Texas Water Development Board Report Pecos Valley Aquifer, West Texas: Structure and Brackish Groundwater by John E. Meyer, P.G. Matthew R. Wise, P.G. Sanjeev Kalaswad, Ph.D., P.G. September 6, 2011 Texas Water Development Board Edward G. Vaughan Chairman, Boerne Joe M. Crutcher Vice Chairman, Palestine Thomas Weir Labatt III Member, San Antonio Lewis H. McMahan Member, Dallas Billy R. Bradford, Jr. Member, Brownsville Monte Cluck Member, Gruver Melanie Callahan Interim Executive Administrator The Texas Water Development Board freely grants permission to copy and distribute its materials. The agency would appreciate acknowledgment. Published and distributed by the Texas Water Development Board P.O. Box 13231, Capitol Station Austin, Texas 78711-3231 September 6, 2011 (Printed on recycled paper) iii This page is intentionally blank. iv Table of Contents 1. Executive summary .................................................................................................................... 1 2. Introduction ................................................................................................................................ 3 3. Study Area .................................................................................................................................. 5 3.1 Location, topography, and climate .................................................................................. 5 3.2 Geologic history .............................................................................................................. 8 3.2.1 Paleozoic Era ............................................................................................................. 9 3.2.2 Mesozoic Era ........................................................................................................... 10 3.2.3 Cenozoic Era ............................................................................................................ 10 3.3 Summary of water demands and supplies in the study area ......................................... 11 4. Previous Investigations ............................................................................................................. 12 5. Data Collection and Analysis ................................................................................................... 13 5.1 Data sources and processing ......................................................................................... 13 5.1.1 Well identification numbers ..................................................................................... 15 5.1.2 Water well reports .................................................................................................... 15 5.1.3 Geophysical well logs .............................................................................................. 17 5.1.4 Water quality data .................................................................................................... 18 5.1.5 Static water level data .............................................................................................. 19 5.1.6 Hydraulic properties................................................................................................. 19 5.2 Availability of project data to customers ...................................................................... 21 6. Hydrogeologic Setting .............................................................................................................. 21 6.1 Hydrostratigraphy ......................................................................................................... 21 6.1.1 Stratigraphic unit interpretation ............................................................................... 21 6.1.2 Lithologic descriptions............................................................................................. 32 6.1.3 Net sand and sand percent maps .............................................................................. 33 6.1.4 Structural geometry .................................................................................................. 36 6.2 Aquifer determination analysis ..................................................................................... 47 6.3 Water levels, saturated thickness .................................................................................. 48 6.4 Water quality ................................................................................................................. 51 6.4.1 Aquifers.................................................................................................................... 51 6.4.2 Parameters of concern for desalination .................................................................... 51 6.4.3 Brackish water volume estimates............................................................................. 57 6.4.4 Sources of salinity .................................................................................................... 61 7. Resistivity analysis of geophysical well logs ........................................................................... 62 7.1 Interpretive techniques .................................................................................................. 64 7.1.1 BRACS well 1376.................................................................................................... 65 7.1.2 BRACS well 994...................................................................................................... 65 7.2 Results ........................................................................................................................... 68 8. Database description ................................................................................................................. 69 8.1 Table relationships ........................................................................................................ 70 8.1.1 Well Locations ......................................................................................................... 70 8.1.2 Foreign Keys ............................................................................................................ 71 8.1.3 Digital Well Reports ................................................................................................ 71 8.1.4 Geophysical Well Logs ............................................................................................ 72 8.1.5 Well Geology ........................................................................................................... 72 v 8.1.6 Well construction ..................................................................................................... 72 8.1.7 Water Quality ........................................................................................................... 72 8.1.8 Static Water Level.................................................................................................... 73 8.1.9 Aquifer Hydraulic Properties ................................................................................... 73 8.1.10 Aquifer Determination ............................................................................................. 73 8.2 Supporting data sets ...................................................................................................... 73 8.2.1 GIS data set development ........................................................................................ 73 8.2.2 Processes to create data sets ..................................................................................... 73 8.2.3 Map projection parameters ...................................................................................... 75 9. Future improvements ................................................................................................................ 75 10. Conclusions ....................................................................................................................... 76 11. Acknowledgments............................................................................................................. 76 12. References ......................................................................................................................... 77 13. Appendices ........................................................................................................................ 82 13.1 GIS Data Sets ................................................................................................................ 82 List of Figures Figure 2-1. Study area in Trans-Pecos West Texas. ................................................................ 4 Figure 3-1. Oil and gas activity in the project area.. ................................................................ 6 Figure 3-2. Regional water planning areas in the study area. .................................................. 7 Figure 3-3. Groundwater management areas in the study area. ............................................... 8 Figure 3-4. Groundwater conservation district in the study area. ............................................ 9 Figure 3-5. Regional geologic elements of the Trans-Pecos of West Texas.. ....................... 11 Figure 5-1. BRACS project well control. .............................................................................. 14 Figure 5-2. Wells with aquifer test information. .................................................................... 20 Figure 6-1. BRACS aquifer regions in the project area. ........................................................ 22 Figure 6-2. Location of stratigraphic cross-sections