Oahu Q = ·s:::> 

I 

HAWAII l / 

.,_,.,. t.=7.? ~ 

Caribbean Islands Aquifer 
REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM 

OF THE 

U.S. GEOLOGICAL SURVEY 

SUMMARY OF PROJECTS, 1978-84 

Edited by 

Ren )en Sun 

U.S. Geological Survey Circular 1'002 
U·NITED STATES DEPARTMENT OF THE INTERIOR 

DON~LD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1986 

Free on application to Distribution Branch, Text Products Section,. 

U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304-4658 
CONTENTS 

Page 

Abstract ....................................................................•....................•.•..•.....•...•....•.•..............•...... 1 

Introduction ...................................•...............................•....................•......•...•...•..•........•...........• 1 

by Ren Jen Sun 

Completed phase I regional aquifer-system analysis projects ................................................................ 9 

Central Valley regional aquifer-system study, California ................•.....•...•.........•.•........•.......•........ 9 

by Gilbert L. Bertoldi and Ren Jen Sun 

Introduction .•....•....................•....................••............•...•.......•............•.......•...•.••............ 9 

Significant results ......•..........•....................................•...•.............................................. 13 

Published reports ......•......................................................•.•..•.....•..•......•.••..•.....•.•.••...... 15 

References cited .............................................................•.•..•.•..........•..•....••...•...••.•..••... 16 

Floridan regional aquifer-system study ............................•...............•..........•................•....•..•.•.. 17 

by Peter W. Bush and Richard H. Johnston 

Introduction .............................................................................•...............•................... 17 

Hydrogeologic framework ..•................................................................ : ...•..•.••..........•...... 17 

Conceptual model ...•...................................•.......................•........•.....•..............•.•......•.. 18 

Digital flow model ......................................................................................................... 18 

Geochemistry ...............................................•......•....•..........•.....••........•.......•..•.........•.•. 26 

Potential for development ..........................................................................•.....•..•........... 26 

Published reports .................................................................•...•......•.•.............•........•.•.. 26 

References cited .............................................................•....•....•......•.............•...•.•...•.... 28 

High Plains regional aquifer-system study .................................................•...•...•...................... 30 

by John B. Weeks ..............•...................................•...............•..........•.................•........... 30 

Introduction .•........................................................................•.....•.....•..............•.•......... 30 

Geohydrology ...............................................................•..............................•....... : .•..•... 30 

Ground-water pumpage ..................................................•....•........•..................•..•.......•... 34-

Fiow models .....................................................................•......•.........•........•......•...•..... 40 

Published reports .........................................................................••......•........................ 43 

References cited ........................................................................................................... 48 

Northern Great Plains regional aquifer-system study .................................••.....•..•.............•........ 50 

by George A. Dinwiddie and Joe S. Downey 

Introduction .•....................................................•...................•..•.......••......•................... 50 

Geohydrology and model simulation ................•.................•.........•.........................•.......... 50 

Published reports .......................................................•............................•..•......•........... 68 

References cited .................................................................................•........•..•....•........ 71 

Northern Midwest regional aquifer-system study .................................•.•.......•.....•.....•............•.. 72 

by Harley L. Young, Donald I. Siegel, Richard J. Mandie, and Angleo L. Kontis 

Introduction .......................................................•................•.•........•...............•............. 72 

Geologic and hydrologic data ................................•..........................•...............•....•......... 73 

Flow models ........................•.............................•...........................•....•......•...•............. 75 

Geochemical data ......................................................................................................... BO 

Published reports .............................................................................•............................ 86 

References cited ..........................................................•..•....•.............................•....•..... 87 

Ill 
IV 

Page 

Snake River Plain regional aquifer-system study ...............•.................................•...•.•..•.......•...•. SB 

by Gerald F. Lindholm 

Introduction ...........................................•....................................•.....•.......................... 88 

Geohydrologic framework .........................•.................................................•........•.........• 89 

Water budgets and ground-water and surface-water relations ..................•..•.............•...........• 89 

Water quality and geochemistry ....................................................................................... 93 

Water use ................................................................................................................... 95 

Simulation of ground-water flow in the eastern part of the Snake River Plain .. ; ........................ 97 

Simulation of ground-water flow in the western part of the Snake River Plain ........................ 102 

Summary ................................................................................................................... 104 

Published reports ......................................................................................................... 105 

References cited ..•..........................................................................•............................ 106 

Southwest alluvial-basin regional aquifer-systems study ............................................................ 107 

Study in parts of Colorado, New Mexico, and Texas .......................................................... 107 

by David W. Wilkins 

Introduction ........................................................................................................... 107 

General geology and hydrology ................................................................................. 107 

Geologic studies ..................................................................................................... 1 08 

Geochemical studies ................................................................................................ 108 

Recharge models .................................................................................................... 109 

Simulations ........................................................................................................... 113 

Published reports .................................................................................................... 114 

References cited ................................................................................•.................... 115 

Study in southern and central Arizona and parts of adjacent states ...................................... 116 

by Thomas W. Anderson 

lntroduction ........................................................................................................... 116 

Geohydrologic setting ......... ~ .................................................................................... 116 

Regional categorization of basins ............................................................................... 119 

Summary of basin characteristics ............................................................................... 119 

Summary .............................................................................................................. 129 

Published reports .................................................................................................... 129 

References cited ..................................................................................................... 131 

Active phase I regional aquifer-system analysis projects ................................................................... 132 

Central Midwest regional aquifer-system study ........................................................................ 132 

by Donald G. Jorgensen, Robe·rt B. Leonard, Donald C. Signor, and John 0. Helgensen 

lntroduction ................................................................................................................ 132 

Progress of the study .................................................................................................... 132 

Results ...................................................................................................................... 134 

Published reports ......................................................................................................... 139 

References cited .......................................................................................................... 140 

Columbia Plateau basalt regional aquifer-system study .............................................................. 141 

by John Vaccaro 

lntroduction ................................................................................................................ 141 

Hydrogeologic framework ............................................................................................. 141 

Results and scheduled work .......................................................................................... 145 
v 

Page 

Published report ..........................•.......................................................................•....... 145 

References cited .......................................................................................................... 145 

Great Basin regional aquifer-system study .............................................................................. 146 

by James R. Harrill 

Introduction ................................................................................................................ 146 

Progress of the study ................................................................................................... 147 

Significant results ........................................................................................................ 147 

Published reports ......................................................................................................... 151 

Gulf Coastal Plain regional aquifer-system study ...................................................................... 152 

by Hayes F. Grubb 

lntroduction ................................................................................................................ 152 

Conceptual geohydrologic framework .............................................................................. 152 

Data sources .............................................................................................................. 156 

Simulation of ground-water flow .................................................................................... 157 

Published reports .......................................................................... · ............................... 161 

References cited .......................................................................................................... 161 

Northeast glacial regional aquifer-system study ....................................................................... 162 

by Forest P. Lyford 

lntroduction ................................................................................................................ 162 

Progress and findings ................................................................................................... 162 

Published report .......................................................................................................... 167 

References cited .......................................................................................................... 167 

Northern Atlantic Coastal Plain regional aquifer-system study .................................................... 168 

Introduction, by Harold Meisler ...................................................................................... 168 

Hydrogeologic framework, by Henry Trapp, Jr .................................................................. 168 

Simulation of ground-water flow, by P. Patrick Leahy and Mary Martin ................................. 169 

Saltwater-freshwater relations, by Harold Meisler ............................................................... 176 

Geochemistry, by LeRoy L. Knobel and Francis H. Chapelle ................................................ 186 

Saltwater, by Harold Meisler .......................................................................................... 190 

Published reports ......................................................................................................... 192 

References cited .......................................................................................................... 193 

Oahu Island regional aquifer-system study, Hawaii, .................................................................. 195 

by Charles J. Ewart 

Introduction ................................................................................................................ 195 

Progress and results ..................................................................................................... 197 

References cited .......................................................................................................... 204 

Southeastern Coastal Plain regional aquifer-system study .......................................................... 205 

by Robert L. Wait, Robert A. Renken, Rene A. Barker, Roger W. Lee, and Virginia Stricker 

Introduction ................................................................................................................ 205 

Regional geologic setting .............................................................................................. 206 

Hydrogeologic framework ............................................................................................. 206 

Hydrology .................................................................................................................. 212 

Ground-water flow simulations ....................................................................................... 213 

Geochemistry ....................................................................................... · ....................... 219 

Published reports ......................................................................................................... 220 

References cited .......................................................................................................... 222 
VI 

Page 

Upper Colorado River Basin regional aquifer-system study ......................................................... 223 

by 0. James Taylor, Geoffrey Freethey, and Kent C. Glover 

Introduction .................. ,, ............................................................................................. 223 

Progress and results ...............................................................................•..................... 223 

Published re.ports ......................................................................................................... 233 

References cited .......................................................................................................... 233 

Phase I regional aquifer-system analysis projects started in 1984 ........................................................ 234 

Caribbean Islands regional aquifer-system study ...................................................................... 234 

by Fernando Gomez-Gomez 

Introduction ................................................................................................................ 234 

Hydrogeologic framework ............................................................................................. 234 

Summary ................................................................................................................... 241 

References cited .......................................................................................................... 241 

Michigan Basin regional aquifer-system study ........................................................................ 242 

by Lindsay A. Swain 

References cited .......................................................................................................... 244 

Southern California alluvial basins regional aquifer-system study ................................................. 245 

by Peter Martin 

Phase II regional aquifer-system analysis projects (followup studies) ................................................... 248 

Central Valley regional aquifer system, California, phase II study ................................................ 248 

by Robert J. Gilliam 

Floridan regional aquifer system, phase II study ...................................................................... 249 

by Peter W. Bush, James A. Miller, and Morris L. Maslia 

Introduction ................................................................................................................ 249 

Petrographic study, central Florida .................................................................................. 249 

Saltwater movement study, Hilton Head Island, South Carolina ........................................... 249 

Effects of increased pumpage, southwest Georgia and northwest Florida ............................... 251 

Regional potentiometric-surface map, 1985 ....................................................................... 251 

Published report ..................................................................... : ..................................... 254 

Reference cited ........................................................................................................... 254 

High Plains regional aquifer system, phase II study .................................................................. 255 

by John B. Weeks 

Introduction ............. · ................................................................................................... 255 

Evaluation of pumpage and irrigation return flow ............................................................... 255 

Evaluation of effects of future pumping ........................................................................... 256 

Published report ........................................... ~ .............................................................. 258 

References cited .......................................................................................................... 258 

Snake River Plain regional aquifer system, phase II study .......................................................... 259 

by Gerald F. Lindholm 

Introduction ................................................................................................................ 259 

Big Lost River Basin .................................................................................................... 259 

American Falls Reservoir area ........................................................................................ 259 

Ground-water flow model combining the eastern and western parts 

of the Snake River Plain .............................................................................................. 259 

Geochemical investigations of sources of water to the Thousand Springs .............................. 260 

Stream-aquifer model for the eastern part of the Snake River Plain ...................................... 261 

Appendix: RASA project chiefs and their addresses ........................................................................ 262 
Figures 

ILLUSTRATIONS 

Page 

1-7. Maps showing: 

1. Location of reports of ~~summary Appraisals of the Nation's 

Ground-Water Resources" by the U.S. Geological Survey ........................ 3 

2. Location of regional aquifer systems identified for study under 

the Regional Aquifer-System Analysis Program of the U.S. 

Geological Survey ............................................................................. 4 

3. Location of areas being investigated during 1978-84 under the 

Regional Aquifer-System Analysis Program of the U.S. Geological Survey .................................................................................. 5 

4. Schematic section showing aquifers and confining units .......................... 7 

5. Location of the Central Valley of California and the principal 

areas of land subsidence .................................................................. 10 

6. Water-surplus and water-deficient areas in California ............................. 12 

7. Areas of A, land subsidence observed during 1961-75 and, 

B, the corresponding 1961 pumpage per unit area ................................. 13 

8. Graph showing volume of land subsidence in major pumping areas in 

San Joaquin Valley and volume of pumped water in the west part of 

the San Joaquin Valley .................................................................................. 14 

9-16. Maps showing: 

9. Translation of hydrogeologic framework into conceptual and 

digital ground-water flow model, Floridan aquifer system ........................ 19 

10. Potentiometric surface of the Upper Floridan aquifer, May 

1980; occurrence of unconfined or loosely confined conditions; 

locations of springs discharging from the Upper Floridan 

aquifer; and areas of long-term water-level decline ................................ 21 

11. Estimated predevelopment discharge from major ground-water 

areas of the Upper Floridan aquifer .................................................... 23 

12. Estimated 1980 discharge from major ground-water areas 

of the Upper Floridan aquifer ......................................... ,. ................. 25 

13. Principal geologic units of the High Plains regional aquifer system ........... 32 

14. Areal extent and age of bedrock units underlying the High 

Plains regional aquifer system ............................................................ 33 

15. Areas where saturated thickness of the High Plains regional 

aquifer system exceeded 200 feet in 1980 ............................................ 35 

16. Dissolved-solids concentrations in ground water in the High 

Plains regional aquifer system ............................................................ 36 

17. Bar graph showing acreage irrigated by ground water and estimated 

ground-water pumpage in the High Plains, 1949-78 .............................................. 37 

18-22. Maps showing: 

18. Water-level changes, from predevelopment to 1980, in the 

High Plains regional aquifer system .................................................... 39 

19. Saturated thickness changes, from predevelopment to 1980, 

in the High Plains regional aquifer system ............................................ 41 

20. Subdivisions used in modeling the High Plains regional aquifer system ...... 42 

21. Study area of the Northern Great Plains regional aquifer system .............. 51 

22. Structural and physiographic features of the northern 

Great Plains ................................................................................... 52 

23. Diagrammatic cross section from ground-water recharge area to 

discharge area showing relation of aquifers and confining units 

underlying the northern Great Plains, from south-central Montana 

to east North Dakota ........... n .......................................................... 53 

VII 
VIII 

Page 

24-28. Maps showing: 

24. Regional flow in the Upper Cretaceous aquifer system (AQ5) 

underlying the northern Great Plains ..............................•........•..........• 54 

25. Regional flow in the Lower Cretaceous aquifer system (AQ4) 

underlying the northern Great Plains ........................................•.......... 55 

26. Regional flow in the Pennsylvanian aquifer system (AQ3) 

underlying the northern Great Plains ......................•........................•... 56 

27. Regional flow in the Mississippian (Madison Limestone) aquifer 

system (AQ2) underlying the northern Great Plains .......................•........ 57 

28. Regional flow in the Cambrian-Ordovician aquifer system (AQ1) 

underlying the northern Great Plains .........•..................•.....•................ 58 

29. Generalized hydrogeologic cross section showing general ground-water flow 

patterns in the Northern Great Plains regional aquifer system ................................ 59 

30. Generalized hydrogeologic cross section showing ground-water discharge 

from aquifers consisting of rocks of Paleozoic to Mesozoic age underlying 

the northern Great Plains ................................................................•....•.......... 60 

31-32. Maps showing: 

31. Simulated rates of .movement of ground water in the Mississippian 

(Madison Limestone) aquifer system (AQ2) underlying the 

northern Great Plains ................................ · ....................................... 62 

32. Simulated rates of movement of ground water in the CambrianOrdovician aquifer system (AQ1) underlying the northern 

Great Plains ................................................................................... 64 

33. Diagrammatic cross section showing general altitudes of brine 

in the Williston basin of the northern Great Plains ....................•............ 65 

34. Generalized hydrogeologic cross section showing discharge 

area of the Cambrian-Ordovician aquifer system (AQI) 

underlying the northern Great Plains ................................................... 65 

35-37. Maps showing: 

35. Simulated drawdowns in the Pennsylvanian aquifer system (AQ3) 

underlying the northern Great Plains, after 5.9 years of pumping 

from the Mississippian aquifer system (AQ2) at a rate of 27.9 cubic 

feet per second and an assumed storage coefficient of 2.0 x 10-6 ••••••••••• 67 

36. Simulated drawdowns in the Cambrian-Ordovician aquifer system 

(AQ1) underlying the northern Great Plains, after 5.9 years of 

pumping from the Mississippian aquifer system (AQ2) at a rate of 

27.9 cubic feet per second and an assumed storage coefficient 

of 2.0 x 10-6 ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 68 

37. General bedrock geology of the northern Midwest and locations 

of test wells drilled during the Northern Midwest regional aquifersystem study ..........................................................................•....... 74 

38. Chart showing stratigraphic configuration of the regional aquifers and 

confining units delineated for the Northern Midwest regional aquifersystem study ................................................................................................ 75 

39-92. Maps showing: 

39. Generalized predevelopment potentiometric surface of the 

St. Peter-Prairie du Chien-Jordan aquifer of the CambrianOrdovician regional aquifer system in the northern Midwest .................... 76 

40. Decline in the potentiometric surface of the Cambrian-Ordovician 

regional aquifer system in the Chicago-Milwaukee area, 1864-1980 ........... n 

41. Potentiometric surface of the St. Peter-Prairie du Chien-..Jordan 

aquifer of the Cambrian-Ordovician regional aquifer system in 

the northern Midwest, 1980 ............................................................... 78 
Page 

42. Location and areal extent of subregional groundwater flow models of the Cambrian-Ordovician regional aquifer 

system in the northern Midwest ...............................................•......... 79 

43. Simulated head decline, 1864-1980, in the St. PeterPrairie du Chien-Jordan aquifer of the Cambrian-Ordovician 

regional aquifer system in the northern Midwest ..............................•.... 80 

44. Simulated head decline, 1864-1980, in the Mount Simon 

aquifer of the Cambrian-Ordovician regional aquifer system 

in the northern Midwest ................................................................... 81 

45. Dissolved-solids concentrations of ground water in the 

St. Peter-Prairie du Chien-Jordan aquifer of the CambrianOrdovician regional aquifer system in the northern Midwest .............•..•... 82 

46. Sulfate concentrations of ground water in the St. Peter-Prairie du 

Chien-Jordan aquifer of the Cambrian-Ordovician regional aquifer 

system in the northern Midwest .....................................................•... 83 

47. Hydrochemical facies of ground water in the St. PeterPrairie du Chien-Jordan aquifer of the Cambrian-Ordovician 

regional aquifer system in the northern Midwest ................................... 84 

48. Distribution of cPSO in ground water in the Cambrian-Ordovician 

regional aquifer system in the northern Midwest ................................... 85 

49. Study area of the Snake River Plain regional aquifer system ................... 90 

50. Generalized geology of the Snake River drainage basin above 

Weiser, Idaho ................................................................................. 91 

51. Thickness of saturated Quaternary basalt underlying the 

Snake River Plain ............................................................................ 92 

52. Configuration of the regional water table in the Snake River 

Plain, spring 1980 ......................................................................•.•... 93 

53. Changes in Snake River Plain ground-water levels due to 

surface-water irrigation ..................................................................... 94 

54. Ground-water discharge to the Snake River from the eastern 

part of the Snake River Plain regional aquifer system ............................. 95 

55. Relation of ground-water levels to ground-water discharge from 

the eastern part of the Snake River Plain regional aquifer system ............. 95 

56. Changes in ground-water budget, 1880 and 1980, the eastern 

part of the Snake River Plain regional aquifer system .... ; .................•...... 96 

57. Areal distribution of dissolved-solids concentrations in ground 

water in the Snake River Plain regional aquifer system ........................•.. 97 

58. Estimated 1980 ground-water pumpage from the Snake River 

Plain regional aquifer system ..........................................................••. 98 

59. Generalized geologic section and conceptual model, eastern part of 

the Snake River Plain regional aquifer system .......................... ~ .•.......••. 99 

60. Simulated transmissivities for modeled aquifer layer 1, eastern part 

of the Snake River Plain regional aquifer system ................................. 100 

61. Simulated and measured water levels in a well near Mud Lake, 

ground-water discharge to the Snake River from Milner to King 

Hill, and model sensitivity to changes in transmissivities, eastern 

part of the Snake River Plain regional aquifer system ........................... 101 

62. Generalized geologic section and conceptual model, western part 

of the Snake River Plain regional aquifer system ................................. 103 

63. Simulated transmissivities for modeled aquifer layer 1, western part 

of the Snake River Plain regional aquifer system ................................. 104 

64. Study area and basin boundaries of alluvial basins in parts of 

Colorado, New Mexico, and Texas ..................................•.......•........ 109 

IX 
X 

65. 

66. 

67. 

68. 

69. 

70. 

71. 

72. 

73. 

74. 

75. 

76. 

n. 

78. 

79. 

80. 

81. 

82. 

83. 

84. 

85. 

86. 

87. 

Page 

Alluvial basins with open and closed surface water drainages, 

in parts of Colorado, New M·exico, and Texas .................................... 110 

Generalized geologic map of the alluvial basins in parts of 

Colorado, New Mexico, and Texas ................................................... 111 

Regional potentiometric surface of the alluvial basin aquifer 

systems in parts of Colorado, New Mexico, and Texas, 1971-80 ............. 112 

Regionalized water quality of the alluvial basin aquifer systems 

in parts of Colorado, New Mexico, and Texas .................................... 113 

Study area and basin boundaries of the· alluvial basin 

aquifer systems in southern and central Arizona and parts 

of adjacent States ...........................................................•............. 117 

Typical sequence of sedimentary units that fill a basin in 

southern and central Arizona and parts of adjacent States .................... 118 

Recharge and discharge components in alluvial basins in 

southern and central Arizona and parts of adjacent States .................... 120 

Annual ground-water withdrawal, 1915-80, from the alluvial 

basin aquifer systems in southern and central Arizona and 

parts of adjacent States .................................................................. 121 

Areas of water-level declines In the alluvial basin 

aquifer systems in southern and central Arizona and 

parts of adjacent States .................................................................. 122 

Generalized categories of basins and modeled basins of 

the alluvial basin aquifer systems in southern and central 

Arizona and parts of adjacent States ................................................. 123 

Generalized characteristics of the aquifer system underlying 

the basins of the southeast category in southern and 

central Arizona and parts of adjacent States ....................................... 124 

Generalized characteristics of the aquifer system underlying 

the basins of the central category in southern and 

central Arizona and parts of adjacent States ....................................... 125 

Generalized characteristics of the aquifer system underlying 

the basins of the west category in southern and 

central Arizona and parts of adjacent States ....................................... 126 

Generalized characteristics of the aquifer system underlying 

the basins of the Colorado River category in southern and 

central Arizona and parts of adjacent States ....................................... 127 

Generalized characteristics of the aquifer system underlying 

the basins of the highland category in southern and 

central Arizona and parts of adjacent States ....................................... 128 

Study area of the Central Midwest regional aquifer system .................... 133 

Generalized geologic section of the Maha and Apishapa 

aquifers of the Great Plains regional aquifer system 

in the central Midwest ................... 

-................................................. 135 

Preliminary potentiometric surface of the Maha aquifer 

of the Great Plains regional aquifer system in the central Midwest .......... 136 

Dissolved-solids concentrations of ground water in Maha aquifer 

of the Great Plains regional aquifer system in the central Midwest .......... 137 

Dominant ions of ground water in the Maha aquifer of the 

Great Plains regional aquifer system in the central Midwest ................... 138 

Study area of the Columbia Plateau basalt regional aquifer system ......... 142 

Extent of the Columbia River Basalt Group ......................................... 143 

Generalized ground-water flow pattern in the Columbia River 

basalt regional aquifer system and idealized vertical 

sections showing basalt interflow structures ....................................... 144 
Page 

88. Study area and types of ground-water flow models, 

Great Basin regional aquifer system .................................................. 148 

89. Regional ground-water flow of the Great Basin regional 

aquifer system .............................................................................. 149 

90. Identified major ground-water flow systems and areas of 

major ground-water discharge of the Great Basin regional 

aquifer svstem ............................................................................... 150 

91. Study area, location of geophysical logs used to define the 

hydrogeologic framework of the Gulf Coastal Plain 

regional aquifer system ................................................................... 154 

92. Generalized outcrop of major aquifers and confining units in 

the Gulf Coastal Plain regional aquifer system study area. 

The Coastal Lowlands confining unit is covered by alluvium 

in northeastern Louisiana and west-central Mississippi ...................•...... 158 

93. Generalized section showing relation of aquifers and confining units 

from southeastern Missouri to Atchafalaya Bay, Louisiana ................................... 159 

94-137. Maps showing: 

94. Areas of subregional ground-water flow models, Gulf Coastal Plain 

regional aquifer system .................................................................. 160 

95. Study area, specific site study area, and prominent glacial aquifers 

in the northeastern United States ..................................................... 163 

96. Physiographic divisions of the northeastern United States in the 

study area of the Northeast glacial regional aquifer system .................... 164 

97. Three major types of geohydrologic areas to group and describe 

the glacial aquifers in the northeastern United States ........................... 165 

98. Generalized transverse and longitudinal geologic sections of valleys 

draining away from glacial ice (type A) ...........................................•.. 166 

99. Generalized geologic section of deposits in an area having extensive 

preglacial lakes (type B) .................................................................. 167 

100. Generalized valley-aquifer system used in a ground-water flow 

model for the study of the Northeast glacial regional aquifer system ....... 167 

101. Location of the northern Atlantic Coastal Plain ................................... 170 

102. Thickness of Coastal-Plain sediments and location of hydrogeologic 

sections in the northern Atlantic Coastal Plain .................................... 171 

103. Hydrogeologic section B-B', from New Jersey to the off-shore 

COST B-2 well, in the northern Atlantic Coastal Plain .......................... 172 

104. Hydrogeologic section C-C'~ Maryland, in the northern Atlantic 

Coastal Plain ........................................................ ~ ....................... 173 

105. Hydrogeologic section D-A, southern North Carolina, in the 

northern Atlantic Coastal Plain ......................................................... 174 

106. Hydrogeologic section A-A', from North Carolina to Long Island, 

New York, in the northern Atlantic Coastal Plain ................................. 175 

107. Comparison of physical and model-simulated systems used 

for steady-state simulations of the Northern Atlantic Coastal 

Plain regional aquifer system ........................................................... 176 

108. Comparison of physical and model simulated systems used for 

transient simulations of the Northern Atlantic Coastal Plain 

regional aquifer system ................................................................... 177 

109. Simulated prepumping potentiometric surface of an aquifer 

consisting of sediments of Upper Cretaceous age (model 

aquifer layer 2), the Northern Atlantic Coastal Plain 

regional aquifer system ................................................................... 178 

110. Simulated prepumping potentiometric surface of an aquifer • 

XI 
XII 

Page 

consisting of sediments of Eocene age (model aquifer layer 7), 

the Northern Atlantic Coastal Plain regional aquifer system ................... 179 

111. Simulated deep percolation to and discharge from the confined 

aquifers of the Northern Atlantic Coastal Plain regional 

aquifer system .............................................................................. 180 

112. Ground-water withdrawals from the Northern Atlantic Coastal 

Plain regional aquifer system, 1900-80 ............................................... 181 

113. Simulated 1980 potentiometric surface of an aquifer consisting 

of sediments of Upper Cretaceous age (model aquifer layer 2), 

the Northern Atlantic Coastal Plain regional aquifer system ................... 182 

114. Simulated 1980 potentiometric surface of an aquifer consisting 

of sediments of Eocene age (model aquifer layer 7), the 

Northern Atlantic Coast regional aquifer system .................................. 183 

115. Hydrogeologic section from southern New Jersey to the 

Continental Slope, showing isochlors and simulated 

saltwater-freshwater interface in the northern Atlantic 

Coastal Plain ................................................................................ 184 

116. Altitudes of the 250 milligrams per liter chloride concentration of 

ground water in the northern Atlantic Coastal Plain ............................. 185 

117. Altitudes of the 10,000 milligrams per liter chloride concentration 

of ground water in the northern Atlantic Coastal Plain .......................... 187 

118. Concentrations of exchangeable sodium on Aquia glauconite 

samples plotted against distance along a flow path in 

southern Maryland ......................................................................... 188 

119. Concentrations of dissolved sodium, calcium plus magnesium, 

and bicarbonate of the Aqia aquifer water plotted against distance 

along a flow path in southern Maryland ............................................. 188 

120. Concentrations of dissolved silica and dissolved oxygen of 

the Aquia aquifer water plotted against distance along a flow 

path in southern Maryland .............................................................. 190 

121. Calcium plus magnesium concentrations plotted against 

bicarbonate concentrations for analyses of water taken 

from the Castle Hayne aquifer in North Carolina .................................. 191 

122. Measured and calculated values of stable carbon isotope 

composition plotted against distance along a flow path 

for water taken from the Aquia aquifer in southern Maryland ................ 192 

123. Rift zones and calderas of Koolau and Waianae Volcanoes 

on the Island of Oahu, Hawaii ......................................................... 196 

124. Geologic structure of an idealized Hawaiian volcano dome .................... 197 

125. Occurrence of ground water in the Oahu regional aquifer 

system, Hawaii .......... ~··································································198 

126. Ten identified aquifers underlying the Island of Oahu, Hawaii ................ 199 

127. Finite-element mesh for the southeast basal water body, 

Oahu, Hawaii. ............................................................................... 200 

128. Simulated potentiometric surface for the southeast basal water 

body, Oahu, Hawaii, prior to development ......................................... 201 

129. Generalized section of Honolulu-Pearl Harbor basal water body, 

Oahu, Hawaii ................................................................................ 202 

130. Finite-element mesh for cross sectional simulation of the 

Honolulu-Pearl Harbor basal water body, Oahu, Hawaii ........................ 202 

131. Simulated contours of seawater percentage for steady-state 

and transient conditions, the Honolulu-Pearl Harbor basal 

water body, Oahu, Hawaii ............................................................... 203 
Page 

132. Study area of the Southeastern Coastal Plain regional 

aquifer system .............................................................................. 207 

133. Location and outcrop areas of major hydrogeologic units 

of the Southeastern Coastal Plain regional aquifer system ..................... 208 

134. Schematic classification of rock-stratigraphic and regional 

hydrogeologic units of the Southeastern Coastal Plain 

regional aquifer system ................................................................... 209 

135. Generalized hydrogeologic section in east-central Georgia ..................... 211 

136. Geology and configuration of the surface of the lowest 

aquifer (A4) and approximate location of updip limit of water · 

containing concentrations of 10,000 milligrams per liter of 

dissolved solids, Southeastern Coastal Plain regional aquifer system ....... 213 

137. Location of major rivers that have significant impact on the 

regional ground-water flow system and potentiometric surface 

of the lowest aquifer (A4), Southeastern Coastal Plain regional 

aquifer system .............................................................................. 214 

138. Relation between hydrogeologic framework and simulated flow 

direction along a hypothetical dip section through Georgia ..................... 215 

139. Areas modeled by regional and subregional models, Southeastern Coastal Plain regional aquifer system ...................................... 216 

140. Schematic section A-A' and B-8', showing simulated aquifers, confining 

units, and boundary conditions, Southeastern Coastal Plain regional 

aquifer system ............................................................................................. 217 

141-160. Maps showings: 

141. Relation between surface drainage system and scale of aquifers 

which discharge into the surface drainage system, Southeastern 

Coastal Plain regional aquifer system ................................................. 218 

142. Simulated hydrologic components, Southeastern Coastal Plain 

regional aquifer system ................................................................... 219 

143. Generalized geologic section along a flow path from Alabama 

to Mississippi showing approximate location of geochemical zones, 

A, B, C, and D, in the southeastern Coastal Plain ............................... 220 

144. Study area of the Upper Colorado River Basin regional 

aquifer system .............................................................................. 224 

145. Principal tectonic features in the Upper Colorado River Basin ................ 225 

146. Areal extent of Paleozoic rocks in the Upper Colorado River Basin ......... 227 

147. Areal extent of Mesozoic rocks in the Upper Colorado River Basin ......... 229 

148. Location of flow models of the Mesozoic aquifer, Upper 

Colorado River Basin regional aquifer system ...................................... 231 

149. Areal extent of Cenozoic rocks in the Upper Colorado River Basin .......... 232 

150. Study area of the Caribbean regional aquifer system ............................ 235 

151. General geology of the Island of Puerto Rico and 

ground-water provinces .................................................................. 236 

152. Generalized subsurface geology of the North Coast 

Ground-Water Province of Puerto Rico .............................................. 237 

153. Generalized subsurface geology of the Island of St. Croix, 

U.S. Virgin Islands, and a typical cross section of the 

Kingshill aquifer ............................................................................ 240 

154. Study area of the Michigan Basin regional aquifer system ..................... 243 

155. Study area of the Southern California Alluvial Basins regional 

aquifer systems ............................................................................. 246 

156. Site-specific investigations of the Floridan aquifer system, 

phase II study ............................................................................... 250 

XIII 
XIV 

157. Estimated predevelopment potentiometric surface of the Upper 

Floridan aquifer in the area of Hilton Head Island and vicinity; 

Page 

A-A' is the proposed line of section for simulation ... ~ ...•........•.....•...•.... 252 

158. May 1980 potentiometric surface of the Upper Floridan 

aquifer in the area of Hilton Head Island; A-A' is the 

proposed line of section for simulation ...•..••....•.....•..•.........•.•...•.•..••.. 253 

159. Study area of the High Plains regional aquifer system, 

phase II study .....•...•....•.............••........•..•••..••••...•...•......••.•....•••••.. 257 

160. Study area of the Snake River Plain regional aquifer system, 

phase II study •.....................•....•............•....•.•...•...••.....................• 260 

TABLES 

Page 

1. Estimated irrigated acreage and volume of ground water pumped for 

i'rrigation in areas of the High Plains during the 1980 growing season •........•.••......•....•.....•............. 38 

2. Relation among previously mapped aquifers to geology and regional 

confining units in the Gulf Coastal Plain regional aquifer system study area .................................. 155 

3. Ground-water pumpage, in million gallons per day, 1980, Gulf Coastal 

Plain regional aquifer system •.•......•.......•.....•........•............•.•....•........••...••..••....••...••..•....••.... 157 

4. Simulated and observed heads in the southeast basal water body, 

Oahu, Hawaii, in feet above sea level .........•......................................•.......•.•..••..........••......... 200 

5 . Zonation of chemical reactions of water along a flow path from 

Alabama to Mississippi in the Southeastern Coastal Plain regional 

aquifer system ..•...•......•..•........................•............................•..............•.....•.............•..•...... 221 
ABBREVIATIONS AND CONVERSION FACTORS 

For the use of readers who prefer to use metric units, 

conversion factors for terms used in this report are listed below. 

Multiply By To obtain 

inch (in.) 

foot (ft) 

mile (mi) 

acre 

acre 

square foot (ft2 ) 

square mile (mi2 ) 

acre foot (acre-ft) 

cubic foot (ft3 ) 

gallon (gal) 

gallon (gal) 

cubic mile (mi3 ) 

foot per day (ft/d) 

inch per year (in./yr) 

square foot per day (ft2 /d) 

cubic foot per second (ft3/s) 

gallon per minute (gal/min) 

gallon per day (gal/d) 

billion gallons per day (Bgal/d) 

million gallons per day(Mgal/d) 

Length 

25.4 

0.3048 

1.609 

Area 

4,047 

0.4047 

0.09294 

2.59 

Volume 

1,233 

0.02832 

3.785 

0.003785 

4.168 

Flow 

0.3048 

25.4 

0.0929 

0.02832 

0.06308 

0.003785 

43.81 

0.04381 

U.S. Geological Survey Data Base 

millimeter (mm) 

meter (m) 

kilometer ( km) 

square meter (m2) 

hectare 

square meter (m2 ) 

square kilometer (km2 ) 

cubic meter (m3 ) 

cubic meter (m3 ) 

liter (L) 

cubic meter (m3 ) 

cubic kilometer (km3) 

meter per day (m/ d) 

millimeter per year (mm/yr) 

square meter per day (m2 I d) 

cubic meter per second (m3 /s) 

liter per second (L/s) 

cubic meter per day (m3 /d} 

cubic meter per second (m3 /s} 

cubic meter per second (m3 /s) 

Two U.S. Geological Survey's data bases frequently mentioned in the report are: 

GWSI: Ground-Water Sites Inventory 

WATSTORE: Water Data Storage and Retrieval System 

XV 

REGIONAL AQUIFER-SYSTEM ANALYSis-SUMMARY OF PROJECTS, 1978-84 

REGIONAL AQUIFER-SYSTEM ANALYSIS 

PROGRAM OF THE U.S. GEOLOGICAL SURVEYSUMMARY OF PROJECTS, 1978-84 

Edited By 

Ren ]en Sun, Reston, Virginia 

ABSTRACT 

The Regional Aquifer-System Analysis Program of 

the U.S. Geological Survey was initiated in 1978 as a 

result of specifications of the appropriations bill of the 

95th Congress, prompted by the 1977 drought. The purpose of this program is to define the regional hydrology 

and geology and to establish a framework of 

background information of geology, hydrology, and 

geochemistry of the Nation's important aquifer 

systems. This information is critically needed to 

develop an understanding of ground-water flow 

systems, and to support better gr':lund-water resources 

management. 

As of 1984, investigations of seven regional aquifer 

systems were completed, nine regional aquifer systems 

were still being studied, and three new studies were 

started. This report summarizes the status of each investigation of the regional aquifer systems under the 

program from 1978 through 1984. The nature of the 

summaries differs somewhat from study to study. For 

those studies which either have been completed or are 

near completion, summaries of results are presented. 

For projects that are not near completion or have just 

been started, discussions may be brief and focus on problem issues or hydrogeologic conditions. 

All reports resulting from the study as of 1984 are 

listed at the end of each summary. A list of project 

chiefs and their offices is also included in the report 

for those who are interested in obtaining additional 

information. 

INTRODUCTION 

Water is essential for plant, animal, and 

human life. The source of the world's freshwater 

supply is precipitation, which is unevenly 

distributed in both time and space. Part of the 

precipitation falling on the Earth's surface is 

evaporated or transpired by plants to the atmosphere, while part flows directly into rivers, 

streams, and lakes, and eventually discharges to 

the sea or returns to the atmosphere by evaporation. The remainder of the precipitation infiltrates past the root zone and gradually moves 

downward to the zone of saturation. Water in the 

zone of saturation is termed "ground water." 

In much of the western United States, where 

precipitation ranges from sparse to moderate, 

ground water forms a vital part of the water supply. Even in the humid East, where precipitation 

normally is plentiful, ground water is used to 

meet water needs during droughts, or as a supplement to surface water. In 1980, about. 90 

billion gallons of ground water were pumped daily 

in the United States. About 5 percent of this pumpage was used for rural water supply, 13 percent 

for public supply, 67 percent for irrigation, and 

15 percent for industrial use. Ground water contributed about 20 percent of the national water 

supply-450 billion gallons per day (Bgal/d) in 

1980. About 34 percent of the water used for 

public supply and 79 percent for rural domestic 

and livestock use in 1980 were supplied by ground 

water (Solley and others, 1983). 

Increases in ground-water use are expected 

to occur during the next decade. These increases 

will be associated with irrigation, urban expansion, and energy production, including such activities as power generation and refining of oil 

shales. In addition, the Nation will look increasingly to ground water as available sites for construction of new surface reservoirs become more 

1 
2 

limited, and as ground-water becomes more 

widely recognized as a major component to the 

Nation's water supply during droughts. These 

projected increases in the use of ground water will 

have widespread impacts on the Nation's aquifer 

systems. 

The withdrawal of water through wells initially results in removal of ground water from 

aquifer storage with an associated lowering of 

water levels. As water levels decline, new 

hydraulic gradients are established in the groundwater system which may either reduce natural 

ground-water discharge to streams, or induce 

ground-water recharge. When pumpage is greater 

than the amount of water that can be obtained 

by increases in recharge or reductions in natural 

discharge, sustained withdrawal from aquifer 

storage and continued lowering of water levels occur. In turn, this increases pumping lifts and, in 

water-table aquifers, causes progressive reduction 

of the saturated thickness of the aquifer. The 

result is an increase in pumping costs, a decrease 

in well yields, and eventually a depletion of the 

ground-water resource. In areas where aquifers 

are covered with thick, compressible, fine-grained 

sediments of low permeability, such as clay and 

silt, land subsidence may occur due to the sustained withdrawal of water from aquifer storage 

thus causing compaction of the overlying thick 

fine-grained sediments by the overburden 

pressure. 

In irrigated areas, where return flow from 

irrigation water recharges the aquifer, constituents such as salts leached from soil or applied 

pesticides, herbicides, and fertilizers may move 

into the aquifer system, thus degrading the 

ground water quality. Water-quality problems 

may also develop in industrial or urban areas, 

especially as a result of waste disposal. Irrigation 

return flow resulted from surface-water irrigation 

may cause ground-water levels to rise, creating 

water-logging problems. 

For several decades, ground-water investigations both within and outside the Geological 

Survey were conducted largely on a local scale 

within county or State boundaries. In evaluating 

the effects of development on ground-water 

resources on the basis of such local investigations, 

questions have often arisen regarding the extent 

of the development effects beyond a study area, 

and the correct way to represent conditions along 

the boundaries of a study area. Moreover, 

hydrologists beginning a local ground-water investigation often find little or no background information on the regional geology, hydrology, or 

water chemistry, and thus have to begin their 

studies from a base of very little knowledge. 

These facts underscore the need for broad regional 

evaluations of the Nation's ground-water 

resources. 

In 1973, the U.S. National Water Commission 

recognized that the depletion of ground-water 

storage had reached serious proportions in certain 

places, and that critically needed information on 

aquifer systems was not readily available to 

water-management officials. The Commission 

recommended to the President and to the Congress of the United States that the U.S. Geological 

Survey conduct continuing intensive investigations of significant aquifer systems giving priority 

to those with falling water levels and 

deteriorating water quality (U.S. National Water 

Commission, 1973, p. 245). In a report dated June 

21, 1977, to the Congress of the United States, 

the Comptroller General of the United States 

stated that, "Although much ground-water data 

have been collected by Federal and State agencies and others, we were told during our study 

that substantially more geological and 

hydrological data-primarily of a more specific 

and detailed nature-will be needed to provide for 

the orderly development, proper use, and conservation of ground-water resources. According to 

Federal and State officials, the lack of such 

specific and detailed data is a major constraint 

to improving ground-water management" (U.S. 

Comptroller General, 1977, p. 30). 

In 1977 the Committee on Appropriations of 

the U.S. House of Representatives, in a report of 

the appropriations for the Department of the Interior and related agencies for fiscal year 1978, 

stated that "The Committee is providing funds 

to initiate a program to identify the water 

resources of the major aquifer systems witp.in the 

United States. This program will establish the 

aquifer boundaries, the quantity ~nd the quality 

of the water within the aquifer, and the recharge 

characteristics of the· aquifer. Although this initiative comes too late to help the present drought 

(1977), the action taken will develop an inventory 

of the major ground-water systems of the United 

States so that in the event of another drought we 

may be able to draw upon the ground-water reservoir system without doing irreparable damage to 

the system. The Committee ·expects the Survey 

to press this program vigorously" (U.S. House of 

Representatives, 1977, p. 36-37). 

As a result of the specifications of the appropriations bill, and in response to Federal and 

State needs for information to support better 
ground-water management, the Geological 

Survey instituted the Regional Aquifer-System 

Analysis (RASA) Program in 1978. On the basis 

of a series of reports presenting the summary appraisals of the Nation's ground-water resources 

by the Geological Survey (fig. 1), and economic 

and hydrologic considerations, 28 regional aquifer 

systems were identified for study under the RASA 

Program (fig. 2). 

This report reviews the reasons for initiating the Regional Aquifer-System Analysis Program and discusses the purpose, approach, and 

status of the program. Findings and accomplishments of each project are discussed. 

Reports produced by each project are also listed. 

As of 1984, 19 RASA projects had been 

started. The geographic locations and status of 

these studies are shown in figure 3. Studies of the 

following seven regional aquifer systems have 

been completed as of 1984: (1) Central Valley, 

California; (2) Floridan; (3) High Plains; (4) Northem Great Plains; (5) N orthem Midwest; (6) Snake 

...... __ f/J., 

~<:=# M occ 

HAWAII D 

River Plain; and (7) Southwest Alluvial basins. 

In some projects, where major technical problems 

or data deficiencies were identified which could 

not be addressed adequately within the context 

of the initial investigation (phase I study), 

followup studies (termed RASA phase II study) 

have been undertaken. For example, during the 

study in the Central Valley, Calif., it was found 

that ground-water quality is being degraded by 

irrigation return flow recharging the aquifer; 

similarly, during the High Plains study, it was 

found that more accurate information on pumpage and on recharge from irrigation return flow 

was necessary for a full understanding of the 

ground-water system and its use for irrigation. 

RASA phase II studies were initiated for both the 

Central Valley and the High Plains to address 

these issues. Except for the Northern Great 

Plains regional aquifer system study, the other 

six completed studies have followup projects. In 

addition to the followup studies, there are eight 

on-going studies within the continental United 

u 

CARIBBEAN 

[::7.:~ 

- EXPLANATION 

BOUNDARY OF WATER-RESOURCES REGIONS-- Letter Indicates chapter 

designation In U.S. Geological Survey Professional Paper 813 series 

Rgure 1.-Location of reports of "Summary Appraisals of the Nation's Ground-Water Resources" by the U.S. Geological Survey. 

3 
4 

0 

Caribbean Islands 

EXPLANATION 

REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM·· Numbering system 

for identification purposes only, not intended to imply priorityQ· "' I( • . 

1, Northern Great Plains 

2, High Plains 

3, Central Valley, California 

4, Northern Midwest 

5, Southwest alluvial basins 

6, Floridan aquifer 

7, Northern Atlantic Coastal Plain 

8, Southeastern Coastal Plain 

9, Snake River Plain 

10, Central Midwest 

11, Gulf Coastal Plain 

12, Great Basin 

13, Northeast glacial valleys 

14, Upper Colorado River Basin 

15, Oahu Island, Hawaii 

16, Caribbean Islands 

17, Columbia Plateau 

18, South-Central Texas 

19, Southern California alluvial basins 

20, Michigan Basin 

21, San Juan Basin 

22, Ohio-Indiana glacial and carbonates 

23, Pecos River Basin 

24, Illinois Basin 

25, Appalachian Valleys and Piedmont 

26, Northern Rockies Intermontane basins 

27, Puget·Willamette Trough 

28, Alluvial basins, Oregon, California, and Nevada 

Figure 2.- Location of regional aquifer systems identified for study under the Regional Aquifer-System Analysis Program of 

the U.S. Geological Survey. 
-

~ 

0 

Caribbean Islands 

EXPLANATION 

STATUS OF THE REGIONAL AQUIFER-SYSTEMS ANALYSIS PROGRAM in 1984 

[Actual or planned duration shown by span of years] 

STUDIES COMPLETED 

PHASE I STUDIES COMPLETED 

PHASE II STUDIES UNDERWAY, FY 1984 

STUDIES UNDERWAY, FY 1984 

1, Northern Great Plains; FY 1978-82 

2, High Plains; FY 1978-82; Phase II study 

~ STUDIES INITIATED, FY 1984 

.. STUDIES PLANNED, FY 1985 

3, Central Valley, California; FY 1978-82; Phase 11 study 

4, Northern Midwest; FY 1979-84 

5, Southwest alluvial basins; FY 1979-84 

6, Floridan aquifer; FY 1979-82; Phase II study 

7, Northern Atlantic Coastal Plain; FY 1980-85 

8, Southeastern Coastal Plain; FY 1980-86 

9, Snake River Plain; FY 1980-84; Phase II study 

10, Central Midwest; FY 1981-86 

11, Gulf Coastal Plain; FY 1981-88 

12, Great Basin; FY 1981-85 

13, Northeast glacial valleys; FY 1982-86 

14, Upper Colorado River Basin; FY 1982-86 

15, Oahu Island, Hawaii; FY 1982:86 

16, Caribbean Islands; FY 1984-87 

17, Columbia Plateau; FY 1983-86 

19, Southern California alluvial basins; FY 1984-87 

20, Michigan Basin; FY 1984-87 

21, San Juan Basin; to be iniated in FY 1985 

5 

Figure 3.- Location of areas being investigated during 1978-84 under the Regional Aquifer-System Analysis Program of the 

U.S. Geological Survey. 
6 

States and one in Oahu Island, Hawaii. Three 

new regional aquifer system studies were initiated during fiscal year 1984, as follows: (1) 

Caribbean, (2) southern California alluvialbasins, and (3) Michigan Basin. 

A regional aquifer system as defined in the 

RASA Program may be of two general types: (1) 

it may be comprised of an extensive set of aquifers 

and confining units which locally may be discontinuous, but which act hydrologically as a single 

aquifer system on a regional scale-examples include, aquifer systems underlying the Great 

Plains, High Plains, Gulf Coastal Plain, and 

Atlantic Coastal Plain; or (2) it may represent a 

set of virtually independent aquifers which share 

so many common characteristics that investigation of a few of these aquifers can establish common principles and hydrogeologic factors controlling the occurrence, movement, and quality 

of ground water throughout the aquifer systems. 

Examples of the second type include the alluvial 

basins of Arizona, and New Mexico, and the 

glacial aquifers of the northeastern United States 

(Bennett, 1979). 

The objective of each RASA study is to define the regional hydrology and geology and to 

establish a framework of background 

information-geologic, hydrologic, and 

geochemical-that can be used for regional assessment of ground-water ·resources and in support of 

more detailed local studies. Each RASA project 

is designed to fit the particul~ needs of the study 

area; however, every project utilizes simulation 

(computer modeling) to help understand and 

analyze ground-water flow patterns and to provide the ability to evaluate effects of development 

on ground-water resources. Available information 

on quality of water throughout the aquifer system 

is ·also assembled and analyzed in all studies. 

Although the studies rely primarily on existing 

data, some new data are collected in each investigation, and some exploratory drilling has · 

been carried out. 

The delineation and continuity of aquifers 

and confining units are dependent on the scale 

of the problem under study. For example, the 

schematic section in figure 4 shows three major 

aquifers, A1, A2, and A3, separated by two confining units, C1 and C2, viewed on a regional 

scale. On a more local scale, however, aquifers A2 

and A3 might be subdivided further, treating the 

discontinuous lenses of low permeability material 

within those aquifers as confining units. Similarly, the .Permeable sand lenses within confining 

units C1 and C2 could be viewed as aquifers if 

their size were significant on a local scale. 

Regional studies normally combined local 

aquifers into a relatively small number of 

regional aquifers. However, many of the studies 

under this program also have considered the 

ground-water system at subregional and even 

local scales, through the establishment of subprojects, to address specific areas of interest. Normally, these subprojects utilize greater resolution 

in the delineation of aquifers and confining units 

than do the regional studies. 

Delineation and correlaion of aquifers and 

confining units in the regional studies is based 

on the hydraulic characteristics of the rocks 

rather than on their geologic age. Thus, an 

aquifer delineated in a RASA study may contain 

several different geologic formations or timestratigraphic units. 

Simulation, using computer-based numerical 

models of ground-water flow, is used in all studies 

to provide quantitative understanding of the 

aquifer systems. However, the regional simulation models developed in the regional studies may 

not always be appropriate for evaluation of effects · 

of development on ground-water resources at a 

local level. The regional simulations are intended 

primarily for regional assessments, to improve 

understanding of regional flow patterns, and to 

provide boundary conditions for subregional or 

local simulation studies. For example, during the 

northern Atlantic Coastal Plain regional aquifersystem study, four sub-regional flow models were 

constructed for the Coastal Plain aquifers underlying the States of New Jersey, Delaware and 

Maryland, Virginia, and North Carolina. A 

regional-flow model was also constructed 

representing the entire Coastal Plain aquifer 

system from Long Island, N.Y., through North 

Carolina. The regional-flow model supplies the 

boundary conditions for each of the subregional 

flow models, and provides an overall view of the 

flow system and its evaluation; the subregional 

flow models provide the resolution needed for 

more detailed analysis of the effects of development on the aquifer system. 

The results of RASA investigations are released through publications of the Survey as 

Hydrologic Investigations Atlases (HA), OpenFi~e Reports (OFR), Water-Resources Investigations Reports (WRffi), Water-Supply Papers 

(WSP), and Professional Papers (PP), or are 

published in outside scientific journals. Upon 

completion of each ~..;\SA project, Professional 
NOT TO SCALE EXPLANATION 

HIGH PERMEABILITY AOUIFER··A1, A2, and 

A3 are explained in text 

LOW PERMEABILITY CONFINING ZONE·· 

C1, and C2 are explained in text 

VERY LOW PERMEABILITY BEDROCK 

~ GROUND-WATER FLOW 

CONFINING ZONE IS MISSING AS DELINEATED 

ON A REGIONAL SCALE 

Figure 4.-Schematic section showing aquifers and confining units. 

Papers are published that summarize and synthesize the results of the project. The Professional 

Paper associated with each project is divided into chapters designated by letters, with the letter 

A reserved for a general chapter summarizing 

and integrating the major project findings. For example, the Professional Paper describing the 

Floridan aquifer system is designated Professional Paper 1403. "Summary of the Hydrology 

of the Floridan Aquifer System in Florida and in 

parts of Georgia, South Carolina, and Alabama" 

is Professional Paper 1403-A; "Hydrogeologic 

Framework of the Floridan Aquifer System in 

Florida and in parts of Georgia, South Carolina, 

and Alabama" is Professional Paper 1403-B; and 

so on. All of the Professional Papers derived from 

RASA studies will be designated by a Professional 

Paper number between 1400 and 1428. 

During the RASA studies, technical problems for which there are no readily available 

solutions are often encountered; for example, 

analyzing hydrologic data from wells that are 

open to many aquifers, or simulating the movement of ground water of different densities in an 

extensive three-dimensional system. To address 

such problems, RASA project personnel have 

devoted considerable effort to develop new techniques. For example, a multiaquifer-well simulation technique was developed during the Northern Midwest RASA study (Bennett and others, 

1982). An improved method of simulating 

variable-density ground-water flow also has been 

7 
8 

developed by Weiss (1982) and Kuiper (1983). The 

RASA Program also supports research by 

specialists within the Geological Survey in areas 

of geohydrology and geochemistry. Numerous 

reports have been prepared by researchers under 

this support, and have contributed not only to the 

RASA Program, but also to the overall understanding of ground-water hydrology, geology and 

geochemistry. However, only reports prepared by 

hydrologists assigned to RASA projects are listed 

in this report. 

Summaries of each RASA project are presented in the following four groups: (1) completed 

phase I projects, (2) active phase I projects, (3) 

newly initiated phase I projects, and (4) active 

phase II projects (followup studies). A list of 

reports released, as of 1984, by each project is also 

included at the end of each summary. The nature 

of the summaries differs somewhat from project 

to project. For those projects which either have 

been completed or are near completion, summaries of the results are presented. For projects 

that are not near completion or have just been 

started, discussion may be brief. 

It should be noted that aquifer names presented in this summary are provisional; these 

names may change when more suitable names 

are selected during investigations. 

For those who are interested in obtaining 

additional information, a list of project chiefs and 

their offices is included in the Appendix. 

REFERENCES CITED 

Bennett, G. D., 1979, Regional ground water systems analysis: 

U.S. Army Corps of Engineers, Water Resources Support Center, Fort Belvoir, Virginia, Water Spectrum, 

v. 11, no. 4, p. 36-42. 

Bennett, G. D., Kontis, A. L., and Larson, S. P., 1982, 

Representation of multiaquifer well effects in threedimensional ground-water flow simulation: Ground 

Water, v. 20, no. 3, p. 334-341. 

Kuiper, L. K., 1983, A numerical procedure for the solution 

of the steady state variable density ground-water flow 

equation: American Geophysical Union, Water 

Resources Research v. 19, no. 1, p. 234-240. 

Solley, W. B., Chase, E. B., and Mann, W. B., IV, 1983, 

Estimated use of water in the United States in 1980: 

U.S. Geological Survey Circular 1001, 56 p. 

U.S. Comptroller General, 1977, Ground water: An overview: 

Report to the Congress of the United States by the Comptroller General of the United States, June 21, 1977, 

46 p. 

U.S. House of Representatives, 1977, Report of Co:JD,mittee on· 

Appropriations for the Department of the Interior and 

related agencies for fiscal year 1978: 95th Congress, 

First Session, House Report no. 95-392. 

U.S. National Water Commission, 1973, Water policies for the 

future-Final report to the President and to the Congress of the United States: Washington, D.C., U.&. 

Government Printing Office, 579 p. 

Weiss, Emanuel, 1982, A model for the simulation of flow of 

variable density ground water in three dimensions 

under steady-state conditions: U.S. Geological Survey 

Open-file Report 82-352, 66 p. 
REGIONAL AQUIFER-SYSTEM ANALYSis-SUMMARY OF PROJECTS, 1978-1984 

COMPLETED PHASE I REGIONAL AQUIFER-SYSTEM 

ANALYSIS PROJECTS 

CENTRAL VALLEY REGIONAL AQUIFER-SYSTEM STUDY, CALIFORNIA 

By Gilbert L. Bertoldi, Sacramento, California, 

and Ren )en Sun, Reston, Virginia 

INTRODUCTION 

The Central Valley of California occupies 

about 12 percent of the total land area of the State 

of California. It is a large alluvium-filled structural basin occupying approximately 20,000 mi2 

of the flatland lying between the Coastal Ranges 

and Valleys to the west and Sierra Nevada Range 

to the east (fig. 5). The aquifer system of the Central Valley is composed of a heterogeneous mixture of continental alluvial materials derived 

from the surrounding mountains. Thickness of 

the sediments averages about 2,900 feet in the 

San Joaquin Valley and 1,500 feet in the 

Sacramento Valley. 

The climate of the Central Valley is arid to 

semiarid, with average annual precipitation 

ranging from 14 to 20 inches in the Sacramento 

Valley, and 5 to 14 inches in the San Joaquin 

Valley. Under predevelopment conditions, there 

was a water deficiency (potential evapotranspiration exceeding precipitation) of between 0 to 40 

in./yr in the Central Valley (fig. 6). 

In order to support an agricultural economy, 

large quantities of water are needed for irrigation. 

It is estimated that, including delivery losses, an 

average of 36 inches of water per acre is used annually. During 1961-77, approximately 22 million 

acre-ft of water was used in an average year. Of 

this 22 million acre-ft of water, about 50 percent · 

of the water was supplied by surface water and 

the remaining 50 percent was ground water. 

In addition to the agricultural use of ground 

water, nearly every city in the San Joaquin 

Valley uses ground water as the principal source 

for municipal and industrial supplies. 

The natural distribution of water in California is very erratic (fig.6). The Central Valley 

has an average annual water deficiency, under 

natural conditions, as great as 40 inches; whereas 

parts of the bordering Sierra Nevada and Coastal 

Ranges have an average annual surplus of water. 

However, because of flat, low land with fertile 

soil, agricultural development and human population tend to be concentrated in the valleys that 

are deficient in precipitation. Fortunately, ground 

water is available everywhere in the Central 

Valley, even where little rain normally falls or 

little surface water exists. 

Since the last half of the 1800's, ground 

water in the Central Valley has been developed 

for irrigation. Early records indicate that 

estimated pumpage was about 250,000 acre-ft in 

the San Joaquin Valley in 1912 (Harding and 

Robertson, 1912) and about 112,000 acre-ft in the 

Sacramento Valley in 1913 (Bryan, 1923). The annual pumpage in the Central Valley has increased from about 362,000 acre-ft in 1912-13to 

about 15 million acre-ft in the drought year, 1977; 

however, the average pumpage in the mid-1970's 

was about 12 million acre-ft. 

Ground water withdrawn from aquifers by 

pumping may or may not be replenished. In some 

parts of the Central Valley, the ground water 

withdrawn can be replenished annmrlly during 

the nonirrigation season by recharge from 

precipitation and streams; in other areas, 

replenishment of aquifers occurs only in years of 

9 
10 

abundant precipitation. In parts of the Central 

Valley, pumping has caused continuous waterlevel declines; in parts of the San Joaquin Valley 

and Tulare Basin, water levels have declined 

nearly 400 feet, depleting the stored ground 

water. 

Page (1984) has shown that throughout the 

Central Valley, about 50 percent ofthe thickness 

of continental sediments is composed of finegrained sediments (clay or silt). As water levels 

decline in aquifers, water stored in the pores of 

the layers consisting of fine-grained materials 

40" 

39" 

38" 

37" 

38" 

0 

35" 0 

124" 

50 

(") 

0 

~ 1> 

\ 

SCALE 1:4,000,000 

50 100 

100 150 KILOMETERS 

121" 

CALIFORNIA 

150MILES 

EXPLANATION 

STUDY AREA 

120" 

' 

NEVADA 

"" ' ' 

"" ' ' 

Mono Lake "" cQ, ' "" 

118" 

' ' 

"" 

AREA WHERE LAND SUBSIDENCE EXCEEDED 1 FOOT 

CAUSED PRIMARILY BY GROUND-WATER PUMPAGE 

Figure 5.- Location of the Central Valley of California and the principal areas of land subsidence 

(from Williamson and Prudic, 1984). 

' ' 

"" ' 
starts to drain into the adjacent aquifers where 

heads have been reduced. 

As a result, the land surface may subside due 

to compaction of the overlying fine-grained 

sediments. Subsidence in the Central Valley 

began in the mid-1920's as ground water was 

developed for irrigation. By 1970, the maximum 

subsidence exceeded 29 feet at one point in the 

San Joaquin Valley. Over 5,000 mi2 of land surface in the Central Valley had subsided more 

than 1 foot by 1970. Figure 7 illustrates the areas 

of land subsidence observed during 1961-75 and 

the corresponding 1961 pumpage per unit area. 

The rate of subsidence in the most severe 

pumping areas in the San Joaquin Valley has 

been decreasing since delivery of surface water 

began in 1968 (fig. 8); however, it may recur if 

pumping reduces water levels below the previous 

maximum lows. For example during the 1976-77 

drought, water levels- declined a maximum of 

nearly 200 feet in 8 months; the subsidence, 

which had nearly ceased after 1972, was as much 

as 0.5 foot in 1977. 

Volume of water released from compacting 

sediments is much greater than that available 

from artesian storage. However, the storage of the 

compacted sediments cannot be restored to its 

original volume; therefore, water is available only 

during compaction as water levels are lowered to 

a given depth. As compaction ceases, water can 

be withdrawn from or returned to artesian 

storage only. Subsidence has also caused damage 

to structures such as aqueducts, roads, bridges, 

buildings, and well casings. In low areas, subsidence also increases the potential for flooding 

and seawater encroachment, which may become 

a problem in the Sacramento Valley where subsidence is only beginning. 

Except at a few localities, quality of ground 

water is good for nearly all purposes in the 

Sacramento Valley; dissolved solids range from 

200 to 1,200 milligrams per liter (mg/L). In the 

San Joaquin Valley, the shallow water body in 

the west is not extensively used because of high 

dissolved solids which range from 1,000 to 5,000 

mg/L. Chloride and sulfate concentrations 

average about 400 and 440 mg/L, respectively. 

. Prior to the importation of surface water, ground 

water for irrigation was pumped from a confined 

aquifer below the water-table aquifer. Originally, 

water levels in the confined aquifer were above 

those in the shallow aquifer. However, irrigation 

pumping caused a reversal of heads, and a 

downward hydraulic gradient developed from the 

shallow aquifer (with poor water quality) to the 

confined aquifer. This downward leakage could 

cause contamination of the lower confined aquifer 

by poor-quality water from the shallow aquifer. 

In addition, pesticide and fertilizer have been applied to the land and minerals in soil such as 

selenium and boron could be leached by irrigation water. All those human activities can contaminate ground-water in water-table and confined aquifers. Dibromochloropropane (DBCP), a 

suspected carcinogen and widely used 

nematocide, was found in ground water in every 

county in the San Joaquin Valley and Tulare 

Basin and has been found in public-water supplies 

of the city of Fresno. 

Because of these problems, water managers 

need accurate and consistent information on the 

behavior of the ground-water flow system in the 

Central Valley and on the potential impact of 

developments on the aquifer system. Previous 

analyses of ground-water flow were conducted 

within limited geographic areas or were limited 

to definition of only a part of the ground-water 

flow system. Ground-water problems in the Central Valley, however, are not strictly limited to 

local areas and in many cases affect the entire 

valley. For example, an increase in pumpage in 

the city of Stockton may have an effect as far 

away as Sacramento. 

In order to provide such needed information 

on a regional scale, the Geological Survey started 

a 4-year study of the regional ground-water flow 

system in the Central Valley in 1978 (Bertoldi, 

1979). The study compiled and analyzed geologic, 

hydrologic, and geochemical information and 

established a valley-wide ground-water data base 

that could be used to construct ground-water flow 

and land-subsidence simulation models. The 

study was completed in 1982. Twenty-two reports 

have been published; several more reports are in 

review and preparation. 

For the first 18 months of the study, data 

were gathered from 600 published reports and 

from files of 150 Federal, State, county, and local 

agencies. These data were coded, stored, and 

analyzed, using various computer programs for 

areal distribution, validity, and suitability. Data 

needed for model simulation generally are 

available from existing information. However, 

geologic information, for the part of the aquifer 

from 100 feet below land surface to the top of 

Tehama Formation of Pliocene age, about 2,500 

feet below land surface, was not available in much 

of the Sacramento Valley. Most wells in the 

Sacramento Valley are less than 200 feet deep 

and therefore provide no information on the 

11 
12 

40' 

35 

SCALE 1:7,500,000 

0 50 100 150 200 MILES 

120' 

OREGON 

I 

I 

115' 

IDAHO 

______ l-------,-------

NEVADA 

1 

I 

I 

I 

I 

I 

I 

I 

UTAH 

~-----

ARIZONA 

0 50 100 150 200 KILOMETERS 

~ 

~ 

EXPLANATION 

WATER SURPLUS AREA 

LINE OF EQUAL ANNUAL WATER 

SURPLUS -- Interval 20 inches 

CENTRAL VALLEY GEOMORPHIC AND 

GROUND-WATER PROVINCE 

ANNUAL WATER DEFICIENCY AREAS--

Precipitation less than evapotranspiration 

CJ 

-

-

0 - 20 inches 

20 - 40 inches 

Greater than 40 Inches 

Figure 6.-Water-surplus and water-deficient areas in California (modified from Thomas and Phoenix, 1976). 
0 50 100MILES 0 50 100 MILES 

0 50 100 KILOMETERS 0 50 100 KILOMETERS 

' 

~'·"" ~UMOO~ 

o'1"~~ ,1t~ 0 ' ~(~()~ ~(/.~() o~, ~<'o ~ ~', 

""" ' ~""" ' 

<()Mono 

38' 

VMono Lake Lake 

~ "'10 

38' ~ 36' ~ ~ ("\ -s ("\ 

~ (!>OJ ~ -;. (!>OJ 

-;. 

35' 35' 

EXPLANATION 

-6-

MAPA 

LINE OF EQUAL LAND SUBSIDENCE, 

1961 -75 -- Interval in feet, is variable --4-

MAPB 

LINE OF EQUAL PUMPAGE PER UNIT 

AREA, 1961 --Interval in feet, is variable 

• STUDYAREA 

Figure 7. -Areas of A, land subsidence observed during 1961-75 and, B, the corresponding 1961 pumpage per unit 

area (modified from Wi lliamson and Prudic , 1984). 

aqutfer below that depth. To remedy this data 

gap, seven deep exploratory wells were drilled 

during the study for the purpose of obtaining: (1) 

geologic logs, (2) core samples, (3) geophysical 

logs, (4) sonic logs, (5) water samples, and (6) 

water-level measurements. 

From examination of the available data, it 

was found that water-quality information was inadequate for the San Joaquin· Valley and nonexistent for an area of 400 mi2 in the Sacramento 

Valley. A one-time sampling was done to fill the 

gap in the water-quality data base. 

Data for water levels, precipitation, soil types, 

pumpage, land use, and streamflow were adequate for initial modeling. A finite-difference 

ground-water flow model incorporating subsidence was developed from the data compiled. 

SIGNIFICANT RESULTS 

Many significant findings that emerged from 

the Central Valley regional aquifer study may 

have application to the general knowledge of 

ground-water hydrology. For example, knowledge 

of the extent of changes in aquifer characteristics 

caused by permanent deformation of sediments 

during subsidence may lead to new concepts in 

ground-water hydrology. Only a few of the 

findings are listed below: 

• Discovery of a compressible clay in the 

Sacramento Valley that is similar to the Corcoran 

13 
14 

Clay Member of the Tulare Formation, a major 

confining unit in the San Joaquin Valley. This 

clay bed occurs in an area where little ground 

water is being used. Hence, there is considerable 

potential for land subsidence should ground water 

be developed in that area because the clay has a 

very high compression index and is over 50 feet 

thick. This discovery is very important to water 

managers when plans to develop ground-water 

resources in that area are considered. 

18~------~--------~--------~--------~--------~--------~~ 

~ I 

I 

0 TIMES OF LEVELING ,.LS 

"' " 16 ESTIMATES OF SUBSIDENCE ,; / 48 6 I 

Based on extensiometer data ·and level- , 

ing along selected lines 

- ESTIMATED PUMPAGE (CUMULATIVE) 

1972 and 1973 were estimated from 

14 Diamond and Williamson (1983), while 42 

1974-77 were obtained from Ireland, 

Poland and Riley (1982) 

tu -CONNECTION BETWEEN POINTS OF SUBSIDENCE 

w w Dashed where approximated u. 

w 

u. w 12 36 a: a: (.) (.) <( < u. u. 0 0 

(/) (/) 

z z 0 0 

:::J 10 30 :::J 

.... .... .s :E :i g. ~ a ~ 

u.i "') ci ~ w (.) r: 1- z ~ w .s c 8 !1 24 U5 ! c m i w :J .'$? ~ 0.. (/) ~ .t- :!: u. ~ (j :J 

0 ...... i 0.. 

w 8 f u. 

::.:! ~ ;:: 0 

:J 6 If 18 w .... ~ ::.:! 

~ cr :J 

.... Qj s g 

cr 

" 

4 12 

2 6 

0 1920 

YEAR 

Figure 8.-Volume of land subsidence in major pumping areas in San Joaquin Valley and volume of 

pumped water in the west part of the San Joaquin Valley (from Williamson and Prudic, 1984). 
•Natural geochemical controls and mechanisms were defined for the Sacramento Valley thus 

establishing baseline information on water quality (Hull, 1984). Future water-quality changes in 

the Sacramento Valley can be evaluated by comparison to the baseline data. 

• Areas where ground water has high concentrations of boron were mapped. This information 

is important for future planning of boron-sensitive 

crops. 

•Estimates of ground-water storage, 

hydraulic conductivity, porosity, and potential 

land subsidence in the Sacramento Valley were 

made on the basis of information resulting from 

more than 10,000 wells augmented by the seven 

deep exploratory test wells. This information was 

not available before this study. 

• Prior to development, the aquifers were 

recharged by precipitation and stream seepage in 

upland and discharged to streams, lakes or 

topographic depressions and by evapotranspiration in the central part of the Valley. The total 

regional circulation through the ground-water 

flow system was estimated to be approximately 

200,000 acre-ft/yr. 

•Since development, about 64 million acre-ft 

of ground water has been removed from aquifer 

storage; 40 million acre-ft of water was removed 

due to lowering of water table, 17 million acre-ft 

was removed due to compaction of fine-grained 

sediments accompanied by land subsidence, and 

7 million acre-ft was removed from the elastic 

storage of the confined aquifer. 

•Simulation indicates that during 1961-77, 

ground-water discharge was about 11.8 million 

acre-ft/yr, of which 94 percent was for irrigation 

(11.1 million acre-ft/yr), 3 percent was for 

municipal water supplies (350,000 acre-ft/yr), and 

3 percent discharged to streams, lakes and topographic depressions (350,000 acre-ft/yr). The 

simulation also indicates that the ground-water 

recharge was about 11 million acre-ft/yr, of which 

81 percent was irrigation return flow (9.0 million 

acre-ft/yr), 14 percent was percolated from 

precipitation (1.5 milion acre-ft/yr), and 5 percent 

was induced from streams and lakes (0.5 million 

acre-ft/yr). The difference between annual groundwater discharge and recharge was 0.8 million 

acre-ft/yr. About 50 percent of this difference was 

derived from the aquifer as the result of watertable declines (0.4 million acre-ft/yr) and another 

50 percent was derived from elastic storage and 

compaction of sediments. 

•The average horizontal hydraulic conductivity of the valley sediments is about 6ft/d. The 

horizontal hydraulic conductivity of sediments in 

the Sacramento Valley is about twice that for 

sediments in the San Joaquin Valley. 

•The average thickness of the continental 

deposits in the Central Valley is about 2,400 feet, 

and increases from north to south with the maximum thickness of about 9,000 feet near 

Bakersfield. 

•Ground-water quality has the potential of 

being degraded by poor quality irrigation return 

flow. However, due to time and budget constraints, this problem was not fully explored 

during the initial phase of this study. A second 

unexpected problem was the potential migration 

of an extensive body of saline water lying beneath 

the freshwater aquifer system. Both problems are 

to be studied during phase II (a followup) study. 

PUBLISHED REPORTS 

1. Bertoldi, G. L., 1979, A plan to study the 

aquifer system of the Central Valley of 

California: U.S. Geological Survey OpenFile Report 79-1480, 48 p. Reprinted in 

Pacific Ground Water Digest, July-August 

1980. 

2. ----1981, Central Valley aquifer project 

in California-an overview: Proceedings of 

American Society of Civil Engineers Water 

Forum 1981, Specialty Conference, San 

Francisco, CA. 

3. Burkham, D. E., and Guay, Richard, 1981, 

Development of curves that represent trends 

in selected hydraulic variables for the 

Sacramento River at Butte City, California: 

U.S. Geological Survey Open-File Report 

81-693, 22 p. 

4. Diamond, Jonathan, and Williamson, A. K., 

1983, A summary of ground-water pumpage 

in the Central Valley, California, 1961-77: 

U.S. Geological Survey Water-Resources Investigations Report 83-4037, 75 p. 

5. French, J. T., Page, R. W., and Bertoldi, G. 

L., 1982, Data for ground-water test hole 

near Zamora, Central Valley aquifer project, 

California: U.S. Geological Survey OpenFile Report 82-510, 72 p. 

6. ----1983a, Data for ground-water test 

hole near Butte City, Central Valley aquifer 

project, California: U.S. Geological Survey 

Open-File Report 83-697, 65 p. 

7. -----1983b, Data for ground-water test 

hole near Nicolaus, Central Valley aquifer 

project, California: U.S. Geological Survey 

Open-File Report 83-273, 70 p. 

15 
16 

8. Fogelman, R. P., 1982, Compilation of selected 

ground-water quality data from the San Joaquin Valley, California: U.S. Geological 

Survey Open-File Report 82-335, 275 p. 

9. ---1983a, Dissolved solids concentrations of ground water in the Sacramento 

Valley, California: U.S. Geological Survey 

Hydrologic Investigations Atlas 645, 

1 sheet. 

10. ----1983b, Ground-water quality in the 

Sacramento Valley, California-Water types 

and potential nitrate and boron problem 

areas: U.S. Geological Survey Hydrologic mvestigations Atlas 651, 1 sheet. 

11. Hull, L. C., 1984, Geochemistry of ground 

water in the Sacramento Valley, California: 

U.S. Geological Survey Professional Paper 

1401-B. 36 p. 

12. Nady, Paul, and Larragueta, Lori, 1983a, 

Development of irrigation in the Central 

Valley of California: U.S. Geological Survey 

Hydrologic Investigations Atlas 649, 

2 sheets. 

13. -----1983b, Estimated average annual 

streamflow into the Central Valley of 

California: U.S. Geological Survey 

Hydrologic Investigations Atlas 657, 

2 sheets. 

14. Page, R. W., 1981a, Data on depths to the Upper Mya zone of the San Joaquin formation 

in the Kettleman City area, San Joaquin 

Valley, California: U.S. Geological Survey 

Open-File Report 81-699, 12 p. 

15. 1981b, Texture maps, a guide to deep 

ground-water basins in the Central Valley, 

California: Proceedings of the American 

Society Civil Engineers Water Forum 1981, 

Specialty Conference, San Francisco, CA. 

16.----1983, Geology of the Tulare Formation and other continental deposits, Kettleman City area, San Joaquin Valley, 

California-with a section on ground-water 

management considerations and use of texture maps: U.S. Geological Survey WaterResources Investigations Report 83-4000, 

24 p. 

17. ----1984, Geology of the fresh groundwater basin in the Central Valley, California, with a section on texture of sediments: 

U.S. Geological Survey Professional Paper 

1401-C [in press]. 

18. Page, R. W., and Bertoldi, G. L., 1983, A 

Pleistocene diatomaceous clay and a 

pumiceous ash: California Geology, January 

1983, p. 14-20. 

19. Prudic, D. E., and Williamson, A. K., 1984, 

Evaluation of a technique for simulating a 

compacting aquifer system in the Central 

Valley of California, USA: Proceedings of 

the 3rd International Symposium of Land 

Subsidence, Venice, Italy, March 1984 [in 

press]. 

20. Swain, L.A., 1981, Ground-water models of 

the Central Valley, California: Proceedings 

of the American Society Civil Engineers 

Water Forum 1981, Specialty Conference, 

San Francisco, CA. 

21. Williamson, A. K., 1981, Evapotranspiration 

of applied water, Central Valley, California 

1957-78: U.S. Geological Survey WaterResources Investigations Report 81-45, 56 p. 

22. Williamson, A. K., and Prudic, D. E. 1984, 

Results of simulation of flow and compaction 

in the regional aquifer system of the Central Valley of California, USA: Proceedings 

of the 3rd International Symposium of Land 

Subsidence, Venice, Italy, March 1984 [in 

press]. 

23. Williamson, A. K., Prudic, D. E., and Swain, 

L. A., 1985, Ground-water flow in the Central Valley California: U.S. Geological 

Survey Professional Paper 1401-D, [in 

press], and Open File Report 85-345, 300 p. 

REFERENCES CITED 

Bertoldi, G. L., 1979, A plan to study the aquifer system of 

the Central Valley of California: U.S. Geological Survey 

Open-file Report 79-1480, 48 p. 

Bryan, Kirk, 1923, Geology and ground-water resources of the 

Sacramento Valley, California: U.S. Geological Survey 

Water-Supply Paper 495, 185 p. 

Harding, S. T., and Robertson, R. D., 1912, Irrigation resources 

of central California: California Conservation Committee Report, p. 172-240. 

Hull, L. C., 1984, Geochemistry of ground water in the 

Sacramento Valley, California: U.S. Geological Survey 

Professional Paper 1401-B, 36 p. 

Page, R. W., 1984, Geology of fresh ground-water basin in the 

Central Valley, California, with a section on texture 

of the sediments: U.S. Geological Survey Professional 

Paper 1401-C [in press] 

Thomas, H. E., and Phoenix, D. A., 1976, Summary appraisal 

of the Nation's ground-water resources, California 

region: U.S. Geological Survey Professional Paper 

813-E, 51 p. 

Williamson, A. K., and Prudic, D. E., 1984, Results of simulation of flow and compaction in the regional aquifer 

system of the Central Valley of California, USA: Proceedings of the 3rd International Synposium of Land 

Subsidence, Venice, Italy, March 1984 [in press]. 

Williamson, A. K., Prudic, D. E., and Swain, L. A., 1985, 

Ground-water flow in the Central Valley California: 

U.S. geological Survey Professional Paper 1401-D, [in 

press], and Open File Report 85-345, 300 p. 
COMPLETED PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

FLORIDAN REGI9NAL AQUIFER-SYSTEM STUDY 

By Peter W. Bush and Richard H. Johnston, Atlanta, Georgia 

INTRODUCTION 

The Floridan aquifer system is one of the 

major sources of ground-water supplies in the 

United States. This highly productive aquifer 

system underlies all of Florida, southeastern 

Georgia, and small parts of adjoining Alabama 

and South Carolina, for a total area of about 

100,000 mi2 • A total of about 3 Bgal/d is 

withdrawn from the aquifer system, and, in many 

areas, the Floridan aquifer system is the sole 

source of freshwater. 

During 1978-83, the Survey conducted a 

regional assessment of the Floridan aquifer 

system that involved the review and synthesis of 

many previous studies, the acquisition of new 

data in selected areas, and the extensive use of 

computer-based models to simulate the groundwater flow. 

The Floridan aquifer system includes several 

Tertiary carbonate formations that are 

hydraulically connected in various degrees to 

form a regional aquifer system. However, locally 

there are significant differences in hydrologic properties, water chemistry, and flow; and developm~nt has proceeded unevenly with large 

withdrawals concentrated in a few areas. 

The approach to studying the Floridan 

aquifer system was to focus on (and document) 

loc~l differences while tying together, in a 

regional analysis, the individual segments of the 

aquifer system. 

A s~ries of regional geohydrologic, 

geochemical, and potentiometric surface maps 

was prepared. Eleven of these maps were published during the course of the study (Johnston 

and others, 1980, 1981; Miller, 1982 a-e; Sprinkle, 

1982 a-d). 

A data-collection program was undertaken to 

fill the data gaps. This work involved a program 

of exploratory drilling, aquifer tests, seismic 

surveys (onshore and offshore), selective 

geochemical sampling, and mass measurement of 

water levels and artesian pressures. A notable example of these activities was the collection of 

hydrologic and geochemical data from an abandoned oil exploratory well 55 miles offshore from 

the east Florida coast (Johnston and others, 1982). 

Computer silpulation involved the design and 

calibration of a "coarse-mesh" regional flow 

model and four subregional flow models. The goal 

of the regional flow model was to understand the 

major features of the flow system. The design of 

the regional flow model and the results of 

simulated predevelopment conditions are described by Bush (1982). The four subregional flow 

models focus on the areas of greatest groundwater development. Preliminary reports describing model design and the results of simulated 

predevelopment conditions were prepared for 

three subregions: southeast Georgia, including 

small adjacent parts of South Carolina and 

Florida (Krause, 1982); west-central Florida 

(Ryder, 1982); and east-central Florida (Tibbals, 

1981). Final reports of the Floridan regional 

aquifer system study comprise nine chapters in 

the U.S. Geological Survey Professional Paper 

1403, designated 1403-A through I. As of 

September 1984, three of the nine chapters have 

been released and are in press, five are in colleague review, and one is still in preparation. 

Throughout the study, the central theme was 

to translate the hydrogeologic fram~work into, 

frrst, a conceptual model, and then into a flow 

model that could be used to quantify aquifer properties and components of the flow system. Figure 

9 illustrates the results of this process for a typical 

area in central Florida. 

HYDROGEOLOGIC FRAMEWORK 

The aquifer system is a sequence of 

hydraulically connected carbonate rocks (principally limestone with some dolomite) that range 

17 
18 

in age from late Paleocene to early Miocene. The 

rocks vary in thickness from a featheredge in outcrop areas to more than 3,500 feet in coastal 

areas. The aquifer system generally consists of an 

upper and lower aquifer separated by a lesspermeable confining unit of highly variable properties. In parts of northern Florida and 

southwestern Georgia, there is little permeability 

contrast within the aquifer system. Thus, in these 

areas, the Floridan acts effectively as one continuous aquifer. The upper and lower aquifers are 

defmed on the basis of permeability contrast and 

their boundaries locally do not coincide with 

either time-stratigraphic or rock-stratigraphic 

wiits. 

Prior to this study, several stratigraphic units 

and two aquifer names were generally associated 

with the carbonate rocks now defined as the 

Floridan aquifer system. In Florida, the term 

"Floridan aquifer" was widely applied although 

its thickness and extent differed among investigators. In Georgia and South Carolina, the 

term "principal artesian aquifer" was applied to 

these carbonate rocks. A major contribution of 

this study was the regional definition of the 

Floridan aquifer system, its component aquifers 

and confining units, and their relation to 

associated stratigraphic units. The regional. 

definition resulted from subsurface hydrogeologic 

studies that used geophysical and lithologic logs, 

faunal data, and hydrologic data. Based on 

analyses of these data, a series of structure contours, isopach maps and sections were prepared 

for the component aquifers and the seven principal stratigraphic units that comprise all or parts 

of the Floridan aquifer system. 

Throughout the coastal areas, the effective 

lower boundary of the aquifer system is a transition from circulating freshwater to underlying 

saline water. The configuration of this transition 

zone agrees, in general, with the principles outlined by Hubbert (1940) for the case of an interface between moving freshwater and static saline 

water. That is, the interface is deepest beneath 

inland areas; it rises seaward and ultimately intersects the top of the aquifer system. In inland 

and updip areas, however, the base of the 

Floridan aquifer system is considered as the contact surface below which rocks have very low 

permeability. This surface generally coincides 

with a facies change to fine-grained clastic rocks 

or bedded anhydrite. 

Low-permeability clastic rocks overlie the 

Floridan aquifer system in much of its area of occurrence. The lithology, thickness, and integrity 

of these low-permeability rocks have a controlling 

effect on the flow in the Floridan aquifer system 

locally. A surficial sand aquifer overlies these lowpermeability rocks in many places. 

CONCEPTUAL MODEL 

A conceptual model of the Floridan aquifer 

system, as shown in figure 9, incorporates the major features of the flow system. The Upper and 

Lower Floridan aquifers are separated by a lesspermeable middle confining unit. The lowpermeability clastic rocks separating the Upper 

Floridan from the surficial aquifer are considered 

an upper confining unit. A freshwater- saltwater 

interface forms the base and lateral boundary of 

the system in coastal areas. Fine-grained clastic 

rocks or bedded anhydrite act as a lower confining 

unit and thus are treated as the base of the 

aquifer system in inland and updip areas. 

DIGITAL FLOW MODEL 

The Trescott-Larson quasi-three-dimensional 

finite-difference model (Trescott, 1975; Trescott 

and Larson, 1976) was used to simulate the 

regional and subregional flow systems. The basic 

structure of the model is shown in figure 9, 

although the subregional models depart from the 

regional model in some degree to accommodate 

local conditions or features. The Upper and Lower 

Floridan aquifers were simulated as active layers; . 

the surficial aquifer was treated as a source-sink 

bed; and the lower confining unit and the 

freshwater-saltwater interface were assumed to 

be no-flow boundaries. However, the Upper 

Floridan, in a strip of area adjacent to its updip 

limit in Georgia, was bounded below by a 

constant-head boundary which simulated a small 

amount of upward leakage from the sand aquifer 

system that underlies the Upper Floridan. The 

other part of the updip limit of the Floridan 

aquifer system was considered as a no-flow boundary, because it is generally a pinchout of the carbonate rocks. 

