHILLIPS

PERRY

SEARCY

MARION

FULTON

SEVIER

MISSISSIPPI

JEFFERSON

NEVADA

POINSETT

GARLAND

COLUMBIA

BAXTER

OUACHITA

BRADLEY

JOHNSON

WASHINGTON

MONROE

GREENE

JACKSON

CARROLL

HOWARD

LINCOLN

CALHOUN

CONWAY FAULKNER

VAN BUREN FRANKLIN

CRAIGHEAD

HEMPSTEAD

RANDOLPH

CLEBURNE

MONTGOMERY

LAWRENCE

ST. FRANCIS

CRAWFORD

CLEVELAND

HOT SPRING

INDEPENDENCE

LITTLE

RIVER

WOODRUFF CRITTENDEN

LAFAYETTE

SEBASTIAN

94° 92° 91° 93°

90°

36°

35°

34°

0 15 0 30 

15

Base from U.S. Geological Survey digital data, 1:2,000,000

DucksElectricIndustrIrrigatiPublic 

Extent of Well type 

galloto repwaterrepres

EX

Figure 35. Wells with reported water use from the Cockfield aquifer in Arkansas, 2010.
124 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Several municipalities using the Cockfield aquifer as their 

sole water-supply source eventually added other sources or 

changed their source with growing population and increasing 

water demands. Water use has correspondingly decreased 

in several counties (figs. 36 and 37; table 22) because many 

municipalities have switched their primary water supply from 

the Cockfield to the Sparta aquifer. McGehee (Desha County) 

used both the Sparta and Cockfield aquifers for a few decades 

in the middle part of the 1990s (Bedinger and Reed, 1961). 

Arkansas City (Desha County) and Kingsland (Cleveland 

County) were supplied solely by the Cockfield aquifer through 

the 1960s (Bedinger and Reed, 1961; Plebuch and Hines, 

1969); however by the late 1970s, those three communities 

relied solely upon the Sparta aquifer for public supply (Lyle 

Godfrey, Arkansas Health Department, written commun., 

2012). In Drew County, Wilmar and Winchester drilled wells 

into the Cockfield aquifer in 1902 and 1916, respectively, 

which were used until at least the 1950s (Onellion, 1956). 

Winchester currently (2013) uses the Sparta aquifer, while 

Wilmar taps the Cook Mountain Formation. Dermott (Desha 

County) began using the Cockfield aquifer in the 1920s and 

added the Sparta aquifer as a supplementary water source in 

1960 (Lyle Godfrey, Arkansas Health Department, written 

commun., 2012). 

Ashley County has been the greatest user of the Cockfield 

aquifer for public supply since ARWUDBS began and is the 

only county with increasing use of this aquifer (table 22). 

Water use from the Cockfield aquifer in Ashley County 

increased by more than 12,000 percent from 1965 to 2010 

(fig. 37). Crossett used the Mississippi River Valley alluvial 

aquifer to provide public supply (Hale, 1926; Hewitt and 

others, 1949) from about 1900 until 1944, when the county 

began to share a well completed in the Cockfield aquifer with 

a lumber company. Three other Ashley County towns reported 

a cumulative use of approximately 0.065 Mgal/d for public 

supply in 1947 (Hewitt and others, 1949). Several publicsupply wells were completed in the Cockfield aquifer near 

Crossett in the 1960s and 1970s, coinciding with an increase 

in use between 1965 and 1970 (Lyle Godfrey, Arkansas Health 

Department, written commun., 2012). 

Public supply accounted for 17 percent of water pumped 

from the Cockfield aquifer in 2010 (Terrance W. Holland, U.S. 

Geological Survey, written commun., 2012). The aquifer ranks 

as the sixth highest-use aquifer for public supply in Arkansas 

after the Sparta, Wilcox, Mississippi River Valley alluvial, 

Arkansas River Valley alluvial, and lower Ozark aquifers. Ten 

municipalities use wells completed in the Cockfield aquifer for 

a source of public-supply water (Terrance W. Holland, U.S. 

Geological Survey, written commun., 2012). Ashley County 

used the largest amount from 2000 to 2010, with Crossett 

pumping a maximum of 1.26 Mgal/d in 2010 (Terrance W. 

Holland, U.S. Geological Survey, written commun., 2012). 

Chicot County had the second highest rate of use for public 

supply in 2010, with Lake Village and Eudora using 0.83 and 

0.51 Mgal/d, respectively in 2010 (Terrance W. Holland, U.S. 

Geological Survey, written commun., 2012).

Rural domestic use from the Cockfield aquifer in south 

and south-central Arkansas has been locally important. 

Domestic users in Cleveland and Dallas Counties pumped a 

combined 0.12 Mgal/d in 1965 (Plebuch and Hines, 1969). 

Chicot County withdrew 0.5 Mgal/d for domestic use around 

the mid-1950s (Onellion and Criner, 1955). Cleveland and 

Dallas Counties together reported 0.12 Mgal/d in 1965 of 

domestic use (Plebuch and Hines, 1969). Ashley, Bradley, 

Calhoun, Columbia, Desha, Drew, Grant, and Lincoln 

Counties also used the Cockfield aquifer for domestic supply 

(Hewitt and others, 1949; Tait and others, 1953; Onellion, 

1956; Bedinger and Reed, 1961; Albin, 1964; Halberg and 

others, 1968). Domestic use of the Cockfield aquifer continues 

to be locally important in southeastern Arkansas; however, 

domestic use is not reported to ARWUDBS and subsequently 

quantifiable data are not available. 

Industrial use from the Cockfield aquifer has been 

locally important. During the oil boom of the early 1920s in 

southern Arkansas, large quantities of water were pumped 

from the Cockfield aquifer to supply water use for oil and 

gas exploration in Union County (Baker and others, 1948). 

In the city of El Dorado, Root Petroleum Company pumped 

0.2 Mgal/d from 1921 to 1935 (Baker and others, 1948). 

El Dorado also relied on the Cockfield aquifer for public 

supply and reportedly pumped as much as 1.5 Mgal/d in the 

1920s and 1930s (Baker and others, 1948). Public supply 

during this period increased greatly because of the population 

increase associated with petroleum production. Eventually, 

growing demand required other water sources, and El 

Dorado completed wells in the Sparta aquifer in 1935 (Baker 

and others, 1948). By the end of the 1940s, reliance on the 

Cockfield aquifer in southern Arkansas was decreasing as 

petroleum exploration and production declined. Since the 

1940s, water supply in this area generally has been furnished 

from the Sparta aquifer and more recently from the Ouachita 

River (see “Sparta Aquifer” section).

Industrial use of the Cockfield aquifer is centered in 

Ashley County. As early as 1947, Ashley County reported 

0.065 Mgal/d from the aquifer for paper and lumber mills 

(Hewitt and others 1949), constituting 5 percent of the total 

industrial water use for the county. The primary traditional 

source for industrial water use in Ashley County was the 

Mississippi River Valley alluvial aquifer; however, more 

recent water-use data from 1990 through 2010 have shown all 

industrial groundwater withdrawals were from the Cockfield 

aquifer (Terrance W. Holland, U.S. Geological Survey, written 

commun., 2012). Over 80 percent of the water used in Ashley 

County in 2010—8.40 Mgal/d—was for industrial purposes 

(Terrance W. Holland, U.S. Geological Survey, written 

commun., 2012). A cone of depression surrounding Crossett 

was attributed to groundwater withdrawals (Pugh, 2010). 
EXPLANA

Annual water withdrawn f

in million gallons per d

2.1 to 4.0 0.6 to 1.01.1 to 2.00.1 to 0.5

No color represents no report

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

0 60 0 60 120 K

Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977;

 Holland, 1981, 1987, 1993, 1999, 2004, 2007

Base from U.S. Geological Survey digital data 1:2,000,000

19651980 1985

1970 1975

Figure 36. Water-use rates for the Cockfield aquifer in southeastern Arkansas from 1965 to 2010. 
94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 

36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° EXPLANA

Annual water withdrawn f

in million gallons per d

2.1 to 4.0 0.6 to 1.0 1.1 to 2.0 0.1 to 0.5 No color represents no report

0 60 0 60 120 K

Base from U.S. Geological Survey digital data 1:2,000,000 Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977; Holland, 1981, 1987, 1993, 1999, 2004, 2007 1990 2005 2010 1995 2000

Figure 36. Water-use rates for the Cockfield aquifer in southeastern Arkansas from 1965 to 2010.—Continued
UNION -100

LEE

-100

DREW

-100

GRANT

-100

DALLAS

-100

PHILLIPS

-100

COLUMBIA

-100

BRADLEY

-66

LINCOLN

-100

CALHOUN

-100

CLEVELAND

-100

ASHLEY

12,425

DESHA

413

CHICOT

131

JEFFERSON

261

94° 92° 91° 93°

90°

36°

35°

34°

0 15 30 0 30 

15

45

 Use of the C

 by countpercent c

No color indicates n

-100 to 01 to 200201 to 400401 to 600> 600

EXPLAN

Base from U.S. Geological Survey digital data, 1:2,000,000

Figure 37. Change in percentage of water use from the Cockfield aquifer in southeastern Arkansas from 1965 to 2010.
128 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Total water use reported from the Cockfield aquifer has 

increased by almost 500 percent from 3.25 to 19.23 Mgal/d 

from 1965 to 2010, with much of this resulting from increased 

industrial use in Ashley County and for irrigation (figs. 35 

and 36; table 22). Total water use increased 2.02 Mgal/d 

from 1965 to 1970 (table 22) when Lonoke and St. Francis 

Counties began reporting use, and several other counties 

(Ashley, Cleveland, Dallas, and Drew) had large increases. 

Water use during the 1970s was stable. A 38-percent increase 

in use was noted between 1975 and 1980 because of increased 

withdrawals during the drought of 1980. Pumping rates as well 

as the number of counties pumping from the Cockfield aquifer 

decreased from 1980 to 1985, decreasing from 17 counties 

reporting a total of 7.15 Mgal/d use in 1980 to 6 counties 

reporting a total of 3.83 Mgal/d use in 1985 (fig. 35; table 22). 

This decrease was likely because of the changes in reporting 

to ARWUDBS. 

Water use from the Cockfield aquifer has increased 

steadily since 1985, with users relying more heavily on the 

aquifer as population grows and as other groundwater sources 

experience depletion. Traditionally, the Cockfield aquifer has 

been used less for irrigation, although irrigation has increased 

in many areas. As early as the 1950s, 20–30 wells in the Grand 

Prairie tapped the Cockfield aquifer for irrigation (Baker, 

1955). Farmers in eastern Arkansas are increasingly turning 

to the Cockfield aquifer to support irrigation as water levels 

decline in the Mississippi River Valley alluvial aquifer. Since 

2000, use of the aquifer has begun in several counties for the 

first time and most of this new use is for irrigation (fig. 35). By 

2005, water use reported for the Cockfield aquifer in Monroe 

and St. Francis Counties was solely for irrigation. From 2000 

to 2010, all water use reported for the Cockfield aquifer in 

Desha County was for irrigation, whereas in 1957 all irrigation 

water came from the Mississippi River Valley alluvial 

Table 22. Water use from the Cockfield aquifer in southeastern Arkansas, 1965–2010. 

[Counties shown are only those with published data. Data from Halberg and Stephens (1966); Halberg (1972, 1977); Holland (1981, 1987, 1993, 1999, 2004, 

2007). Units are million gallons per day]

County 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Arkansas 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.57 0.48 0.38

Ashley 0.08 0.39 0.50 1.01 1.18 2.44 2.81 3.40 8.17 10.02

Bradley 0.29 0.42 0.27 0.38 0.17 0.11 0.10 0.00 0.08 0.10

Calhoun 0.18 0.24 0.26 0.39 0.00 0.00 0.00 0.00 0.00 0.00

Chicot 0.85 0.96 1.16 1.41 2.12 5.00 6.23 1.26 1.93 1.96

Cleveland 0.10 0.40 0.44 0.65 0.05 0.05 0.02 0.00 0.00 0.00

Columbia 0.14 0.27 0.34 0.38 0.00 0.00 0.00 0.00 0.00 0.00

Crittenden 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.57 0.00 0.00

Dallas 0.02 0.07 0.07 0.08 0.00 0.00 0.00 0.00 0.00 0.00

Desha 0.40 0.46 0.34 0.44 0.18 0.38 0.48 0.24 1.58 2.05

Drew 0.12 0.23 0.21 0.48 0.13 0.11 0.12 0.00 0.00 0.00

Grant 0.08 0.23 0.19 0.21 0.00 0.00 0.00 0.00 0.00 0.00

Jefferson 0.31 0.30 0.17 0.23 0.00 0.00 0.00 3.42 1.97 1.12

Lafayette 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01

Lee 0.02 0.02 0.02 0.06 0.00 0.00 0.00 0.00 0.00 0.00

Lincoln 0.08 0.10 0.07 0.07 0.00 0.00 0.00 0.00 0.00 0.00

Lonoke 0.00 0.37 0.30 0.45 0.00 0.00 0.00 0.08 0.90 0.00

Monroe 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.94 0.95

Phillips 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.38 0.00 0.00

Poinsett 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.97

Prairie 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00

St. Francis 0.00 0.20 0.17 0.23 0.00 0.00 0.00 0.00 0.06 0.67

Union 0.55 0.61 0.67 0.67 0.00 0.00 0.00 0.00 0.00 0.00

Total 3.25 5.27 5.19 7.15 3.83 8.09 9.76 9.92 16.11 19.23
Aquifers of the Coastal Plain 129

aquifer (Bedinger and Reed, 1961). A small amount from the 

Cockfield aquifer also has been used to flood fields for duck 

hunting in Arkansas County (Terrance W. Holland, USGS, 

written commun., 2012).

Chicot County was the largest user of the Cockfield 

aquifer prior to 2000. Water use in Chicot County increased 

through the middle 1990s and decreased dramatically in 2000. 

The upward trend resulted from growth in aquaculture, and 

the downward trend resulted from declines in aquaculture 

related to low-cost imports of fish from Vietnam and other 

countries (Kaliba and Engle, 2006). Water use increased 

in Jefferson County in 2000 because of withdrawals by an 

electric company and has decreased in subsequent reporting 

periods (Terrance W. Holland, U.S. Geological Survey, written 

commun., 2013). 

Water Levels

Several reports have examined the water levels of the 

Cockfield aquifer (Ackerman, 1987a; Westerfield, 1994; 

Joseph, 1998b; Schrader and Joseph, 2000; Yeatts, 2004; 

Schrader, 2007a; Pugh, 2010). The potentiometric surface 

generally declines from higher altitudes at the western 

outcrop of the aquifer to lower altitudes in the deeper subcrop 

area to the east (fig. 38). However, pumping centers have 

disturbed predevelopment water levels and flow paths causing 

depressions in the potentiometric surface in several areas 

including western Drew County, southeastern Lincoln County, 

Ashley County near Crossett, southwestern Calhoun County, 

and Chicot County west of the city of Greenville, Miss. 

(Ackerman, 1987a; Joseph, 1998b; Schrader and Joseph, 2000; 

Yeatts, 2004; Schrader, 2007a; Pugh, 2010).

The first study documenting the potentiometric surface 

of the Cockfield aquifer, based on measurements in 1980, did 

not recognize the extensive occurrence of long-term declines. 

However, three wells in Chicot, Drew, and Lincoln Counties 

exhibited considerable long-term declines (Ackerman, 1987a). 

Onellion (1956) speculated that water levels had declined in 

Drew County based on decreases in water pressure, although 

water levels were not measured. The declines in Chicot, 

Drew, and more recently Desha Counties have been attributed 

to withdrawals by the city of Greenville, Miss. (Ackerman, 

1987a; Joseph, 1998b; Pugh, 2010). Water levels declined 

21.62 ft at Eudora (Chicot County) from 1971 to 1991 (well A; 

figs. 38 and 39) (Westerfield, 1994). Later reports showed 

relatively stable water levels from 1998 to 2009 (Joseph, 

1998b; Schrader and Joseph, 2000; Yeatts, 2004; Schrader, 

2007a; Pugh, 2010).

The lowest water levels in the Cockfield aquifer are 

generally in southeastern Lincoln County. Declines in water 

levels in Lincoln County were recognized as early as the 

1960s. Water levels in one domestic well (well B; figs. 38 and 

39) dropped by about 40 ft from 1966 to 1987 (Ackerman, 

1987a). Rebounds in the water levels for this well (fig. 39) 

from 2000 through 2003 are attributed to intermittent use of 

the well during this period (T.P. Schrader, U.S. Geological 

Survey, oral commun., 2013). Domestic use of the Cockfield 

aquifer is common in Lincoln County.

A cone of depression in the Cockfield aquifer has been 

developing near Crossett in Ashley County since 2003 

(Yeatts, 2004). Water levels previously were reported to have 

declined nearly 9 ft in central Ashley County from 1971 to 

1991 (Westerfield, 1994). Schrader and Joseph (2000) noted 

that a cone of depression might be forming in that area. The 

depression at Crossett is centered on a single well (well C; 

figs. 38 and 39). Between 2003 and 2009, the depression 

at Crossett grew to the northwest and southeast because of 

groundwater withdrawals (Pugh, 2010).

Between 2003 and 2006, a new depression formed in the 

potentiometric surface of Cockfield aquifer in southwestern 

Calhoun County (Yeatts, 2004; Schrader, 2007a; Hart 

and others, 2008). This depression further extended to the 

southeast between 2006 and 2009 (Pugh, 2010). A hydrograph 

of well D near the center of that cone of depression is shown 

in figure 39. Water levels declined 1 ft from 2003 to 2009.

No regionally extensive declines have yet been 

observed in the Cockfield aquifer; however, with continued 

development, these individual cones may coalesce to 

encompass broader areas of the extent of the aquifer. 

Published summary statistics for water levels in the Cockfield 

aquifer are available in Schrader (2007a) and Pugh (2010). 

Declines were noted in all counties except Cleveland County 

in the 1986–2006 period (Schrader, 2007a) along with 

Calhoun and Columbia Counties in the 1990–2009 period 

(Pugh, 2010). The largest mean annual decline of 1.46 ft/yr 

was seen in Chicot County from 1990 to 2009. Desha County 

had annual mean declines more than 1 ft/yr in the 1986–2006 

and 1990–2009 periods. 
130 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

UNION

DREW

ASHLEY

CHICOT

DESHA

ARKANSAS

GRANT

DALLAS

JEFFERSON

COLUMBIA

OUACHITA

BRADLEY

LINCOLN

CALHOUN

CLEVELAND

Saline River

Ouachita River

Moro Creek

Mississippi River

Greenville

Crossett 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

60 180

200

280

260

60

180

180

260

!

!

!! !

!

!

!

!

!

!

!! !

!

! !

!

! !

!

!! !

!

!

!

!

!! !

!

!

!

!

!

!

!!

!

!

!

!

!

! !

!

!

!

!

!

! !

!

!

!

43

95

70

98

82

80

65

83

88

81

79

77

62

67

92 96

86

85 70

68

88

99 91

87

86

72

189

174

262

230

201

155

158

234

159

104

307

251

260

289

351

234

267

164

126

134

177

211

194

257

111

107

131

109

113

102

C

D

A

B

0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

34°00'

33°30'

91°30'

92°30'

92°00'

93°00'

91°00'

LOUISIANA

ARKANSAS

MISSISSIPPI

Base from U.S. Geological Survey digital data, 1:24,000

Universal Transverse Mercator, zone 15 North

North American Datum of 1983 

Modified from Pugh, 2010 

EXPLANATION

160

C 68

Outcrop of Cockfield Formation (modified from Hosman, 1988)

Potentiometric contour—Shows altitude at which 

 water level would have stood in tightly cased wells. 

 Dashed where approximately located. Hachures

 indicate depression. Contour interval 20 feet. Datum

 is National Geodetic Vertical Datum of 1929 (NGVD 29)

General direction of groundwater flow

Well, completed in the Cockfield aquifer, used for control—

 Letter, where present, indicates hydrograph shown on

 figure 39. Number is water level in feet above NGVD 29

Area enlarged

ARKANSAS

Figure 38. Potentiometric surface of the Cockfield aquifer in Arkansas, 2009.
Aquifers of the Coastal Plain 131

Water Quality

Water quality in the Cockfield aquifer is generally very 

good throughout its extent, except for an area of high salinity 

in Chicot County and isolated areas of elevated sulfate in parts 

of Grant, Jefferson, Drew, and Bradley Counties. Hewitt and 

others (1949) stated that the quality of groundwater from the 

aquifer was fairly good and quite uniform for all of Ashley 

County. Tait and others (1953) described groundwater from 

the aquifer as being exceptionally soft and containing only 

a moderate amount of dissolved solids for all of Columbia 

County. Plebuch and Hines (1969) described the water 

quality as good throughout Cleveland and Dallas Counties. 

Halberg and others (1968) described groundwater from the 

Cockfield aquifer as varying from a soft, sodium-bicarbonate 

to a hard, calcium-bicarbonate water type and having greater 

dissolved-solids content than water from other formations in 

Grant County. They additionally noted that the sulfate content 

can be high, indicating possible migration of groundwater 

from the overlying Jackson Group (see section “Jackson 

Group”). Halberg and others (1969) also stated that much of 

the groundwater had a high iron content and that the water 

was corrosive locally (indicating low pH). Broom and others 

(1984) cited the aquifer in Union County as having a low 

mineral content with dissolved-solids concentrations ranging 

from less than 100 mg/L to approximately 200 mg/L. 

General Geochemistry and Water Type

Data compiled for this report revealed 247 sites with 

water-quality data for the Cockfield aquifer (table 23). 

A review of these data revealed very good water quality 

throughout most of the aquifer with isolated areas of poorquality groundwater. A spatial analysis of the water-quality 

sites showed distinct patterns for many of the constituents of 

interest. Several of the chemical constituents revealed spatial 

trends related to geochemical processes along regional flow 

paths or leakage of poor-quality groundwater from overlying 

or underlying formations.

Values for pH in the Cockfield aquifer ranged from 5.1 

to 8.8 with a median value of 7.9 (table 23). In general, pH 

values were lowest in the area of aquifer outcrop and subcrop 

(pH ranging from 5.1 to 7.0 in 34 samples). Values of pH 

generally increased (upward to 8.8) in the southeast trending 

1966 1972 1978 1984 1990 1996 2002 2008 2014

Year

30 

40 

50 

60 

70 

80 

90 

100 

110 

120 

130 

Water level, in feet above National Geodetic Vertical Datum of 1929

Water level, in well completed

in the Cockfield aquifer

 Well A (Chicot County)

 Well B (Lincoln County)

 Well C (Ashley County)

 Well D (Calhoun County) 

EXPLANATION

Figure 39. Hydrographs of water levels in wells completed in the Cockfield aquifer in southeastern Arkansas.
132 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

direction of flow within short distances of outcrop and 

subcrop areas (fig. 40A). Increases in pH in the downgradient 

direction are attributed to increased dissolution of carbonate 

minerals with resulting increased buffering of low-pH water 

and increased bicarbonate concentrations. Bicarbonate was 

the dominant anion (greater than 50 percent of anions in 

78 percent of samples) throughout the aquifer, except for 

an area of high salinity in Chicot County. Bicarbonate also 

followed a similar trend to that of pH and with increasing 

concentrations to the southeast in the downgradient direction 

of flow (fig. 40C).

Percent sodium in the Cockfield aquifer followed 

a similar trend of increasing values in the downgradient 

direction of flow (fig. 40B) similar to that of pH and 

bicarbonate. Groundwater throughout most of the aquifer 

is of a strongly sodium-bicarbonate water type. More than 

80 percent of sites had sodium values that were more than 

50 percent of the total cations (in milliequivalents per liter); 

60 percent of these sites had values exceeding 70 percent 

sodium and ranging upward to 98 percent sodium. Increased 

sodium is attributed to cation exchange of calcium for sodium 

at solid-phase exchanges sites, thus increasing sodium in 

solution at the expense of calcium along the flow path. 

Sodium percentages less than 50 percent (generally a calciumbicarbonate water type) occurred in the outcrop and subcrop 

areas generally in Bradley, Calhoun, Dallas, Grant, and Union 

Counties. 

Table 23. Descriptive statistics for selected chemical constituents in groundwater from the Cockfield aquifer in southeastern 

Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 0.2 5.0 124 21.8 193

Magnesium (mg/L) 0.10 1.3 38 6.08 185

Sodium (mg/L) 1.2 77 747 102.76 189

Potassium (mg/L) 0.2 3.0 13 2.16 169

Bicarbonate (mg/L) 1.0 207 504 110 217

Chloride (mg/L) 1.0 13 1,800 207.5 238

Sulfate (mg/L) 0.02 2.4 470 64.7 214

Silica (mg/L) 0.9 15 82 14.55 106

Nitrate (mg/L as nitrogen) 0.01 0.18 89 6.70 223

Dissolved solids (mg/L) 20 241 2,366 306 188

Iron (μg/L) 0.05 70 30,600 2,578 181

Manganese (μg/L) 0.13 25 3,640 474 59

Arsenic (μg/L) 0.03 0.50 7.3 1.59 47

Hardness (mg/L as calcium carbonate) 1.0 16 600 89 183

Specific conductance (μS/cm) 25 406 5,050 758 232

pH (standard units) 5.1 7.9 8.8 0.8 217
LEE

UNION

DREW

DESHA

ASHLEY

CLARK

SALINE

LONOKE

ARKANSAS

PULASKI

CHICOT

GRANT

PERRY

PRAIRIE

PHILLIPS

JEFFERSON

DALLAS

OUACHITA

MONROE

GARLAND

BRADLEY

LINCOLN

CALHOUN

COLUMBIA

YELL

NEVADA CLEVELAND

WHITE FAULKNER WOODR POPECONWAY ST. FRANCIS

LEE

UNION

DREW

DESHA

ASHLEY

CLARK

SALINE

LONOKE

ARKANSAS

PULASKI

CHICOT

GRANT

PERRY

PRAIRIE

PHILLIPS

JEFFERSON

DALLAS

OUACHITA

MONROE

GARLAND

BRADLEY

LINCOLN

CALHOUN

COLUMBIA

YELL

NEVADA CLEVELAND

WHITE FAULKNER WOODR POPECONWAY ST. FRANCIS

UNION

ASH

CLARK

SALINE

LONOK

PULASKI

GRANT

PERRY

JEFFERSO

DALLAS

OUACHITA

GARLAND

BRADLEY

LIN

CALHOUN

COLUMBIA

YELL

NEVADA CLEVELAND

WHI

FAULKNER 

POPECONWAY 

LEE

UNION

DREW

DESHA

ASHLEY

CLARK

SALINE

LONOKE

ARKANSAS

PULASKI

CHICOT

GRANT

PERRY

PRAIRIE

PHILLIPS

JEFFERSON

DALLAS

OUACHITA

MONROE

GARLAND

BRADLEY

LINCOLN

CALHOUN

COLUMBIA

YELL

NEVADA CLEVELAND

WHITE FAULKNER WOODR POPECONWAY ST. FRANCIS

LEE

UNION

DREW

DESHA

ASHLEY

CLARK

SALINE

LONOKE

ARKANSAS

PULASKI

CHICOT

GRANT

PERRY

PRAIRIE

PHILLIPS

JEFFERSON

DALLAS

OUACHITA

MONROE

GARLAND

BRADLEY

LINCOLN

CALHOUN

COLUMBIA

YELL

NEVADA CLEVELAND

WHITE FAULKNER WOODR POPECONWAY ST. FRANCIS

UNION

ASH

CLARK

SALINE

LONOK

PULASKI

GRANT

PERRY

JEFFERS

DALLAS

OUACHITA

GARLAND

BRADLEY

LIN

CALHOUN

COLUMBIA

YELL

NEVADA CLEVELAND

WH

FAULKNER 

POPECONWAY 

35°34°35°34°

35°34°

35°34°

93° 92° 91° 93° 92° 

93° 92° 91° 93° 92° 91° 93° 92° 

93° 92° 91°

35°34°

35°34°

0 60 120 MILES0 60 120 KILOMETERS

Base modified from U.S. Geological Survey digital data, 1:250,000 Geology map modUniversal Transverse Mercator projection, zone 15

5.1 to 6.06.1 to 6.56.6 to 7.07.6 to 8.08.1 to 8.8

7.1 to 7.5

6 to 1011 to 2526 to 5076 to 9091 to 98

51 to 75

pH, in standard units Sodium, in percent of major cations

1 to 8586 to 165166 to 255336 to 425426 to 504

256 to 335

Bicarbonate, in milligrams per l

0 to 1011 to 2526 to 50151 to 250251 to 470

51 to 150

Sulfate, in milligrams per liter

EXPLANATION

0 to 2526 to 100101 to 250501 to 750751 to 1,800

251 to 500

Chloride, in milligrams per liter

EXPLANATION

0 to 5051 to 100101 to 300

301 to 1, 0001,001 to 5,0005,001 to 30,600

Iron, in micrograms per liter

EXPLANATION

EXPLANATION EXPLANATION EXPLANATION

EXPLANATION

Cockfield outcropCockfield subcropCockfield extent

ARKANSAS

Area enlarged

Figure 40. Spatial distribution of selected chemical constituents for groundwater from the Cockfield aquifer in southeastern Arkansas.
134 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Iron 

Iron concentrations in the Cockfield aquifer ranged from 

0.05 to 30,600 μg/L with a median of 70 μg/L. The median 

concentration is below the 300 μg/L secondary drinking-water 

regulation and illustrates the generally low iron concentrations 

throughout the aquifer (fig. 41; table 23). Iron concentrations 

generally are greatest (upward to 30,600 μg/L) in the outcrop 

and subcrop areas of the westernmost extent of the aquifer 

and consistently lower, dominantly less than 200 μg/L, 

throughout the rest of the aquifer (fig. 40D). Two exceptions 

are an area in Chicot County and an area in eastern Grant and 

Jefferson Counties. Upwelling of brines from the Jurassic-age 

Smackover Formation in Chicot County has been identified 

as the cause of elevated salinity identified in the Sparta, 

Cockfield, and alluvial aquifers. Elevated iron concentrations 

ranging from greater than 500 μg/L to 3,730 μg/L in this area 

probably are related to intrusion of poor-quality groundwater 

from underlying formations (see section on “Chloride” below). 

In the area of eastern Grant and Jefferson Counties, elevated 

iron concentrations are possibly the result of infiltration 

of high-iron content in the groundwater from overlying 

formations.

Nitrate

Nitrate concentrations were relatively low throughout 

the aquifer and ranged from 0.01 to 89 mg/L with a median 

concentration of 0.18 mg/L (table 23). Two sites contained 

extremely high nitrate concentrations of 46 and 89 mg/L. 

No information was available to explain these high nitrate 

concentrations, and no other site had nitrate concentrations 

exceeding the Federal MCL of 10 mg/L. Of the 223 sites 

with nitrate data, 213 (96 percent) had nitrate concentrations 

less than 1.0 mg/L. No strong spatial trend was noted in the 

distribution of nitrate concentrations. Additionally, there 

was no strong relation of nitrate concentration to well depth; 

however, all but two sites with nitrate concentrations greater 

than 1.0 mg/L occurred in wells less than 200 ft deep. The 

maximum well depth was 690 ft.

0

50

100

150

200

250

300

350

400

450

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron

Concentrations, in milligrams per liter

500

Concentration, in micrograms per liter

700

800

900

1,000

0

100

200

300

400

500

600

181

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

193

185

189

217

238

214

181

Constituent Constituent

Figure 41. Box plots showing interquartile range of selected chemical constituents in groundwater from the Cockfield aquifer in 

southeastern Arkansas.
Aquifers of the Coastal Plain 135

Sulfate

Although water quality generally is good throughout 

the Cockfield aquifer, poor water quality occurs in two areas: 

(1) an area in the central part of the aquifer in southeastern 

Arkansas with elevated sulfate concentrations, and (2) a 

large area of high salinity (elevated chloride concentrations) 

in Chicot County. The high-salinity area in Chicot County 

that affects several aquifers is discussed in greater detail 

(sources and solubility control) in the section “Mississippi 

River Valley Alluvial Aquifer.” Sulfate concentrations ranged 

from 0.02 to 470 mg/L with a median of 2.4 mg/L (table 23). 

A high density of sites with elevated (greater than 50 mg/L) 

sulfate concentrations occurs in Grant, Jefferson, Drew, and 

eastern Bradley Counties (fig. 40E). Only 4 of 214 samples 

(2 percent) exceeded the Federal secondary drinking-water 

regulation of 250 mg/L sulfate, and 184 of 214 sites (86 

percent) had concentrations that were less than 20 mg/L. 

In Grant and Jefferson Counties, however, a large area of 

elevated sulfate concentrations occurs in which 4 of 24 sites 

exceeded 150 mg/L with a maximum of 220 mg/L. Isolated 

wells with elevated sulfate occur in eastern Bradley and 

western Drew Counties, where four sites with the highest 

sulfate concentrations (greater than 250 mg/L) were located. 

All of these counties are areas where the Cockfield aquifer 

is overlain by deposits of the Jackson Group, which contains 

numerous groundwater sites with sulfate concentrations 

exceeding 250 mg/L and ranging upward to 3,080 mg/L. 

Halberg and others (1968) hypothesized groundwater from 

the Jackson Group was the source for elevated sulfate 

concentrations in groundwater from the Cockfield aquifer in 

Grant County. The larger dataset, and resulting greater spatial 

distribution afforded by this study, supports the theory of 

infiltration of high sulfate groundwater from the overlying 

Jackson Group.

Chloride

A review of chloride concentrations for the Cockfield 

aquifer shows overall low values throughout the aquifer 

with the exception of an area in Chicot County (fig. 40F). 

Bicarbonate dominates the anion chemistry and increases 

with increases in dissolved solids for dissolved-solids 

concentrations up to approximately 500 mg/L (fig. 42A). 

Chloride dominates the anion chemistry for dissolved-solids 

concentrations greater than 500 mg/L as evidenced by the 

strong linear relation between dissolved-solids and chloride 

concentrations at this transition point (fig. 42B). Mixing of 

poor-quality, high-salinity groundwater from underlying 

formations generally accounts for dissolved solids greater 

than approximately 500 mg/L. This concentration represents 

a transition zone from dissolution of carbonate minerals to 

a geochemistry reflecting influx and mixing of high-salinity 

groundwater from other sources. Chloride ranged from 1.0 

to 1,800 mg/L with a median concentration of 13 mg/L 

(fig. 41; table 23); 159 of 238 samples (67 percent) were less 

than 20 mg/L, and only 21 of 238 samples (9 percent) had 

concentrations greater than the Federal secondary drinkingwater regulation of 250 mg/L. All sites having chloride 

concentrations greater than 100 mg/L occurred in Chicot 

County, with the exception of one site in Drew County and 

three sites in Ashley County. Kresse and Clark (2008) used 

chloride concentration data from five monitoring wells 

(Kresse and others, 2000) and 21 domestic wells completed 

in the Cockfield aquifer to construct a chloride concentration 

map. The resulting map showed that the distribution of 

elevated chloride concentrations in the Cockfield aquifer 

was similar to that of the overlying Mississippi River Valley 

alluvial aquifer with the zone of elevated chloride manifested 

as an elongated north-south oriented band. Kresse and Clark 

(2008) suggested that the most likely source was upwelling 

of brine water from the Smackover Formation along the 

intersection of two mapped wrench faults (Zimmerman, 

1992). Mixing curves were developed using bromide/chloride 

ratios from the alluvial aquifer, Tertiary aquifers, and brine 

water from the Smackover Formation, in addition to the use 

of chloride isoconcentration maps and data from early oil 

and gas wells. Additional information and maps of chloride 

concentrations for the Mississippi River Valley alluvial, 

Cockfield, and Sparta aquifers are found in Kresse and Clark 

(2008).

In summary, groundwater quality throughout the 

Cockfield aquifer is good except for isolated areas with 

elevated sulfate and chloride concentrations that are a 

result of influx of poor-quality groundwater from overlying 

or underlying formations. The groundwater typically is 

of a calcium-bicarbonate type in the outcrop area but 

transitions to a sodium-bicarbonate type downdip to the 

east and southeast as a result of cation-exchange processes. 

Groundwater is of a sodium-chloride type in areas of mixing 

of poor-quality, high-salinity groundwater from underlying 

formations. Nitrate concentrations generally were low 

throughout the aquifer.
136 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Sparta Aquifer

The Tertiary-age Sparta Sand is the thickest sand in 

the Mississippi embayment and its importance as an aquifer 

is recognized by the fact that it is second in use only to the 

Mississippi River Valley alluvial aquifer. Veatch (1906) 

included the Sparta Sand as part of the undifferentiated 

Eocene deposits in southern Arkansas. Stephenson and Crider 

(1916) included the strata between the Wilcox Formation 

and the Jackson Formation, including the Sparta Sand, as 

the Claiborne Group. In Arkansas, the Claiborne Group is 

differentiated into the Carrizo Sand, Cane River Formation, 

Sparta Sand, Cook Mountain Formation, Cockfield Formation, 

and the Memphis Sand (Hosman and others, 1968; Payne, 

1968, 1970, 1972, 1975). 

In northeastern Arkansas, the underlying Cane River 

Formation and Carrizo Sand undergo a facies change 

northward of latitude 35 degrees, and the formations become 

sand. The northern sand facies of these two formations are 

generally indistinguishable and undifferentiated from the 

Sparta Sand, and all three formations are grouped together as 

the Memphis Sand in northeastern Arkansas (Counts, 1957; 

Hosman and others, 1968; Payne, 1972; Petersen and others, 

1985). Therefore, in northeastern Arkansas, the Sparta aquifer 

locally is referred to as the Memphis aquifer. In various 

USGS water-use and water-level reports referenced herein 

that address the aquifer as one aquifer throughout the State, 

the most recent being Schrader (2013) and Holland (2007), 

the aquifer is referred to as the “Sparta-Memphis aquifer.” To 

avoid confusion between local terminology and differences 

0 500 1,000 1,500 2,000 2,500

0 500 1,000 1,500 2,000 2,500

Dissolved solids, in milligrams per liter

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

2,000

0

100

200

300

400

500

600

Bicarbonate, in milligrams per liter Chloride, in milligrams per liter

A. Bicarbonate

B. Chloride

Figure 42. Graphs showing relation of concentrations of dissolved solids to A, bicarbonate and B, chloride in groundwater from the 

Cockfield aquifer in southeastern Arkansas.
Aquifers of the Coastal Plain 137

across States, regional hydrogeologic framework models 

designated the Sparta aquifer and Memphis aquifer as part 

of the regional Middle Claiborne aquifer (Arthur and Taylor, 

1990; Hosman and Weiss, 1991; Renken, 1998; Hart and 

Clark, 2008; Clark and Hart, 2009).

Additional confusion is noted for local usage in southern 

Arkansas. In the area of Union County, the Sparta Sand is 

divisible into three distinct hydrogeologic units: the Greensand 

(upper Sparta aquifer), the middle confining unit, and the 

El Dorado sand (lower Sparta aquifer). The terms “Greensand” 

and “El Dorado sand” are informal terms applied to the 

upper and lower major sand units within the Sparta aquifer 

in southern Arkansas. For the sake of clarity, it should be 

noted that the term “Sparta aquifer” is applied to a sequence 

of hydraulically connected sands that are often separated by 

silts and clays and is not an absolutely equivalent term with 

“Sparta Sand,” the formal name for the geologic formation. 

This distinction is important because by Arkansas law, critical 

groundwater area designation criteria for the Sparta aquifer 

are based on the top of the geologic formation rather than the 

top of the aquifer (Arkansas Natural Resources Commission, 

1996). In areas where clays and silts in the Sparta Sand (the 

geologic formation) occur above productive sands, the top of 

the Sparta aquifer does not coincide with the top of the Sparta 

Sand. In this report, the term “Sparta Sand” always will refer 

to the geologic formation (comprising sands, silts, and clays), 

and the term “Sparta aquifer” will refer to the sequence of 

productive, hydraulically connected sands that constitute a 

part of the geologic formation. Use of the term Sparta aquifer 

in the following sections is noted to include the groundwater 

in the saturated part of the Sparta Sand (and Memphis 

Sand) throughout Arkansas. Use of other terms will only be 

used to make distinctions in depositional and stratigraphic 

environments when appropriate. 

Geologic Setting

The Sparta Sand overlies the Cane River Formation 

and is overlain by either the Cook Mountain Formation or 

the Mississippi River Valley alluvium where the formation 

subcrops. The Sparta Sand consists of varying amounts of 

well-sorted, rounded to subrounded, fine- to medium-grained 

quartz sand interspersed with silt, clay, shale, and lignite. 

Layers of coarse sand and fine gravel occur in some areas. 

Glauconite occurs in various areas, particularly in the upper 

part of the formation. Shales within the Sparta Sand are gray 

to dark brown or black (Payne, 1968). The lithology of the 

Sparta Sand is variable vertically and laterally. The lower part 

of the unit generally contains more sand, and the upper part 

generally contains more clay and shale (Hosman and others, 

1968; Petersen and others, 1985). In southern Arkansas, welldeveloped lineations of high sand content occur at a generally 

north/south orientation that is presumed to be normal to the 

shoreline at the time of deposition. This pattern was likely 

created by a system of shifting stream channels, lakes, 

marshes, and swamps that were present in a deltaic-fluvial 

plain (Payne, 1968). Onellion and Criner (1955) describe 

the Sparta Sand in Chicot County as white to gray, fine- to 

medium-grained sand with beds and lenses of sandy or silty 

clay and some thin beds of lignite. The occurrence, thickness, 

and continuity of the sand beds are quite variable, but in 

general, the sands appear to be hydraulically connected. Albin 

(1964) described the Sparta Sand in Bradley and Calhoun 

Counties as gray, very fine- to medium-grained sand and 

brown to gray sandy clay. Ludwig (1973) described the Sparta 

Sand in Nevada, Lafayette, and Miller Counties as gray, fineto medium-grained sand, brown and gray sandy clay, with 

lenses of lignite in the formation as much as 2 ft thick. Ludwig 

(1973) noted that local drillers identify the Sparta Sand in well 

cuttings by its “salt and pepper” appearance as a result of the 

lignite.

The Sparta Sand in northeastern Arkansas is mainly 

composed of thick-bedded, very fine to gravely, well-sorted 

sand, with some argillaceous, micaceous, and lignitic 

materials. Clay layers are minor, but layers as thick as 20 

ft may locally occur and separate the sand hydraulically 

(Hosman and others, 1968). Counts (1957) described the 

Claiborne Group that includes the Sparta Sand in Lonoke, 

Prairie, and White Counties as generally white to lightgray, fine- to medium-grained sand with interbedded gray 

or tan clay and sandy clay, lignitic clay, and lignite. The 

Sparta Sand thickens southward and toward the axis of the 

Mississippi embayment downdip from its depositional extent 

to a maximum thickness of approximately 900 ft (Hosman 

and others, 1968; Petersen and others, 1985; Brahana and 

Broshears, 1989).

In and near Union County, the Sparta Sand is divisible 

into three distinct units. The lower 300 ft consists of thickbedded sands with grains ranging from fine to coarse and 

referred to locally as the El Dorado sand. The El Dorado 

sand overlies the Cane River Formation and regionally dips 

southeastward. The El Dorado sand is faulted against the Cane 

River Formation in some areas. The fault zones are described 

in more detail by Leidy and Taylor (1992). The middle 

50–155 ft of the Sparta Sand are composed of clay and silt 

and is referred to as the middle confining unit, and the upper 

200 ft are composed of thin-bedded, very fine- to fine-grained 

sands and clays. In places, the upper unit is distinctively 

green because of the presence of glauconite and therefore is 

referred to as the Greensand. In some areas of Union County, 

the middle confining unit contains sand that makes the unit 

difficult to distinguish from the Greensand and El Dorado 

sand. However, differences in potentiometric surfaces above 

and below this unit confirm that it effectively isolates the 

upper and lower units of the Sparta aquifer in this area. The 

Greensand is overlain by the Cook Mountain Formation and 

regionally dips southeastward. The Greensand is partially 

in contact with the middle confining unit and the El Dorado 

sand along faults. Differences in static water levels measured 

in sand beds within the Greensand aquifer indicate that some 

clay beds in the Greensand locally act as confining beds. 

In general, the El Dorado sand is more productive than the 
138 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Greensand, and the local flow pattern within the El Dorado 

sand are heavily influenced by groundwater withdrawals 

(Hosman and others, 1968; Broom and others, 1984; Leidy 

and Taylor, 1992; Clark and Hart, 2009).

The Sparta Sand crops out in southern Arkansas, and 

the aquifer is unconfined at its western extent within the 

Mississippi embayment. It becomes confined east of the 

outcrop area as it dips toward the axis of the embayment 

and southward toward the Gulf of Mexico. It is confined by 

the Cook Mountain Formation above and by the Cane River 

Formation below (McKee and Clark, 2003). In and near the 

outcrop area, the Sparta Sand ranges in thickness from 0 

to 200 ft (Petersen and others, 1985). In south-central and 

southwestern Arkansas, the dip is to the east and southeast 

at about 25–50 feet per mile (ft/mi) into the Mississippi 

embayment and the Desha Basin (fig. 8), and the thickness 

ranges from approximately 600–800 ft with percentage 

of sand varying from 60 to 100 percent (Klein and others, 

1950; Terry and others, 1979; Kresse and Huetter, 1999). 

In southeastern Arkansas, the dip is to the south at about 

25–50 ft/mi (Payne, 1968). The Sparta Sand exceeds 800 ft in 

thickness near the axes of the Mississippi embayment and the 

Desha Basin in southeastern Arkansas (Payne, 1968); Pugh 

(2008a) reported a maximum thickness of 900 ft. The Sparta 

Sand does not crop out in northern Arkansas except for some 

exposed erosional remnants along Crowleys Ridge. In the 

Sparta Sand subcrop area, the Sparta aquifer and overlying 

Mississippi River Valley alluvial aquifer are hydraulically 

connected. This area serves as an important recharge area 

to the Sparta aquifer (Hosman and others, 1968; Broom and 

Lyford, 1981). Groundwater in the Sparta Sand generally 

flows toward the axis of the Mississippi embayment and then 

southward (Hosman and others, 1968; Edds and Fitzpatrick, 

1984b; Stanton, 1997; Schrader, 2004, 2006b, 2009, 2013; 

Schrader and Jones, 2007).

Hydrologic Characteristics

Hydraulic properties vary widely in the Sparta aquifer, 

and the highest transmissivity is tied to the thickest sand 

intervals, not necessarily the highest sand percentage (Payne, 

1968). Hosman and others (1968) reported transmissivity 

of the Sparta aquifer ranging from 1,800 to 17,400 ft2/d, 

storage coefficients ranging from 0.0002 to 0.0024, hydraulic 

conductivity ranging from about 11 to 110 ft/d, and specific 

capacities ranging from 7 to 14 (gal/min)/ft. Plebuch and 

Hines (1969) reported well yields as high as 700 gal/min and 

transmissivities from 3,200 to 15,400 ft2/d. 

Pugh (2008a) summarized aquifer-test data from the 

Sparta aquifer as follows: based on data from 16 sites, 

the average specific capacity was 61.7 (gal/min)/ft with 

a minimum of 0.13 (gal/min)/ft and a maximum of 

439 (gal/min)/ft; based on data from 33 sites, the average 

transmissivity was 7,990 ft2/d with a minimum of 23 ft2/d and 

a maximum of 31,000 ft2/d; based on data from 3 sites, the 

average hydraulic conductivity was 13.1 ft/d with a minimum 

of 1.7 ft/d and a maximum of 29 ft/d; and based on data from 

17 sites, the average storage coefficient was 0.00209 with a 

minimum of 0.000017 and a maximum of 0.03. Pugh (2008a) 

also reported that the Sparta aquifer commonly yields 1,000 

gal/min to wells, and that yields may exceed 1,900 gal/min. A 

transmissivity of nearly 7,400 ft2/d and a storage coefficient 

of 0.0009 were reported from the Sparta aquifer in St. Francis 

County (Hosman and others, 1968). Data from 23 aquifer tests 

in northern Arkansas (listed under Memphis Sand) throughout 

the northern Mississippi embayment show transmissivity 

ranging from 2,700 to 54,000 ft2/d, and storage coefficients 

ranging from 0.0001 to 0.2 (Brahana and Broshears, 1989).

The Sparta aquifer outcrop area is recharged by direct 

infiltration, from rivers, and by leakage from overlying 

alluvium and other aquifers with higher hydraulic heads. 

Natural discharge occurs by leakage through the overlying 

and underlying confining units, lateral movement into 

adjacent units with lower hydraulic heads, and discharge to 

rivers within the outcrop area. Groundwater flow is generally 

downdip toward the axis of the embayment and southward 

toward the Gulf of Mexico. The rate of groundwater flow 

within the aquifer varies with local lithology and may be 

affected by local faulting (Payne, 1968; McKee and Clark, 

2003). The above generalized groundwater-flow pattern was 

present in the aquifer prior to aquifer development (Reed, 

1972). Continued, large withdrawals have resulted in waterlevel declines affecting changes in flow direction (discussed 

further under the section “Water Levels”).

Water Use

The Sparta aquifer is an extremely important source 

of groundwater in eastern Arkansas. The aquifer generally 

provides water of excellent quality, and wells often yield 

hundreds to thousands of gallons per minute. The Sparta 

aquifer provided 196.64 Mgal/d in 2010, which was 

2.5 percent of all groundwater used in Arkansas, with over 

700 wells withdrawing water from the aquifer (fig. 43). 

Historically, the Sparta aquifer has been used for public and 

industrial supply, but irrigation use has increased as water 

levels in the Mississippi River Valley alluvial aquifer have 

decreased, particularly in the Grand Prairie region. In the past, 

drilling costs for completing wells in the deeper Sparta aquifer 

had been cost prohibitive; however, as the Mississippi River 

Valley alluvial aquifer became depleted in some areas, the lack 

of other water sources has necessitated drilling in the Sparta 

aquifer to support agriculture (Czarnecki and Schrader, 2013). 

As of 2010, more water was used from the Sparta aquifer for 

irrigation than for any other purpose.
YELL

LEE

UNION

WHITE

POLK

POPE

DREW

PIKE

SCOTT

CLARK

CLAY

ASHLEY

DESHA

BENTON

LOGAN

SALINE

IZARD

LONOKE

PULASKI

ARKANSAS

NEWTON

GRANT

CHICOT

MADISON

STONE

MILLER

SHARP

CROSS

DALLAS

PRAIRIE

BOONE

PHILLIPS

PERRY

SEARCY

MARION

FULTON

SEVIER

MISSISSIPPI

JEFFERSON

NEVADA

POINSETT

GARLAND

COLUMBIA

BAXTER

OUACHITA

BRADLEY

JOHNSON

WASHINGTON

MONROE

GREENE

JACKSON

CARROLL

HOWARD

LINCOLN

CALHOUN

CONWAY FAULKNER

VAN BUREN FRANKLIN

CRAIGHEAD

HEMPSTEAD

RANDOLPH

CLEBURNE

MONTGOMERY

LAWRENCE

ST. FRANCIS

CRAWFORD

CLEVELAND

HOT SPRING

INDEPENDENCE

LITTLE

RIVER

WOODRUFF CRITTENDEN

LAFAYETTE

SEBASTIAN

94° 92° 91° 93°

90°

36°

35°

34°

Base from U.S. Geological Survey digital data, 1:2,000,000

0 15 0 30 

15

Extent of Grand PrWell type 

galloto repwaterrepres

EX

CommeDucksElectricIndustrIrrigatiMiningPublic 

Figure 43. Wells with reported water use from the Sparta aquifer in Arkansas, 2010.
140 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

The majority of Sparta aquifer water use in Arkansas 

currently is centered in the Grand Prairie region (figs. 43 and 

44). Use of the aquifer almost doubled between 1965 and 

1995 (table 24). From 1965 to 1985, the largest amount of 

use occurred in Jefferson County; whereas Arkansas County 

had the most use in 1990, 1995, and 2010 (fig. 44; table 24). 

Although use has decreased in both of these counties, 

Arkansas and Jefferson Counties continue to be the greatest 

users of the aquifer. 

Statewide water use from the Sparta aquifer decreased 

32 percent from the 2000 peak of 287.44 Mgal/d to 

196.64 Mgal/d in 2010 (table 24), primarily because of 

changes in reporting criteria that occurred in Jefferson County 

in 2000. Anecdotal reports from drillers indicated many wells 

drilled around 2000 were dual completed in the Mississippi 

River Valley alluvial and Sparta aquifers. For the 2000 report, 

10 percent of the water use from dual-completed wells was 

reported as use from the Sparta aquifer (Terrance W. Holland, 

U.S. Geological Survey, written commun., 2012). This 

resulted in the greatest one-time reported use from Jefferson 

County of 90.63 Mgal/d, a use that was approximately 

35–40 Mgal/d more than what was reported in 1995 and 

2005.

Jefferson County, especially in the Pine Bluff area, 

has been the largest user of the Sparta aquifer in the State. 

Domestic and industrial wells, including those for railroads 

and ice manufacturing (Veatch, 1906), were present before 

1890 (Klein and others, 1950), and the aquifer was not used 

for public supply until the late 1890s (Veatch, 1906). Water 

use and the number of wells completed in the aquifer in 

Jefferson County steadily increased over time from 5 wells in 

1900 (Klein and others, 1950), to 27 wells in 1950 (Klein and 

others, 1950), and 60 wells in 2010 (Terrance W. Holland, 

U.S. Geological Survey, written commun., 2012).
EXPLANA

Annual water withdrawn 

in million gallons per d

No color represents no report

10.1 to 20.020.1 to 30.0

30.1 to 40.040.1 to 50.00.1 to 10.0

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

0 60 0 60 120 

Base from U.S. Geological Survey digital data 1:2,000,000 Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977; Holland, 1981, 1987, 1993, 1999, 2004, 2007

19651980 1985

1970 1975

Figure 44. Water-use rates for the Sparta aquifer in Arkansas from 1965 to 2010. 
EXPLANA

Annual water withdrawn f

in million gallons per d

No color represents no report

10.1 to 20.0 20.1 to 30.0 30.1 to 40.0 40.1 to 50.0 0.1 to 10.0 0 60 

0 60 120 K

Base from U.S. Geological Survey digital data 1:2,000,000 Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977; Holland, 1981, 1987, 1993, 1999, 2004, 2007 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 

36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 1990 2005 2010 1995 2000

Figure 44. Water-use rates for the Sparta aquifer in Arkansas from 1965 to 2010.—Continued
Aquifers of the Coastal Plain 143

Table 24. Water use from the Sparta aquifer in Arkansas, 1965–2010.

[Counties shown are only those with published data. Data from Halberg and Stephens (1966); Halberg (1972, 1977); Holland (1981, 1987, 1993, 1999, 2004, 

2007). Units are million gallons per day]

County 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Arkansas 17.39 20.26 24.25 36.97 36.50 67.99 76.69 63.40 36.03 58.29

Ashley 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.18 0.00 0.00

Bradley 1.14 1.39 1.34 1.83 1.44 0.91 0.91 1.76 1.70 1.88

Calhoun 0.17 0.19 0.47 0.69 0.53 0.70 0.98 0.61 0.53 0.63

Chicot 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.16 0.52 0.48

Clay 0.20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.12

Cleveland 0.26 0.16 0.16 0.24 0.85 0.98 0.89 1.44 0.73 1.16

Columbia 3.03 5.84 6.02 7.22 7.10 6.50 5.24 2.90 3.61 9.41

Craighead 3.26 0.21 0.19 0.29 0.40 0.68 0.76 22.74 14.14 13.38

Crittenden 0.07 0.05 0.00 0.00 0.00 0.00 0.00 0.50 0.00 0.00

Cross 0.71 0.40 0.40 0.53 0.00 0.00 0.00 4.17 7.02 5.21

Dallas 0.67 1.04 1.19 1.42 1.19 1.07 0.93 1.15 1.47 0.78

Desha 0.83 0.76 1.35 1.73 6.45 6.23 6.65 3.85 5.42 4.36

Drew 1.12 2.45 2.97 3.88 3.06 2.60 3.11 0.88 2.82 2.56

Grant 0.50 1.41 1.41 1.53 1.39 1.41 1.84 1.92 2.60 1.73

Greene 0.22 0.34 0.31 0.63 0.00 0.00 0.00 0.00 0.00 0.00

Hot Spring 0.06 0.15 0.15 0.17 0.00 0.00 0.00 0.00 0.00 0.24

Jackson 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.18 0.42 0.33

Jefferson 44.36 59.30 53.82 71.13 65.00 63.80 53.87 90.63 50.38 45.50

Lafayette 2.63 0.49 0.24 0.46 0.14 0.04 0.30 0.24 0.42 0.75

Lawrence 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5.99 0.13 0.00

Lee 0.09 0.57 0.98 2.84 1.72 3.32 3.29 1.18 0.93 0.94

Lincoln 0.34 1.02 1.20 1.28 1.03 1.12 1.33 2.01 1.20 3.23

Little River 0.00 0.00 0.00 0.00 0.47 0.40 0.24 0.00 0.00 0.00

Lonoke 0.24 0.00 0.00 0.09 3.43 3.08 3.98 23.19 9.35 16.50

Madison 0.00 0.03 0.06 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Miller 0.00 0.25 0.35 0.80 0.09 0.03 0.04 0.01 0.04 0.01

Mississippi 0.00 0.00 0.00 0.00 0.01 0.02 0.15 0.57 0.00 0.00

Monroe 0.24 0.76 0.83 1.67 0.51 0.73 1.80 0.17 0.77 1.33

Nevada 0.00 0.10 0.13 0.16 0.00 0.00 0.00 0.01 0.19 0.00

Ouachita 2.27 7.39 4.28 3.89 0.00 1.23 1.52 2.60 1.03 1.11

Phillips 4.57 9.19 7.56 5.84 6.00 9.27 9.70 1.07 4.14 3.75

Poinsett 0.08 0.46 0.78 1.36 0.02 0.03 0.04 1.28 1.29 2.40

Prairie 6.75 7.72 15.80 20.92 20.70 22.58 24.72 27.65 5.79 10.32

Pulaski 0.00 0.16 0.20 0.30 0.85 0.82 0.52 0.43 0.12 0.93

Saline 0.57 0.20 0.18 0.28 3.43 3.43 3.72 3.35 0.38 0.49

Sevier 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00

St. Francis 0.76 0.29 0.36 0.49 0.00 0.00 0.00 0.77 0.00 0.09

Union 19.07 18.85 17.40 16.07 13.85 14.83 15.23 17.97 15.55 7.59

Woodruff 0.13 0.10 0.10 0.75 0.00 0.00 0.00 1.48 1.21 1.14

Total 111.73 141.53 144.48 185.46 176.16 213.80 218.45 287.44 169.94 196.64
144 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Use of the Sparta aquifer in southern Arkansas is less 

than use in the Grand Prairie or Jefferson County; however, 

the aquifer remains vitally important in southern Arkansas 

as it is the best source for industrial and public supply. In 

southern Arkansas, Union County is the biggest user of the 

Sparta aquifer (fig. 44; table 24). The maximum historic 

withdrawals in Union County most likely occurred during 

the oil boom of the 1920s before consistent water-use record 

keeping began in 1965. From reported water-use data, a 

maximum use of 19.07 Mgal/d occurred in Union County in 

1965, and usage since has decreased (table 24). Water levels 

in the Sparta aquifer have continued to fall until the early to 

mid-2000s. At that time, the Union County Water Alliance, 

a local stakeholder group with local governmental, utilities, 

industrial, commercial, and public representation, led El 

Dorado and other users in Union County in implementing 

large-scale, coordinated conservation and alternative-source 

development efforts. This resulted in considerable decreases 

in withdrawals from the Sparta aquifer (discussed further in 

the “Water Levels” section below). From 2005 to 2010, water 

use in Union County decreased more than 50 percent because 

of conservation efforts and use in 2010 was 60 percent less 

than in 1965 (fig. 45; table 24). Sparta aquifer water use 

in Columbia County decreased by almost 20 percent from 

6.50 Mgal/d in 1990 to 5.24 Mgal/d in 1995 with the 1993 

completion of Lake Columbia and associated water treatment 

and transfer infrastructure. 

Water use from the Sparta aquifer increased in 

northeastern Arkansas beginning about 2000 (fig. 44; 

table 24). Use in Craighead County increased 310 percent 

from 1965 to 2010 (fig. 45), primarily as a result of increasing 

public-supply demand. Irrigation use also has increased in 

Cross and Poinsett Counties since 2000. 

Domestic and Public Supply

The Sparta aquifer accounts for the greatest volume of 

groundwater used for public supply in Arkansas. More than 

115 towns across Arkansas use the Sparta aquifer as their 

water source (fig. 43), withdrawing a combined 57.44 Mgal/d 

in 2010 (Terrance W. Holland, U.S. Geological Survey, 

written commun., 2012). The greatest number of towns using 

groundwater from the Sparta aquifer are in Arkansas and 

Union Counties. Municipalities generally turned to this aquifer 

because of water-quality issues in shallower aquifers or after 

shallower water sources were depleted. Multiple counties 

withdraw exclusively from the Sparta aquifer for their public 

supply, including those in the Grand Prairie, southern, and 

southeastern Arkansas. Craighead County had the most publicsupply use, followed by Arkansas, Jefferson, Union, and 

Phillips Counties.

Municipalities in the Grand Prairie transitioned to the 

Sparta aquifer as water levels declined in the Mississippi River 

Valley alluvial aquifer. Stuttgart (Arkansas County), the largest 

city in the Grand Prairie, originally used the Mississippi 

River Valley alluvial aquifer for its public supply but because 

of declining water levels in this aquifer, the city completed 

its first well into the Sparta aquifer in 1947 (Stephenson 

and Crider, 1916; Engler and others, 1945, 1963; Hale and 

others, 1947). Stuttgart is the largest public user of the Sparta 

aquifer in the Grand Prairie and withdrew 3.13 Mgal/d in 

2010 (Terrance W. Holland, U.S. Geological Survey, written 

commun., 2012). 

The cities of Brinkley (Monroe County), Des Arc 

(Prairie County), Carlisle, and Lonoke (both Lonoke County) 

originally used the Mississippi River Valley alluvial aquifer 

for public supply but have added new wells or completely 

switched to the Sparta aquifer (Stephenson and Crider, 1916; 

Engler and others, 1945, 1963; Halberg and Reed, 1964). The 

cities of DeWitt and Gillett (Arkansas County) tapped the 

Sparta aquifer in the 1950s (Lyle Godfrey, Arkansas Health 

Department, written commun., 2012). As of 2010, Des Arc 

pumped from Mississippi River Valley alluvial wells but 

installed an additional well tapping the Sparta aquifer in 2004. 

Brinkley and Lonoke now (2013) exclusively use the Sparta 

aquifer. 

Use of the Sparta aquifer for public supply began at the 

turn of the 20th century in Pine Bluff (Jefferson County). 

Searching for better quality drinking water, two wells were 

drilled to the aquifer in the late 1890s; one of these wells was 

reported as pumping as much as 1 Mgal/d (Veatch, 1906). Pine 

Bluff completed additional public-supply wells in the Sparta 

aquifer in 1924; pumping was estimated at 2 Mgal/d in 1945 

(Klein and others, 1950). With expanding population, publicsupply pumpage increased to 2.7 Mgal/d in 1948, 3.6 Mgal/d 

in 1958, approximately 8 Mgal/d in 1977, and 11 Mgal/d in 

1999 (Klein and others, 1950; U.S. Army Corps of Engineers, 

1977; Kresse and Huetter, 1999). Use of the Sparta aquifer 

peaked in 2000 and has dropped as the population of Pine 

Bluff has declined (fig. 44; table 24). 
POINSETT

2,900

LONOKE

6,775

PHILLIPS

-18

UNION

-60

ST. FRANCIS

-88

CRITTENDEN

-100

GREENE

-100

CLAY

-40

SALINE

-14

LAFAYETTE

-71

OUACHITA

-51

LEE

944

COLUMBIA

211

GRANT

246

DALLAS

16 CLEVELAND 346

JEFFERSON

3

LINCOLN

850

DESHA

425

DREW

129

BRADLEY

65 CALHOUN 271

MONROE

454

PRAIRIE

53

WOODRUFF

777

CROSS

634

CRAIGHEAD

310

HOT SPRING

300

ARKANSAS

235

94° 92° 91° 93°

90°

36°

35°

34°

0 15 30 

0 30 

15 45

-100 to 1 to 200201 to 4401 to 6601 to 8801 to 1> 1,000

 Use of th

by couperce

No color indicates 

EX

Base from U.S. Geological Survey digital data, 1:2,000,000

Figure 45. Change in percentage of water use from the Sparta aquifer in Arkansas from 1965 to 2010.
146 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Most of the historical groundwater used in Union County 

was drawn by the city of El Dorado (fig. 46). El Dorado 

began public-water supply service in 1909, primarily drawing 

from the Cockfield aquifer (Hale, 1926; Hale and others, 

1947; Baker and others, 1948; Broom and others, 1984). Oil 

was discovered near El Dorado in 1921 (Parker, 2001) and 

the population of El Dorado expanded within weeks of the 

discovery from 4,000 to 15,000 (Buckalew and Buckalew, 

1974), which put a heavy demand on water resources in the 

region. Prior to the oil boom, public supply from the Sparta 

aquifer at El Dorado was estimated to be 0.1 Mgal/d in 1921 

(Baker and others, 1948). In 1922, after the oil discovery, 

El Dorado completed additional public-supply wells into the 

Sparta aquifer to supply the rapidly increasing population 

(Baker and others, 1948). The population of El Dorado 

continued to increase, reaching 25,000 in 1924, while publicsupply use correspondingly increased to 1.5 Mgal/d, with 

0.4 Mgal/d coming from the Sparta aquifer (Hale, 1926; Baker 

and others, 1948). Total El Dorado public-supply water use 

was 1.32 Mgal/d in 1944, of which 1.2 Mgal/d was from the 

Sparta aquifer (Hale and others, 1947; Bakers and others, 

1948). Many rural domestic wells in Union County also were 

completed in the Sparta aquifer during the 1930s and 1940s, 

whereas most domestic wells previously had tapped the 

Cockfield aquifer (Baker and others, 1948; Broom and others, 

1984). The Sparta aquifer has been the sole public-supply 

source for El Dorado since the late 1940s (Bakers and others, 

1948). 

Magnolia (Columbia County) tapped the Sparta aquifer 

as early as 1928 (Hale and others, 1947). An oil discovery near 

Magnolia in 1938 caused population growth and increased 

groundwater withdrawals for public supply (Fancher and 

Mackay, 1946; Tait and others, 1953). Prior to the oil boom, 

Columbia County used 0.25 Mgal/d from the aquifer for 

all uses; in 1950, public-supply use had increased to about 

1.2 Mgal/d (Tait and others, 1953). A larger percentage of 

surface water has been consumed by Magnolia since Lake 

Columbia was constructed and connected to the town’s water 

supply in 1993; correspondingly, water use from the Sparta 

aquifer in Columbia County (table 24) decreased by almost 

Figure 46. Hydrograph showing water use in the Sparta aquifer from the city of El Dorado and Union County and water levels in the 

Monsanto well (location shown as well F on fig. 49) in the Sparta aquifer near El Dorado, Union County, Arkansas. 

-200 

-150 

-100 

-50 

0 

50 

0 

5 

10 

15 

20 

25 

1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 

Year

1970 1975 1980 1985 1990 1995 2000 2005 2010 

Groundwater use, in million gallons per day

Water level, in feet above National Geodetic Vertical Datum of 1929

Groundwater use

 El Dorado—Data from 

Baker and others (1948) 

and Baker (1955)

 Union County—Data from Halberg

and Stephens (1966); Halberg

(1972, 1977); Holland (1981, 1987,

1993, 1999, 2004, 2007)

Water level in well F (Monsanto

well in Union County),

completed in the 

Sparta aquifer 

EXPLANATION
Aquifers of the Coastal Plain 147

20 percent from 1990 (6.50 Mgal/d) to 1995 (5.24 Mgal/d) 

and further decreased to 2.90 Mgal/d by 2000 (Terrance W. 

Holland, U.S. Geological Survey, written commun., 2012). 

Total use of the aquifer has since risen to 9.41 Mgal/d in 2010, 

which corresponds with an increase in industrial use. Publicsupply withdrawals have remained between 0.5 Mgal/d and 

1.3 Mgal/d since 2000 (Terrance W. Holland, U.S. Geological 

Survey, written commun., 2012). 

The Sparta aquifer has many municipalities in other areas 

in southern Arkansas. Carthage, Fordyce (both Dallas County), 

and Rison (Cleveland County) were documented as using the 

aquifer in 1965 and continue, as of 2010, to draw from the 

aquifer (Plebuch and Hines, 1969). Albin (1964) reported that 

the Sparta aquifer at Camden (Ouachita County) was nearing 

maximum sustainable yield in the mid-1960s, but Camden 

now gets their water from the Ouachita River (Arkansas 

Department of Health, 2013). 

Public-supply use of the Sparta aquifer in eastern 

Arkansas is not as intensive as in central and southern 

Arkansas. In southeastern Arkansas, the Mississippi River 

Valley alluvial and Cockfield aquifers are the primary 

groundwater sources. Only Dermott in the most northwestern 

part of Chicot County pumps from the Sparta aquifer (fig. 43). 

Many smaller municipalities in Drew County completed 

wells in the Sparta aquifer in the 1930s and 1940s (Hale and 

others, 1947). Monticello, the largest user in Drew County, 

first tapped the Sparta aquifer in 1910 (Hale and others, 1947) 

and withdrew 2.28 Mgal/d from the aquifer in 2010 (Terrance 

W. Holland, U.S. Geological Survey, written commun., 2012). 

Winchester (Drew County) originally drew from the Cockfield 

aquifer but switched to the Sparta aquifer (Onellion, 1956). In 

northeastern Arkansas, there is less use of the Sparta aquifer 

as the Mississippi River Valley alluvial or Wilcox aquifers are 

viable water sources (Counts, 1957; Ryling 1960; Plebuch, 

1961; Halberg and Reed, 1964). In northeastern Arkansas, 

Jonesboro (Craighead County) is the largest city using the 

Sparta aquifer and withdrew 11.20 Mgal/d in 2010 (Terrance 

W. Holland, U.S. Geological Survey, written commun., 2012). 

Other cities using the Sparta aquifer in eastern Arkansas 

include Brinkley (Monroe County), Marianna (Lee County), 

Wynne (Cross County), and Helena (Phillips County).

Irrigation 

Rice farming began in the Grand Prairie region of 

Arkansas around 1905 (Engler and others, 1945; Sniegocki, 

1964; Gates, 2005). Rice yields were greatly improved by 

irrigation, and fields were initially irrigated with groundwater 

from the Mississippi River Valley alluvial aquifer. By 

1915, the Mississippi River Valley alluvial aquifer was 

being depleted faster than it was being recharged, and large 

water-level declines in the Mississippi River Valley alluvial 

aquifer were noticed in 1927 (Engler, 1963; see the section 

“Mississippi River Valley Alluvial Aquifer”). Development 

of the Sparta aquifer for irrigation supply consequently 

increased in areas where the Mississippi River Valley alluvial 

aquifer had been effectively dewatered. It is unknown when 

the Sparta aquifer first began to be used for irrigation supply, 

but Thompson (1936) noted about 10 irrigation wells, Engler 

and others (1945) documented 11 wells, and Sniegocki 

(1964) recorded 40 wells in the Sparta aquifer in the Grand 

Prairie region. As of 2010, 173 irrigation wells were reported 

as completed in the Sparta aquifer in Arkansas County and 

64 in Lonoke County (fig. 43). Drought in the early 1980s 

dramatically increased water use for irrigation (Mahon and 

Poynter, 1993). Use of the Sparta aquifer has increased over 

6,500 percent in Lonoke County and about 235 percent in 

Arkansas County from 1965 to 2010 (fig. 45; table 24). There 

is little irrigation use outside the Grand Prairie (fig. 43), 

although irrigation use has been increasing in Poinsett and 

Cross Counties. 

Many rice farmers inundate their fields in winter to 

provide habitat for migratory waterfowl. “Duck tours,” guided 

duck hunting trips, are a lucrative business in the Grand 

Prairie, and this practice can bring more income to farmers 

than their rice crops. Arkansas and Prairie Counties used 

water from the Sparta aquifer to flood agricultural fields for 

duck hunting in 2010 (fig. 43). Arkansas County withdrew 

1.02 Mgal/d in 2010, a decrease from 2.03 and 1.89 Mgal/d 

in 2000 and 2005, respectively (Terrance W. Holland, U.S. 

Geological Survey, written commun., 2012).

Industrial Use

Industrial use of the Sparta aquifer is primarily for oil 

and gas processing or development, chemical industry, and 

the lumber and paper industries. Sawmills scattered across 

southern Arkansas primarily tap this aquifer. Chemical and 

oil and gas companies are located in Columbia, Jefferson, 

Lafayette, and Union Counties. Most industrial use occurs in 

Jefferson and Union Counties; however, Broom and Lyford 

(1981) reported 11.6 Mgal/d of use in 1973 in northeastern 

Arkansas for combined public and industrial supply. Several 

oil fields were discovered in the 1920s and 1930s in southern 

Arkansas (Ragsdale, 2003). Water was intensively used in 

the development of the oil fields, and untold amounts of 

water were consumed for this use. The Cockfield aquifer 

was the primary source of water used near El Dorado for this 

purpose (Baker and others, 1948), while near Smackover 

(Union County), water was primarily from the Sparta aquifer 

(Baker and others, 1948). For refining and other processes, 

companies tapped the Sparta aquifer (Baker and others, 1948). 

One refinery pumped between 0.2 and 1.5 Mgal/d from the 

Cockfield aquifer from 1921 to 1935, when it began to draw 

from the Sparta aquifer (Baker and others, 1948). Refiners 

in Union County started withdrawing 0.4 Mgal/d in 1923 

and steadily increased to 0.7 Mgal/d in 1924, 1.1 Mgal/d in 

1926, 4.0 Mgal/d in 1938, and 5.0 Mgal/d in 1947 (Baker 

and others, 1948). The peak of the oil boom occurred in 1925 

and declined thereafter because of poor oil conservation and 

drilling practices (Ragsdale, 2003); consequently, water use in 

the oil fields waned after this time (Baker and others, 1948). 
148 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

A majority of water use from the Sparta aquifer in Union 

County was centered in El Dorado (fig. 46). As of 1953, 

water use from the Sparta aquifer had reached its safe yield 

of 15 Mgal/d near El Dorado (Baker and others 1948; Baker, 

1955). Use in Union County reached a high of 19.07 Mgal/d 

in 1965, declined through 1985, increased from 1985 to 2000, 

and decreased thereafter to 7.59 Mgal/d in 2010 (fig. 46; 

table 24). Industrial use in Union County was 3.98 Mgal/d 

in 2010 (Terrance W. Holland, U.S. Geological Survey, 

written commun., 2012). Decreases in use are attributed to the 

implementation of conservation measures and development of 

alternative water sources. To remove the critical groundwater 

area designation for the Sparta aquifer by the ANRC, further 

reduction in use is required to reach the sustainable yield goal 

of 5.9 Mgal/d (Hays, 1999) that will allow water levels of the 

Sparta aquifer to rise to the top of the formation. 

Just east of Magnolia (Columbia County), oil was 

discovered in 1938 (Fancher and Mackay, 1946), and many 

wells were drilled in the 1940s and 1950s to support oil 

production and refining (Tait and others, 1953). Unlike oil 

fields to the east in Union County that tapped the Cockfield 

aquifer, oil fields in Columbia County used water exclusively 

from the Sparta aquifer. Water use in Columbia County was 

estimated to have increased from 0.25 Mgal/d in 1928 to about 

0.60 Mgal/d in 1941 from the Sparta aquifer prior to intensive 

water use for oil development (Tait and others, 1953; Baker, 

1955). In 1950, after the oil boom had slowed and much 

infrastructure was in place for oil development, Magnolia 

used an estimated 2.7 Mgal/d (Tait and others, 1953). Tait 

and others (1953) suggested that 3 Mgal/d is the optimum 

withdrawal rate of the Sparta aquifer at Magnolia. Sparta 

water use in Columbia County increased from 0.33 Mgal/d in 

1950 to 3.03 Mgal/d in 1965 (fig. 47) and to 7.22 Mgal/d in 

1980 (table 24). 

Use of the Sparta aquifer in Columbia County decreased 

from 1985 through 2000 (fig. 47; table 24) resulting from 

completion of Lake Columbia as an alternative water source. 

There was a long-term overall increase of 211 percent from 

1965 to 2010 (fig. 45) as a result of increased industrial 

withdrawals in 2010. Industrial use of the Sparta aquifer 

in Columbia County increased 160 percent from 2005 to 

2010 (Terrance W. Holland, U.S. Geological Survey, written 

commun., 2012). Major industries in Columbia County 

currently include lumber, chemical, and steel companies. 

Figure 47. Hydrograph showing water use and water levels in well E (location shown on fig. 49) in the Sparta aquifer in Columbia 

County, Arkansas. 

-60 

-40 

-20 

0 

20 

40 

60 

80 

Water level, in feet above National Geodetic Vertical Datum of 1929

0 

2 

6 

10 

12 

4 

8 

Groundwater use, in million gallons per day

Year

1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 

Groundwater use (Columbia County) 

Water level in well E, completed in

the Sparta aquifer (Columbia

County) 

EXPLANATION
Aquifers of the Coastal Plain 149

Large water users in Jefferson County included paper 

mills, railroads, and food companies. Two paper mills 

constructed in the late 1950s in Pine Bluff began using the 

Sparta aquifer, which dramatically increased total water use 

with a combined use of 31.8 Mgal/d in 1958 (Bedinger and 

others, 1960) and 40 Mgal/d in the mid-1970s (U.S. Army 

Corps of Engineers, 1977). Since construction of these paper 

mills, industrial water use has grown at a more moderate 

pace (Kresse and Huetter, 1999). Industrial water use from 

the aquifer in Jefferson County has fluctuated between 25 

and 35 Mgal/d from 2000 to 2010 and was 31.79 Mgal/d in 

2010 (Terrance W. Holland, U.S. Geological Survey, written 

commun., 2012). 

Water Levels

Water-level declines in the Sparta aquifer are a major 

concern for users in Arkansas. Multiple studies have 

documented water-level trends in the Sparta aquifer (Bedinger 

and others, 1960; Albin and others, 1967b; Reed, 1972; 

Ryals, 1980; Edds and Fitzpatrick, 1984b, 1985, 1986, 1989; 

Ackerman, 1987b; Westerfield, 1995; Stanton, 1997; Joseph, 

1998a, 2000; Schrader, 2004, 2006b, 2008b, 2009, 2013; 

Schrader and Jones, 2007). Severe water-level declines were 

noted in southern and east-central Arkansas after development 

of the Sparta aquifer for primarily public and industrial uses 

in these areas, and overall declines since predevelopment 

are shown in figure 48. Selected potentiometric maps from 

predevelopment to 2009 are shown in figure 49, which 

provides a general overview of changing water levels over 

time. The 2009 potentiometric surface (fig. 49J) documented 

eight cones of depression in the Sparta aquifer (Schrader, 

2013). Major cones of depression occurred in (1) Pine 

Bluff (Jefferson County); (2) El Dorado (Union County); 

and (3) Magnolia (Columbia County) with minor cones in 

(4) Poinsett and Cross Counties, west of Crowleys Ridge; 

(5) northern Cleveland County; (6) northeastern Bradley 

County; (7) eastern Calhoun County; and (8) northern Ashley 

County. Declines also have been noted at Camden (Ouachita 

County) and West Memphis (Crittenden County) (Ackerman, 

1987b). 
Base from U.S. Geological Survey digital data, 1:100,000 Universal Transverse Mercator projection, zone 15 North American Datum of 1983 Data modified from Mahon and Poynter, 1993; T.P. Schrader, U.S. Geological Survey, written commun., 2013 YELL LEE UNION WHITE POLK POPE DREW PIKE SCOTT CLARK CLAY ASHLEY DESHA BENTON LOGAN SALINE IZARD PULASKI LONOKE ARKANSAS NEWTON GRANT CHICOT MADISON STONE MILLER SHARP CROSS DALLAS PRAIRIE BOONE PHILLIPS PERRYSEARCY MARION FULTON SEVIER MISSISSIPPI JEFFERSON NEVADA POINSETT GARLAND COLUMBIA BAXTER OUACHITA BRADLEY JOHNSON WASHINGTON MONROE GREENE JACKSON CARROLL HOWARD LINCOLN CALHOUN CONWAY FAULKNER VAN BUREN FRANKLIN CRAIGHEAD HEMPSTEAD RANDOLPH CLEBURNE MONTGOMERY LAWRENCEST. FRANCIS CRAWFORD CLEVELAND HOT SPRING INDEPENDENCE LITTLE RIVER WOODRUFF CRITTENDEN LAFAYETTE SEBASTIAN 94° 92° 91° 93° 90° 36°35° 34° 

E

0 15 30 0 30 6

15 

45 A. Predevelopment to 2011 B. 2003 to 2011 UNION COUNTY 0 

0 

E

ARKANSAS UNION COUNTY

Figure 48. A, change in water levels for the Sparta aquifer in Arkansas from predevelopment to 2011; B, change in water levels for the Sparta aquife

to 2011.
Potentiometric contours modified from Albin and others, 1967b; Reed

Base from U.S. Geological Survey digital data, 1:2,000,000Universal Transverse Mercator projection, zone 15North American Datum of 1983 

35°

34°

92°

94°

93°

80

100 60

60

40

20

60

80

100

140

140

160

240

40

180

200

220

0

-160

280

240

220

180

140

60

100

80

20

20

60

40

-60

-20

-40

40

0

-100

200

240

160

120

240

220

100

80

-160

-80

-20

A. Predevelopment

B. 1965

35°

34°

36°

92°

91°

90°

94°

93°

100

240

120

140

160

180

200

220

260

200

220

280

240

240

220

200

160

180

Crowleys RidgeExtent of Sparta aquifer (Clark and Hart, 2009)Inset area boundary

C

EXPLANATION

251 to 300

201 to 250

151 to 200

101 to 150

51 to 100

1 to 50

-49 to 0

Well used for control—Letter indicates hy figures 46, 47, 50, and 51

280 Potentiometric contour—Shows altitude a

 in tightly cased wells. Dashed where ap 20 feet. Datum is National Geodetic Vert

80 KILOMETERS

200 40 60 80 MILES

40 60200

UNION

LEE

CLAY

ASHLEY

DESHA

MILLER

SALINE

GRANT ARKANSAS

LONOKE

CHICOT

DALLAS

PRAIRIE

PHILLIPS

JEFFERSON

BRADLEY

MISSISSIPPI

OUACHITA

MONROE

COLUMBIA

NEVADA

LINCOLN

JACKSON

CALHOUN

WOODRUFF

CRITTENDEN

CLEVELAND

ST FRANCIS

LAFAYETTE

HOT SPRING

GREENE

CRAIGHEAD

PULASKI

CROSS

DREW

POINSETT

35°

34°

36°

94° 93° 92° 91°

90°

Saline River

Ouachita Ri ver

Mississippi River

Arkansas River

White River

Lake

Columbia

Missouri River

Little

Saline River

Ouachita Ri ver

Mississippi River

Arkansas River

White River

Lake

Columbia

Jonesboro

West Memphis

Stuttgart

Pine Bluff

El Dorado

Magnolia

Camden

Lonoke

Jonesboro

West Memphis

Stuttgart

Pine Bluff

El Dorado

Magnolia

Camden

Lonoke

F E

D

C

A

B

F E

D

C

A

B

Figure 49. Selected potentiometric contours of water levels in the Sparta aquifer in Arkansas.
Extent of Sparta aquifer (Clark and Hart, 2009) Inset area boundary EXPLANATION

401 to 450

351 to 400

301 to 350

251 to 300

201 to 250

151 to 200

101 to 150

51 to 100

1 to 50

-49 to 0

-99 to -50

-149 to -100

-199 to -150

60 Potentiometric contour—Shows altitude at which water level would have stood in tightly 

 cased wells. Dashed where approximately located. Contour interval 20 and 40 feet. Datum is National Geodetic Vertical Datum of 1929 (NGVD 29)

Potentiometric contours modified from Ackerman, 

Edds and Fitzpatric

Base from U.S. Geological Survey digital data, 1:2,000,000Universal Transverse Mercator projection, zone 15North American Datum of 1983 

200 40 

40 60200

C. 1980 D. 1986

220

260

280

80

60

40

20

-20

0

-160

60

-60

-20

140

100

120

140

180

-100

-120

-806

0

180

100

80

220

220

80

-140

-40

0

40

160

80

240

35°

34°

36°

92°

91°

90°

94°

93°

220

280

220

260

260

180

160

100

280

220

80

60

40

-20

20

0

-160

40

60

-60

60

-20

140

200

100

240

120

340

160

140

120

180

220

200

180

200

300

80

260

260

420

Area enlarged

ARKANSAS

Inset

220

180140

60

100 80

20

20

60

40

-60

-20

-40

40

0

200

160

120

240

220

100

80

-160

-80

-20

140

240

2

260

280

200

180

160

120

-100

-120

-140

35°

34°

92°

94°

93°

80

60

60

40 20

60

100

140

140

160

40

180

200

220

0

280 -160

440

300

40 20

-20

40

0

220

-60

Figure 49. Selected potentiometric contours of water levels in the Sparta aquifer in Arkansas.—Continued
Extent of Sparta aquifer (Clark and Hart, 2009) Inset area boundary EXPLANATION 100

301 to 350

251 to 300

201 to 250

151 to 200

101 to 150

51 to 100

1 to 50

-49 to 0

-99 to -50

-149 to -100

-199 to -150

180 Potentiometric contour—Shows altitude at which water level would have stood in

 tightly cased wells. Dashed where approximately located. Contour intervals 20  and 25 feet. Datum is National Geodetic Vertical Datum of 1929 (NGVD 29)

Base from U.S. Geological Survey digital data, 1:2,000,000 Potentiometric contours modified from Westerfield, 1995; JosephUniversal Transverse Mercator projection, zone 15North American Datum of 1983 

8

200 40 

40 60200

220

80

60

40

20

-20

0

-160

-60

60

-20

140

120

100

140

-100

-120 -806

0

180

100

80

220

80

-140

-40

0

40

160

40

20

100

120

160

240

-180

200

200

35°

34°

36°

92°

91°

90°

94°

93°

220

220 260

180

160

100

80

60

40

20

-20

0

40

60

-60

60

-20

140

200

120

100

240

160

140

120

200

180

200

300

80

60

240

20

60

60

120

-180

0

0

-50

-150

-175

-100

-125

-75

25

50

75

100

50

100

125

150 175

200

275

250

300

175

150

200

50

75

225

35°

34°

92°

94°

93°

100

200

250

325

175

-25

-50

0

25

50

75

100 125

150

225

275

300

250

275 300

225

-175

-25

25

0

0

50

50

75

1

50

75

E. 1993 F. 1997

Area enlarged

ARKANSAS

Inset

Figure 49. Selected potentiometric contours of water levels in the Sparta aquifer in Arkansas.—Continued
Extent of Sparta aquifer (Clark and Hart, 2009) Inset area boundary 180 EXPLANATION

301 to 350

251 to 300

201 to 250

151 to 200

101 to 150

51 to 100

1 to 50

-49 to 0

-99 to -50

-149 to -100

-199 to -150

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 (NGVD 29)

Base from U.S. Geological Survey digital data, 1:2,000,000 Potentiometric contours modified from Schrader, 2004Universal Transverse Mercator projection, zone 15North American Datum of 1983 

200 40 

40 60200

220

80

60

40

20

-20

0

-160

-60

140

60

100 120

140

-100

-120

-806

0

180

100

80

220

-140

-40

0

40

160

40

20

120

160

240

-180

200

200

-20

0

60

240

160

260

100

-806

35°

34°

36°

92°

91°

90°

94°

93°

220

220

260

180

160

100

80

40

20

-20

0

40

60

-60

60

-20

140

200

120

100

160

140

120

200

180

200

80

60

240

20

60

-180

-80

80

180

160

200

300

320

220

260 240 300

160

40

240

0

-20

140

240

220

80

120

300

260

220

180

140

60

0

80

100

20

20

60

180

200

-180 -140

-160

60

40

40

2

20

-60

-20

-40

40

80

0

-80

-100

-120

280

200

240

160

120 260

200

60

35°

34°

92°

94°

93°

320

300

80

10060 6

40

40

20

60

8

100

-80

-180

0

20

18

-80

300

240

40 220

180

220

200

G. 2001 H. 2003

Area enlarged

ARKANSAS

Inset

Figure 49. Selected potentiometric contours of water levels in the Sparta aquifer in Arkansas.—Continued
Extent of Sparta aquifer (Clark and Hart, 2009) Inset area boundary 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 (NGVD 29) 240 EXPLANATION

301 to 350

251 to 300

201 to 250

151 to 200

101 to 150

51 to 100

1 to 50

-49 to 0

-99 to -50

-149 to -100

Base from U.S. Geological Survey digital data, 1:2,000,000 Potentiometric contours modified from Schrader 200Universal Transverse Mercator projection, zone 15North American Datum of 1983 

200 40 

40 60200

35°

34°

36°

92°

91°

90°

94°

93°

320

300

80

100

60

60

40

40

20

60

80

100

-80

-140

0

20

120

140

140

180

160

160

-80

300

240

220

40

200

220

180

200

220

40

40

60

220 240

200

240

120

140

240

220

240

160

260

180

220

180

140

60

0

80

100

20

20

60

200

-160

-140

20

40

40

20

20

-60

-20

-40

40

-80

80

0

-100

-120

0

200

240

160 120

220

160

100

120

-20

140

220

180

140

60

0

80

100

20

20

60

200

-140

40

40

20

-60

-20

-40

40

-80

80

0

-100

-120

0

200

240

160 120

160

100

120

-20

140

240

260

100

60

-100

80

20

40

320

80

100

60

60

40

40

20

60

8

100

-80

-140

0

20

240

40

220

180

220

200

40

40

60

240

200

240

120

140

80

300

260

-60

-20

-40

0

40

I. 2007

J. 2009

Area enlarged

ARKANSAS

Inset

Figure 49. Selected potentiometric contours of water levels in the Sparta aquifer in Arkansas.—Continued
156 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Northeastern Arkansas

The first cone of depression in the potentiometric surface 

of the Sparta aquifer in the southwestern corner of Poinsett 

County in northeastern Arkansas was first depicted in the 

1995 surface with the contour at 150 ft above NGVD 29 (not 

shown on fig. 49; Stanton, 1997). The 1996–97 potentiometric 

surface of the Sparta aquifer illustrated that the 150-ft contour 

had enlarged from the southwestern corner of Poinsett County 

to central Poinsett County (fig. 49F; Joseph, 1998a). In the 

2001 surface, the cone of depression at the 140-ft contour had 

elongated south into Cross County (fig. 49G; Schrader, 2004). 

However the surfaces for 2003 (fig. 49H), 2005 (not shown on 

fig. 49; Schrader and Jones, 2007), and 2007 (fig. 49I) depict 

the cone of depression at the 140-ft NGVD contour primarily 

in western Poinsett County and only extending into Cross 

County beginning in 2005 (Schrader, 2006b, 2009; Schrader 

and Jones, 2007). In 2009, the 140-ft contour covered a large 

part of western Cross County (fig. 49J). While irrigation 

pumping from the Sparta aquifer increased in these counties 

throughout this time period (table 24), increased use may not 

be the sole cause of an enlarged cone of depression (Schrader, 

2008b, 2013). Hydrologic connection and transfer of water 

from the Sparta aquifer to the highly stressed Mississippi 

River Valley alluvial aquifer also may have exacerbated waterlevel declines in Cross and Poinsett Counties west of Crowleys 

Ridge. Support for this hypothesis is that water levels in two 

wells in the Sparta aquifer mirror those in a nearby well in the 

Mississippi River Valley alluvial aquifer (fig. 50). 

Another depression in the Sparta potentiometric surface 

has been noted in Crittenden County, near the Memphis, 

Tenn., metropolitan area (Schrader, 2008b). The depression 

from Memphis extends into the eastern part of Crittenden 

1957 1962 1967 1972 1977 1982 1987 1992 1997 2002 2007

Year

Water level, in feet above National Geodetic Vertical Datum of 1929

120

130

140

150

160

170

180

190

200

Water level, in well completed

 in the Mississippi River

 Valley alluvial aquifer

Water level, in well completed

in the Sparta aquifer

 Well A (Poinsett County)

 Well B (Poinsett County)

EXPLANATION

ARKANSAS

POINSETT COUNTY

Sparta aquifer well B

Sparta aquifer well A

Mississippi River Valley

alluival aquifer well

POINSETT COUNTY

8.9 miles 6.7 miles

Figure 50. Hydrographs showing water levels in wells A and B in the Sparta aquifer (locations of wells shown on fig. 49) and water 

levels in a well in the Mississippi River Valley alluvial aquifer in Poinsett County, Arkansas.
Aquifers of the Coastal Plain 157

County, and includes West Memphis, Ark. Intensive pumping 

at Memphis has resulted in considerable water-level declines 

in Arkansas of approximately 50 ft from predevelopment to 

2011 (fig. 48; Schrader, 2009). The depression extended from 

Memphis to just east of West Memphis in the 2003, 2005, 

and 2007 surfaces (Schrader, 2006b, 2008b, 2009; Schrader 

and Jones, 2007). Plebuch (1961) also recorded water-level 

declines of 28 ft from 1934 to 1958 at West Memphis. 

