~ f~~" u *~"} ~~~~~~~i/ ~~ TEXAS DEPARTMENT OF WATER RESOURCES REPORT 234 GEOHYDROLOGY OF COMAL, SAN MARCOS, AND HUECO SPRINGS By William F. Guyton & Associates June 1979 TEXAS DEPARTMENT OF WATER RESOURCES Harvey Davis, Executive Director TEXAS WATER DEVELOPMENT BOARD A. l. Black, Chairman John H. Garrett, Vice Chairman Milton Potts Glen E. Roney George W. McCleskey W. O. Bankston TEXAS WATER COMMISSION Felix McDonald, Chairman Dorsey B. Hardeman, Commissioner Joe R. Carroll, Commissioner Authorization for use or reproduction of any original material contained in this publicatiun, 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 SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS INTRODUCTION 3 Purpose 3 Scope 3 Area of Investigation 3 Previous Investigations 4 Acknowledgements 4 Metric Conversions 4 DESCRIPTION OF SPRINGS 7 Comal Springs. 7 San Marcos Springs 7 Hueco Springs. 7 EDWARDS (BALCONES FAULT ZONE) AQUIFER. 8 Geology. 8 Recharge 8 Natural Discharge 9 Storage . 9 Bad Water Line 9 Withdrawals of Water Through Wells 11 Effects of Withdrawals . 11 GEOLOGY IN VICINITY OF SPRINGS 15 General . 15 Stratigraphy 15 iii TABLE OF CONTENTS-Continued Page Glen Rose Formation 15 Walnut Formation 15 Edwards Group 15 Georgetown Formation. 19 Del Rio Formation 19 Buda Formation 19 Eagle Ford Group 19 Austin Group 19 Taylor Group 19 Navarro Group 19 Quaternary Alluvium 20 Structural Geology . 20 Detailed Geology of Comal, San Marcos, and Hueco Springs Localities 20 Comal Springs. 20 San Marcos Springs 25 Hueco Springs. 25 Recent Geohydrologic Subdivision of Edwards Aquifer by the U.S. Geological Survey 31 SPRING FLOW . 39 ComaI Springs. 39 San Marcos Springs 39 Hueco Springs. 46 CHEMICAL QUALITY OF WATER 46 Comal Springs. 46 San Marcos Springs 54 Hueco Springs. 54 TEMPERATURE OF WATER 54 iv TABLE OF CONTENTS-Continued Page Comal Springs. 55 San Marcos Springs 55 Hueco Springs _ 55 TRITIUM CONTENT OF WATER 55 Comal Springs. 57 San Marcos Springs 57 Hueco Springs. 57 Wells. 57 SPRING FLOW CORRELATION STUDIES. 61 Long-Term Recharge and Discharge. 61 Recent Correlations by U.S. Geological Survey 61 Study by William F. Guyton & Associates 65 Studies by U.S. Bureau of Reclamation 66 Digital Model by Texas Department of Water Resources 67 Similarity of Fluctuations in Flow of San Marcos and Hueco Springs. 68 RECHARGE AREAS FOR SPRINGS 68 Comal Springs. 71 San Marcos Springs 71 Hueco Springs. 71 Local Water Balance. 72 POSSIBILITIES OF POLLUTION 72 Present Records _ 72 Legal Control of Pollution. 72 Comal Springs. 72 San Marcos Springs 72 Hueco Springs. 79 v TABLE OF CONTENTS-CONTINUED Page EFFECTS ON SPRING FLOW CAUSED BY WITHDRAWALS FROM WELLS 79 Comal Springs. 79 San Marcos Springs 79 Hueco Springs. 80 POSSIBILITIES OF MAINTAINING COMAL AND SAN MARCOS SPRING FLOWS AT PREDETERMINED RATES 80 FUTURE STUDIES. 81 General Edwards Program 81 Special Studies Related to ComaI, San Marcos, and Hueco Springs 81 REFERENCES 83 TABLES 1. Ground-Water Recharge and Discharge, Edwards Aquifer Northeast of San Antonio. 45 2. Chemical Analyses of Water From Comal, San Marcos, and Hueco Springs 47 3. Temperature of Water From Hueco Springs , 56 4. Minor Elements in Water From Comal, San Marcos, and Hueco Springs 73 5. Nutrients and Bacteria in Water From Comal, San Marcos, and Hueco Springs. 75 6. Insecticides and Herbicides in Water From Comal and San Marcos Springs . 78 FIGURES 1. Edwards (Balcones Fault Zone) Aquifer, San Antonio Region 5 2. Recharge and Discharge of the Edwards Aquifer and Discharge From Wells and Major Springs 10 3. Surface Geology of the Edwards Aquifer Area Northeast of San Antonio Showing Water-Quality Features and Locations of Springs, Observation Wells, and Test Holes 13 4. Elevation of the Top of the Glen Rose Formation, and Surface Geology of the Edwards Aquifer Area Northeast of San Antonio . 17 5. Surface Geology of ComaI Springs Locality 21 6. Geologic Cross-Section Through ComaI Springs Locality. 23 7. Surface Geology of San Marcos Springs Locality 27 vi TABLE OF CONTENTS-Continued Page 8. Geologic Cross-Section Through San Marcos Springs Locality 29 9. Surface Geology of Hueco Springs Locality 33 10. Geologic Cross-Section Through Hueco Springs Locality 35 11. Geohydrologic Subdivision of the Edwards Aquifer Northeast of San Antonio 37 12. Flow of Comal, San Marcos, and Hueco Springs, 1881-1928 41 13. Flow of Comal, San Marcos, and Hueco Springs and Precipitation at New Braunfels and San Marcos, 1928-1975. 43 14. Surface Geology of the Edwards Aquifer Area Northeast of San Antonio Showing Tritium Analyses of Water From Wells and Springs and Surface-Drainage Divides. 