The Flow System 

The major features of the flow system are illustrated and summarized by a potentiometric 

surface map of the Upper Floridan aquifer constructed from more than 2,700 water-level or 

pressure-head measurements made in May 1980 

(fig. 10). Superimposed on figure 10 is a delineation of areas where the aquifer system is unconfined or loosely confined (the definition of loosely 
FEET A 400 

GEOLOGIC UNITS IN 

HYDROGEOLOGIC FRAMEWORK 

Pleistocene/ Pleistocene sands and A' 

Holocene sands Hawthorn Formation 

Sealevel ~~i~~=~~~~=~~~~~!f -400 

-800 •• 

-1200 

-1600 

-2000 

-2400 

-2800 

-3200 

-2600 

30' 

25' 

VERTICAL SCALE GREATLY 

EXAGGERATED 

0 

85' 

~ GEORGIA 

ALABAMA ) 

100 

Trace of 

hydrogeologic 

section 

200 MILES 

0 100 200 KILOMETERS 

0 10 20 30 MILES 

0 10 20 30 KILOMETERS 

80' 

HYDROGEOLOGIC 

UNITS IN 

CONCEPTUAL 

MODEL 

. Surficial aquifer 

Upper a ·. 

confining '-'flit 

Upper 

Floridan 

aquifer 

"'CCn =le fin ng J.Jnit 

EQUIVALENT UNITS IN 

DIGITAL GROUND-WATER 

FLOW MODEL 

Recharge/discharge at surface 

translated into source-bed leakage 

to/from Upper Floridan aquifer and 

discharge to springs or streams via 

head-dependent source-sinks 

. · . ' . ~ 

., 

~ .. shJde b~c 

.. ~ ~c nfl I gull ~ Lower Floridan ~ 

aquifer 

Freshwater-saltwater "1-----------. interface 

' ' ~-

' COCttth~t > 

a fA.Iluifer 

-:.~ I lqo ~~~f1ing 

... j I 

·-~~/ ~fliT ~~:_- -=-~-~ 

Missing 

confining 

unit 

Impermeable boundary 

(Lower confining unit 

or freshwatersaltwater interface) 

NOTES: Source bed node blocks 

are all constant head; heads 

vary a really but are constant 

with time 

Vertical leakage across 

confining beds is controlled 

by head gradients between 

aquifers and confining-unit 

leakage coefficients 

Aquifer properties vary 

greatly, but are constant 

with time 

Figure 9.-Translation of hydrogeologic framework into conceptual and digital ground-water flow model, 

Floridan aquifer system. 

confined hereafter used in this report is that the 

confining unit 'is less than 100 feet thick, 

breached, or both). 

The configuration of the potentiometric surface indicates that, in South Carolina and 

Georgia, the direction of flow is generally east and 

southeast from the topographically high outcrop 

areas toward the Atlantic coast and Florida. In 

Alabama and western Florida, flow is generally 

south from the outcrop_ areas toward the Gulf 

coast. In peninsular Florida, the general flow 

direction is from the central inland areas toward 

the Gulf and Atlantic coasts. Thus, regional 

recharge occurs primarily in northern outcrop 

and peninsular inland areas, and regional 

discharge occurs in coastal areas. 

The degree of confinement of the Upper 

Floridan is the characteristic that most strongly 

19 
20 

influences. the distribution of natural recharge, 

flow, and discharge. Most of the natural recharge, 

flow, and discharge occurs in the unconfined and 

loosely confined areas. Potentiometric contours 

that are distorted as they cross streams indicate 

the interaction between streams and the Upper 

Floridan aquifer, and typify unconfined and 

loosely confined conditions. Smoother, less 

distorted contours are associated with tightly confined (the definition of tightly confined hereafter 

used in this report is that the confining unit is 

more than 100 feet thick) parts of the system that 

have less interaction with the surface drainage 

features. 

Before development, the flow system was in 

a state of dynamic equilibrium in which natural 

recharge to the Floridan aquifer system was 

balanced by natural discharge. The predevelopment recharge area is estimated to be about 

67,000 mi2; the discharge area is estimated to be 

about 55,000 mi2 , of which about 27,000 mi2 was 

land discharge area. The total predevelopment 

recharge, and therefore discharge, simulated by 

the regional flow model was about 21,500 ft3/s. 

This is equivalent to 4.4 in./yr of water distributed 

evenly over the entire estimated recharge area. 

The dominant feature of the Floridan aquifer 

system, both before and after development, is 

discharge through springs. The locations of the 

springs are shown in figure 10. Nearly all of the 

springs occur in unconfined and loosely confined 

areas. In the early 1980's, the average total 

discharge from about 300 known Upper Floridan 

springs was about 13,000 ft3

/s. In addition to 

discharge. from known springs, point discharges 

to streams and lakes in unconfined and loosely 

confined areas is appreciable. About 7,000 ft3

/s 

discharge to streams and lakes, in addition to 

spring flow, was simulated by the regional flow 

model. Spring flow and point discharge to streams 

and lakes accounted for a very high percentage 

of the total aquifer discharge. Before groundwater development, simula.ted spring flow and 

point discharge to surface-water bodies was 88 

percent of the 21,500 ft3

/s simulated discharge, or 

about 19,000 ft3

/s. Diffuse upward leakage, which 

occurs primarily in the confined areas, accounted 

for the remaining fraction of the total simulated 

predevelopment discharge, about 12 percent or 

2,500 ft3/s. 

Most of the recharge necessary to sustain 

spring flow and aquifer discharge to streams and 

lakes occurs relatively close to the discharge 

points. Recharge to the Upper Floridan is highest 

in unconfined and loosely confined spring areas 

and averages 10 to 20 in./yr. The proximity of 

high recharge to high discharge implies a 

vigorous and well developed shallow flow system 

in the unconfmed and loosely confined parts of the 

Upper Floridan aquifer. 

The distribution of transmissivity is generally related to the degree of confinement. All of 

the areas of very high transmissivity (greater 

than 1,000,000 ft2/d) and much of the area of high 

transmissivity (250,000 to 1,000,000 ft2/d) occur 

where the aquifer is either unconfined or loosely 

confined. 

Areas of very high transmissivity are characterized by extensive development of secondary 

permeability (solution openings) in the carbonate 

rock. Solution openings ranging from slightly 

widened joints to caves and large sinkholes 

characterize the upper part of the aquifer system. 

The resulting permeability distribution is extremely complex and marked differences in 

transmissivity occur within short distances. 

In contrast to ground-water flow in unconfined and loosely confined areas, flow in parts of 

the aquifer that are deeply buried and tightly confined is very sluggish. These areas are in 

southeastern Georgia and northeastern Florida, 

south Florida, and western panhandle Florida. 

Springs and points of discharge to streams and 

lakes are practically nonexistent in these areas; 

natural discharge occurs almost exclusively by 

diffuse upward leakage through thick confining 

units. As would be expected in areas of sluggish 

flow, rates of recharge and discharge are considerably lower than the rates in unconfined and 

loosely confined areas. Recharge and diffuse upward leakage average less than 5 in./yr in tightly confmed areas. Transmissivity is also generally 

lower in deeply buried and tightly confined areas. 

Comparatively little is known about the 

Lower Floridan aquifer because in most areas 

wells obtain sufficient supplies from the Upper 

Floridan; thus, there is little reason to drill into 

the Lower Floridan. Aquifer-test data or well performance information are therefore minimal. 

Freshwater flow is considerably less in the Lower 

Floridan than in the Upper Floridan. The lack of 

field data precludes precise areal definition of 

transmissivity of the Lower Floridan aquifer. The 

Lower Floridan aquifer in south Florida includes 

a highly permeable cavernous unit known as the 

''Boulder Zone." This zone contains saline water 

and has been used for underground disposal of 

treated sewage through injection wells. 
30' 

25' 

MISSISSIPPI 

I ALABAMA 

I 

SCALE 1 :6,500,000 

0 50 100 MILES 

GULF 

OF 

MEXICO 

0 50 100 KILOMETERS 

-

EXPLANATION 

UNCONFINED OR LOOSELY CONFINED AREAS 

OF THE UPPER FLORIDAN AQUIFER--

Unconfined-upper confining unit Is absent or 

very thin. Loosely confined-upper confining 

unit Is generally less than 100 feet thick, 

breached, or both 

AREAS WHERE LONG-TERM WATER-LEVEL 

DECLINE IS GREATER THAN 10 FEET IN 

THE UPPER FLORIDAN AQUIFER 

-4o-- POTENTIOMETRIC CONTOUR-- Shows altitude 

of potentiometric surface of the Upper 

Floridan aquifer. Dashed where approximately 

located. Contour Interval, in feet, Is variable. Hachures Indicate depressions. 

Datum is sea level 

Q .. b _ ()A 

0 •. 0~ 

ATLANTIC 

OCEAN 

APPROXIMATE UPDIP LIMIT OF THE 

UPPER FLORIDAN AQUIFER 

SPRING OR GROUP OF SPRINGS IN THE 

UPPER FLORIDAN AQUIFER 

STUDY AREA 

Figure 10.-Potentiometric surface of the Upper Floridan aquifer, May 1980; occurrence of unconfined or loosely confined conditions; locations of springs discharging from the Upper Floridan aquifer; and areas of long-term water-level 

decline. 

21 
22 

To quantify and summarize the areal 

distribution of predevelopment flow, the 

estimated predevelopment discharge from the 

major ground-water areas of the Upper Floridan 

aquifer is shown in figure 11. Regionally, and in 

every area except south Florida, the 

predominance of spring discharge and aquifer 

discharge to surface-water bodies over diffuse upward leakage is apparent. The five areas that are 

predominantly unconfined or loosely confined 

(Dougherty Plain-Apalachicola, ThomasvilleTallahassee, Suwannee, west-central Florida, and 

east-central Florida), although comprising only 

about 50 percent of the occurrence of the Floridan 

aquifer system, contribute nearly 90 percent of 

the simulated total predevelopment discharge. 

The Suwannee area is the most active part of the 

aquifer system in terms of ground-water flow. 

More than one-fourth of the simulated total 

predevelopment discharge, close to 6,000 ft3/s, occurred there. 

In tightly confined panhandle Florida, diffuse upward leakage occurred over the major part 

of the area. But confinement is lacking in the 

eastern third of the panhandle and along the outcrop, allowing direct aquifer discharge to streams. 

Similarly, in the southeast Georgia-northeast 

Florida and southwest South Carolina area, about 

three-quarters of the simulated predevelopment 

discharge leaked to four major rivers crossing the 

areally small northern outcrop. Diffuse upward 

leakage occurred over a much larger area, but accounted for a minor part of the total discharge in 

the area. Only in south Florida, where the 

Floridan aquifer is tightly confined, was diffuse 

upward leakage the major part of predevelopment 

discharge. The simulated 100 ft3/s predevelopment discharge from south Florida represents less 

than 1 percent of the total regional discharge. 

Pumping Effects 

The general characteristics of the flow system 

described herein have not been altered appreciably by development. However, similarity of 

the 1980 flow system to the predevelopment flow 

system does not mean that ground-water development has not brought significant changes. In 

1980, about 3 Bgal/d of water were pumped from 

the aquifer system (almost all from the Upper 

Floridan) for all uses. This is equal to about 20 

percent of the estimated predevelopment recharge 

or discharge. This pumpage has resulted in longterm regional water-level declines of more than 

10 feet in three broad areas (fig. 10): (1) coastal 

Georgia, adjacent South Carolina and northeastern Florida; (2) west-central Florida; and (3) 

panhandle Florida. The effect of ground-water 

development on the potentiometric surface is particularly evident at Savannah and Brunswick, 

Ga., and at Fernandina Beach and Fort Walton 

Beach, Fla., where deep cones of depression have 

formed. Saltwater encroachment as a result of 

pumping has occurred in some coastal 

areas, but its extent has· been local. 

Pumpage has been and continues to be 

balanced primarily by the diversion of natural 

discharge from the aquifer system and by induced 

recharge rather than by depletion of aquifer 

stm;age. The transient response of the aquifer 

system to changes in pumping rates dissipates· 

fairly rapidly (days or weeks) in most areas. Thus, 

on the average (that is, excluding the effects of 

seasonal changes in stresses), the aquifer system 

is considered to be approximately at equilibrium 

(steady-state conditions) except during short 

periods following sustained increases in pumpage. 

As of 1980, about 4 70 Mgal!d, mostly for industrial use, were being withdrawn from the 

coastal strip of southeastern Georgia and northeastern Florida. As a result, what began as a 

trough-like depression of water levels in the 

1940's in coastal Georgia and northeastern 

Florida has spread inland to become the largest 

area of significant water-level declines in the 

Floridan aquifer system. 

The overall extent of this broad area of 

regional water-level decline reflects the potential 

for increasing recharge, and diverting natural 

discharge to wells. Figure 10 shows that in the 

area of southeast Georgia and northeast Florida 

the regional water-level decline is coincident with 

a tightly confined part of the aquifer. Thus, there 

is little potential for increasing recharge or reducing upward leakage near the pumping 

centers. Therefore, the area of pumping influence 

in northeast Florida and southeast Georgia has 

spread southwestward to the region of loosely confined or unconfined areas where natural recharge 

is greater. 

In west-central Florida, about 1 Bgal/d is 

pumped. The phosphate industry and irrigation 

account for the major part of the pumpage. As a 

result, a regional depression exists in the potentiometric surface southeast of Tampa. Although 

the pumping rate is greater in west-central 

Florida than in southeast .Georgia and northeast 

Florida, the area of influence and magnitude of 

water-level decline is smaller in west-central 
30 

25' 

I 

' 

MISSISSIPPI 

0 

I ALABAMA 

I \---... _ I '-.... 

I 

88 

PERCENT SPRING FLOW 

21,500 

---:;oo 

SCALE 1:6,500,000 

50 100 MILES 

0 50 100 KILOMETERS 

GULF 

OF 

MEXICO 

GEORGI~ 

(" fouTHEAST GEORGIA -

,-. ./ NORTHEAST FLORIDA · 

SOUTHWEST SOUTH CARO 

1220 

6 

o .. oo 

0 .. oA 

o . -

ATLANTIC 

OCEAN 

o' 

EXPLANATION 

5 

PERCENT SPRINGFLOW AND DISCHARGE 

TO SURFACE-WATER BODIES 

PERCENT DIFFUSE UPWARD LEAKAGE 

~ CUBIC FEET PER SECOND 

21,500 TOTAL DISCHARGE 

----:;co-- PERCENT OF TOTAL DISCHARGE-· 

Values associated with largest circle are regional totals; 

others are area totals 

APPROXIMATE UPDlP LIMIT OF THE 

UPPER FLORIDAN AQUIFER 

BOUNDARY OF MAJOR GROUND 

WATER AREAS 

Figure 11.-Estimated predevelopment discharge from major ground-water areas of the Upper Floridan aquifer. 

23 
24 

Florida. This is mainly because the potential for 

increasing recharge, and diverting natural 

discharge to wells, is greater in west-central 

Florida than in southeast Georgia and northeast 

Florida. Figure 10 shows that most of the area 

of net water-level decline in west-central Florida 

occurs in places where the aquifer system is under 

tightly confined conditions. However, the center 

of heaviest pumping in west-central Florida is in 

the northern part of area of the ~egional waterlevel declines. This center is close to a region of 

loosely confined or unconfined areas, thus enhancing the potential for inducing recharge. 

In the Fort Walton Beach area of panhandle 

Florida, pumping of about 15 Mgal/d has caused 

a regional depression in the potentiometric surface. This relatively low pumping rate has caused 

a regional depression because, in this area, 

transmissivity is much lower than that in either 

southeast Georgia and northeast Florida, or westcentral rlorida. In much of the area of water-level 

declines in panhandle Florida, transmissivity is 

less than 10,000 ft2/d. Confinement in the vicinity 

of Fort Walton Beach is at least as tight as in any 

other part of the aquifer system. The area of appreciable water-level declines appears to have 

spread eastward to a loosely confined area. 

However, the very low transmissivity limits the 

ability of the aquifer to transmit water that is 

available in the loosely confined area to wells. 

Because of continually increasing pumpage, the 

area of water-level declines in panhandle Florida · 

continues to enlarge. Because of the proximity of 

loosely confined conditions to the east, the 

panhandle area of water-level declines is expected 

to grow less rapidly in that direction than in other 

directions. 

Simulation of 1980 pumpage by the regional 

flow model indicates that development has caused 

the total recharge area to expand from about 

67,000 mi2 before development to about 76,000 

mi2 in 1980. Recharge to or discharge from the 

simulated aquifer system increased from a 

predevelopment total of about 21,500 ft3

/s to about 

24,100 ft3/s in 1980. The recharge area has increased by about the same percentage as the 

recharge rate due to development. Therefore, the 

1980 recharge rate per unit area was nearly the 

same as the predevelopment rate, about 4 to 5 

in./yr. 

If steady-state conditions are assumed, about 

60 percent of 1980 pumpage was supplied by increased recharge. About half of the remaining 40 

percent of the pumpage was obtained from reduction in spring flow and discharge to surface-water 

bodies, and the other half was obtained from 

reduction in upward leakage. Because the total 

flow rate of spring discharge and discharge to 

surface-water bodies is much greater than the 

total flow rate of diffuse upward leakage, groundwater development has reduced the total spring 

flow and discharge to surface-water bodies less 

than 5 percent, however, the reduction in total 

diffuse upward leakage is about 30 percent. 

To quantify and summarize the areal 

distribution of 1980 flow conditions, figure 12 

shows the discharge from the major ground-water 

areas of the Upper Floridan aquifer. Regionally, 

spring discharge and point discharge to surfacewater bodies were the predominant forms of 

discharge from the 1980 flow system, as they were 

from the predevelopment flow system; simulations suggest that about three-fourths of 1980 

discharge was spring flow or discharge to surfacewater bodies. The remaining fourth was the sum 

of the pumpage (17 percent) and the diffuse upward leakage (8 percent). Ground-water development has not appreciably affected the groundwater divides that separate the eight major 

ground-water areas. The percentage of total 

discharge that occurred in each area under 1980 

conditions was not significantly different from 

that simulated before development. 

Central Florida is the most heavily developed 

part of the aquifer system. Roughly half of the 

total1980 pumpage was withdrawn from the two 

central Florida areas-east-central and westcentral Florida. These two areas accounted for 

about 29 percent of the total 1980 discharge, an 

increase of about 3 percent over the predevelopment discharge (figs. 11 and 12). Figure 12 shows 

that in central Florida, about 60 percent of the 

aquifer discharge is spring flow or direct 

discharge to surface-water bodies; about 30 percent is pumpage, and about 10 percent is diffuse 

upward leakage. 

Pumpage in the area of southeast Georgia, 

northeast Florida, and southwest South Carolina 

accounted for about 25 percent of the total 1980 

pumpage; this area is the only one in which 

spring flow and direct discharge to surface-water 

bodies has been supplanted by pumpage (figs. 11 

and 12). 

Figure 12 shows that in each of the four contiguous areas west of the southeast Georgianortheast Florida-southwest South Carolina area, 

pumpage is a minor fraction of the ground-water 

discharge in the area. Even in the Dougherty 
MISSISSIPPI 

0 

0 

I ALABAMA 

I 

75 

PERCENT SPRING FLOW AND 

~SCHARGETOSURFAC~ 

WATER BODIES 

24,1 00 

100 

SCALE 1 :6,500,000 

50 100 MILES 

50 100 KILOMETERS 

GULF 

OF 

MEXICO 

-- GEORGI~ 

l;" fouTHEAST GEORGIA· 

./NORTHEAST FLORIDA· 

SOUTHWEST SOUTH CAROLINA 

~'~ 4 

ATLANTIC 

OCEAN 

o' 

EXPLANATION 

5 

PERCENT SPRINGFLOW AND DISCHARGE 

TO SURFACE-WATER BODIES 

PERCENT PUMPAGE 

PERCENT DIFFUSE UPWARD LEAKAGE 

~ CUBIC FEET PER SECOND 

24,100 TOTAL DISCHARGE 

100 --PERCENT OF TOTAL DISCHARGE--

Values associated with largest circle are regional totals; others are area totals 

APPROXIMATE UPDIP LIMIT OF THE 

UPPER FLORIDAN AQUIFER 

BOUNDARY OF MAJOR GROUND 

WATER AREAS 

Figure 12.-Estimated 1980 discharge from major ground-water areas of the Upper Floridan aquifer. 

25 
26 

Plain-Apalachicola area, where irrigation 

withdrawals have soared in recent years, pumpage represents only about 11 percent of the 

average ground-water discharge in the area (fig. 

12). Spring flow and discharge to surface-water 

bodies constitute about 87 percent of the 1980 

discharge in each of the four areas. 

In terms of flow, the south Florida area, under 

1980 conditions, is an insignificant part of the 

Floridan aquifer system, as it was during predevelopment time. Discharge from the area is 

only about 1 percent of the total discharge from 

the Floridan aquifer system. 

In summary, the major part of the 1980 flow 

system is largely unchanged from predevelopment conditions. Large-discharge springs are still 

the dominant feature of the aquifer system. 

Although pumping has caused recharge rates to 

increase locally, the greatest recharge still occurs 

in areas near springs. Even after development, 

ground-water flow remains sluggish in areas 

where the aquifer is deeply buried relative to flow 

in areas where the aquifer is close to land surface 

or loosely confined. 

GEOCHEMISTRY 

The water chemistry in the Upper Floridan 

is generally related to flow and proximity to the 

saltwater-freshwater interface. In the unconfined 

or loosely confined areas, where flow is vigorous, 

concentrations of dissolved solids are low. Where 

the system is more tightly confined and flow is 

more sluggish; concentrations of dissolved solids 

are high. In Florida, south of Lake Okeechobee 

and in parts of the St. Johns River valley, residual 

saltwater remains unflushed from the system and 

concentrations of dissolved solids are high. Concentrations of dissolved solids also are higher in 

coastal areas near the saltwater-freshwater 

interface. 

Several distinct hydrochemical facies 

characterize the water chemistry in the Upper 

Floridan. The principal chemical processes 

leading to the development of the hydrochemical 

facies are: 

• Dissolution of aquifer minerals toward 

equilibrium as ground water moves from 

recharge to discharge areas. 

• Mixing of fresh ground water with saltwater 

along the freshwater-saltwater transition zone in 

coastal areas; or with residual saltwater where 

the saltwater is unflushed by freshwater in areas 

comprised of low-permeability rocks. 

•Cation exchange between water and aquifer 

minerals. In the unconfined or loosely confined 

areas, dissolution of calcite is the principal pro-· 

cess and a calcium-bicarbonate hydrochemical 

facies occurs. In coastal areas or where the system 

is more tightly confined, mixing of freshwater 

with saltwater or unflushed residual saltwater 

produces a sodium-chloride facies. In western 

panhandle Florida, cation exchange has produced 

a unique occurrence of a sodium-bicarbonate 

facies in the Upper Floridan. 

POTENTIAL FOR DEVELOPMENT 

A considerable area of the Floridan aquifer 

system remains highly favorable for development 

of large ground-water supplies. This area is 

largely inland and is characterized by high 

transmissivity as well as minimal development 

as of 1980. Simulation suggests that new pumping centers in parts of southeast Georgia and 

north-central Florida can supply large 

withdrawals, while relatively shallow cones of 

depression will develop. The major constraint on 

future development is degradation of water quality rather than limitation of water quantity. The 

possibility of saltwater encroachment in coastal 

areas and upconing of deep saltwater in some inland areas are important factors to consider for 

future development. 

PUBLISHED REPORTS 

Abstracts 

1. Bush, P. W., 1982, Southeast Tertiary 

limestone aquifer flow system: American 

Society of Civil Engineers, Irrigation and 

Drainage Division, Proceedings of the N ationa! Specialty Conference on Environmentally Sound Water and Soil Management, p. 

237-239. 

2. Freeman-Lynde, R. P., Popenoe, Peter, and 

Meyer, F. W., 1982, Seismic stratigraphy of 

the western Straits of Florida: Geological 

Society of America, Abstracts with Programs, v. 14, nos. 1 and 2, p. 18. 

3. Johnston, R. H., 1979, Southeastern Tertiary 

limestone aquifer study: Geological Society 

of America, Abstracts with Programs, v.l1, 

no. 4, p. 184. 

4. ----1980, The saltwater-freshwater interface in the Tertiary limestone aquifer 

system, southeast Atlantic outer-continental 
shelf: Geological Society of America, 

Abstracts with Programs, v. 12, no. 7, p. 456. 

5. ----1983, Overview of the Floridan 

aquifer system: American Society of Civil 

Engineers, Annual Convention, October 

17-21, 1983. 

6. Miller, J. A., 1980, Relation of lowpermeability zones, geologic structure, and 

ground-water flow pattern, Tertiary 

limestone aquifer system, southeastern 

United States: Geological Society of 

America, Abstracts with Programs, v. 12, 

no. 7, p. 484. 

7. -----1983, Regional hydrogeologic 

framework of the Floridan aquifer: 

Geological Society of America, Southeastern 

Section, 32nd Annual Meeting, March 

16-18, 1983. 

8. Ryder, P. D., 1981, Digital model of 

predevelopment flow in the Floridan aquifer 

system in west-central Florida: Ground 

Water in Florida, Proceedings of the First 

Annual Symposium on Florida 

Hydrogeology, p. 133. 

9. Sprinkle, C. L., 1980, Mapping water quality 

of the Tertiary limestone aquifer system, 

southeastern United States: Geological 

Society of America, Abstracts with Programs, v. 12, no. 7, p. 527-528. 

10. -----1982, Geochemistry of water from 

two wells in the Tertiary limestone aquifer 

system, Georgia and Florida: Geological 

Society of America, Abstracts with Programs, v. 14, nos. 1 and 2, p. 85. 

11. ---1983, Modeling mass transfer in the 

Tertiary limestone aquifer system, 

southeastern United States: Geological 

Society of America, Abstracts with Programs, v. 15, no. 2, p. 97. 

Reports 

1. Bush, P. W., 1982, Predevelopment flow in the 

Tertiary limestone aquifer system, 

southeastern United States: a regional 

analysis from digital modeling: U.S. 

Geological Survey Water-Resources Investigations Report 82-905, 41 p. 

2. Johnston, R. H., 1978, Planning report for the 

southeastern limestone regional aquifer 

system analysis: U.S. Geological Survey 

Open-File Report 78-516, 26 p. 

3. -~--1983, The saltwater-freshwater interface in the Tertiary limestone aquifer, 

southeast Atlantic outer-continental shelf of 

the USA: Journal of Hydrology, v. 61, p. 

239-249. 

4. Johnston, R. H., Bush, P. W., Krause, R. E., 

Miller, J. A., and Sprinkle, C. L., 1982, Summary of hydrologic testing in Tertiary 

limestone aquifer, Tenneco offshore exploratory well-Atlantic OCS, lease-block 

427 (Jacksonville NH 17 -5): U.S. Geological 

Survey Water-Supply Paper 2180, 15 p. 

5. Johnston, R. H., Healy, H. G., and Hayes, L. 

R., 1981, Potentiometric surface of the Tertiary limestone aquifer system, 

southeastern United States, May 1980: U.S. 

Geological Survey Open-File Report 81-486, 

1 sheet. 

6. Johnston, R. H., Krause, R. E., Meyer, F. W., 

Ryder, P. D., Tibbals, C. H., and Hunn, J. 

D., 1980, Estimated potentiometric surface 

for the Tertiary limestone aquifer system, 

southeastern United States, prior to development: U.S. Geological Survey Open-File 

Report 80-406, 1 sheet. 

7. Krause, R. E., 1982, Digital model evaluation 

of the predevelopment flow system of the 

Tertiary limestone aquifer system, 

southeast Georgia, northeast Florida, and 

southern South Carolina: U.S. Geological 

Survey Water-Resources Investigations 

Report 82-173, 27 p. 

8. Matthews, S. E. and Krause, R. E., 1984, 

Hydrogeologic data from the U.S. Geological 

Survey test wells near Waycross, Ware 

County, Georgia: U.S. Geological Survey 

Water-Resources Investigations Report 

83-4204, 29 p. 

9. Meyer, F. W., 1984, Disposal of liquid wastes 

in cavernous dolostones beneath 

southeastern Florida: International Association of Hydrogeologists, Monograph Series 

[in press]. 

10. Miller, J. A., 1982a, Configuration of the base 

of the upper permeable zone of the Tertiary 

limestone aquifer system, southeastern 

United States: U.S. Geological Survey 

Water-Resources Investigations Report 

81-1177, 1 sheet. 

11. ----1982b, Geology and configuration of 

the base of the Tertiary limestone aquifer 

system, southeastern United States: U.S. 

Geological Survey Open-File Report 

81-1176, 1 sheet. 

12. ----1982c, Geology and configuration of 

the top of the Tertiary limestone aquifer 

27 
28 

system, southeastern United States: U.S. 

Geological Survey Open-File Report 

81-1178, 1 sheet. 

13. 1982d, Thickness of the Tertiary 

limestone aquifer system, southeastern 

United States: U.S. Geological Survey OpenFile Report 81-1124, 1 sheet. 

14. ---1982e, Thickness of the upper 

permeable zone of the Tertiary limestone 

aquifer system, southeastern United States: 

U.S. Geological Survey Water-Resources Investigations Report 81-1179, 1 sheet. 

15. ----1984, Hydrogeologic framework of 

the Floridan aquifer system in Florida and 

in parts of Georgia, South Carolina, and 

Alabama: U.S. Geological Survey Professional Paper 1403-B [in press]. 

16. Ryder, P. D., 1982, Digital model of 

predevelopment flow in the Tertiary 

limestone (Floridan) aquifer system in westcentral Florida: U.S. Geological Survey 

Water-Resources Investigations Report 

81-54, 61 p. 

17. ---1984, Hydrology of the Floridan 

aquifer system in west-central Florida: U.S. 

Geological Survey Professional Paper 

1403-F [in press]. 

18. Smith, C. A., Lidz, Lauralee., and Meyer, F. 

W., 1982, Data on selected deep wells in 

south Florida: U.S. Geological Survey OpenFile Report 82~348, 144 p. 

19. Sprinkle, C. L., 1982a, Chloride concentration 

in water from the ·upper permeable zone of 

the Tertiary limestone aquifer system, 

southeastern United States: U.S. Geological 

Survey Water-Resources Investigations 

Report 81-1103, 1 sheet. 

20. 1982b, Dissolved-solids concentration in water from the upper permeable zone 

of the Tertiary limestone aquifer system, 

southeastern United States: U.S. Geological 

Survey Water-Resources Investigations 

Report 82-94, 1 sheet. 

21. ----1982c, Sulfate concentration in 

water from the upper permeable zone of the 

Tertiary limestone aquifer system, 

southeastern United States: U.S. Geological 

Survey Water-Resources Investigations 

Report 81-1101, 1 sheet.· 

22. 1982d, Total hardness of water from 

the upper permeable zone of the Tertiary 

limestone aquifer system, southeastern 

United States: U.S. Geological Survey 

Water-Resources Investigations Report 

81-1102, 1 sheet. 

23. Tibbals, C. H., 1981, Computer simulation of 

the steady-state flow system of the Tertiary 

(Floridan) limestone aquifer system in eastcentral Florida: U.S. Geologi_cal Survey 

Water-Resources Investigations Report 

81-681, 31 p. 

24. Tibbals, C. H., and Grubb, H. F., 1982, Aquifer 

test results, Green Swamp area, Florida: 

U.S. Geological Survey Water-Resources Investigations Report 82-35, 29 p. 

REFERENCES CITED 

Bush, P. W., 1982, Predevelopment flow in the Tertiary 

limestone aquifer system, southeastern United States; 

a regional analysis from digital modeling: U.S. 

Geological Survey Water-Resources Investigations 

Report 82-905, 41 p. 

Hubbert, M. K., 1940, The theory of ground-water motion: 

Journal of Geology, v. 48, no. 8, p. 785-944. 

Johnston, R. H., Bush, P. W., Krause, R. E., Miller, J. A., and 

Sprinkle, C .. L., 1982, Summary of hydrologic testing 

in Tertiary limestone aquifer, Tenneco offshore exploratory well-Atlantic OCS, lease-block 427 (Jacksonville NH 17-5): U.S. Geological Survey Water-Supply 

Paper 2180, 15 p. 

Johnston, R. H., Healy, H. G., and Hayes, L. R., 1981, Potentiometric surface of the Tertiary limestone aquifer 

system, southeastern United States, May 1980: U.S. 

Geological Survey Open-File Report 81-486, 1 sheet. 

Johnston, R. H., Krause, R. E., Meyer, F. W., Ryder, P. D., 

Tibbals, C. H., and Hunn, J. D., 1980, Estimated potentiometric surface for the Tertiary limestone aquifer 

system, southeastern United States, prior to development: U.S. Geological Survey Open-File Report 80-406, 

1 sheet. 

Krause, R. E., 1982, Digital model evaluation of the 

predevelopment flow system of the Tertiary limestone 

aquifer system, southeast Georgia, northeast Florida, 

and southern South Carolina: U.S. Geological Survey 

Water-Resources Investigations Report 82-173, 27 p. 

Miller, J. A., 1982a, Configuration of the base of the upper 

permeable zone of the Tertiary limestone aquifer 

system, southeastern United States: U.S. Geological 

Survey Water-Resources Investigations Report 81-1177, 

1 sheet. 

---1982b, Geology and configuration of the base of the 

Tertiary limestone aquifer system, southeastern United 

States: U.S. Geological Survey Open-File Report 

81-1176, 1 sheet. 

---1982c, Geology and configuration of the top of the 

Tertiary limestone aquifer system, southeastern United 

States: U.S. Geological Survey Open-File Report 

81-1178, 1 sheet. 

---1982d, Thickness of the Tertiary limestone aquifer 

system, south-eastern United States: U.S. Geological 

Survey Open-File Report 81-1124, 1 sheet. 

---1982e, Thickness of the upper permeable zone of the 

Tertiary limestone aquifer system, southeastern United 

States: U.S. Geological Survey Water-Resources Investigations Report 81-1179, 1 sheet. 

Ryder, P. D., 1982, Digital model ofpredevelopment flow in 

the Tertiary limestone aquifer system in west-central 

Florida: U.S. Geological Survey Water-Resources Investigations Report 81-54, 61 p. 

Sprinkle, C. L., 1982a, Chloride concentration in water from 

the upper permeable zone of the Tertiary limestone 

aquifer system, southeastern United States: U.S. 

Geological Survey Water-Resources Investigations 

Report 81-1103, 1 sheet. 
---1982b, Dissolved-solids concentration in water from 

the upper permeable zone of the Tertiary limestone 

aquifer system, southeastern United States: U.S. 

Geological Survey Water-Resources Investigations 

Report 82-94, 1 sheet. 

---1982c, Sulfate concentration in water from the upper permeable zone of the Tertiary limestone aquifer 

system, southeastern United States: U.S. Geological 

Survey Water-Resources Investigations Report 81-1101, 

1 sheet. 

---1982d, Total hardness of water from the upper 

permeable zone of the Tertiary limestone aquifer 

system, southeastern United States: U.S. Geological 

Survey Water-Resources Investigations Report 81-1102, 

1 sheet. 

Tibbals, C. H., 1981, Computer simulation of the steady-state 

flow system of the Tertiary (Floridan) limestone aquifer 

system in east-central Florida: U.S. Geological Survey 

Water-Resources Investigations Report 81-681, 31 p. 

Trescott, P. C., 1975, Documentation of finite-difference model 

for simulation of three-dimensional ground-water flow: 

U.S. Geological Survey Open-File Report 75-438, 99 p. 

Trescott, P. C., and Larson, S. P., 1976, Supplement to OpenFile Report 75-438, Documentation of finite-difference 

model for simulation of three-dimensional ground-water 

flow: U.S. Geological Survey Open-File Report 76-591, 

21 p. 

29 
30 

COMPLETED PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

HIGH PLAINS REGIONAL AQUIFER-SYSTEM STUDY 

By John B. Weeks, Denver, Colorado 

INTRODUCTION 

The High Plains regional aquifer system 

underlies about 17 4,000 mi2 in parts of Colorado, 

Kansas, Nebraska, New Mexico, Oklahoma, 

South Dakota, Texas, and Wyoming. The aquifer 

system is the shallowest and most abundant 

source of water in one of the major agricultural 

areas in the United States. About 20 percent of 

the irrigated land in the United States is in the 

High Plains, and about 30 percent of the ground 

water used for irrigation in the United States is 

pumped from the High Plains aquifer system. In 

1980, about 170,000 wells pumped about 18 

million acre-ft of water to irrigate nearly 14 

million acres. 

The irrigated-agricultural economy of the 

High Plains is dependent on the aquifer system 

for continued growth and prosperity. However, 

declining water levels and decreasing water supplies threaten the future of irrigation using 

ground water in parts of the High Plains. 

National concern about the economic impact 

of declining water supplies in the High Plains was 

responsible for the initiation of a regional study 

of the High Plains aquifer system in 1978. The 

regional study was completed in 1982. 

GEOHYDROLOGY 

Previous hydrologic studies of the region have 

not kept pace with ground water development. 

Many water-resource studies of small areas such 

as individual counties or groups of counties have 

been made, but few studies of larger areas within 

the High Plains have been made. Previous investigations provide a wealth of information, but 

without continuity across political boundaries. In 

developing the geohydrologic framework of the 

High Plains aquifer system, hydrologists assembled, organized, and assimilated the 

hydrogeologic data available from many previous 

studies. 

Physical Setting 

The High Plains occupies the southern part 

of the Great Plains physiographic province, which 

lies east of the Rocky Mountains. The region extends from southern South Dakota to northwestern Texas. The High Plains is characterized 

by flat to gently rolling terrain, which is a remnant of a vast plain formed by sediments 

deposited by streams flowing eastward from the 

Rocky Mountains. 

Most of the High Plains has a middle-latitude 

dry continental climate with abundant sunshine, 

moderate precipitation, frequent winds, low 

humidity, and a high rate of evaporation. Mean 

annual precipitation increases eastward across 

the High Plains by about 1 inch every 25 miles 

from less than 16 inches near the western side 

of the study area to about 28 inches in eastern 

Nebraska and central Kansas. Typically, about 

75 percent of the precipitation falls as rain during the growing season. However, much of the 

rain falls during local thunderstorms; therefore, 

large variations in rainfall can occur from place 

to place and year to year. 

Persistent wind and high summer 

temperature cause high rates of evaporation. 

Mean annual evaporation from Class A pans 

ranges from about 60 inches in northern 

Nebraska and southern South Dakota to about 

105 inches in western Texas and southeastern 

New Mexico. Because of these conditions, most of 

the water that enters the soil is returned to the 

atmosphere by evapotranspiration, and little 

precipitation is available to recharge the ground-
water system, except in sand-dune areas where 

water can readily percolate to the water table. 

Aquifer System 

The High Plains aquifer system consists 

mainly of near-surface deposits of late Tertiary 

or Quaternary age (Gutentag and Weeks, 1980). 

The principal geologic units that comprise the 

High Plains aquifer system are shown in figure 

13. The Tertiary rocks include part of the Brule 

Formation of the White River Group, the 

Arik.aree Group, and the Ogallala Formation. The 

Quaternary deposits consist of alluvial, dunesand, and valley-fill deposits. Except for dune 

sand, the Quaternary deposits are combined and 

are shown in figure 13 only in areas where they 

do not overly Tertiary aquifer units. In northern 

Texas, some collapse structures, filled with 

Triassic, Jurassic, and Lower Cretaceous rocks 

that have secondary permeability, are considered 

part of the aquifer system; however, they are 

minor and are not shown in figure 13. 

The Ogallala Formation is the· principal 

geologic unit of the High Plains aquifer system 

and underlies about 134,000 mi2 (fig. 13). Maximum thickness of the Ogallala is about 700 feet. 

During deposition of the Ogallala, aggrading 

streams filled valleys eroded into pre-Ogallala 

rocks. Braided streams flowed eastward from the 

mountains, transporting rock debris, which was 

deposited as a heterogeneous sequence of clay, 

silt, sand, and gravel. 

Dune-sand deposits, consisting predominantly of very fine to medium grained wind blown 

sand, are part of the High Plains aquifer system. 

Ofthe 174,000 mi2 underlain by the High Plains 

aquifer system, about 19 percent is covered by 

dune sand. The most extensive area of dune sand 

is in west-central Nebraska, where the deposits 

cover an area of 20,000 mi2 with a maximum 

thickness of about 300 feet. Large areas also are 

covered by dune-sand deposits south of the Arkansas River in Kansas (fig. 13). Throughout the 

High Plains, the areas covered by dune sands are 

important recharge areas of the aquifer system. 

Bedrock that underlies the High Plains 

aquifer system ranges in age from Permian to 

Tertiary. The areal extent and age of the bedrock 

are shown in figure 14. Some bedrock units may 

yield water to wells; although, the bedrock units 

generally have low permeability. Bedrock of 

marine origin contains evaporites and saline 

water that affect the quality of water in the 

overlying aquifer. This is particularly true in 

areas underlain by Permian bedrock and areas 

south of the Canadian River underlain by Lower 

Cretaceous rocks. 

Flow System 

Climate and geology control the hydrology of 

the High Plains aquifer system. Precipitation, 

temperature, and soil characteristics limit the 

amount of recharge. Lithology, structure, and 

topography control ground-water movement and 

discharge. 

Recharge to the aquifer system, which is 

generally unconfined, is entirely from precipitation and seepage from streams. Because evapotranspiration greatly exceeds precipitation, little 

or no recharge occurs from precipitation except 

in areas covered by sandy soil which have high 

permeability, low field capacity, and rapid infiltration rates. 

Recharge on the High Plains is highly 

variable. Estimated recharge ranges from 0.024 

in./yr in parts of Texas to 6 in./yr in sand-dune 

areas in Kansas and Nebraska (Gutentag and 

others, 1984). The volume of recharge to the 

aquifer system has been estimated by model 

simulation (Luckey and others, 1985). The 

simulated average annual recharge to the aquifer 

system was about 5.7 million acre-ft or 0.6 in./yr 

over the entire area of the aquifer system. About 

80 percent of the recharge occurs north of 39 · 

degrees-latitude where evapotranspiration is low 

and dune sands are prevalent. 

Ground water in the High Plains aquifer 

system generally flows from west to east in 

response to the slope of the water table. Based on 

regional hydraulic gradient and aquifer properties, the velocity of water moving through the 

aquifer system is about 1 ft/d. 

Hydraulic conductivity and specific yield are 

the two principal properties that control groundwater flow in an unconfined aquifer. Both properties, depending on the characteristics of the 

sediments, can vary horizontally and vertically. 

The average hydraulic conductivity of the High 

Plains aquifer system is about 60 ft/d. For most 

(68 percent) of the aquifer area, hydraulic conductivity ranges from 25 to 100 ft/d, although it may 

be as much as 300 ft/d for individual lithologic 

units. The specific yield of most (76 percent) of the 

aquifer area is 10 to 20 percent, although the 

values range from 3 to 35 percent for individual 

lithologic units. The average specific yield is 

about 15 percent. 

31 
32 

35" 

WYOMING 

-------

NEW MEXICO 

QUATERNARY 

~ Undivided 

W!J\%@ Dune sand 

.. 

100" 

------------

IOWA 

------

MISSOURI 

-------'. 

\-----

TEXAS SCALE 1 :9,000,000 r--- 0 100 200 MILES 

0 100 200 KILOMETERS 

EXPLANATION 

TERTIARY 

ISSSJ Ogallala Formation 

~ Arikaree Group or Formation 

EJ] Brule Formation 

AREA OF THE HIGH PLAINS 

REGIONAL AQUIFER SYSTEM 

Figure 13.-Principal geologic units of the High Plains regional aquifer system. 
35" 

WYOMING 

Wheatland Fault 

-------

NEW MEXICO 

AGE OF BEDROCK UNITS UNDERLYING 

THE HIGH PLAINS REGIONAL 

AQUIFER SYSTEM 

- Tertiary 

~ Upper Cretaceous 

EIJ Lower Cretaceous 

[K%i@i\J Jurassic and Triassic 

[~~ ~ Permian 

100" 

TEXAS 

EXPLANATION 

0 

0 

u 

0 

.. 

95" 

------------

IOWA 

-------

-----~ 

\-----

SCALE 1 :9,000,000 

100 200MILES 

100 200 KILOMETERS 

FAULT-- U, upthrown side; 

D, downthown side 

AREA OF THE HIGH PLAINS 

REGIONAL AQUIFER SYSTEM 

Figure 14.-Areal extent and age of bedrock units underlying the High Plains regional aquifer system. 

33 
34 

Ground water from the High Plains aquifer 

system discharges to streams, springs, and seeps, 

and to the atmosphere by evapotranspiration. 

Streams that originate in the High Plains 

generally are ephemeral in upstream reaches and 

perennial where channels are incised into the 

water table. Ground.;water discharge by 

evapotranspiration is greatest in stream valleys 

in which phreatophytes grow. In sand hills in 

Nebraska, evaporation from numerous lakes 

which are hydraulically connected to the aquifer 

system may equal or exceed seepage to streams. 

Ground-water discharge from the High Plains 

aquifer syste~ has been estimated by model 

simulation (Luckey and others, 1985). The 

simulated. annual discharge to streams or lakes 

is 2.3 million acre-ft. About 85 percent of the 

discharge occurs north of 39 degrees-latitude 

where recharge is greatest. 

Saturated thickness of the aquifer system 

ranges from zero, where the deposits comprising 

the aquifer system are unsaturated, to about 

1,000 feet in west-central Nebraska. The average 

saturated thickness is about 200 feet. About 46 

percent of the area underlain by the High Plains 

aquifer system has less than 100 feet of saturated 

thickness, whereas only 5 percent has more than 

600 feet of saturated thickness. The saturated 

thickness of the aquifer is greater than 600 feet 

only in Nebraska and Wyoming (Weeks and 

Gutentag, 1981). Areas where the saturated 

thickness of the aquifer system exceeded 200 feet 

in 1980 are shown in figure 15. 

Salt dissolution has affected the thickness of 

the High Plains aquifer system. Many evaporite 

beds in the Permian rocks underlying the High 

Plains are susceptible to dissolution by ground 

water. Sinkholes associated with salt dissolution 

have been forming since Permian time. Collapse 

structures have been filled by younger material 

in large areas in southwestern Kansas, 

Oklahoma, and northern Texas. 

The volume of water stored in the High Plains 

aquifer system depends on the saturated 

thickness and specific yield of the aquifer. The 

total volume of drainable water in storage (product of specific yield, saturated thickness, and 

area) in 1980 was estimated to be 3.25 billion 

acre-ft (Gutentag and others, 1984). About 65 percent of the water in aquifer storage is in 

Nebraska, where recharge and saturated 

thickness are greatest because of the presence of 

dune sands. About 12 percent of the water in 

aquifer storage is in Texas, 10 percent in Kansas, 4 percent in Colorado, 3.5 percent in 

Oklahoma, 2 percent each in South Dakota and 

Wyoming, and 1.5 percent in New Mexico. 

The quality of water in the High Plains 

aquifer system generally is suitable for irrigation; 

however, the water does not meet U.S. Environmental Protection Agency drinking water 

standards in many places. The concentrations of 

dissolved solids, fluoride, chloride, and sulfate exceed recommended limits for drinking-water in 

parts of the aquifer in all States (Krothe and 

others, 1982). 

Most of the water in the High Plains aquifer 

system contains 250 to 500 milligrams per liter 

(mg/L) of dissolved solids and is a calcium bicarbonate type water. Ground water containing more 

than 500 mg/L dissolved solids generally is a 

mixed type of water, with calcium, sodium, 

sulfate, and chloride the most prevalent ions. The 

concentration of dissolved solids in water from the 

High Plains aquifer system is shown in figure 16. 

About 62 percent of the aquifer area contains 

water with 250 to 500 mg/L dissolved solids; only about 3 percent of the area contains water exceeding 1,000 mg/L dissolved solids, most of which 

is in Texas. Generally, concentrations of dissolved 

solids are least in areas covered by sand, because 

recharge is relatively high and the sand contains 

few readily soluble minerals. 

Bedrock underlying the aquifer system affects 

the chemical composition of water in the aquifer 

in parts of all states in the High Plains. In some 

areas, water at the base of the aquifer in contact 

with bedrock dissolves minerals contained in the 

bedrock and transports them through the aquifer 

by diffusion or ground-water flow in response to 

hydraulic-head differences. In some areas, dissolution of minerals from reworked bedrock in the 

aquifer sediments has affected water chemistry. 

In most areas of the High Plains aquifer system, 

where the concentrations of dissolved solids exceed 1,000 mg/L, the chemical composition of the 

water is affected by the underlying bedrock. 

GROUND-WATER PUMPAGE 

Water from the High Plains aquifer system 

is the principal source of supply for irrigation in 

the area. Rapid development of irrigation in the 

High Plains in recent years has made the area 

one of the major agricultural regions of the 

United States. About 95 percent of all water 

pumped from the aquifer system is used for 

irrigation. 
Ground-water irrigation in the High Plains 

was sporadic until the drought of the 1930's. By 

1949, about 2 million acres of land, mostly in 

southern High Plains, were irrigated. Centerpivot irrigation systems, which were adaptable to 

sandy soil and rolling terrain, were developed 

during the 1960's. Center pivots made land 

available for irrigation that previously was not 

WYOMING 

-------

40 ° 

----

35. 

NEW MEXICO 

___________ j 

suitable, particularly in the northern parts of the 

High Plains. About 13 million acres ofland were 

irrigated in 1978. 

Historical Pumpage 

Historical information on ground-water 

pumpage for irrigation was needed for a ground-

-----

IOWA 

------

KANSAS 

MISSOURI 

----- --', 

\-----

TEXAS SCALE 1:9,000,000 r---- 0 100 200 MILES 

0 100 200 KILOMETERS 

EXPLANATION 

AREAS WHERE THE SATURATED THICKNESS OF THE HIGH PLAINS 

REGIONAL AQUIFER SYSTEM EXCEEDED 200 FEET IN 1980 

AREAS WHERE THE SATURATED THICKNESS OF THE HIGH PLAINS 

REGIONAL AQUIFER SYSTEM WAS LESS THAN 200 FEET IN 1980 

AREA OF THE HIGH PLAINS REGIONAL AQUIFER SYSTEM 

Figure 15.-Areas where saturated thickness of the High Plains regional aquifer system exceeded 200 feet in 1980. 

35 
36 

40 " 

35 " 

WYOMING 

-------

Riuer 

NEW MEXICO 

,... __ _ 

100 " 95 " 

------------

IOWA 

-----

-- - -------

I..; 

I 

I 

KANSAS 

MISSOURI 

----~ 

-----

TEXAS SCALE 1 :9,000,000 I -- 0 

0 100 

EXPLANATION 

CONCENTRATION OF DISSOLVED SOLIDS, 

IN MILLIGRAMS PER LITER 

[[]] Less than 250 

~ 250 - 500 

- 500-1000 

~ Greater than 1000 

AREA OF THE HIGH PLAINS 

REGIONAL AQUIFER SYSTEM 

100 200 MILES 

200 KILOMETERS 

Figure 16.-Dissolved-solids concentrations in ground water in the High Plains regional aquifer system. 
water flow model. Adequate data on ground-water 

pumpage in the High Plains were not available. 

Therefore, a method for estimating pumpage from 

irrigation requirement was developed (Heimes 

and Luckey, 1982). Irrigation requirement is 

defined as the volume of water required in addition to precipitation for all of the irrigated crops 

grown in a given area, on the basis of average 

climatic conditions. 

Irrigated acreage in the High Plains, based 

on the census of agriculture of the U.S. Department of Commerce (1949-78), is shown in figure 

17. The graph shows that the total acreage irrigated by ground water in the High Plains increased from slightly more than 2 million acres 

in 1949 to about 13 million acres in 1978. This 

rapid increase in irrigated acreage has resulted 

in a corresponding increase in ground-water 

pumpage. 

The Blaney-Criddle formula (U.S. Department of Agriculture, 1967) was selected to 

estimate irrigation requirement on the High 

Plains. Ground-water pumpage was estimated by 

adjusting irrigation requirement for the efficiency 

of irrigation. The efficiency of irrigation is defined 

as the ratio of irrigation requirement to the water 

pumped. The efficiency of irrigation generally 

ranges from about 40 to 90 percent and depends 

on many factors, such as the type of irrigation 

system, crop and soil types, and climate. Figure 

17 shows estimated ground-water pumpage in the 

High Plains assuming an average irrigation efficiency of65 percent for period 1949-78. Pumpage 

for irrigation during 1978 was estimated at about 

23 million acre-ft, which is almost 20 million acreft more than the estimated pumpage for irrigation during 1949. 

1980 Pumpage Study 

The objective of the 1980 pumpage study was 

to provide an estimate of the quantity of ground 

water withdrawn for irrigation during 1980. 

Historical pumpage estimates based on irrigation 

requirement were made because measured data 

on historical ground-water withdrawals generally 

are not available. Calculations of irrigation requirement give reasonable estimates of historical 

withdrawals, but changes in irrigation techniques 

caused by increased energy costs and decreasing 

water availabililty are likely to reduce the accuracy of these estimates. Consequently, a sampling program was designed to provide an 

estimate of ground-water withdrawal for irrigation during 1980 based on measured data. A pilot 

37 

24,------------------------------.~ 

22 8 Ill ~ 22 u. 

~ w 

t5 20 

:J 

20 5 

<{ 

...J 

~ 18 z 18 0 

:J 

...J 

ffi. 16 

1-

~ 14 

0 

z 

16 ~ 

~ 

ui 

14 (!) 

<{ 

0.. 

::J 

0 

a: 12 12 ~ 

(!) 

J: 

1-

10 

0.. 

a: 10 w 

0 

~ ~ w 

~ 

8 8 0 

z 

::J 

(!) 6 6 2 

a: (!) 

a: 

w 

(!) 

4 

0 4 w 

~ i:5 ::JE a: 

u 

<{ 

2 2 ~ 

0 

1949 1954 1959 1964 1969 1974 1978 

YEAR 

Figure 17. -Acreage irrigated by ground water and 

estimated ground-water pumpage in the High Plains, 

1949-78. 

program was conducted in 1979 to test methods 

and instrumentation for application to the 1980 

pumpage-sampling program (Luckey and others, 

1980; Heimes and Luckey, 1980). 

The 1979 pilot program was designed to: (1) 

develop a statistical approach to sampling 

ground-water pumpage for irrigation, (2) test instrumentation and develop procedures for 

measuring the annual volume of ground water 

pumped from selected irrigation wells, (3) determine the relation between the annual volume of 

ground water pumped and the acreage irrigated, 

and (4) develop a suitable approach to map irrigated cropland for the entire High Plains in 

order to extend the sampled information. 

For the pilot program, the stratified random 

sampling technique was used to select 250 sites 

in two areas. Sites were stratified by crop and by 

area. The annual volume of ground water pumped 

at each site was computed by multiplying the 

pumping rate by the total time of pumping. During the pilot program, various approaches were 

evaluated for mapping the irrigated cropland. 

For 1980, 15 counties, strategically located 

throughout the High Plains, were selected for 

data collection, and sampling sites were selected 

w 
38 

randomly within the counties (Heimes and 

Luckey, 1983). Discharge from wells, time-ofpumping, crop type, and crop-acreage data were 

collected at each of the sampling sites during the 

growing season. These data were used to compute 

the average depth of water applied at each site. 

The relation between irrigation requirement 

calculated using the Blaney-Criddle formula, and 

the sampled water application were used to 

estimate water application in unsampled areas of 

the High Plains. Estimates of application were 

combined with 1980 irrigated-acreage data to 

calculate the volume of water pumped during the 

1980 growing season. 

Irrigated acreage for the 1980 growing season 

was compiled using Landsat imagery. Fifty-nine 

Landsat scenes covering the High Plains were 

analyzed by computer to separate irrigated 

cropland from other land-cover categories. 

Estimates of irrigated acreage, derived from the 

computer classification of Landsat data, subsequently were aggregated into cells of 1-minute 

latitude by 1-minute longitude (1-minute cells). 

This aggregation made the irrigated-acreage data 

compatible with other hydrologic and geologic 

data compiled for . this study. Data for the 

1-m.inute cells were aggregated to estimate irrigated acreage for 1-degree cells. 

The volume of ground water pumped for irrigation was computed by multiplying the water 

application by irrigated acreage. The volume of 

ground water pumped for irrigation was then 

estimated for each 1-degree cell, and summed up 

by State. The estimated volume of water pumped 

in 1980 for irrigation by State is summarized in 

table 1. The estimated total volume of water 

pumped during the 1980 growing season was 

17,817,000 acre-ft which was applied to 

13,385,000 acres. Three States (Kansas, 

Nebraska, and Texas) accounted for about 88 percent of this pumpage. Texas, which accounts for 

20 percent of the area and 29 percent of the total 

pumpage, was the most densely irrigated area. 

South Dakota, which accounts for 2. 7 percent of 

the area, but only 0.1 percent of the total pumpage, virtually was unirrigated. 

Irrigation requirement in the High Plains 

generally is much larger than the amount of 

ground-water recharge. Consequently, pumpage 

for irrigation in large parts of the High Plains 

greatly exceeds the recharge rate, and water 

levels in these areas are declining. 

Water-Level Changes 

Water-level changes from predevelopment to 

1980 in the High Plains aquifer system are shown 

in figure 18. Areas of water-level decline caused 

by irrigation pumpage are found in all States except South Dakota, where irrigation development, 

relative to other High Plains States, is sparse. 

The largest area of water-level declines exceeding 

50 feet occurred south of the Canadian River in 

New Mexico and Texas. The maximum waterlevel decline in the High Plains of nearly 200 feet, 

occurred south of the Canadian River in Floyd 

County, Texas (Luckey and others, 1981). 

Table 1.-Estimated irrigated acreage and volume of ground water pumped for irrigation in areas of the High Plains during 

the 1980 growing season 

Area of High Plains aquifer Irrigated acreage Volume of groundState system within State during 1980 water pumped 

(square miles) (acres) (acre-feet) 

Colorado 14,900 767,000 985,000 

Kansas 30,500 2,795,000 4,215,000 

Nebraska 63,650 5,101,000 6,240,000 

New Mexico 9,450 325,000 519,000 

Oklahoma 7,350 389,000 540,000 

South Dakota 4,750 20,000 24,000 

Texas 35,450 3,878,000 5,169,000 

Wyoming 8,000 110,000 125,000 

Total 174,050 13,385,000 17,817,000 
35' 

WYOMING 

--------

NEW MEXICO 

,. __ _ 

100' 

TEXAS 

EXPLANATION 

0 

L 

0 

WATER-LEVEL CHANGES, IN FEET 

• Rise more than 10 

~ 10to -10 

- -10to -50 

- Decline more than 50 

.. 

AREA OF THE HIGH PLAINS 

REGIONAL AQUIFER SYSTEM 

95' 

------

IOWA 

--------

MISSOURI 

-----~ 

\-----

SCALE 1:9,000,000 I-- 100 200 MILES 

100 200 KILOMETERS 

Figure 18.-Water-level changes, from predevelopment to 1980, in the High Plains regional aquifer system. 

39 
40 

North of the Canadian River, water levels 

have declined more than 50 feet in parts of Texas, 

Oklahoma, and Kansas. Water levels have declined 10 to 50 feet in large areas in eastern Colorado, western Kansas, and southern Nebraska. 

Water-level declines in these areas are less 

severe, primarily because irrigation started later. 

Water-level nses in Nebraska (fig. 18) are due 

to recharge from surface-water irrigation. In Kansas and Oklahoma, water-level rises probably 

represent recovery from abnormally low water 

levels during the drought of 1933-40. In Texas, 

the water-level rise is attributed to the clearing 

sandy soil of native vegetation for cultivation, 

resulting in increased recharge. 

Significant declines in water levels (more 

than 10 feet) have occurred in 29 percent of the 

area underlain by the aquifer system, and significant rises in water level (more than 10 feet) have 

occurred in only 1 percent of the aquifer area. A 

total of 50,000 mi2 (32 million acres) of the aquifer 

area have had water-level declines in excess of 10 

feet, and more than 12,000 mi2 (7. 7 million acres) 

have had water-level declines in excess of 50 feet. 

Saturated-Thickness Changes 

Changes in saturated thickness of the High 

Plains aquifer system (in percent) from 

predevelopment to 1980 are shown in figure 19. 

Changes in saturated thickness are important 

because large changes in saturated thickness may 

affect well yield and pumping cost, or cause partially penetrating wells to go dry. 

Two areas with significant increases in 

saturated thickness (greater than 10 percent) occur in Nebraska (fig. 19). In each of these areas, 

recharge to the aquifer system from surface-w~ter 

irrigation has resulted in an increase in saturated 

thickness of more than 10 percent. Saturated 

thickness has increased more than 10 percent in 

one area in Texas. In this area, recharge to the 

aquifer system has increased because of land-use 

changes. 

Areas of significant decreases in saturated 

thickness generally are found where the aquifer 

system has been pumped for irrigation for many 

years. Saturated thickness has decreased more 

than 25 percent in one-quarter of the High Plains 

of New Mexico and Texas where -large-scale irrigation began in the 1930's. Saturated thickness 

also has decreased more than 25 percent in parts 

of Kansas and Oklahoma. 

In Colorado, northwestern Kansas, Nebraska, 

and Wyoming, most of the irrigation has taken 

place since 1960. Saturated thickness decreased 

10 to 25 percent in areas of Colorado and Kan-

·sas, and in a smaller area of Nebraska (fig. 19). 

In these areas, ground-water pumpage is beginning to reduce saturated thickness significantly, 

and well yields may decline in the future. 

Significant (greater than 10 percent) increases in saturated thickness have occurred in 

only 1 percent of the aquifer area mostly in 

Nebraska (about 1,700 mi2 or 1.1 million acres). 

Significant decreases· (more than 10 percent) in 

saturated thickness have occurred in 25 percent 

of the area, (about 44,000 mi2 or 28 million acres); 

saturated thickness has decreased more than 25 

percent in 14,000 mi2 (9 million acres). About 166 

million acre-ft of water have been removed from 

aquifer storage since pumping began. About 16 

percent of this decrease in aquifer storage has occurred in Kansas and 70 percent has occurred in 

Texas. No significant regional changes in 

saturated thickness of the High Plains aquifer 

system have occurred in South Dakota. 

FLOW MODELS 

The High Plains aquifer system was divided 

into three parts for simulation by digital models 

of ground-water flow as shown in figure 20. The 

southern High Plains subdivision includes most 

of the area (29,000 mi2

) south of approximately 

35 degrees-latitude, the central High Plains subdivision includes the area (48,500 mi2

) between 

35 and 39 degrees-latitude, and the northern High 

Plains subdivision includes the area (96,500 mi2

) 

north of 39 degrees-latitude. A narrow strip, approximately 12 miles wide, joins the southern and 

central High Plains subdivisions; another strip, 

approximately 32 miles wide, joins the central 

and northern High Plains subdivision (fig. 20). 

Model Development 

The flow models used in this study can 

simulate two-dimensional ground-water flow in 

a heterogeneous, isotropic, unconfined aquifer. 

Two-, rather than three-, dimensional groundwater flow models were used because, on a 

regional scale, the vertical components of flow in 

the aquifer system were so small that they could 

be neglected. The models have a network of nodes 

spaced 10 miles apart in both the north-south and 

east-west directions. Four categories of informa-
40. 

35. 

WYOMING 

-------

NEW MEXICO 

100. 95. 

------------

IOWA 

NEBR' -

------

KANSAS 

MISSOURI 

______ _JI 

-----

TEXAS SCALE 1:9,000,000 I-- 0 

0 

EXPLANATION 

SATURATED-THICKNESS CHANGES, 

IN PERCENT 

- Increase more than 10 

§I 10to -10 

rniiiiiill -1 0 t 0 - 25 

B Decrease more than - 25 

AREA OF THE HIGH PLAINS 

REGIONAL AQUIFER SYSTEM 

100 200 MILES 

100 200 KILOMETERS 

Figure 19. -Saturated thickness changes, from predevelopment to 1980, in the High Plains regional aquifer system. 

41 
42 

40' 

35' 

WYOMING 

--------

NEW MEXICO 

r------

1 

100' 

TEXAS 

0 

0 

EXPLANATION 

AQUIFER AREAS SIMULATED BY 

DIGITAL FLOW MODELS 

- Northern High Plains 

- Central High Plains 

- Southern High Plains 

-

AREA OF THE HIGH PLAINS 

REGIONAL AQUIFER SYSTEM 

95' 

---------

IOWA 

--------

_____ ..J 

. \- --~-

I 

SCALE 1:9,000,000 ~--

100 200 MILES 

100 200 KILOMETERS 

Figure 20.-Subdivisions used in modeling the High Plains regional aquifer system. 
tion were needed for the flow models: (1) aquifer 

geometry (vertical and areal extent of the aquifer 

system); (2) boundary conditions; (3) aquifer 

parameters (hydraulic conductivity and specific 

yield); and ( 4) stresses on the aquifer (recharge 

and discharge). In addition, some simulations required an initial water-level configuration. All 

the data were stored in a data base designed to 

provide input to the model (Luckey and Ferrigno, 

1982). The models integrate all of the input data 

and generate a water-level configuration and 

water budget for the aquifer system (Luckey and 

others, 1985). 

Model Sensitivity 

Sensitivity analyses were performed on the 

flow models to determine how changes in different 

model input parameters affect the simulation 

results (Luckey and others, 1985). The sensitivity 

analyses for the predevelopment-period models indicated that the models were about equally sensitive to changes in recharge and changes in 

hydraulic conductivity. The analyses further indicated that these two model inputs are highly 

interrelated and as long as an increase in one is 

accompanied by a similar increase in the other, 

the simulations will have a small mean residual 

between observed and calculated water levels. 

Hence, the models could be used to accurately 

estimate recharge only if the hydraulic conductivity is know accurately or vice versa. The 

development-period models are sensitive to 

changes in net pumpage and specific yield and insensitive to hydraulic conductivity. Specific yield 

and net pumpage are also highly interrelated and 

one cannot be accurately determined through a 

model analysis unless the other is accurately 

known. 

Calibration of the predevelopment-period 

models provided the initial conditions for the 

calibration of the development-period models. 

Likewise, calibration of the development-period 

models for the southern, central, and northern 

High Plains can be used as the initial conditions 

for projecting future water levels. 

PUBLISHED REPORTS 

Abstracts 

1. Avery, Charles, 1981, Pumpage-data collection in part of the High Plains, Nebraska 

and Wyoming: Proceedings of the lOth annual Rocky Mountain Ground Water Conference, April 30-May 2, 1981, Laramie, 

WY, p. 46. 

2. Gaydos, Leonard; Thelin, Gail; Donovan, 

Walter; Koch, Carol; Morse, Anthony; 

Jones, Harry; and Heimes, Frederick, 1982, 

One billion pixels; analysis and reduction of 

Landsat data for the High Plains 

hydrological model: American Society of 

Photogrammetry, Proceedings, 48th Annual 

Meeting, Denver, CO, March 1982, p. 562. 

3. Gutentag, E. D., Jorgensen, D. G., and Kenny, J. F., 1979, Impact of energy availability 

on irrigation in western Kansas: Ground 

Water, v. 17, no. 5, p. 48. 

4. Gutentag, E. D., Krothe, N. C., and Oliver, 

J. W., 1981, Effects of dissolution ofPermian 

salt on the High Plains aquifer in northwestern Oklahoma and southwestern Kansas: American Geophysical Union EOS 

Transactions, v. 62, no. 45, p. 872. 

5. Gutentag, E. D., and Weeks, J. B., 1981, 

Evaluating vertical variability of 

transmissivity and specific yield for the 

High Plains regional aquifer system: 

Geological Society of America Abstracts 

with Programs, Rocky Mountain Section, 

v. 13, no. 4, p. 199. 

6. -----1984, Ground-water resource 

assessment-the High Plains aquifer, 

western United States: 29th Midwest 

Groundwater Conference, October 1-3, 1984, 

Lawrence, KS, Program with abstracts, p. 3. 

7. Heimes, F. J., and Thelin, G. P., 1980, 

Development and application of Landsatderived irrigation crop-land maps and wateruse determination in the High Plains, in 

Identifying irrigated lands using remote 

sensing: State of the art: Missouri River 

Basin Commission, Proceedings of Symposium, Sioux Falls, SD, 1979, p. 76-77. 

8. Kolm, K. E., and Case, H. L., ill, 1983, A twodimensional, finite- difference model of the 

High Plains aquifer in South Dakota: 

Geological Society of America Abstracts 

with Programs, v. 15, no. 5, p. 312. 

9. Krothe, N.C., 1981, Quality of ground water 

in the High Plains aquifer: American 

Geophysical Union EOS Transactions, v. 62, 

no. 45, p. 872. 

10. Luckey, R. R., and Nethaway, C. D., Jr., 1980, 

Design and implementation of a data base 

to store areal hydrologic information: 

American Geophysical Union EOS Transactions, v. 61, no. 46, p. 953. 

43 
44 

11. Pettijohn, R. A., and Chen, H. H., 1984, 

Hydrologic characteristics and ground-water 

availability in the High Plains aquifer 

system in Nebraska: 29th Midwest Groundwater Conference, October 1-3, 1984, 

Lawrence, KS, Program with abstracts, p. 3. 

12. Thelin, G. P., and Heimes, F. J., 1980, 

Estimating areal extent of irrigated 

cropland using Landsat digital data: 

American Geophysical Union EOS Transac~ 

tions, v. 61, no. 46, p. 953. 

Reports 

1. Ashworth, J. B., 1980, Results of test hole 

drilling: Texas Department of Water 

Resources Report LP-129, 41 p. 

2. -----1984, Hydraulic characteristics of 

the High Plains aquifer as determined from 

core analysis, in Whetstone, G. A., ed., Proceedings of the Ogallala Aquifer Symposium 

II: Texas Tech University, Lubbock, TX, 

June 1984, p. 278-291. 

3. Avery, C. F., 1983, Pumpage data from irrigation wells in eastern Laramie County, 

Wyoming, and Kimball County, Nebraska: 

U.S. Geological Survey Open-File Report 

83-29, 23 p. 

4. Avery, C. F., and Pettijohn, R. A., 1984, 

Generalized potentiometric- surface map of 

the High Plains aquifer system in Wyoming, 

1981: U.S. Geological Survey WaterResources Investigations Report 84-4033, 

scale 1:250,000, 1 sheet. 

5. Borman, R. G., 1983, Predevelopment and 

1980 water table in the northern High 

Plains of Colorado; and water-level changes, 

predevelopment to 1980 and 1975 to 1980: 

U.S. Geological Survey Hydrologic Investigations Atlas 670, scale 1:500,000 and 

1:1,000,000, 1 sheet. 

6. Borman, R. G., and Gaggiani, N. G., 1982, 

Generalized altitude and configuration of 

the water table in parts of Larimer, Logan, 

Sedgwick, and Weld Counties, Colorado: 

U.S. Geological Survey Water-Resources Investigations Report 82-4055, scale 

1:500,000, 1 sheet. 

7. Borman, R. G., Lindller, J. B., Bryn, S. M., and 

Rutledge, John, 1983, The Ogallala aquifer 

in the High Plains of Colorado--Saturated 

thickness in 1980; saturated-thickness 

changes, predevelopment to 1980; hydraulic 

conductivity; specific yield, and predevelopment and 1980 probable well yields: U.S. 

Geological Survey Hydrologic Investigations 

Atlas 671, scale 1:500,000 and 1:1,000,000, 

1 sheet. 

8. Borman, R. G., and Meredith, T. S., 1983, 

Geology, altitude, and depth of the bedrock 

surface beneath the Ogallala Formation in 

the northern High Plains. of Colorado: U.S. 

Geological Survey Hydrologic Investigations 

Atlas 669, scale 1:500,000, 1 sheet. 

9. Borman, R. G., Meredith, T. S., and Bryn, S. 

M., 1982, Geology, altitude, and depth of the 

bedrock surface; water table in 1980; and 

saturated thickness of the Ogallala aquifer 

in 1980 in the southern High Plains of Colorado: U.S. Geological Survey Hydrologic Investigations Atlas 673, scale 1:500,000, 

1 sheet. 

10. Borman, R. G., and Reed, R. L., 1982, Location of irrigation wells and application rates 

for irrigated cropland during 1980 in the 

northern High Plains of Colorado: U.S. 

Geological Survey Hydrologic Investigations 

Atlas 675, scale 1:500,000, 1 sheet. 

11. Cobb, P. M., Colarullo, S. J., and Manoutchehr, Heidari, 1983, A ground-water flow 

model for the Great Bend aquifer, southcentral Kansas: Kansas Geological Survey 

Open-File Report 83-20, 220 p. 

12. Cooley, M.E., 1984a, Linear features determined from Landsat imagery in the Texas 

and Oklahoma Panhandles: U.S. Geological 

Survey Open-File Report 84-589, scale 

1:500,000, 1 sheet. 

13. -----1984b, Linear features determined 

from Landsat imagery in western Kansas: 

U.S. Geological Survey Open-File Report 

84-241, scale 1:500,000, 1 sheet. 

14. DeAngelis, Robert, 1980, Irrigated cropland, 

1978, Hockley and Lamb Counties, Texas: 

U.S. Geological Survey Open-File Report 

80-168, scale 1:250,000, 1 sheet. 

15. Dugan, J. T., 1984, Hydrologic characteristics 

of Nebraska soils: U.S. Geological Survey 

Water-Supply Paper 2222, 12 plates, 19 p. 

16. Feder, G. L., and Krothe, N.C., 1981, Results 

of a reconnaissance water-quality sampling 

program of the Ogallala aquifer in Colorado, 

Kansas, Nebraska, Oklahoma, South 

Dakota, and Texas: U.S. Geological Survey 

Water-Resources Investigations Report 

81-65, 7 p. 

17. Gutentag, E. D., Heimes, F. J., Krothe, N.C., 

Luckey, R. R., and Weeks, J. B., 1984, 
Geohydrology of the High Plains aquifer in 

parts of Colorado, Kansas, Nebraska, New 

Mexico, Oklahoma, South Dakota, Texas, 

and Wyoming: U.S. Geological Survey Professional Paper 1400-B, 63 p. 

18. Gutentag, E. D., and Weeks, J. B., 1980, 

Water table in the High Plains aquifer in 

1978 in parts of Colorado, Kansas, 

Nebraska, New Mexico, Oklahoma, South 

Dakota, Texas, ~nd Wyoming: U.S. 

Geological Survey Hydrologic Investigations 

Atlas 642, scale 1:2,500,000, 1 sheet. 

19. Hart, D. L., Jr., and McAda, D. P., 1985, 

Geohydrology of the High Plains aquifer in 

southeastern New Mexico: U.S. Geological 

Survey Hydrologic Investigations Atlas 679, 

scale 1:500,000 and 1:1,000,000, 1 sheet. 

20. Havens, J. S., 1982a, Altitude and configuration of the 1980 water table in the High 

Plains regional aquifer, northwestern 

Oklahoma: U.S. Geological Survey OpenFile Report 81-100, scale 1:250,000,2 sheets. 

21. ----1982b, Altitude and configuration of 

the predevelopment water table in the High 

Plains regional aquifer, northwestern 

Oklahoma: U.S. Geological Survey OpenFile Report 81-275, scale 1:250,000, 2 sheets. 

22. -----1982c, Generalized altitude and configuration of the base of the High Plains 

regional aquifer, northwestern Oklahoma: 

U.S. Geological Survey Open-File Report 

81-1117, scale 1:250,000, 2 sheets. 

23. -----1982d, Saturated thickness of the 

High Plains regional aquifer in 1980, northwestern Oklahoma: U.S. Geological Survey 

Open-File Report 81-760, scale 1:250,000, 

2 sheets. 

24. -----1983, Water-level changes in the 

High Plains regional aquifer, northwestern 

Oklahoma, predevelopment to 1980: U.S. 

Geological Survey Open-File Report 

83-4073, scale 1:500,000, 1 sheet. 

25. Havens, J. S. and Christenson, S. C., 1984, 

Numerical simulation of the High Plains 

regional aquifer, northwestern Oklahoma: 

U.S. Geological Survey Water-Resources Investigations Report 83-4269, 27 p. 

26. Heimes, F. J., 1984, The High Plains regional 

aquifer-estimating 1980 ground-water 

pumpage for irrigation, in Whetstone, G. A., 

ed., Proceedings of the Ogallala Aquifer 

Symposium II: Texas Tech University, Lubbock, TX, June 1984, p. 26-39. 

27. Heimes, F. J., and Luckey, R. R., 1980, 

Evaluating methods for determining water 

use in the High Plains in parts of Colorado, 

Kansas, Nebraska, New Mexico, Oklahoma, 

South Dakota, Texas, and Wyoming; 1979: 

U.S. Geological Survey Water-Resources Investigations Report 80-111, 118 p. 

28. -----1982, Method for estimating 

historical irrigation requirements from 

ground water in the High Plains aquifer in 

parts of Colorado, Kansas, Nebraska, New 

Mexico, Oklahoma, South Dakota, Texas, 

and Wyoming: U.S. Geological Survey 

Water-Resources Investigations Report 

82-40, 64 p. 

29. -----1983, Estimating 1980 ground-water 

pumpage for irrigation on the High Plains 

in parts of Colorado, Kansas, Nebraska, 

New Mexico, Oklahoma, South Dakota, 

Texas, and Wyoming: U.S. Geological 

Survey Water-Resources Investigations 

Report 83-4123, 36 p. 

30. Jonas, Peter, and Wright, Bruce, 1979a, Irrigated cropland, 1978, Cherry County, 

Nebraska: U.S. Geological Survey Open-File 

Report 79-1629, scale 1:250,000, 1 sheet. 

31. -----1979b, Irrigated cropland, 1978, 

Todd County, South Dakota: U.S. Geological 

Survey Open-File Report 79-1627, scale 

1:250,000, 1 sheet. 

32. Johnson, Robert, 1980a, Irrigated cropland, 

1978, Chase, Dundy, and Perkins Counties, 

Nebraska: U.S. Geological Survey Open-File 

Report 80-641, scale 1:250,000, 1 sheet. 

33. -----1980b,. Irrigated cropland, 1978, 

Cheyenne and Sherman Counties, Kansas: 

U.S. Geological Survey Open-File Report 

80-640, scale 1:250,000, 1 sheet. 

34. Johnson, Thomas, 1980, Irrigated cropland, 

1978, Kit Carson County, Colorado: U.S. 

Geological Survey Open~ File Report 80-639, 

scale 1:250,000, 1 sheet. 

35. -----1980, Irrigated cropland, 1978, 

Laramie County, Wyoming: U.S. Geological 

Survey Open-File Report 80-638, scale 

1:250,000, 1 sheet. 

36. Klemt, W. B., 1981, Neutron-probe 

measurements of deep soil moisture as an 

indication of aquifer recharge rates: Texas 

Department of Water Resources Report 

LP-142, 31 p. 

37. Knowles, Tommy, 1981, GWSIM-111, groundwater simulation program documentation 

and user's manual: Texas Department of 

Water Resources Report UM-36, 84 p. 

45 
46 

38. ·----1984, Assessment of the groundwater resources of the Texas High Plains, 

in Whetstone, G. A., ed., Proceedings of the 

Ogallala Aquifer Symposium II: Texas Tech 

University, Lubbock, TX, June 1984, 

p. 217-237. 

39. Knowles, Tommy, Nordstrom, Phillip, and 

Klemt, W. B., 1981a, Evaluating the 

ground-water resources of the High Plains 

of Texas, basic data for middle third of 

region: Texas Department of Water 

Resources Final Report LP-173, v. 3, 477 p. 

40. 1981b, Evaluating the ground-water 

resources of the High Plains of Texas, basic 

data for southern third of region: Texas 

Department of Water Resources Final 

Report LP-173, v. 4, 389 p. 

41. 1982a, Evaluating the ground-water 

resources of the High Plains of Texas: Texas 

Department of Water Resources Final 

Report LP-173, v. 1, 174 p. 

42. 1982b, Evaluating the ground-water 

resources of the High Plains of Texas, basic 

data for northern third of region: Texas 

Department of Water Resources Final 

Report LP-173, v. 2, 451 p. 

43. Kolm, K. E., and Case, H. L., ill, 1983, A twodimensional, finite- difference model of the 

High Plains aquifer in South Dakota: U.S. 

Geological Survey Water-Resources Investigations Report 83-4175, 34 p. 

44. 1984, Evaluation of techniques for 

identifying irrigated crop types and 

estimating acreages from Landsat imagery 

in the High Plains of South Dakota: Journal of Photogrammetric Engineering and 

Remote Sensing, v. 50, no. 10, p. 1479-1490. 

45. Krothe, N. C., and Oliver, J. W., 1982, 

Sulphur isotopic composition and water 

chemistry in water from the High Plains 

aquifer, Oklahoma Panhandle and 

southwestern Kansas: U.S. Geological 

Survey Water-Resources Investigations 'D~--_. on 1 n nn __ 

46. Krothe, N.C., Oliver, J. W., and Weeks, J. B., 

1982, Dissolved solids and sodium in water 

from the High Plains aquifer in parts of Colorado, Kansas, Nebraska, New Mexico, 

Oklahoma, South Dakota, Texas, and 

Wyoming: U.S. Geological Survey 

Hydrological Investigations Atlas 658, scale 

1:2.500,000, 2 sheets. 

47. Lindner-Lunsford, J. B., and Borman, R. G., 

1985, Potential well yields from the Ogallala 

aquifer in the northern High Plains of Colorado: U.S. Geological Survey Hydrologic Investigations Atlas 685, scale 1:1,000,000, 

1 sheet. 

48. Loskot, C. L., Case, H. L., Ill, and Hern, D. 

· G., 1984, Geologic and hydraulic data from 

a test-drilling program in the High Plains 

area of South Dakota, 1979-80: U.S. 

Geological Survey Open-File Report 84-148, 

31 p. 

49. Luckey, R. R., 1984a, Projected effects of 

ground-water development in the southern 

High Plains of Texas and New Mexico: 

American Water Works Association, Dallas, 

TX, June 10-14, 1984, Proceedings, 

p. 1345-1362. 

50. -----1984b, The High Plains regional 

aquifer-flow system simulation of the central and northern High Plains, in 

Whetstone, G. A., ed., Proceedings of the 

Ogallala Aquifer Symposium II: Texas Tech 

University, Lubbock, TX, June 1984, 

p. 48-66. 

51. Luckey, R. R., and Ferrigno, C. F., 1982, A 

data-management system for areal· interpretive data for the High Plains in parts of 

Colorado, Kansas, Nebraska, New Mexico, 

Oklahoma, South Dakota, Texas, and 

Wyoming: U.S. Geological Survey WaterResources Investigations Report 82-4072, 

112 p. 

52. Luckey, R. R., Gutentag, E. D., and Weeks, 

J. B., 1981, Water-level and saturatedthickness changes, predevelopment to 1980, 

in the High Plains aquifer in parts of Colorado, Kansas, Nebraska, New Mexico, 

Oklahoma, South Dakota, Texas, and 

Wyoming: U.S. Geological Survey 

Hydrologic Investigations Atlas 652, scale 

1:2,500,000, 2 sheets. 

53. Luckey, R. R., Heimes, F. J., and Gaggiani, 

N. G., 1980, Calibration and testing of 

selected portable flowmeters for use on large 

irrigation systems: U.S. Geological Survey 

Water-Resources I~1vestigations Report 

80-72, 21 p. 

54. Martinko, E. A., Poracsky, J., Kipp, E. R., 

Krieger, H., and Gunn, K., 1981, Crop 

phenology and Landsat-based irrigated 

lands inventory in the High Plains: 

Lawrence, KS, University of Kansas, Applied Remote Sensing Program Final Report 

NAG 2-57, 129 p. 

55. McAda, D. P., 1984, Projected water-level 

declines in the Ogallala aquifer in Lea 

County, New Mexico: U.S. Geological 
Survey Water-Resources Investigations 

Report 84-4062, 84 p. 

56. Muller, D. A., 1980, Results of surface electrical resistivity surveys: Texas Department 

of Water Resources Report LP-130, 27 p. 

57. Nordstrom, P. L., 1984, Estimation of specific 

yield using drillers' lithologic descriptions, 

in Whetstone, G. A., ed., Proceedings of the 

Ogallala Aquifer Symposium II: Texas Tech 

University, Lubbock, TX, June 1984, 

p. 265-277. 

58. Pabst, M. E., and Stullken, L. E., 1981, 

Altitude and configuration of the water 

table in the High Plains aquifer of Kansas, 

1980: U.S. Geological Survey Open-File 

Report 81-1004, scale 1:500,000, 1 sheet. 

59. 1982a, Altitude and configuration of 

the water table in the High Plains aquifer 

of Kansas, 1960: U.S. Geological Survey 

Open-File Report 82-429, scale 1:500,000 [in 

press]. 

60. 1982b, Altitude and configuration of 

the water table in the High Plains aquifer 

. of Kansas, 1965: U.S. Geological Survey 

Open-File Report 82-449, scale 1:500,000 [in 

press]. 

61. -----1982c, Altitude and configuration of 

the water table in the High Plains aquifer 

of Kansas, 1970: U.S. Geological Survey 

Open-File Report 82-448, scale 1:500,000, 

1 sheet. 

62. Pettijohn, R. A., and Chen, H. H., 1983a, 

Geohydrology of the High Plains aquifer 

system inN ebraska: U.S. Geological Survey 

Water-Resources Investigations Report 

82-502, scale 1:175,000, 3 sheets. 

63. -----1983b, Hydraulic conductivity, 

specific yield, and pumpage-High Plains 

aquifer system, Nebraska: U.S. Geological 

Survey Water-Resources Investigations 

Renort 82-4014. scale 1:175.000. 3 sheets. 

64. -----1984a, Hydrologic analysis of the 

High Plains aquifer system in Box Butte 

County, Nebraska: U.S. Geological Survey 

Water-Resources Investigations Report 

84-4046, 54 p. 

65. -----1984b, Hydrologic characteristics 

and ground-water availability in the High 

Plains aquifer system in Nebraska, in 

Whetstone, G. A., ed., Proceedings of the 

Ogallala Aquifer Symposium II: Texas Tech 

University, Lubbock, TX, June 1984, 

p. 238-264. 

66. Stullken, L. E., and Pabst, M. E., 1985a, 

Altitude and configuration of the water 

table in the High Plains aquifer of Kansas, 

1975: U.S. Geological Survey WaterResources Investigations Report 81-144, 

scale 1:500,000. 

67. ---1985b, Altitude and configuration of 

the water table in the High Plains aquifer 

of Kansas, pre-1950: U.S. Geological Survey 

Open-File Report 82-117, scale 1:500,000, 

1 sheet. 

68. Thelin, G. P., 1984, The High Plains aquifermapping irrigated agriculture using Landsat data, in Whetstone, G. A., ed., Proceedings of the Ogallala Aquifer Symposium 

II: Texas Tech University, Lubbock, TX, 

June 1984, p. 40-4 7. 

69. Thelin, G. P., Johnson, T. L, and Johnson, R. 

A., 1979, Mapping irrigated cropland on the 

High Plains using Landsat, in Deutsch, M., 

Wiesnet, D. R., and Rango, A., eds., Satellite 

hydrology: American Water Resources 

Association Proceedings, Pecora Symposium, 5th, Sioux Falls, SD, p. 715-721. 