Grand Prairie and Jefferson County

Water-level declines in the Sparta aquifer were first 

observed at Pine Bluff (Jefferson County) around the turn 

of the 20th century (Veatch, 1906; figs. 48 and 49). Veatch 

(1906) described a Pine Bluff well in which the water level 

dropped 15 ft from 1899 to 1900. The water level in another 

well at Pine Bluff dropped 35 ft from 1899 to 1949 (Klein and 

others, 1950). Other water levels in wells at Pine Bluff fell 

16 ft in 7 years during a period of increased use in the 1940s 

(Klein and others, 1950). In 1958, after a year of substantial 

increase in use (approximately 37 Mgal/d) at two paper mills, 

a decline of 115 ft was observed in a well near the center of 

the pumping from April 1958 to May 1959 (Bedinger and 

others, 1960). Water-level declines at well D near Pine Bluff 

(fig. 51; location of well shown in fig. 49) were directly related 

to increases in water use in Jefferson County. A similar decline 

was observed in well D; water levels fell approximately 170 ft 

from the early 1950s to 1975 (fig. 51). Although there was 

a large increase in water use from 1995 to 2000, this was 

because of changes in reporting; water levels were stable from 

1999 to 2001. Corresponding to decreased water use from 

2000 to 2010, water-level rises of approximately 5 ft were 

recorded in Jefferson County between 2005 and 2007 (fig. 51; 

Schrader, 2009).

Year

194019451950195519601965197019751980198519901995200020052010

Water level, in feet above National Geodetic Vertical Datum of 1929

-100

-50

0

50

100

150

200

Groundwater use, in million gallons per day

0

10

20

30

40

50

60

70

80

90

100

Groundwater use

 Arkansas County

 Jefferson County

Water level in well, completed

 in the Sparta aquifer

 Well C (Arkansas County)

 Well D (Jefferson County)

EXPLANATION

Figure 51. Hydrographs showing water use and water levels in wells C and D (locations of wells shown on fig. 49) in the Sparta aquifer 

in Arkansas and Jefferson Counties, Arkansas.
158 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

In the mid-20th century, large industrial withdrawals 

and seasonal irrigation use began in Jefferson County, which 

put further demand on the aquifer. The 1959 potentiometric 

contours of the Sparta aquifer showed a cone of depression 

at the 40-ft contour around Pine Bluff (Bedinger and others, 

1960). By the 1980s, the center of the cone of depression 

had shifted to the east of Pine Bluff, where many industrial 

users were located (Edds and Fitzpatrick, 1984b, 1985, 1986; 

Ackerman, 1987b). The 1993 surface (fig. 49E) revealed the 

center of the cone of depression had dropped to the -60-

ft contour (Westerfield, 1995); the 2001, 2003, and 2005 

surfaces showed the center of the cone of depression at the 

-80-ft contour (Schrader, 2004, 2006b; Schrader and Jones, 

2007). Rises in the potentiometric surface were seen in the 

2007 and 2009 surfaces (Schrader, 2009, 2013).

The cone of depression centered near Pine Bluff 

encroached into Arkansas County as irrigation wells were 

drilled to the Sparta aquifer. In Arkansas County, water 

levels in the Sparta aquifer have fallen over 150 ft since the 

late 1930s (T.P. Schrader, U.S. Geological Survey, written 

commun., 2012). Water levels in well C fell 110 ft from 1951 

to 2001 but rebounded from 2001 to 2005 in conjunction 

with decreased pumping in 2000 and 2005 (fig. 51; location 

of well shown in fig. 49). 

The 1980 potentiometric surface of the Sparta aquifer 

revealed expansion of the cone of depression at the 60-ft 

contour from Jefferson County into Arkansas County 

(fig. 49C) (Ackerman, 1987b). By 2001, the closed 60-ft 

contour encompassed all or parts of Jefferson, Lonoke, 

Prairie, Arkansas, Lincoln, and Drew Counties (Schrader, 

2004) (fig. 49G). The 2007 potentiometric surface (fig. 49I) 

showed western Arkansas County circumscribed by the 

depression with closure at the 40-ft contour (Schrader, 2009). 

Lincoln County had two smaller cones of depression with 

closure at the 40-ft contour (fig. 49I). Also, as early as the 

mid-1950s, Onellion (1956) hypothesized that water levels 

had declined in Drew County because of changes in water 

pressure, but water levels were not recorded at that time. 

Water levels of the Sparta aquifer have declined in 

central Arkansas. Artificial-recharge approaches have been 

evaluated for alleviation of water-level declines in the 

Mississippi River Valley alluvial and the Sparta aquifers 

(Crider, 1906; Sniegocki, 1953, 1963a, b; Steinbrugge and 

others, 1954; Engler and others, 1963; Sniegocki and Reed, 

1963; Sniegocki and others, 1963, 1965; Signor and others, 

1970; Fitzpatrick, 1990; Hays, 2001) but generally have 

not been initiated because economic considerations have 

not supported artificial recharge. Surface-water diversions 

are planned for the White and Arkansas Rivers to provide 

irrigation water and thus decrease dependence on the 

Mississippi River Valley alluvial and Sparta aquifers (see 

section “Mississippi River Valley Alluvial Aquifer”; U.S. 

Army Corps of Engineers, 2007, 2013b).

Southern Arkansas

Smaller cones of depression in the Sparta aquifer have 

developed in northern Ashley County, northeastern Bradley 

County, eastern and southern Calhoun County, northcentral 

Cleveland County, and eastern Ouachita County (fig. 49; 

Schrader, 2013). A depression in eastern Cleveland County 

appeared only in the 1993 surface (fig. 49E). The depression 

in north-central Cleveland County was first noted in 2003 

(fig. 49H; Schrader, 2006b) and has since deepened (figs. 49I

and 49J; Schrader, 2013). The depression in Calhoun County 

was first identified in the 1996–97 surface (fig. 49F; Joseph, 

1998a) and had expanded and deepened in the following 

surfaces from 1999 through 2009 (figs. 49G–J; 1999 surface not 

shown in fig. 49; Joseph, 2000). A second cone of depression 

in Calhoun County developed to the south of the original 

cone in 2003 (fig. 49H), and was seen in subsequent surfaces 

(figs. 49I and 49J). In 1997 (fig. 49F) and 1999 (not shown on 

fig. 49), a cone of depression was noted in northeastern Bradley 

County at the 25-ft contour. It was not seen in either the 2001 

or 2003 surfaces, but the 2007 surface (figs. 49I) showed the 

cone expanded at the 40-ft contour to also include Drew and 

northwestern Ashley Counties. By 2009 (fig. 49J), the cone 

had contracted back into mostly Bradley County and had 

reduced again in size in the 2011 surface (not shown on fig. 49; 

Schrader, 2014). Lower water levels in the Sparta aquifer in 

eastern Ouachita County have centered around the city of 

Camden. While the impact of pumping was seen in all surfaces 

around Camden since 1965 (figs. 49B–J), a cone of depression 

was seen in 1986 (fig. 49D) and again in 1997 (fig. 49F).

Heavy pumping for industrial and public supply lowered 

water levels at Magnolia (Columbia County). Early industrial 

development for paper and lumber increased water use tenfold 

from 1928 to 1950, and water levels declined 75 ft over that 

time (Tait and others, 1953; Baker, 1955). Water levels at 

Magnolia declined from when measurements began in the 

1940s through the 1990s (fig. 47). Water levels in Columbia 

County declined an average of 3.0 ft/yr from 1969 to 1995 

(Joseph, 2000). A cone of depression in the Sparta aquifer 

had formed beneath Magnolia and expanded to coalesce 

with the cone of depression in Union County when the first 

potentiometric surface was created for 1965 (fig. 49B). Depths 

in well E (fig. 47; location of well shown in fig. 49) declined 

from the 1940s through the 1980s, reaching a minimum 

altitude of -36.8 ft in 1986. Construction of Lake Columbia and 

installation of a surface-water supply system in 1993 resulted 

in decreased withdrawals from the Sparta aquifer, resulting in 

a much smaller size of the cone of depression centered beneath 

Magnolia (Hays and others, 1998). With diminishment of the 

cone between 1993 and 2007 (figs. 49E–I), water levels in 

well E rose 64.8 to 28.3 ft by 2010 (fig. 47; location of well 

in fig. 49). However, recent increased industrial usage of the 

Sparta aquifer in Columbia County threatens further waterlevel recovery. From 2007 to 2009, water levels in the aquifer 

declined in the county and the center of the cone of depression 

deepened from the 20-ft to 0-ft contour (figs. 49I and J). 
Aquifers of the Coastal Plain 159

In the El Dorado (Union County) area, water levels for 

the Sparta aquifer dropped 240 ft from 1922 to 1953, while 

water use over that same period increased from less than 

1 Mgal/d to 15 Mgal/d (Baker, 1955). Industrialization began 

in earnest following World War II, and dramatic water-level 

declines were noted throughout the Sparta aquifer in this area 

(fig. 46; Johnson, 2004). Water levels for the Sparta aquifer 

dropped steadily as water use increased. As of 1964, water 

levels near El Dorado were declining about 12.5 ft/yr (Albin, 

1964). Decline of the Sparta aquifer at El Dorado was first 

noticed in the 1965 potentiometric surface (Albin and others, 

1967b); the cone of depression in Union County deepened and 

expanded through 2003 (figs. 49B–H). Maximum drawdown 

in the El Dorado area exceeded 360 ft in 1993 relative to water 

levels in about 1920, when development first began in the 

area. Water levels in Union County in the mid-1990s had been 

declining at rates more than 1 ft/yr for over a decade (Hays 

and others, 1998), and saltwater intrusion caused by intensive 

pumping increased near the cone of depression (Broom and 

others, 1984). Simulated results (Hays and others, 1998) 

indicated that if pumping rates from the 1990s continued to 

2027, water levels would approach or fall below the top of the 

Sparta aquifer at the major pumping centers in Arkansas and 

Louisiana. 

In 1996, the Sparta aquifer was declared a critical 

groundwater area by ANRC in Bradley, Calhoun, Columbia, 

Ouachita, and Union Counties. In the late 1990s, Federal, 

State, and local agencies, industries, and citizens implemented 

conservation measures and alternative source development 

efforts aimed at raising the Sparta aquifer water levels. 

The Union County Water Conservation Board (UCWCB) 

was formed and approved by ANRC in 1999. In an effort 

to conserve water levels in the aquifer, UCWCB instituted 

several water conservation measures, including (1) public 

education about water conservation practices, (2) industrial 

water reuse and sharing, and (3) reuse of reclaimed treated 

wastewater at local golf courses (Johnson, 2004). 

In addition, a temporary 1-cent sales tax was adopted 

in 2002 by the citizens of Union County to help pay for a 

pumping facility on the Ouachita River as an alternative water 

source to local industry. This funding, in combination with a 

grant from the EPA, was used to construct a pumping station 

and pipeline from the Ouachita River to major industrial 

groundwater users in the El Dorado area. The river intake, 

pumping facility, and 5 miles of a 48-inch pipeline were 

completed in 2004. The facility is capable of producing 

10 Mgal/d and could expand to produce another 19 Mgal/d 

(Johnson, 2004). Lion Oil began using the water from the 

Ouachita River in December 2004, El Dorado Chemical 

converted in February 2005, and Chemtura (Formerly 

Great Lakes Chemical) in October 2005; Pilgrim’s Pride 

ceased operations in 2009. The funding also allowed for the 

installation of eight real-time water-level monitors (Scheiderer 

and Freiwald, 2006). These monitors were installed in 2003 

in six existing and two new wells (fig. 52). More information 

on data collected from these monitors can be found on the 

UCWCB Website (http://www.ucwcb.org/). As a result, wells 

in Union County were the first to show a rise in water levels in 

Arkansas since 2003 (Schrader, 2009).

Based on model simulations of sustainable yield for the 

Sparta aquifer in Union County, withdrawals would need to 

be reduced to 28 percent of the 1997 use levels from around 

20 Mgal/d to approximately 6 Mgal/d in order to bring water 

levels up to the top of the Sparta Sand (Hays, 2000). After 

the conversion of three main industrial users to the Ouachita 

River, industrial users used 4.8 Mgal/d of Ouachita River 

water in 2005 (Freiwald and Johnson, 2007). Industrial 

and public supply water use decreased 80 and 50 percent, 

respectively, from 2000 to 2010 (Terrance W. Holland, 

U.S. Geological Survey, written commun., 2012). Overall 

groundwater withdrawals in Union County were reduced by 

an estimated 7.5 Mgal/d (Freiwald and Johnson, 2007). These 

voluntary conservation measures were estimated to have 

decreased overall groundwater use 15 to 20 percent in Union 

County (Union County Water Conservation Board, 2007).

The cone of depression in the Sparta aquifer in Union 

County was projected to coalesce with other cones of 

depression in Columbia County and northern Louisiana 

Parishes; however, the efforts undertaken to reduce 

groundwater use led to rising water levels (figs. 46–48, and 

53) and a smaller cone of depression from 2004 to present 

(2013) (figs. 49I and J; Schrader, 2014). In the 2009 surface, 

the center of the cone of depression was enclosed at the 

-40-ft contour (fig. 49J), which represents a rise from the 

deepest -200-ft contour in the 1999 surface (Joseph, 2000). 

The area which the cone of depression at the -60-ft contour 

encompassed also was reduced 41 percent in size from 

1993 to 2011 (Schrader, 2014). Increases in water levels 

in individual wells ranged from 0.5 to 60.2 ft across Union 

County (Schrader, 2013), although some seasonal fluctuations 

were observed (fig. 53). Water levels in the Monsanto, Airport 

El Dorado, and Welcome Center wells had risen after the 

implementation of the conservation measures outlined above 

(fig. 53). Directly after the Lion Oil (2004) and El Dorado 

Chemical (2005) conversions to surface water, water-level 

rises of about 30 ft were noted in the Monsanto well by late 

2005 (fig. 53). After the Chemtura (2006) conversion, rises 

were seen in multiple wells. Additional rises were noted after 

Pilgrim’s Pride ceased operation in 2009 (fig. 53). 
OUACHITA NEVADA CALHOUN BRADLEY UNION CLAIBORNE UNION LINCOLN WEBSTER ASHLEY MOREHOUSE DREW COLUMBIA Shumaker Union School Marysville Airport El DoradoMonsanto Welcome Center Lawson-Urbana Hampton Warren Camden Homer Bastrop Strong Stephens Hilo Truxno El Dorado #8 El Dorado #17 Junction City D'Arbonne Farmerville Spencer Huttig Magnolia Emerson Smackover Harrell LOUISIANA ARKANSAS 0 5 

0 1

5 

U.S. Geo

real

Union C

auto

El Dorad

mon

U.S. Geo

mon

EXPLA

33° 30' 93° 92° 33° 00' 

Base from U.S. Geological Survey digital data Data modified from Freiwald and Johnson, 2007

Figure 52. Location of water-level and water-quality monitoring wells in the Sparta aquifer of southern Arkansas and northern Louisiana.
Aquifers of the Coastal Plain 161

Deductive Analyses, Projections of Aquifer 

Conditions, and Sustainable Use

Groundwater often is overlooked by water managers, 

in part, because groundwater cannot be directly observed. 

Another consequence of the hidden nature of groundwater 

is that the collection of information and development of 

a competent understanding of groundwater behavior is 

challenging. This is partly the result of the expansive scale 

of groundwater flow and the fact that groundwater moves 

very slowly in most systems. Consequently, understanding 

groundwater flow necessitates the development and use of 

approaches that are somewhat different than those applied to 

surface water. Important questions that groundwater managers 

and groundwater scientists may pose include: How much 

water is stored in a given aquifer? At what rate can water be 

produced? Where does groundwater flow, what are the sources 

and outlets? What is a sustainable long-term yield? How long 

will the aquifer produce water if pumping rate is exceeded? 

How will aquifer yields and groundwater flow paths be 

affected by naturally or human-induced changes? These and 

other more specific questions can be effectively addressed by 

digital simulations of aquifers using groundwater-flow models. 

Groundwater-flow models simulate the physical aquifer 

system and hydrologic processes affecting groundwater 

flow using a set of governing equations. Construction of a 

groundwater-flow model is time-consuming, labor-intensive, 

data-intensive, and expensive; however, the utility of 

groundwater-flow models in understanding and simulating 

groundwater behavior has made them a tool of great value. 

Thus, the tremendous investments that have been made in 

developing and maintaining groundwater models in Arkansas 

are warranted for purposes of effective water management. 

Long-term water-level declines and imminent problems 

associated with the extensive development of groundwater as a 

resource led to development of a regional analog groundwaterflow model of the Sparta aquifer in the late 1960s (Reed, 

1972). The model was used to simulate the effects of potential 

increases in groundwater withdrawals. Reed (1972) simulated 

the period from 1966 to 1990, incorporating a simulated 

2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

Year

Water level, in feet below land surface

100

150

200

250

300

350

400

Industrial change in groundwater use

Water level, by well completed in the Sparta aquifer

 Smackover

 Magnolia

 Union School

Monsanto

Airport

Welcome Center

EXPLANATION

Lion Oil conversion

El Dorado Chemical conversion

Chemtura conversion 

Pilgrim's Pride ceased operations 

Figure 53. Hydrographs showing effects of change in industrial groundwater use on water levels in wells (location of wells shown in 

fig. 52) completed in the Sparta aquifer in southern Arkansas.
162 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

average increase in pumpage of 80 percent; a value based on 

then-current estimates of water-use increase rates (fig. 54). The 

model results indicated that by 1990 approximately 10 percent 

of the projected pumpage would be supplied from storage 

with the remainder from recharge or stream capture. The 

model projected water-level declines of approximately 170 ft 

at El Dorado, 130 ft at Pine Bluff, and 40 ft at West Memphis 

over the simulation period from 1966 to 1990. These model 

results indicated that projected withdrawal rates in several 

areas would not be sustainable for the long term. Another 

notable projection from this early model was that water levels 

would decline below the top of the aquifer in some areas, 

including the area of El Dorado. 

The City of Memphis, Tenn., depends upon the Sparta 

aquifer as a source of public-supply water, and withdrawals 

increased from 200 to more than 250 Mgal/d from 1985 to 

2005 (Robinson and Brooks, 2010). The Memphis pumping 

center is in hydraulic connection with the Sparta aquifer 

across the border in Arkansas. ANRC and other water planners 

and managers in Arkansas have tracked declines caused by 

pumping at Memphis (Edds and Kilpatrick, 1985; Joseph, 

1998a; Schrader, 2009) and have considered implications for 

Arkansas groundwater users. The USGS conducted a series 

of studies in the 1980s to better understand the groundwater 

flow in the Memphis and West Memphis area. These studies 

included development of groundwater-flow models for 

simulation of the Sparta aquifer (termed Memphis aquifer 

in reports) and other major aquifers in the Memphis area 

(Brahana, 1982; Brahana and Broshears, 1989). Brahana 

(1982) developed a two-dimensional digital-flow model of 

the Sparta aquifer and used it to estimate aquifer response 

to hypothetical pumpage projections. An improved threelayer, digital-flow model was then constructed to simulate 

the regional flow system in the Memphis area (fig 54; 

Brahana and Broshears, 1989). Model results determined that 

pumping during the time of their study accounted for almost 

all discharge from the Memphis aquifer. Model simulations 

indicated that lateral inflow, including flow from Arkansas to 

the west, replaced 42 percent of pumped water. Simulations 

indicated that continued pumping at the Memphis pumping 

center would result in expanding water-level declines in 

Arkansas. 

Understanding of conditions in the Sparta aquifer in 

Arkansas was advanced by modeling conducted as part of the 

USGS Gulf Coast RASA model investigation (Williamson and 

others, 1990), which covered 290,000 mi2

 across Alabama, 

Arkansas, Florida, Illinois, Kentucky, Mississippi, Missouri, 

Tennessee, Texas, and all of Louisiana (fig. 54). An important 

subproject of the larger national effort was the Mississippi 

embayment aquifer system study (Arthur and Taylor, 1990, 

1998; fig. 54), which was described as comprising five major 

aquifers and two confining units in the Tertiary System Wilcox 

and Claiborne Groups: (1) upper Claiborne aquifer, (2) middle 

Claiborne confining unit, (3) middle Claiborne aquifer that 

comprises the Sparta Sand in most of Arkansas and includes 

the upper part of the Memphis Sand in east-central Arkansas, 

(4) lower Claiborne confining unit, (5) lower Claiborne-upper 

Wilcox aquifer, (6) middle Wilcox aquifer and, (7) lower 

Wilcox aquifer. 

A digital groundwater-flow model was developed to 

represent the aquifer system using five layers representing 

the five major aquifers (Arthur and Taylor, 1990, 1998). 

Model results showed that flow in the Mississippi embayment 

aquifer system generally moves downdip from the outcrop 

areas and then upward through the confining units as flow 

paths approach the Mississippi embayment axis. Shorter flow 

paths occur near outcrop areas where the shallow water table 

intersects land surface. Model results generally indicated 

that groundwater leakage through confining layers between 

adjacent aquifers was less than 0.1 in/yr. A notable exception 

is the heavily pumped Memphis area where as much as 4.0 in/

yr moves from the upper Claiborne aquifer down to the 

middle Claiborne/Sparta aquifer. Arthur and Taylor (1990, 

1998) noted that simulated water-level declines were greater 

in the middle Claiborne/Sparta aquifer than in any of the 

other aquifers in the Mississippi embayment aquifer system 

because of pumping stress. Consequently, flow from adjacent 

units in the subcrop areas generally was into the middle 

Claiborne aquifer. Comparison of the predevelopment and 

1987 groundwater-flow model budgets indicated that 1985 

pumpage from the five major aquifers was predominantly 

from: (1) increased recharge in the outcrop areas of the 

upper Claiborne and Sparta aquifers and (2) reduction of 

discharge from those two aquifers to the Mississippi River 

Valley alluvial aquifer (Arthur and Taylor, 1990, 1998). The 

total contribution from aquifer storage was relatively small. 

Arthur and Taylor (1998) determined that the five aquifers 

had potential for additional groundwater development. The 

middle Claiborne aquifer exhibited the greatest potential for 

additional development, but simulation results showed that a 

20-percent increase in pumping relative to 1985 rates would 

produce substantial water-level declines by 2000. This is about 

30 ft below 1987 levels in the Sparta aquifer at El Dorado and 

about 20 ft after 13 years at Pine Bluff. These results indicated 

that the simulated withdrawal rates were, in some areas, not 

sustainable for the long term. Several of the embayment 

models referenced herein were derived from or benefitted in 

some fashion from this RASA model. 

Extensive use of the Sparta aquifer in southern Arkansas, 

particularly in Union and Columbia Counties, resulted in 

withdrawals that substantially exceeded recharge. Water 

levels were documented as declining at rates more than 

1 ft/yr through the 1980s and 1990s (Joseph, 2000). Regional 

cones of depression centered on El Dorado and Monroe, La., 

coalesced by 1990 (Joseph, 1998a, 2000). As water levels 

began to drop below the top of the formation, water users 

and managers began to question the ability of the aquifer 

to supply water for the long term and began to evaluate 

management approaches to protect the aquifer. Groundwaterflow models were and are an important part of the aquifer 

evaluation and management for the Sparta aquifer in southern 

Arkansas.
GULF OF MEXICO

TEXAS

OKLAHOMA

ALABAMA G

ARKANSAS

LOUISIANA

MISSISSIPPI

TENNESSEE

MISSOURI

KANSAS

FLORIDA

KENTUCKY

ILLINOIS

100° 90°

30°35°

Base from U.S. National Park ServiceNatural Earth physical map at 500 meters per pixelAlbers Equal Area Conic projection

0 100 200 MILES

0 100 200 KILOMETERS

EXPLANATION

Mississippi embayment aquifer system—Modified from Arthur and Taylor, 1990, 1998Mississippi Embayment Regional Aquifer Study (MERAS)—Modified from Clark and others, 2009, 2011a,bMemphis aquifer regional flow system—Modified from Brahana, 1982; Brahana and Broshears, 1989Sparta aquifer groundwater flow model—Modified from Fitzpatrick and others, 1990; McWreath and other Kilpatrick, 1992; Hays 1998, 1999, 2001Sparta model extent—Modified from McKee and Clark, 2003; Czarnecki, 2009Sparta regional groundwater flow model extent—Modified from Reed, 1972Gulf Coast Regional Aquifer-System Analysis (RASA) study areas—Modified from Williamson and others, 

Figure 54. Extent of area for historical groundwater flow-simulation models constructed for regional analysis of the Sparta aquifer in the Mississippi 

United States.
164 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

In 1985, the USGS, in cooperation with the Arkansas Soil 

and Water Conservation Commission (now called the Arkansas 

Natural Resources Commission), the Louisiana Department of 

Transportation and Development, the El Dorado Water Utility, 

the Union County Water Alliance, UCWCB, and Louisiana 

Sparta Groundwater Conservation District Commission began 

a series of projects to study the hydrogeologic characteristics 

of the Sparta aquifer. These studies also evaluated regional 

water-availability, water-level, and water-quality effects of 

long-term pumping trends. A primary tool for the projects was 

a groundwater-flow model of the Sparta aquifer (Fitzpatrick 

and others, 1990; McWreath and others, 1991) encompassing 

an area of approximately 12,000 mi2 in southern Arkansas 

and northern Louisiana (fig. 54). Three model scenarios by 

Fitzpatrick and others (1990) tested differing pumping rates 

for the 1985–2005 simulation period. The first scenario carried 

the 1985 pumping rate as a constant through to 2005 and 

resulted in water levels with little change over the simulation 

period. For the second scenario, pumping rates in the area of 

the Grand Prairie (fig. 5) were doubled that resulted in waterlevel declines of 30–70 ft over the 20-yr simulation period; 

effects on water levels in southern Arkansas were minimal. 

For the third scenario, pumping rates were doubled across 

the entire model area that resulted in simulated water-level 

declines of 40–130 ft in the Grand Prairie, 80–200 ft in the 

Pine Bluff area, and 20–40 ft near El Dorado. Model results 

showed that whereas 1985 pumping rates appeared to be only 

slightly more than steady-state condition, projected increases 

in pumping would be unsustainable for the long term.

In 1990, the ANRC and the city of El Dorado water 

managers and planners became increasingly concerned 

about saltwater intrusion and declining Sparta groundwater 

levels. El Dorado stakeholders were considering options 

for protecting the aquifer and needed to know the degree of 

influence of potential local management approaches and the 

local effects of pumping activities further removed from the 

city. This problem particularly arose as a result of extensive 

use from the Sparta aquifer near Magnolia, Ark., and Monroe, 

La. Kilpatrick (1992) updated the Sparta model with the thencurrent, 1990 water-use data and ran scenarios to address the 

following specific questions posed by ANRC and the city of 

El Dorado (fig. 54):

4. The city of Magnolia was completing a reservoir in 1991 

that would enable a switch from Sparta groundwater to 

surface water for public supply, leading to the question: 

What effect will the anticipated reduction of pumpage in 

the Magnolia area have on water levels in the El Dorado 

area?

5. What effect will future increases in pumping rates in the 

Monroe, La., area have on water levels in the El Dorado 

area?

6. What effect would changing the locations of El Dorado 

supply wells have on water levels in the El Dorado cone 

of depression?

Scenario 1a of Kilpatrick (1992) addressed the 

completion in 1991 by the city of Magnolia of a surface-water 

reservoir capable of providing 5 Mgal/d to replace use of the 

Sparta aquifer. Model simulations into 2020 showed dramatic 

results in the Magnolia area of water levels rebounding 

to the point that the cone of depression beneath Magnolia 

disappeared; however, effects on water levels in the El Dorado 

area were minor. Scenario 1b in which pumping in El Dorado 

increased by 25 percent from 1990 to 2019, with the decrease 

in pumping at Magnolia from the switch from groundwater to 

surface water, resulted in water-level declines to a level at or 

near the top of the El Dorado sand by 2020, well below the top 

of the Sparta Sand. 

Scenario 2 explored the effect that a 25-percent increase 

in pumping would have in the Monroe area on water levels in 

the El Dorado area. Results showed that the simulated changes 

in pumping in the Monroe area had very little effect on water 

levels in the El Dorado area. Scenario 3 tested the effect of 

redistributing the location of the El Dorado public-supply 

wells on water levels in the cone of depression. Model results 

showed that the modest 25-percent increase in pumpage 

over the 30-year simulation period resulted in substantial, 

additional water-level declines. Thus, redistribution of city 

wells would have minimal influence. Kilpatrick (1992) 

noted that any additional declines in water levels would 

further induce the flow of saltwater toward the cone of 

depression in the potentiometric surface of the Sparta aquifer 

in the El Dorado area. These model results were integral to 

understanding that the causes of the water-level declines 

for the Sparta aquifer in the El Dorado area were local and 

consequently would require local remedial action.

The issue of declining Sparta groundwater levels resulted 

in the designation by the ANRC of the Sparta aquifer in 

southern Arkansas as a critical groundwater area in 1996. 

This designation was designed to focus needed attention and 

resources, to encourage conservation and management, and 

to achieve sustainable use of the aquifer. To evaluate potential 

direct management approaches for the Sparta aquifer in the 

Union County area, the USGS, working with ANRC and 

the Union County Water Alliance, updated the previously 

completed Sparta groundwater flow model with 1997 wateruse data (Hays and others, 1998; fig. 54). The effort was 

unique in that all major aquifer users in Bradley, Calhoun, 

Columbia, Ouachita, and Union Counties in Arkansas 

were queried to assess accuracy of then-current water use 

and develop a realistic database of minimum, median, and 

maximum predicted water use for a 30-year forecast period. 

Five potential pumping scenarios were tested to evaluate the 

effects of static, increased, decreased, and redistributed water 

withdrawals from the Sparta aquifer for the period 1998–

2027. Model results for Scenario 1 showed that maintaining 

pumpage at then-current rates would result in relatively 

minor additional declines in water levels, affecting an area 

less than 10 ft away from the center of the El Dorado cone of 

depression. Scenario 2 applied increasing pumping rates from 

the then-current rates, resulting in declines of more than 130 ft 
Aquifers of the Coastal Plain 165

near El Dorado and 220 ft near Pine Bluff. Scenario 3 applied 

minimum-forecast pumping rates provided by major water 

users for facilities in Bradley, Calhoun, Columbia, Ouachita, 

and Union Counties. This resulted in simulated water levels 

that were substantially higher near the major pumping centers 

of Monroe and El Dorado (more than 70 ft and 180 ft of 

rebound, respectively). Maximum-forecast pumping rates 

input for Scenario 4 resulted in drastic water-level declines 

of more than 110 ft near El Dorado. Scenario 5 explored 

potential future effects of increased irrigation use from the 

aquifer because of overuse and water-level declines noted in 

the Mississippi River Valley alluvial aquifer. In the scenario, 

total pumpage in Lonoke and central Prairie Counties was 

increased by twice the then-current rate of increase, resulting 

in extensive water-level declines with maximum declines of 

more than 100 ft. 

The differences in simulated water-level distributions 

under the various water-use scenarios explored by Hays and 

others (1998) were substantial and effectively demonstrated 

the importance and potential efficacy of water-management 

planning. Hays and Fugitt (1999) demonstrated that the 

aquifer could not meet growing water-use demands and also 

noted that water levels in Union County would drop below 

the top of the primary producing sand unit (locally termed 

the El Dorado sand) by 2008 under then-current water-use 

trends. The result of water levels dropping below the top of 

the El Dorado sand, including loss of yield, decreased water 

quality, and compaction and loss of storage, motivated further 

cooperation between stakeholders and further action towards 

greater protection of the aquifer.

Arkansas’ water-resources policy and programs have 

moved forward with the goal of conjunctive use of the 

State’s groundwater and surface-water resources at optimized 

levels that are sustainable. This sustained yield-conjunctive 

use strategy has been supported using groundwater models 

developed largely through the USGS and the ANRC 

cooperative program. The ANRC and other State water 

planners have advocated sustainable yield groundwater 

protection as a means of achieving specific goals. These goals 

include preventing groundwater-level declines, assuring longterm viability of aquifers to provide certain yields, preventing 

litigation, providing groundwater supplies for drought, 

preventing groundwater-quality degradation, protecting 

riparian rights, and providing courts with an objective means 

for determining and prioritizing uses. Arkansas’ water policy 

has tended to follow a deferred perennial yield strategy, which 

accepts that current groundwater levels or levels defined by 

the critical groundwater area designation are reasonable or 

acceptable.

The Sparta critical groundwater area designation, 

coupled with the work of Hays and others (1998), focused 

regional attention on the declining water levels for the Sparta 

aquifer in southern Arkansas and particularly in the area of 

El Dorado and Union County. Stakeholders in Union County 

reviewed the historical Sparta water-use and water-level data 

and posed the following questions: How much water can 

the Sparta provide for the long term? By what amount must 

Sparta groundwater use be decreased to be sustainable? These 

questions had to be answered before serious, focused, and 

cost-effective management and protection approaches could be 

designed. Only then could the amount of water needed from 

alternative water-supply sources be quantified. 

Hays (1999; fig. 54) conducted a modeling study to 

determine sustainable yield from the Sparta aquifer in Union 

County to address these questions. Sustainable yield is a 

critical element in identifying and designing viable watersupply alternatives (Alley and others, 1999). With sustainable 

yield defined and total water demand identified in a given area, 

any unmet demand that must be supplied from alternative 

water sources can be determined by calculating the difference. 

The Sparta aquifer groundwater-flow model provided a tool 

capable of determining sustainable yield using an iterative 

approach. The sustainable yield of the aquifer was calculated 

by establishing the top of the Sparta Sand as the minimum 

acceptable water level in Union County and varying pumpage 

to achieve this target water level. A stabilization yield also was 

determined that reflected the amount of water the aquifer could 

provide while maintaining target water levels. Sustainable 

and stabilization yields were estimated for two pumping 

conditions: (1) simulation of future pumpage outside of Union 

County by accelerating at the rate of increase observed from 

1985 to 1997, and (2) simulation of future pumpage outside 

of Union County by accelerating at twice the rate of increase 

observed from 1985 to 1997. Results of the study provided 

three primary conclusions: (1) Sparta water-use outside of 

Union County was not a major control on water levels within 

the county, (2) withdrawals would have to be reduced to about 

88–91 percent of 1997 rates to stabilize water levels above the 

top of the Sparta Sand, and (3) the yield from the aquifer was 

determined not to be great enough to support a doubling of 

the rate of increase in pumpage in Union County over the long 

term. Irrespective of how withdrawals from the Sparta aquifer 

were changed outside of Union County, withdrawals within 

Union County had to be reduced to about 25–28 percent of 

1997 rates—a 72–75-percent reduction in use—to cause water 

levels to rise permanently back to the top of the Sparta Sand 

and thereby achieving a sustainable yield and addressing State 

critical groundwater area designation criteria.

The projected local and regional negative consequences 

of continued unabated expansion of Sparta withdrawals 

detailed in Hays and others (1998), Hays (1999), Hays 

and Fugitt (1999), and Hays and McKee (2003) provided 

important impetus for passage of Arkansas legislative Act 

1050 of 1999. This act allowed counties within designated 

Arkansas critical groundwater areas to establish local 

Conservation Boards with management, regulatory, and 

taxing authority to plan, guide, and implement management 

approaches targeting achievement of modeled sustainable 

yields. Model results ultimately were used to guide a largescale, coordinated conservation, and alternative-source 
166 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

development effort that resulted in rebound of Sparta aquifer 

water levels in Union County for the first time in more than 

100 years of pumping. Model results indicated that rebound of 

water levels would occur with implementation of conservation 

and use of alternative sources. Results also highlighted the 

need for monitoring of aquifer conditions. Beginning in 2002, 

the UCWCB, in cooperation with the USGS and the EPA, 

began intensive monitoring of Sparta aquifer recovery with 

eight continuously monitored wells (Scheiderer and Freiwald, 

2006). By 2006, groundwater levels had risen more than 

60 ft in the immediate area of El Dorado and more than 10 

ft as far away as 56 mi southeast of the city. The potential 

irreparable damage to the aquifer and water quality that might 

have occurred with continued unsustainable withdrawals 

was avoided by implementation of the intensive, sciencebased management approach. The Sparta aquifer recovery 

in Union County is a nationally recognized success, and the 

USGS, ANRC, and UCWCB were awarded the Department of 

Interior National Conservation Award for the effort in 2008. 

Results of previous studies provided impetus to consider 

augmented recharge of the Sparta aquifer. Consequently, in 

2000, the Arkansas State Senate requested that ANRC and 

USGS evaluate the hydrogeologic feasibility of augmented 

recharge approaches. Using the Sparta groundwater-flow 

model of Hays and others (1998), Hays (2001) simulated 

the effects of constructing a series of lakes and canals along 

the Sparta outcrop area. The basic concept of augmented 

recharge is to increase the amount of water being introduced 

into the aquifer at the outcrop belt so that more water will 

be available for pumping and for use downgradient from the 

recharge zone. Model results showed that recharge from the 

simulated lakes and canals provided notable benefit to aquifer 

conditions. Simulated total flow through the Sparta aquifer 

was greater with the presence of canals; 80 Mft3

/d with the 

canals compared to about 62 Mft3/d without the canals. Water 

levels in the aquifer also showed considerable improvement. 

The zone of positive influence on water levels extended from 

the recharge area eastward to the Mississippi River with the 

canal simulations. Aquifer water levels increased 5 ft or more 

with the canal simulation across a broad area comprising all 

or a substantial part of 15 counties. Increases of 20 ft or more 

were noted in El Dorado, Pine Bluff, and Stuttgart. Although 

water levels in the aquifer increased substantially with 

augmented recharge, water levels continued to decline through 

the 30-year simulations, with or without additional recharge. 

This indicates that water was still being removed at a greater 

rate than the aquifer could supply for the long term. 

In 2001, the Louisiana Sparta Groundwater Conservation 

District Commission funded a study to determine limitations 

of the Sparta aquifer for meeting groundwater needs. A 

secondary purpose was to test hypothetical conservation 

approaches on hydraulic heads in Sparta wells in Louisiana 

from 2000 to 2025 using the USGS-developed Sparta model 

(Hays and others, 1998; Meyer, Meyer, LeCroix, Hixson, Inc., 

and others, 2002). A sustained maximum pumpage rate of 

52 Mgal/d simulated a recovery in water levels and indicated 

a need to reduce withdrawals by 18 Mgal/d from the thencurrent pumpage rate of approximately 70 Mgal/d. 

The intense use of the Sparta groundwater flow model 

in the 1980s through the 1990s and the ongoing need for 

management input warranted improvement of the model. 

McKee and Clark (2003) worked to modify, recalibrate, 

and convert the Sparta model (fig. 54), addressing potential 

improvements identified by Hays and others (1998) in a 

cooperative study involving USGS, USACE, and ASWCC. 

Modifications to the previous Sparta model included 

rediscretizing the model grid, extending the model area 

northward, updating the surfaces representing the top and 

bottom of the Sparta Sand, and changing the model platform 

from MODFLOWARC used by Hays and others (1998) to 

MODFLOW–2000. The updated model was used to simulate 

the effects of four pumping scenarios on hydraulic heads 

over the period 1998–2027. The most intense pumping 

continued to occur in the El Dorado and Pine Bluff areas, 

which had extensive cones of depression. Results of McKee 

and Clark (2003) reported simulated drawdowns with respect 

to the center of the cones of depression in each area. In 

scenario 1a of McKee and Clark (2003), withdrawals were 

held constant for 30 years at 1990–97 rates, resulting in 

projected water-level declines of 10 ft and 17 ft in the center 

of the cones in El Dorado and Pine Bluff, respectively. With 

these withdrawals extended indefinitely under steady-state 

conditions (scenario 1b), water levels declined an additional 

7 ft and 27 ft in the center of the cones in El Dorado and 

Pine Bluff, respectively. Scenario 2 tested the effect of 

decreasing withdrawals in El Dorado and Pine Bluff for 

industries that were considering alternative water sources. 

Simulated water levels under scenario 2 recovered more than 

165 ft and 120 ft in the center of the cones in El Dorado and 

Pine Bluff, respectively. The area of Union County where 

simulated water levels were below the top of the Sparta Sand 

decreased from 52 percent in 1997 to 7 percent by 2027. 

For scenario 3, most withdrawals had a simulated increase 

of 25 percent over 30 years with selected industrial wells in 

Pine Bluff and El Dorado having reduced withdrawals. The 

model results showed recoveries of 124 ft and 100 ft in the 

center of the cones in El Dorado and Pine Bluff, respectively. 

Results for the targeted industrial reductions in scenarios 2 and 

3 showed the potential effectiveness of the specific watersource alternatives and management approaches to achieve 

sustainable yields that were being considered at the time.

Czarnecki (2009) used the Sparta model by McKee and 

Clark (2003) to explore potential groundwater withdrawal 

scenarios at the Pine Bluff public-supply well field. The 

Pine Bluff well field was within a critical groundwater area, 

and local water managers and ANRC wanted to evaluate 

potential effects of various potential withdrawal rates. The 

model simulated a 50-year period from 1998 to 2048 for 

each scenario. Model results showed a water-level decline 

of about 20 ft for the baseline scenario, which applied the 

1990–97 reported water use of 25.4 Mgal/d. Scenarios 1 and 

2 at the Pine Bluff well field simulated water-use reductions 
Aquifers of the Coastal Plain 167

of 7.2 Mgal/d and 12 Mgal/d, respectively, as compared to 

the then-current rates. Simulated results indicated that water 

levels were approximately 90 ft and 65 ft higher, respectively, 

compared to the baseline scenario. Scenarios 3 and 4 applied 

water-use rates that were within 10 percent of then-current 

water-use levels; simulated results were very similar (within 

10 ft at the well field) to the baseline scenario results. An 

important observation of the study was that an overall 

downward trend of water levels occurred in the area, even for 

the scenarios that applied decreased withdrawals at the Pine 

Bluff well field. This indicates that pumping from the Sparta 

aquifer outside the well field had a considerable effect and 

exceeded levels that would be sustainable.

The USGS initiated a National Water Census (http://

water.usgs.gov/watercensus/) from 2004 to 2012 involving 

Federal, State, local governments, and the private sector to 

assess regional groundwater-flow systems and groundwater 

availability across the conterminous United States (Reilly 

and others, 2008). The Mississippi embayment was a focus 

region and included the Mississippi Embayment Regional 

Aquifer Study (MERAS; fig. 54; Clark and Hart, 2009; Clark 

and others, 2011b). A numerical groundwater-flow model 

was developed to simulate the effects of human activities 

and climate variability on aquifer systems and surface-water 

bodies. The MERAS model resulted in 13 layers covering 

78,000 mi2

 and representing multiple aquifers, including the 

Sparta aquifer. MERAS simulations showed that the confined 

middle Claiborne aquifer, which includes the Sparta Sand, 

exhibited dramatic water-level declines of more than 100 ft 

occurring across 7,529 mi2 (13.3 percent of the model area) 

by 2007. The largest declines of more than 300 ft in the 

middle Claiborne aquifer (Sparta aquifer) occurred in southern 

Arkansas. 

The importance of the MERAS model lies primarily in 

the future utility of the model as a management tool that can 

be updated to address new and continuing questions arising 

from changing human activities and natural conditions that 

challenge water managers and stakeholders. The tools and 

databases integral to the MERAS model include a database 

of over 2,600 geophysical logs used in the construction of 

the hydrogeologic framework (Hart and Clark, 2008). The 

MERAS model represents the current state-of-the-science 

modeling tool for the Sparta and other aquifers of eastern 

Arkansas. It is an integrated tool capable of being updated to 

address diverse issues and questions for years to come. Since 

initial development of the MERAS model, two updates have 

been implemented as of 2013 (Clark and others, 2013) in the 

effort to continually improve upon the ability to accurately 

simulate groundwater flow. 

Clark and others (2011a) used the MERAS model (Clark 

and others, 2011b) in an ANRC-USGS cooperative study to 

simulate groundwater flow and water-level altitudes for the 

period 2007–37. The study focused on the Bayou Meto and 

Grand Prairie agricultural area, which was designated as the 

Grand Prairie critical groundwater area by ANRC in 1998 

(Arkansas Natural Resources Conservation Commission, 

2009). The ANRC was concerned about potential water-level 

declines from an increasing number of wells and an increasing 

demand on the Sparta aquifer in the Bayou Meto and Grand 

Prairie area, resulting from increased reliance on the aquifer 

for agricultural use. In scenario 1, the study compared 

simulated water levels resulting from continuance of 2005 

pumping rates. In scenario 2, the study simulated the addition 

of new Sparta wells in the Bayou Meto and Grand Prairie area 

at a rate of 13 wells per year. Simulated water-level declines 

in scenario 1 ranged from 20 to 40 ft. The additional pumping 

wells in scenario 2 resulted in considerably greater water-level 

declines and caused cones of depression by 2037 in Lonoke 

and Arkansas Counties. Water-level declines ranged from 40 to 

50 ft across most of the Bayou Meto and Grand Prairie area in 

scenario 2. A maximum water-level decline of approximately 

102 ft occurred in Lonoke County. Model results emphasized 

the substantial effects that additional agricultural pumping 

from the Sparta aquifer would have in the Bayou Meto and 

Grand Prairie areas if the Mississippi River Valley alluvial 

aquifer continues to be unable to meet demands. These results 

also showed that increased agricultural usage would cause 

increased water-level declines in public-supply wells that 

depend on the Sparta for public supply, ultimately decreasing 

long-term water availability for public-supply use. 

The prevalence of long-term water-level declines and 

regional cones of depression in large areas of the Sparta 

aquifer highlight the need for greater knowledge and better 

definition of sustainable yield for this aquifer. The work 

of Hays (1999) and Clark and others (2011a, b) provides a 

preliminary estimate of sustainable yield for the aquifer in the 

El Dorado and Pine Bluff areas. The importance of the Sparta 

aquifer in other areas of Arkansas, however, requires a more 

detailed and broader-scale assessment of sustainable use and 

deferred perennial yield for the aquifer throughout the State.

Water Quality

The Sparta aquifer is sand dominated and generally 

yields freshwater of very high quality throughout its extent in 

Arkansas. The groundwater is cited as a sodium-bicarbonate 

water type throughout most of its extent (Tait and others, 

1953; Onellion, 1956; Payne, 1968; Ludwig, 1973; Broom 

and others, 1984; Terry and others, 1986). Calcium and 

magnesium are cited as occurring in appreciable amounts 

only in very small areas (Payne, 1968). In the northeastern 

part of the State, groundwater from the Sparta is reported 

as a calcium-bicarbonate water type with dissolved-solids 

concentrations ranging from 200 to 500 mg/L (Ryling, 1960; 

Plebuch; 1961; Halberg and Reed, 1964; Hosman and others, 

1968; Broom and Lyford, 1981). Only a few areas of the 

State experience problems with use of groundwater from the 

Sparta aquifer, and these dominantly are related to problems of 

elevated salinity.
168 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

General Geochemistry and Water Type

The percent sodium calculated from data gathered for this 

study was plotted using a geographical information system 

(fig. 55). This spatial analysis revealed an overall pattern 

of low sodium occurring dominantly in the area of outcrop, 

with an overall increasing trend in sodium percentage in 

the downgradient direction of flow (fig. 55). Low sodium is 

herein defined as any water type where sodium is less than 

50 percent of the total cations (calcium, sodium, magnesium, 

and potassium) in milliequivalents per liter. The above finding 

suggests that cation exchange along a given flow path accounts 

for the transitioning of an initial calcium-bicarbonate to a 

sodium-bicarbonate water type with increased residence time 

in the aquifer. In the northeastern part of the State, from St. 

Francis to Craighead Counties, the groundwater is a strongly 

calcium-bicarbonate water type. Percent sodium in this area 

generally is less than 25 percent, and no sodium-bicarbonate 

water type is encountered in this area. Hosman and others 

(1968) similarly classified groundwater from the Sparta in 

northeastern Arkansas dominantly as a calcium-magnesiumbicarbonate water type, with other areas of the State 

containing a sodium-bicarbonate water type. Geophysical log 

analysis by Clark and Hart (2009) indicated sand content in 

the Sparta from 80 to 100 percent in much of the northeastern 

part of the State and from 0 to 60 percent over much of the 

southern part of the State. This implies an increase in clay 

content for the Sparta in the southern part of the State. Higher 

cation-exchange capacity on clay surfaces results in greater 

opportunity for cation exchange in the southern part of the 

State as compared to the northeastern part of the State. 

Values of pH are invaluable indicators for tracking 

groundwater flow paths from recharge to discharge areas 

and for preliminary identification of rock type. Values of 

pH ranged from 4.0 to 9.0 with a median of 7.5 (table 25). 

Values generally increased in the downgradient (southeasterly) 

direction of flow. Values of pH were lowest (4.0 to 6.5) in the 

outcrop area in the southwestern part of the State but increased 

to greater than 8.0 within a short distance of the outcrop area 

(fig. 55). In Sparta subcrop areas in the northeastern part of 

the aquifer, pH values were generally greater than 6.5. The 

absence of pH values less than 6.5 in the northeastern part 

of the State may be ascribed to the fact that the Sparta does 

not crop out throughout most of this area; thus, recharge 

has moved through overlying units that likely buffer the 

infiltrating, low-pH water prior to its moving into the Sparta 

aquifer. Values of pH generally increased in the downgradient 

direction, but this trend is most pronounced in the southern 

part of the State.

The increase of pH along a given flow path possibly 

results from the increased dissolution of carbonates, consistent 

with similar increases in bicarbonate concentrations in the 

downgradient direction of flow (not shown on fig. 55). The 

lowest bicarbonate concentrations (less than 50 mg/L) were 

found in the outcrop area in southern Arkansas, with sharp 

increases occurring in the downgradient direction. Conversely, 

in the northeastern part of the State, most bicarbonate 

concentrations are greater than 100 mg/L and generally 

increase to greater than 400 mg/L in the downgradient 

direction. Dissolved-solids concentrations similarly reflect the 

trend of increasing carbonate concentrations, as bicarbonate 

is the dominant anion in groundwater from the Sparta aquifer. 

Hosman and others (1968) similarly noted that dissolvedsolids concentrations are lower in outcrop areas and increase 

as the water moves downgradient, mainly as a result of 

increases in sodium, bicarbonate, and chloride. 
Aquifers of the Coastal Plain 169

Arkansas River Arkansas River Arkansas River

Arkansas River Arkansas River Arkansas River

36°

35°

34°

36°

35°

34°

36°

35°

34°

36°

35°

34°

36°

35°

34°

36°

35°

34°

91° 94° 92° 93°

90°

91° 94° 92° 93°

90°

91° 94° 92° 93°

90°

91° 94° 92° 93°

90°

91° 94° 92° 93°

90°

91° 94° 92° 93°

90°

Geology map modified from Hosman and others, 1968; 

Petersen and others, 1985 

Base modified from U.S. Geological Survey digital data, 1:250,000

Transverse Mercator projection, Central meridian 93 ̊00'W

0 100 200 MILES

0 100 200 KILOMETERS

pH, in standard units

4.0 to 5.55.6 to 6.56.6 to 7.57.6 to 8.08.1 to 9.1

EXPLANATION

Nitrate, in milligrams per liter

0.01 to 0.250.26 to 1.501.51 to 5.005.01 to 10.0010.01 to 15.0015.01 to 33.00

EXPLANATION

Sodium, in percent of major cations

0 to 2526 to 5051 to 6566 to 7576 to 8586 to 100

EXPLANATION

Iron, in micrograms per liter

0 to 5051 to 100101 to 300301 to 1,0001,001 to 2,5002,501 to 34,800

EXPLANATION

Sulfate, in milligrams per liter

0 to 56 to 1011 to 2526 to 5051 to 7576 to 131

EXPLANATION

Chloride, in milligrams per liter

0 to 2526 to 5051 to 100101 to 250251 to 500501 to 1,0001,001 to 2,646

EXPLANATION

EXPLANATION

Sparta outcrop

Sparta subcrop

Sparta extent

Crowleys Ridge

Figure 55. Spatial distribution of selected chemical constituents for groundwater from the Sparta aquifer in Arkansas.
170 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Table 25. Descriptive statistics for selected chemical constituents in groundwater from the Sparta aquifer in Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 0.1 7 130 18 415

Magnesium (mg/L) 0.01 1.7 84 7.62 415

Sodium (mg/L) 0.04 44 700 87.1 412

Potassium (mg/L) 0.4 3.04 56 4.27 366

Bicarbonate (mg/L) 2.0 146 1,280 134 412

Chloride (mg/L) 0.3 8.1 2,650 136 673

Sulfate (mg/L) 0.02 3.8 131 11 448

Silica (mg/L) 1.0 14 74.6 8.87 338

Nitrate (mg/L as nitrogen) 0.01 0.09 33 2.23 427

Dissolved solids (mg/L) 12 186 2,210 228 440

Iron (μg/L) 0.05 111 34,800 2,560 333

Manganese (μg/L) 0.13 28.7 1,090 144 192

Arsenic (μg/L) 0.03 0.07 5.67 0.65 135

Hardness (mg/L as calcium carbonate) 1.0 25 477 70 374

Specific conductance (μS/cm) 22 321 8,870 482 692

pH (standard units) 4.0 7.5 9.0 0.9 446
Aquifers of the Coastal Plain 171

Nitrate

Nitrate concentrations were low throughout most of the 

Sparta aquifer, with a median concentration of 0.09 mg/L (as 

nitrogen) and 85 percent of all nitrate concentrations were 

less than 1.0 mg/L. Nitrate concentrations ranged from 0.01 to 

33 mg/L (table 25). The MCL of 10 mg/L (U.S. Environmental 

Protection Agency, 2009) was exceeded in only 1.5 percent 

of samples. The highest nitrate concentrations occurred in the 

outcrop area, where the formation is exposed and wells are 

shallow, thus increasing the vulnerability to surface sources 

of nitrogen (fig. 55). A strong inverse relation was noted for 

nitrate and well depth (fig. 56A). Most wells with nitrate 

concentrations greater than 2 mg/L occurred in wells less 

than 50 ft deep. Except for isolated areas of elevated nitrate 

concentrations in the outcrop area, concentrations dominantly 

were less than 0.25 mg/L downgradient from and northeast of 

the outcrop area. In these areas, overlying formations protect 

the groundwater from surface sources of contamination. 

Dilution, denitrification processes, and low groundwater-flow 

velocities also may serve to prevent appreciable transport of 

nitrate to areas downgradient from the outcrop area.

0 200 400 600 800 1,000 1,200 1,400 1,600

0 500 1,000 1,500 2,000 2,500 3,000

0 500 1,000 1,500 2,000 2,500 0 500 1,000 1,500 2,000 2,500

Well depth, in feet below land surface

Iron, in micrograms per liter

Dissolved solids, in milligrams per liter Dissolved solids, in milligrams per liter

0

20

40

60

80

100

120

140

0

100

200

300

400

500

600

700

800

0

200

400

600

800

1,000

1,200

1,400

0

5

10

15

20

25

30

35

Sulfate, in milligrams per liter

Bicarbonate, in milligrams per liter

Chloride, in milligrams per liter

Nitrate, in milligrams per liter as nitrogen

A B

C D

Figure 56. Relation between A, well depth and nitrate; B, iron and sulfate; C, dissolved solids and bicarbonate; and D, dissolved solids 

and chloride for groundwater from the Sparta aquifer in Arkansas.
172 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Iron

Iron concentrations in 333 samples ranged from 0.05 to 

34,800 μg/L with a median of 111 μg/L (fig. 57; table 25). 

Similar to nitrate, iron concentrations are greater in the 

outcrop area and generally below 1,000 μg/L for areas 

downgradient from and north of the outcrop area. An area 

of high concentrations also occurs along the Arkansas River 

(fig. 55). Hosman and others (1968) also noted that higher 

concentrations of iron occurred generally in groundwater 

along the outcrop of the Sparta Sand throughout the 

Mississippi embayment. Iron concentrations more than 

1,000 μg/L occur in isolated areas in the northeastern part 

of the State. The Sparta subcrops beneath alluvial deposits 

bearing iron-rich groundwater that potentially is the source for 

the elevated iron. The lower iron concentrations downgradient 

from the outcrop area are attributed to changes in redox 

conditions that result in iron mineralization along the flow 

path.

0

50

100

150

200

250

300

350

400

450

Concentrations, in milligrams per liter

500

Concentration, in micrograms per liter

700

800

900

1,000

0

100

200

300

400

500

600

333

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

415

415

412

412

673

448

333

Constituent Constituent

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron

Figure 57. Interquartile range of selected chemical constituents for groundwater from the Sparta aquifer in Arkansas.
Aquifers of the Coastal Plain 173

Sulfate

Sulfate concentrations generally are low throughout the 

Sparta aquifer, with a median concentration of 3.8 mg/L for 

448 samples (fig. 57; table 25). Of the 448 samples, 300 had 

sulfate concentrations less than 5 mg/L and 88 were less than 

1.0 mg/L. Sulfate concentrations were very low compared to 

other aquifers. The low sulfate concentrations were at least 

half the concentration capable of being derived naturally from 

evaporation of recharging precipitation (Kresse and Fazio, 

2002). Sites with sulfate concentrations between 10 and 51 

mg/L generally occurred in or near the outcrop area of the 

Sparta Sand. Concentrations decreased within short distances in 

the downgradient direction of flow to concentrations typically 

less than 5 mg/L (fig. 55). This result lends additional support to 

the hypothesis that changes in redox conditions control iron and 

sulfate concentrations. Iron- and sulfate-reducing conditions 

along the groundwater-flow path may result in the formation 

of iron-sulfide minerals thus reducing the concentration 

of each constituent. Support for this theory is found in the 

inverse correlation of iron and sulfate concentrations; iron 

concentrations are less than 50 μg/L for sulfate concentrations 

between 20 and 140 mg/L. Sulfate concentrations generally 

are less than 10 mg/L for iron concentrations greater than 

approximately 50 μg/L (fig. 56B). 

The reduction of sulfate to hydrogen sulfide is directly 

related to the abundance of available sulfate. Similar to the 

relation between iron and sulfate, dissolved iron (Fe2+) and 

hydrogen sulfide (H2S) tend to be inversely related according to 

a hyperbolic function, such that when Fe2+ concentrations are 

high, H2S concentrations tend to be low and vice versa. This 

reflects the rapid reaction kinetics of Fe2+ with H2S to produce 

relatively insoluble ferrous sulfides (Chapelle and others, 2009). 

Where abundant sulfate is available, the resulting sulfide binds 

with ferrous iron in solution to form iron sulfide minerals and 

controls soluble iron and sulfate concentration.

Elevated sulfate concentrations south of the Arkansas 

River are exceptions to the generally low concentrations 

beyond the area of outcrop. The greatest sulfate concentrations 

(as much as 131 mg/L) were from wells located in this 

area. Elevated concentrations also were noted from wells 

completed in the Cockfield aquifer in this area. The source of 

sulfate is interpreted as leakage of water from the overlying 

Jackson Group (Halberg and others, 1968), which outcrops 

in southern Arkansas and exhibits some of the highest sulfate 

concentrations of any aquifer in the State (see “Jackson Group” 

section). The fact that the Jackson Group, the Cockfield 

aquifer, and the Sparta aquifer all contain elevated sulfate 

concentrations in this area suggests a high level of connectivity 

and interchange of water between these hydrogeologic units. 

Maximum and median sulfate concentrations in all three 

hydrologic systems, respectively, were 3,080 and 110 mg/L 

for the Jackson Group, 470 and 2.4 mg/L for the Cockfield 

aquifer, and 131 and 3.8 mg/L for the Sparta aquifer. The trend 

of lower maximum concentrations with depth is consistent 

with the uppermost Jackson Group as the possible source of 

sulfate. It should be noted, however, that the top of the Sparta 

aquifer is approximately 600 ft below land surface with a clay 

confining unit between the Cockfield and Sparta aquifers. A 

high level of communication between these aquifers could 

only result from thinning of the confining unit, increased sand 

content of the confining unit, vertical fractures in the confining 

unit, or possible flow along unmapped faults in Jefferson and 

Drew Counties. Sand thickness maps do not reveal anomalous 

sand percentages for these areas (Clark and Hart, 2009). More 

information is needed to validate the above potential transport 

mechanisms. 

The possibility also exists for the elevated sulfate 

concentrations being the result of incorrectly identified 

completion depths, leakage across formations through a 

poorly cased annulus section (or no casing), or wells that are 

screened through one or more producing formations. However, 

the likelihood of this occurring only in Jefferson and Drew 

Counties is low. Only three wells in Jefferson County and one 

well in Drew County had concentrations greater than 25 mg/L, 

ranging up to 131 mg/L. No elevated sulfate concentrations 

were noted in earlier publications. Klein and others (1950) list 

20 wells in Jefferson County with concentrations from 0.6 to 10 

mg/L, and Onellion (1956) listed 17 wells in Drew County with 

concentrations from 0.9 to 7.0 mg/L.

Chloride

Chloride concentrations in 673 samples ranged from 

0.3 mg/L to 2,650 mg/L (table 25). Except for isolated areas 

of the State, chloride concentrations in the Sparta generally 

are low, as indicated by a median concentration of 8.1 mg/L 

(fig. 57; table 25). Chloride concentrations are defined as 

elevated when exceeding 100 mg/L, which follows the 

definition first established in Kresse and Clark (2008). The 

secondary drinking-water regulation for public-supply systems 

is 250 mg/L, which is based on aesthetic characteristics that 

include taste. For dissolved-solids concentrations less than 

approximately 500 mg/L, bicarbonate dominates the anion 

chemistry. For dissolved-solids concentrations greater than 

500 mg/L, a positive, strongly linear relation is noted between 

dissolved-solids and chloride concentrations, and chloride 

generally dominates the anion chemistry (fig. 56D). Three main 

areas of elevated chloride concentrations are (1) an elongated 

band of elevated chloride concentrations trending in a northwest 

to southeast direction within Ouachita and Union Counties, (2) 

an area in Chicot County, and (3) an area extending eastward 

from Prairie County through Monroe and Lee Counties. 

Elsewhere, chloride concentrations are low. Approximately 

70 percent of 1,223 samples were below 20 mg/L, 

reflecting chloride derived from rainwater concentrated by 

evapotranspiration processes (Kresse and Fazio, 2002; Kresse 

and Clark, 2008). 

An elongated band of slightly elevated chloride 

concentrations (maximum of 475 mg/L) extends from 

southeastern Ouachita County to southeastern Union County 

in the southern part of the aquifer (fig. 55). Broom and others 

(1984) reported on an isolated area of high salinity in central 

Union County and attributed the source of elevated chlorides 
174 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

to high-salinity water in a faulted graben in Union County. 

Although no water wells were completed inside of the graben, 

estimates based on electric logs in Sparta wells in the graben 

indicated that chloride concentrations might be as high as 2,500 

mg/L. Alignment of the graben and the spatial distribution 

of chloride concentrations nearby indicated that increased 

pumping from a nearby public supply led to movement of highsalinity water within the graben into previously unaffected parts 

of the aquifer west of the graben (Broom and others, 1984). 

With the exception of Broom and others (1984) discussed 

above, few studies have performed a detailed assessment of 

groundwater quality in Ouachita and Union Counties. Terry 

and others (1986) reported on water resources, including the 

Sparta aquifer in Ouachita and Union Counties, but did not 

address salinity issues and listed specific conductance ranging 

from 20 μS/cm in a sample from Lafayette County to 4,610 μS/

cm in a sample from Ouachita County. Chloride concentrations 

ranged from 612 to 1,120 mg/L in three wells listed as Sparta 

wells (Terry and others, 1986), but these wells later were 

discovered to actually be completed in the Wilcox and Cane 

River Formations (T.P. Schrader, U.S. Geological Survey, 

oral commun., 2012). Albin (1964) reported on groundwater 

resources in Bradley, Calhoun, and Ouachita Counties and 

listed chemical analyses for 34 well-water samples from the 

Sparta aquifer with a maximum chloride concentration of 

84 mg/L. No areas of high salinity were noted for the Sparta 

aquifer in Ouachita County. Currently (2013), no defined 

sources for the band of elevated chloride concentrations have 

been identified in this area. 

The occurrence of saline water in the Sparta aquifer in 

Chicot County was first noted by Onellion and Criner (1955). 

They described a well drilled to a depth of 1,064 ft in southcentral Chicot County that reportedly encountered brackish 

water and subsequently was backfilled and completed at a 

depth of 150 ft. Data from electric logs of oil test wells in the 

county also indicated that water from the Sparta was saline, but 

that freshwater might possibly exist in the northern part of the 

county (Onellion and Criner, 1955). Payne (1968) described a 

saline-water tongue for a downdip area of the Sparta in eastern 

Louisiana and southeastern Arkansas, which corresponded to 

the area described by Onellion and Criner (1955). Payne noted 

that the area of saline water generally represents an area of 

discharge where the dominant component of flow is upward and 

lies beyond the limits of extensive flushing by freshwater. 

A well was drilled into the Sparta aquifer in Chicot County 

near the center of a zone of elevated chloride concentrations in 

the Mississippi River Valley alluvial aquifer (Kresse and others, 

2000) (see “Mississippi River Valley Alluvial Aquifer” section). 

A sample from the well had a chloride concentration of 2,646 

mg/L compared to a chloride concentration of only 36 mg/L 

from a well in southeastern Ashley County and a concentration 

of 171 mg/L from a well in northeastern Chicot County (Kresse 

and others, 2000). Kresse and Clark (2008) attributed the 

occurrence of saline water in the Sparta aquifer and overlying 

formations to brine water from the Smackover Formation 

moving up along the intersection of two mapped wrench faults 

(Zimmerman, 1992). The lack of data prevents an assessment 

of the spatial extent of the saline water in the Sparta aquifer for 

Chicot County. Fresh groundwater may be present in eastern 

Chicot County if similar trends for an elongated north-south 

band noted for the occurrence of saline water in the alluvial and 

Cockfield aquifers exist in the Sparta aquifer.

A third area of elevated chloride concentrations is found 

northeast of the White River and primarily confined to Prairie, 

Monroe, and Lee Counties. Chloride concentrations in wells 

south of the White River and north of Monroe and Lee Counties 

are low and mostly less than 25 mg/L (fig. 55). Chloride 

concentrations for wells northeast of the White River range 

up to 1,100 mg/L in Monroe County, and several wells have 

chloride concentrations between 500 and 1,000 mg/L. Many 

older publications did not differentiate the Cockfield, Cane 

River, or Sparta Sand Formations of the Claiborne Group; 

however, any indication of salinity in the Claiborne Group and 

the underlying Wilcox aquifer provides important information 

on salinity issues related to the Sparta aquifer. Stephenson 

and Criner (1916) provided some of the first evidence for the 

occurrence of high-salinity groundwater from the Sparta in 

northeastern Arkansas. The public supply for Brinkley (Monroe 

County) during the time of their report contained water that was 

cited as being “slightly brackish.” Application of the well depth 

to the recently developed geologic framework by Hart and 

others (2008) indicates that the well was completed in the lower 

part of the Sparta aquifer.

Counts (1957) stated that no wells were completed in 

the Sparta aquifer in Lonoke, Prairie, and White Counties. 

Interpretation of electric logs, however, indicated that 

freshwater could be drawn from the upper sands of the 

Claiborne Group to a maximum depth of approximately 500 ft. 

An increase of salinity in the lower beds corresponding to the 

Sparta aquifer was inferred for groundwater in the downdip 

direction (to the southeast) and below a depth of 500 ft. 

Halberg and Reed (1964) reported that in parts of Prairie, 

Monroe, and Lee Counties, some sands of the Claiborne Group 

yielded brackish water. Two wells in Monroe County were 

noted as yielding moderately mineralized water “that contains 

much sodium and chloride.” An electric log for one well in 

Lee County indicated saline water in the Claiborne Group 

below 700 ft, generally corresponding to the depth of high 

salinity water inferred by Counts (1957). Hosman and others 

(1968) reported elevated chloride concentrations in Monroe 

and Lee Counties that were attributed to upward movement 

of mineralized water from lower aquifers and noted that the 

occurrence of mineralized, high-salinity groundwater coincided 

within a zone of transition. This transition zone is where the 

marine clays of the Cane River undergo a facies change to sand 

to the north, with a corresponding apparent increase in vertical 

permeability. Because the Carrizo Sand contained saline 

water and had a hydrostatic head 10 ft higher than the Sparta 

(Hosman and others, 1968), upward movement of high-salinity 

water from underlying formations was indicated as the source 

of saline water in the Sparta aquifer.

Morris and Bush (1986) investigated the occurrence of 

high-salinity water in the alluvial aquifer near Brinkley in 

Monroe County. An oil and gas test well open to the Nacatoch 
Aquifers of the Coastal Plain 175

Sand, which was flowing artesian, was sealed off because of 

saline water contamination at the surface. Mixing curves for 

bromide/chloride, iodide/chloride, and boron/chloride showed 

Sparta and alluvial aquifer wells plotted on the same line as 

the Nacatoch wells, indicating an upwelling of groundwater 

from the Nacatoch aquifer as the source. Morris and Bush 

(1986) hypothesized two possible sources: (1) leakage of 

saltwater from the Nacatoch aquifer into the Sparta aquifer 

along a fault and (2) saltwater intrusion from the Nacatoch 

aquifer into the Sparta aquifer through abandoned oil and 

gas test wells. The potentiometric surface of the Nacatoch 

aquifer was cited as high enough in the area to force water 

into the Sparta or alluvial aquifer through a breached well 

casing (Morris and Bush, 1986). Earlier documentation of 

high salinity in the Sparta aquifer by Stephenson and Criner 

(1916), however, tends to rule out contamination by oil 

and gas test wells. Clark and Hart (2009) developed a sand 

percentage map for the upper and lower Claiborne aquifer 

within the Mississippi embayment and showed a well-defined 

zone of increased sand for the Claiborne Group in the general 

vicinity of the elevated chloride concentrations in the Sparta 

aquifer in northeastern Arkansas. This sand zone lends some 

support to the theory proposed by Hosman and others (1968), 

and described in the preceding paragraph, for upwelling of 

saltwater from formations underlying the Sparta.

In summary, the quality of groundwater from the 

Sparta aquifer is very good. The groundwater generally is a 

sodium-bicarbonate type; however, a calcium-bicarbonate 

water type is found in northeastern Arkansas and in the 

outcrop area in southern Arkansas. Elevated iron and 

nitrate concentrations occur dominantly in the outcrop area 

with lower concentrations in the downgradient direction 

of flow. Generally, pH, bicarbonate, and dissolved-solids 

concentrations increase with increased residence time along 

the flow path moving downgradient from the outcrop, as well 

as the shallow subcrop in the northeastern part of the State. 

These effects are attributed to the increased dissolution of 

carbonate minerals. Areas of high salinity are noted in isolated 

areas of the Sparta, predominantly as a result of inferred 

upwelling from high-salinity groundwater in underlying 

formations.

Cane River Aquifer

The Cane River Formation (hereinafter referred to as 

the “Cane River aquifer” when referring to the saturated 

part of the formation) comprises an aquifer of mixed clastic 

lithology with resultant variable water quality and water yield. 

Areas where good quality water can be extracted from the 

Cane River aquifer are generally in or very near the outcrop 

in southwestern Arkansas. Hosman and others (1968) listed 

the Cane River as a distinct aquifer in southern Arkansas; 

where locally extensive, water-producing sands were clearly 

identified in and near the outcrop area. Because the sand units 

are thin and regionally discontinuous, the clay-dominated 

lithology of the Cane River Formation in southern Arkansas 

was listed as part of the regional lower Claiborne confining 

unit (Arthur and Taylor, 1990; Hosman and Weiss, 1991; 

Hart and others, 2008; Clark and Hart, 2009). In northeastern 

Arkansas, the formation changes from a clay-dominated to 

sand-dominated facies that cannot be differentiated from 

the Sparta Sand or the Carrizo Sand. These three formations 

collectively are referred to as the Memphis Sand aquifer or in 

regional geologic framework analysis as the middle Claiborne 

aquifer (Hosman and Weiss, 1991; Hart and others, 2008; 

Clark and Hart, 2009). 

Geologic Setting

The Cane River Formation (Spooner, 1935) is a 

sequence of marine clays and shales that includes minor 

amounts of marls, silts, and marine sand. The Cane River 

was incorporated as a part of the undifferentiated Eocene 

(Veatch, 1906; Stephenson and Crider, 1916). The Cane River 

Formation represents the most extensive marine transgression 

during Claiborne time. At the margins of the embayment, 

the formation becomes extremely variable in lithology. 

The sand content exceeds 40 percent in parts of Desha and 

Lincoln Counties. The orientation of the high-sand content 

area is normal to the presumed sea shoreline during Cane 

River deposition. Other sand bodies, such as those located 

in Columbia County, have an orientation parallel to the 

presumed shoreline. The occurrence of massive sand bodies 

and the pattern of sand distribution are believed to represent a 

combination of channel sands near the seaward extremities of 

the ancestral Mississippi River and other large rivers. These 

rivers fed sediment that developed offshore and nearshore 

sand bars near the mouths of river-delta distributaries (Payne, 

1972).

The Cane River overlies the Carrizo Sand and is overlain 

by the Sparta Sand. Well-developed sand bodies normally are 

found only around the margins of the Mississippi embayment 

(Hosman and others, 1968; Payne, 1972). Regionally, the sand 

percentage decreases south and southwest of the embayment; 

in southeastern Arkansas, the Cane River virtually contains 

no sand. The sand accumulation extending from northern 

Louisiana, through parts of southwestern Arkansas, and into 

northern Mississippi probably represents a marginal edge of 

a delta of the ancestral Mississippi River (Payne, 1972). In 

the subsurface of southern Arkansas, the Cane River becomes 

a marine clay and serves as a confining unit (Onellion and 

Criner, 1955; Hosman and others, 1968; Petersen and others, 

1985). In northern Arkansas, the Cane River undergoes a 

facies change and north of latitude 35 degrees, the marine 

clay becomes sand. This northern sand facies of the Cane 

River is included as the middle part of the Memphis Sand 

and is generally indistinguishable from the Sparta aquifer. 

Although the Cane River is undifferentiated, a massive sand 

(Winona Sand of Mississippi) and overlying clay (Zilpha Clay 

of Mississippi) are easily observed in electric logs in Lee and 

Phillips Counties (Hosman and others, 1968; Payne, 1972). 

Tait and others (1953) report that in Columbia County, 

the Cane River Formation consists mainly of shale and silty 

shale with thin beds of sand in the south and becomes sandier 
176 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

in the northern part of the county. Some sand beds attain a 

thickness of 40–50 ft. Plebuch and Hines (1969) described 

the Cane River in Clark, Cleveland, and Dallas Counties as 

consisting of sand, clay, and sandy clay with some ferrous 

cement. Ludwig (1973) describes the Cane River Formation in 

Hempstead, Miller, and Nevada Counties as being composed 

of sand, silt, clay, and lignite. Zachry and others (1986) 

reported that in Columbia and Union Counties, the Cane 

River dominantly is composed of claystone with thin scattered 

sandstone units near its outcrop in Columbia County. 

The strike of the Cane River Formation is inferred to 

be approximately northeast to southwest and parallel to the 

general structure of the Mississippi embayment (Stephenson 

and Crider, 1916). In south-central and southwestern Arkansas, 

the regional dip of the Cane River is to the east and southeast 

at 25–50 ft/mi toward the Mississippi embayment and the 

Desha Basin. Major regional structural elements experienced 

considerable growth during the deposition of the Cane River, 

as noted by the thickening of the formation within these 

structures. In Arkansas, these structural features include the 

Gulf Coast geosynclines, the Mississippi embayment, and the 

Desha Basin. Normal faulting is common in the Cane River 

(Payne, 1972). In Hempstead, Miller, and Nevada Counties, 

the Cane River is cut by several northeast-southwest trending 

faults with displacement of as much as 280 ft (Ludwig, 1972). 

In a faulted graben in Union County, the lower half of the 

Cane River (about 150 ft) is in contact against the Wilcox 

Group (Broom and others, 1984).

The reported thickness of the Cane River Formation 

varies greatly, likely because of the fact that for some time the 

Claiborne Group was undifferentiated. Payne (1972) reported 

that the thickness ranged from 200 to 750 ft thick, which 

is in agreement with most historical reports. Generally the 

formation thickens from west to east. A minimum thickness of 

200 ft is noted in western Arkansas in the area of Hempstead, 

Miller, and Nevada Counties (Ludwig, 1973). The formation 

reaches a maximum thickness of 600–750 ft (Payne, 1972). 

Hydrologic Characteristics

The Cane River is considered an important aquifer 

along the margin of the Mississippi embayment in southern 

Arkansas. In this area, the Cane River comprises an aquifer 

system composed of poorly connected sand bodies of which 

each are 25 ft or more in thickness. The hydraulic conductivity 

of the aquifer is estimated to be 5.3 to 6.7 ft/d for sand units 

that are 25–50 ft thick and conservatively estimated to be 13.4 

ft/d for sand units that are 100–125 ft thick (Payne, 1972).

Near the outcrop and subcrop areas, the aquifer is under 

water-table conditions. Downdip from these areas, the aquifer 

becomes confined by overlying and underlying beds and 

is under artesian conditions (Petersen and others, 1985). In 

Chicot County, the Cane River is not considered an aquifer 

because it is composed of fine-grained materials (Onellion and 

Criner, 1955). The Cane River gradually changes downslope 

to a relatively uniform confining clay bed (Hosman and 

others, 1968; Payne, 1972; Petersen and others, 1985). In 

Union County, the Cane River Formation is considered to be 

a confining unit with little capacity for transmission of fluids, 

with the exception of possible fluid transfer along fault zones 

(Broom and others, 1984).

Yields of the Cane River are variable but are sufficient 

for public supply in the smaller towns in southwestern 

Arkansas. Public-supply wells for three cities in Lafayette 

County produced 120, 300, and 920 gal/min (Ludwig, 1972), 

and two public-supply wells in Dallas County each produced 

50 gal/min (Plebuch and Hines, 1969). Wells in Columbia 

County may yield as much as 300 gal/min (Tait and others, 

1953). Shallow wells in the outcrop area generally yield 

between 5 and 10 gal/min (Hosman and others, 1968).

The principal source of recharge to the aquifer is 

infiltration of precipitation through exposures in the outcrop 

area in the western part of the Mississippi embayment (Hosman 

and others, 1968). Recharge may occur through younger 

sedimentary materials, when the Cane River outcrop is covered. 

A minor amount of recharge takes place by upward movement 

of water from the underlying Carrizo aquifer and the overlying 

Wilcox aquifer. Water is lost from the aquifer from pumping 

wells and from natural discharge of upward leakage through 

confining units. A very minor component of natural discharge 

may occur as base flow into streams incised into the Cane River 

(Hosman and others, 1968; Payne, 1972).

Regional flow of water is generally south and southeast 

toward the Gulf Coast geosyncline and the Mississippi Alluvial 

Valley. Upward flow from the aquifer occurs through overlying 

leaky confining units. This occurs when the hydraulic head of 

the Cane River is more than the hydraulic head of the overlying 

Sparta aquifer (Payne, 1972; Petersen and others, 1985). A 

potentiometric-surface map was created for the Cane River by 

Ludwig (1973) and Terry and others (1986). The direction of 

flow was to the south and east. Ludwig (1973) noted that water 

levels were not affected by pumping. Although historical waterlevel measurements have been made in the Cane River aquifer, 

recent water levels in the aquifer have not been measured.

Water Use

Although present in many areas of southern Arkansas, 

water-quality concerns have restricted use of the Cane River 

aquifer. In many areas in southeastern Arkansas, the aquifer 

is too salty for most uses (Hewitt and others, 1949; Onellion 

and Criner, 1955; Onellion, 1956; Bedinger and Reed, 1961; 

Albin, 1964). Historically in southwestern Arkansas, the 

greatest use has been for domestic supply. The aquifer also was 

a source of public-supply water in Lafayette County (Ludwig, 

1973) and Dallas County (Plebuch and Hines, 1969). Lower 

yields inadequate for public-supply use were noted in wells in 

northern and western Columbia County and in Union County, 

north of El Dorado (Baker and others, 1948; Tait and others, 

1953). Twenty-three wells reported use from the aquifer in 

2010 (fig. 58). Also, water use for irrigation was reported 

from the aquifer for the first time in 2007 in Lafayette County 

(Terrance W. Holland, U.S. Geological Survey, written 

commun., 2012).
EXPL

IrrigationPublic su

Extent of CWell type a

gallons to represwater-usrepresen

94° 92° 91° 93°

90°

36°

35°

34°

YELL

LEE

UNION

WHITE

POLK

POPE

DREW

PIKE

SCOTT

CLARK

CLAY

ASHLEY

DESHA

BENTON

LOGAN

SALINE

IZARD

PULASKI LONOKE

ARKANSAS

NEWTON

GRANT

CHICOT

MADISON

STONE

MILLER

SHARP

CROSS

DALLAS

PRAIRIE

BOONE

PHILLIPS

PERRY

SEARCY

MARION

FULTON

SEVIER

MISSISSIPPI

JEFFERSON

NEVADA

POINSETT

GARLAND

COLUMBIA

BAXTER

OUACHITA

BRADLEY

JOHNSON

WASHINGTON

MONROE

GREENE

JACKSON

CARROLL

HOWARD

LINCOLN

CALHOUN

CONWAY FAULKNER

VAN BUREN FRANKLIN

CRAIGHEAD

HEMPSTEAD

RANDOLPH

CLEBURNE

MONTGOMERY

LAWRENCE

ST. FRANCIS

CRAWFORD

CLEVELAND

HOT SPRING

INDEPENDENCE

LITTLE

RIVER

WOODRUFF CRITTENDEN

LAFAYETTE

SEBASTIAN

0 15 0 30 

15

Base from U.S. Geological Survey digital data, 1:2,000,000

Figure 58. Wells with reported water use from the Cane River aquifer in Arkansas, 2010.
178 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Reported water use for the Cane River aquifer is shown 

in table 26. It appears that the amount of use reported for 

1965 by Halberg and Stephens (1966) might have been 

underestimated, as Ludwig (1973) assessed 3.04 Mgal/d 

were withdrawn in 1965. In 1965, a steam generation plant 

withdrew 1.8 Mgal/d in the town of Stamps in Lafayette 

County (Ludwig, 1973). It is unknown how long this plant 

was operated.

Lafayette County has consistently been the largest 

user of the Cane River aquifer, primarily for public supply 

(fig. 59). Municipalities using the aquifer included Bradley, 

Lewisville, and Stamps (all Lafayette County) and Sparkman 

(Dallas County), whose wells were drilled in the early 1930s 

(Hale and others, 1947). Lewisville used 0.1 Mgal/d in 1960 

and 1965, while Stamps used 0.18 and 0.19 Mgal/d (Ludwig, 

1973). Cities in Lafayette County have continued use of the 

aquifer (2013) as their public-supply source, while in the mid2000s, Sparkman switched from the Cane River aquifer to the 

Ouachita River. 

Table 26. Water use from the Cane River aquifer in Arkansas, 1965–2010. 

[Counties shown are only those with published data. Data from Halberg and Stephens (1966); Halberg (1972, 1977); Holland (1981, 1987, 1993, 1999, 2004, 

2007). Units are million gallons per day]

County 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Columbia 0.06 0.09 0.10 0.16 0.00 0.00 0.00 0.00 0.00 0.00

Dallas 0.06 0.04 0.13 0.15 0.00 0.00 0.00 0.00 0.00 0.00

Hot Spring 0.02 0.07 0.08 0.08 0.00 0.00 0.00 0.00 0.00 0.00

Lafayette 0.32 2.08 2.47 3.68 1.30 0.19 1.43 0.13 0.67 0.65

Miller 0.14 0.50 0.42 0.92 0.59 0.23 0.27 0.00 0.00 0.00

Nevada 0.05 0.39 0.13 0.16 0.05 0.02 0.02 0.00 0.00 0.00

Ouachita 0.17 0.18 0.15 0.12 0.00 0.00 0.00 0.00 0.04 0.08

Total 1

0.82 3.35 3.48 5.27 21.91 20.44 21.72 0.13 0.71 0.73

1

Ludwig (1973) reported that total water use from the Cane River aquifer in 1965 was 3.04 million gallons per day.

2

In the 1985–95 reports, withdrawals in Greene County were reported to the Cane River aquifer; these were later removed. The published totals are slightly 

different from Holland (1987, 1993, 1999).
EXPLANA

Annual water withdrawn f

in million gallons per d

No color represents no report

0.01 to 0.10

0.11 to 0.50

0.51 to 1.00

1.01 to 1.50

0 60 0 60 1

Base from U.S. Geological Survey digital data 1:2,000,000 Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977;

 Holland, 1981, 1987, 1993, 1999, 2004, 2007

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

19651980 1985

1970 1975

Figure 59. Water-use rates for the Cane River aquifer in Arkansas from 1965 to 2010. 
94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 

36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° EXPLANA

Annual water withdrawn 

in million gallons per 

No color represents no repor

0.01 to 0.10 0.11 to 0.50 0.51 to 1.00 1.01 to 1.50 

0 60 0 60 

1990 2005 2010 1995 2000 Base from U.S. Geological Survey digital data 1:2,000,000 Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977; Holland, 1981, 1987, 1993, 1999, 2004, 2007

Figure 59. Water-use rates for the Cane River aquifer in Arkansas from 1965 to 2010.—Continued
Aquifers of the Coastal Plain 181

Water Quality

Areas where good quality water can be extracted from 

the Cane River aquifer are generally in or very near the 

outcrop. The outcrop extends in a narrow band from the very 

southwestern corner of the State up through central Arkansas. 

Changes in lithology and sand thickness throughout the 

extent of the Cane River affect water quality as the aquifer 

dips to greater depths below land surface. In the southern 

and southeastern part of the State, data from electric logs 

indicate that the water is too saline for most uses (Hewitt and 

others, 1949; Onellion and Criner, 1955; Broom and others, 

1984). In northeastern Arkansas, the Cane River changes from 

a clay-dominated to sand-dominated facies and cannot be 

differentiated from the Sparta Sand or the Carrizo Sand.

Plebuch and Hines (1969) described groundwater from 

the Cane River aquifer in Clark, Cleveland, and Dallas 

Counties as soft with generally low iron concentrations. In 

other areas, however, iron concentrations were high enough 

to require treatment for certain uses. Ludwig (1973) reported 

that freshwater possibly could be obtained from most of 

the area comprising Hempstead, Lafayette, Miller, and 

Nevada Counties, although groundwater was increasingly 

mineralized in the downgradient direction of flow. These 

results were based on electric logs and chemical analysis of 

groundwater from wells serving as sources of public supply. 

Dissolved-solids and chloride concentrations ranged upward 

to 679 and 142 mg/L, respectively, and iron concentrations 

were generally less than 0.3 mg/L (Ludwig, 1972). South 

of this area, groundwater was described as a soft, sodiumbicarbonate water type with a moderately high mineral 

content that increased with depth (Tait and others, 1953). 

Further north in Hot Spring County, groundwater from the 

aquifer was described as very soft with low dissolved-solids 

concentrations, high iron concentrations, and low pH that 

could cause corrosion (Halberg and others, 1968). Hosman 

and others (1968) noted that the chemical characteristics of the 

groundwater varied with dissolved-solids concentrations; at 

lower dissolved-solids concentrations, a calcium-bicarbonate 

water type was predominant. As dissolved-solids increased, 

the groundwater transitioned first to a sodium-bicarbonate, 

then to a sodium-bicarbonate chloride type, and finally 

to a sodium-chloride type at the highest dissolved-solids 

concentrations. Dissolved-solids concentrations generally 

increased with depth, and the highest dissolved-solids 

concentrations in the aquifer were associated with fault 

zones. Outside of fault zones, dissolved-solids concentrations 

typically were less than 1,000 mg/L (Hosman and others, 

1968).

General Geochemistry and Water Type

Available data for the Cane River aquifer from the USGS 

NWIS and ADEQ databases yielded 45 groundwater sites with 

associated water-quality data. In general, the water quality 

is very good compared to Federal drinking-water standards 

(U.S. Environmental Protection Agency, 2009). A review of 

the USGS NWIS and ADEQ data supports earlier assessments 

of the groundwater from the aquifer being a soft, sodiumbicarbonate water type. Median concentrations for calcium 

(5.8 mg/L), magnesium (1.5 mg/L), and sodium (53 mg/L) 

indicate that sodium is the most prominent cation, giving 

the groundwater its overall soft-water identification (fig. 60; 

table 27). A review of cation (calcium, magnesium, sodium, 

and potassium) data supports the geochemical transitioning 

of groundwater from a calcium- to a sodium-dominated water 

type (Hosman and others, 1968). Spatial analysis reveals that 

calcium-dominated groundwater occurs only in the outcrop 

area. Abundant clay in the aquifer provides a high cationexchange capacity. The result is that sodium replaces calcium 

at solid-phase exchange sites along the flow path. This results 

in a transitioning to sodium-dominated groundwater (sodium 

more than 50 percent of total cations) downgradient from 

the outcrop area (fig. 61). Isolated areas of elevated chloride 

(sodium-chloride water type) were observed in the aquifer and 

are discussed below.

Values of pH in the Cane River aquifer range from 4.5 to 

8.6 with a median of 7.7 standard units (table 27). The lowest 

pH values are associated with sites in the outcrop area with 

large increases in pH occurring over short distances from the 

outcrop area (fig. 61). The average pH value for precipitation 

in southern Arkansas is approximately 4.7 standard units 

(Kresse and Fazio, 2002), which explains the lower pH values 

of groundwater in the outcrop area (recharge zone) for the 

Cane River aquifer. The infiltrating water is rapidly buffered 

along the flow path by dissolution of carbonate minerals, 

which is reflected by the very low bicarbonate concentrations 

(less than 20 mg/L) for groundwater in the outcrop area 

compared to the high concentrations (more than 100 mg/L) at 

short distances from the outcrop area (fig. 61).
182 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

0

50

100

150

200

250

300

350

400

450

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron

Concentrations, in milligrams per liter

500

Concentration, in micrograms per liter

700

800

900

1,000

0

100

200

300

400

500

600

40 40

40

44

45

45

28

28

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

Constituent Constituent

Figure 60. Interquartile range of selected chemical constituents for groundwater from the Cane River aquifer in Arkansas.

