Hydrogeology and Hydrochemistry of the Ogallala Aquifer, Southern High Plains, Texas Panhandle and Eastern New Mexico

RI0177. Hydrogeology and Hydrochemistry of the Ogallala Aquifer, Southern High Plains, Texas Panhandle and Eastern New Mexico, by Ronit Nativ. 64 p., 35 figs., 1 table, 1988. ISSN: 0082335X: Print.

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ABSTRACT
The Ogallala aquifer, which underlies the Southern High Plains, consists of the saturated sediments of the Neogene Ogallala Formation. The aquifer is the main source of water for the High Plains of Texas and New Mexico and is being severely depleted by extensive pumpage for irrigation. Contamination from evaporating saline lakes, agricultural chemicals and fertilizers, and oil field brines is locally affecting the chemical composition of Ogallala ground water. The impact of chemicals and brines may increase in the future because many of these contaminants may still be moving downward through the unsaturated zone toward the water table. Furthermore, the aquifer overlies Permian evaporites that were being considered as a potential repository for the isolation of high-level nuclear wastes. All of these concerns necessitated the characterization of the hydrogeology and hydrochemistry of the Ogallala aquifer, which are controlled primarily by the subjacent paleotopography and by the thickness, permeability, and mineralogy of the Ogallala Formation.

Two different hydrogeologic provinces were observed in the study area. Increased thickness of formation and saturated section, as well as higher porosity and hydraulic conductivity values, characterize the first province, which is located along paleovalleys filled with coarse fluvial sediments. These paleovalleys trend from northwest to southeast, and ground-water flow lines follow their orientations. Within this first province the hydrochemical composition is relatively constant (Ca-HCO₃ to mixed-cation-HCO₃ water, depleted in δ¹⁸O, δD, and tritium). In the second hydrogeologic province the formation is thinner and less permeable and sediments are mainly fine-grained eolian clastics. In this province ground water discharges into the overlying Ogallala Formation from the Cretaceous, Triassic, and Permian aquifers. In the second province cross-formational movement of water and low permeability in the Ogallala Formation result in variable hydrochemical facies and isotopic composition that differ from those of the first hydrogeologic province. Superimposed permeable strata in the Ogallala and underlying formations and hydraulic-head differences locally allow cross-formational flow, as documented by chemical and isotopic similarities of ground water in the study area.

On the basis of both the rapid recharge rates calculated using tritium as a tracer and the slightly enriched values of δ¹⁸O and δD in ground water with respect to precipitation, it is assumed that the most likely method of ground-water recharge is focused percolation of partly evaporated playa-lake water.

Keywords: discharge, eastern New Mexico, hydrochemistry, hydrogeology, isotopes, Ogallala aquifer,oil field brines, playa lakes, recharge, saline lakes, Southern High Plains, Texas Panhandle, Texas



CONTENTS

Abstract

Introduction

Data and Methods

Hydrologic Setting

Physiography and climate

General hydrology of the Ogallala aquifer

Geologic Framework

Quaternary strata

Tertiary Ogallala Formation

Cretaceous strata

Triassic strata

Permian strata

Hydrogeology

Distribution of porosity and hydraulic conductivity

Potentiometric surface

Recharge

Discharge

Vadose and saturated zones

Hydrochemistry

Chemical and isotopic composition of Ogallala ground water

Effects of lithology and structure

Effects of the thickness of the vadose zone

Effects of natural recharge from precipitation

Effects of underlying aquifers

Cretaceous aquifers

Triassic Dockum aquifer

Permian aquifers

Effects of oil field brine contamination

Conclusions

Acknowledgments

References

Appendices

1. Mean values for chemical parameters of ground water in the major aquifers, Southern High Plains

2. Analytical data from ground-water samples from the Southern High Plains aquifers, 1984-85

3. Mean values for chemical parameters of brines in various stratigraphic units, Southern High Plains

4. Isotopic analyses of precipitation samples collected in the Southern High Plains and Rolling Plains

5. Calculation of recharge rate based on tritium values in ground water in the Ogallala aquifer, Southern High Plains

Figures

1. Location map of the study area, precipitation sampling stations, and wells sampled for ground water

2. Generalized soil map of the study area

3. Mean annual precipitation map of the study area

4. Subcrop map at the base of the Ogallala Formation

5. Isopach map of Ogallala and Quaternary deposits

6. Percent-sand and gravel map of Ogallala and Quaternary deposits

7. Estimates of permeability at the base of the Triassic

8. Estimates of permeability at the top of the Permian

9. Estimates of permeability at the base of the Cretaceous and the top of the Triassic

10. Specific yield map of the Ogallala aquifer

11. Hydraulic conductivity map of the Ogallala aquifer

12. Water-table-surface map of the Ogallala aquifer

13. Graphs of Potentiometric surface versus ground-level elevation in the Ogallala aquifer

14. Map showing changes in Potentiometric surface in the Ogallala aquifer, predevelopment through 1980

15. Map showing Potentiometric surfaces of ground water in the Cretaceous and Permian aquifers where they underlie the Ogallala Formation

16. Potentiometric-head-difference map between the Ogallala aquifer and each of the underlying aquifers

17. Plot of isotopic composition of precipitation and ground water in the study area

18. Distribution map of tritium values in Ogallala ground water

19. Map showing present-day flowing springs in the study area

20. Map showing annual pumpage and recharge of the Ogallala aquifer

21. Map showing thickness of the vadose zone above the Ogallala water table

22. Map showing approximate saturated thickness of the Ogallala Formation

23. Plot of change in saturated thickness of the Ogallala aquifer between 1960 and 1980

24. Map showing total dissolved solids content in Ogallala ground water

25. Map showing hydrochemical facies of Ogallala ground water

26. Piper diagrams of ground water in the Ogallala and Cretaceous aquifers

27. Salinity diagram of mean ion concentration in ground water in various aquifers, Southern High Plains

28. Distribution map of δ¹⁸O values in the study area

29. Distribution map of δ³⁴S values in the study area

30. Plot of hydrochemical facies versus saturated thickness, Ogallala aquifer

31. Map showing arsenic concentrations in Ogallala ground water

32. Salinity diagrams of Ogallala water contaminated by saline lakes and oil field brines

33. Salinity diagrams of ground water in Ogallala, Cretaceous, and Triassic rocks

34. Piper diagram of oil field brines from 16 formations in the Southern High Plains

35. Bivariate plots of oil field brines in the study area

Table

1. Estimates of annual recharge into the Ogallala aquifer, Southern High Plains



Citation
Nativ, Ronit, 1988, Hydrogeology and Hydrochemistry of the Ogallala Aquifer, Southern High Plains, Texas Panhandle and Eastern New Mexico: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 177, 64 p.