70. Watts, K. R., and Stullken, L. E., 1981, 

Generalized configuration of the base of the 

High Plains regional aquifer in Kansas: 

U.S. Geological Survey Open-File Report 

81-344, scale 1:500,000, 1 sheet. 

71. Weeks, J. B., 1978a, High Plains regional 

aquifer-system analysis, in Baird, F. L., ed., 

The multi-faceted water crisis of west Texas: 

Symposium, Lubbock, TX, 1978, Proceedings, Texas Tech University, p. 195-201. 

72. -----1978b, High Plains regional aquifer 

system analysis: in Ground-water Management Districts Association Conference, 5th, 

Amarillo, TX, 1978, Proceedings, p. 13-16. 

73. -----1978c, Plan of study for the High 

Plains regional aquifer-system analysis in 

parts of Colorado, Kansas, Nebraska, New 

Mexico, Oklahoma, South Dakota, Texas, 

and Wyoming: U.S. Geologiclfl Survey 

Water-Resources Investigations Report 

78-70, 28 p. . 

74.-----1979, High Plains regional aquifersystem analysis-progress report: in 

Groundwater Management Districts 

Association Conference, 6th, Colorado 

Springs, CO, 1979, Proceedings, p. 10-13. 

75. 1981, Effects ofpumpage on the High 

Plains aquifer: in Groundwater Management Districts Association Conference, 8tli, 

Lubbock, TX, December 2-4, 1981, Proceedings, p. 97-108. · 

76. Weeks, J. B., and Gutentag, E. D., 1981, 

Bedrock geology, altitude ofbase, and 1980 

47 
48 

saturated thickness of the High Plains 

aquifer in parts of Colorado, Kansas, 

Nebraska, New Mexico, Oklahoma, South 

Dakota, Texas, and Wyoming: U.S. 

Geological Survey Hydrologic Investigations 

Atlas 648, scale 1:2,500,000, 2 sheets. 

77. 1984, The High Plains regional 

aquifer-geohydrology, in Whetstone, G. A., 

ed., Proceedings of the Ogallala Aquifer 

Symposium II: Texas Tech University, Lubbock, TX, June 1984, p. 6-25. 

78. Wright, Bruce, 1980a, Irrigated cropland, 

1978, Curry County, New Mexico: U.S. 

Geological Survey Open-File Report 80-169, 

scale 1:250,000, 1 sheet. 

79. 1980b, Irrigated cropland, 1978, 

Texas County, Oklahoma: U.S. Geological 

Survey Open-File Report 80-170, scale 

1:250,000, 1 sheet. 

80. Wyatt, A. W., Smith, D. D., and McReynolds, 

Don, 1981a, Hydrologic atlas for Armstrong 

County, Texas: High Plains Underground 

Water Conservation District No. 1, Lubbock, 

TX, scale 1:126,720, 4 sheets. 

81. 1981b, Hydrologic atlas for Bailey 

County, Texas: High Plains Underground 

Water Conservation District No. 1, Lubbock, 

TX, scale 1:126,720, 4 sheets. 

82. 1981c, Hydrologic atlas for Castro 

County, Texas: High Plains Underground 

Water Conservation District No. 1, Lubbock, 

TX, scale 1:126,720, 4 sheets. 

83. 1981d, Hydrologic atlas for Cochran 

County, Texas: High Plains Underground 

Water Conservation District No. 1, Lubbock, 

TX, scale 1:126,720, 4 sheets. 

84. ----1981e, Hydrologic atlas for Crosby 

County, Texas: High Plains Underground 

Water Conservation District No. 1, Lubbock, 

TX, scale 1:126,720, 4 sheets. 

85. 1981f, Hydrologic atlas for Deaf 

Smith County, Texas: High Plains 

Underground Water Conservation District 

No. 1, Lubbock, TX, scale 1:126,720, 

4 sheets. 

86. ----1981g, Hydrologic atlas for Floyd 

County, Texas: High Plains Underground 

Water Conservation District No. 1, Lubbock, 

TX, scale 1:126,720, 4 sheets. 

87. 1981h, Hydrologic atlas for Hale 

County, Texas: High Plains Underground 

Water Conservation District No. 1, Lubbock, 

TX, scale 1:"126,720, 4 sheets. 

88. 198-li, Hydrologic atlas for Hockley 

Couhty, Texas: High Plains Underground 

Water Conservation District No. 1, Lubbock, 

TX, scale 1:126,720, 4 sheets. 

89. 1981j, Hydrologic atlas for Lamb 

County, Texas: High Plains Underground 

Water Conservation District No. 1, Lubbock, 

TX, scale 1:126,720, 4 sheets. 

90. 1981k, Hydrologic atlas for Lubbock 

County, Texas: High Plains Underground 

Water Conservation District No. 1, Lubbock, 

TX, scale 1:126,720, 4 sheets. 

91. 19811, Hydrologic atlas for Lynn 

County, Texas: High Plains Underground 

Water Conservation District No. 1, Lubbock, 

TX, scale 1:126,720, 4 sheets. 

92. ---1981m, Hydrologic atlas for Parmer 

County, Texas: High Plains Underground 

Water Conservation District No. 1, Lubbock, 

TX, scale 1:126,720, 4 sheets. 

93. 1981n, Hydrologic atlas for Potter 

County, Texas: High Plains Underground 

Water Conservation District No. 1, Lubbock, 

TX, scale 1:126,720, 4 sheets. 

94. -----1981o, Hydrologic atlas for Randall 

County, Texas: High Plains Underground 

Water Conservation District No. 1, Lubbock, 

TX, scale 1:126,720, 4 sheets. 

REFERENCES CITED 

Gutentag, E. D., Heimes, F. J., Krothe, N. C., Luckey, R. R., 

and Weeks, J. B., 1984, Geohydrology of the High Plains 

aquifer in parts of Colorado, Kansas, Nebraska, N~w 

Mexico, Oklahoma, South Dakota, Texas, and Wyoming: U.S. Geological Survey Professional Paper 1400-B, 

63 p. 

Gutentag, E. D., and Weeks, J. B., 1980, Water table in the 

High Plains aquifer in 1978 in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, 

Texas, and Wyoming: U.S. Geological Survey 

Hydrologic Investigations Atlas 642, scale 1:2,500,000, 

1 sheet. 

Heimes, F. J., and Luckey, R. R., 1980, Evaluating methods 

for detel"Jilining water use in the High Plains in parts 

of Colorado, Kansas, Nebraska, New Mexico, 

Oklahoma, South Dakota, Texas, Wyoming; 1979: U.S. 

Geological Survey Water-Resources Investigations 

Report 80-111, 118 p. 

---1982, Method for estimating historical irrigation requirements from ground water in the High Plains 

aquifer in parts of Colorado, Kansas, Nebraska, New 

Mexico, Oklahoma, South Dakota, Texas, and Wyoming: U.S. Geological Survey Water-Resources Investigations Report 82-40, 64 p. 

---1983, Estimating 1980 ground-water pumpage for irrigation on the High Plains in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, 

Texas, and Wyoming: U.S. Geological Survey WaterResources Investigations Report 83-4123, 36 p. 

Krothe, N.C., Oliver, J. W., and Weeks, J. B., 1982, Dissolved 

solids and sodium in water from the High Plains aquifer 

in parts of Colorado, Kansas, Nebraska, New Mexico, 

Oklahoma, South Dakota, Texas, and Wyoming: U.S. 

Geological Survey Hydrologic Investigations Atlas 658, 

scale 1:2,500,000, 2 sheets. 
Luckey, R. R., and Ferrigno, C. F., 1982, A data-management 

system for areal interpretive data for the High Plains 

in parts of Colorado, Kansas, Nebraska, New Mexico, 

Oklahoma, South Dakota, Texas, and Wyoming: U.S. 

Geological Survey Water-Resources Investigations 

Report 82-4072, 112 p. 

Luckey, R. R., Gutentag, E. D., Heimes, F. J., and Weeks, J. 

B., 1985, Digital simulation of ground-water flow in the 

High Plains aquifer in parts of Colorado, Kansas, 

Nebraska, New Mexico, Oklahoma, South Dakota, 

Texas, and Wyoming: U.S. Geological Survey Professional Paper 1400-D, [in press]. 

Luckey, R. R., Gutentag, E. D., and Weeks, J. B., 1981, Waterlevel and saturated-thickness changes, predevelopment 

to 1980, in the High Plains aquifer in parts of Colorado, 

Kansas, Nebraska, New Mexico, Oklahoma, South 

Dakota, Texas, and Wyoming: U.S. Geological Survey 

Hydrologic Investigations Atlas 652, scale 1:2,500,000, 

2 sheets. 

Luckey, R. R., Heimes, F. J., and Gaggiani, N. G., 1980, 

Calibration and testing of selected portable flowmeters 

for use on large irrigation systems: U.S. Geological 

Survey Water-Resources Investigations Report 80-72, 

21 p. 

U.S. Department of Agriculture, 1967, Irrigation water requirements: Soil Conservation Service, Engineering 

Division, Technical Release no. 21, 88 p. 

U.S. Department of Commerce, 1949-78, Census of agriculture: 

Bureau of the Census, agricultural data for 1949, 1954, 

1959, 1964, 1969, 1974, and 1978 for Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, 

Texas, and Wyoming. 

Weeks, J. B., and Gutentag, E. D., 1981, Bedrock geology, 

altitude of base, and 1980 saturated thickness of the 

High Plains aquifer in parts of Colorado, Kansas, 

Nebraska, New Mexico, Oklahoma, South Dakota, 

Texas, and Wyoming: U.S. Geological Survey 

Hydrologic Investigations Atlas 648, scale 1:2,500,000, 

2 sheets. 

49 
50 

COMPLETED PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

NORTHERN GREAT PLAINS REGIONAL AQUIFER-SYSTEM STUDY 

By George A. Dinwiddie, Reston, Virginia, and Joe S. Downey, Denver, Colorado 

INTRODUCTION 

The study area of the Northern Great Plains 

regional aquifer system is about 250,000 mi2 and 

includes North Dakota and parts of South 

Dakota, Montana, Wyoming, and Nebraska (fig. 

21). It is bounded on the west by the central and 

northern Rocky Mountains, on the east by the 

Red River of the North, on the south by the cen-

.tral High Plains, and on the north by the United 

States-Canadian border. The Northern Great 

Plains mostly is underlain by sandstone, shale, 

and some evaporite deposits. The principal 

aquifers generally crop out along the flanks of the 

Williston and Powder River basins and along 

other major structural features (fig. 22). 

Ground water generally flows northeastward 

across the study area. The source of recharge is 

precipitation in topographically high areas near 

the Black Hills uplift, Bighorn Mountains, the 

eastern flank of the northern Rocky Mountains, 

and other major structurally high areas. Ground 

water mostly discharges into topographically low 

areas of eastern North Dakota and South Dakota 

and occurs as outflow into Canada. Some groundwater discharge also occurs as diffuse upward 

leakage into overlying aquifers. 

Flow characteristics vary significantly between the dominantly carbonate aquifers of 

Paleozoic age (such as the Madison Limestone) 

and the dominantly clastic aquifers of Mesozoic 

age (such as the Dakota Sandstone) and Cenozoic 

age. Potential for flow moving among aquifers exists near recharge and discharge areas and in the 

interior part of the study area, where hydraulic 

heads va.rY significantly between aquifers. 

Development of ground-water supplies in the 

Northern Great Plains will be needed for the 

growth of energy resources, power generation, industrial expansion, increasing irrigation, and 

domestic and municipal water use. Streamflow 

has historically satisfied many of the water needs; 

however, surface water is fully appropriated in 

much of the area and is not always a dependable 

source because streamflows are extremely 

variable. Long-term, large-scale water needs require the development of ground water. 

The Madison Limestone aquifer study, a 

federally funded program initiated in 1975, was 

designed to address the problems of water supplies associated with development of coal 

resources and the proposed coal-slurry pipelines 

in the Fort Union coal region (fig. 21). The Northern Great Plains regional aquifer system study, 

started in 1978 for the purpose of studying the 

aquifer system regionally underlying the Northern Great Plains; subsequently, the Madison 

Limestone aquifer study was merged into the 

Northern Great Plains regional aquifer system 

study which was completed in 1982. Significant 

results of the study are briefly discussed below. 

GEOHYDROLOGY AND MODEL SIMULATION 

The Northern Great Plains aquifer system is 

one of the largest confined systems in the United 

States, extending more than 600 miles from 

mountainous recharge areas in Montana, Wyoming, and South Dakota to discharge areas in 

eastern Dakotas and the Canadian Province of 

Manitoba. Five major aquifer systems were identified in the Northern Great Plains. In descending 

order, they are: the Upper Cretaceous aquifer 

system which mostly includes sediments of Late 

Cretaceous age but also includes the surficial 

glacial and Tertiary sediments; the Lower 

Cretaceous aquifer system; the Pennsylvanian 
45" 

---

IDAHO 

I 

I 

I 

I 

I 

I -------: 

110 " 105" 100" 

" Great I 1 p~ ~ ~ 

-- ---r---- ____ __ j_ ___ l Lake I 

1 SCALE 1:10,000,000 I 

40" UTAH 0 100 200 MILES 

0 100 200 KILOMETERS 

t------- - KANSAS 

EXPLANATION 

~}i} ~~ FORT UNION COAL REGION 

TEST WELL DRILLED BY THE U.S. GEOLOGICAL SURVEY 

• Well penetrating the Madison aquifer 

.A. Well penetrating the Pierre shale 

APPROXIMATE STUDY AREA OF THE NORTHERN GREAT PLAINS REGIONAL AQUIFER SYSTEM 

Figure 21.- Study area of the northern Great Plains regional aquifer system. 

aquifer system; the Mississipian (Madison 

Limestone) aquifer system; and the CambrianOrdovician aquifer system. The relation between 

the aquifer systems is shown in figure 23. All 

aquifer systems crop out and receive recharge in 

the highlands in the western part of the study 

area. Recharge also occurs in outcrop areas 

around the Black Hills uplift in South Dakota. 

The major recharge area for the Mississippian 

aquifer system (Madison Limestone) in the Black 

Hills uplift area is a plateau on the west flank 

of the Black Hills uplift where the limestone contains many caves and sinkholes. The Wyoming 

State Engineer's Office (1974) states that the 

recharge in this plateau area (187 ,000 acres) is 

about 6.8 in./yr or about 146 ft 3/s. Virtually all 

streams lose a part of flow as they cross the 

aquifer-system outcrop areas (Swenson, 1968; 

Wyoming State Engineer's Office, 1974). 

Streamflow measurements on several 

streams located at the east side of the Black Hills 

uplift indicate that as much as 10 ft 3/s of flow is 

lost from streams crossing the outcrop of the 

Mississippian (Madison Limestone) aquifer 

system (Swenson, 1968). Prior to sealing stream 

channels in 1937, about 100 ft 3/s of estimated 

streamflow loss was reported by Powell (1940). 

Based on similar aquifer lithology and degree of 

51 
52 

weathering, it is reasonable to assume that most 

streams at the western mountainous areas, such 

as the Bighorn Mountains, could lose nearly the 

same amount of flow, 100 ft3/s, as the streams 

cross the comparable outcrop areas of rocks of 

Paleozoic age. 

Recharge enters the Lower Cretaceous 

aquifer system either by precipitation in the outcrop areas or by upward leakage from underlying 

aquifers. Miller and Rahn (1974) reported that 

about 0.8 in./yr of water was recharged in outcrop 

,.. \ 

45° \ 

40° 

110° 105° 

' 

areas of Lower Cretaceous sandstone near the 

Black Hills uplift. Assuming an outcrop area for 

the Lower Cretaceous aquifer system of about 334 

mi2 (H. L. Case, U.S. ~ological Survey, written 

commun., 1982), approximately 20 ft 3/s of water 

could recharge the Lower Cretaceous aquifer 

system. Recharge from streamflow loss probably 

is small in the Black Hills uplift area. Brown 

(1944) noted that no loss in streamflow could be. 

detected from gaged streams that cross the outcrop of the Cretaceous rocks, in contrast to water 

100° 

UTAH 0 100 200 MILES t-- ------------- 0 100 200 KILOMETERS KANSAS 

EXPLANATION 

MOUNTAIN RANGES OF THE EASTERN FLANK OF THE NORTHERN ROCKY MOUNTAINS 

Little Rocky 6 Pryor 11 Uinta 

2 Little Belt 7 Bighorn 12 Sierra Madre 

3 Judith 8 Absaroka 13 Medicine Bow 

4 Big Snowy 9 Owl Creek 14 Laramie 

5 Beartooth 10 Wind River 

APPROXIMATE STUDY AREA OF THE NORTHERN 

GREAT PLAINS REGIONAL AQUIFER SYSTEM 

Figure 22. -Structural and physiographic features of the northern Great Plains (modified from Peterson, 1981). 
losses to the Paleozoic rocks; therefore, most of 

the recharge ofthe Cretaceous aquifer system probably is from the underlying Paleozoic rocks. 

Although surface-water data indicate that 

large quantities of water enter the five aquifer 

systems along outcrop areas in the western 

highlands, not all this water recharges the deep, 

regional flow system and flows eastward to 

discharge areas. A large part of the recharged 

water discharges within short distances through 

springs and seeps along the flanks of the mountains (Swenson, 1968; Rahn and Gries, 1973; and 

Hodson, 1974) the remainder eventually enters 

the regional flow system. 

On the basis of simulation, the conceptualized 

flow pattern of the five aquifer systems is shown 

in figures 24-30. Recharge rates shown in figures 

25-29 are of the water that recharges the deep 

regional flow system. Water in the Upper 

FEET A 

6000 

3000 

Sea level 

-3000 

Bighorn 

Mountains 

-6000 H 

-9000 

-12,000 

Basement rocks 

(Precambrian) 

VERTICAL SCALE GREATLY EXAGGERATED 

Cretaceous aquifer discharges toward the 

Missouri River or upward to the overlying surficial aquifers (figs. 24). Discharge from the Lower 

Cretaceous aquifer system is mainly upward to 

overlying aquifers in eastern North Dakota and 

South Dakota and to the subcrop of the Lower 

Cretaceous aquifer system in the glacial Lake 

Agassiz basin of North Dakota (figs. 25 and 29). 

Discharge from aquifer systems consisting of 

rocks of Paleozoic age-the Pennsylvanian aquifer 

system, the Mississippian (Madison Limestone) 

aquifer system, and the Cambrian-Ordovician 

aquifer system-principally is upward to the 

overlying aquifers and to the Red River of the 

North. However, in eastern North Dakota, 

ground water in the Pennsylvanian aquifer 

system flows downward into the CambrianOrdovician aquifer system and then discharges 

to the Red River of the North or to land surface 

A' 

0 50 100 MILES 

.---r--1 

0 50 100 KILOMETERS 

EXPLANATION 

AQUIFERS-· AQ Indicates aquifers, number Indicates position of an 

aquifer. 1 is the lowest 

CONFINING UNITS-· TK represents confining unit, number Indicates 

position of confining unit. 1 Is the lowest 

FAULT-- Arrows Indicate direction of movement 

Figure 23.-Diagrammatic cross section from ground-water recharge area to discharge 

area showing relation of aquifers and confining units underlying the northern Great 

Plains, from south-central Montana to east North Dakota. 

53 
54 

45" 

40" 

115" 

ALBERTA 

I 

I 

110" 105" 

/ 

I 

' I 

I 

\ 

ONTARIO 

IDAHO I -- ____.-

------._; 

Gr~:;, I I Pt<>fle 

Lake 1 I 

----;--------------l 1 SCALE 1.10,000,000 

UTAH I 

I 0 100 200 MILES r--------

0 100 200 KILOMETERS 

EXPLANATION 

APPROXIMATE LIMIT OF UPPER CRETACEOUS ROCKS 

KANSAS 

:::::>- GENERAL DIRECTION OF GROUND-WATER FLOW 

APPROXIMATE STUDY AREA OF THE NORTHERN GREAT PLAINS' REGIONAL AQUIFER SYSTEM 

NOTE: Recharge to the aquifer is generally in outcrop areas and from shallow glacial 

deposits. Discharge from the aquifer is to rivers and streams, by evapotranspiration, 

and through wells 

Figure 24.- Regional flow in the Upper Cretaceous aquifer system (A05) underlying the northern Great Plains. 
50" 

45 

40" 

ALBERTA 

IDAHO 

I 

I 

I 

UTAH 0 100 200 MILES 

0 100 200 KILOMETERS 

EXPLANATION 

RECHARGE AREA-- Generally areas of groundwater recharge. Numbers represent rate 

of recharge in cubic feet per second 

Recharge in highlands 

, 

, 

\ 

I 

I oNTARIO 

\ 

KANSAS 

DISCHARGE AREA-- Approximate areas of principal 

ground-water discharge. Numbers represent 

rate of discharge in cubic feet per second 

Upward leakage to overlying glacial deposits 

~ 

~ 

Recharge from underlying Mississippian 

and Pennsylvanian aquifers 

APPROXIMATE LIMIT OF LOWER 

CRETACEOUS ROCKS 

Upward leakage to overlying Cretaceous 

tP~tN aqu ifers and through wells 

:;;:> GENERAL DIRECTION OF GROUND-WATER FLOW 

• APPROXIMATE STUDY AREA OF THE NORTHERN 

GREAT PLAINS REGIONAL AQUIFER SYSTEM 

NOTE: Generally there is upward leakage from the 

Lower Cretaceous aquifer to overlying aquifers 

at a rate of approximately 75 cubic feet per 

second distributed evenly throughout the area 

Figure 25.- Regional flow in the Lower Cretaceous aquifer system (A04) underlying the northern Great Plains. 

55 
56 

45' 

40' 

115' 110' 105' 

ALBERTA 

IDAHO 

UTAH 0 100 200 MILES 

0 100 200 KILOMETERS 

EXPLANATION 

RECHARGE AREA-- Generally areas of groundwater recharge. Numbers represent rate 

of recharge in cubic feet per second 

/ 

/ 

\ 

I 

I 

\ 

ONTARIO 

NEBRASKA 

KANSAS 

DISCHARGE AREA-- Approximate areas of principal 

ground-water discharge. Numbers represent 

rate of discharge in cubic feet per second 

~ Recharge in highlands [.{f.)M Discharge to Lower Cretaceous aquifers 

APPROXIMATE STUDY AREA OF THE NORTHERN 

GREAT PLAINS REGIONAL AQUIFER SYSTEM 

GENERAL DIRECTION OF GROUND-WATER 

FLOW 

APPROXIMATE LIMIT OF PENNSYLVANIAN 

AND PERMIAN ROCKS 

GEOLOGIC STRUCTURE-- Locations of paleostruclures that may affect the flow of ground water 

BRINE AREA-- Areas within which the total dissolved 

solids in ground water is greater than 100,000 

milligrams per liter 

Figure 26.- Regional flow in the Pennsylvanian (lquifer system (AQ3) underlying the northern Great Plains. 
45 ' 

40 ' 

115' 

ALBERTA 

IDAHO 

--------; Great I Salt 

Lake J 

I 

I 

I 

11 0' 

-- ---.-------

UTAH 0 100 

0 100 

105' 

200 MILES 

200 KILOMETERS 

NEBRASKA 

\ 

/ 

/ 

I 

I 

\ 

oNTARIO 

I i--------------- KANSAS 

EXPLANATION 

RECHARGE AREA-- Generally areas of ground- DISCHARGE AREA-- Approximate areas of principal 

ground-water discharge. Numbers represent 

rate of discharge in cubic feet per second 

water recharge. Numbers represent rate 

of recharge in cubic feet per second 

m Recharge in highlands 

BRINE AREA-- Areas within which the total 

dissolved solids in ground water is greater 

than 100,000 milligrams per liter 

GENERAL DIRECTION OF GROUND-WATER FLOW 

APPROXIMATE STUDY AREA OF THE NORTHERN 

GREAT PLAINS REGIONAL AQUIFER SYSTEM 

F:?z J Discharge to Lower Cretaceous aquifers 

~ Discharge to underlying Cambrian and 

~ Ordovician aquifers 

GEOLOGIC STRUCTURE-- Locations of paleostructures that may affect the flow of ground water 

APPROXIMATE LIMIT OF MADISON LIMESTONE 

Figure 27.-Regional flow in the Mississippian (Madison Limestone) aquifer system (A02) underlying the northern 

Great Plains. 

57 
58 

45' 

40' 

ALBERTA 

IDAHO 

I 

I 

I 

UTAH 0 

0 

105' 

100 200 MILES 

100 200 KILOMETERS 

EXPLANATION 

RECHARGE AREA-- Generally areas of groundwater recharge. Numbers represent rate 

of recharge in cubic feet per second 

/ 

/ 

\ 

I 

I ONTARIO 

\ 

I r--------

KANSAS 

DISCHARGE AREA-- Approximate areas of principal 

ground-water discharge. Numbers represent 

rate of discharge in cubic feet per second 

!£~ Recharge in highlands ~ Discharge to land surface 

~. t:?.:9.:.r_;~ Recharge from aquifers overlying Mississippian 

~ BRINE AREA·· Areas within which the total 

~ dissolved solids in ground water is greater 

than 100,000 milligrams per liter 

.. 

APPROXIMATE STUDY AREA OF THE NORTHERN 

GREAT PLAINS REGIONAL AQUIFER SYSTEM 

GEOLOGIC STRUCTURE·· Locations of paleostructures that may affect the flow of ground-water 

::;;::> GENERAL DIRECTION OF GROUND WATER FLOW 

APPROXIMATE LIMIT OF CAMBRIANORDOVICIAN ROCKS 

APPROXIMATE LIMIT OF ORDOVICIAN ROCKS 

Figure 28.- Regional flow in the Cambrian-Ordovician aquifer system (AQ1) underlying the northern Great Plains. 

/ 
through springs where aquifer systems consisting 

of rocks of Paleozoic age crop out. 

Because of the slow rate of movement of 

ground water indicated by model simulation (figs. 

31 and 32) and the short length of time (12,000 

to 14,000 years) since ice covered southern 

Manitoba of Canada, it is possible that the water 

being discharged from the Paleozoic rocks 

through springs is a mixture of brine from the 

deeper part of the aquifer systems and glacial 

meltwater that recharged the aquifer systems 

while it was covered by glacial ice. The range in 

concentrations of dissolved solids indicates that 

the water may be a mixture of three flow components: (1) flow from the brine area, (2) water 

FEET A 

6000 

3000 

Sea level 

-3000 

-6000 

-9000 

-12,000 

NOTE: Ground water leaves the area through the lower Cretaceous (AQ4) aquifer at a rate of 20 cubic feet per second 

Basement rocks 

(Precambrian) 

VERTICAL SCALE GREATLY EXAGGERATED 

recharged from the Pleistocene glacial ice, and (3) 

freshwater flowing from the south along a flow 

path from the Black Hills uplift (fig. 22). Van 

Everdingen (1968) estimated that about 0.1 ft 3/s 

of water having concentrations of dissolved solids 

ranging from 29,000 to 63,000 milligrams per 

liter (mg/l) was discharging from springs along 

the outcrop of the Paleozoic rocks. The dominant 

ions are sodium and chloride. 

A body of brine is located at the eastern flank 

of the Williston basin (figs. 22, 26-28 and 33) 

where movement of ground water is sluggish (figs. 

31 and 32). Three hypotheses concerning movement of ground water and the brine are: 

(1) The brine is static. 

A' 

Pennsylvanian-Permian 

0 50 100 MILES 

,--,---, 

0 50 100 KILOMETERS 

EXPLANATION 

--

(+10) 

(- 10) 

AQUIFERS --AQ Indicates aquifers, number Indicates position of an 

aquifer. 1 is the lowest 

CONFINING UNITS -· TK represents confining unit, number Indicates 

position of confining unit 1 Is the lowest 

DIRECTION OF GROUND-WATER FLOW 

RECHARGE TO THE AQUIFER--Number indicates rate in cubic feet 

per second 

DISCHARGE FROM THE AQUIFER-· Number indicates rate in cubic feet 

per second 

FAULT·· Arrows indicate direction of movement 

Figure 29.- Generalized hydrogeologic cross section showing general ground-water 

flow patterns in the northern Great Plains regional aquifer system. 

59 
60 

(2) The brine is a very slow-moving segment of 

the regional ground-water flow. 

(3) The brine is moving as part of the adjustment of the flow system to the melting of 

the Pleistocene ice. 

The first hypothesis is similar to that described by Hubbert (1969) in which freshwater 

flowing through a synclinal structure comes into 

FEET B 3000 

2000 

1000 

Sealevel 

-1000 

-2000 

contact with static, dense brine along a sharp 

fluid interface. Hubbert shows that a body of 

saline water under these conditions does not lie 

uniformly in the deepest part of the structure but, 

rather, is displaced upward along the base of the 

outflow flank. That is, while the inflow flank is 

occupied by moving freshwater, the outflow flank 

contains static brine in the lower part of the 

B' 

Missouri River 

0 25 SOMILES 

0 25 50 KILOMETERS 

EXPLANATION 

AQUIFERS 

__.. DIRECTION OF GROUNO.WATER MOVEMENT 

GEOLOGIC CONTACt .. Dashed where doubtful. 

Figure 30.-Generalized hydrogeologic cross section showing ground-water discharge from aquifers consisting of rocks 

of Paleozoic to Mesozoic age underlying the northern Great Plains (modified from Swenson, 1968). Line of section shown 

in figure 22. 
aquifer and moving freshwater above. The flow 

of freshwater in the Williston basin is around the 

dense brine area as well as above, reflecting that 

the structure is actually a basin rather than a 

simple syncline. The flow above the brine apparently is by upward leakage to the overlying 

aquifers rather than within the upper part of the 

Mississippian aquifer system. However, simula-

. tions of the flow system containing variabledensity fluids indicate that the brine in the 

Mississippian aquifer system is not completely 

static as assumed in Hubbert's hypothesis. 

Simulation shows that consistent flow with 

low velocity flows eastward and northeastward, 

through the brine body, in both the CambrianOrdovician and Mississippian aquifer systems. 

This suggests that a small component of the 

regional flow actually moves directly across the 

Williston basin from west to east, through the 

areas containing the brine, thus supporting the 

second hypothesis. This interpretation probably 

explains the origin of the brine, which can be attributed to dissolution of salt from beds of halite 

as ground water flows through the Williston 

basin, as described by Grossman (1968). The process of dissolution of halite is enhanced by increasing water temperature with depth. Water 

having higher salinity usually is found in regions 

of high temperature. Reduction in salinity in updip areas on the eastern flank of the Williston 

basin is presumably due at least in part to 

precipitation of halite associated with cooler 

temperature, although dilution by freshwater undoubtedly also is a factor. Precipitation of halite 

reduces permeability gradually over a long period 

of time and tends to decrease the ground-water 

flow velocity. Although some flow exists, flow 

velocity within the Williston brine area appears 

to be very low and nearly static. Flow velocity is 

extremely low relative to those elsewhere in the 

aquifer system, and most of the freshwater flow 

seems to be deflected around the body of the brine 

to the north or south or discharges upward 

through the confining units into overlying 

aquifers. Thus, both the hydraulics and the density distribution seem to be fairly close to those 

that would be expected in a system containing a 

body of static brine. 

Concerning the third hypothesis regarding 

brine movement, the brine would have been set 

in motion at the end of the Pleistocene glaciation, 

seeking a new equilibrium with recharge and 

discharge. This readjustment could still be in progress, thus contributing to the apparent movement of the brine. However, flow velocity computed from simulation suggests that a simple flow 

across the Williston basin is more likely than the 

adjustment of the brine body to hydrologic 

changes of the Pleistocene glaciation. 

In summary, the second hypothesis, that the 

brine represents a sluggish segment of the 

regional ground-water flow across the Williston 

basin, seems to agree best with simulations and 

field data. The origin of the brine appears to have 

been the dissolution of halite. As the density of 

the brine increases, freshwater is diverted around 

the brine to the north and south or discharges upward into overlying aquifers. Although the second 

hypothesis seems reasonable, the other 

·hypotheses probably also can explain the field 

situation to some degree. The configuration of the 

brine on the outflow side of the Williston basin, 

and the generally low velocity, approximate the 

static conditions of the brine described by Hubbert (1969), even though the brine is not thought 

to be completely static. Distribution of water having high salinity may shift slightly in response 

to hydrologic changes at the end of the Pleistocene 

glaciation. 

Saline water is found also in other parts of 

the study area-for example, in deeper parts of 

the Powder River basin-although not at the concentrations encountered in the Williston basin. 

However, similar processes presumably control 

the distribution and movement of the saline 

water. 

Because the highland recharge areas were 

not covered by major ice during the Pleistocene 

(ice was generally limited to the area north and 

east of the Missouri River), recharge continued 

to be available to the underlying aquifers. 

Therefore, dissolution of halite along the western 

edge of the Williston basin probably existed 

during the glaciation period. Because of the short 

geologic time periods and low flow velocity, the 

brine resulting from dissolution of halite probably 

would not leave the hydrologic system but would 

tend to remain in the same general location 

shown in figures 27 and 28. 

It has been noted that recharge and discharge 

may have been significantly different during the 

Pleistocene glaciation. Such hydrologic variation 

may affect the regional ground-water flow pattern. Evidence of the presence of water at the base 

of the continental ice has been discussed by Robin 

(1955), McGinnis (1968), Weertman (1972), and 

Downey (1983). The water is the result of melting 

at the base of the ice because of geothermal and 

61 
&2 

45 

40" 

11 

ALBERTA 

I 

~---~NADA UN 

IDAHO 

I 

I 

I 

UTAH 

110" 

0 100 

0 100 

SIMULATED RATES OF MOVEMENT OF 

GROUND-WATER IN FEET PER YEAR 

~ 50to75 

UIIIl]] 10 to 20 

~ 2to10 

[[I] Less than 2 

; 

; 

\ 

I 

I 

\ 

ONTARIO 

200 MILES 

200 KILOMETERS KANSAS 

EXPLANATION 

APPROXIMATE LIMIT OF MADISON LIMESTONE 

• HIGHLAND RECHARGE AREA 

APPROXIMATE STUDY AREA OF THE NORTHERN 

GREAT PLAINS REGIONAL AQUIFER SYSTEM 

Figure 31.-Simulated rates of movement of ground water in the Mississippian (Madison Limestone) aquifer system 

(AQ2) underlying the northern Great Plains. 
frictional heat. McGinnis (1968) estimated that 

the heat available to a temperate ice sheet from 

the geothermal and frictional heat could produce 

about 0.32 ftNyr of meltwater per square foot of 

ice surface. During the late Pleistocene, the continental ice covered an area of about 121,500 mi2 

in the Northern Great Plains. Based on 0.32 ft3/yr 

per square foot of ice surface, about 7 mi3/yr of 

water were available to recharge the underlying 

aquifers. The water would be under significant 

hydrostatic pressure from the weight of the 

overlying ice. 

Widespread recharge to aquifers must have 

existed in the areas covered by the continental 

ice. The configuration of ice over the Northern 

Great Plains varied during the Pleistocene (Flint, 

1971), and the resulting distribution of recharge 

similarly would also have varied. Highlands to 

the west of the study area that form the present 

recharge areas would presumably also be the 

recharge areas prior to glaciation, as well as during glacial and interglacial periods of the 

Pleistocene. However, during periods of strong 

glacial advance, recharge would also occur over 

the northern and eastern parts of the study area. 

The regional ground-water flow under these conditions must have been to the south toward the 

only available discharge areas. With successive 

retreats and advances of the continental ice, directions of regional ground-water flow probably 

varied accordingly, generating a complex history 

of ground-water movement. However, dissolution 

of halite in the deeper parts of the Williston basin 

must have occurred throughout the flow history, 

and velocity of ground-water movement in the 

areas of brine accumulation must have been low 

regardless of the variation of the flow directions. 

Hypothetical calculation shows that repeated 

changes in flow directions would probably have 

no major effects on the location of the highsalinity water. In terms of the deep brine, the 

glacial changes probably caused some minor transient disturbances but no major redistributions 

of the brine. 

In summary, the flow pattern prior to glaciation was presumably similar to that at present, 

sustained by recharge in highlands to the west. 

Glaciation produced repeated variation of flow 

directions, but, in general, the glaciation did not 

cause major changes in distribution of the brine. 

The Cambrian-Ordovician aquifer system, 

like the Mississippian (Madison Limestone) 

aquifer system, contains dense brine on the 

eastern flank of the Williston basin (fig. 27) and 

has freshwater flowing around the brine to the 

northeast. The Cambrian-Ordovician aquifer 

system apparently discharges partly to a number 

of saline lakes in eastern North Dakota. The component of flow to the north and east of the 

Williston basin is, accordingly, larger than in the 

Mississippian (Madison Limestone) aquifer 

system. The hypothesis of discharge to saline 

lakes is supported by several factors. The lakes 

lie in the eastern discharge area of the CambrianOrdovician aquifer system and are associated 

with depressions that overlie deposits of fine sand 

and gravel (fig. 34). The origin of these lake 

depressions has been attributed to artesian water 

discharging from deep aquifer systems (Laird, 

1944). A supporting hypothesis (Downey, 1969, p. 

12) suggests that, during Pleistocene glaciation, 

meltwater from the base of the ice sheet (Gow and 

others 1968; McGinnis, 1968) was forced into the 

underlying Mesozoic-Paleozoic aquifer systems by 

hydrostatic pressure. Upon deglaciation, the 

hydrostatic pressure was removed, allowing large 

quantities of water to move rapidly out of the 

systems. This rapid movement of water through 

overlying sediments resulted in erosion of the 

overlying sediments, forming the depressions in 

which the lakes exist today. 

Geologic evidence and water chemistry suggest that these lakes now function as drains for 

the regional ground-water flow system. Test 

drilling indicates that thick deposits of glacial 

sand and gravel underlie the depressions and are 

hydraulically connected with the underlying 

Paleozoic aquifer systems (Downey, 1973). 

Chemical analyses of water samples taken from 

the test holes and lakes (Downey, 1971) indicate 

a chemical similarity to the water taken from the 

Cambrian-Ordovician aquifer system. These 

analyses indicate that the water is able to move 

. upward from the Paleozoic aquifer systems 

through the glacial sand and gravel deposits to 

discharge points at bottoms of the lakes. 

Vertical leakage through confining units are 

major contributors to ground-water discharge. 

Leakage occurs both through the confining units 

and along fractures associated with lineaments 

in the confining units (Weimer and others, 1982). 

Confining units are not present everywhere, 

having been removed by erosion or absent 

because of nondeposition. In those areas where a 

confining unit is absent, such as in eastern South 

Dakota, good hydraulic connection exists between 

aquifer systems, and one aquifer system may 

discharge to an adjoining aquifer system at a rate 

63 
64 

40" 

1 • 

ALBERTA 

I 

~---~NADA UNIT r. ~:;;7~-::c:- -- ,.

IDAHO 

--------; 

I 

I 

I 

/ 

/ 

\ 

I 

I 

\ 

oNTARIO 

__ .---

i\r,1}:./____ i 

\j ;----- ------l SCALE 1:10,000,000 1 

UTAH 0 100 

0 100 

SIMULATED RATES OF MOVEMENT OF 

GROUND-WATER IN FEET PER YEAR 

-

Greater ITIIIJJ 10 to 20 than 75 

- 50 to 75 ~ 2 to 10 

~ 20 to 50 g Less 

than 2 

200 MILES 

200 KILOMETERS 

EXPLANATION 

-

-

I r-------

1 KANSAS 

HIGHLAND RECHARGE AREA 

APPROXIMATE STUDY AREA OF THE NORTHERN 

GREAT PLAINS REGIONAL AQUIFER SYSTEM 

Figure 32.-Simulated rates of movement of ground water in the Cambrian-Ordovician aquifer system (AQ1) underlying the northern Great Plains. 
FEET 

1000 

800 

400 

200 

Sea level 

c 

FEET A 

6000 

3000 

Sea level 

-3000 

-6000 

- POOO 

-12,000 

MONTANA 

Basement rocks 

(Precambrian) 

A' 

NORTH DAKOTA 

VERTICAL SCALE GREATLY EXAGGERATED 0 50 100MILES 

- ,--,---, 

0 50 100 KILOMETERS 

EXPLANATION 

AREAS OF BRINE·· Based on concentrations of total dissolved solids 

greater than 100,000 milligrams per liter 

FAULT·· Arrows indicate direction of movement 

Figure 33.- Diagrammatic cross section showing general altitudes of brine in the Williston 

basin of the northern Great Plains. Line of section, shown in figure 22. 

VERTICAL SCALE GREATLY EXAGGERATED 0 

0 2.5 5 KILOMETERS 

EXPLANATION 

f:#Jt\:W/.l CAMBRIAN-ORDOVICIAN AQUIFER 

_. DIRECTION OF GROUND-WATER MOVEMENT 

C' 

Figure 34.-Generalized hydrogeologic cross section showing discharge area of the Cambrian-Ordovician aquifer system 

(AQ1) underlying the northern Great Plains (cross section modified from Downey, 1978). Line of section, shown in 

figure 22. 

65 
66 

that is dependent on head differences between the 

two aquifers and their vertical hydraulic conductivities. Where a confining unit is thick and unfractured, leakage through the confining unit will 

be low. Leakage along fractures is dependent on 

the degree of fracturing, cross-sectional area of 

the fractures, and interconnection among 

fractures. 

Geochemical facies maps for the CambrianOrdovician, Mississippian, Pennsylvanian, and 

Lower Cretaceous aquifer systems have been used 

to indicate areas where upward leakage is occurring. Similar water types at the same location 

in adjoining aquifers suggest that water is able 

to move between the two aquifers through confining units. This type of geochemical data is of 

value in adjusting vertical leakage of the confining units in simulation. 

Except where they are fractured, beds of 

halite are considered to be impermeable. 

Geochemical evidence (J. F. Busby, U. S. 

Geological Survey, written commun., 1982) indicates that there is extensive leakage between 

the Cambrian-Ordovician, Mississippian, and 

Pennsylvanian aquifer systems and that low vertical permeability of Triassic and Jurassic formations limits the upward leakage between the 

Paleozoic aquifer systems and the Mesozoic 

aquifer systems. This suggests that extensive 

development of the Paleozoic aquifer systems probably would not affect the Mesozoic aquifer 

systems in most of the study area within a 

reasonable time frame (40 years). 

Future development of the regional aquifer 

system in the N orthem Great Plains should take 

into account that part of the water withdrawn 

from wells may come from storage in the confining unit except where a confining unit is absent or highly fractured. The quality of water 

from the confining units may be entirely different 

from the quality of water from the aquifer 

systems. 

Leakage between the Mississippian aquifer 

system and· the Lower Cretaceous aquifer system 

in eastern South Dakota has been noted in 

several studies (Swenson, 1968) and was the basis 

for Swenson's theory of recharge to the artesian 

basin of the Dakotas. He proposed that water 

enters the Madison Limestone in the Black Hills 

uplift area, moves generally eastward across approximately two-thirds of the State of South 

Dakota, and is discharged vertically through confining units to the Lower Cretaceous aquifer 

system. 

In the area of high upward leakage from the 

underlying aquifers to the Lower Cretaceous 

aquifer system, the confining unit between the 

under lying aquifer system and the Lower 

Cretaceous aquifer system is thin or absent. 

Geochemical facies maps indicate that water from 

the Pennsylvanian aquifer system is similar to 

water in the underlying Mississippian aquifer 

system and that vertical leakage is occurring between these two aquifer systems. Swenson (1968) 

indicates that the chemistry of the water from the 

Lower Cretaceous (Dakota) aquifer system is also 

similar to waters in the Mississippian and Pennsylvanian aquifer systems in the area of high upward leakage. 

Simulation indicates that the theory advanced by Swenson (1968) concerning the groundwater flow of the Lower Cretaceous aquifer 

system in South Dakota is basically correct. Additional geochemical data (K. D. Peter, U.S. 

Geological Survey, written commun., 1982) also 

support the conclusion that water is moving upward from the Mississippian and Pennsylvanian 

aquifer systems into the Lower Cretaceous 

aquifer system in eastern South Dakota and 

North Dakota. 

Geologic structure appears to be an important 

control (Weimer and others, 1982) on the rate and 

direction of ground-water movement in the Northem Great Plains. For example, the Casper 

Mountain fault (fig. 22) appears to prevent 

ground-water flow to the south from the Powder 

River basin, and the major fault system bounding 

the Bighorn Mountains on the east limits 

recharge to the Powder River basin. Recharge 

from the Bighorn Mountains appears to be channeled by geologic structures associated with major zones of lineaments and moves northeastward 

(figs. 26-28) across the northern part of the 

Powder River basin, south of the Cedar Creek anticline, to join the flow system recharged from the 

Black Hills uplift area. This flow system continues around the southern part of the Williston 

basin northeastward to the discharge area in northeastern North Dakota and eastern Manitoba of 

Canada. The Weldon-Brockton fault zone (fig. 22) 

appears to act as a major channel for ground 

water movement (figs. 27 -28) from the Big Snowy 

Mountains and associated highlands in Montana 

to discharge areas in Canada north of the 

Williston basin. 

Simulated drawdowns in selected aquifers 

after a hypothetical pumping for 5.9 years at a 

rate of 27.9 ft3/s (18 Mgal/d) from the Mississip-
pian aquifer system (Madison Limestone) with an 

assumed uniform storage coefficient of 2.0 x 10-

6 

indicate the degree of hydrologic connection 

among the aquifer systems. The pumping of the 

Mississippian aquifer (Madison Limestone) 

system results in large drawdowns in the overlying Pennsylvanian aquifer system and much 

larger drawdowns in the underlying CambrianOrdovician aquifer system, (figs. 35-36). 

The digital model developed for the Northern 

Great Plains regional aquifer system may be used 

45. 

I 

I 

IDAHO I 

I 

---------, 

to evaluate the regional effects of planned 

development schemes (Downey and Paulson, 

1974). However, the accuracy of evaluations 

depends on the accuracy of the data used in the 

model. During the Northern Great Plains 

regional aquifer system study, the accuracy of 

hydraulic-head data varied greatly from one area 

to another; therefore, the error range of the 

simulations is quite large. The other aquifer 

parameters such as hydraulic conductivity and 

storage coefficient were all estimated. 

Mr;:;, I I \-J Lake 1_ ----.------ __ l ____ l 

SCALE 1:10,000,000 1 

NEBRASKA 

40. UTAH 0:===;==10=0~---200MILES t-- _ ------------- 0 100 200 KILOMETERS KANSAS 

EXPLANATION 

~ LOCATION OF WELL FIELD-- Number is drawdown, in feet 

-50- LINE OF EQUAL DRAWDOWN --Interval is 20 feet 

- HIGHLAND RECHARGE AREA 

APPROXIMATE STUDY AREA OF THE NORTHERN GREAT PLAINS REGIONAL 

AQUIFER SYSTEM 

Figure 35.- Simulated drawdowns in the Pennsylvanian aquifer system (A03) underlying the northern Great Plains, 

after 5.9 years of pumping from the Mississippian aquifer system (A02l at a rate of 27.9 cubic feet per second and 

an assumed storage coefficient of 2.0 X 10·

8 • 

67 
68 

PUBLISHED REPORTS Reports 

Abstract 

1. Anna, L. 0., 1984, Geologic framework of the 

ground-water system in Jurassic and 

Cretaceous rocks in the Northern Great 

Plains in parts of Montana, North Dakota, 

South Dakota, and Wyoming: U .S. 

Geological Survey Professional Paper 

1402-B [in press]. 

45° 

40° 

1. Hoxie, D. T., 1981, A "black hole" pressure 

anomaly in the Newcastle Sandstone, 

Powder River basin, Wyoming and Montana: Annual Rocky Mountain Ground 

Water Conference, Laramie, WY, April 

30-May 2, 1981, Proceedings of lOth Annual 

Meeting, p. 43. 

IDAHO 

I 

I 

I 

I 

I 

I 

UTAH 0 100 200 MILES 

0 100 200 KILOMETERS 

2. Butler, R. D., 1984, Hydrogeology of Dakota 

aquifer system, Williston Basin, North 

Dakota in Jorgensen, D. G. and Signor, D. 

NEBRASKA 

I r--------

1 KANSAS 

EXPLANATION 

~ LOCATION OF WELL FIELD-- Number is drawdown, in feet 

-50- LINE OF EQUAL DRAWDOWN --Interval in feet, is variable 

- HIGHLAND RECHARGE AREA 

APPROXIMATE STUDY AREA OF THE NORTHERN GREAT PLAINS REGIONAL 

AQUIFER SYSTEM 

Figure 36.-Simulated drawdowns in the Cambrian-Ordovician aquifer system (AQ1) underlying the northern Great Plains, 

after 5.9 years of pumping from the Mississippian aquifer system (AQ2) at a rate of 27.9 cubic feet per second and 

an assumed storage coefficient of 2.0 X 10-•. 
C., eds., Geohydrology of the Dakota aquifer: 

National Water Well Association, Proceedings of the First C. V. Theis Conferences 

on Geohydrology, October 5-6, 1982, Lincoln, 

NE, p. 99-108. 

3. Case, H. L., III, 1984, Hydrology of Inyan 

Kara and Dakota-Newcastle aquifer system, 

South Dakota in Jorgensen, D. G. and 

Signor, D. C., eds., Geohydrology of the 

Dakota aquifer: National Water Well 

Association, Proceedings of the First C. V. 

Theis Conferences on Geohydrology, October 5-6, 1982, Lincoln, NE, p. 147-165. 

4. Cooley, M. E., 1984a, Linear features determined from Landsat imagery in Montana: 

U.S. Geological Survey Open-File Report 

83-936, scale 1:500,000, 2 sheets. 

5. -----1984b, Linear features determined 

from Landsat imagery in North Dakota: 

U.S. Geological Survey Open-File Report 

83-937, scale 1:500,000. 

6. ----1984c, Linear features determined 

from Landsat imagery in South Dakota and 

parts of adjacent states: U.S. Geological 

Survey Open-File Report 83-548, scale 

1:500,000. 

7. ----1984d, Linear features determined 

from Landsat imagery in Wyoming: U.S. 

Geological Survey Open-File Report 83-935, 

scale 1:500,000, 2 sheets. 

8. 1984e, Divisions of potential fracture 

permeability based on distribution of structures and linear features in sedimentary 

rocks, Northern Great Plains-Rocky Mountains region of Montana, North Dakota, 

South Dakota, Wyoming, and northern 

Nebraska: U.S. Geological Survey 

Miscellaneous Investigations Map 1-1687, 

scale 1:1,000,000, [in press]. 

9. Dodge, K. A., and Levings, G. W., 1980, 

Measurements of discharge, gain or loss in 

flow, and chemical quality of the Poplar and 

Redwater Rivers, northeastern Montana, 

October 24-25,1979: U.S. Geological Survey 

Open-File Report 80-1210, 16 p. 

10. Downey, J. S., 1982a, Geohydrology of the 

Madison and associated aquifers in parts of 

Montana, North Dakota, South Dakota, and 

Wyoming: U.S. Geological Survey ~n-File 

Report 82-914, 130 p. 

11. -----1982b, Machine-readable data files 

from the Madison Limestone and Northern 

Great Plains regional aquifer-system 

analysis projects, Montana, Nebraska, 

North Dakota, South Dakota, and 

Wyoming: U.S. Geological Survey WaterResources Investigations Report 82-4107, 

26 p. 

12.----1983, Bedrock aquifers of the Northern Great Plains: American Society of Civil 

Engineers Specialty Conference, Jackson, 

WY, July 1983, Proceedings, p. 29-35. 

13. -----1984, Hydrodynamics of the 

Williston Basin in the Northern Great 

Plains in Jorgensen, D. G. and Signor, D. C., 

eds, Geohydrology of the Dakota aquifer: 

National Water Well Association, Proceedings of the First C. V. Theis Conferences 

on Geohydrology, October 5-6, 1982, Lincoln, 

NE, p. 92-98. 

14. Downey, J. S., and Weiss, E. J., 1980, 

Preliminary data set for three-dimensional 

digital model of the Red River and Madison 

aquifers: U.S. Geological Survey Open-File 

Report 80-746, 8 p. 

15. Druse, S. A., Dodge, K. A., and Hotchkiss, W. 

R., 1981, Base flow and chemical quality of 

streams in the northern Great Plains area, 

Montana and Wyoming, 1977-78: U.S. 

Geological Survey Water-Resources Investigations Report 81-692, 60 p. 

16. Feltis, R. D., Lewis, B. D., Frasure, R. L., 

Rioux, R. P., Jauhola, C. A., and Hotchkiss, 

W. R., 1981, Selected geologic data from the 

Northern Great Plains area of Montana: 

U.S. Geological Survey Water-Resources Investigations Report 81-415, 66 p. 1 17. Henderson, Thomas, 1985, Geochemistry of 

ground water in two sandstone aquifer 

systems in the Northern Great Plains in 

parts of Montana, North Dakota, South 

Dakota, and Wyoming: U.S. Geological 

Survey Professional Paper 1402-C, 84 p. 

18. Hotchkiss, W. R., 1982, The ground-water 

resource in Montana in GroundWater Conference [Planning a Ground-water Strategy], 

Helena, Montana, 1982, Summary Proceedings: Montana Environmental Quality 

Council, p. 5-8. 

19. Kolm, K. E., and Peter, K. D., 1984, A possible relation · between lineaments and 

leakage through confining layers in South 

Dakota in Jorgensen, D. G. and Signor, D. 

C., eds., Geohydrology of the Dakota aquifer: 

National Water Well Association, Proceedings of the First C. V. Theis Conferences 

on Geohydrology, October 5-6, 1982, Lincoln, 

NE, p. 121-134. 

69 
70 

20. Larson, L. R., and Daddow, R. L., 1984, 

Ground-water quality data from the Powder 

River structural basin and adjacent areas, 

northeastern Wyoming: U.S. Geological 

Survey Open-File Report 83-939 [in press]. 

21. Lenfest, L. W., Jr., 1984, Evapotranspiration 

rates at selected sites in the Powder River 

basin, Wyoming and Montana: U.S. 

Geological Survey Water-Resources Investigations Report 82-4105, [in press]. 

22. Levings, G.W., 1981a, Selected drill-stem-test 

data from the Northern Great Plains area 

of Montana: U.S. Geological Survey WaterResources Investigations Report 81-326, 

20 p. 

23. 1981b, Selected hydrogeologic data 

from the northern Great Plains area of Montana: U.S. Geological Survey Open-File 

Report 81-534, 241 p. 

24. 1982a, Potentiometric-surface map 

of water in the Eagle Sandstone and 

equivalent units in the northern Great 

Plains of Montana: U.S. Geological Survey 

Open-File Report 82-565, scale 1:1,000,000. 

25. 1982b, Potentiometric-surface map 

of water in the Fox Hills-Lower Hell Creek 

aquifer in the northern Great Plains of Montana: U.S. Geological Survey Open-File 

Report 82-564, scale 1:1,000,000. 

26. 1982c, Potentiometric-surface map of 

water in the Judith River Formation in the 

northern Great Plains area of Montana: U.S. 

Geological Survey Open-File Report 82-562. 

27. ---1982d, Potentiometric-surface map 

of water in the Lakota Formation and 

equivalent units in the northern Great 

Plains of Montana: U.S. Geological Survey 

Open-File Report 82-563, scale 1:1,000,000. 

28. Levings, J. F., 1983, Hydrogeology and 

simulation of water flow in the Kootenai 

aquifer of the Judith Basin, central Montana: U.S. Geological Survey WaterResources Investigations Report 83-4146, 

39 p. 

29. Levings, J. F., Levings, G. W., Feltis, R. D., 

Hotchkiss, W. R., and Lee, R. E., 1981, Selective annotated bibliography of geology and 

ground-water resources for the Montana 

part of the northern Great Plains regional 

aquifer-system analysis: U.S. Geological 

Survey Water-Resources Investigations 

Report 81-401, 91 p. 

30. Lewis, B. D., and Hotchkiss, W. R., 1981, 

Thickness, percent sand, and configuration 

of shallow hydrogeologic units in the Powder 

River Basin, Montana and Wyoming: U.S. 

Geological Survey Miscellaneous Investigations Map 1-1317. 

'31. Lohmeyer, D. H., 1980, Preliminary 

potentiometric-surface map showing 

freshwater heads for the Lower Cretaceous 

rocks in the Northern Great Plains of Montana, North Dakota, South Dakota, and 

Wyoming: U.S. Geological Survey Open-File 

Report 80-757, scale 1:1,000,000. 

32. 1985, Freshwater heads and groundwater temperatures in aquifers of the Northern Great Plains of Montana, North Dakota, 

South Dakota, and Wyoming: U.S. 

Geological Survey Professional Paper 

1402-D, 11 p. 

33. Lohmeyer, D. H., Anna, L. 0., and Busby, J. 

F., 1982, Preliminary data for Northern 

Great Plains test well 1, NW114NE1/4 sec. 

11, T.55N.~ R77W., Sheridan County, 

Wyoming: U.S. Geological Survey Open-File 

Report 82-446, 80 p. 

34. Peter, K. D., 1984, Hydrochemistry of Lower 

Cretaceous sandstone aquifers, Northern 

Great Plains: in Jorgenson, D. G. and 

Signor, D. C., eds. Geohydrology of the 

Dakota aquifer: National Water Well 

Association, Proceedings of the First C. V. 

Theis Conferences on Geohydrology, October 5-6, 1982, Lincoln, NE, p. 197-208. 

35. Rioux, R. P., and Dodge, K. A., 1980, 

Hydrologic data from the Bull Mountains 

area, south-central Montana: U.S. Bureau 

of Land Management report, 146 p. 

36. Stenzil, Sheila, Buss, Rebecca, and Busby, J. 

F., 1980, Maps showing dissolved-solids concentration of waters in the Red River Formation and Mission Canyon Limestone in 

North Dakota, South Dakota, and parts of 

Wyoming and Montana: U.S. Geological 

Survey Open-File Report 80-748, scale 

1:1,000,000, 2 sheets. 

37. U.S. Geological Survey, 1979, Plan of study 

for the Northern Great Plains regional 

aquifer-system analysis in parts of Montana, 

North Dakota, South Dakota, and Wyoming: U.S. Geological Survey WaterResources Investigations Report 79-34, 20 p. 

38. Weimer, R. J., Emme, J. J., Farmer, C. L., Anna, L. 0., Davis, T. L., and Kidney, R. L., 

1982, Tectonic influences of sedimentation, 

Early Cretaceous, east flank of Powder 

River basin, Wyoming and South Dakota: 
Colorado School of Mines Quarterly, v. 77, 

no. 4, 61 p. 

39. Weiss, Emanuel, 1982a, A computer program 

for calculating relative transmissivity input 

arrays to aid model calibration: U.S. 

Geological Survey Open-File Report 82-44 7, 

18 p. 

40. 1982b, A model for the simulation of 

flow of variable density ground water in 

three dimensions under steady-state conditions: U.S. Geological Survey Open-File 

Report 82-352, 66 p. 

REFERENCES CITED 

Brown, C. B., 1944, Report on an investigation of water losses 

in streams flowing east out of the Black Hills, South 

Dakota: U.S. Department of Agriculutre Soil Conservation Service Special Report 8, 45 p. 

Downey, J. S., 1969, Glacial Lake Agassiz, in Pederson, D. 

T., and Reid, J. R., eds., Geology of northeastern North 

Dakota: North Dakota Geological Survey Miscellaneous 

Series 39, p. 12. 

---1971, Ground-water resources of Walsh County, 

northeastern North Dakota: U.S. Geological Survey 

Hydrologic Investigations Atlas 431, scale 1:126,000, 

1 sheet. 

---1973 Ground-water resources, Nelson and Walsh 

Counties, North Dakota: North Dakota Geological 

Survey Bulletin 57, pt. ill., and North Dakota State 

Water Commission County Ground-Water Studies 17, 

pt. m., 67 p. 

---1983, Bedrock aquifer of the northern Great Plains; 

American Society of Civil Engineers, Specialty Conference Proceedings, Jackson Hole, WY, July 1983, 

p. 29-35. 

Downey, J. S., and Paulson, Q. F., 1974, Predictive modeling 

of effects of the planned Kindred Lake on ground-water 

levels and discharge, southeastern North Dakota: U.S. 

Geological Survey Water-Resources Investigations 

30-7 4, 22 p., 7 plates. 

Flint, R. F., 1971, Glacial and Quaternary geology: New York, 

John Wiley and Sons, Inc., 892 p. 

Gow, A. J., Veda, H. T., and Garfield, D. E., 1968, Antarctic 

ice sheet: Preliminary results of fll'st core hole to 

bedrock; Science, v. 161, no. 3845, p. 1011-1013. 

Grossman, I. G., 1968, Origin of the sodium sulfate deposits 

of the northern Great Plains of Canada and the United 

States: U.S. Geological Survey Journal of Research, 

chapter B, p. 104-109. 

Hodson, W. G., 1974, Records of water wells, springs, oil- and 

gas-test holes, and chemical analyses of water for the 

Madison Limestone and equivalent rocks in the Powder 

River Basin and adjacent areas, northeastern Wyoming: Wyoming State Engineer report, 27 p. 

Hubbert, M. K., 1969, The theory of ground-water motion and 

related papers: New York, Hafner Publishing Co; 310 p. 

Laird, W. M., 1944, The geology and ground water resources 

of the Emerado quadrangle: North Dakota Geological 

Survey Bulletin 17, 35 p. 

McGinnis, L. D., 1968, Glaciation as a possible cause of 

mineral deposition: Economic Geology, v. 63, p. 390-400. 

Miller, R. H., and Rahn, P. H., 1974, Recharge to the Dakota 

Sandstone from outcrops in the Black Hills, South 

Dakota: Bulletin of the Association of Engineering 

Geologists, v. 11, no. 3, p. 221-234. 

Peterson, J. A., 1981, Stratigraphy and sedimentary facies of 

the Madison Limestone and associated rocks in parts 

of Montana, North Dakota, South Dakota, Wyoming, 

and Nebraska: U.S. Geological Survey Open-File Report 

81-642, 83 p. 

Powell, B. F., 1940, Construction history and technical details 

of Sheridan Dam: Black Hills Engineer, v. 26, 

p. 180-196. 

Rahn, P. H., and Gries, J. P., 1973, Large springs in the Black 

Hills, South Dakota and Wyoming: South Dakota 

Geological Survey Reports oflnvestigations 107,46 p. 

Robin, G. de Q., 1955, Ice movement and temperature distribution in glaciers and ice sheets: Journal of Glaciology, 

v. 2, no. 18, p. 523-532. 

Swenson, F. A., 1968, New theory of recharge in the artesian 

basin of the Dakotas: Geological Society of America 

Bulletin, v. 79, p. 163-182. 

Van Everdingen, R. 0., 1968, Studies of formation waters in 

western Canada-Geochemistry and hydrodynamics: 

Canadian Journal of Earth Sciences, v. 5, p. 523-543. 

Weertman, Johannes, 1972, General theory of water flow at 

the base of a glacier or ice sheet: Reviews of Geophysics 

and Space Physics, v. 10., no. 1, p. 287-533. 

Weimer, R. J., Emme, J. J., Farmer, C. L., Anna, L. 0., Davis, 

T. L., and Kidney, R. L., 1982, Tectonic influences of 

sedimentation, Early Cretaceous, east flank of Powder 

River basin, Wyoming and South Dakota: Colorado 

School of Mines Quarterly, v. 77, no. 4, 61 p. 

Wyoming State Engineer's Office, 1974, Underground water 

supply in the Madison Limestone: Cheyenne, WY, 

117 p. 

71 
72 

COMPLETED PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

NORTHERN MIDWEST REGIONAL AQUIFER-SYSTEM STUDY 

By Harley L. Young, Donald I. Siegel, Richard J. Mandie, 

and Angelo L. Kontis, Madison, Wisconsin 

INTRODUCTION 

The Northern Midwest regional aquifersystem study was started in 1978 and completed 

in 1984. The study was designed to investigate 

the hydrogeology, ground-water availability, and 

chemical quality of the ground water in an 

aquifer system consisting of rocks of Cambrian 

and Ordovician age, in parts of lllinois, Indiana, 

Iowa, Minnesota, Missouri, and Wisconsin (fig. 

37), and to describe the regional interaction of all 

components of the aquifer system (Steinhilber and 

Young, 1979). This aquifer system is referred to 

as the Cambrian-Ordovician aquifer system in 

this report. The rocks forming the aquifer system 

are mainly sandstone and dolomite. The aquifer 

system is used extensively for industrial and 

rural water supplies in the six states and is the 

primary source of water for many metropolitan 

areas. The study area is about 161,000 mi2 and 

its border delimits either the natural physical or 

hydrologic boundaries of the aquifer system. 

The aquifer strata were deposited in shallow 

seas that encroached on the Precambrian rock 

surface, which slopes generally southward from 

Minnesota and Wisconsin, but eastward from 

eastern Wisconsin. Structural basins are located 

in southwestern Iowa, south-central lllinois, and 

Michigan. The aquifer system crops out in an arc 

around the Wisconsin Arch and thickens toward 

the basins where it is deeply buried beneath 

younger sedimentary rocks (fig. 37). The aquifer 

system contains three distinct aquifers-St. PeterPrairie du Chien-Jordan aquifer, IrontonGalesville aquifer, and Mount Simon aquifer. The 

aquifers consist primarily of sandstone and are 

separated by shale, shaly dolomite, or siltstone 

confining units, as shown in figure 38. Where the 

Maquoketa Shale is present, it and the underlying dolomite and shale strata of the Galena, 

Decorah, Platteville, and Glenwood Formations 

form a major confining unit that overlies the 

three aquifers. 

The Cambrian-Ordovician aquifer system is 

a leaky-artesian system; and movement of groun4 

water is partly controlled by internal confining 

units of low permeability. In the outcrop area, 

water-table conditions prevail in shallow parts of 

the aquifer system and where the system is thin. 

Much of the recharge in upland areas discharges 

to streams through local flow systems, which are 

no more than a few miles in length. The re .. 

· mainder of the recharge moves slowly downward 

to deeper formations and downgradient to the 

regional ground-water flow system. 

Regional ground-water movement in the confined part of the system is generally. Q.way from 

the structural highs in the north toward the structural lows (basins) in the south and east (fig. 39). 

The rate of ground-water movement is very slow . 

and the flux along flow paths into the basins 

decreases due to a reduction in permeability and 

a progressive loss of water from the continuous, 

although small, upward leakage. 

In the late 1800's, when wells first were 

drilled into the confined areas of the aquifer 

system in eastern Wisconsin, northeastern TIlinois, and along stream valleys in eastern Iowa, 

the wells were flowing. The hydraulic head at 

that time was as much as 140 feet above Lake 

Michigan in Milwaukee and 130 feet above the 

Lake in Chicago. Flowing wells are still common 

in valleys of the Mississippi River and its major 

tributaries. 
The Cambrian-Ordovician aquifer system 

supplies a major part of the water needs in the 

study area. Many metropolitan areas depend on 

it for all or part of their water supplies. Hydraulic 

heads in the aquifer system have declined hundreds of feet since the late 1800's in the heavily 

pumped Chicago-Milwaukee area (fig. 40) and to 

a somewhat lesser extent in other major metropolitan areas. Projections of future water needs 

indicate continuing or increasing demands and, 

therefore, continuing water-level declines are expected. The Illinois State Water Survey has 

monitored pumpage and water-level declines and 

has reported on aquifer characteristics and water 

availability and quality (Schicht and others, 1976; 

Sasman and others, 1982). In addition, the Illinois 

State Geological Survey has studied the geologic 

framework and geochemistry of the aquifer 

system. These agencies have contributed to the 

planning of the Illinois Division of Water 

Resources (1980) for its allocation of water from 

Lake Michigan. Control of the allocation process 

gives the Division indirect control of deep-well 

pumpage. 

The aquifer system contains highly mineralized water in several places, especially in its 

deepest parts, which generally coincide with 

regional discharge areas or structurally low 

areas. These areas are mainly in the 

southwestern, southern, and eastern parts of the 

study area. Water from highly mineralized zones 

may be induced into freshwater zones by large 

withdrawals of freshwater, such as those presently occurring in northeastern Illinois, 

southeastern Wisconsin, and central Iowa. 

GEOLOGIC AND HYDROLOGIC DATA 

State agencies and the District Offices of 

the U.S.· Geological Survey provided the geologic 

data for the study, consisting of contour and 

isopach maps of the top of each aquifer and confining unit. The state maps were combined into 

regional maps and converted into a computerized 

data base (Kontis and Mandie, 1980) that provided easy input to flow models. Structure contour maps of the tops of ten units described in 

figure 38 were produced: (1) the Precambrian 

basement surface; (2) the Mount Simon, (3) Eau 

Claire, and (4) Ironton Sandstones; (5) the St. 

Lawrence Formation of Cambrian age; (6) the St. 

Peter Sandstone; (7) the Galena Dolomite and (8) 

Maquoketa Shale of Ordovician age; (9) the combined Silurian and Devonian rocks; and (10) the 

combined Mississippian and Pennsylvanian 

rocks. Isopach maps were made of the total section between successive structural surfaces. 

Although geologic data are available for each 

formation, very little information exists on 

hydraulic properties, head distribution, and water 

quality within the aquifer system, except in outcrop areas. In most of the study area, wells are 

open to more than one formation. To obtain data 

on individual aquifers at various points, deep test 

wells were drilled at seven sites (fig. 37). Inflatable packers, pressure transducers, and 

submersible pumps were used to obtain hydraulic 

conductivity, head, and water ~quality in individual aquifers. After testing was completed, 

piezometers were installed in three to four 

discrete zones within the test wells. These 

piezometers are now part of the U.S. Geological 

Survey's ground-water monitoring network and 

provide long-term benefit for monitoring water 

quality and head in the Cambrian-Ordovician 

aquifer system. 

The most important of the seven deep well 

·test sites was the 3,4 75-foot well near Zion, IL, 

(Nicholas and others, 1984). The well reached 

Precambrian basement at a depth of 3,435 feet 

(2,849 feet below sea level) and encountered saline 

water below a depth of about 1,800 feet. 

Piezometers were installed at different depths. 

The observed head in the Mount Simon was about 

50 and 55 feet higher than the heads in the St. 

Peter-Prairie du Chien-Jordan aquifer and the 

Ironton-Galesville aquifer, respectively. Head 

data from the test well indicated that the head 

in the Ironton-Galesville was the lowest. This fact 

indicates that ground water flows into the 

Ironton-Galesville aquifer from both the overlying 

and the underlying aquifers, resulting from 

regional pumping stress and the significantly 

higher transmissivity of the Ironton-Galesville 

aquifer. 

Head data for predevelopment conditions are 

sparse in many areas, especially for deeper 

aquifers, however, they are sufficient for primary 

studies. The preparation of the potentiometric 

surface map for the St. Peter-Prairie du ChienJordan aquifer shown in figure 39 was based on 

those sparse data. The predevelopment heads in 

the deeper Ironton-Galesville and Mount Simon 

aquifers probably were similar to those shown in 

figure 39. The broadly spaced, smooth contours 

in Iowa, northern Missouri, and Illinois mark 

areas of strong confinement beneath the Maquoketa Shale and younger strata. Regional flow 

is southeastward to the Illinois Basin. 

73 
74 

p ·t 

Illinois Basin .. SCALE 1:7,000,000 

0 50 100 150 

50 100 150 200 KILOMETERS 

EXPLANATION 

K CRETACEOUS FORMATIONS s SILURIAN FORMATIONS 

JURASSIC FORMATIONS Om ORDOVICIAN-AGE MAQUOKETA SHALE 

PERMIAN FORMATIONS 0 ORDOVICIAN FORMATIONS OLDER THAN 

THE MAQUOKETA SHALE 

p 

p PENNSYLVANIAN FORMATIONS £ C~MBRIAN FORMATIONS 

M MISSISSIPPIAN FORMATIONS p(;x PRE€AMBRIAN-AGE SANDSTONE 

0 DEVONIAN FORMATIONS p£s PRECAMBRIAN-AGE CRYSTALLINE ROCK 

CONTACT 

e LOCATION OF TEST WELL DRILLED FOR THIS PROJECT 

- STUDYAREA 

Figure 37.-General bedrock geology of the northern Midwest and locations of test wells drilled 

during the northern Midwest regional aquifer-system study. (Modified from maps of individual states 

produced by state agencies, dated from 1966 to 1982). 
Designation of layers used 

Geologic system Hydrogeologic unit in the regional flow model 

Aquifer Confining unit 

Quaternary Drift 

6 

Cretaceous Cretaceous aquifer-only in Minnesota and Iowa 

Pennsylvanian 

Mississippian Pennsylvanian-Mississippian-Devonian confining unit 4-6 

Devonian 

Silurian Silurian aquifer-includes basal Devonian in Illinois and Indiana 4 

Maquoketa confining unit-consists of the Maquoketa Shale and the Galena, 

Decorah, Platteville, and Glenwood formations or equivalents, where 3-4 

Ordovician overlain by the Maquoketa. Equivalents in Missouri and southern Illinois 

are the Maquoketa Shale through the Joachim Dolomite 

St. Peter-Prairie du Chien-Jordan aquifer-in Missouri and Hlinois, includes 3 the St. Peter through Eminence formations 

St. Lawrence-Franconia confining unit-in Missouri and Illinois, includes the 2-3 Potosi through Davis formations 

Ironton-Galesville aquifer-not present in southern Illinois, southwestern ~ Iowa, and Missouri 

Cambrian Eau Claire confining unit- Bonneterre Formation is the equivalent in Missouri 1-2 and western Iowa 

Includes overlying Elmhurst Sandstone Member of the 

Eau Claire Formation in Illinois 

Mount Simon aquifer Mount Simon Sandstone is main component. Equiv- 1 

alent in Missouri is the Lamotte Sandstone 

Precambrian Includes underlying Hinckley Sandstone in Minnesota 

Figure 38.-Stratigraphic configuration of the regional aquifers and confining units delineated for the northern Midwest 

regional aquifer-system study. 

The 1980 potentiometric surface for the St. 

Peter-Prairie du Chien-Jordan aquifer shows little change in head in the recharge. areas, but 

significant declines in most of the confined area 

(figs. 39 and 41). The area of most significant head 

decline is in the Chicago-Milwaukee area, where 

the potentiometric surface of the CambrianOrdovician aquifer system has declined as much 

as 850 feet in the vicinity of Chicago (Sasman and 

others, 1982) and 375 feet in the vicinity of 

Milwaukee (fig. 40). Water levels in some Chicago 

area wells are 100 to 150 feet below sea level. 

Pumpage has increased almost steadily to about 

180 Mgal/d in the Chicago area and about 33 

Mgal/d in southeastern Wisconsin in 1980. 

FLOW MODELS 

The complexities of the regional ground-water 

flow system were studied by development and 

calibration of a regional digital flow model and 

three subregional models (fig. 42). The models 

simulate the flow systems and can be used to 

estimate water-level changes based on projected 

future pumping. A quasi three-dimensional flow 

model (Trescott, 1975) was used to simulate the 

five aquifers and four confining units in the 

regional flow model. A uniform node spacing of 

16 miles was used for the regional flow model. 

The three lower aquifers-St. Peter-Prairie du 

Chien-Jordan aquifer, Ironton-Galesville aquifer, 

and Mount Simon aquifer-are of primary interest; the upper two aquifers-drift and 

Cretaceous aquifer and Silurian aquifer-serve as 

sources and sinks for the lower three aquifers. 

Two significant modifications to the Trescott 

(1975) model code were necessary to simulate the 

Cambrian-Ordovician aquifer system. Saline 

water, including brine in the deep structural 

basins, is represented in the model by the addition of a function to simulate flow in ground water 

with variable densities. Simulation of multiaquifer well effects (Bennett and others, 1982) 

was also added to the model to incorporate the 

variation in yield from, and hydraulic head of, 

each aquifer penetrated by the well. 

75 
76 

In addition to the regional flow model, subregional flow models were constructed for areas 

of local interest. The subregional flow models are: 

(1) a two-dimensional flow model of northeastern 

Missouri (Imes, 1984), (2) a quasi threedimensional flow model of northeastern Wisconsin (Emmons, in press), and (3) a two-dimensional 

--- ..... _ _ _ MINNESOTA 

--------

SCALE 1 7,500,000 

0 50 100 150 200 MILES 

0 50 100 150 200 KILOMETERS 

flow model of the Jordan aquifer in Iowa (M.R. 

Burkart and R.C. Buchmiller, U.S. Geological 

Survey, written commun., 1984). Although 

unrelated to the regional aquifer-system study, 

two U.S. Geological Survey cooperative program 

studies to evaluate ground-water flow benefited 

from joint data-collection efforts. The studies are 

ILLINOIS 

Superior 

MICHIGAN 

--------r--- 0 

' I 

INDIANA 

EXPLANATION 

_ 600_ POTENTIOMETRIC CONTOUR·· Shows.altitude of potentiometric surface. 

Interval, in feet, is variable. Datum is sea level 

~ GENERALIZED GROUND-WATER FLOW DIRECTION 

STUDY AREA 

Figure 39.- Generalized predevelopment potentiometric surface of the St. Peter-Prairie du Chien-Jordan aquifer of 

the Cambrian-Ordovician aquifer system in the northern Midwest. 
of the Minneapolis-St. Paul area (Guswa and 

others, 1982), and of Brown County, Wisconsin 

(K.rohelski, in press). 

tions, and then for transient conditions to 

' simulate the effects of ground-water development 

from 1864 to 1980. Simulated drawdown is less 

than 50 feet throughout central Wisconsin, northcentral Tilinois, extreme northeastern Iowa, and The regional flow model was initially calibrated for steady-state predevelopment condiag· 

I ,. I /~ I I I / --------,--·-----1 I I / 

I t I' I ~-------~-~-

' 1 II / 

I i ~~ f I I \ I 

I 'I I ;d~\ J ..-------. --,. I I --~ ! _____ _._ ___ r__ , 

I I I ,' 

I I tl / i ! i //~ 

i ! I I@ 

-- j__------··j ~~~~g~~~~~.- fjl-p 

i i 

• I I I I· I l ! f : ., ·--,----·.L.----, I I I i l---~-~1 1 

43" 

I • I I I' I 

.,. ___ j_ .. J I ~-~·-----/1 

i ;/ ! I I I I 

. r-----~----

·---1--------~ I ·---

' I I I 

I I I I 

1 r 

SCALE 1:1,500,000 

0 10 20 30 

0 10 20 30 40 KILOMETERS 

EXPLANATION 

_ 2oo-- LINE OF EQUAL HEAD DECLINE-- Dashed where location is approxi!'Tia.te. 

Interval is 100 feet with supplementary 25- and 50-foot lines 

Figure 40.- Decline in the potentiometric surface of the Cambrian-Ordovician aquifer system in the Chicago-Milwaukee 

area, 1864-1980. 

77 
78 

southern Minnesota (figs. 43-44), where the Maquoketa Shale is absent and the aquifers of the 

Cambrian-Ordovician aquifer system are mainly 

unconfined or loosely confined. 

Large coalescing drawdown cones have developed in the Cambrian-Ordovician aquifer 

system in northeastern Illinois, northwestern Indiana, eastern Wisconsin, central and east-central 

Iowa, and central Missouri (figs. 43-44), where the 

aquifer system is tightly confined. Heads in the 

95° 

-·------- MINNESOTA 

40° ------... - MlpSOURI 

SCALE 1 7,500,000 

0 50 100 150 200 MILES 

0 50 100 150 200 KILOMETERS 

St. Peter-Prairie du Chien-Jordan aquifer most 

closely depict the composite head conditions in the 

Cambrian-Ordovician aquifer system. The large 

areal extent of the cone for the St. Peter-Prairie 

du Chien-Jordan aquifer shows that the aquifer 

system is tightly confined and that a major source 

of the water pumped is probably from storage in 

the aquifer. The pattern is similar for the IrontonGalesville and the Mount Simon aquifers (fig. 44), 

except in Iowa and Missouri where these aquifers 

ILLINOIS 

Superior 

MICHIGAN 

--------r---

' ' I 

INDIANA 

EXPLANATION 

--aoo-- POTENTIOMETRIC CONTOUR -- Shows altitude of potentiometric surface. Dashed where location 

is approximate. Interval, in feet, is variable. Datum is sea level 

STUDY AREA 

Figure 41.- Potentiometric surface of the St. Peter-Prairie du Chien-Jordan aquifer of the Cambrian-Ordovician aquifer 

system in the northern Midwest, 1980. 
95 ' 

-·------- MINNESOTA 

.Mason City 

IOWA 

·oes Moines 

3 

40 ' --- -----~- --

r---, 

1 

I 

I 

I 

I 

I 

EXPLANATION 

I I REGIONAL GROUND-WATER FLOW MODEL "-- _ _, 

D SUBREGIONAL GROUND-WATER FLOW MODEL 

1, NE Missouri 

2, NE Wisconsin 

3, Iowa 

:!? . . . . SEPARATE STUDY AREAS 

4, Minneapolis- St. Paul 

5, Brown County, Wisconsin 

STUDY AREA 

Superior 

I --------h .. : I 

I: 

' I 

\: 

, I 

INDIANA 

ILLINOIS 

SCALE 1:7,500,000 

0 50 100 150 200 MILES 

0 50 100 150 200 KILOMETERS 

Figure 42.- Location and areal extent of and subregional ground-water flow models of the Cambrian-Ordovician regional 

aquifer system in the northern Midwest. 

79 
80 

are little used. The extensive drawdown cone in 

eastern Wisconsin and northeastern Illinois and 

the drawdown cone in eastern Iowa and northwestern Illinois terminate near the edge of the 

Maquoketa Shale confining unit, showing the effect of recharge from the overlying unconfined 

aquifers. The drawdown cones spread farther in 

the confined area away from the outcrop area, 

because the primary source of pumped water 

there is probably from aquifer storage. 

95° 

-------. MINNESOTA 

40 ° 

SCALE 1 : 7,500,000 

0 50 100 150 200 MILES 

0 50 100 150 200 KILOMETERS 

GEOCHEMICAL DATA 

More than 3,000 chemical analyses of ground 

water were available in the study area. Major 

sources of the data were the W ATSTORE data 

base of the U.S. Geological Survey, publications 

of State and Federal agencies, and scientific journals. In addition, about 200 water samples were 

collected during the study. These samples were 

Superior 

ILLINOIS 

MICHIGAN 

-----r--- 0 

' I 

EXPLANATION 

-100- LINE OF EQUAL SIMULATED HEAD DECLINE ··Interval, in feet, is variable 

STUDY AREA 

Figure 43.-Simulated head decline, 1864-1980, in the St. Peter-Prairie du Chien-Jordan aquifer of the CambrianOrdovician aquifer system in the northern Midwest. 
analyzed for major ions, trace metals, and 

radiochemical species. In addition, 85 samples 

were analyzed for the isotopes of oxygen and 

hydrogen in water and carbon in bicarbonate, and 

9 were analyzed for the isotopes of sulfur in 

sulfate. 

Detailed evaluation of ground-water quality 

was restricted to the shallow drift and Cretaceous 

aquifer and the St. Peter-Prairie du Chien-Jordan 

40 ' 

·-------

-----

I 

' I 

I 

' ' I 

' 

95 . 

MINNESOTA 

-------·----·-------

IOWA 

----------... ----·-

MISSOURI 

SCALE 1 : 7,500,000 

0 50 100 150 200 MILES 

0 50 100 150 200 KI LOMETERS 

aquifer, for which the areal distribution of data 

was considered sufficient to evaluate the trends 

and variation in concentrations of major dissolved constituents. In most of Wisconsin and northcentral Illinois, the St. Peter-Prairie du ChienJordan, Ironton-Galesville, and Mount Simon 

aquifers are unconfined and are hydraulically 

connected, thus water quality in these aquifers 

is probably similar. 

-- WISCONSIN 

ILLINOIS 

Superior 

MICHIGAN 

--------r--- 0 

' I 

INDIANA 

' ' I 

I 

EXPLANATION 

- 100- LINE OF EQUAL SIMULATED HEAD DECLINE -- Interval , in feet, is variable 

STUDY AREA 

Figure 44. - Simulated head decline, 1864-1980, in the Mount Simon aquifer of the Cambrian-Ordovician aquifer system 

in the northern Midwest. 

81 
82 

Ground water in outcrop areas and beneath 

the Maquoketa Shale confining unit to depths 

below land surface of about 2,000 feet generally 

has concentrations of dissolved solids of less than 

1,000 milligrams per liter (mg!L). The water is of 

a calcium-magnesium-bicarbonate type. However, 

concentrations of dissolved solids tend to increase 

greatly where the aquifer is deeper and the for95 ° 

-- -- .. .. MINNESOTA 

40 ° 

SCALE 1 . 7,500,000 

0 50 100 150 200 MILES 

0 50 100 150 200 KILOMETERS 

mation is thicker. Ground water becomes a 

sodium-chloride brine in deeper parts of the structural basins. Commonly, the transition to higher 

concentrations of dissolved solids in the confined 

areas is accompanied by substantial increases in 

sulfate concentration and the occurrence of a 

calcium-sodium-sulfate type water (figs. 45 and 

46). 

Superior 

MICHIGAN 

--------r---

' ' I 

INDIANA 

EXPLANATION 

_ 500 __ LINE OF EQUAL DISSOLVED-SOLIDS CONCENTRATION-- Dashed where location 

is approximate. Interval, in milligrams per liter, is variable 

STUDY AREA 

Figure 45.- Dissolved-solids concentrations of ground water in the St. Peter-Prairie du Chien-Jordan aquifer of the 

Cambrian-Ordovician aquifer system in the northern Midwest. 
In recharge areas of Wisconsin, southern 

Minnesota, northeastern Iowa, and north-central 

Illinois, the calcium-magnesium-bicarbonate type 

water (Ca-Mg-HC03) (fig. 4 7) in the aquifer 

system is identical to that in the overlying glacial 

drift. It probably resulted from dissolution of carbonate minerals in the soil by carbon dioxide-rich 

recharge water. In northwestern Iowa and 

southwestern Minnesota, however, the water in 

--·------. MINNESOTA ) 

-----

SCALE 1 : 7.500.000 

0 50 100 150 200 MILES 

50 100 150 200 KILOMETERS 

both the glacial drift and the CambrianOrdovician aquifer system is of a calcium-sodiumsulfate-bicarbonate (Ca-N a-SO 4-HC03) type 

resulting from the oxidation of pyrite in the 

overlying Dakota Formation. Dissolved solids in 

this ground water can exceed 1,000 mg/L. The 

water is generally undersaturated with respect 

to gypsum; this fact, and its negative values of 

o34S (standard expression of the ratio of the less 

Su~ 

MICHIGAN 

--------r---

' ' I 

INDIANA 

EXPLANATION 

_ 500 __ LINE OF EQUAL CONCENTRATION OF SULFATE-- Dashed where location is 

approximate. Interval, in milligrams per liter, is variable 

STUDY AREA 

Figure 46.- Sulfate concentrations of ground water in the St. Peter-Prairie du Chien-Jordan aquifer of the CambrianOrdovician aquifer system in the northern Midwest. 