Table 27. Descriptive statistics for selected chemical constituents in groundwater from the Cane River aquifer in Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 1.0 5.8 65 13.4 40

Magnesium (mg/L) 0.07 1.5 18 3.45 40

Sodium (mg/L) 0.8 53 964 223 40

Potassium (mg/L) 0.4 2.3 17 3.99 40

Bicarbonate (mg/L) 1.0 145 460 127 44

Chloride (mg/L) 0.7 8.0 1,410 314 45

Sulfate (mg/L) 0.02 3.0 37 7.65 45

Silica (mg/L) 7.4 11 28 5.45 31

Nitrate (mg/L as nitrogen) 0.01 0.18 6.1 0.98 43

Dissolved solids (mg/L) 30 158 2,660 622 40

Iron (μg/L) 0.05 120 52,000 9,580 28

Manganese (μg/L) 0.13 20 293 77.6 18

Arsenic (μg/L) 0.03 0.03 0.03 0.03 4

Hardness (mg/L as calcium carbonate) 4 22 240 46 42

Specific conductance (μS/cm) 22 245 4,610 1,020 45

pH (standard units) 4.5 7.7 8.6 1.1 44
LEE

UNION

DREW

CLARK

ASHLEY

GRANT

DESHA

SALINE LONOKE

ARKANSAS

PULASKI

CHICOT

PRAIRIE

MILLER

PHILLIPS

JEFFERSON

DALLAS

NEVADA OUACHITA

COLUMBIA

MONROE

BRADLEY

LINCOLN

CALHOUN HEMPSTEAD

HOT SPRING

CLEVELAND

LAFAYETTE

LEE

UNION

DREW

CLARK

ASHLEY

GRANT

DESHA

SALINE LONOKE

ARKANSAS

PULASKI

CHICOT

PRAIRIE

MILLER

PHILLIPS

JEFFERSON

DALLAS

NEVADA OUACHITA

COLUMBIA

MONROE

BRADLEY

LINCOLN

CALHOUN HEMPSTEAD

HOT SPRING

CLEVELAND

LAFAYETTE

LEE

UNION

DREW

CLARK

ASHLEY

GRANT

DESHA

SALINE LONOKE

ARKANSAS

PULASKI

CHICOT

PRAIRIE

MILLER

PHILLIPS

JEFFERSON

DALLAS

NEVADA OUACHITA

COLUMBIA

MONROE

BRADLEY

LINCOLN

CALHOUN HEMPSTEAD

HOT SPRING

CLEVELAND

LAFAYETTE

LEE

UNION

DREW

CLARK

ASHLEY

GRANT

DESHA

SALINE LONOKE

ARKANSAS

PULASKI

CHICOT

PRAIRIE

MILLER

PHILLIPS

JEFFERSON

DALLAS

NEVADA OUACHITA

COLUMBIA

MONROE

BRADLEY

LINCOLN

CALHOUN HEMPSTEAD

HOT SPRING

CLEVELAND

LAFAYETTE

UNION

CLARK

GR

SALINE 

PU

MILLER

DALLAS

NEVADA OUACHITA

COLUMBIA

CALHOU

HEMPSTEAD

HOT SPRING

LAFAYETTE

UNION

CLARK

GRA

SALINE 

PU

MILLER

DALLAS

NEVADA OUACHITA

COLUMBIA

CALHOU

HEMPSTEAD

HOT SPRING

LAFAYETTE

94° 93° 

35°34°

94° 93° 92° 91°

35°34°

94° 93° 92° 91°

35°34°

94° 93° 

35°34°

94° 93° 92° 91°

35°34°

94° 93° 92° 91°

35°34°

0 0 

Geology map m

Base modified from U.S. Geological Survey digital data, 1:250,000Universal Transverse Mercator projection, zone 15

Sodium, in percent of major cations

0 to 3031 to 5051 to 7576 to 8586 to 9091 to 98

EXPLANATION

pH, in standard units

4.5 to 5.05.1 to 5.55.6 to 6.56.6 to 7.57.6 to 8.08.1 to 8.6

EXPLANATION

Bicarbonate, in milligra

1 to 2021 to 5051 to 100101 to 250251 to 350351 to 460

EXPLANATION

Nitrate, in milligrams per liter

0 to 0.250.26 to 0.50.51 to 12 to 2.52.6 to 6.1

EXPLANATION

Chloride, in milligrams p

0 to 1011 to 5051 to 150151 to 250251 to 500501 to 1,410

EXPLANATION

Silica, in milligrams per liter

0 to 1011 to 1516 to 2021 to 2526 to 28

EXPLANATION

Area enlarged

ARKANSAS

Cane River outcropCane River extent

EXPLANATION

Figure 61. Spatial distribution of selected chemical constituents for groundwater from the Cane River aquifer in Arkansas.
184 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Nitrate

Nitrate concentrations generally were low in the 

Cane River aquifer, ranging from 0.01 to 6.1 mg/L with a 

median of 0.18 mg/L as nitrogen (table 27). No site had a 

concentration that exceeded the MCL of 10 mg/L, and only 

5 of 43 sites had concentrations exceeding 0.5 mg/L. Nitrate 

concentrations greater than 1.0 mg/L occurred only in the 

outcrop area, demonstrating the vulnerability of shallow 

groundwater. Concentrations were less than 0.5 mg/L for all 

sites downgradient from the outcrop area, indicating one or 

more of the following conditions: (1) less connection with 

the surface because of greater depth and the presence of 

confining units, (2) dilution, (3) slow groundwater velocities, 

or (4) denitrification under reducing conditions hypothesized 

for groundwater downgradient from the outcrop area.

Iron

Similar to other Tertiary aquifers reviewed in this report, 

iron concentrations in the Cane River aquifer generally were 

greatest in the outcrop area (ranging up to 52,000 μg/L) and 

lowest (mostly less than 300 μg/L) downgradient from the 

outcrop area. Lower iron concentrations downgradient from 

the outcrop area are hypothesized to be the result of changes 

in redox zonation along the flow path, leading to possible 

mineralization of iron sulfides and other minerals formed 

under reducing conditions. A more detailed discussion for this 

theory of reducing conditions leading to formation of iron 

sulfides is found in the “Water Quality” section for the Sparta 

aquifer.

Silica

Silica concentrations in the Cane River aquifer ranged 

from 7.4 to 28 mg/L with a median of 11 mg/L (table 27). 

Similar to iron and some other constituents, the highest silica 

concentrations (more than 15 mg/L) occurred solely in the 

outcrop area, decreasing to less than 15 mg/L downgradient 

from the outcrop area. Likely mechanisms accounting for 

this spatial distribution include greater relative abundance 

of amorphous forms of quartz in the outcrop area, which 

results from weathering and diagenesis that contributes 

higher solubility forms of silica, and competition of silica, 

phosphorus, and other ions in solution for exchange sites on 

minerals along the flow path away from the outcrop area. Soil 

development and shallow groundwater processes can provide 

a source of mobile silica involving opal and microcrystalline 

forms of quartz cements (Basile-Doelsch and others, 2005; 

Macaulay, 2005). Organic compounds formed by celluloseconsuming fermentative bacteria can raise silica solubility 

to concentrations more than 110 mg/L and enhance silica 

dissolution. These organic compounds are unstable in many 

subsurface environments and can break down resulting 

in later precipitation of amorphous silica at relatively low 

temperatures (as low as 20° C) (Turner and others, 2002). 

It should be noted that higher concentrations of silica in the 

outcrop area of the Cane River also were noted for other 

Cretaceous and Tertiary aquifers including the Sparta and 

Cockfield aquifers. Silica behavior and early diagenesis has 

been implicated in control of aquifer hydraulic properties in 

the shallow Tertiary aquifers (Androes, 2006). Future studies 

are needed to elucidate this spatial geochemical phenomenon 

that has yet to be addressed in current and past publications.

Sulfate

Sulfate concentrations in the Cane River aquifer ranged 

from 0.02 mg/L to 37 mg/L with a median of 3.0 mg/L 

(fig. 60; table 27). These represent some of the lowest median 

and maximum sulfate concentrations of any of the aquifers 

in the Coastal Plain. No spatial relation was noted for the 

distribution of sulfate concentrations in the Cane River 

aquifer.

Chloride

Chloride concentrations ranged from 0.7 to 1,410 mg/L 

with a median of 8.0 mg/L (fig. 60; table 27). This median 

demonstrates the overall low chloride concentrations in 

groundwater from the Cane River aquifer, dominantly derived 

from rainwater concentrated by evapotranspiration processes 

(Kresse and Fazio, 2002; Kresse and Clark, 2008). Of the 

45 wells with chloride data, 26 (58 percent) had concentrations 

less than 10 mg/L. Only eight wells had concentrations 

exceeding the Federal secondary drinking-water regulation 

of 250 mg/L. A spatial distribution of chloride revealed 

concentrations greater than 250 mg/L generally occurring in 

Dallas and eastern Ouachita Counties. The four wells with 

chloride concentrations greater than 500 mg/L occurred in 

eastern Ouachita County (fig. 61). 

In summary, water quality from the Cane River aquifer 

is good with respect to Federal drinking-water standards. 

Groundwater generally is a calcium-bicarbonate water type 

in the outcrop area but transitions to a sodium-bicarbonate 

water type as a result of cation-exchange processes. Nitrate 

concentrations were less than the MCL of 10 mg/L for all 

samples. Salinity increases downdip from the outcrop area, 

and chloride concentrations can exceed the Federal secondary 

drinking-water regulation of 250 mg/L in some areas.

Carrizo Aquifer

The Carrizo Sand (hereinafter referred to as the 

“Carrizo aquifer” where referring to the saturated part of the 

formation) comprises an aquifer of limited use only in and 

near the outcrop area in southwestern Arkansas. Although 

the hydrologic characteristics associated with the Carrizo 

aquifer were deemed favorable for future development in 

south-central Arkansas (Hosman and others, 1968), abundant 

groundwater from overlying formations supplies water needs 

in that area of the State. In the northeastern part of the State, 

sand units within the Carrizo cannot be differentiated from 
Aquifers of the Coastal Plain 185

those of the overlying Cane River Formation and Sparta Sand. 

In previous regional geohydrologic framework analyses, the 

Carrizo aquifer was included in the lower Claiborne-upper 

Wilcox aquifer (Arthur and Taylor, 1990; Hosman and Weiss, 

1991) or the lower Claiborne aquifer (Hart and others, 2008; 

Clark and Hart, 2009). 

Geologic Setting

The Tertiary-age Carrizo Sand unconformably overlies 

the Wilcox Group and is overlain by the Cane River 

Formation. The Carrizo consists predominately of fine to 

coarse, micaceous, massive-bedded quartz sands with minor 

amounts of interbedded clays and silts and occasional lenses 

of lignite. The lithology is composed of more than 80 percent 

sand in the majority of Arkansas. The Carrizo was deposited 

as valley and channel fills and as beach sands over an irregular 

erosion surface (Payne, 1975). In Clark, Cleveland, and Dallas 

Counties, the Carrizo consists mainly of very fine to medium 

sand with minor clay and lignite (Plebuch and Hines, 1969).

Formation and sand-thickness maps (Payne, 1975) 

indicate a thickening along relatively narrow sinuous bands 

elongated in a northerly direction, likely normal to the 

shoreline of the early Claiborne sea. These deposits likely 

represent an ancient delta or fluvial plain. The pattern of 

deposition of the Carrizo is believed to have resulted from 

deposition in shore and nearshore environments during initial 

advance of the Claiborne sea over an erosional surface that 

was developed on sediments of the Wilcox Group by an 

ancestral Mississippi River system. The elongated areas of 

thickened Carrizo is interpreted to be the result of infilling of 

preexisting channels and valleys during Carrizo time. The lack 

of seaward gradation of the sand to clay ratio is indicative of a 

lack of appreciable deposition on the steep seaward side of the 

delta.

The Carrizo Sand and overlying Cane River Formation 

undergo facies changes north of latitude 35 degrees, and 

both formations become sand. This northern sand facies of 

the Cane River Formation and the underlying Carrizo Sand 

are generally indistinguishable from the Sparta Sand and 

are grouped together as the Memphis Sand (Counts, 1957; 

Hosman and others, 1968; Payne, 1972; Petersen and others, 

1985). The Claiborne Group in Cross, Lee, Lonoke, Monroe, 

Prairie, St. Francis, and Woodruff Counties was noted to 

be undifferentiated (Halberg and Reed, 1964). In parts of 

southern Lonoke and Prairie Counties, however, the Carrizo 

and the Sparta Sand can be recognized in the subsurface. Wells 

completed in the Carrizo aquifer were as far north as Prairie 

and Lee Counties.

The regional dip of the Carrizo Sand is into the Desha 

Basin, the Mississippi embayment, and the Gulf Coast 

geosynclines. Some movement of major structural features 

took place during Carrizo time. Normal faulting is extensive 

in southern Arkansas (Payne, 1975). The Carrizo dips toward 

the east-southeast in southern Arkansas, to the southeast in 

central and eastern Arkansas, and to the northeast into the 

Desha Basin in extreme southeastern Arkansas at a rate of 

20–50 ft/mi. The Carrizo is discontinuous and highly variable 

in thickness, notably in parts of Columbia, Ouachita, and 

Union Counties, where thicknesses of 30 ft or less occur. The 

thickness in the subsurface ranges from zero ft in areas of 

nondeposition to nearly 400 ft in southeastern Arkansas in the 

Desha Basin (Hosman and others, 1968; Payne, 1975; Petersen 

and others, 1985). The Desha Basin in southeastern Arkansas 

is a major negative structural element seen on the top of the 

Carrizo. Normal faulting is extensive in southern Arkansas as 

shown on structural maps (Plebuch and Hines, 1969; Payne, 

1975; Hosman, 1982; Petersen and others, 1985). Thickness 

of the Carrizo in Clark, Cleveland, and Dallas Counties varies 

considerably over short distances, ranging from about 60 to 

200 ft (Plebuch and Hines, 1969). The Carrizo crops out in a 

narrow band, 2–5 miles wide, through southern Hempstead, 

central Miller, and central Nevada Counties. 

Hydrologic Characteristics

Recharge to the Carrizo aquifer comes from rainfall on 

the outcrop, seepage from the overlying Mississippi River 

Valley alluvial aquifer, and lateral flow from the Sparta 

aquifer downdip into the Carrizo south of latitude 35 degrees. 

Discharge from the Carrizo occurs by withdrawals from 

wells and natural discharge by leakage through the overlying 

confining beds. Regional flow of water is generally downdip 

toward the axes of the Mississippi embayment and the Desha 

Basin (Hosman and others, 1968; Payne, 1975).

The Carrizo aquifer is not considered a major aquifer 

in Arkansas because of its erratic distribution, and therefore 

available hydrologic data are limited. There is an increase 

in permeability with increasing sand thickness. Results of 

45 aquifer tests provided the following hydraulic conductivity 

values: 29 ft/d for sands from 25 to 100 ft thick, 40 ft/d for 

sands from 100 to 200 ft thick, and 53 to 60 ft/d for sands 

from 200 to more than 300 ft thick (Payne, 1975). A single 

aquifer test in Hot Spring County yielded a transmissivity 

of about 550 ft2/d, a hydraulic conductivity of about 13 ft/d, 

and a specific capacity of 2 (gal/min)/ft (Hosman and others, 

1968). A well in Miller County yielded 100 gal/min and had a 

specific capacity of 3 (gal/min)/ft (Ludwig, 1973). Except in 

the outcrop area, the aquifer is under artesian conditions, and 

the regional flow is downdip to the east and southeast into the 

Desha Basin and the Mississippi embayment (Payne, 1975). 

In southern Arkansas, groundwater flow in the Carrizo aquifer 

is confined by the Wilcox Group below and the Cane River 

Formation above (Hosman and others, 1968). 
186 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Water Use

The Carrizo is only a minor aquifer in Arkansas and 

mainly used for domestic supply in southwestern Arkansas. 

Hosman and others (1968) noted that in south-central 

Arkansas the aquifer was untapped, where the hydrology of 

the Carrizo was most favorable for future development. Older 

reports state that the aquifer was not commonly utilized, 

perhaps because of high iron concentrations or limited 

available information on the aquifer’s extent and water 

availability (Halberg and others, 1968; Plebuch and Hines, 

1969). Most withdrawals from the Carrizo were domestic 

users within 5–10 mi of its outcrop (Albin, 1964; Terry and 

others, 1986). The Carrizo was evaluated for industrial use at 

Pine Bluff; however, the poor water quality rendered its use 

unsuitable (Hosman, 1964).

Published water-use data for the Carrizo aquifer are 

only available from 1965 to 1980 (table 28). Ludwig (1973) 

reported that 0.23 Mgal/d was withdrawn from Miller County 

wells in 1965, slightly higher than what was reported in 

Halberg and Stephens (1966). Prairie County users withdrew 

the most water from 1970 to 1980, but Ludwig (1973) 

attributed most use of the Carrizo to domestic use in Miller 

County (table 28). The city of Fouke (Miller County) obtained 

its water supply from a well screened in the Carrizo aquifer 

(Ludwig, 1973); however, later inventories reported the water 

source for Fouke was the Wilcox aquifer (Baker and others, 

1991). No wells currently are recorded in the ARWUDBS for 

this aquifer. A few commercial enterprises that do not meet 

the reporting requirements for ARWUDBS use the aquifer 

in Miller and Nevada Counties (Lyle Godfrey, Arkansas 

Department of Health, written commun., 2012). 

Water Quality

Databases accessed for this study contained waterquality results for only 12 wells completed in the Carrizo 

aquifer. Although groundwater quality of the aquifer 

generally is good in and near the outcrop area, it degrades 

downgradient and becomes unusable for most purposes 

because of increased chloride concentrations (Hosman 

and others, 1968; Terry and others, 1986). Most wells 

completed in the Carrizo are located in a southwest to 

northeast trending line, which trends from western Miller 

County into southern Saline County. Few data were 

available for the Carrizo aquifer in Clark, Cleveland, and 

Dallas Counties, but in south-central Dallas and southern 

Cleveland Counties the aquifer probably contained more 

than 1,000 mg/L dissolved solids, making it unsuitable for 

most uses (Plebuch and Hines, 1969). The Carrizo aquifer 

contains freshwater throughout much of Hempstead, 

Lafayette, Little River, Miller, and Nevada Counties except 

in south-central Lafayette County (Ludwig, 1973). One 

well completed in the Carrizo produced groundwater of a 

soft, sodium-bicarbonate type, but another well in eastern 

Grant County had 280 mg/L chloride (Halberg and others, 

1968). Most reports listed groundwater from the Carrizo 

as a soft, sodium-bicarbonate water type with a low to 

moderate mineral concentration (Hosman and others, 1968; 

Ludwig, 1972; Terry and others, 1986). Hosman and others 

(1968) stated that water type varies with dissolved-solids 

concentration and noted that the water is either a calcium/

magnesium-bicarbonate or a sodium-bicarbonate type for 

groundwater with low dissolved-solids concentrations and 

evolves to a sodium-bicarbonate-chloride water type for 

dissolved-solids concentrations greater than 400 mg/L.

General Geochemistry and Water Type

Median concentrations for most constituents in the 

Carrizo aquifer reveal an overall good quality, sodiumbicarbonate groundwater with low iron concentrations. All 

samples had percent sodium (as a percentage of the total 

cations) values indicative of a sodium-bicarbonate water 

type. Six samples had sodium greater than 95 percent, and 

11 of 12 samples exceeded 80 percent (fig. 62). Values of 

pH ranged from 7.2 to 8.4 with a median of 7.9 (table 29), 

and no strong spatial trend was evident, likely a result 

of the paucity of data. Bicarbonate concentrations were 

less than 250 mg/L in 8 of 12 samples. Two samples 

had concentrations of 449 and 518 mg/L and were in 

southeastern Ouachita and southeastern Lee Counties, 

respectively (fig. 62).

Table 28. Water use from the Carrizo aquifer in Arkansas, 

1965–80. 

[Counties shown are only those with published data. Data from Halberg and 

Stephens (1966); Halberg (1972, 1977); Holland (1981). Units are million 

gallons per day]

County 1965 1970 1975 1980

Hempstead 0.00 0.06 0.09 0.10

Hot Spring 0.02 0.06 0.06 0.07

Miller 0.09 0.06 0.08 0.18

Nevada 0.00 0.03 0.04 0.06

Ouachita 0.05 0.07 0.06 0.08

Prairie 0.00 0.18 0.19 0.25

Total 0.16 0.46 0.52 0.74
YELL

UNION

DREW

LEE

PIKE

CLARK

DESHA

ASHLEY

SALINE LONOKE

ARKANSAS

PULASKI

CHICOT

GRANT

PERRY

PRAIRIE

JEFFERSON

DALLAS

SCOTT

PHILLIPS

NEVADA

GARLAND

OUACHITA

COLUMBIA

LINCOLN

HOT SPRING

WHITE LOGAN

MONROE

BRADLEY

CALHOUN

HEMPSTEAD

HOWARD HOWARDHOWARD HOWARD

MONTGOMERY

CLEVELAND

ST. FRANCIS

FAULKNER

CONWAY WOODRUFF

YELL

UNION

DREW

LEE

PIKE

CLARK

DESHA

ASHLEY

SALINE LONOKE

ARKANSAS

PULASKI

CHICOT

GRANT

PERRY

PRAIRIE

MILLER

JEFFERSON

DALLAS

SCOTT

PHILLIPS

NEVADA

GARLAND

OUACHITA

COLUMBIA

LINCOLN

HOT SPRING

WHITE LOGAN

MONROE

BRADLEY

CALHOUN

HEMPSTEAD

MONTGOMERY

CLEVELAND

LAFAYETTE MILLERLAFAYETTE

MILLERLAFAYETTE MILLERLAFAYETTE

ST. FRANCIS

FAULKNER

CONWAY WOODRUFF

YELL

UNION

DREW

LEE

PIKE

CLARK

DESHA

ASHLEY

SALINE LONOKE

ARKANSAS

PULASKI

CHICOT

GRANT

PERRY

PRAIRIE

JEFFERSON

DALLAS

SCOTT

PHILLIPS

NEVADA

GARLAND

OUACHITA

COLUMBIA

LINCOLN

HOT SPRING

WHITE LOGAN

MONROE

BRADLEY

CALHOUN

HEMPSTEAD

MONTGOMERY

CLEVELAND

ST. FRANCIS

FAULKNER

CONWAY WOODRUFF

YELL

UNION

DREW

LEE

PIKE

CLARK

DESHA

ASHLEY

SALINE LONOKE

ARKANSAS

PULASKI

CHICOT

GRANT

PERRY

PRAIRIE

JEFFERSON

DALLAS

SCOTT

PHILLIPS

NEVADA

GARLAND

OUACHITA

COLUMBIA

LINCOLN

HOT SPRING

WHITE LOGAN

MONROE

BRADLEY

CALHOUN

HEMPSTEAD

MONTGOMERY

CLEVELAND

ST. FRANCIS

FAULKNER

CONWAY WOODRUFF

0 30 60 MILES

0 30 60 KILOMETERS

93° 92° 91°

34°35°

94° 93° 92° 91° 94°94° 94°

34°35°

93° 92° 91°

34°35°

93° 92° 91°

34°35°

Base modified from U.S. Geological Survey digital data, 1:250,000 Geology map modified from Petersen and others, 1985Universal Transverse Mercator projection, zone 15

EXPLANATION EXPLANATION

EXPLANATION EXPLANATION

125 to 150151 to 250251 to 500501 to 600601 to 750751 to 2,765

Dissolved Solids, in milligrams per liter

36 to 100101 to 150151 to 250251 to 350351 to 518

Bicarbonate, in milligrams per liter

0 to 6061 to 7071 to 8081 to 8586 to 9091 to 98

Sodium, in percent of major cations

Chloride, in milligrams per liter

3 to 1011 to 2021 to 5051 to 250251 to 500501 to 1,350

Figure 62. Spatial distribution of selected chemical constituents for groundwater from the Carrizo aquifer in Arkansas.
188 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Nitrate

Nitrate concentrations in the Carrizo aquifer ranged 

from 0.01 to 1.1 mg/L with a median of 0.09 mg/L as 

nitrogen (table 29). All but one of the nitrate samples had 

concentrations below 1.0 mg/L, which is well below the 

Federal MCL of 10 mg/L as nitrogen. All well depths were 

more than 195 ft, ranging from as much as 400 ft in the 

outcrop area up to 2,050 ft for a well in Jefferson County. 

In most aquifers of the Coastal Plain, nitrate concentrations 

showed an inverse relation with depth and were dominantly 

more than 1.0 mg/L for well depths less than 50–100 ft. The 

paucity of data prevented a rigorous statistical analysis of well 

depth and nitrate concentrations in the Carrizo aquifer. The 

somewhat greater depths for wells completed in the Carrizo 

aquifer compared to other Tertiary aquifers may render the 

groundwater producing zone less vulnerable to surface sources 

of nitrogen and other contaminants. Other Tertiary aquifers in 

Arkansas (Jackson Group, Cockfield, Sparta, Cane River, and 

Wilcox aquifers) generally had nitrate concentrations more 

than 5 mg/L in groundwater from wells with depths less than 

approximately 150 ft.

Iron

Iron concentrations for nine wells in the Carrizo aquifer 

ranged from 0.05 to 1,000 μg/L with a median of 130 μg/L 

(fig. 63; table 29). Only three of the nine wells had iron 

concentrations that exceeded the Federal secondary drinkingwater regulation of 300 μg/L. All iron concentrations were 

relatively low compared to other aquifers in the State. Samples 

were too few to evaluate the spatial distribution of iron 

concentrations throughout the Carrizo aquifer.

Table 29. Descriptive statistics for selected chemical constituents in groundwater from the Carrizo aquifer in Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; NA, not analyzed; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 0.5 3.9 20 7.2 12

Magnesium (mg/L) 0.35 1.0 7 2.09 11

Sodium (mg/L) 6.2 130 1,050 271 12

Potassium (mg/L) 0.6 2.67 11 2.81 12

Bicarbonate (mg/L) 36 197 518 144 12

Chloride (mg/L) 3.0 34 1,350 363 12

Sulfate (mg/L) 0.02 3.0 90 24.3 12

Silica (mg/L) 9.25 12 30 5.82 9

Nitrate (mg/L as nitrogen) 0.01 0.09 1.1 0.3 11

Dissolved solids (mg/L) 125 329 2,770 701 12

Iron (μg/L) 0.05 130 1,000 372 9

Manganese (μg/L) 0.13 0.13 120 41.6 7

Arsenic (μg/L) NA NA NA NA NA

Hardness (mg/L as calcium carbonate) 4.0 15 79 27 12

Specific conductance (μS/cm) 127 572 4,680 1,200 12

pH (standard units) 7.2 7.9 8.4 0.4 12
Aquifers of the Coastal Plain 189

Sulfate

Sulfate concentrations in 12 samples from the Carrizo 

aquifer were low compared to that in many other aquifers 

and ranged from 0.02 to 90 mg/L with a median of 3.0 mg/L 

(fig. 63; table 29). The second highest sulfate concentration 

was 22 mg/L, which demonstrates the overall low sulfate 

concentration of groundwater from the Carrizo. The maximum 

concentration of 90 mg/L was in a sample from a well in 

northwestern Ouachita County. No pattern of increasing 

sulfate concentrations was noted downdip from the outcrop 

area, and too few well sites were available for a meaningful 

interpretation of the spatial distribution of sulfate.

Chloride and Dissolved Solids

Chloride concentrations in 12 samples from the Carrizo 

aquifer ranged from 3.0 to 1,350 mg/L with a median of 

34 mg/L (fig. 63; table 29). The maximum concentration 

was for a well in southeastern Ouachita County that was 

approximately 30 mi from the outcrop area. Hosman 

and others (1968) and Terry and others (1986) noted that 

groundwater downdip from the outcrop area becomes unusable 

as a result of increasing chloride concentrations. Only two 

other wells were higher than the Federal secondary drinkingwater regulation of 250 mg/L for chloride, and these wells 

were in Jefferson (277 mg/L) and Prairie (310 mg/L) Counties 

northeast of the outcrop area (fig. 62). The distribution of 

dissolved-solids concentrations was similar to the distribution 

of chloride concentrations, which is typical. The highest 

concentrations were in areas outside of the outcrop area 

(fig. 62). Four of the five wells with dissolved solids exceeding 

the Federal secondary drinking-water regulation of 500 mg/L 

were far removed from the outcrop area.

9

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

12 11

12

12

12

12

9

0

50

100

150

200

250

300

350

400

450

Concentrations, in milligrams per liter

500

Concentration, in micrograms per liter

700

800

900

1,000

0

100

200

300

400

500

600

Constituent Constituent

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron

Figure 63. Interquartile range of selected chemical constituents for groundwater from the Carrizo aquifer in Arkansas.
190 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

In summary, samples from the Carrizo aquifer reveal an 

overall good quality, sodium-bicarbonate groundwater with 

low iron concentrations as compared to many other aquifers of 

the Coastal Plain. Nitrate concentrations from data compiled 

for this report were extremely low throughout the aquifer. 

Sulfate and chloride concentrations generally are low for areas 

near the outcrop but appreciably increase with distance from 

the outcrop area.

Wilcox Aquifer

The Wilcox Group contains a major lower aquifer, termed 

the lower Wilcox aquifer, and minor aquifers associated 

with sands of the upper Wilcox Group (Hosman and others, 

1968). In later regional framework and embayment models, 

three units were used to represent the Wilcox Group: the 

lower Claiborne-upper Wilcox aquifer, the middle Wilcox 

aquifer, and the lower Wilcox aquifer (Arthur and Taylor, 

1986; Brahana and Mesko, 1988; Renken, 1998; Hart and 

others, 2008; Clark and Hart, 2009). The lower Claiborneupper Wilcox aquifer included all sand beds below the clay 

beds of the lower Claiborne Group and included sand beds 

present in the upper Wilcox Group. In Arkansas, this model 

unit included the Carrizo Sand of the Claiborne Group and 

sand units in the upper Wilcox Group that are hydraulically 

connected to the lower Claiborne Group. The middle Wilcox 

aquifer included the irregular and discontinuous sand beds 

that are interbedded with layers of clay, silt, and lignite within 

the upper unit of the Wilcox Group. The lower Wilcox aquifer 

included thin, interbedded layers of lignitic sands and clays of 

the lower Wilcox unit. Water-use (Holland, 2007) and waterlevel reports (Pugh, 2010) refer to the combined sands simply 

as the Wilcox aquifer. For purpose of this report, the saturated 

part of the Wilcox Group most often will be referred to as the 

“Wilcox aquifer,” unless summarizing historical reports that 

reference the aquifer according to divisions cited above. 

Geology

The Wilcox Group is a predominantly unconsolidated 

sequence comprising two distinct lithologic units: a lower 

unit of mostly sand and an upper predominately shale or 

clay unit (Cushing and others, 1964). The Wilcox is of 

Eocene age and extends throughout most of eastern and 

southern Arkansas. Most of the beds of the Wilcox of eastern 

Arkansas are considered to be nonmarine in origin (Renfroe, 

1949). The Wilcox (Crider and Johnson, 1906) generally is 

undifferentiated, except in central Arkansas where the Berger 

and Saline Formations and the Detonti Sand may be identified 

(Gordon and others, 1958). Although undifferentiated, the 

upper and lower units of the Wilcox are recognizable in the 

State. 

The upper unit of the Wilcox Group predominates in 

the southern part of Arkansas and consists of complexly 

interbedded layers of clay, sandy clay, thin and discontinuous 

sand, and lignite (Joseph, 1998b). The thin sands of this unit 

serve as aquifers primarily in the southern extent of the Wilcox 

(Hosman and others, 1968). In southern Arkansas, the Wilcox 

overlies the Midway Group, and crops out in a discontinuous 

band 1–3 mi wide (Joseph, 1998b) and commonly is overlain 

by terrace deposits and alluvium of Quaternary age. The 

Wilcox becomes progressively thicker downdip from the 

outcrop, ranging in thickness from only a few feet at the 

outcrop to about 1,100 ft in Bradley County in southern 

Arkansas (Albin, 1964; Petersen and others, 1985). The 

Wilcox dips toward the axis of the Mississippi embayment 

at about 50 ft/mi in southern Arkansas (Hosman and others, 

1968). 

In northeastern Arkansas, the upper and lower Wilcox 

Group units are present. The upper Wilcox Group unit is 

composed of thin, interbedded layers of lignitic sands and 

clays. The lower predominately sand unit may contain as 

many as three major sand units, although they are collectively 

referred to as the lower Wilcox aquifer (Hosman and others, 

1968). Where differentiated in northeastern Arkansas, the 

Wilcox contains the Flour Island Formation, the Fort Pillow 

Sand, and the Old Breastworks Formation (Renken, 1998). 

Of note, the lower sand contains the “1,400-foot” sand as first 

used by Klaer (1940), which is a common term for this aquifer 

in northeastern Arkansas. The Wilcox contains sand beds 

more than 200 ft thick east of Crowleys Ridge in northeastern 

Arkansas (Petersen and others, 1985). The maximum 

thickness of the lower Wilcox aquifer where it contains 

freshwater is 300 ft. In most of the northern half of the 

embayment, the lower Wilcox aquifer is more than 80 percent 

sand (Hosman and others, 1968). The lower Wilcox unit is 

confined by an overlying clay bed of the Wilcox Group and an 

underlying clay bed of the Midway Group. The Wilcox crops 

out in the area of Crowleys Ridge (fig. 64) in Clay, Craighead, 

and Green Counties (Broom and Lyford, 1981). The Wilcox 

dips toward the axis of the Mississippi embayment at about 

20 ft/mi in the north (Hosman and others, 1968). Locally, 

the upper part of the Wilcox is unconformably overlain by 

the Carrizo Sand. Where sand is present in the upper Wilcox 

Group, it is difficult to differentiate from the Carrizo Sand 

(Hosman and others, 1968).

The Wilcox crops out in northern Nevada and Hempstead 

Counties and underlies the Cane River Formation throughout 

Columbia and Union Counties (Zachry and others, 1986). In 

this area, the Wilcox is dominantly composed of clay with 

thin discontinuous sand units and thin lignite beds in some 

areas. Near Columbia and Union Counties, the Wilcox Group 

ranges from 350 to 550 ft in thickness but does not make a 

good aquifer because of the lithology and water quality. In 

fact, the Wilcox has been examined as a potential reservoir 

for hydrocarbons in some parts of eastern Arkansas. A few 

sandstones show staining that were possibly hydrocarbons, but 

the Wilcox was not considered to have good potential as an oil 

reservoir (Renfroe, 1949).
YELL

LEE

UNION

WHITE

POLK

POPE

DREW

PIKE

SCOTT

CLARK

CLAY

ASHLEY

DESHA

BENTON

LOGAN

SALINE

IZARD

LONOKE

PULASKI

ARKANSAS

NEWTON

GRANT

CHICOT

MADISON

STONE

MILLER

SHARP

CROSS

DALLAS

PRAIRIE

BOONE

PHILLIPS

PERRY

SEARCY

MARION

FULTON

SEVIER

MISSISSIPPI

JEFFERSON

NEVADA

POINSETT

GARLAND

COLUMBIA

BAXTER

OUACHITA

BRADLEY

JOHNSON

WASHINGTON

MONROE

GREENE

JACKSON

CARROLL

HOWARD

LINCOLN

CALHOUN

CONWAY FAULKNER

VAN BUREN FRANKLIN

CRAIGHEAD

HEMPSTEAD

RANDOLPH

CLEBURNE

MONTGOMERY

LAWRENCE

ST. FRANCIS

CRAWFORD

CLEVELAND

HOT SPRING

INDEPENDENCE

LITTLE

RIVER

WOODRUFF CRITTENDEN

LAFAYETTE

SEBASTIAN Crowleys 

Extent of Well type 

galloto repwaterrepres

EX

CommeElectricIndustrIrrigatiMiningPublic 

36°

35°

34°

90°

94° 92° 91° 93°

Base from U.S. Geological Survey digital data, 1:2,000,000

0 15 0 30 

15

Figure 64. Wells with reported water use from the Wilcox aquifer in Arkansas, 2010. 
192 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Hydrologic Characteristics

Wells completed in the Wilcox aquifer typically yield 

from 500 to more than 2,000 gal/min (Hosman and others, 

1968). An aquifer test in Mississippi County resulted in a 

transmissivity value of 21,390 ft2/d, a storage coefficient of 

0.0002, and a hydraulic conductivity of 174 ft/d. An aquifer 

test in Hot Spring County resulted in a transmissivity value of 

2,406 ft2/d, a storage coefficient of 0.00002, and a hydraulic 

conductivity of 60 ft/d (Hosman and others, 1968). Pugh 

(2008a) noted that specific capacity for the aquifer ranged 

from 0.25 to 641 (gal/min)/ft with a mean of 142 (gal/min)/ft 

(12 tests). Transmissivity ranged from 39 to 32,000 ft2/d with 

a mean of 10,700 ft2/d (14 tests). The estimated hydraulic 

conductivity for the aquifer was 9.73 ft/d based on the mean 

transmissivity value (Pugh, 2008a). Wells near Blytheville had 

yields from 200 to 1,800 gal/min (Halberg and Reed, 1964). 

Discharge from the aquifer is mainly to wells (Westerfield, 

1994). Pumping from the aquifer has caused substantial 

declines in local water levels. 

In most of Arkansas, the potentiometric surface of the 

Wilcox aquifer is below land surface (Hosman and others, 

1968). However, where the lower Wilcox unit is confined in 

northeastern Arkansas, the potentiometric surface may rise 

above land surface (Joseph, 1998b). Regional groundwater 

flow is toward the axis of the Mississippi embayment 

(Westerfield, 1994; Joseph, 1998b; Schrader and Joseph, 

2000; Yeatts, 2004; Schrader, 2007a; Pugh, 2010). Cones of 

depression associated with pumping centers locally affect the 

groundwater movement (Hosman and others, 1968). 

The main source of recharge to the Wilcox aquifer in 

the southern part of the State is infiltration of precipitation in 

the outcrop areas. In the northern part of the State where the 

aquifer subcrops, recharge is by leakage from the overlying 

Carrizo Sand and other overlying formations (Hosman and 

others, 1968). Pumping from the Wilcox aquifer in southern 

Arkansas has caused substantial declines in water levels in 

some areas.

Water Use

The Wilcox aquifer generally yields water of excellent 

quality, and users often refer to the water as having the 

best water quality in the State (Scott and others, 1998). 

Approximately 150 wells were reported to use water from the 

aquifer as of 2010 (fig. 64). Good water quality and yields 

have led to its use for public, domestic, and industrial supplies. 

Several municipalities in eastern Arkansas historically 

have used the aquifer for public supply (Baker, 1955) with 

65 percent of water from the aquifer being used for this 

purpose (Terrance W. Holland, U.S. Geological Survey, 

written commun., 2012). Water use from the aquifer has been 

greatest in Crittenden, Greene, and Mississippi Counties. East 

of the outcrop area in Chicot, Desha, Jefferson, and Union 

Counties, salinity limits usage of the deeper parts of the 

aquifer (Klein and others 1950; Onellion and Criner, 1955; 

Bedinger and Reed, 1961; Terry and others, 1986).

Total water use from the Wilcox aquifer peaked in 

1995 and has since declined to amounts comparable to 

those of 1980. The aquifer is nevertheless an important, 

high-quality water source in Arkansas. Water-use rates for 

the Wilcox increased from 1965 through 1980 but declined 

in 1985 (table 30). Decreases in use are likely attributed to 

reduced irrigation following heavy use of the aquifer during 

the drought in the 1980s. In addition, changes were made 

associated with reporting procedures with the switch to the 

ARWUDBS system that affected reported usage. Use of the 

aquifer again increased in 1990 and peaked at 40.98 Mgal/d 

in 1995. Water use dropped 10.59 Mgal/d from 1995 to 2000 

following a large decrease in use by Mississippi County. It 

subsequently increased to 36.52 Mgal/d in 2010. Mississippi 

County historically had the greatest water use from the aquifer 

when several municipalities depend on the aquifer for public 

supply (figs. 64 and 65). Industrial use is also important in 

Mississippi County with industries using approximately 

1.66 Mgal/d in 2010 (Terrance W. Holland, U.S. Geological 

Survey, written commun., 2012). 

Most early use of the Wilcox aquifer around the 1900s 

occurred east of Crowleys Ridge (figs. 64 and 65) and 

primarily was for domestic supply. However, industrial use 

for lumber, ice, and railroad companies in Cross and Greene 

Counties was locally important (Stephenson and Crider, 1916). 

The Wilcox aquifer was also tapped by users on Crowleys 

Ridge, whereas users to the east and west of the ridge that 

could access Quaternary deposits used the Mississippi River 

Valley alluvial aquifer during the early part of the last century 

(Stephenson and Crider, 1916). Beginning in the 1920s, 

public-water suppliers east of Crowleys Ridge depended 

heavily on the aquifer (Hale and others, 1947; Counts and 

other, 1955; Ludwig, 1973). Towns in Crittenden, Mississippi, 

and St. Francis Counties reported average water usage ranging 

from 0.05 to 5.4 Mgal/d during the 1940s through the 1960s 

(Hale and others, 1947; Counts and others, 1955; Ryling, 

1960; Plebuch, 1961; Halberg and Reed, 1964; Ludwig, 1973). 

The greatest public-supply use of the Wilcox aquifer was 

in Crittenden and Mississippi Counties with Crittenden County 

using 2.5 Mgal/d in 1959 (Plebuch, 1961) and Mississippi 

County using 5.4 Mgal/d in 1957 (Ryling, 1960). Use in 

these counties has continued to increase. West Memphis 

(Crittenden County) was the largest user of the Wilcox aquifer 

in 2010 (5.04 Mgal/d) and Blytheville (Mississippi County) 

used 4.35 Mgal/d (Terrance W. Holland, U.S. Geological 

Survey, written commun., 2012). Other municipalities using 

the Wilcox aquifer are Marion (Crittenden County), Osceola 

(Mississippi County), and Paragould (Greene County). Total 

public-supply use of the Wilcox aquifer in Arkansas was 

23.8 Mgal/d in 2010, which is about 65 percent of total use 

of this aquifer in 2010 (Terrance W. Holland, U.S. Geological 

Survey, written commun., 2012).
Aquifers of the Coastal Plain 193

Notable changes in water use occurred as new 

communities began to tap the Wilcox aquifer. Water use 

increased in Greene County from 1965 to 1970 after the 

installation of two wells in Paragould (table 30). Increased 

use in Poinsett County from 1970 to 1980 was because of the 

drilling of multiple new public-supply wells. An increase of 

use from the aquifer of approximately 10 Mgal/d from 1990 to 

1995 is attributed to use as cooling water for power generation 

(table 30; Pugh, 2010). 

Counts (1957) suggested that the Wilcox aquifer could 

be developed in the future as a supplemental water source 

for the Mississippi River Valley alluvial aquifer in Prairie 

County. The Mississippi River Valley alluvial aquifer has 

been depleted in some areas of Prairie and Lonoke Counties 

over the past 70 years (Engler and others, 1945, 1963; Counts 

and Engler, 1954; Plebuch, 1962; Albin and others, 1967b; 

Ackerman, 1989a, b; Mahon and Poynter, 1993; Westerfield 

and Poynter, 1994; Joseph, 1999; Schrader, 2006a, 2008a, 

2010). While it is difficult to determine when the Wilcox 

aquifer originally was tapped for irrigation, wells in the Grand 

Prairie have increased in the last 20 years. In Lonoke County, 

use of the Wilcox increased more than 1,000 percent from 

1965 to 2010 (fig. 66). In 2010, 2.13 Mgal/d was withdrawn 

from the aquifer in Prairie County for irrigation purposes 

(Terrance W. Holland, written commun., 2012). Irrigation 

use was also prevalent in Lafayette, Lonoke, Mississippi, 

and Poinsett Counties. All of the irrigation wells in Poinsett 

County were located west of Crowleys Ridge.

Total water use from the Wilcox aquifer in southern and 

southwestern Arkansas is less than in northeastern Arkansas; 

however, the Wilcox aquifer is very important in those areas 

for domestic supply near its outcrop area. Many residences 

have wells completed in the Wilcox and depend on it for 

drinking water. Schools and small businesses also are reported 

to use water from the Wilcox aquifer in those areas (Counts 

and others, 1955; Onellion and Criner, 1955; Albin, 1964; 

Halberg and others, 1967; Plebuch and Hines, 1969; Ludwig, 

1973; Terry and others, 1986). Domestic use has declined in 

recent years as more residents convert to public-supply use. 

However, small amounts are assumed to be withdrawn for 

domestic supply in Lafayette, Miller, and Nevada Counties. 

Rosston (Nevada County) is the only town in southern 

Arkansas using the Wilcox aquifer for public supply. The town 

installed a well in 1928 that pumped 0.03 Mgal/d from 1945 to 

1965 and 0.06 Mgal/d in 2010 (Hale and others, 1947; Counts 

and other, 1955; Ludwig, 1973; Terrance W. Holland, U.S. 

Geological Survey, written commun., 2013).

Table 30. Water use from the Wilcox aquifer in Arkansas, 1965–2010. 

[Units are million gallons per day; Data from Halberg and Stephens (1966); Halberg (1972, 1977); Holland (1981, 1987, 1993, 1999, 2004, 2007). Only counties 

with published data for consumption of groundwater from the Wilcox aquifer are shown]

County 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Clark 0.07 0.13 0.19 0.52 0.00 0.00 0.00 0.00 0.00 0.00

Clay 0.26 0.17 0.18 0.50 0.00 0.00 0.00 2.97 0.33 0.80

Craighead 0.38 0.44 0.62 0.95 0.47 1.83 2.42 0.79 0.81 0.77

Crittenden 2.25 3.56 4.77 9.76 6.8 5.05 7.85 5.75 8.09 7.12

Cross 0.05 0.00 0.00 0.00 0.00 0.00 0.00 1

0.32 0.00 0.35

Greene 1.20 2.18 2.19 4.48 1.21 1.59 2.07 7.12 5.55 5.78

Hempstead 0.00 0.06 0.08 0.10 0.00 0.00 0.00 0.00 0.00 0.00

Hot Spring 0.43 2.20 0.29 0.30 0.00 0.00 0.00 0.00 0.00 0.00

Lafayette 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02

Lee 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.05

Lonoke 0.17 0.32 0.55 0.76 1.35 1.72 2.14 0.76 0.51 1.92

Miller 0.14 0.09 0.14 0.31 0.66 0.43 0.49 0.03 0.10 0.02

Mississippi 6.83 10.41 10.9 10.00 8.12 16.85 22.31 1

7.49 6.57 9.92

Nevada 0.08 0.04 0.07 0.09 0.00 0.00 0.00 0.76 0.18 0.22

Poinsett 1.37 1.53 3.04 5.28 2.14 3.38 3.70 0.59 2.85 3.32

Prairie 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.22 2.17

Pulaski 0.05 0.59 0.47 0.30 0.00 0.00 0.00 0.00 0.00 0.00

Saline 0.63 0.14 0.18 0.28 0.00 0.00 0.00 1

1.31 0.93 2.74

St. Francis 0.15 0.20 0.16 0.21 0.00 0.00 0.00 0.00 0.33 0.56

White 0.12 0.46 0.50 2.10 0.00 0.00 0.00 1.43 0.54 0.76

Total 14.18 22.52 24.33 35.94 20.75 30.85 40.98 30.39 27.01 36.52

1

Unpublished data from Terrance W. Holland, U.S. Geological Survey, written commun., 2013.
1965 1980 1985 1970 1975 0 60 

0 60 120 K

EXPLANA

Annual water withdrawn f

in million gallons per d

2.1 to 4.0 4.1 to 6.0 6.1 to 8.0 8.1 to 10.0 10.1 to 12.0 0.1 to 2.0 No color represents no report

94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 

36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° Base from U.S. Geological Survey digital data 1:2,000,000 Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977; Holland, 1981, 1987, 1993, 1999, 2004, 2007

Figure 65. Water-use rates for the Wilcox aquifer in Arkansas from 1965 to 2010.
94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

EXPLANA

Annual water withdrawn f

in million gallons per d

No color represents no reporte

2.1 to 4.04.1 to 6.06.1 to 8.08.1 to 10.010.1 to 12.00.1 to 2.0

0 60 0 60 120 K

Base from U.S. Geological Survey digital data 1:2,000,000 Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977;

 Holland, 1981, 1987, 1993, 1999, 2004, 2007

19902005 2010

1995 2000

Figure 65. Water-use rates for the Wilcox aquifer in Arkansas from 1965 to 2010.—Continued
ST. FRANCIS 273 CRITTENDEN 216 CROSS 600POINSETT 142 CRAIGHEAD 103 GREENE 382CLAY 208 SALINE 335 NEVADA 175 WHITE 533 MISSISSIPPI 45 LONOKE 1,029 HOT SPRING -100 MILLER -86 CLARK -100 PULASKI -100 94° 92° 91° 93° 90° 36°35° 34° 0 15 30 

0 30 

15 45 Use of the 

by coupercen

-100 to 0 1 to 200 201 to 40

401 to 60

> 600 E

No color indicates 

Base from U.S. Geological Survey digital data, 1:2,000,000

Figure 66. Change in percentage of water use from the Wilcox aquifer in Arkansas from 1965 to 2010.
Aquifers of the Coastal Plain 197

The limited extent and poor quality of groundwater 

from the aquifer in some areas has prevented its use. It 

was too mineralized for most uses in Desha and Lincoln 

Counties (Bedinger and Reed, 1961). A report by Klein and 

others (1950) hypothesized that wells drilled to the Wilcox 

in Jefferson County would not yield water or was too salty. 

Domestic use was present in Chicot County, but its high 

mineral and iron concentration precluded its use for other 

purposes (Onellion and Criner, 1955). Wells in parts of Cross, 

Poinsett, Prairie, and Woodruff Counties were reported to 

contain high dissolved solids (Broom and Lyford, 1981). A 

small part of the Wilcox underlies eastern Jackson County but 

is not very thick in that area (less than 25 ft) and has not been 

considered a water source, although it may have good quality 

water (Albin and others, 1967a). 

Water Levels

Water-level declines in the Wilcox aquifer have been 

associated with the development and growth of large pumping 

centers (Westerfield, 1994; Joseph, 1998b; Schrader and 

Joseph, 2000; Yeatts, 2004; Schrader, 2007a; Pugh, 2010). 

In northeastern Arkansas (fig. 67), water-level declines 

and coalescing cones of depression were recorded at major 

pumping centers near Paragould (Greene County) and West 

Memphis (Crittenden County) (Joseph, 1998b; Schrader 

and Joseph, 2000; Yeatts, 2004). Flowing-artesian wells in 

Crittenden County were common around the late 1920s and 

early 1930s. By the late 1950s, these wells ceased to flow, 

and water levels had fallen to a maximum of 22 ft below the 

land surface (Plebuch, 1961). Water levels in West Memphis 

declined 30 ft from 1929 to 1951 (Plebuch, 1961). Near 

West Memphis, well A (fig. 68) had a water-level decline of 

approximately 25 ft from 1983 to 2012 (location of wells 

shown in fig. 67). Declines at Paragould were approximately 

26 ft from 1967 to 2012 (well B, figs. 67 and 68).

The 1991 and 1996–97 potentiometric surfaces of the 

Wilcox aquifer showed minimum levels at the 180–200 ft 

altitude near Paragould and at the 150–170 ft altitude near 

West Memphis (Westerfield, 1994; Joseph, 1998b). In 2000, 

minimum levels in the depression near Paragould had shifted 

slightly to the southwest along Crowleys Ridge, and the 

minimum levels at West Memphis had dropped some 30 ft 

to an altitude of 130 ft (Schrader and Joseph, 2000). A 2006 

study showed the contours under West Memphis had declined 

another 10 ft to an altitude of 120 ft (Schrader, 2007a). A 2009 

study showed contours south of Paragould declined some 20 

ft to an altitude of 170 ft (fig. 67). Pumping near Blytheville 

(Mississippi County) does not appear to have made as large an 

impact on the potentiometric surfaces; however, large waterlevel declines previously have been documented elsewhere in 

Mississippi County. Stephenson and Crider (1916) measured 

three wells in Mississippi County in 1912. These wells were 

revisited in 1958 by Ryling (1960) with reported declines of 

25–30 ft over the period of measurement. Water levels in the 

Mississippi County well (well C, fig. 68) dropped 21 ft from 

1968 to 2010.

Cones of depression were noted in the 2006 

potentiometric surface in Nevada County near Rosston and 

in southeastern Clark County (Schrader, 2007a). The cone 

in Nevada County is centered near a single well. From 2003 

to 2009, water levels in this well dropped 17.7 ft, which was 

the largest decline documented in the southern extent of the 

aquifer (Pugh, 2010). Previous work in the 1970s had reported 

the lowest water levels in the southern part of the State near 

the Rosston public supply well (Ludwig, 1973). The lowest 

water levels of the aquifer were recorded in 2009 at the 

depression in southeastern Clark County (fig. 67; Pugh, 2010).
198 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Base from U.S. Geological Survey digital data, 1:24,000

Universal Transverse Mercator, zone 15

North American Datum of 1983

Modified from Pugh, 2010

Area enlarged

ARKANSAS

Paragould

West

Memphis

CLAY

CROSS

POINSETT

GREENE

CRAIGHEAD

ST. FRANCIS

LEE

CRITTENDEN

MISSISSIPPI

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 (NGVD 29)

General direction of groundwater flow

Well completed in Wilcox aquifer, 

 northeastern Arkansas—Number is

 water level in feet above NGVD 29.

 Letter, where present, corresponds 

 to hydrograph in figure 68

EXPLANATION

180

!

114

A

35°00’

36°00’

90°00’

91°00’

90° 30’

35° 30’

36° 30’

0 10 20 MILES

0 10 20 KILOMETERS

210

210

200

190

180

160

150

140

170

190

180

120

130 130

200

180

180

190

170

140

130

160

170

220

130

139

174

174

184 175

171

165

207 181

199

201

187

186

184

187

184

179

171

140

136

296

180

352

168

168

160

153 154

114

133

131

133

203

195

195 187

193

296

368

190

A

C

B

Figure 67. Potentiometric surface of the Wilcox aquifer in Arkansas, 2009.
Aquifers of the Coastal Plain 199

Base from U.S. Geological Survey digital data, 1:24,000

Universal Transverse Mercator, zone 15

North American Datum of 1983

Modified from Pugh, 2010

Area enlarged

ARKANSAS

Little Missouri River

Ouachita River

CLARK

DALLAS

NEVADA

OUACHITA

HEMPSTEAD

HOT SPRING

Outcrop of Wilcox aquifer (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 

 (NGVD 29)

General direction of groundwater flow

Well completed in Wilcox aquifer, southern

 Arkansas—Number is water level in feet above

 NGVD 29

EXPLANATION

280

!

231

34°30'

93°30'

92°30'

93°00'

34°00'

33°30'

0 10 20 MILES

0 10 20 KILOMETERS

220

240

260

280

300

320

340

180

200

160

240

260

220

180

200

340

300

320

280

360

380

280

260

360

380

275

311

243

256

312

393 342

333

344

400

346

265

147

212

231

257

!

!

!

!

!

!

!!

!

!

!

!

!

!

!

!

Figure 67. Potentiometric surface of the Wilcox aquifer in Arkansas, 2009.—Continued
200 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Water Quality

The distinctive lithologic characteristics of the sandrich lower Wilcox unit and the clay-rich upper Wilcox unit, 

coupled with the relative thickness of the two units across 

Arkansas, exercise a strong control on yields and water 

quality. Because of these stratigraphic differences, a distinct 

trend exists in the water quality from the northeast to the west. 

Producing wells in Miller County in southwestern Arkansas 

to approximately Lonoke County in central Arkansas are 

completed almost solely in the outcrop area; however, in the 

extreme northeastern part of the State and east of Crowleys 

Ridge, numerous wells have been completed in a broad area 

downgradient from the outcrop and subcrop areas. Waterquality differences are related to the facies change for the 

Wilcox Group, which are discussed in further detail below.

For most of the western extent of the aquifer, the Wilcox 

aquifer is a viable groundwater supply only in the outcrop 

area. The water becomes brackish or saline within a short 

distance downdip from the outcrop and is unfit for most 

purposes (Plebuch and Hines, 1969; Ludwig, 1973; Terry and 

others, 1986). Plebuch and Hines (1969) describe groundwater 

from the Wilcox in Clark, Cleveland, and Dallas Counties 

as a sodium-bicarbonate type, with water increasing in 

dissolved-solids concentrations and becoming a sodiumchloride type downdip. Broom and others (1984) noted 

that the Wilcox and Carrizo aquifers are indistinguishable 

in Union County, are hydraulically connected, and used 

solely for injection of brine. Hewitt and others (1949) 

noted abundant saltwater at depths of 1,000 ft in Ashley 

County. Onellion and Criner (1955) additionally noted that 

groundwater was too salty for any use based on electric 

logs from wells in Chicot County. Ludwig (1972) described 

groundwater from the Wilcox as a soft to moderately 

hard, sodium-bicarbonate type for most of Hempstead, 

Lafayette, Miller, and Nevada Counties. The southern 

extent of freshwater coincided with a fault system extending 

through central Lafayette, Miller, and Nevada Counties. 

Groundwater south of the fault zone contained more than 

1,000 mg/L dissolved solids based on electric logs (Ludwig, 

1973). Halberg and others (1968) reported that groundwater 

from the Wilcox in Hot Spring and Grant Counties was 

a soft, sodium-bicarbonate type. They also stated that 

iron concentrations could be high and that groundwater 

Figure 68. Hydrographs of water levels in wells completed in the Wilcox aquifer in Arkansas.

1960 1966 1972 1978 1984

Year

1990 1996 2002 2008 2014

100 

120 

140 

160 

180 

200 

220 

240 

Water level, in feet above National Geodetic Vertical Datum of 1929

Water level, in well completed

in the Wilcox aquifer

 Well A (Crittenden County)

 Well B (Greene County)

 Well C (Mississippi County) 

EXPLANATION
Aquifers of the Coastal Plain 201

from shallow wells was slightly acidic. Hosman and others 

(1968) noted that water type varied with dissolved-solids 

concentrations as follows: (1) when dissolved-solids 

concentrations were low, water was a calcium-magnesiumbicarbonate or a sodium-bicarbonate type; (2) increases 

in dissolved solids up to 400 mg/L were attributed to 

predominantly sodium and bicarbonate; and (3) increases in 

dissolved solids greater 400 mg/L were attributed to increases 

in sodium, bicarbonate, and chloride. 

In the northeastern part of the State, east of Crowleys 

Ridge, the Wilcox is a much more regionally important 

aquifer and was cited as the second most important aquifer in 

Mississippi County (Ryling, 1960). Counts (1957) stated that 

the Wilcox was “... the most important mineral resource in 

parts of Lonoke, Prairie, and White Counties.” Groundwater 

in the Wilcox was reported as a very soft, sodium-bicarbonate 

type with generally low mineralization (Ryling, 1960; 

Plebuch, 1961; Halberg and Reed, 1964; Broom and Lyford, 

1981). Broom and Lyford (1981) reported dissolved-solids 

concentrations from 100 to 150 mg/L in the area east of 

Crowleys Ridge. To the west of the ridge in parts of Cross, 

Poinsett, Prairie, and Woodruff Counties, the report listed 

dissolved solids in excess of 1,000 mg/L. Ryling (1960) cited 

much of the groundwater from the Wilcox in Mississippi 

County as being under flowing artesian conditions at rates 

of 300 gal/min. Broom and Lyford (1981) reported yields 

exceeding 2,000 gal/min. The high yields and good water 

quality associated with the Wilcox reveal the importance of 

this water resource for eastern Arkansas.

General Geochemistry and Water Type

Much of the following discussion is focused on 

differences in groundwater geochemistry between the two 

areas described above: (1) the main outcrop area for the 

Wilcox Group, generally extending from Miller County in 

extreme southwestern Arkansas through Lonoke County 

in central Arkansas, hereinafter referred to as the “western 

extent” and (2) an area east of Crowleys Ridge in northeastern 

Arkansas, hereinafter referred to as the “eastern extent.” 

Increases of pH along a given flow path often reflect the 

degree of carbonate dissolution by infiltrating low-pH and 

poorly buffered precipitation. Thus, pH can be used to assist 

in tracking flow paths for carbonate-dominated groundwater 

that is typical of most aquifers of the Coastal Plain in 

Arkansas (see sections on Sparta and Cockfield aquifers). 

Because of the absence of wells downgradient from the 

Wilcox outcrop area, no well-defined pH trends are evident 

in the western extent (fig. 69). Values of pH less than 6.0 

dominantly occurred in the outcrop area in central Arkansas, 

with the higher values, greater than 8.0, occurring in and 

near the subcrop areas. Only 37 of 137 sites had pH values 

less than 7.0, and most of these were in the western extent of 

the aquifer. In the eastern extent of the aquifer, no samples 

exhibited pH values less than 6.0 with the majority having 

pH values greater than 7.5. Because the aquifer is confined at 

all of the sites in the eastern extent, sufficient buffering has 

occurred for recharging water within the overlying units prior 

to entering the aquifer.

The exchange of calcium for sodium occurs on solidphase exchange sites as groundwater travels through the 

unsaturated and saturated zones. This results in an overall 

increase in sodium at the expense of calcium in solution. 

When sodium is greater than 50 percent of the major cations 

(calcium, magnesium, potassium, and sodium), the resultant 

groundwater is deemed sodium-dominated with respect 

to cations. For most aquifers, calcium is derived from 

dissolution of carbonates and is the dominant major cation 

in the early stages of geochemical evolution; therefore, 

calcium-bicarbonate is the dominant water type in this less 

geochemically evolved groundwater. Groundwater generally 

transitions to a sodium-bicarbonate water type further along 

the flow path, as calcium exchanges for sodium on clay 

exchange sites. Groundwater from the Wilcox generally does 

not show a well-defined trend in its western extent, although 

most of the calcium-dominated groundwater occurs in the 

outcrop areas from Nevada to White Counties. In the eastern 

extent of the aquifer, practically all of the sites exhibit a 

strongly sodium-bicarbonate water type. Nearly half of the 

sites have sodium constituting greater than 90 percent of the 

total cations, which reflects a more geochemically evolved 

groundwater at greater distances from the subcrop area 

(fig. 69). 
LEE WHITE UNION DREW CLARK CLAY DESHA ASHLEY SALINE

CROSS

ARKANSAS

PULASKI

GRANT

PHILLIPS

DALLAS

POINSETT

GREENE

LINCOLN

CRAIGHEAD

ST. FRANCIS

HOT SPRING

LONOKE

CHICOT

PRAIRIE

MILLER

JEFFERSON

MISSISSIPPI

NEVADA

OUACHITA

MONROE

JACKSON

COLUMBIA

BRADLEY

CALHOUN

WOODRUFF CRITTENDEN

CLEVELAND

LAFAYETTE

LEE

WHITE

UNION

DREW

CLARK

CLAY

DESHA

ASHLEY

SALINE

CROSS

ARKANSAS

PULASKI

GRANT

PHILLIPS

DALLAS

POINSETT

GREENE

LINCOLN

CRAIGHEAD

ST. FRANCIS

HOT SPRING

LONOKE

CHICOT

PRAIRIE

MILLER

JEFFERSON

MISSISSIPPI

NEVADA

OUACHITA

MONROE

JACKSON

COLUMBIA

BRADLEY

CALHOUN

WOODRUFF CRITTENDEN

CLEVELAND

LAFAYETTE

UNION

CLARK

SALINE

PULASKI

GRANT

DALLAS

HOT SPRING

MILLER

JEFF

NEVADA

OUACHITA

COLUMBIA

BRADLEY

CALHOUN

CLEVELAN

LAFAYETTE

LEE

WHITE

UNION

DREW

CLARK

CLAY

DESHA

ASHLEY

SALINE

CROSS

ARKANSAS

PULASKI

GRANT

PHILLIPS

DALLAS

POINSETT

GREENE

LINCOLN

CRAIGHEAD

ST. FRANCIS

HOT SPRING

LONOKE

CHICOT

PRAIRIE

MILLER

JEFFERSON

MISSISSIPPI

NEVADA

OUACHITA

MONROE

JACKSON

COLUMBIA

BRADLEY

CALHOUN

WOODRUFF CRITTENDEN

CLEVELAND

LAFAYETTE

LEE

WHITE

UNION

DREW

CLARK

CLAY

DESHA

ASHLEY

SALINE

CROSS

ARKANSAS

PULASKI

GRANT

PHILLIPS

DALLAS

POINSETT

GREENE

LINCOLN

CRAIGHEAD

ST. FRANCIS

HOT SPRING

LONOKE

CHICOT

PRAIRIE

MILLER

JEFFERSON

MISSISSIPPI

NEVADA

OUACHITA

MONROE

JACKSON

COLUMBIA

BRADLEY

CALHOUN

WOODRUFF CRITTENDEN

CLEVELAND

LAFAYETTE

UNION

CLARK

SALINE

PULASKI

GRANT

DALLAS

HOT SPRING

MILLER

JEFF

NEVADA

OUACHITA

COLUMBIA

BRADLEY

CALHOUN

CLEVELAN

LAFAYETTE

36°

35°

34°

36°

35°

34°

36°

35°

34°

36°

35°

34°

36°

35°

34°

36°

35°

34°

94° 93° 92° 91°

90°

94° 93° 92° 91°

90°

94° 93° 9

94° 93° 9

94° 93° 92° 91°

90°

94° 93° 92° 91°

90°

0 100 0 100 

Base modified from U.S. Geological Survey digital data, 1:250,000Universal Transverse Mercator projection, zone 15

Geology map modified fr

Petersen and 

Nitrate, in milligrams per liter

0.01 to 0.020.03 to 0.100.11 to 0.500.51 to 5.005.01 to 10.0010.01 to 19.00

EXPLANATION

Sodium, in percent of major cations

0 to 2526 to 5051 to 6061 to 8081 to 9091 to 99

EXPLANATION

4.9 to 5.55.6 to 6.06.1 to 7.07.1 to 7.57.6 to 8.08.1 to 8.9

pH, in standard units

EXPLANATION

Chloride, in milligrams per lite

1 to 1011 to 2526 to 100101 to 350351 to 1,0001,001 to 150,000

EXPLANATION

Sulfate, in milligrams per liter

0 to 56 to 1011 to 2021 to 5051 to 100101 to 430

EXPLANATION

Iron, in micrograms per liter

0 to 5051 to 100101 to 300301 to 1,0001,001 to 5,0005,001 to 220,000

EXPLANATION

EXPLANATION

Wilcox outcropWilcox subcrop

Wilcox extentCrowleys Ridge

Figure 69. Spatial distribution of selected chemical constituents in groundwater from the Wilcox aquifer in Arkansas.
Aquifers of the Coastal Plain 203

Nitrate

Similar to most of the Tertiary aquifers of eastern 

Arkansas, higher nitrate concentrations generally occurred 

only in the outcrop and subcrop areas for the Wilcox aquifer. 

The median nitrate concentration was 0.11 mg/L (table 31), 

and only two wells had nitrate concentrations greater than 

the Federal MCL of 10 mg/L. All but two wells in the 

eastern extent of the aquifer had nitrate concentrations less 

than 0.5 mg/L; most had concentrations less than 0.1 mg/L 

(fig. 69). The most vulnerable areas to contamination are those 

where the aquifer is exposed in the outcrop or shallow subcrop 

areas. A comparison of well depth to nitrate concentrations 

revealed that all nitrate concentrations greater than 2.0 mg/L 

occurred in wells less than approximately 120 ft deep (fig. 70). 

Simple dilution or denitrification processes possibly serve as 

the primary controls on the occurrence of appreciable nitrate 

downgradient from outcrop and subcrop areas. In addition, low 

velocities add a temporal element to the transport of nitrate.

Table 31. Descriptive statistics for selected chemical constituents in groundwater from the Wilcox aquifer in Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 0.3 4.4 24,000 2,260 112

Magnesium (mg/L) 0.01 1.2 2,600 244 112

Sodium (mg/L) 0.5 37.8 73,000 6,930 110

Potassium (mg/L) 0.1 2.1 840 81.8 104

Bicarbonate (mg/L) 2.0 110 512 101 134

Chloride (mg/L) 0.8 4.8 150,000 12,600 140

Sulfate (mg/L) 0.02 3.4 430 52.7 136

Silica (mg/L) 4.6 11 66 11 90

Nitrate (mg/L as nitrogen) 0.01 0.11 19 2.33 122

Dissolved solids (mg/L) 14 128 253,000 23,700 113

Iron (μg/L) 0.05 130 220,000 20,800 111

Manganese (μg/L) 0.13 10 1,800 287 38

Arsenic (μg/L) 0.03 0.52 1.0 0.48 6

Hardness (mg/L as calcium carbonate) 1.0 21 71,000 6,060 136

Specific conductance (μS/cm) 16 205 13,500 1,200 146

pH (standard units) 4.9 7.5 8.9 0.8 137

0 500 1,000 1,500 2,000 2,500

Well depth, in feet below land surface

0

2

4

6

8

10

12

14

16

18

20

Nitrate, in milligrams per liter as nitrogen

Figure 70. Relation of well depth and nitrate in groundwater from the Wilcox aquifer in Arkansas.
204 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Iron

No well-defined patterns or spatial trends were 

revealed for iron concentrations in the Wilcox aquifer. Iron 

concentrations ranged from 0.05 to 220,000 μg/L with a 

median of 130 μg/L (fig. 71; table 31), which is below the 

Federal secondary drinking-water regulation of 300 μg/L. 

A trend of lower iron concentrations along flow paths was 

noted for other Tertiary-age aquifers in eastern Arkansas. 

This trend was particularly noticeable for the Sparta and 

Cockfield aquifers, which had elevated concentrations of 

iron almost solely in or near the outcrop areas with lower 

concentrations downdip from outcrop areas. This trend was 

attributed to iron-reducing conditions in the outcrop areas 

and subsequent precipitation of iron minerals with changing 

redox conditions in the downgradient direction of flow. The 

Wilcox is an exception to this general trend, as noted by the 

relatively high concentrations of iron throughout the eastern 

extent of the aquifer downgradient from the subcrop area. 

The highest iron concentration occurred in a site in southern 

Arkansas that also exhibited the highest chloride, sulfate, and 

other constituent concentrations (fig. 69). This study did not 

focus on dissolved oxygen (or other gases), dissolved organic 

matter, ammonia, or other redox-sensitive constituents 

besides sulfate and iron. Thus, no definitive statements can be 

made with respect to the distribution of iron concentrations in 

the Wilcox in regard to redox zonation. Iron concentrations 

exceeding the Federal secondary drinking-water regulation 

(300 μg/L) are found predominantly in eastern Clay, 

Craighead, and Poinsett Counties, and throughout most 

of Mississippi County. In the western extent, elevated 

concentrations are found dominantly in Hot Spring, Saline, 

and Lonoke Counties.

0

50

100

150

200

250

300

350

400

450

Concentrations, in milligrams per liter

500

Concentrations, in micrograms per liter

700

800

900

1,000

0

100

200

300

400

500

600

111

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

112 112

110

134

140

136

111

Constituent Constituent

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron 

Figure 71. Interquartile range of selected chemical constituents in groundwater from the Wilcox aquifer in Arkansas.
Aquifers of the Coastal Plain 205

Sulfate

Sulfate concentrations generally are low throughout the 

Wilcox aquifer, except for downgradient from the outcrop 

areas in the western extent (fig. 69). Sulfate concentrations 

ranged from 0.02 to 430 mg/L with a median of 3.4 mg/L 

(fig. 71; table 31). Only three wells had sulfate concentrations 

exceeding 100 mg/L; two were in Union County at a great 

distance downgradient from the outcrop area, and one 

was in eastern Miller County. In the eastern extent of the 

aquifer, nearly all of the wells had concentrations less than 

5 mg/L. The only exception was for the northeastern part of 

Mississippi County, where concentrations exceeded 10 mg/L 

(upward to 25 mg/L). 

Chloride and Dissolved Solids

Chloride concentrations for the Wilcox aquifer generally 

are extremely low, except for areas downgradient from the 

outcrop and subcrop areas in the western extent. Groundwater 

in these areas becomes saline and is unfit for most uses 

(Plebuch and Hines, 1969; Ludwig, 1972; Terry and others, 

1986). The low chloride concentrations are reflected in 

the median concentration of 4.8 mg/L (fig. 71; table 31), 

the lowest median for chloride of any aquifer reviewed in 

this study. Chloride concentrations in the eastern extent of 

the aquifer generally were below 5.0 mg/L. The highest 

concentrations (upward to 150,000 mg/L) occurred at great 

distances from the outcrop and subcrop areas in the western 

extent of the aquifer in Union County (fig. 69). These water 

samples were taken from oil exploration wells and were not 

meant to be used as freshwater sources. In the eastern extent 

of the aquifer, only one well exhibited a slightly elevated 

chloride concentration of 170 mg/L. This well was located 

in Lee County in an area that was identified in earlier reports 

as an elongated zone of high salinity for several aquifers 

extending from Lee, Monroe, and Prairie Counties (Counts, 

1957; Halberg and Reed, 1964; Hosman and others, 1968; 

Morris and Bush, 1986). For more information on this highsalinity zone see the sections on the Sparta and Mississippi 

River Valley alluvial aquifers.

Spatial patterns for dissolved solids in the Wilcox 

aquifer tend to follow that of chloride concentrations, as 

high-salinity groundwater had chloride as the dominant 

anion. The median concentration for dissolved solids was 

128 mg/L, and only nine sites had concentrations greater 

than the secondary drinking-water regulation of 500 mg/L 

(U.S. Environmental Protection Agency, 2009). These data 

demonstrate the overall good quality of groundwater from the 

Wilcox. Hosman and others (1968) noted that groundwater 

transitions from a sodium-bicarbonate to a sodium-chloride 

type water for dissolved-solids concentrations greater than 

400 mg/L throughout the Mississippi embayment. Data 

compiled for Arkansas in this report showed a slightly 

different evolution of water types in the Wilcox. Calciumbicarbonate was the dominant water type for dissolved-solids 

concentrations up to approximately 100 mg/L, and calcium 

was the dominant cation in all but one sample within this 

range. For dissolved-solids concentrations greater than 

approximately 100 mg/L, 67 of 80 samples (84 percent) had 

sodium exceeding 50 percent of the total cations. Groundwater 

dominantly was represented by sodium-bicarbonate, with 

calcium-bicarbonate as the secondary water type. Sodiumchloride water type generally occurred only for dissolvedsolids concentrations more than approximately 800 mg/L. Six 

of seven samples with dissolved-solids concentrations greater 

than approximately 800 mg/L (upward to 253,000 mg/L) had 

chloride concentrations greater than 50 percent of the total 

anions (up to 98 percent). 

In summary, groundwater from the Wilcox aquifer is 

of very good quality, with the exception of high salinity and 

elevated dissolved solids downgradient from the outcrop and 

subcrop areas for most of the western extent of the aquifer. 

Numerous groundwater samples had iron concentrations 

that exceeded the secondary drinking-water regulation of 

300 μg/L. Generally, the overall best water quality is located 

in the eastern extent of the aquifer in northeastern Arkansas. 

Groundwater generally evolves from a calcium-bicarbonate 

to a sodium-bicarbonate water type at dissolved-solids 

concentrations greater than 100 mg/L. For dissolved-solids 

concentrations greater than 800 mg/L, groundwater is 

represented by a sodium-chloride water type.

Nacatoch Aquifer

Cretaceous formations in Arkansas (Nacatoch Sand, 

Ozan Formation, Tokio Formation, and the Trinity Group) and 

the aquifers comprised by these formations are not included 

in any of the regional hydrogeologic framework models 

of the Mississippi embayment (Arthur and Taylor, 1990; 

Hart and others, 2008; Clark and Hart, 2009). The Midway 

Group, a thick clay sequence serving as a lower confining 

layer for the Wilcox aquifer, is the oldest hydrogeologic unit 

included in the aquifers of the Mississippi embayment aquifer 

system. The Nacatoch aquifer was included as the McNairyNacatoch aquifer in the Gulf Coast RASA study by Hosman 

and Weiss (1991) and the Groundwater Atlas of the United 

States for segment 5 (Arkansas, Louisiana, and Mississippi) 

of Renken (1998). Because the McNairy Sand does not occur 

in Arkansas, the saturated part of the Nacatoch Sand often is 

referred to, and listed in various USGS reports, as simply the 

Nacatoch aquifer (Holland, 2007; Schrader and Blackstock, 

2010). This will be the nomenclature used within this report. 

Geology

The Nacatoch Sand of southwestern Arkansas is 

a Cretaceous-age formation of interbedded lithologies, 

predominated by generally unconsolidated sands with local 

lenses and beds of fossiliferous sandy limestone (Counts and 

others, 1955; Plebuch and Hines, 1969). The Nacatoch Sand 

is named after its type exposure at Nacatoch Bluff on the east 
206 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

bank of the Little Missouri River in Clark County, Ark., where 

about 50 ft of the upper Nacatoch Formation are exposed. 

Veatch (1906) defined the Nacatoch as the beds lying between 

the Marlbrook Marl and the Arkadelphia Marl, including the 

Saratoga Chalk. Stephenson (1927) and Dane (1929) separated 

the Saratoga Chalk from the Nacatoch and established the 

essentials of the definition of the formation that are used today.

Considerable sea transgressions and regressions occurred 

after the lower Cretaceous. While the lower Cretaceous 

deposition in Arkansas occurred mainly in nearshore 

environments, transgression resulted in finer-grained, 

carboniferous marls and chalks being deposited during the 

upper Cretaceous (Veatch, 1906). The contact of the Nacatoch 

Sand with the underlying Saratoga Chalk is sharp and slightly 

irregular, indicating an unconformity. The sediments of both 

formations suggest that they were deposited in a shallow 

nearshore environment. Dane (1929) noted that the lithologic 

variability and sedimentary structure within the Nacatoch 

represent changing conditions characteristic of a nearshore, 

shallow-water environment. The variation in sand content 

represents input switching among multiple sediment sources.

The Nacatoch Sand includes three distinct lithologic 

units: a lower unit comprising interbedded clays, marls, and 

sands; a middle unit comprising fossiliferous, glauconitic 

sand; and an upper principal water-bearing unit. The upper 

unit consists of unconsolidated, crossbedded, gray, finegrained quartz sand. In southwestern Arkansas, the Nacatoch 

unconformably overlies the Saratoga Chalk, Marlbrook 

Marl, or Ozan Formation. The Nacatoch Sand is overlain 

unconformably by the Arkadelphia Marl where the Nacatoch 

Sand serves as an aquifer in southwestern Arkansas. 

Formation thickness ranges from 150 to nearly 600 ft (Boswell 

and others, 1965; Zachry and others 1986). The Nacatoch 

generally has a higher sand percentage to the west and north, 

with the exception of an anomalously high sand content along 

the eastern border of Union County (Dollof and others, 1967). 

The Nacatoch Sand crops out in southwestern Arkansas 

along a belt 3–8 mi wide that extends southwest from central 

Clark County to the west of Hempstead County. In Little River 

County, the Nacatoch is covered by Quaternary alluvial and 

terrace deposits (Counts and others, 1955). In southwestern 

Arkansas, the Nacatoch dips south and southeast at a rate 

of about 30 ft/mi (Veatch, 1906; Boswell and others, 1965; 

Ludwig, 1972). Spooner (1935) noted structural control on 

Nacatoch lithology with sand being abundant over structurally 

high areas and grading rapidly to finer sediment on the 

flanks. The Nacatoch is faulted downdip in Bradley, Calhoun, 

Hempstead, Little River, Lafayette, Miller, Nevada, and 

Ouachita Counties (Petersen and others, 1985). The lower 

sand unit in the Nacatoch Sand is a petroleum producing 

formation in the Smackover Field of southern Arkansas 

(Weeks, 1938).

The Nacatoch Sand is present in the subsurface across 

most of northeastern Arkansas; formation thickness ranges 

up to 380 ft (Caplan, 1954). In northeastern Arkansas, the 

formation is composed of glauconitic sands interbedded 

with gray laminated clays. Localized calcareous and 

fossiliferous layers occur in the formation. In much of 

northeastern Arkansas, the formation rests unconformably 

on Paleozoic rocks and is overlain by Quaternary alluvium. 

In Lonoke, Pulaski, and White Counties, the Nacatoch rests 

unconformably on Paleozoic rocks and is overlain by Eocene 

strata, primarily of the Midway Group. The Nacatoch strikes 

to the northeast roughly parallel to the trend of the Paleozoic 

rocks and the Fall Line and dips to the southeast (Stephenson 

and Crider, 1916; Petersen and others, 1985). Near 

southwestern Lawrence County, the Nacatoch dips at about 

40 ft/mi to the southeast. In this area, sand content increases 

downdip and makes up 40–60 percent of the formation 

in extreme southeastern Randolph and eastern Lawrence 

Counties (Lamonds and others, 1969). 

Hydrologic Characteristics

Hydraulic test data for the Nacatoch aquifer are sparse. 

Aquifer tests in Clark and Hempstead Counties yielded 

transmissivities of 161 ft2/d and about 480 ft2/d, respectively. 

Aquifer tests on wells at Hope, in Hempstead County, and 

Prescott, in Nevada County, resulted in transmissivities of 

about 480 ft2/d (Ludwig, 1973). 

Most wells completed in the Nacatoch aquifer are 

relatively low yielding. Throughout southwestern Arkansas, 

well yields were reported from 1 to more than 300 gal/min 

(Counts and others, 1955). Flowing artesian wells in the lower 

stream valleys of Nevada County yield less than 5 gal/min, 

whereas many wells in southwestern Arkansas reported yields 

as high as 300 gal/min (Boswell and others, 1965). Wells in 

Hempstead and Nevada Counties can be expected to yield 

from 150 to 300 gal/min (Counts and others, 1955; Ludwig, 

1973). Wells yielding 200 to 500 gal/min can be expected in 

Jackson County; however, electric logs indicate that the water 

is saline (Albin and others, 1967a). Flowing artesian wells 

indicate the Nacatoch is under confined conditions away from 

the outcrop area. Renfroe (1949) defined the Nacatoch aquifer 

as an artesian aquifer in areas of northeastern Arkansas. In 

parts of eastern Arkansas, the Nacatoch Sand, downdip from 

the Fall Line, is porous but does not contain water; however, 

gas is found in these areas.

In southwestern Arkansas, the Nacatoch aquifer receives 

direct recharge from precipitation in its outcrop area, and 

in northeastern Arkansas, the aquifer receives recharge 

through the alluvium and terrace deposits where it subcrops. 

(Stephenson and Crider, 1916; Boswell and others, 1965; 

Petersen and others, 1985). In southwestern Arkansas, the 

regional direction of groundwater flow is to the southeast 

(Schrader and Blackstock, 2010; Schrader and Rodgers, 

2013). Flow directions may be locally controlled by clay 

content and faulting (Boswell and others, 1964). Groundwater 

flow rates and direction have been altered by pumping at 

Hope (Hempstead County), where water levels in the aquifer 

declined 40 ft from 1942 to 1969 (Ludwig, 1973), and a cone 

of depression developed in the potentiometric surface. In 
Aquifers of the Coastal Plain 207

northeastern Arkansas, groundwater moved southeast in the 

direction of the aquifer dip (Stephenson and Crider, 1916; 

Petersen and others, 1985; Schrader and Blackstock, 2010; 

Schrader and Rodgers, 2013).

Water Use

Use of the Nacatoch aquifer has been restricted to 

areas near its outcrop and subcrop areas in southwestern and 

northeastern Arkansas, respectively. The water is considered 

too saline for use in other areas, such as Craighead, Jackson, 

Monroe, and Poinsett Counties (Albin and others, 1967a; 

Hines and others, 1972; Broom and Lyford, 1981). Few early 

wells were completed in the Nacatoch in east-central Arkansas 

(Stephenson and Crider, 1916). Water-use reports since 1965 

show use only in Clay, Greene, and Lawrence Counties in 

northeastern Arkansas (fig. 72). Primary use of the aquifer 

has been for public and industrial supply. Domestic wells 

also tap the aquifer in eastern Lawrence and southeastern 

Randolph Counties (Lamonds, 1969). Countywide domestic 

use is attributed to the primary aquifer present in the county, 

therefore domestic use for Randolph County would not 

be attributed the Nacatoch aquifer and is not presented in 

table 32. Poor water-quality downdip from the outcrop area 

has restricted the aquifer’s use in parts of southwestern 

Arkansas (Terry and others, 1986). 

Veatch (1906) reported that the Nacatoch aquifer had 

been extensively developed in southwestern Arkansas and 

stated “over a thousand wells” had been developed between 

Arkadelphia (Clark County) and Texarkana (Miller County), 

which was most likely an overestimation because later work 

recorded just over 400 wells completed in the aquifer (Boswell 

and others, 1965). Many wells that were flowing artesian 

wells had been abandoned and allowed to flow because of the 

lack of concern for conserving this resource (Veatch, 1906). 

Other flowing artesian wells were present in the Nacatoch in 

southern Clark County (Boswell and others, 1965; Plebuch 

and Hines, 1969), but yields and water levels in the aquifer 

were declining as a consequence of unrestricted artesian flows. 

Water use from the Nacatoch aquifer has varied over 

the years. Boswell and others (1965) reported 1.2 Mgal/d 

were produced prior to 1965, primarily by municipalities and 

industries in southwestern Arkansas. Use of groundwater 

from the aquifer increased 174 percent from 1965 to 1980 

(table 32), the peak year for use of water from the Nacatoch 

aquifer. Use decreased from 1980 to 1995, jumped to a second 

high in 2000, and again decreased after 2000. Water use from 

the aquifer in 2010 was approximately 66 percent public 

supply, 4 percent for industrial supply, 10 percent for electric 

supply, and the remainder for mining, domestic, and livestock 

uses (Terrance W. Holland, U.S. Geological Survey, written 

commun., 2012). As of 2010, 33 wells completed in the 

Nacatoch were registered in ARWUDBS.
YELL LEE UNION WHITE POLK POPE DREW PIKE SCOTT CLARK CLAY ASHLEY DESHA BENTON LOGAN SALINE IZARD LONOKE PULASKI ARKANSAS NEWTON GRANT CHICOT MADISON STONE MILLER SHARP CROSS DALLAS PRAIRIE BOONE PHILLIPS PERRYSEARCY MARION FULTON SEVIER MISSISSIPPI JEFFERSON NEVADA POINSETT GARLAND COLUMBIA BAXTER OUACHITA BRADLEY JOHNSON WASHINGTON MONROE GREENE JACKSON CARROLL HOWARD LINCOLN CALHOUN CONWAY FAULKNER VAN BUREN FRANKLIN CRAIGHEAD HEMPSTEAD RANDOLPH CLEBURNE MONTGOMERY LAWRENCE ST. FRANCIS CRAWFORD CLEVELAND HOT SPRING INDEPENDENCE LITTLE RIVER WOODRUFF CRITTENDEN LAFAYETTE SEBASTIAN Base from U.S. Geological Survey digital data, 1:2,000,000 94° 92° 91° 93° 90° 36°35° 34° Extent of 

Well type 

galloto repwaterrepres

EX

CommeElectric IndustrMining Public 

0 15 0 30 

15 

Figure 72. Wells with reported water use from the Nacatoch aquifer in Arkansas, 2010. 
Aquifers of the Coastal Plain 209

Northeastern and southwestern Arkansas generally 

exhibited the same patterns of water use from the Nacatoch 

aquifer. Hempstead County generally had the most use in 

southwestern Arkansas and Clay County in northeastern 

Arkansas (fig. 73). Southwestern Arkansas had the greatest 

use in 1980, and northeastern Arkansas had the greatest use in 

1990. Groundwater use in southwestern Arkansas usually was 

more than in northeastern Arkansas except for reporting years 

1990, 1995, and 2010. From 1965 to 2010, use decreased in 

southwestern Arkansas, while use increased in northeastern 

Arkansas (fig. 74; table 32). 

Table 32. Water use from the Nacatoch aquifer in Arkansas, 1965–2010.

[Counties shown are only those with published data. Data from Halberg and Stephens (1966); Halberg (1972, 1977); Holland (1981, 1987, 1993, 1999, 2004, 

2007). Units are million gallons per day]

County 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Clay 0.25 0.51 0.63 1.55 1.13 1.98 1.72 1

1.28 0.97 1.22

Greene 0.00 0.06 0.08 0.16 0.09 0.23 0.00 1

0.40 0.48 0.46

Lawrence 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01

Northeast total 0.25 0.57 0.71 1.71 1.22 2.21 1.72 1

1.68 1.46 1.69

Clark 0.44 0.55 0.64 1.73 0.91 0.29 0.34 0.54 0.43 0.15

Hempstead 1.12 1.72 1.44 1.98 0.15 0.20 0.32 1.83 1.92 1.29

Hot Spring 0.00 0.00 0.00 0.24 0.00 0.00 0.00 0.00 0.00 0.00

Howard 0.00 0.14 0.22 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Little River 0.20 0.04 0.04 0.06 0.00 0.00 0.00 0.00 0.00 0.00

Miller 0.14 0.03 0.04 0.06 0.00 0.00 0.00 0.00 0.00 0.00

Nevada 0.21 0.45 0.55 0.68 1.11 0.44 0.36 1

0.08 0.18 0.21

Ouachita 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01

Southwest total 2.11 2.93 2.93 4.75 2.17 0.93 1.02 1

2.45 2.54 1.66

Total 2.36 3.50 3.64 6.46 3.39 3.14 2.74 1

4.13 4.00 3.35

1

Unpublished data from Terrance W. Holland, U.S. Geological Survey, written commun., 2013.
EXPLANA

Annual water withdrawn 

in million gallons per 

0.01 to 0.20 0.21 to 0.40 0.41 to 0.60 0.61 to 0.80 0.81 to 1.00 No color represents no repor

0 60 0 60 120 

Base from U.S. Geological Survey digital data 1:2,000,000 Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977; Holland, 1981, 1987, 1993, 1999, 2004, 2007 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 

36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 1965 1980 1985 1970 1975

Figure 73. Water-use rates for the Nacatoch aquifer in Arkansas from 1965 to 2010. 
Figure 73. Water-use rates for the Nacatoch aquifer in Arkansas from 1965 to 2010.—Continued

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

EXPLANA

Annual water withdrawn f

in million gallons per d

0.01 to 0.200.21 to 0.400.41 to 0.600.61 to 0.800.81 to 1.00

No color represents no report

0 60 0 60 120 K

Base from U.S. Geological Survey digital data 1:2,000,000 Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977;

 Holland, 1981, 1987, 1993, 1999, 2004, 2007

19902005 2010

1995 2000
MILLER -100 NEVADA 0 CLARK -66 LITTLE RIVER -100 GREENE 667 CLAY 388 HEMPSTEAD 15 94° 92° 91° 93° 90° 36°35° 34° 0 15 30 

0 30 

15 45 EXP

No color indicates 

 Use of the 

by coupercen

-100 to 0 1 to 200 201 to 60

> 600 Greene County used 1970 values, because 1965 values were not available Base from U.S. Geological Survey digital data, 1:2,000,000

Figure 74. Change in percentage of water use from the Nacatoch aquifer in Arkansas from 1965 to 2010.
Aquifers of the Coastal Plain 213

Public Supply

Water use from the Nacatoch aquifer for public supply 

currently (2013) is greater in northeastern Arkansas than in 

southwestern Arkansas. Clay County Regional Water District 

is the largest user of the Nacatoch for public supply with a 

total of 0.64 Mgal/d, which accounted for approximately 

19 percent of total Nacatoch water use in 2010. Piggott 

(0.35 Mgal/d) and Rector (0.17 Mgal/d) in Clay County 

were other large users in 2010 (Terrance W. Holland, U.S. 

Geological Survey, written commun., 2012). The well in 

Piggott was drilled in 1923 and, at one point, was a flowing 

artesian well (Hale and others, 1947). 

Hope (Hempstead County) is the largest user for public 

supply in southwestern Arkansas, using 15 percent of the 

total water withdrawn from the aquifer. Hope completed two 

wells in the Nacatoch in 1933, after completing one well in 

the Tokio aquifer in 1918 (Hale and others, 1947; Counts 

and others, 1955). Hope has drilled additional wells into both 

aquifers over the years but now supplements its groundwater 

with surface water. 

Prescott (Nevada County) drilled two wells in the 

Nacatoch aquifer in 1925 and 1948 (Hale and others, 1947; 

Counts and others, 1955) but currently (2013) withdraws 

water only from the Little Missouri River. Water use for 

Nevada County decreased (fig. 73) after Prescott switched 

water sources between 1985 and 1990. Smaller communities 

in the area, including Gurdon (Clark County) and Emmet 

(Nevada County), tap the aquifer for public supply. Also, 

a school district in Hempstead County continues to use a 

well drilled in 1948 (Counts and others, 1955; Terrance W. 

Holland, U.S. Geological Survey, written commun., 2012).

Industry

Industrial use from the Nacatoch aquifer in Clark County 

was dominated by lumber and paper companies in the mid1900s. Counts and others (1955) recorded five different 

lumber companies with wells withdrawing from the aquifer. 

Lumber-processing facilities currently (2013) depend on the 

aquifer in Clark County. Ice and gas companies also were 

recorded users of the aquifer. In 2010, the largest single 

use of the aquifer was for cooling water at a powerplant in 

Hempstead County. In northeastern Arkansas, mining interests 

are active users of the aquifer in Greene and Lawrence 

Counties. 

Water Levels

Southwestern Arkansas has experienced water-level 

declines in the Nacatoch aquifer since its early and intense 

development. During early development, many flowing 

artesian wells were unrestricted and allowed to flow freely, 

causing a decline in water levels of approximately 7 ft over 

17 years near Prescott (Nevada County) (Veatch, 1906). 

Veatch (1906) created a potentiometric-surface map from 

water levels measured in 1902. Water levels were highest 

north of Hope at the northern limit of the aquifer outcrop and 

decreased to the south. 

The ANRC and USGS monitor water levels in the 

Nacatoch aquifer as part of a long-term, statewide program 

(Schrader, 1998, 1999, 2007b; Schrader and Scheiderer, 2004; 

Schrader and Blackstock, 2010; Schrader and Rogers, 2013). 

In southwestern Arkansas, recent potentiometric-surface 

maps have shown the same pattern as in Veatch (1906), 

where groundwater-surface altitudes gradually decrease 

from the outcrop of the aquifer to the south (Schrader and 

Blackstock, 2010). Water levels in some wells declined by 

approximately 40 ft at Hope from 1942 to 1969 as a result 

of large groundwater withdrawals, mostly for public supply 

and industry. A cone of depression has been documented in 

this area since 1967 (Ludwig, 1973; Schrader, 1999; Schrader 

and Scheiderer, 2004; Schrader and Blackstock, 2010). Water 

levels rose in well A near the cone of depression at Hope in 

2010 (figs. 75 and 76), corresponding to decreasing water use 

in Hempstead County. The 2011 potentiometric surface depicts 

a cone of depression near Hope (fig. 76).

Two other cones of depression in the Nacatoch aquifer 

potentiometric surface were noted in southern Clark and 

north-central Hempstead Counties (fig. 76). The Clark 

County depression was first identified in 2002 (Schrader and 

Scheiderer, 2004), whereas the Hempstead County depression 

was first identified in 2008 (Schrader and Blackstock, 2010). 

Groundwater altitudes in each of these depressions have 

dropped a foot since construction of the 2005 potentiometricsurface map (Schrader, 2007b).

In well B, near Prescott (Nevada County), water 

levels declined more than 30 ft from the mid-1950s to the 

mid-1970s (figs. 75 and 76). Dramatic water-level rises of 

approximately 70 ft were later identified in well B from 1985 

to 1990, when the drinking-water supply of Prescott switched 

from groundwater to the Little Missouri River (Schrader and 

Blackstock, 2010). Water levels have stabilized since the early 

1990s.

