Report 273 GROUND- WA TER AVAILABILITY OF THE LOWER CRETACEOUS FORMATIONS IN THE HILL COUNTRY OF SOUTH- CENTRAL TEXAS TEXAS DEPARTMENT OF WATER RESOURCES January 1983 “‘._ __ __.. TEXAS DEPARTMENT OF WATER RESOURCES REPORT 273 GROUND-WATER AVAILABILITY OF THE LOWER CRETACEOUS FORMATIONS IN THE HILL COUNTRY OF SOUTH-CENTRAL TEXAS John B. Ashworth, Geologist January 1983 TEXAS DEPARTMENT OF WATER RESOURCES Charles E. Nemir, Executive Director TEXAS WATER DEVELOPMENT BOARD Louis A. Beecherl Jr., Chairman George W. McCleskey, Vice Chairman Glen E. Roney Lonnie A. “Bo” Pilgrim W. 0. Bankston Louie Welch TEXAS WATER COMMISSION Lee B. M. Biggart, Chairman Felix McDonald, Commissioner John D. Stover, Commissioner Authorization for use or reproduction of any original material contained in this publication, i.e., not obtained from other sources, is freely granted The Department would appreciate acknowledgement. Published and distributed by the Texas Department of Water Resources Post Office Box 13087 Austin, Texas 78711 TABLE OF CONTENTS Page CONCLUSIONS . INTRODUCTION Purpose and Scope Location and Extent 2 Geography. 2 Topography and Drainage. 2 Population. 2 Economy and Land Use 3 Vegetation . 3 Climate. 3 Previous Investigations . 3 Acknowledgements. 3 Well-Numbering System 7 Definition of Terms . 8 Metric Conversions . 9 GEOLOGY AS RELATED TO THE OCCURRENCE OF GROUND WATER. 9 Depositional History 9 Stratigraphy 9 Structure . 10 STRATIGRAPHY OF THE WATER-BEARING UNITS. 19 Pre-Cretaceous Rocks 19 Trinity Group. 19 Lower Trinity Aquifer 19 iii TABLE OF CONTENTS-Continued Page Middle Trinity Aquifer . 19 Upper Trinity Aquifer 33 Fredericksburg Group 33 Quaternary Alluvium 33 CHEMICAL QUALITY OF GROUND WATER AS RELATED TO USE 33 General Chemical Quality of Ground Water 33 Public Supply. 39. Primary Standards 42 Secondary Standards 42 Domestic and Livestock 43 Irrigation 44 Industrial 44 Treatment of Water . 44 Chemical Quality of Ground Water from the Trinity Group Aquifer 44 OCCURRENCE OF GROUND WATER IN THE TRINITY GROUP AQUIFER. 47 Recharge, Movement, and Discharge 47 Hydraulic Characteristics 48 Water Levels . 48 Utilization and Development . 60 AVAILABILITY OF GROUND WATER IN THE TRINITY GROUP AQUIFER 60 GROUND-WATER PROBLEMS. 60 RECOMMENDATIONS . 61 SELECTED REFERENCES 63 TABLES 1. Stratigraphic Units and Their Water-Bearing Properties . 12 2. Source and Significance of Dissolved-Mineral Constituents and Properties of Water 40 iv TABLE 0 F CONTENTS-Continued Page 3. Results of Pumping Tests . 55 4. Results of Laboratory Analyses of Cores from Test Wells 56 WELL DATA, BY COUNTIES Page Numbers Records of Selected Chemical Analyses of Water Wells, Springs, Water From Selected and Oil and Gas Tests Well and Springs (Table 5) (Table 6) Well-Location Maps Bandera 66 73 77 Bexar 79 83 85 Blanco 87 95 101 Comal 103 108 109 Gillespie 111 114 117 Hays 119 122 123 Kendall 125 139 147 Kerr 149 157 161 Medina 163 164 165 Real 167 168 169 Uvalde 171 172 173 FIGURES 1. Map Showing Location of Study Region . 2 2. Map Showing Average Annual Precipitation, 1931-60, and Charts of Average Monthly Precipitation for Period of Record at Selected Stations. 5 3. Diagram of Well-Numbering System. 7 4. Map Showing Regional Structural Trends. 11 5. Geologic Map. 13 6. Geologic Section A-A' 15 v TABLE OF CONTENTS-Continued Page 7. Geologic Section B·B' . 17 8. Map Showing Approximate Altitude of and Depth to the Base of the Cretaceous System 21 9. Map Showing Approximate Altitude of and Depth to the Top of the Lower Trinity Aquifer 23 ·10. Map Showing Approximate Total Thickness of the Lower Trinity Aquifer. 25 11. Map Showing Approximate Altitude of and Depth to the Top of the Cow Creek Limestone of the Middle Trinity Aquifer. 29 12. Map Showing Approximate Altitude of and Depth to the Top of the Hensell Sand and Bexar Shale of the Middle Trinity Aquifer . 31 13. Map Showing Approximate Altitude of and Depth to the Top of the Middle Trinity Aquifer. 35 14. Map Showing Approximate Total Thickness of the Middle Trinity Aquifer 37 15. Map Showing Sulfate, Chloride, and Dissolved-Soilds Content in Water from Selected Wells and Springs . _ . 45 16. Hydrographs comparing Water Levels in Low.~r and Middle Trinity Wells and the Gain in Base Flow of the Guadalupe River between the Comfort and Spring Branch Gages . 49 17. Map Showing Approximate Altitude of and Depth to Water Levels in Wells Completed in the Middle Trinity Aquifer, Winter of 1977-78 . 51 18. Map Showing Approximate Altitude of and Depth to Water Levels in Wells Completed in the Lower Trinity Aquifer, 1975-78 . 