83 
84 

·------. 

-----

I 

' ' I 

' ' I 

MINNESOTA 

SCALE 1 : 7,500,000 

Ca-MgHC03 

0 50 100 150 200 MILES 

0 50 100 150 200 KILOM ETERS 

Ca-MgHC03 

ILLINOIS 

Superior 

MICHIGAN 

--------r--· 

' ' I 

INDIANA 

EXPLANATION 

FACIES ZONE BOUNDARY-· Queried where uncertain 

STUDY AREA 

Figure 47.- Hydrochemical facies of ground water in the St. Peter-Prairie du Chien-Jordan aquifer of the CambrianOrdovician aquifer system in the northern Midwest. 

abundant sulfur-34 ion with respect to the more 

common sulfur-32 ion) of sulfur in sulfate, indicates that pyrite is the primary source of the 

sulfur. 

Ground water changes from a calcium-magnesium-bicarbonate type to a sodium-calciumsulfate-bicarbonate (Na-Ca-S04-HC03) type and 

then to a sodium-chloride (Na-Cl) type along the 

major flow paths from northwestern Iowa to the 

Illinois Basin. The changes may be due to ion exchange of calcium and magnesium for sodium in 

clay or due to membrane filtration that could 

result in the precipitation of calcite coincident 

with increases in sodium and chloride. 

The evolution of the water quality in the 

Cambrian-Ordovician aquifer system is com-
85 

Superior 

---.. ___ _ ·--- MINNESOTA 

A. WISCONSIN 

MICHIGAN 

--------r---

INDIANA 

-----

SCALE 1 : 7,500,000 

0 50 100 150 200 MILES 

0 50 100 150 200 KILOMETERS 

EXPLANATION 

-- 10-- Ll N E OF EQUAL o '80 .. Dashed where location is approximate. lnterval,in parts permil, is variable 

WELL SAMPLED FOR CHEMICAL ANALYSIS DURING THIS STUDY 

& Open to Mount Simon aquifer 

• Open to St. Peter· Prairie du Chien· Jordan aquifer 

• Open to glacial drift or Cretaceous aquifers 

WELL WITH ANALYSIS FROM OTHER SOURCES 

0 Open to St. Peter· Prairie du Chien ~ Jordan aquifer 

STUDY AREA 

Figure 48.- Distribution of o180 in ground water in the Cambrian-Ordovician aquifer system in the northern Midwest. 
86 

plicated because of many possible geochemical 

processes and the effects of Pleistocene glaciation 

on the aquifer system. The hydrochemical facies 

of ground water shown in figure 4 7 may, in part, 

reflect the water types before or during the 

Pleistocene. Analysis of the isotopic composition 

of the ground water strongly indicates that the 

source of much of the ground water in the con-

. fined part of the Cambrian-Ordovician aquifer 

system, other than in the deep basins, probably 

was recharge from glacial meltwater (Siegel and 

Mandie, 1984). The water is isotopically depleted 

in o11iO (standard expression of the ratio of the 

less abundant oxygen-18 ion with respect to the 

more common oxygen-16 ion) with respect to 

modern precipitation (fig. 48). This indicates that 

the source of the ground water was precipitation 

in a climate similar to that at latitudes hundreds 

of miles north of the study area and suggests that 

the water probably was recharged during 

Pleistocene glaciations. 

Pleistocene recharge probably also was a factor in the occurrence of a plume of water in central Iowa that has much lower concentrations of 

dissolved solids than in neighboring waters (fig. 

45). The distribution of o180 and the concentration of lithium, radium-226, and bromide show a 

correlation with the plume. ·Concentrations of 

dissolved solids generally increase downgradient; 

however, in Iowa they increase from northeast to 

southwest, whereas the regional flow is 

southeastward across the State. This may suggest 

that the direction of paleoflow was perpendicular 

to the direction of flow today, possibly due to 

emplacement of subglacial meltwater by very 

high hydraulic gradients from ice loading. 

PUBLISHED REPORTS 

Abstracts 

1. Alexander, E. C., Jr., Siegel, D. I., and Milske, 

J. A., 1983, Isotopic studies of the Mt. Simon 

aquifer, southern Minnesota: American 

Geophysical Union EOS, v. 64, no. 18, 

p. 225. 

2. Franz, K. E., and Siegel, D. I., 1984, 

Geochemical trends in the sandstone 

aquifer, eastern Wisconsin: American 

Geophysical Union EOS, v. 65, no. 16, 

p. 212. 

3. Shedlock, R. J., and Eikenberry, S. E., 1982, 

Saline formation waters in the CambrianOrdovician aquifer in northwest Indiana: 

Geological Society of America, NorthCentral Section, 16th Annual Meeting, West 

Lafayette, IN, 1982, Abstracts with Programs, v. 15, no. 5, p. 287. 

4. Siegel, D. 1., 1983, Sulfur isotope chemistry, 

Cambrian-Ordovician aquifer, north-central 

United States: American Geophysical Union 

EOS v. 64, no. 45, p. 704. 

5. Siegel, D. 1., and Franz, K. E., 1984, Isotopic 

studies of the sanqstone aquifer, eastern 

Wisconsin: Geophysical Society of America 

97th Annual Meeting~ Reno, NV, Abstracts 

with Programs, v. 16, no. 6, p. 655. 

6. Siegel, D. 1., Kontis, A. L., and Mandie, R. J., 

1982, The chemical evolution of water quality in the Cambrian-Ordovician aquifer, 

north-central United States: American 

Geophysical Union EOS, v. 63, no. 33, 

p. 612. 

7. Siegel, D. 1., and Mandie, R. J., 1982, 

Geochemical evidence of Pleistocene glacial 

meltwater recharge to the CambrianOrdovician aquifer in the north-central 

United States: American Geophysical Union 

EOS v. 63, no. 18, p. 325-326. 

8. -----1983, Geochemical evidence for 

glaciation of the Driftless Area, 

southwestern Wisconsin: Geological Society of America• 96th Annual Meeting, Indianapolis, IN, 1983, Abstracts with Programs, v. 15, no. 6, p. 687. 

9. Woodward, D. G., and Delin, G. N., 1982, 

Potentiometric surface of :regional aquifers 

in the Hollandale embayment, southeastern 

Minnesota: American Geophysical Union 

EOS, v. 63, no. 33, p. 612. 

Reports 

1. Bennett; G. D., Kontis, A. L., and Larson, S. 

P., 1982, Representation of multiaquifer 

well effects in three-dimensional groundwaterflow simulation: GroundWater, v. 20, 

no. 3, p. 334.:341. 

2. Delin, G. N., and Woodward, D. G., 1984, 

Hydrogeologic setting and potentiometric 

surfaces of regional aquifers in the Hollandale Embayment, southeastern Minnesota; 

1970-80: U.S. Geological Survey WaterSupply Paper2219, 56 p. 

3. Fassnacht; T. L.; 1982, A seismic reflection 

study of the Precambrian basement along 

the Illinois-Wisconsin State line: Northern 

Illinois University, Master of Science thesis, 

103 p. 

4. Horn, M. A., 1983, Ground-water-use trends 

in the Twin Cities metropolitan area, Min-
nesota, 1880-1980: U.S. Geological Survey 

Water-Resources Investigations Report 

83-4033, 37 p. 

5. Imes, J. L., 1984, The ground-water flow 

system in northern Missouri, with emphasis 

on the Cambrian-Ordovician aquifer: U.S. 

Geological Survey Professional Paper 1305 

[in press]. 

6. Kontis, A. L., and Mandie, R. J., 1980, Database system for Northern Midwest Regional 

Aquifer-System Analysis: U.S. Geological 

Survey Water-Resources Investigations 

Report 80-104, 23 p. 

7. Mossier, J. H., 1983a, Bedrocktopography and 

isopachs of Cretaceous and Quaternary 

strata, east-central and southeastern Minnesota: Minnesota Geological Survey 

Miscellaneous Map Series M-52, 2 pls. 

8. --'---1983b, Paleozoic lithostratigraphy of 

southeastern Minnesota: Minnesota 

Geological Survey Miscellaneous Map 

Series M-51, 8 pls. 

9. Nicholas, J. R., Sherrill, M.G., and Young, 

H. L., 1984, Hydrology of the CambrianOrdovician aquifer system at a test well in 

northeastern Illinois: U.S. Geological 

Survey Water-Resources Investigations 

Report 84-4165 [in press]. 

10. Siegel, D. I., and MandleR. J., 1984, Isotopic 

evidence for glacial meltwater recharge to 

the Cambrian-Ordovician aquifer, northcentral United States: Quaternary 

Research, v. 22, p. 328-335. 

11. Steinhilber, W. L., and Young, H. L., 1979, 

Plan of study for the Northern Midwest 

Regional Aquifer-System Analysis: U.S. 

Geological Survey Water-Resources Investigations Report 79-44, 20 p. 

12. Visocky, A. P., Sherrill, M. G., and Cartwright, Keros, 1985, Geology, hydrology, 

and water quality of the Cambrian and Ordovician systems in northern Illinois: Illinois State Geological Survey, Illinois State 

Water Survey, and U.S. Geological Survey 

Cooperative Groundwater Report 10, 136 p. 

13. Woodward, D. G., 1983, Trends in municipal 

wells and aquifer utilization in southeastern 

Minnesota, 1880-1980: U.S. Geological 

Survey Water-Resources Investigations 

Report 83-4222, 86 p. 

14. -----1984a, Areal lithologic changes in 

aquifers in southeastern Minnesota as determined from natural-gamma borehole logs: 

National Water Well Association Conference on Surface and Borehole 

Geophysical Methods in Ground Water Investigations, San Antonio, TX, February 

7-9, 1984, Proceedings, p. 788-800. 

15. ---.,--1984b, Hydrogeologic framework 

and properties of regional aquifers in the 

Hollandale embayment, southeastern Minnesota: U.S. Geological Survey Hydrologic 

Investigations Atlas 677, 2 sheets [in press]. 

REFERENCES CITED 

Bennett, G. D., Kontis, A. L., and Larson, S. P., 1982, 

Representation of multiaquifer well effects in threedimensional ground-water flow simulation: Ground 

Water, v. 20, no. 3, p. 334-341. 

Emmons, P. J., An evaluation of the bedrock aquifer system 

in northeastern Wisconsin: U.S. Geological Survey 

Water-Resources Investigations Report 85-4199 [in 

press]. 

Guswa, J. H., Siegel, D. I., and Gillies, D. C., 1982, Preliminary 

evaluation of the ground-water-flow system in the Twin 

Cities metropolitan area, Minnesota: U.S. Geological 

Survey Water-Resources Investigations Report 82-44, 

65 p. 

Illinois Division of Water Resources, 1980, In the matter of 

allocation of water from Lake Michigan: Illinois Department of Transportation Opinion and Order LMO 80-4, 

December 15, 1980. 

Imes, J. L., 1984, The ground-water system in northern 

Missouri, with emphasis on the Cambrian-Ordovician 

aquifer: U.S. Geological Survey Professional Paper 

1305, [in press]. 

Kontis, A. L., and Mandie, R. J., 1980, Data-base system for 

Northern Midwest Regional Aquifer-System Analysis: 

U.S. Geological Survey Water-Resources Investigations 

Report 80-104, 23 p. · 

Krohelski, J. T., Hydrogeology, ground-water use and quality, Brown County, Wisconsin with a section on bedrock 

geology by Bruce A. Brown: University of WisconsinExtension, Geological and Natural History Survey Information Circular [in press]. 

Nicholas, J. R., Sherrill, M. G., and Young, H. L.,Hydrogeology 

of the Cambrian-Ordovician aquifer system at a test 

well in northeastern Illinois: U.S. Geological Survey 

Water Resources Investigations Report 84-4165 [in 

press]. 

Sasman, R. T., Benson, C. R., Ludwiga, R. S., and Williams, 

T. L., 1982, Water-level trends, pumpage, and chemical 

quality in the Cambrian- Ordovician aquifer in lllinois, 

1971-1980: Illinois State Water Survey Circular 154, 

64 p. 

Schicht, R. J., Adams, J. R., and Stall, J. B., 1976, Water 

resources availability, quality, and cost in northeastern 

Illinois: illinois State Water Survey Report of Investigation 83, 90 p. 

Siegel, D. I., and Mandie, R. J., 1984, Isotopic evidence for 

glacial melt-water recharge to the CambrianOrdovician aquifer, north-central United States: 

Quaternary Research,v. 22, p. 328-335. 

Steinhilber, W. L., and Young, H. L., 1979, Plan of study for 

the Northern Midwest Regional Aquifer-System 

Analysis: U.S. Geological Survey Water-Resources Investigations Report 79-44, 20 p. 

Trescott, P. C., 1975, Documentation of finite-difference model 

for simulation of three-dimensional ground-water flow: 

U.S. Geological Survey Open-File Report 75-438, 103 p. 

87 
88 

COMPLETED PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

SNAKE RIVER PLAIN REGIONAL AQUIFER-SYSTEM STUDY 

By Gerald F. Lindholm, Boise, Idaho 

INTRODUCTION 

The economy of southern Idaho is based 

largely on agriculture, and a key to successful 

agriculture is an adequate supply of good-quality 

water for irrigation. In the past, most water for 

irrigation was obtained from the Snake River. Today (1984), ground water is also a major source. 

As water use increases, so does competition for 

the right to use water. It follows that a better 

understanding of the hydrologic system in the 

Snake River Plain is needed. 

The Snake River Plain is an area of about 

15,600 mi2 that extends across southern Idaho into eastern Oregon (fig. 49) and is included in the 

69,200- mi2 drainage basin of the Snake River 

above Weiser, Idaho. Along its 502-mile course 

from Heise to Weiser, the Snake River descends 

2,930 feet. The surface of the Plain decreases in 

altitude from about 6,000 feet above sea level in 

the northeast to 2,100 feet in the west. Surrounding mountains are as much as 12,000 feet 

above sea level. 

Average annual precipitation on much of the 

Plain is less than 10 inches, one-third to one-half 

of which falls during the April through September 

growing season. Most water available to the Plain 

originates as snow on surrounding mountains 

where annual precipitation is as much as 60 

inches. 

The Snake River Plain regional aquifersystem study began in 1979 (Lindholm, 1981) and 

was completed in 1984. For study purposes, the 

Plain was divided into eastern and western parts 

on the basis of geology and hydrology (fig. 49). 

Geophysical studies indicate that the 10,800-

mi2 eastern Plain is basically a downwarp. Most 

of the fill consists of Quaternary basalt. Near the 

margins, unconsolidated sedimentary rocks 

overlie and are intercalated with the basalt (fig. 

50). Tops of basalt flows are typically broken and 

have high hydraulic conductivities. Consequently, thick sections of basalt, which include 

many flows, store and yield large quantities of 

water. In places, the basalt aquifer may be several 

thousand feet thick; however, the upper 200 to 

500 feet are thought to be the most permeable. 

An estimated 200 to 300 million acre-ft of water 

are stored in the top 500 feet of the regional 

aquifer system. In much of the eastern Plain; the 

regional aquifer system is unconfined. 

About two-thirds of the ground water discharged from the eastern Plain is through a series 

of springs that flow to the Snake River between 

Milner and King Hill. Included in that reach are 

11 of the 65 springs in the United States that 

discharge an average of more than 100 ft3/s 

(Meinzer, 1927, p. 42-51). The hydrologic boundary between the eastern and western parts of the 

Plain includes a 40-mile reach of the Snake River 

where springs are most concentrated. A second 

series of springs between Blackfoot and Neeley 

account for most of the remaining discharge. 

The western Plain is bounded by well-defined 

high-angle faults and is a graben. Quaternary and 

Tertiary sedimentary rocks of variable thickness 

are the predominant fill material (fig. 50). In the 

Boise River Valley, most water is obtained from 

unconfined alluvial sand and gravel. Elsewhere, 

rocks are predominantly fine grained; included 

sand and gravel aquifers are largely confined. 

Ground-water discharge to the Snake River in the 

western Plain is small relative to that in the 

eastern Plain. A geothermal aquifer system 

underlies much of the western Plain. 
GEOHYDROLOGIC FRAMEWORK 

Investigators have used a variety of surface 

geophysical techniques to define the regional 

structural (crustal) features of the Snake River 

Plain (Whitehead, 1984a). However, little work 

has been done with the specific objective of defining the geohydrologic framework. The approach 

in this study was to use results of previous studies 

as a starting point and concentrate interpretive 

efforts on the geologic section that most likely 

contains significant amounts of water. 

In about two-thirds of the Snake River Plain, 

Quaternary basalt of the Snake River Group contains and readily yields large quantities of water 

to wells. Most of the wells on the Plain penetrate 

only a few tens of feet of the basalt aquifer; accordingly, aquifer thickness is largely unknown. 

Zohdy and Stanley (1973) demonstrated the 

usefulness of vertical electrical-resistivity soundings to help define the thickness of major rock 

types in the eastern Plain. After drill-hole data 

were assetnbled and analyzed during this study, 

electrical-resistivity soundings were made to help 

define the thickness of the Quaternary basalt. 

About 400 miles of resistivity profiles were 

generated. These new profiles supplemented 

about 300 miles of previous resistivity profiling. 

Other surface geophysical techniques were also 

investigated and gravity modeling was used in 

areas where no other geophysical data were 

available. 

To help verify subsurface interpretations 

based on surface geophysics, a 1, 123-foot deep test 

hole was drilled in Gooding County on the eastern 

Plain (fig. 49). About 75 percent of the hole was 

cored; the remainder of the hole was drilled by 

rotary methods. Five zones were isolated in the 

hole and piezometers installed to determine head 

changes with depth (Whitehead and Lindholm, 

1984). 

Quaternary basalt underlying the eastern 

Plain is estimated to be as much as 5,000 feet 

thick, of which a maximum of about 3,500 feet 

may be saturated (fig. 51). Thickness of the 

Quaternary basalt is greatest near the center of 

the eastern Plain between Arco and Lake 

Walcott. Individual basalt flows average 20 to 25 

feet in thickness. The top of each flow, generally 

less than 6 feet thick, is typically fine grained, 

vesicular, highly broken, and has high hydraulic 

conductivity. The remainder of the flow is typically coarse grained, massive, ~nd may be broken 

vertically. Hydraulic conductivity of the massive 

basalt is dependent on the degree of fracturing 

and is typically low. It follows that transmissivity 

of the total basalt section is largely dependent on 

the number of individual flows and the thickness 

of permeable flow tops. 

Porosity and hydraulic conductivity of volcanic rocks in the Snake River Plain appear to 

decrease with depth. Most water probably moves 

through the highly conductive upper 200 to 500 

feet of the Quaternary basalt. Miocene basaltic 

and rhyolitic rocks with lower hydraulic conductivity underlie the Quaternary basalt. 

Ninety miles of the north wall of the Snake 

River canyon, from Milner to King Hill, were 

mapped during this study to determine geologic 

controls on the location and magnitude of springs 

issuing from the basalt. Results are being 

prepared to present as maps and sections in the 

U.S. Geological Survey Miscellaneous Geologic 

Investigations series. 

Fine-grained Quaternary-Tertiary sediments, 

which predominate in the western Plain (fig. 50), 

are as much as 5,000 feet thick near the IdahoOregon State line. Alluvial sand and gravel in the 

Boise River Valley (fig. 49) are several hundred 

feet thick in places. Quaternary basalt in the central and eastern parts of the western Plain are 

as much as 2,000 feet thick. Locally, the basalt 

yields large quantities of water, although 

saturated thickness is generally less than 500 feet 

(fig. 51). Miocene basalt, stratigraphically 

equivalent to the Columbia River Basalt Group, 

underlies most of the western Plain. 

Whitehead (1984b) summarized current 

understanding of the geohydrologic framework of 

the Snake River Plain and presented a series of 

illustrations, including maps, showing saturated 

and total thicknesses of the Quaternary basalt, 

geologic sections, resistivity profiles, gravity 

model profiles, and a table of physical and wateryielding characteristics of rocks underlying the 

Snake River Plain. 

WATER BUDGETS AND GROUND-WATER AND 

SURFACE-WATER RELA liONS 

Only a small part of the water available to 

the Snake River Plain regional aquifer system 

originates from precipitation falling on the Plain. 

Therefore, it was necessary to consider the entire 

89 
90 

118 " 112" 

MONTANA 

44" 

42" 

0 

I 1------- 0 50 100 KILOMETERS 

EXPLANATION 

EASTERN SNAKE RIVER PLAIN 

~~~~j WESTERN SNAKE RIVER PLAIN 

AREA OF SNAKE RIVER PLAIN 

BOUNDARY OF SNAKE RIVER BASIN 

GAGING STATION 

0 WELL REFERENCED IN TEXT 

, LINE OF SECTION 

Figure 49. - Study area of the Snake River Plain regional aquifer system. 

Snake River drainage basin above Weiser, Idaho, 

to study the water budget. 

Existing hydrologic data were evaluated for 

adequacy, and additional data needs were identified. Supplemental data were collected on 

precipitation, streamflow, withdrawals, irrigation 

return flow, ground-water levels, and spring 

flows. 

Data collection was concentrated in 1980. 

Water levels were measured in about 1,600 wells 

in spring of 1980 and repeated in about 800 wells 

in August 1980. Configuration of the regional 

water table in spring of 1980 is shown in figure 

52. Annual water budgets from 1934 through 

1980 for the entire Snake River drainage basin 

and annual ground-water budgets from 1912 

through 1980 for the eastern Plain and from 1930 

through 1980 for the western Plain were also 

estimated and reported by Kjelstrom (1984). 

Millions of acre-feet of surface water are 

diverted annually for irrigation and have greatly 

increased the amount of water available for 

ground-water recharge. In one area south of the 

Snake River near Twin Falls, ground-water levels 

rose as much as 200 feet in 5 years after the start 

of irrigation (fig. 53). In much of the eastern Plain, 

water levels rose several tens of feet over tens of 

years as indicated by water levels observed in 

wells in Jerome and near Fort Hall (fig. 53). 

Water levels in the western Plain also rose in 
118. 

MONTANA 

44. 

42. 

I 

Bear/l 1 

~~.:;i i#JL- --- ----r;;ke\J l 

SCALE 1:5,000,000 

0 50 

0 50 100 KILOMETERS 

NEVADA 

I 

I 

Grear I Salt 

I [ _______ _ 

EXPLANATION 

GEOLOGIC UNITS 

Quaternary-Tertiary sedimentary rocks, undifferentiated 

Quaternary-Tertiary basalt, undifferentiated 

Quaternary-Tertiary silicic volcanic rocks, 

undifferentiated 

Tertiary basalt 

Tertiary volcanic rocks, undifferentiated 

AREA OF SNAKE RIVER PLAIN 

BOUNDARY BETWEEN EASTERN 

AND WESTERN PLAIN 

BOUNDARY OF SNAKE RIVER 

BASIN 

Pre -Tertiary rocks, undifferentiated, mainly sedimentary, 

includes small outcrops of Tertiary rocks 

H Cretaceous granitic rocks of the Idaho batholith 

Figure 50. -Generalized geology of the Snake River drainage basin above Weiser, Idaho (modified from Whitehead, 1984b). 

response to surface-water irrigation (well near 

Nampa, fig. 53). 

As ground-water levels rose, discharge to 

rivers increased. Long-term data on gaining 

reaches of the Snake River that include the major springs are the key to understanding 

hydrologic changes in the eastern Plain. To supplement existing data, additional spring 

discharge measurements were made at various 

places and times during the study. Kjelstrom 

(1984) documented changes in ground-water 

discharge to reaches of the Snake River that include major groups of springs (fig. 54). 

Discharge from the group of springs between 

Blackfoot and Neeley (fig. 54) has been relatively 

constant over the period of record (1912-80). 

Upgradient from the springs, considerable 

acreage was irrigated prior to the start of 

91 
92 

discharge-data collection and, despite an increase 

in surface-water diversions of about 1.5 million 

acre-ft from 1912 through 1952, ground-water 

discharge remained relatively stable. It seems 

likely that by 1912, ground-water recharge and 

discharge affecting the reach from Blackfoot to 

Neeley were approximately in balance. 

In the reach from Milner to King Hill, some 

increase in ground-water discharge probably occurred between the start of irrigation (1880's) and 

the start of hydrologic-data collection (1902). A 

40-year trend of increased ground-water 

discharge started in 1912 (fig. 54), the result of 

major increases in surface water irrigated acreage 

following completion of reservoirs and diversion 

structures on the Snake River. In the early 

1950's, spring discharge stabilized, implying a 

temporary balance between recharge and 

discharge that lasted for several years. A period 

of overall decrease in ground-water discharge 

followed and continued to 1980. The decrease 

probably is due to a combination of factors, including increase in withdrawals of ground water, 

decrease in diversions of surface water, increase 

in efficiency of irrigation (largely the use of 

sprinklers), and climatological changes. 

EXPLANATION 

THICKNESS, IN FEET 

~ Less than 500 

ITIJ] 500 to 1500 

~ 1500to2500 

rniiiiil 2500 to 3500 

~ Greater than 3500 

AREA OF SNAKE RIVER PLAIN 

Figure 51. - Thickness of saturated Quaternary basalt underlying the Snake River Plain (modified from Whitehead, 1984b). 
Water-level data for the eastern Plain are 

sparse prior to the 1950's. Therefore, correlation 

of pre-1950 water-level data with ground-water 

discharge is not possible. However, since the 

1950's, there is a good correlation between 

ground-water levels and ground-water discharge 

to the reach of the Snake River from Milner to 

King Hill (fig. 55). 

The net result of 100 successive years of irrigation on the eastern Plain is shown by the 

ground-water budgets for 1880 and 1980 (fig. 56). 

Before irrigation, about two-thirds of the total 

recharge was drainage from tributary basins. In 

1980, tributary basins supplied about 20 percent 

of the recharge; two-thirds of the recharge was 

44° 

42° 

I 

5lo 

C!JII 

~II C3 0 - 0 

I 

I 

SCALE 1:3,000,000 

25 50 MILES 

percolation of excess surface water diverted for 

irrigation. The remainder was from precipitation 

on the Plain and Snake River losses. The imbalance between recharge and discharge in 1980 

(400,000 acre-ft) was water taken from aquifer 

storage. From 1880 to 1980, the amount of annual 

ground-water recharge increased from about 3.2 

to 6. 7 million acre-ft. 

WATER QUALITY AND GEOCHEMISTRY 

Several thousand surface- and ground-water 

samples have been collected on and near the 

Snake River Plain. Analyses from the U.S. 

EXPLANATION 

-4000- WATER·TABLE CONTOUR .. Shows altitude of the regional water 

table. lnterval100, 200, and 400 feet. Datum is sea level 

GENERAL DIRECTION OF GROUND-WATER FLOW 

AREA OF SNAKE RIVER PLAIN 

Figure 52.-Configuration of the regional water table in the Snake River Plain, spring 1980 (modified from Lindholm 

and others, 1983). 

93 
94 

~ LLI 

LL 

~ 

w 

en 

~ 

...J 

LLI 

~ ...J 

a: 

LLI 

1-

~ 

200 

160 

120 

80 

40 

1920 

Near Twin Falls 

1930 

YEAR 

1940 1950 1960 

Figure 53.-Changes in Snake River Plain ground-water 

levels due to surface-water irrigation (locations shown in 

fig. 49). 

Geological Survey files and published reports 

were assembled and used to determine the 

relative proportion of major ions in streams entering the Plain and the range of solute concentrations and areal distribution of selected constituents in ground water. Previous investigations 

emphasized local variations, both temporal and 

spatial, in water quality. The approach taken during this study was to describe regional variations 

of ion concentrations in water and determine how 

water reacts ·with the rocks through which it 

flows. 

Ion concentrations in surface water flowing 

onto the Plain vary, depending on rock types in 

the tributary basin. Surface water from areas 

underlain by granitic rocks of the Idaho batholith 

is typically the least mineralized; surface water 

from areas underlain by pre-Cretaceous carbonate 

rocks is the most mineralized. 

Concentrations of dissolved solids are less 

than 400 milligrams per liter (mg/L) at 78 percent of the 1,123 ground-water and spring sampling sites across the Snake River Plain. The 

areal distribution of concentrations of dissolved 

solids is shown in figure 57. Concentrations of 

dissolved solids are least in areas of exposed 

basalt and thin soil cover in the eastern Plain and 

greatest in areas of fine-grained sedimentary 

rocks and in the intensively irrigated areas. Concentrations of chloride are less than 20 mg/L at 

60 percent of1,649 sampling sites. Areas ofhigh 

and low chloride concentrations generally coincide with areas of high and low dissolved solids 

<W. H. Low, U.S. Geological Survey, written commun., 1984). 

Geochemistry of the aquifer system in the 

eastern Plain was defined by four indirect 

methods: (1) identification of minerals in the 

weathered rocks, (2) comparison of thermodynamic mineral indices with plausible ion 

reactions, (3) comparison of stable-isotope ratios 

in ground water with weathered mineral products 

from the rocks, and (4) calculation of chemical 

budgets. 

Water and rock samples were collected in 

areas of recharge, from intermediate points along 

ground-water flowpaths, and in areas of 

discharge. Water samples were analyzed for common cations and anions, trace metals, and stable 

isotopes. Rock samples from outcrops and the subsurface were analyzed to determine mineralogic 

composition and weathering products. 

Solutes in ground. water in the eastern Plain 

are generally in equilibrium with minerals in the 

rock framework. Alteration minerals in the rock 

framework were identified by petrographic 

microscope, scanning-electron microscope, and 

energy -dispersive X -ray fl. uorescence methods. 

Chemical equations were written for weathering 

of the minerals identified and compared with 

water-mineral saturation indices. The validity of 

the proposed reactions was evaluated using 

isotopes of carbon and sulfur, which comprise 80 

percent of the anions in most of the water 

samples. 

The most plausible reactions controlling the 

ion concentrations appear to be the weathering 

of plagioclase to clay minerals; dissolution of 

olivine, anhydrite, and pyrite; and precipitation 

of calcite and quartz. About 25 percent of the 

solute load is from weathering of the rock 

framework or from man's activities; the remainder is in recharge water from tributary 

drainage basins. 

The same geochemical processes may take 

place in the western Plain but were not defined. 

Concentrations of dissolved solids in thermal 

waters in the western Plain are similar to those 

in the overlying cold-water system. Reactions controlling solutes in thermal waters are also · 

similar, but ion exchange processes produce 

higher concentrations of sodium and. lower concentrations of calcium and magnesium; the pH is 

also. higher. Preliminary results of carbon-14 age 

dating of water from selected geothermal wells 

suggest that residence time of some geothermal 

waters may be about 17,700 ±4,000 years. 
0 7 

z 

0 

u 

w 

en 

a: 

w 

Q.. 6 

tu 

w 

u. 

u 

Cii 

::> 5 u 

u. 

0 

en 0 

z <( 4 en 

::> 

0 J: 1-

~ 

w· 3 (.!) 

a: <( 

J: 

u 

en 

0 

2 

§ N 0 0 0 0 0 0 fiS as o; N (") c;; .... 0) 0) 0) 0) 1B 

YEAR 

Figure 54.- Ground-water discharge to the Snake River from the eastern part of the Snake River 

Plain regional aquifer system (locations shown in fig . 49). 

WATER USE 

Irrigation is by far the largest consumptive 

use of water on the Snake River Plain. Therefore, 

the delineation of past and present irrigated areas 

was needed to determine stresses on the 

hydrologic system and to calculate recharge rates 

for ground-water flow simulation models. 

Irrigation on the Snake River Plain started 

along the Boise River in about 1843. Development 

was slow until the 1880's, when Congress encouraged reclamation of desert lands and expansion of irrigated acreage in the arid West. The 

Desert Land Act of 1877, a survey of irrigable 

lands in 1889, and the Carey Act of 1894 provided 

incentive, and rapid irrigation development 

followed. By 1899, about 550,000 acres were irrigated with surface water. The Reclamation Act 

of 1902 stimulated further expansion by providing funds for construction of major instream 

storage facilities and canals. By 1929, about 2.2 

million acres were irrigated with surface water. 

Increases in irrigated lands from 1929 through 

1945 were moderate, owing to depressed economic 

conditions, World War II, and full appropriation 

of surface-water rights. In the 1940's, demand for 

irrigation water increased, and because surface646 

1-

ww 

~u 650 

z~ ;i§ 

wen 654 

1-o <(z 

3:<( 140 o...J 

1-3: 

J:O 1-...J 

150 Q..W 

WID 

0 

160 w 

(.!) 0 7000 a: z <( • 0 J:a:U 

uww en2:en 

-a: a: 6500 Ow w a::..: Q.. 

~~ tu <(en w 3:wu. 6000 

' J: u 01-Cii 

zo:> ::>1-u 

~ ~ 5500 

(.!) LCi 

0) 

WATER YEAR 

Figure 55.- Relation of ground-water levels to groundwater discharge from the eastern part of the Snake River 

Plain regional aquifer system (locations shown in fig. 49). 

95 
96 

water rights were fully appropriated, ground 

water became a logical source of supply. By 1966, 

ground water was used to irrigate about 700,000 

acres. In the 1960's, installation of large pumping stations on the Snake River began. Where the 

river is deeply entrenched, water is lifted several 

hundred feet to supply the adjacent irrigated 

uplands. 

In 1980, about 3.1 million acres of land, or 

32 percent of the Snake River Plain, were irrigated (Lindholm and Goodell, 1984). About 13 

million acre-ft of surface water were withdrawn 

to irrigate 2.0 million acres. Another 2.3 million 

acre-ft were pumped from 5,300 wells to irrigate 

1.0 million acres. The remaining 0.1 million acres 

were irrigated with combined surface and ground 

water. 

Acreage irrigated in 1980 was determined 

from single-date digital multispectral scanner 

(Landsat) data by the Idaho Department of Water 

Resources Image Analysis Facility through a 

cooperative agreement with the U.S. Geological 

Survey. Source of water (surface, ground, or combined) was determined from published data, 

aerial photographs, and field checking. Historical 

acreages were estimated from published maps for 

1899, 1929, 1945, and 1966. Although methods 

of defining irrigated areas varied, the location and 

relative numbers of acres determined are adequate for comparisons. 

Ground-water and river pumpage in 1980 

were estimated using electrical powerconsumption data because nearly all pumps on 

the Plain are electrically powered. Field 

measurements were made on 79 wells and river 

pumping stations in 1980 to determine the power 

consumption per acre-foot of water pumped per 

foot of lift. On the eastern Plain, river pumping 

stations are typically 100 to 500 horsepower, pumping lifts from the Snake River are less than 200 

feet, and the median drawdown in wells is 6 feet 

(Bigelow and others, 1984). Water commonly is 

distributed by sprinklers. On the western Plain, 

most irrigation wells are completed in sand and 

gravel aquifers that yield a moderate supply. 

River pumping stations are generally less than 

100 horsepower on the western Plain, pumping 

lifts from the Snake River are similar to those on 

the eastern Plain but in places are as much as 500 

feet, and median drawdown in wells is 56 feet. 

Gravity irrigation is more common on the 

Western Plain. 

For comparative purposes, volumes of ground 

water pumped in 1980 were grouped into 

1880 

4 

w TOTAL 3.2 

(!) 3 a: 1-

w <t: w Tributary basins 2 J: LL 

u w w a: a: u 

<t: 

LL 

0 0 (/) 

z w 0 (!) ::::i a: _J 

<t: ~ 2 J: TOTAL 3.2 u z (/) 3 0 

Snake River gains 

4 

1980 

Irrigation return 

4 

w 

(!) 3 1- a: w <t: w J: LL 2 u w w a: a: u 

<t: 

LL 

0 0 (/) 

z w 0 Pumped (!) ::::i a: _J 

<t: ~ 2 J: 

u 

(/) ~ 

0 3 

4 

5 TOTAL 7.1 

6 

Snake River gains 

7 

Figure 56.- Changes in ground-water budget, 1880 and 

1980, the eastern part of the Snake River Plain regional 

aquifer system (area south of the Snake River from Neeley 

to Salmon Falls Creek excluded). 

15-minute blocks (fig. 58). Ground-water pumpage 

is greatest on the eastern Plain in areas where 

surface water is 'not available and where 

topography limits irrigation to locally supplied 

sprinkler systems. 

Other consumptive uses of water (public 

supply, industrial, rural, domestic, and stock) are 

small relative to irrigation. The quantity of water 

use was obtained from the State-Federal Water 

Use data base or was estimated. Hydroelectric 

power generation is the largest nonconsumptive 

use of water. 
44" 

42" 

EXPLANATION 

DISSOLVED-SOLIDS CONCENTRATIONS, 

IN MILLIGRAMS PER LITER 

ITIIIIJ Less than 200 

§ 200to400 

lliiiliiim Greater than 400 

AREA OF SNAKE RIVER PLAIN 

Figure 57.-Areal distribution of dissolved-solids concentrations in ground water in the Snake River Plain regional 

aquifer system. 

SIMULATION OF GROUND-WATER FLOW IN 

THE EASTERN PART OF THE SNAKE RIVER PLAIN 

A two-dimensional parameter estimation 

model (Garabedian, 1984) with 4 mile x 4 mile 

cells, which incorporated a nonlinear least-square 

regression technique, was used to estimate 

transmissivity, leakance, and boundary fluxes of 

the regional aquifer system in the eastern Plain. 

After the parameters were estimated with the 

parameter-estimation model, a four-layered, 

three-dimensional, finite-difference model 

(Trescott, 1976; Trescott and Larson, 1976) with 

the same cell size was used to simulate groundwater flow in the eastern part of the Snake River 

Plain (S. P. Garabedian, U.S. Geological Survey, 

written commun., 1984). Boundaries ofthe models 

were no-flow, constant-flux, and head dependent 

rivers and springs. It was assumed that there is 

no underflow between eastern and western parts 

of the Snake River Plain, owing to the apparent 

sink formed by the Snake River. Based on 

geologic and hydrologic conditions, the eastern 

Plain was then artificially subdivided into 40 

97 
98 

44" 

42" 

I 

I 

~~o (!)IJ: 

~ 11(3 0 - 0 

I 

I 

SCALE 1 :3,000,000 

25 50 MILES 

EXPLANATION 

PUMPAGE, IN ACRE-FEET 

PER SQUARE MILE 

No pumpage 

Less than 50 

50 to99 

100 to499 

Greater than or equal to 500 

TOTAL VOLUME PUMPED, IN THOUSANDS. OF ACRE-FEET 

EXAMPLE: Pumpage for irrigation in 1980 was between 

100 and 499 acre-feet per square mile. The total was 

54,000 acre-feet. 

AREA OF SNAKE RIVER PLAIN 

NOTE: Each complete block represents an area of 

15 minutes latitude by 15 minutes longitude 

Figure 58.- Estimated 1980 ground-water pumpage from the Snake River Plain regional aquifer system (modified from 

Bigelow and others, 1984). 

zones. Parameter values within each zone were 

assumed to be uniform. Throughout the modeling 

process, special efforts were made to keep values 

of geohydrologic parameters within reasonable 

ranges, consistent with what is known. 

The two-dimensional parameter estimation 

model suggested that transmissivity ranges front 

0.05 to 44 ft 2

/s. The values are generally consistent with the ranges estimated by Mundorff and 

others (1964) using a flow-net analysis, by Norvitch and others (1969) using an analog model, 

and by Newton (1978) using a digital flow modeL 

Along the margins of the Plain, and in the central part where better head control was available 

during this study, transmissivity values obtained 

by the parameter-estimation model were lower 

than those obtained previously. 

Simulated and measured .ground-water discharge to subreaches of the Snake River were 

similar. The coefficient of correlation between 

simulated and measured hydraulic head is 0.996 

and standard error of estimates of head is 40 feet. 
GEOLOGY 

A 

FEET ABOVE 

SEA LEVEL 

6000 

5000 

4000 

3000 

2000 

VERTICAL SCALE GREATLY EXAGGERATED 

A' 

0 20 40 MILES 

EXPLANATION 0 20 40 KILOMETERS 

Ed BASALT ~~Zi~fl RHYOLITE ~;:N\i:; J SEDIMENTS 

MODEL LAYERS 

A 

FEET ABOVE 

SEA LEVEL 

6000 

5000 

4000 

3000 

2000 

A' 

1000 -L------------------------------------------------------------~ VERTICAL SCALE GREATLY EXAGGERATED 0 20 40 MILES 

0 20 40 KILOMETERS 

EXPLANATION 

._ GENERAL DIRECTION OF GROUND-WATER FLOW 

1,2,3,4 AQUIFER LAYER IDENTIFIERS USED IN THE FLOW MODEL 

Figure 59.- Generalized geologic section and conceptual model, eastern part of the Snake 

River Plain regional aquifer system (location of section shown in fig. 49). 

The flow model is more sensitive to changes in 

recharge than to changes in transmissivity. 

Parameter values estimated from the calibrated two-dimensional parameter estimation 

model were the initial input data for the fourlayered, three-dimensional steady-state and transient flow models. The basalt aquifer was artificially subdivided into four aquifer layers in 

order to simulate head changes with depth (fig. 

59). Modeled aquifer layers 1 and 2 are 200 and 

99 
100 

300 feet thick and represented the basalts having 

the highest hydraulic conductivity. Most wells are 

completed in the upper 200 feet; consequently, 

less is known about hydraulic conditions in layer 

2 and little is known about conditions in layers 

3 and 4. On the basis of scant evidence, simulated 

hydraulic conductivities in the modeled aquifer 

layers 3 and 4 were reduced by one-third and twothirds of the observed values. 

Simulated transmissivities for modeled 

aquifer layer 1 are shown in figure 60. 

115 ° 114 . 

SCALE 1:2,000,000 

0 25 

Transmissivity is greatest in the central part of 

the eastern Plain. The area of relatively low 

transmissivity comprising model zones 12 and 22 

(fig. 60) probably is related to a major rift zone; 

the low transmissivity area comprising zone 15 

is composed of sediments interlayered with 

basalt. 

The model was tested for anisotropy of the 

basalt aquifer. Although inconclusive, test results 

suggest that transmissivity is slightly greater in 

the direction perpendicular to the longitudinal 

113. 112° 

L_l 

I 

_____ _L_ 

L, 

l 

~l 

L, 

~-

\ 

r--~ - J I 

EXPLANATION 

1 I 

: (60) : 

AREA OF ZONE·· Bold number used to identify zone. 

Number in parenthesis is average transmissivity 

of zone, in feet squared per second 

BOUNDARY OF GROUND-WATER MODEL 

AREA OF EASTERN SNAKE RIVER PLAIN 

Figure 60.- Simulated transmissivities for modeled aquifer layer 1, eastern part of the Snake River Plain regional 

aquifer system. 
axis of the eastern Plain. The results are consistent with geologic evidence; fractures and faults 

in southeast-trending rift zones may increase 

hydraulic conductivity in that direction. 

The storage coefficient of aquifer layer 1 

varies from 0.05 to 0.20 according to the rock type. 

Aquifer layers 2, 3, and 4 were assigned a uniform 

storage coefficient of 0.0001. 

4~0 ~----------~---------------~----------~---------------~----~---------------~-----------r------------~-----------. 

...J 

~ 4560 ...J 

~ rn 

w 4540 

~ aJ 

<( 

~ 4520 LL 

~ 

u..i 

c 

~ 4500 

~ <( 

...J 

w 4480 

~ ...J 

ri: 

w i 4460 

r:i 

w 

;;:: 

a: 

w 

~ 

<Co 

zz 

rna 

au 

~--~ 

wa: 

<!lw 

CX:n.. 

~tu 

~~ 

Cu 

a: iii 

W::J 

i~ c 

z 

::J 

a 

a: 

(!J 

4440 

9000 

8000 

7000 

6000 

5000 

Well near Mud Lake 

4000 ~----------~----------~~----------~----~------L-----~----~------~----~ 

1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 

YEAR 

Figure 61.-Simulated and measured water levels in a well near Mud Lake, ground-water discharge 

to the Snake River from Milner to King Hill, and model sensitivity to changes in transmissivities, 

eastern part of the Snake River Plain regional aquifer system. 

101 
102 

Transient simulations, using 5-year time 

steps from 1890 to 1980, were made to determine 

hydrologic changes in the eastern Plain resulting 

from continued use of surface water for irrigation. 

Simulated and measured water levels and 

discharge to subreaches of the Snake River were 

comparable (fig. 61). Model response to changes 

in transmissivity is also shown in figure 61. 

The flow model was used to simulate preirrigation hydrologic conditions and to determine 

probable aquifer response to hypothetical future 

water-resource development in the eastern Plain. 

If 1980 conditions of recharge and discharge 

are extended to the year 2010, the model indicates 

that water levels may decline 2 to 8 feet in most 

of the eastern Plain with greater declines along 

the boundaries. Spring flow may decrease about 

5 percent and river leakage into the aquifer may 

increase 9 percent. As an extreme example, if 

ground-water withdrawals were increased by 

2,400 ft3/s in order to irrigate another 1 million 

acres in the eastern Plain, head declines of 10 to 

50 feet and decreases in spring flow of 20 percent 

might be expected within 30 years. 

SIMULATION OF GROUND-WATER FLOW IN 

THE WESTERN PART OF THE SNAKE RIVER PLAIN 

Geologic complexities and general lack of 

data for model input dictated that major emphasis 

on the western Plain be given to development of 

a conceptual flow model. · 

Rather than a single regional aquifer, a number of local aquifers collectively operate as a 

regional aquifer system. Basalt of the Snake 

River Group, particularly in the vicinity of Moun~ 

tain Home, yields large quantities of water, but 

areal extent is small. Alluvial sand and gravel 

aquifers in the Boise River Valley yield moderate 

to large amounts of water to wells. Elsewhere, 

sand lenses in the predominantly fine-grained 

Quaternary-Tertiary Bruneau Formation and 

Idaho Group are the best aquifers. Thermal water 

in the Tertiary Banbury Basalt, Idavada 

Volcanics, and Columbia River Basalt Group is 

confined. The thermal water is used mainly for 

space heating in the Boise area and for irrigation 

south of the Snake River. 

Nat ural recharge to shallow aquifers is from 

tributary basin underflow, leakage of streams 

that drain the tributary basins, and direct 

precipitation. Deeper aquifers are recharged 

laterally from faulted margins of the Plain and 

by vertical leakage. As in the eastern Plain, use 

of surface water for irrigation for more than 100 

years has effected major changes in the hydrologic 

system. In 1980, infiltration of surface water applied for irrigation provided about two-thirds of 

the recharge. Since the start of irrigation, groundwater levels in the Boise River Valley have risen 

several tens of feet (well near Nampa, fig. 53). In 

the lower Boise River Valley, high water levels 

necessitate drainage ditches to relieve waterlogging. Ground water in the western Plain also 

discharges to the Snake River and its tributaries. 

Owing to the magnitude of flow in the Snake 

River, estimation of river gains is difficult at best. 

A three-layer finite-difference flow model 

(Trescott, 1976; Trescott and Larson, 1976) with 

2 mile x 2 mile grid cells was developed by G. 

D. Newton (U.S. Geological Survey, written commun., 1984) to simulate the conceptualized 

system in the western Plain (fig. 62). The steadystate model was calibrated to 1980 hydrologic conditions. The transient model simulated 1890-1980 

conditions in 10-year time increments. Transient 

calibration helped refine initial estimates of 

transmissivity, recharge and discharge rates, 

specific yield, and vertical hydraulic conductivity. 

Calibration in 10-year increments was uncertain 

because long-term hydrologic data were generally 

lacking. Therefore, the model also was calibrated 

to several successive 1-year periods using 

monthly time steps. All rivers were modeled as 

leaky connections to the aquifer system; canals 

and drains in the lower Boise River Valley were 

similarly modeled. 

The top aquifer layer, about 500 feet thick, 

is largely alluvial sand and gravel west of Boise. 

East of Boise, the top layer includes basalt of the 

Snake River Group and Bruneau Formation, and 

sediments of the Bruneau Formation and Idaho 

Group. Simulated transmissivities for modeled 

aquifer layer I are highly variable and range from 

0.01 to 0.22 ft2/s (fig. 63). Transmissivity is 

highest in the Boise River Valley and lowest 

along the margins of the western Plain where 

fine-grained sediments predominate. 

Modeled aquifer layer 2 represents several 

thousand feet of predominantly fine-grained 

sediments. The estimated transmissivity is about 

0.005 ft2/s. 

Modeled aquifer layer 3 represents Tertiary 

volcanic rocks, some of which are exposed along 

the boundaries of the western Plain. Thickness 

of the volcanic rocks is largely unknown but is 

assumed to be several thousand feet. Estimated 

transmissivity ranges from about 0.01 to 0.2 ft2/s. 

Water in modeled aquifer layer 3 is confined by 

the fine-grained sediments in modeled layer 2, 
FEET 

4000 

2000 

Sea level 

-2000 

-4000 

-6000 

-8000 

FEET 

4000 

2000 

-6000 

-8000 

B 

GEOLOGY 

VERTICAL SCALE GREATLY EXAGGERATED 

EXPLANATION 0 

CONTACT .. Dashed where approximately 

located, queried where inferred 

5 

~ FAULT .. Arrows show relative direction of movement 

MODEL LAYERS 

B 

Recharge from irrigation and precipitation 

t + 

VERTICAL SCALE GREATLY EXAGGERATED 

EXPLANATION 

- LOW-PERMEABILITYROCKS 

- DIRECTION OF WATER MOVEMENT 

0 

0 5 

10 KILOMETERS 

5 10 MILES 

10 KILOMETERS 

1,2,3 AQUIFER LAYER IDENTIFIERS USED IN THE FLOW MODEL 

B' 

B' 

Figure 62.- Generalized geologic section and conceptual model, western part of the Snake 

River Plain regional aquifer system (location of section shown in fig. 49). 

103 
104 

which have an average vertical hydraulic conductivity of about 3 x 10- 9 ft/s. Although hydraulic 

heads are high in layer 3, the volume of recharge 

to upper layers is probably small and is masked 

by other sources of recharge. 

Storage coefficients of 0.10, 0.002, and 0.001 

were assigned for layers 1, 2, and 3 to yield the 

best simulation results. By removing all pumpage 

and recharge from irrigation return flow 

resulting from surface-water irrigation, preirrigation hydrologic conditions were simulated. The 

116' 

OREGON 

43' 

SCALE 1:2,000,000 

transient model was used to simulate possible 

aquifer conditions to the year 2010, using 1980 

recharge rates. Model response suggests that 

future water-level declines can be expected if 

ground-water withdrawals increase. 

SUMMARY 

Large quantities of good-quality ground and 

surface water are available on the Snake River 

Plain. For study purposes, the Plain was divided 

into eastern and western parts. As much as 3,500 

115' 114' 

\ 

~ 

0 25 50 MILES 

0 25 50 KILOMETERS 

EXPLANATION 

,--

1

--, AREA OF ZONE-· Bold number used to identify zone. 

: (o. 2o) l Number in parenthesis is average transmissivity 

' ' of zone, in feet squared per second 

• MODEL AREA REFERENCED IN TEXT 

BOUNDARY OF GROUND-WATER MODEL 

AREA OF WESTERN SNAKE RIVER PLAIN 

' Figure 63.- Simulated transmissivities for modeled aquifer layer 1, western part of the Snake River Plain regional 

aquifer system. 
feet of saturated Quaternary basalt underlie the 

eastern Plain. The upper 200 feet have the 

highest hydraulic conductivity, and estimated 

transmissivity ranges from 0.05 to 44 ft2/s. An 

estimated 200 to 300 million acre-ft of water are 

stored in the upper 500 feet. The thickness of the 

basalt aquifer was estimated largely from 

electrical-resistivity soundings. Interpretations of 

surface geophysical data were checked by drilling a 1,123-foot test hole. In the western Plain, 

generally fine-grained Tertiary sedimentary 

rocks predominate; water in the western Plain is 

obtained from unconfined alluvial sand and 

gravel aquifers in the Boise River Valley, from 

basalt east of Boise, and from confined sand 

aquifers in other areas. Volcanic rocks underlying the fine-grained sedimentary rocks in the 

western Plain contain confined thermal water. 

Prior to irrigation, streamflow and underflow 

from tributary drainage basins were the major 

sources of recharge to the Snake River Plain 

regional aquifer system. In 1980, infiltration of 

surface water used for irrigation supplied about 

two-thirds of the recharge in the eastern Plain. 

Over the years, ground-water levels rose several 

tens of feet, owing to surface-water irrigation. As 

water levels rose, ground-water discharge, largely 

spring flow, increased. From 1912 to the early 

1950's, ground-water discharge from the eastern 

Plain to the reach of the Snake River from Milner 

to King Hill increased by about 2,600 ft3/s. Since 

the 1950's, ground-water discharge has decreased 

owing to increased ground-water withdrawals, 

decreased surface-water diversions, and more efficient use of irrigation water. In 1980, about 3.1 

million acres were irrigated on the Snake River 

Plain-2.0 million acres by surface water, 1.0 

million acres by ground water, and the remainder 

by combined surface and ground water. Surfacewater diversions totaled 13 million acre-ft; all 

were diverted by gravity except about 1 million 

acre-ft, which were pumped from rivers, mainly 

the Snake River. About 2.3 million acre-ft of 

ground water were pumped for irrigation from 

5,300 wells. 

Steady-state and transient finite-difference 

ground-water flow models were developed for the 

eastern and western Plain. Steady-state models 

were calibrated to 1980 hydrologic conditions; 

transient models were calibrated from preirrigation to 1980. The models reasonably simulated 

current and past hydrologic conditions. They were 

used to evaluate aquifer response to possible 

future ground-water development. Should 

ground-water withdrawals increase, additional 

water-level declines and decreases in groundwater discharge to the Snake River are expected. 

Water quality is generally good. Most solutes 

originate in tributary basins, and concentrations 

of ions change little as water flows from areas of 

recharge to areas of discharge. 

PUBLISHED REPORTS 

Abstracts 

1. Garabedian, S. P., 1982, Application of a 

parameter estimation technique to the 

regional aquifer underlying the eastern 

Snake River plain, Idaho: American 

Geophysical Union EOS Transaction, v. 63, 

no. 45, p. 926. 

2. Wood, W. W., and Low, W. H., 1984, Aqueous 

geochemistry of the eastern Snake River 

Plain olivine basalt aquifer, Idaho: 

Geological Society of America 97th Annual 

Meeting, Reno, NV, Abstracts with Programs, v. 16, no. 6, p. 700. 

Reports 

1. Bigelow, B. B., Goodell, S. A., and Newton, 

G. D., 1984, Water withdrawn for irrigation 

in 1980 on the Snake River Plain, Idaho and 

eastern Oregon: U.S. Geological Survey 

Open-File Report 84-434, scale 1:1,000,000, 

2 sheets. 

2. Bisdorf, R. J., 1983, Schlumberger soundings 

on the Snake River Plain near Nampa, 

Idaho: U.S. Geological Survey Open-File 

Report 83-412, 56 p. 

3. Garabedian, S. P., 1984, Application of a 

parameter estimation technique to modeling 

the regional aquifer under lying the eastern 

Snake River Plain, Idaho: U.S. Geological 

Survey Open-File Report 84-461, 119 p; 

4. Johnson, G. S., Brockway, C. E., and Luttrell, 

S. P., 1984, Application of a numerical 

ground-water flow model to the Mud Lake 

area in southeastern Idaho: Moscow, Idaho, 

University of Idaho, Technical Completion 

Report, 60 p. 

5. Kjelstrom, L. C., 1984, Flow characteristics 

of the Snake River and water budget for the 

Snake River ·Plain, Idaho and eastern 

Oregon: U.S. Geological Survey Open-File 

Report 84-052, scale 1:1,000,000, 2 sheets. 

6. Lindholm, G. F., 1981, Plan of study for the 

regional aquifer-system analysis of the 

105 
106 

Snake River Plain, Idaho and eastern 

Oregon: U.S. Geological Survey Open-File 

Report 81-689, 37 p. 

7. Lindholm, G. F., Garabedian, S. P., Newton, 

G. D., and Whitehead, R. L., 1983, Configuration of the water table, March 1980, 

in the Snake River Plain regional aquifer 

system, Idaho and eastern Oregon: U.S. 

Geological Survey Open-File -Report 

82.;.1022, scale 1:500,000. 

· 8. Lindholm, G. F., and Goodell, S. A., 1984, Irrigated acreage and other land uses in 1980 

on the Snake River Plain, Idaho and eastern 

Oregon: U.S. Geological Survey Open-File 

Report 84-452, scale 1:500,000. 

9. Newton, G. D., 1985, Computer programs for 

common map projections: U.S. Geological 

Survey Bulletin 1642, 33 p. 

10. Whitehead, R. L., 1984a, Compilation of 

selected geophysical references for the 

Snake River Plain, Idaho and eastern 

Oregon: U.S. Geological Survey Open-File 

Report 84-587, scale 1:1,000,000. 

11. -----1984b, Geohydrologic framework of 

the Snake River Plain, Idaho and eastern 

Oregon: U.S. Geological Survey Open-File 

Report 84-051, scale 1:1,000,000, 3 sheets. 

12. Whitehead, R. L., and Lindholm, G. F, 1985, 

Results of geohydrologic test drilling in the 

eastern Snake River Plain, Gooding County, 

Idaho: U.S. Geological Survey WaterResources Investigations Report 84~4294, 

30 p. 

REFERENCES CITED , 

Bigelow, B. B., Goodell, S. A., and Newton, G. D., 'i984, Water 

withdrawn for irrigation in 1980 on the Snake River 

Plain, Idaho and eastern Oregon: U.S. Geological 

Survey Open-File Report 84-434, scale 1:1,000,000, 

2 sheets. 

Garabedian, S. P., 1984, Application of a parameter estimation technique to modeling the regional aquifer underlying the eastern Snake River Plain, Idaho: U.S. 

Geological Survey Open-File Report 84-461, 119 p. 

Kjelstrom, L. C., 1984, Flow characteristics of the Snake River 

and water budget for the Snake River Plain, Idaho and 

eastern Oregon: U.S. Geological Survey Open-File 

Report 84-052, scale 1:1,000,000, 2 sheets. 

Lindholm, G. F., 1981, Plan of study for the regional aquifersystem analysis of the Snake River Plain, Idaho and 

eastern Oregon: U.S. Geological Survey Open-File 

Report 81-689, 37 p. 

Lindholm, G. F., Garabedian, S. P., Newton, G. D., and 

Whitehead, R. L., 1983, Configuration of the water 

table, March 1980, in the Snake River Plain regional 

aquifer system, Idaho and eastern Oregon: U.S. 

Geological Survey Open-File Report 82-1022, scale 

1:500,000. 

Lindholm, G. F., and Goodell, S. A., 1984, Irrigated acreage 

and other land uses in 1980 on the Snake River Plain, 

Idaho and eastern Oregon: U.S. Geological Survey 

Open-File Report 84-452, scale 1:500,000. 

Meinzer, 0. E., 1927, Large springs inthe United States: U.S. 

Geological Survey Water-Supply Paper 557, 93 p. 

Mundorff, M. J., Crosthwaite, E: G., and Kilburn, Chabot, 

1964, Ground water for irrigation in the Snake River 

Plain in Idaho: U.S. Geological Survey Water-Supply 

Paper 1654, 224 p. 

Newton, G. D., 1978, Application of a simulation model to the 

Snake River Plain aquifer: Moscow, Idaho, University 

of Idaho, unpublished thesis, 82 p. 

NorVitch, R. F., Thomas, C. A., and Madison, R. J., 1969, Artificial recharge to the Snake Plain aquifer; an evaluation of potential and effect: Idaho Department of 

Reclamation, Water Information Bulletin no. 12, 59 p. 

Trescott, P. C., 1976, Documentation of finite-difference model 

for simulation of three-dimensional ground-water flow: 

U.S. Geological Survey Open- File Report 75-438, 103 p. 

Trescott, P. C., and Larson, S. P., 1976, Documentation of 

finite-difference model for simulation of threedimensional ground-water flow; supplement to U.S. 

Geological Survey Open-File Report 75-438: U.S. 

Geological Survey Open-File Report 76-591, 20 p. 

Whitehead, R. L., 1984a, Compilation of selected geophysical 

references for the Snake River Plain, Idaho and eastern 

Oregon: U.S. Geological Survey Open-File Report 

84-582, scale 1:1,000,000. 

---1984b, Geohydrologic framework of the Snake River 

Plain, Idaho and eastern Oregon: U.S. Geological 

Survey Open-File Report. 84-051, scale 1:1,000;000, 

3. sheets. 

Whitehead, R. L., and Lindholm, G. F., 1984, Results of 

geohydrologic test drilling in the eastern Snake River 

Plain, Gooding County,-Idaho: U.S. Geological Survey 

Water-Resources Investigations Report 84-4294, 30 p. 

Wood, S. H., and Anderson, J. E., 1981, Geology (chapter 2) in 

Mitchell, J. C., ed., Geothermal investigations in Idaho, 

Part 11, Geological, hydrological, geochemical, and 

geophysical investigations of the Nampa-Caldwell and 

adjacent areas, southwestern Idaho: Idaho Department 

of Water Resources, Water Information Bulletin no. 30, 

p. 9-31. 

Zohdy, A. A. R., and Stanley, W. D., 1973, Preliminary interpretation of electrical sounding curves obtained across 

the Snake River Plain from Blackfoot to Arco, Idaho: 

U.S. Geological Survey Open-File Report, 19 p. 
COMPLETED PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

SOUTHWEST ALLUVIAL-BASIN 

REGIONAL AQUIFER-SYSTEMS STUDY 

Hundreds of isolated alluvial basins are 

in the southwestern United States. Some of 

·them have surface-water outflow, others do not. 

It is impossible to study all alluvial-basin aquifer systems at once. Therefore, basin aquifers 

were selected to be studied under the RASA 

Program to understand the occurrence, movement, and water quality of ground water in 

these alluvial-basin aquifer systems. It is hoped 

that the results of the study can be transferred 

to other basin aquifer systems which need to be 

evaluated in the future. Geographically, the 

study was divided into two parts. Alluvial 

basins in parts of Colorado, New Mexico, and 

Texas were investigated by the U.S. Geological 

Survey in Albuquerque, NM, and alluvial 

basins in parts of southern and central Arizona 

and parts of adjacent States were investigated 

by the Geological Survey in Tucson, AZ. Following are discussions of these studies. 

STUDY IN PARTS OF COLORADO, NEW MEXICO, AND TEXAS 

By David W. Wilkins, Albuquerque, New Mexico 

INTRODUCTION 

The study of aquifer systems under lying the 

southwest alluvial basins in parts of Colorado, 

New Mexico, and Texas was started in 1978 and 

completed in 1984, except for report writing. The 

study covers a total area of 70,000 mi2 within or 

adjacent to three physiographic provinces (fig. 64). 

The northern part of the study area is in the 

Southern Rocky Mountains Province, the central 

part is in the Basin and Range Province, and the 

west-central part is in the Colorado Plateau Province. The Great Plains Province is east of the 

study area. Except for a small area in its southwest corner, the study area is bounded by the Continental Divide on the west. 

GENERAL GEOLOGY AND HYDROLOGY 

Two types of basins occur in the study area: 

(1) open basins are within the Rio Grande rift, (2) 

closed basins are predominantly in southwest 

New Mexico and west Texas having no surfacewater outflow (fig. 65). The Rio Grande rift is a 

fault-bounded structural feature with uplifted 

blocks on the east and on the west. Uplifted blocks 

to the east of the basins generally rise several 

thousand feet above the valley floor of the basins. 

The basins are bounded on the north, east, and 

west mainly by Quaternary and Tertiary 

volcanics, and Mesozoic and Paleozoic rocks (fig. 

66). The southern boundary of the study area is 

not defined by structural or hydrologic boundaries 

but is arbitrarily placed at the Mexico-United 

States International Boundary. Alluvial 

sediments in the basins were derived from the 

surrounding highlands and mountains and are of 

Cenozoic age. These are composed of flood-plain 

deposits and sediments of the Santa Fe Group. 

The Santa Fe Group is a rock-stratigraphic unit 

that consists of unconsolidated to moderately consolidated lenticular deposits of gravel, sand, and 

clay interbedded in some places with volcanics. 

Most municipal and industrial wells in the study 

area are completed in the Santa Fe Group. Wells 

in these sediments may produce up to 3,000 

gal/min. 

Precipitation in the uplifted mountainous 

blocks east and west of the basins is high and is 

the source of the surface water which eventually 

recharges the aquifers near the base of the mountains. Very little of the surface runoff is 

debouching onto the alluvial fans because of high 

rates of infiltration through arroyos. Most 

recharge to aquifers underlying the basins is near 

mountain fronts. The other major recharge in the 

open basins is the seepage of the Rio Grande river 

and irrigation return flows. The regional potentiometric surface of the alluvial basins (fig. 67) 

107 
108 

indicates that ground-water flow in most basins 

is from the east and west margins of the basins 

toward the basin axis and then southward. Exceptions to this flow pattern are the Animas Basin 

and lower part of the Salt Basin. Within these 

basins, flow is northward (figs. 64 and 67). 

Wilkins (1984) has described the ground-water 

flow system and the aquifer characteristics of 

each basin. 

Quality of ground water changes areally and 

vertically. Kelly (1974) reported that ground 

water underlying the Rio Grande river from near 

Espanola to east of Socorro, NM, has concentrations of dissolved solids less than 1,000 

milligrams per liter (mg/L) from land surface to 

a depth of about 2,000 feet. Below this depth, concentrations of dissolved solids are as much as 

3,000 mg/L. Concentrations of dissolved solids increase to a range of 3,000 to 10,000 mg/L below 

about 1,900 feet in the Jornada del Muerto Basin 

to the south Qocation of the Basin is shown in fig. 

64). A vertical profile along the Rio Grande in the 

Mesilla Basin, further to the south, shows water 

with concentrations of dissolved solids from 1,000 

to 3,000 mg/L in the flood-plain sediments. Within 

100 feet below the water table, concentrations of 

dissolved solids normally are less than 1,000 

mg/L; however, concentrations increase with 

depth. At a depth of about 4,000 feet below the 

water table, concentrations of dissolved solids 

may range from 3,000 to 10,000 mg/L (Wilson and 

others, 1981). Recharge waters are characterized 

by a calcium bicarbonate type such as that found 

in the San Luis and Espanola Basins (figs. 64 and 

68). A sodium bicarbonate type water is found in 

the central part of many closed basins and at the 

lower end of some open basins (figs. 64, 65, and 

68). The predominant chemical process responsible for sodium bicarbonate type water is probably ion exchange on clay minerals. In many 

sodium bicarbonate type water areas a finegrained lithology is present. Calcium or 

magnesium sulfate or chloride type waters probably result from the dissolution of gypsum or 

salts. These latter three types of water are found 

in many closed basins. Sodium sulfate or sodium 

chloride type waters are also found in many closed 

basins. 

GEOLOGIC STUDIES 

Geologic studies were initiated early during 

the study with the objective of selecting representative basins and of characterizing these selected 

basins. Basin boundaries were delineated on the 

basis of bedrocks or faults that separated the 

basins into distinct hydrologic areas. Topographic and surface-water divides were also considered. This process resulted in dividing the 

alluvial basins in the study area into 22 basins, 

shown in figure 64. 

The characterization studies were based upon 

driller's logs, geophysical logs, and published 

reports. Estimates of percent sand and clay were 

derived from the logs and were used to estimate 

the relative permeability of the sediments which 

generally are correlated with the permeability 

values resulting from calibrated ground-water 

flow models. 

Subsurface configuration of the basins could 

not be defined with available data. Surface 

geophysical surveys were conducted in 16 basins, 

Birch (1980a, 1980b) interpreted existing gravity 

data to define volume of sediments and bottom 

of alluvial material. Birch (1980a and b) 

estimated the average thickness of sediments in 

the Albuquerque-Belen Basin probably is about 

4,920 feet; 2,400 feet in Mesilla Basin; 1,600 feet 

in Mimbres Basin; 2,600 feet in Tularosa-Hueco 

Basin; 2,400 feet in Jornada del Muerto Basin; 

1,600 feet in Palomas Basin; and 2,000 feet in 

Engle Basin. Seismic refraction data were used 

to define the size and shape of the basins and to 

estimate the depth of alluvial sediments. 

GEOCHEMICAL STUDIES 

Prior to this study, few geochemical studies 

had been done. Data stored in the WATSTORE 

file of the U;S. Geological Survey, having identifiable sources of water, were evaluated for cation and anion balance. Four basins, San Luis, 

Albuquerque-Belen, Socorro, and Mesilla, were 

selected for geochemical studies and are discussed below. 

San Luis Basin.-The geochemical study 

in the San Luis Basin suggests that chemical data 

of ground water are insufficient. Data were collected from 15,000 wells in the basin,. but only 

data from 99 wells were useful. Primary conclusions are that ground water in the aquifer north 

of the Rio Grande changes in water chemistry 

from calcium bicarbonate to sodium bicarbonate 

due to cation exchange on clays. 

Albuquerque..;Belen Basin.-The study in the 

Albuquerque-Belen Basin verified the existence 

of a layer of silt and clay at depth on the mesa 

west of Albuquerque. It is suggested that groundwater flow enters the Albuquerque-Belen Basin 

from the San Juan Basin to the west. The ground-
water flow direction in the southern end of the 

basin is upward over a bedrock layer, which probably is the basin boundary. 

Socorro Basin.-The geochemical study in 

the Socorro Basin was useful in verifying the 

suspected mixing of water upwelling along faults 

with ground water at shallower depths. These 

upward-flowing waters are geothermal. 

Mesilla Basin.-The major geochemical process in the Rio Grande flood plain of the Mesilla 

38° 

36 ° 

<!10 

ZIO 

Nw olx 

a:~ 

<!13: 

~~ I 

I 

108° 

COLORADO 

PLATEAU 

106° 

Basin is mixing of water flowing from the uplifted 

recharge areas with water in the flood-plain 

sediments. The study also confirmed the location 

and temperature of the geothermal water. 

RECHARGE MODELS 

Prior to this study, data on aquifer recharge 

in the basins were not available. Three models 

were developed to estimate recharge. The 

"mountain-front recharge model" provides 

104° 

EXPLANATION 

AREA OF ALLUVIAL FILL-- Indicates 

only that basin fill is alluvium not 

necessarily saturated alluvium 

STUDY AREA 

PROVINCE BOUNDARY 

CONTINENTAL DIVIDE 

BASIN BOUNDARY-- Number and 

name listed below 

1, San Luis 

2, Espanola 

3, Santo Domingo 

I 

I 

I 

I 

GREAT 

PLAINS 

PROVINCE 

4, Albuquerque-Belen 

5, Socorro 

6, La Jencia 

34 ° 

30° 

I 

I 

I 

0 

SCALE 1 :6,000,000 

50 100 MILES 

0 50 100 KILOMETERS 

7, San Agustin 

8, San Marcial 

9, Engle 

10, Palomas 

11, Jornada Del Muerto 

12, Mesilla 

13, Tularosa-Hueco 

14, Mimbres 

15, Hachita 

16, Playas 

17, Animas 

18, Lordsburg 

19, Salt 

20, Eagle 

21, Redlight Draw 

22, Presidio 

Figure 64.- Study area and basin boundaries of alluvial basins in parts of Colorado, New Mexico, and Texas. 

109 
110 

estimates of volumes and locations of recharge 

supplied from streams with drainage areas on 

relativly impervious bedrock masses. Recharge 

occurs as flow crosses permeable alluvial fan 

deposits at the toe of the mountains. These results 

are applied to simulation of specific basins. 

Simulation suggests that the estimated recharge 

is reasonable . During development of the 

"mountain-front recharge model," the following 

108. 106 . 

38. 

36 . 

34 . 

32° 

SCALE 1:6,000,000 

0 50 100 MILES 

30° 

0 50 100 KILOMETERS 

runoff equations were established empirically. If 

precipitation is less than 7.36 inches, runoff may 

be calculated as: 

Q=1.074 X lo-sx AL216 X p 2.749 X so.535 

If precipitation is greater than 7 .36, the runoff 

may be calculated as: 

where: 

104. 

Q=7.621 xlo-s x A0977 x p 3.s9s 

EXPLANATION 

AREASTHATHAVENOSURFACE 

WATER DRAINAGE 

AREAS THAT HAVE SURFACE 

WATER DRAINAGE 

STUDY AREA 

Figure 65. -Alluvial basins with open and closed surface water drainages, in parts of Colorado, New Mexico, and Texas. 
Q is runoff, in cubic feet per second, 

A is the drainage area, in square miles, 

P is precipitation, in inches, and 

S is slope of the drainage channel, in feet 

per mile. 

The second recharge model (the mountain 

water-balance model) was developed to estimate 

direct recharge within uplifted mountainous 

38' 

36' 

34' 

30' 

I 

10 

lo 

'<t 

<t...J :r:l~ 1-10 :::>,(.) 

<1:10 

Z I O 

Nw o/x

0::::!: 

<tis; 

~~ I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

0 

108' 

SCALE 1:6,000,000 

50 

106' 

100 MILES 

0 50 100 KILOMETERS 

areas composed of relatively impervious rocks, 

such as Quaternary or Tertiary volcanics. The 

"mountain water-balance model" was especially 

useful for estimating recharge entering the San 

Luis Basin from the San Juan Mountains on the 

west. The model uses precipitation, types of 

vegetation, and ambient temperature to estimate 

recharge within a particular drainage basin. 

Some water drains to streams through local flow 

104' 

EXPLANATION 

QUATERNARY AND TERTIARY 

SEDIMENTARY ROCKS·· 

Includes floodplain sediments of 

the Rio Grande and its tributaries 

and the Santa Fe Group of 

Pliocene and Pleistocene age. 

These sediments collectively are 

the principal aquifer in the study 

area. Wells in these sediments 

will produce from a few gallons 

per minute to several thousand 

gallons per minute 

QUATERNARY AND TERTIARY 

VOLCANICS--

Usually appear as mesas in the 

study area. In places the 

volcanics overlie the sediments 

of the Santa Fe Group, and can 

be interbedded with sediments of 

the Santa Fe Group. May be 

saturated and are considered 

part of the aquifer system where 

they occur at depth 

MESOZOIC AND PALEOZOIC 

ROCKS UNDIVIDED·-

Considered bedrock and 

impermeable, in this study 

PRECAMBRIAN ROCKS, BEDROCK 

AND IMPERMEABLE 

STUDY AREA 

Figure 66.- Generalized geologic map of the alluvial basins in parts of Colorado, New Mexico, and Texas. 

111 
112 

systems. The remaining water is assumed to flow 

through permeable rock and recharge the alluvial 

sediments at the toe of the mountains. Results 

from this recharge model and water budgets in 

the San Luis Basin suggest that there is some 

lateral ground-water movement from areas in the 

San Juan Mountains to adjacent downgradient 

areas. 

34 

30" 

10 

'o I<( 

::cj~ <(...J 

1-10 

:::>lu 

106" 

-t-----------~bf.f'I~~ <(JO 

ZJU 

21~ a:~ 

<1:1$: 

~~ I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

SCALE 1:6,000,000 

0 50 100 MILES 

0 50 100 KILOMETERS 

The third recharge model is a "valley evapotranspiration (ET) model." The model takes into 

account precipitation, depth to water, types of 

natural vegetation and crops, irrigated acreage, 

and consumptive use of vegetation and crops. In 

irrigated areas of the San Luis Basin, it is 

estimated that about 90 percent of the precipitation is returned to the atmosphere by 

104" 

EXPLANATION 

-6600- POTENTIOMETRIC CONTOUR 00 

Shows altitude at which water 

level would have stood in tightly 

cased wells, 1971-80. Contour 

interval 200 feet. Datum is sea 

level 

AREA OF ALLUVIAL FILL 

STUDY AREA 

Figure 67.- Regional potentiometric surface of the alluvial basin aquifer systems in parts of Colorado, New Mexico, 

and Texas, 1971-80. 
evapotranspiration during the growing season 

and about 27 percent is returned during the 

nongrowing season. 

SIMULA liONS 

For basins where sufficient data were available, the ground-water flow systems were 

I 

10 

Ia 

'oct 

r/~ oct-' 1-10 ::::>,(.) 

---t-----------------

octiO 

Zl(.) 

2j~ tr:::E 

octl3 

~~ I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

0 

0 

SCALE 1 :6,000,000 

50 100 MILES 

50 100 KILOMETERS 

simulated by computer-based models. Basins 

selected for simulation were the San Luis, 

Albuquerque-Belen, Mesilla, and Animas Basins. 

San Luis Basin.-Cross-sectional simulations 

were made to evaluate the conceptualized flow in 

the vertical direction. Several sections, located 

where the most data were available, were 

simulated. The simulated depth of the basin 

EXPLANATION 

WATER QUALITY 

Calcium sulphate, calcium chloride, ·magnesium sulphate, or 

magnesium chloride water 

Sodium sulphate or sodium chloride 

water 

Sodium bicarbonate water 

Calcium bicarbonate or magnesium 

bicarbonate water 

Undefined 

STUDY AREA 

Figure 68.- Regionalized water quality of the alluvial basin aquifer systems in parts of Colorado, New Mexico, and Texas. 

113 
114 

aquifer was stopped at 3,200 feet during the crosssectional simulation. Extending the depth beyond 

3,200 feet had no significant improvement on 

results. Sensitivity of dividing the aquifer into 

several layers having different thicknesses was 

tested by the cross-sectional simulation. The tests 

indicated that better results can be obtained 

where a given layer is not more than 1.5 times 

the thickness of the layer above. 

A three-dimensional flow model (Trescott, 

1975; Trescott and Larson, 1976) was used to 

simulate the aquifer underlying the San Luis 

Basin north of the Colorado-New Mexico State 

line. Because ground-water development in the 

basin was begun in the late 1800's, there were 

few data available to define the predevelopment 

steady-state conditions. Information on hydrologic 

changes since 1950 was used for the transient 

calibration. Simulation indicates that in 1980 

about 80 percent of ground-water withdrawals 

were from salvage of evapotranspiration, 14 percent from aquifer storage, and 6 percent from 

reduction· in discharge as stream baseflow. 

Albuquerque-Belen Basin.-The ground-water 

flow model of the Albuquerque-Belen Basin is also 

a three-dimensional model representing the 

aquifer to a depth of 6,180 feet with 6 active 

layers. Both steady-state and transient simulations were made. The flood plain was represented 

by a constant-head boundary. This assumption is 

maqe on the basis that no long-term water-level 

fluctutations in the flood-plain aquifer existed 

prior to 1975. Simulation confirms the results of 

the geochemical study in the basin that upwelling 

of flow exists at the southern end of the .basin. 

Simulation also suggests that changes in 

recharge will not totally disappear for about 800 

years; that indicates that· the aquifer system 

underlying the basin. does not reach equilibrium 

easily. Simulation also suggests that. about 25 

percent of the water withdrawn from 1907 to 1979 

was from aquifer storage outside the flood plain. 

About 75 percent was from the Rio Grande and 

flood plain aquifer, assuming that 

evapotranspiration remained constant. 

MesillaBasin.-The Mesilla Basin was simulated with a 5-layer model. The flood plain of the 

Rio Grande was represented in the model with as 

much detail as possible. Data for irrigation pumpage, evapotranspiration, domestic and industrial 

use, and irrigation return flows were compiled or 

estimated from the late 1800's to 1975. Flow in 

rivers and drains was routed. Simulation indicates that most hydrologic details observed in 

the flood plain of the Rio Grandf3 .. ca1;1 be 

simulated. Simulated average. volume of groundwater discharge to.the river or. drains froll11940 

to 1975 was within about 5 percent of .the observed values. In 1960 about. 75 .percent of the 

pumped ground water was induced from su.rl'acewater bodies and the remainder was from aquifer 

storage. . . . 

Animas Basin.-A two-dimensional flow 

model was used to simulate the a,quifer. system 

underlying the Animas .Basin in .southwestern 

New Mexico. This model 'Vas done und~r contract 

by the New Mexico Bureau of Mines and Mineral 

Resources (O'Brien and Stone, 1983). The model 

serves as a type model that could be used to 

simulate a closed-basin aquifer system in which 

vertical flow is insignificant .. The two-dimensional 

flow model produced acceptable results. During 

the transient calibrations, change in head from 

1948 to 1955 were simulated to withinlOfeet of 

the observed head changes. From 1948 to 1981, 

the simulated head changes were within 18 feet 

of . the observed draw:downs. Sensitivity tests 

showed that the aquifer system is most ~ensitive 

to increases in transmissivity and· withdrawal 

and to decreases in storage coefficient and 

transmissivity (O'Brien and Stone, 1983,.p. 50). 

PUBLISHED REPORTS 

1. Birch, F. S., 1980a, Geophysical evaluation of 

basin hydrologic characteristics in central 

Rio Grande, part 1: .Gravity models of the 

Albuquerque-Belen Basin: University of 

New Mexico, contract no~ 1408000117879, 

30 p. 

2. -----1980b, Three dimensional gravity 

modeling of basin hydrologic parameters in 

New Mexico: University ofNew Mexico, contract no. 1408000117899, 26 p. 

3. ------1982, Gravity models of the Albuquerque basin, Rio Grande rift, New Mexico: Geophysics, v. 47, no. 8, August 1982, 

p. 1182-1197. 

4. Crouch, T. M., 1980, Potentiometric surface, 

and 1969-80 water-level changes in the unconfined valley-fill aquifers of the San Luis 

Basin, Colorado and New Mexico: U.S. 

Geological Survey Hydrologic Investigations 

Atlas 683 

5. Hearne, G. A., 1983, Supplement to the New 

Mexico three dimensional model (supplement to U.S. Geological Survey Open-File 

Report 80-421): U.S. Geological Survey 

Open-File Report 82-857, 90 p. 
6. Jiracek, G. R., 1982, Geophysical evaluation 

of basin hydrologic characteristics in the 

central Rio Grande rift, part 3: Electrical 

resistivity investigations: University of New 

Mexico, contract no. 1408000117879, 109 p. 

7. Kentron International, Inc., 1980, Revised 

three-dimensional water resources flow 

model: contract no. GS07502355 task 

80-001, 39 p. 

8. O'Brien, K. M., and Stone, W. J., 1981, Water 

level data compiled for hydrogeologic study 

of Animos Valley, Hidalgo County, New 

Mexico: New Mexico Bureau of Mines and 

Mineral Resources, Open-File Report 130, 

55 p. 

9. -----1982a, Drill hole and testing data 

compiled for hydrogeologic study of Animas 

Valley, Hidalgo County, New Mexico: New 

Mexico Bureau of Mines and Mineral 

Resources, Open-File Report 132, 79 p. 

10. -----1982b, Water-quality data compiled 

for hydrogeologic study of Animas Valley, 

Hidalgo County, New Mexico: New Mexico 

Bureau of Mines and Mineral Resources, 

Open-File Report 131, 25 p. 

11.-----1983, A two-dimensional hydrologic 

model ofthe Animas Valley, Hidalgo County, New Mexico: New Mexico Bureau of 

Mines and Mineral Resources Open-File 

Report 133, 60 p. 

12. Stone, W. J., and Mizell, N. H., 1979, 

Availability of geological and geophysical 

data for the eastern half of the U.S. 

Geological Survey's Southwestern Alluvial 

Basins regional aquifer study: New Mexico 

Bureau of Mines and Mineral Resources, 

Open-File Report 109, 80 p. 

13. Wilkins, D. W., 1984, Geohydrology of the 

southwest alluvial basins regional aquifersystem analysis, parts of Colorado, New 

Mexico, and Texas: U.S. Geological Survey 

Water-Resources Investigations Report 

84-4224, [in press]. 

14. Wilkins, D. W., Scott, W. B., and Kaehler, C. 

A., 1980, Planning report for the Southwest 

Alluvial Basins (east) regional aquifersystem analysis, parts of Colorado, New 

Mexico and Texas: U.S. Geological Survey 

Open-File Report 80-564, 39 p. 

REFERENCES CITED 

Birch, F. S., 1980a, Geophysical evaluation of basin hydrologic 

characteristics in central Rio Grande, Part I, gravity 

models of the Albuquerque- Belen Basin: University of 

New Mexico, contract no. 1408000117879, 30 p. 

----1980b, Three-dimensional gravity modeling of basin 

hydrologic parameters in New Mexico: University of 

New Mexico, contract no. 1408000117899, 26 p. 

Kelly, T. E., 1974, Reconnaissance investigation of ground 

water in the Rio Grande drainage basin-with special 

emphasis on saline ground-water resources: U.S. 

Geological Survey Hydrologic Investigation Atlas 510, 

4 sheets. 

O'Brien, K. M., and Stone, W. J., 1983, A two-dimensional 

hydrologic model of the Animas Valley, Hidalgo County, New Mexico: New Mexico Bureau of Mines and 

Mineral Resources Open-File Report 133, 60 p. 

Trescott, P. C., 1975, Documentation of finite-difference model 

for simulation of three-dimensional ground-water flow: 

U.S. Geological Survey Open- File Report 75-438,32 p. 

Trescott, P. C., and Larson, S. P., 1976, Documentation of 

finite-difference model for simulation of threedimensional ground-water flow: U.S. Geological Survey 

Open-File Report 76-591, 21 p. [Supplement to OpenFile Report 75-438.] 

Wilkins, D. W., 1984, Geohydrology of the southwest alluvial 

basins, regional aquifer-systems analysis, parts of Colorado, New Mexico, and Texas: U.S. Geological Survey 

Water-Resources Investigations Report 84-4224, [in 

press]. 

Wilkins, D. W., Scott, W. B., and Kaehler, C. A., 1980, Planning report for the Southwest Alluvial Basins (east) 

regional aquifer-systems analysis, parts of Colorado, 

New Mexico, and Texas: U.S. Geological Survey OpenFile Report 80-564, 39 p. 

Wilson, C. A., White, R. R., Orr, B. R., and Roybal, G. R., 1981, 

Water resources of the Rincon and Mesilla Valleys and 

adjacent areas, New Mexico: U.S. Geolo~cal Survey 

Open-File Report 81-487, 305 p. 

115 
116 

COMPLETED PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

STUDY IN SOUTHERN AND CENTRAL ARIZONA 

AND PARTS OF ADJACENT STATES 

By Thomas W. Anderson, Tucson, Arizona 

INTRODUCTION 

The study of the alluvial-basin regional 

aquifer systems in southern and central Arizona 

and parts of California, Nevada, and New Mexico covering an area of about 82,000 mi2 (fig. 69) 

was started in 1978. All activities were completed 

in 1984, except for report writing. The area contains 72 basins that are virtually separate 

hydrologic entities. The boundaries between 

basins mainly correspond to surface-water 

drainage divides, ground-water divides, or areas 

of minimal interbasin connection. The study area 

is characterized by sharply rising mountains that 

separate wide, flat basins filled with varying . 

amounts of alluvial deposits. These deposits form 

the major aquifers and store large amounts of 

water. Altitude of the land surface generally increases from the southwest toward the north and 

northeast. Climatic factors have a wide rangeprecipitation increases and evaporation and 

temperature decrease from southwest to 

northeast. 

GEOHYDROLOGIC SETTING 

The basins of the study area are the result 

of formation of the Basin and Range topography 

about 10 to 15 million years ago (Scarborough and 

Peirce, 1978, Shafiqullah and others, 1980). Movement along high-angle normal faults downdropped the basins in relation to the mountain 

masses. The result was a series of generally 

northwest-trending basins. Basin subsidence was 

a gradual process that was accompanied by 

deposition of locally derived sediments within the 

internally drained basins. The bedrock of the 

mountains consists of igneous, metamorphic, and 

sedimentary rocks that are virtually impermeable. These rocks underlie the basins and 

form the side and bottom boundaries of the 

alluvial basin aquifers. 

The basins are filled with alluvial deposits 

that range from a few thousand feet to more than 

10,000 ft in thickness. Basin subsidence and sediment deposition occurred at varying rates 

throughout the study area; as a result, the 

thickness, areal extent, and grain size of the 

alluvial deposits are highly variable. The 

sediments range in grain size from clay to gravel 

and may vary from unconsolidated to highly consolidated in a single basin. The general sequence 

of sedimentary units, in ascending order, consists 

of: (1) sedimentary rocks deposited prior to 

development of the Basin and Range topography, 

(2) lower and upper basin fill, and (3) stream 

alluvium (fig. 70). The sedimentary units are 

distinguishable on the basis of structural relation, 

degree of consolidation and deformation, sources 

of clasts, age, and water-bearing characteristics. 

The sedimentary units reflect different conditions 

of deposition. Although each basin is unique, 

general spatial patterns in character, thickness, 

and extent of the sedimentary units can be 

documented among groups of basins. 

The sedimentary rocks deposited prior to 

development of the Basin and Range topography 

consist of moderately to highly consolidated continental deposits that range from clay to gravel 

and also include some volcanic rocks. The 

sedimentary rocks were faulted and tilted along 

with the underlying bedrock. These sedimentary 

rocks are deeply buried in the basins. Although 

a few wells penetrate these sedimentary rocks 

near the basin edges, little is known about their 

hydrologic characters. 
The basin-fill sediments, which constitute 

the principal aquifers in most basins, were 

deposited during and after the formation of the 

Basin and Range topography. The lower basin fill 

is moderately to highly consolidated, has extensive fine-grained material, and contains 

evaporites that range from disseminated gypsum 

36' 

34° 

NEVADA 

Las Vegas. 

' ' 

"" 

114° 

I 

I r-- 112' 

UTAH ------ ARIZONA 

SCALE 1:5,000,000 

0 50 100 MILES 

0 50 100 KILOMETERS 

EXPLANATION 

to massive halite deposits. The lower basin fill 

was deposited in topographically closed basins. 

The upper basin fill was deposited during a transition period in which the basins changed from 

a closed basin to an integrated drainage system. 

The upper basin fill is less consolidated, generally is thinner, and contains fewer fine-grained 

110' 108° 

•Durango 

COLORADO 

Gallup 

NEW MEXICO 

• Silver City 

I 

__ _j 

ALLUVIAL DEPOSITS -- Locally may include 

evaporite deposits and volcanic rocks 

BEDROCK OF THE MOUNTAINS 

BASIN BOUNDARY 

STUDY AREA 

Figure 69.- Study area and basin boundaries of the alluvial basin aquifer systems in southern and central Arizona 

and parts of adjacent States. 

117 
118 

sediments than the lower basin fill. Both lower 

and upper basin fills grad~ laterally from coarsegrained sediments at the basin margins to finegrained sediments near the basin center. 

The stream alluvium was deposited contemporaneously with the establishment of the present 

surface-drainage system. The alluvium ranges 

from clay to boulders and is unconsolidated. 

Where saturated, the stream alluvium forms the 

most productive part of the aquifers. 

The sedimentary units are hydraulically interconnected and form a single aquifer system 

within most basins. The basins are interconnected 

in a dendritic pattern-much like the surface 

drainage-and form an integrated regional 

ground-water flow system. The individual basinaquifer system serves mainly as a subsurface 

reservoir with only small areas of interconnection 

between the basin aquifers. A small quantity of 

ground water flows from basins of higher altitude 

to those of lower altitude. 

The chemistry of ground water generally is 

good and is similar from basin to basin. Concentrations of dissolved solids generally are less than 

1,000 milligrams per liter (mg/L). Where appreciable gypsum or halite is present, such as in 

the fine-grained facies of the lower basin fill, concentrations of dissolved solids may increase 

severalfold. Trace elements, such as mercury, 

NOT TO SCALE 

lead, arsenic, and nitrate associated with the rock 

matrix in which the ground water occurs, locally 

restrict the use of the water. 

Ground water generally is unconfined. Confined conditions occur in a few basins where extensive fine-grained deposits overlie the principal 

water-bearing formation. Depth to water ranges 

from land surface near perennial streams to more 

than 500 feet below land surface near the mountain fronts in some basins. An estimated 900 

million acre-ft of recoverable water was stored in 

the upper 1,200 feet of the alluvial deposits of the 

basins prior to development (Freethey and Anderson, 1985). This amount is much greater than the 

amounts of water that move into and out of the 

aquifers annually. 

Sources of recharge are: (1) infiltration of 

streamflow along major streams, (2) infiltration 

of streamflow along mountain fronts, and (3) subsurface inflow from adjacent basins (fig. 71). The 

average annual recharge to all basins in the study 

area was estimated to be 2.5 million acre-ft before 

development. In general, ground water discharges 

to the atmosphere as evapotranspiration, through 

springs, to the downgradient adjacent basin as 

subsurface outflow, or to streams where head in 

the aquifer is higher than the stage in the stream. 

The specific flow characteristics in a basin or for 

a group of basins are dependent on the hydraulic 

Fi~ure 70.- Typical sequence of sedimentary units that fill a basin in southern and central Arizona and parts of 

adjacent States. 
properties of the aquifer material and on the total 

flow through the aquifer. 

Ground-water development in the study area 

has been principally for irrigation and has 

resulted in the depletion of surface-water flow in 

several basins and water-level declines in 

developed basins. The greatest development 

began after World War IT. Ground-water pumpage increased from 1. 7 million acre-ft in 1942 to 

3.8 million acre-ft in 1952 and to 4.8 million acreft in ·1962 (fig. 72). During 1950-80, an average 

of 4.8 million acre-ft per year was pumped. Pumpage in individual basins was 2 to more than 100 

times greater than the estimated annual 

recharge. Through 1980, an estimated 184 million 

acre-ft of water was pumped from the basins (U.S. 

Geological Survey, 1982). Of the estimated total 

pumpage, not all was derived from aquifer 

storage; some pumpage was balanced by irrigation return flow, and leakage from canals and 

streams. 

The major developed basins have experienced water-level declines that range from less 

than 50 feet to more than 400 feet (fig. 73). The 

magnitude of water-level decline varies from 

basin to basin and reflects the characteristics of 

the geohydrologic environment and the 

magnitude and duration of pumping. Associated 

with water-level declines are the problems of 

decreases of well yield, changes in water quality, 

and the potential for land subsidence and earth 

fissuring. The severity of these problems is a function of the magnitude and duration of pumping 

and character of the aquifer material in a basin. 

REGIONAL CATEGORIZATION 

OF BASINS 

Conceptual models of the basin aquifer 

systems in the study area were developed on the 

basis of geologic and hydrologic data. Representative basins were analyzed using numerical 

models. The model results and related 

geohydrologic data were used to categorize basins 

into groups. The response of the basin aquifer 

systems to development therefore can be 

evaluated for a specific basin on the basis of the 

categorization. 

The principal geologic property that controls 

the occurrence and movement of ground water in 

the alluvial basins is the texture of the sediments. 

The important hydrologic factor is the total annual flow through the basin, which represents the 

annual renewable source of water. On the basis 

of the similarity of these geohydrologic factors, 

the alluvial basins in the study area are grouped 

into five categories and are named geographically 

as: (1) southeast, (2) central, (3) west, (4) Colorado 

River and (5) highland (fig. 74). 

Flow simulation of basin aquifer systems of 

each category requires different input data. 

Aquifers underlying 12 alluvial basins (fig. 74) 

were simulated to test the concepts of the 

categorization. Simulation suggests that 

hydraulic conductivity, recharge rate, and extent 

and integrity of a confining unit constitute the 

most important information for steady-state conditions of the southeast category. Specific yield, 

pumpage, and pumping location constitute the 

most important information for transient conditions of the central and west categories. Streamaquifer interaction, evapotranspiration, and 

return of excess irrigation water constitute the 

most important information for the Colorado 

River and highland categories, because infiltration of surface water is a major inflow component 

in these basins. 

SUMMARY OF BASIN CHARACTERISTICS 

Southeast Category 

The aquifer systems underlying the basins 

·in the southeast category consist of at least two 

saturated units, the upper basin fill and the lower 

basin fill, separated by a low-permeability finegrained confining unit (fig. 75a). The lower 

saturated unit may include at least the upper part 

of the sediments deposited before the formation 

of the Basin and Range topography. Mudstone 

and evaporites may be found in the lower basin 

fill. 

The major ground-water co-mponents are 

streamflow infiltration along the mountain front 

and along the major streams. Ground-water 

discharge before development was through 

evapotranspiration, stream baseflow, and subsurface outflow to downgradient adjacent basins. 

Because of similarities in geohydrologic 

characteristics, the Big Sandy River basin in the 

northwestern part of the area is included in this 

category despite its geographical location (fig. 7 4). 

Development of basins in the southeast category has resulted in a gradual reduction of 

natural discharge, increase in streamflow infiltration, and a small change in the volume of water 

stored in the aquifer. Models of the basin aquifers 

of the southeast category need to be multilayered 

and allow for flow through leaky confining units. 

119 
120 

Subsurface inflow 

from upgradient basin 

RECHARGE 

: ~ t7 ~L ~ :: .... ::::::: :: ::::.: .. ~ate'-< · . . :. :. :. :. :. :. :. :. :. :. : .. table' ~S 

DISCHARGE 

Figure 71.- Recharge and discharge components in alluvial basins in southern and central Arizona and parts of 

adjacent States. 
YEAR 

Figure 72. -Annual ground-water withdrawal, 1915-80, from the alluvial basin aquifer systems in southern and 

central Arizona and parts of adjacent States. 

Central Category 

Sediments of the aquifer systems underlying the basins of the central category are the 

thickest in the study area. Few wells have 

penetrated the sediments that were deposited 

before the formation of the Basin and Range 

topography; therefore, little is known about their 

extent and character. Typically, aquifers underlying the basins of this category contain as much 

as 5,000 feet oflower basin fill and less than 1,000 

feet of upper basin fill (fig. 76A). Evaporites 

typically are found in the lower basin fill. Fine 

grained sediments commonly comprise more than 

60 percent of the sediments near the center of the 

basins. The upper basin fill grades laterally to 

coarse material near the mountain fronts. Stream 

alluvium along major streams is as much as 300 

feet thick. 

Aquifer recharge consists of small to moderate amounts of mountain-front recharge and 

streamflow infiltration. Subsurface inflow from 

adjacent upgradient basins is also a significant 

recharge source in several basins (fig. 76B). Before 

development, ground water discharged principally as evapotranspiration. Subsurface outflow 

to adjacent downgradient basins was significant 

in several basins. Discharge to streams was small. 

Development has greatly decreased the 

amount of discharge as evapotranspiration and 

stream baseflow. Most of the pump age is from 

aquifer storage. Further increases in pumpage 

will cause further decline in water levels. Models 

used to simulate the alluvial aquifers underlying 

the basins of the central category need to be 

multilayered for simulating vertical-flow components and variable hydraulic characteristics 

with depth in the basins. 

West Category 

The aquifer systems underlying the basins 

of the west category contain sediments deposited 

before the formation of the Basin and Range 

topography, which are overlain by moderate- to 

coarse-grained lower basin fill. The lower basin 

fill is the principal aquifer in the basins of this 

category. Upper basin fill is thin and generally 

above the water table (fig. 77 A). Stream alluvium 

is not typical of this category and is found only 

along the lower Gila River. 

Recharge in this category is small and consists of minor amounts of mountain-front 

recharge, subsurface inflow from upgradient 

basins, and streamflow infiltration (fig. 77B). 

Discharge is also small and consists of 

evapotranspiration and subsurface outflow to adjacent downgradient basins. Discharge to streams 

is insignificant. 

Because natural recharge, discharge, and 

streamflow are small in the basins of this 

category, no significant capture of natural 

discharge or increase in streamflow infiltration 

has occurred following pumping (fig. 77C), except 

locally along the Gila River. Ground-water pumpage is derived almost entirely from aquifer 

storage (fig. 77D). Multilayered models need to be 

used to simulate the aquifer systems underlying 

the basins ofthis category. The Big Sandy River 

basin southeast of Kingman is excluded from this 

category, despite its western geographic location. 

121 
122 

36' 

34° 

32' 

NEVADA 

Las Vegas. 

' ' 

"" 

114° 112' 

I 

1 UTAH r-- ARiZONA---

SCALE 1:5,000,000 

0 

0 50 

50 100 MILES 

100 KILOMETERS 

EXPLANATION 

ALLUVIAL DEPOSITS -- Locally may include 

evaporite deposits and volcanic rocks 

BEDROCK OF THE MOUNTAINS 

WATER- LEVEL DECLINE 

0-50 feet 

- 50-200 feet 

- greater than 200 feet 

BASIN BOUNDARY 

STUDY AREA 

NEW MEXICO 

Figure 73.-Areas of water-level declines in the alluvial basin aquifer systems in southern and central Arizona and parts 

of adjacent States. 
36' 

34' 

32' 

NEVADA 

Las Vegas. 

' ' "' ' 

114' 112' 

I 

I UTAH r---ARiZONA---

• Flagstaff 

CALIFORNIA 

0 

0 

It?~ .................. 

)(I .. 

c 0 ................... 

SCALE 1 :5,000,000 "'""-.. .., 

50 100 MILES 

50 100 KILOMETERS 

EXPLANATION 

BOUNDARY OF GENERAL CATEGORIC 

ALLUVIAL BASINS 

_ 5_ BASIN BOUNDARY-- Number indicates 

modeled basir,s listed below 

1, Mohave 

2, Parker 

3, McMullen 

4, Harquahala 

5, Waterman 

6, Avra Basin 

?, Tucson 

8, Lower San Pedro 

9, Benson 

10, Upper San Pedro 

11, Willcox 

12, Douglas 

STUDY AREA 

108' 

.Durango 

COLORADO 

Gallup 

NEW MEXICO 

• Silver City 

l 

__ _j 

Figure 74.- Generalized categories of basins and modeled basins of the alluvial basin aquifer systems in southern 

and central Arizona and parts of adjacent States. 

123 
124 

Sediments deposited before formation 

of the Basin and Range topography 

A. Generalized physical system 

100% 

3: 

0 

...J 

u. 

z 

0 

3: 

0 

...J 

u. 

..... 

::::::> 

0 

100°!. 0 

(/) 

c 

(/) 

,E>. co E.o Cll oQl s:;; ..... -o ..... ::J u 1_2 :;::::: CD 

.. o::: 

- Qj :;:co c Cs:;; e ... - = a;.~ 

c :s o.c 

co- a; E -c 

- ..... Ql c ~ 

l ~ :::t - :::1'6' (/) (/)CIJ 

J Ql 

"0 

c 

::::::> 

B. Generalized water budget 

gl 

CD 

tD 

Cll 

.0 

E I-.~ 

~ 

Ci5 

c 

.2 

~ Q. 

tD 

c 

!.! 

0 

a. 

Cll 

> 

w 

..._ 

w 

(!) 

<( 

a.. 

::;: 

:::> 

a.. 

..... 

w 

w 

lL 

g 

"' J 

VERTICAL SCALE GREATLY EXAGGERATED 

MAGNITUDE OF FLOW COMPONENT 

C. Generalized flow-component response 

to pumpage 

VOLUME REMOVED FROM STORAGE 

D. Generalized change in storage in response 

to pumpage 

Figure 75. - Generalized characteristics of the aquifer system underlying the basins of the southeast category in southern 

and central Arizona and parts of adjacent States. 
Stream alluvium 

A. Generalized physical system 

100o/o r--------------------------------------------, 

Cll 

c 

3: 

0 Ql 

..J Cl 

u. ni z .t:: 

0 

~ 

c 

_g 

C: 

·a; 

c 

;:) 

0 

:::!: 0 

Ql 

Cll 

ra 

..0 

E 

ra 

~ 

3: Ci5 

0 

..J 

u. 

1-

::::> 

0 

100o/o L-------------------------------------------~ 

B. Generalized water budget 

w 

(!) 

<( 

a. 

:::;; 

::;) 

a. 

w 

(!) 

<( 

a. 

:::;; 

=> 

a. 

VERTICAL SCALE GREATLY EXAGGERATED 

MAGNITUDE OF FLOW COMPONENT 

c. Generalized flow-component response 

to pumpage 

VOLUME REMOVED FROM STORAGE 

D. Generalized change in storage in response 

to pumpage 

Figure 76.- Generalized characteristics of the aquifer system underlying the basins of the central category in southern 

and central Arizona and parts of adjacent States. 

125 
126 

Upper basin fill 

1 

t;; 

w 

"-

~ _j_ 

----------------------------4T014MILES ----------------------~ 

A. Generalized physical system 

100o/o r-------------------------------------------0 

rn 

c 

3: rn 

0 C1l <1l 

...J Cl E.o u.. «; o<1l 

z .c ~u 

-::::J (.) c 3::!::: ~ .Q Q!:: 

~ ;;::til 

c:c 

-o C!l-

£ o.r:: roE -c 

~C!l 

<1l ::J(.) 

~ rn«l .o_ 

ii5 ::JU 

(/)til 

0 c 

.Q 

Iii 

..... 

·c. 

II) 

c 

!! 

0 

a. 

3: as 

> 

w 0 

...J 

u.. 

1-

:::J 

0 

100% L-------------------------------------------~ 

B. Generalized water budget 

w 

(!) 

<( 

0.. 

::;: 

::J 

0.. 

w 

(!) 

<( 

0.. 

::;: 

::J 

0.. 

VERTICAL SCALE GREATLY EXAGGERATED 

/ Stream infiltration 

/ Evapotranspiration 

MAGNITUDE OF FLOW COMPONENT 

c. Generalized flow-component response 

to pumpage 

VOLUME REMOVED FROM STORAGE 

D. Generalized change in storage in response 

to pumpage 

Figure n.-Generalized characteristics of the aquifer system underlying the basins of the west category in southern 

and central Arizona and parts of adjacent States. 
I, 

-,-' --.,, 

Upper basin fill 

Stream alluvium 

iii 

w 

u. 

§ 

N 

_1 

1------------- 5T014 MILES----------

A. Generalized physical system 

100% 

:5: 

0 

...J 

u.. 

z 

0 

:5: 

0 

...J 

u.. 

I-

=> 

0 

100% 

Q) 

Ol 

:u 

.c:: 

0 

~ 

..... 

c:: 

g 

C:: 

:§ 

c:: 

:::J 

0 

:::!: 

.....-

C/l 

c:: 

C/l 

111 

E.c 

oGl 

~u 

-:::J c:: 3::!::: .2 0!::: 

iii :;:111 

.!:.c:: ~ Q).!? 

:E o.c:: 

!11 ..... 

E 't:C:: :::JQ) 111 <flO 

~ .cal 

w :::Ju 

(/)!11 

7 :;: 

(jj 

u 

c:: 

::::> 

B. Generalized water budget 

J c:: 

0 

Q) ~ C/l Q. 111 til .0 c:: E <II 

... 111 0 ~ 0. 

Ci5 <II 

> w 

L......:. 

w 

Cl 

<( 

a. 

::;: 

:::> 

a. 

VERTICAL SCALE GREATLY EXAGGERATED 

MAGNITUDE OF FLOW COMPONENT 

C. Generalized flow-component response 

to pumpage 

VOLUME REMOVED FROM STORAGE 

D. Generalized change in storage in response 

to pumpage 

Figure 78.- Generalized characteristics of the aquifer system underlying the basins of the Colorado River category in 

southern and central Arizona and parts of adjacent States. 

127 
128 

I. 

A. Generalized physical system 

100% 

3: 

0 

....J 

u. 

z 

0 

3: 

0 

....J 

u. 

1-

:::> 

0 

100% 

!I) 

c 

!I) 

Ql ., Cl E.o 

:;; ...----. oGl .c. ... :o 0 -::;, 

~ c :i::!: 0 O:!: 

c :; ;:10 

c.c. _g ~ -o 

Q)-

C:: £ .,_ 

OS:: 

m -c: 

ll .... Q) 

:::lo 

Ill., .a_ 

:::l'O 

(/)10 

:i: 

.2 

-Q; 

u 

c 

:::> 

B. Generalized water budget 

LESS THAN 1 TO 8 MILES 

:i: 

;: 

0 ~ Q) ~ Ill c. "' Ill .0 c 

., 

E ~ 

Q) -

0 .... 0. - "' (I) > w ....__ 

L.....-.. 

w 

C) 

<( 

Q. 

::;; 

::J 

Q. 

w 

~ Q. 

::;; 

::J 

Q. 

VERTICAL SCALE GREATLY EXAGGERATED 

MAGNITUDE OF FLOW COMPONENT 

C. Generalized flow-component response 

to pumpage 

VOLUME REMOVED FROM STORAGE 

D. Generalized change in storage in response 

to pumpage 

Figure 79.-Generalized characteristics of the aquifer system underlying the basins of the highland category in southern 

and central Arizona and parts of adjacent States. 
Colorado River Category 

Basins of the Colorado River category are 

filled with sediments that consist of a 

fanglomerate over lain by a marine estuarine 

deposit of the same age as the lower basin fill. The 

lower basin fill unit, in turn, is overlain by the 

upper basin fill. Stream alluvium overlies and occupies the channels which had cut into the basin 

fills. 

Flow in the aquifer systems underlying the 

basins of the Colorado River category is totally 

dominated by flow in the Colorado River. Infiltration of Colorado River water is the main source 

of recharge to the aquifer systems. Discharge 

before development was almost entirely through 

evapotranspiration by phreatophytes and 

riparian vegetation (fig. 78B). Stream alluvium 

that underlies the flood-plain area is the principal 

aquifer. Ground-water flow occurs laterally and 

longitudinally in the basins. Surface water infiltrates and flows away from the river and 

discharges as evapotranspiration. 

Ground-water withdrawal from the aquifer 

systems underlying basins of this category has 

minimal effect on the aquifer system because of 

the immensity of seepage from the Colorado 

River. Ground water pumped from the flood-plain 

area is mainly induced from the river. In places, 

evapotranspiration may decrease and minor 

amounts of water may be withdrawn from aquifer 

storage; however, increasing the hydraulic gradient by pumping will also result in more induced flow from the river. The aquifer systems in this 

category can be simulated with two-dimensional 

models. 

Highland Category 

The aquifer systems under lying the basins 

of the highland category contain thin basin-fill 

deposits of limited areal extent that occur in the 

flood plain of the streams that drain the 

area.These alluvial deposits are superimposed on 

a sequence of older, consolidated sedimentary 

rocks (fig. 79A). Many of the streams are perennial. Recharge occurs as underflow from the adjacent consolidated-rock aquifers and as 

streamflow infiltration (fig. 79B). Mountain-front 

recharge only occurs locally. Before development, 

ground water discharged as evapotranspiration 

and as stream baseflow. 

The response of aquifers to development is 

dependent upon the magnitude of the development and its proximity to the perennial stream, 

if one is present. Typically, the result will be more 

induced streamflow infiltration, less discharge as 

stream baseflow, and reduced evapotranspiration. 

Ground-water pumpage from the aquifer systems 

in the basins of this category could result in some 

amount of water being withdrawn from aquifer 

storage (fig. 79D). Two-dimensional models are 

adequate to simulate the aquifer systems in this 

category. 

SUMMARY 

The study area is composed of 72 alluvial 

basins. The basins are filled with alluvial deposits 

that range from a few thousand feet to more than 

10,000 feet in thickness. In almost all basins, the 

general vertical sequence of sedimentary units is, 

in ascending order, sediments deposited before 

the formation of the Basin and Range topography, 

lower and upper basin fill, and stream alluvium. 

Each of the hydrogeologic units has different 

physical, geologic, and hydrologic properties 

largely because of differences in the depositional 

environment and source area of the sedimentary 

material. 

An estimated 900 million acre-ft of recoverable water was stored in the upper 1,200 feet of 

the sediments before development. The amount 

of water entering and leaving the basin aquifers 

is estimated to be about 2.5 million acre-ft per 

year. From the beginning of development through 

1980, an estimated 184 million acre-ft of water 

has been pumped. Although a part of this volume 

has been balanced by recharge, water levels have 

declined more than 400 feet in some basins. 

The basins of the study area are grouped 

into five categories on the basis of geologic and 

hydrologic properties. The groups. are: (1) 

southeast, (2) central, (3) west, (4) Colorado River, 

and (5) highland. The character of the sediments 

filling the basins and the important flow components are similar within a category. The effect 

of development on the aquifer system and 

changes in flow components generally can be 

evaluated for each category by model simulation. 

PUBLISHED REPORTS 

Abstracts 

1. Robertson, F. N. 1984a, Isotopic content of 

ground water along the Colorado River in 

129 
130 

Arizona and California: Geologi~al Society 

of America, Abstracts with Program, 

November 8, .1984. 

2. -~-~-:-1984b, Trace elements in ,ground 

water in southern Arizona, in Water Today 

and Tomorrow, Amerjcan Society of Civil 

Engineers, Irrigation and Drainage Division, Specialty Conference, Proceedings, 

Flagstaff, AZ, ·1984. 

3. Tucci, Patrick, Schmoker, J. W., and Robbins, 

S. L. , 1982, Density of basin-fill deposits 

calculated from borehole-gravity data in 

four basins in central and southern Arizona: 

Societ:y of Exploration Geophysicists, Expanded Abstracts· with Biographies, 1983 

Technical Programs, p. 2~-31. ' 

Reports 

1. Anderson, ·T. W. , 1979, Development of 

ground-water models of alluvial basins in 

south-central Arizona: Proceedings of the 

23rd Annual· Arizona Water Symposium, 

Arizona Department of Water Resources 

Report 2, p. 13-17. 

2. ----1980, Study plan for the regional 

aquifer-system analysis of alluvial basins in 

south-central Arizona and adjacent states: 

United State Geological Survey Open-File 

Report 80-1197, 22 p. 

3. -----1983, Implications of deep percolation to ground-water systems in southcentral Arizona based on numerical-model 

studies: Proceedings of the 1982 Deep Percolation Symposium, October 26, 1982, 

Arizona Department of Water Resources 

Report 4, p. 30-40. 

4. -----1984, Southwest alluvial basins, 

RASA study-An overview, in Water Today 

and Tomorrow: American Society of Civil 

Engineers, Irrigation and Drainage Division, Specialty Conference, Proceedings, 

Flagstaff, AZ, 1984, p. 606-613. 

5. DeCook, K. J., and Wilson, L. G., 1980, 

Ground-water recharge from urban runoff 

and irrigation returns: Proceedings of the 

Deep Percolation Symposium, May 1-2, 

1980, Arizona Department of Water 

Resources Report 1, p. 37-52. 

6. Evans, L. G. and Haimson, J. S., 1982, 

SWAB/RASA aquifer parameter study: 

Arizona Department of Water Resources, 

final report for U.S. Geological Survey contract 14-08-0001-18268, 21 p. 

7. Fennessy, P. J., Carter, K. G., and Keith, S. 

J., 1980, Summary of literature information 

on recharg~ in arid-semiarid basins: University of Arizona, Water Resources Research 

Center R~port, 259 p. 

8. Fields, R. 1., and Vetter, E. F., 1984, A datamanagement system for use in a· groundwater modeling and resources evaluation 

environment: U.S. Geological Survey WaterResources Investigations Report 84-4014. 

9. Freethey, G. W., 1982, Hydrologic analysis of 

the upper San Pedro Basin from the Mexico• 

United States international boundary to 

Fairbank, Arizona: U.S. Geological Survey 

Open-File Report 82-752, 64 p. 

10. -----1984, Ground-water modeling, 

alluvial basins of Arizona, in Water Today 

and Tomorrow: American Society of • Civil 

Engineers, Irrigation and Drainage .Division, Specialty Conference, Proceedings, 

Flagstaff, AZ, 1984, p. 6'75-682 .. 

11. Freethey, G. W., and Anderson, T. W., 1985, 

Predevelopment hydrologic conditions in the 

alluvial basins of Arizona and ~djacent parts 

of California and New. Mexico: U.S. 

Geological Survey Hydrologic Investigations 

Atlas 664, scale 1:500,000, 3 sheets, [in 

press]. 

12. Keith, S. J., Paylore, Patricia, DeCook, K. J., 

and Wilson, L. G., 1982, Bibliography on 

ground-water recharge in arid and semiarid 

areas: University of Arizona, Water 

Resources Research Center Report, 149 p. 

13. Kisser, K. G., and Haimson, J. S., 1981, 

Estimations of aquifer characteristics using 

drillers' logs: Arizona and Nevada Academy 

of Sciences, Proceedings of 1981 meeting of 

American Water Resources Association and 

Hydrology Section, May 1-2, 1981, v. 11, 

p. 112-116. 

14. Oppenheimer, J. M., and Sumner, J. S., 1980, 

Regional geophysics assessment of 

southwest alluvial basins: University of 

Arizona, final report for U.S. Geological 

Survey contract 14-08-0001-18228, 50 p. 

15. ----1981, Gravity modeling of the basins 

in the Basin and Range Province, Arizona: 

Arizona Geological Society Digest, v. XIII, 

p. 111-115. 

16. Pool, D. R., 1984, Aquifer geology of alluvial 

basins of Arizona, in Water Today and 

Tomorrow: American Society of Civil 

Engineers, Irrigation and Drainage Division, Specialty Conference, Proceedings, 

Flagstaff, AZ, 1984, p. 683-690. 
17. Tucci, Patrick, 1982, Use of a threedimensional model for the analysis of the 

ground-water flow system in Parker Valley, 

Arizona and California: U.S. Geological 

Survey Open-File Report 82-1006, 54 p. 

18. -----1984, Surface resistivity studies for 

water-resources investigations, near Tucson, 

Arizona: Proceedings, Conference on 

geophysical methods in water-resources investigations, San Antonio, TX, February 

6-9, 1984. 

19. Tucci, Patrick, Schmoker, J. W., and Robbins, 

S. L., 1982, Borehole gravity surveys in 

basin-fill deposits of central and southern 

Arizona: U.S. Geological Survey Open-File 

Report 82-473, 23 p. 

20. Wilson, L. G., DeCook, K. J., and Neuman, 

S. P., 1980, Regional recharge research for 

southwest alluvial basins: University of 

Arizona, Water Resources Research Center 

Report, 389 p. 

21. Winograd, I. J., and Robertson, F.N., 1982, 

Deep oxygenated ground water-anomaly or 

common occurrence: Science, v. 216, 11 

June, 1982, p. 1227-1230. 

REFERENCES CITED 

Anderson, T. W., 1980, Study plan for the regional aquifer" 

system analysis of alluvial basins in south-central 

Arizona and adjacent States: U.S. Geological Survey 

Open-File Report 80-1197, 22 p. 

Freethey, G. W., and Anderson, T. W., 1985, Predevelopment 

hydrologic conditions in the alluvial basins of Arizona 

and adjacent parts of California and New Mexico: U.S. 

Geological Survey Hydrologic Investigations Atlas 664, 

scale 1:500,000, 3 sheets, [in press]. 

Scarborough, R. B., and Peirce, H. W. 1978, Late Cenozoic 

basins of Arizona, in Callender, J. F., Wilt, J. C., and 

Clemons, R. E., eds., The Land of Cochise: New Mexico Geological Society Guidebook, 29th Field Conference, p. 253-259. 

Shafiqullah, M., Damon, P. E., Lynch, D. J., Reynolds, S. J., 

Rehrig, W. A., and Raymond, R. H., 1980, K-Ar 

geochronology and geologic history of southwestern 

Arizona and adjacent areas: Arizona Geological Society 

Digest, v. 12, p. 201-260. · 

Trescott, P. C. 1975, Documentation of finite-difference model 

for simulation of three-dimensional ground-water flow: 

U.S. Geological Survey Open-File Report 75-438, 32 p. 

Trescott, P. C., and Larson, S. P., 1976, Documentation of 

finite-difference model for simulation of threedimensional ground-water flow: U.S. Geological Survey 

Open-File Report 76-591, 21 p. [Supplement to OpenFile Report 75-438.] 

U.S. Geological Survey, 1982, Annual summary of groundwater conditions in Arizona, spring 1980 to spring 1981: 

U.S. Geological Survey Open-File Report 82-368, scale 

1:1,000,000, 2 sheets. 

131 
132 

REGIONAL AQUIFER-SYSTEM ANALYSIS-SUMMARY OF PROJECTS, 1978-1984 

ACTIVE PHASE I 

REGIONAL AQUIFER-SYSTEM A~ALYSIS PROJECTS 

CENTRAL MIDWEST REGIONAL AQUIFER-SYSTEM STUDY 

By Donald G. Jorgensen, Robert B. Leonard, Donald C. Signor, 

and john 0. Helgesen, Lawrence, Kansas 

INTRODUCTION 

The Central Midwest regional aquifer system study was started in 1980 and is scheduled 

for completion in 1986. The study area extends 

eastward from the foothills of the Rocky Mountains in Colorado to the valleys of the Missouri 

and Mississippi Rivers, and extends southward 

from northern Nebraska to south-central Arkansas. The area includes the Ozark Plateau and a 

large part of the Great Plains (fig. 80). 

The sedimentary rocks under lying the 

study area, except in the St. Francois Mountains, 

are generally water-yielding formations and 

range in thickness from a featheredge where they 

pinch out against the St. Francois Mountains to 

more than 40,000 feet in the Anadarko Basin in 

central Oklahoma. The ,igneous and metamorphic 

basement rocks that underlie the water-yielding 

formations generally do not yield significant 

quantities of water to wells. Therefore, the surface of the basement rock effectively forms the 

base of the ground-water flow system in the study 

area. 

Hydraulic properties of the various rocks in 

the study area differ greatly. These rocks include 

sandstone, shale, and evaporites of Cretaceous, 

Jurassic, and Permian age; limestone and shale 

of Pennsylvanian and Mississippian age and 

Dolomite and sandstone of Silurian, Ordovician, 

and Cambrian age. Except in the Ozark Plateau, 

little is known about the ground-water flow, and 

it is probable that not all aquifers have been identified. In much of the study area, the wateryielding rocks are deeply buried, and groundwater related data are scarce except for data collected incidentally by the. petroleum industry. 

Be~ause the cost of· collecting additional 

hydrologic data in the deep subsurface is prohibitive, special efforts and techniques are needed to evaluate and analyze existing data. 

PROGRESS OF THE STUDY 

The aquifers studied consist generally of 

Early Cretaceous and older rocks. These aquifers 

constitute the major components of the regionalflow system within the study area. Local aquifers 

are not studied unless they are hydrologically important components of the regional-flow system. 

Available maps and reports of previous investigations, along with readily accessible data 

describing hydrologic and geologic characterstics, 

were examined to define the regional 

hydrogeologic units and to form a conceptual 

model of the ground-water flow system. 

Data have been collected on water quality, 

water use, water levels, hydraulic properties, 

geohydrologic-unit thicknesses,. and altitude. The 

data bases in which the collated data are stored 

are nearly complete. Maps and tables are now being prepared from the information stored in these 

data bases. 
A ground-water flow model for the entire 

study area incorporating variable-density effects 

is being constructed and used. Subregional flow 

models are being used to simulate the freshwater 

flow system of the Ozark area, and to simulate 

flow conditions in the Great Plains aquifer 

system. A model simulating flow into and out of 

the water-table aquifer has also been developed 

and models of water chemistry are being tested. 

Several special studies have been undertaken 

to evaluate specific items of particular importance 

in understanding the hydrology in the study area. 

40 " 

35" 

I --------1 

WYOMING 

BL~CK :HILLS 

I 

I 

I 

Ci) ~ ~o <:7 

r------- --- 1 

I 

~ Cl) 

<: _, ::.::> :::::! 

0 ~ COLORADO ~ 0 

0 ~ 

"-

>-

G 

0 

ct 

---------, 

NEW MEXICO (!) I 

I 

I 

I 

I 

TEXAS I 

The special studies, some of which have been completed, are 

• Geohydrology of the aquifers in the 

Ozark area. 

•Geohydrology of the aquifers consisting 

of Lower Cretaceous rocks in the Great Plains 

aquifer system. 

•Hydrology and geochemistry of the transition zone between the freshwater flow system 

in the Ozark area and the saline water flow 

system in the western part of the Interior Plains. 

•Ground-water and surface-water relationships in the Ozark area. 

MINNESOTA 

-------

IOWA 

WISCONSIN 

ILLINOIS 

ST. 

FRANCOIS 

MTNS. 

SCALE 1:10,000,000 OKLAHOMA 

0 100 200 MILES 

0 100 200 KILOMETERS 

EXPLANATION 

STUDY AREA 

BOUNDARY SHOWING APPROXIMATE EXTENT OF 

GREAT PLAINS AQUIFER SYSTEM 

BOUNDARY SHOWING APPROXIMATE EXTENT OF OZARK AREA 

Figure 80.- Study area of the Central Midwest regional aquifer system. 

133 
134 

• Recharge to and discharge from the shallow 

water-table. 

• Hydrogeologic controls of recharge to 

the Great Plains aquifer system along the 

foothills of the Rocky Mountains. 

An evaluation of past and future impacts on 

the regional flow system resulting from development of ground water is being conducted. 

RESULTS 

Results from several of the special studies 

listed above have been important in developing 

the overall description of the Central Midwest 

regional aquifer system and in defining the 

following major regional geohydrologic units: 

•Confining units consisting of Late Cretaceous and younger rocks. 

•The Great Plains aquifer system in the 

Great Plains, consisting of "Early" Cretaceous 

rocks. 

•Confining units of Jurassic, Triassic, Permian, and Pennsylvanian age rocks. 

• An aquifer system consisting ·of rocks of 

Early Paleozoic age outside the Ozark area 

(western part of Interior Plains). 

•The Springfield Plateau aquifer consisting of limestones of Mississippian age in the 

Ozark area. 

•The confining unit that separates the 

Springfield Plateau aquifer from the underlying 

Ozark aquifer in the Ozark Area. 

•The Ozark aquifer consisting mostly of dolomites of Lower Ordovician and Cambrian age in 

the Ozark area. 

• A confining unit of shale and dolomite 

that separates the Ozark aquifer and the underlying St. Francois aquifer. 

•The St. Francois aquifer of sandstone of 

Cambrian age. 

•The crystalline basement. 

· The confining units of Late Cretaceous and 

younger rocks overlying the Great Plains aquifer 

system in the Great Plains consist mainly of shale 

and range in thickness from featheredge at the 

outcrop to about 8,000 feet in the Denver basin. 

The shale has extremely low permeability except 

where microfractures that exist to depths of about 

800 feet, markedly increase the vertical 

permeability. 

The Great Plains aquifer system in the Great 

Plains, generally referred to as the ''Dakota 

aquifer" in the hydrologic literature is one of the 

most extensive aquifer systems in North America. 

The .aquifer system commonly consists of an upper unit (Maha aquifer) and a lower unit 

(Apishapa aquifer) separated by a confining unit 

(fig. 81). Both the Maha and Apishapa aquifers 

consist primarily of loosely cemented fine sand. 

In the study area, regional ground-water flow 

through the Great Plains aquifer system is eastnortheastward towards discharge areas (fig. 82). 

Thick shale, salt, and anhydrite of Jurassic 

to Pennsylvanian age restrict vertical flow between the Great Plains aquifer system and the 

under lying aquifers. The shale has very low 

permeability, and the anhydrite and salt are virtually impermeable. Thus, these sediments form 

a very effective confining unit. 

Lower Paleozoic rocks, exclusive of the Ozark 

area, comprise a separate regional aquifer system 

in the study area. This aquifer system contains 

a large quantity of saline water. Permeable zones, 

resulting from paleokarst development in 

dolomite, exist in this aquifer system. 

Within the Ozark area, the Springfield Plateau E,tnd Ozark aquifers are important sources of 

water. The Springfield Plateau aquifer, the upper aquifer, is composed mainly of fractured 

limestone . of Mississippian age. The Ozark 

aquifer, except in northwestern Arkansas, usually yields more water than the Springfield 

Plateau aquifer and is composed mostly of fractured dolomite of Ordovician and Cambrian age. 

At most locations, the two aquifers are separated 

by a confining unit of Chattanooga Shale. The 

basal water-yielding unit in the Ozark area is the 

St. Francois aquifer consisting of sandstone of 

Cambrian age. 

Throughout the study area, the basement 

is composed mostly of fractured igneous and 

metamorphic rocks of Cambrian and Precambrian age. The rocks generally have moderate to 

low permeability, depending on the degree of fracturing. Because there is no information indicating 

the magnitude. or direction of flow through the 

basement rock, it is being treated :regionally in 

this study as a no-flow boundary of the delineated 

aquifer system. 

Rapid interchange of surface water and 

ground water characterizes the Ozark Plateaus, 

especially at. locations where the fractured 

limestone and dolomite of the Springfield Plateau 

and Ozark aquifers crop out or are near land surface. Many springs are present and karst 

topography is well developed locally. Large gains 

and losses of streamflow are evident in much of 

the Ozark area, thus determination of the relations between the aquifers and streams is essential in evaluating the ground.;water flow system 
Ol ~ c:: 

> Q) ·-- C:: -- ;:> -- c:: _9'C:J 0 

u 

West 

NOT TO SCALE 

tf!:kk{{j SANDSTONE 

Bill SHALE 

-SALT 

EXPLANATION 

~ LIMESTONE 

~ ANHYDRITE 

135 

East 

Figure 81.- Generalized geologic section of the Maha and Apishapa aquifers of the Great Plains regional aquifer system in 

central Midwest. 

in the Ozark area. Accordingly, a study was made 

of the Ozark area in parts of Arkansas, Kansas, 

Missouri, and Oklahoma to determine the flow 

characteristics of selected springs and streams. 

Hedman and others (1984) summarized flowduration data for continuous-record spring- and 

streamflow-gaging stations. They also included 

low-flow frequency data for continuous-record 

spring- and streamflow-gaging stations and for 

miscellaneous-measurement sites as well as 

values of mean annual runoff. A finding of particular interest is that the difference between annual precipitation and runoff (which represents 

the sum of consumptive use and evapotranspiration) has a relatively uniform value of about 29 

inches across the Ozark area; although the annual precipitation ranges from 34 to 56 inches. 

Information describing flow to and from the 

water-table aquifer is needed as data-input for 

simulating the regional ground-water flow 

system. As a part of this study, Dugan (1984) 

developed a procedure to determine such flow. In 

general, the amount of water moving through the 

unsaturated zone above the water table is a function of many factors, such as soil type, slope of 

land surface, vegetation, soil permeability, waterretention properties, depth to the water table, and 

climatic factors such as precipitation, solar radiation, and temperature. 

Determining the direction of flow in an 

aquifer containing water with different densities 

at different locations is a complex problem. 

Analysis usually is accomplished by modeling the 

flow of the variable density fluid in three dimen-
136 

OKLAHOMA 

NEW MEXICO --------l 0 100 

MINNESOTA 

IOWA 

I 

I 

\ 

I 

I 

\ 

I 

I -----1 

L... 

200MILES \ 

TEXAS : 0 100 200 KILOMETERS \ 

EXPLANATION 

-1800- POTENTIOMETRIC CONTOUR·· Shows altitude of potentiometric 

surface. Contour Intervals 200 and 1000 feet. Datum Is sea level 

~ GENERALIZED GROUND-WATER FLOW DIRECTION 

LIMIT OF MAHA AQUIFER 

Figure 82.-Preliminary pqtertiometric surface of the Maha aquifer of the Great Plains regional aquifer system in the 

central Midwest (modified frqm Helgesen and others, 1982). 
40° 

105° 

~--------

----

------

NEW MEXICO 

DISSOLVED SOLIDS, IN 