Water-level declines in wells completed in the Nacatoch 

aquifer in northeastern Arkansas were recorded in Clay (well 

C) and Greene (well D) Counties from the 1960s and 1970s 

until the late 1990s (figs. 75 and 76). Water levels have 

stabilized since 1990 with the decrease in use of the Nacatoch 

aquifer (table 32). Interestingly, a localized potentiometric 

high that had not been noted previously appeared in the 2011 

surface in southeastern Clay County (fig. 76).
214 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Figure 75. Hydrographs of water levels in wells completed in the Nacatoch aquifer in Arkansas.

1942 1948 1954 1960 1966 1972 1978

Year

1984 1990 1996 2002 2008 2014

Water level, in feet above National Geodetic Vertical Datum of 1929

100 

120 

140 

160 

180 

200 

220 

240 

260 

280 

300 

EXPLANATION

Water level, in well completed

in the Nacatoch aquifer

 Well A (Hempstead County)

 Well B (Nevada County)

 Well C (Clay County)

 Well D (Greene County) 
Aquifers of the Coastal Plain 215

; ;

"

197

177

260

280

200

300

220

320

180

340

360

380

160

260

200

220

340

300

180

200

360

400

280

240

260

260

240

280

300

320

220

217

216 217

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

268

218

*

143

94°00' 93°30'

34°00'

33°30'

93°00'

0 10 20 KILOMETERS

0 10 20 MILES

Base from U.S. Geological Survey digital data, 1:24,000

Universal Transverse Mercator, zone 15 North

North American Datum of 1983 

Modified from Schrader and Rodgers, 2013

Hope

A

B

LITTLE 

RIVER

SEVIER

HOWARD

PIKE

HEMPSTEAD

MILLER

LAFAYETTE

COLUMBIA

NEVADA

CLARK

TEXAS

ARKANSAS

EXPLANATION

250

B 268

*

177

Southwestern study area

Outcrop of Nacatoch Sand

Approximate northern limit of Nacatoch aquifer

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 (NGVD 29)

Well, completed in the Nacatoch aquifer, used for control—

 Letter, where present, indicates hydrograph shown on

 figure 75. Number is water level in feet above NGVD 29

Flowing artesian well—Number is water level in 

 feet above NGVD 29

Area enlarged

ARKANSAS

Figure 76. Potentiometric surface of the Nacatoch aquifer in Arkansas, February–March 2011.
216 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

271 265

256

235

258

263

242

243

250

238

* 233

C

D

CLAY

GREENE

ARKANSAS

MISSOURI

270

260

250

240

240

250

90°40' 90°20'

36°20'

36°00'

EXPLANATION

Northeastern study area

Approximate western limit of Nacatoch aquifer

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

 (NGVD 29)

Control point—Letter, where present, corresponds to

 hydrograph in figure 75. Number is water level in feet 

 above NGVD 29 in 2011. Asterisk indicates well last

 measured in 2008

250

256 C

0 5 10 KILOMETERS

0 5 10 MILES

Base from U.S. Geological Survey digital data, 1:24,000

Universal Transverse Mercator, zone 15 North 

North American Datum of 1983

Modified from Schrader and Rodgers, 2013

Area enlarged

ARKANSAS

Figure 76. Potentiometric surface of the Nacatoch aquifer in Arkansas, February–March 2011.—Continued
Aquifers of the Coastal Plain 217

Water Quality

The Nacatoch aquifer is an important source of 

groundwater in the southwestern part of the State. It is also 

a good-quality source of water in the extreme northeastern 

part of the State. Geological controls on lithology and 

structure explain its occurrence and viability as an aquifer 

in these areas. The Nacatoch crops out in a narrow band in 

the southwestern part of the State, extending from western 

Hempstead County to northeastern Clark County (fig. 77).

Freshwater occurs almost solely in an isolated area in and 

near this area of outcrop (Terry and others, 1986). The upper 

part of the Nacatoch is composed of sand and is the principal 

water-bearing part of the formation in this area (Counts and 

others, 1955; Ludwig, 1973). Counts and others (1955) noted 

that water quality in the Nacatoch varied considerably in 

southwestern Arkansas. Within 2–20 mi from the outcrop 

area, the groundwater was too salty for most uses. The change 

in water quality along flow paths downgradient from the 

recharge area is gradual in some areas, degrading to unusable 

over 20 mi, or abrupt, changing from less than 100 mg/L to 

greater than 1,000 mg/L in less than 4 mi. Similarly, Plebuch 

and Hines (1969) stated that chloride concentrations in 

Clark County were low but increased rapidly downgradient 

to concentrations unsuitable for most uses within 2–17 mi 

from the outcrop. Within a distance of 3 mi along the 

northeastern edge of the outcrop area in Clark County, 

chloride concentrations were noted to increase from 7.0 to 

7,560 mg/L and dissolved solids from 92 to 12,300 mg/L. 

Near the outcrop area in Hempstead, Little River, and Nevada 

Counties, groundwater was soft or moderately hard with low 

chloride concentrations (Ludwig, 1972). Downgradient from 

the outcrop area, however, sodium and chloride concentrations 

increased with a concomitant increase in dissolved solids. 

Counts (1955) hypothesized that because the Nacatoch was 

a marine deposit, the original salt content had never been 

flushed completely from the formation, accounting for the 

higher salinity in the downgradient and deeper parts of the 

aquifer. Groundwater from the Nacatoch generally had very 

low iron concentrations (Counts and others, 1955; Ludwig, 

1973) as well as low sulfate and nitrate concentrations (Counts 

and others, 1955).

The Nacatoch aquifer provides a productive source 

of groundwater in the southwestern part of the State near 

the outcrop (hereinafter referred to as the “southwestern 

extent” of the aquifer). This is because of the higher sand 

content in the upper unit compared to the lower unit of the 

Nacatoch that consists of a mixture of interbedded clays, 

marls, and sands (Counts and others, 1955; Plebuch and 

Hines, 1969). The lithology in central Arkansas consists of 

bluish-gray, calcareous, fossiliferous sandstones and clays 

(Stephenson and Crider, 1916). Elevated dissolved-solids 

concentrations in groundwater from this area render the water 

unusable (Boswell and others, 1965; Petersen and others, 

1985). In northeastern Arkansas (hereinafter referred to as 

the “northeastern extent” of the aquifer), the sand content 

of the Nacatoch increases to 40–60 percent, and the aquifer 

once again becomes a viable aquifer (Renfroe, 1949; Caplan, 

1954; Lamonds and others, 1969). The Nacatoch is a silty 

and fine-grained sand in Jackson County but transitions to a 

clean, medium- to coarse-grained sand in Clay, Greene, and 

Lawrence Counties. The aquifer thickens in these counties to 

approximately 200 ft and yields are as much as 500 gal/min 

in parts of Clay and Greene Counties. In Craighead County, 

the aquifer yielded slightly saline to brine water, and one 

sample in Monroe County contained chloride concentrations 

of 21,500 mg/L (Broom and Lyford, 1981). Because the 

northeastern extent contained only 8 of 132 wells in the 

combined water-quality database used for this report, most of 

the following detailed discussion, especially with respect to 

spatial trends for the various constituents, is confined to the 

southwestern extent of the aquifer.

General Geochemistry and Water Type

The Nacatoch aquifer is similar to other Cretaceous and 

Tertiary aquifers and tends to have increasing pH values along 

the flow path resulting from increased dissolution of carbonate 

minerals. The Nacatoch is somewhat unique, however, in 

that only 1 of 129 samples, including samples from wells in 

the outcrop area, had a pH value less than 7.0 (value of 4.7). 

Because the average pH of precipitation for southern Arkansas 

is approximately 4.7 standard units (Kresse and Fazio, 2002), 

pH values for Cretaceous and Tertiary aquifers often are 

much lower than 7.0 for many shallow wells in the recharge 

(outcrop) area. Downgradient from the outcrop area, pH 

values tend to increase along a given flow path as a result of 

buffering by carbonate minerals. Values of pH for groundwater 

from the Nacatoch ranged upward to 9.0 with a median of 8.4 

(table 33). Only 25 of 129 samples had pH values less than 

8.0. Lower groundwater velocities coupled with an abundance 

of carbonate minerals throughout the formation may result 

in dissolution of carbonates and associated buffering of 

acidic recharge within a relatively short distance along the 

flow path. Additionally, many of the wells completed in the 

Nacatoch produce from sands at relatively great depths. Out 

of 129 wells with well-depth information, only 13 were less 

than 100 ft deep, and 39 wells were more than 500 ft deep 

with a maximum of 2,231 ft in depth. The increased vertical 

distance and traveltime of infiltrating recharge water allows 

greater time for rock/water interaction, including dissolution 

of carbonate minerals.

The lowest pH values (4.7–7.5) in the Nacatoch aquifer 

occurred in or near the outcrop area and trended progressively 

upward to values exceeding 8.0 in the downgradient 

(southeasterly) direction of flow (fig. 77). Because pH 

generally increases with increasing dissolution of carbonates 

along the flow path, bicarbonate concentrations generally 

followed the trend of increasing pH. The lowest concentrations 

(less than 200 mg/L) occurred in and near the outcrop and 

progressively increased in the downgradient direction of flow. 

The highest bicarbonate concentrations were in wells located 

in the eastern and western sections of the outcrop area in the 

southwestern extent of the aquifer (fig. 77). 
HEMPSTEAD COLUMBIA LITTLE RIVER NEVADA CLARK SEVIER HOT SPRING LAFAYETTE OUACHITA DALLAS MILLER UNION HOWARD HEMPSTEAD COLUMBIA LITTLE RIVER NEVADA CLARK SEVIER HOT SPRING LAFAYETTE OUACHITA DALLAS MILLER UNION HOWARD HEMPSTEAD COLUMBIA LITTLE RIVER NEVADA CLARK SEVIER HOT SPRING LAFAYETTE OUACHITA DALLAS MILLER UNION HOWARD HEMPSTEAD 

LITTLE RIVER 

SEVIER 

LAFAYET

MILLER 

HOWARDHEMPSTEAD COLUMBIA LITTLE RIVER NEVADA CLARK SEVIER HOT SPRING LAFAYETTE OUACHITA DALLAS MILLER UNION HOWARD HEMPSTEAD 

LITTLE RIVER 

SEVIER 

LAFAYET

MILLER 

HOWARD 93° 94° 34° 33° 30’ 93° 94° 34° 33° 30’ 93° 94° 34° 33° 30’ 

94° 34° 33° 30’ 93° 94° 34° 33° 30’ 94° 34° 33° 30’ 

EXPLANATION Iron, in micrograms per liter 0.05 to 50 51 to 100 101 to 300 301 to 1,000 1,001 to 38,000 Iron, in micrograms per liter 0.05 to 50 51 to 100 101 to 300 301 to 1,000 1,001 to 38,000 

Bicarbonate, in milligrams per liter 2 to 50 51 to 100 101 to 200 201 to 300 301 to 968 Bicarbonate, in milligrams per liter 2 to 50 51 to 100 101 to 200 201 to 300 301 to 968 EXPLANATION Sulfate, in milligrams per liter 0.8 to 5 6 to 10 11 to 25 26 to 50 51 to 10 101 to 2,800 Sulfate, in milligrams per liter 0.8 to 5 6 to 10 11 to 25 26 to 50 51 to 10 101 to 2,800 EXPLANATION pH, in standard units 4.7 to 6.0 6.1 to 7.0 7.1 to 7.5 7.6 to 8.0 8.1 to 8.5 8.6 to 9.0 pH, in standard units 4.7 to 6.0 6.1 to 7.0 7.1 to 7.5 7.6 to 8.0 8.1 to 8.5 8.6 to 9.0 EXPLANATION EXPLANATION Nacatoch outcrop Nacatoch extent Base modified from U.S. Geological Survey digital data, 1:250,000 Universal Transverse Mercator projection, zone 15 Geology map modified 

Areas enlarged ARKANSAS 0 20 40 MILES 0 20 40 KILOMETERS CLAY GREENE CLAY GREENE CLAY GREENE CLAY GREENE CLAY GREENE CLAY GREENE CLAY GREENE 90°45’ 90°30’ 90°15’ 36° 15’ 36° 30’ 90°45’ 90°30’ 90°15’ 90°45’ 90°30’ 90°15’ 90°45’ 90°30’ 90°15’ 90°45’ 90°30’ 90°15’ 90°45’ 90°30’ 90°15’ 36° 15’ 36° 30’ 36° 15’ 36° 30’ 36° 15’ 36° 30’ 36° 15’ 36° 30’ 36° 15’ 36° 30’

Figure 77. Spatial distribution of selected chemical constituents for groundwater from the Nacatoch aquifer in Arkansas.
Aquifers of the Coastal Plain 219

Rock/water interactions in the aquifer can change the 

major chemical composition and resulting water type along 

the groundwater-flow path. The exchange of calcium for 

sodium on solid exchange sites certainly is one of the most 

important processes affecting inorganic chemistry in aquifers 

of the Coastal Plain (Kresse and Fazio, 2002; Kresse and 

Clark, 2008; Kresse and others, 2012) Only 32 sites had 

sufficient data for calculating percent sodium of total cations 

in the Nacatoch aquifer. These data, however, were sufficient 

to note general trends in water type. Generally, sites with 

sodium less than 50 percent of the total cations, indicating a 

calcium-bicarbonate water type, were located in or less than 

about 1 mi from the outcrop area. Sites further downgradient 

had sodium percentages more than 50 percent and ranging 

upward to 99 percent (not shown on fig. 77).

Nitrate

Nitrate concentrations were extremely low in most 

samples from the Nacatoch aquifer. Nitrate concentrations 

ranged from 0.01 to 5.9 mg/L as nitrogen with a median 

of 0.25 mg/L (table 33). No concentrations exceeded the 

Federal MCL of 10.0 mg/L as nitrogen (U.S. Environmental 

Protection Agency, 2009). Out of 127 sites, 118 had nitrate 

concentrations less than 1.0 mg/L, of which 106 were less than 

0.5 mg/L. The highest nitrate concentrations were in and near 

the outcrop area in the southwestern extent, with the lowest 

(less than 0.5 mg/L as nitrogen) occurring downgradient from 

the outcrop area (fig. 77). In the vicinity of the outcrop, well 

depths are shallower, and all nitrate concentrations greater 

than 2.0 mg/L occurred in wells with depths of 60 ft or less 

(fig. 78). All groundwater samples from the northeastern 

extent had nitrate concentrations less than 0.5 mg/L. Similar 

to other aquifers in the Coastal Plain, the highest nitrate 

concentrations tend to occur in and near the outcrop area. 

Well depths are shallow in these areas, and the aquifer is more 

vulnerable to surface (fertilizers, applied animal waste) and 

shallow subsurface (septic tanks) sources of nitrate.

Iron

Iron is ubiquitous in groundwater for aquifers throughout 

the State and can present problems for most uses. Groundwater 

from the Nacatoch aquifer, however, contained some of 

the lowest iron concentrations for any aquifer in the State. 

Iron concentrations ranged from 0.05 to 38,000 μg/L with a 

median of 80 μg/L (fig. 79; table 33). Only 8 of 38 samples 

had iron concentrations exceeding the secondary drinkingwater regulation of 300 μg/L (U.S. Environmental Protection 

Agency, 2009). All samples from the northeastern extent 

(Clay and Greene Counties) had iron concentrations less than 

50 μg/L. Most of the highest iron concentrations (ranging 

up to 7,400 μg/L) were in the extreme northeastern part of 

the outcrop area in Clark County (fig. 77), with the highest 

concentration of 38,000 μg/L from an unused oil-exploration 

well in Union County (not shown on map). Downgradient 

from the outcrop area, iron concentrations were generally 

less than 100 μg/L. Higher iron concentrations in and near 

the outcrop area were noted for other Cretaceous and Tertiary 

aquifers. Lower concentrations downgradient from outcrop 

areas were attributed to iron-sulfide mineralization as a 

dominant control on iron solubility (see sections on Sparta and 

Cockfield aquifers for detailed discussion). 

Table 33. Descriptive statistics for selected chemical constituents in groundwater from the Nacatoch aquifer in Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 1.0 17 2,100 438 40

Magnesium (mg/L) 0.1 3.1 570 97 40

Sodium (mg/L) 6.5 168 20,000 3,740 40

Potassium (mg/L) 0.8 3.0 119 27.5 40

Bicarbonate (mg/L) 2.0 260 968 118 123

Chloride (mg/L) 3.0 45 30,000 4,240 132

Sulfate (mg/L) 0.8 21 2,800 251 131

Silica (mg/L) 7.4 13 63 13.6 41

Nitrate (mg/L as nitrogen) 0.01 0.25 5.9 0.78 127

Dissolved solids (mg/L) 94 444 55,400 10,900 40

Iron (μg/L) 0.05 80 38,000 6,200 38

Manganese (μg/L) 0.13 10 1,800 382 21

Arsenic (μg/L) 0.03 0.52 1.0 0.48 6

Hardness (mg/L as calcium carbonate) 4.0 33 6,700 807 131

Specific conductance (μS/cm) 38 706 53,000 6,080 130

pH (standard units) 4.7 8.4 9.0 0.6 129
220 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

0 200 400 600 800 1,000 1,200

Well depth, in feet below land surface

0

1

2

3

4

5

6

7

Nitrate, in milligrams per liter as nitrogen

Figure 78. Relation of well depth and nitrate concentrations in groundwater from the Nacatoch aquifer in Arkansas.

0

50

100

150

200

250

300

350

400

450

Concentrations, in milligrams per liter

500

Concentration, in micrograms per liter

700

800

900

1,000

0

100

200

300

400

500

600

38

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

40

40

40

123

131

132

38

Constituent Constituent

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron 

Figure 79. Interquartile range of selected chemical constituents in groundwater from the Nacatoch aquifer in Arkansas.
Aquifers of the Coastal Plain 221

Sulfate

Earlier reports (Counts and others, 1955; Ludwig, 1972) 

noted the low concentrations of nitrate, iron, and sulfate 

concentrations in groundwater from the Nacatoch aquifer. 

Inspection of data compiled for this report confirmed these 

observations. Sulfate concentrations ranged from 0.8 to 

2,800 mg/L with a median of 21 mg/L (fig. 79; table 33). Of 

131 samples with sulfate concentration data, 118 (90 percent) 

were less than 50 mg/L, 55 (42 percent) were less than 

10 mg/L, and 35 (27 percent) were less than 5 mg/L. Only 

three samples had sulfate concentrations greater than the 

secondary drinking-water regulation of 250 mg/L (U.S. 

Environmental Protection Agency, 2009). These three 

samples were (1) from unused oil-exploration wells in Union 

County (not shown on figures), (2) were not used as watersupply sources, and (3) were far removed from the outcrop 

area where high-salinity, high-dissolved-solids groundwater 

is known to occur. In and near the outcrop area, sulfate 

concentrations generally were less than 50 mg/L (fig. 77). The 

lowest concentrations (less than 5 mg/L) were from wells in 

the outcrop area and along the extreme eastern (Clark County) 

and western (Little River and Miller Counties) parts of the 

southwestern extent of the aquifer (regardless of proximity 

to outcrop area). This distribution was the inverse of that 

observed for bicarbonate concentrations, which were highest 

in the extreme eastern and western part of the outcrop area 

(fig. 77). In the central part of the outcrop area (Hempstead 

and Nevada Counties), sulfate concentrations generally were 

lowest and increased downgradient. Higher clay content and 

gypsum mineralization in the central part of the aquifer may 

account for the higher sulfate concentrations downgradient 

from the outcrop area. However, data on mineralogy, redox 

zonation, or other aquifer characteristics were not available 

to make definitive statements in regard to specific rock/

water interaction that would explain occurrence and spatial 

distribution for sulfate or other constituents. All samples from 

wells in the northeastern extent had sulfate concentrations less 

than 10 mg/L.

Chloride

Increasing salinity downgradient from the outcrop area in 

the southwestern extent of the Nacatoch aquifer is documented 

in numerous earlier reports (Counts and others, 1955; Plebuch 

and Hines, 1969; Ludwig, 1973; Terry and others, 1986). 

Data collected for this report corroborate these earlier studies 

and reveal a strong spatial component to the occurrence 

and distribution of elevated chlorides. Although chloride 

concentrations generally increased downgradient from the 

outcrop area in Hempstead and Nevada Counties, the gradient 

is not as sharp as noted for sites in the southwestern and 

northeastern parts of the outcrop area (fig. 77). Groundwater in 

Hempstead and Nevada Counties has chloride concentrations 

that are below the secondary drinking-water regulation of 

250 mg/L as far as 13 mi from the outcrop area. Thus, goodquality, low-salinity groundwater can be extracted in a much 

broader area in these counties. However, much sharper 

concentration gradients and higher concentrations are noted 

for groundwater from sites located in the western and eastern 

parts of the outcrop area. Chloride concentrations sharply 

increased in a southeasterly direction in Miller County from 

355 mg/L, to 565 mg/L, and finally to 1,670 mg/L, all within 

a distance of 0.7 mi. In the eastern part of the outcrop area 

(Clark County), one well containing a chloride concentration 

of 7,560 mg/L was less than 0.8 mi from the outcrop area 

and less than 1.5 mi from a well containing a chloride 

concentration of only 10 mg/L. 

Four exploratory wells in Union County contained 

chloride concentrations ranging from 3,500 to 30,000 mg/L. 

These wells were at a distance of approximately 60 mi from 

the outcrop area, where high salinity would be expected in 

the Nacatoch aquifer (not shown on fig. 77). Samples from all 

wells in the northeastern extent (Clay and Greene Counties) 

contained chloride concentrations less than 100 mg/L. One 

well located in Monroe County (not shown on fig. 77) was 

located in an area of high salinity that occupies a narrow band 

extending from Prairie County, through Monroe County, and 

into Lee County. This area was noted in past publications 

as containing high salinity that affected all Quaternary- and 

Tertiary-age aquifers (Stephenson and Criner, 1916; Counts, 

1957; Halberg and Reed, 1964; Morris and Bush, 1986). See 

the section on Mississippi River Valley alluvial and Sparta 

aquifers for detailed information on this area of high salinity 

groundwater.

In summary, the Nacatoch aquifer is a viable and 

important source of water for parts of the southwestern and 

extreme northeastern parts of the State. In the southwestern 

extent, freshwater mainly is obtained from areas in or near 

to the outcrop area. This is especially true for the eastern 

and western parts of the outcrop area. Salinity increases in 

a downgradient direction from the outcrop area to a point 

where the groundwater is not suitable for most uses. Gradients 

of increasing chloride concentrations are sharpest in the 

western and eastern parts of the outcrop, with a larger area of 

freshwater downgradient from the outcrop area in the central 

part of the outcrop area. Concentrations of sulfate, iron, and 

nitrate generally are very low throughout the Nacatoch aquifer. 

Values for pH, bicarbonate, and sodium tend to increase 

downgradient from the outcrop area as a result of mineral 

dissolution coupled to cation exchange. 

Ozan Aquifer

The Cretaceous-age Ozan Formation comprises an 

aquifer that is used in isolated parts of southwestern Arkansas. 

This aquifer is not listed in any regional reports, is one of the 

least-used aquifers, and contains some of the poorest-quality 

groundwater of any aquifer in the State. For purposes of 

this report, the saturated part of the Ozan Formation will be 

referred to hereinafter as the “Ozan aquifer.”
222 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Hydrogeologic Setting

The Ozan Formation is a mixed limey, clayey, and 

primarily sand unit that ranges in thickness from 0 to 

about 200 ft thick. The Ozan unconformably overlies the 

Brownstone Marl and grades conformably into the Annona 

Chalk above (Dane, 1929; Boswell and others, 1965). The 

formation is difficult to differentiate from the underlying 

Brownstone Marl but in some areas can be distinguished by 

a glauconitic sand bed (known as the Buckrange sand lentil) 

at the base of the formation or by a common occurrence of 

smooth, convex oyster shells (Dane, 1929; Counts and others, 

1955; Plebuch and Hines, 1969). The upper part of the Ozan 

consists of gray sandy marl with a few beds of sand and sandy 

limestone. The formation changes facies from a sandy clay 

and marl to a chalk and marl in Little River County (Counts 

and others, 1955). 

A considerable change in sea depth occurred in Arkansas 

following the Lower Cretaceous. While Lower Cretaceous 

units in Arkansas dominantly were nearshore deposits, 

deepening water resulted in more clayey and carboniferous 

sediments being deposited during the Upper Cretaceous 

(Veatch, 1906), resulting in the formation of mainly marls 

and chalks. The base of the Ozan shows evidence of nearly 

continuous, very slow deposition, indicating a period of 

nondeposition as an explanation of the unconformity at the 

base. The upper part of the Ozan indicates increased sediment 

supply, as evidenced by the increased sand content and 

micaceous nature of the sediment.

The Ozan Formation outcrop extends from northeastern 

Clark County towards the southwest into Oklahoma. The 

outcrop is from 1 to 4 mi wide and is covered by terrace and 

alluvial deposits through large areas (Boswell and others, 

1965). From central Union County eastward, the sand content 

and thickness increase rapidly, indicating an approach to 

the sea strand line and the presence of a sedimentary trough 

(Dollof and others, 1967). While the extent is limited, 

an equivalent of the formation does appear at depth in 

northeastern Arkansas. In this area, the formation ranges up 

to 150 ft thick and consists of a dark-gray, silty to sandy, 

micaceous, calcareous marl with shale layers. 

Hydrologic Characteristics

Hydrologic data for the Ozan aquifer are limited because 

of its lack of importance as a regional water supply. Most 

wells completed in the Ozan are used for domestic water 

supply (Boswell and others, 1965). Aquifer yields are limited, 

and the water is highly mineralized. Most producing wells 

are located in Clark County (Counts and others, 1955), and 

some of these were listed as flowing artesian wells (Plebuch 

and Hines, 1969); however, most of these wells are no longer 

flowing, possibly because of decades of unrestricted flow. A 

few wells are completed in Hempstead and Sevier Counties, 

but the water in these counties is not suitable for drinking. A 

flowing artesian well yielding approximately 1 gal/min was 

noted in Sevier County (Counts and others, 1955). The Ozan 

dominantly receives recharge in the outcrop area.

Zachry and others (1986) investigated the potential 

of injecting wastewaters from petroleum exploration into 

Cretaceous aquifers in southern Arkansas, demonstrating 

the poor water quality in this area. They concluded that 

the variability of sand thickness and sand distribution 

prevented confident prediction of lateral movement of 

water within the Nacatoch, Ozan, and Tokio Formations. 

Vertical movement towards Tertiary aquifers was projected 

to be slow or nonexistent. Fractures were hypothesized to 

provide for enhancement of potential lateral movement of 

water within the formation but would have little influence 

on vertical movement into Tertiary aquifers as a result of the 

characteristics of the confining units.

Water Use

Eleven domestic wells were recorded in Clark County, 

and 2 other wells were recorded in Hempstead and Sevier 

County, but their use was restricted because of high chloride 

concentrations (Counts and others, 1955; Boswell, 1965). 

Plebuch and Hines (1969) estimated that 0.13 Mgal/d was 

withdrawn from the Ozan aquifer in Clark County in 1965. 

Water-use data for the Ozan are only available from 1965 to 

1980 (table 34), and no use has been reported for this aquifer 

thereafter.

Water Quality

Wells completed in the Ozan aquifer occur dominantly 

in the outcrop area, which extends along an extremely narrow 

band extending from western Little River County (near the 

State border) through northeastern Clark County. The Ozan 

contains some of the poorest quality water of any of the 

aquifers in the Coastal Plain. Limited use of groundwater 

from the Ozan has been cited in several reports. Plebuch 

and Hines (1969) noted that the aquifer generally contained 

groundwater with dissolved-solids concentrations of more 

than 1,000 mg/L in Clark County and was used only because 

no other water source was available. Counts and others 

(1955) noted that the aquifer yielded only small amounts of 

highly mineralized water for domestic purposes, although 

Table 34. Water use from the Ozan aquifer in southwestern 

Arkansas, 1965–80. 

[Data from Halberg and Stephens (1966); Halberg (1972, 1977); Holland 

(1981). Only counties with published data for consumption of groundwater 

from the Ozan aquifer are shown]

County 1965 1970 1975 1980

Clark 0.13 0.15 0.19 0.52
Aquifers of the Coastal Plain 223

noting that some of the water was not suitable for even 

that purpose. Boswell and others (1965) reported that even 

groundwater from the Ozan outcrop area contained dissolvedsolids concentrations of more than 1,000 mg/L and that it was 

an important aquifer only in Clark County because no other 

water source was present.

As a consequence of limited use, the Ozan aquifer has 

received limited attention in terms of aquifer characterization 

and documentation of water quality. Older reports contain 

sparse water-quality information, and most of this information 

is related to salinity problems. Counts and others (1955) 

reported chloride concentrations ranging from 32 to 

2,100 mg/L in the Ozan aquifer. One well in Sevier County 

was reported as containing a chloride concentration of 

1,100 mg/L and was not used at the time of sampling. Only 

wells in Hempstead County yielded less mineralized water, 

containing dissolved-solids concentrations from 400 to 

500 mg/L (Counts and others, 1955). Boswell and others 

(1965) calculated dissolved-solids concentrations from 

specific conductance values and cited a range from 600 to 

greater than 4,000 mg/L.

General Geochemistry and Water Type

Only 14 sites had water-quality data from the Ozan 

aquifer. These data dominantly included major anions 

(bicarbonate, chloride, sulfate), nitrate, and field parameters 

including pH and specific conductance; only 2 wells contained 

information related to major cations (calcium, magnesium, 

sodium, potassium). Thus, no meaningful analysis can be 

made with regard to water type. However, certain assumptions 

can be made in regard to the evolution of geochemistry with 

existing data, and these are discussed further in “Conceptual 

Model of Groundwater Geochemical Evolution” at the end of 

this section.

Values of pH ranged from 6.8 to 8.6 with a median of 

8.3 (table 35). All pH values except one were greater than 7.5. 

No trends were noted in the spatial distribution of pH, except 

that the highest values tend to occur in the eastern part of the 

aquifer in Clark County (fig. 80). Generally, areas of higher 

pH correlated to areas of higher bicarbonate concentrations, 

indicating dissolution of carbonate minerals as a primary 

catalyst for buffering the low pH of rainwater and increasing 

pH. However, the distribution and concentrations of other 

anions indicate additional rock/water reactions and possible 

mixing with other water sources to explain the evolution of 

groundwater geochemistry. For instance, several sites with low 

bicarbonate concentrations were in the extreme eastern extent 

of the aquifer in Clark County, but samples from these wells 

exhibit some of the highest pH values and highest sulfate 

concentrations (fig. 80). Further discussion on the occurrence 

and distribution of the major anions is found below.

Nitrate

Nitrate concentrations ranged from 0.02 to 1.9 mg/L 

as nitrogen with a median of 0.43 mg/L (table 35). All 

concentrations were below the MCL of 10 mg/L. Insufficient 

data were available to assess any relations of nitrate with 

depth. However, wells with nitrate concentrations exceeding 

0.5 mg/L were less than 200 ft below the land surface. Well 

depths ranged up to 380 ft.

Table 35. Descriptive statistics for selected chemical constituents in groundwater from the Ozan aquifer in southwestern Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 0.8 3.4 6.0 2.6 2

Magnesium (mg/L) 0.35 1.32 2.3 0.97 2

Sodium (mg/L) 33.6 477 920 443 2

Potassium (mg/L) 1.62 2.21 2.8 0.59 2

Bicarbonate (mg/L) 96 261 560 154 14

Chloride (mg/L) 5.3 479 2,100 771 14

Sulfate (mg/L) 4.9 230 517 151 14

Silica (mg/L) 11.1 12.1 13 0.95 2

Nitrate (mg/L as nitrogen) 0.02 0.43 1.9 0.54 12

Dissolved solids (mg/L) 136 1,230 2,330 1,090 2

Iron (μg/L) 20 600 1,180 580 2

Manganese (μg/L) 19.8 19.8 19.8 0.13 1

Arsenic (μg/L) 0.03 0.03 0.03 0.03 1

Hardness (mg/L as calcium carbonate) 6.0 98 400 128 13

Specific conductance (μS/cm) 213 2,550 7,200 2,370 14

pH (standard units) 6.8 8.3 8.6 0.4 14
PIKE CLARK HOWARD NEVADA HEMPSTEAD SEVIER LITTLE RIVER HOT SPRING PIKE CLARK HOWARD NEVADA HEMPSTEAD SEVIER LITTLE RIVER HOT SPRING PIKE CLARK HOWARD NEVADA HEMPSTEAD SEVIER LITTLE RIVER HOT SPRING PIKE CLARK HOWARD NEVADA HEMPSTEAD SEVIER LITTLE RIVER HOT SPRING 94° 93°30’ 34° 33° 94° 93°30’ 34° 33° 94° 93°30’ 34° 33° 94° 93°30’ 34° 33° 0 10 20 MILES 0 10 20 KILOMETERS 

Chloride, in milligrams per liter 5 to 25 26 to 50 51 to 250 251 to 1,000 1,001 to 2,100 pH, in standard units 6.8 to 7.0 7.1 to 7.5 7.6 to 8.2 8.3 to 8.4 8.5 to 8.6 Sulfate, in milligrams per liter 5 to 25 26 to 100 101 to 250 251 to 500 501 to 517 Bicarbonate, in milligrams per liter 96 to 100 101 to 200 201 to 300 301 to 500 501 to 560 EXPLANATION EXPLANATION EXPLANATION EXPLANATION 

Base modified from U.S. Geological Survey digital data, 1:250,000 Universal Transverse Mercator projection, zone 15 Geology map modified from Boswell and others, 1965; Haley and others, 1993

Figure 80. Spatial distribution of selected chemical constituents in groundwater from the Ozan aquifer in southwestern Arkansas.
Aquifers of the Coastal Plain 225

Iron

Only two wells had iron analyses, with concentrations 

of 20 and 1,180 μg/L. These two samples reveal that iron 

concentrations vary widely, similar to other Cretaceous 

and Tertiary aquifers of the Coastal Plain. Typically, iron 

concentrations in Coastal Plain aquifers tend to be higher in 

the outcrop area and decrease downgradient. This is attributed 

to increasing reducing conditions and formation of ironsulfide minerals along the flow path. However, data were 

inadequate to make any assessment of the spatial distribution 

of iron for the Ozan aquifer. 

Sulfate

Sulfate concentrations ranged from 4.9 to 517 mg/L with 

a median of 230 mg/L, which is the highest median sulfate 

concentration of any aquifer in the State (fig. 81; table 35). 

However, groundwater from the Jackson Group (table 21) 

contained the overall highest sulfate concentrations of any 

aquifer. A general relation was observed between sulfate 

and bicarbonate concentrations. Four wells had sulfate 

concentrations greater than 300 mg/L (ranging upward to 

517 mg/L) with associated bicarbonate concentrations that 

were less than 300 mg/L. Conversely, five wells had sulfate 

concentrations less than 300 mg/L and associated bicarbonate 

concentrations that were greater than 400 mg/L (upward to 

542 mg/L) (fig. 82A).

Chloride 

Chloride concentrations ranged from 5.3 to 2,100 mg/L 

with a median of 479 mg/L (fig. 81; table 35). Chloride 

exceeded the Federal secondary drinking-water regulation 

of 250 mg/L (U.S. Environmental Protection Agency, 

2009) dominantly at sites located in central Clark County 

with the exception of one site located in northeastern 

Little River County that had a chloride concentration of 

1,100 mg/L (fig. 80). Six wells with chloride concentrations 

NO DATANO DATANO DATANO DATA

14

14

14

14

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

2,000

700

800

900

1,000

0

100

200

300

400

500

600

Concentrations, in milligrams per liter

Concentration, in micrograms per liter

Constituent Constituent

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron 

Figure 81. Interquartile range of selected chemical constituents in groundwater from the Ozan aquifer in southwestern Arkansas.
226 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

exceeding 250 mg/L in Clark County ranged in depth from 

150 to 360 ft. These were located in the outcrop area, and 

the depths are relatively shallow compared to other highchloride occurrences in Cretaceous and Tertiary aquifers 

in southwestern Arkansas. Because the outcrop generally 

represents the area of recharge and shallow well depths, 

flushing of residual salinity would normally occur resulting in 

lower chloride concentrations. Other Cretaceous formations 

generally contained freshwater in and near the outcrop with 

higher salinity occurring downgradient. No mechanisms for 

the cause of high chloride were provided in older reports. The 

authors also cannot provide mechanisms confidently because 

of the lack of information for this unusual occurrence. Counts 

and others (1955) noted the low well yields from a dominant 

sandy-clay facies of the Ozan in the area of outcrop, and one 

plausible explanation for elevated chloride concentrations may 

be that residual connate water in the high percentage clayey 

deposits of the Ozan Formation have not been sufficiently 

flushed over time. Another possible explanation is that 

elevated chloride concentrations result from the upwelling of 

high-salinity groundwater from underlying formations.

Conceptual Model of Groundwater Geochemical 

Evolution

Although only two samples had analysis of dissolved 

solids, all samples had field specific conductance, which 

is a reasonable proxy for assessing changes in constituent 

concentrations with increased residence time in the 

aquifer. Specific conductance and chloride show a positive 

linear relation when specific conductance values exceed 

2,000 μS/cm (fig. 82B). Analysis of the geochemical data 

shows that bicarbonate or sulfate is the dominant anion 

(by weight) for specific conductance values less than 

approximately 2,000 μS/cm. Therefore, certain assumptions 

can be made in regard to geochemical evolution of 

groundwater in the Ozan aquifer based on extensive review of 

other aquifers in the Coastal Plain. 

0 100 200 300 400 500 600

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

Specific conductance, in microsiemens per centimeter Specific conductance, in microsiemens per centimeter

Bicarbonate, in milligrams per liter Specific conductance, in microsiemens per centimeter

100

200

300

400

500

600

Sulfate, in milligrams per liter

0

10

20

30

40

50

60

70

80

90

Bicarbonate, in percent of anions

500

1,000

1,500

2,000

2,500

Chloride, in milligrams per liter

0

10

20

30

40

50

60

70

Sulfate, in percent of anions

0 0

A B

C D

Figure 82. Relation of A, bicarbonate and sulfate; relation of specific conductance and B, chloride; C, percent bicarbonate; and 

D, percent sulfate in groundwater from the Ozan aquifer in southwestern Arkansas.
Aquifers of the Coastal Plain 227

Groundwater from the Ozan aquifer appears to be 

dominated by bicarbonate in the early stages along the 

groundwater flow path with short residence time within the 

aquifer. This is reflected in two samples with bicarbonate 

greater than 50 percent of anions and values of specific 

conductance less than 1,000 μS/cm (fig. 82C). A sharply 

decreasing trend is noted for percent bicarbonate when specific 

conductance is greater than 1,000 μS/cm. Therefore, this 

fits the model of early-stage carbonate-mineral dissolution 

observed for many aquifers of the State. This model typically 

results in a calcium-bicarbonate to sodium-bicarbonate 

water type with increased carbonate dissolution and cation 

exchange. For samples with specific conductance values 

between approximately 1,000 and 2,200 μS/cm, sulfate is the 

dominant anion (fig. 82D). Groundwater with higher sulfate 

than bicarbonate concentrations is theorized to be derived 

from dedolomitization processes in the aquifer, in which 

gypsum dissolution leads to calcite precipitation (see sections 

on Tokio and Trinity aquifers). Groundwater with specific 

conductance values exceeding approximately 2,200 μS/cm has 

chloride as the dominant anion (ranging from 64 to 87 percent 

of total anions). Chloride additionally exhibits a positive linear 

relation with specific conductance for specific conductance 

values greater than 2,200 μS/cm (fig. 82B). The increasing 

chloride concentration may result from dissolution of residual 

salts (or saline water) that have not been flushed from the 

original marine deposits or from leakage of high-salinity water 

from underlying formations. Thus, one model of geochemical 

evolution of groundwater in the Ozan aquifer is carbonate 

dissolution in the early phases resulting in a bicarbonate water 

type, transitioning to a sulfate-dominated water type with 

dissolution of gypsum, and eventually to a chloride water 

type by mixing with high-salinity water. Groundwater with 

elevated chloride concentrations would be expected to contain 

elevated sodium (sodium-chloride type water), which is a 

concern for consumptive use (U.S. Environmental Protection 

Agency, 2009). One groundwater sample contained chloride 

and sodium concentrations of 1,100 mg/L and 920 mg/L, 

respectively, which may be a problem for individuals with a 

restricted sodium diet.

In summary, groundwater from the Ozan aquifer is some 

of the least used and poorest quality water in the State. Several 

reports mentioned that use of the aquifer as a domestic source 

was predicated on the fact that no other water source was 

available. High chloride concentrations occur in groundwater 

within the outcrop area of the Ozan aquifer, which is atypical 

of most Cretaceous and Tertiary aquifers of the Coastal Plain. 

Elevated sulfate concentrations and pH from wells located 

in the northeastern extent are attributed to possible gypsum 

dissolution coupled to calcite precipitation. 

Tokio Aquifer

Cretaceous formations in Arkansas (Nacatoch Sand, Ozan 

Formation, Tokio Formation, and the Trinity Group) and the 

aquifers comprised by these formations are not included in 

any of the regional hydrogeologic framework models of the 

Mississippi embayment (Arthur and Taylor, 1990; Hosman 

and Weiss, 1991; Hart and others, 2008; Clark and Hart, 

2009); however, the Tokio was included in the hydrologic 

investigations atlas for Segment 5 (Arkansas, Louisiana, 

and Mississippi) of Renken (1998) as the Tokio-Woodbine 

aquifer. The aquifer is referred to as the Tokio aquifer in 

various USGS water-use and water-level reports referenced 

herein; the most recent being Holland (2007) and Schrader 

and Rodgers (2013). This report will follow this terminology 

and for purpose of this report, the saturated part of the Tokio 

Formation yielding groundwater to wells in Arkansas will be 

referred to hereinafter as the “Tokio aquifer.”

Geology

The Tokio Formation is a Cretaceous-age, clastic 

formation primarily comprising sand and gravel units with 

interbedded clay and marl, ranging in thickness from 50 

to more than 300 ft (Boswell and others, 1965). The Tokio 

Formation initially was included with strata named as the 

Bingen Sand by Hill (1888). Stephenson (1927) divided the 

Bingen Sand into the Tokio Formation and the Woodbine 

Formation, discarding the term Bingen Sand. During the 

Cretaceous age, a considerable change of sea depth occurred 

in Arkansas after deposition of the Lower Cretaceous 

formations. While deepening water resulted in more clayey 

and carboniferous rocks being deposited during the Upper 

Cretaceous, Lower Cretaceous units in Arkansas, including 

the Tokio Formation, mainly were nearshore deposits (Veatch, 

1906).

The Tokio Formation unconformably overlies 

consolidated rocks of Mississippian and Pennsylvanian age in 

Clark and northeastern Nevada Counties (Plebuch and Hines, 

1969); overlies the Trinity Group in Pike, Nevada, Miller, 

and most of Hempstead Counties (Petersen and others, 1985); 

and overlies the Woodbine Formation in Little River, Sevier, 

Howard, and northwestern Hempstead Counties (Boswell and 

others, 1965). The Tokio is overlain by the Brownstown Marl, 

although in an area of Union County, the Brownstone Marl 

is absent and the Tokio is overlain by the Ozan Formation 

(Boswell and others, 1965; Zachry and others, 1986). The 

formation outcrops from Clark County southwestward to 

Sevier County and attains a maximum width of about 10 mi in 

Howard County (Schrader and Blackstock, 2010). The Tokio 

consists of discontinuous, interbedded gray clay and poorly 

sorted crossbedded sands, lignite, and scattered carbonaceous 

materials. In some areas, there is a prominent basal gravel 

(Counts and others, 1955; Boswell and others, 1965; Dollof 

and others, 1967; Plebuch and Hines, 1969; Petersen and 

others, 1985). 

The Tokio Formation dips at about 60 ft/mi to the 

southeast away from the outcrop and ranges in thickness from 

50 to more than 300 ft (Boswell and others, 1965), obtaining 

its maximum thickness in Miller County (Dollof and others, 

1967). A fault zone through the Tokio occurs across Miller, 
228 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Little River, Lafayette, Hempstead, Nevada, Ouachita, 

Calhoun, and Bradley Counties (Petersen and others, 1985, 

pl. 8). Dane (1929) identified the Tokio as a nearshore 

marine deposit. The presence of lignite and terrestrial plant 

fossils indicates nearshore deposition. The basal gravel is 

interpreted as a beach deposit formed by a transgressing sea 

with the gravel mainly being reworked from older Cretaceous 

formations (Dane, 1929).

In southern Sevier County and parts of Howard and 

Hempstead Counties, the Tokio comprises three distinct 

aquifers, including a basal sand that grades to gravel to 

the east and two upper sands (Boswell and others, 1965). 

Toward the east, the clay layers separating the sands thin, and 

the sands merge into a single massive sand aquifer, which 

is prevalent over most of Hempstead, southern Pike, and 

northern Nevada Counties.

Hydrologic Characteristics

The Tokio aquifer receives direct recharge at its outcrop 

and from the overlying alluvial deposits where it subcrops 

(Boswell and others, 1965). At its outcrop, the Tokio weathers 

into a sandy soil, facilitating percolation of surface and 

rainwater into the sand (Counts and other, 1955). Well depths 

and yields vary throughout the aquifer. Ludwig (1972) listed 

well depths ranging from less than 30 ft to 1,200 ft below land 

surface for parts of Hempstead, Lafayette, and Little River 

Counties. Most wells in the Tokio have low yields, but some 

produce 150–300 gal/min. Many are flowing artesian wells 

that typically produce less than 20 gal/min. The Tokio is the 

most important source of water from flowing artesian wells in 

southwestern Arkansas. Wells in central Hempstead County 

yield as much as 300 gal/min. Wells flowing at rates as much 

as 90 gal/min occur adjacent to streams (Counts and others, 

1955). Wells in northwestern Little River County penetrated 

a 15- to 20-ft thick, water-bearing sand that produced yields 

of less than 10 gal/min (Ludwig, 1973). The prevalence 

of artesian wells in the Tokio indicates that the aquifer is 

confined away from the outcrop and the potentiometric surface 

is above land surface. An aquifer test in southern Howard 

County resulted in a transmissivity of about 170 ft2/d and a 

storage coefficient of 0.000044. A test using a public-supply 

well in Hempstead County resulted in a transmissivity of 

about 600 ft2/d (Boswell and others, 1965). 

Water Use

The Tokio aquifer dominantly has been used as a source 

of domestic water supply. Counts and others (1955) recorded 

143 domestic wells in the Tokio aquifer in Clark, Hempstead, 

Howard, Nevada, Pike, and Sevier Counties in southwestern 

Arkansas. Many of these wells originally were flowing. An 

estimated 66 percent of water was lost from the total 3 Mgal/d 

that was withdrawn in southwestern Arkansas as a result of 

uncontrolled flowing artesian wells (Boswell and others, 

1965). Domestic-supply and livestock use continued into the 

late 1960s and early 1970s in Clark County and northwestern 

Little River County near Winthrop (Plebuch and Hines, 1969; 

Ludwig, 1973). For 2010, there were 18 wells registered in 

ARWUDBS from the Tokio (fig. 83). Current (2013) use is 

for domestic purposes in Hempstead County and for livestock 

purposes in Howard County.

Several towns in southwestern Arkansas have used 

the Tokio aquifer for public supply. Hope (Hempstead 

County) tapped the aquifer in 1918 (Hale and others, 1947). 

Hope drilled additional wells into the Nacatoch aquifer 

in 1933 (Hale and others, 1947). The city continues to 

use groundwater from this and the Nacatoch aquifers but 

supplements with surface water. Hope withdrew 1.83 Mgal/d, 

which was 64 percent of its total public-supply use from 

this aquifer in 2010 (Terrance W. Holland, U.S. Geological 

Survey, written commun., 2012). Other small communities in 

the area including Okolona (Clark County), Mineral Springs 

(Howard County), Blevins (Hempstead County), and Ben 

Lomond (Sevier County) tap the Tokio for public supply. 

Prescott (Nevada County) formerly had one well in the Tokio, 

which was completed in 1912, and two wells in the Nacatoch 

(Counts and others, 1955) but now solely withdraws water 

from the Little Missouri River. Also, wells historically were 

used at several schools in the area (Counts and others, 1955).

A small amount of industrial use, including gas 

production near Prescott, a cement company in Howard 

County, and a handful of lumber operations occurred in the 

past (Counts and others, 1955). Current industrial use of the 

aquifer only occurs in Miller County (Terrance W. Holland, 

U.S. Geological Survey, written commun., 2012). 

Historical use of the Tokio aquifer by county is listed in 

table 36. Use of groundwater from the aquifer increased about 

200 percent from 1965 to 1980 (fig. 84), the peak year for use 

of water from the aquifer. Use decreased from 1980 to 1995 

and then jumped to a second high in 2000. Since 2000, water 

use from the Tokio has declined. Approximately 73 percent 

of water used from the Tokio aquifer is for public supply, 7 

percent for industrial use, and the remainder for domestic and 

livestock uses (Terrance W. Holland, U.S. Geological Survey, 

written commun., 2012). 
YELL

LEE

UNION

WHITE

POLK

POPE

DREW

PIKE

SCOTT

CLARK

CLAY

ASHLEY

DESHA

BENTON

LOGAN

SALINE

IZARD

LONOKE

PULASKI

ARKANSAS

NEWTON

GRANT

CHICOT

MADISON

STONE

MILLER

SHARP

CROSS

DALLAS

PRAIRIE

BOONE

PHILLIPS

PERRY

SEARCY

MARION

FULTON

SEVIER

MISSISSIPPI

JEFFERSON

NEVADA

POINSETT

GARLAND

COLUMBIA

BAXTER

OUACHITA

BRADLEY

JOHNSON

WASHINGTON

MONROE

GREENE

JACKSON

CARROLL

HOWARD

LINCOLN

CALHOUN

CONWAY FAULKNER

VAN BUREN FRANKLIN

CRAIGHEAD

HEMPSTEAD

RANDOLPH

CLEBURNE

MONTGOMERY

LAWRENCE

ST. FRANCIS

CRAWFORD

CLEVELAND

HOT SPRING

INDEPENDENCE

LITTLE

RIVER

WOODRUFF CRITTENDEN

LAFAYETTE

SEBASTIAN

94° 92° 91° 93°

90°

36°

35°

34°

Base from U.S. Geological Survey digital data, 1:2,000,000

0 15 0 30 

15

Extent of Well type 

galloto repwaterrepres

EX

IndustrPublic 

Figure 83. Wells with reported water use for the Tokio aquifer in Arkansas, 2010.
230 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Table 36. Water use from the Tokio aquifer in Arkansas, 1965–2010. 

[Counties shown are only those with published data. Data from Halberg and Stephens (1966); Halberg (1972, 1977); Holland (1981, 1987, 1993, 1999, 2004, 

2007). Units are million gallons per day]

County 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Clark 0.00 0.00 0.02 0.06 0.04 0.01 0.01 1

0.06 0.07 0.06

Hempstead 0.67 0.68 2.15 3.00 2.86 1.10 1.66 3.46 2.10 2.12

Howard 0.69 0.62 0.97 1.11 0.14 0.00 0.00 1

0.06 0.50 0.54

Miller 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.15

Nevada 0.37 0.47 0.55 0.68 0.00 0.00 0.00 0.00 0.00 0.00

Pike 0.12 0.41 0.43 0.82 0.06 0.03 0.02 0.00 0.00 0.00

Sevier 0.15 0.17 0.25 0.35 0.79 1.15 0.54 2.36 1.73 0.00

Total 2.00 2.35 4.37 6.02 3.89 2.29 2.23 1

5.94 24.40 2.87

1

Unpublished data from Terrance W. Holland, U.S. Geological Survey, written commun., 2013.

2

In the 2005 report, 0.08 million gallons per day in Sharp County was inadvertently reported as being withdrawn from the Tokio aquifer when it should have 

been applied to the Everton Formation. Therefore, the published total is slightly different from Holland (2007). 
19651980 1985

1970 1975

EXPLAN

Annual water withdrawn 

in million gallons per 

No color represents no repo

0.01 to 0.100.11 to 0.400.41 to 0.80

0.81 to 1.40

1.41 to 1.80

0 60 0 60 

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

Base from U.S. Geological Survey digital data 1:2,000,000 Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977;

 Holland, 1981, 1987, 1993, 1999, 2004, 2007

Figure 84. Water-use rates for the Tokio aquifer in Arkansas from 1965 to 2010. 
EXPLANA

Annual water withdrawn 

in million gallons per 

No color represents no repor

0.01 to 0.10 0.11 to 0.40 0.41 to 0.80 0.81 to 1.40 1.41 to 1.80 

94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 

36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 0 60 

0 60 

Base from U.S. Geological Survey digital data 1:2,000,000 Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977; Holland, 1981, 1987, 1993, 1999, 2004, 2007 1990 2005 2010 1995 2000

Figure 84. Water-use rates for the Tokio aquifer in Arkansas from 1965 to 2010.—Continued
Aquifers of the Coastal Plain 233

Water Levels

Long-term ANRC and USGS cooperative monitoring 

has documented water-level changes in the Tokio aquifer 

(Schrader, 1998, 1999, 2007b; Schrader and Scheiderer, 2004; 

Schrader and Blackstock, 2010; Schrader and Rogers, 2013). 

The potentiometric surface for the Tokio aquifer is highest 

within the outcrop area in northeastern Howard County 

(fig. 85), with groundwater flowing to the south and primarily 

southeast (Counts and others, 1955; Boswell and others, 1965; 

Plebuch and Hines, 1969; Petersen and others; 1985; Schrader 

and Blackstock, 2010; Schrader and Rodgers, 2013). No 

appreciable changes in water levels were noted between the 

1996, 1999, and 2001 investigations (Schrader and Scheiderer, 

2004), but the addition of a single well changed the position 

of the 300-ft contour in Howard County for the 2008 

potentiometric-surface map (Schrader and Blackstock, 2010). 

A cone of depression in southern Howard County appeared in 

the 2011 potentiometric surface (fig. 85). Many reports cite the 

possibility of a cone of depression forming 5 mi northwest of 

Hope; however, data are insufficient in the southern part of the 

study area to confirm this situation (Schrader, 2007; Schrader 

and Blackstock, 2010; Schrader and Rodgers, 2013). Ludwig 

(1973) previously reported that large withdrawals from 

Prescott and Hope did not appear to affect the potentiometric 

surface between 1950 and 1968. 

Water levels in well A (figs. 85 and 86) near the possible 

cone of depression northwest of Hope have declined with 

increasing use. A large decline was documented between 

1990 and 2000, when water use increased from 1.10 Mgal/d 

to 3.46 Mgal/d in Hempstead County, a 215-percent increase. 

Water levels additionally appear to have slowly declined at 

Prescott; water-level changes in well B previously have been 

associated with changes in water use in Nevada County. Water 

levels near the outcrop and artesian-flow areas have remained 

relatively constant since the 1950s (well C in northeastern 

Hempstead County and well D in southwestern Howard 

County; figs. 85 and 86). 

Water Quality

Similar to other Tertiary-age aquifers in southwestern 

Arkansas, water quality varies with flow direction as 

controlled by formation dips to the southeast. The Tokio 

aquifer crops out in a narrow band from southeastern Sevier 

through western Clark Counties with a small, isolated 

outcrop located in extreme western Little River County. 

Most producing wells are located within the larger outcrop 

belt. Chloride concentrations increased to the southeast in 

the downgradient (downdip) direction of groundwater flow 

(Counts and others, 1955; Plebuch and Hines, 1969; Ludwig, 

1972). Counts and others (1955) stated that bicarbonate and 

sulfate were high, indicating a moderately high sodiumbicarbonate to sodium-sulfate water type. Plebuch and Hines 

(1969) and Ludwig (1973) listed groundwater from the Tokio 

as a soft to moderately hard, sodium-bicarbonate water type 

throughout most of its extent, except for areas of increased 

chloride concentration downgradient from the outcrop area. 

Iron concentrations were cited as being high in some areas, 

ranging up to 54 mg/L (Counts and others, 1955; Ludwig, 

1972). 
234 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Base from U.S. Geological Survey digital data, 1:24,000

Universal Transverse Mercator, zone 15

North American Datum of 1983

Modified from Schrader and Rodgers, 2013

0 10 20 KILOMETERS

0 10 20 MILES

LITTLE

RIVER

SEVIER

HOWARD

PIKE

CLARK

HEMPSTEAD

MILLER

LAFAYETTE COLUMBIA

NEVADA

320

300

280

340

240

260

220

200

380

400

180

440

160

460

140

480

240

360

240

220

420

C

A

D

B 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

437

283

299

269

271

219

207

215

225

279 250

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

437

283

299

269

271

219

207

215

225

279 250

* * **

*

*

*

*

*

!

!!

!

! !

!

! !

!

!

!

!

!

! !

!!

!

!! !

!

! !

! !

!

!

!

!

!

!

!

"

"

Hope

Prescott

94°00' 93°30'

93°00'

34°00'

33°30'

Area enlarged

ARKANSAS

EXPLANATION

Southwestern study area

Outcrop of Tokio Formation

Approximate boundary of artesian flow

Approximate northern limit of Tokio aquifer

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 (NGVD 29)

Control point—Letter, where present,

 corresponds to hydrograph on figure 86. 

 Number is water level in feet above 

 NGVD 29 in 2011. Asterisk indicates 

 well last measured in 2008

Flowing artesian well—Number is water

 level in feet above NGVD 29

214 B

271

250

!

*

Figure 85. Potentiometric surface of the Tokio aquifer in Arkansas, spring 2011.
Aquifers of the Coastal Plain 235

General Geochemistry and Water Type

Similar to other Cretaceous- and Tertiary-age aquifers 

reviewed in this report, pH values generally were lowest 

in the outcrop area, reflecting rainwater recharge values. 

Values of pH increased abruptly within short distances in the 

downgradient direction of flow as buffered by dissolution 

of aquifer carbonate minerals (fig. 87). Values of pH ranged 

from 5.4 to 9.1 standard units with a median of 8.3 (table 37). 

The median value demonstrates the high-pH characteristic of 

Tokio groundwater. Only 20 of 158 samples were less than 

7.0, and 102 of the 158 samples were greater than 8.0. Values 

of pH were highest, greater than 8.5, in the southwestern 

and northeastern outcrop areas. In the southwestern part 

of the outcrop area, bicarbonate concentrations were very 

low, which is at odds with application of the carbonate 

buffering explanation of high pH mentioned earlier. In this 

area, sulfate was the dominant anion. Detailed discussion of 

sulfate geochemistry and explanation of high pH values in the 

southwestern area are found in the “Sulfate” section below.

Most Cretaceous and Tertiary aquifers have sodium 

as the dominant cation downgradient from their respective 

outcrop areas, and the Tokio aquifer follows this pattern. Only 

29 samples had sufficient major cation data for calculating 

percent sodium of total cations (in milliequivalents per liter). 

Samples having percent sodium less than 50 percent of 

the total cations were from wells in the outcrop area at the 

origin of the groundwater flow path where groundwater is 

less geochemically evolved (fig. 87). At the beginning of the 

flow path, calcium is often the dominant cation, and cationexchange processes have not appreciably affected groundwater 

chemistry. The exchange of calcium for sodium on solid-phase 

exchange sites increases sodium in solution at the expense 

of calcium, and groundwater transitions ultimately from a 

calcium- to a sodium-bicarbonate water type along a given 

flow path. Fifteen samples had greater than 90 percent sodium. 

All of these wells were located within 2–5 mi of the outcrop 

area except for one site located on the southern edge of the 

outcrop area in Howard County. 

Figure 86. Hydrographs of water levels in wells completed in the Tokio aquifer in Arkansas.

1965 1970 1975 1980 1985 

Year

1990 1995 2000 2005 2010 

100 

150 

200 

250 

300 

350 

400 

450 

500 

Water level, in feet above National Geodetic Vertical Datun of 1929

EXPLANATION

Water level, in well completed

in the Tokio aquifer

 Well A (Hempstead County)

 Well B (Nevada County)

 Well C (Hempstead County)

 Well D (Howard County) 
PIKE HOWARDMONTGOMERY HEMPSTEAD LITTLE RIVER NEVADA CLARK SEVIER GARLAND HOT SPRING MILLER PIKE HOWARDMONTGOMERY HEMPSTEAD LITTLE RIVER NEVADA CLARK SEVIER GARLAND HOT SPRING MILLER 

HOWARDM

LITTLE RIVER 

SEVIER 

MILLE

PIKE HOWARDMONTGOMERY HEMPSTEAD LITTLE RIVER NEVADA CLARK SEVIER GARLAND HOT SPRING MILLER PIKE HOWARDMONTGOMERY HEMPSTEAD LITTLE RIVER NEVADA CLARK SEVIER GARLAND HOT SPRING MILLER 

HOWARDM

LITTLE RIVER 

SEVIER 

MILL

94°00’ 93°30’ 94°00’ 93°30’ 94°00’ 

94°00’ 93°30’ 94°00’ 93°30’ 94°00’ 

34° 00’ 34° 30’ 33° 30’ 34° 00’ 34° 30’ 33° 30’ 34° 00’ 34° 30’ 33° 30’ 34° 00’ 34° 30’ 33° 30’ 34° 00’ 34° 30’ 33° 30’ 34° 00’ 34° 30’ 33° 30’ 0 20 40 MILES 0 20 40 KILOMETERS EXPLANATION Tokio outcrop Tokio extent 5.4 to 6.5 6.6 to 7.0 7.1 to 7.5 7.6 to 8.0 8.1 to 8.5 8.6 to 9.1 pH, in standard units Specific conductance, in microsiemens per centimeter at 25 degrees Celsius 41 to 100 101 to 250 251 to 500 501 to 1,000 1,001 to 2,500 2,501 to 4,760 Sodium, in percent of majo

15 to 25 26 to 50 51 to 60 61 to 70 71 to 80 81 to 99 Bicarbonate, in milligrams per liter 2 to 10 11 to 25 26 to 50 51 to 250 251 to 500 501 to 691 Sulfate, in milligrams per liter 1 to 10 11 to 25 26 to 50 51 to 100 101 to 250 251 to 397 Chloride, in milligrams per 

2 to 10 11 to 25 26 to 100 101 to 250 251 to 500 501 to 1,200 EXPLANATION EXPLANATION EXPLANATION EXPLANATION EXPLANATION EXPLANATION Area enlarged ARKANSAS Base modified from U.S. Geological Survey digital data, 1:250,000 Universal Transverse Mercator projection, zone 15 Geology map 

Figure 87. Spatial distribution of selected chemical constituents in groundwater from the Tokio aquifer in Arkansas.
Aquifers of the Coastal Plain 237

Nitrate

Nitrate concentrations in 154 samples generally were 

low in samples from the Tokio aquifer, ranging from 0.01 to 

4.1 mg/L as nitrogen with a median of 0.18 mg/L (table 37). 

All samples were below the Federal MCL of 10 mg/L as 

nitrogen (U.S. Environmental Protection Agency, 2009). 

Typical of other aquifers in the Coastal Plain, higher nitrate 

concentrations generally were in or near outcrop areas, with 

low concentrations downgradient. Three of the four samples 

with nitrate concentrations greater than 1.0 mg/L were in the 

outcrop area. There was a relatively greater density of nitrate 

concentrations more than 0.5 mg/L in the southwestern part 

of the aquifer. Overall low nitrate concentrations precluded 

an effective relation between nitrate and well depth. 

However, the two highest nitrate concentrations of 2.0 and 

4.1 mg/L were in wells with depths of 25 and 16 ft. Well 

depths ranged upward to 1,500 ft. 

Iron

The Tokio aquifer generally had the lowest median and 

maximum iron concentrations of any of the Cretaceous- and 

Tertiary-age aquifers in Arkansas. Iron concentrations ranged 

from 0.05 to 4,000 μg/L with a median of 80 μg/L (fig. 88; 

table 37). The median concentration is below the Federal 

secondary drinking-water regulation of 300 μg/L (U.S. 

Environmental Protection Agency, 2009). Iron concentrations 

generally were lower in and near the outcrop area, although 

no strong spatial trend was evident for iron concentrations. 

Several wells that had concentrations exceeding 1,000 μg/L 

were located 6 mi or more downdip from the outcrop area. 

Ludwig (1973) stated that elevated iron concentrations were 

not necessarily indicative of iron originating in the Tokio 

aquifer; instead, he hypothesized it resulted from a mixing of 

water in uncased wells from shale formations overlying the 

Tokio. This could explain the lack of spatial trends noted for 

other Cretaceous and Tertiary aquifers, such as higher iron 

concentrations in outcrop areas.

Table 37. Descriptive statistics for selected chemical constituents in groundwater from the Tokio aquifer in Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 0.7 5.3 66 14.8 29

Magnesium (mg/L) 0.07 1.2 9.2 1.95 29

Sodium (mg/L) 1.99 196 694 204 29

Potassium (mg/L) 0.7 2.62 29 5.3 28

Bicarbonate (mg/L) 2.0 27 691 152 156

Chloride (mg/L) 2.3 11 1,200 205 159

Sulfate (mg/L) 1.0 31 397 59.4 158

Silica (mg/L) 4.8 13.2 28.5 6.1 26

Nitrate (mg/L as nitrogen) 0.01 0.18 4.1 0.41 154

Dissolved solids (mg/L) 52 498 1,820 502 29

Iron (μg/L) 0.05 80 4,000 736 117

Manganese (μg/L) 0.13 4.09 2,100 446 21

Arsenic (μg/L) 0.03 0.03 0.03 0.03 6

Hardness (mg/L as calcium carbonate) 2.0 48 700 135 155

Specific conductance (μS/cm) 41 435 4,760 808 159

pH (standard units) 5.4 8.3 9.1 0.8 158
238 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Sulfate

Sulfate concentrations for the Tokio aquifer ranged from 

1.0 to 397 mg/L with a median of 31 mg/L (fig. 88; table 37). 

This median concentration was an order of magnitude higher 

than in the Sparta, Cockfield, Carrizo, Cane River, and 

Wilcox aquifers. Only the Ozan and Jackson Group aquifers 

had higher sulfate concentrations, with medians of 230 and 

110 mg/L, respectively. Therefore, the Tokio exhibits a wider 

range and higher concentrations of sulfate compared to other 

Cretaceous and Tertiary aquifers. Counts (1955) stated that 

bicarbonate and sulfate concentrations frequently were high 

in the Tokio, indicating a moderately high sodium-bicarbonate 

to sodium-sulfate water type. However, Ludwig (1972) had 

little mention of elevated sulfate in the aquifer. The spatial 

distribution of sulfate suggests very different geochemical 

processes controlling groundwater-evolution trends in various 

parts of the Tokio. 

Prior to this discussion, a review of general salinity 

trends is useful. Conceptually, salinity is represented by the 

quantity of dissolved salts in water, which is directly related to 

the dissolved-solids concentration. Only 29 of 160 wells with 

water-quality data had analyses for dissolved solids. However, 

159 of the wells had specific conductance values. Specific 

conductance exhibited a strong linear relation with dissolved 

solids with a coefficient of determination (R2

) value of 0.99 

(fig. 89A) from a regression analysis (Helsel and Hirsch, 

2002), making specific conductance an excellent proxy for 

dissolved solids by the equation:

DS = (0.556 × SC) + 35.7 (1)

where 

DS is the concentration of dissolved solids in 

milligrams per liter, and

SC is the specific conductance in microsiemens 

per centimeter.

An inspection of the spatial distribution of specific 

conductance values revealed steep gradients for increases 

in groundwater salinity downgradient from the outcrop 

area (fig. 87). Specific conductance values exceeding 

0

50

100

150

200

250

300

350

400

450

Concentrations, in milligrams per liter

500

Concentration, in micrograms per liter

700

800

900

1,000

0

100

200

300

400

500

600

117

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

29 29

29

156

159

158

117

Constituent Constituent

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron

Figure 88. Box plots showing interquartile range for selected chemical constituents in groundwater from the Tokio aquifer in Arkansas.
Aquifers of the Coastal Plain 239

2,500 μS/cm are located within 1–5 mi of the outcrop areas 

in the southwestern and northeastern parts of the aquifer. 

Conversely, no values exceeding 2,500 μS/cm are noted in 

the central part. Even as far as 15–20 mi from the outcrop 

area, specific conductance values are less than 2,500 μS/cm in 

the central part of the aquifer. This situation is similar to the 

Nacatoch aquifer, which exhibited sharper salinity gradients 

in the southwestern and northeastern parts of the aquifer 

compared to the central part. 

These abrupt increases in salinity, indicated by increases 

in specific conductance, appear to be the result of different 

processes in the southwestern and northeastern areas of the 

aquifer. In the northeastern part of the aquifer, the higherconductance groundwater is dominated by chloride and 

bicarbonate as the major anions. Six samples have chloride 

concentrations exceeding 500 mg/L, and 14 samples have 

bicarbonate concentrations exceeding 250 mg/L and ranging 

upward to 432 mg/L (fig. 87). The increase in salinity in the 

northeastern area is similar to other Cretaceous aquifers, 

where salinity tends to increase within short distances in 

the downgradient direction of flow. There usually is a clear 

transition from a calcium- or sodium-bicarbonate water in 

and near the outcrop area to a sodium-chloride water type 

downgradient. In the extreme southwestern part of the aquifer, 

sulfate is the dominant anion, rather than bicarbonate or 

chloride. Only 4 of 27 wells in the southwestern part of the 

aquifer had chloride concentrations exceeding 250 mg/L, and 

all but 2 wells had bicarbonate concentrations less than 50 

mg/L (many less than 10 mg/L) (fig. 87). When sulfate was 

the dominant anion (sulfate greater than 50 percent of anions 

in milliequivalents per liter), bicarbonate concentrations 

generally were less than approximately 25 mg/L. An inverse 

relation was noted between percent sulfate and bicarbonate 

concentrations (fig. 89B). Additionally, sulfate-dominated 

groundwater generally occurred in less mineralized water. 

When sulfate was the dominant anion, conductance values 

generally were less than approximately 800 μS/cm (fig. 89C), 

which correlates to a dissolved-solids concentration of about 

480 mg/L. Thus, sulfate concentrations did not increase with 

increasing dissolved solids along the flow path, typical of 

other Cretaceous aquifers, but rather constitutes the major 

anion chemistry in this area.

0 1,000 2,000 3,000 4,000 5,000

Specific conductance, in microseimens per centimeter

0 100 200 300 400 500 600 700 800

Bicarbonate, in milligrams per liter

0 1,000 2,000 3,000 4,000 5,000

Specific conductance, in microseimens per centimeter

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000

Specific conductance, in microsiemens per centimeter

0

10

20

30

40

50

60

70

80

90

100

Sulfate, in percent of anions

0

200

400

600

800

1,000

1,200

1,400

Chloride, in milligrams per liter

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

2,000

Dissolved solids,

in milligrams per liter

0

10

20

30

40

50

60

70

80

90

100

Sulfate, in percent of anions

A B

C D

R2 = 0.99

Figure 89. Relation of A, specific conductance and dissolved solids; B, sulfate and bicarbonate; C, specific conductance and sulfate; 

and D, specific conductance and chloride in groundwater from the Tokio aquifer in Arkansas.
240 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

For Arkansas aquifers, bicarbonate concentrations 

generally exceed sulfate concentrations. One mechanism that 

results in high (greater than 20 mg/L) sulfate concentrations is 

diffusion from fine-grained sediments. Fine-grained sediments 

often contain several hundred milligrams per liter of sulfate, 

whereas concentrations in coarse-grained sediments are less 

than 50 mg/L (Chapelle, 2001). Although abundant clays are 

noted for most of the Cretaceous formations in southwestern 

Arkansas, this mechanism does not account for the increases 

in sulfate with concomitant decreases in bicarbonate 

concentrations. This mechanism also does not explain the high 

pH values (greater than 8.5 standard units) in this area.

A second viable mechanism that results in elevated 

sulfate concentrations is dedolomitization. Sacks (1996) 

noted that high-sulfate groundwater in Florida was controlled 

by gypsum and dolomite dissolution linked with calcite 

precipitation. This process, referred to as dedolomitization, 

accounts for increased sulfate concentrations with concomitant 

decreases in bicarbonate for several areas of the country 

(Appelo and Postma, 1999). Gypsum (a mineral composed 

of calcium and sulfate) is cited as a source of sulfate in other 

Cretaceous and Tertiary aquifers in southwestern Arkansas. 

Thus, dedolomitization provides a plausible explanation 

for elevated sulfate that is consistent with the geochemistry 

of groundwater, particularly bicarbonate and chloride, 

in the southwestern part of the aquifer. Only a limited 

number of samples had major cation chemistry (table 37) 

including calcium, magnesium, sodium (29 samples), and 

potassium (28 samples), whereas most samples had major 

anion chemistry including bicarbonate (156), chloride 

(159) and sulfate (158). This precludes detailed analysis of 

mineral equilibrium constraints on resulting groundwater 

geochemistry. Availability of more detailed geochemical 

data sets would enable such an analysis and provide a more 

confident determination of dissolved-species sources.

Chloride 

Similar to other Cretaceous aquifers in southwestern 

Arkansas, salinity was noted to increase to the southeast in the 

downdip direction of groundwater flow (Counts and others, 

1955; Plebuch and Hines, 1969; Ludwig, 1973). Chloride 

exhibited a positive, linear relation with specific conductance 

values greater than 1,000 μS/cm, indicating dominance of 

chloride in the higher salinity groundwater (fig. 89D). The 

elevated salinity in southern Arkansas led Zachry and others 

(1986) to investigate the potential of injecting wastewaters 

from petroleum exploration into Cretaceous aquifers in 

southern Arkansas as the groundwater was too saline for other 

uses. 

Chloride concentrations from the Tokio aquifer ranged 

from 2.3 to 1,200 mg/L with a median of 11 mg/L (fig. 88; 

table 37). This median concentration is capable of being 

derived naturally from evapotranspiration of infiltrating 

precipitation (Kresse and Fazio, 2002). Similar to the 

Nacatoch aquifer, gradients of increasing salinity are sharper 

along the northeastern and southwestern parts of the aquifer. 

Chloride concentrations exceeding 500 mg/L occurs within 

1–5 mi of the outcrop area in the western and eastern parts 

of the aquifer. In the central part of the aquifer, chloride 

concentrations are less than approximately 300 mg/L as much 

as 20 mi from the outcrop area (fig. 87). Thus, the central 

part of the aquifer affords a much larger area of low-salinity 

groundwater for various uses. There was no variation in 

formation structure or dominant stratigraphy to explain the 

observed chloride distribution. Further investigations into 

the spatial variation in geochemistry for the Tokio aquifer 

ultimately will require a more indepth analysis of stratigraphy, 

sediment mineralogy, and redox zonation.

In summary, good-quality water is obtained from the 

Tokio aquifer throughout much of its extent. Sharp increases 

in salinity are noted in the extreme southwestern and 

northeastern parts of the aquifer, limiting use at distances 

more than approximately 5 mi downdip from the outcrop area. 

In the central part of the aquifer, salinity increases are more 

gradual, affording a larger area of low-salinity, high-quality 

water for multiple uses. In the southwestern part of the aquifer, 

sulfate is the dominant anion. Dedolomitization is a likely 

process that may account for the high-sulfate, low-bicarbonate 

groundwater in this area of the aquifer; however, this theory 

requires further analysis to achieve greater confidence.

Trinity Aquifer

Cretaceous formations in Arkansas (Nacatoch Sand, Ozan 

Formation, Tokio Formation, and the Trinity Group) and the 

aquifers comprised by these formations are not included in 

any of the regional hydrogeologic framework models of the 

Mississippi embayment (Arthur and Taylor, 1990; Hart and 

others, 2008; Clark and Hart, 2009). Although the Nacatoch 

was included in the Gulf Coast RASA by Hosman and Weiss 

(1991), no older Cretaceous formations were included in their 

model. Renken (1998) included the Trinity as a minor aquifer 

in the Ground Water Atlas of the United States for Segment 5 

(Arkansas, Louisiana, and Mississippi). USGS water-use 

reports referenced herein record use from the “Trinity 

aquifer,” although it accounts for the lowest use of any aquifer 

in Arkansas. For purpose of this report, the saturated part of 

the Trinity Group yielding water to wells will be referred to 

hereinafter as the “Trinity aquifer.” The following sections 

describe the geology, hydrologic characteristics, use, water 

levels, and water quality of the Trinity aquifer in Arkansas.

Geologic Setting

The Trinity Group is a sequence of clastic rocks ranging 

from less than 100 ft thick in outcrop areas to more than 

1,000 ft thick at downdip locations. The Trinity is a locally 

important aquifer in southwestern Arkansas and comprises 

six distinct units (Counts and others, 1955). The basal unit is 

the Pike Gravel, overlain by the Delight Sand, overlain by the 
Aquifers of the Coastal Plain 241

Dierks Limestone, overlain by the Holly Creek Formation, 

overlain by the De Queen Limestone, and finally overlain by 

the Paluxy Sand. The three important water-bearing sands 

of the Trinity are the Pike Gravel, the Ultima Thule Gravel 

Member of the Holly Creek Formation, and the Paluxy Sand 

Formation (Boswell and others, 1965).

The Trinity Group is named for type exposures on the 

Trinity River in Texas. The Lower Cretaceous Series Trinity 

Group unconformably overlies rocks of Paleozoic age and is 

unconformably overlain by the Upper Cretaceous Woodbine 

and Tokio Formations (Miser and Purdue, 1919; Boswell and 

others, 1965). The Trinity crops out in a belt 5–10 mi wide 

that extends from Pike County westward into southeastern 

Oklahoma. The outcrop is irregular and may cap outlying 

hills (Veatch, 1906; Counts and others, 1955; Boswell and 

others, 1965). The strike of the beds is generally westward, 

and the dip is generally to the south at about 50 ft/mi. The dip 

increases to the south and may exceed 100 ft/mi (Miser and 

Purdue, 1919). The Trinity attains a maximum thickness of 

more than 2,500 ft (Boswell and others, 1965).

The Pike Gravel is the thickest and most persistent gravel 

unit of the Trinity Group. It consists of rounded pebbles 

and cobbles intermixed and interbedded with sand and clay 

(Counts and others, 1955). The Pike Gravel is a resistant 

unit and forms an even, though dissected, southward-dipping 

upland. The gravel is composed mainly of dense white, 

gray, brown, black, or red novaculite and lesser amounts 

of quartz, quartzite, and sandstone gravel. The Pike Gravel 

ranges in thickness from 20 to 50 ft thick near the outcrop to 

a maximum known thickness of about 100 ft downdip (Miser 

and Purdue, 1919; Counts and others, 1955). 

The Ultima Thule Gravel is similar in lithology to the 

Pike Gravel but is comprised of finer materials (Boswell and 

others, 1965). The sand and clay separating the Ultima Thule 

and Pike gravels thin to the west and the Ultima Thule rests 

directly on the Pike Gravel or Paleozoic rocks into Oklahoma 

(Miser and Purdue, 1919). The Ultima Thule Gravel thickens 

to the west, reaching a maximum thickness of approximately 

40 ft near the State line (Counts and others, 1955). The 

Paluxy Sand generally consists of well-sorted, fine white sand 

interbedded with clay and limestone and local gravel lenses 

(Boswell and others, 1965). The Paluxy Sand has a maximum 

thickness of about 900 ft. The Paluxy Sand is present in 

southern Howard and Sevier Counties (Boswell and others, 

1965). 

The lowest beds of the Trinity Group represent nearshore 

deposits of the advancing Cretaceous sea that were followed 

by overlying limestone and marls indicating deeper waters. 

The upper sand represents shallow-water conditions, which 

mark the beginning of the Upper Cretaceous (Veatch, 1906). 

Hydrologic Characteristics

The upper Paluxy Sand is the principal water-bearing 

sand in the group. Well yields range from 0 to 200 gal/min, 

and flowing artesian wells were common at lower altitudes. 

A flowing artesian well in the Saline River bottoms in Sevier 

County yielded about 100 gal/min (Counts and others, 1955). 

Counts and others (1955) provided a table that listed 16 of 

35 wells as “flowing.” Public-supply wells in western Sevier 

County generally are completed in the upper and lower 

gravels at depths of 145–450 ft and have reported yields as 

high as 200 gal/min. Flowing artesian wells that yield from 

1 to 50 gal/min were reported in Howard County (Counts and 

others, 1965). Wells screened in the Pike Gravel in southern 

Pike County initially were under flowing artesian conditions 

but ceased to flow as potentiometric surfaces declined with 

large withdrawals and overpumping. One aquifer test showed 

a transmissivity of about 1,300 ft2/d and a storage coefficient 

of about 0.00004 (Boswell and others, 1965). In Pike County, 

the Trinity is a calcareous clay with little potential to yield 

water. The Trinity aquifer receives recharge in the outcrop 

area, and the direction of groundwater flow is southward 

(Boswell and others, 1965).

Water Use

The Trinity aquifer is present in several counties in 

southwestern Arkansas, but the clayey sediments common 

throughout the extent impede its use from a water-quality and 

yield standpoint. Five wells are recorded in the ARWUDBS 

for this aquifer in 2010 (fig. 90). Multiple wells in the outcrop 

area were also in use for domestic and livestock supply but do 

not meet registration requirements. 

Veatch (1906) reported a scattering of well completion 

attempts into the Trinity aquifer in southwestern Arkansas, 

but only one well was completed in central Howard County. 

Counts and others (1955) reported 37 wells completed 

in the Trinity aquifer, including public-supply wells at 

Murfreesboro (Pike County), DeQueen, Horatio, Lockesburg 

(Sevier County), and Mineral Springs (Howard County). The 

public-supply well for the town of Horatio was drilled in 

1921. Public-supply wells were drilled for Murfreesboro and 

Mineral Springs in the mid-1930s (Hale and others, 1947). 

Horatio and Lockesburg continue (2013) to use the Trinity 

aquifer (fig. 90), Murfreesboro uses the Little Missouri River, 

and Mineral Springs uses groundwater from the Tokio aquifer. 

Albin (1960) estimated that Murfreesboro used 0.07 Mgal/d 

in 1960, which quickly increased to 0.215 Mgal/d in the later 

1960s because of increased industrial demands. 
YELL LEE UNION WHITE POLK POPE DREW PIKE SCOTT CLARK CLAY ASHLEY DESHA BENTON LOGAN SALINE IZARD LONOKE PULASKI ARKANSAS NEWTON GRANT CHICOT MADISON STONE MILLER SHARP CROSS DALLAS PRAIRIE BOONE PHILLIPS PERRYSEARCY MARION FULTON SEVIER MISSISSIPPI JEFFERSON NEVADA POINSETT GARLAND COLUMBIA BAXTER OUACHITA BRADLEY JOHNSON WASHINGTON MONROE GREENE JACKSON CARROLL HOWARD LINCOLN CALHOUN CONWAY FAULKNER VAN BUREN FRANKLIN CRAIGHEAD HEMPSTEAD RANDOLPH CLEBURNE MONTGOMERY LAWRENCE ST. FRANCIS CRAWFORD CLEVELAND HOT SPRING INDEPENDENCE LITTLE RIVER WOODRUFF CRITTENDEN LAFAYETTE SEBASTIAN Base from U.S. Geological Survey digital data, 1:2,000,000 94° 92° 91° 93° 90° 36°35° 34° Extent of 

Well type 

galloto repwaterrepres

EX

Public 

0 15 0 30 

15 

Figure 90. Wells with reported groundwater use for the Trinity aquifer in Arkansas, 2010. 
Aquifers of the Coastal Plain 243

Use of the Trinity aquifer has been restricted to a few 

counties in southwestern Arkansas (figs. 90–91). Estimated 

use from the aquifer in 2010 was available only for Columbia 

and Sevier Counties with a combined total of 0.86 Mgal/d 

(table 38). Sevier County generally had the most use. 

Although no data were published for Sevier County from 1985 

through 1995, Horatio and Lockesburg were assumed to have 

used the aquifer for public supply. Approximately 20 percent 

of water used from the Trinity in Sevier County is for public 

supply (Terrance W. Holland, U.S. Geological Survey, written 

commun., 2012). Domestic use of the Trinity is still (2013) 

widespread and common; however, water use is assumed to be 

underestimated because domestic wells are not required to be 

registered. In addition, livestock wells generally do not meet 

the minimum-use requirement for registration. In 1990–2000, 

water use attributed to those two purposes was reported for 

Howard County (fig. 90).

Water Levels

The Trinity aquifer is recharged by infiltration of 

precipitation in the outcrop area. The direction of flow is 

southward with regional dip of the formation (Boswell and 

others, 1965). Water levels have not been monitored following 

measurements taken by Boswell and others (1965) in the 

mid-1960s. High rates of withdrawal from the Trinity probably 

contributed to potentiometric-head declines in formerly 

flowing artesian wells with water-level declines of more than 

40 ft below the land surface in the mid-1960s (Boswell and 

others, 1965). 

Water Quality

The Trinity aquifer crops out in an east-west trending 

band from western Sevier County to near the southeastern 

extent of Pike County. Only 32 wells with limited waterquality data were available, and these data were from wells 

located only in Sevier and Howard Counties. Generally, 

water quality from the Trinity is good, although chloride 

and sulfate can be somewhat elevated locally (Counts 

and others, 1955; Boswell and others, 1965). Counts and 

others (1955) noted that although sulfate concentrations 

generally were less than 30 mg/L, a few samples had sulfate 

concentrations exceeding 100 mg/L. Chloride concentrations 

generally were below 10 mg/L, except for one sample that 

exceeded 100 mg/L. Boswell and others (1965) reported that 

groundwater varied from a calcium-magnesium bicarbonate 

to a sodium-bicarbonate water type and that dissolved-solids 

concentrations usually were less than 300 mg/L, indicating 

overall good quality water.
94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° 94° 93° 

36° 35° 34° 94° 93° 92° 91° 90° 36° 35° 34° EXPLANA

Annual water withdrawn f

in million gallons per d

0.01 to 0.10 0.11 to 0.20 0.21 to 0.30 0.31 to 0.40 0.41 to 0.50 

Water use from Trinity Aquife

No color represents no report

0 60 0 60 120 K

Base from U.S. Geological Survey digital data 1:2,000,000 Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977; Holland, 1981, 1987, 1993, 1999, 2004, 2007 1965 1980 1985 1970 1975

Figure 91. Water-use rates for the Trinity aquifer in Arkansas from 1965 to 2010.
94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

94° 93° 

36°

35°

34°

94° 93° 92° 91°

90°

36°

35°

34°

EXPLANA

Annual water withdrawn 

in million gallons per 

0.01 to 0.100.11 to 0.200.21 to 0.300.31 to 0.400.41 to 0.50

No color represents no repor

0 60 0 60 120 

Base from U.S. Geological Survey digital data 1:2,000,000 Data modified from Halberg and Stephens, 1966; Halberg, 1972, 1977;

 Holland, 1981, 1987, 1993, 1999, 2004, 2007

19902005 2010

1995 2000

Figure 91. Water-use rates for the Trinity aquifer in Arkansas from 1965 to 2010.—Continued
246 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

General Geochemistry and Water Type

Generally, groundwater from the Trinity aquifer is of a 

calcium-magnesium water type, transitioning to a sodiumbicarbonate water type downdip from the outcrop area, similar 

to other Cretaceous- and Tertiary-age aquifers in southern 

Arkansas. Sodium was less than 50 percent of the total cations 

for locations in the outcrop area. Groundwater from wells at 

a distance from 5 to 25 mi downdip from the outcrop area 

contained as much as 98 percent sodium (fig. 92). Values of 

pH ranging from 6.2 to 7.5 occur only in the outcrop area. 

Values of pH from about 5 to 20 mi downgradient from the 

outcrop area generally were greater than 8.5 and ranged 

upward to 9.2 (fig. 92).

For many aquifers in Arkansas, bicarbonate 

concentrations tend to increase with increasing pH and 

dissolved-solids concentrations, indicating dissolution of 

carbonate minerals. Therefore, groundwater tends to evolve 

toward a strongly bicarbonate water type with bicarbonate 

accounting for the highest percentage of total anions at 

higher dissolved-solids concentrations. The only exception 

to this situation is when groundwater is affected by saltwater 

intrusion or mixing with poor-quality groundwater. Several 

geochemical relations indicate that reactions other than 

simple dissolution of carbonate minerals affect groundwater 

geochemical evolution in the Trinity aquifer. This is discussed 

in greater detail later in this section.

Table 38. Water use from the Trinity aquifer in Arkansas, 1965–2010. 

[Counties shown are only those with published data. Data from Halberg and Stephens (1966); Halberg (1972, 1977); Holland (1981, 1987, 1993, 1999, 2004, 

2007)]

County 1965 1970 1975 1980 11985 1990 1995 2000 2005 2010

Columbia 0.00 0.00 0.00 0.00 -- 0.00 0.00 0.00 0.03 0.02

Howard 0.13 0.22 0.30 0.35 -- 0.23 0.08 0.42 0.00 0.00

Pike 0.00 0.00 0.01 0.02 -- 0.00 0.00 0.00 0.00 0.00

Sevier 0.99 0.49 0.65 0.89 -- 0.00 0.00 2

0.94 20.16 0.84

Total 1.12 0.71 0.96 1.26 -- 0.23 0.08 1.36 0.19 0.86

1

Water use from the Trinity aquifer was not reported in 1985. 

2

Unpublished data from Terrance W. Holland, U.S. Geological Survey, written commun., 2013.
HOWARD PIKE

HEMPSTEAD

LITTLE RIVER

MONTGOMERY

SEVIER

HOWARD PIKE

HEMPSTEAD

LITTLE RIVER

MONTGOMERY

SEVIER

HOWARD PIKE

HEMPSTEAD

LITTLE RIVER

MONTGOMERY

SEVIER

HOWARD PIKE

HEMPSTEAD

LITTLE RIVER

MONTGOMERY

SEVIER

0 10 20 MILES

0 10 20 KILOMETERS

Geology map modified from Petersen and others, 1985;

Haley and others, 1993

Base modified from U.S. Geological Survey digital data, 1:250,000

Transverse Mercator projection, Central meridian 93 ̊00'W

94°00’ 93°30’ 94°00’ 93°30’

94°00’ 93°30’ 94°00’ 93°30’

34°

00’

34°

15’

33°

45’

34°

00’

34°

15’

33°

45’

34°

00’

34°

15’

33°

45’

34°

00’

34°

15’

33°

45’

pH, in standard units

6.2 to 7.07.1 to 7.57.6 to 8.08.1 to 8.58.6 to 9.2

Sulfate, in milligrams per liter

1 to 56 to 1011 to 2526 to 5051 to 116

Sodium, in percent of major cations

4 to 1011 to 2526 to 5051 to 7576 to 98

Bicarbonate, in milligrams per liter

4 to 1011 to 5051 to 100101 to 150151 to 433

EXPLANATION

EXPLANATION

EXPLANATION

EXPLANATION

Figure 92. Spatial distribution of selected chemical constituents in groundwater from the Trinity aquifer in Arkansas.
248 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Nitrate

Nitrate concentrations generally are low in the Trinity 

aquifer. Nitrate concentrations ranged from 0.04 to 29 mg/L 

in 26 samples with a median of 0.26 mg/L as nitrogen 

(table 39). One well, only 25 ft deep, exceeded a nitrate 

concentration of 1.0 mg/L with a nitrate concentration of 

29 mg/L. Two wells, 130 ft and 260 ft northwest of the 25-ft 

deep well, had nitrate concentrations less than 0.5 mg/L, 

indicating the elevated nitrate for the 25-ft well was from an 

extremely localized source of nitrogen. 

Iron

Iron concentrations are extremely low in the Trinity 

aquifer with a median of 60 μg/L for 29 samples (fig. 93; 

table 39). Only one groundwater sample exceeded the 

Federal secondary drinking-water regulation of 300 μg/L 

(U.S. Environmental Protection Agency, 2009). This 

sample was taken from a well located in the outcrop area. 

Iron concentrations for several Cretaceous and Tertiary 

aquifers were noted to have higher iron concentrations in 

their outcrop areas compared to increasing concentrations 

downgradient, resulting from possible changes in redox 

conditions along the flow path.

Sulfate

Sulfate concentrations ranged from 1.0 to 116 mg/L 

with a median of 16 mg/L (fig. 93; table 39). Concentrations 

exceeded 25 mg/L in seven wells located approximately 

5–17 mi from the outcrop area in the southeastern part 

of the aquifer in southern Howard County (fig. 92), with 

five of these wells exceeding 50 mg/L. In this same area, 

all chloride concentrations were less than 15 mg/L, and 

bicarbonate concentrations generally were lower than sulfate 

concentrations (fig. 92). For other Cretaceous aquifers, salinity 

increased downdip from the outcrop area with chloride as the 

dominant anion. Increasing chloride concentrations generally 

result from ineffective flushing of residual marine-derived 

salinity or upwelling of high-salinity water from underlying 

formations. Six of seven wells exceeding 25 mg/L sulfate in 

this area had sulfate concentrations exceeding that of chloride 

and bicarbonate. Therefore, some process is thought to have 

accounted for the increased sulfate. This situation also was 

noted for the Tokio aquifer for an area in southeastern Sevier 

County, where increases in sulfate with concomitant decreases 

in bicarbonate were attributed to dedolomitization mechanisms 

(see section on “Tokio aquifer”). Although further research 

is required to validate such assumptions, dedolomitization 

appears to be the most likely process accounting for the 

chemistry of groundwater where sulfate is the anion of highest 

concentration in the Trinity aquifer.