53 19. Hydrographs of Water Levels in Selected Wells 59 vi GROUND-WATER AVAILABILITY OF THE LOWER CRETACEOUS FORMATIONS IN THE HILL COUNTRY OF SOUTH-CENTRAL TEXAS CONCLUSIONS of sulfate and chloride. High concentrations of iron, nitrate, and fluoride are also common problems. The The Trinity Group aquifer is essentially the dissolved-solids content generally increases downdip only ground-water source for all but the extreme toward the south and southeast. There had been no updip, northern portion of the study region and is widespread pollution of the aquifer in the study region divided, in ascending order, into the lower, middle, although local problems do exist. The chemical quality and upper aquifer units. of the water produced from a well can often be improved by properly casing off zones of undesirable The lower Trinity aquifer, which includes the water. The yield and life expectancy of a well can Hosston Sand and Sligo Limestone Members of the likewise be improved by utilizing proper well completion Travis Peak Formation, yields small to large and development procedures. quantities of ground water. The quality is good in the Kerrville to Bandera area but becomes slightly Although approximately 200,000 acre-feet more saline throughout the remainder of the study (247 hm3) of rainfall is estimated to be available as area. The water is utilized for municipal purposes in recharge to the aquifer annually, much of this recharge is Kerrville and Bandera and for irrigation in a few lost by natural rejection, principally to springs. During other localities. Because of its depth and poor dry periods, recharge is limited and water levels decline. quality, overall development of the lower Trinity Also, continuous heavy pumpage results in rapid aquifer has been minimal. The lower Trinity is not water-level declines due to the aquifer’s rather low present in Gillespie and portions of Blanco and Kerr capability to transmit water. Therefore, moderate to Counties. severe water-level declines can be expected over a major part of the study region where both drought and heavy The middle Trinity aquifer is comprised of the concentrated pumpage occur. Cow Creek Limestone, Hensell Sand, the lower member of the Glen Rose Limestone, and is the most widely utilized of the three aquifer units. The INTRODUCTION middle Trinity aquifer yields small to moderate quantities of fresh to slightly saline water throughout the study region. Purpose and Scope The upper Trinity aquifer produces water from The ground-water study of the Lower Cretaceous the upper member of the Glen Rose Limestone. formations in south-central Texas, commonly referred to Yields are generally very small due to the low as the Hill Country, was conducted during the period porosity and permeability of the limestone, and the from December 1974 to October 1978. The primary chemical quality is normally poor because of the purpose of the study was to describe the hydrologic presence of evaporite beds. This unit is utilized only characteristics of the Trinity Group, which includes the for limited domestic and livestock purposes. Glen Rose Formation and the Hensell Sand, Bexar Shale, Cow Creek Limestone, Hammett Shale, Sligo Limestone, Chemical quality of water in the Trinity Group and Hosston Sand Members of the Travis Peak aquifer is variable. Water acceptable for human Formation. consumption, although very hard, is available over most of the study region. Poor quality of water in Principal objectives of the investigation included: the Trinity is usually due to excessive concentrations (a) collection and evaluation of previously compiled -_ geologic and hydrologic data; (b) determination of the minimum of 780 feet (240 m) in the drainage basins in quantity and quality of the available ground waters on a the east. regional basis; (c) determination of the hydrological characteristics of the various formations; Four major drainage basins occupy the study (d) determination of hydrologic connections between region. Drainage in the Nueces River basin is to the formations; (e) determination of the annual amount of south. In the San Antonio River basin, drainage is to the recharge and discharge of the aquifers; and (f) the southeast. And in the Guadalupe and Colorado River initiation of a continuing ground-water quality basins the drainage is to the east. The larger rivers are monitoring program. dominantly effluent and form wide valleys. The smaller creeks and streams are characterized by two dominant For the purpose of this report, hydrologic: data types: the perennial spring-fed streams, and the were gathered primarily from high-capacity wells which intermittent creeks that only transport precipitation include public supply, industrial, and irrigation wells. runoff. Many of the-streams revert underground when Also an attempt was made to inventory all perennial encountering cavernous zones or areas of gravel springs. accumulation and later resurface as gravity springs. Most of these streams that are perennial in their lower reaches are diverted underground where they cross the Balcones Location and Extent fault zone. Most of this water is probably captured in the down-faulted Edwards Formation. The area of investigation includes the southern edge of the Edwards Plateau and extends southeastward into the Balcones fault zone. It includes all or parts of the following 11 counties: Bandera, Bexar, Blanco, Comal, Gillespie, Hays, Kendall, Kerr, Medina, Real, and Uvalde.