~~~~~~~~~~~~~~~~~~~~~<>!!!!~::. 

~ N $ ~ ~~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ••• 0 •• •• • ••••• 0 •••••• •• •• 0 ••• •••• 

• • • • • 0 0 •• •• • 0 •• • 0 0 ••••••••• 0 0 •• 

• : • •••• 0 ••• 0 ••••••• 0 •• 0 0 ••••• • 

_ _J__ _____________ _ 

OKLAHOMA 

--------l 

TEXAS 

0 

SCALE 1:7,500,000 

100 

MINNESOTA 

------

I 

I -----1 

200 MILES 

L 

I 

I 

I 0 100 200 KILOMETERS \ 

EXPLANATION 

MILLIGRAMS PER LITER 

IIIIIJ Less than 2000 ~ Greater than 20,000 

~ 2000 to 10,000 NO DATA 

[illill] 10,000 to 20,000 LIMIT OF MAHA AQUIFER 

Figure 83.- Dissolved-solids concentrations of ground water in Maha aquifer of the Great Plains regional aquifer system 

in the central Midwest (modified from Leonard and others, 1983). 

137 
138 

40" 

MONTANA 

------

------

-------

OKLAHOMA 

NEW MEXICO - - - - ----l 

p::;;\);\)J SODIUM CHLORIDE 

f_: ,; ~- ~ :C.'j SODIUM BICARBONATE 

B~~{H.1 SODIUM SULPHATE 

LIMIT OF MAHA AQUIFER 

TEXAS : 

EXPLANATION 

0 

0 

MINNESOTA 

IOWA 

I 

I 

-----1 100 200MILES 

100 200 KILOMETERS 

CALCIUM SULFATE 

CALCIUM BICARBONATE 

NO DATA 

'-

\ 

\ 

Figure 84.- Dominant ions of ground water in the Maha aquifer of the Great Plains regional aquifer system in the central Midwest (modified from Leonard and others, 1983). 
sions. This modeling requires more data than are 

available for most of the study area. Jorgensen 

and others (1982) have developed a technique to 

be applied between two points in a flow system 

containing variable density water that determines whether a component of flow exists between the two points. This technique requires less 

information than the three-dimensional variable 

density modeling technique. 

The Great Plains aquifer system is one of 

the most extensive aquifer systems in North 

America. No regional data synthesis and evaluation of the aquifer characteristics had been undertaken since the classic work by Darton (1905). 

During the RASA study, Helgesen and others 

(1982) summarized the important work and the 

changes in concepts that have occurred since Darton's 1905 study and concluded that conceptualization of the geohydrology was handicapped by the 

confusing nomenclature used in describing the 

various sandstone units of Lower Cretaceous age, 

which had been collectively called the "Dakota 

aquifer." Also, Leonard and others (1983), described the geohydrology and hydrochemistry of 

the Maha aquifer which is considered to be the 

upper part of the Great Plains aquifer system. 

Figure 83 shows the distribution of dissolved 

solids and figure 84 shows the distribution of 

predominant ions in the water of the Maha 

aquifer. As used therein, "predominant ion" 

refers to the most abundant cation or anion in the 

water, as measured, in milliequivalents per liter. 

For simplicity, mixed anion or cation types are 

included within the dominant types shown in 

figure 84. Their inclusion does not significantly 

alter the interpretation. 

The potentiometric surface of the water in 

the Maha aquifer indicates that ground water 

generally flows laterally from the Rocky Mountain foothills toward outcrop areas to the east. 

However, the distribution of dissolved solids 

shown in figure 83 strongly suggests zones of 

recharge near the northeast corner of New Mexico, and the northwest corner of Nebraska near 

the Black Hills, with an intervening zone of 

stagnation. Local recharge also occurs along the 

southern and eastern boundaries of the Great 

Plains aquifer system where the Maha aquifer 

crops out or is truncated at shallow depth beneath 

the High Plains aquifer. 

Concentrations of dissolved solids exceeding 

20,000 milligrams per liter (mg/L) in the Denver 

basin and ranging from about 2,000 to 10,000 

mg/L along the Rocky Mountain front, west of the 

basin, suggests minimal recharge of freshwater 

in the foothill areas. Recharge from west of the 

Denver basin probably is restricted by low 

permeability resulting from facies change, including pinchout of sandstone to the west, and 

faults that constitute barriers to lateral flow. 

These interpretations are preliminary and 

subject to revision; however, the chemical data 

shown in figures 83 and 84 reveal the complexity 

of the Great Plains aquifer system. In particular, 

when combined with the hydrologic data, they 

suggest extensive vertical leakage through 

presumed confining units, localized recharge at 

the truncated eastern boundary, and a partial 

barrier to recharge along the Rocky Mountain 

front. 

PUBLISHED REPORTS 

1. Dugan, J. A., 1984, Hydrologic properties of 

soils in parts of Arkansas, Colorado, Kansas, Missouri, Nebraska, New Mexico, 

Oklahoma, South Dakota, and Texas: U.S. 

Geological Survey Hydrologic Investigations 

Atlas 678 [in press]. 

2. Hedman, E. R., Skelton, John, and Freiwald, 

D. A., 1984, Flow characteristics for selected 

springs and streams in the Ozark subregion, 

Arkansas, Kansas, Missouri, and 

Oklahoma: U.S. Geological Survey 

Hydrologic Investigations Atlas 688 [in 

press]. 

3. Helgesen, J. 0., Jorgensen, D. G., Leonard, 

R. B., and Signor, D. C., 1982, Regional 

study of the Dakota aquifer ·(Darton's 

Dakota revisited): Ground Water, v. 20, 

no. 4, p. 410-414. 

4. Jorgensen, D. G., Gogel, Tony, and Signor, D. 

C., 1982, Determination of flow in aquifers 

containing variable density water: Ground 

Water Monitoring Review, v. 2, no. 2, 

p. 40-45. 

5. Jorgensen, D. G., and Signor, D. C., 1981, Plan 

of study for the Central Midwest regional 

aquifer system analysis in parts of Arkansas, Colorado, Kansas, Missouri, Nebraska, 

New Mexico, South Dakota, and Texas: U.S. 

Geological Survey Water-Resources Investigations Report 81-206, 28 p. 

6. -----Ceds.), 1984, Geohydrology of the 

Dakota aquifer: National Water Well 

Association, Proceedings of the First C. V. 

Theis Conferences on geohydrology, Oct. 5-6, 

1982, Lincoln, NE, 24 7 p. 

139 
140 

7. Leonard, R. B., Signor, D. C., Jorgensen, D. 

G., and Helgesen, J. 0., 1983, Geohydrology 

and hydrochemistry of the Dakota aquifer, 

central United States: American Water 

Resources Association Water Resources 

Bulletin, v. 19, no. 6, p. 903-911. 

8. Signor, D. C., 1985, Ground-water sampling 

during artificial recharge: equipment, 

techniques, and data analyses: in Artificial 

Recharge of Ground Water, Tak.ashi Asano, 

ed: Boston, MA, Butterworth Publishers, 

chapter 6, 51-202 p., 36 illustrations. 

9. Signor, D. C., Kontis, A. L., Jorgensen, D. G., 

and Mandie, R. L., 1980, Ground-water flow 

regime based on preliminary data: 

American Geophysical Union EOS, v. 61, 

no. 46, p. 952. 

REFERENCES CITED 

Darton, N. H., 1905, Preliminary report on geology and 

underground water resources of the Central Great 

Plains: U.S. Geological Survey Professional Paper 32, 

83 p. 

Dugan, J. A., 1984, Hydrologic properties of soils in parts of 

Arkansas, Colorado, Kansas, Missouri, Nebraska, New 

Mexico, Oklahoma, South Dakota, and Texas: U.S. 

Geological Survey Hydrologic Investigations Atlas 678 

[in press]. 

Hedman, E. R., Skelton, John, and Freiwald, D. A., 1984, Flow 

characteristics for selected springs and streams in the 

Ozark subregion, Arkansas, Kansas, Missouri, and 

Oklahoma: U.S. Geological Survey Hydrologic Investigations Atlas 688 [in press]. 

Helgesen, J. 0., Jorgensen, D. G., Leonard, R. B., and Signor, 

D. C., 1982, Regional study of the Dakota aquifer (Darton's Dakota revisited): Ground Water, v. 20, no. 4, 

p. 410-414. 

Jorgensen, D. G., Gogel, Tony, and Signor, D. C., 1982, Determination of flow in aquifers containing variable density water: Ground Water Monitoring Review, v. 2, 

no. 2, p. 40-45. 

Jorgensen, D. G., and Signor, D. C., 1980, Plan of study for 

the Central Midwest regional aquifer system analysis 

in parts of Arkansas, Colorado, Kansas, Missouri; 

Nebraska, New Mexico, Oklahoma, South Dakota, and 

Texas: U.S. Geological Survey Water-Resources Investigations Open-File Report, 81-206, 28 p. 

Leonard, R. B., Signor, D. C., Jorgensen, D. G., and Helgesen, 

J. 0., 1983, Geohydrology and hydrochemistry of the 

Dakota aquifer, central United States: American Water 

Resources Association Water Resources Bulletin, v. 19, 

no. 6, p. 903-911. 
ACTIVE PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS. 

COLUMBIA PLATEAU BASALT REGIONAL AQUIFER-SYSTEM STUDY 

By John Vaccaro, Tacoma, Washington 

INTRODUCTION 

The basaltic rocks that comprise the regional 

aquifer system underlying the Columbia Plateau 

are located in central and eastern Washington, 

northern Oregon, and a small part of northwestern Idaho (fig. 85). The Plateau covers about 

70,000 mi2 entirely within the drainage of the Columbia River and is bordered on the west by the 

Cascade Range, on the north and east by the 

Rocky Mountains, and on the south by the Blue 

Mountains. Major tributaries to the Columbia 

River on the Plateau are the Snake, Spokane, 

John Day, Yakima, Palouse, and Deschutes 

Rivers. The topography of the Plateau is varied 

and includes: (1) major mountains consisting of 

a geologically young folded region of large anticlines and synclines, and (2) low relief features. 

Rocks of the Columbia River Basalt Group 

underlie the Columbia Plateau and compose a 

multilayered aquifer system which, for study purpos~s, has been conceptualized as a three-layered 

aquifer system. The three aquifer layers correspond to three basalt formations-the Saddle 

Mountains, W anapum, and Grande Ronde 

Basalts (Swanson and others, 1979) (fig. 86). The 

Saddle Mountains Basalt, less extensive than the 

other basalts, is the youngest formation, and is 

unconfined where it is not overlain by saturated 

unconsolidated deposits. The W anapum Basalt 

under lies most of the study area and is loosely 

confined where it is overlain either by the Saddle Mountains Basalt or unconsolidated 

sediments. The Grande Ronde Basalt under lies 

the entire study area and is loosely confined 

wh~re it is overlain by younger basalts or by 

sediments of Holocene and Pliocene age. Both the 

Wanapum and Grande Ronde Basalts are unconfined near their respective margins. All basalts 

are connected hydraulically either directly or 

through sedimentary interbeds. 

These three major aquifers form the regional ground-water flow system that provides 

water for most municipal, industrial, and 

domestic needs and for most of the irrigated lands 

outside of the Columbia Basin Irrigation Project 

and the Yakima River Basin. 

The predominant economic activity in the 

study area is agriculture, and the importance of 

this activity to the economy of Washington and 

Oregon underlines the need to better understand 

the ground-water flow system. 

The Columbia Plateau Basalt regional 

aquifer system study was started in 1982 and is 

scheduled for completion in 1986. The study was 

designed to address some of the hydrologic problems currently being encountered on the 

plateau. These problems include: (1) declining 

water levels of as much as 20 ft/yr (Cline, 1984), 

(2) the occurrence of sodium-enriched water, (3) 

the need for additional ground water for expanding irrigated land, (4) the lack of knowledge of 

the effects of increased development of the aquifer 

system, (5) the lack of know ledge of the interaction between ground water and surface water 

and (6) the potentiality of using the low: 

permeability zones of the deep basalts as a national repository site for solidified high-level 

nuclear wastes near Richland, W A. 

HYDROGEOLOGIC FRAMEWORK 

Rocks that comprise the Columbia River 

Basalt Group were emplaced through extrusion 

of numerous individual lava flows through fissure 

eruptions. These individual lava flows range in 

thickness from a few inches to more than 300 feet ' and average about 110 feet (Swanson and Wright, 

141 
142 

125' 124' 123' 118 ' 117' 116' 

49 ' -------------__g~_NAQ.~----- --,----r--·-- UNITED STATES 

WASHINGTON 

48' 

47 ' 

46 ' 

§ 

~ 

0 

\,) 

45 ' !"$ 

~ Q:; 

44' 

43' 

0 

0 50 

50 

~ ~ 

~ 

~ 

0 

"' 0 

SCALE 1:5,000,000 

100 

OREGON 

150 MILES 

100 150 KILOMETERS 

~0 

'} 

..'- \ ' \ 

l 

' ~ "'-l 

0 "- c. \ 

~ 

1;:. 

-z. 

(/) 

Figure 85. -Study area (shaded) of the Columbia Plateau basalt regional aquifer system. 

1978). The structure of a lava flow generally consists of three units (fig. 87): the flow top, the entablature, and the colonnade. The flow tops may 

also include the basal part of the overlying flow 

that consists of pillow-palagonite complexes 

(Swanson and Wright, 1978). Ground-water flow 

is predominantly horizontal and occurs in the flow 

tops, which average about 5 to 30 percent of the 

total flow thickness. In general, the entablature 

and colonnade are denser than the flow tops. 

Because fractures are generally oriented vertically, flow through fractures in the entablature 

and colonnade is predominantly in the vertical 

direction. 

The basalt flows are locally interbedded with 

sediments that function either as confining units 

or aquifers. The lithology of the interbeds varies 

from shalelike material to sand and gravel with 

fine-grained materials predominating. There are 

generally more interbeds in the younger basalt 

formation than in the older basalt. Basalt flows 

underlying the Columbia Plateau have been 

grouped into three major aquifers in this study. 

Movement of ground water in each aquifer is con-
124' 123' 118' 117 ' 116' 115' 

49' --,------r-----

WASHINGTON 

48' 

\ 

' '"-. 

' 47' "\. \ 

46' 

§ 

8 

0 

1.1 

45' ~ 1.1 

~ 

44' OREGON 

43' 

50 

0 50 

SCALE 1:5,000,000 

100 150 MILES 

100 150 KILOMETERS 

EXPLANATION 

SADDLE MOUNTAINS BASALT 

~ WANAPUM BASALT 

~ GRANDERONDEBASALT 

f.&~tGJl PRE-YAKIMA BASALT SUBGROUP 

EXTENT OF COLUMBIA RIVER 

BASALT GROUP 

STUDY AREA 

Figure 86.-Extent of the Columbia River Basalt Group. 

sidered to be lateral with some vertical flow 

through sedimentary interbeds and fractures. 

The hydrogeologic framework and generalized pattern of regional ground-water flow is 

depicted in figure 87. On a regional scale, water 

levels measured in the spring of 1983 indicate 

that the ground-water flow reasonably agrees 

with the conceptualized flow pattern shown in 

figure 87. Because of pumping, local geologic 

structures, and the inhomogeneity and anisotropy 

of the aquifer system, local variations in groundwater flow are common. For example, the 

regional water-level data show that in some areas 

ground-water flow is downward and that gradual, 

143 
144 

Southwest 

(Downgradient) 

GENERALIZED GROUND-WATER FLOW PATTERN Northeast 

(Upgradient) 

Saddle 

Columbia Mountains Mabton Rocky 

Potentiometric surface Columbia 

River 

River Basalt interbed Coulee 

-~'" ~ \ j._,...t-::~~~ ~=-=~ 

NOT TO SCALE A' 

EXPLANATION 

ESJ . 

' 

D 

UNCONSOLIDATED HOLOCENEPLIOCENE SEDIMENTS 

SEDIMENTARY INTERBEDS 

STRATIGRAPHY 

Basalt Stratigraphy Sediment Stratigraphy A " _o , • . C . • • ' . • O•. ··' 0 -··-· .. ' (glacio-fluvial, · .: :~ :-~: Holocene- · 

. fluvial, lacustrine .>~ Pliocene · ':~ :eolian, and ash fa[l ·.:,: sediments ·,::;· · 

· .. m~t er!a~s) ',';'~:; ~:\ :~; ~'; :., :~ ;;\/ 

Saddle 

Mountains 

Basalt 

c. Saddle Mountains - Miocene ::::J 

e c. Wanapum lnterbed sediments ::::J 

(!) e (informally called (Ellensburg 

- Cl "Mabton") and Latah iii .0 1/) ::::J Formations) ttl (/) 

Ill - Q; iii Wanapum 1/) 

> ttl Basalt a: Ill 

ttl ttl 

:0 E Wanapum - Grande (fluvial, E ~ Ronde lnterbed lacustrine, ::::J ttl 

0 >- (informally called and 

(.) "Vantage") volcaniclastic 

Grande 

materials) 

Ronde 

Basalt 

pre-Yakima< olumbia River Basalts 

,: ''Basement' ' roc s (pre-Columbia River· '(,-;>/,'~ ,":\ 

-' -; -_-; ._-, :.. .. ;Bas " /' ... I\\ - \ \'- lilt Group rocks) ,' ;--.,; ,-::~, :~ •-/-:..•(-•/!,, 

A' 

ARROWS INDICATE GENERAL DIRECTION 

OF GROUND-WATER FLOW 

VERTICAL SECTION 

DIAGRAM SHOWING A SERIES 

OF LAVA FLOWS 

Broken basalt 

Dense flow center 

with vertical joints 

lnterbed, flow top, 

flow bottom 

Dense flow center 

with vertical joints 

Dense flow center 

with vertical joints 

DIAGRAM SHOWING 

STRUCTURE OF 

INDIVIDUAL LAVA FLOW 

-------L.~~0c<c..:~..._ Vesicular 

base 

Figure 87.- Generalized ground-water flow pattern in the Columbia River basalt regional aquifer system and idealized vertical sections showing basalt interflow structures. 
almost linear, changes of head occur with depth. 

Locally, however, changes of head with depth 

may be small within the basalt unit but quite 

large, up to 200 feet, at or near the boundaries 

between two basalt units. 

RESULTS AND SCHEDULED WORK 

As of 1984, the following work had been 

completed: 

•The hydrogeologic framework for Washington State has been defined. This includes areal 

extent, thickness, tops and bottoms, and structural features for the three aquifers and the two 

major sedimentary interbeds. 

• An observation well network was set up 

and two mass water-level measurements were 

made in the spring of 1983 and 1984. 

• Potentiometric surface maps were prepared 

for the three basalt aquifers and the overlying 

sedimentary deposits for the spring of 1983. 

•Conceptualization and development of a 

computer program of a recharge model was made. 

•The first draft of a report documenting 

the recharge model was completed. 

•The meteorological data base such as temperature, wind velocity, radiation, and others for 

input to the recharge model was established. 

• Average annual runoff and precipitation 

maps were constructed. 

•Computer programs for plotting, manipulating, and retrieving the hydrogeologic data 

were completed. 

•Files of more than 4,000 wells in the 

U.S. Geological Survey's GWSI data base were 

revised. 

The following work is in progress: 

• Estimating ground-water pumpage and 

recharge rates. 

• Developing a regional ground-water flow 

model. 

• Preparing soil maps. 

• Developing computer programs to estimate horizontal hydraulic conductivity values on 

the basis of specific-capacity test data. 

• Determining boundary conditions for model 

simulations. 

• Determining the location and altitude of 

surface-water bodies and identifying underlying 

geohydrologic units. 

• Establishing rainfall-runoff relations. 

•Generating land-use data for 1979 and 

1983 on half-mile blocks through Landsat 

imagery. 

• Estimating irrigation acreage associated 

with crop types. 

• Using a model to estimate evapotranspiration. 

• Developing the hydrogeologic framework 

for the Oregon and Idaho part of the study area. 

•Completion of the 1984 potentiometric map. 

Scheduled future work includes the following items: 

•Complete maps for water levels, average 

annual precipitation, basalt-unit thickness, 

hydraulic conductivity, irrigation rates, and 

average annual runoff. 

•Complete a computerized data base which 

will contain land-use data, model-node locations, 

locations and altitudes of water levels of the 

surface-water bodies, thickness of hydrogeologic 

units, and recharge and discharge rates. 

•Construct pumpage maps, which will show 

location and average annual pumping rates. 

•Calibrate the regional ground-water flow 

model, which will be used to evaluate current, 

predevelopment, and projected future conditions. 

PUBLISHED REPORT 

Bauer, H. H., Vaccaro, J. J. and Lane, R. C., 1984, 

Ground-water levels in the Columbia River 

Basalt Group and overlying materials, 

spring 1983, southeastern Washington 

State: U.S. Geological Survey WaterResources Investigations Report 84-4360. 

REFERENCES CITED 

Cline, D. R., 1984, Ground-water levels and pumpage in eastcentral Washington, including Odessa-Lind area, 1967 

to 1981: Washington State Department of Ecology, 

Water-Supply Bulletin no. 55, 34 p. 

Swanson, D. A., and Wright, T. L., 1978, Bedrock geology of 

northern Columbia Plateau and adjacent areas in the 

Channel Scabland, Ch. 3, in Baker, V. R., and Nummedal, D., eds, Planetary Geology Program: National 

Aeronautic and Space Administration, 186 p. 

Swanson, D. A., Wright, T. L., Hooper, P.R., and Bentley, R. 

D., 1979, Revisions in stratigraphic nomenclature of the 

Columbia River basaltic group: U.S. Geological Survey 

Bulletin 1457 -G, 59 p. 

145 
146 

ACTIVE PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

GREAT BASIN REGIONAL AQUIFER-SYSTEM STUDY 

By James R. Harrill, Carson City, Nevada 

INTRODUCTION 

The Great Basin regional aquifer system 

study was started in 1980 and is scheduled for 

completion in 1985. The study area encompasses 

about 140,000 mi2 in parts of Nevada, Utah, and 

adjacent States (fig. 88). The area is characterized 

by generally north-trending mountain ranges 

which have a width ranging from 5 to 15 miles. 

The mountain ranges rise 1,000 to 5,000 feet 

above adjoining valleys. The widths of the valleys 

are about the same as widths of the adjacent 

mountain ranges. The valleys are typically 

elongated, and many extend more than 50 miles 

iii a north or northeast direction. The area has 

a complex geologic history that includes major 

episodes of sedimentation, igneous activity, 

orogenic deformation, and continental rifting. A 

major tectonic change occurred about 17 million 

years ago with the onset of extensional faulting, 

which has formed the major basins and ranges 

that characterize the topography. The Great 

Basin contains a regional aquifer system in that 

most of its separate valley basins share common 

geologic and hydrologic characteristics. Currently, some 242 hydrographic areas are recognized within the study area. Most include one or 

more structural basins and associated basin-fill 

aquifers. A special situation exists in eastern 

Nevada and western Utah, where permeable carbonate rocks underlying the basin-fill deposits 

form. a complex ground-water flow system that 

reflects the characteristics of both basin-fill and 

carbonate aquifers. 

In recent years, much of the study area has 

been considered for use by the MX missile system; 

large coal-fired powerplants are being constructed 

at several locations, and the potential for disposal 

of solidified high-level radioactive waste at the 

Nevada Test Site is being studied. These activities will greatly affect the ground-water 

resources in much of the study area within the 

next several· decades. 

Impacts from existing and anticipated 

developments would have both regional and, local 

effects. · However, most of the known water 

resources, which include the surface water and 

much of the ground water in basin-fiiled deposits, 

are either used or appropriated to the extent of 

current estimates of their availability. Therefore, 

continued development in some of the more in- . 

tensively developed basins requires new sources 

of water or new methods of managing the existing 

resources to make more water available. This 

regional aquifer-system study will provide. ari 

areal perspective so that effec~t:; of intensive 

development can be evaluated on both a local and 

regional basis. 

The objective of this study is to describe the 

aquifer sy~temsin the Great Basin and, to the extent possible, develop techniques that can be used 

for quantitative evaluation of the aquifer systems. 

The approach has been strongly influenced by 

the diverse nature of the ground-water flow 

systems and the large number of basins. Some 

hydrologic characteristics can be. described on a 

regional basis. However, a detailed appraisal of 

242 individual areas is not feasible .. Consequently, the approach taken was to study selected 

typical areas, identify key hydrologic processes, 

and then attempt to transfer the knowledge 

developed to areas of similar hydrology. Initial efforts have been directed towa:r.d .d~scribing. the 

regional hydrology, conducting .detailed studies 

of representative areas, and. studying selected 

hydrologic processes. Efforts during the final part 

of the study would be directed.toward developing 
a regional approach of evaluating the aquifers in 

the area of the Great Basin. 

PROGRESS OF THE STUDY 

As of 1984, efforts to describe the regional 

system were mostly complete. Findings are being 

presented as maps or reports which are in various 

stages of preparation. These are: 

•U.S. Geological Survey Hydrologic Atlases 

showing: 

•Generalized water-level contours in all 

basin-fill and consolidated rock aquifers 

within the carbonate rock province. 

• Regional hydrogeology. 

• Regional flow systems. 

• Data reports such as: 

•A series of 1:250,000 quadrangle maps 

showing quality of ground water in the 

region. 

• A summary of selected hydrologic data 

collected by the MX missile siting investigation. 

•A field canvas of wells drilled in Utah 

as part of the MX missile program. 

Study of important hydrologic processes is 

also in progress, as described below. 

Recharge.-The Desert Research Institute of 

the University of Nevada was contracted to investigate the mechanics of recharge processes at 

selected sites in both northern and southern 

Nevada. Results of the work were being compiled 

into a report. In addition, a technique to estimate 

recharge based on the mass balance of chloride 

between precipitation and ground water has been 

developed and applied to selected areas. 

Evapotranspiration. -Efforts to better 

understand the process of evapotranspiration 

have been directed toward measuring 

evapotranspiration rates under field conditions. 

Two field sites have been instrumented-one near 

Soda Lakes, about 50 miles east of Carson City, 

NV, and the other is in Smith Creek Valley, about 

40 miles west of Austin, NV. Weather stations 

were established at each site to obtain continuous 

meteorologic data. The Bowan-ratio technique 

(which measures evapotranspiration on the basis 

of humidity gradients) was also used to provide 

a comparison with the eddy correlation 

measurements. Data were collected during part 

of the 1982 growing season and through the 1983 

growing season, which were wetter than normal. 

Reports of this study are interesting and useful 

for estimating ground-water discharge. 

Basin flow models.-Eight basins were 

selected for ground-water flow modeling, which 

collectively represent most conditions present in 

the study area (fig. 88). Two basins were modeled as parts of cooperative studies with State and 

local agencies, and the results are available for 

use in this study. Of the remaining six models, 

all were calibrated for steady-state conditions, two 

were calibrated for transient conditions, and the 

remaining are in final stages of transient calibrations. Grid spacing differs in each model depending on the basin characteristics and ranges from 

2,000 feet to 2 miles. The model for Smith Creek 

Valley was completed and stressed for several proposed development alternatives. 

Regional flow models.-Two regional flow 

models were being constructed, one is the carbonate rock province between the Great Salt Lake 

Desert and Death Valley, and the other is a 

smaller scale model of the Fish Springs flow 

system that drains northward toward the Great 

Salt Lake Desert (fig. 88). The primary purpose 

of these models is to test hypotheses concerning 

the regional flow system and to ensure that information used to describe the regional flow 

system is internally consistent. Both models were 

run for steady-state conditions. The large regional 

carbonate-rock flow model is being restructured 

with a grid spacing half the initial size of 10 by 

15 miles to allow for more detailed analyses. 

Regional-scale analysis.-Intermediate and 

final results of this study were being evaluated 

in terms of their significance to the overall 

regional flow system. Constraints posed by 

geochemical, geologic, geophysical, and 

hydrologic evidence was generally in good agreement among all elements, and overall analysis 

based on various techniques of investigation appeared to be converging. 

SIGNIFICANT RESULTS 

Regional flow is driven by hydraulic gradients that extend over long distances. Figure 89 

shows the regional flow of the Great Basin aquifer 

system based primarily on the lowest water-level 

altitudes in each basin. The regional flow is apparently toward either the Colorado River or major regional discharge areas. The 242 identified 

basin areas had been grouped into 39 major flow 

systems (fig. 90). Of these, 14 are single-basin 

systems, the rest are multibasin systems. Large 

multibasin systems outside the carbonate-rock 

province are generally coincident with major 

drainage systems. Large multibasin systems 

within the carbonate-rock province typically have 

little surface-water flow; instead they may contain ground-water flow paths that are more than 

147 
148 

40° 

35° 

120. 

OREGON I 

I 

115° 

IDAHO 

___ j_ _ _____ ___ _ 

CALI FORNIA 

EXPLANATION 

BASIN FLOW MODEL BY THIS STUDY ·· Number 

indicates basin study areas listed below 

1, Paradise Valley 

2, Dixie Valley 

3, Smith Creek Valley 

4, Stagecoach Valley 

5, Tule Valley 

6, Milford Area 

BASIN FLOW MODEL BY COOPERATIVE STUDY 

(RESULTS USED BY THIS STUDY) -- Number 

indicates basin study areas listed below 

7, Carson Valley 

8, Las Vegas Valley 

.___ __ 

UTAH 

SCALE 1:5,500,000 

0 50 100 150MILES 

0 50 100 150 KILOMETERS 

REGIONAL MODELS 

Carbonate rock province 

~ Fish Springs flow system 

~ White River flow system 

HYDROGRAPHIC AREA BOUNDARY 

A EVAPOTRANSPIRATION SITE 

STUDY AREA 

Figure 88.- Study area and types of ground-water f low models, Great Basin regional aquifer system. 
100 miles long and traverse several basins. 

Discharge from these multibasin systems within 

the carbonate-rock province is typically to large 

springs and is usually consumed by evapotranspiration in the vicini-ty of the springs. 

120' 

Geochemical studies of the White River 

ground-water flow system suggest that the system 

can be further subdivided into several subsystems, with relatively small quantities of flow 

between the subsystems.--- Analy ~i~ of 

115 ' 

OREGON 1 IDAHO 

-- ..--......__5000 I 

r------- j_ / --- -- ----------1--

:/# . NEVADA , .. o.r.,-c;·,; . 

I ~ ~ 

I 

~ 

40 ' I ~ I 

I 

I 

CALIFORNIA 

0 

._ __ 

UTAH 

SCALE 1:5,500,000 

50 100 150MILES 

35' ' ' 0 50 100 150 KILOMETERS 

POTENTIOMETRIC CONTOUR·- Shows 

-5000- altitude of potentiometric surface. 

Approximately located. Contour 

interval1000 feet. Datum is sea level 

CARBONATE ROCK PROVINCE 

STUDY AREA 

EXPLANATION 

REGIONAL DISCHARGE AREAS 

1, Colorado and Virgin Rivers 

2, Great Salt Lake Desert 

3, Death Valley 

4, Carson Sink 

5, Walker Lake 

6, Pyramid Lake 

7, Black Rock Desert 

Figure 89.- Regional ground-water flow of the Great Basin regional aquifer system. 

149 
150 

aeromagnetic data suggests that subsurface 

masses of igneous rock probably act as barriers 

and provide significant controls on regional flow 

in parts of east-central Nevada and western Utah. 

Regional analysis of hydrologic conditions in 

southwestern Utah suggests that the 

transmissivity of the carbonate rocks is higher 

than originally anticipated, and that some degree 

of hydraulic continuity exists between basins 

throughout that part of the area. Much of this con120. 

40. 

CALIFORNIA 

35° 

115. 

0 

;..'f\ River 

-.1''~ -----------

ARIZONA 

SCALE 1:5,500,000 

50 100 150 MILES 

0 50 100 150 KILOMETERS 

EXPLANATION 

~ MAJORLAKE 

MAJOR FLOW SYSTEM BOUNDARY .. 

Dashed where uncertain 

AREA OF MAJOR GROUND-WATER DISCHARGE 

AS EVAPOTRANSPIRATION 

STUDY AREA 

Figure 90. -Identified major ground-water flow systems and areas of major ground-water discharge of the Great Basin 

regional aquifer system. 
tinuity is inferred from information obtained at 

shallow depth. For example, shallow test drilling 

in the Sevier Desert ofUtah(fig. 88) suggests that 

Sevier Lake is not the final terminus of the Sevier 

flow system but that there may be some leakage 

west and north to the Great Salt Lake Desert flow 

system. Finally, there appears to be some degree 

of hydraulic continuity between the deep carbonate aquifer and the overlying basin-fill aquifer 

throughout most ofthe carbonate-rock province. 

Smith Creek Valley is generally typical of 

closed basins. Simulation of several proposed 

development alternatives using the Smith Creek 

Valley flow model illustrates that long-term 

response to pumping is a function of both the location and rate of pumping. Efficient capture of 

natural discharge with minimal water~level 

declines is hydrologically a viable alternative. 

However, less strategic distributions of pumping, 

which still provide for reasonably efficient cap-· 

ture of discharge, may be preferable because of 

the additional freedom allowed in locating pumping centers. Locating pumping centers remote 

from areas of natural discharge results in long 

periods of aquifer-storage reduction and declining 

water levels regardless of pumping rate. Pumping in excess of the estimated predevelopment 

rate of recharge is hydrologically a feasible alternative because of the large quantities of water 

stored in the basin-fill aquifers. However, 

economic considerations associated with declining 

water levels and aquifer-storage reduction will 

most likely ultimately cause the pumping rate to 

be reduced as the thickness of saturation is reduced. Simulation of Smith Creek Valley flow system 

suggests that recovery from sustained overpumping may be more efficient if pumping is close to 

the general area of natural discharge than if 

pumping is remote from the area of discharge. 

PUBLISHED REPORTS 

Abstracts 

1. Miffiin, M. D., and Harrill, J. R., 1981, 

Hydrogeologic characteristics of the Great 

Basin: Geological Society of America 

Abstracts with Programs 1981, 94th Annual 

meeting v. 13, no. 7, p. 510. 

2. Plume, R. W., 1984, Use of aeromagnetic data 

to define some properties of a carbonate-rock 

aquifer in eastern Nevada: Geological Society of America Abstracts with Programs 

1984, 97th Annual Meeting, v. 16, no. 6, 

p. 624. 

3. Thomas, J. M., Welch, A. H., and Preissler, 

A. M., 1984, Geochemical evolution of 

ground water in a hydrologically closed 

basin, northern Basin and Range Province, 

Nevada: Practical Applications of GroundWater Geochemistry Conference, Banff, 

Canada, June 1984, Conference 

Proceedings. 

4. Welch, A. H., and Thomas, J. M., 1984, 

Aqueous geochemistry and isotope 

hydrology of the White River System, 

eastern Nevada: Geological Society of 

America Abstracts with .Programs 1984, 

97th Annual Meeting v. 16, no. 6, p. 689. 

REPORTS 

1. Bunch, R. L., and Harrill, J. R., 1984, Compilation of selected hydrologic data from the 

MX missile-siting investigation, east-central 

Nevada and western Utah: U.S. Geological 

Survey Open-File Report. 84-702, 123 p. 

2. Gates, J. S., 1984, Hydrogeology of northwestern Utah and adjacent parts of Idaho 

and·Nevada: Utah Geological Association 

publication 13, p. 239-248. 

3. Harrill, J. R., 1984, Great Basin aquifer 

systems, Nevada-Utah-an Overview, in 

Water Today and Tomorrow: American 

Society of Civil Engineers, Irrigation and 

Drainage Division, Specialty Conference 

Proceedings, Flagstaff, AZ, 1984, 

p. 590-597. 

4. Harrill, J. R., Welch, A. H., and Preissler, A. 

M., 1984, Hydrogeologic controls on groundwater flow in Stagecoach Valley, Nevada, in 

Lintz, Joseph, Jr., ed., Western geological 

excursions: Reno, University of Nevada, 

Mackay School of Mines, v. 3, p. 117-120. 

5. Harrill, J. R., Welch, A. H., Prudic, D. E., 

Thomas, J. M., Carman, R. L., Plume, R. W., 

Gates, J. S., and Mason, J. L., 1983, Aquifer 

systems in the Great Basin region of 

Nevada, Utah, and adjacent states-a study 

plan: U.S. Geological Survey Open-File 

Report 82-445, 49 p. 

6. Scheafer, D. H., Thomas, J. M., and Duffrin, 

B. G., 1984, Principal facts for gravity stations in Dixie, Fairview, and Stingaree 

Valleys, Churchill and Pershing Counties, 

Nevada: U.S. Geological Survey Open-File 

Report 84-586, 15 p. 

151 
152 

ACTIVE PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

GULF COASTAL PLAIN REGIONAL AQUIFER-SYSTEM STUDY 

By Hayes F. Grubb, Austin, Texas 

INTRODUCTION 

The Gulf Coastal Plain regional aquifer 

system study was started in 1980 and is scheduled 

for completion in 1988. The study area includes 

about 225,000 mi2 of the Gulf Coastal Plain in 

parts of Alabama, Arkansas, Florida, Illinois, 

Kentucky, Mississippi, Missouri, Tennessee, and 

Texas and all of Louisiana (fig. 91). The thick 

wedge of sediments of Tertiary and younger age, 

yields large quantities of water for municipal, industrial, and agricultural use. 

In addition to the objectives of all RASA 

studies, specific objectives or approaches of this 

study include: (1) evaluation of effects of highly 

saline water on the regional flow system, and (2) 

evaluation of potential for compaction of confining 

units as a result of changes in fluid pressures. 

The principal findings of the study, as of 

1984, consist largely ofthe development of a conceptual framework for studying the regional 

aquifers, identification of data sources, compilation of the data into computer files, and 

preliminary simulations of the ground-water flow 

system. 

CONCEPTUAL GEOHYDROLOGIC FRAMEWORK 

A regional geohydrologic framework was 

developed based on the concept of the aquifer 

system. This concept recognizes the interconnection of aquifers and associated confining units and 

provides guidelines for simulation of the groundwater flow on a regional scale where geologic 

units are aquifers in one part and confining units 

in another part of the study area. 

Three aquifer systems are delineated in the 

study area: the Mississippi Embayment aquifer 

system, the Texas Coastal Uplands aquifer 

system, and the Coastal Lowlands aquifer system 

(fig. 92). The designation of these aquifer systems 

is based upon differences in geohydrology, 

regional flow patterns, and the presence of two 

or more significant aquifers of regional extent. 

The differences in flow patterns and the distribution of sediment characteristics provided the 

basis for delineating the three aquifer systems. 

Ground-water flow in the Mississippi Embayment 

aquifer system is generally from the outcrop areas 

around the margin of the Mississippi embayment 

toward the Mississippi River. In the Texas 

Coastal Uplands aquifer system the flow is 

generally from the outcrop areas toward the Gulf 

of Mexico. The bulk of fine-grained sediments that 

comprise the confining units in the Mississippi 

Embayment aquifer system and in the Texas 

Coastal Uplands aquifer system are generally 

massive clay layers that can be correlated over 

large areas, both at the surface and in the subsurface. By contrast, the fine-grained sediments 

that comprise the confining units within the 

Coastal Low lands aquifer system typically occur 

in thinner layers, cannot be correlated over large 

areas, and occur as isolated bodies throughout the 

aquifer system. 

Mississippi Embayment Aquifer System 

The Mississippi Embayment aquifer system 

consists of sediments of Tertiary age above the 

uppermost massive marine clay of the Midway 

Group and below the lowermost massive marine 

clay of the Jackson Group, or the Jackson and 

Vicksburg Groups where they are undifferentiated (table 2). The Upper Cretaceous sediments 

that under lie the Paleocene Midway Group in an 
area of about 25,000 mi2 in the northernmost part 

of the Mississippi embayment are also included 

in the Mississippi Embayment aquifer system. 

The Upper Cretaceous sands are laterally isolated 

from the extensive aquifers of Cretaceous age to 

the south and southeast by calcareous and clayey 

strata of low permeability. The sediments which 

make up the Mississippi Embayment aquifer 

system are exposed at land surface from the 

southern tip of Illinois to the Jackson-Vicksburg 

outcrop belt in central Louisiana, central 

Mississippi, and southwestern Alabama. The 

eastern limit of this aquifer system is the contact 

between sediments of Cretaceous and Paleozoic 

age in western Kentucky and the outcrop belt of 

the Ripley Formation of Cretaceous age in northeastern Mississippi and western Tennessee. The 

western limit of this aquifer system is the TexasLouisiana State line, which runs in a north-south 

direction approximately through the center of the 

surface expression of the Sabine uplift, which 

disrupts the general outcrop pattern of the Tertiary sediments. 

Eleven aquifers of regional significance have 

been mapped by previous investigations in the 

Mississippi Embayment aquifer system (table 2), 

the oldest is the Ripley Formation of Cretaceous 

age (Boswell and others, 1965) and the youngest 

is the Mississippi River Valley alluvial aquifer 

of Holocene and Pleistocene age (Boswell and 

others, 1968). Identified aquifers of Eocene age, 

in ascending order, are: (1) lower Wilcox aquifer 

(Hosman and others, 1968), (2) Wilcox Group 

(Hosman and others, 1968), (3) Carrizo Sand and 

Meridian-Upper Wilcox aquifer (Hosman and 

others, 1968), (4) Carrizo and Meridian Sand 

aquifer (Payne, 1975), (5) Sparta hydraulic system 

(Payne, 1968), (6) Sparta Sand (Hosman and 

others, 1968), (7) Memphis aquifer (Hosman and 

others, 1968), (8) Cockfield Formation (Hosman 

and others, 1968), and (9) Cockfield aquifer 

system (Payne, 1970). The number of aquifers to 

be delineated in the Mississippi Embayment 

aquifer system during this study has not been 

decided. Similarly, the delineation of aquifers in 

the other two aquifer systems-Texas Coastal 

Uplands aquifer system and the Coastal 

Lowlands aquifer system-is also pending. 

Texas Coastal Uplands Aquifer System 

The Texas Coastal Uplands aquifer system 

consists of sediments of Tertiary age above the 

uppermost massive clay of the Midway Group and 

below the lowermost massive clay of the Jackson 

Group, or the Jackson and Vicksburg Groups 

where they are undifferentiated. The sediments 

which make up the Texas Coastal Uplands 

aquifer system are exposed at land surface 

gulfward of a narrow band of the Midway outcrop, 

and extend to a narrow outcrop band of the 

Jackson and Vicksburg Groups which is located 

about 100 miles inland from the Gulf of Mexico. 

The southwestern limit of this aquifer system extends beyond the Rio Grande into Mexico but this 

area is not included in this study. The eastern 

limit of this aquifer system is the Texas-Louisiana 

State line. Many of the aquifers and confining 

units of the Texas Coastal Uplands aquifer 

system extend laterally into equivalent 

hydrologic units that are part of the Mississippi 

Embayment aquifer system. 

Seven aquifers of regional significance have 

been identified by different investigators in the 

Texas Coastal Uplands aquifer system (table 2). 