Table 39. Descriptive statistics for selected chemical constituents in groundwater from the Trinity aquifer in Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 0.4 13 54 20.7 9

Magnesium (mg/L) 0.2 2.2 11 4.38 9

Sodium (mg/L) 3.6 8.5 261 89.6 9

Potassium (mg/L) 1.24 2.8 9.3 2.32 9

Bicarbonate (mg/L) 4.0 67 433 109 30

Chloride (mg/L) 3.0 6.0 695 124 30

Sulfate (mg/L) 1.0 16 116 34.6 30

Silica (mg/L) 10 12 16 1.89 9

Nitrate (mg/L as nitrogen) 0.04 0.26 29 5.6 26

Dissolved solids (mg/L) 42 192 683 189 9

Iron (μg/L) 0.05 60 2,200 544 29

Manganese (μg/L) 4.29 4.29 4.29 0.13 1

Arsenic (μg/L) 0.03 0.03 0.03 0.03 1

Hardness (mg/L as calcium carbonate) 8.0 185 440 114 30

Specific conductance (μS/cm) 75 501 2,650 458 30

pH (standard units) 6.2 8.4 9.2 0.6 30
Aquifers of the Coastal Plain 249

Chloride

All but one chloride concentration was less than or 

equal to 15 mg/L, even as far as 13 mi from the outcrop 

area in southern Howard County. The one sample had an 

elevated chloride concentration of 695 mg/L and was from a 

shallow 25-ft well in Sevier County. Counts and others (1955) 

described this well as “almost dry.” If the well was completed 

in a low-permeable, clayey section of the Trinity, it is 

possible that salinity originated during deposition in a marine 

environment that had not been adequately flushed. Because 

of the overall low chloride concentrations in higher yielding 

wells in the area, the geochemistry of groundwater from 

this well is simply an anomaly but assists in understanding 

localized water-quality problems in other aquifers of the 

Coastal Plain that have varying amounts of clay interbedded 

with sand lenses. In the absence of anthropogenic effects 

on water quality, poor-quality, higher-salinity groundwater 

often is explained by mixing with groundwater bound in 

low-permeable, clay-rich deposits that experience inadequate 

flushing of residual connate water at the time of deposition. 

The overall low salinity in samples from wells throughout the 

aquifer suggests that any saline water that originated in more 

permeable sands has been adequately flushed.

In summary, good-quality groundwater is found 

throughout the Trinity aquifer. Sulfate concentrations can be 

locally elevated, although all concentrations were less than 

the 250 mg/L secondary drinking-water regulation. Wells with 

elevated sulfate generally had low bicarbonate concentrations, 

which is hypothesized as resulting from dedolomitization 

processes. All chloride concentrations but one were less than 

or equal to 15 mg/L at distances as great as 15 mi from the 

outcrop area, demonstrating the low overall salinity in the 

aquifer. 

0

50

100

150

200

250

300

350

400

450

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron

Concentrations, in milligrams per liter

500

Concentration, in micrograms per liter

700

800

900

1,000

0

100

200

300

400

500

600

29

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

9

9

9

30

30

30

29

Constituent Constituent

Figure 93. Interquartile range of selected chemical constituents in groundwater from the Trinity aquifer in Arkansas.
250 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Aquifers of the Interior Highlands

The Interior Highlands of northern and western Arkansas 

have less reported groundwater use than other areas of the 

State. This reflects a combination of processes including: 

(1) prevalent and increasing use of surface water, (2) less 

intensive agricultural uses, (3) lower population and industry 

densities, (4) less potential yield of the resource, and (5) lack 

of detailed reporting. Reported use in 2010 for all aquifers 

of the Interior Highlands was approximately 115 Mgal/d, 

1.5 percent of the total reported groundwater use in Arkansas 

of 7,873.75 Mgal/d. The various aquifers of the Interior 

Highlands generally occur in shallow, fractured, wellindurated, structurally modified bedrock of this mountainous 

region of the State. Rocks of the Interior Highlands are 

characterized by secondary, relatively low-porosity fractures 

and bedding planes. By comparison, the relatively flat-lying, 

unconsolidated sediments of the Coastal Plain have greater 

porosity, storage, and yields because they are composed of 

coarse-grained, uncemented sands and gravels. The laterally 

expansive and relatively continuous Coastal Plain aquifers 

contrast markedly with the more discontinuous aquifers and 

ancient bedrock in the highlands. The Interior Highlands have 

experienced multiple episodes of structural modification, 

uplift, and erosion causing truncation, dissection, and excision. 

Consequently, yields of aquifers in the Interior Highlands are 

lower, and domestic supply is the dominant use. Surface water 

is the greatest supplier when large volumes are required for 

population growth and industry.

Disparity in total water use for aquifers in the Coastal 

Plain and Interior Highlands arises from the major uses of 

groundwater in Arkansas. For example, irrigation use, which 

is almost solely from the Mississippi River Valley alluvial 

aquifer in eastern Arkansas, accounts for nearly 94 percent 

of the total groundwater used in the State. Thus, groundwater 

use from all other aquifers is insignificant compared to 

irrigation. Unfortunately, the magnitude of use for irrigation 

overshadows the important use of groundwater for thousands 

of households, numerous small-community supply systems 

(parks, stores, and small communities), and livestock supply, 

among other uses in the Interior Highlands.

Spatial trends in groundwater geochemistry in the Interior 

Highlands differ greatly from trends for aquifers in the Coastal 

Plain. In the Coastal Plain, the prevalence of long regional 

flow paths results in regionally predictable and mappable 

geochemical changes. In the Interior Highlands, groundwater 

flow paths are short and topographically controlled (from 

hilltops to valleys) within relatively small watersheds. Thus, 

dense data coverage from numerous wells would be required 

to effectively characterize these groundwater basins and define 

small-scale geochemical changes along any given flow path. 

Small-scale potentiometric-surface maps constructed in the 

Interior Highlands confirm the dominant control of topography 

on groundwater-flow directions (Leidy and Morris, 1990b; 

Kresse and Hays, 2009). Changes in geochemistry dominantly 

are related to rock type and residence time along individual 

flow paths.

The aquifers of the Interior Highlands are discussed from 

youngest to oldest in the following sections: the Arkansas 

River Valley alluvial aquifer, Ouachita Mountains aquifer, 

Western Interior Plains confining system, the Springfield 

Plateau aquifer, and the Ozark aquifer. The Western Interior 

Plains confining system, Springfield Plateau aquifer, and 

Ozark aquifer are regional hydrogeologic units, and regional 

nomenclature is adhered to in this report. The reader should 

refer to figure 5 for locations of cities and counties discussed 

in this section.

Arkansas River Valley Alluvial Aquifer

The alluvial deposits of the Arkansas River are one of the 

most important sources of water in the Arkansas Valley section 

of the Ouachita Province. This water provides a valuable 

source of irrigation and public-supply use. Groundwater in 

alluvium of the Arkansas River Valley, hereinafter referred to 

as the Arkansas River Valley alluvial aquifer, is considered 

a distinct aquifer from approximately the State border at 

Fort Smith to Little Rock. In the Mississippi Alluvial Plain 

in eastern Arkansas, it is difficult to distinguish between 

groundwater from the alluvial deposits of the Arkansas River 

and those of the Mississippi Alluvial Plain. Consequently, all 

alluvial deposits east of Little Rock are considered part of the 

Mississippi River Valley alluvial aquifer.

The following sections provide information on the 

geohydrology and geochemistry of groundwater from 

the Arkansas River Valley alluvial aquifer. Much of this 

information was summarized from available historical and 

recent publications, which provide more detailed information.

Geologic Setting

The Arkansas River Valley region is a synclinorium 

generally lying between dipping rocks of the Boston 

Mountains to the north and the highly folded rocks of the 

Ouachita Mountains to the south. Alluvial deposits overlie 

consolidated rocks along the Arkansas River and its major 

tributaries. They comprise terrace and flood-plain deposits 

that occur along the river in discontinuous segments 3–43 mi 

in length and 1–5 mi across the river valley (fig. 3). In some 

locations, the alluvium and terrace deposits are absent, and 

the river is bordered by consolidated rocks of the Interior 

Highlands (Bedinger and others, 1963; Cordova, 1963). Tops 

of older terraces lie 50 ft or more above the present flood plain 

and consist of interbedded gravel, clay, and sand. Younger 

terrace deposits lie 20–40 ft above the present flood plain 

and are composed of a coarsening downward sequence of 

clay, sand, and gravel. Flood-plain alluvial deposits consist 

of gravel, sand, silt, and clay. Younger terraces typically are 

hydraulically well connected with alluvium, whereas older 

terraces have bases far above the surface of the adjacent 
Aquifers of the Interior Highlands 251

alluvium (Bedinger and others, 1963). The alluvial deposits 

typically are about 40 ft thick near Fort Smith and thicken 

downstream to about 80 ft near Little Rock (Cordova, 1963). 

The alluvium represents several environments of 

deposition and characteristic deposits including point bar, 

swale, channel fill, natural levee, and backswamp. These 

can be distinguished on the basis of lithologic character and 

topographic expression. Infiltration of rainfall is an important 

source of groundwater recharge. Recharge is higher in areas 

that are underlain by the highly permeable point-bar and 

natural-levee deposits, and lower in backswamp and channelfill deposits (Bedinger and others, 1963). Lithologic logs near 

Van Buren were used to determine why some wells did not 

have sufficient yield for use as irrigation water (Tim Kresse, 

U.S. Geological Survey, unpub. data, 2013). Percent sand 

thickness was calculated from each available log and overlain 

onto a photomosaic map to examine the areal distribution of 

sand thickness in relation to geomorphologic features (fig. 94). 

Several abandoned channels were identified from the map, 

and a consistent association was noted between higher sand 

percentages near the river on the point-bar (concave) side of 

abandoned channels and lower sand percentage on the convex 

side of the channel. Point-bar and channel deposits are located 

on the concave side and are characterized by coarser, higherpermeable deposits. Backswamp areas are located on the 

convex side of the channel and are characterized by finer, less 

permeable deposits. Modern-day point-bar deposits are easily 

recognizable on figure 94 as lighter colored sands and gravels 

on the concave side of the Arkansas River meander bend. The 

distribution of these deposits of varying permeability was in 

agreement with anecdotal information from farmers about the 

distribution of productive wells in the area and the proximity 

of low-permeable zones during irrigation well pumping (Tim 

Kresse, U.S. Geological Survey, unpub. data, 2013).

Hydrologic Characteristics

Recharge to the Arkansas River Valley alluvial aquifer 

primarily is by downward percolation of precipitation in 

addition to leakage from the river (Bedinger and others, 1963; 

Kilpatrick and Ludwig, 1990a). Recharge in the vicinity of 

the Atkins well field (Pope County), which is underlain largely 

by backswamp deposits, was about 3 in/yr, whereas the 

average rate of recharge in nearby channel deposits was about 

10 in/yr (Bedinger and others, 1963). Although absent locally 

beneath some channel-fill deposits, in most places 30–60 ft 

of saturated sand and gravel are present. The saturated 

thickness generally increases with distance downstream 

from Fort Smith. Wells completed in the sands and gravels 

in the lower part of the Arkansas River Valley alluvial 

aquifer are capable of yielding 300–700 gal/min of water and 

predominantly are used for sources of irrigation and public 

supply (Bedinger and others, 1963; Kilpatrick and Ludwig, 

1990a). Water levels range from approximately 5 to 30 ft 

below the ground surface (Kilpatrick and Ludwig, 1990a). 

Transmissivity values range from 5,348 to 21,390 ft2

/d, and 

storage coefficient ranges from 0.0001 to 0.009 (Bedinger and 

others, 1963).

Groundwater in the Arkansas River Valley alluvial 

aquifer is largely unconfined. Historically, the water table 

sloped toward the river and larger tributary streams during 

normal and low river stages. During high river stages, the 

groundwater gradient is reversed with groundwater flowing 

away from the river. Local water-table highs are common 

beneath the more permeable surface materials where recharge 

rates are high. Locally, pumping can modify the shape of 

the water-table surface. Pumping for irrigation historically 

has had little pronounced effect because irrigation wells are 

widely spaced and pumpage is small. Withdrawals for public 

supply are nearly continuous and are concentrated in small 

areas. Bedinger and others (1963) noted that pumping for 

public supply near Atkins had a pronounced effect on the 

water table. The well fields near Ozark (Franklin County) 

and Dardanelle (Yell County), which are near the river, also 

had cones of depression extending from well fields to the 

river, which induced recharge from the river. Kline and others 

(2006), Kresse and others (2006), and Kresse and Clark (2008) 

also documented influx of river water into the Dardanelle 

well field. However, geochemical mixing curves indicated 

that a maximum of only 20 percent of the groundwater from 

the public-supply well was river water with greatly reduced 

mixing in other wells. They also noted that some wells near 

the river in adjacent well fields with similar production history 

showed very little, if any, influx of river water based on the 

same mixing approaches. 

Bedinger and others (1963) contended that only when 

continuously pumping public-supply wells are in close 

proximity to the river will any appreciable influx of water 

occur from the Arkansas River. Similar findings were noted in 

southeastern Arkansas (Kresse and Clark, 2008). The lowest 

chloride concentrations occurred in wells next to the Arkansas 

River, in spite of intensive local and regional irrigation 

pumping, with the highest concentrations in backswamp 

deposits further from the river. Kresse and Clark (2008) 

hypothesized that recharge predominantly occurred through 

coarse natural levee and channel deposits near the river in this 

area, similar to that proposed for the Arkansas River Valley 

alluvial aquifer in the western part of the State.

Groundwater-Flow Simulation Models

The groundwater-flow system of the Arkansas River 

Valley alluvial aquifer south of Dardanelle in Yell County was 

simulated by Kline (2003). A two-layer model was developed 

to characterize groundwater flow and to investigate the degree 

of groundwater connectivity with the Arkansas River. Results 

indicated that groundwater pumping induced flow from 

the river into the aquifer. Further work by Kline and others 

(2006) and Kresse and others (2006) used hydrographs and 

geochemical data to quantify the degree of interaction between 

groundwater and the Arkansas River and validate the results of 

the model. 
Alma Dyer Van Buren Fort Smith SEBASTIAN COUNTY CRAWFORD COUNTY Image from Arkansas State Land Information Board, 2006 Natural Color County Mosaic Universal Transverse Mercator, zone 15 North American Datum of 1983 0 1 2 KILOMETERS 0 1 2 MILES !! !! !! !! !! !!! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! !!! !! !! ! 

! ! ! !! ! ! ! ! ! ! ! !! ! ! ! !! !! !! !! !! !!! ! ! ! ! ! !! ! ! ! ! ! ! ! ! ! ! ! ! !!! !! !! ! ! ! ! !! ! ! ! ! ! ! ! !! ! ! ! 94°21' 94°15' 94°09' 

35°27' 35°21' EXPLANAT

Sand perc

0 to 20 20 to 40 40 to 60 60 to 80 80 to 100 !!!!! ARKANSAS Area enlarged

Figure 94. Percent sand calculated from lithologic logs for the Arkansas River Valley alluvium in west-central Arkansas.
Aquifers of the Interior Highlands 253

Water Use

Groundwater from the Arkansas River Valley alluvial 

aquifer is, and historically has been, an important source of 

irrigation and public supply. Currently (2013), only the cities 

of Dardanelle and Maumelle are using the Arkansas River 

Valley alluvial aquifer as a source of public-supply water. 

In the past, the cities of Atkins, Dardanelle, Morrilton, and 

Ozark used the aquifer for public supply, but of these cities, 

only Dardanelle has continued and expanded the use of the 

aquifer as a sole public-supply water source. Bedinger and 

others (1963) described the use from these four systems 

and calculated the remaining development potential of the 

Arkansas River Valley alluvial aquifer based on aquifer 

thickness, extent, and average yields. During 1959, Atkins 

used three wells that yielded about 75–250 gal/min and 

pumped about 162,000 gal/d; Dardanelle used three wells that 

yielded about 300 gal/min and pumped about 225,000 gal/d; 

Morrilton used four wells that yielded about 200–500 gal/min 

and pumped about 681,000 gal/d; and Ozark used five wells 

to pump about 300,000 gal/d. Assuming natural recharge to 

the aquifer of 10 in/yr, Bedinger and others (1963) calculated 

that 130 Mgal/d could be pumped from the aquifer without 

overdraft of groundwater storage or inducting water from the 

river. In 1959, groundwater was pumped at an average rate of 

3.2 Mgal/d from the aquifer, which is less than 3 percent of the 

amount regionally available from natural recharge (Bedinger 

and others, 1963). 

Dardanelle continues to depend solely upon groundwater 

for public supply. Drilling efforts were part of the plan for 

continued long-term use of the aquifer. A review of data from 

2003 through 2009 revealed total withdrawals increased 

from 1.1 to 2.2 Mgal/d with production from nine wells 

completed at depths of about 65 ft with each well pumping 

about 200 gal/min. Total reported use for Dardanelle in 2010 

was 2.03 Mgal/d. In 2010, Dardanelle installed a horizontal 

interceptor well system 300 ft from the river that produced 

more than 2.5 Mgal/d. The interceptor well consists of a 13-ft 

by 16-ft caisson installed 45 ft below ground level with five 

12-inch diameter lateral screens ranging from 150 to 250 ft in 

length. The collector well system replaced the nine production 

wells in January 2011 as the city’s primary water supply, but 

the nine wells are maintained as a backup water supply. A 

pumping rate of more than 3.0 Mgal/d from the interceptor 

well was reported in 2012 (Bill Smith, Dardanelle Water 

Works, oral commun., 2012). With improved directionaldrilling techniques and innovative well design, Dardanelle 

has demonstrated that groundwater from the Arkansas River 

Valley alluvial aquifer may contain great potential as a 

valuable and productive water supply in other areas along the 

river. 

In Maumelle, pumping from the Arkansas River Valley 

alluvial aquifer began in 1941 when wells were installed to 

provide water for the production of ammonium picrate (picric 

acid); water use continued until the plant was deactivated in 

March 1945. In 1972, the city of Maumelle converted those 

wells for public supply and installed two additional wells. 

Nine additional wells were installed to provide water for 

the growing municipality from 1995 through 2012 (Barry 

Heller, Maumelle Water Management, oral commun., 2013). 

Maumelle currently (2013) pumps from 13 wells completed 

in the Arkansas River Valley alluvial aquifer with a reported 

average use of 2.74 Mgal/d in 2010 (Terrance W. Holland, 

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

In addition to its important use as a source for publicsupply water, the Arkansas River Valley alluvial aquifer 

continues to be a valuable source for irrigation along 

the Arkansas River. In 2010, the reported irrigation use 

was 2.6 Mgal/d, which was pumped from 34 wells for 

approximately 2,960 acres of cropland (Terrance W. Holland, 

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

Water Quality

General Geochemistry and Water Quality

Groundwater in the Arkansas River Valley alluvial 

aquifer is generally of good quality and appropriate for 

most uses, although elevated iron concentrations can require 

treatment for public supply and other uses. Values of pH 

ranged from 4.9 to 9.5 with a median of 8.0 (table 40). The 

relatively high median pH value results from the dissolution 

of carbonate minerals in the alluvial deposits. Groundwater 

from the aquifer principally has been identified as a calciumbicarbonate type and is characterized by wide variations in 

dissolved-solids concentrations (Bedinger and others, 1963; 

Kresse and others, 2006). Data compiled for this report 

confirm this dominant calcium-bicarbonate water type and 

contain more analyses of total anions (bicarbonate, chloride, 

sulfate) than for total cations (calcium, magnesium, sodium, 

potassium). Bicarbonate was greater than 50 percent in 462 of 

493 (94 percent) samples. Calcium was greater than 50 percent 

for 75 of 81 (93 percent) samples having sufficient cation data 

for calculation of the dominant cation.
254 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Nitrate

Nitrate concentrations in the Arkansas River Valley 

alluvial aquifer ranged from 0.01 to 67 mg/L with a 

median of 1.1 mg/L in 457 samples (table 40). The median 

concentrations for all other aquifers in Arkansas, with the 

exception of the Springfield Plateau and Ozark aquifers, 

were less than 0.3 mg/L. The shallow depths and relatively 

high recharge to the aquifer are consistent with increased 

vulnerability to surface (for example, fertilizer and manure) 

and near-surface (for example, septic tanks) sources of 

nitrogen. Out of 457 samples with nitrate analyses, 58 

(12.7 percent) had concentrations exceeding the Federal 

MCL of 10 mg/L. The greatest density of elevated nitrate 

concentrations was along the western (Crawford County) 

and the eastern (Conway, Faulkner, Pope, and Yell Counties) 

extents of the aquifer (fig. 95). The lower concentrations of 

nitrate in the central part of the aquifer (Franklin, Johnson, and 

Logan Counties) are hypothesized in this report to result from 

denitrification. Further evidence for denitrification as a control 

on nitrate concentrations in this part of the aquifer is provided 

in the discussions of iron, arsenic, and sulfate.

Table 40. Descriptive statistics for selected chemical constituents in groundwater from the Arkansas River Valley alluvial aquifer in 

western Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 0.5 58 433 60.4 143

Magnesium (mg/L) 1.69 16 70 10.4 139

Sodium (mg/L) 0.9 14 236 34.8 117

Potassium (mg/L) 0.08 1.6 48 5.12 102

Bicarbonate (mg/L) 8.0 231 1,050 150 503

Chloride (mg/L) 1.0 12 980 52.3 661

Sulfate (mg/L) 0.2 17 253 26.8 518

Silica (mg/L) 0.18 22 39.5 7.77 66

Nitrate (mg/L as nitrogen) 0.01 1.1 67 8.63 457

Dissolved solids (mg/L) 88 319 887 152 88

Iron (μg/L) 0.05 70 15,500 1,300 336

Manganese (μg/L) 0.13 338 1,360 403 17

Arsenic (μg/L) 0.03 0.76 6.8 1.78 15

Hardness (mg/L as calcium carbonate) 20 240 1,300 134 570

Specific conductance (μS/cm) 89 507 2,920 273 655

pH (standard units) 4.9 8.0 9.5 0.6 649
Aquifers of the Interior Highlands 255

YELL

SCOTT

POPE

LOGAN

PERRY

CONWAY

FAULKNER

SEBASTIAN

PULASKI

FRANKLIN

JOHNSON

SALINE

CRAWFORD VAN BUREN

YELL

SCOTT

POPE

LOGAN

PERRY

CONWAY

FAULKNER

SEBASTIAN

PULASKI

FRANKLIN

JOHNSON

SALINE

CRAWFORD VAN BUREN

YELL

SCOTT

POPE

LOGAN

PERRY

CONWAY

FAULKNER

SEBASTIAN

PULASKI

FRANKLIN

JOHNSON

SALINE

CRAWFORD VAN BUREN

0 100 200 MILES

0 100 200 KILOMETERS

Arkansas River

Arkansas River

Arkansas River

Geology map modified from

Haley and others, 1993

Base modified from U.S. Geological Survey digital data, 1:250,000 

Universal Transverse Mercator projection, zone 15

94°00' 93°00'

35°20'

35°00'

94°00' 93°00'

35°20'

35°00'

94°00' 93°00'

35°20'

35°00'

Alluvial deposits

Terrace deposits

EXPLANATION

0 to 50

51 to 100

101 to 300

301 to 1,000

1,001 to 5,000

5,001 to 15,500

Iron, in micrograms

per liter

0.01 to 0.25

0.26 to 0.50

0.51 to 1.00

1.01 to 5.00

5.01 to 10.00

10.01 to 67.00

Nitrate, in milligrams

per liter

1 to 10

11 to 25

26 to 50

51 to 100

101 to 250

251 to 980

Chloride, in milligrams

per liter

EXPLANATION

EXPLANATION

EXPLANATION

ARKANSAS

Van

Buren

Ozark

Dardanelle

Atkins

Maumelle

Morrilton

Area enlarged

Figure 95. Spatial distribution of selected chemical constituents in groundwater from the Arkansas River Valley alluvial aquifer in 

western Arkansas.
256 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Iron and Arsenic

Iron concentrations in the Arkansas River Valley alluvial 

aquifer ranged from 0.05 to 15,500 μg/L with a median 

of 70 μg/L (fig. 96; table 40). For 336 samples with iron 

analyses, only 37 (11 percent) exceeded the Federal secondary 

drinking-water regulation of 300 μg/L. Iron concentrations 

ranged from 155 to 15,500 μg/L with a median of 2,955 μg/L 

near Van Buren. The large median iron concentration likely 

indicates iron-reducing conditions and dissolution of iron 

oxyhydroxides (Chappelle and others, 2009). In this area, 

arsenic concentrations ranged from 0.38 to 6.8 μg/L with 

a median of 1.3 μg/L; all concentrations were below the 

drinking-water standard of 10 μg/L (U.S. Environmental 

Protection Agency, 2009). Iron correlated positively to 

arsenic with an R2 value of 0.76, indicating reduction of 

iron oxyhydroxides as a possible source of arsenic. Ironreducing conditions were similarly noted in the aquifer near 

Dardanelle by Kresse and others (2006). A review of waterquality data from the Dardanelle area (Kresse and others, 

2006) also revealed a positive correlation between iron and 

arsenic with an R2

 value of 0.77. Arsenic concentrations 

ranged as much as 19 μg/L in this area. Kresse and Fazio 

(2003) provided evidence for reductive dissolution of iron 

oxyhydroxides as the source of elevated iron and arsenic in the 

Mississippi River Valley alluvial aquifer along the Arkansas 

River in southeastern Arkansas. Detailed studies by Sharif 

and others (2008a, b) confirmed reductive dissolution of iron 

oxyhydroxides as the source of elevated iron and arsenic 

concentrations in this area. Holocene-age alluvial deposits 

contain abundant dissolved organic matter that provides a 

substrate for microbial respiration. This substrate results in 

utilization of electron acceptors such as oxygen, nitrate, iron 

oxyhydroxide, and sulfate thus increasing reducing conditions 

in the deeper sections of the aquifer. Reduction of iron 

oxyhydroxides likely is the source of elevated iron and arsenic 

concentrations in the Arkansas River Valley alluvial aquifer in 

the western part of the State.

336

143

139 117

503

661 518

336

0

50

100

150

200

250

300

350

400

450

Concentrations, in milligrams per liter

500

Concentration, in micrograms per liter

700

800

900

1,000

0

100

200

300

400

500

600

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

Constituent Constituent

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron

Figure 96. Interquartile range of selected chemical constituents in groundwater from the Arkansas River Valley alluvial aquifer in 

western Arkansas.
Aquifers of the Interior Highlands 257

The spatial distribution of iron concentrations shows that 

the highest density of elevated iron concentrations, similar to 

that of nitrate, occurred in the western and eastern parts of the 

aquifer (fig. 95). All but one iron concentration in the central 

part of the aquifer were less than 100 μg/L. This suggests 

that the more energetically favorable terminal electron 

acceptors—oxygen, nitrate, and iron oxyhydroxides—have 

been exhausted, and geochemical conditions have evolved to 

favor sulfate-reducing conditions and the precipitation of ironsulfide minerals. The inverse relation of iron and sulfate in the 

aquifer supports the theory of iron-sulfide mineralization as a 

control on iron in solution (fig. 97). Where iron-oxide supply 

has been exhausted in an aquifer and an appreciable sulfate 

and an organic substrate are available for sulfate-reducing 

bacteria, sulfate will be reduced to hydrogen sulfide, which 

quickly reacts with the soluble iron. Chapelle and others 

(2009) noted that sulfide was inversely related to dissolved 

iron, reflecting the rapid reaction kinetics of iron with 

hydrogen sulfide to produce relatively insoluble iron-sulfide 

minerals. Because sulfate concentrations are much greater than 

iron concentrations throughout most aquifers, any appreciable 

reduction of sulfate can remove a large fraction of the soluble 

iron.

Sulfate

Sulfate concentrations generally were low throughout 

the Arkansas River Valley alluvial aquifer and ranged from 

0.2 to 253 mg/L with a median of 17 mg/L (fig. 96; table 40). 

Of 518 samples with sulfate data, 470 (91 percent) had 

concentrations less than 50 mg/L, and 295 (57 percent) 

had concentrations less than 20 mg/L. Only one sample 

(253 mg/L) had a concentration greater than the secondary 

drinking-water regulation of 250 mg/L. In areas with sulfate 

concentrations exceeding approximately 30 mg/L, iron 

is virtually absent (less than 50 μg/L), suggesting sulfate 

reducing conditions in areas with higher sulfate concentrations 

(fig. 97). No discernible trends were noted in the spatial 

distribution of sulfate concentrations.

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000

Iron, in micrograms per liter

0

20

40

60

80

100

120

140

160

Sulfate, in milligrams per liter

Figure 97. Relation of iron and sulfate concentrations in groundwater from the Arkansas River Valley alluvial aquifer in western 

Arkansas.
258 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Chloride

Chloride concentrations in the Arkansas River Valley 

alluvial aquifer ranged from 1.0 to 980 mg/L with a median 

of 12 mg/L (fig. 96; table 40). Only 4 of 661 samples with 

chloride analyses exceeded the Federal secondary drinkingwater regulation of 250 mg/L; however, 32 samples exceeded 

100 mg/L and are elevated as defined for this report. Bedinger 

and others (1963) hypothesized that natural variation in 

dissolved-solids content, salinity, and water type was related 

more to the movement of water from adjacent or underlying 

formations than from movement of groundwater within the 

alluvium. However, Kresse and others (2006) indicated that 

increases in salinity and dissolved-solids concentrations 

were the direct result of the type of deposits penetrated by 

wells in the aquifer in the Dardanelle area. They showed 

that groundwater in underlying formations was of better 

quality with lower salinity than water in the Arkansas River 

Valley alluvial aquifer. Higher chloride and dissolved-solids 

concentrations were noted for wells in two different areas of 

the aquifer: (1) areas with deposits having a higher percentage 

of clay and located further from the river, which correlates 

to areas of backswamp deposits, and (2) areas near to and 

directly affected by influx of higher salinity water from 

the Arkansas River. Trend lines for bromide and chloride 

concentrations in each area reflected differences in the source 

of salinity. Groundwater in backswamp areas contained 

higher bromide/chloride ratios and plotted along a trend line 

associated with evapotranspiration (fig. 98). Conversely, 

groundwater between the river and public-supply wells in the 

Dardanelle area had lower bromide/chloride ratios and plotted 

along a line with river water as an end member. Chloride 

concentrations in the river averaged approximately 200 mg/L 

during the study (Kresse and others, 2006), and the production 

well closest to the river had a maximum chloride concentration 

of 112 mg/L. Petersen (1988) provided a summary of water 

quality for four sites on the Arkansas River for 1975 through 

1985 and showed maximum chloride concentrations ranging 

from 220 to 550 mg/L with means ranging from 90 to 

150 mg/L for the four sites.

Kresse and Clark (2008) noted a relation between 

groundwater quality and the type of deposits that compose 

the Mississippi River Valley alluvial aquifer south of the 

Arkansas River in southeastern Arkansas. This was based 

on geochemical data for approximately 2,500 irrigation 

wells completed in the Mississippi River Valley alluvial 

aquifer south of the Arkansas River from Little Rock to 

the Mississippi River. This analysis showed that the lowest 

chloride concentrations were in wells completed in coarsergrained levee and channel deposits that tend to lie closest 

to the Arkansas River. The highest chloride concentrations 

were in wells completed in finer-grained backswamp deposits 

located away from the river (see Mississippi River Valley 

alluvial aquifer). Kresse and Clark (2008) hypothesized that 

a combination of rapid recharge and advective flushing in 

the relatively coarser channel and levee deposits near the 

river maintained low chloride concentrations in groundwater, 

which closely reflect that of evaporated rainwater. The 

fine-grained, clay-rich deposits associated with backswamp 

areas likely restrict recharge, induce increased ratios between 

evapotranspiration and recharge, and experience minimal 

flushing of salts concentrated during evapotranspiration. 

Although the spatial variability of various types of deposits 

is on a smaller scale for the Arkansas River Valley alluvium 

in the Interior Highlands, it is likely that restricted recharge 

through the lower permeable deposits results in groundwater 

of higher dissolved-solids concentration.

The highest chloride concentrations in the Arkansas 

River Valley alluvial aquifer generally occurred at further 

distances from the Arkansas River from Fort Smith to Little 

Rock. This situation is hypothesized to be the result of 

evapotranspiration in backswamp areas at greater distances 

from the river as proposed by Kresse and others (2006) and 

Kresse and Clark (2008). In the isolated areas where chloride 

concentrations were elevated next to the river, including an 

area in Franklin County, past pumping associated with public 

supply was likely the cause. In other words, past pumping 

for public supply resulted in the induced influx of water 

from the river into the alluvial aquifer. Bedinger and 

others (1963) also noted that pumping at the well fields in 

Dardanelle and Ozark had induced infiltration of river water 

into the aquifer. 

In summary, groundwater in the Arkansas River Valley 

alluvial aquifer is of overall good quality, with the exception 

of elevated iron concentrations that often require treatment 

for use in public-supply systems. Chloride concentrations can 

be slightly elevated in backswamp areas or where influenced 

by an influx of water from the Arkansas River. Only 4 of 

661 samples with chloride analyses exceeded the Federal 

secondary drinking-water regulation of 250 mg/L. Reducing 

conditions in various parts of the aquifer were hypothesized 

as controls on the distribution and concentration of nitrate, 

iron, and sulfate.

0 50 100 150 200

Chloride, in milligrams per liter

0

0.2

0.4

0.6

0.8

1

Bromide, in milligrams per liter

River

Evapotranspiration

Figure 98. Relation of chloride and bromide concentrations in 

groundwater samples from the Arkansas River Valley alluvial 

aquifer near Dardanelle, Arkansas (from Kresse and Clark, 2008).
Aquifers of the Interior Highlands 259

Ouachita Mountains Aquifer

A thick sequence of Paleozoic rock formations in 

the Ouachita Mountains serves as an important source of 

groundwater supply for domestic users, in addition to a 

limited number of small commercial- and community-supply 

systems. The shallow saturated section of the combined 

formations in the Ouachita Mountains will hereinafter be 

referred to as the “Ouachita Mountains aquifer” (tables 2 and 

4). Renken (1998) used a similar nomenclature in his listing 

of the “Ouachita Mountains aquifer” as a minor aquifer of 

Segment 5 (Arkansas, Louisiana, and Mississippi) of the 

Ground Water Atlas of the United States. Assignment of 

boundaries for various aquifers of Arkansas, and particularly 

those of the Ouachita Mountains, can be a daunting task. 

The Ouachita Province includes two sections: the Arkansas 

(River) Valley and the Ouachita Mountains (table 2). The 

Arkansas Valley lies between dipping rocks of the Boston 

Mountains to the north and the highly folded and deformed 

rocks of the Ouachita Mountains to the south and includes 

geologic formations that extend into both areas (fig. 3; 

Cordova, 1963; Kilpatrick and Ludwig, 1990a). Waterresources investigations in the Ouachita Mountains generally 

included an area south of the Arkansas Valley (Albin, 1965; 

Renken, 1998), which resulted in an arbitrary divide that 

omitted large, continuous exposures of formations that cross 

the divide to the north, particularly in Sebastian and Logan 

Counties. Some of these formations are included in Ouachita 

Mountains and Arkansas Valley sections and also extend into 

the Boston Mountains north of the river. For example, the 

Atoka Formation is exposed across a large part of the Boston 

Mountains physiographic region and is a major formation of 

the Western Interior Plains confining system. It extends as far 

south as Scott County in the heart of the Ouachita Mountains 

physiographic region (Haley and others, 1993). 

Physiographic province and section boundaries often 

do not coincide with geologic or hydrologic boundaries. The 

Arkansas Valley section as identified on physiographic and 

regional hydrogeologic maps (Fenneman, 1938; Albin, 1965; 

Renken, 1998) includes formations that more appropriately 

belong to the Boston Mountains section of the Ozark Plateaus 

to the north or the Ouachita Mountains section of the 

Ouachita Province to the south. Including these formations 

as part of the Arkansas Valley for this report would result 

in (1) reproducing geologic, hydrologic, and water-quality 

discussions for either region in a separate section on the 

Arkansas Valley; (2) arbitrary boundaries of the Arkansas 

Valley cutting through continuously exposed formations 

(and possible groundwater flow paths) properly belonging to 

other sections; and (3) omitting important information, such 

as spatial water-quality trends or groundwater flow paths for 

aquifers in the Ouachita Mountains or Boston Mountains 

by arbitrary divides imposed by those defining the Arkansas 

Valley. For purposes of this report, the Arkansas River and 

associated alluvial deposits serve as a southern limit of the 

Western Interior Plains confining system (coinciding with 

the Boston Mountains section) and the northern limit of the 

Ouachita Mountains. Therefore, the Ouachita Mountains 

aquifer includes all formations extending north to the Arkansas 

River (and associated alluvial deposits), west to the State line, 

and south and east to the boundary with the Coastal Plain. 

Geology

Rocks forming the Ouachita Mountains aquifer are 

dominantly of sedimentary origin, ranging in age from 

Cambrian to Middle Pennsylvanian (table 4). These rocks 

were deposited by a regionally extensive sinking trough 

(geosyncline) that extended at minimum from central 

Oklahoma to central Arkansas. The geosyncline formed 

throughout most of the Paleozoic Era accounting for 

approximately 46,000 ft of accumulated sediment deposited in 

the trough. Lithification and compression of the sediments at a 

later time formed shales, sandstone, conglomerates, limestone, 

chert, and novaculite, ultimately resulting in deformation of a 

complexly folded and thrust-faulted arch (anticlinorium). 

Orogenic activity into the Middle Pennsylvanian Epoch 

formed the rocks into a complexly folded and thrust-faulted 

anticlinorium in which many of the folds were broken by 

thrusts or high-angle reverse faults. The folds were overturned 

to the south, resulting in the dips off the fold axes to the north 

(Purdue, 1910; Albin, 1965; Stone and Bush, 1984). A long 

period of epeirogenic uplift and erosion subsequently occurred 

resulting in the present-day mountains (Albin, 1965; Stone 

and Bush, 1984). The present-day physiography is represented 

by long even-crested ridges and flat-intermontane basins. The 

higher ridges and crest-forming rocks typically consist of the 

more resistant quartz formations (Albin, 1965; Kresse and 

Hays, 2009). Major faults are essentially parallel to trends of 

the axes of folds, which generally lie along east-west trending 

lines throughout the Ouachita Mountains. Consequently, wells 

of similar water-yielding capacity typically lie on east-west 

trends relative to each other. The best places to drill wells 

in the Ouachita Mountains generally are on the flanks of 

anticlines (in synclinal valleys) and off the noses of plunging 

anticlines (Albin, 1965; Halberg and others, 1968). 

Hydrologic Characteristics

Formations in the Ouachita Mountains are dominated 

by thick sequences of shale, siltstones, and quartz (sandstone, 

chert, novaculite), with minor occurrences of carbonates 

and other rocks. Similar lithologies coupled with structural 

modification have created an extremely high degree of 

hydraulic connectively between the formations. The rock 

sequence serves effectively as a single aquifer from a regional 

perspective, and a detailed discussion of lithology and 

depositional environment for each formation is not provided. 

For additional information, the reader is directed to Purdue 

and Miser (1916), Albin (1965), Halberg and others (1968), 

Stone and Bush (1984), and McFarland (2004).
260 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Primary porosity in rocks of the Ouachita Mountains was 

greatly decreased by compaction and lithification as sediments 

filled the synclinal trough and compression occurred during 

orogenic episodes. Secondary porosity and permeability are 

provided by faults, joints, fractures, bedding planes, and other 

structural features. These secondary permeability features 

generally result in low yields compared to unconsolidated 

sediments of Coastal Plain aquifers. Groundwater yields 

generally are sufficient for only domestic use. Groundwater 

geochemistry reflects the dominant aquifer rock types, with 

better quality water generally produced from quartz formations 

and poorer quality water from shale formations.

Groundwater availability afforded by secondary-porosity 

processes is strongly dependent on the degree of fracturing 

related to the tensile strength of the rock (Albin, 1965; 

Halberg and others, 1968; Stone and Bush, 1984; Cole and 

Morris, 1986; Kresse and Hays, 2009). Quartz formations 

such as the Bigfork Chert and Arkansas Novaculite are 

very brittle and prone to dense fracturing. Most researchers 

working in the Ouachita Mountains identified the Bigfork 

Chert as the most productive water-bearing formation in the 

region (Albin, 1965; Halberg and others, 1968; Stone and 

Bush, 1984; Cole and Morris, 1986; Kresse and Hays, 2009). 

Well yields have a fairly large range depending on individual 

formations and lithology but typically are low throughout 

the aquifer. Albin (1965) noted that most wells yielded less 

than 10 gal/min, and yields more than 50 gal/min were rare. 

The maximum recorded yield of 350 gal/min was for a well 

completed in the Bigfork Chert. Wells continuously yielding 

more than 10 gal/min for a week generally were considered 

“large-yield” wells. Wells in Hot Spring County generally 

yielded from 2 to 7 gal/min, with a few wells yielding 20 gal/

min or more (Halberg and others, 1968). The average pumping 

rate measured in this area was 21 gal/min with a reported 

maximum of 40 gal/min. A well completed in the Bigfork 

Chert in Garland County was pumped at 30 gal/min over 

a 3-day period, resulting in drawdown of only 1–2 inches 

(Kresse and Hays, 2009). Specific capacities ranged from 0.1 

to 9.0 (gal/min)/ft of drawdown (Albin, 1965; Halberg, 1968), 

and transmissivities ranged from 134 to 2,674 ft2

/d (Albin, 

1965). In spite of the few relatively high reported yields cited 

above, all publications cautioned that the aquifer should not 

be considered as a source of water supply unless the required 

quantity was small (Albin, 1965; Halberg and others, 1968; 

Stone and Bush, 1984).

Most wells in the Ouachita Mountains aquifer are less 

than 100 ft deep but can be as much as 700 ft deep. Static 

water levels generally are less than 20 ft below land surface, 

and flowing-artesian wells are common throughout the region 

(Albin, 1965; Kresse and Hays, 2009). Pumping water levels 

may be as much as 150 ft below land surface in the deepest 

wells. Of the 35 wells surveyed in Garland County, 83 percent 

were less than or equal to 200 ft deep, and all were less than 

400 ft deep (Kresse and Hays, 2009). Of these wells, 25 were 

located in valleys and had a mean depth of 16 ft compared to 

a mean depth of 75 ft for wells located at higher elevations. 

Generally, wells in the valleys were completed in the Stanley 

Shale and those at higher elevations were completed in the 

Bigfork Chert. 

Seasonal water-level fluctuations in the Ouachita 

Mountains aquifer generally were less than 10 ft. Larger 

fluctuations are common in abnormally wet or dry years 

because the groundwater reservoirs generally have small 

storage capacities and are recharged by rapid infiltration of 

local precipitation (Albin, 1965). Kresse and Hays (2009) 

collected water-level data for seven wells (two Stanley 

Shale, one Hot Springs Sandstone, three Bigfork Chert, and 

one Arkansas Novaculite) from October 2007 through April 

2009. Substantial water-level rises occurred for the quartz 

formations compared to the shale formations from December 

through May (wet season), reflecting greater storage in the 

quartz formations. Smaller rises in water levels were noted for 

wells in the quartz formations compared to shale formations 

for individual rain events. However, water levels slowly 

increased to maximum overall rises of 8–15 ft during the 

wet season in the quartz formations. Conversely, there were 

only episodic increases and decreases relative to a similar 

base level for wells in shale formations throughout this 

same period. Kresse and Hays (2009) hypothesized that the 

brittle nature and intense fracturing of the quartz formations 

resulted in substantially greater fracture porosity compared 

to shale formations. This provided greater permeability and 

storage for the quartz formations, with the result of an overall 

large rise in water levels in the wet season and smaller rises 

during individual rain events. The lower permeability and 

secondary porosity in the shale formations resulted in rapid 

filling of the fractures and causing large, short-term waterlevel rises, followed by rapid water-level declines driven by 

steep hydraulic gradients. Aquifer tests for several wells in 

both types of formations confirmed that yields and storage 

properties were substantially lower in the shale formations 

than in the quartz formations. 

Because of the similar rock types in the Boston and 

Ouachita Mountains regions, groundwater flow within both 

of these systems is likely explained by a similar conceptual 

model. Kresse and others (2012) proposed a general 

conceptual model explaining groundwater flow for a part 

of the Boston Mountains. They hypothesized that flow was 

controlled by secondary-porosity features (fractures, bedding 

planes), which provide limited groundwater storage and low 

yields generally sufficient only for domestic supply, and 

that flow paths were confined by small-scale topographic 

boundaries with short flow paths from elevated areas to valley 

floors in individual, small-scale watersheds. Topographic 

basins in the Ouachita Mountains generally are defined by 

the folded strata resulting in synclinal and anticlinal basins. 

Consequently, Halberg and others (1968) postulated that flow 

directions would reflect the structural geology, orientation, and 

hydraulic connection of the major east-west trending faults 

and likely have little interbasin flow of groundwater. Kresse 

and Hays (2009) tested this postulation using water levels 

from 53 shallow (less than 400 ft deep) wells and 24 springs 
Aquifers of the Interior Highlands 261

in Garland County to construct a potentiometric-surface map. 

The map indicated a high degree of topographic control on 

shallow groundwater flow, with groundwater flow confined 

to individual synclinal and anticlinal basins. This observation 

adds support to the conceptual model of groundwater flow 

of topographically controlled, short flow paths within local 

watersheds in the Ouachita Mountains aquifer.

Water Use

Determination of accurate values for the amount of water 

used from the Ouachita Mountains aquifer is difficult, and 

reported total use from the aquifer should be viewed with 

caution. The greatest use of groundwater from the Ouachita 

Mountains aquifer is for domestic supply. Domestic wells 

and wells producing less than 50,000 gal/d are exempt from 

reporting requirements; consequently, various methods that 

are used to estimate domestic water use commonly result in 

an underestimation of total groundwater use from the aquifer. 

Although Albin (1965) noted overall low yields and stated 

that wells in the aquifer that yield more than 10 gal/min are 

considered “large-yield wells,” some wells can yield between 

10 and 50 gal/min, which are more than sufficient for many 

communities. Records from the ADH indicate that 72 wells 

are used by camps and other recreational areas, conference 

centers, rest areas, stores, and even sources of public supply. 

Five separate communities used wells completed in the 

Atoka, Bigfork Chert, Stanley Shale, and Arkansas Novaculite 

Formations for purpose of public supply. This demonstrates 

that many formations within the Ouachita Mountains aquifer 

are capable of supplying sufficient volumes of water for a 

small community.

Water Quality

Past research indicated that groundwater in the Ouachita 

Mountains aquifer primarily is of a mixed calcium- and 

sodium-bicarbonate type and chemically is suitable for 

most domestic and farm uses. However, some groundwater 

exhibited high hardness and contained concentrations of iron, 

manganese, chloride, and nitrate in excess of concentrations 

recommended for various uses. The most common complaint 

from domestic users was that the groundwater can be hard and 

high in iron (Albin, 1965; Halberg and others, 1968; Cole and 

Morris, 1986; Kresse and Hays, 2009).

General Geochemistry and Water Type

Bicarbonate was the dominant anion in 90 of 116 samples 

(78 percent) with complete anion (chloride, sulfate, 

bicarbonate) analyses and was greater than 50 percent of 

the total anions in 78 of the 116 samples (67 percent) for the 

Ouachita Mountains aquifer. The remaining samples had 

chloride or sulfate as the dominant anion or were of a mixed 

type. For samples with complete cation (calcium, magnesium, 

sodium, potassium) analyses, calcium was the dominant 

cation in 59 of 125 samples (47 percent) and greater than 

50 percent in 37 of 125 samples (30 percent). Sodium was 

the dominant cation in 48 of 125 samples (38 percent) and 

greater than 50 percent in 23 of 125 samples (18 percent). The 

remaining samples generally had magnesium as the dominant 

cation. Therefore, groundwater is predominantly a calciumbicarbonate type throughout the aquifer. Generally, samples 

with the highest percent sodium occur in the southern part 

of the aquifer in wells completed in the Stanley Shale and in 

the northern part in wells completed in the shale-rich Atoka 

and McAlester Formations (fig. 99). These areas represent 

the transition from a calicium-bicarbonate to a sodiumbicarbonate or a sodium-chloride water type.

Values of pH for the Ouachita Mountains aquifer 

ranged from 3.3 to 8.6 in 137 samples with a median of 7.0 

(table 41). To better assess the extreme variability of pH, 

it is useful to understand the difference in geochemistry of 

the source rocks, which are dominantly shale and quartz. A 

study by Kresse and Hays (2009) in Garland County revealed 

substantial differences in groundwater geochemistry based 

on rock type. Low specific-conductance values were noted 

for groundwater from quartz formations (Bigfork Chert, 

Arkansas Novaculite, and Hot Springs Sandstone). All but one 

sample exhibited values less than 50 μS/cm with a median of 

30 μS/cm. These low specific-conductance values reflect a low 

dissolved-solids concentration attributable to the low solubility 

of quartz and the lack of carbonate minerals. Specificconductance values for the shale formations (Stanley Shale, 

Womble Shale, and the undifferentiated Missouri Mountain 

Shale and Polk Creek Shale) ranged from 97 to 490 μS/cm 

with a median of 293 μS/cm. These high specific-conductance 

values reflect high dissolved-solids concentrations attributable 

to the abundance of carbonate and other soluble minerals in 

the shale rocks. Values of pH in groundwater from shale rock 

ranged from 5.8 to 7.4 with a median of 6.6. Conversely, 

pH values in groundwater from quartz rocks ranged from 

3.6 to 6.1 with a median of 4.4. Increased pH was attributed 

to dissolution of mineral species with buffering capacity, 

particularly carbonate minerals, resulting in a positive 

correlation of pH and conductance (Kresse and Hays, 2009).

Spatial patterns of pH and specific conductance generally 

followed formation outcrop patterns for the Ouachita 

Mountains aquifer. Generally, the lowest pH values (3.3–5.0) 

were from the eastern part of the aquifer, where the Bigfork 

Chert, Arkansas Novaculite, and Hot Springs Sandstone 

Formations have extensive outcrop. High pH values (8.1–8.6) 

occur in the south, dominantly represented by wells completed 

in the Stanley Shale, and also occur in the western and 

northern parts of the aquifer, where shale-dominated rocks 

of the Atoka Formation predominate in outcrop. A few of 

these wells also were completed in the shale-rich McAlester 

Formation (fig. 99). 
YELL POLKSCOTT PIKE POPE LOGAN SALINE GRANT PERRY GARLAND CLARK PULASKI MONTGOMERY HOT SPRING SEBASTIAN HOWARD SEVIER FRANKLIN DALLAS JOHNSON POPE JOHNSON POPE JOHNSON POPE JOHNSON CRAWFORD YELL POLKSCOTT PIKE LOGAN SALINE GRANT PERRY GARLAND CLARK PULASKI MONTGOMERY HOT SPRING SEBASTIAN HOWARD SEVIER FRANKLIN DALLAS CRAWFORD YELL POLKSCOTT PIKE LOGAN SALINE GRANT PERRY GARLAND CLARK PULASKI MONTGOMERY HOT SPRING SEBASTIAN HOWARD SEVIER FRANKLIN DALLAS CRAWFORD YELL POLKSCOTT PIKE LOGAN SALINE GRANT PERRY GARLAND CLARK PULASKI MONTGOMERY HOT SPRING SEBASTIAN HOWARD SEVIER FRANKLIN DALLAS CRAWFORD 

Base modified from U.S. Geological Survey digital data, 1:250,000 Universal Transverse Mercator projection, zone 15Arkansas River Arkansas River Arkansas River Arkansas River 

251 to 500 1 to 10 11 to 25 26 to 50 51 to 100 101 to 250 Chloride, in mil

per liter 1,001 to 3,050 15 to 50 51 to 100 101 to 250 251 to 500 501 to 1,000 Specific conductance, in microsiemens per centimeter at 25 degrees Celsius 8.1 to 8.6 3.3 to 5.0 5.1 to 6.0 6.1 to 6.5 6.6 to 7.0 7.1 to 8.0 76 to 98 2 to 10 11 to 25 26 to 40 41 to 50 51 to 75 Sodium, in percent per major cations pH, in standard 

EXPLANATI

EXPLANATIO

EXPLANATION 94°00’ 93°00’ EXPLANATION 94°00’ 93°00’ 94°00’ 93°00’ 94°00’ 93°00’ 35°00’ 34°30’ 35°00’ 34°30’ 35°00’ 34°30’ 35°00’ 34°30’ 

Figure 99. Spatial distribution of selected chemical constituents in groundwater from the Ouachita Mountains aquifer in western Arkansas.
Aquifers of the Interior Highlands 263

Specific conductance values follow the same general 

trend represented by pH values. The lowest conductance 

values (15–50 μS/cm) occur in the eastern part of the aquifer, 

represented by the quartz formations listed above. A generally 

increasing trend in conductance occurs in the southern part 

of the aquifer, represented by wells dominantly completed in 

the Stanley Shale with numerous samples having conductance 

values ranging from 250 to 500 μS/cm. Lower values (ranging 

from 15 to 100 μS/cm) in the southern part of the aquifer 

were from wells completed in the Jackfork Sandstone. The 

highest specific conductance values (ranging from 1,000 

to 3,050 μS/cm) were from wells completed in the Atoka 

Formation in Scott County (fig. 99). The Atoka Formation is 

dominantly shale rock with some traceable sandstone units in 

the Ouachita Mountains. In general, the spatial distribution 

of pH and specific conductance values reflected source-rock 

types (Kresse and Hays, 2009).

Groundwater from quartz formations generally has 

lower conductance values than shale formations, reflecting 

lower dissolved-solids concentrations. This indicates 

that groundwater from quartz formations of the Ouachita 

Mountains aquifer is a highly desirable drinking-water 

source from the standpoint of hardness issues; however, the 

corresponding low pH values can present other problems 

related to leaching of metals in plumbing fixtures. Certain 

trace metals have solubility values that increase substantially 

at low pH values. These metals can be leached from pumps, 

pipes, fixtures, and other metallic parts of the waterdistribution system, which leads to higher concentrations 

that affect taste, pitting and corrosion of pipes, and staining 

of plumbing fixtures (Hem, 1989). Dissolved aluminum and 

copper were higher in groundwater from the quartz formations 

than in groundwater from shale formations as a result of 

the low pH in groundwater from quartz formations. This 

interpretation was substantiated by an inverse correlation of 

these metals with pH from a regression analysis. 

Nitrate

Nitrate concentrations in the Ouachita Mountains aquifer 

ranged from 0.01 to 15 mg/L with a median of 0.14 (table 41), 

which reflects the generally low nitrate concentrations 

throughout the aquifer. Out of 101 samples with nitrate 

analyses, 40 had concentrations less than 0.10 mg/L and 

72 were less than 1.0 mg/L. Only 4 of the 101 samples had 

concentrations exceeding the Federal MCL of 10 mg/L 

as nitrogen. No regional spatial trend was found in the 

distribution of nitrate. Although low concentrations can be 

found throughout the aquifer, a greater number of low (0.01 

to 0.10) concentrations occur in the eastern part of the aquifer. 

Generally, decreasing nitrate concentrations were related 

to increasing well depth rather than to spatial variability, 

reflecting the differences in vulnerability based on regolith 

thickness, rock type, and other surface features. Nitrate 

concentrations greater than 2.0 mg/L occurred in wells less 

than 200 ft deep. Correlation of nitrate concentrations with 

nitrogen sources was outside the scope of this report and was 

not addressed in previous reports.

Table 41. Descriptive statistics for selected chemical constituents in groundwater from the Ouachita Moutains aquifer in western 

Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 0.04 13.9 303 30.7 136

Magnesium (mg/L) 0.01 4.25 307 27 136

Sodium (mg/L) 0.67 12 284 41.1 135

Potassium (mg/L) 0.08 1.2 24 3.88 124

Bicarbonate (mg/L) 1.0 89 511 107 118

Chloride (mg/L) 0.9 7.0 500 62.1 152

Sulfate (mg/L) 0.02 9.15 535 56.1 137

Silica (mg/L) 1.1 13.2 46.8 11.1 102

Nitrate (mg/L as nitrogen) 0.01 0.14 15 3.17 101

Dissolved solids (mg/L) 14 152 953 152 125

Iron (μg/L) 0.05 170 14,000 2,320 108

Manganese (μg/L) 0.13 71.8 2,600 403 86

Arsenic (μg/L) 0.03 0.03 7.2 1.76 41

Hardness (mg/L as calcium carbonate) 0 62 410 82 116

Specific conductance (μS/cm) 15 241 3,050 401 157

pH (standard units) 3.3 7.0 8.6 1.2 137
264 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Iron

Iron concentrations in the Ouachita Mountains aquifer 

ranged from 0.05 to 14,000 μg/L with a median of 170 μg/L 

(fig. 100; table 41). No spatial pattern was noted for iron; 

high and low concentrations occurred in shale and quartz 

formations. Iron is abundant in numerous minerals in alluvial 

sediments and sedimentary rocks throughout Arkansas. 

Controls on solubility generally are related to changes in redox 

zonation, which can result in dissolution or precipitation of 

various iron-rich minerals based on the presence or absence of 

oxygen and the availability of electron donors and acceptors. 

Although iron was cited as problematic for wells completed 

in the Ouachita Mountains aquifer (Albin, 1965; Halberg and 

others, 1968; Cole and Morris, 1986; Kresse and Hays, 2009), 

no studies currently (2013) have been completed to identify 

iron sources and transport pathways. Higher concentrations 

of some trace metals (barium, lithium, manganese, and 

strontium) are noted in shale formations, whereas other trace 

metals occur in higher concentrations from quartz formations 

related to the low pH values (Wagner and Steele, 1985; Kresse 

and Hays, 2009). Although no relations were noted for the 

spatial distribution or sources of iron, evidence shows some 

control on iron solubility by possible sulfate reduction as 

described in the next section.

0

50

100

150

200

250

300

350

400

450

Concentrations, in milligrams per liter

500

Concentration, in micrograms per liter

700

800

900

1,000

0

100

200

300

400

500

600

108

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

136

136

135

118

152 137

108

Constituent Constituent

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron

Figure 100. Interquartile range of selected chemical constituents in groundwater from the Ouachita Mountains aquifer in western 

Arkansas.
Aquifers of the Interior Highlands 265

Sulfate

Sulfate concentrations generally were low throughout 

the Ouachita Mountains aquifer. Of 137 samples, 72 wells 

(53 percent) had concentrations less than 10 mg/L, 124 wells 

(91 percent) had concentrations less than 50 mg/L, and 

only 1 well had a concentration greater than the Federal 

secondary drinking-water regulation of 250 mg/L. Sulfate 

was substantially greater in shale formations than in quartz 

formations in the Ouachita Mountains aquifer (Kresse and 

Hays, 2009). Grouping all data by aquifer codes confirmed 

that concentrations greater than 10 mg/L (up to 535 mg/L) 

generally occurred in groundwater from the Stanley Shale, 

McAlester Formations, and Atoka Formation (51 of 88 

combined analyses greater than 10 mg/L). Nevertheless, 

low concentrations can be found throughout the aquifer in 

groundwater from all formations. This is demonstrated by 

the low concentrations throughout the southern part of the 

aquifer, an area with numerous wells completed in the Stanley 

Shale. The lowest concentrations (generally less than 5 mg/L) 

generally occurred in the Bigfork Chert, Arkansas Novaculite, 

Hot Springs Sandstone, and Jackfork Sandstone (only 6 of 

44 combined analyses more than 10 mg/L). 

Various constituent relations suggest that sulfate 

reduction in groundwater from shale formations may serve 

as a control on iron solubility. Iron and sulfate had inverse 

correlations with nitrate, indicating that denitrification 

occurred prior to iron and sulfate reduction. Nitrate 

concentrations greater than 0.5 mg/L occurred where iron 

concentrations generally were less than 1,200 μg/L. Iron 

concentrations greater than approximately 500 μg/L with 

corresponding nitrate concentrations more than 0.5 mg/L 

normally represent mixing of groundwater from different 

zones in the aquifer, which is typical of open-hole completions 

in bedrock aquifers (fig. 101A). Nitrate concentrations were 

greater than 0.5 mg/L for sulfate concentrations generally less 

than 30 mg/L (fig. 101B).

Sulfate concentrations in the Ouachita Mountains aquifer 

were inversely correlated with iron concentrations (fig. 101C). 

The reduction of sulfate to hydrogen sulfide is directly related 

to the abundance of available sulfate. Studies have shown 

that dissolved iron (Fe2+) and hydrogen sulfide (H2

S) tend 

to be inversely related according to a hyperbolic function. 

When Fe2+ concentrations are high, H2S concentrations tend 

to be low and vice versa, which reflects the rapid reaction 

kinetics of Fe2+ with H2S to produce relatively insoluble 

ferrous sulfides (Chapelle and others, 2009). The transition 

from iron- to sulfate-reducing conditions occurs when higher 

sulfate concentrations are available for sulfate-reducing 

bacteria to produce sulfide, and the resulting precipitation of 

iron-sulfide minerals acts as a sink for soluble iron. Kresse 

and others (2012) provided evidence for the geochemical 

evolution of redox zonation in similar shale formations in 

the Boston Mountains area. A series of reduction steps from 

denitrification, through iron reduction, and ultimately to 

sulfate reduction occurred with increasing dissolved-solids 

concentrations, corresponding to increasing residence time in 

the aquifer. 

Elevated (more than 2.0 mg/L) nitrate concentrations 

in the Ouachita Mountains aquifer dominantly occurred 

in association with dissolved-solids concentrations less 

than 200 mg/L (fig. 101D). Iron concentrations greater 

than 2,000 μg/L occurred in association with dissolvedsolids concentrations less than 250 mg/L (fig. 101E). When 

dissolved-solids concentrations exceeded 250 mg/L, all 

but one of the iron concentrations were less than 200 μg/L. 

Although it appears that nitrate and iron concentrations 

overlap, the inverse correlation between iron and nitrate 

(fig. 101A) indicates that redox zonation varies for dissolvedsolids concentrations less than 200 mg/L, depending on 

conditions along local flow paths in different parts of the 

aquifer. Sulfate concentrations increased with increasing 

dissolved solids, and sulfate concentrations exceeding 50 

mg/L (up to 535 mg/L) occurred where dissolved-solids 

concentrations were greater than 250 mg/L (fig. 101F). All of 

these relations support a conceptual model of redox zonation 

that fits the theory by Kresse and others (2012) for shale 

formations in the Boston Mountains. Shale formations are 

rich in labile organic material, which drives the reduction of 

initially oxygenated water by aerobic and anaerobic bacteria. 

These redox processes proceed sequentially from the most to 

the least energetic microbially mediated reaction (Appelo and 

Postma, 1999). Oxygen is the first terminal electron acceptor, 

followed by nitrate, manganese oxide, iron oxyhydroxide, 

sulfate, and carbon dioxide. Data indicate that nitrate and iron 

reduction dominate the redox zonation for dissolved-solids 

concentrations less than 250 mg/L. Concentrations of nitrate 

and iron appear to overlap along the continuum of increasing 

dissolved-solids concentrations (representing increased 

residence time in the aquifer) between approximately 100 and 

200 mg/L. Because nitrate reduction precedes iron reduction, 

this relation appears to violate redox zonation theory. 

However, the inverse correlation of iron and nitrate (fig. 101A) 

shows that elevated concentrations for these constituents 

are mutually exclusive. Either process can be dominant in 

this region based on the abundance and availability of the 

respective electron acceptors and dissolved organic matter. 

Dissolved-solids concentrations more than 250 mg/L are 

characterized by: (1) the virtual disappearance of iron and 

nitrate, (2) the dominance of higher sulfate concentrations, and 

(3) hypothesized sulfate-reducing conditions. This corresponds 

closely with groundwater-quality data from shale formations 

in the Boston Mountains (Kresse and others, 2012), which 

indicate that sulfate reduction dominates over iron reduction 

for dissolved-solids concentrations exceeding approximately 

290 mg/L (see “Western Interior Plains Confining System” 

section). Therefore, geochemical evolution of groundwater in 

shale formations appears to be similar throughout the Ouachita 

Mountains and Interior Highlands. This model of redox 

zonation accounts for controls on iron solubility, which was 

not evident from a review of the spatial distribution of iron 

concentrations or relation to geologic formations. 
266 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

Iron, in micrograms per liter

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

Iron, in micrograms per liter

0 200 400 600 800 1,000

Dissolved solids, in milligrams per liter

0 100 200 300 400 500 600

Sulfate, in milligrams per liter

0 200 400 600 800 1,000

Dissolved solids, in milligrams per liter

0 200 400 600 800 1,000

Dissolved solids, in milligrams per liter

0

2

4

6

8

10

12

14

16

Nitrate, in milligrams per liter

0

50

100

150

200

250

300

Sulfate, in milligrams per liter

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

Iron, in micrograms per liter

0

2

4

6

8

10

12

14

16

Nitrate, in milligrams per liter

0

2

4

6

8

10

12

14

16

Nitrate, in milligrams per liter

0

100

200

300

400

500

600

Sulfate, in milligrams per liter

A B

C D

E F

Figure 101. Relation of concentrations for A, nitrate and iron; B, nitrate and sulfate; C, sulfate and iron; D, nitrate and dissolved 

solids; E, iron and dissolved solids; and F, sulfate and dissolved solids in groundwater from the Ouachita Mountains aquifer in western 

Arkansas.
Aquifers of the Interior Highlands 267

Chloride

High salinity can be a problem in some aquifers, 

especially for some of the Tertiary and Cretaceous aquifers 

of the Coastal Plain, but chloride concentrations were low 

throughout the Ouachita Mountains aquifer. Shale formations 

formed from marine deposits often retain residual salts. 

Through the process of uplift and erosion, coupled to 

continuous flushing by meteoric water over time, much of the 

original salinity is often flushed from the aquifer. However, 

wells that penetrate low-porosity, hydraulically isolated 

zones that still retain high levels of chloride often result in 

production of slightly brackish water.

Chloride concentrations in the Ouachita Mountains 

aquifer ranged from 0.9 to 500 mg/L with a median of 

7.0 mg/L (fig. 100; table 41). Out of 152 samples, 143 

(94 percent) had concentrations that were less than 100 mg/L, 

117 (77 percent) were less than 25 mg/L, and only 3 samples 

exceeded the Federal secondary drinking-water regulation 

of 250 mg/L. Chloride concentrations, similar to sulfate, 

generally increased with an increase in dissolved solids. 

All chloride concentrations more than 50 mg/L occurred 

at dissolved-solids concentrations greater than 200 mg/L. 

Extremely low chloride concentrations occur in the eastern 

part of the aquifer. The greatest density of elevated (greater 

than 100 mg/L) chloride concentrations occur in Scott County. 

Wells in this area are completed in the shale-dominated rocks 

of the Atoka Formation. For quartz formations, only 1 of 

44 samples had a concentration that was greater than 10 mg/L 

(54 mg/L), and 38 of the 44 samples were less than 10 mg/L.

In summary, groundwater quality in the Ouachita 

Mountains aquifer is good with respect to Federal primary 

drinking-water standards. Problems in regard to taste, staining, 

and other aesthetic properties are related to elevated levels of 

iron, which is a common complaint among domestic users. 

Geochemical data indicate that an important control on iron 

solubility is sulfate reduction, which occurs dominantly in 

groundwater with dissolved-solids concentrations greater 

than 250 mg/L. Nitrate was somewhat elevated (greater than 

1.0 mg/L) in numerous wells; however, only 4 of 101 samples 

exceeded the Federal MCL of 10 mg/L. Concentrations more 

than 1.0 mg/L generally occurred in wells less than 200 ft in 

depth. As is the case with most aquifers, shallow groundwater 

is more vulnerable to surface sources of contamination. 

Western Interior Plains Confining System

The Boston Mountains (fig. 3) are represented by a 

group of formations that comprise dominantly fractured 

shale and sandstone rocks, which are characterized by low 

secondary porosity and permeability with resulting low yields. 

Regional hydrogeologic framework studies (Imes and Emmett, 

1994) characterize this system of formations as a regional 

confining unit, referred to as the Western Interior Plains 

confining system (table 5). Although regionally designated as 

a confining system, these formations are important locally as 

valuable sources of water supply. Unfortunately, there are no 

reports that view this collection of rocks as a regional aquifer 

system because of the dominance of shale formations and low 

well yields. However, historical reports discuss hydrologic 

characteristics and water quality for individual formations in 

this system of rocks. Historical and current USGS water-use 

reports use the term “rocks of Paleozoic age, undifferentiated” 

to refer to the total reported groundwater use from all shallow 

rock formations of the Interior Highlands, including those 

of the Ouachita Mountains, the Boston Mountains, and the 

Ozark and Springfield Plateaus regions. Although this report 

retains the accepted regional nomenclature of Western Interior 

Plains confining system for this system of formations, it is 

implied and often referred to in the following discussion as an 

important aquifer system in Arkansas.

Geologic Setting

The Western Interior Plains confining system comprises 

11 different predominantly clastic (sand, siltstone, shale) 

formations of Upper Mississippian and Pennsylvanian age 

(tables 2 and 5). These formations are relatively thin in the 

northern Boston Mountains and thicken considerably to the 

south at rates of approximately 180 ft/mi. Total thickness of 

the formations is more than 6,000 ft beneath the Arkansas 

River Valley (Imes and Emmett, 1994). The lithology and 

hydrogeological characteristics of these formations are very 

similar. Consequently, a detailed discussion of each formation 

is not integral to the understanding of this shallow aquifer 

system. For additional information on the stratigraphy of the 

individual formations composing the confining system, the 

reader is referred to McFarland (2004). A general knowledge 

of the basic rock types is sufficient to understanding the 

hydrologic characteristics and geochemistry of groundwater 

from the Western Interior Plains confining system.

Hydrologic Characteristics

The Western Interior Plains confining system (fig. 3) 

consists of alternating sequences of low-permeable shale 

and siltstone, and low- to moderate-permeable sandstone, 

with minor occurrences of limestone and coal. Regionally, 

the confining system impedes the flow of water to and 

from the underlying Springfield Plateau aquifer (Imes 

and Emmett, 1994). The designation of these combined 

formations as a “confining system” is a consequence of the 

marked permeability contrast between the high porosity karst 

limestone of the Springfield Plateau aquifer compared to the 

low fracture porosity in the Western Interior Plains confining 

system. Porosity in the well-indurated clastic rocks of the 

Western Interior Plains confining system is dependent upon 

weathering and resultant fracture development. Chemical and 

physical weathering processes result in the development of 

secondary porosity through expansion and fracturing of the 

rocks. Fractures tend to exhibit denser distribution and larger 

apertures near the surface because of unloading expansion 
268 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

that is a mechanical response to decreased compressive stress 

as overlying rocks are eroded and removed. The hydraulic 

properties of the Western Interior Plains confining system 

exhibit low primary porosity, secondary porosity from 

fractures associated with compression, uplift and weathering, 

and low yields that rarely exceed 1–5 gal/min, similar to that 

of the shale- and sandstone-dominated Ouachita Mountains 

aquifer.

Imes and Emmett (1994) noted that local groundwaterflow systems in the Western Interior Plains confining system 

are dominantly present in the upper 300 ft of the weathered 

confining system. This is because fractures generally have 

a larger aperture near the surface and diminishing width 

with depth. Porosity and permeability generally decrease to 

a magnitude insufficient to support production from wells 

at depths more than approximately 300 ft (Cordova, 1963; 

Kilpatrick and Ludwig, 1990b; Imes and Emmett, 1994; 

Kresse and others, 2012). Kresse and others (2012) reported 

on 58 wells in the central part of the Western Interior Plains 

confining system with depths ranging from 25 to 385 ft with 

a median of 87 ft. Many wells in the Western Interior Plains 

confining system often go dry during pumping, particularly 

during drought periods (Cordova, 1963; Kresse and others, 

2012). The quantity of groundwater available in the Western 

Interior Plains confining system is related directly to the 

density, size, openness, and degree of interconnection of 

fractures (Cordova, 1963). 

Groundwater generally is recharged by precipitation 

that infiltrates in upland areas, percolates to the water table, 

flows downgradient toward lowland areas, and discharges 

into streams (Imes and Emmett, 1994). A conceptual model 

of groundwater flow for the Western Interior Plains confining 

system is controlled by expansion fractures with limited 

groundwater storage and has sufficient yields almost solely 

for use as domestic supply. Groundwater flow paths are 

constrained by small-scale topographic boundaries with flow 

from elevated areas to valley floors in small stream systems 

(Cordova, 1963; Imes and Emmett, 1994; Kresse and others, 

2012). Regional hydraulic heads and flow gradients probably 

have changed little since predevelopment because of the poor 

hydraulic connection between lower and higher permeability 

zones. Water-level measurements in any one well represent 

averages of all the water-yielding layers in the Western Interior 

Plains confining system (Imes and Emmett, 1994).

Because of the low porosity of the Western Interior 

Plains confining system, well yields generally are sufficient 

only for household, small public-supply, and nonirrigation 

farm uses. Cordova (1963) noted that most wells yielded 

less than 60 gal/min, which is the maximum yield in the 

Western Interior Plains confining system. Thicker sandstone 

units in the Atoka Formation and the Batesville Sandstone 

in the eastern part of the confining system commonly yield 

5–10 gal/min to wells less than 300 ft deep (Albin and others, 

1967a). Kilpatrick and Ludwig (1990b) also noted that yields 

typically are less than 10 gal/min. Well yields for 16 shallow 

wells in southwestern Washington County ranged from 2 to 

19 gal/min (Muse, 1982). Water levels in the Western Interior 

Plains confining system typically range from near land 

surface to approximately 50 ft below land surface. Seasonal 

fluctuations are approximately 10 ft with drawdowns from 

pumping as much as 45 ft (Cordova, 1963; Albin and others, 

1967a).

Water Use

Difficulties exist when attempting to gather information 

on use of groundwater in the Interior Highlands. Before 

development of surface-water resources, wells were common 

throughout the region for domestic and livestock supply and 

less common for public supply, commercial, and industrial 

purposes (Purdue and Miser, 1916; Cordova, 1963; Albin and 

others, 1967a; Lamonds, 1972). Because domestic and publicsupply systems serving less than 50,000 gal/d are not required 

to report their groundwater use, there is no way to accurately 

quantify the number of domestic and livestock wells currently 

in use. Thirteen wells were reported as completed in the Atoka 

Formation of the Western Interior Plains confining system in 

2010 (Terrance W. Holland, U.S. Geological Survey, written 

commun., 2013). These wells were mainly used for public 

supply or parks. Several schools, stores, parks, and some 

commercial businesses also withdraw water from the Western 

Interior Plains confining system (Lyle Godfrey, Arkansas 

Health Department, written commun., 2012).

Water Quality

Little groundwater-quality monitoring has been done 

in the past related to the Western Interior Plains confining 

system. Most water-resource investigations in the Ozark 

Plateaus have concentrated on the Springfield Plateau and 

Ozark aquifers. Kilpatrick and Ludwig (1990a) reported 

that overall geochemistry in the area is closely related to 

the mineral concentration of the rock, although no detailed 

discussions were provided to explain this observation. The 

water was described as a calcium-magnesium-bicarbonate 

type, hard, and high in iron, with areas of slightly saline water 

and occasional high nitrate concentrations (Kilpatrick and 

Ludwig, 1990a). 

Groundwater in formations of the Western Interior 

Plains confining system was noted to have bicarbonate as 

the principal anion with sodium, calcium, or magnesium 

dominating the cations dependent on the formation type 

(Cordova, 1963). Lamonds (1972) stated that groundwater 

ranged from a calcium- to a sodium-bicarbonate type with 

dissolved-solids concentrations ranging from 20 to 1,200 

mg/L. Dissolved-solids concentrations for groundwater 

in sandstones of the Atoka Formation typically ranged up 

to 200 mg/L, whereas groundwater from shale formations 

typically had dissolved-solids concentrations greater 

than 200 mg/L. Cordova (1963) attributed sodium- and 

magnesium-chloride water types to proximity of hydrocarbon 

accumulations and attributed the sulfate water type to 
Aquifers of the Interior Highlands 269

oxidation of pyrite. Cordova also noted that iron concentration 

varied widely, ranging from nondetectable to 19 mg/L. Odors 

of hydrogen sulfide and iron staining on plumbing fixtures 

were the major complaints of household residents (Cordova, 

1963). 

Albin and others (1967a) reported on water resources of 

Jackson and Independence Counties, which are located in the 

eastern extent of the Western Interior Plains confining system. 

Analyses for the Atoka Formation indicated that groundwater 

generally was of good quality with low concentrations for 

most chemical constituents; though, in a few areas, the water 

was hard with elevated iron concentrations. The poorest 

quality groundwater was noted in groundwater from the 

Fayetteville Shale, which contained elevated concentrations of 

iron, sodium, sulfate, chloride, and dissolved solids relative to 

other formations (Albin and others, 1967a). Lamonds (1972) 

also noted that groundwater from black shale can be high in 

sulfide and sulfate. 

The primary scope of previously described earlier reports 

was a general assessment of the quantity and quality of 

surface and subsurface waters throughout the State. Detailed 

geochemical evaluations to assess rock/water interactions 

and microbially mediated processes affecting geochemical 

evolution of groundwater, in addition to anthropogenic sources 

affecting groundwater quality, were outside the scope of these 

earlier reports. Recent groundwater studies (Kresse and Hays, 

2009; Kresse and others, 2012; Warner and others, 2013) 

collected a more extensive and comprehensive geochemical 

database. These recent studies also provided an analysis 

of isotopic compositions to better understand rock/water 

interactions and evolution of groundwater geochemistry with 

respect to rock type in the Interior Highlands. These recent 

studies confirmed the poor quality of groundwater quality 

from shale formations and showed marked differences in 

the geochemistry of groundwater from quartz formations 

(sandstone, chert, and novaculite) and shale formations in the 

Interior Highlands.

General Geochemistry and Water Type

There is no definitive spatial trend for various chemical 

constituents in the Western Interior Plains confining system, 

which contrasts markedly with the strong trend noted for 

most of the aquifers of the Coastal Plain. One explanation for 

the lack of spatial trends is the predominance of relatively 

short, local flow paths, and small fracture size. These affect 

groundwater residence time and the amount of flushing in 

the Western Interior Plains confining system. The nature of 

the alternating geologic formations and differing associated 

mineralogies across the areal extent of the Western Interior 

Plains confining system are also a factor. 

A detailed analysis of groundwater geochemistry in the 

central part of the Western Interior Plains confining system 

was performed by Kresse and others (2012) as part of an 

assessment of potential effects of gas-extraction activities 

in the Fayetteville Shale. This study used groundwater data 

from 127 wells completed dominantly in the Atoka and Bloyd 

Formations. Out of 282 groundwater samples compiled for 

this report, 260 (92 percent) samples were from the Atoka 

(191 samples) and Bloyd (69 samples) Formations, with the 

remaining 22 samples distributed among other formations. 

Because Kresse and others (2012) reported on groundwater 

quality and geochemistry using data dominantly from the 

Atoka and Bloyd Formations, their study can be used to 

explain the variation in geochemistry for most of the Western 

Interior Plains confining system, as these two formations 

constitute the greatest area of exposure throughout the 

confining system.

Much of the variation in groundwater geochemistry 

within the Western Interior Plains confining system can be 

explained by the dominant geology in the region, which 

mainly consists of alternating shale and sandstone units. 

In most areas, shale dominates the lithology with minor 

occurrences of thin sandstone units within any one vertical 

section. In some other areas, thicker sandstone units occur. 

Distinct geochemical differences were noted in groundwater 

extracted from shale compared to groundwater extracted from 

quartz formations in the Ouachita and Boston Mountains 

areas, which are dominated by these clastic lithologies (Kresse 

and Hays, 2009; Kresse and others, 2012). These differences 

in groundwater geochemistry were definable, reproducible, 

and consistent across both areas and were controlled by 

mineralogy. This is primarily related to the presence or 

absence of carbonate minerals, as well as redox zonation for a 

given section of aquifer penetrated by each well. Much of the 

following discussion on the evolution of geochemistry in the 

Western Interior Plains confining system is taken from Kresse 

and Hays (2009) and Kresse and others (2012).

Similar to most aquifers in Arkansas, groundwater in the 

Western Interior Plains confining system generally is a strong 

bicarbonate water type. Bicarbonate accounted for more 

than 50 percent of the total anions in 202 of 249 (81 percent) 

samples with complete anion (chloride, sulfate, bicarbonate) 

analyses. Eighty-three of these 202 samples had percent 

bicarbonate exceeding 90 percent. Bicarbonate concentrations 

ranged up to 980 mg/L with a median of 129 mg/L (fig. 102; 

table 42). For samples with bicarbonate as the dominant anion, 

groundwater ranged from calcium- and calcium-magnesiumbicarbonate to a sodium-bicarbonate water type. Bicarbonate 

concentrations increased with increasing dissolved-solids 

concentrations. This relation indicates that dissolution of 

carbonate minerals accounts for the increasing bicarbonate 

concentrations, which drives the concomitant increases in 

dissolved solids (fig. 103A). Shale formations in the Western 

Interior Plains confining system have abundant carbonate 

minerals because the source sediments accumulated in marine 

environments (McFarland, 2004). Similarly, increasing values 

of pH correlated to increasing concentrations of bicarbonate 

and dissolved solids (figs. 103B, C). 
270 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

0

50

100

150

200

250

300

350

400

450

Concentrations, in milligrams per liter

500

Concentration, in micrograms per liter

700

800

900

1,000

0

100

200

300

400

500

600

163

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

262

262

257

256

282 267

163

Constituent Constituent

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron

Figure 102. Interquartile range of selected chemical constituents in groundwater from the Western Interior Plains confining system in 

northern Arkansas.

Table 42. Descriptive statistics for selected chemical constituents in groundwater from the Western Interior Plains confining system in 

northern Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 0.1 16.4 160 24.9 262

Magnesium (mg/L) 0.07 4.98 211 17.1 262

Sodium (mg/L) 0.9 12.3 844 74.7 257

Potassium (mg/L) 0.13 0.8 11 1.87 128

Bicarbonate (mg/L) 2.0 129 980 137 256

Chloride (mg/L) 0.9 5.0 1,100 78.2 282

Sulfate (mg/L) 0.02 4.7 1,030 80.6 267

Silica (mg/L) 0.18 11 47.7 8.2 252

Nitrate (mg/L as nitrogen) 0.01 0.09 18 1.95 214

Dissolved solids (mg/L) 7.0 176 2,460 346 129

Iron (μg/L) 0.05 27 13,800 2,410 163

Manganese (μg/L) 0.13 100 4,370 519 218

Arsenic (μg/L) 0.03 0.03 16.9 1.28 200

Hardness (mg/L as calcium carbonate) 4.0 73 1,100 131 195

Specific conductance (μS/cm) 13 267 3,500 388 280

pH (standard units) 3.5 6.6 8.8 1.1 266
Aquifers of the Interior Highlands 271

0 2 4 6 8 10

Calcium plus magnesium/bicarbonate, equivalent ratio

0 200 400 600 800 1,000

Dissolved solids, in milligrams per liter

0 200 400 600 800 1,000 1,200

Bicarbonate, in milligrams per liter

0 200 400 600 800 1,000

Dissolved solids, in milligrams per liter

0 500 1,000 1,500 2,000 2,500 3,000

Dissolved solids, in milligrams per liter

0 200 400 600 800 1,000 1,200 1,400

Dissolved solids, in milligrams per liter

0

10

20

30

40

50

60

70

80

Sodium/chloride, equivalent ratio

0

50

100

150

200

250

300

350

400

Chloride, in milligrams per liter

3

4

5

6

7

8

9

10

pH, in standard units

0

50

100

150

200

250

300

350

400

Sulfate, in milligrams per liter

3

4

5

6

7

8

9

10

pH, in standard units

0

200

400

600

800

1,000

1,200

Bicarbonate, in milligrams per liter

A B

C D

E F

Figure 103. Relation of A, dissolved solids and bicarbonate; B, bicarbonate and pH; C, dissolved solids and pH; D, calcium plus 

magnesium/bicarbonate and sodium/chloride; E, dissolved solids and sulfate; and F, dissolved solids and chloride in groundwater from 

the Western Interior Plains confining system in northern Arkansas.
272 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Similar to most aquifers in Arkansas, recharge of slightly 

acidic precipitation with a mean pH value of approximately 

4.7 (Kresse and Fazio, 2002) is neutralized with the 

dissolution of carbonate minerals. This results in increasing 

pH values along a continuum of increased residence time with 

resultant increasing dissolved-solids concentrations in the 

Western Interior Plains confining system (Kresse and Fazio, 

2002; Kresse and Hays, 2009; Kresse and others, 2012). 

Values of pH ranged from 3.5 to 8.8 (table 42), and 16 samples 

had pH values less than 4.7. Values of pH lower than the pH 

of rainwater are attributed to formation of carbonic acid by 

dissolution of carbon dioxide with recharging precipitation in 

the unsaturated zone of carbonate-free sandstone units (Kresse 

and Hays, 2009; Kresse and others, 2012). Bicarbonate 

concentrations and pH values show no clearly discernible 

spatial trends. However, some groupings of lower values for 

pH (for example, in extreme southern Van Buren County; 

fig. 104) suggest that wells may be producing from areal 

extensive sandstone units. Similarly, a grouping of higher 

pH values in northern Faulkner County may indicate wells 

completed in predominately shale rocks (fig. 104).

In addition to mineral dissolution, cation exchange is 

one of the more important rock/water interaction processes 

affecting groundwater geochemistry and resulting water type. 

Cation exchange occurs when groundwater is in contact with 

clays and weathered shale surfaces. Kresse and others (2012) 

showed that sodium/chloride equivalent ratios were inversely 

correlated to calcium plus magnesium/bicarbonate ratios. This 

suggests that cation exchange was actively occurring in the 

Western Interior Plains confining system, increasing sodium 

while decreasing calcium in solution. Data compiled for this 

report showed a similar relation between these two ratios for 

the Western Interior Plains confining system (fig. 103D). The 

lowest sodium/chloride ratios occur in groundwater with the 

lowest dissolved-solids concentrations and lowest pH values. 

Sodium/chloride ratios increase with increasing dissolved 

solids, indicating that cation exchange progresses with 

increasing residence time in the aquifer. Ultimately, this results 

in sodium/chloride equivalent ratios nearly 70 times the oneto-one ratio resulting from dissolution of sodium-chloride salts 

(Kresse and others, 2012).

Nitrate

Nitrate concentrations in the Western Interior Plains 

confining system ranged from 0.01 to 18 mg/L as nitrogen 

with a median of 0.09 mg/L (table 42). Of 214 samples with 

nitrate data, 169 (79 percent) were less than 0.5 mg/L and 186 

(87 percent) were less than 1.0 mg/L, reflecting the overall 

low nitrate concentrations in groundwater from the Western 

Interior Plains confining system. Only two samples had nitrate 

concentrations exceeding the Federal MCL of 10 mg/L as 

nitrogen. Generally, higher nitrate concentrations occurred 

near the southern boundary of Van Buren County in the same 

area as wells with low pH values (fig. 104) and, therefore, 

low dissolved-solids concentrations (fig. 103C). An inverse 

relation noted for nitrate and dissolved solids confirmed this 

observation in that most nitrate concentrations are more than 

1.0 mg/L when dissolved-solids concentrations are less than 

125 mg/L. Kresse and others (2012) similarly noted that 

nitrate concentrations were highest in groundwater samples 

with low pH and low dissolved-solids concentrations. Low 

pH and low dissolved-solids concentrations in groundwater 

were noted by Kresse and others (2012) as occurring in 

poorly buffered sandstone units. This suggests that sandy 

soils developed in these areas have increased permeability 

and concomitantly increased vulnerability to surface and 

shallow subsurface (for example, septic systems) sources of 

nutrients. By comparison, clayey soils developed in regions 

of weathered shale outcrops have less permeable soils that 

retard transport of nutrients to the water table. Kresse and 

others (2012) also showed inverse correlations of nitrate 

with iron and manganese concentrations. This suggests that 

nitrate is removed from the system by denitrification with 

increased residence time along the flow path. These relations 

suggest that the occurrence and distribution of nitrate is related 

to degree of vulnerability associated with soils of varying 

permeability, reduction of nitrate with increased residence 

time in the aquifer, or a combination of both processes. No 

relation was noted between well depth and nitrate in the 

Western Interior Plains confining system. For many of the 

aquifers in the Coastal Plain, nitrate generally was inversely 

correlated to well depth.

Iron

Iron concentrations in the Western Interior Plains 

confining system ranged from 0.05 to 13,800 μg/L with a 

median of 27 μg/L (fig. 102; table 42). Iron concentrations 

were below the Federal secondary drinking-water regulation 

of 300 μg/L in 120 of 163 (74 percent) samples. Groupings 

of concentrations exceeding 500 μg/L generally occur in 

Faulkner County and into eastern Conway County and 

similarly throughout Cleburne and White Counties (fig. 104). 

However, wells with high iron concentrations occur next to 

wells with low concentrations, indicating the lack of a welldefined and consistent spatial distribution trend. The lack 

of any spatial trend suggests that the occurrence of iron is a 

function of mineralogical and reduction-oxidation processes 

occurring with increased residence time along localized and 

relatively short groundwater flow paths.

Kresse and others (2012) showed that dissolved iron was 

lowest (less than 500 μg/L) in groundwater with dissolved 

solids less than 60 mg/L, generally correlating to regions with 

high nitrate concentrations. Iron concentrations increased with 

increasing dissolved-solids concentrations up to approximately 

290 mg/L and decreased for dissolved-solids concentrations 

greater than 290 mg/L. Arsenic concentrations had similar 

trends with increasing dissolved solids. Kresse and others 

(2012) hypothesized that sulfate reduction dominates redox 

zonation at dissolved solids more than 290 mg/L, removing 

iron from solution with the precipitation of iron sulfide 

minerals. For a more detailed discussion, see the later section 

“Conceptual Model of Groundwater Geochemical Evolution.”
Aquifers of the Interior Highlands 273

YELL

POPE

WHITE

SCOTT

LOGAN

IZARD

NEWTON

STONE

MADISON

PERRY

SHARP

SEARCY

JOHNSON

WASHINGTON

BENTON

CONWAY

VAN BUREN

PULASKI

FAULKNER

BOONE

MARION

CLEBURNE

LONOKE

CRAWFORD

BAXTER

INDEPENDENCE

CARROLL FULTON

SALINE

SEBASTIAN

YELL

POPE

WHITE

SCOTT

LOGAN

IZARD

NEWTON

STONE

MADISON

PERRY

SHARP

SEARCY

JOHNSON

WASHINGTON

BENTON

CONWAY

PRAIRIE

VAN BUREN

PULASKI

FAULKNER

FRANKLIN

BOONE

MARION

CLEBURNE

LONOKE

CRAWFORD

BAXTER

INDEPENDENCE

JACKSON

CARROLL FULTON

SALINE

SEBASTIAN WOODRUFF

PRAIRIE

FRANKLIN

LONOKE

JACKSON

WOODRUFF

PRAIRIE

FRANKLIN

JACKSON

WOODRUFF

YELL

POPE

WHITE

SCOTT

LOGAN

IZARD

NEWTON

STONE

MADISON

PERRY

SHARP

SEARCY

JOHNSON

WASHINGTON

BENTON

CONWAY

VAN BUREN

PULASKI

FAULKNER

BOONE

MARION

CLEBURNE

CRAWFORD

BAXTER

INDEPENDENCE

CARROLL FULTON

SALINE

SEBASTIAN

0 40 80 MILES

0 40 80 KILOMETERS

94°00' 93°00' 92°00'

94°00' 93°00' 92°00'

35°30'

36°00'

35°00'

35°30'

36°00'

35°00'

35°30'

36°00'

35°00'

94°00' 93°00' 92°00'

Western Interior Plains 

confining system 

(modified from Imes

and Emmett, 1994)

EXPLANATION

pH, in standard units 

3.5 - 5.0

5.1 - 6.0

6.1 - 6.5

6.6 - 7.0

7.1 - 7.5

7.6 - 8.0

Nitrate, in milligrams per liter 

0.01 to 0.05

0.06 to 0.50

0.51 to 1.00

1.01 to 5.00

5.01 to 10.00

10.01 to 17.50

Iron, in micrograms per liter 

0 to 1

2 to 100

101 to 300

301 to 2,500

2,501 to 5,000

5,000 to 13,800

EXPLANATION

EXPLANATION

EXPLANATION

Area enlarged

ARKANSAS

Arkansas River

Arkansas River

Arkansas River

Base modified from U.S. Geological Survey digital data, 1:250,000

Universal Transverse Mercator projection, zone 15

Figure 104. Spatial distribution of selected chemical constituents in groundwater from the Western Interior Plains confining system in 

northern Arkansas.
274 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Sulfate

Sulfate concentrations generally were low throughout the 

Western Interior Plains confining system. Only three samples 

were higher than the secondary drinking-water regulation 

of 250 mg/L. Sulfate concentrations ranged from 0.02 to 

1,030 mg/L with a median of 4.7 mg/L (fig. 102; table 42). Out 

of 267 samples, 243 (91 percent) had concentrations less than 

50 mg/L. Cordova (1963) attributed sulfate in groundwater 

to oxidation of pyrite; however, Kresse and others (2012) 

hypothesized that appreciable sulfate concentrations results 

from gypsum dissolution. Sulfate concentrations increased 

with increasing dissolved-solids concentrations (fig. 103E). 