59 15. Relationship Between the Flow of Comal Springs and the Water Level in Well DX-68-23-302. 62 16. Relationship Between the Flow of Comal Springs and the Water Level in Well AY-68-37-203. 63 17. Comparison of Observed and Computed Annual Average Discharge of Comal Springs 63 18. Relationship Between the Flow of San Marcos Springs and the Water Level in Well LR-67-09·102 64 19. Relationship Between the Water Level in Well DX-68-23-302 and the Discharge of Regional Underflow at San Marcos Springs 65 20. Comparison of Observed and Computed Annual Average Discharge of San Marcos Springs. 65 21. Comparison of Observed and Computed Annual Average Discharge of Hueco Springs 65 22. Correlation of Year-End Water Levels in Beverly Lodges Well With Change in Storage in the Edwards Aquifer 66 23. Correlation of Average Yearly Water Levels in Beverly Lodges Well With Comal Springs Flow 67 24. Correlation of Average Yearly Water Levels in Beverly Lodges Well With Estimated San Antonio and San Pedro Springs Flow . 68 25. Comparison of Calculated and Measured Water Levels in Beverly Lodges Well, 1934-1961 69 26. Historical and Simulated Sum of Spring Flows, 1947·1971 . 70 27. Annual Flow of San Marcos Springs Versus Annual Flow of Hueco Springs, 1945-1974 70 vii GEOHYDROLOGY OF COMAL, SAN MARCOS, AND HUECO SPRINGS SUMMARY, CONCLUSIONS, AND aquifer was discharged through six major spring outlets: RECOMMENDATlONS Leona Springs along the Leona River south of Uvalde in Uvalde County, San Pedro and San Antonio Springs at Comal, San Marcos, and Hueco Springs are major San Antonio in Bexar County, Comal Springs, Hueco natural discharge points for the Edwards (Balcones Fault Springs, and San Marcos Springs. The water moved Zone) aquifer, hereafter referred to in this section as the generally from west to east, and the springs served as Edwards aquifer. Comal Springs are in the city of New natural spillways for the aquifer. Since withdrawals from Braunfels in Comal County and are the largest group of wells began, the spring flow has decreased, with the total springs in Texas. San Marcos Springs occur in the city of reduction in volume of spring flow being roughly equal San Marcos in Hays County and are the second largest to the total volume of withdrawals from wells. group of springs in Texas. Hueco Springs are a smaller group of springs near the Guadalupe River about 3 miles Estimates of storage of water in the aquifer range 3 north of New Braunfels in Comal County. All three from about 15 million acre-feet (18.5 billion m ) to 3 groups of springs occur along major faults in the about 45 million acre·feet (55.5 billion m ). Balcones Fault Zone. The first substantial withdrawals of water from The formations comprising the Edwards aquifer in wells penetrating the aquifer were in the late 1800's. In the area of the three groups of springs, from top to 1934, the total withdrawal from wells was about 3 bottom, are the Georgetown Formation, the Person and 100,000 acre·feet (123 million m ). Withdrawals Kainer Formations of the Edwards Group, 'and the reached their maximum in 1971, when they were 3 Walnut Formation. The aquifer considered in this report 407,000 acre·feet (502 million m ). In 1974, 3 occurs in an area about 5 to 30 miles (8.0 to 48.3 km) withdrawals were 364,000 acre-feet (449 million m ). wide and 175 miles (282 km) long extending from a The primary effects of the withdrawals have been ground-water divide at Brackettville in Kinney County reductions in spring flows during periods of drought. on the west through parts of Uvalde, Medina, Atascosa, Comal Springs were dry, for the first time on record, for Bexar, Guadalupe, and Comal Counties to a about 5 months from July 1956 to November 1956. The ground-water divide northeast of Kyle in Hays County. lowest recorded flow for San Marcos Springs also The formations range in total thickness in this area from occurred at that time. about 400 to 1,000 feet (122 to 305 mi. The daily average flow reported for Comal Springs The Edwards aquifer is recharged principally by has ranged from a minimum of zero in 1956 to a seepage of water from streams crossing its outcrop, and maximum of 534 cubic feet per second (15.1 m 3 /s) in by direct infiltration of precipitation falling on its 1973. Prior to 1948, the lowest daily average flow outcrop areas. Average recharge for the period 1934-73 reported was 245 cubic feet per second (6.9 m 3 /s) in is estimated at slightly less than 600,000 acre·feet (740 1939. The average annual discharge for Comal Springs 3 million m ) per year. Annual recharge during this period during the period 1945·73 was 184,000 acre·feet (227 3 ranged between a minimum of less than 50,000 acre-feet million m ) per year.