All are of Eocene age and range from the oldest 

in sediments of the Wilcox Group to the youngest 

in sediments of the Y egua Formation of the 

Claiborne Group. The seven identified aquifers 

are: (1) Lower Wilcox (Jones and others, 1976), (2) 

Upper Wilcox (Jones and others, 1976), (3) 

Carrizo-Wilcox aquifer (Klemt and others, 1976), 

(4) Carrizo Sand (Payne, 1975), (5) Sparta Sand 

(Payne, 1968), (6) Queen City Sand (Payne, 1972), 

and (7) Yegua aquifer system (Payne, 1970). 

Coastal lowlands Aquifer System 

The Coastal Lowlands aquifer system consists 

of sediments of Miocene and younger age above 

the uppermost massive clay of the Vicksburg 

Group or the Jackson and Vicksburg Groups 

where they are undifferentiated. The sediments 

which make up the Coastal Lowlands aquifer 

system are exposed at land surface in Alabama, 

Florida, Louisiana, Mississippi and Texas, and extend gulfward from the Jackson-Vicksburg outcrop belt to the Gulf of Mexico. The eastern limit 

of this aquifer system is the Escambia River in 

Florida and the Alabama River and Big Escambia Creek in southwestern Alabama. Sediments 

of Miocene age extend beyond the eastern limit 

of the aquifer system but they are thin and are 

significant only as a source of recharge to the 

Floridan aquifer system. The Coastal Lowlands 

aquifer system extends to the west beyond the Rio 

Grande into Mexico but this area is not included 

in this study. 

153 
154 

es· 

MISSOURI KENTUCKY 

---, 

I 

I 

TENNESSEE 

OKLAHOMA 

ARKANSAS 

Gulf 

of Mexico 

SCALE 1:10,000,000 

0 100 200 MILES _ 

0 100 200 KILOMETERS 

EXPLANATION 

LOCATION OF WELL WITH LOGS 

"' LOCATION OF TWO OR MORE WELLS 

A .-._A' LINE OF SECTION ON FIGURE 93 

LINE DIVIDING BASE OF THE FLOW SYSTEM-- Coastal Uplands confining 

unit is the base of the flow system to the north of line. The top of the 

geopressured zone Is the base of the flow system to the south of line 

STUDY AREA 

Figure 91.- Study area, location of geophysical logs used to define the hydrogeologic framework of the Gulf Coastal 

Plain regional aquifer system. 
Mississippi Embayment aquifer system 

Geologic unit 

System Series Group 

(/) 

:::l 

0 

CD 

(.) 

,f9 

~ 

u 

~ CD 

(.) 

0 

UJ 

CD 

c 

CD 

(.) 

0 

CD 

co 

CL 

(/) 

:::l ~ 0 CD CD a.u 

a.ro 

:::::>Q) 

u 

CD 

c 

0 

.0 

'(ij 

u 

X 

0 

.s2 

3: 

Aquifers, (references), and confining 

units 

Mississippi River Valley Alluvial aquifer (Boswell, and 

others, 19681 

Coastal Lowlands confining unit 1 

Cockfield aquifer system !Payne, 19701 

Cockfield Formation (Hosman and others, 19681 

Memphis aquifer (Hosman and others, 19681 

Sparta Sand (Hosman and others, 19681 

Sparta hydraulic system (Payne, 19681 

Carrizo and Meridian Sand aquifer (Payne, 19751 

Carrizo Sand and Meridian-Upper Wilcox aquifer (Hosman 

and others, 19681 

Wilcox Group (Hosman and others, 19681 

Lower Wilcox aquifer (Hosman and others, 19681 

Coastal Uplands confining unit 1 

Ripley Formation (Boswell and others, 19651 

1 The confining units are defined as the massive clay section (with interbedded sands) of 

the Midway Group and the undifferentiated Jackson and Vicksburg Groups that are 

recognizable on geophysical logs. The recognizable lithologic unit may not be equivalent 

to the geologic unit as determined by fossils or other means of correlation and dating, because 

the upper or lower part of either the Midway Group or the undifferentiated Jackson and 

Vicksburg Groups may be sandy and therefore included in the adjacent aquifer. 

Texas Coastal Uplands aquifer system 

Geologic unit 

System Series Group 

CD ~ C ~ 

Aquifers, (references), and confining 

units 

C "0 CD £ "0 _5 g 15 g ~ 15 ~ Coastal Lowlands confining unit 1 

UJ == ro u 0 J > 

CD 

c: 

CD 

(.) 

0 

UJ 

CD 

c: 

CD 

(.) 

0 

CD 

C5 

CL 

CD 

c: 

0 

.0 

'(ii 

u 

X 

0 

.s2 

3: 

Yegua aquifer system !Payne, 1970! 

Queen City Sand (Payne, 1972) 

Sparta Sand (Payne, 1968) 

Carrizo Sand (Payne, 1 975) 

Carrizo-Wilcox aquifer (Kiemt and others, 1976) 

Upper Wilcox (Jones and others, 1976) 

Lower Wilcox (Jones and others, 1976) 

Coastal Uplands confining unit 1 

Coastal Lowlands aquifer system 

Geologic unit 

System Series Group 

CD 

c: 

CD 

(.) 

.Q 

a: 

CD 

c: 

CD 

(.) 

0 

~ 

CD Cl 

Aquifers, (references), and confining 

units 

Chicot Reservoir (Jones and others, 1956) 

Chicot aquifer (Meyer and Carr, 1979) 

Evangeline aquifer !Whitfield, 1975) 

Evangeline aquifer (Meyer and Carr, 19791 

Jasper aquifer (Whitfield, 19751 i 

"'C"i 

~ co 

~------------------------_, ~ ~ 

"2000-foot" sand of the Baton Rouge area 

ITorak and Whiteman, 1982) 

g =a .. 

~c3 g-

~ 

CDC:§:; 

~ -g g ~ -g ~ Coastal Lowlands confining unit 1 

~ro~ ~ro~ 0 -, > 

155 

Table 2.-Relation among previously mapped aquifers to geology and regional confining units in the Gulf Coastal Plain regional 

aquifer systems study area. 
156 

At least three aquifers of regional significance in the Coastal Lowlands aquifer system 

have been identified by other investigators. The 

oldest is in sediments of Miocene age and the 

youngest in sediments of Pleistocene-Holocene 

age. Subdivision into aquifers within this aquifer 

system is difficult due to the discontinuous nature 

of the sediments, which were deposited in fluvial 

and deltaic environments. This problem is illustrated by the aquifers mapped by different investigators in Mississippi and Louisiana. The 

Miocene aquifer system mapped by Gandl (1982) 

includes equivalent units that were mapped as 

the Jasper aquifer by Whitfield (1975) and the 

"2000-foot" sand of the Baton Rouge area by 

. Torak and Whiteman (1982) as shown in table 2. 

Investigation of vertical head gradients in areas 

having heavy pumping suggests that this 

regional aquifer system probably can be differentiated into five aquifers regionally. 

Regional Confining Units 

Two regional confining units, the Coastal 

Uplands confining unit and the Coastal Lowlands 

confining unit, are the major restrictions to vertical flow in the study area. The Coastal Uplands 

confining unit is comprised of the predominantly 

fine-grained marine sediments of the Midway 

Group. The Coastal Uplands confining unit is 

assumed to be the base of the ground-water flow 

system in the overlying Texas Coastal Uplands 

aquifer system. The Coastal Lowlands confining 

unit is comprised predominantly of thick marine 

clays of the undifferentiated Jackson and 

Vicksburg Groups which separate the Texas 

Coastal Uplands and the Mississippi Embayment 

aquifer systems from the Coastal Lowlands 

aquifer system down dip of the JacksonVicksburg outcrop belt. Sand beds near the top 

of the Midway Group or near the top or base of 

the Jackson and Vicksburg Groups are considered 

to be part of the adjacent aquifers. The top and 

base of these confining units are determined by 

lithology (clay being indicative of low permeability sediments) rather than by the geologic age of 

the sediments. 

The data available for mapping these confining units are mostly derived from geophysical 

logs obtained in oil and gas wells. Therefore, the 

confining units are defined as the massive clay 

sections with interbedded sands of the Midway 

Group (Coastal Uplands confining unit) and the 

undifferentiated Jackson and Vicksburg Groups 

(Coastal Lowlands confining unit) that can be 

recognized on geophysical logs. 

Two confining units within the Texas Coastal 

Uplands and the Mississippi Embayment aquifer 

systems can be correlated across the study area 

by use of geophysical logs. They correspond 

closely to the Cook Mountain Formation and part 

of the Cane River Formation of the· Claiborne 

Group. These confining units are defined in terms 

of lithology rather than being restricted to a 

geologic unit. 

Local vertical resistance to flow within the 

Coastal Lowlands aquifer system is typically due 

to numerous clay layers that are discontinuous 

and generally cannot be correlated over large 

areas by use of geophysical logs. In the Houston, 

TX, area, Meyer and Carr (1979, p~ 5) report that 

about one-half ofthe total thickness of the Chicot 

aquifer consists of discontinuous clay layers. 

DATA SOURCES 

Data that are useful in defining the regional 

geohydrologic framework are abundant in the 

study area. Hundreds of thousands of wells have 

been drilled for oil and gas exploration and production, and geophysical logs are. available from 

commercial sources for many of these wells. The 

Petroleum Information Corporation1 has compiled 

additional data for many oil and gas wells in its 

Well History Control System. 

Major sources of hydraulic head and chemical data other than the U.S. Geological Survey's 

W ATSTORE file are the files of the Texas Department of Water Resources and brine data from the 

Petroleum Data System at the University of 

Oklahoma. 

Estimates of pumpage at state level have 

been made throughout the study area by the U.S. 

Geological Survey in cooperation with State and 

other Federal agencies at 5-year intervals since 

about 1950 (Solley and others, 1983). Additional 

detail is needed for use of pumpage in groundwater flow models; therefore, the pumpage data 

at the county level will be compiled and used to 

estimate the amount of pumpage for each grid 

block of the flow models. 

Pumpage data for 1980 are summarized by 

state and aquifer systems in table 3 and show that 

more than one-half of the pumpage is from the 

Mississippi River Valley alluvial aquifer. Pumpage from aquifers in Arkansas is about twice 

that of any other state within the study area. 

l.The use of company names or brand names in this report are 

for identification purposes only and do not imply endorsement by the 

U.S. Geological Survey. 
Geophysical logs were selected for use in 

defining the regional geohydrologic framework. 

Location and general information about the wells 

and conditions at the time of logging were entered 

into a computer-based file along with the 

thickness, resistivity, spontaneous potential, and 

depth to each sand bed with a thickness exceeding 

20 feet. Geologic units were correlated across the 

study area and the depth to the top of each unit 

was entered into the computer file. Of 1,011 

selected logs, 887 have been interpreted and 

entered into the computer file. An average of 22 

sand beds per well have been identified for almost 

7 million feet of logged section. The vertical relation of the aquifers and confining units as defined from the geophysical logs is shown in figure 93. 

A computer-based file of selected chemical 

analysis of ground water has also been constructed. About half of the nearly 52,000 analyses 

have data on well depths (or depth of sample collection), and about 75 percent of the analyses have 

data for dissolved solids. 

SIMULATION OF GROUND-WATER FLOW 

Both regional and subregional finitedifference ground-water flow models are being 

used for simulation of the ground-water flow 

within the Gulf Coastal Plain regional aquifer 

system. The regional model will encompass the 

entire study area including those parts of the 

aquifers that contain saline water. The 

subregional models will be limited to smaller 

areas as shown in figure 94, and to those parts 

of the aquifers containing fresh to moderately 

saline water. 

The regional model consists of a rectangular 

grid that is divided into blocks which are 10 miles 

on each side. The model probably will consist of 

11 aquifers; however, the details of how each 

aquifer will be delineated has not been finalized. 

Flow of ground water in all of the aquifers, with 

the exception of the Upper Cretaceous aquifer, 

will be simulated using a variable-density flow 

model developed by Kuiper (1983). Spatial variation in water density and water temperature, is . 

calculated from data obtained from geophysical 

logs. 

The subregional models consist of rectan., 

gular grids with blocks that are 5 miles on each 

side. Four of these blocks cover the same area as 

a single block in the regional model. The number 

of aquifers in the subregional models probably 

will range from two for the Mississippi River 

Valley alluvial aquifer, a subregional flow system 

of the Mississippi Embayment aquifer system, to 

six for the entire Mississippi Embayment aquifer 

system. 

Preliminary model runs have been made 

using aquifer thicknesses calculated from data obtained from geophysical logs and with uniform · 

values of hydraulic conductivity assigned to 

aquifers and confining units. Initial results have 

demonstrated that: (1) there is at least a small 

volume of water that moves vertically upward 

from the Mississippi Embayment aquifer system 

through the Coastal Low lands confining unit 

(marine clays of the undifferentiated Jackson and 

Vicksburgs Group) and discharges to areas at or 

near land surface, and (2) the vertical hydraulic 

conductivity of the thick sequence of interbedded 

sand and clay within the Coastal Lowlands 

aquifer system is almost as small as the vertical 

hydraulic conductivity of the thick clay units that 

are are ally persistent over part of the study area 

and mapped as the regional confining units. 

Table 3.-Ground-water pumpage, in million gallons per day, 1980, Gulf Coastal Plain regional aquifer system 

Mississippi Embayment aquifer system 

State Mississippi Aquifers in Upper Coastal Texas Coastal Total 

River Valley sediments of Cretaceous Lowlands Uplands 

alluvial aquifer Tertiary age aquifer aquifer system aquifer system 

Arkansas 3,745 199 6 3,950 

Louisiana 234 82 1,148 1,754 

Mississippi 1,140 154 146 1,440 

Missouri 102 5 4 111 

Tennessee 2 251 7 260 

Texas 1,269 458 1,727 

Total 5,223 691 17 2,853 458 9,242 

157 
158 

25" 

---1 

I 

I 

95 " 

MISSOURI 

OKLAHOMA 

TEXAS 

Gull 

EXPLANATION 

UPPER CRETACEOUS AQUIFER 

ol 

KENTUCKY 

TENNESSEE 

Mexico 

SCALE 1:10,000,000 

0 100 200 MILES 

0 100 200 KILOMETERS 

- COASTAL UPLANDS CONFINING UNIT 

TEXAS COASTAL UPLANDS AQUIFER SYSTEM 

MISSISSIPPI EMBAYMENT AQUIFER SYSTEM 

COASTAL LOWLANDS CONFINING UNIT-- The Coastal Lowlands confining unit 

is covered by alluvium in northeastern Louisiana and westcentral Mississippi 

COASTAL LOWLANDS AQUIFER SYSTEM 

STUDY AREA 

\ 

\ 

Figure 92. - Generalized outcrop of major aquifers and confining units in the Gulf Coastal Plain regional aquifer system 

study area . The Coastal Lowlands confining unit is covered by alluvium in northeastern Louisiana and west-central 

Mississippi. 
159 

FEET 

A A' 2000 

Sea 

level 

-2000 

-4000 

-6000 

-8000 

-10,000 

-12,000 

-1 4,000 

VERTICAL SCALE GREATLY EXAGGERATED 

AQUIFER SYSTEMS 

EXPLANATION 

MISSISSIPPI EMBAYMENT REGIONAL AQUIFER SYSTEM 

j,/;;<.J Aquifers (unnamed) 

Mississippi River Valley alluvial aquifer 

[;)m{:(f(;;J Upper Cretaceous aquifer 

~ Confining unit (unnamed) 

COASTAL LOWLANDS REGIONAL AQUIFER SYSTEM 

- Aquifers (unnamed) 

- Confining unit (unnamed) 

N 

0 

rJ) 

:::;: 

a: 

< 

I 

0 50 100MILES 

0 50 100 KILOMETERS 

REGIONAL CONFINING UNIT 

1!111 Coastal uplands 

- Coastallowlands 

ZONE OF ABNORMALLY HIGH PRESSURE 

WELL AND NUMBER 

DISSOLVED SOLIDS EQUAL TO 10,000 

MILLIGRAMS PER LITER 

Figure 93.- Generalized section showing relation of aquifers and confining units from southeastern Missouri to Atchafalaya Bay, 

Louisiana, (location of section shown in fig. 91 ). 
160 

35 

---, 

I 

I 

TEXAS 

gs· 

I 

I 

MISSOURI 

---l 

1-------

OKLAHOMA 

Gulf 

of 

EXPLANATION 

KENTUCKY 

TENNESSEE 

Mexico 

SCALE 1:10,000,000 

0 100 200 MILES 

0 100 200 KILOMETERS 

AREA OF SUBREGIONAL GROUND-WATER FLOW MODELS 

-

[£] . 

. 

Mississippi River valley alluvial aquifer in the 

Mississippi Embayment aquifer system 

Mississippi embayment aquifer system 

Coastal Lowlands aqu ifer system of Alabama, 

Florida, Louisiana, and Mississippi 

STUDY AREA 

CJ] Coastal Lowlands aquifer system of Texas 

Texas Coastal Uplands aquifer system 

Upper Cretaceous aquifer in the Mississippi 

Embayment aquifer system 

NOTE: The models of the Texas Coastal 

Uplands aquifer system and the 

Mississippi Embayment aquifer system 

extend for a short distance beyond the 

landward extent of the Coastal Lowlands 

aquifer system 

Figure 94. -Areas of subregional ground-water flow models, Gulf Coastal Plain regional aquifer system. 
Three cross-sectional models across the 

Mississippi embayment indicate that a major 

component of ground-water flow prior to largescale development was across the axis of the embayment from east of the Mississippi River to 

discharge areas west of the river (Weiss, 1983). 

PUBLISHED REPORTS 

Abstract 

1. Weiss, J. S., 1983, Simulation of ground-water 

flow across the Mississippi embayment: 

Geological Society of America 96th annual 

meeting, Indianapolis IN, Abstracts with 

Programs, v. 15, no. 6, 716 p. 

Reports 

1. Grubb, H. F., 1984, Planning report for the 

Gulf Coast regional aquifer-system analysis, 

Gulf of Mexico Coastal Plain, United States: 

U.S. Geological Survey Water-Resources Investigations Report 84-4291, 30 p. 

2. Hosman, R. L., 1982, Outcropping Tertiary 

units in southern Arkansas: U.S. Geological 

Survey Miscellaneous Investigations Series 

Map I-1405, scale 1:250,000, 1 sheet. 

3. Kuiper, L. K., 1983, A numerical procedure 

for the solution of the steady-state variabledensity groundwater flow equation: 

American Geophysical Union Water 

Resources Research v. 19, no. 1, February 

1983, p. 234-240. 

4. MacCary, L. M., 1984, Relationship of formation factor to depth of burial in aquifers 

along the Texas Gulf Coast, in Surface and 

Borehole Geophysical Methods in GroundWater Investigations: National Water Well 

Association, Conference Proceedings, 

p. 722-742. 

REFERENCES CITED 

Boswell, E. H., Cushing, E. M., and Hosman, R. L., 1968, 

Quaternary aquifers in the Mississippi embayment, 

with discussions of quality of the water by H. G. Jeffery: U.S. Geological Survey Professional Paper 448-E, 

p. E1-E15. 

Boswell, E. H., Moore, G. K., and MacCary, L. M., 1965, 

Cretaceous aquifers in the Mississippi embayment, with 

discussions of quality ofthe water by H. G. Jeffery: U.S. 

Geological Survey Professional Paper 448-C, p. Cl-C37. 

Gandl, L. A., 1982, Ch;:j.racteristics of aquifers designated as 

potential drinking water sources in Mississippi: U.S. 

Geological Sur~ey Water-Resources Investigations 

Report 81-550, 0 p. 

Hosman, R. L., Long, A T., Lambert, T. W., and others, 1968, 

Tertiary aquife1 in the Mississippi embayment, with 

a discussion of uality of the water by H. G. Jeffery: 

U.S. Geological Survey Professional Paper 448-D, 

p. D1-D19. I 

Jones, P. H., Hendrick~, E. L., Ireland, Burdge, and others, 

1956, Water resdurces of southwestern Louisiana: U.S. 

Geological Surv~y Water- Supply Paper 1364, 460 p. 

Jones, P. H., Stevens, P.R., Wesselman, J. B., and Wallace, 

R. H., Jr., 1976, tegional appraisal of the Wilcox Group 

in Texas for sub1._urface storage of fluid wastes: Part!-

Geology: U.S. <fieological Survey Open-File Report 

76-394, 107 p. I 

Klemt, W. B., Duffin,~. L., and Elder, G. R., 1976, Groundwater resources of the Carrizo aquifer in the Winter 

Garden area of exas: Texas Water Development Board 

Report 210, 30 r· 

Kuiper, L. K., 1983, A numerical procedure for the solution 

of the steady-st4te variable-density groundwater flow 

equation: Water Resources Research. v. 19, no. 1. 

p. 234-240. : 

Meyer, W. R., and Carr~ J. E., 1979, A digital model for simulation of ground-tater hydrology in the Houston area, 

Texas: Texas D~partment ofWater Resources Limited 

Publication 103, 27 p. 

Payne, J. N., 1968, H drologic significance of the lithofacies 

of the Sparta S d in Arkansas, Louisiana, Mississippi, 

and Texas: U.S. Geological Survey Professional Paper 

569-A, 17 p. ! 

-----1970, Geohy&ologic significance oflithofacies ofthe 

Cockfield For~tion of Louisiana and Mississippi and 

of the Y egua ormation of Texas: U.S. Geological 

Survey Profess"onal Paper 569-B, 14 p. 

-----1972, Hydro ogic significance of lithofacies of the 

Cane River Fo ation or equivalents of Arkansas, Louisiana, Mississi pi, and Texas: U.S. Geological Survey 

Professional P per 569-C, 17 p. 

----1975, Geohy ologic significance oflithofacies of the 

Carrizo Sand o Arkansas, Louisiana, and Texas and 

the Meridian and of Mississippi: U.S. Geological 

Survey Profess onal Paper 569-D, 11 p. 

Solley, W. B., Chase E. B., and Mann, W. B. IV, 1983, 

Estimated use of water in the United States: U.S. 

Geological Surtey Circular 1001, 56 p. 

Torak, L. J., and Whi~eman, C. D., Jr., 1982, Applications of 

digital modelirg for evaluating the ground-water 

resources of th "2,000-foot" sand of the Baton Rouge 

area, Louisia~: Louisiana Department of Transportation and Dev lopment Water-Resources Technical 

Report 27, 87 . 

Weiss, J. S., 1983, Si ulation of ground-water flow across the 

Mississippi em ayment: Geological Society of America 

Abstracts with Programs, 96th annual meeting, Indianapolis, IN,'v. 15, no. 6, p. 716. 

Whitfield, M. S., Jr., 975, Geohydrology of the Evangeline 

and Jasper aq ifers of southwestern Louisiana: Louisiana Depart ent of Conservation, Louisiana 

Geological S ey, and Louisiana Department of Public 

Works Water- esources Bulletin 20, 72 p. 

161 
162 

ACTIVE PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

NORTHEAST GLACIAL REGIONAL AQUIFER-SYSTEM STUDY 

By Forest P. Lyford, Albany, New York 

INTRODUCTION 

The regional assessment of the Northeast 

glacial aquifers was started in 1981 and is 

scheduled for completion in 1986 (Lyford and 

others, 1984). The purpose of the study is to investigate the sand and gravel aquifers that were 

formed during advances and retreats of the continental glaciers in the northeastern United 

States. Glacial sand and gravel aquifers,. though 

consisting of many geographically separated independent systems (fig. 95), share many geologic, 

hydrofogfc, ·' and geochemical characteristics 

because of their common depositional origins and 

physiographic settings. 

This study will document the hydrologic 

characteristics of the glacial aquifers in the northeastern United States through study of the variations in magnitude and areal distribution of key 

components of the aquifers and through evalua.: 

tion of the response of the aquifers to pumping 

and to climatic stresses. 

The study area includes most of the 

glaciated parts of the northeastern United States 

and extends approximately as far west as the edge 

of the glaciated Appalachian Plateau in Ohio. The 

areas of Long Island, NY, and Cape Cod, MA, are 

excluded from the study because . the groundwater hydrology of these systems has been extensively studied. The. study area includes· several 

physiographic provinces, which range from mountainous areas. such . as the White Mountains of 

New Hampshire and Maine, the Green Mountains of Vermont, and the Adirondack and Catskill Mountains of New York; to low-lying areas 

along the· Great Lakes, the·. St. Lawrence River 

valley, the Hudson and Mohawk River valleys; 

and. seaboard ·lowland areas . along the Atlantic 

Coast (fig. ·96). 

· PROGRESS AND FINDINGS 

Aquifer Geometry 

The study area has been subdivided into 

three major geohydrologic areas to group and 

describe aquifer systems that have similar 

characteristics. These subdivisions, shown in 

fiiDITe 97, are based largely on the geology of 

gl~cial deposits and physiography. 

Much of the study area and most of the productive glacial aquifers are in type A areas (fig. 

97), where aquifers were formed largely in valleys 

that generally drained away from glacial ice. In 

type A areas, stratified drift commonly fills 

valleys or narrow lowlands, bordered by uplands 

or ridges. The stratified drift generally exhibits 

a succession of overlapping, shingled depositional 

profiles classified as morphosequences (Koteff, 

197 4). Each morphosequence ideally grades down 

valley from coarse-grained heterogeneous icecontact deposits to a valley train capped by pebbly coarse sand that may overlie lacustrine 

deposits. Generalized transverse and longitudinal 

sections of valleys draining away from glacial ice 

are shown in figure 98. 

Glacial aquifers in type B areas (fig .. 97) were 

formed largely in lake- or marine~dominated terranes where fine-grained stratified drift 

predominates. Commonly, a surfical.aquifer, consisting of medium to very fine sand overlies silt 

and clay as shown in figure 99. Ice-contact 

deposits, which are commonly scattered beneath 

the lacustrine clay, probably reflect local ice-front 

positions and meltwater channels in the decaying 

ice. In southern Maine, northwestern Vermont, 

and south of Lake Ontario, marine or lake-bottom· 

silt and clay immediately underlie the land sur-
80' 75' 70' 

CANADA 

45 ' 

Woos~ Atlantic 

Ocean 

40' OHIO 

0 50 100 150 200 MILES 

0 50 100 150 200 KILOMETERS 

EXPLANATION 

-._ PROMINENT GLACIAL AQUIFER 

• LOCATION OF AQUIFER GEOMETRY STUDY 

• LOCATION OF INDUCED INFILTRATION STUDY 

A LOCATION OF TRIBUTARY-STREAM LOSS STUDY 

STUDY AREA 

Figure 95.- Study areas, specific site study area, and prominent glacial aquifers in the northeastern United States 

(modified from McGuinness, 1964). 

face over large areas. Coarse-grained stratified 

drift has limited distribution in type B areas. 

Glacial aquifers in type C areas (fig. 97) are 

characterized by valleys that drained toward 

glacial ice. Glacial drift is commonly several hundred feet thick in type C areas and consists 

largely of lake-bottom silt and clay that are inter layered in places with till composed of reworked lacustrine sediments. Coarse sediments, 

a minor fraction of the valley fill, may have 

originated in two ways: (1) as alluvium or possibly 

deltaic deposits of north-draining streams 

deposited during intervals between ice readvances and, (2) as local outwash deposited by 

meltwater at the base of an ice tongue during advance or retreat of the ice. The origin of buried 

coarse-grained sediments in a type C area is being studied near Dryden in central New York 

(fig. 95). 

In support of aquifer geometry studies and to 

determine the application of surface geophysics, 

several methods, including electromagnetic 

surveys and marine seismic reflection, are being 

tested in several depositional environments to aid 

163 
164 

80' 75 ' 70' 

I ""\._.....-r' 

CANADA 

;' l 

45' 

Atlantic 

PENNSYLVANIA 

Ocean 40' 

0 50 100 150 200 MILES 

0 50 100 150 200 Kl LOM ETERS 

Figure 96.- Physiographic divisions of the northeastern United States in the study area (shaded) of the Northeast glacial 

regional aquifer system (from Fenneman, 1938). 

in determining the subsurface distribution of 

glacial materials. Preliminary results indicate 

that these methods are useful for interpolation of 

the subsurface geology between points where 

geologic data are available, and for mapping the 

distribution of buried coarse-grained material. 

Studies of low-flow characteristics of streams 

will help identify the elements of aquifer 

geometry that strongly influence the hydrology 

of glacial aquifers as well as interaction between 

aquifers and streams. Earlier studies in Connecticut and New York indicate that low flow is 

chiefly a function of the size of the area covered 

by coarse-grained stratified drift. Low-flow 

studies, as part of this study conducted in Connecticut, have shown that the percent of area 

covered by wetlands is also a significant factor affecting low flow (Robert Melvin, U.S. Geological 

Survey, written commun., 1983). Studies of 

geologic and physiographic controls on low flow 

in streams are underway in other parts of the 

study area. 

Regional Analysis of Water Chemistry 

The water-quality data in the U.S. Geological Survey's WATSTORE file are being analyzed 

to define water chemistry in glacial aquifers and 

to determine relations between rock minerals and 

water chemistry. Statistical analysis of concentrations of dissolved solids from water samples 

taken from stratified drift and shallow bedrock 

wells (generally less than 200 feet deep) indicates 

that the chemistry of water in drift is similar to 

that of the adjoining bedrock. Studies of the areal 

distribution of various constituents and of the 

geologic and hydrologic factors that affect water 

chemistry are in process. 

Hydrologic Budget of Glacial Aquifers 

Streamflow and water-level data are being 

analyzed to determine the hydrologic budget of 

selected glacial aquifers. Recharge and discharge 

of an entire basin have been studied by many 

investigators; however, information on recharge 
80' 75° 

CANADA 

45° 

Atlantic 

Ocean 

40' 

0 50 100 150 200 MILES 

0 50 100 150 200 KILOMETERS 

EXPLANATION 

GEOHYDROLOGIC AREAS 

TYPEA D Aquifers formed largely in valleys that drained away from glacial ice 

TYPE B ~~f1i~it4 

TYPE C ~)}\:J 

Aquifers formed largely in terranes that were dominated 

by large bodies of water 

Aquifers formed largely in valleys that drained 

toward glacial ice 

STUDY AREA 

Figure 97.-Three major types of geohydrologic areas to group and describe the glacial aquifers in the northeastern United States. 

and discharge of sand and gravel aquifers within 

a basin is lacking. Analytical and modeling 

techniques are being used to evaluate groundwater runoff in aquifers of different geometry. 

Recharge to glacial aquifers from tributary 

streams that flow across the valleys is an important component of the hydrologic budget for certain valley-fill aquifers. Field studies to quantify 

the recharge process from tributary streams are 

underway in the Asaph area of Pennsylvania and 

the North Conway area of New Hampshire 

(fig. 95). 

Hydraulic Properties of Aquifers Near Streams 

A well field near a stream in a glacial aquifer 

may strongly affect the flow in the stream. The 

controlling factors are the hydraulic conductivities of streambed and aquifer materials, and the 

head difference between the stage in the stream 

and head in the aquifer near the stream. Five 

sites have been selected for studies of these controlling factors. These sites are: (1) Wooster well 

field on Killbuck Creek, OH; (2) Dover well field 

on the Rockaway River, NJ; (3) Cannondale well 

165 
166 

West TRANSVERSE SECTION East 

Kame terrace 

NOT TO SCALE 

I 

t- z a: 0 0 

t3 ~ w t- en ::J 

0 

en 

South LONGITUDINAL SECTION North 

Kame 

terrace 

deposits 

(projected) 

NOT TO SCALE 

z ti; 

0 ~ t3 ~ w en en w 3: 

Fluvial valley 

train deposits 

·,::. 

Figure 98. - Generalized transverse and longitudinal geologic sections of valleys draining away from glacial ice 

(type A). 

field on the Norwalk River, CT; (4) Fairfield Hills 

well field on the Pootatuck River, CT; and (5) 

Kirkwood well field on the Susquehanna River, 

NY (fig. 95). Techniques that are used to determine hydraulic properties of aquifer materials 

near streams and of streambeds include: (1) 

simultaneous measurement of seepage loss or 

gain and head in aquifers near the stream, (2) 

chemical analyses of water from the stream and 

nearby wells to estimate quantity of water 

diverted from the streams, (3) temperature 

surveys in wells to determine the ground-water 

flow rate, and (4) flow modeling. 

Simulation of Glacial Aquifers 

Flow models are being used to evaluate and 

synthesize concepts of ground-water flow in 

glacial aquifers and to analyze sensitivity of flow 

to geohydrologic factors. A three-dimensional conceptual model consisting of three layers representing an idealized valley-aquifer system is 

depicted in figure 100. In the valley part, layers 

1 and 2 represent coarse-grained material 

separated by a confining layer. In the upland 

area, layer 1 represents a layer of soil or 

weathered till at land surface; layer 2 represents 

a layer of till or fractured bedrock; and layer 3 

represents bedrock throughout the modeled area. 

These features of a glacial aquifer are commonly 

observed in the northeastern United States. The 

flow model is being used to evaluate variations 

in ground-water runoff with time, the relation 

between aquifer head and ground-water runoff, 

and the response of streamflow to pumping 

stresses. 

Bibliography of Previous Investigations 

A bibliography that summarizes published information on ground-water studies related to 
Stream Stream 

Silt and clay deposits 

Figure 99. - Generalized geologic section of deposits in an area having extensive preglacial lakes (type B) . 

Figure 100.-Generalized valley-aquifer system used in a ground-water 

flow model for the study of the Northeast glacial regional aquifer system. 

glacial aquifers in the study area includes about 

750 references. Types of information contained in 

each reference such as well data, modeling 

results, and description of water quality have 

been identified. 

PUBLISHED REPORT 

1. Lyford, F. P., Dysart, J. E. , Randall, A. D., 

and Kontis, A. L., 1984, Glacial aquifer 

systems in the northeastern United 

States-A study plan: U.S. Geological 

Survey Open-File Report 83-928, 33 p. 

REFERENCES CITED 

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

States: New York, McGraw-Hill, 714 p. 

Koteff, Carl, 1974, The morphologic sequence concept and 

deglaciation of southern New England, in Coates, D. 

R., ed., Glacial geomorphology: Binghamton, N.Y., 

State University of New York, Publications in Geomorphology, p. 121-144. 

Lyford, F. P., Dysart, J. E., Randall, A. D., and Kontis, A. L., 

1984, Glacial aquifer systems in the northeastern 

United States-A study plan: U.S. Geological Survey 

Open-File Report 83-928, 33 p. 

McGuinness, C. L., 1964, Generalized maps showing annual 

runoff and productive aquifers in the conterminous 

United States: U.S. Geological Survey Hydrologic Investigations Atlas 194. 

167 
168 

ACTIVE PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

NORTHERN ATLANTIC COASTAL PLAIN 

REGIONAL AQUIFER-SYSTEM STUDY 

By Harold Meisler, Trenton, New jersey 

INTRODUCTION 

The northern Atlantic Coastal Plain is a 

gently rolling to flat region of about 50,000 mi2 • 

The study area extends along the Atlantic coast 

from Long Island, NY, to North Carolina (fig. 

101). It is underlain by a wedge of predominantly 

unconsolidated sediments that thickens from a 

feather edge at the Fall Line to 8,000 feet along 

the coast of Maryland and 10,000 feet at Cape 

Hatteras, NC, (fig. 102). The sediments consist 

mostly of sand, silt, clay, and gravel of Jurassic 

to Holocene age. Limestone occurs in North 

Carolina. A regional aquifer system study of the 

Northern Atlantic Coastal Plain was begun in 

1979 and is scheduled for completion in 1986 

(Meisler, 1980). 

This sedimentary wedge forms a complex 

aquifer system in which the sand, gravel, and 

limestone function as aquifers, whereas the clay 

and silt act as confining units. Withdrawal of 

water from this system, principally for municipal 

and industrial use, has grown from about 100 

Mgal/d in 1900 to about 1,200 Mgal/d in 1980. 

Recharge to the northern Atlantic Coastal 

Plain aquifer system is derived from precipitation 

and occurs chiefly in upland and interfl uvial 

areas. It ranges from 10 to 25 in./yr, but most of 

this water flows only through the shallow unconfined parts of the system and discharges to local 

streams that dissect the Coastal Plain. A small 

amount of the precipitation, generally less than 

1 in/yr, recharges the deeper confined aquifers. 

Under natural conditions, discharge from the 

deeper aquifers is primarily upward across the 

confining units into shallower aquifers and 

ultimately into the sea or coastal estuaries, 

sounds, and bays. 

HYDROGEOLOGIC FRAMEWORK 

By Henry Trapp, Jr., Trenton, New Jersey 

Northern Atlantic Coastal Plain sediments 

range in age from Jurassic . to Holocene. Late 

Jurassic sediments have been identified in a few 

wells near the coast, but for the most part, the 

Jurassic sediments are offshore (fig. 103), and do 

not contain freshwater. In general, the lowermost 

Coastal Plain deposits are fluvial or fluviodeltaic 

in origin, and contain discontinuous lenses of 

sand, silt, clay, gravel, and lignite. Younger 

deposits successively overlap older ones (figs. 

103-105). In the Cretaceous section, there is a 

general upward transition from fluvial and 

fluviodeltaic to marginal-marine to marine 

deposits. The marine parts of the section consist 

primarily of glauconitic sand, silt, clay, and some 

limestone beds, which are traceable over longer 

distances than the more lenticular nonmarine 

beds. The Tertiary sediments are predominantly 

marine except for the Upper Miocene and 

Pliocene beds, which are, in part, nonmarine. The 

Pleistocene section includes glacial drift on Long 

Island, and marine, dune, alluvial and terrace 

deposits elsewhere. The Holocene section includes 

alluvial, terrace, and marine deposits, beaches, 

and dunes. 

For this study, the Coastal Plain sediments 

have been grouped into ten regional aquifers (fig. 

106), consisting principally of sand, gravel, or 

limestone, separated by nine confining units, consisting principally of clay and silt. A regional 

aquifer may coincide with a recognized local 

aquifer in one area and comprise several local 

aquifers in another, or it may constitute only part 

of an aquifer. None of the regional aquifers ex-
tends over the entire study area. Because they ~e 

delineated on the basis of permeability contrast, 

and the distribution of permeable zones changes 

from place to place, the regional aquifers replresent sediments of different ages in different are~s. 

SIMULATION OF GROUND-WATER FLOW 

By P. Patrick Leahy and Mary Martin, 

Trenton, New Jersey 

Ground-water flow in the northern Atlantic 

Coastal Plain regional aquifer system was 

simulated using a multilayered finite-differe~ce 

flow model (Leahy, 1982) that includes ten 

aquifers and nine confining units. The grid u$ed 

has 85 rows and 32 columns. The grid sizes b.re 

variable; however, most of them are 7 milesl x 

7 miles or 49 mi2 • : 

The aquifer system is bounded laterally ~nd 

below by no-flow boundaries. The bottom bo"P.ndary corresponds to the sloping contact betw~en 

Coastal Plain sediments and the underlyi~g, 

nearly impermeable, crystalline rocks or c1bnsolidated rocks of Mesozoic age. The Fall Ll'· ne 

represents an irregular no-flow boundary at he 

updip limit of the aquifer system to the north nd 

west. The downdip offshore no-flow bounda~ to 

the east and south represents an assu~ed 

saltwater-freshwater interface located where ~he 

ground water contains concentrations of chlo*de 

of 10,000 milligrams per liter (mg!L) as delinea)ted 

by Meisler (1981). The southwestern boundarp is 

coincident with a major ground-water di~ide 

located at the Pee Dee River in South Carol~na. 

However, in the deepest part of the aqu~fer 

system, ground water appears to flow north~ast 

in South Carolina toward North Carolina bene~th 

the shallower ground-water divide. Therefore, ithe 

southwestern boundary of the lowest aquifer 1vas 

defined as a constant-head boundary instea~ of 

a no-flow boundary. The northeastern no-fl.ow 

boundary of the aquifer system occurs at th~ intersection of the Fall Line and an estimated !~cation where ground water contains concentrat~ons 

of chloride of 10,000 mg/L northeast of Lbng 

Island. 

During steady-state simulations, two !top 

boundary conditions were used to represent )the 

shallow aquifers. One of the top boundaries ~as 

water-table altitudes specified as constant heads 

(fig. 107). In this case, the water-table aquifer ~as 

not simulated; however, the flow recharged ftom 

the water-table aquifer to the deeper aquifers was 

simulated. The other top boundary was use~ to 

simulate the water-table aquifer and streams as 

part of the aquifer system (fig. 108). In this case, 

the base flow discharged from the water-table 

aquifer and recharge rate to the deeper aquifer 

system were simulated. 

Simulation of the steady-state flow system 

using water-table altitudes as a constant-head 

boundary yields heads in every cell and a value 

of flow into or out of the constant-head cells. The 

flow out of the constant-head cells represents the 

component of flow recharging to the deeper 

aquifers and is herein referred to as deep percolation. Deep percolation is treated as a known flow 

for the second conceptualization of the top boundary condition. 

The second conceptualization includes the 

water-table aquifer and streams as part of the 

aquifer system and is necessary in order to 

simulate transient water levels in aquifer-outcrop 

areas where pumping centers are located and 

water levels are declining. These water-level 

declines cannot be simulated using the watertable constant-head boundary. 

Simulation of the flow system using the second conceptualization includes ground-water 

recharge of 10 to 25 in./yr from precipitation to 

the water-table aquifer, and streams acting as 

local drains. The streambed leakance (hydraulic 

conductivity divided by streambed thickness) controls the amount of ground water discharged to 

or recharged from streams as base flow or seepage 

depending on head difference between the aquifer 

and the stage in the stream. A water budget for 

each model cell is used to compute an effective 

streambed leakance. Inasmuch as recharge (QRE) 

is given and deep percolation (DP) is computed by 

the steady-state simulation, the discharge (BF) to 

a stream is then calculated. Using the calculated 

discharge and the known altitudes for the water 

table (hwt) and stage of streams (hs), streambed 

leakances (TKs) can be calculated. Because of the 

large grid size used in the model, numerous 

streams exist in every cell and one average 

representative stream elevation must be 

estimated for each model cell. Also, regional 

lateral flow in the water-table aquifer is assumed 

to be negligible. 

Simulating ground-water flow under prepumping conditions results in virtually 

equivalent values of head and of deep percolation 

using either a constant-head boundary to represent the water-table aquifer, or simulating the 

water-table aquifer and streams as part of the 

aquifer system. However, using the latter ap169 
170 

80' 

40' 

PENNSYLVANIA 

Atlantic 

Ocean 

SCALE 1:11,000,000 

0 50 100 MILES 

r---r---1 

0 50 100 KILOMETERS 

EXPLANATION 

FALL LINE 

STUDY AREA 

Figure 101.- Location of the northern Atlantic Coastal 

Plain. 

proach, the water-table altitude, deep percolation, 

and discharge to or recharge from streams are 

able to change in response to pumping stresses 

during transient simulations. 

Figures 109 and 110 show the simulated 

prepumping potentiometric surfaces for two 

selected aquifers, a deep aquifer consisting of 

sediments of Late Cretaceous age (model aquifer 

layer 2) and a shallow aquifer consisting of 

sediments of Eocene age (model aquifer layer 7). 

From the potentiometric surface of the shallower 

aquifer, the discharge to major surface-water 

bodies may be deduced. The influence of major 

rivers, estuaries, and embayments on the flow 

system is apparent. In contrast, the potentiometric surface of the deeper aquifer shows 

smoother contours reflecting a deeper regional 

ground-water flow. Although the streams and 

rivers seem to affect the flow pattern in the updip part of the deeper aquifer, most of the groundwater flow is not influenced by the presence of 

overlying surface-water bodies. Flow lines in the 

deeper aquifer are several tens of miles long and 

cross State boundaries. The flat hydraulic gradient suggests that the ground-water flow is sluggish in areas away from outcrops. 

The simulated prepumping potentiometric 

surfaces show that: (1) recharge to the confined 

aquifers generally is downward along or near the 

Fall Line, and (2) discharge from the deeper confined aquifers usually is upward leakage through 

confining units into the ocean or coastal estuaries 

and bays. 

Figure 111 shows the simulated flow to and 

out of the overlying water-table aquifer under 

steady-state conditions. The flow ranges up to 20 

in./yr of recharge into the confined aquifers and 

up to 17 in./yr of discharge from the confined 

aquifers. In general, however, recharge is 1 in./yr 

or less, indicating that only a small part of the 

water in the water-table aquifer infiltrates to the 

deeper confined aquifers. High infiltration rates 

are located in areas where the water-table aquifer 

is directly connected with the underlying aquifers 

and there is no intervening confining unit. Examples of this relation occur between the glacial 

aquifer and the Magothy aquifer in Long Island, 

and between the surficial and Castle Hayne 

aquifers in North Carolina. 

Generally, development of ground water in 

the northern Atlantic Coastal Plain began in the 

late 1800's. Pumpage for 1900 was estimated to 

be 100 Mgal/d; most of it was for water supply of 

Brooklyn and Queens on Long Island. 

Withdrawals have steadily increased and total 

pumpage in 1980 was estimated to be about 1,200 

Mgal/d (fig. 112). These estimates do not include 

domestic and irrigation usage obtained from 

shallow water-table aquifers, because the impact 

of these water-table pumpages is negligible 

regionally. Water-level declines resulting from 

deep-aquifer withdrawals are observed in every 

State in the study area. 

Estimates of pumpage from 1900 to 1980 

were used in determining the average pumpage 

for ten pumping periods for the simulation. 

Figures 113 and 114 show the simulated 1980 

potentiometric surfaces for a deeper Late 

Cretaceous aquifer and a shallow Eocene aquifer, 

respectively. Pumping in the deeper aquifer has 

reduced water levels in Virginia to more than 100 

feet below sea level and to more than 50 feet 

below sea level in New Jersey. Pumping in the 

shallower aquifer reduced water levels to more 

than 50 feet below sea level in North Carolina 

and Delaware. 

Sources of pumped water in the Coastal Plain 

are: (1) an increase in deep percolation from the 

overlying water-table aquifer to deeper confined 

aquifers corresponding to a decrease in discharge 

to streams; (2) water withdrawn from· aquifer 

storage; and (3) a reduction in upward discharge 
from the confined aquifers through overlying confining units to surface-water bodies, including the 

ocean. Preliminary simulation indicates that the 

aquifer system approaches steady-state conditions 

within a 5-year pumping period. Therefore, water 

is released from aquifer storage with an accompanying water-level decline for a relatively short 

PENNSYLVANIA 

OHIO 

40" 

WEST VIRGINIA 

35" 

SOUTH CAROL! NA 

period oftime after increases in pumpage. Pumping has caused a long-term decrease in groundwater discharge to streams in areas of increased 

infiltration to the deeper aquifers. In other areas, 

pumping has resulted in a decrease in discharge 

from the deeper aquifers upward to the overlying 

aquifers and lower water levels in the deeper 

0 

0 

Atlantic 

Ocean 

SCALE 1 :5,500,000 

50 100 MILES 

50 100 KILOMETERS 

EXPLANATION 

-2000- LINE OF EQUAL THICKNESS OF COASTAL-PLAIN 

SEDIMENTS-- Interval in feet, is variable 

A 

~ 

A' TRACE OF HYDROGEOLOGIC SECTION·· 

Numbers indicate the control wells 

AXIS OF STRUCTURAL FEATURE 

AREA OF INTENSIVE SAMPLING OF 

AQUIA-AQUIFERWATER 

--.- FALL LINE 

STUDY AREA 

Figure 102.- Thickness of Coastal-Plain sediments and location of hydrogeologic sections in the northern Atlantic 

Coastal Plain. 

171 
172 

aquifers, possibly causing migration of the 

freshwater-saltwater transition zone, toward 

pumping centers. 

Simulation has indicated: (1) the need for 

rigorous definition of confining-unit leakance, (2) 

< <( 

z 

0 

j:: 

(.) 

FEET B w C/) 

Sea 

level 

-1000 

-2000 

-3000 

- 4000 

-5000 

- 6000 

- 7000 

- 6000 

-9000 

B' 

PLEISTOCENE 

MIOCENE 

OLIGOCENE 

EOCENE AND 

PALEOCENE 

UPPER 

CRETACEOUS 

LOWER 

CRETACEOUS 

0 

UPPER 

JURASSIC 

50 

the importance of discretization scale in the 

simulation of regional flow as related to the purpose of the simulation, and (3) the importance of 

the boundary condition representing the 

freshwater-saltwater transition zone. 

D 

.. 

.. 

EXPLANATION 

AQUIFER-- Predominantly sand. Number 

corresponds to layer number used in the 

three-dimensional flow models 

AQUIFERS (WHERE DEFINED) OR SEDIMENTS 

OF MIOCENE, PLIOCENE, AND 

QUATERNARY AGE 

AQUIFERS(WHERE DEFINED) OR SEDIMENTS 

OF PALEOCENE, EOCENE, AND 

OLIGOCENE AGE 

AQUIFERS (WHERE DEFINED) OR SEDIMENTS 

IN UPPER PART OF CRETACEOUS SECTION--

Predominantly marine and marginal marine 

AQUIFERS (WHERE DEFINED) OR SEDIMENTS 

IN LOWER PART OF CRETACEOUS SECTION--

Predominantly nonmarine 

[IZJ JURASSIC SEDIMENTS 

~ CONFINING BED(S) (WHERE DEFINED) 

~ 

I 

100 MILES 

BASEMENT 

CONTROL WELL-- Number was assigned for this 

investigation 

HYDROGEOLOGIC CONTACT ·- Dashed where 

approximately located, queried where 

inferred 

0 50 100 KILOMETERS 

Figure 103.-Hydrogeologic section 8-8', from New Jersey to the offshore COST 8-2 well, in the northern Atlantic Coastal 

Plain (location of section shown in fig. 102). 
FEET 

c 500 

Sea 

level 

- 500 

- 1000 

- 1500 

- 2000 

- 2500 

- 3000 

- 3500 

- 4000 

- 4500 

- 5000 

- 5500 

-6000 

- 6500 

-7000 

C' 

0 

0 

VERTICAL SCALE GREATLY EXAGGERATED 

-

-

-

g: 

I 

EXPLANATION 

AQUIFER -- Predominantly sand. Number 

corresponds to layer number used in the 

three-dimensional flow models 

AQUIFERS OF MIOCENE, PLIOCENE, 

AND QUATERNARY AGE 

173 

AQUIFERS OF PALEOCENE AND EOCENE AGE 

AQUIFERS IN UPPER PART OF CRETACEOUS 

SECTION -- Predominantly marine and 

marginal marine 

AQUIFERS IN LOWER PART OF CRETACEOUS 

SECTION-- Predominantly nonmarine 

CONFINING BED(S) 

BASEMENT 

CONTROL WELL -- Number was assigned for 

this investigation 

- WASTEGATE FORMATION OF HANSEN, 1982 

25 50 MILES 

25 50 KILOMETERS 

Figure 104.- Hydrogeologic section C-C', Maryland, in the northern Atlantic Coastal Plain (location of section shown in fig. 102). 
174 

FEET D 

400 

200 

Sea 

level 

- 200 

-400 

-600 

-600 

-1000 

-1200 

~ 

-

-

-

~ 

~ 

~ 

~ 

N 

~ 

I 

A 

0 25 50 KILOMETERS 

EXPLANATION 

AQUIFER-- Predominantly sand. Number corresponds to layer 

number used in the three-dimensional flow models 

AQUIFERS OF MIOCENE, PLIOCENE, AND QUATERNARY AGE 

AQUIFERS IN UPPER PART OF CRETACEOUS SECTION--

Predominantly marine and marginal marine 

AQUIFERS IN LOWER PART OF CRETACEOUS SECTION --

Predominantly nonmarine 

CONFINING BED(S) 

UNDIFFERENTIATED LAYERS 4, 3, AND 2 

BASEMENT 

CONTROL WELL-- Number was assigned for this investigation 

Figure 105.- Hydrogeologic section D-A, southern North Carolina, in the 

northern Atlantic Coastal Plain (location of section shown in fig. 102). 
FEET 

- 1000 

-2000 

-3000 

A 

<( 

0 

NORTH CAROLINA 

"t> 

c: 

::. 

0 

Cl) 

VIRGINIA MARYLAND I DEL I 

VERTICAL SCALE GREATLY EXAGGERATED 0 

t; um 

~ 

-

~ 

-

~ 

~ 

i 

0 50 

EXPLANATION 

AQUIFER-- Predominantly sand. Number corresponds to layer 

number used in the three-dimensional flow models 

AQUIFER-- Predominantly limestone and lime sand, layer 7 

AQUIFERS OF MIOCENE, PLIOCENE, AND QUATERNARY AGE 

AQUIFERS OF PALEOCENE, EOCENE, AND OLIGOCENE AGE 

AQUIFERS IN UPPER PART OF CRETACEOUS SECTION--

Predominantly marine and marginal marine 

AQUIFERS IN LOWER PART OF CRETACEOUS SECTION--

Predominantly nonmarine 

CONFINING BED(S) 

BASEMENT-· Configuration of the basement drawn on the 

basis of the contour maps of the basement prepared under 

the study of the Northern Atlantic Coastal Plain Regional 

Aquifer System Analysis 

CONTROL WELL-- Number was assigned for this investigation 

NEW JERSEY 

50 

100 KILOMETERS 

Figure 106.- Hydrogeologic section A-A', from North Carolina to Long Island, New York, in the northern Atlantic Coastal 

Plain (location of section shown in fig. 102). 

175 
176 

SAL TWA TER-FRESHWA TER RELATIONS 

By Harold Meisler 

with depth within a transition zone between the 

· deepest freshwater and the underlying saltwater. 

Salty ground water underlies freshwater in 

the eastern part of the northern Atlantic Coastal 

Plain. Chloride concentrations generally increase 

The zone containing concentrations of chloride 

ranging from 1,000 to 18,000 milligrams per liter 

(mg/L) (the approximate chloride concentration in 

seawater) is depicted in a section across southern 

· New Jersey and the adjacent Continental Shelf 

Fall line 

NOT TO SCALE 

X X 

X t 

l x 

PHYSICAL SYSTEM 

MODELED SYSTEM 

Water-table constant head node- ~ X 

X X t t 

• 

X X - t - X X X - t - ,. Jp I 

-i ti r 

EXPLANATION . 

~ CONFINING-UNIT LEAKAGE . 

---·- FLOW WITHIN AQUIFER 

t DP, DEEP PERCOLATION 

- NO-FLOW BOUNDARY 

Atlantic Ocean 

""'-

~ ~L,,,, ~units 

X X X 10 

t DtP t I 9 

r:~ 8 

r "" 7 

,... I'll 

3-6 

2 

Aquifer 1 

Figure 107.- Comparison of physical and model-simulated systems used for steady-state simulations of the 

Northern Atlantic Coastal Plain regional aquifer system. 
(fig. 115). Altitudes of the 250 and 10,000 mg/L 

concentrations of chloride are shown in figures 

116 and 117, respectively. 

The saltwater-freshwater transition zone 

generally deepens inland from the coast except 

in New Jersey, where it is deepest along the coast, 

and locally in North Carolina (fig. 117). The transition zone is shallowest in North Carolina, particularly in the vicinities of the Cape Fear River 

and Albemarle Sound, and deepens northward to 

Maryland and the coast of New Jersey. It is 

relatively shallow, however, in the vicinity of 

Delaware Bay. Concentrations of chloride of less 

than 5,000 mg/L extend about 55 miles off the 

New Jersey coast (fig. 115). The offshore extension of the transition zone decreases southward 

toward southern Virginia. 

Depth to the saltwater-freshwater transition 

zone is partly controlled by the natural flow pattern of the fresh ground water in the aquifer 

system. Areas where the transition zone is 

relatively shallow generally coincide with areas 

PHYSICAL SYSTEM 

of natural ground-water discharge-the most prominent of these are Delaware Bay, lower 

Chesapeake Bay, Albemarle Sound, and the Cape 

Fear River. 

The effect of eustatic sea-level fluctuations on 

the location and development of the transition 

zone in New Jersey was analyzed by means of a 

finite-difference cross-sectional flow model 

(Meisler, and others, 1984). The model simulates 

the sedimentary wedge from the Delaware River 

to the Continental Slope (fig. 115) as a highly 

anisotropic porous medium (ratio of simulated 

lateral to vertical hydraulic conductivity ranges 

from 1,000:1 to 1 million:1). Simulated steadystate freshwater flow is separated from static 

saltwater (18,000 mg/L of chloride) by a sharp interface. Freshwater pressure at the simulated interface equals the pressure exerted by a column 

of static seawater. 

Positions of the interface in a steady-state 

condition of the aquifer system were simulated 

for several hypothetical sea levels and for difORE 

MODELED SYSTEM 

I 

Constant stage in stream 

hs 

TKS 

. TKC 

. 

TKC 

. 

I 

ORE 

NOT TO SCALE 

EXPLANATION 

ORE, GROUND-WATER RECHARGE 

BF, BASE FLOW (BF =ORE- DP) 

DP, DEEP PERGOLA TION 

hwt' WATER-TABLE HEAD 

h5 , STREAMHEAD 

f . 

i 

TKc, CONFINING UNIT LEAKAGE 

TK5 , STREAM BED LEAKAGE 

(TK5 = BF/(hwt - h5 )) 

--·- FLOW WITHIN AQUIFER 

Figure 108.- Comparison of physical and model-simulated systems used for transient simulations of the Northern Atlantic 

Coastal Plain regional aquifer system . 

177 
178 

ferent distributions of vertical and lateral 

hydraulic conductivity. The simulated sea levels 

range from present sea level to 150 feet below present sea level. Simulated hydraulic conductivities 

range from 1 to 20 ft/d lateral conductivity, and 

PENNSYLVANIA 

WEST VIRGINIA 

-r--------------

35" 

SOUTH CAROLINA 

1 x 10- 6 to 3.3 x 10- 4 ft/d for vertical conductivity. The simulated interface position is sensitive to anisotropy (ratio of lateral conductivity 

to vertical conductivity) and to sea level. Increasing anisotropy causes the interface to be 

0 

0 

Atlantic 

Ocean 

SCALE 1 :5,500,000 

50 100MILES 

50 100 KILOMETERS 

EXPLANATION 

-25- POTENTIOMETRIC CONTOUR-- Shows altitude of potentiometric 

surface. Contour interval 25 feet. Datum is sea level 

AREA OF AQUIFER 

FALL LINE 

STUDY AREA 

Figure 109.-Simulated prepumping potentiometric surface of an aquifer consisting of sediments of Upper Cretaceous 

age (model aquifer layer 2), the Northern Atlantic Coastal Plain regional aquifer system. 
shallower and to extend farther offshore. Lowering sea level causes the interface to be deeper and 

to extend farther offshore. 

A comparison of several interfaces, computed 

for different sea levels, with observed isochlors is 

PENNSYLVANIA 

OHIO 

40° 

WEST VIRG INIA 

35° 

SOUTH CAROLINA 

shown in figure 115. The most probable distribution of hydraulic cbnductivities (2.5 to 10 ft/d for 

lateral hydraulic conductivities and 8.3 x 10-s 

to 3.3 x 10 - 4 ft/d for vertical conductivity) and 

a constant anisotropic ratio of 30,000:1 were used 

0 

0 

Atlantic 

Ocean 

SCALE 1 :5,500,000 

50 100 MILES 

50 100 KILOMETERS 

EXPLANATION 

-2&-- POTENTIOMETRIC CONTOUR-- Shows altitude of potentiometric 

surface. Contour interval25 feet. Datum is sea level 

AREA OF AQUIFER 

FALL LINE 

STUDY AREA 

Figure 110.- -Simulated prepumping potentiometric surface of an aquifer consisting of sediments of Eocene age (model 

aquifer layer 7), the Northern Atlantic Coastal Plain regional aquifer system. 

179 
180 

PENNSYLVANIA 

WEST VIRGINIA 

Atlantic 

Ocean 

35· 

SCALE 1:5,500,000 

SOUTH CAROL! 0 50 100 MILES 

0 50 100 KILOMETERS 

EXPLANATION 

RECHARGE TO DEEP AQUIFERS DISCHARGE FROM DEEP AQUIFERS 

IN INCHES PER YEAR IN INCHES PER YEAR 

~ 10to20 - 10to17 

~ 1to10 k//Y/J 1 to 10 

OIIl] Oto 1 l<:>: q 0 to 1 

/'...../" FALL LINE STUDY AREA 

Figure 111.-Simulated deep percolation to and discharge from the confined aquifers of the Northern Atlantic Coastal 

Plain regional aquifer system. 
> 

< c 

a: 

w 

ll.. 

en 

z 

0 

....1 

...J 

< (!J 

u. 

0 

en 

z 

0 

::J 

...J 

~ 

~ 

...J' 

a: 

~ c 

:I: 

I-

~ 

1200 

1100 

1000 

900 

800 

700 

600 

500 

400 

300 

200 

_, / 

100 

1910 1920 

/ 

/ 

/ 

/ 

"--- Long Island ·- .... ,... " / --------- 1 

1930 1940 

YEAR 

1950 

/ 

/ 

/ 

/ 

I 

I 

1960 

I 

I 

I 

I 

/ 

,. .... / / / / 

1970 

.,. .... , 

1980 

Figure 112.-Ground~water withdrawals from the Northern Atlantic Coastal Plain regional 

aquifer system, 1900-80. 

181 
182 

35 ° 

PENNSYLVANIA 

WEST VIRGINIA 

Atlantic 

Ocean 

-r--------------

SOUTH CAROLINA 

- 50-

0 

SCALE 1:5,500,000 

50 100MILES 

0 50 100 KILOMETERS 

EXPLANATION 

POTENTIOMETRIC CONTOUR-- Shows altitude of potentiometric 

surface. Contour interval 50 feet. Datum is sea level 

AREA OF AQUIFER 

FALL LINE 

STUDY AREA 

Figure 113.-Simulated 1980 potentiometric surface of an aquifer consisting of sediments of Upper Cretaceous age 

(model aquifer layer 2), the Northern Atlantic Coastal Plain regional aquifer system. 
35 ° 

WEST VIRGINIA 

J 

I 

I 

PENNSYLVANIA 

Atlantic 

Ocean 

-r--------------

SOUTH CAROLINA 

- 50-

0 

SCALE 1:5,500,000 

50 100MILES 

0 50 100 KILOMETERS 

EXPLANATION 

POTENTIOMETRIC CONTOUR·· Shows altitude of poten~iometrlc 

surface. Contour interval 50 feet. Datum is sea level 

AREA OF AQUIFER 

FALL LINE 

STUDY AREA 

Figure 114.- Simulated 1980 potentiometric surface of an aquifer consisting of sediments of Eocene age (model aquifer 

layer 7), the Northern Atlantic Coast regional aquifer system. 

183 
184 

FEET E 2000 

2000 

4000 

New Jersey 

VERTICAL SCALE GREATLY EXAGGERATED 

Shoreline 

E' 

Continental Shelf 

0 10 

0 10 20 KILOMETERS 

EXPLANATION 

--150- SIMULATED INTERFACE (10,000 milligrams per liter of chloride)-- Number 

is sea level used for simulation, in feet, relative to present sea level. 

--5000- - LINE OF EQUAL CHLORIDE CONCENTRATION 

--Interval, in milligrams per liter, is variable. 

Lateral hydraulic conductivity 

Vertical hydraulic conductivity = 30•

000 

Figure 115.- Hydrogeologic section from southern New Jersey to the Continental Slope, showing isochlors 

and simulated saltwater-freshwater interface in the northern Atlantic Coastal Plain (location of section shown 

infig.117). 

to compute the interfaces shown in figure 115. 

The offshore position of the center of the transition zone (10,000 mg/L isochlor) estimated from 

field data coincides approximately with the interface computed for a sea level of 50 feet below present sea level. Onshore the estimated 10,000 mg/L 

isocholor coincides with the interface computed 

for a sea level of 100 feet below present sea level 

(fig. 115). 

These simulations suggest that the position 

of the freshwater-saltwater transition zone 

estimated from field data in southern New Jersey, 

and the occurrence of relatively fresh ground 

water (compared to seawater) in the offshore area 

reflect sea levels that were probably between 50 

to 100 feet below present sea level. Although the 

average sea level during the Quaternary period 

probably was in this range, it is likely that the 

observed and estimated transition zone reflects 

sea-level conditions for a longer period of time 

that includes the Pliocene and part of the 

Miocene. The saltwater-freshwater transition 

zone off the coast of southern New Jersey is 

presently moving slowly landward in response to 

the most recent sea-level rise which started about 

16,000 years ago. Estimates of lateral groundwater velocity suggest that this movement probably is at a rate of about 0.2 mile per 10,000 

years (Meisler and others, 1984). Ground-water ·· 

development in southern New Jersey, however, 

has probably increased the lateral velocity, but 

the magnitude of the influence of pumping has 

not yet been investigated. 

Farther south, in southeastern Virginia and 

North Carolina, the transition zone is much 

shallower, and relatively fresh ground water 

(compared to seawater) probably does not extend 

very far offshore (fig. 117). Here, the position of 

the transition zone probably reflects higher 

average sea levels than those suggested for New 

Jersey. Indeed, depositional environments inferred from sediments of Middle Miocene age and 

younger indicate that marine submergence was 

generally more prevalent to the south. The broad 

saltwater-freshwater transition zone probably 

developed as a result of saltwater circulation 

caused by large-scale sea-level fluctuations during 

the later Tertiary and Quaternary. Repeated advance and retreat of the salty ground water 

caused the saltwater and freshwater to mix. 
35. 

WEST VIRGINIA 

SOUTH CAROLINA 

--800 -

PENNSYLVANIA 

0 

0 

EXPLANATION 

Atlantic 

Ocean 

SCALE 1 :5,500,000 

50 100 MILES 

50 100 KILOMETERS 

WATER-QUALITY-ZONE CONTOUR-- Shows altitude of 250 milligrams per liter 

chloride concentration. Contour interval, in feet, is variable. Datum is sea level 

EASTERN LIMIT OF DEEP FRESHWATER WEDGE 

LIMIT OF 250 MILLIGRAMS PER LITER CHLORIDE CONCENTRATION 

IN COASTAL PLAIN SEDIMENTS 

~ FALLLINE 

STUDY AREA 

Figure 116. - Aititudes of the 250 milligrams per liter chloride concentration of ground water in the northern Atlantic 

Coastal Plain. 

185 
186 

GEOCHEMISTRY 

By LeRoy L. Knobel, Trenton, New Jersey 

and Francis H. Chapelle, Towson, Maryland 

The chemical nature of ground water in the 

study area is highly variable (Back, 1966). This 

variability results from both the mineralogical 

complexity of the sediments and the diverse 

nature of flow patterns. 

The environment . of deposition causes the 

most striking differences in the mineralogy of the 

sediments, which were deposited under marine, 

marginal marine, and nonmarine conditions. The 

resulting differences in mineralogical composition 

and their effect on the chemical character of the 

ground water are discussed below. 

Nonmarine Sediments 

Nonmarine sediments, which occur primarily 

in the Lower Cretaceous and the lower part of the 

Upper Cretaceous, are commonly fluviodeltaic 

deposits-they generally consist of quartz sand 

with minor amounts of silicate minerals and interbedded silt and clay lenses. The clay lenses are 

usually light colored, consist mostly of illite, 

kaolinite, and montmorillonite, and contain 

significant quantities of pyrite and lignite. Hard 

beds rich in iron minerals occasionally occur at 

or near the contacts of sandy and clayey layers. 

These sediments commonly grade laterally into 

marginal marine deposits. 

Precipitation entering the nonmarine 

sediments in the outcrop areas is saturated with 

dissolved oxygen and has a low pH. The dissolved 

oxygen reacts with lignite and pyrite to produce 

ferric hydroxide, dissolved carbon dioxide, and 

hydrogen and sulfate ions (Chapelle, 1984). The 

dissolved carbon dioxide dissociates into additional hydrogen and bicarbonate ions. The 

hydrogen ions are consumed by hydrolysis of 

silicate minerals such'asthefeldspars and micas 

to produce dissolved silica (Si02) and the following dissolved ions: calcium (Ca2 + ), magnesium 

(Mgt+), sodium (N a+), potassium (K +),.and bicarbonate (HC03 -). The composition of silicate 

minerals is variable and controls which ions are 

actually released into the ground water (Faust 

and Aly, 1981). 

Ca2 + and Mg2+ released by weathering of 

the silicate minerals are removed from solution 

by cation exchange processes and are replaced by 

N a+. The source of sodium on cation exchange 

minerals is probably either from loading of the 

exchange sites during episodes of saltwater intrusion or from formation of sodium-rich clay-by 

weathering processes prior to deposition of the 

clay. The sulfate ion (804 - 2) produced by the 

dissolution of pyrite is reduced to sulfide or remains in the ground water as 804 - 2 depending 

on local conditions. Precipitated ferric hydroxide 

(Fe(OH)3) is commonly observed as secondacy 

mineralization in the nonmarine sediments. · · 

Marine Sediments 

Glauconitic Sediments. -Glauconite-rich 

sediments constitute a significant part of the 

marine deposits of the northern Atlan~ic Coastal 

Plain, primarily in the aquifers composed· • of 

sediments of Late Cretaceous and early Tertiary 

age. The Aquia aquifer in southern Maryland (fig. 

102) is typical of these sediments and will be lised to summarize the chemical processes. The 

Aquia aquifer is composed primarily of quartz 

sand, glauconite, and shell debris. The shell 

material is composed of magnesium calcite and 

aragonite and is commonly associated with secondary calcite cementation. Detrital lignite is found 

throughout these sediments. 

Glauconite has a high capacity to exchange 

ions adsorbed onto its surface for ions in the 

ground water. Because glauconite is formed iri a 

marine environment, the exchange sites are initially occupied by sodium; changes in water 

chemistry due to ion exchange reflect changes in 

the exchangeable cation composition of 

glauconite. Analyses of paired samples of ground 

water and glauconite from the Aquia aquifer in 

Maryland indicate that the exchangeable cation 

composition of glauconite changes systematically 

along flow paths in a manner related to changes 

in the concentrations of cations in the ground 

water. Cation exchange reactions thus appear to 

be procesSes,that 'simultaneously alter water and 

glau~onite composition along a flow path 

(Chapelle and &11obef, 1983). Because the exchange reaction is rapid, any Ca2+ in solution 

would exchange for Na +·on glauconite, a process 

that c,ontinues.until sodium is no longer available 

and Ca2+ is the dom.inant ion both in ground 

water and on glauc;oll.ite. The concentrations of 

Na+ on Aquia glauconite are plotted in figure 

118 as a function of distance along a flow path. 

Examination of figure 118 indicates that the exchange front in the Aquia aquifer is currently 

more than 30 miles along the hydraulic gradient. 

Ground water in the outcrop area of the 

· Aquia aquifer in southern Maryland is !calciummagnesium bicarbonate in character,'· ·and 
35' 

WEST VIRGINIA 

SOUTH CAROLINA 

--800-

E E' ,________. 

PENNSYLVANIA 

VIRGINIA Atlantic 

Ocean 

SCALE 1:5,500,000 

0 50 100 MILES 

0 50 100 KILOMETERS 

EXPLANATION 

WATER-QUALITY-ZONE CONTOUR-- Shows altitude of 10,000 milligrams per liter 

chloride concentration. Contour interval, in feet, is variable. Datum is sea level 

TRACE OF HYDROGEOLOGIC SECTION 

LIMIT OF 10,000 MILLIGRAMS PER LITER CHLORIDE CONCENTRATION 

IN COASTAL PLAIN SEDIMENTS 

'----.... FALL LINE 

STUDY AREA 

Figure 117. -Altitudes of the 10,000 milligrams per liter chloride concentration of ground water in the northern Atlantic 

Coastal Plain. 

187 
188 

changes to sodium bicarbonate downgradient. To 

explain the chemical processes further, the concentrations of Ca2 + + Mg2 +, N a + and HC03 - in 

Aquia water were plotted as a function of distance 

along a flow path as shown in figure 119. The 

aquifer can be divided into three regions based 

on changes in water chemistry. 

Region I.-This region includes the outcrop area. 

a: 

w 

D.. 

II) 

~ 

< 

a: 

~ 

:::i 

...J 

~ 

~ 

~-

:::> 

15 

0 

II) 

Ca2 + + Mg2 + and HC03 - concentrations increase to a peak and begin to decrease as 

water flows downgradient, due to the rapid 

dissolution of high-magnesium calcite shell 

material in the presence of C02 • Because 

w 40 1-

z 

0 Exchangeable Sodium u 30 :::> 

< ...J 

~ 

~ 20 

0 

II) 

~ 

< 10 a: 

~ 

~ 0 

0 10 20 30 

high-magnesium calcite has a higher solubility than low-magnesium calcite, the water 

becomes saturated with respect to the latter 

and precipitation of calcite occurs 

simultaneously with dissolution of the shell 

material. These processes account for the 

distribution of ions in the ground water occurring in Region I as well as for the observed 

distribution of secondary calcite cementation 

in this area (Chapelle, 1983). Ion exchange is 

not a significant process in Region I because 

the exchange capacity of the glauconite has 

been used up. 

40 50 60 

DISTANCE ALONG A FLOWPATH, IN MILES 

Figure 118.-Concentrations of exchangeable sodium on Aquia glauconite samples plotted against distance along 

a flow path in southern Maryland. 

ffi 5.0 1-

:::i 

a: 

w 

D.. 

l:3 4 .0 ...J 

0 

::!!: 

:::i 

...J 

~ 3.0 

~ 

z 

0 

i= < 2.0 a: 

1-

z 

w 

u 

z 8 1.0 

0 

0 

REGION I 

10 

oCb 

0 0 

6 

20 

REGION II 

0 

30 40 50 

DISTANCE ALONG FLOWPATH, IN MILES 

60 

EXPLANATION 

0 Sodium 

0 Bicarbonate 

6 Calcium plus Magnesium 

Delineations of regions I, II , Ill 

are explained in the text. 

Figure 119.-Concentrations of dissolved sodium, calcium plus magnesium, and bicarbonate of the 

Aquia aquifer water plotted against distance along a flow path in southern Maryland (modified from 

Chapelle, 1983). 
Region !I.-This region is downgradient from 

Region I. The aquifer is confined and 

therefore is closed off from atmospheric C02 • 

The .water chemistry exhibits rising N a+ 

concentrations and declining Ca2+ + Mg2 + 

concentrations. These changes in the water 

chemistry are primarily due to ion 

exchange. 

Region III....,... This region is downgradient from 

Region II and extends to the downdip boundary of the aquifer. The water is characterized by low Ca2 + + Mg2 + concentrations 

and increasing Na+ and HC03 - concentrations. The concentrations of Ca2 + + Mg2 + 

decrease as a result of ion-exchange, causing 

the water to become undersaturated with 

respect to both high- and low-magnesium 

calcite. Dissolution of these minerals occurs 

and HC03 - concentration increase. Comparison of figures 118 and 119 shows that 

sodium increases in concentrations in 

ground water in Regions II and III, coinciding with the availability of N a+ on 

glauconite. 

In the outcrop area of the Aquia aquifer, the 

ground water contains dissolved oxygen and incongruent dissolution of glauconite is an important chemical process that consumes dissolved oxygen and releases Si02 into the ground water. 

This process continues until the dissolved oxygen 

is consumed. Figure 120 shows the change of concentrations of dissolved oxygen and Si02 along a 

flow path in the Aquia aquifer in southern 

Maryland. These patterns are consistent with 

observations on weathering of glauconite made 

by Wolff (1967). The chemical processes summarized here have been described in detail by 

Chapelle (1983) and Chapelle and Knobel (1983). 

Diatomaceous Sediments.-Marine sediments 

of the lower Chesapeake Group of Miocene age 

in southern Maryland, Delaware, and the 

Mary land Eastern Shore generally consist of 

quartz sand interbedded with silt and clay. These 

deposits contain substantial quantities of 

diatomaceous material in the lower parts of the 

section (Cushing and others, 1973). Diatom shells 

are composed of amorhpous silica which is less 

stable in ground water than crystalline quartzas a result, concentrations of dissolved silica ar~ 

elevated in these sediments. In addition to high 

silica concentrations, dissolution of shell material 

generates . calcium-bicarbonate water which is 

modified by ion exchange to form a sodium bicarbonate water. 

Limestone Deposits.-The Coastal Plain of 

North Carolina contains extensive deposits of 

molluscan limestone with substantial secondary 

recrystallization, which grades laterally into 

bryozoan limestone and downward into 

calcareous sand (Brown and others, 1972). 

Chapelle (1983) developed a model to predict the 

chemical composition of ground water resulting 

from carbonate dissolution reactions in the 

presence of carbon dioxide. The model indicates 

that two moles of bicarbonate will be produced for 

each mole of calcium plus magnesium. Ca2+ + 

Mg2+ values plotted against HC03 - values for 

all available analyses of ground water from the 

Castle Hayne aquifer in North Carolina show a 

good match between observed data and modelderived values, suggesting that the model is a 

good representation of the chemical system in this 

area (fig. 121). 

Origin of Carbon 

Foster (1950) noted that ground water in the 

Atlantic and Gulf Coastal Plains has anomalously 

high bicarbonate concentrations; several times 

higher than those that could be generated by reactions involving dissolved C02 gas in recharge 

water in outcrop areas. Foster (1950) concluded 

that C02 was being generated within the aquifer 

system. 

Stable carbon isotopes used in conjunction 

with major-ion water chemistry are useful in helping to identify the sources of HC03 - in ground 

water. It is a common practice to relate 13C/ 12C 

ratios to the Peedee Belemnite (PDB) carbonate 

standard according to the following expression. 

(1ac; 12C)sample - (1ac; 12C)PDB 

(13Cf 12C)PDB X 1000 

If the carbon-containing substance is 

isotopically lighter than the PDB standard (for example, has less 13C relative to 12C), then it would 

have a negative value of 013C. Conversely, if the 

substance is isotopically heavier than the PDB 

standard, then it would have positive values of 

()13C. 

Stable carbon isotope data for Aquia water 

are plotted versus distance along a flow path as 

shown by figure 122. The bicarbonate becomes 

enriched with the heavier isotope (13

C) as the 

distance along a flow path increases. This increase is more pronounced in Region III and corresponds to the rapid rise of HC03 - concentrations (see figs. 119 and 122). The authors, using 

mass balance techniques, concluded that the increases in both the heavier carbon isotope in 

189 
190 

bicarbonate and the bicarbonate concentrations 

in the ground water require an aquifer-generated 

source of C02 that is enriched in the heavy 

isotope. They also noted that in Region III where 

C02 is being generated, anoxic conditions exist 

(fig. 120). 

Winograd and Farlekas (197 4) noted similar 

trends along three hydrochemical sections inN ew 

Jersey and also concluded that an aquifergenerated source of C02 was required. It is significant to note that the observations of Winograd 

andFarlekas were based on a study of sediments 

deposited in a nonmarine to marginal marine environment whereas the observations of the 

0 

0 0 

00 

0 0 

0 

authors were based on a study of marine 

sediments. This suggests that similar processes 

may generate C02 in aquifers of widely varying 

characteristics. The possible sources of aquifer~ 

generated C02 include: (1) bacterially-mediated 

fermentation of lignitic material, and (2} 

bacterially-mediated methanogenesis. 

SALTWATER 

By Harold Meisler 

The saltwater-freshwater transition zone is 

characterized by increases in concentrations of 

chloride with increasing depth. Also, concentrations of calcium, magnesium, sodium, potassium, 

0 

0 

10 20 30 40 50 60 

a: 

w 

..... 

~ 

a: 

w 

0.. 

en 

w 

...J 

0 

::!\: 

~ 

...J 

~ 

~ 

z 

w 

(!:I 

> 

~ 

c 

w 

~ 0 

en 

en 

c 

DISTANCE ALONG FLOW PATH IN MILES 

0.1 

0 

0 10 20 30 40 50 

DISTANCE ALONG FLOW PATH IN MILES 

Figure 120.-Concentrations of dissolved silica and dissolved oxygen of the A quia 

aquifer water plotted against distance along a flow path in southern Maryland. 
and sulfate generally increase as concentrations 

of chloride increase. Bicarbonate, on the other 

hand, tends to decrease as concentrations of 

chl9ride increase (Meisler, and others, 1984). 

The relation of concentrations of these ions 

to concentrations of chloride indicates that the 

saltwater-freshwater transition zone in North 

Carolina is primarily a mixture of seawater and 

fresh sodium bicarbonate water. In the area from 

Virginia to New Jersey, the transition zone appearsto be largely a mixture of sodium-calcium 

chloride brine and fresh sodium bicarbonate 

water. The brine has concentrations of chloride 

several times higher than that of seawater. It differs significantly from seawater, also, in having 

higher concentrations of calcium and sodium and 

lower concentrations of potassium, sulfate, and 

bicarbonate. A comparison of the equivalent fractions of the principal cations of the most concentrated ground-water samples (Meisler, and others, 

1984, table 2) with seawater indicates that, proportionately, the brine has significantly more 

calcium and less magnesium and potassium than 

does seawater. The occurrence of a similar brine 

beneath the transition zone in North Carolina is 

indicated by interpretation of geophysical logs 

(Meisler, 1981) and by chemical analyses of water 

samples taken from depths of greater than 6,000 

feet from a well at Cape Hatteras. (Meisler, and 

others, 1984). 

10.5 r------r------r------.------.-------r------, 

a: 

w 

1-

::::i 

9.0 

ffi 7.5 D.. 

rn 

w 

..J 

0 

::!: 

::::i 

...J 

~ 6.0 

~ 

z~ 

0 

~ a: 

t-

~ 4.5 

u 

z 

0 

u 

w 

~ z 

g 3.0 

a: 

tS 

iii 

0 0 

0 0 

0 

0.8 1.6 2.4 3.2 4.0 4.8 

CALCIUM PLUS MAGNESIUM, IN MILLIMOLES PER LITER 

Figure 121.-Calcium plus magnesium concentrations plotted against bicarbonate concentrations 

for analyses of water taken from the Castle Hayne aquifer in North Carolina. · 

191 
192 

z 

0 

i= 

c;; 

-15r-----------r-r---------.-------.---.-----------.---------~~--------~ 

Region I 

I 

ctl 

Region II Region Ill 

2 -10 ~ 

~I a. 

~I 8 

w 

D.. 

~ ~ 

z 

0 

m 

cr: 

() 

w 

...J 

m 

~ UJ 

::::l 

~I ..c 

~I 0 

..... 

]I 

Q) 

~I ·x 

~I -5 

a. <(I 

I 

I 

I 

0 Measured stable carbon isotope composition value of Aquia water 

6 Stable carbon isotope composition value of Aquia water as calculated 

using equation A3.1 (Plummer and others, 1983, p. 685) 

10 20 30 40 50 60 

DISTANCE ALONG A FLOWPATH, IN MILES 

Figure 122.-Measured and calculated values of stable carbon isotope composition plotted against distance along a flow 

path for water taken from the Aquia aquifer in southern Maryland. 

The origin of brines in the Atlantic Coastal 

Plain is not well understood. Two possible sources 

are: (1) leaching of evaporitic strata, and (2) concentration of dissolved solids through membrane 

filtration. Graf(1982) discusses three of the most 

important mechanisms in the development of the 

overpressured zones in aquifers, that are needed 

to drive membrane filtration. One of these, tectonic compression, is not applicable to the northern Atlantic Coastal Plain. A second mechanism, 

abnormally high geothermal gradients, appears 

to be ruled out by the geothermal data available. 

The third mechanism, rapid accumulation of finegrained sediments, has been evaluated by 

Bredehoeft and Hanshaw (1968, p. 1097); they 

concluded that "a sedimentation rate of 500 m 

[1640 ft] per 1 million years (reasonable for the 

Gulf Coast) will create fluid pressures approaching lithostatic***." In the northern Atlantic Coastal Plain, however, sedimentation rates 

have generally been 80 to 160 feet per 1 million 

years in the outer Continental Shelf and considerably lower on the emerged Coastal Plain. 

Head measurements in the Atlantic Coastal Plain 

wells and reported pressures in several offshore 

oil-test wells do not indicate excess fluid 

pressures. Any excess pressure generated has probably been dissipated laterally. 

Manheim and Horn (1968, p. 229-233), in 

their discussion of the origin of the Atlantic 

Coastal Plain brines conclude that leaching of 

evaporitic strata along with updip movement of 

the brine accounts for the present distribution of 

highly saline water. Indeed, drilling and 

geophysical data (Hathaway and others, 1979, p. 

529) have indicated the presence of evaporitic 

strata beneath the Continental Shelf and Slope. 

PUBLISHED REPORTS 

Abstracts 

1. Harsh, J. F., and Laczniak, R. J., 1983, Finitedifference model of ground-water flow in the 

northern Atlantic Coastal Plain of Virginia 

and adjoining states: Geological Society of 

America Abstracts with Programs 1983, 

96th Annual meeting v. 15, no. 6, p. 592. 

2. Leahy, P. P., and Meisler, Harold, 1982, An 

analysis of the distribution of fresh and 
saline ground water in the New Jersey 

Coastal Plain and Continental Shelf: 

American Geophysical Union EOS Transactions, v. 63, no. 18, p. 322. 

3. Martin, M. M., and Leahy, P. P., 1983, Conceptualization and simulation of groundwater flow in the New Jersey Coastal Plain: 

American Geophysical Union EOS Transactions, v. 64, no. 18, p. 224. 

4. Meisler, Harold, Leahy, P. P., and Trapp, 

Henry, Jr., 1981, Simulation of the multiple aquifer system of the northern Atlantic 

Coastal Plain, North Carolina to New York: 

Geological Society of America Abstracts 

with Programs 1981, 94th Annual meeting 

v. 13,no. 7,p. 509. 

5. Meng, A. A., III, and Harsh, J. F., 1983, The 

hydrogeologic framework of the northern 

Atlantic Coastal Plain of Virginia: 

Geological Society of America Abstracts 

with Programs 1983, 96th Annual meeting, 

v. 15, no. 6, p. 642. 

Reports 

1. Chapelle, F. H., and Knobel, L. L., 1983, 

Aqueous geochemistry and the exchangeable cation composition of glauconite 

in the A quia aquifer, Mary land: Ground 

Water, v. 21, no. 3, p. 343-352. 

2. Knobel, L. L., and Leahy, P. P., 1981, 

DUROV, a FORTRAN program for plotting 

chemical parameters on a hydrochemical 

facies diagram: U.S. Geological Survey 

Water Resources Division Bulletin, Oct.-

Dec., p. 34-41. 

3. Leahy, P. P., 1982, A three-dimensional 

ground-water flow model modified to reduce 

computer-memory requirements and better 

simulate confining-bed and aquifer pinchouts: U.S. Geological Survey WaterResources Investigations Report 82-4023, 

59 p. 

4. Meisler, Harold, 1980, Plan of study for the 

northern Atlantic Coastal Plain regional 

aquifer system analysis: U.S. Geological 

Survey Water-Resources Investigations 

Report 80-16, 27 p. 