For dissolved-solids concentrations less than 100 mg/L, sulfate 

was less than 10 mg/L. For dissolved-solids concentrations 

between 100 and 200 mg/L, sulfate was less than 25 mg/L. 

All sulfate concentrations greater than 50 mg/L occurred at 

dissolved-solids concentrations greater than 200 mg/L. This 

is a region that was shown by Kresse and others (2012) to 

be under iron- and possibly sulfate-reducing conditions in 

which pyrite would be stable. Additionally, increases in sulfate 

generally correlated to increases in calcium/bicarbonate 

equivalent ratios more than 1.0 and up to 8.0. This correlation 

suggested that excess calcium not accounted for by dissolution 

of carbonate minerals may be derived from dissolution of 

gypsum.

Chloride

Chloride concentrations generally are low in groundwater 

throughout the Western Interior Plains confining system. 

Chloride concentrations ranged from 0.9 to 1,100 mg/L with 

a median concentration of 5.0 mg/L (fig. 102; table 42). Out 

of 282 samples, 195 (69 percent) were less than 10 mg/L, 

and only 5 samples exceeded the Federal secondary drinkingwater regulation of 250 mg/L. Residual salinity from the 

marine environment in which shales of the Atoka and Bloyd 

Formations were deposited generally has been flushed over 

time by infiltrating precipitation. In low permeability zones 

or hydraulically isolated areas that have not been flushed over 

time, higher salinity water can be released into the well bore. 

This raises chloride concentrations above the generally low 

concentrations found across much of the Western Interior 

Plains confining system. Chloride concentrations increase 

with increasing dissolved solids (fig. 103F). This suggests 

that higher chloride concentrations in groundwater are more 

likely in regions of more evolved groundwater with a longer 

residence time along a given flow path, affording greater rock/

water interaction over time. 

Conceptual Model of Groundwater Geochemical 

Evolution

A general analysis of abundant groundwater geochemical 

data enabled the development of a conceptual model for 

the evolution of groundwater geochemistry in the shallow 

Western Interior Plains confining system. Kresse and others 

(2012) used nonparametric statistical analysis to show that 

groundwater from the Atoka and Bloyd Formations have a 

similar geochemistry. This suggested that the geochemistry in 

both formations results from similarities in mineralogy of the 

interbedded sandstone and shale. Because 92 percent of the 

samples compiled for this report were from these formations, 

this general model may be applied to the system as a whole 

and is discussed in more detail in the following paragraphs. 

Kresse and others (2012) evaluated data from 127 

groundwater samples primarily from the Atoka and Bloyd 

Formations to construct a geochemical model for evolving 

water type. A plotting of water types along a continuum 

of increasing dissolved solids showed that major ion 

geochemistry is not random but follows a predictable pattern 

based on rock type and rock/water interaction. The continuum 

of increasing dissolved solids represents increased residence 

time in the aquifer system. The lowest pH values, ranging 

from 4.2 to 5.8, occurred in groundwater with dissolved-solids 

concentrations less than approximately 30 mg/L (fig. 105). 

Although chloride concentrations increased with increasing 

dissolved-solids concentrations, chloride was found to 

be the dominant anion almost solely for dissolved-solids 

concentrations less than 30 mg/L. The geochemistry of these 

samples resembled that of evaporated rainwater with minor 

addition of silica and trace metals (Kresse and Fazio, 2002). 

Much of this groundwater is theorized to be derived from 

carbonate-free sandstone units. Similar findings were noted 

in the Ouachita Mountains aquifer near Hot Springs (Garland 

County), where well-defined, thick sequences of quartz 

formations and shale formations allowed the association 

of unique groundwater chemistry for each rock type. 

Groundwater from the quartz formations was soft and acidic 

(7 of 11 samples had pH values less than 4.7 and 3 samples 

were less than 4.0), indicating a quartz source rock with little 

to no buffering capacity (Kresse and Hays, 2009).

In general, groundwater with dissolved-solids 

concentrations greater than 30 mg/L had bicarbonate as 

the dominant anion and shale as the dominant rock type. 

Groundwater with dissolved-solids concentrations between 

31 and 95 mg/L exhibited a mixture of calcium-bicarbonate 

and mixed-bicarbonate water types. For groundwater with 

dissolved-solids concentrations between 96 and 249 mg/L, 

calcium-bicarbonate was the dominant water type in 24 

of the 40 samples. A majority of the remaining samples 

had increasing sodium percentages and sodium as one of 

two major cations representing groundwater transitioning 

toward sodium as the dominant cation. For groundwater with 

dissolved-solids concentrations greater than 250 mg/L, 20 of 

51 samples were a sodium-bicarbonate water type with sodium 

percentages ranging from 52 to 99 percent of the total cations. 

The remaining samples primarily were calcium-bicarbonate 

water types with a few transitional water types (fig. 105). 

Kresse and others (2012) described the effects of 

reduction-oxidation (redox) processes in the Western Interior 

Plains confining system using redox-sensitive inorganic 

constituents and methane for 51 groundwater samples. 
Aquifers of the Interior Highlands 275

Using the same continuum of increased residence time for 

groundwater to investigate evolution of redox zonation in 

the aquifer system is informative and enables refining of the 

geochemical model. Shale formations in the Western Interior 

Plains confining system are rich in labile organic material, 

which drives the reduction of oxygenated water by aerobic and 

fermentation bacteria. As recharging water enters an aquifer 

system having abundant organic matter, oxygen first will 

be used as a terminal electron acceptor; followed by nitrate, 

manganese oxide, iron oxyhydroxide compounds, and sulfate; 

and finally carbon dioxide with the generation of methane. 

Depending on the available supply of electron donors (carbon) 

and electron acceptors (oxidizers), redox zonation can stop 

at any point along this continuum or proceed through each 

sequence to methane production (Kresse and others, 2012). 

Kresse and others (2012) noted that the highest nitrate 

concentrations occurred for groundwater with dissolved-solids 

concentrations less than approximately 100 mg/L. Conversely, 

the highest iron concentrations occurred in association with 

dissolved-solids concentrations greater than 90 mg/L. Data 

compiled for this report confirmed that nitrate concentrations 

generally were less than 0.5 mg/L for dissolved-solids 

concentrations greater than 100 mg/L. For dissolved-solids 

concentrations greater than approximately 90 to 100 mg/L, 

nitrate has been consumed, resulting in the prevalence of 

manganese- and iron-reducing conditions. Iron and manganese 

had well-defined inverse correlations with nitrate, thus 

confirming this assumption. As nitrate is depleted, iron and 

manganese oxides are reduced, releasing iron and manganese 

into solution. Iron concentrations generally increased to 

approximately 290 mg/L, at which point, iron concentrations 

steadily decreased to low and nondetectable concentrations 

for dissolved solids exceeding 500 mg/L (fig. 106A). Arsenic 

concentrations (fig. 106B) behaved in a similar fashion. Kresse 

and others (2012) hypothesized that beyond a dissolved-solids 

concentration of 290 mg/L, sulfate reduction dominates over 

iron reduction with free sulfide combining with iron (and 

arsenic) to precipitate as iron-sulfide minerals. 

0 100 200 300 400 500 600 700 800

Dissolved solids, in milligrams per liter

3

4

5

6

7

8

9

pH, in standard units

Dissolved

solids Water type 

EXPLANATION

Less than 30

31 to 95

96 to 249

Greater than 250

Sodium-chloride plus mixed-chloride

Calcium-bicarbonate plus mixed-bicarbonate

Calcium-bicarbonate plus transitional

Sodium-bicarbonate plus calcium-bicarbonate

Figure 105. Relation between dissolved-solids concentrations and pH values with a depiction of the evolution of chemical water types 

for groundwater from the Western Interior Plains confining system in northern Arkansas (from Kresse and others, 2012).
276 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

0 100 200 300 400 500 600 700 800

0 100 200 300 400 500 600 700 800

Dissolved solids, in milligrams per liter

0

1

2

3

Arsenic, in micrograms per liter

0

1

2

3

4

5

6

Iron, in milligrams per liter

Reduction of iron3+ to iron2+ Reduction of sulfate

Formation of iron-arsenic sulfide

Reduction of iron3+ to iron2+ Reduction of sulfate

Formation of iron-arsenic sulfide

A

B

From Kress and others, 2012

Figure 106. Relation between dissolved-solids concentrations and A, iron and B, arsenic concentrations in groundwater from the 

Western Interior Plains confining system in northern Arkansas.
Aquifers of the Interior Highlands 277

Biogenic methane was detected in 32 of 51 samples 

with 7 of the samples having methane concentrations 

greater than 0.5 mg/L (maximum of 28.5 mg/L). Methane 

concentrations increased with increasing dissolved-solids 

concentrations. Concentrations greater than 1.0 mg/L 

generally occurred at dissolved-solids concentrations 

more than 475 mg/L. Therefore, the conceptual model 

for geochemical evolution in the Western Interior Plains 

confining system is one where increased groundwater 

residence time in the shallow aquifer system drives rock/

water interaction, particularly cation exchange. This results 

in transitioning from a calcium- to a sodium-bicarbonate 

water type along the flow path. Microbial-mediated redox 

zonation similarly transitions with increasing residence 

time in the aquifer through oxygen consumption; reduction 

of nitrate, iron and manganese oxides, and sulfate; and 

eventually to the production of biogenic methane (Kresse 

and others, 2012).

In summary, water quality generally is good throughout 

the Western Interior Plains confining system. Groundwater 

with elevated iron, nitrate, sulfate, and chloride occurs 

in localized areas, depending on rock type and position 

along a flow path. Groundwater varies from a soft, slightly 

acidic type, typically encountered in wells completed in 

sandstone rocks, to a calcium-and sodium-bicarbonate 

water type dependent on the amount of cation exchange in 

the groundwater system. Reducing conditions are found 

throughout the Western Interior Plains confining system, 

predominantly for groundwater from shale rock, with a 

complete redox zonation from nitrate-reducing conditions to 

production of methane.

Springfield Plateau Aquifer

The Springfield Plateau aquifer (fig. 3) lies within 

the Springfield-Salem Plateaus section of the Ozark 

Plateaus (fig. 3; tables 2 and 5) and comprises a sequence 

of limestone and cherty limestone of Mississippian age. 

The Ozark Plateaus (Ozarks) are a region of unique and 

complex hydrogeology and physiography. The Ozarks are 

characterized by a predominantly mantled karst terrain 

where aquifer anisotropy and heterogeneity, and variability 

in aquifer hydraulic characteristics are the norms. This 

variability is noted on a small spatial scale where (1) 

groundwater-flow velocities vary from 10-6 ft/s to several 

feet per second, (2) a well may produce 0.01 gal/min or 

1,000 gal/min, (3) groundwater chemistry may not reflect 

interaction with the aquifer matrix compared in one 

location and nearby may be mineral saturated and actively 

precipitating authigenics, (4) surface-derived contaminants 

may be effectively ameliorated within a short distance or 

may travel great distances with little to no attenuation, 

and (5) a subsurface may be essentially lifeless or home 

to numerous cave-related species. Groundwater flow and 

quality within the Ozark Plateaus are controlled by (1) the 

lithologies of the rocks exposed at the surface that convey 

groundwater flow; (2) stratigraphic relations of these different 

lithologies; and (3) geologic structure, including the physical 

modifications to the rocks that have occurred over time.

Geologic Setting

The Ozarks are referred to locally and regionally 

as the “Ozark Mountains.” Geologic structure of the 

Ozarks, however, is characterized by a lack of any intense 

modification over an expanse of geologic time; therefore, 

the Ozarks generally are not considered a true mountain 

range. The great topographic relief in the area results from 

erosional dissection of the plateaus that has been controlled 

to a degree by presence of structural features such as faults 

and fracture zones as well as by lithology. The Ozarks were 

formed by a structural dome that has been uplifted during 

several periods since Precambrian time (Nunn and Lin, 2002; 

Tennyson and others, 2008; Cox, 2009). The core of the dome 

is in southeastern Missouri. Sedimentary units in Arkansas 

drape off of the southern and southwestern margins of the 

dome with gentle regional dips generally ranging from 10 to 

100 ft/mi and steeper dips being common near faults (Frezon 

and Glick, 1959). Widespread extensional fracturing, jointing, 

and faulting of Ozarks’ rocks occurred with uplift (Hudson and 

Cox, 2003), creating secondary porosity that has provided key 

nucleation points for initiation of dissolution of the carbonate 

rocks and karst development. 

The karstic bedrock of the region is overlain by 

weathered regolith that greatly varies in thickness from 

near zero in many areas to more than 100 ft. Areas of low 

topographic relief, including plateau tops and valley floors, 

tend to have greater thicknesses of regolith. Steep areas tend 

to have lesser thicknesses of regolith, although thicknesses 

are variable within all areas. The regolith mantles the 

underlying karst topography, which typifies the Ozarks’ karst 

and distinguishes the region from classic occurrences of karst 

elsewhere. The regolith is a clay-rich, typically low-permeable 

unit that contains variable amounts of chert. This material is 

derived from weathering of the original Mississippian and, 

in some areas, Pennsylvanian capping units and comprises 

refractory impurities and weathering products—predominantly 

chert and clay. The regolith generally is present as a silt-loam 

surface soil overlying a clay-loam subsoil, which can vary 

from being well-drained and exhibiting moderate permeability 

to very tight with low permeability. Chert constitutes up to 

90 percent of the regolith in some areas. The chert is present 

from sand to boulder size and is present as remnant layers that 

remain in weathered soil profiles. These layers often create 

barriers to infiltration of recharge water. Where present in 

considerable thickness, the regolith is a strong impediment 

to infiltration of precipitation and leakage from surface 

water, protecting the underlying karst aquifer from rapid 

input of surface-derived contaminants. However, the variable 

thickness of the regolith and the variable clay content render 

the protective qualities of the regolith somewhat sporadic 

throughout the Ozarks. 
278 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

The Boone Formation comprises the Springfield 

Plateau aquifer (Imes and Smith, 1990; Imes and Emmett, 

1994) and is exposed across most of the Springfield 

Plateau. However, outlier remnants of confining clastics 

are observed in the southern area of the Springfield Plateau 

where the upper Mississippian section is represented by the 

Batesville Sandstone and the Fayetteville Shale (Adamski 

and others, 1995; table 5). These sandstone and shale 

units typically are well-cemented and exhibit low matrix 

porosity and permeability but exhibit moderate porosity and 

permeability where weathered or highly fractured. Owing to 

the predominance of low-permeable shale and sandstone, the 

Upper Mississippian and Pennsylvanian strata are included in 

the Western Interior Plains confining system hydrogeologic 

unit to the south in the Boston Mountains (Imes and Smith, 

1990; Imes and Emmet, 1994; Adamski and others, 1995). 

The Boone Formation has a thickness of about 200–500 ft 

(McFarland and others, 1979) but is variably eroded across the 

plateau. The basal St. Joe Limestone Member of the Boone 

Formation is a relatively pure limestone. Above the St. Joe, the 

Boone Formation contains abundant chert, which can exceed 

70 percent of the interval. Matrix porosity and permeability of 

the Boone Formation are very low (Stanton, 1993), but where 

fracturing has occurred, carbonate dissolution has greatly 

enhanced porosity and permeability (Nunn and Lin, 2002). 

Solutioning of the fractures ultimately created the karst terrain 

that typifies the area.

Bedrock in the Ozarks shows evidence of multiple 

episodes of water movement and carbonate dissolution 

defining distinct karst development events through time 

(Stoffell and others, 2008). Exposure of Ordovician strata 

associated with the Ordovician-Mississippian unconformity 

resulted in dissolution and some paleokarst development. 

Widespread dissolution features associated with the lead 

and zinc ore-bearing fluids that moved from the Arkoma 

Basin (Leach and Rowan, 1986) are observed across the 

Ozarks region. Lead and zinc were mined commercially 

where faults conveyed mineral-saturated fluids up from 

depth. Hypogene indicators such as diagnostic calcite 

isotopic compositions (Brahana and others, 2009), collapse 

breccias (McKnight, 1935), and isotopic dating (Brannon and 

others, 1996) show that this episode of fluid movement and 

dissolution was a separate occurrence predating recent karst 

development. Exposure of Mississippian strata associated 

with the Mississippian-Pennsylvanian unconformity resulted 

in meteoric diagenesis followed by pedogenesis, regolith 

formation, and paleokarst development on the Pitkin 

Limestone (Webb, 1994). The Ozarks once again showed 

active karst development as uplift, denudation, and abundant 

precipitation; recharge initiated dissolution of soluble 

carbonate lithologies. 

The recent period of dissolution and karst development 

has had a very visible impact on the modern karst land surface, 

controlling subsurface flow and ultimately the surface flow in 

the region. The hydrogeology of the region is typical of karst 

with focused flow paths that are well connected to the surface 

and deliver water from input to discharge points at streams 

and springs at velocities of tens to thousands of feet per day 

(Funkhouser and others, 1999; Mott and others, 2000; Hudson 

and others, 2005; Hudson and Turner, 2007). Abundant karst 

features are apparent—ponors, losing stream reaches, springs, 

caves, and sink holes. However, recent karst development 

often reactivated and followed previous dissolution-enhanced 

flow paths that originally developed during ancient exposure 

periods (such as at the Ordovician-Mississippian and the 

Mississippian-Pennsylvanian unconformities; Webb, 1994) 

or hypogene episodes (such as Mississippi Valley Type ore 

emplacement; Leach and Rowan, 1986; Brannon and others, 

1996; Brahana and others, 2009). Another very important 

phenomenon caused by karst development is interbasin 

transfer of water. Dye tracing studies and observations of 

drainage-area and discharge relations show the abundant 

occurrence and transfer of groundwater across surface-water 

drainage-basin divides (Sullavan, 1974; Brahana and Davis, 

1998; Mott and others, 2000). Consideration of interbasin 

movement of water is an important point for protection and 

management of groundwater because contributing zones 

are not apparent at the surface, and contaminants can be 

introduced into groundwater from unexpected locations. This 

interbasin transfer has been shown to be driven more by local 

hydraulic gradients than by interbasin structure and karst 

development (Mott and others, 2000). 

Hydrologic Characteristics

The Springfield Plateau aquifer generally is unconfined 

across the Springfield Plateau and confined in the Boston 

Mountains. The highly soluble nature of carbonate rocks 

of the Boone Formation has given rise to development of 

the distinctive karst terrain and pervasive occurrence of 

karst features, such as caves, springs, and sinkholes. There 

is hydraulic connection of surface water and groundwater 

as well as the variable aquifer characteristics that typify 

the area (fig. 107). Karst aquifers are typified by a bimodal 

distribution of porosity—primary matrix porosity and small 

fracture porosity. This results in low porosity values for 

individual small-scale samples that are pervasive through 

the aquifer matrix and constitute a large proportion of total 

porosity. Secondary fractures and dissolution-enhanced 

porosity are significant within focused areas but represent a 

smaller proportion of the total porosity. The control of these 

porosity types on permeability leads to two end-member flow 

types—diffuse and focused flow (Alley and others, 2002; 

Ghasemizadeh and others, 2012). The bimodal nature of karst 

porosity enables spring and stream base flow to be maintained. 

The slower diffuse flow allows for sustained groundwater 

input to streams and springs, even during dry periods. The 

faster focused flow provides extremely rapid response and 

short transit times for precipitation events. An observable 

and prominent feature associated with karst aquifers is caves, 
Aquifers of the Interior Highlands 279

which serve as a window into the Springfield Plateau aquifer 

and allow the study of environments in the saturated and 

unsaturated zones. Large cavernous conduits and solution 

features allow for deep and rapid circulation of groundwater. 

Conduits and dissolution-enhanced fracturing help integrate 

flow to spring resurgences (Harvey, 1980). As a result, 

high-discharge springs are common throughout the exposed 

sections of the Springfield Plateau aquifer.

High hydraulic conductivities of as much as 1,000 

ft/d (Stanton, 1993) associated with the Springfield Plateau 

aquifer result from the development of secondary porosity 

through diagenetic processes, which particularly results from 

dissolution of bedrock along joints, fractures, and bedding 

planes rather than from primary, matrix-type porosity. 

Enhancement or enlargements of fractures, bedding planes, 

and conduits by carbonate dissolution is an active, ongoing 

process (Adamski and others, 1995). Hydraulic conductivity 

of matrix porosity blocks is much lower, on the order of 10−7

ft/d or even less (Van den Heuvel, 1979; Peterson and others, 

2002). Development of secondary porosity has produced 

anisotropic and heterogeneous hydraulic characteristics 

for the aquifer. The presence of smaller-scale matrix, 

Undifferentiated Ordovician units

St. Joe Limestone member of Boone Formation

Boone

Formation

Ozark confining unit 7

8

Sinkhole 10

1 Perched aquifer

above chert lense

Potentiometric

surface

2

3

3

4

5

6

6

Normal fault

9

Recharge

 Meteoric water 

 Diffuse infiltration

 - small aperature fractures

 - regolith

 Focused: localized

 - sinkholes

 - large aperature fractures

 Focused: indirect

 - losing stream

Groundwater flow

 Diffuse flow

 Conduit flow

Discharge

 Inter-aquifer flow

 Spring

 Evapotranspiration

 Withdrawals

EXPLANATION

1

2

3

4

5

6

7

8

9

10

Figure not to scale Modified from Kindinger and others, 2000

Figure 107. Conceptual model of karst hydrogeologic setting for the Springfield Plateau aquifer in northern Arkansas.
280 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

small-aperture fracture, and small-conduit porosity combined 

with the dissolution-enhanced conduits results in a bimodal 

permeability distribution. Water movement may be described 

relative to the two flow end members of diffuse flow and 

focused (conduit) flow previously defined. Because of the 

low rock-matrix hydraulic conductivity, a large fraction of 

groundwater transfer is through the focused-flow component 

of the aquifer (Imes and Smith, 1990; Kilpatrick and Ludwig, 

1990b). Rapid input of surface water, rapid-flow velocities, 

rapid mass transfer, and minimal attenuation of contaminants 

are associated with this component of flow. More timeaveraged flow, maintenance of streamflows during dry periods, 

low-flow velocities, and effective attenuation of contaminants 

are behaviors associated with the diffuse component of flow. 

Fracture and bedding-plane apertures typically decrease 

with depth as lithostatic pressure increases (Drogue, 1980). 

Correspondingly, groundwater storage, hydraulic conductivity, 

and well yields decrease with depth in the Springfield 

Plateau aquifer (Lamonds, 1972), and well depths rarely 

exceed 300 ft in the aquifer (Imes and Emmett, 1994). 

Most well depths associated with data compiled for this 

report were less than 200 ft. Average values of horizontal 

conductivity from groundwater simulations are 22 ft/d 

(Imes and Emmett, 1994) with vertical conductivities about 

an order of magnitude lower (Adamski and others, 1995). 

However, hydraulic conductivities as high as 886–2,100 ft/d 

occur locally (Vandike, 1997). Transmissivity values range 

from approximately 1,700 to 8,600 ft2

/d (Imes and Emmett, 

1994). Wells yields reflect the porosity types. Where wells 

intersect highly porous and permeable zones, yields of 10 

gal/min to more than 100 gal/min are common. Where wells 

are completed in zones with little secondary development of 

porosity and permeability, well yields are typically less than 

10 gal/min. Most wells yield less than 20 gal/min throughout 

the extent of the aquifer (Adamski and others, 1995; Peterson 

and others, 2002; McFarland and Prior, 2005; Gillip, 2007).

Most recharge to the Springfield Plateau aquifer is by 

infiltration of precipitation in the aquifer’s outcrop area. 

Where confined, recharge occurs by leakage through overlying 

units (Adamski and others, 1995). Recharge to the aquifer 

occurs as diffuse and focused recharge (Alley and others, 

2002; Healy, 2010). Diffuse recharge occurs by infiltration of 

precipitation through the overlying regolith; however, most 

potential recharge water moving through the soil zone is lost 

to evapotranspiration, particularly during the growing season 

(Brahana, 2011b). Diffuse recharge likely amounts to a small 

percentage of the total recharge compared to focused recharge 

through karst features such as sinkholes, fractures and 

conduits, and losing stream reaches (Alley and others, 2002; 

Brahana and others, 2005). The distribution of recharge is 

not well understood for the Springfield Plateau aquifer. Karst 

features allow for rapid recharge, thus allowing the influx 

of surface-derived contaminants into the aquifer with little 

attenuation (Jagucki and others, 2009). Consequently, karst 

aquifers such as the Springfield Plateau aquifer have a high 

susceptibility to contamination.

Discharge from the Springfield Plateau aquifer is 

primarily through springs, withdrawals by wells, and 

interaquifer flow to the underlying Ozark aquifer system 

(Branner, 1937; Harvey, 1980; Brahana and Davis, 1998; 

Czarnecki and others, 2009; Hudson and others, 2011; Vardy, 

2011). Seeps and springs are the predominant discharge 

points for the aquifer. Springs generally occur near the base 

of the Boone Formation coincident with structural lows and 

the underlying Ozark confining unit (Kilpatrick and Ludwig, 

1990a; Adamski and others, 1995; Murray and Hudson, 

2002; Bolyard, 2007; Hudson and others, 2011). Where the 

underlying Ozark confining unit is absent or incompetent, 

groundwater discharges from the Springfield Plateau aquifer 

to the underlying Ozark aquifer (Imes and Emmet, 1994). 

Groundwater withdrawals by pumping do not appear to have 

caused distinguishable differences in potentiometric surfaces 

over time in northern Arkansas (Gillip, 2007).

Water Levels

Long-term groundwater-level measurements for the 

Springfield Plateau aquifer are limited. Only one record exists 

that has more than 15 years duration and was measured at 

an interval adequate to capture seasonal variability (fig. 108; 

see fig. 109 for location of the well). Direct correlation of 

seasonal water-level variations is weak (R2 = 0.063). The 

potentiometric surface (Imes and Emmet, 1994) reflects 

relatively higher groundwater levels in high-altitude areas 

such as Benton, Carroll, Boone, Washington, Madison, and 

Newton Counties. A lower potentiometric surface occurs in 

lower altitude areas west towards Oklahoma, south towards 

the Arkansas River Valley, and east towards the Mississippi 

Alluvial Plain. An NWIS query revealed 543 wells with both 

land-surface altitude and water-level data. The potentiometric 

surface for the aquifer generally reflects topography and 

exhibits a strong correlation with land-surface altitude (R2 = 

0.98). However, a regional correlation between land-surface 

altitude and groundwater level below land surface cannot fully 

explain groundwater movement in the Springfield Plateau 

aquifer at more localized scales. Small-scale variation in flow 

is the result of fractures, faults, conduits, and other structures 

that facilitate or vertically and laterally impede flow (Leidy 

and Morris, 1990b; Brahana and Davis, 1998; Turner and 

Hudson, 2008; Hudson and others, 2011). Numerous dyetracing studies have shown hydraulic connectivity across 

watershed divides (interbasin flow) (Adamski and others, 

1995; Brahana and Davis, 1998; Adamski, 2000; Gillip, 

2007; Brahana, 2011a, b). This connectivity can occur across 

considerable distances outside a given watershed (Mott and 

others, 1999; Murray and Hudson, 2002). 
Aquifers of the Interior Highlands 281

Water Use

The Springfield Plateau aquifer is widely used 

throughout northwestern Arkansas. Historically, the 

aquifer was used extensively for domestic, public-supply, 

commercial, and industrial purposes. Several towns were 

sited near areas of large springs, which were frequently used 

to power grain and lumber mills and to supply residents 

of the growing population. Several domestic and livestock 

wells were recorded in Carroll and Boone Counties (Brahana 

and others, 1991, 1993). At the time of this report (2013), 

numerous domestic and livestock wells were still in use. 

Because domestic and water-supply systems serving less 

than 50,000 gal/d are not required to report water use, total 

use of groundwater from the Springfield Plateau aquifer is 

unknown. The wider distribution of surface-water systems 

has largely supplanted use of the Springfield Plateau aquifer 

as a source of water supply. There were three public-supply 

wells in Carroll County reporting use from the Springfield 

Plateau in 2010. A limited number of small communitysupply systems, as well as restaurants, resorts, recreational 

vehicle parks, and shops, are registered as using this aquifer 

with ADH (Lyle Godfrey, Arkansas Department of Health, 

written commun., 2012). 

Water Quality

Groundwater quality resulting from rock/water 

interaction in the Springfield Plateau aquifer generally is good. 

The water can be used without treatment as an important 

source of water supply throughout the Ozarks, although low 

yields limit its use primarily to domestic supply. Iron is the 

most frequent naturally derived constituent exceeding Federal 

drinking-water regulations (Lamonds, 1972; Steele, 1981). 

Hardness related to dissolved carbonate minerals can present 

problems related to scaling of pipes, water heaters, and 

other plumbing fixtures (Lamonds, 1972; Leidy and Morris, 

1990b; Imes and Emmett, 1994; Adamski, 2000). Surfacederived, anthropogenic contaminants primarily related to 

livestock agricultural activities also affect water quality as a 

result of rapid influx of surface water with little attenuation 

in many areas. The aquifer constitutes a large part of the 

karst landscape of the Ozark Plateaus. This karst network 

creates a hydrologic system of great complexity with intimate 

groundwater/surface-water interaction, which makes the 

system highly vulnerable to surface-derived contamination. 

Anthropogenic contaminant sources can affect the natural 

groundwater geochemistry and water quality. Common 

contaminants include nutrients, fecal bacteria, and pesticides. 

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

Year

411

412

413

414

415

416

417

418

419

420

421

422

Water level, in feet above

National Geodetic Vertical Datum of 1929 

16N12W25DCB1 Webb Cabin

Figure 108. Water levels in a well completed in the Springfield Plateau aquifer in northern Arkansas.
282 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Agriculture in the form of beef and dairy cattle, swine, 

and poultry operations accounts for the greatest land-use 

activity in this region. Contamination of the aquifer often 

is derived from these activities (Peterson and others, 2000). 

Nationally, Arkansas ranks second in poultry production, 

and the three top counties for agricultural sales in Arkansas 

are located in the northwestern region of the State (U.S. 

Department of Agriculture, 2010). Another common source 

of contamination is septic systems, which are the primary 

means of domestic waste treatment in rural and in many 

suburban areas in the Ozarks. The thin, poorly developed 

soils in the Ozarks make installation of effective, functioning 

septic systems a challenge, resulting in frequent contamination 

of groundwater. A vulnerability map created for Arkansas 

(Arkansas Soil and Water Conservation Commission, 1991) 

generally listed the entire Ozarks of northern Arkansas at the 

highest vulnerability index. The spatial distribution of karst 

features, as well as the variable thickness and composition 

of soils in the overlying regolith, results in variable vertical 

permeability and resultant variable vulnerability. 

General Geochemistry and Water Quality

The predominant carbonate rock hosting the Springfield 

Plateau aquifer is limestone. Numerous reports have 

documented the dominant calcium-bicarbonate water type 

resulting from dissolution of the parent rock (Lamonds, 1972; 

Leidy and Morris, 1990b; Imes and Emmett, 1994; Adamski, 

1997; Huetter and others, 1997). Groundwater derives acidity 

from carbonic, nitric, sulfuric, and other acids formed from 

natural and anthropogenic sources of carbon dioxide, sulfur 

dioxide and hydrogen sulfide, and nitrogen oxides. Gas 

sources include vehicle, industrial, and other anthropogenic 

emissions, in addition to carbon dioxide and organic acids 

derived from plant respiration and organic-matter decay in 

soil. This acidity drives dissolution of limestone and resultant 

increases in dissolved calcium and bicarbonate concentrations 

(Wagner and others, 1975). Because limestone is the dominant 

rock type of the Springfield Plateau aquifer and dolomite is 

more common in the Ozark aquifer, researchers frequently 

use calcium/magnesium ratios to differentiate groundwater in 

these two aquifers. Dolomite has equal parts of calcium and 

magnesium, and groundwater from predominant dolostone 

formations composing the Ozark aquifer generally reflects 

this one-to-one ratio. These ratios are considerably higher in 

groundwater from limestone of the Springfield Plateau aquifer. 

Calcium/magnesium equivalent ratios for 134 samples from 

the Springfield Plateau aquifer ranged from 1.2 to 359 with a 

median of 17. This median ratio reflects the higher calcium/

magnesium ratio typical of groundwater from the Springfield 

Plateau aquifer. All ratios, except for the minimum of 1.2, 

were greater than 2.0, and all but 11 of the 134 samples 

were greater than 5.0. No strong spatial trend was evident in 

calcium/magnesium ratios, though a greater density of lower 

ratios occurs near the contact of the Springfield Plateau with 

Ordovician-age formations of the Ozark Plateaus in Boone 

and Independence Counties (fig. 109). Limestone often 

contains varying amounts of magnesium. Consequently, 

lower calcium/magnesium ratios in some areas result from a 

higher admixture of magnesium in the limestone or migration 

of Ozark aquifer groundwater across the Chattanooga 

confining layer in areas where it is absent or incompetent. 

Additionally, some wells labeled as completed in the 

Springfield Plateau aquifer may penetrate and receive water 

from upper units of the Ozark aquifer. The relation of calcium 

and bicarbonate shows the overall strong calcium-bicarbonate 

type water of the Springfield Plateau aquifer. Calcium 

was strongly correlated to bicarbonate with an R2

 of 0.78. 

The addition of magnesium to this analysis improved the 

correlation by only a small degree to an R2 of 0.81 (fig. 110).

Low pH from precipitation recharging the aquifer is 

quickly buffered by carbonate minerals in the overlying 

regolith and bedrock of the Boone Formation. Values of pH 

subsequently increase to values exceeding 6.0 throughout 

the aquifer. Values of pH ranged from 6.0 to 9.1 with a 

median of 7.2 (table 43). Sixty-seven percent (110 of 163 

samples) of the samples had pH values greater than 7.0. 

No correlation was established between dissolved-solids 

concentrations and pH values, and the entire range of pH 

values was found throughout the range of dissolved-solids 

concentrations (58 to 515 mg/L), which strongly suggests that 

buffering occurs in the weathered regolith and unsaturated 

bedrock prior to recharging the aquifer. Knierim and others 

(2011, 2013) and Pollock and others (2011) characterized 

basic geochemical changes, nutrient and carbon alterations, 

and isotopic behavior as groundwater moved through soils 

into diffuse and focused karst flow paths in the Ozarks. 

They noted modification of acidity and behavior of soil 

and regolith as a storage zone for organic carbon and other 

nutrients. For example, median calcium concentrations in 

the soil and regolith zones for sites from two different study 

locales were 5.0 and 5.9 mg/L, respectively, and median 

dissolved inorganic carbon (predominantly bicarbonate) 

concentrations were 13.1 and 1.7 mg/L, respectively. These 

results indicated considerable modification of recharge water 

in the soil and regolith zones prior to reaching the epikarst. 

Pollock and others (2011) used hydrograph separation mixing 

models to rigorously quantify source-water contributions to 

streams in caves and flow from springs during storm events 

and to measure evolution of groundwater geochemistry. A 

key finding was the importance of the soil and regolith zone 

on groundwater chemistry very early on for karst flow paths. 

Soil and regolith were found to be of particular importance 

in controlling chemistry during high-flow events. A metadata 

analysis for this study showed no spatial correlation for the 

distribution of pH values throughout the aquifer based on data 

compiled for this report.
BENTON

NEWTON

STONE

MADISON

BOONE

MARION

WASHINGTON

CARROLL

CRAWFORD VAN BUREN

SEARCY

BAXTER

16N12W25DCB

0 200 400 KILOMETERS

0 200 400 MILES

94°00' 92°00' 93°00'

36°20'

36°00'

Area enlarged

ARKANSAS

Base modified from U.S. Geological Survey digital data, 1:250,000 Geo

Universal Transverse Mercator projection, zone 15

EXPLANATION

Atoka FormationBloyd Shale and Prairie Grove 

Member of the Hale Formation

Cane Hill Member of the Hale FormationCretaceous rocks

Chattanooga Shale (Lower Mississippian and 

Upper Devonian), Clifty Limestone (Middle Devonian), and Penters Chert (Lower Devonian)

Boone FormationMoorefield Formation

Pitkin Limestone

Ruddell Shale Cason S

OrdoPlatt(Mid

Cotter a

Powell St. Pete

(Mid

Lafferty, St. Clair, and Brassfield Limestones

Water bodies

Geologic formations of the Ozark Plateaus

Undiffer

Figure 109. Spatial distribution of calcium/magnesium ratios (from milliequivalent concentrations) in groundwater from the Springfield Plateau aquif
284 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

0 1 2 3 4 5 6 7

Calcium plus magnesium, in milliequivalents per liter

0 1 2 3 4 5 6

Calcium, in milliequivalents per liter

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

Bicarbonate, in milliequivalents per liter

R2 = 0.7778 R2

 = 0.8104

A B

Figure 110. Relation of bicarbonate to A, calcium and B, calcium plus magnesium in groundwater from the Springfield Plateau aquifer 

in northern Arkansas.

Table 43. Descriptive statistics for selected chemical constituents in groundwater from the Springfield Plateau aquifer in northern 

Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 0.04 55 109 20.4 134

Magnesium (mg/L) 0.01 1.7 21 3.31 134

Sodium (mg/L) 0.2 4.3 51 6.38 132

Potassium (mg/L) 0.1 1.2 15 1.58 132

Bicarbonate (mg/L) 39 164 316 65 119

Chloride (mg/L) 1.2 7.6 47 6.8 134

Sulfate (mg/L) 0.48 3.9 90 11.2 134

Silica (mg/L) 5.3 9.7 19 1.85 129

Nitrate (mg/L as nitrogen) 0.01 1.8 20 2.77 166

Dissolved solids (mg/L) 58 193 515 69 134

Iron (μg/L) 0.05 5.6 3,300 338 126

Manganese (μg/L) 0.13 0.13 1,410 198 129

Arsenic (μg/L) 0.03 0.03 2.52 0.39 90

Hardness (mg/L as calcium carbonate) 0.1 140 323 54 115

Specific conductance (μS/cm) 102 349 693 112 161

pH (standard units) 6.0 7.2 9.1 0.5 163
Aquifers of the Interior Highlands 285

Adamski (2000) noted that groundwater from springs 

and wells was geochemically different. In general, median 

concentrations of dissolved solids, calcium, magnesium, and 

bicarbonate were greater in samples from wells than from 

springs. Additionally, groundwater from wells was more 

saturated with respect to calcite than from springs. Springs 

typically receive a large component of flow from focusedflow conduits in the flow system. Rapid flow through large 

conduits in spring basins results in minimal contact with 

carbonate rock. This is because the size of the conduits 

(solution channels) and shorter residence times result in a 

lesser degree of rock/water interaction for springs. In contrast, 

the low yield of many wells indicates that most boreholes 

receive a large component of flow from the more diffuse part 

of the flow system. This diffuse flow is through small conduits 

and fractures and is characterized by lower permeability, 

increased residence time, and increased rock/water interaction 

(Adamski, 2000; Pollock and others, 2011; Knierim and 

others, 2013). 

Water-quality monitoring during storm events 

substantiates the shorter residence time and reduced rock/

water interaction for groundwater moving through conduits 

that feed springs. Generally, concentrations of rock-derived 

dissolved constituents (for example, calcium, magnesium, 

and bicarbonate) have been observed to decrease substantially 

during storm events within hours of the storm. Conversely, 

concentrations of surface-derived constituents (for example, 

nitrate, chloride, phosphate, fecal bacteria) often increase over 

the rise and peak of storm events (Widmann, 1982; Steele 

and others, 1985; Adamski, 1987; Parr, 1987; Wickliff, 1988; 

Davis and others, 2000; Pollock and others, 2011; Knierim 

and others, 2013). Pollock and others (2011) described marked 

changes in groundwater chemistry for storm events compared 

to base-flow events. There was less rock/water interaction 

modifying recharging waters during the rapid input stormevent periods, but there was effective delivery of dissolved 

constituents such as nitrate from the surface and regolith 

zones. For example, median calcium and dissolved inorganic 

carbon concentrations were 38.4 mg/L and 24.8 mg/L, 

respectively, during base flow, and 20.3 mg/L and 11.8 mg/L, 

respectively, during times of stormflow. By comparison, the 

nitrate concentration did not change substantially but remained 

near 2.7 mg/L for base flow and stormflow. Nitrate remained 

essentially constant even as flows increased by orders of 

magnitude, indicating considerable transport of dissolved mass 

into and through the aquifer during storm events.

Nitrate

The terms “elevated,” “background,” and “baseline” 

as applied to groundwater nitrate concentrations can, from a 

quantitative perspective, have different meanings in different 

comparative contexts and defining these terms as used for the 

discussion of nitrate in groundwater of the Ozarks is of great 

importance. The typical contexts are comparing watershed 

to watershed, within a watershed, between different land 

uses, land-use intensity, time steps, areas of differing scales, 

and between contaminant source inputs. One definition 

of “elevated” nitrate would be the Federal MCL of 10.0 

mg/L as nitrogen, which was established based on potential 

health effects from consumption of high-nitrate water. This 

definition, however, does not address concentrations that are 

greater than background levels and can result in environmental 

effects, such as promotion of algal growth in streams. 

Several studies of the Springfield Plateau aquifer have 

been conducted in areas that are dominantly forested and 

provide a better understanding of representative background 

nitrate concentrations in relatively pristine areas. Steele (1983) 

sampled 74 springs in three relatively pristine (forested) 

areas in northwestern Arkansas with mean and median nitrate 

concentrations of 0.32 mg/L and 0.15 mg/L as nitrogen, 

respectively. Steele and Adamski (1987) sampled 48 springs 

and noted that seasonal mean nitrate concentrations in 

dominant forested areas ranged from 0.16 to 0.40 mg/L for 

the same sites sampled in different seasons. None of these 

sites were completely forested because there were homes with 

septic systems located throughout the spring basin; therefore, 

a true background concentration is probably less than this 

range of concentrations. Kresse and others (2011) established 

what they considered a conservative estimate for a background 

nitrate concentration of 0.40 mg/L as nitrogen based on review 

of data in these previous studies. The term “elevated” nitrate 

as used in this report refers to nitrate concentrations exceeding 

the 0.40 mg/L background concentration estimated in the 

above studies.

Because soils are generally thin, rocky, and poorly 

suited for row-crop farming, poultry, cattle, and swine 

production is the predominant agricultural activity in the 

Ozarks. The karst terrain enables rapid infiltration of surface 

water into the subsurface, which renders groundwater highly 

vulnerable to surface-derived contamination. This results 

in widespread influx of nutrients and fecal bacteria from 

waste generated by agricultural activities and septic tanks. 

Nitrogen and phosphorus associated with these activities 

are the dominant nutrients posing environmental threats to 

surface and subsurface waters in the Ozarks. Because most 

of the phosphorus is strongly bound to clays and organic 

matter in soils, little phosphorus moves in the dissolved state. 

Conversely, nitrate is the most soluble form of nitrogen and 

is conservative in transport. Consequently, nitrate is more 

persistent than phosphorus in the subsurface and poses the 

largest threat to groundwater resources in the Ozarks. 

Numerous studies in northwestern Arkansas have 

reported on the occurrence, sources, transport pathways, and 

fate of nitrate in the Springfield Plateau aquifer (Keener, 

1972; Coughlin, 1975; MacDonald and others, 1976; Ogden, 

1979; Cox and others, 1980; Leidy and Morris, 1990b; Davis 

and others, 2000). Most of these studies found a wide range 

of elevated nitrate concentrations with a small percentage 

that exceeds the Federal MCL of 10.0 mg/L. Most studies 

attributed nitrate contamination to an abundance of septic 

systems and chicken houses in northwestern Arkansas. Other 
286 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

studies have attributed elevated nitrate and other surfacederived contaminants to urban sources (Gillip, 2007; Kresse 

and others, 2011; Vardy, 2011). Concentrations of nitrate in 

166 samples from the Springfield Plateau aquifer compiled 

for this report ranged from 0.01 to 20 mg/L with a median of 

1.8 mg/L. Only three samples exceeded the Federal MCL of 

10 mg/L. Contrary to most of the aquifers of the Coastal Plain, 

the occurrence of nitrate in the Springfield Plateau aquifer was 

not correlated with well depth. Concentrations of more than 

5.0 mg/L as nitrate were found uniformly throughout the range 

of well depths from as shallow as 5 ft upwards to 250 ft.

Several variables can affect the transport of nitrate 

to the subsurface including nitrogen form and loading, 

soil type, regolith thickness, attenuation processes such as 

denitrification, plant uptake, as well as presence of karst 

features and other focused-flow pathways. A well-defined 

relation was noted for the Springfield Plateau aquifer between 

increases in agricultural land use and increases in nitrate. 

Adamski (1997) used regression analysis that revealed a 

positive correlation between nitrate concentrations and percent 

agricultural land use in 103 sampled sites across the Ozark 

Plateau in Arkansas, Kansas, Missouri, and Oklahoma. Kresse 

and others (2011) similarly applied regression analysis using 

groundwater samples from 823 sites (springs and wells) in 

northern Arkansas that showed a similar positive, though 

weak linear, correlation between the two variables. Although 

the sites included samples from groundwater throughout 

the Ozark Plateaus aquifer system, most were from the 

Springfield Plateau aquifer. Bar graphs also were employed 

to show a positive relation between increasing mean nitrate 

concentrations for 10 percent incremental increases in 

agricultural land use using the same dataset (fig. 111A). An 

overall mean nitrate concentration of 2.4 mg/L was exceeded 

by the mean nitrate concentration for agricultural land use that 

exceeded 40 percent. Most domestic wells that were sampled 

had a septic system nearby that could affect the groundwater 

sample from the well. Thus, inclusion of data from domestic 

wells can skew the analysis, regardless of surrounding land 

use. To overcome this problem, the regression of nitrate and 

land use was conducted for spring sites only, which generally 

would not be associated with nearby septic systems. The 254 

spring sites in the database were extracted and similarly tested 

for relation to agricultural land use. For springs, a much more 

consistent stepwise increase in nitrate concentration was noted 

for increasing agricultural land use, indicating the well data 

were affected by septic systems. Hence, the water chemistry of 

springs better reflects the influence of increasing agricultural 

land use (fig. 111B). The mean nitrate concentration for 

all spring sites was 2.6 mg/L, which was exceeded for all 

agricultural land-use percentage categories more than 40 

percent, similar to that of wells and springs. Higher mean 

nitrate concentrations occurred for each percent agricultural 

land-use category as compared to both wells and springs. The 

spring data showed that effects on nitrate concentrations in 

groundwater were discernible at any level of agricultural land 

use. Even at the lowest agricultural land-use category from 

0 to 10 percent, the mean nitrate concentration for 46 samples 

was 0.9 mg/L, almost twice the background concentration 

of 0.4 mg/L. This finding demonstrates the effects of even 

small land-use changes on the concentration of nitrate in 

groundwater and indicates that agricultural land use of more 

than 40 percent has an effect on groundwater quality in the 

Springfield Plateau aquifer.

Elevated nitrate concentrations in previous groundwater 

studies of the Springfield Plateau aquifer were attributed to 

karst features that allow rapid movement of groundwater with 

minimal attenuation of surface-derived contaminants. None of 

these studies, however, produced data to quantitatively test the 

influence of karst. One problem in assessing other variables 

affecting the occurrence and concentration of nitrate was the 

overriding variable of land use (Adamski, 1997; Kresse and 

others, 2011). To separately test the influence of karst terrain 

features on nitrate transport in dominant agricultural land-use 

areas, Kresse and others (2011) used the density of mapped 

sinkholes as a surrogate representing the degree of karst 

development in north-central Arkansas (Newton and Searcy 

Counties). Only springs were sampled to reduce the local 

influence of septic systems. Sampling locations were limited 

to agricultural land-use areas to remove land use as the main 

control on nitrate occurrence. Following these constraints, 

34 springs were sampled in an area of highly developed karst 

as indicated by a high density of mapped sinkholes (Group 

I), and 22 springs were sampled in an area of less developed 

karst as indicated by an area devoid of mapped sinkholes 

(Group II). A statistically significant difference (p<0.01) 

occurred between the two groups; nitrate concentrations were 

greater for Group I springs. A weak point in the analysis was 

that total acres of agricultural land use were greater in Group 

I than in Group II, indicating that land use likely remained 

a controlling variable between the two sites. Regression 

analysis of nitrate concentrations from all springs did show 

a positive correlation to agricultural land use. To account for 

this land-use inconsistency, an analysis of covariance was 

conducted to investigate the importance of karst development 

as an additional important variable in nitrate occurrence. 

The analysis revealed that nitrate concentrations for Group 

I springs were greater than Group II springs for increasing 

agricultural land use (fig. 112). The occurrence of karst 

features accounted for approximately 12 percent of the 

variation between the two groups. This indicates that while 

nitrate concentrations in springs generally increase with 

increasing agricultural land use, concentrations generally are 

greater in areas where karst development (represented by 

sinkholes) is greater. The occurrence of sinkholes and other 

karst features thus provided more direct and rapid transport of 

contaminants to groundwater (Kresse and others, 2011).
Aquifers of the Interior Highlands 287

0–10 10–20 20–30 30–40 40–50 50–60 60–70 70–80 >80

0–10 10–20 20–30 30–40 40–50 50–60 60–70 >70

Agricultural land use, in percent of total land use

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Mean nitrate, in milligrams per liter (mg/L) as nitrogen

0

1

2

3

4

5

6

From Kresse and others, 2011

B. Springs

A. Wells and springs

105

68

96

88

119

131

93 78

42

Mean = 2.4 mg/L

46

22

34

35

44

30

25

10

Mean = 2.6 mg/L

EXPLANATION

105 Number of samples

Figure 111. Relation of agricultural land use in percent of total land use to mean nitrate concentrations in groundwater from A, wells 

and springs and B, springs in the Ozark Plateaus aquifer system in northwest Arkansas.
288 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Nitrate concentrations in the Springfield Plateau and 

Ozark aquifers have been compared in several studies, and 

higher mean and median concentrations have consistently 

been noted for the Springfield Plateau (Leidy and Morris, 

1990b; Smith and Steele, 1990; Steele and McCalister, 

1990, Adamski, 1997; Huetter and others, 1997; Kresse 

and others, 2011). For example, mean and median nitrate 

concentrations in 190 samples taken from the Springfield 

Plateau aquifer were 2.9 and 1.8 mg/L, respectively, compared 

to 0.47 and 0.10 mg/L, respectively, for 101 samples from 

the Ozark aquifer (Kresse and others, 2011). Most of the 

studies referenced above were in northwestern Arkansas, 

where the Ozark aquifer is confined and often overlain by 

exposures of the Boone Formation. Lower concentrations in 

the Ozark aquifer were attributed to protection from overlying 

formations. However, in areas of northeastern Arkansas and 

southeastern Missouri where the Ozark aquifer is exposed, 

mean and median nitrate concentrations remained low, 

similar to where the aquifer is confined (Kresse and others, 

2011) (see section “Ozark Aquifer”). This finding suggests 

greater vulnerability to surface-derived contaminants for the 

Springfield Plateau aquifer compared to the Ozark aquifer. 

No definitive attributes have been identified to explain the 

higher vulnerability of the Springfield Plateau aquifer because 

the geology for both aquifers hosts abundant karst features 

(sinkholes, springs, and losing streams).

Recent research in northwestern Arkansas has been 

conducted at plot scale for assessing fate of nitrate in the 

Springfield Plateau aquifer (Peterson and others, 2002; Laincz, 

2011). In these studies, nitrate transport was traced from its 

source through active microbial zones in soil, regolith, and 

epikarst, and ultimately into bedrock solution channels. The 

purpose was to determine controls on nitrate transport and 

the effectiveness of various zones in the aquifer system in 

removing nitrate. Results from one study indicated piston 

flow in the soil matrix with nitrate moving in pulses and the 

soil serving as a reservoir for nitrate (Peterson and others, 

2002). Another study documented nitrate attenuation processes 

(denitrification) in the interflow zone between the soil and 

focused-flow (bedrock) zones, which can remove as much as 

33 percent of infiltrating nitrate (Laincz, 2011).

Bacteria

The increasing occurrence of pathogens in groundwater 

from the Springfield Plateau aquifer has been one of the 

primary water-quality factors limiting its use (Knierim and 

others, 2013).The potential occurrence of pathogens in 

groundwater usually is indicated by surrogate measurement 

of indicator bacteria, for example fecal coliform, fecal 

streptococcus, and Escherichia coli (E. coli). Fecal indicator 

bacteria commonly are detected in groundwater from the 

aquifer and are detected with great frequency in springs, 

where conduit flow and rapid transport prevent effective 

filtering. Bacteria in springs and wells in northwestern 

Arkansas have been documented at rates ranging from 42 to 

80 percent of the sampling sites (Keener, 1972; Coughlin, 

1975; MacDonald and others, 1976; Ogden, 1979; Cox and 

others, 1980; Leidy and Morris, 1990b; Davis and others, 

0 10 20 30 40 50 60 70

Agricultural land use, in percent of total land use

0

1

2

3

4

5

6

7

Nitrate, in milligrams per liter as nitrogen

Group I springs

Group II springs

From Kresse and others, 2011

Figure 112. Analysis of covariance for nitrate concentrations and agricultural land use for Group I (highly developed karst) and Group 

II (less developed karst) springs.
Aquifers of the Interior Highlands 289

2000). Bacteria sources are related to agricultural and urban 

land use, and bacteria survival and transport in the aquifer are 

controlled by degree of karst development, hydrologic flow 

condition, and sediment concentrations (Marshall and others, 

1998). Davis and others (2005) found that fecal-coliform 

bacterial concentrations, including E. coli, were controlled 

by groundwater-flow conditions with bacteria concentrations 

varying by several orders of magnitude from base-flow to 

storm-flow conditions. Bacteria concentrations in spring 

water rapidly increased during the rising limb of stormevent hydrographs prior to breakthrough of nitrate and other 

conservative constituents, and the concentrations declined 

prior to the falling limb of the storm. Bacteria likely resided 

within sediment in the groundwater system, and the bacteria 

flux was associated with resuspension of sediment during the 

onset of turbulent flow. The survival period for bacteria in 

groundwater was at least 4 months (Davis and others, 2005).

Sediment

Sediment, especially clay, is a contaminant that is 

virtually nonexistent in clastic aquifers in the State but is an 

important contaminant in karst settings, particularly from an 

ecosystem standpoint. Sediment commonly is associated with 

karst environments in urban land-use settings of the Ozarks. 

Sediment also is important in facilitating bacterial transport 

(Marshall and others, 1998; Davis and others, 2005). Gillip 

(2007) described large volumes of sediment that moved 

through karst and caves near urban areas in northwestern 

Arkansas as development denuded the landscape, exposing 

and enabling mobilization of the clayey regolith. Individual 

storm events were observed to deposit more than 3 ft of 

sediment in caves with considerable effects on the karst 

ecosystems. Gillip (2007) also showed the dynamic nature 

of sediment transport in karst as noted by deposition 

followed by removal of sediment during succeeding lowerprecipitation events. Caving expeditions coupled with surface 

reconnaissance showed movement of sediment through 

fractures and conduits directly into caves during urbandevelopment activities (Phillip D. Hays, U.S. Geological 

Survey, written commun., 2013). Ting (2005) used europiumlabeled clays to demonstrate the effectiveness of suspendedphase transport in karst conduits and showed that the average 

transport velocity for a given mass of suspended material 

was more than the average transport velocity for dissolved 

material. Ting hypothesized that this discrepancy was the 

result of size exclusion and rapid preferential movement of 

suspended material through larger conduits.

Pesticides

Because of the limited use of pesticides in the Ozarks 

relative to its pervasive use in row-crop areas of eastern 

Arkansas, very little sampling has been performed to 

document the occurrence of pesticides in groundwater from 

the Springfield Plateau aquifer. One regional study sampled 

for pesticides in groundwater from the Ozark Plateaus in 

Arkansas, Kansas, Missouri, and Oklahoma (Adamski, 

1997). Pesticides were detected in 80 of 229 (35 percent) 

groundwater samples from 73 of 215 sites (9 sites in northern 

Arkansas). Twenty pesticides were detected, with a maximum 

of 5 detected in any one sample. The most commonly detected 

pesticides were tebuthiuron (31 samples), atrazine (30), 

prometon (25), desethylatrazine, a metabolite of atrazine (19), 

and simazine (18). These are herbicides that commonly are 

used on pastures and other noncrop areas. Pesticides were 

detected statistically (p<0.01) more often in groundwater from 

the Springfield Plateau aquifer than from the Ozark aquifer 

(Adamski, 1997). Pesticide detections additionally were 

related to nitrate concentrations in samples from agricultural 

sites. Median nitrate concentrations were statistically greater 

in samples with pesticide detections, further substantiating the 

increased vulnerability of the aquifer to surface contamination.

Iron

Iron concentrations in 126 samples from the Springfield 

Plateau aquifer ranged from 0.05 to 3,300 μg/L with a median 

of 5.6 μg/L (fig. 113; table 43). Only five samples had iron 

concentrations exceeding the Federal secondary drinkingwater regulation of 300 μg/L. Potential sources include: 

(1) iron mobilized from overlying regolith that contains 

abundant iron oxyhydroxide minerals that gives the unit its 

prevalent bright red coloration, (2) weathering of abundant 

pyrite that occurs in the Boone Formation limestone, and 

(3) iron sulfides associated with the Mississippi Valley Type 

ore mineralization that is common along fault zones in the 

Ozarks. The oxidation of iron-sulfide minerals as a source of 

iron is unlikely because of an observed inverse relation of iron 

and sulfate concentrations (graph not shown). Mobilization 

of iron from the regolith with onset of reducing conditions 

may explain elevated iron in isolated areas. This process is 

particularly common near landfills, waste lagoons, and other 

sources of abundant organic matter that provides a substrate 

for microbial activity using terminal electron acceptor 

processes (Hobza, 2005; Bolyard, 2007; Wagner, 2007). 

Regardless of the source, iron concentrations generally are low 

throughout the Springfield Plateau aquifer.
290 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Chloride

Chloride concentrations for 134 sites in the Springfield 

Plateau aquifer ranged from 1.2 to 47 mg/L with a median 

of 7.6 mg/L (fig. 113; table 43). Imes and Emmett (1994) 

reported concentrations generally are less than 10 mg/L in 

the aquifer throughout the Ozark Plateaus. Several studies 

noted the co-occurrence of nitrate and chloride in the aquifer, 

indicating that chloride may be derived from the same 

sources as nitrate (Ogden, 1979; Davis and others, 2000; 

Kresse and others, 2011; Vardy, 2011). Although a positive 

linear relation was noted between nitrate and chloride for 

this report, considerable variation occurred with an R2

 of 

only 0.12. This indicates that attenuation processes affecting 

the transport and resultant concentration of nitrate in 

groundwater are not affecting chloride, which is nonreactive 

(conservative) in transport within the hydrologic system. No 

spatial trend was noted for chloride concentrations.

Sulfate

Sulfate concentrations for 134 sites in the Springfield 

Plateau aquifer ranged from 0.48 to 90 mg/L with a median of 

3.9 mg/L (fig. 113; table 43). Imes and Emmett (1994) noted 

that sulfate concentrations generally are less than 10 mg/L. No 

spatial trend was noted for sulfate concentrations. As noted 

for iron, an inverse relation of iron and sulfate concentrations 

tends to rule out oxidation of iron-sulfide minerals as a source 

of sulfate. Because all but one sulfate concentration greater 

than 20 mg/L had ratios of calcium plus magnesium divided 

by bicarbonate that were more than 1.0, dissolution of gypsum 

may account for the increased sulfate concentrations. 

In summary, groundwater from natural rock/water 

interaction processes in the Springfield Plateau aquifer is 

generally of good quality. Because of the steep topography 

and poor soils in the Ozarks, agriculture in the form of beef 

and dairy cattle, swine, and poultry operations accounts 

134

134 132

119

134 134 126

126

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

0

50

100

150

200

250

300

350

400

450

500

700

800

900

1,000

0

100

200

300

400

500

600

Concentrations, in milligrams per liter

Concentration, in micrograms per liter

Constituent Constituent

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron

Figure 113. Interquartile range of selected chemical constituents in groundwater from the Springfield Plateau aquifer of northern 

Arkansas.
Aquifers of the Interior Highlands 291

for the greatest land-use activity. Nutrients, bacteria, and 

pesticides from agricultural activities, home septic systems, 

and infiltration of urban runoff are the dominant threats to 

groundwater quality in the aquifer. Numerous studies have 

documented elevated nitrate and fecal bacteria in groundwater 

from springs and wells. A positive correlation between 

agricultural land use and nitrate concentrations validates 

concerns over agricultural wastes and the vulnerability of the 

aquifer to anthropogenic contaminants. Recent studies have 

shown a direct correlation between areas of greater karst 

development and increased vulnerability of the aquifer to these 

agricultural waste sources. Inorganic constituents, including 

chloride, sulfate, and iron, generally were low throughout the 

aquifer, revealing a relative high quality of groundwater for all 

water-supply uses.

Ozark Aquifer

The Ozark aquifer (fig. 3) is exposed and generally 

unconfined within the Salem Plateaus section of the Ozark 

Plateaus (Ozarks) province (table 2). The aquifer underlies 

and is confined below the Springfield Plateau aquifer in the 

Springfield Plateau and Boston Mountains regions of the 

Ozarks (tables 2 and 5). The aquifer comprises a sequence 

of formations predominated by dolostones along with minor 

limestone, sandstone, and shale intervals of Ordovician age. 

These formations contribute to the unique and complex 

hydrogeology and physiography of the Ozarks. The karst 

of the carbonates in the upper Ozark aquifer presents a 

physiographic and hydrologic environment in the Salem 

Plateau similar in aspect and complexity to that seen for the 

Springfield Plateau.

The upper, carbonate-dominated part of the Ozark aquifer 

comprises the Clifty Limestone, Penters Chert, Lafferty 

Limestone, St. Clair Limestone, Brassfield Limestone, Cason 

Shale, Fernvale Limestone, Kimmswick Limestone, Plattin 

Limestone, Joachim Dolomite, St. Peter Sandstone, Everton 

Formation, Powell Dolomite, Cotter Dolomite, and Jefferson 

City Dolomite (table 5). The carbonate-dominated limestones 

and dolomites of Ordovician age are the predominant waterbearing units of the upper part of the aquifer. This differs 

from the lower part of the aquifer in predominant lithologies, 

groundwater levels, exposure and confinement, yields, and 

geochemistry, and hereinafter will be commonly referred to 

in this report as the “upper Ozark aquifer.” The lower part 

of the aquifer includes the confined Roubidoux Formation, 

Gunter Member of the Gasconade Dolomite, Van Buren 

Formation, Eminence Dolomite, and Potosi Dolomite. The 

combined Roubidoux and Gunter Member of the Gasconade 

Dolomite are the primary water-bearing units of the lower part 

of the aquifer in Arkansas and are predominated by sandstone 

lithology with abundant dolomite and shaly intervals common 

in the Roubidoux Formation. The combined water-bearing 

units of the Roubidoux and Gunter Member of the Gasconade 

Dolomite are referred to hereinafter in this report as the “lower 

Ozark aquifer.” Similar to the Springfield Plateau aquifer, 

groundwater movement and groundwater quality of the Ozark 

aquifer are controlled by regional and local geology. Geologic 

factors include the presence and composition of the regolith 

mantle, the lithologies of the rocks that convey groundwater 

flow, stratigraphic relations of these different lithologies, and 

geologic structure.

Geologic Setting

The fundamental structural feature defining the Ozark 

Plateaus is a broad dome that has been uplifted during several 

periods since Precambrian time to bring the plateaus to their 

current altitude (Nunn and Lin, 2002; Tennyson and others, 

2008; Cox, 2009). The core of the dome is in southeastern 

Missouri. Sedimentary units in Arkansas lie along the southern 

and southwestern margins of the dome with gentle regional 

dips generally ranging from 10 to 100 ft/mi and steeper dips 

being common proximal to faults (Frezon and Glick, 1959). 

Regional extensional fracturing, jointing, and faulting of rocks 

in the Ozark Plateaus occurred with uplift of the formations 

(Hudson and Cox, 2003) creating secondary porosity that has 

provided key nucleation points for initiation of dissolution of 

the carbonate rocks and karst development. Topographic relief 

resulted from erosional dissection of the Ozark Plateaus rather 

than from intense folding and faulting. This erosion has been 

controlled to a degree by structural features such as faults and 

fracture zones as well as by lithology. 

Regolith mantles most areas of the underlying karstic 

bedrock where the formations of the Ozark aquifer are 

exposed on the Salem Plateau. In many areas of the regolith, 

thickness varies from near zero to more than 100 ft and 

typically comprises a silt-loam surface soil overlying a 

clay-loam subsoil. The regolith usually is clay-rich, low in 

permeability, and impedes recharging water. The regolith 

mantling the Salem Plateau generally contains less chert than 

the regolith over the Springfield Plateau. This compositional 

difference may make the Salem Plateau regolith a more 

competent barrier to surface-derived contamination. This has 

been theorized to explain observational differences in lower 

nitrate concentrations in the Ozark aquifer compared to the 

Springfield Plateau aquifer (see “Water Quality” section 

below).

The younger Ordovician-age rocks constituting the 

upper Ozark aquifer only require a brief description because 

yield and water quality are similar throughout. The Fernvale 

Limestone is generally observed as a massive, zero to more 

than 100 ft in thickness, coarsely crystalline, light-gray to 

pink limestone present in the Ozarks of northern Arkansas. 

The Fernvale is very similar to the underlying Kimmswick, 

which is generally less than 50 ft in thickness. The Plattin 

Limestone is a gray, thin-bedded limestone and is usually less 

than 100 ft in thickness. The Joachim Dolomite is generally 

described as a fine-grained dolostone or dolomitic limestone 

with thin beds of shale. Sand is abundant at the base of the 

formation with thin sandstones commonly occurring above 
292 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

the St. Peter Sandstone. The Joachim is absent in the western 

Ozarks and is as thick as 100 ft in the central and eastern 

Ozarks. The St. Peter Sandstone is usually observed as a 

massive-bedded, medium- to fine-grained, well-rounded, 

poorly cemented, white sandstone. The formation ranges from 

less than 1.0 ft to as much as 175 ft in thickness. The Everton 

Formation exhibits considerable spatial variation in lithologic 

character and comprises dolostone, sandstone, and limestone 

intervals in varying proportions. The Everton Formation 

includes members of thick, friable sandstone that are similar 

to the overlying St. Peter Sandstone. Thickness of the Everton 

Formation varies from about 300 ft to more than 650 ft. The 

Powell Dolomite usually is observed as a fine-grained, light to 

green-gray dolostone from less than 50 ft to more than 200 ft 

in thickness, with thin beds of shale, sandstone, and occasional 

chert. The Jefferson City and Cotter Dolomites constitute a 

thick interval of 1,000 ft or more of light- to dark-tan, fineto medium-grained dolostone with common chert and some 

thin beds of sandstone and shale. These two formations are 

indistinguishable in Arkansas (McFarland, 1998). 

The lower Ozark aquifer comprises the Roubidoux 

Formation and the Gasconade Dolomite for which the 

Gunter Sandstone Member is the primary water-yielding 

unit. These formations do not crop out in Arkansas. The 

Roubidoux consists of dolomite, sandstone, and chert. The 

dolomite is light gray to brown in color, finely granular to 

medium crystalline, and is sandy and cherty at some locations 

(Caplan, 1960; Howe and Konig, 1961; Imes and Emmet, 

1994; Adamski and others, 1995). The sandstones consist 

of discontinuous beds of white to light-gray, fine to medium 

quartz (Snyder, 1976; McDonald and others, 1977) and are 

loosely to well cemented by silica or carbonate materials 

(Caplan, 1960). The Roubidoux Formation ranges from 100 ft 

to more than 450 ft in thickness in northern Arkansas. 

The Gunter Sandstone Member at the base of the 

undifferentiated Gasconade Formation represents the oldest 

Ordovician rock present in northern Arkansas and rests 

unconformably on the Cambrian Eminence Dolomite. The 

Gasconade Formation comprises light brownish-gray, fine- to 

medium-crystalline dolomites that frequently contain chert 

(Caplan, 1960; Prior and others, 1999). The upper part of 

the Gasconade Formation contains relatively small amounts 

of chert; however, the formation may contain as much as 

50 percent chert by volume above the Gunter Sandstone 

Member (Prior and others, 1999). The Gasconade Formation 

ranges from about 300 to over 700 ft in thickness (Caplan, 

1960; Melton, 1976). The Gunter Sandstone is mainly 

composed of white to light-gray, fine- to coarse-grained quartz 

sandstone and sandy dolostone (McQueen, 1931; Knight, 

1954; Caplan, 1960; Melton, 1976; Snyder, 1976; MacDonald 

and others, 1977; Adamski and others, 1995; Imes and Emmet, 

1994; Prior and others, 1999a). The sand generally is loosely 

cemented by silica or carbonate material (Grohskopf and 

McCracken, 1949). The Gunter Sandstone Member typically 

averages about 30 ft in thickness (Caplan, 1960; Melton, 

1976; Prior and others, 1999) but is locally reported to be 

approximately 100–120 ft in thickness (Caplan, 1960; Melton, 

1976; Prior and others, 1999). The Gunter Sandstone Member 

may be locally absent (Caplan, 1960; Prior and others, 1999). 

The tops and thicknesses of the Roubidoux Formation 

and the Gunter Sandstone encountered in wells in northern 

Arkansas were identified by Lamonds and Stephens (1969). 

Structural maps of the Roubidoux and the Gunter are 

presented by Caplan (1960), Lamonds (1972), Melton (1976), 

MacDonald and others (1977), and Prior and others (1999). 

A limited number of wells are drilled to the Roubidoux and 

the Gunter. As a result, data used to compile the structural 

maps are limited. Prior and others (1999) used 174 wells and 

provided the most comprehensive structural map available at 

this time (2013). 

Karst-development processes and history are an 

important aspect of the geology controlling groundwater 

hydrology in the Ozarks. The exposed formations of the Ozark 

aquifer present an example of a dynamic and developing 

karst aquifer. Also evident are episodes of karst development 

through geologic time that results in overlap and interplay of 

recent and paleokarst features. Karst aquifers are typified by 

a combination of diffuse and focused flow. The slower flow 

occurs through diffuse flow paths and allows for sustained 

groundwater input to streams and springs, even during 

dry periods. Extremely rapid response and transit times 

occur during precipitation events and are provided through 

preferential flow paths and karst features. In karst systems, 

large cavernous conduits allow for deep and rapid circulation 

of recharge. Conduits and dissolution-enhanced fracturing 

help integrate flow to spring resurgences (Harvey, 1980). As a 

result, springs are common throughout the exposed sections of 

the Ozark aquifer. 

Bedrock in the Ozarks shows evidence of multiple 

episodes of water movement and carbonate dissolution, 

which defines distinct karst-development events through time 

(Stoffell and others, 2008). Exposure of Ordovician strata 

associated with the Ordovician-Mississippian unconformity 

caused dissolution and initial paleokarst development. 

Widespread dissolution features associated with the lead and 

zinc ore-bearing fluids that moved from the Arkoma Basin 

(Leach and Rowan, 1986) are observed across the Ozarks 

region. Lead and zinc were commercially mined where faults 

conveyed mineral-saturated fluids up from depth. Hypogene 

indicators, such as diagnostic calcite isotopic compositions 

(Brahana and others, 2009), collapse breccias (McKnight, 

1935), and isotopic dating (Brannon and others, 1996), show 

that this episode of fluid movement and dissolution was a 

separate occurrence predating recent karst development. 

The formations of the Ozark aquifer once again showed 

active karst development as uplift, denudation, and abundant 

precipitation, and recharge initiated further dissolution of the 

soluble carbonate lithologies. 

The recent period of dissolution and karst development 

has had very visible impact on the modern karst land surface, 

on controlling subsurface flow, and ultimately on surface flow 

in the region. The hydrogeology of the region is typical of 
Aquifers of the Interior Highlands 293

karst with focused flow paths that are well connected to the 

surface and delivers water from input to discharge points at 

streams and springs at velocities of tens to thousands of feet 

per day (Funkhouser and others, 1999; Mott and others, 2000; 

Turner and others, 2007; Hudson and others, 2011). Abundant 

karst features are apparent including ponors, losing stream 

reaches, springs, caves, and sink holes. However, recent karst 

development in the Ozark aquifer has often reactivated and 

followed previous dissolution-enhanced flow paths. These 

flow paths originally developed during ancient exposure 

periods (for example, at the Ordovician-Mississippian 

unconformity; Webb, 1994) or hypogene episodes (such as 

Mississippi Valley Type ore emplacement; Leach and Rowan, 

1986; Brannon and others, 1996; Brahana and others, 2009).

Hydrologic Characteristics

The upper Ozark aquifer is generally unconfined across 

the Salem Plateau and confined in the Springfield Plateau and 

Boston Mountains. The highly soluble nature of the carbonate 

rocks of the dolostones and limestones that comprise the 

upper Ozark aquifer has resulted in development of the 

hydrologically heterogeneous karst terrain. Karst features 

include caves, springs, and sinkholes, which result in the direct 

hydraulic connection of surface water and groundwater and 

create the highly variable aquifer characteristics that typify the 

area. In the upper Ozark aquifer, high hydraulic conductivity 

values typically result from secondary porosity created by 

dissolution of bedrock along joints, fractures, and bedding 

planes, rather than from primary, matrix-type porosity. 

Enhancement of fractures, bedding planes, and conduits by 

carbonate dissolution is an active, ongoing process (Adamski 

and others, 1995). Diagenetic processes have developed 

secondary porosity features and have produced anisotropic 

and heterogeneous hydraulic characteristics in the aquifer. At 

one end of the porosity-permeable continuum, smaller-scale 

matrix, small-aperture fracture, and small-conduit porosity 

give rise to diffuse groundwater flow in the aquifer. At the 

other end of the porosity-permeable continuum, dissolutionenhanced porosity creates the focused (conduit) groundwater 

flow. Because of the low rock-matrix permeability, a large 

fraction of groundwater transfer is through the focusedflow component of the aquifer (Imes and Smith, 1990). The 

rapid recharge of surface water, rapid flow velocities, rapid 

mass transfer, and minimal attenuation of contaminants are 

associated with this component of flow. The time-averaged 

groundwater flow, base flow of streams during dry periods, 

low groundwater-flow velocities, and effective attenuation 

of contaminants are behaviors associated with the diffuse 

component of flow. 

In the unconfined upper Ozark aquifer, precipitation 

provides recharge to the aquifer where exposed. Recharge can 

be rapid and result in highly variable water levels, substantial 

seasonal changes, and groundwater-gradient reversals (Aley, 

1988). In areas where the Ozark aquifer is overlain by the 

Springfield Plateau aquifer, most recharge occurs through 

downgradient flow originating in the outcrop area for the 

Ozark aquifer and leakage from the overlying Springfield 

Plateau aquifer. Leakage of water between the Springfield 

Plateau and Ozark aquifers is impeded by shales (primarily 

the Chattanooga Shale) and dense, low-permeable limestones 

and dolostones (Imes and Emmett, 1994; Adamski and others, 

1995). In some areas, the Chattanooga Shale is absent and the 

potential is increased for hydraulic connection between the 

two aquifers.

Well yields are relatively low within the upper Ozark 

aquifer and are comparable to those of the exposed Springfield 

Plateau aquifer, reflective of the generally low permeability. 

Wells within the upper Ozark aquifer are generally less 

than 300 ft in depth (Lamonds, 1972) and have yields of 

approximately 5–10 gal/min (Lamonds, 1972; Leidy and 

Morris, 1990b). Data on the hydraulic properties of the upper 

Ozark aquifer are scarce. The hydraulic conductivity of the 

combined upper and lower Ozark aquifer is estimated to range 

from greater than 1,000 ft/d to less than 1.0×10-2 ft/d (Imes 

and Emmet, 1994). 

The Roubidoux Formation, Gasconade Dolomite, 

Eminence Dolomite, and Potosi Dolomite form aquifers of 

generally high yield (Harvey, 1980). Only the Roubidoux 

and Gunter Sandstone are commonly used in Arkansas and 

are grouped and discussed for the purposes of this report as 

the “lower Ozark aquifer.” Where these units are exposed in 

Missouri, multiple studies have been conducted using dye 

traces and other approaches (Gott, 1975; Aley and Aley, 1987; 

Imes and Kleeschult, 1996). Results indicate a complex karst 

hydrologic system having long, interwoven flow paths that 

change drastically in terms of basin boundary extents and 

dominant flow paths with changing hydrologic condition 

(Mesko and Imes, 1995; Imes and Fredrick, 2002). Secondary 

porosity is provided by fractures, joints, bedding planes, vugs, 

dissolution conduits, and other karst features. This contributes 

to the high permeability values and the ability of the aquifer to 

convey great amounts of water. Secondary-porosity features 

are observed to decrease with depth (Lamonds, 1972). High 

yields at depth in the lower Ozark aquifer are attributed 

dominantly to porous sandstone layers, as reported for the 

Roubidoux Formation and Gunter Sandstone Member, rather 

than high hydraulic conductivity provided by karst features. 

Emerging data indicate the potential for localized karst-flow 

systems at depth within the Ozark aquifer (Brahana, 2011a). 

Though observations of paleokarst and solutional development 

are difficult to identify at depth, evidence provided by Palmer 

(2011) has shown that deep-seated dissolution has occurred 

within the Ozarks. Orndorff and others (2006) also provided 

evidence of karst development at depth in confined aquifers.

 The lower Ozark aquifer is under confined conditions 

(Prior and others, 1999) and receives recharge from rainfall 

and streamflow interception in its outcrop areas in southern 

Missouri (Lamonds, 1972; Melton, 1976; MacDonald and 

others, 1977; Harvey, 1980; Prior and others, 1999). Harvey 

(1980) further detailed important recharge components and 

listed sinkholes, infiltration through conduits, and losing 
294 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

streams as the primary mechanisms of recharge. Some 

recharge occurs as leakage from the upper Ozark aquifer (Imes 

and Emmett, 1994; Adamski and others, 1995); however, 

the majority of recharge is attributed to lateral flow from the 

outcrop areas (Imes and Emmett, 1994; Adamski and others, 

1995). The direction of groundwater flow generally follows 

the regional dip toward the south. Wells in Missouri intercept 

some of the groundwater in the lower Ozark aquifer before it 

reaches Arkansas (Prior and others, 1999). 

Wells in the lower Ozark aquifer are among the most 

productive in the region (Lamonds, 1972); yields from the 

Roubidoux Formation range from less than 10 gal/min to 

about 600 gal/min (Caplan, 1960; Lamonds, 1972; Melton, 

1976; MacDonald and others, 1977; Kilpatrick and Ludwig, 

1990b; Prior and others, 1999). Yields from the Gunter 

Sandstone Member range from less than 100 gal/min to about 

600 gal/min (Lamonds, 1972; Melton, 1976; MacDonald, 

1977; Kilpatrick and Ludwig, 1990b; Imes and Emmett, 1994; 

Adamski and others, 1995; Renken, 1998; Prior and others, 

1999; Czarnecki and others, 2014). Prior and others (1999) 

noted that wells were drilled to the deeper Gunter Sandstone 

Member only when yields from the Roubidoux Formation 

were insufficient. The wells often were dually completed, 

making it difficult to determine yields for the individual 

formations. Caplan (1960) reported that combined yields 

from the lower Ozark aquifer can be as much as 300 gal/min, 

although yields commonly are 50 gal/min or less. Melton 

(1976) noted that the distribution of well yields is not uniform, 

indicating that local lithologic differences and distribution of 

secondary porosity may affect well yields.

Data on the hydraulic properties of the Roubidoux 

Formation and the Gunter Sandstone Member in Arkansas 

are scarce. The hydraulic conductivity of the Ozark aquifer 

as a whole is estimated to range from more than 1.0×10-3 ft/s 

to less than 1.0×10-8 ft/s (Imes and Emmet, 1994). Specific 

capacity values ranged from 0.1 to 3.8 (gal/min)/ft for the 

Roubidoux Formation, and several wells experienced no 

measurable drawdown while pumping. A single specific 

capacity of 0.1 (gal/min)/ft was reported from a well 

completed in the Gasconade Formation (Melton, 1976; 

MacDonald and others, 1977). Potentiometric surfaces of the 

lower Ozark aquifer are presented by Lamonds (1972), Melton 

(1976), MacDonald and others (1977), and Prior and others 

(1999) and generally show an overall southerly direction of 

flow following the regional deep of the formation constituting 

the aquifer.

Water Levels

Water-level data for the Ozark aquifer are scarce. 

Where available, the data are very nonspecific in terms of 

the individual formation in which the well is completed, or 

if the well is completed in the lower Ozark aquifer compared 

to the upper Ozark aquifer. Most historical water levels were 

measured in open-hole wells, and the determination and 

assignment of the primary groundwater-yielding formation 

are difficult. This paucity of data results in (1) potentiometric 

maps that lack in detail, (2) a vertical distribution of head 

gradients that cannot be individually determined, and (3) an 

inability to understand groundwater flow in the aquifer, 

particularly at small, subregional scales.

The understanding of groundwater flow in the upper 

Ozark aquifer is derived from various reports and analysis 

of NWIS data performed for this report. Problems in 

understanding groundwater flow lies in the fact that the Ozark 

aquifer is not differentiated in most reports, although the 

dominantly unconfined upper Ozark aquifer has hydrologic 

characteristics vastly different from those of the deeper and 

confined lower Ozark aquifer. For the upper Ozark aquifer, 

precipitation provides direct recharge to the aquifer where 

exposed in Arkansas, and groundwater follows short (usually 

less than 10 mi), local flow paths that terminate near streams 

(Adamski and others, 1995). Therefore, recharge can be rapid 

and results in highly variable water levels with substantial 

seasonal changes. This also contributes to groundwater 

gradient reversals (Aley, 1988). The potentiometric surface of 

the combined (upper and lower Ozark aquifer undifferentiated) 

Ozark aquifer averages from about 700 to 1,000 ft of altitude 

(Adamski and others, 1995). The potentiometric surface 

generally is a subdued reflection of the topography where the 

upper Ozark aquifer crops out and is unconfined (Lamonds, 

1972; Leidy and Morris, 1990b). Meta-analysis statistics 

conducted on data (altitude and water-level data from NWIS) 

compiled for this report from 1,081 wells showed that water 

levels closely correspond to land-surface altitudes with a 

correlation coefficient of 0.92. Groundwater-flow directions 

are lateral and outward from areas of high to low altitude. 

Small groundwater basins with short flow paths originating at 

higher altitudes and with discharge occurring at lower altitudes 

at streams and springs account for much of the overall 

groundwater-flow budget (Imes and Emmett, 1994; Adamski 

and others, 1995; Pugh, 1998, 2008b; Schrader, 2001a, 2005; 

Czarnecki and others, 2014). 

Much of the understanding of groundwater flow in the 

lower Ozark aquifer is derived from extrapolation of data 

from Missouri. Water levels in the Roubidoux Formation of 

the lower Ozark aquifer vary spatially and temporally and 

may vary by as much as 200 ft/yr. Variations in the resulting 

potentiometric surface reflect topographic relief, changes in 

pumping, and regional formation dip (Kilpatrick and Ludwig, 

1990b). Water levels from the Gunter Sandstone of the lower 

Ozark aquifer vary spatially and temporally and vary by 

approximately 100 ft in a period of a few years (Edds and 

Remsing, 1986; Freiwald and Plafcan, 1987). Representative 

hydrographs showing water levels from wells completed in 

the upper and lower Ozark aquifers are shown in figure 114. 

The upper Ozark aquifer generally shows greater and more 

rapid water-level change than the lower Ozark aquifer because 

it is shallower and more exposed to direct infiltration of 

locally recharging precipitation. Water-level changes in the 

lower Ozark are more subdued and slower in response to 

precipitation. This lag time for the lower Ozark as compared 

with the upper Ozark aquifer results from the greater distance 

of the wells in Arkansas from the recharge area located to 
Aquifers of the Interior Highlands 295

the north in Missouri. Water levels in the Ozark aquifer are 

measured on a 3-year rotational basis; measurements were 

last made in 2010 in 56 wells and 5 springs by the USGS in 

collaboration with ANRC (Czarnecki and others, 2014). No 

continuous water-level monitoring sites are active for the 

Ozark aquifer. 

Water levels in the lower Ozark aquifer generally rise 

to altitudes of approximately 400–1,000 ft and typically are 

within about 200 ft below land surface (Lamonds, 1972). 

Water-level altitudes for the lower Ozark aquifer show a much 

less well-defined relation with land surface than the upper 

Ozark aquifer or the Springfield Plateau aquifer. Water-level 

and elevation data compiled from 1,085 wells for this report 

show that water levels correspond poorly to land-surface 

altitudes with a correlation coefficient of 0.70, as compared to 

correlation coefficients of 0.92 and 0.98 for the upper Ozark 

and Springfield Plateau aquifers, respectively. This lack of 

correlation between water-level and land-surface altitudes for 

the lower Ozark aquifer is a reflection of the lesser control of 

topography, the less frequent occurrence of short, small-basin 

flow paths, and the predominance of long, regional flow paths. 

Regional flow within the lower Ozark aquifer is to the 

south and southeast following the dip of the units toward the 

Arkansas River and Mississippi Alluvial Plain (Lamonds, 

1972, Czarnecki and others, 2014). Evidence of upward 

leakage from the lower Ozark aquifer into the embayment 

aquifers is seen in water-budget and geochemical data 

(Mesko and Imes, 1995; also see the “Mississippi River 

Valley Alluvial Aquifer” section in this report). The paucity 

of well control points for the lower Ozark aquifer in 

northern Arkansas greatly limits the confidence and detail 

of groundwater-flow interpretation and any delineation 

of topographic and other local controls on water levels. 

Additional data are needed to better understand the flow 

system in the lower Ozark aquifer (Lamonds, 1972; Imes and 

Emmett, 1994; Czarnecki and others, 2014). Potentiometric 

surfaces generated for the undifferentiated Ozark aquifer 

using the relatively scarce available water-level data 

(fig. 115) have changed little through time (Pugh, 1998; 

Schrader, 2001a, 2005; Pugh, 2008b; Czarnecki and others, 

2014). Therefore, more recent potentiometric surfaces 

(Czarnecki and others, 2014) resemble predevelopment 

surfaces constructed by Imes and Emmett (1994). The St. 

Francois confining unit, the lower confining unit for the 

Ozark aquifer, limits the downward flow of groundwater 

and hydrologically separates the Ozark aquifer from the St. 

Francois aquifer (Adamski and others, 1995). 

1962

1966

1970

1974

1978

1982

1986

1990

1994

1998

2002

2006

2010

2014

Year

Water level, in feet above National Geodetic Vertical Datum of 1929,

for 18N09W15BCB1, well completed in the upper Ozark aquifer 

430

450

470

490

510

530

550

Water level, in feet above National Geodetic Vertical Datum of 1929,

for 18N06W10CBC1, well completed in the lower Ozark aquifer 

560

580

600

620

640

660

680

18N09W15BCB1—Well completed in the upper Ozark aquifer

18N06W10CBC1—Well completed in the lower Ozark aquifer

EXPLANATION

Figure 114. Water levels in wells completed in the upper and lower Ozark aquifer of northern Arkansas.
SHARP FULTON IZARD STONE INDEPENDENCE BENTON WASHINGTON MADISON CARROLL NEWTON SEARCY BOONE MARION BAXTER ARKANSAS MISSOURI 400 500700 600 900 

700 600 800 700 600 800 1,000 1,100 1,000 1,100 1,200 1,200 1,200 900 1,200 900 800 1,100 1,000 800 900 700 300 800 500 Beaver Lake Bull Shoals Lake Norfolk Lake Stra

Whit 

e River 

Osage CrWhite River Osage Cree Il k linois River Kings River Buffalo River Crooked Cr 

400 400 400400 600 800 600600 800 600 600 600 400 400 400 600400 600 8001,000 1,000 1,000 1,200 1,200 1,000 1,000 1,000 489 794 658 9111,190 1,073 654 666 663 988 489 53

497 440 355 554 390 405540 934 794 817 778 767 709 

809 838 764 715 565 561518 590 490 658 681 475 734 979 930 642 658 911 995 803766 580 547551 552 567556 1,144 1,156 1,046 1,068 1,106 1,174 1,190 1,054 1,066 1,073 890 662 400435 455 495 340 435 18N09W15BCB1 18N06W10CBC

EXPLANATION Outcrop of Ozark aquifer Potentiometric contour—Shows altitude at which water level would have stood in tightly cased wells. Dashed where approximately located. Contour interval 100 feet. Datum is National Geodetic Vertical Datum of 1929 (NGVD 29) General direction of groundwater flow Fault (Haley and others, 1993) Observation well completed in the Ozark aquifer— Measurement made in February and March 2010. Value is the water-level altitude above NGVD 29 778 400 500 Observation well completed in the 

 hydrograph is presented (fig. 114 Measurement made in February a

 is the water-level altitude above Spring in the Ozark aquifer—Meas

 February 2010. Value is the water

above NGVD 29 Control point—Intersection of land-

 and stream within area where the  unconfined. Altitude values deter 1:500,000 topographic map 455 497 18N06W10CBC1 Fayetteville 94°30' 94°00' 93°30' 93°00' 92°30' 92°00' 91°30' 

36°30' 36°00' Base from U.S. Geological Survey digital data, 1:500,000 and other scales Universal Transverse Mercator, zone 15 North North American Datum of 1983 Modified from Czarnecki and others, 201

0 10 40 KILOMETERS 0 10 40 MILES 20 3020 30 Area enlarged ARKANSAS

Figure 115. Potentiometric surface of the Ozark aquifer in northern Arkansas, 2010. 
Aquifers of the Interior Highlands 297

Several studies have investigated long-term water-level 

trends within the Ozark aquifer to identify areas at risk for 

groundwater decline and to quantify the effect of water users 

converting from groundwater to surface-water sources (Pugh, 

2008b; Czarnecki and others, 2014). The sparse and limited 

number of water levels greatly limits effective assessment 

and prediction of sustainable water levels for the Ozark 

aquifer. Nevertheless, declines had been noted in northwestern 

Arkansas (Benton, Carroll, and Washington Counties), which 

is an area of development and population growth (Czarnecki 

and others, 2014). Czarnecki and others (2014) reported recent 

decreases in the rate of water-level decline in some wells and 

increases in water levels for others. This positive news was 

related to the expansion of rural water-supply districts that 

have predominately converted to surface-water sources.

Deductive Analysis and Projections of 

Groundwater Movement

Groundwater often receives less focus in terms of 

monitoring and management efforts than does surface water 

because it is less visible, hydrologic and geochemical changes 

typically occur more slowly, and it responds less quickly 

to external processes or boundary conditions. Furthermore, 

collecting information and developing an effective 

understanding of groundwater behavior is more challenging 

than for surface water. Digital simulation of groundwater 

has been an important tool for evaluating basic aquifer 

characteristics such as recharge rates, storage, permeability, 

flow rates, and flow paths. Groundwater-flow models are 

also important as a tool to predict aquifer responses to future 

conditions such as changes in pumping, land-development 

effects, and climatic effects. Although numerous localscale and regional investigations of groundwater have been 

conducted across the Ozarks, groundwater-flow models 

rarely have been used. Investigations that have developed 

groundwater-flow models specific to the Ozarks of Arkansas 

are Imes and Emmett (1994), Mesko and Imes (1995), and 

Czarnecki and others (2009). 

A regional groundwater-flow model for the Ozarks was 

developed by Imes and Emmett (1994) as part of the USGS 

Central Midwest RASA to assess regional groundwater 

resources and to better understand hydraulic properties of the 

aquifer and groundwater flow. Simulation results indicated 

that the hydraulic conductivity of the Ozark aquifer is 

approximately 10 ft/d in the southern Ozarks of Arkansas and 

about 25 percent of precipitation occurring over the outcrop 

area of the Ozark aquifer infiltrated as recharge to the aquifer. 

Of that total, about 78 percent entered small-scale watersheds, 

flowing along short flow paths to quickly discharge into 

nearby streams and springs. The remainder (6 percent of 

precipitation) ended up in deeper, longer flow paths as regional 

groundwater flow. The pumping rates at that time (1990) were 

found to have little to no effect on the simulated regional water 

budget and potentiometric surfaces compared to simulated 

predevelopment conditions. These results illustrate the great 

differences in the predominantly karst aquifers of the Ozarks 

and the granular aquifers of the Mississippi embayment. 

Results also highlighted the prevalence of small-scale 

watersheds and associated short groundwater flow paths in the 

surficial aquifers in the overall groundwater-flow budget.