5. -----1981, Preliminary delineation of 

salty ground water in the northern Atlantic Coastal Plain: U.S. Geological Survey 

Water-Resources Investigations Report 

81-71, 25 p. 

6. Meisler, Harold, Leahy, P. P., and Knobel, L. 

L., 1984, Effect of eustatic sea-level changes 

on saltwater-freshwater relations in the 

northern Atlantic Coastal Plain: U.S. 

Geological Survey Water-Supply Paper 

2255, 28 p. 

7. Meng, A. A., III, and Harsh, J. F., 1984, 

Hydrogeologic framework of the Virginia 

Coastal Plain: U.S. Geological Survey OpenFile Report 84-728, 78 p. 

8. Trapp, Henry, Jr., Knobel, L. L., Meisler, 

Harold and Leahy, P. P., 1984, Test well DOCE 88 at Cambridge, Dorchester County, 

Maryland: U.S. Geological Survey WaterSupply Paper 2229, 48 p. 

9. Zapecza, 0. S., 1984, Hydrogeologic 

framework of the New Jersey Coastal Plain: 

U.S. Geological Survey Open-File Report 

84-730, 61 p. 

REFERENCES CITED 

Back, William, 1966, Hydrochemical facies and ground-water 

flow patterns in the northern part of Atlantic Coastal 

Plain: U.S. Geological Survey Professional Paper 498-A, 

42 p. 

Bredehoeft, J. D., and Hanshaw, B. B., 1968, On the 

maintenance of anomalous pressures: I, Thick sedimentary sequences: Geological Society of America Bulletin, 

v. 79, p. 1097-1106. 

Brown, P.M., Miller, J. A., and Swain, F. M., 1972, Structural and stratigraphic framework, and spatial distribution of permeability of the Atlantic Coastal Plain, North 

Carolina to New York: U.S. Geological Survey Professional Paper 796, 79 p. 

Chapelle, F. H., 1983, Groundwater geochemistry and calcite 

cementation of the Aquia aquifer in southern Maryland: 

Water Resources Research, v. 19, no. 2, p. 545-558. 

-----1984, The occurrence of dissolved oxygen and the 

origin of ferric-hydroxide cemented hardbeds in the 

Patuxent aquifer, Maryland, in Canadian-American 

Conference of Practical Applications of Ground-Water 

Geochemistry: Alberta Research Council and National 

Water Well Association Meeting, Banff, Canada, June 

22-26, Proceedings. 

Chapelle, F. H. and Knobel, L. L., 1983, Aqueous geochemistry 

and the exchangeable cation composition of glauconite 

in the Aquia aquifer, Maryland: Ground Water, v. 21, 

no. 3, p. 343-352. 

Cushing, E. M., Kantrowitz, I. H., and Taylor, K. R., 1973, 

Water resources of the Delmarva Peninsula: U.S. 

Geological Survey Professional Paper 822, 58 p. 

Faust, S. D., and Aly, 0. M., 1981, Chemistry of natural 

waters: Ann Arbor Science Publishers, Inc., Ann Arbor, MI, 400 p. 

Foster, M. D., 1950, The origin of high sodium bicarbonate 

waters in the Atlantic and Gulf Coastal Plains: 

Geochimica et Cosmochimica Acta, v. 1, p. 33-48. 

Graf, D. L., 1982, Chemical osmosis, reverse chemical osmosis, 

and the origin of subsurface brines: Geochimica et 

Cosmochimica Acta, v. 46, no. 8, p. 1431-1448. 

Hansen, H. J., 1982, Part one, Hydrogeologic framework and 

potential utilization of the brine aquifers of the Waste 

Gate Formation, a new unit of the Potomac Group 

underlying the Delmarva Peninsula, in Hansen, H. J., 

and Doyle, J. A., Waste Gate Formation, Maryland 

Department of Natural Resources Geological Survey 

Open-File Report, p. 1-50. 

193 
194 

Hathaway, J. C., and others, 1979, U.S. Geological Survey core 

drilling on the Atlantic shelf: Science, v. 206, no. 4418, 

p. 515-527. 

Leahy, P. P., 1982, A three-dimensional ground-water-flow 

model modified to reduce computer-memory requirements and better simulate confining-bed and 

aquifer pinchouts: U.S. Geological Survey WaterResources Investigations Report 82-4023, 

59 p. 

Manheim, F. T., and Horn, M. K., 1968, Composition of deeper 

subsurface waters along the Atlantic Continental 

Margin: Southeastern Geology, v. 9, no. 4, p. 215-236. 

Meisler, Harold, 1980, Plan of study for the northern Atlantic Coastal Plain regional aquifer system analysis: U.S. 

Geological Survey Water-Resources Investigations 

Report 80-16, 27 p. 

----1981, Preliminary delineation of salty ground water 

in the northern Atlantic Coastal Plain: U.S. Geological 

Survey Open-File Report 81-71, 25 p. 

Meisler, Harold, Leahy, P. P., and Knobel, L. L., 1984, Effect 

of eustatic sea-level changes on saltwater-freshwater 

relations in the northern Atlantic Coastal Plain: U.S. 

Geological Survey Water-Supply Paper 2255, 28 p. 

Plummer, L. N., Parkhurst, D. L., and Thornstenson, D. C., 

1983, Development of reaction models for ground-water 

systems: Geochimica et Cosmochimica Acta, v. 4 7, 

p. 665-686. 

Winograd, I. J., and Farlekas, G. M., 1974, Problems in 

carbon-14 dating of water from aquifers of deltaic origin, 

an example from the New Jersey Coastal Plain, in 

Isotope Techniques in Groundwater Hydrology 1974, 

v. II, IAEA, Vienna, p. 69-93. 

Wolff, R. G., 1967, X-ray and chemical study of weathering 

glauconite: American Mineralogist, v. 52, p. 1129-1138. 
ACTEVE PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

OAHU ISLAND REGIONAL AQUIFER-SYSTEM STUDY, HAWAII 

By Charles J. Ewart, Honolulu, Hawaii 

INTRODUCTION 

Several recent studies have concluded that 

the ground-water resource of the Island of Oahu 

will be near maximum development by the year 

2000. Estimates of the long-term potential of 

ground-water development of the Oahu regional 

aquifer system range between 480 and 635 

Mgal/d. In 1980, the ground-water withdrawal 

rate was about 400 Mgal/d, which is 85 percent 

of the island's total water use. Development of 

this magnitude unquestionably imposes substantial stresses on the aquifer system. To establish 

background information and to evaluate the i~­

pact of the potential development, a study of the 

Oahu regional aquifer system was started in 1982 

and is scheduled for completion in 1986. 

The Island of Oahu has a land area of 604 mi2 

and was formed through the building and subsequent coalescence of two shield volcanoes, the 

Waianae and Koolau Volcanoes (fig. 123). The 

Waianae Volcano forms the western part of Oahu, 

with the Koolau Volcano making up the eastern 

part. A long period of quiescence followed the initial mountain-building phase. During the 

quiescence, both volcanoes were deeply eroded. 

The Waianae Volcano, which is older, became dormant first, thus allowing the westward dipping 

flows of the Koolau Volcano to overlap the erodea surface of the Waianae Volcano in the central 

part of the island. 

Volcanic activity resumed at the southeastern 

end of the Koolau Range after a long erosional 

period. This renewed activity produced the rocks 

of the Honolulu Volcanic Series. These rocks are 

confined to relatively small scattered areas. 

Because the lava flows tended to be ponded in 

deep valleys, and in general are very dense and 

of low permeability, they do not constitute an important aquifer. The bulk of the Koolau Volcano 

consists of thin-bedded, highly permeable basaltic 

lava flows. An andesitic veneer is common to most 

Hawaiian volcanoes, but is absent in the Koolau 

rock mass. In contrast, much of the Waianae 

range has the andesite veneer, making the surficial lavas somewhat less permeable than those 

of the Koolau rock mass. 

Isostatic adjustment resulted in the subsidence of Oahu to a significant depth, thus 

submerging permeable lava flows originally extruded subaerially, and placing them in hydraulic 

contact with the surrounding ocean water. Shifts 

in sea level and erosion· allowed deposits of 

marine and terrestrial sediments to accumulate 

behind barrier reefs, forming coastal plains in 

some areas (fig. 124). The most prominent example of this on Oahu is the southern Oahu 

coastal plain (fig. 123). 

Due to the complexity of the volcanic rocks, 

a local terminology has developed in Hawaii to 

describe the occurrence of ground water. A body 

of ground water floating on and in hydrodynamic 

equilibrium with saltwater is termed "basal 

ground water" or "basal water" in Hawaii. 

Ground water stored in lavas between low 

permeability intrusion dikes is termed "dikeimpounded ground water." In areas where water 

levels are much higher than the expected basal 

water table but the geological reason for this occurrence is unknown (ground water is impeded 

by low permeability dikes, ash beds, or other low 

permeability rocks), the ground water is referred 

to as "high-level ground water." The dikeimpounded or high-level ground water eventually 

seeps through or over the low permeability dikes 

195 
196 

or barriers and discharges into a basal groundwater body, as shown in figure 125, or leaks to 

streams in valleys that have cut deep into the 

aquifer. In places, perched ground water also occurs. The perched water is an unconfined ground 

water separated from an underlying basal water 

21° 

45 ' 

21 ° 

30' 

21° 

15' 

158° 15' 

0 

0 

158°00' 

rl t 

SCALE 1:500,000 

10 

10 20 KILOMETERS 

20 MILES 

body by an unsaturated zone due to the presence 

of ash beds or other low permeability materials 

overlying the basal water body (fig. 125). The 

Oahu regional aquifer system is divided into 

several aquifers using the technical terms 

discussed above. 

157° 45' 

0 OKAUAI 

NIIHAU 

OAH~ MOLOKAI 

c:::::::::::J~MAUI LANAI'Q 0 

~ 

KAHOOLAWE 

50 

HAWAII~ 100 150MILES v 0 50 100 150 KILOMETERS 

Main 

fissure 

EXPLANATION 

w %iml CALDERA 

RIFT ZONE 

Figure 123.-Rift zones and calderas of Koolau and Waianae Volcanoes on the Island of Oahu, Hawaii (modified from 

Macdonald, 1972). 
PROGRESS AND RESULTS 

An annotated bibliography has been comiled. Compilation of a hydrologic data base for all 

aquifers is virtually completed. From available 

data, interpretation of information on hydrology 

and hydraulics of three of the ten identified 

aquifers (fig. 126) has been completed. Because 

all the aquifers are interrelated to some extent, 

the ten identified aquifers are grouped into five 

areas for simulation purposes. They are: 

1. Southeast basal water body (southeast 

area). 

2. Honolulu-Pearl Harbor basal water body 

(southern area). 

3. Koolau dike-impounded water body and 

the northeast basal water body (windward area). 

4. Kawailoa, Waialua, and Mokuleia basal 

water bodies (north-central area). 

5. Waianae dike-impounded and basal water 

bodies (Waianae area). 

The Schofield high-level water body is tributary to the southern and the north-central 

areas. Therefore, the Schofield high-level water 

body is included in the simulation of both the 

southern and the north-central areas. 

The ground-water flow model selected for 

aquifer evalu.ation is AQUIFEM as described by 

Pinder and Voss (1979), and modified by Voss 

(1984a) as AQUIFEM-SALT. The modified code 

simulates an aquifer containing a freshwater 

body that freely floats on seawater. The flow 

model will be used to simulate each of the five 

areas outlined above. The southeast area was the 

first area selected for simulation. This area comprises the leeward (south) side of Oahu's eastern 

end, and the aquifer consists principally of thinbedded, gently dipping and highly permeable lava 

flows from the Koolau Volcano. The aquifer is 

bounded on the north and.west by near-vertical 

volcanic dikes of low permeability, and on the 

south and east by the Pacific Ocean and Koko 

volcanics (fig. 127). 

Recharge to the southeast basal water body 

is greatest near the crest of the Koolau Range, 

and water flows principally from north to south, 

generally along the direction of the lava flows. 

Natural discharge from the southeast basal water 

body occurs as diffuse leakage upward through 

the coastal sediments along the southern coast. 

A northeast-trending dike zone internally 

divides the southeast basal water body into the 

Waialae aquifer on the west and the WailupeHawaii-Kai aquifer on the east (fig. 127). 

Recharge to these aquifers of 6 and 9 Mgal/d, 

respectively, has created 2 freshwater lenses that 

"float" on underlying seawater. In the W aialae 

· aquifer area, rainfall is greater than in the 

neighboring Wailupe-Hawaii-Kai aquifer area, 

and the poorly permeable coastal sediments are 

thicker, thus impeding the coastal discharge of 

ground water. The greater rainfall and thick low 

permeability coastal sediments cause freshwater 

heads in the W aialae aquifer to be 9 to 15 feet 

above sea level. Lesser rainfall and thinner low 

permeability coastal sediments allowing easier 

discharge to the sea result in freshwater heads 

of 1 to 5 feet above sea level in the W ailupeHawaii-Kai aquifer. The Koko volcanics (fig. 127) 

are posterosional volcanics that lie seaward of the 

Caldera 

-- ANDESITES, primary 

Dikes 

.._ ______ Uneroded state ------..-~~------ Eroded state -------~ 

Figure 124.-Geologic structure of an idealized Hawaiian volcano dome (from Cox, 1954}. 

197 
198 

former shoreline, and consist of tuff and recent 

lavas underlain by coralline material. Ground 

water in the Koko volcanics is probably not 

hydraulically connected with the southeast basal 

water body and the water in the volcanics is not 

potable (Takasaki and Mink, 1982). Therefore, the 

Koko volcanics are not included in the simulation 

of the southeast area. 

Ground-water flow was simulated by using 

a finite-element mesh constructed for the 

discretization of the aquifer. Average annual 

recharge was determined for each element by use 

of a water balance approach (Thornthwaite and 

Mather, 1955). The model simulates head changes 

only in the freshwater flow field. The base of the 

freshwater aquifer is either a confining unit 

underlying the aquifer or the freshwatersaltwater interface, depending on the position of 

the interface during the time of interest. If the 

simulated freshwater-saltwater interface is below 

the confining unit underlying the aquifer, then 

the aquifer base is the confining unit; otherwise, 

the aquifer-base boundary is the freshwatersaltwater interface. The position of the 

freshwater-saltwater interface is determined by 

assuming static equilibrium between the 

freshwater and saltwater. Data from several wells 

provided a general distribution of heads. Because 

most of the historic head data were obtained after 

development began in 1899, the predevelopment 

heads were estimated by calibrating the model by 

matching the simulated head to observed head 

data after development and then "turning off' the 

simulated pumpage and allowing the simulation 

to continue until the heads recovered to an 

equilibrium condition . The simulated and 

observed head data match closely, as shown in 

table 4. The simulated predevelopment potentiometric surface for the southeast basal water 

body is shown in figure 128. 

Because of the assumptions used in the 

model-namely, a sharp interface between the 

freshwater and saltwater, no vertical movement, 

and a constant saltwater head in the aquiferthis model cannot be used to analyze the movement of a freshwater lens. However, it is appropriate for long-term analysis of the aquifer 

system regionally. 

The model selected to evaluate the movement of a freshwater lens is SUTRA CV oss, l984b). 

SUTRA is a finite-element simulation model for 

saturated-unsaturated fluid density-dependent 

/ Perched spring 

-----·"" 

Figure 125. -Occurrence of ground water in the Oahu regional aquifer system, Hawaii (modified from Stearns and 

Macdonald, 1946). 
ground-water flow with energy or solute 

transport. The principal objective of using 

SUTRA is to gain an understanding of the 

dynamics of the freshwater and saltwater movement. Of particular interest is the size and movement of the transition zone between freshwater 

and saltwater in response to natural and maninduced stresses on the aquifer system. 

The most heavily developed aquifer in Hawaii 

is the Honolulu-Pearl Harbor basal water body. 

This aquifer consists of thin-bedded overlapping 

21" 

45' 

21. 

30' 

21° 

15' 

158"15' 

WAIANAE 

BASAL WATER 

BODY---" 

0 

0 

SCALE 1:500,000 

10 

10 

158" 00' 

20MILES 

20 KILOMETERS 

Koolau lava flows, with generally higher horizontal permeability. A thick freshwater lens has been 

formed because ground-water discharge to the 

ocean is inhibited by a thick wedge of poorly 

permeable coastal sediments, locally termed 

"caprock." Along the base of the lens, the 

freshwater and saltwater are separated by a transition zone of variable thickness (fig. 129). 

Natural discharge from the Honolulu-Pearl 

Harbor basal water body is by upward leakage 

through the caprock and through springs that 

157" 45' 

t:J OKAUAI 

NIIHAU 

OAH~ MOLOKAI 

c:;:~MAUI LANAI u ..:\._..) 

0 

KAHOOLAWE 

50 

HAWAII~ 100 150MILES v 0 50 100 150 KILOMETERS 

Figure 126.-Ten identified aquifers underlying the Island of Oahu, Hawaii (modified from Dale and Takasaki, 1976). 

199 
200 

21 ' 

20 ' 

157' 45' 

0 

0 

EXPLANATION 

MODEL AREA 

DIKE ZONE 

2 

0 

L 

SCALE 1:125,000 

2 

3 4 

157' 40' 

10 20 MILES 

10 20 KILOMETERS 

3 4 

5 KILOMETERS 

Figure 127.- Finite-element mesh for the southeast basal water body, Oahu, Hawaii. 

5 MILES 

Table 4.-Simulated and observed heads in southeast basal water body, Oahu, Hawaii, in feet above sea level 

Node 

number 41 45 62 76 78 144 163 206 237 277 316 317 

Observed 

head 9.6 11.5 10.6 8.5 9.5 2.7 3.7 2 2 3.7 0.81 1. 3 2.2 

Simulated 

head 9.7 11 2 10.4 8.2 10.2 2.8 3.8 2.4 3.8 0.40 1.4 2.4 
originate near the contact between basalt and 

caprock. In order to assess the applicability of the 

SUTRA model to the Honolulu-Pearl Harbor 

basal water body, the flow of freshwater and 

saltwater was simulated for a generalized cross 

section. Initial hydrologic parameter values for 

21 . 

20 ' 

157'45' 

0 

the Honolulu-Pearl Harbor basal water body were 

those determined by other investigators. A finiteelement mesh of rectangular elements of variable 

size was constructed to represent the aquifer 

system (fig. 130). Constant freshwater recharge 

was put into nodes at the top part of the upstream 

157• 40' 

OAHU 

10 20 MILES 

SCALE 1:125,000 

2 3 4 5 MILES 

2 3 4 5 KILOMETERS 

EXPLANATION 

MODEL AREA 

(<.> <: >" • ..... < ..... ,., 

"'., ~.., "'.~" "., r DIKE ZONE 

POINTS OF GROUND-WATER OBSERVATION AND NODE NUMBER 

--4- POTENTIOMETRIC CONTOUR-- Shows altitude of potentiometric 

surface. Contour interval1 foot. Datum is sea level 

Figure 128.-Simulated potentiometric surface for the southeast basal water body, Oahu, Hawaii, prior to development. 

201 
202 

boundary (constant flux) while the bottom part of 

the same upstream boundary was assumed to be 

a no-flow boundary. The downstream seawater 

boundary is a specified-pressure boundary which 

is equivalent to the depth of the sea at the respective position. A regional ground-water discharge 

North 

of 20 Mgal/d per mile of coastline was used for the 

steady-state simulation. The simulated contours 

of seawater percentage for the steady-state, and 

transient conditions, are shown in figure 131 

which seem to be consistent with the observed 

data. 

South 

Figure 129.-Generalized section of Honolulu-Pearl Harbor basal water body, Oahu, Hawaii. 

Recharge area SPECIFIED-PRESSURE NODES Coastal discharge area 

(/) p~l~mG 

w 

0 

0 

z CAPROCK X 

::::> 

....J 

lL 

~ 

z 

<( 

f--

(/) 

z 

0 

(/) 

w 

0 

0 

z 

a: u w 

1-

<( 

~ J: 

CJ) 

w 

a: 

1.1.. >-

a: 

0 

z 

::::> 

BASALT 

w 

a: a: ::::> w (/) 1- (/) <( w 

a: 

a.. ~ <( 0 w w CJ) lL 

u 

w 

a.. 

(/) 

0 

CD 

s 

0 

....J 

lL 

6 

z 

5( eat 

i 

fil 

1 

j j 

1--- 4000 feet ~ § 

N ~ lo-----< 1+-o 

Figure 130.-Finite-element mesh for cross sectional simulation of the Honolulu-Pearl Harbor basal water body, Oahu, Hawaii. 
During the transient simulation, a cyclic 

pumping stress was applied to the steady-state 

condition. Pumping was assumed to withdraw 

150 percent of the estimated regional groundwater discharge (30 Mgal/d per mile of coastline) 

for 6 months, followed by 6 months of recovery. 

This cyclic pumping schedule roughly corresponds 

to that of the agricultural industry water use (the 

largest water users) in southern Oahu. During the 

simulated 65 years of cyclic pumping, the 

freshwater lens shrank considerably, and the 

freshwater-saltwater transition zone moved landward and upward to a significant degree (fig. 131). 

The SUTRA finite-element model was successfully used to simulate the flow of fresh and 

saline ground water. The initial phase of testing 

300 

1500 

>- 0:: 

< 0 

z 

::::::> 

0 

aJ 

....J 

~ L1. 

z 

FRESHWATER 

BASALT 

for suitability of the model is completed. Extensive use of the model is underway to better 

understand the interrelation of the aquifer 

parameters. 

The first phase of using SUTRA model did 

not fully utilize the transport aspect of the model, 

except to demonstrate that the general nature of 

a freshwater lens and the freshwater-saltwater 

transition zone could be reproduced. The next 

phase of using SUTRA will be to investigate the 

nature of the freshwater-saltwater transition zone 

and its movement in relation to; (1) boundary conditions, (2) long- and short-term stresses, (3) 

values of dispersivity, (4) sea-level changes, (5) 

movement of sea-water, and (6) other aquifer 

characteristics. 

SALTWATER 

12,000 16,000 20,000 24,000 28,000 

HORIZONTAL DISTANCE, IN FEET FROM INFLOW BOUNDARY 

EXPLANATION 

DIAGONAL LINE REPRESENTS CONTACT BETWEEN 

BASALT AND CAPROCK 

_ 10 _ STEADY-STATE CONTOUR-- Contours in percent 

seawater. Interval is 10 percent 

__ 10_ _ TRANSIENT CONTOUR-- Contours in percent 

seawater. Interval is 10 percent 

Pumping stress applied at location labeled "pumping center". 

Transient contours shown after 65 years of cyclic pumping 

at a rate of 30 million gallons per day for 6-month pumping 

and 6-month recovery 

32,000 36,000 

Figure 131.-Simulated contours of seawater percentage for steady-state and transient conditions, the HonoluluPearl Harbor basal water body, Oahu, Hawaii. 

203 
204 

REFERENCES CITED 

Cox, D. C., 1954, Water development for Hawaiian sugarcane 

irrigation: The Hawaiian Planters' Record, v. 54, 

p. 175-197. 

Dale, R. H., and Takasaki, K. J., 1976, Probable effects of increasing pumpage from the Schofield ground-water 

body, Island of Oahu, Hawaii: U.S. Geological Survey 

Water-Resources Investigations Report 76-47, 45 p. 

Macdonald, G. A., 1972, Volcanoes: Englewood Cliffs, New 

Jersey, Prentice-Hall Inc., 510 p. 

Pinder, G. F., and Voss, C. 1., 1979, AQUIFEM, a finiteelement model for aquifer evaluation (documentation): 

Department of Water Resources Engineering, Royal Institute of Technology, Stockholm, Sweden, Report 7911; 

TRITAVAT - 3806, 107 p. 

Stearns, H. T., and Macdonald, G. A., 1946, Geology and 

ground-water resources ofthe Island of Hawaii: Hawaii 

Division Hydrography Bulletin 9, 363 p. 

Takasaki, K. J., and Mink, J. F., 1982, Water resources of 

southeastern Oahu, Hawaii: U.S. Geological Survey 

Water-Resources Investigations Report 82-628, 89 p. 

Thornthwaite, C. W. and Mather, J. R., 1955, The water 

balance: Publications in climatology, Laboratory of 

Climatology, v. 8, no. 1, 104 p. 

Voss, C. I., 1984a, AQUIFEM-SALT, a finite-element mod~l 

for aquifers containing a seawater interface:· U.S. 

Geological Survey Water-Resources Investigations 

Report 84-4263, 37 p. 

-----1984b, SUTRA, a finite-element simulation model 

for saturated-unsaturated, fluid-density-dependent 

ground-water flow with energy transport or chemicallyreactive single-species solute transport: U.S. Geological 

Survey Water-Resources Investigations Report 84-4369, 

409 p. 
ACTIVE PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

SOUTHEASTERN COASTAL PLAIN REGIONAL AQUIFER-SYSTEM STUDY 

By Robert L. Wait, Robert A. Renken, Rene A. Barker, Roger W. Lee 

and Virginia Stricker, Atlanta, Georgia 

INTRODUCTION 

Clastic sediments of Cretaceous and Tertiary 

age in South Carolina, Georgia, Alabama, 

Mississippi, and adjacent areas of northern 

Florida and southwestern North Carolina comprise a major aquifer system that underlies an 

area of about 130,000 mi2 and is informally called 

the Southeastern Coastal Plain aquifer system. 

This aquifer system extends from the 

southwestern flank of the Cape Fear arch in 

North Carolina into the Mississippi embayment 

in northern Mississippi (fig. 132). The 

Southeastern Coastal Plain aquifer system is 

located between three adjacent regional aquifer 

systems: the Northern Atlantic Coastal Plain to 

the northeast; the Floridan aquifer system to the 

south and southeast; and the Gulf Coastal Plain 

to the west. 

No previous hydrologic studies have considered the Southeastern Coastal Plain aquifer 

system as a single system. The solutions to problems such as multicounty declines in water levels 

or the degradation of ground-water supplies due 

to saltwater encroachment need to be examined 

regionally. One of the merits of the regional 

investigation is that a comprehensive view is obtained of the whole system, rather than only a 

small part of it. The Southeastern Coastal Plain 

regional aquifer system study was started in 1979 

and is scheduled for completion in 1986. 

For the most part, this study is based on information from previous studies. However, some 

additional data were collected to fill major gaps 

in information. For example, three test wells were 

drilled between 1980 and 1983 (one in western 

Alabama; one each in central and eastern South 

Carolina) to fill voids in the data. In addition, a 

four-State mass measurement of water levels was 

made in 1982 to evaluate the decline of water 

levels in different hydrogeologic units. Water 

samples were collected from 105 wells over the 

four-State area and were filtered and measured 

for pH, conductivity, temperature, trace metals, 

stable and radioactive isotopes, nutrients, and 

dissolved gases. 

The clastic sediments that comprise the 

Southeastern Coastal Plain regional aquifer 

system have been grouped into seven major 

hydrogeologic units; some of these are highly 

interconnected with the interfingering and partially over lying carbonate rocks of the Floridan 

aquifer system. The composition, texture, and 

bedding character of the major hydrogeologic 

units vary considerably from place to place. Sand 

aquifers of this system are massive to thinly bedded, fine to coarse grained, quartzose, and 

feldspathic, with minor amounts of glauconitic 

sand, sandstone, gravel, and occasional limestone 

beds. Chalk, clay, shale, and mudstone form the 

confining units that separate the major aquifers. 

Rainfall ranges from 44 to 64 inches in the 

study area. Most of the rainfall that enters this 

clastic system is discharged to nearby streams 

and rivers. In outcrop areas, the predominant flow 

is downward or upward near streams. However, 

in middip and downdip areas where the major 

aquifers are confined by thick clay, chalk, and 

shale, the predominant flow direction is 

horizontal. 

205 
206 

The average hydrologic conditions in the 

study area can be summarized as follows: 

• precipitation is approximately 50 in./yr, 

• overland runoff is approximately 7 in./yr, 

• evapotranspiration is approximately 

35 in./yr, and 

• recharge to the aquifer system is 

approximately 8 in./yr. 

Most of this recharge eventually discharges 

into streams or rivers as base flow through 

shallow, local scale aquifers; however, a small 

amount, about 1 in./yr, recharges downward into the deeper aquifers. This deep recharge eventually discharges either into streams or rivers as 

base flow or discharges upward through confining units into overlying aquifers. This conceptualized recharge pattern has been demonstrated 

to be reasonable by preliminary simulations as 

discussed later. 

Five geochemical zones have been identified 

for ground water flowing from recharge areas into the deeper parts of the system. The quality of 

the ground water has been adversely affected 

locally by heavy pumping which has caused an 

increase in concentrations of dissolved solids in 

several areas. Similarly, high concentrations of 

dissolved solids near major streams in central 

Alabama may be associated with potentiometric 

lows caused by natural ground-water discharges 

there. 

REGIONAL GEOLOGIC SETTING 

Coastal Plain sediments in the southeastern 

United States form a thick wedge of unconsolidated to poorly consolidated clastic and carbonate rocks of Jurassic to Holocene age. They are 

underlain in most places by relatively impervious 

metamorphic, sedimentary, and igneous rocks of 

Paleozoic and early Mesozoic age that are, in part, 

a southeastern extension of the Piedmont Province. In other places, they are underlain by 

sedimentary rocks of Paleozoic age which are a 

southwestern extension of the Appalachian 

Mountains. These rocks form the base of the 

Atlantic Coastal Plain. 

Except where they are covered by younger 

strata, the aquifers and confining units that comprise the Southeastern Coastal Plain regional 

aquifer system crop out in adjacent bands from 

Mississippi to South Carolina (fig. 133). These 

units extend seaward from the inner Coastal 

Plain margin to the Atlantic Ocean, Gulf of Mexico, or Peninsular Florida. 

The Coastal Plain sediments of the 

southeastern United States are the product of 

cyclical advance and retreat of ancient seas over 

the Paleozoic-Mesozoic basement complex during 

Jurassic to Holocene time and were deposited 

under marine, marginal marine, and nonmarine 

conditions. The fluctuating depositional conditions, resulting from an ever-shifting shoreline, 

caused the lithology-and, therefore, the 

hydraulic conductivity-of these sediments to differ greatly from place to place. The variation of 

hydraulic conductivity significantly affects the occurrence and flow of ground water within the 

Southeastern Coastal Plain. Consequently, the 

texture, bedding character, and composition of the 

aquifers and confining units greatly control the 

regional ground-water movement. 

Clastic Tertiary and Cretaceous aquifers are 

the focus of this investigation; however, ·in 

Florida, southern Georgia, southern Alabama, 

and southwest South Carolina, the Southeastern 

Coastal Plain aquifer system is partly over lain 

by, and is hydraulically connected to, highly 

permeable carbonate rocks of the Floridan aquifer 

system. The limestone units that comprise the 

Floridan aquifer system generally grade into or 

interfinger with the clastic rocks that compose the 

Southeastern Coastal Plain regional aquifer 

system. Low-permeability rocks of Oligocene to 

Pliocene age make up the upper confining unit 

of the Floridan aquifer system (fig. 133) and are, 

in turn, over lain by a surficial aquifer consisting 

of unconsolidated sand and gravel of Pliocene to 

Holocene age. Aquifers of the Southeastern 

Coastal Plain regional aquifer system consist of 

quartzose, feldspathic, locally glauconitic, coarse 

to fine sand, with minor amounts of gravel and 

limestone; confining unitst that bound and 

separate these aquifers are composed of clay, 

mudstone, shale, marl, and chalk. 

HYDROGEOLOGIC FRAMEWORK 

The Southeastern Coastal Plain regional 

aquifer system consists of interbedded strata 

having wide areal distribution and containing 

numerous aquifers and confining units. The 

aquifers are hydraulically connected in varying 

degrees and can be treated as a single system.· The 

arrangement, distribution,- and. physical attributes of individual aquifers and confming units 

that serve as conduits for the regional groundwater flow constitute the hydrogeologic 

framework. 
85 ' 

TENNESSEE 

35 ' 

Atlantic 

Ocean 

30 ' 

Gulf of Mexico FLORIDA 

SCALE 1:8,000,000 

0 100 200 MILES 

0 100 200 KILOMETERS 

EXPLANATION 

STUDY AREA 

AREA OF OUTCROP OR SHALLOW SUBCROP OF THE 

SOUTHEASTERN COASTAL PLAIN AQUIFER SYSTEM 

• TESTWELLS 

~· LINE OF CROSS SECTION 

Figure 132.- Study area of the Southeastern Coastal Plain regional aquifer system. 

The hydrogeologic framework established for 

this study is designed to evaluate permeability, 

and is therefore unlike sedimentary basin studies 

that usually center on the study of the 

stratigraphic characteristics of the rocks that 

have paleoenvironmental significance. The 

physical limits of an aquifer may locally parallel 

boundaries of a stratigraphic unit defined by 

lithology, time, or mode of deposition; however, 

the limits of a regionally-extensive body of 

hydraulically interconnected permeable rock do 

not always fall within such boundaries. Rocks 

that are stratigraphically equivalent may be an 

aquifer in one location and a confining unit in 

another location. 

Consequently, the hydrogeologic units 

delineated herein cannot be described adequately 

by existing nomenclatural schemes, in part due 

to their regional extent, and in part due to their 

poor correspondence with physical boundaries of 

rock- and time-stratigraphic units. Therefore, the 

hydrogeologic units have been given a provisional 

alphanumeric designation; regional aquifers are 

designated by the letter A, and regional confining 

207 
208 

units by the letter C. A sequential number is 

assigned to each hydrogeologic unit to indicate its 

relative position in the hydrogeologic section. 

Figure 134 shows the relation between rockstratigraphic units and the regional hydrogeologic units. 

Strata that together comprise a regional 

hydrogeologic unit were combined according to: 

TENNESSEE 

35° 

30° 

Gulf of Mexico 

SCALE 1:8,000,000 

(1) their degree of interconnection, (2) the uniformity and continuity of the strata, (3) their overall 

distribution, (4) their ability to be mapped over 

a wide area with definable physical boundaries, 

and (5) hydraulic heads in the strata. Many of the 

local water-yielding units within the regional 

aquifer system have been largely treated as 

discrete aquifers or confining units at the State 

85 ° 

,,---"" 

SOUTH 

CAROLI NA 

Atlantic 

Ocean 

0 100 200 MILES 

0 100 200 KILOMETERS 

SOUTHEASTERN COASTAL PLAIN 

AQUIFER SYSTEM 

~ A1 

C1 

- A2 

C2 

[£] A3 

C3 

- A4 

EXPLANATION 

~22 1 SURFICIALAQUIFER 

0 UPPER CONFINING UNIT 

0 FLORIDAN AQUIFER SYSTEM 

UPDIP LIMIT OF FLORIDAN (MODIFIED ---- FROM MILLER, 1984) 

Figure 133.- Location and outcrop areas of major hydrogeologic units of the Southeastern Coastal Plain regional 

aquifer system. 
or county level. However, several of these discrete 

aquifers and confining units are grouped into 

regional aquifers or confining units if they can 

be shown to behave regionally as a single 

hydrologic unit. 

MISSISSIPPI ALABAMA 

The Southeastern Coastal Plain sediments 

are divided into 7 hydrogeologic units (Renken, 

1984); 4 regional aquifer units, A1 to A4, 

numbered downward, separated by 3 regional 

confining units, C1 to C3 (fig. 134). The uppermost 

GEORGIA SOUTH CAROLINA 

209 

North Centrai·East West East West East South·West North·East 

'• , .... ·::Oo\ i::: )caiahoula sariii"sicine ·•c::.: ........... . 

'. Glendon, Mariari"ria a~d Mint Springs For,;aii~ri~ ' 

< ' Fo~~si Hii1 F=ci~;;;~i;c;~ • •..• ..•. ·.···· · ······ ··.·: .. ·.,• .. .... , •, .. · ... ·;· ···· · .· .. . · .· ·. ·· :·:.·:·.·.:-:·-·.·. ··-:·· """""""" ....... ':' """""""" """"""" Yazoo Formation """""""" 

Ocala Limestone 

::::::::; ~o?k.fv1?.~~~~i ~ .~?r_m.~~~~~;::::::: _G()SI)Ort .sa_nd: :~~~A~v~o~n~P~a~r~k~F~o~r~m~at~i~o~n~~~~~~~ :::::::::::: :sparta S~nd : :::: :::::::: ::Lisbon Formation : l ............... .. . . . . 

::: :: :::::::: .Tallahatta: :: :: :: : :: Formation: :: :: ::::::::: :: :: :: _TaJ.Ia.hatt(l.Fo_rm_ation :: 

: : . M~·rid'i~~ 's~~d ~iember: : : : : : : : : : ~~~:~ ;~:~;~: : : : : : :_:_;_:_T;.;_u.:.;~.c_:_. a;. h~· o_;_, .. :.;.~.;_.~~F:.;.~.;_~m;,; .. _;.~:..;ti_:_~~-~_.:,~:..;. ~;.-.:,._/J?:2:=:::;:~~;.;_.:.,:_;..;_;;,;..;_;.;_;;_:;.;,J~ 

HYDROGEOLOGIC UNITS 

[f:}:f;' j Surficial aquifer 

~ Upper confining unit 

~ Floridan aquifer 

t> ,\ I A1 

f~ ~~ l C1 

[J] A2 

t~~~J C2 

EXPLANATION 

I~ :.< :·1 A3 

~ C3 

f(:Mt:;[j A4 

~ Base of system 

A,C 

IS DELINEATED REGIONAL AQUIFER LAYER OR 

CONFINING LAYER·· Number indicates the 

sequence order numbered downward. A 1, C1 

are also referred to in flow models 

.. 

; ~ ~: ,· 

Figure 134.- Schematic classification of rock-stratigraphic and regional hydrogeologic units of the Southeastern Coastal Plain 

regional aquifer system . 
210 

unit, A1, extends across southwest Alabama and 

southern Mississippi into Louisiana, where it 

becomes part of the Gulf Coastal Plain regional 

aquifer system. Comprised largely of Oligiocene 

and Miocene clastics and minor limestone beds, 

it is underlain in southern Mississippi by 

calcareous marine clay (Yazoo Formation, 

regional confining unit C1) that separates the A1 

aquifer from underlying permeable strata. In 

southwest Alabama, the A1 unit is interbedded 

and interconnected with the upper part of the 

Floridan aquifer system. Although aquifer unit 

A1 has been mapped regionally, it is not 

simulated as an active layer in the regional 

ground-water flow model; rather, it is referred to 

as a source-sink layer. 

The A2 regional aquifer consists of a thick sequence of sand, sandstone, gravel, and minor 

limestone beds, all of Paleocene to late Eocene 

age. Locally, sands of Late Cretaceous age in 

South Caroli:aa are included as part of the A2 

aquifer. The sediments that comprise the A2 

aquifer were deposited largely under marine conditions except in Mississippi where they grade into a thick fluvial sequence. The A2 aquifer is 

largely quartzose sand (but contains glauconitic 

and feldspathic sand in places), fine to coarse 

grained, massive to thinly bedded, and is locally 

stratified by interbedded to inter-laminated clay, 

shale, marl, and mudstone. 

The outcrop area of the A2 aquifer is shown 

in figure 133. This aquifer connects to the west 

with the Gulf Coastal Plain regional aquifer 

system that can be mapped as far west as Texas. 

The A2 aquifer is the uppermost regionallyextensive clastic aquifer except in southwestern 

Alabama and southern Mississippi where 

younger sand aquifers are present. The highly 

permeable Floridan aquifer system partly 

overlies, and is hydraulically interconnected with, 

the less permeable A2 aquifer in Georgia, 

southwest South Carolina, and southern 

Alabama. In most places, the Floridan aquifer 

system and the underlying A2 aquifer are not 

separated by an intervening confining unit. The 

boundary between the two aquifer . systems 

represents a facies transition separating 

predominantly carbonate rocks from underlying 

predominantly clastic rocks. The Floridan aquifer 

system has permeability values that are 

generally one or more orders of magnitude higher 

than those of the A2 aquifer. The top of the A2 

aquifer is coincident with the base of the Floridan 

aquifer system (Miller, 1982), where the two 

systems are juxtaposed (fig. 135). The A2 aquifer 

in most places grades seaward from sand, sand.:. 

stone, gravel, and minor limestone beds into low~ 

permeability rocks that mark the downdip limit 

of the aquifer. In southeastern Georgia, however~ 

the A2 aquifer grades downdip into permeable 

limestone that is part of the Floridan aquifer 

system (fig. 135). 

The permeable clastic rocks of the A2 aquifer 

are separated from underlying aquifers by two extensive, separate confining units (C2 and C3) that 

range from Paleocene to Late Cretaceous in age 

(fig. 134). Locally, in updip areas of the Coastal 

Plain in northeast Georgia and northwest South 

Carolina, ·no underlying confining unit is present, 

and the A2 aquifer is .hydraulically connected 

with underlying massively-bedded, quartzose, 

nonmarine Cretaceous sand that is part of the A3 

aquifer. The C2 confining unit is largely covered 

by overlapping rocks of the A2 aquifer (fig. 133) 

but crops out in eastern Alabama (Tuscahoma 

Formation and equivalents) and in eastern South 

Carolina (parts of the Black Mingo. aJJ.d Peedee 

Formations). Although the lithology of this confining unit varies, the C2 confining unit consists 

everywhere of low-permeability rocks that effectively separate the overlying A2 aquifer and the 

underlying A3 aquifer. 

To the west, in central Alabama, the C2 confining bed grades laterally into fine-grained 

glauconitic sand with minor interbedded silty 

clay that is part of the A2 aquifer (fig. 134). Consequently, a deeper, regionally extensive confining unit (C3) in these places separates the A2 

aquifer from the underlying permeable strata, the 

A3 aquifer. Where the C3 confining unit 

underlies the A2 aquifer, this confining unit is 

largely equivalent to the outcropping massive 

clay of the Porters Creek Formation of Paleocene 

age and to chalk and shale of the Late Cretaceous 

Selma Group. 

The area of outcrop of the A3 aquifer is shown 

in figure 133. In western South Carolina and 

eastern Georgia, this aquifer crops out in a discontinuous pattern where it is covered by younger, 

overlapping rock. In the subsurface, the A3 

aquifer extends as a continuous unit from eastern 

Alabama into North Carolina where it is continuous with aquifers that are part of the Northern Atlantic Coastal Plain regional aquifer 

system. To the west, the A3 aquifer grades by 

facies change laterally into calcareous shale and 

chalk that are part of the C3 confining unit 

(Selma Group, fig. 134). Locally, glauconitic 
quartz sand of Late Cretaceous age in northern 

Mississippi (Ripley Formation) is considered part 

of the A3 aquifer. This aquifer extends north and 

northwest into the northernmost reaches of the 

Mississippi embayment where it is part of the 

Gulf Coastal Plain regional aquifer system. 

FEET A 1000 

The A3 aquifer is mostly massive to thinly 

bedded, largely quartzose, fine to coarse-grained 

quartz sand that is glauconitic to feldspathic in 

places; highly permeable, sandy, glauconitic 

limestone of local extent (Clayton Formation) is 

also part of the aquifer. In downdip areas, the A3 

A' 

0 20 40 KILOMETERS 

EXPLANATION 

HYDROGEOLOGIC UNITS 

D 

~ 

~ -

-

~ 

~ 

~ 

[I] . 

0 

Floridan aquifer 

A2 

C2 

A3 

C3 

A4 

Base of system 

CONTACT-- Dashed where approximately located, queried where inferred 

WELL 

Figure 135.-Generalized hydrogeologic section in east-central Georgia (location of section shown in fig. 132). 

211 
212 

aquifer grades into calcareous shale and chalk; 

locally in southeast Georgia, however, the aquifer 

grades into permeable limestone that is part of 

the Floridan aquifer system (fig. 135). 

Fissile, carbonaceous to varicolored clay and 

shale found in the sub-surface of South Carolina 

and Georgia combine with outcropping and subsurface clay and chalk of the Midway (Paleocene) 

and Selma (Late Cretaceous) Groups of Alabama 

and Mississippi to form confining unit C3. This 

confining unit is everywhere thick and effective, 

separating aquifers A3 and A4. 

The A4 aquifer is the most regionally extensive clastic aquifer underlying the Southeastern 

Coastal Plain. Correlative sands of this aquifer 

extend in the subsurface or outcrop from Tennessee eastward into central North Carolina. This 

aquifer crops out in a wide band in Mississippi 

(fig. 133) but the outcrop width gradually 

diminishes in central Georgia where the aquifer 

is completely covered by onlapping Late 

Cretaceous and Tertiary rocks. Aquifer A4 is not 

known to crop out in eastern Georgia or in South 

Carolina. 

Aquifer A4 includes sediments of Early and 

Late Cretaceous age and is composed of medium 

to coarse, massively to thinly bedded, sand and 

sandstone mostly offluviodeltaic origin. Locally, 

this aquifer contains various trace minerals 

ranging from limonite to glauconite; very locally, 

sediments of this aquifer are of marginal marine 

origin. Interbedded varicolored and mottled clay, 

shale, and siltstone form local confining units 

within the aquifer. A major subsurface part of this 

aquifer consists of sand that is part of the 

Tuscaloosa Group. However, four other rockstratigraphic units are included in the upper part 

of this aquifer (fig. 136), thus illustrating the poor 

regional correspondence of a regionally extensive 

aquifer with previously defined rock-stratigraphic 

units 

Deeply buried sedimentary rocks of Jurassic 

age that underlie Early Cretaceous rocks in parts 

of Alabama, Mississippi, Georgia, and Florida are 

not considered to be part of the regional 

hydrogeologic framework of the ·Southeastern 

Coastal Plain regional aquifer system because 

they contain water everywhere with concentrations of dissolved solids greater than 10,000 

milligrams per liter(mg/1). The southernmost extent of ground water having concentrations of 

dissolved solids less than 10,000 mg/1 in aquifer 

A4 is shown in figure 136. Downdip of the line 

representing the limit of 10,000 mg/1 concentration of dissolved solids, there is considered to be 

little or no ground-water movement in the 

aquifer. 

HYDROLOGY 

Ground water originates as precipitation that 

enters the aquifer system in outcrop areas. Annual precipitation ranges between 44 to 64 in./yr 

over the entire study area (Cederstrom and 

others, 1979); however, outcropping rocks of the 

aquifer system that are adjacent to the inner 

margin of the Coastal Plain receive lesser 

amounts of precipitation. Only a small part of the 

precipitation enters the regional ground-water 

flow system; the majority either discharges. to 

streams as (1) direct runoff, and (2) through 

shallow and intermediate aquifer systems as base 

flow, or is transpired by plants, or evaporates. 

Runoff in outcrop areas of the regional aquifer 

system is generally 10 to 20 in/yr, except in 

western Alabama where it ranges between 20 to 

25 in/yr (Busby, 1966). ·Major rivers that are considered to have a significant impact on the 

regional ground-water flow· system are shown in 

figure 137. 

Aquifers extend downdip under younger 

· sediments, and generally contain freshwater for 

a distance of about 100 miles or more downdip of 

the outcrop. Where the regional aquifer system 

is overlain by rocks of the Floridan aquifer 

system, the clastic aquifers are -little used because 

of the abundance of. water available from the 

Floridan. Ground-water development in the 

Southeastern Coastal Plain regional aquifer 

system is largely limited to rural use. However, 

in places, municipal and agricultural use has 

resulted in local water-level declines of as much 

as 100 feet from predevelopment water levels. 

The general pattern of ground-water flow 

within the Southeastern Coastal Plain regional 

aquifer system is controlled by variations in 

aquifer permeability and the distribution of 

recharge and discharge. Water enters the aquifer 

system in upland outcrop areas where the groundwater movement is through relatively short 

distances and predominantly in the vertical direction; whereas ground-water flow in middip and 

. downdip areas is relatively slow and 

predominantly in the horizontal plane. In places, 

ground water may flow parallel to the strike of 

the aquifers (fig. 137). The shift from 

predominantly vertical flow in updip areas to 

largely horizontal flow in middip areas (fig. 138) 

can be attributed to: (1) a diminishing downdip 
interconnection between surface drainage and the 

aquifers, and (2) an overall decrease in vertical 

hydraulic conductivity combined with an increase 

in thickness of the confining units in a downdip 

direction. Distinctions between regional and local 

ground-water flows and the determination of the 

relative importance of vertical and horizontal 

TENNESSEE 

35' 

30' 

Gulf of Mexico 

SCALE 1:8,000,000 

flows are made possible through use of simulation. 

GROUND-WATER FLOW SIMULATIONS 

Computer models of the Southeastern Coastal 

Plain regional aquifer system are being used to 

85 ' 

~--· ---~ 

SOUTH 

CAROLINA 

Atlantic 

Ocean 

0 100 200 MILES 

0 100 200 KILOMETERS 

~ AQUIFER ABSENT 

~ AREA OF OUTCROP 

COFFEE SAND 

CIJ EUTAW AND McSHAN FORMATIONS 

MWCW I TUSCALOOSA GROUP/FORMATION 

~ I 

- ATKINSON FORMATION 

EiJ CAPE FEAR FORMATION 

EXPLANATION 

FALL LINE OF COASTAL PLAIN 

STRUCTURE CONTOUR·· Shows altitude of A4 

--1ooo ~ aquifer. Dashed where approximately located. 

Contour interval500 feet. Datum is sea level 

APPROXIMATE UPDIP LIMIT OF WATER CONTAINING 

10,000 MILLIGRAMS PER LITER DISSOLVED 

SOLIDS 

LOCATION OF PICKENS-GILBERTOWN 

FAULT SYSTEM 

STUDY AREA 

Figure 136.- Geology and configuration of the surface of the lowest aquifer (A4) and approximate location of 

updip limit of water containing concentrations of 10,000 milligrams per liter of dissolved solids, Southeastern Coastal 

Plain regional aquifer system. 

213 
214 

help estimate predevelopment potentiometric surfaces and hydrologic properties of the aquifers and 

confining units, and to simulate ground-water 

movement. The models additionally are being 

used to help test the validity of the delineated 

regional hydrogeologic framework. 

Because hydrologic conditions within the 

regional aquifer system were not known initially 

for large parts of the study area, the strategy for 

calibrating the regional flow model was to: (1) accept a plausible set of boundary conditions; (2) 

make preliminary estimates of recharge, 

TENNESSEE 

35. 

30 . 

J Gulf of Mexico 

SCALE 1:8,000,000 

transmissivity, leakance of confining units, and 

conductance of riverbeds; and (3) refine these 

preliminary estimates by way of trial- and-error 

simulations. The objective of model calibration is 

to simulate potentiometric surfaces and regional 

ground-water flow conditions consistent with the 

observed data and the delineated geohydrologic 

framework. 

The models utilize a three-dimensional finitedifference code described by McDonald and Harbaugh (1984). Four subregional models that 

overlap are directly linked with the regional 

ss· 

,----"""' SOUTH 

CAROLINA 

FLORIDA 

so· 

Atlantic 

Ocean 

0 100 200 MILES 

- 200-

0 100 200 KILOMETERS 

EXPLANATION 

FALL LINE-OF COASTAL PLAIN 

UPDIP LIMIT OF AQUIFER A4 

ALTITUDE OF POTENTIOMETRIC SURFACE-- Interval, 

in feet, is variable. Datum is sea level 

GENERAL DIRECTION OF REGIONAL 

GROUND-WATER FLOW 

SOUTHERN EXTENT OF GROUND WATERWITH LESS THAN 

10,000 MILLIGRAMS PER LITER DISSOLVED SOLIDS 

STUDY AREA 

~igure _137.- Location of major rivers that have significant impact on the regional ground-water flow system and potentlometnc surface of the lowest aquifer (A4), Southeastern Coastal Plain regional aquifer system. 
model (fig. 139) and share a common data base. 

Although the regional model is less detailed than 

the subregional models, it simulates flow across 

the boundaries of the subregional models and 

calculates a water budget for the entire aquifer 

system. 

As shown in figure 140, the regional model 

is comprised of three active aquifers (A2, A3, and 

A4) which are overlain by an aquifer assumed to 

have constant water levels and to act as a source 

or sink. In addition to the Upper Floridan aquifer 

(Miller, 1984), the source-sink aquifer includes the 

'surficial aquifer' as shown in figure 134. To effectively simulate the interconnection between 

the A2 aquifer and the Lower Floridan aquifer 

(Miller, 1984), these aquifers are combined into 

a single aquifer in the simulation model as shown 

in figure 140. 

Boundary Conditions 

To properly simulate observed hydraulic conditions near the boundaries of the modeled area, 

the appropriate conditions must be specified for 

the model boundaries. Zero ground-water flow in 

the horizontal direction is maintained by no-flow 

boundaries to represent conditions along the Fall 

Line (updip limit of the Southeastern Coastal 

Plain regional aquifer system) and along the 

downdip limits these represent either the loss of 

permeability by facies change or the freshwatersaltwater interface which is defined as water in 

place that contains concentrations of at least 

10,000 mg/L of dissolved solids. The constanthead boundary conditions atop parts of the 

Southeastern Coastal Plain regional aquifer 

system are derived from potentiometric surfaces 

simulated by flow models of the Floridan aquifer 

system and the Gulf Coastal Plain regional 

aquifer system. Flow across all model boundaries 

is monitored during simulations to ensure that 

realistic hydrologic conditions are being 

simulated. 

Model Sensitivity 

The steady-state model is most sensitive to 

changes in rates of recharge. The potentiometric 

surface simulated directly results from recharge 

into outcrop areas. Different recharge rates affect 

the simulated rates of aquifer-to-stream leakage 

by roughly the same percent that the recharge 

rate differs. When recharge is held constant, the 

model is more sensitive to variation in leakance 

of confining units and conductance of streambeds 

than it is to comparable changes in 

transmissivity. The model is more sensitive to 

changes in transmissivity in updip areas where 

hydraulic gradients are steep than it is to changes 

in transmissivity in downdip areas where 

hydraulic gradients are relatively flat. 

The model's sensitivity was tested also to 

changes in the location of no-flow boundaries used 

to simulate the presumed effect of the downdip 

limits of the freshwater-saltwater interface. 

Changing the location of the southern no-flow 

boundary through a distance of about 40 miles in 

a southeast-to-northwest (inland) direction, produces simulated head differences that are 

everywhere less than 10 feet, and average less 

~ 

~ 

~ 

EXPLANATION 

Simulated as constant head 

(source sink) boundary conaition 

Simulated aquifer 

Simulated confining unit 

Basa of Floridan Aquifer System 

General direction of regional 

ground-water flow 

Figure 138.-Relation between hydrogeologic framework and simulated flow direction along a hypothetical dip section 

through Georgia. 

215 
216 

than 5 feet, over the affected parts of the 

simulated aquifer system. Differences of such 

magnitude and distribution are considered inconsequential to the model's capability of satisfying the objectives of the study. 

Preliminary Results of Simulation 

Limited by the model's grid block size of 8 

miles to a side, the regional flow model can 

simulate discharge as base flow adequately only 

as· 

MISSOURI 

-------

35 ° 

Jo • 

Gulf of Mexico 

to major streams in the Southeastern Coastal 

Plain. All major rivers simulated in the regional 

model have drainage basins exceeding 1,000 mi2 • 

To simulate recharge and discharge rates that are 

consistent with the model's grid scale, stream 

reaches within drainage basins ofless than 1,000 

mi2 are considered to be of local or intermediate 

scale and are not modeled (fig. 141). 

Consequently, the regional model cannot 

simulate recharge that is discharged directly to 

these streams which drain the shallower aquifers. 

OHIO 

0 

VIRGINIA 

SCALE 1:11 ,000,000 

100 

Atlantic 

Ocean 

200 MILES 

200 KILOMETERS 

EXPLANATION 

r---, 

I I ._ __ _J REGIONAL MODEL 

SUBREGIONAL MODEL 

1, Mississippi 

2, Alabama 

3, Georgia 

4, South Carolina 

STUDY AREA 

Figure 139. -Areas modeled by regional and subregional models, Southeastern Coastal Plain regional aquifer system. 
Therefore R = P - DRO - ET (1) , the amount of simulated recharge 

associated with the regional scale ground-water 

flow system is less than the total recharge to the 

entire aquifer system. 

Where, R = total recharge, in./yr, 

Recharge in the outcrop area can be calculated by the following equation: 

90 ' as· 

A 

35' 

30 ' 

0 100 200 300 MILES 

25' 0 100 200 300 KILOMETERS 

A a A' I I 

i,:,:::·:.: ~\~~~/~~~ ~~~e~~~:i:f~~~ -::::· -:: SS 

-- - - - C1 

•~• ~ ~~ri'~'• :_:•• @'!:: mf\Mi\!Mi~,,w.·::m; i!,% y·~·W! I ~: 

t ;:(Nt}) ?I::t{U~· .. )M_;;;:;-;wmm ~~,~@\(fH.§-g ~;:;.}-:w_~~i:f:t:~nrJWi~;=;w{ * A3 

1 ~--~E.;g~~:;-%-:.i)?r::.i{w©.;J(:ls~:ff.~%::·0ti J, 1(~-? i.: ~ ~: 

EXPLANATION 

[/}X/1 SIMULATED AQUIFER 

m SIMULATED CONFINING UNIT 

PERIPHERAL BOUNDARIES 

Constant head 

I Noflow 

SS Source or sink layer · 

B 

P = precipitation, in./yr, 

DRO = direct runoff (does not 

include base flow), in./yr, 

ET = evapotranspiration, in./yr. 

80 ' 

UPPER BOUNDARIES 

b 

I 

B' 

I 

Floridan aquifer 

[JiilliJ Constant head (source-sink) 

+ Direct recharge (in outcrop areas) 

LOWER BOUNDARY 

- Noflow 

A,C 

IS DELINEATED REGIONAL AQUIFER LAYER OR 

CONFINING LAYER -- Number indicates the 

sequence order numbered downward . A 1, C1 

are also referred to in flow models 

Figure 140.- Schematic section A-A' and B-B', showing simulated aquifers, confining units, and boundary conditions, 

Southeastern Coastal Plain regional aquifer system. 

217 
218 

-c~ r r" ~ ~ ,..,,, ~~;} -...... r --... """' 

r::_.t.J-y-_,u.r~.LL/!(/1) _/ 

I11 JIIjl ·, jj 'If' ' I I 1.' I ' I I I I I 1 1 /I Precipitation 1 1 lj /I ' I ' ' ' I ' I ' I I I 

I I ' I I! I ' I I I 'I '! I I I' I I I I' I I 

REGIONAL FLOW 

0 5 MILES 

0 5 KILOMETERS 

EXPLANATION 

.... GENERAL DIRECTION OF GROUND-WATE~R FLOW 

..._, SURFACE WATER DRAIN 

Figure 141.- Relation between surface drainage system and scale of aquifers which discharge into the surface 

drainage system, Southeastern Coastal Plain regional aquifer system. 

Equation 1 can be modified to show the difference between simulated recharge (r) associated 

with the regional flow system and the total 

recharge (R) to the entire aquifer system; thus: 

r = P - DRO - ET - BF, or 

r = R - BF (2) 

Where, r = simulated regional recharge, in./yr, 

BF = base flow to rivers discharged by local and intermediate flow systems 

which are not simulated, 

in./yr. 

The relatively small component of simulated 

regional recharge (r) that does not discharge to 

major rivers can be expressed by: 

Where, 

dp = r - bf (3) 

dp = simulated deep infiltration of ground water, 

in./yr, 

bf = simulated base flow discharge to major rivers 

from the regional scale 

flow system, in./yr. 

The schematic diagram of the water budget 

(inset, fig. 142) illustrates the results of combining 

the simulated hydrologic components with 

estimates of precipitation, total runoff, and base 

flow which are assumed to be known. The 

estimated evapotranspiration (ET) rate of about 

35 in./yr results from the difference between the 

estimated average precipitation (about 50 in./yr) 

and the estimated average total runoff (about 15 

in./yr) which is the sum of direct runoff and base 

flow. The base flow of approximately 7 in./yr 

through local and intermediate scale groundwater flow systems (BF) is the area-weighted 

average of base flow provided by Stricker (1983, 

table 1, p. 8) for 26 nonsimulated stream reaches 

in the outcrop area of the regional aquifer system, 

all of which have drainage areas ofless than 1,000 

mi2 • The estimated 7 in./yr of direct runoff to 

streams (DRO) is the rounded-off result of subtracting the sum of the nonsimulated base flow (BF) 

and the simulated base flow discharged from the 

regional scale aquifer systems (bf, about 0.75 

in./yr) from total runoff(about 15 in./yr). The total 

recharge (R) of about 8 in./yr is the difference between precipitation (P) and the sum of 
EXPLANATION 

WATER BUDGET SCHEMATIC, showing general distribution 

of water resulting from: 

Nonslmulated 

P, Precipitation 

ET, Evapotranspiration 

ORO, Direct runoff 

R, Total recharge; the percolation of precipitation 

below land surface that is neither lost to 

direct runoff or ET 

BF, Base flow to small streams 

Simulated 

r, Component of total recharge that percolated 

below level of small streams 

bf, Base flow to major streams through regional 

· aquifer system - · 

dp, Deep penetration; component of total recharge 

that percolates below level of major streams 

~ 

~ 

~ 

~ ""' 

----

In outcrop area, under predominately unconfined conditions 

Under predominately confined conditions 

Small stream; interacts primarily with 

local scale flow system 

Major stream; interacts primarily with 

intermediate-to-regional scale flow system 

Hydraulic head 

Figure 142.-Simulated hydrologic components, Southeastern Coastal Plain regional aquifer system. 

evapotranspiration (ET) and direct runoff(DRO); 

total recharge also equals the sum of base flow 

to the unmodeled streams (BF) and the simulated 

regional recharge (r). 

The model-simulated recharge (r) to the 

regional aquifer systems is about l in./yr. The 

regional aquifer system discharge to major rivers 

as base flow (bf) is about 0.75 in./yr; the remainder 

of about 0.25 in./yr (dp) discharges diffusively upward through confining units into the overlying 

Floridan aquifer system and its equivalents. The 

simulated values of r, bf, and dp are rounded to 

the nearest 0.25 in./yr. The sum of simulated 

boundary flow among the Southeastern Coastal 

Plain aquifer system and the adjacent Gulf 

Coastal Plain and Northern Atlantic Coastal 

Plain regional aquifer systems is less than 10 ft3/s. 

The ratio of total recharge (R) to simulated 

recharge (r) is 10 to 1 and the boundary outflow 

is 250 to 1. 

GEOCHEMISTRY 

Water from all aquifers in the Southeastern 

Coastal Plain regional aquifer system have a 

similar chemical evolution as the water moves 

down the hydraulic gradient from outcrop 

recharge areas to deeper downgradient parts of 

the aquifers. In the recharge area and at shallow 

depth (Zone A, fig. 143), the concentrations of 

dissolved solids are less than 50 mg/L, the water 

is calcium or sodium-bicarbonate dominated, pH 

is about 4.5 to 6.0, dissolved oxygen concentrations are 2 to 10 mg/L. At greater depth (Zone B) 

the concentrations of dissolved solids range from 

100 to 200 mg/L, the water is sodium and bicarbonate dominated, pH is about 6.0 to 7.0, with 

negligible dissolved oxygen, and concentrations 

of dissolved iron range from 500 to 20,000 mg/L. 

Downgradient from the recharge area (Zones C 

and D) the concentrations of dissolved solids 

range from 300 to 500 mg/L, the water is sodium 

bicarbonate dominated with increased chloride, 

pH is about 7.0 to 9.0, and the concentrations of 

dissolved iron are less than 300 mg/L. Further 

downgradient (Zone E, not shown in fig. 143) the 

concentrations of dissolved solids range from 

1,000 to 30,000 mg/L, the water is sodium and 

chloride dominated, pH is about 8.0 to 9.0, and 

the concentrations of dissolved iron range up to 

5,000 mg/L. 

Zones A through D were examined in greater 

detail in Mississippi and Alabama (fig. 143) to 

gain further insight concerning the types of 

geochemical reactions that occur after water 

recharges the aquifers. The various geochemical 

reactions associated with each zone are summarized in table 5. A fifth zone (zone E, not included in table 5) is characterized as a zone where 

freshwater is mixed with sodium-chloride brine. 

Evidence of water-quality degradation is 

observed in several locations; large ground-water 

withdrawals at major pumping centers in 

219 
220 

FEET Southwest 

1500 

Ripley 10 12 11 15 14 16 

1000 

Form ~tion \ \ // 

500 

~ 

Northeast 

TENNESSEE 

' ' / r' 9 17 

8 I 21 j ~18 

87' 

11 '-: I I ~ 15 \ 16 • -19 ',<$>~ 

Sea level ~'b' v "

· . / " \ 12 - :· \ 20 ~,., (i ~,~ 

~p 1$'0 

500 '>0 

1 • 10 I 22 ' '>e .... __ 

13 ALABAMA 

1000 

1500 

2000 

2500 

Gulf of Mexico 

3000 

3500 

VERTICAL SCALE GREATLY EXAGGERATED 0 20 40 MILES 0 100 200 MILES 

0 20 40 KILOMETERS 0 100 200 KILOMETERS 

EXPLANATION 

A Geochemical zone, explained in text 

EXPLANATION 

Sampling well, number assigned 

during this study 

Line of section 

Figure 143.- Generalized geologic section along a flow path from Alabama to Mississippi showing approximate location of geochemical zones, A, B, C, and D, in the southeastern Coastal Plain. 

Mississippi, Alabama, and coastal South Carolina 

have resulted in higher concentrations of 

dissolved solids and chloride. An anomalous low 

in the potentiometric surface of the A4 aquifer in 

central Alabama (fig. 137) may have contributed 

to the observed increase in concentrations of 

dissolved solids and chloride there. 

Detailed study of zones A and B indicates that 

the geochemical character of ground water 

associated with calcareous clastic aquifers differs 

from that of sand aquifers that are noncalcareous. 

Sand aquifers that are calcareous contain water 

of calcium and bicarbonate dominance in zones 

A and B, but do not attain high concentrations 

of dissolved iron in zone Bowing to precipitation 

of siderite. In noncalcareous sand aquifers, water 

develops high dissolved iron concentrations in 

zone B and the iron is precipitated in zone C. 

PUBLISHED REPORTS 

Abstracts 

1. Faye, R. E., 1982, Coastal Plain faults affect 

ground water flow: American Society of 

Civil Engineers Irrigation and Drainage 

Division National Specialty Conference, 

Proceedings, Environmentally Sound Water 

and Soil Management, Orlando, FL, July 

21-23, 1982, p. 251. 
Table 5. -Zonation of chemical reactions of water along a flow path from Alabama 

to Mississippi in the Southeastern Coastal Plain regional aquifer system 

[Location of the flow path is shown in fig. 143] 

Recharge zone: Rainfall-input chemistry, atmospheric carbon dioxide + soil carbon 

dioxide + dissolved oxygen 

Zone A: Calcite dissolution 

Sodium feldspar hydrolysis to kaolinite 

Oxidation of carbonaceous matter by dissolved oxygen 

Zone B: Calcite dissolution 

Sodium feldspar hydrolysis to kaolinite 

Ferric iron reduction to siderite to saturation of siderite 

Oxidation of carbonaceous matter 

Silica precipitation 

Zone C: Calcite dissolution 

Sodium feldspar hydrolysis to kaolinite 

Siderite precipitation 

Ferric iron reduction 

Oxidation of carbonaceous matter 

Silica precipitation 

Zone D: Smectite precipitation 

Calcite dissolution 

Na-Ca cation exchange 

Gypsum dissolution 

Sulfate reduction 

FeS2 precipitation 

Ferric iron reduction 

Oxidation of carbonaceous matter 

Silica dissolution 

2. Lee, R. W., 1983a, Carbon-13, deuterium, and 

oxygen isotopes in Tertiary and Cretaceous 

aquifers of the Southeastern Coastal Plain 

of the United States: Geological Society of 

America Annual Meeting, Indianapolis, IN, 

October 30, 1983, abstract no. 27679. 

3.-----1983b, Chemical evolution of ground 

waters in Cretaceous aquifers in eastern 

Mississippi and western Alabama: 

Geological Society of America Southeastern 

Section, Tallahassee, FL, March 10, 1983, 

p. 97, abstract no. 25054. 

4. Wait, R. L., 1983, Hydrology of the 

Southeastern sand aquifer: American 

Society of Civil Engineers, Houston, TX, October 1983. 

5. Renken, R. A., Mahon, G. L., and Davis, M. 

E., 1985, A hydrogeologic framework for 

Coastal Plain sand aquifers of the 

southeastern United States: Geological 

Society of America Southeastern Section, 

March22, 1985, Knoxville, TN, v.17, no. 2, 

abstract no. 72831. 

Reports 

1. Aucott, W. R., and Speiran, G. K., 1984a, 

Potentiometric surfaces of the Coastal Plain 

aquifers of South Carolina prior to development: U.S. Geological Survey WaterResources Investigations Report 84-4208, 

5 sheets. 

2.-----1984b, Potentiometric surfaces of 

November 1982 and declines in the potentiometric surfaces between the period prior 

to development and November 1982 for the 

Coastal Plain aquifers of South Carolina: 

U.S. Geological Survey Water-Resources Investigations Report 84-4215, 7 sheets. 

3.-----1984c, Water-level measurements for 

the Coastal Plain aquifer~ at South Carolina 

prior to development: U.S. Geological 

Survey Open-File Report 84-803. 

4.-----1984d, Ground water flow ~n the 

Coastal Plain Aquifers of South Carolina: 

Ground Water [in press]. 

221 
222 

5. Brooks, R., Clarke~ J. S., and Faye, R. E., 1984, 

Hydrology of the Gordon aquifer system of 

east-central Georgia: Georgia Geologic 

Survey Information Circular 73 [in press]. 

6. Clark, J. S., Brooks, R., and Faye, R. E., 1984, 

Hydrology of the Dublin and Midville 

, B,quifer systems of east-central Georgia: 

Georgia Geologic Survey Information Circular 7 4 [in press]. 

7. Clarke, J. E., Faye, R. E., and Brooks, R., 

1983a, Hydrol_ogy of the Clayton aquifer of 

southwest Georgia: U.S. Geological Survey 

Open-File Report 83-755, 56 p. 

8. ____ ...:_1983b, Hydrology of the Providence 

aquifer of southwest Georgia: Georgia 

Geologic Survey Hydrologic Atlas 11, 

5 sheets. 

. · 9. Davis, M. E., Sparkes, A. K., and Peacock, B. 

S., 1983, Results of a test well in the 

Nanafalia Formation near Melvin, Choctaw 

County, Alabama: U.S. Geological Survey 

Open-File Report 82-4108, 17 p. 

10. Faye, R. E., and Prowell, D. C., 1982, Effects 

of late Cretaceous and Cenozoic faulting on 

the .geology and hydrology of the Coastal 

Plain near the Savannah River, Georgia, 

and South Carolina: :U.S. Geological Survey 

Open-File Report 82-156, 73 p. 

11. Feder, G. L., and Lee, R. W., 1981, Waterquality reconnaissance of Cretaceous 

aquifers in the Southeastern Coastal Plain: 

U.S. Geological Surv~y Open-File Report 

81-696, 10 p. 

12. Lee, R. W., 1984, Ground-water quality data 

from the southeastern coastal plain, 

Mississippi, Alabama, Georgia, South 

Carolina and North Carolina: U.S. 

Geological Survey .Open-File Report 84-237, 

20 p. 

13. Lee·, R. W., 1985; Geochemistry of groundwater in Cretaceous sediments of the 

Southeastern Coastal Plain, eastern 

Mississippi-western Alabama: Water 

Resources Research v. 21, no. 10, 

p. 1545-1556 

14. Renken, R. A., 1984, The hydrogeologic 

framework for the Southeastern Coastal 

Plain aquifer system of the United States: 

U.S. Geological Survey Water-Resources Investigations Report 84-4243, 26 p. 

15. Stricker, V. A., 1983, Base flow of streams in 

the outcrop area of southeastern sand 

aquifer, South Carolina, Georgia, Alabama, 

and Mississippi: U.S. Geological Survey 

Water-Resources Investigations Report 

83-4106, 17 p. 

16.~----, 1985, Approximate potentiometric 

surface for aquifer unit A4, Southeastern 

Coastal Plain aquifer system: U.S. 

Geological Survey Water-Resources Investigations Report 84-4364, 1 sheet . 

REFERENCES CITED 

Busby, M. W., 1966, Annual runoff in the conterminous United 

States: U.S. Geological Survey Hydrologic Investigations Atlas 212. 

Cederstrom, D. J., Boswell, E. H., and Tarver, G. R., 1979, 

Summary appraisals of the Nation's ground-water 

resources-South Atlantic-Gulf Region: U.S. Geological 

Survey Professional Paper 813-0, 35 p. 

McDonald, M.G., and Harbaugh, A. W., 1984, A modular 

three-dimensional finite-difference ground-water flow 

model: U.S. Geological Survey Open-File Report 83-875, 

528 p. 

Miller, J. A., 1982, Geology and configuration of the base of 

the Tertiary limestone aquifer system, southeastern 

United States: U.S. Geological Survey Open-File Report 

81-1176, 1 sheet. 

-----1984, Hydrogeologic framework of the Floridan 

aquifer system in Florida and in parts of Georgia, South 

Carolina, and Alabama: U.S. Geological Survey Professional Paper 1403-B, [in press] 

Renken, R. A., 1984, The hydrogeologic framework for the 

Southeastern Coastal Plain aquifer system of the 

United States: U.S. Geological Survey Water-Resources 

Investigations Report 84-4243, 26 p. 

Stricker, V. A., 1983, Base flow of streams in the outcrop area 

of southeastern sand aquifer, South Carolina, Georgia, 

Alabama, and Mississippi: U.S. Geological·Survey, 

Water-Resources Investigations Report 83-4106, 17 p. 

Toth, J. A., 1963, A theoretical analysis of groundwater flow 

in small drainage basins: Journal of Geophysical 

Research, v. 68, p. 4795-4812. 
ACTIVE PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

UPPER COLORADO RIVER BASIN REGIONAL AQUIFER-SYSTEM STUDY 

By 0. James Taylor, Denver, Colorado, Geoffrey Freethey, Salt Lake City, Utah, 

and Kent C. Glover, Cheyenne, Wyoming 

INTRODUCTION 

Water shortage is common in the Colorado 

River Basin and increasing water demand is expected. The Colorado River Compact of 1922 

divided the Colorado River Basin into an upper 

and a lower basin in order to allocate water supplies. The Upper Colorado River Basin has a 

drainage area of about 113,500 mi2 in western 

Colorado, eastern Utah, southwestern Wyoming, 

northeastern Arizona, and northwestern New 

Mexico. 

Local studies of the ground-water resources 

in the Upper Colorado River Basin are numerous; 

however, regional studies are few. Some regional 

studies have been described by Iorns and others 

(1965), the Upper Colorado Region State-Federal 

Interagency Work Group (1971), and Price and 

Arnow (197 4). To obtain additional regional information systematically on hydrology, geology, 

and water chemistry of the Upper Colorado River 

Basin aquifer system, in 1981, the U.S. Geological 

Survey started the Upper Colorado River Basin 

regional aquifer study, scheduled for completion 

in 1986. Excluded from this study is the upper 

part of the San Juan River Basin, which will be 

investigated in a separate study. The remaining 

study area is about 100,000 mi2 (fig. 144). 

The area covered by this study contains a 

variety of landforms: rugged mountains, broad 

plains, deeply dissected canyons, relatively flat 

flood plains, and many erosional features. Consolidated sedimentary formations of Paleozoic, 

Mesozoic, and Cenozoic age attain a maximum 

thickness of tens of thousands of feet. These formations include aquifers within beds of fractured 

limestone, dolomite, sandstone, and shale. Lowpermeability limestone, dolomite, shale, and 

evaporite deposits act as confining units. Igneous 

rocks, especially volcanic rocks, are also present 

in part of the study area~ but they are not regional 

aquifers. · 

The study area has been subjected to repeated tectonism. The predominant tectonic 

features are numerous basins and uplifts (fig. 

145). The resulting structural relief is nearly 

30,000 feet above the basin floors in places. 

Because of this relief, several aquifers that are 

deeply buried in basins are exposed on the 

margins of uplifts, where precipitation partly 

recharges the aquifers. Aquifers within 

stratigraphically younger formations tend to be 

exposed and recharged over extensive areas. 

Annual precipitation ranges from approximately 6 inches on the plains of Utah to about 

40 inches in mountainous areas. Precipitation, in 

form of snowmelt and rainfall, is the only source . 

of recharge to the aquifers. 

PROGRESS AND RESULTS 

Ground-water flow systems have been classified into three major groups. In descending 

order, they are: (1) Cenozoic-rock aquifers, (2) 

Mesozoic-rock aquifers, and (3) Paleozoic-rock 

aquifers. These flow systems are being studied individually in U.S. Geological Survey offices in 

Colorado, Utah, and Wyoming. Studies of the flow 

systems are being integrated to ensure that in· 

teractions among the three identified flow 

systems are investigated. Within each flow 

system, rocks are grouped into aquifers and confining units on the basis of lithology, depositional 

environment, and hydrologic characteristics. A 

total of 11 hydrogeologic units has been identified 

for the Upper Colorado River Basin regional 

aquifer system. 

223 
224 

40 ' 

35' 

115 ' 11 0' 105 ' 

IDAHO 

WYOMING 

I 

I 

. 

l--

1 

---··--r·--·--··-··----J 

: I 

I 

I 

I 

I 

I 

. 

I 

. 

. 

I 

. 

I 

I 

I 

I 

I 

I 

. 

I 

I 

I I 

. 

I 

_ _j_ 

t----·-------

NEW MEXICO 

ARIZONA 

SCALE 1 :6,000,000 

50 100 150 MILES 

0 50 100 150 KILOMETERS 

EXPLANATION 

////// 

~:j~~ ~ AREA EXCLUDED FROM STUDY 

STUDY AREA 

Figure 144.-Study area of the Upper Colorado River Basin regional aquifer system. 
40' 

35 ' 

115' 

IDAHO 

I 

. 

' 

----- I -r------- ' 

I 

' ' I 

. ' 

I 

I 

. • 

I 

f --------.... 

: I 

I 

UTAH 

ARIZONA 

110' 

EXPLANATION 

GREAT 

WYOMING 

(~AWLINS PLIFT 

105' 

I 

. 

' [ __ 

J_ 

COLORADO 

NEW MEXICO 

SCALE 1"6,000,000 

50 100 150 MILES 

0 50 100 150 KILOMETERS 

APPROXIMATE BOUNDARY OF UPLIFTS AND BASINS 

~~~~~~ AREA EXCLUDED FROM STUDY 

STUDY AREA 

Figure 145.-Principal tectonic features in the Upper Colorado River Basin (modified from Grose, 1972). 

225 , 
226 

Paleozoic Rocks 

Paleozoic rocks extend over most of the study 

area (fig. 146). These rocks were subdivided into 

four hydrogeologic units. In descending order, 

they are: (1) an upper Palezoic aquifer and confining unit which contains sandstone, red beds, 

and evaporites of Mississippian, Pennsylvanian, 

and Permian age; (2) a middle Paleozoic aquifer 

which contains limestone and dolomite of Devonian and Mississippian age; (3) a lower Paleozoic 

aquifer and confining unit which contains 

limestone and dolomite of Cambrian and Ordovician age; and (4) a basal Paleozoic aquifer which 

contains sandstone and quartzite of Cambrian 

age. Due to the great depth of the lower two units, 

very few drillers' logs are available. Therefore, 

the analysis of Paleozoic rocks will be limited to 

the upper two hydrogeologic units. 

Structure contours drawn to represent the 

top of each hydrogeologic unit indicate considerable relief because of the numerous basins 

and uplifts. Isopach maps indicate a large range 

in thickness, especially for the uppermost 

hydrogeologic unit. Potentiometric surface maps 

were prepared from shut-in pressures obtained 

during drill-stem tests. The potentiometric surface maps indicate that the upper two 

hydrogeologic units are recharged by precipitation in uplifted areas. Water moves through the 

formations toward the valleys and discharges to 

major streams and tributaries. Maps of concentrations of dissolved solids generally substantiate 

the identified flow pattern. In areas of recharge, 

the concentrations of dissolved solids are relatively low. Water quality deteriorates downgradient and with depth. In some basins, concentrations of dissolved· solids exceed 400,000 

milligrams per liter (mg/L) at depth. 

A detailed analysis of the major flow systems 

is underway. Hydraulic conductivity data have 

been obtained by interpreting drill-stem tests 

(Teller and Chafin, 1984) and from literature. 

Reported values of hydraulic conductivities for 

Paleozoic sandstones range from 3 x 10-s to 100 

ft/d; reported values for Paleozoic carbonate rocks 

range from 6 x lo-s to 600ft/d. The discharge 

of major aquifers to valley streams is being 

estimated by determining base flow from analysis 

of historical streamflow data at major gaging stations. Quality data of streamwater collected at 

gaging stations during base-flow periods are being analyzed to identify which aquifers are 

discharging to streams. Hydrogeologic sections in 

selected areas are in preparation, and will be used 

to interpret and simulate the vertical flow components between aquifers. 

Model simulation is being used to evaluate 

the flow system ofthe Paleozoic-rock aquifers in 

parts of south-central Utah and northwestern Colorado. The simulation includes the middle and upper Paleozoic aquifers and their associated confining units. The simulation is used to evaluate 

the hydrologic effects and. potential of groundwater development. 

Mesozoic Rocks 

Based on hydrogeologic characteristics, the 

Mesozoic-age rocks were divided into three units. 

In descending order, they are: (1) an upper 

Mesozoic aquifer and confining unit which contains shale and sandstone of Jurassic and 

Cretaceous age; (2) a midqle Mesozoic aquifer 

which contains sandstone and shale of Triassic 

and Jurassic age; and (3) a lower Mesozoic confining unit which contains siltstone, and 

mudstone of Triassic age. The three hydrogeologic 

units have been described in detail by Freethey 

and others (1984). Figure 14 7 shows the areal extent of the Mesozoic rocks. 

Preliminary analysis of stratigraphic data indicates that Jurassic and Triassic sandstones constitute a regional aquifer (the middle Mesozoic 

aquifer), that extends over about 75 percent of the 

Upper Colorado River Basin. Aggregate thickness 

of this hydrogeologic unit increases westward to 

more than 2,000 feet, but saturated thickness is 

less than aggregate thickness where the 

hydrogeologic unit ·crops out. Cretaceous sandstone underlies about 50 percent of the Upper Colorado River Basin. Although the Cretaceous sandstone yields water to wells, the water quality 

generally is poor. Most of the Mesozoic rocks are 

laterally discontinuous and are only locally 

significant as sources of water. 

Water-level data are . being compiled and 

potentiometric surface maps were constructed for 

the significant formations of the Mesozoic-rock 

aquifers. They are the Glen Canyon Group, Entrada Sandstone, Morrison Formation, lower 

Cretaceous Sandstone, and Mesaverde Group. 

The Glen Canyon Group is the most laterally continuous system. 

Ground-water occurrence and direction of 

movement can be determined in areas where the 

Mesozoic rocks are not deeply buried. Potentiometric surface maps of the Mesozoic-rock 

aquifers indicate that the regional movement of 

ground water is toward the large river vall~ays, 
40 ' 

35 ' 

115' 110' 

IDAHO 

WYOMING 

105' 

I 

. ' 

l--

----- I ,--- -- ----------~ 

I 

' I 

: I I 

. ' 

' I 

' ' I 

I 

' ' I 

' 

I 

I 

I ' 

I 

' ' I 

I 

' 

r-----------

I 

r~:Ei't~~~7':t~~"'fi~~:;-------- ------JEXPLANATION 

1_ (;/~{{j PALEOZOIC ROCKS 

0 

jj~j/~ //-';~~~ AREA EXCLUDED FROM STUDY 

STUDY AREA 

------ -w-----·-· 

NEW MEXICO 

SCALE 1:6,000,000 

50 100 150 MILES 

50 100 150 KILOMETERS 

Figure 146. -Areal extent of Paleozoic rocks in the Upper Colorado River Basin (modified from King and Beikman, 

1974, and Rocky Mountain Association of Geologists, 1972). 

227 
228 

mainly those of the Colorado, Green, Yampa, and 

San Juan Rivers (fig. 144). Small river valleys 

control ground-water discharge locally. PotentiQmetric data indicate. vertical movement of 

water also takes place from one formation to 

another, but the direction of movement is governed largely by the relative locations of recharge 

and discharge. 

Quality of ground water is related to: (1) 

distance and time of travel from the recharge 

areas to the discharge areas, and (2) solubility of 

minerals in the sediments. Ground water in the 

upper Mesozoic aquifer and in the middle 

Mesozoic aquifer generally is fresh with calciumbicarbonate dominance where the formations are 

near land surface or close to recharge · areas. 

Ground water is briny with sodium-chloride 

dominance in deep basins. Large concentrations 

of dissolved solids are pre~ent where ground 

water flows through formations containing 

evaporites. 

Available data indicate that hydraulic conductivity in unfractured Mesozoic sandstone 

ranges from about 1 x 10-4 to 10 ft/d, and 

ranges from 1 x 10-2 to 200 ft/d for fractured 

sandstones. 

Intrinsic permeability was determined from 

two Mesozoic rock core samples using solutions 

that simulated freshwater (dissolved solids of 540 

mg/L) and brine (dissolved solids of 70,800 mg/L). 

Intrinsic permeability values obtained using the 

brine were 31 and 7 4 percent greater than those 

obtained using freshwater. The largest difference 

in permeability was in the rock core having the 

greatest quantity of silt- and clay-sized particles, 

and is thought to be due to flocculation of clay by 

the saline water with a resulting increase in 

permeability. 

Intrinsic permeability using freshwater was 

determined from four Mesozoic rock core samples 

with various pressures on the core to simulate 

burial depths ranging from 400 to 6,000 feet. A 

decrease of intrinsic permeability values with increased pressure was evident but small, ranging 

from 8 to 11 percent. The largest percentage of 

decrease was in the rock core having the largest 

mean grain-sized particles. 

Two studies have been started to aid quantitative evaluation of the hydrologic characteristics of the Mesozoic aquifers. The first is a comprehensive compilation of hydraulic and lithologic 

properties of aquifers and confining units. The 

compilation is essential to the assessment of 

ground-water recharge and discharge areas and 

to an understanding of the interformational and 

intraformational ground-water movement. The 

second study consists of model simulation. Two 

models simulating ground-water flow in the 

Navajo Sandstone have been completed. One 

model simulates ground-water flow near the Sail 

Rafael swell and the other near Lake Powell (fig. 

148). Both models are generalized and are not 

suitable for specific evaluations.· Simulation of.the 

Navajo Sandstone near the San Rafael swell supports the concept that the aquifer is primarily 

recharged on the west side of the swell. Water 

moves around the swell to the east. Simulation 

of the Navajo Sandstone near Lake Powell was 

used to analyze the possible far-reaching effects 

caused by filling the impounded Lake Powell. 

This model simulates the local effects of the· inundation of the Navajo Sandstone by Lake Powell 

due to construction of Glen Canyon Dam. The 

simulation indicates that the hydraulic conductivity of the Navajo Sandstone was increased by 

fractures. Hydraulic conductivity values used in 

the model range from 0.25 to 3.5 ft/d. However, 

fracturing of the Navajo probably occurs near the 

synclinal axes because in the model the hydraulic 

conductivity had to be increased by a factor of 

three to obtain a reasonable match with observed conditions. A third model is being prepared for 

the region near the Four Corners area (fig. 148) 

and is a multilayered model. This model is to 

evaluate various ground-water flow definitionsfor 

the Mesozoic aquifers in the modeled area, and 

to determine which of these definitions is best 

suited to describe the regional aquifer system. 

Cenozoic Rocks 

The Cenozoic rocks are sedimentary rocks of 

Tertiary age. Aquifers of Tertiary age overlie 

much of the northern half of the study area itnd 

are exposed at the surface in the Green River and 

in the Great Divide-Washakie, Piceance, and Uinta basins (figs. 145 and 149). Tertiary rocks have 

been divided into four hydrogeologic units. In 

descending order, they are: (1) an u,pper Tertiary 

aquifer which contains sandstone, conglomerate, 

claystone and tuffofEocene, Oligocene, Miocene, 

and· Pliocene . age; (2) a middle Tertiary aquifer 

and confining unit which contain claystone, sandstone, shale, limestone, and conglomerate of 

Eocene and Oligocene age; (3) a lower Tertiary 

aquifer and confining unit which contain shale 

and sandstone of Paleocene and Eocene age; and 

(4) a basal Tertiary aquifer which contains sand-
40' 

35' 

115' 

IDAHO 

., 

' 

110' 

----- I -r·----- . 

I 

' I 

' ' 

I 

I ----- ----""' 

: I 

I 

UTAH 

ARIZONA 

EXPLANATION 

:> ·.:J MESOZOIC ROCKS 

105' 

WYOMING 

NEW MEXICO 

SCALE 1:6,000,000 

0 50 100 

I 

I 

[ __ 

I 

I 

I 

I 

' ' 

\ 

150 MILES 

0 50 100 150 KILOMETERS 

////// 

;;;::: AREA EXCLUDED FROM STUDY 

STUDY AREA 

Figure 147. -Areal extent of Mesozoic rocks in the Upper Colorado River Basin (modified from King and Beikman, 1974). 

229 
230 

stone, mudstone, shale, and coal of Paleocene and 

Eocene age. 

The hydraulic properties of the Tertiary formations vary markedly from basin to basin. Formations such· as the Wasatch of the lower Tertiary aquifer are water yielding in the Green 

River and Great Divide-Washakie basins, but do 

not transmit significant quantities of water to 

wells in the Piceance and Uinta basins. Lake 

deposits in the Green River Formation of the 

same hydrogeologic unit form a regional aquifer 

in the Piceance basin where they are fractured; 

elsewhere, this hydrogeologic unit is a confining 

unit. Because of the large variability of the 

hydraulic properties of the Tertiary aquifers, as 

well as the relative hydrologic isolation of the major Tertiary basins, the Uinta, Piceance, and 

Wyoming basins are discussed separately. 

In the Uinta basin, the Duchesne River Formation of the middle Tertiary aquifer is most productive; however, it is limited in areal extent to 

the northern half of the basin. The Uinta Formation of the same hydrogeologic unit is used extensively for water supplies. An inventory of water 

wells undertaken as part of the study indicates 

that the Green River and Wasatch Formations 

are not used extensively for water supply. The 

North Horn Formation (the basal Tertiary 

aquifer) is also not used for water supply. 

The thickness and depth of burial of the Tertiary aquifer have been mapped from geologic and 

geophysical logs throughout the Uinta basin as 

part of the study. The total thickness of Tertiary 

sediments in the north-central part ofthe.Uinta 

basin exceeds 15,000 feet. For this reason, few 

wells have been drilled through the entire Tertiary sequence. 

Aquifer characteristics of the Tertiary rocks 

in the Uinta basin are dependent upon the 

relative amount of sandstone and degree of fracturing. The Duchesne River and Uinta Formations consist of varying amounts of sand interbedded with shale. However, the most 

permeable zones are the rocks that were extensively fractured. Estimates of hydraulic conductivity for the Duchesne River Formation range 

from less than 1 ft/d for unfractured rocks to 500 

ft/d for fractured rocks. Work is planned to 

establish a regional relation between hydraulic 

conductivity and fracture pattern. The hydraulic 

conductivity of the formations underlying the 

Uinta Formation is generally less than 1 ft/d. 

The Piceance basin (fig. 145) is the largest 

area of oil-shale development in the western 

United States. The important Tertiary aquifer in 

the Piceance basin is the Uinta Formation and 

parts of the Parachute Creek Member of the 

Green River Formation. The depth of burial and 

thickness of these formations have been mapped 

in the principal area of oil-shale development, and 

many hydrologic studies have been completed 

there. The role of this study in this area is 

primarily to extend the results of other investigations southward from the area of oil-shale 

development to the part of the structural basin 

that lies south of the Colorado River. 

In Wyoming, the Fort Union Formation and 

the Wasatch Formation and their equivalents are 

the most important hydrogeologic units of the 

Tertiary aquifer. The Wasatch and Green River 

Formations interfinger around the periphery of 

both the Green River and Washakie basins. 

Sparse well data show that the Wasatch Formation also occurs in the deep parts of these basins, 

where the formation is completely overlain by 

confining units of the Green River Formation. 

The Fort Union and Wasatch Formations, or their 

equivalents, are found throughout most of the 

study area in Wyoming. The thickness of formations of the Tertiary aquifer has been mapped 

utilizing existing data and limited field reconnaissance. However, it has been difficult to identify formation contacts in the subsurface. The 

similar lithology of the Fort Union and Wasatch 

Formations has prevented accurate determinations of their contact from geologic and 

geophysical logs. Accordingly, a generalized map 

of the combined thickness of the Fort Union and 

Wasatch Formations has been made. The maximum combined thickness of these units is about 

11,000 feet near Pinedale, WY. Areas of thickness 

greater than 7,000 feet occur near -Flaming Gorge 

Reservoir and in the center of the Great Divide 

and Washakie basins. 

The ability of the Wasatch and Fort Union 

Formations to transmit and store water is being 

evaluated. Hydraulic characteristics of the formations were evaluated from sparse aquifer-test, 

specific-capacity, and drill-stem test data. The 

most reliable estimates of the aquifer properties 

have been made in the northern Green River 

basin. A series of aquifer tests made at different 

depths indicate that the hydraulic conductivity 

of the Wasatch Formation, which is about 2 ft/d, 

is fairly uniform from land surface to a depth of 

2,000 feet. However, at 5,000 feet below land surface, the hydraulic conductivity is much lower 

(7 x lo-s ft/d) , and below 7,000 feet the hy-
40 ' 

35' 

115 ' 

IDAHO 

----- I ,---------------~ 

: I 

I 

UTAH 

t- --------- ' ' I 

ARIZONA 

110' 105' 

I 

I 

' 

l--

WYOMING 

COLORADO 

NEW MEXICO 

SCALE 1:6,000,000 

50 100 150 MILES 

0 50 100 150 KILOMETERS 

EXPLANATION 

AREA OF FLOW MODEL 

NEAR SAN RAFAEL SWELL 

~///// '/////. AREA EXCLUDED FROM STUDY /////, 

AREA OF FLOW MODEL 

NEAR LAKE POWELL STUDY AREA 

AREA OF FLOW MODEL 

NEAR FOUR CORNERS 

Figure 148.- Location of flow models of the Mesozoic aquifer, Upper Colorado River Basin regional aquifer system. 

231 
232 

draulic conductivity of the Wasatch is further 

reduced (5 x 10- 4 ftld). 

Potentiometric surface maps have been prepared in many areas where the Wasatch Formation is exposed at the surface. These maps 

115" 

40" 

35" 

I 

' I 

. 

. 

I 

IDAHO 

r---- ------------

ARIZONA 

110" 

generally show that recharge occurs on the 

periphery of the basins and in upland areas, and 

ground water discharges to streams in the center 

of the basins. In the Great Divide basin (fig. 145), 

water in the Wasatch Formation discharges to 

105" 

I 

. 

[ __ WYOMING 

COLORADO 

SCALE 1.6,000,000 

50 100 150 MILES 

0 50 100 150 KILOMETERS 

EXPLANATION 

CENOZOIC ROCKS 

AREA EXCLUDED FROM STUDY 

STUDY AREA 

Figure 149. -Areal extent of Cenozoic rocks in the Upper Colorado River Basin (modified from King and Beikman, 1974). 
salt flats and phreatophytes. The rate of 

evapotranspiration is large enough to prevent formation of permanent lakes in the Great Divide 

basin. 

Water-level data are available for the 

Wasatch Forma~ion in areas overlain by the 

Green River Formation. Flowing wells are common, and heads are scheduled to be measured. A 

preliminary examination of available water-level 

data has shown little variation in heads with 

depth. The data examined to date primarily represent the Wasatch Formation in outcrop areas. As 

additional data are collected and interpreted, it 

is anticipated that head variation with depth will 

be observed. 

Quality of Water 

Water-quality investigations in the Upper 

Colorado River Basin are intended to supplement 

hydrologic investigations and to serve as an independent check on ground-water flow directions, 

velocities, and aquifer properties. 

A water-quality data base has been made 

that includes information from the W ATSTORE 

data base of the U.S Geological Survey, from 

petroleum companies, and from published reports. 

Maps showing concentrations of dissolved solids 

have been prepared for the principal 

hydrogeologic units (Freethey and others, 1984). 

The water-quality trend provides an independent 

check of recharge, ground-water movement, and 

discharge interpreted from potentiometric-surface 

maps and simulations. 

Additional water samples have been collected 

from the principal hydrogeologic units for 

analyses of stable isotopes and carbon-14. This 

isotope-and carbon-14 information will help 

develop chemical-reaction models. The stableisotope information provides independent determinations of mixing of water between the 

hydrogeologic units. This mixing generally occurs 

between freshwater from recharge areas and 

brine in the deep hydrogeologic units. Each of 

these determinations will aid in refining the concepts of ground-water flow in the Upper Colorado 

River Basin. 

PUBLISHED REPORTS 

Reports 

1. Freethey, G. W., Kimball, B. A., Wilberg, D. 

E., and Hood, J. W., 1984, General 

hydrogeology of aquifers of Mesozoic age, 

Upper Colorado River Basin-excluding the 

San Juan Basin-Colorado, Utah, Wyoming, 

and Arizona: U.S. Geological Survey OpenFile Report 84-716. 

2. Kimball, B. A., 1984, Ground water age determinations, Piceance Creek Basin, Colorado: 

National Water Well Association, Proceedings, First Canadian/ American Conference on Hydrogeology, June 22-26, 1984, 

Banff, Alberta, Canada, p. 267-283. 

3. Taylor, 0. J., Hood, J. W., and Zimmerman, 

E. A., 1983, Plan of study for the regional 

aquifer-systems analysis of the Upper Colorado River Basin in Colorado, Utah, 

Wyoming, and Arizona: U.S. Geological 

Survey Water-Resources Investigations 

Report 83-4184, 23 p. 

4.-----1984, Hydrogeologic framework of 

the Upper Colorado River Basin-excluding 

the San Juan Basin-Colorado, Utah, 

Wyoming, and Arizona: U.S. Geological 

Survey Hydrologic Investigations Atlas 687 

[in press]. 

5. Teller, R. W., and Chafin, D. T., 1984, Selected 

drill-stem test data for the Upper Colorado 

River Basin: U.S. Geological Survey WaterResources Investigations Report 84-4146. 

REFERENCES CITED 

Freethey, G. W., Kimball, B. A., Wilberg, D. E., and Hood, 

J. W., 1984, General hydrogeology of aquifers of 

Mesozoic age, Upper Colorado River Basin-excluding 

the San Juan Basin-Colorado, Utah, Wyoming, and 

Arizona: U.S. Geological Survey Open-File Report 

84-716. 

Grose, L. T., 1972, Tectonics, in Geologic atlas of the Rocky 

Mountain region: Denver, Rocky Mountain Association 

of Geologists, p. 35-44. 

Iorns, W. V., Hembree, C. H., and Oakland, G. L., 1965, Water 

resources of the Upper Colorado River Basin-Technical 

Report: U.S. Geological Survey Professional Paper 441, 

370 p. 

King, P. B., and Beikman, H. M., 1975, Geologic map of the 

United States, exclusive of Alaska and Hawaii: U.S. 

Geological Survey Special Geologic Map, scale 

1:2,500,000, 3 sheets. 

Price, Don, and Arnow, Ted, 1974, Summary appraisals of the 

Nation's ground-water resources-Upper Colorado 

Region: U.S. Geological Survey Professional Paper 

813-C, 40 p. 

Rocky Mountain Association of Geologists, 1972, Geologic atlas 

of the Rocky Mountain region: Denver, 331 p. 

Teller, R. W., and Chafin, D. T., 1984, Selected drill-stem test 

data for the Upper Colorado River Basin: U.S. 

Geological Survey Water-Resources Investigations 

Report 84-4146. 

Upper Colorado Region State-Federal Interagency Work 

Group, 1971, Upper Colorado Region Comprehensive 

Framework Study-Main Report and Appendices I-XV, 

XVII-XVIII. 

233 
234 

REGIONAL AQUIFER-SYSTEM ANALYSis-SUMMARY OF PROJECTS, 1978-1984 

PHASE I 

REGIONAL AQUIFER-SYSTEM ANALYSIS 

PROJECTS STARTED IN 1984 

CARIBBEAN ISLANDS REGIONAL AQUIFER-SYSTEM STUDY 

By Fernando Gomez-Gomez, San Juan, Puerto- Rico 

INTRODUCTION 

The Caribbean Islands regional aquifer 

system includes Puerto Rico, its offshore islands 

(Vieques, Culebra, and Mona), and the U.S. 

Virgin Islands (St. Croix, St. Thomas, and St. 

John.) However, the regional aquifer system 

study will investigate only the aquifers underlying the islands of Puerto Rico and St. Croix (fig. 

150). 

The island ·of Puerto Rico has an area of 

about 3,300 mi2 • It consists of a series of east-towest mountain ranges with a maximum altitude 

of about 4,400 feet, flanked on the north and south 

by foothills. Extensive coastal plains as much as 

8 -miles in width exist along the north and south 

coasts. Rainfall ranges from 200 inches in the rain 

forests of the northeast to 35 inches in the 

lowlands of the southwest. The annual average 

rainfall is about 75 inches. Streamflow varies 

seasonally with precipitation and topography 

(Bogart and others, 1964). The average runoff (25 

years of record) is about 23 in./yr (GOmez-Gomez 

and Heisel, 1980). 

HYDROGEOLOGIC FRAMEWORK 

The geology of Puerto Rico is complex and 

varied. The central core of the island consists 

largely of volcanic and intrusive rocks of late 

Cretaceous and early Tertiary age. These rocks 

are interbedded with lava flows and thin beds of 

limestone, which have been partly recrystallized 

in many places. The volcanic rocks and interbedded limestones have been complexly faulted, 

folded, metamorphosed, and intruded by dioritic 

rocks. Clastic sediments and limestones of 

Oligocene and Miocene age were deposited to the 

north and south of the central mountain core. The 

older clastic sediments are poorly sorted mixtures 

of gravel, sand, and fine-grained materials. These 

sediments grade upward into thick beds of 

relatively pure limestone.· The limestones have 

been subjected to intensive solutional activity at 

their outcrop areas. A mature karst topography 

has developed . mostly along the north coast 

(Giusti, 1978). 

The principal aquifers in Puerto Rico are as 

follows: 

1. Alluvial deposits of Quaternary age along 

the coastal areas and in some interior 

stream valleys. 

2. Limestone formations of Middle Tertiary 

age on the north and south coasts. 

3. Volcan-ic and igneous rocks of Late. Cretaceous and Early Tertiary age in the 

interior. 

Six ground-water provinces (McGuinness, 

1948) have been defined in Puerto Rico as follows 

(fig. 151): 

(1) North Coast, 

(2) South Coast, 

(3) East Coast, 

(4) West Coast, 

(5) Lajas.JV alley, and 

(6) Interior. · 
68" 67" 

19" 

18" Isla de Mona 

SCALE 1:2,500,000 

0 20 40 MILES 

0 20 40 KILOMETERS 

66" 

Atlantic Ocean 

Caribbean Sea 

Isla de 

Culebra 

~ 

Isla de Vieques 

65° 

VIRGIN ISLANDS 

~.~ St. Thomas St. John 

St. Croix 

~ 

Figure 150.-Study area (shaded) of the Caribbean Islands regional aquifer system. 

North Coast Ground-Water Province 

The North Coast Ground-Water Province extends for approximately 90 miles in length and 

averages 9 miles in width. It is comprised primarily of Tertiary limestones which dip north at approximately 5 degrees (fig. 152). The North Coast 

Ground-water Province has been further subdivided into six areas (fig. 151): 

(1) Aguada-Rio Grande de Arecibo, 

(2) Rio Grande de Arecibo-Rio Grande de 

Manati, 

(3) Rio Grande de Manati-Rio Cibuco, 

(4) Rio Cibuco-Rio de La Plata, 

(5) Rio de La Plata-Rio de Bayamon, and 

(6) Rio de Bayamon-Rio Grande. 

These subdivisions follow general drainage patterns of the principal rivers in the area. 

1. Aguada-Rio Grande de Arecibo.-This 

area, from Aguada to Rio Grande de Arecibo, is 

an elevated limestone plateau about 25 miles long 

and 12 miles in width. It is characterized by rolling hills on the northern half and intense karst 

development on the southern half. A water-table 

aquifer occurs within the Aymamon and Aguada 

Limestones. In the southern part of the outcrop 

areas, the older rocks of the Cibao Formation and 

Lares Limestone are a water-table aquifer. Depth 

to the water table normally exceeds 400 feet 

below land surface, except in lower areas along 

the narrow river valleys. Ground-water development has been minimal in this area (less than 10 

Mgal/d). Yields to wells range from 50 gal/min in 

the inland areas to as much as 1,500 gal/min in 

the vicinity of Rio Camuy. There is no information on yields from the older Cibao Formation and 

Lares Limestone. These formations dip toward 

the coast to depths of as much as 2,500 feet. Wells 

within one mile from the coast tapping the watertable aquifer are generally saline. 

2. Rio Grande de Arecibo-Rio Grande de 

Manati.-The principal aquifers in this area occur within stream-valley alluvium and limestone 

rocks. Alluvial deposits of Quaternary age as 

much as 300 feet thick consist of fine-grained 

sand, gravel, and clay. Yields to wells range from 

50 to 800 gal/min. Water-table and artesian 

aquifers exist in the limestone units. The watertable aquifer within the Aymamon and Aguada 

Limestones is the most productive. Yields to wells 

range from 150 to more than 2,000 gal/min. 

Within the outcrop areas of the Montebello 

Limestone Member of the Cibao Formation and 

Lares Limestone yields of wells are generally 

poor, seldom exceeding 100 gal/min. However, 

artesian conditions occur within these formations 

at depths in excess of 1,500 feet with initial heads 

of about 400 feet above sea level and well yields 

in excess of 2,000 gal/min. Ground-water 

withdrawals from the water-table aquifers are 

about 20 Mgalld, and 7 Mgal/d from the artesian 

system. The quality of the water in the watertable aquifer has been affected by seawater encroachment and chemical spills. 

-235 
236 

3. Rio Grande de Manati-Rio Cibuco.-The 

principal aquifer in this area occurs in the 

Aymamon and Aguada Limestones. The artesian 

system formed by the deeper Montebello Member 

of the Cibao Formation and Lares Limestone is 

known to occur toward the western section of the 

area. The Montebello Limestone, however, pinches out east of the Rio Grande de Manatl. There 

is no information on the possible occurrence of the 

artesian system east of the town of Manatl. 

Alluvial deposits are locally important within the 

Rio Grande de Manati lower valley. In the Rio 

18" 

30' 

18" 

67"30' 67" 66"30' 66" 65"30' 

SCALE 1:1,500,000 

Atlantic Ocean 0 10 20 MILES 

2 3 4 5 6 0 10 20 KILOMETERS 

7 

18--+ :·.Y 

17 ----.f i ...,... 

16 --t:t;L::2:::~ (:;: ;: ~--- 9 

L2Jill 

-

D 

~ 

-

(]!)[05~~~~------10 

LAJAS 15 14 13 12 VALLEY 11 

Caribbean Sea 

EXPLANATION 

UNCONSOLIDATED ALLUVIAL AND OLD ALLUVIAL DEPOSITS J QUATERNARY 

LIMESTONE J TERTIARY 

MASSIVE ANDESITIC TUFFS, SHALES, AND STRATIFIED ASH AND TUFF J CRETACEOUS 

AND 

VOLCANIC AND IGNEOUS ROCKS -- Granitoid intrusives including 

diorites, quartz diorites, granites, and other holocrystalline types TERTIARY 

SERPENTINITE 

BOUNDARY OF AQUIFER AREAS 

GROUND-WATER PROVINCES 

NORTH COAST 

1 Aguada to Rio Grande de Arecibo 

2 Rio Grande de Arecibo to Rio Grande de Manatl 

3 Rio Grande de Manatlto Rio Cibuco 

4 Rio Cibuco to Rio de La Plata 

5 Rio de La Plata to Rio de Bayamon 

6 Rio de Bayamon to R(o Grande 

EAST COAST 

7 Fajardo 

8 Naguabo - Humacao 

9 Yabucoa 

10 Maunabo 

J CRETACEOUS? 

SOUTH COAST 

11 Ponce to Patillas 

12Tallaboa 

13 Guayanilla 

14 Yauco 

15 Guanica 

WEST COAST 

16 Guanajibo 

17 Yaguez 

18 Ai'iasco 

19 Culebrinas 

LAJAS VALLEY 

INTERIOR 

20 Caguas-Juncos vaUeys 

21 Cayey valley 

Figure 151.-General geology of the Island of Puerto Rico and ground-water provinces. 
Cibuco Valley sediments are mostly composed of 

silty-clay and are not productive. 

Yields to wells in the water-table aquifer 

range from 200 to more than 2,000 gal/min. In 

the artesian aquifer initial heads of 500 feet above 

sea level and well yields of 1,000 gal/min were 

67" 66'30' 

18 

37 ' 

30" 

reported. Production from the alluvial deposits 

are usually less than 800 gal/min. Pumpage exceeds 30 Mgal/d. Seawater encroachment occurs 

in the water-table aquifer near the coast. 

4. Rfo Cibuco-Rfo de La Plata.-The 

principal aquifer in the area is also within the 

66' 

SCALE 1:500,000 

0 5 

Atlantic Ocean 

18 

30' 

18 

22 

30 

EXPLANATION LOCATION SHOWN ON FIGURE 150 

~ SURFICIAL DEPOSITS UNCONSOLIDATED 

- CAMUY FORMATION 

- AYMAMON LIMESTONE 

- AGUADA LIMESTONE 

67 ' 

FEET 

A 1000 

Sea level 

-1000 

-2000 

- 3000 

-4000 

-5000 

-6000 

66'30' 

- CIBAO FORMATION 

- LARES LIMESTONE 

R00M MUCARABONESSAND 

SAN SEBASTIAN FORMATION 

AND VOLCANIC ROCKS 

VERTICAL EXAGGERATION 14 x EXPLANATION 

[illill]] 

-

~ 

-

D 

-

AYMAMON LIMESTONE 

AGUADA LIMESTONE 

CLASTIC MEMBER OF THE 

CIBAO FORMATION 

MONTEBELLO LIMESTONE MEMBER 

OF THE CIBAO FORMATION 

GUAJATACA MEMBER 

QUEBRADA ARENAS LIMESTONE MEMBER 

OF THE CIBAO FORMATION 

-

-

-

D 

~ 

RIO INDIO LIMESTONE MEMBER 

OF THE CIBAO FORMATION 

LARES LIMESTONE 

MUCARABONES SAND 

SAN SEBASTI..(N FORMATION 

VOLCANIC ROCKS 

A' 

Figure 152.- Generalized subsurface geology of the North Coast Ground-Water Province of Puerto Rico. 

237 
238 

Aymamon and Aguada Limestones. Alluvial 

deposits occur in the upper reaches of the Rio 

Cibuco. The occurrence of an artesian system 

within the Cibao Formation and Lares Limestone 

is uncertain. Yields to wells in the water-table 

aquifer range from 200 to 2,000 gal/min. In the 

alluvial aquifers, well yields seldom exceed 150 

gal/min. Withdrawals in the area exceed 20 

Mgal/d. Seawater encroachment occurs in the 

coastal areas. A major chemical spill has affected 

a large segment of the aquifer near the town of 

Vega Alta. 

5. Rio de La Plata-Rio de Bayamon.-The 

Aguada Limestone forms the principal freshwater 

aquifer in the area. Most of the overlying 

Aymamon Limestone contains saline water 

because of its proximity to the coast. The Cibao 

Formation, which underlies the Aguada 

Limestone, is composed mostly of clay and marl 

and yields little water to wells. The Mucarabones 

Sand, a local aquifer, underlies the Cibao Formation. Alluvial deposits as much as 200 feet thick 

occur along the entire section. 

Yields to wells from the Aguada Limestone 

range from 200 to 600 gal/min. Wells tapping the · 

Mucarabones Sand near metropolitan San Juan 

produce as much as 100 gal/min. The alluvial 

deposits contain freshwater as a thin lens (about 

100 feet thick) floating above a saline water body. 

Total withdrawals from the area are about 10 

Mgalld. Seawater encroachment occurs in the 

Campanillas and Levittown areas. 

6. Rio de Bayamon-Rio Grande.-The most 

productive aquifer in the metropolitan San Juan 

area is formed by clastic sediments and beach 

deposits of Tertiary and Quaternary age. The 

Mucarabones Sand underlies the Aymamon and 

Aguada Limestones on the western part of the 

section. Most of the Aymamon and Aguada 

Limestones contain saline water throughout the 

area. 

Yields to wells from the unconsolidated 

deposits range from 30 to 150 gal/min. Wells tapping the Aguada Limestone in the eastern part 

can yield as much as 800 gal/min. Withdrawals 

are less than 10 Mgal!d. Urban development has 

reduced recharge to the ground-water system. 

Seawater encroachment occurs throughout the 

area. 

Recharge to the aquifers along the north coast 

is mostly from precipitation. Discharge occurs 

mostly to streams in the coastal areas or to the 

seabed. Ground-water contamination with toxic 

organic compounds has been detected in water 

samples taken from 25 wells. Seawater encroachment as a result of overpumping is becoming 

widespread near the north coast. 

South Coast Ground-Water Province 

The South Coast Ground-Water Province conists of an alluvial plain and four alluvial valleys 

cut into Tertiary Limestones. Volcanic rocks 

underlie most of the eastern third of the south 

coast. The alluvial plain extends about 40 .miles 

from Ponce to Patillas, averaging 3 miles in width 

from the coast to the foothills. The alluviated 

valleys from west to east include the areas of (1) 

Guanica, (2) Yauco, (3) Guayanilla, and (4) 

Tallaboa (fig. 151). 

The alluvial plain consists of a series of 

coalescing fans formed by fast flowing intermittent streams. Sediments of Holocene to 

Pleistocene age . are mostly coarse-grained sand 

and gravel in the apex of the major fans, becoming finer-grained toward the coast and interfluvial areas. They range in thickness from 100 

feet at the shoreline toward the east to as much 

as 3,000 feet near Santa Isabel. 

Yields to wells along the alluvial plain range 

from 150 gal/min in the interfluvial areas to as 

much as 3,000 gal/min near·Gminica, averaging 

500 gal/min. Wells penetrating the Ponce 

Limestone below alluvium can yield as much as 

900 gal/min. Ground.:water withdrawals from the 

alluvial plain are about 120 Mgal/d. Although no 

significant seawater encroachment occurs, persisting cones of depression in water· levels may 

induce seawater contamination. Organic industrial chemicals have been detected in wells 

near Patillas, Guayama, and Juana Diaz. 

The four alluvial valleys are very similar in 

composition and hydrogeologic characteristics. 

The alluvium is as much as 200 feet thick, mostly 

composed of sand and gravel. Streams flow perennialy in each valley. The Ponce Limestone and 

Juana Diaz Formation of Tertiary age underly the 

four valleys. Total thickness of the Tertiary units 

may be as much as 4,000 feet thick near the coast, 

thinning to 150 feet near Guanica. 

Yields to wells tapping the alluvium range 

from 150 to 3,000 gal/min.· Several wells·also tapping the Ponce Limestone yield as much as 2,000 

gal/min. However, water from the limestone is 

more mineralizedthan·from the·alluvium, probably due to the existence of connate seawater in 

the limestone. The Ponce Limestone and Juana 

Diaz Formation are not considered an aquifer in 

the outcrop areas; Total ground-water 
withdrawals from the four alluvial valleys are 

about 20 Mgal/d. The aquifers were overpumped 

through 1980, but presently are underutilized due 

to availability of surface water and reduction in 

irrigated acreage. 

East Coast Ground-Water Province 

The East Coast Ground-Water Province includes the alluvial valleys in Fajardo, NaguaboHumacao, Yabucoa, and Maunabo (fig. 151). The 

alluvium in most of the areas consists of clay and 

silt, except in the Y abucoa and Maunabo Valleys, 

where coarse-grained sand predominates. The 

deposits range from 100 feet thick near Fajardo 

to 400 feet near Y abucoa. 

Yields to wells range from 100 to 2,000 

gal/min. The most productive wells occur in the 

Yabucoa Valley. Water withdrawals from the 

area are about 10 Mgalld. High concentrations of 

manganese and iron occur in wells at Humacao, 

Yabucoa, and Maunabo. 

West Coast Ground-Water Province 

The West Coast Ground-Water Province includes the alluvial valleys of (1) Rio Guanajibo, 

(2) Rio Yaguez, (3) Rio Grande de Aiiasco, and (4) 

Rio Culebrinas (fig. 151). The alluvium is mostly 

detrital clay, sand, silt, and gravel of Quaternary 

age ranging in thickness from 60 feet to as much 

as 450 feet. Limestone deposits of Tertiary or Upper Cretaceous age and unknown thickness occur 

beneath the alluvial deposits in the western Rio 

Guanajibo Valley. Yields to wells tapping the 

alluvium range from 50 gal/min to as much as 400 

gal/min in the Rio Guanajibo Valley. Wells tapping the limestone in the Rio Guanajibo Valley 

can produce as much as 1,500 gal/min. 

Withdrawals are about 8 Mgalld, most of it in the 

Rio Guanajibo Valley. 

lajas Valley 

The Lajas Valley (fig. 151) includes about 40 

mi2 of volcanic rocks of Cretaceous age in 

southeastern Puerto Rico. Limestone rocks of 

Cretaceous age (?) extend throughout the area 

overlain by unconsolidated deposits of Quaternary age. The thickness of the limestones is 

unknown, while the clastic deposits are as much 

as 200 feet thick. Most of the unconsolidated 

deposits are fine grained and yield little water to 

wells. Well yields from the limestone can be as 

much as 2,000 gal/min. However, most of the 

water in the valley is saline because of low 

recharge and of connate salty water. Actual 

withdrawals are less than 1 Mgalld mostly from 

wells tapping alluvial fans along the edge of the 

valley. 

Interior Province 

The Interior Province (fig. 151) includes the 

, central volcanic core of Puerto Rico, extending 

from west to east over an area of about 2,000 mi2 • 

The principal aquifers in the area occur in 

sedimentary, volcanic, and intrusive rocks of Late 

Cretaceous or Early Tertiary age. The most important aquifers are in the alluvial valleys of 

Caguas-Juncos and Cayey areas. The alluvium 

consists mostly of clay, sand, and gravel at 

Caguas-Juncos and clay with rock fragments at 

Cayey. Thickness of the unconsolidated deposits 

range from as much as 120 feet near Caguas to 

less than 35 feet in Cayey. Yields to wells average 

200 gal/min in the Caguas-Juncos area and 150 

gal/min in the Cayey area. Wells that tap fractured systems in the volcanic rocks can yield from 

15 gal/min to as much as 450 gal/min. 

Withdrawals from the Interior Province are about 

15 Mgal/d. 

Kingshill Aquifer in St. Croix 

The Island of St. Croix, with an area of 82 

mi2 , is underlain by volcanic and sedimentary 

rocks of Late Cretaceous and Early Tertiary age. 

These rocks have been intruded by gabbro and 

diorite of Tertiary age. The east and west parts 

of the island are separated by a graben filled with 

volcanic ash overlain by marl and limestone 

known as the Kingshill Marl (fig. 153). 

The Kingshill aquifer in St. Croix is the most 

important ground-water system in the U.S. 

Virgin Islands. It covers about 30 mi2 in central 

St. Croix. Locally, it varies from marl to sandstone of Miocene to Oligocene age lying unconformably on bedrock. Alluvial deposits blanket 

the area to a thickness less than 20 feet except 

in stream courses where they are 200 feet thick. 

Ground water in the Kingshill aquifer occurs 

under water table conditions in the alluvial 

deposits and Kingshill Marl. Yields to wells may 

be as much as 100 gal/min, but are usually about 

30 gal/min. Withdrawals are about 800,000 gal/d. 

Saline water has affected numerous wells. Its 

source is either saltwater encroachment from the 

coast or upward coning of underlying saline 

water. 

239 
240 

17" 

45' 

64.55' 

~ 

~ 

-

D 

~ 

64.50' 64 °45' 

Caribbean Sea 

Caribbean Sea 

EXPLANATION 

ALLUVIUM AND BEACH DEPOSITS 

KINGSHILL MARL 

JEALOUSY FORMATION 

DIORITE INTRUDED INTO MOUNT EAGLE VOLCANICS 

MOUNT EAGLE VOLCANICS 

64°40' 

J 

l 

I 

I 

I 

I 

I 

I 

I 

J 

0 

0 

64°35' 

~ Buck Island 

SCALE 1:250,00 

2 4 MILES 

2 4 KILOMETERS 

QUATERNARY 

TERTIARY 

CRETACEOUS 

FEET ,-----------------------------------------------------------------------------------, 

A' 

100 

-100 

-200 

-300 

EXPLANATION 

t::\/inf.l ALLUVIUM D UNDEFINED 

g KINGSHILL MARL POTENTIOMETRIC SURFACE 

- JEALOUSY FORMATION WELL 

MOUNT EAGLE GROUP 

Figure 153. - Generalized subsurface geology of the Island of St. Croix, U.S. Virgin Islands, and a typical cross section 

of the Kingshill aquifer. 
SUMMARY 

The information above shows that the most 

important ground-water areas in Puerto Rico are 

the limestone aquifers of the north coast and the 

alluvial aquifers of the south coast. In the U.S. 

Virgin Islands, the Kingshill aquifer of St. Croix 

is the only significant ground-water area. The 

Caribbean Islands regional aquifer system study 

will concentrate in these three areas. The 

regional aquifer system study will entail compilation of existing information and development of 

computer-based flow models to understand the 

flow systems, to evaluate the potential for 

seawater encroachment near the coast, and to 

study the effects of change in irrigation patterns. 

An ongoing cooperative investigation with the 

Department of Natural Resources of the Commonwealth of Puerto Rico includes studying the 

occurrence and movement of ground water in the 

North Coast Ground-Water Province. This 

cooperative project involves developing flow 

models (Torres-Gonzalez and Wolansky, 1984); 

therefore, the effort of the Caribbean Islands 

regional aquifer system study on the north coast 

interacts closely with the cooperative study and 

will be concentrated on geochemistry as well as 

the interconnection between streams and the 

shallow water-table aquifers. The regional aquifer 

system study also will entail some exploratory 

drilling to fill the information gap in the data 

base. 

In St. Croix, a ground-water flow model of the 

Kingshill aquifer will be developed and 

calibrated. Saltwater encroachment as a result of 

ground-water development also will be 

investigated. 

REFERENCES CITED 

Bogart, D. B., Arnow, Ted, and Crooks, J. W., 1964, Water 

resources of Puerto Rico, a progress report: Commonwealth of Puerto Rico Water Resources Bulletin 4, 

120 p. 

Giusti, E. V., 1978, Hydrogeology of the karst of Puerto Rico: 

U.S. Geological Survey Professional Paper 1012, 68 p. 

Gomez-Gomez, Fernando, and Heisel, J. E., 1980, Summary 

appraisals of the Nation's ground water resources 

Caribbean Region: U.S. Geological Survey Professional 

Paper 813-U, 32 p. 

McGuinness, C. L., 1948, Groundwater resources of Puerto 

Rico: Puerto Rico Aqueduct and Sewer Service, 613 p. 

Torres-Gonzalez, A. and Wolansky, R. M., 1984, Planning 

report for the comprehensive appraisal of the ground 

water resources of the north coast limestone area of 

Puerto Rico: U.S. Geological Survey Open-File Report 

84-427, 32 p. 

241 
242 

PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS STARTED IN 1984 

MICHIGAN BASIN REGIONAL AQUIFER-SYSTEM STUDY 

By Lindsay A. Swain, Reston, Virginia 

Michigan lies in a great structural bedrock 

depression-the Michigan Basin. The youngest 

bedrocks are at the center of the basin, and the 

oldest bedrocks crop out along the basin circumference. The important aquifers in the 

Michigan Basin are glacial aquifers and sandstone aquifers of the Marshall and Saginaw Formations of Paleozoic age. The Michigan Basin 

regional aquifer system study is designed to in-

:vestigate the glacial aquifers and the underlying 

sandstone aquifers which cover about two-thirds 

of the lower peninsula of the State of Michigan · 

(fig. 154). The study is scheduled for completion 

within 4 to 5 years. 

Approximately 43 percent of Michigan's population, and nearly 100 percent of the State's 

domestic water supplies, are dependent on ground 

water (Bedell, 1982). In 1980, about 220 Mgal/d 

of ground water were pumped for water supplies 

(Solley and others, 1983). Of this, about 60 percent of the water was pumped from the glacial 

aquifers, 25 percent from the Saginaw and Marshall Formations, and the remaining 15 percent· 

from other hydrogeologic units, such as the unnamed redbeds and Grand River Formation of 

Pennsylvanian age. 

Nearly all of the study area is overlain by 

glacial deposits which range from a few inches to 

about 1,000 feet. Well yields in the glacial 

deposits are highly variable, depending on the 

thickness and characteristics of the deposits, 

whether the deposits are till, lacustrine sand and 

clay, or outwash sanc:l and gravel. The distribution and characteristics of the glacial deposits are 

not well delineated nor is there a good understanding of the interconnection between the 

glacial deposits and under lying bedrock aquifers. 

The sandstone of the Marshall and Saginaw 

Formations is the major aquifer to supply 

freshwater to the communities in the basin. In the 

Lansing-East Lansing area, where the Saginaw 

Formation is the principal source of water supply, a cone of depression has extended over 100 

mi2 • Water levels near the pumping center are as 

much as 160 feet below the predevelopment level. 

In the Flint area, where both the Saginaw and 

Marshall Formations are used for public water 

supply, water having high chloride concentrations has migrated to the pumping centers; some 

of the well fields eventually were abandoned 

because of this migration. Areal and vertical 

distributions of saline water beneath the 

freshwater are not known; neither is the origin 

of the saline water. In places, the saline water 

may be as shallow as 100 feet below land surface; 

in other areas, the saline water may be more than 

1,000 feet in depth. Where the Marshall Formation is confined, formations both above and below 

contain evaporite deposits. Water leaking 

through the confining . units may dissolve the 

evaporites reswting in the accumulation of saline 

water in the Marshall Formation. Saline water 

in the Saginaw. Formation seems different from 

that in the Marshall Formation and appears 

unrelated to the confining units. The predominant area where the Saginaw Formation contains 

saline water is in the Saginaw Bay area. 

To ensure that suffic~ent ground water can 

be developed in the basin, it is critical to know 

the relation between development of ground 
44 • 0 ~~~~ebago 

WISCONSIN 

42. 

ILLINOIS 

82° 

ONTARIO 

I I ~====~==5=0==~----~ OHIO I 0 50 

-250-

100 KILOMETERS 

EXPLANATION 

AREA WHERE SAGINAW FORMATION IS OVERLAIN BY GRAND 

RIVER FORMATION OR JURASSIC REDBEDS OR BOTH 

AREA WHERE THE SAGINAW FORMATION SUBCROPS 

AREA WHERE THE MARSHALL FORMATION SUBCROPS 

COLDWATER SHALE 

LINE OF EQUAL THICKNESS OF MARSHALL FORMATION --

Interval 250 feet, dashed where approximately located 

STUDY AREA 

Figure 154.- Study area of the Michigan Basin regional aquifer system. 

Georgian 

Bay 

ONTARIO 

243 
244 

water in the Michigan Basin and the movement 

of the saline water. The origin of the saline water 

is also important as it may be critical to understand the movement of the saline water to the 

freshwater aquifer system due to development. 

The study will use variable density flow 

models to evaluate all hypotheses and to understand the flow system, from land surface down to 

a major confining unit of the Coldwater Shale of 

early Mississippian age, before development and 

after development. The Coldwater Shale was 

chosen as the lower boundary of the flow system 

due to its low permeability. Therefore, the study 

area is bound by the contact between the Coldwater Shale and the Marshall Formation, the 

lowermost formation of the studied aquifer 

system (fig. 154). The established flow models will 

be used to evaluate the impact of future 

development. 

REFERENCES CITED 

Bedell, D. J., 1982, Municipal water withdrawals in 

Michigan: Michigan Department of Natural 

Resources, Water Management Division, 43 p. 

Solley, W. B., Chase, E. B., and Mann, W. B., IV, 

1983,Estimated use of water in the United States 

in 1980: U.S.Geological Survey Circular1001, 

56 p. 
PHASE I REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS STARTED IN 1984 

SOUTHERN CALIFORNIA ALLUVIAL BASINS 

REGIONAL AQUIFER-SYSTEM STUDY 

By Peter Martin, San Diego, California 

The southern California alluvial basins 

regional aquifer system study is scheduled for 

completion within 4 to 5 years. The study area 

is shown in figure 155. The study will be conducted in two parts: (1) the first part will produce 

a comprehensive bibliography and a report that 

will characterize regional ground-water conditions and identify the major ground-water problems and issues; and (2) the second part of the 

study will describe and categorize the regional 

geohydrology of the alluvial basins and analyze 

the major problems and issues that affect the 

utilization of ground water. 

The geohydrology of the alluvial basins will 

be described using extensive data files and 

published reports. In basins where there is a scarcity of data, field investigations may be necessary 

to collect additional data. An attempt will be 

made to use geostatistics to extrapolate data from 

basins with extensive data to basins with limited 

data of the same category. 

The study area includes 88 identified alluvial 

basins which will be grouped according to common characteristics and relationships. Elements 

that will be used to categorize the basins include: 

(1) depositional history of the basin fill, (2) groundwater flow characteristics, (3) recharge and 

discharge characteristics, and (4) water quality. 

Three major water problems or issues have 

been selected for detailed investigations. They 

are: (1) saltwater intrusion in coastal basins, (2) 

flow between aquifer layers, and (3) the quantity 

and distributuion of recharge in coastal and 

desert basins. The study plans for the different investigations are discussed below. 

Saltwater Intrusion In Coastal BasinsNearly all of the alluvial coastal basin aquifers 

in southern California are affected by saltwater 

intrusion. Data on hydraulic characteristics and 

water quality in coastal basins will be analyzed 

to determine the natural geohydrologic and 

human activities that may affect the rate of 

saltwater intrusion. Field investigations may be 

necessary where there are little or no data. 

Geohydrologic and human activities that will be 

studied include: the presence of offshore faults 

and their effect on ground-water movement, the 

presence of permeable buried channel deposits in 

otherwise impermeable clay layers, tidal movement of saltwater into stream channels and 

subsequent vertical movement into underlying 

aquifers, the presence of multiple aquifer layers 

and the movement of saltwater between pumped 

and unpumped aquifers, the distribution and 

quantity of pump age, and artificial recharge and 

other management alternatives used to control 

saltwater intrusion.The relative importance of 

the various controlling factors on movement of 

saltwater will be evaluated using mathematical 

ground-water flow models. Solute-transport 

models may be used to simulate saltwater movement due to pumping. 

Flow Between Aquifer Layers-In general, 

there are at least three distinct aquifers in the 

coastal basins: (1) a shallow perched aquifer, that 

is virtually unconfined, in the upper part of 

alluvial deposits of Holocene age; (2) a principal 

freshwater aquifer, that is generally confined, 

comprising the lower part of the Holocene 

245 
246 

San 

OREGON ! IDAHO 

-----------------T·----------_1·----------T----------

SCALE 1:7,500,000 

: i I . : i I . 

i \ 

i \ : NEVADA j UTAH 

I . 

\ 

\ 

i 

\ r··-

i 

ARIZONA 

50 100 150 200 MILES 

EXPLANATION 

STUDY AREA 

Figure 155.-Study area (shaded) of the Southern California 

Alluvial Basins regional aquifer system. 

alluvium and nearly all sediments of Pleistocene 

to mid-Pliocene age; and (3) a deep saline-water 

aquifer that occurs in the consolidated rocks of 

Tertiary age and that underlies the principal 

freshwater aquifer. The desert basins also contain 

at least three distinct aquifers: (1) unconsolidated 

alluvial deposits of Pliocene to Holocene age that 

comprise the principal aquifer, (2) loosely consolidated sedimentry deposits of Tertiary age, and 

(3) consolidated rocks of pre-Tertiary age. 

The mathematical models will be used to help 

gain an understanding of the ground-water flow 

between aquifer layers in coastal and desert 

basins. The aquifer system will be divided into 

several layers to simulate water movement 

among different water-bearing zones in coastal 

basins and among the interbedded alluvial and 

lacustrine deposits in desert basins. The models 

will be used to identify the parameters that have 

the greatest control over flow between aquifer 

layers and to determine the acceptable range in 

values of these parameters. The models will also 

be used to help evaluate the potential for waterquality degradation during different levels of 

stresses in the principal aquifer. Data required 

for the models will be compiled from existing 

reports and data files. If necessary, new data will 

be collected. 

Geochemical techniques will also be used to 

help determine the amount of ground-water flow 

between aquifer layers. Concentrations of common dissolved ions, trace elements, and isotopes 

will be used to quantify the flow contributed to 

the sample wells from each aquifer layer. In some 

of the basins, this will require sample collection, 

especially for isotope analyses. 

Quantity And Distribution Of Recharge In 

Coastal Or Desert Basins-In southern California, 

aquifer recharge is derived from: (I) infiltration 

of streamflow, (2) infiltration of precipitation, and 

(3) irrigation return flow. Recharge from streams 

is usually estimated from the decrease in 

streamflow between two gaging stations; 

however, in the arid and semiarid basins of 

southern California, this method is impractical 

due to the large number of small streams and the 

poorly integrated drainage network. Several 

methods that have been used to estimate infiltration of streamflow include: (1) rainfall runoff relationship, (2) basin characteristics, (3) channel 

geometry, and ( 4) model simulation. The differences between methods and the effectiveness 

of the methods will be evaluated with field 

observations. 

Infiltration of precipitation in coastal basins 

is usually estimated from rainfall-infiltration 

functions developed for a particular basin. The 

transferability of the rainfall-infiltration functions, from basin to basin within each category 

of the basins, will be evaluated in depth. Direct 

infiltration of precipitation in desert basins is 

usually considered negligible. To determine 

qualitatively if recharge from precipitation is occuring in the desert, soil core samples will be 

analyzed to determine tritium concentrations 

with depth. 

The quantity and quality of irrigation return 

flow are major problems affecting the utilization 

of ground water in southern _California. The use 

of water for irrigation typically adds dissolved 

constituents in ground water. Consequently, as 

agricultural activities increase in a basin, the 

quality of the ground water is degraded. Problems 

common to agricultural areas include high concentrations of nitrate, dissolved solids, and pesticides. This study will delineate areas where 

agricultural activities have significantly degraded the ground-water quality. An attempt will 

be made to relate the degree of contamination in 

the principal aquifer to the thickness of the un-
saturated zone and the history of irrigation in 

selected basins. In basins where there is a large 

unsaturated zone and the principal aquifer has 

not been contaminated, the perched water table 

will be sampled to determine the vertical migration of irrigation return flow. 

Note from the editor-The activity of the 

Southern California Alluvial Basin Regional 

Aquifer-System Study was temporarily suspended 

in 1985. All resources related to this study were 

transferred to Central Valley, California, to intensify a phase II (followup) study. 

247 
248 

REGIONAL AQUIFER-SYSTEM ANALYSIS-SUMMARY OF PROJECTS, 1978-1984 

PHASE II 

REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

(followup studies) 

CENTRAL VALLEY REGIONAL AQUIFER SYSTEM, 

CALIFORNIA, PHASE II STUDY 

By Robert J. Gilliom, Sacramento, California 

A regional study of the Central Valley aquifer 

system conducted during 1978-82 identified 

several water-resource issues that are important 

to water management in the area but could not 

be adequately addressed within the regional scope 

of the study. One of the key water issues for the 

Central Valley is the effect of extensive irrigation 

on the water quality and flow system of the 

aquifers. This issue has recently come to the 

forefront of public, political, and scientific attention, with the discovery that subsurface 

agricultural drainage water from certain parts of 

the western San Joaquin Valley contains 

undesirably high concentrations of some trace 

elements, particularly selenium. 

The U.S. Geological Survey, in cooperation 

with the U.S. Bureau of Reclamation, is 

conducting a comprehensive regional study of the 

sources, occurrence, and movement of selenium 

and other trace elements in the hydrologic system 

of the western San Joaquin Valley. Phase II of 

the Central Valley regional aquifer system study 

is a complementary part of the overall study plan 

for the San Joaquin Valley which specifically 

focuses on (1) detailed eval nation of the 

hydrogeology of the aquifer system at a shallow 

depth (less than 200 feet) that may be affected by 

poor quality of irrigation return flow, and (2) a 

regional study of the ground-water quality of the 

entire San Joaquin Valley-both eastern and 

western parts. 

The hydrogeologic evaluation of the aquifer 

system at a shallow depth in the western San Joaquin Valley is the main focus of Phase II. The 

s~udy area with the poorest quality of irrigation 

return flow will consist of a ground-water flow 

model that relies on the extensive data collections 

and geochemical process studies that are 

separately funded as parts of the cooperative 

study with the U.S. Bureau of Reclamation. 

Simulation will be used to help characterize the 

shallow ground-water flow system, to provide 

quantitative estimates of rates and directions of 

flow including irrigation return flow, and to help 

understand subsurface movement of selenium 

and other chemical constituents. Preliminary 

ground-water flow models will be constructed at 

two scales: (1) agricultural field, and (2) alluvial 

fan (the Panoche fan) which covers about 200-300 

mi2 • Each model will provide insight into (1) interaction of the shallow water-bearing zone and 

the regional aquifer system, and (2) processes 

responsible for subsurface movement of chemical 

constituents. 

The regional study of ground-water quality 

in the San Joaquin Valley is the main focus of the 

Phase II study. The study will be developed by 

using recently collected data for the western part 

of the Valley and by extending the same type of 

data-collection effort for the eastern part of the 

Valley. The study will focus on major ions, and 

trace elements, with selective analyses for 

pesticides. Analyses of data for these sampling 

programs will involve statistical analyses of the 

areal distribution of chemical constituents in relation to hydrogeologic and environmental factors 

potentially affecting the ground-water quality, 

and application of geochemical models to assess 

the measured chemistry in relation to estimated 

equilibrium concentrations. 
PHASE II REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

FLORIDAN REGIONAL AQUIFER SYSTEM, PHASE II STUDY 

By Peter W. Bush, james A. Miller, Atlanta, Georgia, 

and Morris L. Maslia, Doraville, Georgia 

INTRODUCTION 

The Floridan regional aquifer-system study 

investigated and described the flow system from 

a regional and subregional perspective. During 

the course of that study, local aspects of the 

system that merited continued or more detailed 

work were noted but were not dealt with in order 

to fulfill the broader objectives of the initial study. 

The purpose of the Floridan regional aquifersystem phase II study is to investigate some of 

these local aspects. The phase II study was started 

in 1983 and is scheduled for completion in 1986. 

Four investigations are part of the phase II study. 

The locations of these investigations are shown 

in figure 156. A brief description of each activity 

follows. 

PETROGRAPHIC STUDY, CENTRAL FLORIDA 

A 2,000-foot test well was continuously cored 

in central Florida during the initial study. As part 

of the phase II studies, petrography of the cores 

was studied in detail to determine the effect that 

original carbonate depositional environment and 

postdepositional mineralogic change (diagenesis) 

have had on the porosity and permeability of the 

Floridan aquifer system. Thin sections of the core 

were examined with a petrographic microscope. 

X-ray analysis and scanning electron microscopy 

were used on selected core samples, and laboratory values of porosity and permeability were obtained from selected core intervals. 

Results of this petrographic study show that 

the primary control on carbonate porosity is the 

original depositional environment of the rock. Six 

general depositional environments were identified; only one high-energy, relatively coarsegrained limestone (foraminiferal grainstone) 

showed appreciable primary porosity and 

permeability. Dolomite in the core occurs both as 

a fine-grained primary deposit and as a fine to 

coarse-crystalline replacement (diagenetic) 

material. The replacement dolomites show considerable porosity and permeability, indicating 

that diagenesis is a secondary, but very important, factor in determining carbonate permeability. Anhydrite and gypsum that formed in a 

tidal-flat environment fill practically all the pore 

space in the carbonate rocks in certain horizons. 

Replacement dolomites appear to have formed in 

a mixed meteoric-seawater zone, during several 

episodes of dolomitization. 

Results of this petrographic study have been 

summarized in the article "Petrology of Lower 

and Middle Eocene Carbonate Rocks, Floridan 

aquifer, central Florida" by P. A. Thayer and J. 

A. Miller, published in volume 34 of Transactions 

of the Gulf Coast Association of Geological 

Societies (1984). 

SALTWATER MOVEMENT STUDY, 

HILTON HEAD ISLAND, SOUTH CAROLINA 

The potential exists for saltwater contamination of coastal freshwater supplies in areas 

where the Floridan aquifer system is unconfined 

or loosely confined. One such area is Hilton Head 

Island, a rapidly growing resort area along the 

southern coast of South Carolina. The freshwater 

supplies of the island are obtained from wells tapping the Upper Floridan aquifer. In 1984, water 

quality in the upper part of the Upper Floridan 

on the island was good. However, concentrations 

of chloride in water in the lower part of the Upper Floridan are greater than 250 milligrams per 

liter (mg!L), and water throughout the Upper 

249 
250 

Floridan 3 or 4 miles northeast of the island 

ranges from slightly saline t o very saline with 

depth. 

Head Island, and limestone of the Upper Floridan 

may crop out in the sea. Confinement by clay increases southeast and southwestward from the 

The Upper Floridan aquifer in the vicinity island. 

of Hilton Head Island is loosely confined by clastic 

materials, primarily sand and clay. The clastic 

materials thin a few miles northeast of Hilton 

Before ground-water development, the configuration of the Upper Floridan potentiometric 

surface suggests that the direction of natural flow 

30 ' 

25' 

0 

I 

I 

I 

GEORGI! 

<" tl 

,....., -- ..... 

r-./ Saltwater movement 

r study, Hilton Head ALABAMA / Island, South Carolina 

/ 

/ 

,_ -- / 

I ..... - ' 0 Effects of increased pumpa '- ,..... _, southwest Georgia I ··-··--· _:::::: ____ _ 

\ ··-··-·--·--·· 

GULF 

OF 

MEXICO 

Ta 

SCALE 1:6,500,000 

50 100 MILES 

0 50 100 KILOMETERS o .. o_ .. t;l" o .. oa 

0 

EXPLANATION 

SITE SPECIFIC INVESTIGATION, PHASE II STUDY 

APPROXIMATE UPDIP LIMIT OF THE 

UPPER FLORIDAN AQUIFER 

AREA OF THE UPPER FLORIDAN AQUIFER 

ATLANTIC 

OCEAN 

0 

jl 

Figure 156.-Site-specific investigations of the Floridan aquifer system, phase II study. 
in the aquifer in the vicinity of Hilton Head 

Island was east-northeastward, from the Savannah area across Hilton Head Island to a natural 

discharge area coincident with the loosely confined part of the Upper Floridan northeast of the 

island (fig. 157). 

Large withdrawals from the Upper Floridan 

centered in Savannah have created a deep 

regional cone of depression. The area influenced 

by the cone includes the vicinity of Hilton Head 

Island. Pumping at Savannah has reversed the 

original seaward gradient. The present direction 

of ground-water flow is west-southwestward from 

the area where the aquifer is loosely confined 

northeast of Hilton Head Island toward Savannah, as suggested by the 1980 potentiometric surface of the Upper Floridan (fig. 158). The Savannah pumping, combined with local pumping on 

Hilton Head Island, have reduced heads on the 

island about 10 to 30 feet. By 1980, heads were 

below sea level, but monitoring of concentrations 

of chloride over the past 25 years has not shown 

definite long-term changes in the freshwatersaltwater transition zone beneath the island. It 

is hypothesized that the transition zone has not 

moved appreciably from its predevelopment position, even though heads have been lowered 

substantially. 

Nevertheless, the transition zone is in a 

transient state, presumably seeking a new 

equilibrium position. A key question is, how fast 

is the transition zone moving toward a new 

equilibrium position? Is the movement on the 

order of geologic time, or hundreds of years, or 

tens of years? To answer these questions, the objective of the phase II study in the vicinity of 

Hilton Head Island is to determine the sensitivity 

of the transition zone to changes in freshwater 

discharge and to variations of properties and conditions in the Upper Floridan aquifer. The scope 

of the investigation is limited to a sensitivity 

analysis because detailed field data (specifically 

changes in pressure, density, concentrations of 

chloride, and aquifer properties with depth) are 

limited. 

A finite-element model for simulating density-dependent ground-water flow with solute 

transport is being used to determine how the position of the transition zone reacts to changes in 

freshwater discharge and to variations in aquifer 

properties and conditions. The model simulates 

cross-sectional flow along a flow path (proposed 

section shown in figs. 157-158). The first series 

of simulations are of predevelopment conditions. 

These simulations are used to test which aquifer 

properties and boundary conditions control the 

flow system, and test whether variation of these 

factors within reasonable limits can produce a 

simulated flow system compatible with the 

predevelopment flow system simulated during the 

initial study of the aquifer system. 

If the series of predevelopment simulations 

are successful, the results will be used as initial 

conditions for transient simulations that include 

solute transport (chlorides) over a timespan 

equivalent to that of ground-water development, 

or about 80 to 90 years. The 1984 boundary conditions will be used in a series of pumping periods 

over the simulated timespan. These simulations 

will test the hypothesis that it is possible for the 

transition zone to have remained virtually in its 

predevelopment position even as flow conditions 

changed during the 80 to 90 years of development 

in the area. 

EFFECTS OF INCREASED PUMPAGE, 

SOUTHWEST GEORGIA AND 

NORTHWEST FLORIDA 

The Upper Floridan aquifer in southwest 

Georgia is relatively thin (generally less than 200 

feet), has varying transmissivity, and is loosely 

confined. In contrast, the Upper Floridan in 

northwest Florida is relatively thick (generally 

400 to 500 feet), has much lower transmissivity, 

and is tightly confined. Ground-water development in both of these areas is increasing rapidly. 

Based on the initial study of the Floridan aquifer 

system in these two areas, a paper will be writ-

. ten to compare each area's response to the 1980 

and projected future ground-water development. 

Emphasis will be placed on discussion of the different flow regimens as well as the methods of 

analysis necessitated by the very different 

hydrologic conditions that occur in southwest 

Georgia and northwest Florida. 

REGIONAL POTENTIOMETRIC-SURFACE MAP, 

1985 

As part of the initial study, an aquifer-wide 

potentiometric-surface map of the Upper Floridan 

was constructed (Johnston and others, 1981). The 

map was based on water-level and pressure-head 

measurements made simultaneously in May 1980 

in more than 2,700 wells tapping the Upper 

Floridan. It is planned that a similar 

251 
252 

82' 

SCALE 1:1,250,000 

I 

,--J 

--~ 

10 20 30 MILES 0~00 KILOMETERS · .. 

10 20 30 KILOMETERS 

EXPLANATION 

- AREA OF HILTON HEAD ISLAND 

-20- ESTIMATED PREDEVELOPMENT POTENTIOMETRIC CONTOUR--

Shows altitude of potentiometric surface of the Upper Floridan 

aquifer. Contour interval, in feet, is variable. Datum is sea level 

APPROXIMATE UPDIP LIMIT OF THE UPPER FLORIDAN AQUIFER 

A--A' PROPOSED LINE OF SECTION FOR SIMULATION 

Figure 157.-Estimated predevelopment potentiometric surface of the Upper Floridan aquifer in the area of Hilton 

Head Island and vicinity; A-A' is the proposed line of section for simulation. 
82' 81 ' 

SCALE 1:1,250,000 

A' 

0 

I 

,--J 

----~ 

10 20 30 MILES 0~0 KILOMETERS · .. 

0 10 20 30 KILOMETERS 

EXPLANATION 

AREA OF HILTON HEAD ISLAND 

-20- MAY 1980 POTENTIOMETRIC CONTOUR-- Shows altitude of 

potentiometric surface of the Upper Floridan aquifer. 

Contour interval, in feet, is variable. Datum is sea level 

APPROXIMATE UPDIP LIMIT OF THE UPPER FLORIDAN AQUIFER 

A--A' PROPOSED LINE OF SECTION FOR SIMULATION 

Figure 158.-May 1980 potentiometric surface of the Upper Floridan aquifer in the area of Hilton Head Island; 

A-A' is the proposed line of section for simulation. 

253 
254 

potentiometric-surface map will be constructed for 

May 1985 based on a similar mass measurement 

of water levels in Alabama, Florida, Georgia, and 

South Carolina. The May 1985 potentiometricsurface map will be evaluated and compared with 

the May 1980 map. 

PUBLISHED REPORT 

Thayer, P. A., and Miller, J. A., 1984, Petrology 

of Lower and Middle Eocene carbonate 

rocks, Floridan aquifer, central Florida: Gulf 

Coast Association of Geological Societies, 

Transactions, v. XXXIV, p. 421-434. 

REFERENCE CITED 

Johnston, R. H., Healy, H. G., and Hayes, L. R., 1981, Potentiometric surface of the Tertiary limestone aquifer 

system, southeastern United States, May 1980: U.S. 

Geological Survey Open-File Report 81-486. 
PHASE II REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

HIGH PLAINS REGIONAL AQUIFER SYSTEM, PHASE II STUDY 

By john B. Weeks, Denver Colorado 

INTRODUCTION 

The initial High Plains regional aquifer study 

provided a regional description of the aquifer 

system and calibrated regional ground-water flow 

models. The models were calibrated on the basis 

of water-level changes from predevelopment to 

1980. Pumpage and irrigation return flow are two 

poorly known factors, however, they are critical 

for simulation. An indirect method for estimating 

pumpage was developed during the initial study· 

irrigation return flow was adjusted during modei 

calibrations. The accuracy of pumpage estimates 

and an independent estimate of irrigation return 

flow are essential to developing more accurately 

calibrated flow models. 

The ground-water flow models developed 

during the initial study are capable of projecting 

future water levels in the aquifer resulting from 

the strategies proposed by a study of the Economic 

Development Administration (EDA) of the U.S. 

Department of Commerce. However, the accuracy 

of the water- level projections cannot be evaluated 

unless the accuracy of information on pumpage 

and irrigation return flow are evaluated, which 

was not pursued during the initial study. For this 

reason, a phase II study was started in 1982 and 

is scheduled for completion in 1986. 

EVALUATION OF PUMPAGE AND 

IRRIGATION RETURN FLOW 

During the initial phase of the High Plains 

regional aquifer-system study, pumpage was 

estimated on the basis of reported crop acreage, 

calculated irrigation demand, and reported irrigation efficiency. Pumpage in 1980 was estimated 

using irrigated acreage determined from Landsat 

imagery associated with a random sample of 

measured pumpage and irrigated acreage 

(Heimes and Luckey, 1983). The procedure was 

found to be inexpensive for estimating pumpage 

for large areas; but, the accuracy of the procedure 

has not been determined. 

The estimates of historical pumpage were 

used in development of the ground-water flow 

models during the initial study. During model 

development, part of the simulated historical 

pumpage was allowed to return to the aquifer as 

irrigation return flow. The percentage of pumpage that became irrigation return flow varied 

with time and location, but return flow ranged 

from 30 to 55 percent of the gross pumpage. 

Although the percentage of return flow is consistent with reported estimates, a method to 

estimate the return flow independently is needed 

to verify the results obtained from model 

analyses. 

Based on existing hydrologic data, two areas 

were selected to evaluate pumpage and irrigation 

return flow (fig. 159). One area includes Castro 

and Parmer Counties in the southern High Plains 

of Texas. These two counties were selected 

because the Texas Department of Water 

Resources and the Underground Water Conservation District No. 1 have long-term annual 

water-level records. Digital Landsat data are also 

available for the area since 197 4. The second area 

is in the Upper Republican Natural Resources 

District (NRD) which includes Chase, Perkins, 

and Dundy Counties in Nebraska. These three 

counties were selected because the NRD has installed flowmeters on all irrigation wells. Meter 

installation began in 1978 and was completed in 

1980. Digital Landsat data are available since 

197 4. The period of analysis for each area will be 

255 
256 

for about 10 years, 1974-84, depending on the 

availability of data. 

Pumpage Estimates 

Pumpage data were collected during the 1983 

and 1984 irrigation seasons from about 50 irrigation systems in each of the two areas using portable flowmeters and time-of-operation sensors. In 

Nebraska, pumpage from nearly all wells was 

measured by the NRD using inline volumetric 

flowmeters. The NRD data will be used to 

measure the accuracy of the pumpage data collected using portable flowmeters. In Texas, no 

metering program exists to measure pumpage. 

Therefore, 12 volumetric inline flowmeters were 

installed as calibration sites for the portable 

flowmeters. 

Pumpage and irrigated acreage data, collected during 1983 and 1984, are being used to 

estimate total pumpage in each area for the entire period, 197 4-84. The estimated total pumpage 

will then be compared to the measured pumpage 

in Nebraska to evaluate the accuracy of the 

estimates. In Nebraska, the total1983 pumpage 

measured by portable flowmeters and time-ofoperation sensors at 52 sites was within 3 percent 

of the total pumpage measured by inline 

flowmeters. This ind~cates that reasonably accurate measurements can be made with portable 

flowmeters and time-of-operation sensors. 

Irrigated acreage is being mapped in both 

areas for selected years using Landsat imagery. 

Irrigated acreage obtained from Landsat is being 

compiled by the National Mapping Division 

(NMD) of the U.S. Geological Survey for test areas 

in Nebraska and Texas for 1974, 1976, 1978, 

1980, 1982, and 1983. The acreage data are being 

digitized and stored in a computerized data base. 

Estimates of total pump age for selected years 

during 197 4-83 are being made for both test areas 

by estimating the irrigation application rate and 

multiplying that number by the irrigated acreage 

determined from Landsat imagery. Two approaches to estimate application rate for the years 

in which measured data are not available are 

being evaluated: (1) development of a time series 

using measured application rates, and (2) development of relations between measured application 

rates and the calculated consumptive-use. 

Irrigation Return-Flow Estimates 

Irrigation return flow is being estimated 

from the difference between pumpage and change 

in aquifer storage. Change in aquifer storage is 

being determined from maps of water-level 

change and specific yield. Maps of water-level 

change are being prepared for the period 1975 

through 1983 for both test areas. Drillers' logs are 

being used to estimate and prepare maps of 

specific yield. On a volumetric basis, the difference between total pumpage and change in 

aquifer storage is assumed to be the irrigation 

return flow plus changes in recharge and 

discharge due to natural stresses, if any. The 

estimates of pumpage and irrigation return flow 

will be compared to values resulting from the 

calibrated ground-water flow models. 

Maps of specific yield are being prepared 

for both areas. For the area in Nebraska, 

lithologic logs were compiled from 532 wells 

which represent about 18 percent of the estimated 

3,000 wells in the area. For the area in Texas, 

lithologic logs were compiled for Castro, Parmer, 

and adjoining counties. For Castro and Parmer 

Counties, 996 logs were processed which represent about 12 percent of the estimated 8,000 wells 

in the area. For bordering areas in Texas, about 

300 additional logs were processed. The lithologic 

logs were processed by a computer program and 

averaged specific yield was determined for each 

log. The average specific yield for each county was 

estimated to be: 

Chase County, NE 12.3 percent 

Dundy County, NE 14.7 percent 

Perkins County, NE 12~2 percent 

Castro County, ·TX 18.4 percent 

Parmer County, TX 19.5 percent 

A map of water-level change for the period 

1978-82 for the test area in Nebraska was 

prepared using data from 384 wells. Maps of 

water-level change for the period 1975-84 for the 

area in Texas were prepared using data from 125 

wells. Maps of water-level change were digitized 

and stored in a data base. Change in aquifer 

storage is being comp.uted from that data base. 

EVALUATION OF EFFECTS OF FUTURE PUMPING 

The results of the EDA study of the High 

Plains have been published in a report by High 

Plains Associates (1982); recommendations to the 

U.S. Congress also have been made by the High 

Plains Study Council (1982). Additionally, more 

detailed reports have been published by investigators in each of the six individual States. 

These reports will be used to estimate future 

pumpage for the 40-year period from 1980 to 

2020. 
Ground-water flow models of the High Plains 

aquifer are being used to evaluate the effects of 

pumpage on the aquifer from 1980 to 2020. 

Simulated results will be presented in maps of 

water-level and saturated-thickness changes. 

Finite-difference models ofthe northern, central, and southern High Plains aquifers have been 

developed and calibrated during the initial study. 

During the phase II study, these calibrated 

models are being used to project future water 

35. 

100° gs• 

SOUTH DAKOTA t _____ ___ ---

WYOMING 

IOWA 

NEBRASKA 

-------

MISSOURI 

I 

------- I ' 

--------r-_j ___ - - ------- ______ _11 

r----

NEW MEXICO 

1 

' r-------, 

' I I 

I 

I 

Parmer ~ Castro 

County County 

I 

-----

TEXAS SCALE 1:9,000,000 ~- -

0 100 200 MILES 

___________ j 0 100 200 KILOMETERS 

EXPLANATION 

AREA OF THE HIGH PLAINS REGIONAL AQUIFER SYSTEM 

l%cm;q PUMPAGE SAMPLING AREA 

Figure 159. - Study area of the High Plains regional aquifer system, phase II study. 

257 
258 

levels under three different development 

strategies. The strategies are: (1) a baseline condition where future water use is based on the projected need, (2) a voluntary-reduction strategy 

where water use is slightly reduced from the projected need, and (3) a mandatory-reduction 

strategy where water use is greatly reduced from 

the· projected need. 

Projections of water-level and saturated-thickness changes have been completed for the three 

strategies in the southern High Plains. For the 

baseline condition, the total projected pumpage 

is 113 million acre-ft between 1980 and 2020. The 

projected pumpage for the same period for the 

voluntary-reduction strategy is 109 million acreft and for the mandatory-reduction strategy is 88 

million acre-ft. Under the baseline condition, 

much of the southern High Plains would experience severe water-level declines; by the year 

2020, much of the· area in the southern High 

Plains would have less than 25 feet of saturated 

thickness remaining. Similar conditions would occur under the voluntary-reduction strategy 

because the pumpage is only slightly less. 

However, under the mandatory-reduction 

strategy, water-level declines would be less severe 

and approximately 124 million acre-ft of 

drainable water would remain in aquifer storage 

by the year 2020. This remaining water in aquifer 

storage is about 40 percent of the total volume 

pumped from the aquifer from predevelopment to 

the year 2020 under the baseline condition. 

PUBLISHED REPORT 

Stephens, D. M., Heimes, F. J., and Luckey, R. 

R., 1984, Irrigation data from Chase, Dundy, and Perkins Counties, southwestern 

Nebraska, 1983: U.S. Geological Survey 

Open-File Report 84-4 71, 31 p. 

REFERENCES CITED 

Heimes, F. J., and Luckey, R. R., 1983, Estimating 1980 

ground-water pumpage for irrigation on the High Plains 

in parts of Colorado, Kansas, Nebraska, New Mexico, 

Oklahoma, South Dakota, Texas, and Wyoming: U.S. 

Geological Survey Water-Resources Investigations 

Report 83-4123, 36 p. 

High Plains Associates, 1982, Six-state High PlainS Ogallala 

aquifer regional resources study; a report to the .U.S. 

Department of Commerce and the High Plains Study 

Council: High Plains Associates, Austin, TX, 438 p. 

High Plains Study Council, 1982, A summary of results of the 

Ogallala aquifer regional study, with recommendations 

to the Secretary of Commerce and Congress: High 

Plains Study Council, 61 p. 
PHASE II REGIONAL AQUIFER-SYSTEM ANALYSIS PROJECTS 

SNAKE RIVER PLAIN REGIONAL AQUIFER SYSTEM, PHASE II STUDY 

By Gerald F. Lindholm, Boise, Idaho 

INTRODUCTION 

During phase I of the Snake River Plain 

regional aquifer-system study, several areas were 

identified for more detailed study. Long-term 

regional hydrologic changes were successfully 

simulated using quasi three-dimensional groundwater flow models. However, in key local areas 

the desired degree of understanding was not 

satisfactorily achieved with the large-scale 

regional flow models. Data need to be collected 

and incorporated into smaller scale local flow 

models that will be developed during phase II 

studies. A stream-aquifer model of the eastern 

Snake River Plain is also scheduled to be 

developed. The following are brief descriptions of 

these key studies. 

BIG LOST RIVER BASIN 

The Big Lost River basin contributes major 

quantities of water to the eastern part of the 

Snake River Plain (fig. 160). Estimates of water 

yield from most tributary basins have been made 

during the phase I study. However, all estimates 

are long-term annual averages that do not account for short-term variations in precipitation 

and irrigation. Since the 1950's, concern has increased about declines in ground-water levels and 

decreases in ground-water discharge from the 

eastern Snake River Plain. Consequently, there 

is concern about the amounts of water available 

to the Plain from tributary drainage basins. This 

phase II study is to address those concerns. A 

ground-water flow model will be used to test different hypotheses concerning water yield to the 

Snake River Plain from the Big Lost River basin. 

AMERICAN FALLS RESERVOIR AREA 

About 1.8 million acre-ft of ground water 

are discharged annually to the Snake River and 

American Falls Reservoir between Blackfoot and 

Neeley (figs. 49 and 160). In the 10-mile reach 

from Blackfoot to the high-water line of the reservoir, the Snake and Portneuf Rivers receive large 

quantities of ground water, largely from springs. 

Discharge data suggest that gains have remained 

relatively stable since 1912, although irrigation 

in and upstream from that area has increased 

significantly. The American Falls area was included in the regional flow model developed 

during the phase I study. Although a reasonable 

transient simulation was achieved, the level of 

detail was inadequate to answer specific questions about the effect of irrigation on groundwater and surface-water relations. A detailed 

quasi three-dimensional model to simulate 

ground-water movement in the American Falls 

Reservoir area will be developed and calibrated. 

Data will be collected in 1985 on irrigation diversions, return flows, water levels, river gains, 

pumpage, and water chemistry. Test holes will be 

drilled and piezometers installed to help define 

the flow system locally. 

GROUND-WATER FLOW MODEL 

COMBINING THE EASTERN AND WESTERN 

PARTS OF THE SNAKE RIVER PLAIN 

During the phase I study, separate groundwater flow models were developed for the eastern 

and western parts of the Snake River Plain. The 

dividing line includes about 40 miles of the Snake 

River where numerous springs discharge several 

259 
260 

thousand cubic feet per second from the eastern 

part of the Snake River Plain (figs. 49 and 160). 

Water budget analyses indicate that virtually all 

water in both the eastern and western parts of 

the Plain can be accounted for without underflow 

along the dividing line. The Snake River in this 

area is a regional sink and gains water from both 

the east and west sides of the river. The 

hypothesis that there is no underflow along the 

dividing line needs to be tested. A ground-water 

flow model that combines parts of the eastern and 

western Plain would be developed and used for 

the test. Initial parameter values, including 

boundary flux, would be obtained from models 

developed during the phase I study. A fine mesh 

and several layers would be needed to increase 

118° 

OREGON 

44° 

42° 

0 

0 50 100.KILOMETERS 

model sensitivity. During the phase I study, 

springs were simulated either as constant flux or 

leaky boundary with constant head representing 

the spring levels. In the phase II study, springs 

would be simulated as a seepage face. After model 

calibration, sensitivity tests would be run to 

determine the validity of assumptions made during the phase I study. 

GEOCHEMICAL INVESTIGATIONS OF SOURCES 

OF WATER TO THE THOUSAND SPRINGS 

Sources of water discharging as springs in the 

thousand Springs area are inadequately defined. 

During the phase I study, maps and sections were 

I 

\ 

112. 

MONTANA 

\ .. \ .. J \. ,-.. .r0--· " 

EXPLANATION 

L!J EAST AND WEST MODELS EASTERN SNAKE RIVER PLAIN 

2 THOUSAND SPRINGS t~:-_~(/ WESTERN SNAKE RIVER PLAIN 

[2] BIG LOST RIVER BASIN AREA OF SNAKE RIVER PLAIN 

0 AMERICAN FALLS RESERVOIR AREA BOUNDARY OF SNAKE RIVER BASIN 

Figure 160. -Study area of the Snake River Plain regional aquifer system, phase II study. 
prepared to describe the geology of the north 

Snake River canyon wall between Milner and 

King Hill (fig. 49). Geologic controls on spring 

locations were determined and quantity of 

discharge estimated. The actual points of 

emergence of some springs are not always apparent. In places, spring vents are masked by 

talus deposits; elsewhere, springs issue from the 

canyon floor as much as 200 feet below other 

springs. A test hole about 12 miles upgradient 

from the springs penetrated a basalt aquifer (Tertiary Banbury Basalt), which is separated from 

the overlying Snake River Plain aquifer by a 

200-foot thick zone of sediments. The altitude of 

the top of the lower aquifer is about the same as 

the floor of the Snake River canyon. As such, it 

seems probable that some springs issuing from 

the canyon floor may be from the Tertiary Banbury Basalt. Effects of possible future development of the lower aquifer on spring flow and the 

overlying Snake River Plain aquifer are 

unknown. 

Geochemical techniques are proposed to attempt to differentiate sources of water from 

various springs. Water samples will be analyzed 

for major ions, trace elements, and stable isotopes 

of hydrogen, oxygen, carbon, and sulfur. Mineralwater saturation indices for the Snake River 

Group and Banbury Basalt will be calculated. 

Mineralogic evidence collected during the initial 

study shows that the Banbury Basalt is more 

weathered than basalt of the Snake River Group 

and contains secondary minerals. Mineral-water 

saturation indices for water from the Banbury 

Basalt probably are more positive than those for 

water from the Snake River Group. If true, 

sources of spring water may be differentiated. 

STREAM-AQUIFER MODEL FOR 

THE EASTERN PART OF THE SNAKE RIVER PLAIN 

Ground- and surface-water systems in the 

Snake River Plain are closely interrelated. 

During the phase I study, historical changes in 

ground water and surface water resulting from 

100 years of irrigation were defined. Percolation 

of large quantities of excess surface water 

diverted for irrigation raised water levels several 

tens of feet in much of the Snake River Plain and 

as much as 200 feet locally. Ground-water 

discharge subsequently increased, largely as 

spring flow; flow in the Snake River changed accordingly. The increase in river discharge was appropriated for hydropower generation, irrigation, 

and other uses. When surface water was fully appropriated, ground water became a feasible alternative source. The result was a reversal of the 

original trends; ground-water levels began to 

decline and spring flow decreased. Increased competition for water made holders of junior water 

rights concerned about the reliability of their 

supply and a conflict of interest developed between proponents of hydropower generation and 

irrigation. The relation between ground and surface water is now generally recognized, and concern has developed that increased use of ground 

water will adversely impact availability of surface water. Many considerations are necessary to 

properly manage conjunctive use of ground and 

surface water. One of the tools that can be used 

is a stream-aquifer model. A stream-aquifer 

model of the eastern part of the Snake River Plain 

will be developed to study the hydrologic impacts 

of the conjunctive use of ground and surface 

water. 

261 
262 

APPENDIX: RASA PROJECT CHIEFS AND THEIR ADDRESSES 

Regional Aquifer-System Analysis Program 

Sun, Ren J en, Program Coordinator 

Office of Ground Water, Water Resources 

Division 

U.S. Geological Survey, National Center, 

Mail Stop 411 

12201 Sunrise Valley Drive 

Reston, Virginia 22092 

1. Completed Phase I Regional AquiferSystem Analysis Projects. 

Central Valley regional aquifer-system study, 

California 

Bertoldi, Gilbert L., Project Chief 

(Resigned) 

Page, Ronald W., Hydrologist 

U.S. Geological Survey 

Federal Building, Room W-2235 

2800 Cottage Way 

Sacramento, California 95825 

Floridan regional aquifer-system study 

Johnston, Richard H., Project Chief 

(retired) 

Bush, Peter W., Hydrologist 

U.S. Geological Survey 

649 Federal Bldg., 

300 East 8th Street 

Austin, Texas 78701 

High Plains regional aquifer-system study 

Weeks, John B. Project Chief 

U.S. Geological Survey 

Bldg. 53, Denver Federal Center 

Mail Stop 412 

Lakewood, Colorado 80225 

Northern Great Plains regional aquifersystem study 

Dinwiddie, George A., Project Chief 

U.S. Geological Survey, National Center 

Mail Stop 410 

12201 Sunrise Valley Drive 

Reston, Virginia 22092 

Northern Midwest regional aquifer-system 

study 

Young, Harley L., Project Chief 

U.S. Geological Survey 

1815 University Avenue, 2nd Floor 

Madison, Wisconsin 53705-4042 

Snake River Plain regional aquifer system 

study 

Lindholm, Gerald F., Project Chief 

U.S. Geological Survey 

230 Collins Road 

Boise, Idaho 83702 

Southwest alluvial basins regional aquifersystem study 

Study in parts of Colorado, New Mexico, 

and Texas 

Wilkins, David W., Project Chief 

U.S. Geological Survey 

Western Bank Building, Room 720 

505 Marquette, N.W. 

Albuquerque, New Mexico 87102 

Study in southern and central Arizona 

and adjacent states 

Anderson, Thomas W., Project Chief 

U.S. Geological Survey 

Federal Bldg., FB-44 

301 W. Congress Road 

Tucson, Arizona 85701 

2. Active Phase I Regional Aquifer-System 

Analysis Projects 

Central Midwest regional aquifer-system 

study 

Jorgensen, Donald G., Project Chief 

U.S. Geological Survey 

1950 Constant Avenue, Campus West 

University of Kansas 

Lawrence, Kansas 66046 
Columbia Plateau basalt regional aquifersystem study 

Vaccaro, John J., Project Chief 

U.S. Geological Survey 

1201 Pacific Avenue, Suite 600 

Tacoma, Washington 98402 

Great Basin regional aquifer-system study 

Harrill, James R., Project Chief 

U.S. Geological Survey 

Federal Bldg., Room 224 

705 North Plaza Street 

Carson City, Nevada 89701 

Gulf Coastal Plain regional aquifer-system 

study 

Grubb, Hayes F., Project Chief 

U.S. Geological Survey 

211 East 7th Street, 3rd Floor 

Austin, Texas 78701 

Northeast glacial regional aquifer-system 

study 

Lyford, Forest P., Project Chief 

U.S. Geological Survey 

353 U.S. Post Office & Courthouse 

Albany, New York 12201 

Northern Atlantic Coastal Plain regional 

aquifer-system study 

Meisler, Harold, Project Chief 

U.S. Geological Survey 

810 Bear Tavern Road 

Suite 206 

West Trenton, New Jersey 08628 

Oahu Island regional aquifer-system study, 

Hawaii 

Ewart, Charles J., Project Chief 

U.S. Geological Survey 

300 Ala Moana Blvd., Room 6110 

Honolulu, Hawaii 96850 

Southeastern Coastal Plain regional aquifersystem study 

Miller, James A., Project Chief 

U.S. Geological Survey 

Richard B. Russell Federal Bldg., 

Suite 772 

75 Spring Street, S.W. 

Atlanta, Georgia 30303 

Upper Colorado River Basin regional aquifersystem study 

Cenozoic aquifer system 

Glover, Kent C., Project Chief 

U.S. Geological Survey 

2120 Captial Avenue, Room 4004 

Cheyenne, Wyoming 82003 

Mesozoic aquifer system 

Freethey, Geoffrey, Project Chief 

U.S. Geological Survey 

Administration Bldg., Room 1016 

1745 West 1700 South 

Salt Lake City, Utah 84104 

Paleozoic aquifer system 

Taylor, 0. James, Project Chief 

U.S. Geological Survey 

Bldg. 53, Denver Federal Center 

Mail Stop 415, Box 25046 

Lakewood, Colorado 80225 

Phase I Regional Aquifer-System Analysis 

Projects started in 1984. 

Caribbean Islands regional aquifer-system 

study 

Gomez-Gomez, Fernando, Project Chief 

U.S. Geological Survey 

GSA Center, Bldg. 652 

Highway 28, Pueblo Viejo 

San Juan, Puerto Rico 00936 

Michigan Basin regional aquifer-system 

study 

Mandie, Richard J., Project Chief 

U.S. Geological Survey 

6520 Mercantile Way, Suite 5 

Lansing, Michigan 48910 

Southern California alluvial basins 

regional aquifer-system study 

Martin, Peter, Project Chief 

U.S. Geological Survey 

5201 Ruffin Road, Suite F. COC 

Annex 

San Diego, California 92123 

263 
264 

Phase II Regional Aquifer-System Analysis 

Projects (followup studies) 

Central Valley regional aquifer system, 

California, phase II study 

Gilliom, Robert J., Project Chief 

U.S. Geological Survey 

Federal Building, Room W-2235 

2800 Cottage Way 

Sacramento, California 95825 

Floridan regional aquifer system, phase II 

study 

Bush, Peter W., Project Chief 

U.S. Geological Survey 

649 Federal Bldg. 

300 East 8th Street 

Austin, Texas 78701 

High Plains regional aquifer system, 

phase II study 

Weeks, John B., Project Chief 

U.S. Geological Survey 

Bldg. 53 Denver Federal Center 

Mail Stop 412 

Lakewood, Colorado 80225 

Snake River Plain regional aquifer 

system, phase II study 

Lindholm, Gerald F., Project Chief 

U.S. Geological Survey 

230 Collins Road 

Boise, Idaho 83702 

*U.S. GOVERNMENT PRINTING OFFICE: 1986-491-405:20111