Regional groundwater-flow simulations were conducted 

by Mesko and Imes (1995) linking simulations of two 

regional-scale models: the Ozark Plateaus Aquifer System 

model (Imes and Emmett, 1994) and the Mississippi 

embayment Aquifer System Model (Brahana and Mesko, 

1988). Historical hydrogeological data in the Mesko and Imes 

study indicated the potential for groundwater to move from the 

Ozarks aquifer system to beneath the Fall Line or escarpment 

into the northern Mississippi embayment, ultimately to 

discharge to overlying embayment aquifers or directly to 

streams. The quantity of water simulated by the linked Ozark 

model moving from the Ozark Plateaus aquifer system 

under the Fall Line into the Mississippi embayment was 

650–800 ft3/s more than the quantity simulated by the MERAS 

model. The most likely explanation for this difference was 

groundwater discharge to streams. Therefore, the results were 

initially interpreted as indicating that a considerable volume 

of groundwater might be discharging to embayment streams. 

To determine if these differences in simulated groundwater 

flow could be explained by discharge to base flow in streams, 

low-flow seepage measurements were made on the Black 

and Current Rivers and their major tributaries in 1987. The 

seepage data indicated that groundwater contributed about 

1,000 ft3/s to the streams. These results were in precise 

agreement with model results confirming the scale and great 

importance of groundwater contribution to streamflow (Mesko 

and Imes, 1995).

Availability of water has been a limiting factor for growth 

in the Ozarks; nevertheless, groundwater has historically 

been an important part of the resource base. Relatively 

minor attention and resources were focused on development 

of groundwater because of limited fiscal resources of the 

region and the regional groundwater system of the Ozarks 

is incredibly complex and challenging to characterize. As a 

result, an understanding of the Ozark Plateaus aquifer system 

is not at the same level as other important regional aquifers, 

and the available tools for assessing the system are insufficient 

to address evolving needs. Currently (2013), USGS is working 

on a regional assessment of groundwater availability of the 

Ozark Plateaus aquifer system as part of a USGS Groundwater 

Resources Program initiative (http://water.usgs.gov/ogw/

gwrp/activities/regional.html), whose objectives are to assess 

(1) growing demand and the role of groundwater as a resource 

for agricultural, industrial, and public-supply uses (Emmett 

and others, 1978; Dintelmann and others, 2006; Richards and 

Mugel, 2008; Richards, 2010), (2) regional climate variability 

and pumping affecting groundwater levels and groundwater 

and surface-water flow paths (Macfarlane and Hathaway, 

1987; Imes and Emmett, 1994), (3) effects of the gradual 

shifting to greater dependence upon surface water in some 
298 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

areas (Morgan, 2012) and, (4) potential effects on water use 

from shale-gas production (U.S. Environmental Protection 

Agency, 2010). Specific objectives related to the Ozark Plateaus 

aquifer system assessment include deductive analyses and 

projections of aquifer conditions using a newly developed 

groundwater flow model to (1) better understand groundwater 

movement in the Ozark Plateaus aquifer system, (2) quantify 

current water use and evaluate effectiveness of water-use 

monitoring approaches, (3) evaluate how groundwater 

and surface-water resources have changed over time, and 

(4) provide information to help project the systems response 

to future changes. The Ozark system model encompasses 

approximately 69,000 mi2 extending north to the Missouri 

River, south to the Arkansas River, west into Oklahoma and 

Kansas, and east to the Mississippi embayment. Groundwater 

use, groundwater levels, surface-water levels, streamflow, 

precipitation, temperature, land use, geophysical, and drillers’ 

logs have been compiled to define hydrogeology and hydraulic 

properties of the system. These data were used to develop a 

conceptual model and ultimately can be used to construct a 

numerical model of the system.

Water Use

There were 108 wells reported in the Ozark aquifer in 

2010. Of those, 79 wells withdrew groundwater from the 

lower Ozark aquifer (comprised of the Roubidoux Formation 

and Gunter Member of the Gasconade Formation), and the 

remaining wells withdrew from the upper Ozark aquifer 

(fig. 116; Terrance W. Holland, U.S. Geological Survey, written 

commun., 2013). Primary use of the Ozark aquifer is for public 

supply; 76.45 Mgal/d was withdrawn for public supply in 

2010. The high costs associated with drilling prevent smaller 

community-supply systems from using the more productive 

lower Ozark aquifer; although, some gas stations, campgrounds, 

mobile home parks, and resorts withdraw a small amount of 

groundwater in rural areas, but most others rely on wells in the 

upper Ozark aquifer.

The Roubidoux and Gunter units together compose 

the lower Ozark aquifer and account for the greatest yields 

and overall use in the Ozarks. Total reported use from the 

Roubidoux and Gunter in 2010 was 50.73 Mgal/d and 

26.58 Mgal/d, respectively. Primary use of both units is 

public supply; 99.8 percent of use from the Roubidoux and 

80.9 percent of use from the Gunter in 2010 was for public 

supply. Cherokee Village in Sharp County withdrew the most 

water from the lower Ozark aquifer in 2010 at 9.72 Mgal/d; 

all withdrawals were from wells listed as completed in the 

Roubidoux (Terrance W. Holland, U.S. Geological Survey, 

written commun., 2013). Decatur (Benton County) withdrew 

the most water from the Gunter Member in 2010 at 5.08 Mgal/d 

(Terrance W. Holland, U.S. Geological Survey, written 

commun., 2013). Other large users include the public supplies 

of Holiday Island (Carroll County), Corning (Clay County), and 

Mammoth Spring (Fulton County).

The Rubidoux and Gunter units were suggested as 

potential future groundwater supply sources in Randolph 

and Lawrence Counties by Lamonds and others (1969). In 

Randolph County, one community tapped the Roubidoux 

in 1980 and the deeper Gunter in 2010; another community 

tapped the Roubidoux in 1978 (Lyle Godfrey, Arkansas Health 

Department, written commun., 2012). In Lawrence County, the 

Gunter was tapped in the late 1990s for public supply. 

While groundwater use from the lower Ozark aquifer 

is substantial, and some wells have been drilled into the 

lower Ozark aquifer in recent years, use of the aquifer has 

decreased. Surface-water use has increased dramatically, and 

the vast majority of the population in northern Arkansas is 

served by surface water, especially in Benton and Washington 

Counties (see “Overview of Aquifers of Arkansas” section). 

Beaver Lake was developed in the 1960s by the U.S. Army 

Corps of Engineers primarily to provide water to the major 

cities in northwestern Arkansas: Fayetteville and Springdale 

(Washington County) and Rogers and Bentonville (Benton 

County) (Amy Wilson, Beaver Water District, written commun., 

2012). Many other water districts have formed throughout 

northern Arkansas—Carroll-Boone Water District, BentonWashington Regional Public Water Authority, and Madison 

County Regional Water District—to deliver surface water to 

smaller communities from Beaver Lake (Davis and Shephard, 

2010). Bull Shoals, originally developed for hydroelectric 

generation and flood control, is currently (2013) providing 

water to many users in Marion County (U.S. Army Corps of 

Engineers, 2010). Thus, numerous wells in the lower Ozark 

aquifer have been abandoned.

Many communities have sought out surface water as a 

public-supply source because of quantity and quality issues 

with groundwater. Some municipalities have struggled to 

provide adequate supplies for growing demands with limited 

groundwater sources. Other areas tapping the lower Ozark 

aquifer have naturally occurring radon, radium, fluoride, and 

other undesirable constituents that have impaired use and 

increased treatment costs (Adamski, 1996). For some of these 

communities, like the Nail-Swain Water Association (Newton 

County), ADH issued Administrative Orders restricting 

groundwater use (U.S. Army Corps of Engineers, 2010). 

Development of an alternative water source for these areas is 

a top priority, and a project is underway to deliver water from 

Bull Shoals to multiple rural communities (U.S. Army Corps 

of Engineers, 2010; Ozark Mountain Regional Public Water 

Authority, 2013).

Irrigation use from the Ozark aquifers was estimated at 

approximately 20 Mgal/d in 2010 (Terrance W. Holland, U.S. 

Geological Survey, written commun., 2012). About 70 percent 

of irrigation water use is from the upper Ozark aquifer and 

occurs in counties in the aquifer’s far eastern extent, where 

row crops like cotton, rice, and soybeans are commonly 

grown. Depth to water in most of these wells is approximately 

100 ft. Agricultural use throughout the rest of the Ozark 

Plateaus is likely to be smaller in scale, mainly for growing 

fruit (Lamonds, 1972) that does not have the large water 

requirements of row crops. In addition, approximately 6 Mgal/d 

were withdrawn for two fish hatcheries in 2010 from the Gunter 

Member. 
YELL

LEE

UNION

WHITE

POLK

POPE

DREW

PIKE

SCOTT

CLARK

CLAY

ASHLEY

DESHA

BENTON

LOGAN

SALINE

IZARD

PULASKI LONOKE

ARKANSAS

NEWTON

GRANT

CHICOT

MADISON

STONE

MILLER

SHARP

CROSS

DALLAS

PRAIRIE

BOONE

PHILLIPS

PERRY

SEARCY

MARION

FULTON

SEVIER

MISSISSIPPI

JEFFERSON

NEVADA

POINSETT

GARLAND

COLUMBIA

BAXTER

OUACHITA

BRADLEY

JOHNSON

WASHINGTON

MONROE

GREENE

JACKSON

CARROLL

HOWARD

LINCOLN

CALHOUN

CONWAY FAULKNER

VAN BUREN FRANKLIN

CRAIGHEAD

HEMPSTEAD

RANDOLPH

CLEBURNE

MONTGOMERY

LAWRENCE

ST. FRANCIS

CRAWFORD

CLEVELAND

HOT SPRING

INDEPENDENCE

LITTLE

RIVER

WOODRUFF CRITTENDEN

LAFAYETTE

SEBASTIAN

Base from U.S. Geological Survey digital data, 1:2,000,000

36°

35°

34°

94° 92° 91° 93°

90°

0 15 0 30 

15

Shallow Gunter a

*

(

The following sy

) Undifferi

CommeElectricIndustrIrrigatioMiningPublic 

Extent of Well type 

galloto repwaterrepres

EX

Figure 116. Wells with reported groundwater use from the Ozark aquifer in northern Arkansas, 2010.
300 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Domestic and livestock use are known to be 

underestimated for the Ozark aquifer. Domestic wells 

have been widely used since the 1880s (Purdue and Miser, 

1916). Use has been reported in the shallower upper Ozark 

aquifer (Albin and others, 1967a; Lamonds and Stephens, 

1969; Lamonds 1972; Kilpatrick and Ludwig, 1990b) but 

has often been poorly estimated—records have been spotty 

and estimation methods were inaccurate. Also, many wells 

fail to meet the 50,000 gal/d reporting requirement or are 

coregistered as a domestic well and therefore exempt from 

the water-use reporting program. For example, a well 

producing from the Ozark aquifer for livestock purposes, 

such as a chicken house or other animal operation, and also 

has a waterline to an adjacent house or garden for domestic 

purposes, would not have to report use as a coregistered well. 

Commercial groundwater use of the Ozark aquifer was 

estimated at 0.1 Mgal/d in 2010 (Terrance W. Holland, U.S. 

Geological Survey, written commun., 2013). Most use in the 

Ozarks is seasonal for recreational activities including resorts, 

parks, campgrounds, and golf courses. Commercial use is also 

suspected to be underreported because many wells may not 

meet the 50,000 gal/d reporting requirement. No industrial 

use was recorded for the Ozark aquifer in 2010, but previous 

industrial users have included concrete companies. In 1985, 

1.53 Mgal/d was reported for commercial use (Kilpatrick and 

Ludwig, 1990a).

Water Quality

The Ozark aquifer, together with the Springfield Plateau 

aquifer, is one of the major aquifers of the Ozark Plateaus. 

Similar to the Springfield Plateau aquifer, the Ozark is a karst 

aquifer within carbonate rocks described in previous sections. 

Additionally, agriculture in the form of beef and dairy cattle, 

swine, and poultry operations is the predominant land use 

in this region of steep topography and thin soils (Adamski, 

1997). There is a high degree of connectivity between the 

surface and groundwater, expressed in the occurrence of 

sinkholes, solution fractures, caves, losing streams, large 

springs, and other karst features. This leads to nutrients, 

bacteria, and other surface-derived contaminants that are 

associated with the agricultural activities as posing the greatest 

threat to groundwater quality in the Ozark aquifer, particularly 

that of the upper Ozark aquifer (Peterson and others, 2000). 

The karst geology is well developed with the upland areas 

of the Salem Plateau estimated to have 1 to 10 sinkholes per 

100 mi2 (Harvey, 1980). Spring discharges that exceed 100 

ft3/s are common (Imes and Smith, 1990). The surface extents 

of the Ozark aquifer and the Springfield Plateau aquifer in 

northern Arkansas are mapped at the highest groundwater 

vulnerability index in the State (Arkansas Soil and Water 

Conservation Commission, 1991). 

There are 16 formations that constitute the upper 

Ozark aquifer (table 5), which dominantly are represented 

by dolostones composed of or containing a high percentage 

of dolomite. Water-quality data in USGS NWIS commonly 

are reported by the well-completion depth and formation 

penetrated by the driller. Water-quality data in USGS NWIS 

from the upper part of the Ozark aquifer are reported from 7 of 

the 16 upper Ozark formations: Fernvale Limestone, Everton 

Formation, Joachim Dolomite, St. Peter Sandstone, Cotter 

Dolomite, Jefferson City Dolomite, and Powell Dolomite. 

Well depths in the upper Ozark aquifer ranged from 19 to 

1,210 ft, although 71 percent of the wells were less than 

500 ft deep. By comparison, well depths for the lower Ozark 

aquifer in Arkansas ranged from 506 to 3,534 ft, with 45 of 

62 wells (73 percent) being more than 1,000 ft. The following 

sections discuss water quality of the Ozark aquifer. Historical 

publications often do not separate the shallow upper Ozark 

aquifer from the lower Ozark aquifer, especially with respect 

to regional studies. The following discussion will focus on the 

upper and lower Ozark aquifers separately where the data are 

available and meaningful differences exist in geochemistry 

and water quality. 

General Geochemistry and Water Type

Groundwater from the carbonate rocks constituting the 

Ozark aquifer is of a hard to very hard, calcium-magnesiumbicarbonate type (Albin and others, 1967a; Lamonds and 

others, 1969; Lamonds, 1972; MacDonald and others, 1977; 

Harvey, 1980; Kilpatrick and Ludwig, 1990b; Leidy and 

Morris, 1990b; Imes and Emmett, 1994; Adamski and others, 

1995; Prior and others, 1999; Kresse and Fazio, 2004). Pure 

dolomite minerals contain an equal number of calcium and 

magnesium ions. Dissolution of the dominant dolomite 

mineralogy in the Ozark aquifer produces a groundwater 

reflective of this rock chemistry and has approximately equal 

equivalent concentrations of calcium and magnesium. Some 

spatial variation is imparted by variable mineralogy and 

lithology and from formation to formation. Kresse and Fazio 

(2004) compared calcium/magnesium ratios in groundwater 

from individual formations of the upper Ozark aquifer and 

noted slightly higher median, mean, and maximum calcium/

magnesium ratios in the combined St. Peter Sandstone and 

Everton Formation exposures compared to the Powell, Cotter, 

and Jefferson City Dolomites. Calcite cement in the lower 

part of the St. Peter Sandstone was noted as influencing the 

higher ratio. Calcium-magnesium ratios exceeding 1.0 for the 

upper Ozark aquifer, where exposed, probably are influenced 

by occurrence of limestone or calcite cement in various 

formations of the Ozark aquifer.

Data compiled for this report generally support the 

dominant calcium-magnesium water type for groundwater 

from the Ozark aquifer and reflect the dominant dolomitic 

geochemistry of rocks constituting the Ozark aquifer. The 

upper Ozark aquifer had calcium/magnesium equivalent ratios 

ranging from 0.5 to 32.5 with a median of 1.2. The lower 

Ozark aquifer had ratios ranging from 0.4 to 26.2 with a 

median of 1.1. All but the maximum ratio of 26.2 in the lower 

Ozark aquifer were less than 2.0 and demonstrate the narrow 
Aquifers of the Interior Highlands 301

range of low ratios nearing the 1:1 ratio of pure dolomite. 

Conversely, 24 of 123 of the calcium/magnesium ratios for 

the upper Ozark aquifer exceeded 2.0. These 24 sites reflected 

ratios typical of that from the Springfield Plateau aquifer. 

Comparison of calcium/magnesium ratios from the upper 

Ozark aquifer to surface geology revealed that the higher 

ratios occurred in samples from wells located in outcrop areas 

of the Springfield Plateau aquifer (Boone Formation; fig. 117). 

By comparison, in areas where the Ozark aquifer is exposed 

(Fernvale Limestone through Jefferson County Dolomite; 

fig. 117), calcium/magnesium ratios are near 1.0 (fig. 117). 

Groundwater in the upper Ozark aquifer exhibiting higher 

calcium/magnesium ratios similar to those of the Springfield 

Plateau aquifer may be explained by (1) incorrect aquifer 

designation indicating that these wells are actually completed 

in the Springfield Plateau aquifer, (2) open-hole completions 

where wells penetrate rocks of the Ozark and Springfield 

Plateau aquifers, or (3) leakage from the Springfield Plateau 

aquifer down into the upper Ozark aquifer where the 

Chattanooga Shale confining layer is incompetent or absent. 

Harvey (1980) noted higher calcium/magnesium ratios for 

the Ozark aquifer on the Springfield Plateau and attributed 

slow leakage of water from overlying limestone formations 

to the increased ratios. Kresse (1991) compared calciummagnesium ratios in groundwater from the Springfield Plateau 

and Ozark aquifers in Searcy County. Some wells that were 

cased and receiving groundwater only from the upper Ozark 

aquifer had ratios similar to that of the Springfield Plateau 

aquifer. Because the Chattanooga Shale was absent in Searcy 

County, Kresse (1991) attributed leakage from the overlying 

Springfield Plateau aquifer as the source of the higher ratios.

Values of pH ranged from 4.8 to 8.7 with a median 

of 7.3 in the upper Ozark aquifer (table 44). Values ranged 

from 6.7 to 8.4 with a median of 7.7 in the lower Ozark 

aquifer (table 45). For both aquifers, pH showed no trend 

with increasing well depth or dissolved solids. For the upper 

aquifer, R2 values for relations of pH to well depth and 

dissolved-solids concentrations were 0.0003 and 0.0135 

(fig. 118A, B), respectively, and were 0.0031 and 0.0687, 

respectively, in the lower aquifer (fig. 118C, D). Thus, 

median pH values and relations of pH to well depth and 

dissolved solids are similar in the less geochemically evolved 

groundwater for the upper Ozark aquifer compared to that 

in the more geochemically evolved groundwater for the 

lower Ozark aquifer. This suggests that infiltrating, low-pH 

rainwater (average of 4.7 standard units; Kresse and Fazio, 

2002) is rapidly buffered by carbonate minerals in the 

overlying regolith and unsaturated bedrock prior to reaching 

the aquifer. This interpretation is supported by additional 

work conducted by Pollock and others (2011) who observed 

well-buffered regolith and cave drip water in the unsaturated 

zone above a cave in the upper Ozark aquifer.

No strong spatial trend was noted for the distribution 

of dissolved solids in the lower Ozark aquifer. However, a 

general trend of increasing dissolved solids was observed 

moving from the south toward the northeast, especially 

in the eastern extent. The greatest frequency of dissolved 

solids greater than 300 mg/L occurred in the exposed 

sections of the Powell, Cotter, and Jefferson City Dolomites 

as compared to the St. Peter and Everton Formations (not 

shown in fig. 117). Bicarbonate exhibited strong positive 

correlations with dissolved-solids concentrations for the 

upper (fig. 118E) and the lower (fig. 118F) Ozark aquifers, 

with R2 values of 0.9235 and 0.7387, respectively. The spatial 

distribution of bicarbonate was similar to that of dissolved 

solids with higher concentrations observed to the northeast. 

Kresse and Fazio (2004) noted lower mean, median, and 

maximum bicarbonate and dissolved-solids concentrations 

in groundwater from the St. Peter and Everton Formations 

compared to other formations of the upper Ozark aquifer. 

There is insufficient evidence to discern if these differences 

are attributable to the solubility of carbonate minerals 

between the formations or if the higher concentrations 

are an artifact of longer residence time and greater rock/

water interaction in the Powell, Cotter, and Jefferson City 

Dolomites along longer flow paths.
302 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

NEWTON STONE

WASHINGTON MADISON

CLAY

GREENE

LAWRENCE

CRAIGHEAD

POPE JACKSON JOHNSON VAN BUREN POINSETT CRAWFORD FRANKLIN

CLEBURNE

BENTON

IZARD SHARP

BOONE

SEARCY

FULTON

MARION

CARROLL BAXTER

RANDOLPH

LAWRENCE

FRANKLIN

RANDOLPH

LAWRENCE

FRANKLIN

RANDOLPH

LAWRENCE

FRANKLIN

RANDOLPH

INDEPENDENCE

NEWTON STONE

WASHINGTON MADISON

CLAY

GREENE

CRAIGHEAD

POPE JACKSON JOHNSON VAN BUREN POINSETT CRAWFORD CLEBURNE

BENTON

IZARD SHARP

BOONE

SEARCY

FULTON

MARION

CARROLL BAXTER

INDEPENDENCE

NEWTON STONE

WASHINGTON MADISON

CLAY

GREENE

CRAIGHEAD

POPE JACKSON JOHNSON VAN BUREN POINSETT CRAWFORD CLEBURNE

BENTON

IZARD SHARP

BOONE

SEARCY

FULTON

MARION

CARROLL BAXTER

INDEPENDENCE

NEWTON STONE

WASHINGTON MADISON

CLAY

GREENE

CRAIGHEAD

POPE JACKSON JOHNSON VAN BUREN POINSETT CRAWFORD CLEBURNE

BENTON

IZARD SHARP

BOONE

SEARCY

FULTON

MARION

CARROLL BAXTER

INDEPENDENCE

0 30 60 MILES

0 30 60 KILOMETERS

36°30'

36°00'

36°30'

36°00'

36°30'

36°00'

93°00' 91°00'

93°00' 91°00'

93°00' 91°00'

93°00' 91°00'

36°30'

36°00'

ARKANSAS

Area enlarged

Calcium to 

magnesium ratio

0.5 to 1.0

1.1 to 3.0

3.1 to 5.0

5.1 to 10.0

10.1 to 20.0

20.1 to 32.5

Nitrate, in milligrams 

per liter

0 to 0.1

0.2 to 0.3

0.4 to 0.5

0.6 to 1.0

1.1 to 5.0

5.1 to 7.2

Sulfate, in milligrams 

per liter

0 to 5

6 to 10

11 to 20

21 to 40

41 to 50

51 to 138

Chloride, in milligrams 

per liter

1 to 5

6 to 10

11 to 20

21 to 30

31 to 50

51 to 113

EXPLANATION

EXPLANATION

EXPLANATION

EXPLANATION

Base modified from U.S. Geological Survey digital data, 1:250,000 Geology map modified from Haley and others, 1993

Universal Transverse Mercator projection, zone 15

EXPLANATION

Atoka Formation

Bloyd Shale and Prairie Grove 

Member of the Hale Formation

Cane Hill Member of the Hale

Formation

Cretaceous rocks

Sand and clay

Chattanooga Shale (Lower Mississippian 

and Upper Devonian), Clifty Limestone 

(Middle Devonian), and Penters Chert 

(Lower Devonian)

Boone Formation

Moorefield Formation

Pitkin Limestone

Ruddell Shale Cason Shale and Fernvale Limestone (Upper 

Ordovician) and Kimmswick Limestone, 

Plattin Limestone, and Joachim Dolomite 

(Middle Ordovician)

Cotter and Jefferson City Dolomites

Powell Dolomite

St. Peter Sandstone and Everton Formation 

(Middle Ordovician)

Alluvium and terrace deposits Lafferty, St. Clair, and Brassfield Limestones

Water bodies

Geologic formations of the Ozark Plateaus

Upper Qzark aquifer

Upper Qzark aquifer

Upper Qzark aquifer

Lower Qzark aquifer

Figure 117. Spatial distribution of selected chemical constituents in groundwater from the Ozark aquifer in northern Arkansas.
Aquifers of the Interior Highlands 303

Table 44. Descriptive statistics for selected chemical constituents in groundwater from the upper Ozark aquifer in northern Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent Minimum Median Maximum Standard 

deviation

Number 

of wells

Calcium (mg/L) 4.4 63 140 21.13 132

Magnesium (mg/L) 0.8 28 71 14.49 132

Sodium (mg/L) 0.7 2.4 696 61.95 129

Potassium (mg/L) 0.1 1.1 22 2.76 127

Bicarbonate (mg/L) 2.0 313 1,720 169.02 104

Chloride (mg/L) 0.3 4.1 105 12.27 133

Sulfate (mg/L) 0.4 8.8 138 20.40 133

Silica (mg/L) 0.13 9.9 20 2.56 117

Nitrate (mg/L as nitrogen) 0.01 0.62 7.2 1.26 124

Dissolved solids (mg/L) 52 285 1,735 154.64 132

Iron (μg/L) 0.05 5.2 1,600 252.26 112

Manganese (μg/L) 0.13 0.13 40 6.86 123

Arsenic (μg/L) 0.03 0.03 6.96 1.12 73

Hardness (mg/L as calcium carbonate) 20 243 520 101.88 84

Specific conductance (μS/cm) 89 518 2,840 250.98 130

pH (standard units) 4.8 7.3 8.7 0.45 133

Table 45. Descriptive statistics for selected chemical constituents in groundwater from the lower Ozark aquifer in northern Arkansas.

[mg/L, milligrams per liter; μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent or 

characteristic Minimum Median Maximum Standard deviation

Number 

of wells

Calcium (mg/L) 11 45 91 16.95 55

Magnesium (mg/L) 0.07 23 83 13.95 55

Sodium (mg/L) 0.73 2.3 100 29.66 40

Potassium (mg/L) 0.4 1.7 6.1 1.45 27

Bicarbonate (mg/L) 22 270 548 102.16 31

Chloride (mg/L) 1.0 4.0 113 19.08 63

Sulfate (mg/L) 0.4 12 49 10.42 59

Silica (mg/L) 1.7 9.4 14.4 2.54 23

Nitrate (mg/L as nitrogen) 0.01 0.18 29 5.79 48

Dissolved solids (mg/L) 93 276 431 75.85 59

Iron (μg/L) 0.05 30 3,600 667.73 29

Manganese (μg/L) 0.13 10 7,000 1,181.78 35

Arsenic (μg/L) 0.03 0.03 4.5 1.43 12

Hardness (mg/L as calcium carbonate) 50.9 200 400 80.71 51

Specific conductance (μS/cm) 10 459 1,640 231.36 39

pH (standard units) 6.7 7.7 8.4 0.44 43
304 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000

Well depth, in feet below ground surface

0 100 200 300 400 500

Dissolved solids, in milligrams per liter

0 100 200 300 400 500

Dissolved solids, in milligrams per liter

0 20 40 60 80 100 120 140 160

Well depth, in feet below ground surface

0 100 200 300 400 500 600

Dissolved solids, in milligrams per liter

0 100 200 300 400 500 600

Dissolved solids, in milligrams per liter

0

1

2

3

4

5

6

7

8

9

10

0

1

2

3

4

5

6

7

8

9

0

100

200

300

400

500

600

0

1

2

3

4

5

6

7

8

9

10

0

100

200

300

400

500

600

0

1

2

3

4

5

6

7

8

9

pH, in standard units pH, in standard units

pH, in standard units pH, in standard units

Bicarbonate, in milligrams per liter

Bicarbonate, in milligrams per liter

A. Upper Ozark aquifer B. Upper Ozark aquifer

E. Upper Ozark aquifer

C. Lower Ozark aquifer D. Lower Ozark aquifer

F. Lower Ozark aquifer

R2 = 0.0687

R2

 = 0.0003

R2

 = 0.7387 R2

 = 0.9235

R2

 = 0.0031

R2 = 0.0135

Figure 118. Relation of pH to A, well depth and B, dissolved solids in the upper Ozark aquifer and to C, well depth and D, dissolved 

solids in the lower Ozark aquifer; and relation of bicarbonate to dissolved solids in E, the upper Ozark aquifer and F, the lower Ozark 

aquifer.
Aquifers of the Interior Highlands 305

Nitrate

Nitrate concentrations in 124 samples from the upper 

Ozark aquifer ranged from 0.01 to 7.2 mg/L with a median of 

0.62 mg/L (table 44). For purposes of this section, “elevated” 

concentrations of nitrate (expressed as nitrogen) refer to 

concentrations exceeding 0.4 mg/L, which is considered a 

background concentration for nitrate in relatively undisturbed 

areas of the Ozarks (see “Springfield Plateau Aquifer” 

section). For the lower Ozark aquifer, nitrate concentrations 

in 48 samples ranged from 0.01 to 29 mg/L with a median of 

0.18 mg/L (table 45). Two wells in the lower Ozark aquifer 

had concentrations of 28 and 29 mg/L, which was far above 

the maximum concentration in the upper Ozark aquifer. 

However, the median of 0.18 mg/L reflects the overall lower 

nitrate concentrations in the lower Ozark aquifer compared to 

that of the upper Ozark aquifer (median of 0.62 mg/L). 

The two very high nitrate concentrations in a deep, 

confined aquifer pose questions on the transport of nitrate 

to such depths. Prior and others (1999) noted that problems 

in the ability to retrieve samples representing groundwater 

only from the Roubidoux or Gunter geologic units (lower 

Ozark aquifer) were related directly to depth of the casing. 

Casing for domestic wells in the Ozark Plateaus typically is 

advanced only through 1–3 ft of bedrock (effectively casing 

off unconsolidated regolith material) with the remainder of 

the well being an open-hole completion. For deeper publicsupply wells, the casing is advanced through parts of the 

upper, shallow formations to a depth determined by drillers 

and water suppliers, and the remainder is left as an open-hole 

completion. Although the ADH recommends casing entirely 

through overlying, shallow exposed formations, no legally 

binding regulation has been enacted that requires such casing. 

Because overlying formations are not fully cased, or perhaps 

the casing has become compromised during completion 

or deteriorated over time, there is increased opportunity 

for influx of surface-derived contaminants into the deeper 

confined formations of the lower aquifer. No relation was 

found between well depth and nitrate concentrations for the 

lower or upper Ozark aquifers. Several nitrate concentrations 

that exceeded 1.0 mg/L occurred throughout a range of 

500–3,500 ft in the lower Ozark aquifer. One well with a depth 

of 3,420 ft had a concentration of 3.4 mg/L, although most 

concentrations were less than 1.0 mg/L. These elevated nitrate 

concentrations may be ascribed to the increased vulnerability 

of karst aquifers to surface-derived contaminants and to the 

lack of adequate well casing regardless of well depth.

Numerous studies have discussed the occurrence 

of elevated nitrate in groundwater from karst aquifers of 

the Ozark Plateaus, and several have noted lower overall 

concentrations in the Ozark aquifer compared to the 

Springfield Plateau aquifer (Leidy and Morris, 1990b; 

Smith and Steele, 1990; Steele and McCalister, 1990, 

Adamski, 1997; Huetter and others, 1997; Kresse and 

others, 2011). These studies were conducted in northwestern 

Arkansas, which is dominated by exposures of the Boone 

Formation that constitutes the Springfield Plateau aquifer. 

A common hypothesis within these studies was that the 

lower concentrations in the Ozark aquifer were because 

of the protection afforded by overlying formations of the 

Springfield Plateau aquifer and the Ozark aquifer confining 

unit (Chattanooga Shale). Median nitrate concentrations from 

the upper (table 44) and lower (table 45) Ozark aquifers were 

0.62 and 0.18 mg/L, respectively, compared to 1.8 mg/L from 

the Springfield Plateau (table 43). 

To investigate confinement as the dominant control 

on lower nitrate concentrations, Kresse and others (2011) 

compared nitrate data from two separate studies. One study 

(Adamski, 1997) was in northwestern Arkansas where the 

Ozark aquifer is confined by overlying Mississippian-age 

formations. The other study (Kresse and Fazio, 2004) was 

conducted in northeastern Arkansas where the aquifer is 

unconfined, exposed at the surface, and more vulnerable to 

contamination. Kresse and Fazio (2004) sampled groundwater 

from the upper Ozark aquifer in northeastern Arkansas and 

reported median nitrate concentrations in springs of 0.47 mg/L 

and median concentrations in wells of 0.63 mg/L. These data 

compared closely to median concentrations from springs 

(0.40 mg/L) and wells (0.60 mg/L) in the confined upper 

Ozark aquifer sampled in northwestern Arkansas (Adamski, 

1997). Because median nitrate concentrations for the Ozark 

are similar in areas whether confined or exposed, Kresse and 

others (2011) hypothesized that other factors must influence 

the lower vulnerability of the Ozark aquifer to surface-derived 

contaminants.

A positive correlation between nitrate concentrations 

and agricultural land use in northwestern Arkansas for 

groundwater collected dominantly from the Springfield 

Plateau aquifer (see “Springfield Plateau Aquifer” section) 

was shown by Adamski (1997) and Kresse and others (2011). 

One plausible explanation for the lower nitrate concentrations 

in the Ozark aquifer is lower agricultural land use in the 

northeastern part of the Ozark Plateaus, where the Ozark 

aquifer is exposed at the surface. Kresse and others (2011) 

determined percent agricultural land use in the upper Ozark 

aquifer in northeastern Arkansas using data from Kresse 

and Fazio (2004) and plotted nitrate concentrations and 

10 percent increments of increasing agricultural land use to 

investigate the effects of increasing agricultural land use on 

nitrate concentrations (fig. 119A). The results were compared 

to that of Kresse and others (2011) for well and spring nitrate 

concentrations in northwestern Arkansas (fig. 119B). Mean 

nitrate concentrations for the upper Ozark aquifer were 

much lower for all categories of percent agricultural land use 

compared to data taken from the Springfield Plateau aquifer in 

northwestern Arkansas. The overall mean nitrate concentration 

of 0.73 mg/L for data from the upper Ozark aquifer in 

northeastern Arkansas was exceeded for most agricultural 

land-use categories greater than 30–40 percent (fig. 119A), 

and all mean nitrate concentrations for agricultural land use 

below 30 percent were less than about 0.3 mg/L. Conversely, 

the mean nitrate concentrations for agricultural land use below 
306 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

0–10 10–20 20–30 30–40 40–50 50–60 60–70 70–80 >80

Agricultural land use, in percent of total land use

0–10 10–20 20–30 30–40 40–50 50–60 60–70 70–80 >80

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Mean nitrate, in milligrams per liter (mg/L) as nitrogen

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Mean = 2.4 mg/L

Mean = 0.73 mg/L

A. Ozark aquifer (Kresse and Fazio, 2004)

B. Springfield Plateau aquifer (Kresse and others, 2011)

105

68

96

88

119

131

93 78

42

9

7 7 3

9

3

6

8

6

7 Number of samples

EXPLANATION

Figure 119. Nitrate concentrations and agricultural land use for groundwater from A, the Ozark aquifer in northeastern Arkansas and 

B, from the Springfield Plateau aquifer in northwestern Arkansas.
Aquifers of the Interior Highlands 307

30 percent for the Springfield Plateau aquifer in northwestern 

Arkansas were all greater than 1.0 mg/L (upward to 1.9 mg/L) 

(fig. 119B). The highest mean nitrate concentrations for 

the upper Ozark aquifer (fig. 119A) occurred at percent 

agricultural land use between 50–60 percent (mean nitrate 

concentration of 1.2) and 60 to 70 percent (mean nitrate 

concentration of 1.3 mg/L). By comparison, the mean 

nitrate concentrations at these categories, 50–60 percent and 

60–70 percent, for the Springfield Plateau aquifer data were 

2.8 and 3.2 mg/L, respectively (fig. 119B). Therefore, nitrate 

concentrations are much lower in the upper Ozark aquifer 

than in the Springfield Plateau aquifer for similar increases 

in agricultural land use. This finding indicates that the upper 

Ozark aquifer, even where exposed at the surface, is less 

vulnerable to contamination than the Springfield Plateau 

aquifer, regardless of the percent agricultural land use. The 

soils overlying the upper Ozark aquifer, or the geologic units 

of the shallow part of the aquifer itself, may have physical 

characteristics (lower permeability soils, thicker regolith, less 

fracturing and dissolution of rocks, fewer bedding planes, 

and other factors) favoring a lower vulnerability to influx 

of surface-derived contaminants than the soils overlying the 

Springfield Plateau aquifer. 

A general trend of a higher density of elevated nitrate 

concentrations was observed in the eastern part of the upper 

Ozark aquifer, where it is exposed, compared to areas where 

the upper Ozark aquifer is overlain by the Chattanooga Shale 

and the Springfield Plateau aquifer (fig. 117). Therefore, 

some protection is afforded where it is confined by overlying 

formations of the Springfield Plateau aquifer and the Ozark 

confining unit. An important protection and management 

conclusion based on these data is that sufficient casing for 

isolating groundwater from the more vulnerable Springfield 

Plateau aquifer should prevent influx of surface-derived 

contaminants into the upper Ozark aquifer in this area of 

the Ozark Plateaus. No spatial trend was noted for nitrate 

concentrations in the lower Ozark aquifer. The fact that 

elevated nitrate concentrations occur in the confined, lower 

Ozark aquifer at well depths exceeding 1,000 ft suggests 

inadequate casing in these wells. The casing of all overlying 

formations when drilling wells for public supply could prevent 

contamination of the lower Ozark aquifer.

Pesticides 

The occurrence of pesticides in groundwater from 

the Ozark Plateaus in Arkansas, Kansas, Missouri, and 

Oklahoma was investigated by Adamski (1997). Pesticides 

were detected in 14 of 63 (22 percent) of the samples from 

the Ozark aquifer (the upper and lower Ozark aquifer were 

not differentiated). Many of the sampling sites were located 

in northwestern Arkansas. Pesticides were detected at a lower 

rate in the Ozark aquifer compared to the Springfield Plateau 

aquifer, demonstrating the reduced vulnerability of the Ozark 

aquifer to surface-derived contaminants. The most commonly 

detected pesticides were tebuthiuron; atrazine; prometon; 

desethylatrazine, a metabolite of atrazine; and simazine. These 

compounds are herbicides that are commonly used on pastures 

and noncrop areas.

Radium

Radium in groundwater was analyzed as part of the 

Ozarks National Water Quality Assessment study (Adamski 

and others, 1995). The combined radium-226 and radium-228 

activity ranged from 5.1 to 13.9 picocuries per liter (pCi/L) 

in 18 water samples from public-supply wells in Missouri 

in 1983 and ranged from 4.9 to 12.8 pCi/L in samples from 

several public-supply wells in northern Arkansas in 1987–89. 

Depths of these wells ranged from 250 to more than 1,700 

ft below land surface. Only one well in Arkansas had levels 

above the Federal MCL of 5 pCi/L.

Sampling of public-water systems by the ADH revealed 

a systemic radium problem in the lower Ozark aquifer. Three 

systems in Newton County, three in Searcy County, three in 

Boone County, and one each in Marion and Carroll Counties 

have had at least one well with historical violations for the 

combined radium MCL of 5 pCi/L. Contamination above the 

MCL of 5 pCi/L for these public-supply wells presently is 

attributed to an association with early Paleozoic shales within 

the lower Ozark aquifer. The contamination has resulted in 

abandonment of wells and selection of alternate sources of 

drinking water for most of these systems. The Ozark Mountain 

Regional Public Water Association is constructing a surface 

intake on Bull Shoals Lake in eastern Newton County to 

replace many of the public-water suppliers using groundwater 

from the Ozark aquifer (Darcia Routh, Arkansas Department 

of Health, written commun., 2013). 

Iron

Iron concentrations generally are low in groundwater 

from the Ozark aquifer throughout the Ozark Plateaus. Iron 

concentrations ranged from 0.05 to 1,600 μg/L with a median 

of 5.2 μg/L (fig. 120; table 44) in the upper Ozark aquifer and 

from 0.05 to 3,600 μg/L with a median of 30 μg/L in the lower 

Ozark aquifer (fig. 121; table 45). Only 4 of 112 samples 

from the upper Ozark aquifer exceeded the Federal secondary 

drinking-water regulation of 300 μg/L, and 4 of 29 samples 

from the lower Ozark aquifer exceeded this limit.
308 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

0

50

100

150

200

250

300

350

400

450

Concentrations, in milligrams per liter

500

Concentration, in micrograms per liter

700

800

900

1,000

0

100

200

300

400

500

600

112

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

132

132

129

104

133 133 112

Constituent Constituent

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron

Figure 120. Interquartile range of selected chemical constituents in groundwater from the upper Ozark aquifer in northern Arkansas.

55

55 40

31

63 59

29

29

EXPLANATION 

Number of values

75th percentile

50th percentile (median)

25th percentile

0

50

100

150

200

250

300

350

400

450

500

700

800

900

1,000

0

100

200

300

400

500

600

Concentrations, in milligrams per liter

Concentration, in micrograms per liter

Constituent Constituent

Calcium

Magnesium

Sodium

Bicarbonate

Chloride

Sulfate

Iron

Figure 121. Interquartile range of selected chemical constituents in groundwater from the lower Ozark aquifer in northern Arkansas.
Aquifers of the Interior Highlands 309

Sulfate

Sulfate concentrations generally are low in the Ozark 

aquifer and were below the Federal secondary drinkingwater regulation of 250 mg/L in all samples from the upper 

and lower Ozark aquifer. Whereas the maximum sulfate 

concentration in 59 samples from the lower Ozark aquifer 

was 49 mg/L, the upper Ozark aquifer had a maximum of 

138 mg/L, and 6 of 133 samples were greater than 50 mg/L 

(table 44). Sulfate concentrations generally were below 

10 mg/L in areas where formations composing the upper 

Ozark aquifer (Fernvale Limestone through Jefferson 

City Dolomite; fig. 117) are exposed and greater than 

20 mg/L (upward to 138 mg/L) where the upper Ozark 

aquifer is overlain by younger formations (fig. 117). Shale 

formations typically have groundwater with elevated sulfate 

concentrations relative to overlying and underlying aquifers 

(Kresse and Hays, 2009). Leakage through the overlying 

Chattanooga Shale that serves as the Ozark aquifer confining 

unit may be contributing sulfate to the upper Ozark aquifer in 

this area. 

Chloride

Chloride concentrations generally are low throughout the 

Ozark aquifer. Concentrations ranged from 0.3 to 105 mg/L 

with a median of 4.1 mg/L in the upper Ozark aquifer 

(fig. 120; table 44) and ranged from 1.0 to 113 mg/L with 

a median of 4.0 mg/L in the lower Ozark aquifer (fig. 121; 

table 45). Various reports have commented on potential higher 

salinity groundwater in the lower Ozark aquifer, where it dips 

steeply south of the Springfield-Salem Plateaus toward the 

Arkansas River. Lamonds (1972) stated that groundwater in 

the southern extent of the lower Ozark aquifer was assumed to 

be highly mineralized but did not provide spatial information 

on salinity gradients or saltwater-freshwater transition zones. 

MacDonald and others (1977) stated that chloride increases 

with the regional gradient toward the Arkoma Basin and 

calculated salinity concentrations ranging from 2,000 to 

3,000 mg/L using formation density and induction-electric 

logs. Imes and Emmett (1994) stated that the lower Ozark 

aquifer was saline only in the region between the Boston 

Mountains and the Arkansas River. Prior and others (1999) 

stated that most wells advanced into the lower Ozark aquifer 

in the Boston Mountains were reported to contain brine 

and hypothesized that deeper wells in the extreme southern 

Ozark Plateaus probably would encounter increased water 

salinity. A general spatial trend was noted for increases 

in chloride to the south (fig. 117). Wells with the highest 

chloride concentrations, which are located near the southern 

boundary of the Springfield Plateau (Boone Formation), may 

represent an approximate southern boundary of usable fresh 

groundwater in the lower Ozark aquifer. No spatial trends 

were apparent for chloride concentrations in the upper Ozark 

aquifer.

In summary, the Ozark aquifer comprises carbonate 

formations that have weathered to form a karst terrain, which 

increases vulnerability to surface-derived contaminants. 

Because agriculture in the form of dairy and beef cattle, 

poultry, and swine operations is the dominant land use in 

the Ozark Plateaus, nutrients, bacteria, and pesticides pose 

the greatest threat to groundwater quality. Elevated nitrate 

concentrations were noted in groundwater from the upper and 

lower Ozark aquifer, in spite of the fact that the lower Ozark 

aquifer is confined and well depths generally are more than 

1,000 ft. The thin soils and karst features associated with 

the Ozark aquifer coupled with insufficient casing appear 

to facilitate the transport of agricultural contaminants to the 

upper and lower Ozark aquifers. An important protection and 

management conclusion based on these data is that sufficient 

casing for isolating groundwater from the more vulnerable 

Springfield Plateau aquifer may prevent influx of surfacederived contaminants into the upper Ozark aquifer in this area 

of the Ozark Plateaus. 

Summary

Aquifers in Arkansas that currently serve or have 

served as important sources of water supply were described 

with respect to existing State and Federal groundwater 

protection and management programs, geology, hydrologic 

characteristics, water use, water levels, deductive analyses, 

and projections of aquifer conditions using groundwater 

models, and water quality for 16 aquifers. State and Federal 

protection and management programs were described 

according to regulatory oversight, management strategies, 

and ambient groundwater-monitoring programs that currently 

are in place for assessing and protecting groundwater 

resources throughout the State. Information was compiled 

and summarized from about 550 historical and recent 

publications that describe the hydrology and geochemistry 

of each of the aquifers. Additionally, more than 8,000 sites 

with groundwater-quality data were obtained from the U.S. 

Geological Survey National Water Information System and the 

Arkansas Department of Environmental Quality databases and 

entered into a spatial database to investigate distribution and 

trends in groundwater chemical constituents for each of the 

aquifers. 

The 16 aquifers of the State are divided into two major 

physiographic regions: the Coastal Plain of eastern Arkansas 

and the Interior Highlands of western Arkansas. Aquifers in 

the Coastal Plain comprise Cenozoic-age strata consisting 

primarily of Cretaceous, Tertiary, and Quaternary sands, 

gravels, silts, and clays, with groundwater primarily produced 

from coarse-grained sands and gravels within these aquifers. 

Except for isolated areas of Quaternary alluvial deposits that 

serve as valuable sources of groundwater supply, aquifers 

of the Interior Highlands predominantly consist of fractured 

sandstone, shale, chert, and carbonate rocks. These rocks 

are well indurated and primary porosity is low. Secondary 

porosity is created by weathering, fracturing, and dissolution, 

resulting in relatively low storage and low well yields from 

aquifers of the Interior Plains.
310 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Groundwater in the Coastal Plain of Arkansas represents 

one of the most valuable natural resources in the State, driving 

the economic engines of agriculture, while also supplying 

abundant water for commercial, industrial, and public-water 

supply. In terms of age from youngest to oldest, the aquifers 

of the Coastal Plain include: Quaternary alluvial aquifers 

including the Mississippi River Valley alluvial aquifer, 

the Jackson Group, and the Cockfield, Sparta, Cane River, 

Carrizo, Wilcox, Nacatoch, Ozan, Tokio, and Trinity aquifers. 

The Mississippi River Valley alluvial aquifer is the 

most important aquifer in terms of total groundwater used in 

Arkansas. Arkansas ranks fourth nationally in groundwater 

use, and 94 percent of all groundwater used in Arkansas is 

from the Mississippi River Valley alluvial aquifer. Wateruse rates continue to increase for this aquifer; rates in 

2010 from the aquifer were approximately 7,400 million 

gallons per day (Mgal/d). Intensive use has led to (1) severe 

water-level declines resulting in deep cones of depression 

in the potentiometric surface, (2) rates of pumping that 

exceed recharge and are unsustainable in many areas, and 

(3) designation of critical groundwater area status for the 

aquifer in several areas of eastern Arkansas. These conditions 

have led to development of alternate water supplies, including 

construction of major surface-water diversions and the drilling 

of deeper wells into the Sparta aquifer to supplement irrigation 

water demands. Water quality generally is good throughout the 

aquifer. However, elevated iron concentrations in most areas 

preclude use of the aquifer for public-supply, commercial, 

and industrial purposes without treatment. Elevated salinity 

additionally occurs in different areas of eastern Arkansas, 

resulting from upwelling of high-salinity water from 

underlying formations or evapotranspiration in clay-rich 

backswamp areas. 

The Jackson Group in south-central Arkansas is formally 

designated as a regional confining unit, though serving as a 

locally important aquifer for domestic and farm supply for 

six counties up through the 1990s. Low well yields and poor 

water quality, in addition to wider availability of public-supply 

sources, have resulted in no known use from the aquifer at the 

time of this report.

The Cockfield is a principal aquifer in southeastern 

Arkansas and had a reported use of approximately 19 Mgal/d 

in 2010. This aquifer serves dominantly as source of domestic 

supply but has been used for small public-supply systems. It 

has been increasingly used over the years as a public supply 

and more recently for irrigation. Groundwater in the outcrop 

area has low pH and dissolved solids, elevated nitrate and 

iron concentrations, and is a calcium-bicarbonate water type. 

Groundwater downdip from the outcrop area is affected by 

cation exchange and transitions to a sodium-bicarbonate water 

type. Compared to the outcrop area, groundwater downdip 

has higher pH and increasing dissolved solids and lower 

nitrate and iron with more strongly reducing conditions further 

along the flow path. An area of elevated salinity occurs in 

Chicot County with chloride concentrations as high as 1,800 

mg/L that results from upwelling of saline water from great 

depths. Elevated sulfate concentrations in the central part 

of the aquifer were attributed to leakage of high-sulfate 

groundwater from the Jackson Group. 

The Sparta aquifer is the second most important 

aquifer in Arkansas in terms of volume of use and provided 

approximately 196 Mgal/d of water in 2010. The aquifer 

was used in the past dominantly as a source of public and 

industrial supply, although irrigation use has increased over 

the years in response to critically declining water levels in 

the Mississippi River Valley alluvial aquifer. Pumping rates 

that exceed recharge rates have resulted in severe waterlevel declines and the formation of eight separate cones 

of depression in the potentiometric surface. Groundwater 

from the Sparta aquifer generally is of very high quality; 

however, isolated areas contain slightly elevated chloride 

concentrations resulting from upwelling of high-salinity 

water from underlying formations. Changes in geochemistry 

result from a transitioning of calcium-bicarbonate to a 

sodium-bicarbonate water type along the flow path. There 

also are concomitant increases in dissolved solids, decreases 

in iron, and decreases in nitrate with changes in redox 

conditions along the flow path. 

The other aquifers of the Coastal Plain, the Cane River, 

Carrizo, Wilcox, Nacatoch, Ozan, Tokio, and Trinity aquifers, 

generally are used as important local sources of domestic, 

industrial, and public supply. In terms of reported water 

use, the Wilcox is recognized as the most important of these 

aquifers with a reported water use in 2010 of approximately 

37 Mgal/d. All other aquifers have reported uses of less than 

4 Mgal/d each. Use of groundwater from the Cane River, 

Carrizo, Tokio, and Trinity aquifers is solely in and near the 

respective outcrop areas in southeastern Arkansas. These 

aquifers all exhibit increasing salinity at various distances 

downdip from the outcrop areas that renders the groundwater 

unusable for most purposes. Water use for the Nacatoch and 

Wilcox aquifers also is restricted to areas in and near to the 

outcrop area with salinity increasing in the downdip direction 

in southwestern Arkansas. However, there is a higher 

percentage of sand in these aquifers in the northeastern part 

of the State that results in high quality water and in greater 

use of the aquifers in this region. Increasing sand percentages 

also occur for the Cane River and Carrizo Formations in the 

northeastern part of the State. However, these sands cannot 

be distinguished from and are included as part of the Sparta 

aquifer in this region. An increase in salinity downdip from 

the outcrop area for all of these aquifers in southwestern 

Arkansas was attributed to possible residual salinity from 

original marine depositional environments. In southwestern 

Arkansas, all of these aquifers had groundwater with low 

pH, high iron, and were of a calcium-bicarbonate water type 

in and near the outcrop area. The groundwater transitions to 

a sodium-bicarbonate water type with increasing dissolved 

solids, pH, and salinity, as well as lower iron and nitrate 

concentrations in the downdip direction of flow. 

The Interior Highlands of northern and western 

Arkansas has less reported groundwater use than other areas 
Summary 311

of the State. This is the result of a combination of factors 

including (1) prevalent and increasing use of surface water, 

(2) less intensive agricultural uses, (3) lower population and 

industry densities, (4) less potential yield of the resource, and 

(5) lack of detailed reporting. The overall lower well yields 

from aquifers of the Interior Highlands result in domestic 

supply as the dominant use, with minor industrial, public, and 

commercial-supply use. When large volumes are required 

for public and industrial supply with a growing population, 

surface water supplies the majority of these water needs. 

However, surface water is not available for large expanses of 

the rugged and remote Interior Highlands, so locally available 

groundwater is a critical, though small-scale water resource. 

The aquifers of the Interior Highlands generally occur in 

shallow, fractured, well-indurated, structurally modified 

bedrock compared to the relatively flat-lying, unconsolidated 

sediments of the Coastal Plain. 

Spatial trends in groundwater geochemistry of the 

Interior Highlands differ greatly from trends noted for aquifers 

of the Coastal Plain. In the Coastal Plain, the prevalence of 

long regional flow paths resulted in regionally predictable and 

mappable geochemical changes. In the Interior Highlands, 

groundwater moves along short, topographically controlled 

flow paths (from hilltops to valleys) within small watersheds. 

Consequently, dense data coverage from numerous wells 

would be required to effectively characterize these small 

groundwater basins and to define small-scale geochemical 

changes along any given flow path. Dominant changes in 

geochemistry for the Ouachita aquifer and the Western 

Interior Plains confining system were attributed to (1) rock 

type, (2) residence time along individual flow paths, and 

(3) resultant rock/water interaction and changes in redox 

zonation. Generally, groundwater evolves along flow paths 

from a calcium- to a sodium-bicarbonate water type, with 

increasing reducing conditions that result in denitrification, 

elevated iron and manganese, and ultimately to production 

of methane in the more geochemically evolved and strongest 

reducing conditions. 

In the Ozark and Springfield Plateau aquifers, rapid influx 

of surface-derived contaminants such as nitrogen, coupled 

with little to no attenuation processes, is attributed to the karst 

landscape developed on Mississippian- and Ordovician-age 

carbonate rocks. Agriculture in the form of beef and dairy 

cattle, swine, and poultry operations is the predominant land 

use in this region of steep topography and thin soils. There 

is a high degree of connectivity between the surface water 

and groundwater, expressed in the occurrence of sinkholes, 

solution fractures, caves, losing streams, large springs, and 

other karst features. This kart-derived interconnection leads 

to nutrients, bacteria, and other surface-derived contaminants 

associated with agricultural activities posing the greatest 

threat to groundwater quality in the Ozark aquifer. A direct 

correlation was noted for increasing nitrate concentrations 

with increasing percentage of agricultural land use for 

the Springfield Plateau and Ozark aquifers. Additionally, 

areas with a higher density of karst features were shown 

to have higher nitrate concentrations than areas with less 

karst features. Even in areas of similar agricultural land 

use, the presence of karst features was shown to account for 

approximately 12 percent of the variation between nitrate 

concentrations (12 percent greater in areas with dense karst 

features) for increasing agricultural land use.

References

Ackerman, D.J., 1987a, Generalized potentiometric surface 

of the aquifers in the Cockfield Formation, southeastern 

Arkansas, spring 1980: U.S. Geological Survey WaterResources Investigations Report 87–4212, 1 sheet.

Ackerman, D.J., 1987b, Generalized potentiometric surface 

of the aquifers in the Sparta-Memphis aquifer, eastern 

Arkansas, spring 1980: U.S. Geological Survey WaterResources Investigations Report 87–4282, 1 sheet.

Ackerman, D.J., 1989a, Hydrology of the Mississippi River 

Valley alluvial aquifer, South-Central United States—A 

preliminary assessment of the regional flow system: U.S. 

Geological Survey Water-Resources Investigations Report 

88–4028, 74 p.

Ackerman, D.J., 1989b, Potentiometric surfaces of the 

Mississippi River Valley alluvial aquifer in eastern 

Arkansas, spring 1972 and 1980: U.S. Geological Survey 

Water-Resources Investigations Report 88–4075, 1 sheet.

Ackerman, D.J., 1990, Hydrology of the Mississippi River 

Valley alluvial aquifer, South-Central United States: U.S. 

Geological Survey Water-Resources Investigations Report 

90–358, 228 p.

Ackerman, D.J., 1996, Hydrology of the Mississippi River 

Valley alluvial aquifer, South-Central United States: U.S. 

Geological Survey Professional Paper 1416–D, 56 p.

Adamski, J.C., 1987, The effect of agriculture on the quality 

of ground water in a karstified carbonate terrain, northwest 

Arkansas: Fayetteville, University of Arkansas, M.S. thesis, 

124 p.

Adamski, J.C., 1996, Radium and radon in ground water 

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

Oklahoma: U.S. Geological Survey Fact Sheet 181–96, 

1 sheet.

Adamski, J.C., 1997, Nutrients and pesticides in ground 

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

and Oklahoma: U.S. Geological Survey Water-Resources 

Investigations Report, 96–4313, 28 p.

Adamski, J.C., 2000, Geochemistry of the Springfield Plateau 

aquifer of the Ozarks Plateaus Province in Arkansas, 

Kansas, Missouri, and Oklahoma, U.S.A.: Hydrogeological 

Processes, v. 14, p. 849–866.
312 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

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

J.V., 1995, Environmental and hydrologic setting of the 

Ozarks Plateaus study unit, Arkansas, Kansas, Missouri, 

and Oklahoma: U.S. Geological Survey Water-Resources 

Investigations Report 94–4022, 69 p.

Agricultural Research Service, 2013, The ARS pesticide 

properties database: Agricultural Research Service, 

accessed January 17, 2013, at http://www.ars.usda.gov/

services/docs.htm?docid=14199.

Albin, D.R., 1960, Special ground-water report number 1, 

Murfreesboro area: Arkansas Geological and Conservation 

Commission in cooperation with the U.S. Geological 

Survey, 22 p.

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.

Albin, D.R., 1965, Water-resources reconnaissance of the 

Ouachita Mountains, Arkansas: U.S. Geological Survey 

Water-Supply Paper 1809–J, 14 p.

Albin, D.R., Hines, M.S., and Stephens, J.W., 1967, Water 

resources of Jackson and Independence Counties, 

Arkansas: U.S. Geological Survey Water-Supply Paper 

1839–G, 29 p.

Albin, D.R., Stephens, J.W., and Edds, Joe, 1967, Groundwater levels in deposits of Quaternary and Tertiary age, 

spring 1965: Arkansas Geological Survey Water Resources 

Summary, no. 4, 10 p.

Aley, T.J., 1988, Complex radial flow of ground water in 

flat-lying residuum-mantled limestone in the Arkansas 

Ozarks: Proceedings, Second Environmental Problems in 

Karst Terranes and Their Solutions, National Water Well 

Association Conference, p. 159–170.

Aley, T.J., and Aley, Cathy, 1987, Groundwater study—

Ozarks National Scenic Riverways: Ozark Underground 

Laboratory, Protem, Mo., National Park Service Contract 

CX 6000–4–0083, 222 p.

Alley, W.M., Healy, R.W., LaBaugh, J.W., and Thomas, E.R., 

2002, Flow and storage in groundwater systems: Science, 

v. 296, no. 5575, p. 1985–1990.

Alley, W.M., Reilly, T.E., and Franke, O.L, 1999, 

Sustainability of ground-water resources: U.S. Geological 

Survey Circular 1186, 79 p.

Androes, D., 2006, The origin and extent of quartz 

overgrowth cements in anomalous Eocene sandstones and 

siltstones within the Wilcox Group on Crowley’s Ridge: 

Fayetteville, University of Arkansas, M.S. thesis, 148 p.

Appelo, C.A.J., and Postma, Dieke, 1999, Geochemistry, 

groundwater, and pollution: Brookfield, Vt., A.A. Bakema 

Publishers, 536 p.

Arkansas Agriculture Department, 2013, About the 

aquaculture division: Arkansas Agriculture Department, 

accessed March 11, 2013, at http://aad.arkansas.gov/

aquaculture/Pages/default.aspx.

Arkansas Department of Environmental Quality, 1981, 

Groundwater—Elements of an Arkansas State groundwater 

quality protection strategy: Arkansas Department of 

Environmental Quality Water Division, v. 1, 96 p. (Also 

available at http://www.adeq.state.ar.us/water/branch_

planning/publications.htm.)

Arkansas Department of Environmental Quality, 2012, 

Integrated water quality monitoring and assessment report 

(draft): Arkansas Department of Environmental Quality, 

Water Division, prepared pursuant to Sections 305b and 

303d of the Federal Water Pollution Control Act, accessed 

May 10, 2013, at http://www.adeq.state.ar.us/water/reports_

data.htm.

Arkansas Department of Environmental Quality, 2013a, 

Remedial action trust fund, State priority list: Technical 

Branch, Hazardous Waste Division, accessed May 10, 2013, 

at http://www.adeq.state.ar.us/hazwaste/branch_tech/.

Arkansas Department of Environmental Quality, 2013b, 

Arkansas Brownfield Program: Arkansas Department of 

Environmental Quality, accessed May 10, 2013, at 

http://www.adeq.state.ar.us/hazwaste/bf/brownfield/.

Arkansas Department of Environmental Quality, 2013c, 

The Elective Sites Cleanup Program: Enforcement and 

Inspection Branch, Hazardous Waste Division accessed 

May 10, 2013, at http://www.adeq.state.ar.us/hazwaste/

branch_ie/.

Arkansas Department of Environmental Quality, 2013d, List 

of publications: Water Division, Water Quality Planning 

Branch, accessed May 3, 2013, at http://www.adeq.state.

ar.us/water/branch_planning/publications.htm.

Arkansas Department of Health, 1990, Wellhead protection 

program, State of Arkansas: Department of Health, Division 

of Engineering, September 1990.

Arkansas Department of Health, 2009, Source water 

assessment and protection programs: Arkansas Department 

of Health, Division of Engineering, Source Water Protection 

Program, accessed April 3, 2013, at http://www.healthy.

arkansas.gov/programsServices/environmentalHealth/

Engineering/sourceWaterProtection/Pages/default.aspx.

Arkansas Department of Health, 2013, Drinking water 

information for Arkansas: Arkansas Department of Health, 

accessed April 3, 2013, at http://www.healthy.arkansas.gov/

eng/autoupdates/pwslist0.htm.

Arkansas Game and Fish Commission, 1998, Arkansas 

wildlife—A history, K. Sutton, ed.: University of Arkansas 

Press, 328 p. 
References 313

Arkansas Geological Commission, 1980, Ground-water levels 

in observation wells in Arkansas, spring, 1980: Arkansas 

Geological Commission in cooperation with the U.S. 

Geological Survey Water Resources Summary, no. 15, 45 p.

Arkansas Industrial Development Commission, 1980, 

Directory of manufacturers in Arkansas, 1980: Arkansas 

Industrial Development Commission publication, 180 p.

Arkansas Natural Resources Commission, 1990, Water 

management, Arkansas water plan, available at http://anrc.

ark.org/divisions/water-resources-management/arkansaswater-plan.

Arkansas Natural Resources Commission, 1996, The 

designation of the Sparta aquifer within Bradley, Calhoun, 

Columbia, Ouachita, and Union Counties as a critical 

groundwater area: accessed May 31, 2013, at http://

www.anrc.arkansas.gov/Rules%20and%20Regulations/

orders/1995-1_designation_of_sparta_as%20cgwap.pdf.

Arkansas Natural Resources Commission, 1999, Arkansas 

nonpoint source management plan, 1998–2001, as amended: 

Little Rock, Ark., Arkansas Natural Resources Commission.

Arkansas Natural Resources Commission, 2005, Rules for 

the protection and management of groundwater, Title 

IV, effective 2005: Little Rock, Ark., Arkansas Natural 

Resources Commission.

Arkansas Natural Resources Commission, 2009, Order 

designating the Cache critical groundwater area: Arkansas 

Natural Resources Commission, accessed May 31, 2013, 

at http://www.anrc.arkansas.gov/Rules%20and%20

Regulations/orders/nea_critical_gw_designation_2009.pdf.

Arkansas Natural Resources Commission, 2011, Water law in 

Arkansas: Little Rock, Ark., Arkansas Natural Resources 

Commission, 58 p. 

Arkansas Natural Resources Commission, 2012a, Arkansas 

ground-water protection and management report for 2011: 

Little Rock, Ark., Arkansas Natural Resources Commission, 

139 p. 

Arkansas Natural Resources Commission, 2012b, Status 

report to the Arkansas Legislative Council on the Grand 

Prairie area: Demonstration Project and Bayou Meto Water 

Management District Irrigation Project, accessed April 

2, 2013, at http://www.arkleg.state.ar.us/assembly/2011/

Meeting%20Attachments/000/I10445/Exhibit%20H.9%20

-%20ANRC%20-%20Status%20Report.pdf.

Arkansas Natural Resources Commission, 2013a, Arkansas 

groundwater protection and management report for 2012, a 

supplement to the Little Rock, Ark., Arkansas Water Plan: 

Arkansas Natural Resources Commission, 57 p.

Arkansas Natural Resources Commission, 2013b, Fact 

sheet on well metering law: Arkansas Natural Resources 

Commission, accessed November 25, 2013, at https://static.

ark.org/eeuploads/anrc/fact_sheet_act_1426.pdf.

Arkansas Oil and Gas Commission, 2013, General rules and 

regulations, effective February 8, 2013: Little Rock, Ark., 

Arkansas Oil and Gas Commission, accessed April 2, 2013, 

at http://www.aogc.state.ar.us.

Arkansas Pollution Control and Ecology Commission, 

1993, Regulation no. 1—Regulation for the prevention of 

pollution by salt water and other oil field wastes produced 

by wells in all fields or pools, effective March, 16, 1993: 

Little Rock, Ark., Arkansas Pollution Control and Ecology 

Commission, accessed April 4, 2013, at http://www.adeq.

state.ar.us/regs.

Arkansas Pollution Control and Ecology Commission, 2002, 

Regulation no. 20—The Arkansas surface coal mining and 

reclamation code as revised, effective September 26, 2002: 

Little Rock, Ark., Arkansas Pollution Control and Ecology 

Commission, accessed April 4, 2013, at http://www.adeq.

state.ar.us/regs.

Arkansas Pollution Control and Ecology Commission, 2005, 

Regulation no. 17—Arkansas underground injection control 

code, effective February 14, 2005: Little Rock, Ark., 

Arkansas Pollution Control and Ecology Commission, 

accessed April 4, 2013, at http://www.adeq.state.ar.us/regs.

Arkansas Pollution Control and Ecology Commission, 2006, 

Regulation no. 29—Brownfields redevelopment as revised, 

effective March 3, 2006: Little Rock, Ark., Arkansas 

Pollution Control and Ecology Commission, accessed April 

4, 2013, at http://www.adeq.state.ar.us/regs.

Arkansas Pollution Control and Ecology Commission, 

2008, Regulation no. 22—Solid waste management rules, 

effective April 26, 2008: Little Rock, Ark., Arkansas 

Pollution Control and Ecology Commission, accessed April 

4, 2013, at http://www.adeq.state.ar.us/regs.

Arkansas Pollution Control and Ecology Commission, 2009, 

Regulation no. 12—Storage tank regulations as revised, 

effective December 28, 2009: Little Rock, Ark., Arkansas 

Pollution Control and Ecology Commission, accessed April 

4, 2013, at http://www.adeq.state.ar.us/regs.

Arkansas Pollution Control and Ecology Commission, 2011a, 

Regulation no. 34—State water permit regulation, effective 

September 26, 2011: Little Rock, Ark., Arkansas Pollution 

Control and Ecology Commission, accessed April 4, 2013, 

at http://www.adeq.state.ar.us/regs.
314 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Arkansas Pollution Control and Ecology Commission, 2011b, 

Regulation no. 2—Regulation establishing water quality 

standards for surface waters of the State of Arkansas as 

revised, effective September 26, 2011: Little Rock, Ark., 

Arkansas Pollution Control and Ecology Commission, 

accessed April 4, 2013, at http://www.adeq.state.ar.us/regs.

Arkansas Pollution Control and Ecology Commission, 

2012a, Regulation no. 23—Hazardous waste management 

as revised, effective August 12, 2012: Little Rock, Ark., 

Arkansas Pollution Control and Ecology Commission, 

accessed April 4, 2013, at http://ww.adeq.state.ar.us/regs.

Arkansas Pollution Control and Ecology Commission, 2012b, 

Regulation no. 5—Liquid animal waste management 

systems as revised, effective June 22, 2012: Little Rock, 

Ark., Arkansas Pollution Control and Ecology Commission, 

accessed April 4, 2013, at http://www.adeq.state.ar.us/regs.

Arkansas Pollution Control and Ecology Commission, 2012c, 

Regulation no. 15—The Arkansas open-cut mining and land 

reclamation code as revised, effective September 15, 2012: 

Little Rock, Ark., Arkansas Pollution Control and Ecology 

Commission, accessed April 4, 2013, at http://www.adeq.

state.ar.us/regs.

Arkansas Pollution Control and Ecology Commission, 2012d, 

Regulation no. 30—Arkansas remedial action trust fund 

hazardous substances site priority list, effective August 12, 

2012: Little Rock, Ark., Arkansas Pollution Control and 

Ecology Commission, accessed April 4, 2013, at http://

www.adeq.state.ar.us/regs.

Arkansas Soil and Water Conservation Commission, 1991, 

Identification of ground-water vulnerability areas in 

Arkansas: Little Rock, Ark., Arkansas Soil and Water 

Conservation Commission, 12 p.

Arkansas State Board of Health, 2012a, Rules and regulations 

pertaining to public water systems as revised, effective 

March 23, 2012: Little Rock, Ark., Arkansas State Board 

of Health, accessed March 30, 2013, at http://www.healthy.

arkansas.gov/programsServices/environmentalHealth/

Engineering/Pages/RulesRegulations. 

Arkansas State Board of Health, 2012b, Rules and regulations 

pertaining to public water systems as revised, effective 

March 23, 2012: Little Rock, Ark., Arkansas State Board 

of Health, Department of Health Center for Local Public 

Health Branch, Engineering Section, accessed March 30, 

2013, at http://www.healthy.arkansas.gov/programsServices/

environmentalHealth/Engineering/Pages/RulesRegulations.

Arkansas State Planning Board, 1939, Arkansas water 

resources: Little Rock, Ark., Arkansas State Planning 

Board, 92 p.

Arkansas State Plant Board, 2013, Arkansas ground water, 

groundwater pesticide database: Arkansas State Plant 

Board, accessed January 17, 2013, at http://plantboard.

arkansas.gov/Pages/default.aspx. 

Arkansas Water Study Commission, 1956, Water in 

Arkansas—A report on the surface water resources in 

Arkansas: Prepared at the Discretion of the General 

Assembly of Arkansas, 55 p.

Arkansas Water Well Construction Commission, 2011, 

Arkansas Water Well Construction Act, chapter 50 of the 

Arkansas Code, Title 17: Arkansas Water Well Construction 

Commission, accessed on May 10, 2013, at http://www.

arkansas.gov/awwcc/2011_law.pdf. 

Arthur, J.K., 2001, Hydrogeology, model description, and 

flow analysis of the Mississippi River alluvial aquifer in 

northwestern Mississippi: U.S. Geological Survey WaterResources Investigations Report, 2001–4035, 47 p.

Arthur, J.K., and Taylor, R.E., 1990, Definition of the 

geohydrologic framework and preliminary simulation of the 

ground-water flow in the Mississippi embayment aquifer 

system, Gulf Coastal Plain, United States: U.S. Geological 

Survey Water-Resources Investigations Report 86–4364, 

97 p.

Arthur, J.K., and Taylor, R.E., 1998, Ground-water flow 

analysis of the Mississippi embayment aquifer system, 

South-Central United States: U.S. Geological Survey 

Professional Paper, 1416–I, 148 p.

Baker, N.T., 1990, Summary and analysis of water-use data 

collection in eastern Arkansas: U.S. Geological Survey 

Water-Resources Investigations Report 90–4177, 25 p.

Baker, N.T., Manning, C.A., and Beavers, E.A., 1991, 

Inventory of public water supplies in Arkansas: U.S. 

Geological Survey Open-File Report 91–247, 157 p.

Baker, R.C., 1955, Arkansas’ ground-water resources: 

Arkansas Geological and Conservation Commission in 

cooperation with the U.S. Geological Survey Circular, no. 1, 

16 p.

Baker, R.C., Hewitt, F.A., and Billingsley, G.A., 1948, 

Ground-water resources of the El Dorado area, Union 

County, Arkansas: University of Arkansas Bulletin, v. 42, 

no. 12, 39 p.

Bangladesh Agricultural Development Corporation, 1992, 

Final report of the Deep Tubewell II Project, v. 2.1, Natural 

Resources: Report prepared for the Bangladesh Agricultural 

Development Corporation and Overseas Development 

Administration (United Kingdom), Mott MacDonald Ltd. 

and Hunting Technical Services, 401 p.
References 315

Barlow, P.M., and Leake, S.A., 2012, Streamflow depletion 

by wells—Understanding and managing the effects of 

groundwater pumping on streamflow: U.S. Geological 

Survey Circular 1376, 84 p.

Basile-Doelsch, D.I., Meunier, J.D., and Parron, Claude, 2005, 

Another continental pool in the terrestrial silicon cycle: 

Nature, v. 433, no. 7024, p. 399–402.

Bates, B.C., Kundzewicz, Z.W., Wu, Shaohong, and Palutikof, 

J.P., 2008, Climate change and water: Geneva, Switzerland, 

Technical Paper VI of the Intergovernmental Panel on 

Climate Change (IPCC), IPCC Secretariat, 210 p. 

Beaver Water District, 2010, Beaver Lake and its watershed: 

Beaver Water District, accessed October 9, 2012, at http://

www.bwdh2o.org/.

Bedinger, M.S., Emmett, L.F., and Jeffery, H.G., 1963, 

Ground-water potential of the alluvium of the Arkansas 

River between Little Rock and Fort Smith, Arkansas: U.S. 

Geological Survey, Water-Supply Paper, 1669–L, 29 p. 

Bedinger, M.S., and Jeffery, H.G., 1964, Ground water in the 

Lower Arkansas River Valley, Arkansas: U.S. Geological 

Survey Water-Supply Paper 1669–V, 17 p.

Bedinger, M.S., and Reed, J.E., 1961, Geology and groundwater resources of Desha and Lincoln Counties, Arkansas: 

Arkansas Geology and Conservation Commission Water 

Resources Circular 6, 129 p.

Bedinger, M.S., Stephens, J.W., and Edds, Joe, 1960, Decline 

of water levels in the Pine Bluff area: U.S. Geological 

Survey in cooperation with Arkansas Geological and 

Conservation Commission Special Ground-Water Report 

Number 2, 10 p.

Bell, Robert, 2010, History of U.S. aquaculture has roots in 

Arkansas: Arkansas Business, accessed December 11, 2012, 

http://www.arkansasbusiness.com/article/36243/history-ofus-aquaculture-has-roots-in-arkansas?page=all.

Bolyard, S.E., 2007, Migration of landfill contaminants in a 

tilted-block mantled-karst setting in northwestern Arkansas: 

Fayetteville, University of Arkansas, M.S. thesis, 69 p.

Boswell, E.H., Cushing, E.M., Hosman, E.L., and Jeffery, 

H.G., 1968, Quaternary aquifers in the Mississippi 

embayment, with discussion on quality of the water: U.S. 

Geological Survey Professional Paper 448–E, 15 p.

Boswell, E.H., Moore, G.K., MacCary, L.M., Jeffery, H.G., 

and others, 1965, Water resources of the Mississippi 

embayment—Cretaceous aquifers in the Mississippi 

embayment, with discussions on quality of the water: U.S. 

Geological Survey Professional Paper 448–C, 37 p.

Bowman, Steve, and Wright, Steve, 1999, Arkansas Duck 

Hunter’s Almanac: Fayetteville, Ark., Ozark Delta Press, 

272 p.

Brahana, J.V., 1982, Two-dimensional digital groundwater 

model of the Memphis Sand and equivalent units, 

Tennessee, Arkansas, Mississippi: U.S. Geological Survey 

Open-File Report 82–99, 55 p.

Brahana, J.V., and Broshears, R.E., 1989, Hydrogeology and 

ground-water flow in the Memphis and Fort Pillow aquifers 

in the Memphis area, Tennessee: U.S. Geological Survey 

Water-Resources Investigations Report 89–4131, 56 p.

Brahana, J.V., and Davis, R.K., 1998, Methodology for 

delineating ground-water recharge areas of springs in 

the carbonate-rock terrane of northwest Arkansas, and 

application to five separate spring basins within the region, 

in Davis, R.K., Brahana, J.V., and Johnston, J.S., eds., 

Ground water in northwest Arkansas—Minimizing nutrient 

contamination from non-point sources in karst terrane: 

Final report for tasks 94–300 and 95–300 to Arkansas Soil 

and Water Conservation Commission for EPA, Project 

#C9996103–02 and C9996102–03, 56 p.

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

Hydrogeologic data for Boone County, Arkansas: U.S. 

Geological Survey Open-File Report 91–518, 36 p.

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

Hydrogeologic data for Carroll County, Arkansas: U.S. 

Geological Survey Open-File Report 93–150, 32 p.

Brahana, J.V., and Mesko, T.O., 1988, Hydrogeology and 

preliminary assessment of regional flow in the upper 

Cretaceous and adjacent aquifers in the northern Mississippi 

embayment: U.S. Geological Survey Water-Resources 

Investigations Report, 87–4000, 65 p.

Brahana, J.V., Tennyson, Rodney, Terry, Jim, Hays, P.D., and 

Pollock, Erik, 2009, Reactivated basement faulting as a 

hydrogeologic control of hypogene speleogenesis in the 

southern Ozarks of Arkansas, U.S.A., in Stafford, Kevin, 

ed., Advances in hypogene karst studies: National Cave and 

Karst Research Institute Symposium 1, p. 99–110.

Brahana, J.V., Ting, T.E., Mohammed Al-Qinna, Murdoch, 

J.F., Davis, R.K., Laincz, Jozef, Killingbeck, J.J., Szilvagyi, 

Eva, Doheny-Skubic, Margaret, Chaubey, Indrajeet, 

Hays, P.D., and Thomas, Gregg, 2005, Quantification of 

hydrologic budget parameters for the vadose zone and 

epikarst in mantled karst, in Kuniansky, E.L., ed., U.S. 

Geological Survey Karst Interest Group, Proceedings, 

Rapid City, South Dakota, September 12–15, 2005: U.S. 

Geological Survey Scientific Investigations Report 2005–

5160, p. 144–152.

Brahana, J.V., 2011a, Karst hydrogeology of the southern 

Ozarks in Kuniansky, E.L., ed., U.S. Geological Survey 

Karst Interest Group, Proceedings, Fayetteville, Ark., 

April 26–29, 2011: U.S. Geological Survey Scientific 

Investigations Report 2011–5031, p. 119
316 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Brahana, J.V., 2011b, Ten relevant karst hydrogeologic 

insights gained from 15 years of in situ field studies at the 

Savoy Experimental Watershed in Kuniansky, E.L., ed., 

U.S. Geological Survey Karst Interest Group, Proceedings, 

Fayetteville, Ark., April 26–29, 2011: U.S. Geological 

Survey Scientific Investigations Report 2011–5031, 

p. 132–141

Branner, G.C., 1937, Data on springs in Arkansas: Arkansas 

Geological and Conservation Commission unnumbered 

series, 127 p.

Brannon, J.C., Podosek, F.A., and Cole, S.C., 1996, 

Radiometric dating of Mississippi Valley-type ore deposits, 

in Sangster, D.F., ed., Carbonate hosted lead-zinc deposits: 

Society of Economic Geologists Special Publication 4, 

p. 536–545.

Broom, M.E., Kraemer, T.F., and Bush, W.V., 1984, A 

reconnaissance study of the saltwater contamination in 

the El Dorado aquifer, Union County, Arkansas: U.S. 

Geological Survey Water-Resources Investigations Report 

84–4012, 47 p.

Broom, M.E., and Lyford, F.P., 1981, Alluvial aquifer of the 

Cache and St. Francis River Basins, northeastern Arkansas: 

U.S. Geological Survey Open-File Report 81–476, 48 p.

Broom, M.E., and Lyford, F.P., 1982, Alluvial aquifer of the 

Cache and St. Francis River Basins, northeastern Arkansas: 

Arkansas Geological Commission Circular No. 13, 48 p., 

13 pls.

Broom, M.E., and Reed, J.E., 1973, Hydrology of the Bayou 

Bartholomew alluvial aquifer-stream system, Arkansas: 

U.S. Geological Survey Open-File Report 73–34, 91 p.

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

Buckalew, A.R., and Buckalew, R.B., 1974, The discovery 

of oil in south Arkansas, 1920–1924: Arkansas Historical 

Quarterly, v. 32, p. 195–208.

Caplan, W.M., 1954, Subsurface geology and related oil 

and gas possibilities of northeastern Arkansas: Arkansas 

Resources and Development Commission Bulletin 20, 

124 p.

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

rocks in northern Arkansas: Arkansas Geological and 

Conservation Commission Information Circular 21, 17 p.

Cardon, G.E., and Mortvedt, J.J., 2001, Salt affected soils: 

Fort Collins, Colo., Colorado State University Cooperative 

Extension Service, 5 p.

Chapelle, F.H., 2001, Ground-water microbiology and 

geochemistry (2d ed.): New York, John Wiley and Sons, 

Inc., 477 p.

Chapelle, F.H., Bradley, P.M., Thomas, M.A., and McMahon, 

P.B., 2009, Distinguishing iron-reducing from sulfatereducing conditions: Ground Water, v. 47, no. 2, p. 300–305.

Chowdhury, A.A.F., 2002, The impact of the acreage allotment 

program on rice farming: International Advances in 

Economic Research, v. 8, no. 1, p. 49–57.

Clark, B.R., and Hart, R.M., 2009, The Mississippi 

Embayment Regional Aquifer Study (MERAS)—

Documentation of a groundwater-flow model constructed 

to assess water availability in the Mississippi embayment: 

U.S. Geological Survey Scientific Investigations Report 

2009–5172, 61 p.

Clark, B.R., Hart, R.M., and Gurdak, J.J., 2011a, Groundwater 

availability of the Mississippi embayment: U.S. Geological 

Survey Professional Paper 1785, 62 p.

Clark, B.R., Westerman, D.A., and Fugitt, D.T., 2011b, 

Simulation of the effects of groundwater withdrawals on 

water-level altitudes in the Sparta aquifer in the Bayou 

Meto-Grand Prairie area of eastern Arkansas, 2007–37: 

U.S. Geological Survey Scientific Investigations Report 

2011–5215, 9 p.

Clark, B.R., Westerman, D.A., and Fugitt, D.T., 2013, 

Enhancements to the Mississippi Embayment Regional 

Aquifer Study (MERAS) groundwater flow model and 

simulations of sustainable water-level scenarios: U.S. 

Geological Survey Scientific Investigations Report 2013–

5161, 36 p.

Cole, E.F., and Morris, E.E., 1986, Water resources of the 

Ouachita National Forest, Arkansas: U.S. Geological 

Survey Water-Resources Investigations Report 86–4166, 

1 sheet.

Conrad, T.A., 1856, Observations on the Eocene deposit of 

Jackson, Mississippi, with descriptions of thirty-four new 

species of shells and corals: Philadelphia Academy of 

Natural Sciences, Proceedings, v. 7, p. 257–258.

Cordova, R.M., 1963, Reconnaissance of the ground-water 

resources of the Arkansas Valley region: U.S. Geological 

Survey Water-Supply Paper 1669–BB, 33 p.

Coughlin, T.L., 1975, Geologic and environmental factors 

affecting groundwater chemistry in north-central 

Washington County, Arkansas: Fayetteville, University of 

Arkansas, M.S. thesis, 130 p.

Counts, H.B., 1957, Ground-water resources of parts of 

Lonoke, Prairie, and White Counties, Arkansas: Arkansas 

Geology and Conservation Commission Water Resources 

Circular 5, 65 p. 

Counts, H.B., and Engler, K., 1954, Changes in water levels 

in deposits of Quaternary age in eastern Arkansas from 

1938–1953: University of Arkansas, Agriculture Experiment 

Station Report Series 42, 11 p.
References 317

Counts, H.B., Tait, D.B., Klein, H., and Billingsley, G.A., 

1955, Ground-water resources in a part of southwestern 

Arkansas: Arkansas Geological Commission Water 

Resources Circular, no. 2, 35 p. 

Cox, G.D., Ogden, A.E., and Slavik, Gretta, 1980, 

Contamination of Boone-St. Joe Limestone groundwater 

by septic tanks and chicken houses: Arkansas Academy of 

Science Proceedings, v. 34, p. 41–44.

Cox, R.T., 2009, Ouachita, Appalachian, and ancestral Rockies 

deformations recorded in mesoscale structures on the 

foreland Ozark plateaus: Tectonophysics, v. 474, no. 3–4, 

p. 674–683.

Crider, A.F., 1906, Drainage of wetlands in Arkansas by wells: 

U.S. Geological Survey Water-Supply Paper 160, p. 54–58.

Crider, A.F., and Johnson, L.C., 1906, Summary of the 

underground-water resources of Mississippi: U.S. 

Geological Survey Water-Supply Paper 159, 86 p.

Cushing, E.M., Boswell, B.H., and Hosman, R.L., 1964, 

General geology of the Mississippi embayment: U.S. 

Geological Survey Professional Paper 448–B, 28 p.

Czarnecki, J.B., 2006a, Effects of proposed additional 

ground-water withdrawals from the Mississippi River 

Valley alluvial aquifer on water levels in Lonoke County, 

Arkansas: U.S. Geological Survey Scientific Investigations 

Report 2006–5275, 6 p.

Czarnecki, J.B., 2006b, Simulation of various management 

scenarios of the Mississippi River Valley alluvial aquifer in 

Arkansas: U.S. Geological Survey Scientific Investigations 

Report 2006–5052, 14 p.

Czarnecki, J.B., 2007, Simulated ground-water withdrawals 

by Cabot WaterWorks from the Mississippi River Valley 

alluvial aquifer, Lonoke County, Arkansas: U.S. Geological 

Survey Scientific Investigations Report 2007–5030, 39 p.

Czarnecki, J.B., 2008, Evaluation of selected model 

constraints and variables on simulated sustainable yield 

from the Mississippi River Valley alluvial aquifer system in 

Arkansas: U.S. Geological Survey Scientific Investigations 

Report 2008–5138, 21 p.

Czarnecki, J.B., 2009, Effects of potential changes in 

groundwater withdrawals from the Sparta aquifer on 

water-level altitudes in Jefferson County, Arkansas: U.S. 

Geological Survey Scientific Investigations Report 2009–

5234, 8 p.

Czarnecki, J.B., 2010, Groundwater-flow assessment of the 

Mississippi River Valley alluvial aquifer of northeastern 

Arkansas: U.S. Geological Survey Scientific Investigations 

Report 2010–5210, 33 p.

Czarnecki, J.B., Bolyard, S.E., Hart, R.M., and Clark, 

J.M., 2014, Digital surfaces and thicknesses of selected 

hydrogeologic units within the Ozark Plateaus aquifer 

system, northwestern Arkansas: U.S. Geological Survey 

Scientific Investigations Report 2013–5208, 25 p.

Czarnecki, J.B., Clark, B.R., and Reed, T.B., 2003, 

Conjunctive-use optimization model of the Mississippi 

River Valley alluvial aquifer of northeastern Arkansas: U.S. 

Geological Survey Water-Resources Investigations Report 

03–4230, 29 p.

Czarnecki, J.B., Clark, B.R., and Stanton, G.P., 2003, 

Conjunctive-use optimization model of the Mississippi 

River Valley alluvial aquifer of southeastern Arkansas: U.S. 

Geological Survey Water-Resources Investigations Report 

03–4233, 26 p. 

Czarnecki, J.B., Gillip, J.A., Jones, P.M., and Yeatts, D.S., 

2009, Groundwater-flow model of the Ozark Plateau aquifer 

system, northwestern Arkansas, southeastern Kansas, 

southwestern Missouri, and northeastern Oklahoma: U.S. 

Geological Survey Scientific Investigations Report 2009–

5148, 62 p. 

Czarnecki, J.B., Hays, P.D., and McKee, P.W., 2012, The 

Mississippi River Valley alluvial aquifer in Arkansas—A 

sustainable water resource?: U.S. Geological Survey Fact 

Sheet 041–02, 4 p.

Czarnecki, J.B., Pugh, A.L., and Blackstock, J.M., 2013, 

Potentiometric surface of the Ozark aquifer in northern 

Arkansas, 2010: U.S. Geological Survey Scientific 

Investigations Report 2014–5013, 16 p.

Czarnecki, J.B., and Schrader, T.P., 2013, Effects of recent 

climate variability on groundwater levels in eastern 

Arkansas: U.S. Geological Survey Scientific Investigations 

Report 2012–5258, 17 p.

Dall, W.H., 1898, A table of the North American Tertiary 

horizons, correlated with one another and those of Western 

Europe, with annotations: U.S. Geological Survey 18th 

Annual Report, part 2, p. 323–348.

Dane, C.H., 1929, Upper Cretaceous formations of 

southwestern Arkansas: Arkansas Geological Survey 

Bulletin 1, 215 p.

Davies, J., and Exley, C., 1992, Hydrochemical character 

of the main aquifer units of central and north-eastern 

Bangladesh and possible toxicity of groundwater to fish and 

humans, final report: British Geological Survey Technical 

Report WD/92/43R, 70 p.

Davis, R.K., Brahana, J.V., and Johnston, J.S., 2000, Ground 

water in northwest Arkansas—Minimizing nutrient 

contamination from non-point sources in karst terrane: 

Fayetteville, Ark., University of Arkansas, Arkansas Water 

Resources Center, no. MSC–288, 69 p.
318 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Davis, R.K., Hamilton, S., and Brahana, J.V., 2005, 

Escherichia coli survival in springs and streams of mantled 

karst aquifers, northwest Arkansas: Journal of American 

Water Resources Association, v. 41, n. 6, p. 1279–1287.

Davis, R.K., and Shephard, S., 2010, Beaver Lake and its 

watershed 2010, Beaver Water District, 44 p., accessed 

October 9, 2012, at http://www.bwdh2o.org/wp-content/

uploads/2012/03/2010-FINAL-Beaver-Lake-WatershedReport.pdf.

Dintelmann, D., Gutierrez, M., and Gouzie, D., 2006, 

Groundwater potentiometric decline in the Springfield, 

Missouri area: Environmental Geology, v. 50, no. 4, 

p. 541–549.

Dollof, J.H., Rozendal, R.A., Siratovich, E.N., Swain, F.M., 

Jr., and Woncik, J., 1967, Subsurface upper Cretaceous 

stratigraphy of southwestern Arkansas: Gulf Coast 

Association of Geological Survey Transactions, v. 17, 

p. 76–104.

Drogue, C., 1980, Essai d’identification d’un type de 

structure de magasins carbonates fissures: Application 

à l’interprétation de certains aspects du fonctionnement 

hydrogéologìque: Mém sér Soc Géol France, v. 11, 

p. 101–108.

Edds, Joe, and Fitzpatrick, D.J., 1984a, Maps showing the 

altitude of the potentiometric surface and changes in the 

water levels of the alluvial aquifer in eastern Arkansas, 

spring 1983: U.S. Geological Survey Water-Resources 

Investigations Report 84–4264, 1 sheet.

Edds, Joe, and Fitzpatrick, D.J., 1984b, Maps showing altitude 

of the potentiometric surface and changes in water levels 

of the Sparta Sand and Memphis Sand aquifers in eastern 

Arkansas, spring 1983: U.S. Geological Survey WaterResources Investigations Report 84–4265, 1 sheet.

Edds, Joe, and Fitzpatrick, D.J., 1985, Maps showing altitude 

of the potentiometric surface and changes in water levels 

of the Sparta Sand and Memphis Sand aquifers in eastern 

Arkansas, spring 1984: U.S. Geological Survey WaterResources Investigations Report 85–4223, 1 sheet.

Edds, Joe, and Fitzpatrick, D.J., 1986, Maps showing altitude 

of the potentiometric surface and changes in water levels 

of the Sparta Sand and Memphis Sand aquifers in eastern 

Arkansas, spring 1985: U.S. Geological Survey WaterResources Investigations Report 86–4084, 1 sheet.

Edds, Joe, and Fitzpatrick, D.J., 1989, Altitude of the 

potentiometric surface and changes in water levels in the 

Sparta-Memphis aquifer in eastern and southern Arkansas, 

spring 1986: U.S. Geological Survey Water-Resources 

Investigations Report 88–4042, 1 sheet.

Edds, Joe, and Remsing, L.M., 1986, Ground-water levels in 

Arkansas, spring 1986: U.S. Geological Survey Open-File 

Report 86–406–W, 62 p.

Emmett, L.F., Skelton, John, Luckey, R.R., and Miller, D.E., 

and others, 1978, Water resources and geology of the 

Springfield area, Missouri: Missouri Department of Natural 

Resources, 160 p.

Encyclopedia of Arkansas, 2013, Lake Georgia-Pacific in The 

encyclopedia of Arkansas history and culture: Encyclopedia 

of Arkansas, Central Arkansas Library System, accessed 

September 10, 2013, at http://www.encyclopediaofarkansas.

net/encyclopedia/media-detail.aspx?mediaID=7071.

Engle, C.R., 2012, Aquaculture in The encyclopedia of 

Arkansas history and culture: Encyclopedia of Arkansas, 

Central Arkansas Library System, accessed April 13, 2013, 

at http://www.encyclopediaofarkansas.net/encyclopedia/

entry-detail.aspx?entryID=3640.

Engler, Kyle, 1958, Water levels in rice irrigation wells in the 

Grand Prairie region: Arkansas Farm Research, May–June 

1958, v. 7, 12 p.

Engler, Kyle, Bayley, F.H., and Sniegocki, R.T., 1963, Studies 

of artificial recharge in the Grand Prairie region, Arkansas 

environment and history: U.S. Geological Survey WaterSupply Paper 1615–A, 32 p.

Engler, Kyle, Thompson, D.G., and Kazmann, R.G., 1945, 

Groundwater supplies for rice irrigation in the Grand 

Prairie region, Arkansas: University of Arkansas, College of 

Agriculture, Agricultural Experiment Station Bulletin, no. 

457, 56 p.

Fancher, G.H., and Mackay, D.K., 1946, Secondary recovery 

of petroleum in Arkansas: Report to the 56th General 

Assembly of the State of Arkansas under the auspices of the 

Arkansas Oil and Gas Commission, p. 245–250. 

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

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

Fetter, C.W., 1988, Applied hydrogeology (2d ed.): New York, 

Macmillan Publishing Company, 592 p. 

Fisk, H.N., 1944, Geological investigation of the alluvial 

aquifer of the lower Mississippi River: U.S. Department of 

the Army, Mississippi River Commission, 78 p.

Fisk, H.N., 1947, Fine-grained alluvial deposits and their 

effects on Mississippi River activity: U.S. Army Corps of 

Engineers, Waterways Experiment Station, 82 p.

Fitzpatrick, D.J., 1985, Occurrence of saltwater in the 

alluvial aquifer in the Boeuf-Tensas Basin, Arkansas: U.S. 

Geological Survey Water-Resources Investigations Report 

85–4029, 1 sheet.

Fitzpatrick, D.J., 1990, A preliminary assessment of the 

potential for artificial recharge in eastern Arkansas: U.S. 

Geological Survey Water-Resources Investigations Report 

90–4123, 31 p.
References 319

Fitzpatrick, D.J., Kilpatrick, J.M., and McWreath, Harry, 

1990, Geohydrologic characteristics and simulated response 

to pumping stresses in the Sparta aquifer in east-central 

Arkansas: U.S. Geological Survey Water-Resources 

Investigations Report 88–4201, 50 p.

Freeze, R.A., and Cherry, J.A., 1979, Groundwater: New 

Jersey, Prentice-Hall, 604 p.

Freiwald, D.A., 1984, Average annual precipitation and runoff 

in Arkansas, 1951–80: U.S. Geological Survey WaterResources Investigations Report 84–4363, 1 sheet.

Freiwald, D.A., 1987, Streamflow gain and loss of selected 

streams in northern Arkansas: U.S. Geological Survey 

Water-Resources Investigations Report 86–4185, 4 sheets.

Freiwald, D.A., and Grosz, G.D., 1988, Effects of fluctuating 

river-pool stages on ground-water levels in the adjacent 

alluvial aquifer in the lower Arkansas River, Arkansas: U.S. 

Geological Survey Water-Resources Investigations Report 

87–4279, 14 p.

Freiwald, D.A., and Johnson, S.F., 2007, Monitoring of 

Sparta aquifer recovery in southern Arkansas and northern 

Louisiana, 2003–07: U.S. Geological Survey Fact Sheet 

2007–3102, 4 p.

Freiwald, D.A., and Plafcan, Maria, 1987, Ground-water 

levels in Arkansas, spring 1987: U.S. Geological Survey 

Open-File Report 87–459, 66 p.

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

northern Arkansas: U.S. Geological Survey Professional 

Paper 314–H, 18 p.

Funkhouser, J.E., Little, P.R., Brahana, J.V., Kresse, T.M., 

Anderson, M., Formica, S., and Huetter, T., 1999, 

Methodology to study the effects of animal production in 

mantled karst aquifers of the southern Ozarks, in Palmer, 

A.N., Palmer, M.V., and Sasowsky, I.D., eds., Karst 

modeling: Special Publication 5, Karst Waters Institute, 

Charles Town, W. Va., p. 255–258.

Gates, J.B., 2005, Groundwater irrigation in the development 

of the Grand Prairie rice industry, 1896–1950: Papers in the 

Earth and Atmospheric Sciences, paper 172, p. 394–413.

Ghasemizadeh, Reza, Hellweger, Ferdinand, Butscher, 

Christoph, Padilla, Ingrid, Vesper, Dorothy, Field, Malcolm, 

and Alshawabkeh, Akram, 2012, Review—Groundwater 

flow and transport modeling of karst aquifers, with 

particular reference to the North Coast Limestone aquifer 

system of Puerto Rico: Hydrogeology Journal, v. 20, no. 8, 

p. 1441–1461.

Ghil, Michael, 2002, Natural climate variability, in MacCraken, M.C., and Perry, J.S., eds., Encyclopedia of global 

environmental change—Volume 1, the Earth system—

Physical and chemical dimensions of global environmental 

change: Chichester, John Wiley and Sons, p. 544–549.

Gillip, J.A., 2007, The effects of land-use change on water 

quality and speleogenesis in Ozark cave systems—A 

paired cave study of Civil War and Copperhead Caves, 

northwestern Arkansas: Fayetteville, University of 

Arkansas, M.S. thesis, 77 p.

Gillip, J.A., and Czarnecki, J.B., 2009, Validation of a groundwater flow model of the Mississippi River Valley alluvial 

aquifer using water-level and water-use data for 1998–2005 

and evaluation of water-use scenarios: U.S. Geological 

Survey Scientific Investigations Report 2009–5040, 22 p.

Gilmour, J.T., 2000, Water quality in rice production: B.R. 

Wells Rice Research Studies 2000, Arkansas Agricultural 

Experiment Station Research Series, no. 485, p. 171–177.

Gonthier, G.M., 2003, Quality of ground water in Pleistocene 

and Holocene subunits of the Mississippi River Valley 

alluvial aquifer, 1998: U.S. Geological Survey WaterResources Investigations Report 03–4202, 84 p.

Gonthier, G.M., and Mahon, G.L., 1993, Thickness of the 

Mississippi River Valley confining unit, eastern Arkansas: 

U.S. Geological Survey Water-Resources Investigations 

Report 92–4121, 4 sheets.

Gordon, Mackenzie, Jr., Tracey, J.I., Jr., and Ellis, M.W., 1958, 

Geology of the Arkansas bauxite region: U.S. Geological 

Survey Professional Paper 299, 268 p.

Gott, J.D., 1975, Soil survey of Mark Twain National Forest 

area, Missouri: U.S. Department of Agriculture, Soil Survey 

Report, p. 47–50.

Griffis, C.L., 1972, Groundwater surface-water integration 

study in the Grand Prairie of Arkansas: Arkansas Water 

Resources Research Center, no. 11, 330 p.

Grohskopf, J.G., and McCracken, Earl, 1949, Insoluble 

residues of some Paleozoic formations of Missouri, their 

preparation, characteristics, and application: Missouri 

Geological Survey and Water Resources Report of 

Investigations, no. 10, 39 p.

Grosz, G.D., Terry, J.E., and Hall, A.P., 1988, Hydrology of 

the lower Little Red River, Arkansas, and a procedure for 

estimating available streamflow: U.S. Geological Survey 

Water-Resources Investigations Report 88–4008, 106 p.

Guccione, M.J., Prior, W.L., and Rutledge, E.M., 1986, The 

Tertiary and Quaternary geology of Crowley’s Ridge—A 

guidebook: Arkansas Geological Commission Guidebook 

86–4, 39 p.

Halberg, H.N., 1972, Use of water in Arkansas, 1970: State 

of Arkansas Geological Commission, Water Resources 

Summary, no. 7, 17 p.

Halberg, H.N., 1977, Use of water in Arkansas, 1975: State 

of Arkansas Geological Commission Water Resources 

Summary, no. 9, 28 p.
320 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Halberg, H.N., Bryant, C.T., and Hines, M.S., 1968, Water 

resources of Grant and Hot Spring Counties, Arkansas: U.S. 

Geological Survey Water-Supply Paper 1857, 64 p.

Halberg, H.N., and Reed, J.E., 1964, Ground water resources 

of eastern Arkansas in the vicinity of U.S. Highway 70: U.S. 

Geological Survey Water-Supply Paper 1779–V, 38 p.

Halberg, H.N., and Stephens, J.W., 1966, Use of water in 

Arkansas, 1965: State of Arkansas Geological Commission 

Water Resources Summary, no. 5, 12 p.

Hale, H., 1926, City water supplies of Arkansas: Fayetteville, 

Ark., University of Arkansas Engineering Experiment 

Station Bulletin, no. 2, 100 p.

Hale, H., Baker, R.C., Walling, I.W., Parrish, D.M., 

Billingsley, G.A., 1947, Public water supplies of Arkansas: 

Fayetteville, Ark., University of Arkansas Bulletin, 

Research Series, no. 11, 104 p.

Haley, B.R., Glick, E.E., Bush, W.V., Clardy, B.F., Stone, 

C.G., Woodward, M.B., and Zachry, D.L., 1993, Geologic 

map of Arkansas: U.S. Geological Survey, 1 sheet.

Hall, A.P., and Holland, T.W., 1984, Water use in Arkansas, 

1981: U.S. Geological Survey Water Resources 

Investigation 84–4070, 1 sheet.

Hanson, R.T., Newhouse, M.W., and Dettinger, M.D., 2004, A 

methodology to assess relations between climatic variability 

and variations in hydrologic time series in the southwestern 

United States: Journal of Hydrology, v. 287, no. 1–4, 

p. 252–269.

Harrington, A.D., and Childers, R.A., 1985, Arkansas 

directory of manufacturers (1984 ed.): Arkansas Industrial 

Development Foundation, 324 p.

Hart, R.M., and Clark, B.R., 2008, Geophysical log database 

for the Mississippi Embayment Regional Aquifer Study 

(MERAS): U.S. Geological Survey Scientific Investigations 

Report 2008–5192, 8 p.

Hart, R.M., Clark, B.R., and Bolyard, S.E., 2008, Digital 

surfaces and thicknesses of selected hydrogeologic units 

within the Mississippi Embayment Regional Aquifer Study 

(MERAS): U.S. Geological Survey Scientific Investigations 

Report 2008–5098, 33 p.

Harvey, E.J., 1980, Ground water in the Springfield-Salem 

Plateaus of southern Missouri and northern Arkansas: U.S. 

Geological Survey Water-Resources Investigations 80–101, 

66 p.

Hays, P.D., 1999, Sustainable yield estimation for the Sparta 

aquifer in Union County, Arkansas: U.S. Geological Survey 

Water-Resources Investigations Report 99–4274, 18 p.

Hays, P.D., 2000, Sustainable-yield estimation for the Sparta 

Aquifer in Union County, Arkansas: U.S. Geological Survey 

Water-Resources Investigations Report 99–4274, 17 p.

Hays, P.D., 2001, Simulated response to recharge 

augmentation of the Sparta aquifer in southeastern 

Arkansas: U.S. Geological Survey Water-Resources 

Investigations Report 01–4039, 14 p.

Hays, P.D., and Fugitt, D.T., 1999, The Sparta aquifer in 

Arkansas’ critical ground-water areas—Response of the 

aquifer to supplying future water needs: U.S. Geological 

Survey Water-Resources Investigations Report 99–4075, 

6 p.

Hays, P.D., Lovelace, J.K., and Reed, T.B., 1998, Simulated 

response to pumping stress in the Sparta aquifer of 

southeastern Arkansas and north-central Louisiana, 

1998–2027: U.S. Geological Survey Water-Resources 

Investigations Report 98–4121, 25 p.

Hays, P.D., and McKee, P.W., 2003, The Sparta aquifer—A 

sustainable regional resource?: U.S. Geological Survey Fact 

Sheet FS–111–02, 4 p.

Healy, R.W., 2010, Estimating groundwater recharge: 

Cambridge, New York, Cambridge University Press, 256 p.

Helsel, D.R., and Hirsch, R.M., 2002, Statistical methods 

in water resources: U.S. Geological Survey Techniques 

of Water-Resources Investigations, book 4, chap. A3, 

522 pages.

Hem, J.D., 1989, Study and interpretation of the chemical 

characteristics of natural water (3d ed.): U.S. Geological 

Survey Water-Supply Paper 2254, 263 p.

Henry, C., Daniels, M., and Hardke, J., 2013, Water 

management, in Hardke, J.T., ed., Arkansas rice production 

handbook: University of Arkansas Cooperative Extension 

Service, Little Rock, Ark., p. 103–122.

Hewitt, F.A., Baker, R.C., and Billingsley, G.A., 1949, 

Ground-water resources of Ashley County, Arkansas: 

Arkansas University, Institute of Science and Technology, 

Research Series 14, 35 p.

Hill, R.T., 1888, The Neozoic geology of southwestern 

Arkansas, in Annual report of the Geological Survey of 

Arkansas: Little Rock, Ark., Press Printing Co., v. 2, 

p. 1–259.

Hines, M.S., 1975, Flow-duration and low-flow frequency 

determinations of selected Arkansas streams: Arkansas 

Geological Survey, Water Resources Circular 12, 66 p.

Hines, M.S., Plebuch, R.O., and Lamonds, A.G., 1972, 

Water resources of Clay, Greene, Craighead, and Poinsett 

Counties, Arkansas: U.S. Geological Survey Hydrologic 

Atlas 337, 2 maps.

Hobza, C.M., 2005, Ground-water quality near a swine 

waste lagoon in a mantled karst terrane in northwestern 

Arkansas: Fayetteville, University of Arkansas, M.S. thesis, 

76 p.
References 321

Holland, T.W., 1981, Use of water in Arkansas, 1980: State 

of Arkansas Geological Commission Water Resources 

Summary, no. 14, 30 p.

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

of Arkansas Geological Commission Water Resources 

Summary, no. 16, 27 p.

Holland, T.W., 1993, Water use in Arkansas, 1990: U.S. 

Geological Survey Open-File Report 93–48, 9 p.

Holland, T.W., 1999, Water use in Arkansas, 1995: U.S. 

Geological Survey Open-File Report 99–188, 1 sheet.

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

U.S. Geological Survey Scientific Investigations Report 

2004–5230, 31 p.

Holland, T.W., 2007, Water use in Arkansas, 2005: U.S. 

Geological Survey Scientific Investigations Report 2007–

5241, 32 p.

Holland, T.W., and Hall, A.P., 1986, Water use in Arkansas, 

1982: U.S. Geological Survey Water-Resources 

Investigations Report 85–4282, 1 sheet.

Holman, I.P., 2006, Climate change impacts on groundwater recharge—Uncertainty, shortcomings, and the way 

forward?: Hydrogeology Journal, v. 14, no. 5, p. 637–647.

Hon, Rudolph, Doherty, Kevin, Davidson, Thomas, Brandon, 

W.C., Stein, C.L., and McTigue, D.F., 2002, Arsenic sources 

and pathways in the overburden of central Massachusetts: 

Arsenic in New England—A Multi-Discipline Scientific 

Conference, Manchester, N.H., May 29–31, 2002, 2 p. 

Hosman, R.L., 1964, The Carrizo Sand, a potential aquifer 

in south-central Arkansas: U.S. Geological Survey 

Professional Paper 501–D, p. 158–160.

Hosman, R.L., 1982, Outcropping Tertiary units in southern 

Arkansas: U.S. Geological Survey Miscellaneous 

Investigations Series I–1405, 1 sheet.

Hosman, R.L., 1988, Geohydrologic framework, Gulf Coastal 

Plain: U.S. Geological Survey Hydrologic Investigations 

Atlas HA–695, 2 sheets.

Hosman, R.L., 1996, Regional stratigraphy and subsurface 

geology of Cenozoic deposits, Gulf Coastal Plain, SouthCentral United States: U.S. Geological Survey Professional 

Paper 1416–G, 35 p.

Hosman, R.L., Long, A.T., Lambert, T.W., Jeffery, H.G., 

and others, 1968, Tertiary aquifers in the Mississippi 

embayment, with discussions of quality of the water: U.S. 

Geological Survey Professional Paper 448–D, 29 p.

Hosman, R.L., and Weiss, J.S., 1991, Geohydrologic units 

of the Mississippi embayment and Texas coastal uplands 

aquifer systems, South-Central United States: U.S. 

Geological Survey Professional Paper 1416–B, 19 p.

Howe, W.B., and Konig, J.W., 1961, The stratigraphic 

succession in Missouri: Missouri Geologic Survey and 

Water Resources Division, v. 40, 185 p.

Hudson, M.R., and Cox, R.T., 2003, Late Paleozoic tectonics 

of the southern Ozark dome, in Cox, R.T., comp., Field 

trip guidebook for joint South-Central and Southeastern 

sections: Geological Society of America, Tennessee 

Division of Geology Report of Investigations 51, p. 15–32.

Hudson, M.R., Mott, D.N., Turner, K.J., and Murray, K.E., 

2005, Geologic controls on a transition between karst 

aquifers at Buffalo National River, northern Arkansas, 

in Kuniansky, E.L., 2005, U.S. Geological Survey 

Karst Interest Group Proceedings, Rapid City, S.D., 

September 12–15, 2005: U.S. Geological Survey Scientific 

Investigations Report 2005–5160, p. 143.

Hudson, M.R., and Turner, K.J., 2007, Geologic map of 

the Boxley quadrangle, Newton and Madison Counties, 

Arkansas: U.S. Geological Survey Scientific Investigations 

Map 2991, 1:24,000 scale.

Hudson, M.R., Turner, K.J., and Bitting, C., 2011, Geology 

and karst landscapes of the Buffalo National River area, 

northern Arkansas, in Kuniansky, E.L., ed., U.S. Geological 

Survey Karst Interest Group Proceedings, Fayetteville, 

Ark., April 26–29, 2011: U.S. Geological Survey Scientific 

Investigations Report 2011–5031, p. 191–212.

Hudson, M.R., Turner, K.J., and Trexler, C.C., 2009, 

Regional joint analysis for the Buffalo National River area 

of northern Arkansas—Implications for tectonic history 

and landscape influence: Geological Society of America 

Abstracts with Programs, v. 41, no. 7, p. 367.

Huetter, T.A., Van Schaik, E.J., and Kresse, T.M., 1997, 

Report on the third sampling of the Omaha Monitoring 

Area: Arkansas Department of Pollution Control and 

Ecology, WQ97–06–3, 44 p. 

Huff, G.F., and Bonck, J.P., 1993, Saltwater in shallow 

aquifers in east-central and northeastern Louisiana and 

southeastern Arkansas: U.S. Geological Survey Open-File 

Report 93–494, 29 p.

Hunrichs, R.A., 1983, Identification and classification of 

perennial streams of Arkansas: U.S. Geological Survey 

Water-Resources Investigations Report 83–4063, 1 sheet.

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

Ozark Plateaus aquifer system in parts of Missouri, 

Arkansas, Oklahoma, and Kansas: U.S. Geological Survey 

Professional Paper 1414–D, 127 p.

Imes, J.L., and Fredrick, B.S., 2002, Using dye-tracing and 

chemical analyses to determine effects of a wastewater 

discharge to Jam Up Creek on water quality of Big Spring, 

southeastern Missouri, 2001: U.S. Geological Survey Fact 

Sheet 103–02, 1 sheet. 
322 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Imes, J.L., and Kleeschulte, M.J., 1996, Seasonal groundwater level changes (1990–1993) and flow patterns in the 

Fristoe unit of the Mark Twain National Forest, southern 

Missouri: U.S. Geological Survey Water-Resources 

Investigations Report 95–4096, 1 sheet.

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

relation, and geohydrologic properties of regional 

geohydrologic units in southern Missouri: U.S. Geological 

Survey Hydrologic Investigations Atlas HA–711–I, 3 

sheets, scale 1:750,000.

Jagucki, M.L., Katz, B.G., Crandall, C.A., and Eberts, S.M., 

2009, Assessing the vulnerability of public-supply wells 

to contamination—Floridian aquifer system near Tampa, 

Florida: U.S. Geological Survey Fact Sheet 2009–3062, 6 p.

Johnson, Sherrel, 2004, Ouachita River alternative water 

supply project: Union County Water Conservation Board, 

accessed June 13, 2013, at http://ucwcb.org/.

Joseph, R.L., 1998a, Potentiometric surface of the Sparta 

aquifer in eastern and south-central Arkansas, and the 

Memphis Aquifer in east-central Arkansas, October 1996–

July 1997: U.S. Geological Survey Scientific Investigations 

Report 97–4282, 19 p.

Joseph, R.L., 1998b, Potentiometric surfaces of aquifers in 

the Cockfield Formation in southeastern Arkansas and 

the Wilcox Group in southern and northeastern Arkansas, 

October 1996–July 1997: U.S. Geological Survey WaterResources Investigations Report 98–4084, 19 p.

Joseph, R.L., 1999, Status of water levels and selected waterquality conditions in the Mississippi River Valley alluvial 

aquifer in eastern Arkansas, 1998: U.S. Geological Survey 

Water-Resources Investigations Report 99–4035, 54 p. 

Joseph, R.L., 2000, Status of water levels and selected waterquality conditions in the Sparta and Memphis aquifers in 

eastern and south-central Arkansas, 1999: U.S. Geological 

Survey Scientific Investigations Report 2000–4009, 34 p.

Kaliba, A.R., and Engle, C.R., 2006, Chicot County, 

Arkansas—The economic impact of the catfish industry: 

University of Arkansas at Pine Bluff Cooperative Extension 

Program ETB257, 13 p.

Keener, R., 1972, Septic tank contamination of groundwater: 

University of Arkansas, Fayetteville, Ark., 23 p.

Kenny, J.F., Barber, N.L., Hutson, S.S., Linsey, K.S., 

Lovelace, J.K., and Maupin, M.A., 2009, Estimated use of 

water in the United States in 2005: U.S. Geological Survey 

Circular 1344, 52 p.

Kilpatrick, J.M., 1992, Simulated response to future pumping 

in the Sparta aquifer, Union County, Arkansas: U.S. 

Geological Survey Water-Resources Investigations Report 

91–4161, 25 p.

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

resources of the Arkansas River Basin in Arkansas: U.S. 

Geological Survey Open-File Report 88–725, 45 p.

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

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

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

Kindinger, J.L., Davis, J.B., Flocks, J.G., 2000, Subsurface 

characterization of selected water bodies in the St. Johns 

River Water Management District, Northeast Florida: U.S. 

Geological Survey Open-File Report 2000–180, 7 p.

Kinniburgh, D.G., and Smedley, P.L, eds., 2001, Arsenic 

contamination of groundwater in Bangladesh, final report: 

British Geological Survey, BGS Report WC–00–19, v. 2, 267 

p.

Klaer, F.H., Jr., 1940, Memphis, in Meinzer, O.E., Wenzel, 

L.K., and others, Water levels and artesian pressure in 

observation wells in the United States in 1940, pt. 2, 

southeastern States: U.S. Geological Survey Water-Supply 

Paper 907, p. 92–101. 

Klein, Howard, Baker, R.C., and Billingsley, G.A., 1950, 

Ground-water resources of Jefferson County, Arkansas: 

Arkansas University, Institute of Science and Technology 

Research Series 19, 44 p.

Kleiss, B.A., Coupe, R.H., Gonthier, G.J., and Justus, 

B.J., 2000, Water quality in the Mississippi embayment, 

Mississippi, Louisiana, Arkansas, Missouri, Tennessee, and 

Kentucky, 1995–98: U.S. Geological Survey Circular 1208, 

36 p., accessed June 13, 2013, at http://pubs.water.usgs.gov/

circ1208/.

Kline, S.W., 2003, A model for groundwater flow in the alluvial 

aquifer of the Arkansas River at Dardanelle, Arkansas: 

Arkansas Geological Commission Water Resources 

Circular, Issue 18, 70 p.

Kline, S.W., Kresse, T.M., Fazio, J.A., Prior, W.L., Hanson, 

W.D., Miller, R.A., and Treece, T.M., 2006, The Arkansas 

River’s alluvial aquifer in central Arkansas—Physical 

hydrology of the aquifer at Dardanelle [abs.]: Fayetteville, 

Ark., Proceedings of the Arkansas Water Resources Center 

Annual Conference, accessed May 13, 2013, at http://www.

uark.edu/depts/awrc/Publications/2006AWRCConference/

TrifoldLF.pdf.

Knierim, K.J., Pollock, E.D., and Hays, P.D., 2011, Using 

labeled isotopes to trace groundwater flowpaths in a 

northwestern Arkansas cave, in Kuniansky, E.L., ed., U.S. 

Geological Survey Karst Interest Group Proceedings, 

Fayetteville, Ark., April 26–29, 2011: U.S. Geological 

Survey Scientific Investigations Report 2011–5031, p. 67–73.

Knierim, K.J., Pollock, E.D., and Hays, P.D., 2013, Using 

isotopes of dissolved inorganic carbon species and water to 

separate sources of recharge in a cave spring, northwestern 

Arkansas, USA: Acta Carsologica, v. 42, p. 261–276. 
References 323

Knight, R.D., 1954, The Gunter Member of the Gasconade 

Formation (Lower Ordovician) in southern Missouri: 

Missouri Geological Survey and Water Resources Report of 

Investigations, no. 17, p. 51–56.

Konikow, L.F., 2013, Groundwater depletion in the United 

States (1900−2008): U.S. Geological Survey Scientific 

Investigations Report 2013−5079, 63 p., accessed June 13, 

2013, at http://pubs.usgs.gov/sir/2013/5079. 

Kresse, T.M., 1991, A hydrogeological and geochemical site 

characterization of a proposed landfill site, Searcy County, 

Arkansas: Groundwater Journal, v. 29, no. 3, p. 444.

Kresse, T.M., and Clark, B.R., 2008, Occurrence, distribution, 

sources, and trends of elevated chloride concentrations in 

the Mississippi River Valley alluvial aquifer in southeastern 

Arkansas: U.S. Geological Survey Scientific Investigations 

Report 2008–5193, 34 p.

Kresse, T.M., and Fazio, J.A., 2002, Pesticides, water quality, 

and geochemical evolution of ground water in the alluvial 

aquifer, Bayou Bartholomew Basin, Arkansas: Arkansas 

Department of Environmental Quality, Water Quality 

Report WQ02–05–1, 111 p.

Kresse, T.M., and Fazio, J.A., 2003, Occurrence of arsenic 

in ground waters of Arkansas and implications for source 

and release mechanisms: Arkansas Department of Pollution 

Control and Ecology, Water Quality Report WQ03–03–01, 

35 p.

Kresse, T.M., and Fazio, J.A., 2004, Groundwater quality 

and geochemistry in the Strawberry River watershed in 

northeast Arkansas: Arkansas Department of Environmental 

Quality Water Quality Report WQ04–01–1, 54 p.

Kresse, T.M., Fazio, J.A., Hays, P.D., and Stanton, G.P., 

2000, Sources of saltwater intrusion in the alluvial aquifer 

in parts of Chicot County, Arkansas: Proceedings of 

Environmental Hydrology of the Arkansas Water Resource 

Center Annual Conference, April 4–5, 2000, Fayetteville, 

Ark., p. 1–6.

Kresse, T.M., Fazio, J.A., Miller, R.A., and Kline, S.W., 

2006, The Arkansas River’s alluvial aquifer in central 

Arkansas—Geochemistry of the aquifer at Dardanelle 

[abs.]: Fayetteville, Ark., Proceedings of the Arkansas 

Water Resources Center Annual Conference, accessed 

September 29, 2012, at http://www.uark.edu/depts/awrc/

Publications/2006AWRCConference/TrifoldLF.pdf.

Kresse, T.M., and Hays, P.D., 2009, Geochemistry, 

comparative analysis, and physical and chemical 

characteristics of the thermal waters east of Hot Springs 

National Park, Arkansas, 2006–2009: U.S. Geological 

Survey Scientific Investigations Report 2009–5263, 48 p.

Kresse, T.M., Hays, P.D., Hudson, M.R., and Kaufman, J.E., 

2011, The influence of land use and occurrence of sinkholes 

on nitrogen transport in the Ozark Plateaus in Arkansas 

and Missouri, in Kuniansky, E.L., ed., U.S. Geological 

Survey Karst Interest Group Proceedings, Fayetteville, 

Ark., April 26–29, 2011: U.S. Geological Survey Scientific 

Investigations Report 2011–5031, 212 p.

Kresse, T.M., and Huetter, T.A., 1999, Ground-water resources 

and water quality in the vicinity of Pine Bluff municipal 

area, Jefferson County, Arkansas: Arkansas Department of 

Environmental Quality, Water Quality Report WQ99–10–1, 

79 p.

Kresse, T.M., and Van Schaik, E.J., 1996, Preliminary results 

of pesticide investigation, Augusta, Arkansas: Arkansas 

Department of Pollution Control and Ecology, Water 

Quality Report WQ96–11–1, 44 p.

Kresse, T.M., Van Schaik, E.J., Wise, Jim, and Huetter, T.A., 

1997, Occurrence of pesticides in alluvial aquifer of eastern 

Arkansas: Arkansas Department of Pollution Control and 

Ecology, Water Quality Report WQ97–10–1, 39 p.

Kresse, T.M., Warner, N.R., Hays, P.D., Down, Adrian, 

Vengosh, Avner, and Jackson, R.B., 2012, Shallow 

groundwater quality and geochemistry in the Fayetteville 

Shale gas-production area, north-central Arkansas, 2011: 

U.S. Geological Survey Scientific Investigations Report 

2012–5273, 31 p.

Krinitzsky, E.L., and Wire, J.C., 1964, Ground water in 

alluvium of Lower Mississippi Valley (upper and central 

areas): U.S. Army Corps of Engineers, Waterways 

Experiment Station Technical Report 3–658, v. 1–2, 400 p.

Kundzewicz, Z.W., Mata, L.J., Arnell, N.W., Döll, P., 

Kabat, P., Jiménez, B., Miller, K.A., Oki, T., Sen, Z., and 

Shiklomanov, I.A., 2007, Freshwater resources and their 

management, in Parry, M.L., Canziani, O.F., Palutikof, J.P., 

Linden, P.J. van der, and Hanson, C.E., eds., Climate change 

2007—Impacts, adaptation and vulnerability: Contribution 

of Working Group II to the Fourth Assessment Report of the 

Intergovernmental Panel on Climate Change, Cambridge 

University Press, Cambridge, United Kingdom, p. 173–210.

Laincz, Jozef, 2011, Investigation of nitrate processing in the 

interflow zone of mantled karst, northwestern Arkansas, in

Kuniansky, E.L., ed., U.S. Geological Survey Karst Interest 

Group Proceedings, Fayetteville, Ark., April 26–29, 2011: 

U.S. Geological Survey Scientific Investigations Report 

2011–5031, p. 75–83.

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

the Ozark plateaus province, northern Arkansas: U.S. 

Geological Survey Hydrologic Atlas 383, 2 sheets.

Lamonds, A.G., Hines, M.S., and Plebuch, R.O., 1969, Water 

resources of Randolph and Lawrence Counties, Arkansas: 

U.S. Geological Survey Water-Supply Paper 1879–B, 45 p.
324 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Lamonds, A.G., and Stephens, J.W., 1969, Water resources 

data for the Ozark Plateaus Province, Arkansas: U.S. 

Geological Survey Unnumbered Open-File Report, 18 p.

Lautier, Jeffrey, 1981, Geology of the subsurface Eocene 

Cockfield Formation in southern Allen Parish, Louisiana: 

Gulf Coast Association of Geological Societies 

Transactions, v. 31, p. 125–133.

Leach, D.L., and Rowan, E.L., 1986, Genetic link between 

Ouachita foldbelt tectonism and Mississippi Valley-type 

lead-zinc deposits of the Ozarks: Geology, v. 14, p. 931–

935.

Leidy, V.A., and Morris, E.E., 1990a, Ground-water 

quality and preliminary assessment of the potential for 

contamination beneath agricultural lands in central Lonoke 

County, Arkansas: U.S. Geological Survey Water-Resources 

Investigations Report 90–4099, 31 p.

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

quality of ground water in the Boone Formation and Cotter 

Dolomite in karst terrain of northwestern Boone County, 

Arkansas: U.S. Geological Survey Water-Resources 

Investigations Report 90–4066, 57 p.

Leidy, V.A., and Taylor, R.E., 1992, Overview of susceptibility 

of aquifers to contamination, Union County, Arkansas: U.S. 

Geological Survey Water-Resources Investigations Report 

92–4094, 95 p.

Looney, J.W., 1990, An update on Arkansas water law—Is the 

riparian rights doctrine dead?: Arkansas Law Review, v. 43, 

p. 643–708.

Looney, J.W., 1995, Enhancing the role of water districts in 

ground water management and surface water utilization in 

Arkansas: Arkansas Law Review, v. 48, p. 573–630.

Ludwig, A.H., 1973, Water resources of Hempstead, Lafayette, 

Little River, Miller, and Nevada Counties, Arkansas: U.S. 

Geological Survey Water-Supply Paper 1998, 41 p.

Ludwig, A.H., 1992, Flow duration and low-flow 

characteristics of selected Arkansas streams: U.S. 

Geological Survey Water-Resources Investigations Report 

92–4026, 77 p.

Ludwig, A.H., and Terry, J.E., 1980, Methods and applications 

of digital-model simulation of the Red River alluvial 

aquifer, Shreveport to the mouth of the Black River, 

Louisiana: U.S. Geological Survey Water-Resources 

Investigations Report 79–114, 103 p.

Macaulay, Calum, 2005, Low temperature quartz cementation 

of the Upper Cretaceous white sandstone of Lochaline, 

Argyll, Scotland: Department of Geology and Geophysics, 

University of Edinburgh, Departmental Publication 4, 4 p.

MacDonald, H.C., Jeffus, H.M., Steele, K.F., Coughlin, T.L., 

Kerr, K.M., and Wagner, G.H., 1976, Groundwater pollution 

in Arkansas: University of Arkansas at Fayetteville, 

Arkansas Agricultural Experiment Station Special Report, 

no. 25, 7 p.

MacDonald, H.C., Zachry, D.L., Jeffus, H.C., 1977, Northern 

Arkansas groundwater inventory: Arkansas Water 

Resources Center, Fayetteville, Ark., no. MSC–26, 186 p.

Macfarlane, P.A., and Hathaway, L.R., 1987, The 

hydrogeology and chemical quality of groundwaters 

from the lower Paleozoic aquifers in the tri-State region 

of Kansas, Missouri, and Oklahoma: Kansas Geological 

Survey Groundwater Series 9, 37 p.

Mack, L.E., 1963, Water law in Arkansas: Arkansas Industrial 

Development Commission and Arkansas University 

Industrial Research and Extension Center, 74 p.

MacKichan, K.A., 1951, Estimated use of water in the United 

States, 1950, U.S. Geological Survey: U.S. Geological 

Survey Circular 115, 13 p.

MacKichan, K.A., 1957, Estimated use of water in the United 

States, 1955, U.S. Geological Survey: U.S. Geological 

Survey Circular 398, 18 p.

Mahon, G.L., and Ludwig, A.H., 1990, Simulation of groundwater flow in the Mississippi River Valley alluvial aquifer in 

eastern Arkansas: U.S. Geological Survey Water-Resources 

Investigations Report 89–4145, 26 p.

Mahon, G.L., and Poynter, D.T., 1993, Development, 

calibration, and testing of ground-water flow models for the 

Mississippi River Valley alluvial aquifer in eastern Arkansas 

using one-square-mile cells: U.S. Geological Survey WaterResources Investigations Report 92–4106, 33 p., 11 pls.

Mahon, G.L., Terry, J.E., and Peralta, R.C., 1989, Waterresources development alternatives for the Mississippi 

alluvial plain in eastern Arkansas: Proceedings of the 25th 

Annual Conference of the American Water Resources 

Association (AWRA), Herndon, Va., p. 31–35.

Mahon, J.C., 1979, The history of Riceland Foods: Craighead 

County Historical Quarterly, v. 17, p. 10–17.

Manger, W.L., 1983, The geologic provinces of Arkansas: 

Arkansas Naturalist, v. 1, no. 7, p. 1–6.

Marshall, A.S., 2005, Establishing a land subsidence 

observation network using static and kinematic GPS in 

the Grand Prairie region of eastern Arkansas: Fayetteville, 

University of Arkansas, M.S. thesis, 57 p.
References 325

Marshall, David, Brahana, J.V., and Davis, R.K., 1998, 

Resuspension of viable sediment-bound enteric pathogens 

in shallow karst aquifers, in Brahana, J.V., Eckstein, Yoram, 

Ongley, L.K., Schneider, Robert, and Moore, J.E., eds., 

Gambling with groundwater—Physical, chemical, and 

biological aspects of aquifer-stream relations: Las Vegas, 

Nevada, International Association of Hydrogeologists/

American Association of Hydrogeologists, Proceedings, 

p. 179–186.

McArthur, J.M., Ravenscroft, Peter Safiullah, S., and 

Thirlwall, M.F., 2001, Arsenic in groundwater—Testing 

pollution mechanisms for sedimentary aquifers in 

Bangladesh: Water Resources Research, v. 37, no. 1, 

p. 109–117. 

McFarland, J.D., 2004, Stratigraphic summary of Arkansas: 

Arkansas Geological Commission Information Circular 36, 

38 p.

McFarland, J.D., Bush, W.V., Wise, O.A., and Holbrook, D.F., 

1979, A guidebook to the Ordovician-Mississippian rocks of 

north-central Arkansas: Arkansas Geological Commission 

GB–79–1, 25 p.

McFarland, M.L., Lemon, R.G., and Stichler, C.R., 1998, 

Irrigation water quality—Critical salt levels for peanuts, 

cotton, corn and grain sorghum: Texas Agricultural 

Extension Service, Texas A&M University, 4 p.

McFarland, J.D., and Prior, William, 2005, North Arkansas 

ground water investigations—Cave City Graben area: 

Arkansas Geological Commission, Water Resources 

Summary 17, 17 p.

McGee, W.J., 1888, Three formations of the Middle Atlantic 

Slope: American Journal of Science, v. 35, no. 206, p. 120–

143.

McGraw, K., Popp, J., and Miller, W., 2012, Economic 

contribution of agriculture to the Arkansas economy in 

2010: University of Arkansas Cooperative Extension 

Service Research Report 991, 49 p. 

McGuiness, C.L., 1951, Water law with special reference to 

ground water: U.S. Geological Survey Circular 117, 30 p.

McKee, P.W., and Clark, B.R., 2003, Development and 

calibration of a ground-water flow model for the Sparta 

aquifer of southeastern Arkansas and north-central 

Louisiana and simulated response to withdrawals, 

1998–2027: U.S. Geological Survey Water-Resources 

Investigations Report 03–4132, 68 p.

McKee, P.W., Clark, B.R., and Czarnecki, J.B., 2004, 

Conjunctive-use optimization and sustainable-yield 

estimation for the Sparta aquifer of southeastern Arkansas 

and north-central Louisiana: U.S. Geological Survey WaterResources Investigations Report 03–4231, 30 p.

McKnight, E.T., 1935, Zinc and lead deposits of northern 

Arkansas: U.S. Geological Survey Bulletin 853, 311 p.

McQueen, H.S., 1931, Insoluble residues as a guide in 

stratigraphic studies: Missouri Bureau of Geology and 

Mines, 56th Biennial Report of the State Geologist, 1929–

1930, app. 1, p. 102–131.

McWreath, H.C., III, Nelson, J.D., and Fitzpatrick, D.J., 

1991, Simulated response to pumping stresses in the 

Sparta aquifer, northern Louisiana and southern Arkansas: 

Louisiana Department of Transportation and Development 

Water Resources Technical Report No. 51, 51 p.

Melton, R.W., 1976, The regional geohydrology of the 

Roubidoux and Gasconade Formations, Arkansas and 

Missouri: Fayetteville, University of Arkansas, M.S. thesis, 

160 p.

Merrill, R.K., Sims, J.J., Jr., Gann, D.E., and Liles, K.J., 

1985, Newton County geology and mineral resources 

[Mississippi]: Mississippi Office of Geology Bulletin, 

no. 126, 108 p.

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

along the Ozark escarpment in southeastern Missouri and 

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

Meyer, Meyer, LeCroix, Hixson, Inc.; Lazenby and 

Associates; Louisiana Tech University School of Business; 

URS Corporation; Smoot, C.W.; and Frye-Magee, 2002, 

Sparta groundwater study—A study commissioned by the 

Sparta Groundwater Conservation District Commission, 

final report: Sparta Groundwater Conservation District 

Commission, 93 p.

Miser, H.D., and Purdue, A.H., 1919, Gravel deposits of 

the De Queen and Caddo Gap quadrangles, ArkansasOklahoma: U.S. Geological Survey Bulletin 690–B, 

p. 15–30.

Morgan, R., 2012, Water supply and source water protection 

issues in northwest Arkansas, in Annual Watershed and 

Research Conference, 2012, Proceedings: Arkansas Water 

Resources Center, accessed September 29, 2012, at http://

www.uark.edu/depts/awrc/conference.html.

Morris, E.E., and Bush, W.V., 1986, Extent and source of 

saltwater intrusion into the alluvial aquifer near Brinkley, 

Arkansas, 1984: U.S. Geological Survey Water-Resources 

Investigations Report 85–4322, 123 p.

Mott, D.N., Hudson, M.R., and Aley, T.J., 1999, Nutrient 

loads traced to interbasin groundwater transport at Buffalo 

National River, Arkansas, in Harmon, D., ed., Proceedings 

of the 10th Conference on Research and Resource 

Management in Parks and Public Lands, George Wright 

Society, Hancock, Mich., p. 114–121.
326 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Mott, D.N., Hudson, M.R., and Aley, T.J., 2000, Hydrologic 

investigations reveal interbasin recharge contributes 

significantly to detrimental nutrient loads at Buffalo 

National River, Arkansas, in Proceedings of Arkansas 

Water Resources Center Annual Conference MSC–284, 

Fayetteville, Ark., p. 13–20.

Mueller, S.H., Goldfarb, R.J., Farmer, G.L., Sanzolone, R., 

Adams, M., and Theodorakus, P., 2001, A seasonal study 

of the arsenic and groundwater geochemistry in Fairbanks, 

Alaska: U.S. Geological Survey Workshop on Arsenic in the 

Environment, Denver, Colo., February 2001, 4 p. 

Murray, K.E., and Hudson, M.R., 2002, Three-dimensional 

geologic framework modeling for a karst region in the 

Buffalo National River, Arkansas, in Kuniansky, E.L., ed., 

U.S. Geological Survey Karst Interest Group Proceedings, 

Atlanta, Ga., August 20–22, 2002: U.S. Geological Survey 

Scientific Investigations Report 02–4174, 89 p.

Muse, P.S., 1982, Ground-water resource evaluation of 

southwest Washington County, Arkansas: Fayetteville, 

University of Arkansas, M.S. thesis, 175 p.

National Research Council, 2002, Estimating water use in the 

United States—A new paradigm for the National WaterUse Information Program: The National Academies Press, 

Washington, D.C., 190 p., accessed May 3, 2013, at 

http://www.nap.edu/catalog/10484.html.

National Wildlife Federation, 2014, Ecosystem services: 

National Wildlife Federation, accessed March 7, 2014, 

at http://www.nwf.org/Wildlife/Wildlife-Conservation/

Ecosystem-Services.aspx.

Neely, B.L., Jr., 1991, Arkansas floods and droughts in

Paulson, R.W., Chase, E.B., Roberts, R.S., and Moody, 

D.W., compilers, National Water Summary 1988–89—

Hydrologic events and floods and droughts: U.S. Geological 

Survey Water Supply Paper 2375, p. 189–195.

Nichols, T.W., Vendrell, P.F., and Steele, K.F., 1993, 

Completion report, Arkansas State pesticides in ground 

water monitoring project: Fayetteville, Ark., Arkansas Water 

Resources Center, Miscellaneous Report no. 136, 50 p.

Nichols, T.W., Vendrell, P.F., Steele, K.F., and Scott, H.D., 

1996, Completion report, Arkansas State pesticides in 

ground water monitoring project—Phase V, vulnerable 

areas in Jackson, Monroe, Lawrence, and Lonoke Counties: 

Fayetteville, Ark., Arkansas Water Resources Center, 

Miscellaneous Report no. 199, 100 p.

Nickson, R.T., McArthur, J.M., Ravenscroft, Peter, Burgess, 

W.G., and Ahmed, K.M., 2000, Mechanism of arsenic 

release to groundwater, Bangladesh and West Bengal: 

Applied Geochemistry, v. 15, no. 2000, p. 403–413. 

Nordstrom, D.K., Alpers, C.N., Ptacek, C.J., and Blowes, 

D.W., 2000, Negative pH and extremely acidic mine waters 

from Iron Mountain, California: Environmental Science and 

Technology, v. 34, p. 254–258.

Nunn, J.A., and Lin, Guichang, 2002, Insulating effect of coals 

and organic rich shales—Implications for topography driven 

fluid flow, heat transport, and genesis of ore deposits in the 

Arkoma Basin and Ozark Plateau: Basin Research, v. 14, 

no. 2, p. 129–145.

Nuttall, Thomas, 1821, A journal of travels into the Arkansas 

Territory during the year 1819: Philadelphia, Pennsylvania, 

T.H. Palmer, 296 p.

Ogden, A.E., 1979, Hydrogeologic and geochemical 

investigation of the Boone-St. Joe Limestone aquifer in 

Benton County, Arkansas: Fayetteville, Ark., Arkansas 

Water Resources Center, no. PUB–0068, 133 p.

Onellion, F.E., 1956, Geology and ground-water resources 

of Drew County, Arkansas: Arkansas Geology and 

Conservation Commission, Water Resources Circular 4, 

32 p.

Onellion, F.E., and Criner, J.H., Jr., 1955, Ground-water 

resources of Chicot County, Arkansas: Arkansas Geology 

and Conservation Commission Water Resources Circular 3, 

27 p.

Orndorff, R.C., Weary, D.J., and Harrison, R.W., 2006, The 

role of sandstone in the development of an Ozark karst 

system, south-central Missouri: Geological Society of 

America Special Papers, 404, p. 31–38.

Ozark Mountain Regional Public Water Authority, 2013, 

Project history: Ozark Mountain Regional Public Water 

Authority, accessed March 2, 2013, at http://www.

ozarkmountainregionalpwa.org/project-history.html.

Palmer, A.N., 2011, Paleokarst of the U.S.A.—A brief review, 

in Kuniansky, E.L., ed., U.S. Geological Survey Karst 

Interest Group Proceedings, Fayetteville, Ark., April 26–29, 

2011: U.S. Geological Survey Scientific Investigations 

Report 2011–5031, p. 7–15.

Parker, J.S., 2001, A changing landscape—Environmental 

conditions and consequences of the 1920s: Arkansas 

Historical Quarterly, v. 60, no. 1, p. 30–52.

Parr, D.L., 1987, The effect of season and rain events on the 

chemistry of selected spring water in limestone terrain, 

Washington County, Arkansas: Fayetteville, University of 

Arkansas, M.S. thesis, 135 p.

Payne, J.N., 1968, Hydrologic significance of the lithofacies 

of the Sparta Sand in Arkansas, Louisiana, Mississippi, and 

Texas: U.S. Geological Survey Professional Paper 569–A, 

17 p.
References 327

Payne, J.N., 1970, Geohydrologic significance of lithofacies 

of the Cockfield Formation of Louisiana and Mississippi 

and the Yegua Formation of Texas: U.S. Geological Survey 

Professional Paper 569–B, 14 p.

Payne, J.N., 1972, Hydrologic significance of lithofacies 

of the Cane River Formation or equivalents of Arkansas, 

Louisiana, Mississippi, and Texas: U.S. Geological Survey 

Professional Paper 569–C, 17 p.

Payne, J.N., 1975, Geohydrologic significance of lithofacies 

of the Carrizo Sand of Arkansas, Louisiana, and Texas and 

the Meridian Sand of Mississippi: U.S. Geological Survey 

Professional Paper 569–D, 11 p.

Peralta, R.C., Cantiller, R.R.A., and Mahon, G.L., 1992, 

Maximizing sustainable ground water withdrawals 

comparing accuracy and computational requirements for 

steady- and unsteady-state digital modeling approaches, in

Subitzky, Seymour, ed., Selected papers in the hydrologic 

sciences, 1988–1992: U.S. Geological Survey Water-Supply 

Paper 2340, p. 63–74.

Peralta, R.C., Cantiller, R.R.A., and Terry, J.E., 1995, Optimal 

large-scale conjunctive water-use planning—Case study: 

Journal of Water Resources Planning and Management, 

v. 121, no. 6, p. 471–478. 

Peralta, R.C., Yazdanian, A., Killian, P.J., and Shulstad, R.N., 

1985, Future Quaternary groundwater accessibility in the 

Grand Prairie—1993: University of Arkansas, Agricultural 

Experiment Station Bulletin, no. 877, 37 p.

Petersen, J.C., 1988, Statistical summary of selected waterquality data (water years 1975 through 1985) for Arkansas 

rivers and streams: U.S. Geological Survey WaterResources Investigations Report 88–4112, 189 p.

Petersen, J.C., Broom, M.E., and Bush, W.V., 1985, 

Geohydrologic units of the Gulf Coastal Plain in Arkansas: 

U.S. Geological Survey Water-Resources Investigations 

Report 85–4116, 20 p.

Peterson, E.W., Davis, R.K., Brahana, J.V., and Orndorff, 

H.A., 2000, 17-β Estradiol as an indicator of animal 

waste contamination in mantled karst aquifers: Journal of 

Environmental Quality, v. 29, no. 3, p. 826–834.

Peterson, E.W., Davis, R.K., Brahana, J.V., and Orndorff, 

H.A., 2002, Movement of nitrate through regolith covered 

karst terrane, northwest Arkansas: Journal of Hydrology, 

v. 256, p. 35–47.

Plafcan, Maria, 1985, Ground-water levels in the alluvial 

aquifer in eastern Arkansas, 1984: U.S. Geological Survey 

Open-File Report 85–569, 26 p.

Plafcan, Maria, 1986, Ground-water levels in the alluvial 

aquifer in eastern Arkansas, 1985: U.S. Geological Survey 

Open-File Report 86–242, 29 p.

Plafcan, Maria, 1987, Ground-water levels in the alluvial 

aquifer in eastern Arkansas, 1986: U.S. Geological Survey 

Open-File Report 87–545, 31 p.

Plafcan, Maria, and Edds, Joe, 1986, Water level and 

saturated thickness maps of the alluvial aquifer in eastern 

Arkansas, 1984: U.S. Geological Survey Water-Resources 

Investigations Report 86–4014, 1 sheet.

Plafcan, Maria, and Fugitt, D.T., 1987, Water level maps of the 

alluvial aquifer in eastern Arkansas, 1985: U.S. Geological 

Survey Water-Resources Investigations Report 86– 4178, 

1 sheet.

Plafcan, Maria, and Remsing, L.M., 1989, Water level maps 

of the alluvial aquifer in eastern Arkansas, 1986: U.S. 

Geological Survey Water-Resources Investigations Report 

88–4067, 1 sheet.

Plebuch, R.O., 1961, Fresh water aquifers of Crittenden 

County, Arkansas: U.S. Geological Survey Water Resources 

Circular, no. 8, 65 p.

Plebuch, R.O., 1962, Changes in ground-water levels in 

deposits of Quaternary age in northeastern Arkansas: 

U.S. Geological Survey Water Resources Summary, no. 3, 

10 p.

Plebuch, R.O., and Hines, M.S., 1967, Water resources of 

Pulaski and Saline Counties, Arkansas: U.S. Geological 

Survey Water-Supply Paper 1839–B, 25 p.

Plebuch, R.O., and Hines, M.S., 1969, Water resources of 

Clark, Cleveland, and Dallas Counties, Arkansas: U.S. 

Geological Survey Water-Supply Paper 1879–A, 32 p.

Pollock, E.D., Knierim, K.J., Hays, P.D., 2011, Seasonal 

carbon dynamics in a northwestern Arkansas cave—Linking 

climate and cave conditions: U.S. Geological Survey 

Karst Interest Group, U.S. Geological Survey Scientific 

Investigations Report 2011–5020, p. 37–43.

Prior, W.L., Howard, J.M., McFarland, J.D., and Hill, S.S., 

1999, Roubidoux Formation and Gunter Sandstone Member 

of the Gasconade Formation, major aquifers in northern 

Arkansas: Arkansas Geological Commission, Water 

Resources Circular, no. 17, 45 p.

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

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

Pugh, A.L., 2008a, Summary of aquifer test data for 

Arkansas—1940–2006: U.S. Geological Survey Scientific 

Investigations Report 2008–5149, 33 p.

Pugh, A.L., 2008b, Potentiometric surface of the Ozark 

aquifer in northern Arkansas, 2007: U.S. Geological Survey 

Scientific Investigations Report 2008–5137, 16 p.
328 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Pugh, A.L., 2010, Potentiometric surfaces and water-level 

trends in the Cockfield (upper Claiborne) and Wilcox (lower 

Wilcox) aquifers of southern and northeastern Arkansas, 

2009: U.S. Geological Survey Scientific Investigations 

Report 2010–5014, 47 p.

Pugh, A.L., Westerfield, P.W., and Poynter, D.T., 1997, 

Thickness of the Mississippi River Valley alluvial aquifer in 

eastern Arkansas: U.S. Geological Survey Water-Resources 

Investigations Report 97–4049, 1 sheet.

Pugh, A.L., and Westerman, D.A., 2014, Mean annual, 

seasonal, and monthly precipitation and runoff in 

Arkansas, 1951–2011: U.S. Geological Survey Scientific 

Investigations Report 2014–5006, 40 p.

Pulley, H.J., and Beyrouty, C.A., 1996, Effect of salt type on 

soybean growth: Arkansas Soil Fertility Studies, Arkansas 

Agricultural Experiment Station Research Series, no. 45, 

p. 84–87.

Purdue, A.H., 1905, Water resources of the contact region 

between the Paleozoic and Mississippi embayment deposits 

in northern Arkansas: U.S. Geological Survey Water-Supply 

Paper 145, p. 88–119.

Purdue, A.H., 1910, The collecting area of the waters of the 

hot springs, Hot Springs, Arkansas: Journal of Geology, 

v. 18, p. 279–285.

Purdue, A.H., and Miser, H.D., 1916, Description of Eureka 

Springs and Harrison quadrangles (Arkansas-Missouri): 

U.S. Geological Survey Geologic Atlas, Folio 202, 21 p.

Quatrochi, P.M., 1996, Groundwater jurisdiction under the 

Clean Water Act—The tributary groundwater dilemma: 

Boston College Environmental Affairs Law Review, v. 23, 

accessed April 2, 2013, at http://lawdigitalcommons.bc.edu/

ealr/vol23/iss3/.

Ragsdale, J.G., 2003, Oil development in south Arkansas, 

1921–2001: South Arkansas Historical Journal, v. 3, 

p. 18–24, accessed May 1, 2013, at http://www.southark.

edu/old/index.php/volumes-1-4.

Ravenscroft, Peter, 2003, An overview of the hydrogeology 

of Bangladesh, in Rahman, A.A, and Ravenscroft, P., eds., 

Groundwater resources and development in Bangladesh—

Background to the arsenic crisis, agricultural potential and 

the environment: Dhaka, Bangladesh Centre for Advanced 

Studies, University Press Ltd., p. 43–86.

Reed, J.E., 1972, Analog simulation of water-level declines in 

the Sparta Sand, Mississippi embayment: U.S. Geological 

Survey Hydrologic Atlas 434, map, scale 1:250,000. 

Reed, J.E., and Broom, M.E., 1979, Digital model of the 

Bayou Bartholomew alluvial aquifer-stream system, 

Arkansas: U.S. Geological Survey Open-File Report 

79–685, 37 p.

Reed, T.B., 2003, Recalibration of a ground-water flow 

model of the Mississippi River Valley alluvial aquifer of 

northeastern Arkansas, 1918–1998, with simulations of 

water levels caused by projected ground-water withdrawals 

through 2049: U.S. Geological Survey Water-Resources 

Investigations Report 03–4109, 58 p.

Reed, T.B., 2004, Status of water levels and selected waterquality conditions in the Mississippi River Valley alluvial 

aquifer in eastern Arkansas, 2002: U.S. Geological Survey 

Scientific Investigations Report 2004–5129, 53 p. 

Reilly, T.E., Dennehy, K.F., Alley, W.M., and Cunningham, 

W.L., 2008, Ground-water availability in the United States: 

U.S. Geological Survey Circular 1323, 70 p.

Renfroe, C.A., 1949, Petroleum exploration in eastern 

Arkansas with selected well logs: Arkansas Resources and 

Development Commission Bulletin 14, 159 p.

Renken, R.A., 1998, Groundwater atlas of the United 

States—Segment 5, Arkansas, Louisiana, Mississippi: U.S. 

Geological Survey Hydrologic Atlas 730–F, 28 p.

Richards, J.M., 2010, Groundwater-flow model and effects 

of projected groundwater use in the Ozark Plateaus 

aquifer system in the vicinity of Greene County, 

Missouri—1907–2030: U.S. Geological Survey Scientific 

Investigations Report 2010–5227, 106 p.

Richards, J.M., and Mugel, D.N., 2008, Potentiometric surface 

of the Ozark aquifer near Springfield, Missouri, 2006–07: 

U.S. Geological Survey Scientific Investigations Map 3003, 

1 sheet.

Robinson, J.A., and Brooks, J.M., 2010, Public water-supply 

systems and associated water use in Tennessee, 2005: U.S. 

Geological Survey Open-File Report 2010–1226, 100 p.

Rosencrantz, F.L., 1946, The rice industry in Arkansas: The 

Arkansas Historical Quarterly, v. 5, no. 2, p. 123–137.

Ryals, G.N., 1980, Potentiometric maps of the Sparta Sand, 

northern Louisiana and southern Arkansas, 1900, 1965, 

1975, and 1980: U.S. Geological Survey Open-File Report 

80–1180, 1 map.

Ryling, R.W., 1960, Ground-water potential of Mississippi 

County, Arkansas: U.S. Geological Survey Water Resources 

Circular, no. 7, 87 p.

Sacks, L.A., 1996, Geochemical and isotopic composition of 

ground water with emphasis on sources of sulfate in the 

Upper Floridian aquifer in parts of Marion, Sumter, and 

Citrus Counties, Florida: U.S. Geological Survey WaterResources Investigations Report 95–4251, 47 p.

Saucier, R.T., 1994, Geomorphology and Quaternary geologic 

history of the Lower Mississippi Valley, volume I: U.S. 

Army Corps of Engineers, Waterways Experiment Station, 

Vicksburg, Miss., 400 p.
References 329

Scheiderer, R.M., and Freiwald, D.A., 2006, Monitoring the 

recovery of the Sparta aquifer in southern Arkansas and 

northern Louisiana: U.S. Geological Survey Fact Sheet 

2006–3090, 4 p. 

Schrader, T.P., 1998, Status of water levels in aquifers in 

the Nacatoch Sand and Tokio Formation of southwestern 

Arkansas, 1996: U.S. Geological Survey Water-Resources 

Investigations Report 98–4130, 22 p.

Schrader, T.P., 1999, Status of water levels in aquifers in the 

Nacatoch Sand of southwestern and northeastern Arkansas 

and the Tokio Formation of southwestern Arkansas, 1999: 

U.S. Geological Survey Water-Resources Investigations 

Report 99–4208–A, 23 p.

Schrader, T.P., 2001a, Potentiometric surface of the Ozark 

aquifer in northern Arkansas, 2001: U.S. Geological Survey 

Water-Resources Investigations Report 01–4233, 11 p.

Schrader, T.P., 2001b, Status of water levels and selected 

water-quality conditions in the Mississippi River Valley 

alluvial aquifer in eastern Arkansas, 2000: U.S. Geological 

Survey Water-Resources Investigations Report 01–4124, 

52 p.

Schrader, T.P., 2004, Status of water levels and selected 

water-quality conditions in the Sparta-Memphis aquifer in 

Arkansas, spring–summer 2001: U.S. Geological Survey 

Scientific Investigations Report 2004–5055, 57 p.

Schrader, T.P., 2005, Potentiometric surface of the Ozark 

aquifer in northern Arkansas, 2004: U.S. Geological Survey 

Water-Resources Investigations Report 2005–5208, 10 p.

Schrader, T.P., 2006a, Status of water levels and selected 

water-quality conditions in the Mississippi River Valley 

alluvial aquifer in eastern Arkansas, 2004: U.S. Geological 

Survey Scientific Investigations Report 2006–5128, 82 p.

Schrader, T.P., 2006b, Status of water levels and selected 

water-quality conditions in the Sparta-Memphis aquifer in 

Arkansas, spring–summer 2003: U.S. Geological Survey 

Scientific Investigations Report 2006–5021, 43 p.

Schrader, T.P., 2007a, 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, 28 p.

Schrader, T.P., 2007b, Status of water levels in aquifers 

in the Nacatoch Sand of southwestern and northeastern 

Arkansas and the Tokio Formation of southwestern 

Arkansas, February 2005: U.S. Geological Survey Scientific 

Investigations Report 2007–5024, 22 p.

Schrader, T.P., 2008a, Water levels and selected water-quality 

conditions in the Mississippi River Valley alluvial aquifer in 

eastern Arkansas, 2006: U.S. Geological Survey Scientific 

Investigations Report 2008–5092, 72 p.

Schrader, T.P., 2008b, Potentiometric surface in the SpartaMemphis aquifer of the Mississippi embayment, spring 

2007: U.S. Geological Survey Scientific Investigations Map 

3014, 1 sheet.

Schrader, T.P., 2009, Water levels and selected water-quality 

conditions in the Sparta-Memphis aquifer (middle Claiborne 

aquifer), spring–summer 2007: U.S. Geological Survey 

Scientific Investigations Report 2009–5207, 24 p.

Schrader, T.P., 2010, Water levels and selected water-quality 

conditions in the Mississippi River Valley alluvial aquifer in 

eastern Arkansas, 2008: U.S. Geological Survey Scientific 

Investigations Report 2010–5140, 71 p., 2 pls.

Schrader, T.P., 2013, Water levels and water quality in the 

Sparta-Memphis aquifer (middle Claiborne aquifer) in 

Arkansas, spring–summer 2009: U.S. Geological Survey 

Scientific Investigations Report 2013–5100, 51 p., 2 pls, 

accessed September 10, 2013, at http://pubs.usgs.gov/

sir/2013/5100/.

Schrader, T.P., 2014, Water levels and water quality in the 

Sparta-Memphis aquifer (middle Claiborne aquifer) in 

Arkansas, spring–summer 2011: U.S. Geological Survey 

Scientific Investigations Report 2014–5044, 44 p., 2 pls, 

accessed June 25, 2014, at http://dx.doi.org/10.3133/

sir20145044.

Schrader, T.P., and Blackstock, J.M., 2010, Water levels 

in aquifers in the Nacatoch Sand of southwestern and 

northeastern Arkansas and the Tokio Formation of 

southwestern Arkansas, spring 2008: U.S. Geological 

Survey Scientific Investigations Report 2010–5238, 22 p.

Schrader, T.P., and Jones, J.S., 2007, Status of water levels and 

selected water-quality conditions in the Sparta-Memphis 

aquifer in Arkansas and the status of water levels in the 

Sparta aquifer in Louisiana, spring 2005: U.S. Geological 

Survey Scientific Investigations Report 2007–5029, 50 p.

Schrader, T.P., and Joseph, R.L., 2000, Potentiometric 

surface of the Cockfield aquifer in southeastern Arkansas 

and the Wilcox aquifers in southern and northeastern 

Arkansas, 2000: U.S. Geological Survey Water-Resources 

Investigations Report 2000–4206, 22 p.

Schrader, T.P., and Rodgers, K.D., 2013, Water levels 

in aquifers in 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. 

Schrader, T.P., and Scheiderer, R.M., 2004, Status of water 

levels in aquifers in the Nacatoch Sand of southwestern 

and northeastern Arkansas and the Tokio Formation of 

southwestern Arkansas, 2002: U.S. Geological Survey 

Water-Resources Investigations Report 2003–4284, 24 p. 
330 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Scott, H.D., Ferguson, J.A., Hanson, Linda, Fugitt, Todd, 

and Smith, Earl, 1998, Agricultural water management 

in the Mississippi Delta Region of Arkansas: University 

of Arkansas, Arkansas Agricultural Experiment Station 

Research Bulletin, no. 959, 100 p.

Scott, H.D., Selim, H.M., and Johnson, A.B., 2000, MLRA 

134—Southern Mississippi Valley silty uplands, in Water 

and chemical transport in soils of the southern U.S.A.: 

Southern Cooperative Bulletin, no. 395. 

Sharif, M.U., Davis, R.K., Steele, K.F., Kim, B., Hays, P.D., 

Kresse, T.M., and Fazio, J.A., 2008, Distribution and 

variability of redox zones controlling spatial variability 

of arsenic in the Mississippi River Valley alluvial aquifer, 

southeastern Arkansas: Journal of Contaminant Hydrology, 

v. 99, p. 49–67.

Sharif, M.U., Davis, R.K., Steele, K.F., Kim, B., Hays, P.D., 

Kresse, T.M., and Fazio, J.A., 2011, Surface complexation 

modeling for predicting solid phase arsenic concentrations 

in the sediments of the Mississippi River Valley alluvial 

aquifer, Arkansas, U.S.A.: Applied Geochemistry, v. 26, 

p. 496–504.

Sharif, M.U., Davis, R.K., Steele, K.F., Kim, B., Kresse, 

T.M., and Fazio, J.A., 2008, Inverse geochemical modeling 

of groundwater evolution with emphasis on arsenic in the 

Mississippi River Valley alluvial aquifer, Arkansas, U.S.A.: 

Journal of Hydrology, v. 350, p. 41–55.

Signor, D.C., Growitz, D.J., and Kam, W., 1970, Annotated 

bibliography on artificial recharge of ground water, 1955–

67: U.S. Geological Survey Water-Supply Paper 1990, 

141 p.

Skinner, J.H., 1984, Clarification of the definition of aquifer 

in 40 CFR 260.10: Memorandum from John H. Skinner, 

Director, Office of Solid Waste, U.S. Environmental 

Protection Agency, 4 p.

Smith, C.R., and Steele, K.F., 1990, Nitrate concentrations of 

ground water Benton County, Arkansas: Fayetteville, Ark., 

Arkansas Water Resources Center, no. MSC–073, 48 p.

Smith, M.C., Massey, J.H., Branson, J., Epting, J.W., 

Pennington, D., Tacker, P.L., Thomas, J., Vories, E.D., 

and Wilson, C., 2007, Water use estimates for various rice 

production systems in Mississippi and Arkansas: Irrigation 

Science, v. 25, p. 141–147.

Sniegocki, R.T., 1953, Plans for the first year’s work on the 

artificial recharge project, Grand Prairie region, Arkansas: 

U.S. Geological Survey Open-File Report, 16 p.

Sniegocki, R.T., 1963a, Geochemical aspects of artificial 

recharge in the Grand Prairie region, Arkansas: U.S. 

Geological Survey Water-Supply Paper 1615–E, 41 p.

Sniegocki, R.T., 1963b, Problems in artificial recharge through 

wells in the Grand Prairie region, Arkansas: U.S. Geological 

Survey Water-Supply Paper 1615–F, 25 p.

Sniegocki, R.T., 1964, Hydrology of a part of the Grand 

Prairie region, Arkansas: U.S. Geological Survey WaterSupply Paper 1615–B, 72 p.

Sniegocki, R.T., Bayley, F.H., and Engler, K., 1963, 

Equipment and controls used in studies of artificial recharge 

in the Grand Prairie region, Arkansas: U.S. Geological 

Survey Water-Supply Paper 1615–C, 39 p.

Sniegocki, R.T., Bayley, F.H., Engler, K., and Stephens, J.W., 

1965, Testing procedures and results of studies of artificial 

recharge in the Grand Prairie region, Arkansas: U.S. 

Geological Survey Water-Supply Paper 1615–G, 56 p.

Sniegocki, R.T., and Reed, J.E., 1963, Principals of siphons 

with respect to the artificial-recharge studies in the Grand 

Prairie region, Arkansas: U.S. Geological Survey WaterSupply Paper 1615–D, 19 p.

Snyder, R.W., 1976, Stratigraphy of the Roubidoux and 

Gasconade Formations of northern Arkansas: Fayetteville, 

University of Arkansas, M.S. thesis, 65 p.

Southwest Arkansas Water District, 2013, Our history: 

Southwest Arkansas Water District, accessed January 12, 

2013, at http://www.swawd.com/history.

Spooner, W.C., 1935, Oil and gas geology of the Gulf Coastal 

Plain in Arkansas: Arkansas Geological Survey, Bulletin 2, 

516 p.

Stanton, G.P., 1993, Processes and controls affecting 

anisotropic flow in the Boone-St. Joe aquifer in northwest 

Arkansas: Fayetteville, University of Arkansas, M.S. thesis, 

217 p.

Stanton, G.P., 1997, Potentiometric surface and specific 

conductance of the Sparta and Memphis aquifers in eastern 

Arkansas, 1995: U.S. Geological Survey Water-Resources 

Investigations Report 97–4119, 126 p.

Stanton, G.P., and Clark, B.R., 2003, Recalibration of a 

ground-water flow model of the Mississippi River Valley 

alluvial aquifer in southeastern Arkansas, 1918–1998, 

with simulations of hydraulic heads caused by projected 

ground-water withdrawals through 2049: U.S. Geological 

Survey Water-Resources Investigations Report 03–4232, 

48 p.

Stanton, G.P., Joseph, R.L., and Pugh, A.L., 1998, Status 

of water levels and selected water-quality conditions in 

the Mississippi River Valley alluvial aquifer in eastern 

Arkansas, 1994–1996: U.S. Geological Survey WaterResources Investigations Report 98–4131, 72 p.

Stanton, J.S., Peterson, S.M., and Fienen, M.N., 2010, 

Simulation of groundwater flow and effects of groundwater 

irrigation on stream base flow in the Elkhorn and Loup 

River Basins, Nebraska, 1895–2055—Phase two: U.S. 

Geological Survey Scientific Investigations Report 2010–

5149, 78 p., 1 app.
References 331

State Review of Oil and Natural Gas Environmental 

Regulations, 2012, Arkansas hydraulic fracturing State 

review: Arkansas Oil and Gas Commission, accessed on 

April 2, 2013, at http://www.aogc.state.ar.us/notices/AR_

HFR_FINAL.pdf.

Steele, K.F., 1981, Groundwater quality and mineral deposits 

relationships in the Ozark Mountains: Fayetteville, Ark., 

Water Resources Research Center, no. PUB–077, 59 p.

Steele, K.F., 1983, Chemistry of the springs of the Ozark 

Mountains, northwestern Arkansas: Fayetteville, Ark., 

Arkansas Water Resources Research Center, no. 98, 48 p.

Steele, K.F., and Adamski, J.C., 1987, Land use effects on 

ground water quality in carbonate rock terrain: Fayetteville, 

Ark., Arkansas Water Resources Research Center, no. 129, 

71 p.

Steele, K.F., Clayton, W.R., Nichols, T.W., and Vendrell, P.F., 

1993, Completion report, pesticide and nitrate monitoring 

results for Craighead, Mississippi, and Poinsett Counties, 

Arkansas—Phase II: Fayetteville, Ark., Arkansas Water 

Resources Center, no. MSC–200, 27 p.

Steele, K.F., Hill, S.S., Nichols, T.W., Scott, H.D., Vendrell, 

P.F., and Lin, H.S., 1994, Completion report—Ground water 

monitoring project for Arkansas, phase III: Fayetteville, 

Ark., Arkansas Water Resources Center, no. MSC–197, 59 

p.

Steele, K.F., and McCalister, W.K., 1990, Nitrate 

concentrations of ground water from limestone and 

dolomitic aquifers in the northeastern Washington County 

area, Arkansas: Fayetteville, Ark., Water Resources 

Research Center, no. MSC–68, 33 p.

Steele, K.F., Widmann, R.K., Wickliff, D.S., and Parr, D.L., 

1985, The effect of rainstorm events on spring water 

chemistry in limestone terrane: Association of Ground 

Water Scientists and Engineers, Southern Regional Ground 

Water Conference, National Water Well Association, 

Proceedings, p. 51–65.

Steinbrugge, G.W., Heiple, L.R., Rogers, N., and Sniegocki, 

R.T., 1954, Groundwater recharge by means of wells: 

University of Arkansas, Agricultural Experimental Station 

Publication, 119 p.

Stephens, J.W., and Halberg, H.N., 1961, Use of water 

in Arkansas, 1960: State of Arkansas Geological and 

Conservation Commission Water Resources Summary, 

no. 4, 8 p.

Stephenson, L.W., 1927, Notes on stratigraphy of the upper 

Cretaceous formations of Texas and Arkansas: Bulletin of 

the American Association of Petroleum Geologists, v. 11, 

p. 8.

Stephenson, L.W, and Crider, A.F., 1916, Geology and ground 

waters of northeastern Arkansas, with a discussion of Dole, 

R.B., The chemical character of the waters: U.S. Geological 

Survey Water-Supply Paper 399, 315 p.

Stoffell, Barry, Appold, M.S., Wilkinson, J.J., McClean, 

N.A., and Jeffries, T.E, 2008, Geochemistry and evolution 

of Mississippian Valley-type mineralizing brines from the 

tri-State and northern Arkansas districts determined by 

LA–ICP–MS microanalysis of fluid inclusions: Economic 

Geology, v. 103, no. 7, p. 1411–1435.

Stone, C.G., and Bush, W.V., 1984, General geology and 

mineral resources of the Caddo River watershed: Arkansas 

Geological Commission, Information Circular 29, 32 p.

Stone, Nathan, and Selden, George, 2006, Aquaculture 

alternatives in Arkansas: University of Arkansas at Pine 

Bluff Cooperative Extension Program FSA9055, 8 p.

Sullavan, J.N., 1974, Drainage areas of streams in Arkansas—

White River Basin: U.S. Geological Survey Unnumbered 

Open-File Report, 123 p.

Sumner, D.M., and Wasson, B.E., 1990, Geohydrology and 

simulated effects of large ground-water withdrawals on 

the Mississippi River alluvial aquifer in northwestern 

Mississippi: U.S. Geological Survey Water-Supply Paper 

2292, 60 p.

Tacker, Phil, Langston, J., Ferguson, J., and Vories, E., 1994, 

Water management: Rice Production Handbook, University 

of Arkansas Cooperative Extension Service MP 192, 

p. 55–63.

Tacker, Phil, Vories, E.D., and Carman, D., 2010, Water supply 

problems and solutions in the Grand Prairie region of 

Arkansas: American Society of Agricultural and Biological 

Engineers Conference Proceedings, Phoenix, Ariz., 

December 5–8, 2010, 8 p.

Tait, D.B., Backer, R.C., and Billingsley, G.A., 1953, The 

ground-water resources of Columbia County, Arkansas—A 

reconnaissance: U.S. Geological Survey Circular 241, 25 p.

Tennyson, Rodney, Terry, Jim, Brahana, J.V., Hays, P.D., 

and Pollock, Erik, 2008, Tectonic control of hypogene 

speleogenesis in the Southern Ozarks—Implications 

for NAWQA and beyond, in Kuniansky, E.L., ed., U.S. 

Geological Survey Karst Interest Group Proceedings, 

Bowling Green, Ky., May 27–29, 2008: U.S. Geological 

Survey Scientific Investigations Report 2008–5023, 142 p.

Terry, J.E., Bryant, C.T., Ludwig, A.H., and Reed, J.E., 1979, 

Water-resources appraisal of the south Arkansas lignite area: 

U.S. Geological Survey Open-File Report 79–924, 162 p.

Terry, J.E., Bryant, C.T., Ludwig, A.H., and Reed, J.E., 1986, 

Water-resources appraisal of the south-Arkansas lignite 

area: Arkansas Geological Commission Information 

Circular 28–D, 162 p.
332 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

The New York Times, 1907, Roosevelt pleads for water routes: 

The New York Times, accessed January 17, 2013, at 

http://query.nytimes.com/mem/archivefree/pdf?res=F10B14

F8345417738DDDAC0894D8415B878CF1D3.

Thompson, D.G., 1931, Ground-water supplies for rice 

irrigation in the Grand Prairie region, Arkansas: U. S. 

Department of the Interior Press Mem. 49844, 21 p.

 Thompson, D.G., 1936, Arkansas Grand Prairie Region, in

Metnzer, O.E., and Wenzel, L.K., ed., Water levels and 

artesian pressure in observation wells in the United States 

in 1935: U.S. Geological Survey Water-Supply Paper 777, 

p. 5–17.

Ting, T.E., 2005, Assessing bacterial transport, storage and 

viability in mantled karst of northwest Arkansas using clay 

and Escherichia coli labeled with lanthanide series metals: 

Ph.D. Dissertation, University of Arkansas, Fayetteville, 

558 p.

Truman, H.S., 1949, Letter to the speaker concerning 

irrigation in the Grand Prairie area of Arkansas in Peters,

Gerhard, and Woolley, J.T., The American presidency 

project: Accessed June 2, 2013, at http://www.presidency.

ucsb.edu/ws/?pid=13275.

Turner, K.J., and Hudson, M.R., 2008, Improved 

understanding of a karst aquifer system through utilization 

of a 3D geologic model, Buffalo National River, Arkansas: 

Geological Society of America Abstracts with Programs, 

v. 40, no. 3, p. 36.

Turner, K.J., Hudson, M.R., Murray, K.E., and Mott, D.N., 

2007, Three-dimensional geologic framework model for a 

karst aquifer system, Hasty and Western Grove quadrangles, 

northern Arkansas: U.S. Geological Survey Scientific 

Investigations Report 2007–5095, 12 p., CD digital archive.

Turner, J.P., Saunders, J.A., and Cook, R.B., 2002, 

Petrographic evidence for amorphous silica precursors 

and geomicrobiologic processes in silicified and pyritized 

Holocene wood: Paper 216–9, Geological Society of 

America Annual Meeting, 2002, Programs with Abstract, 

p. 493.

Union County Water Conservation Board, 2007, Sparta aquifer 

recovery study Union County, Arkansas: Final Report to the 

EPA, 67 p.

University of Arkansas at Little Rock Water Study Task Force, 

2000, Water for our future: Overcoming regional paralysis, 

114 p., accessed June 2, 2013, at http://ualr.edu/provost/

water.pdf.

University of Arkansas Division of Agriculture, 2013, 

Economic contribution of Arkansas Agriculture, 36 p., 

accessed June 2, 2014, at http://www.uaex.edu/division/

docs/Economic_Contribution_2013.pdf.

U.S. Army Corps of Engineers, 1977, Pine Bluff metropolitan 

area, Arkansas: Summary of Water Supply Studies, Interim 

Report, Vicksburg District, 33 p.

U.S. Army Corps of Engineers, 2007, Grand Prairie region and 

Bayou Meto Basin, Arkansas: General Reevaluation Report, 

118 p., accessed March 11, 2013, at http://www.mvm.usace.

army.mil/Portals/51/docs/missions/projects/Bayou%20

Meto/Volume%2001.pdf.

U.S. Army Corps of Engineers, 2010, Reallocation of water 

storage at Bull Shoals Lake, Arkansas: Ozark Mountain 

Regional Public Water Authority and Marion County 

Region Water District, 362 p., accessed August 28, 

2013, at http://www.swl.usace.army.mil/Portals/50/docs/

planningandenvironmental/BShoals_OzarkWS_FEA_

FONSI_20100817%20.pdf.

U.S. Army Corps of Engineers, 2013a, National inventory 

of dams: U.S. Army Corps of Engineers, accessed May 1, 

2013, at http://geo.usace.army.mil/pgis/f?p=397:1:0.

U.S. Army Corps of Engineers, 2013b, Review plan for 

Grand Prairie Area Demonstration Project, Grand Prairie 

region, Arkansas P2# 109425—Implementation phase: U.S. 

Army Corps of Engineers, 25 p., accessed April 2, 2013, at 

http://www.mvm.usace.army.mil/Portals/51/docs/PPPMD/

Peer%20Review%20Plans/Grand_Prairie_Review_Plan.

pdf.

U.S. Department of Agriculture, 2006, USDA roles in marketbased environmental stewardship: Natural Resources 

Conservation Service, USDA Department Regulation 

no. 5600–003.

U.S. Department of Agriculture, 2010, State facts sheets—

Arkansas: U.S. Department of Agriculture, accessed August 

17, 2013, at http://www.ers.usda.gov/StateFacts/AR.htm.

U.S. Department of Agriculture, 2011, Arkansas 2011 State 

agriculture overview: U.S. Department of Agriculture, 

accessed April 20, 2013, at http://www.nass.usda.gov/

Statistics_by_State/Ag_Overview/AgOverview_AR.pdf.

U.S. Department of Agriculture, 2012, National Agricultural 

Statistics Service Quick Stats: U.S. Department of 

Agriculture, accessed April 20, 2012, at http://quickstats.

nass.usda.gov/.

U.S. Environmental Protection Agency, 1984, Classification 

of injection wells, section 146.5 of subpart A of part 6 

146, underground injection control program—Criteria and 

standards: U.S. Code of Federal Regulations, Title 40, Part 

146, July 1, 1984, p. 371–372.

U.S. Environmental Protection Agency, 1988, 40 CFR Parts 

280 and 281, Technical standards and corrective action 

requirements for owners and operators of underground 

storage tanks (UST), Federal Register, v. 53, no. 185, 

165 p.
References 333

U.S. Environmental Protection Agency, 1994a, Review, 

approval, and evaluation of State management plans: Office 

of Prevention, Pesticides, and Toxic Substances, EPA 

735–B–93–005b, 42 p. 

U.S. Environmental Protection Agency, 1994b, Assessment, 

prevention, monitoring, and response components of State 

management plans: Office of Prevention, Pesticides, and 

Toxic Substances, EPA 735–B–93–005c, 219 p.

U.S. Environmental Protection Agency, 2001, 40 CFR 

Parts 9, 141, and 142, National Primary Drinking Water 

Regulations—Arsenic and clarification to compliance and 

new source contaminants monitoring, final rule: Federal 

Register, v. 66, no. 14, 94 p.

U.S. Environmental Protection Agency, 2009, 2009 Edition of 

the drinking water standards and health advisories: Office of 

Water, Washington, D.C., EPA 822–R–09–011, 12 p.

U.S. Environmental Protection Agency, 2010, Hydraulic 

fracturing research study: Office of Research and 

Development, EPA/600/F–10/002, accessed July 30, 2013, 

at http://www.epa.gov/tp/pdf/hydraulic-fracturing-factsheet.pdf.

U.S. Environmental Protection Agency, 2013, CERCLIS 

public access database: U.S. Environmental Protection 

Agency, Superfund Site Information, NPL Listing for 

Arkansas, accessed May 13, 2013, at http://cfpub.epa.gov/

supercpad/cursites/srchsites.cfm.

U.S. Geological Survey, 2013a, Changes in water-use 

categories: U.S. Geological Survey, accessed June 3, 2013, 

at http://water.usgs.gov/watuse/WU-Category-Changes.

html.

U.S. Geological Survey, 2013b, USGS water data for the 

Nation: USGS National Water Information System (NWIS), 

accessed August 29, 2013, at http://waterdata.usgs.gov/

nwis.

Van den Heuvel, P., 1979, Petrography of the Boone 

Formation, northwest Arkansas: Fayetteville, University of 

Arkansas, M.S. thesis, 92 p.

Vandike, J.E., 1997, Guidebook to the geology and hydrology 

of the Current River Basin: Missouri Division of Geology 

and Land Survey, 27 p.

Van Schaik, E.J., and Kresse, T.M., 1994, Report on the 

third sampling of the El Dorado, Pine Bluff, and Lonoke 

Prototypes: Arkansas Department of Pollution Control and 

Ecology, WQ94–10–1, 45 p. 

Van Schaik, E.J., and Kresse, T.M., 1995, Report on the third 

sampling of the Jonesboro Prototype: Arkansas Department 

of Pollution Control and Ecology, WQ95–11–1, 28 p. 

Van Schaik, E.J., and Kresse, T.M., 1996, Report on the third 

sampling of the Brinkley Prototype: Arkansas Department 

of Pollution Control and Ecology, WQ96–02–1, 40 p. 

Vardy, Renee, 2011, Characterization of urban impact on water 

quality of karst springs in Eureka Springs, Arkansas, in

Kuniansky, E.L., ed., U.S. Geological Survey Karst Interest 

Group Proceedings, Fayetteville, Ark., April 26–29, 2011: 

U.S. Geological Survey Scientific Investigations Report 

2011–5031, p. 44–53.

Vaughn, T.W., 1895, The stratigraphy of northwestern 

Louisiana: American Geologist, v. 15, p. 205–229.

Veatch, A.C., 1906, Geology and underground water resources 

of northern Louisiana and southern Arkansas: U.S. 

Geological Survey Professional Paper 46, 422 p.

Vories, E.D., Tacker, P.L., and Hogan, Robert, 2005, Multiple 

inlet approach to reduce water requirements for rice 

production: Applied Engineering in Agriculture, v. 21, no. 4, 

p. 611−616. 

Wagner, D.M., 2007, In-situ assessment of waste 

storage effectiveness in karst using stable isotope 

biogeochemistry: Fayetteville, University of Arkansas, M.S. 

thesis, 58 p.

Wagner, G.H., and Steele, K.F., 1985, Metal concentrations 

in the groundwater of the Ouachita Mountains, Arkansas, 

U.S.A.: Water, Air, and Soil Pollution, v. 25, p. 339–347.

Wagner, G.H., Steele, K.F., and Zachry, D.L., 1975, Trace 

metal and major elements in water-soluble rocks of 

northwest Arkansas: Arkansas Water Resources Center, 

Fayetteville, Ark, no. PUB–036, 55 p.

Warner, N.R., Kresse, T.M., Hays, P.D., Down, A., Karr, J.D., 

Jackson, R.D., and Vengosh, A., 2013, Geochemical and 

isotopic variations in shallow groundwater in areas of the 

Fayetteville Shale development, north-central Arkansas: 

Applied Geochemistry, v. 35, p. 207–220.

Webb, G.E., 1994, Paleokarst, paleosol, and rocky-shore 

deposits at the Mississippian-Pennsylvanian unconformity, 

northwestern Arkansas: Geological Society of America 

Bulletin, May 1994, v. 106, no. 5, p. 634–648.

Weeks, W.B., 1938, South Arkansas stratigraphy with 

emphasis on the older Coastal Plain beds: American 

Association of Petroleum Geologists Bulletin, v. 22, 

p. 972–978.

Westerfield, P.W., 1989, Ground-water levels in the alluvial 

aquifer in eastern Arkansas, 1987: U.S. Geological Survey 

Open-File Report 89–64, 32 p.

Westerfield, P.W., 1990, Water-level maps of the Mississippi 

River Valley alluvial aquifer in eastern Arkansas, 1987: 

U.S. Geological Survey Water-Resources Investigations 

Report 90–4089, 1 sheet.

Westerfield, P.W., 1994, Potentiometric-surface maps of the 

Cockfield and lower Wilcox aquifers in Arkansas, 1991: 

U.S. Geological Survey Water-Resources Investigations 

Report 93–4137, 2 sheets.
334 Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater

Publishing support provided by

Lafayette and Tacoma Publishing Service Centers

Westerfield, P.W., 1995, Potentiometric surface of the Sparta 

and Memphis aquifers in eastern Arkansas, April through 

July 1993, U.S. Geological Survey Scientific Investigations 

Report 95–4000, 1 sheet.

Westerfield, P.W., and Baxter, C.R., 1990a, Ground-water 

levels in the alluvial aquifer in eastern Arkansas, 1988: 

U.S. Geological Survey Open-File Report 90–383, 32 p.

Westerfield, P.W., and Baxter, C.R., 1990b, Ground-water 

levels in the alluvial aquifer in eastern Arkansas, 1989: 

U.S. Geological Survey Open-File Report 90–558, 35 p.

Westerfield, P.W., and Baxter, C.R., 1990c, Water level maps 

of the Mississippi River Valley alluvial aquifer in eastern 

Arkansas, 1987: U.S. Geological Survey Open-File Report 

90–4089, 1 sheet.

Westerfield, P.W., and Gonthier, G.J., 1993, Water-level maps 

of the Mississippi River Valley alluvial aquifer in eastern 

Arkansas, 1989: U.S. Geological Survey Water-Resources 

Investigations Report 92–4120, 1 sheet.

Westerfield, P.W., and Poynter, D.T., 1993, Ground-water 

levels in the alluvial aquifer in eastern Arkansas, 1992: 

U.S. Geological Survey Open-File Report 93–96, 25 p., 

1 sheet.

Westerfield, P.W., and Poynter, D.T., 1994, Water-level maps 

of the Mississippi River Valley alluvial aquifer in eastern 

Arkansas, spring, 1993: U.S. Geological Survey Open-File 

Report 93–374, 1 sheet.

Westerfield, P.W., and Touschner, S.T., 1991, Ground-water 

levels in the alluvial aquifer in eastern Arkansas, 1990: 

U.S. Geological Survey Open-File Report 91–248, 35 p.

Westerfield, P.W., and Touschner, S.T., 1992, Ground-water 

levels in the alluvial aquifer in eastern Arkansas, 1991: U.S. 

Geological Survey Open-File Report 92–46, 24 p.

Westerfield, P.W., and Touschner, S.T., 1993, Ground-water 

levels in the alluvial aquifer in eastern Arkansas, 1992: 

U.S. Geological Survey Open-File Report 93–96, 25 p.

Whitfield, M.S., Jr., 1975, Geohydrology and water quality 

of the Mississippi River alluvial aquifer, northeastern 

Louisiana: Louisiana Department of Public Works Water 

Resources Technical Report, no. 10, 29 p.

Wickliff, D.S., 1988, The effects of rainstorm events on the 

water chemistry of a river with emphasis on the heavy metal 

content: Fayetteville, University of Arkansas, M.S. thesis, 

95 p.

Widmann, R.K., 1982, Episodic and seasonal effects of 

rainfall on spring water chemistry in a limestone terrane: 

Fayetteville, University of Arkansas, M.S. thesis, 110 p.

Wilbert, L.J., Jr., 1953, The Jacksonian stage in southeastern 

Arkansas: Arkansas Resources and Development 

Commission, Division of Geology Bulletin 19, 125 p.

Williams, F.C., 2012, Agriculture: Encyclopedia of 

Arkansas, accessed December 4, 2012, at http://www.

encyclopediaofarkansas.net/encyclopedia/entry-detail.

aspx?search=1&entryID=385.

Williamson, A.K., Grubb, H.F., and Weiss, J.S., 1990, 

Groundwater flow in the Gulf Coast aquifer systems, 

south-central United States—A preliminary analysis: 

U.S. Geological Survey Water-Resources Investigations 

Report 89–4071, 124 p.

Wilson, C.E., Jr., and Branson, J.W., 2002, Trends in Arkansas 

rice production, in Rice research studies 2002: Arkansas 

Agricultural Experiment Station Research Series 504, 

p. 15–17. 

Wilson, C.E., Jr., Frizzell, D.L., Slaton, N.A., and Norman, 

R.J., 1997, Influence of seeding rates on rice salinity 

tolerance: B.R. Wells Rice Research Studies 1997, Arkansas 

Agricultural Experiment Station Research Series 460, 

p. 175–179.

Yeatts, D.S., 2004, Potentiometric Surfaces in the Cockfield 

and Wilcox aquifers of southern and northeastern Arkansas, 

2003: U.S. Geological Survey Scientific Investigations 

Report 2004–5169, 29 p.

Zachry, D.L., Steele, K.F., Wood, L.J., and Johnston, D.H., 

1986, Stratigraphy and hydrology of upper Cretaceous and 

Tertiary strata, Columbia and Union Counties, Arkansas: 

University of Arkansas, Fayetteville, Ark., 74 p.

Zimmerman, R.K., 1992, Fractured Smackover limestone 

in northeast Louisiana—Implications for hydrocarbon 

exploitation: Gulf Coast Association of Geological Societies 

Transactions, v. 42, p. 401–412.

Kresse and others — Aquifers of Arkansas—Protection, Management, and Hydrologic and Geochemical Characteristics of Groundwater—SIR 2014–5149

I SBN 978- 1- 4113- 3858-6

9 7 8 1 4 1 1 3 3 8 58 6 Printed on recycled paper

ISSN 2328-031X (print)

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20145149