ABSTRACT Salinity in the Northern Segment of the Brazos River Alluvium Aquifer: A Hydro-Forensic Approach Erin P. Noonan, M.S. Mentor: Joe C. Yelderman, Jr., Ph.D. The Brazos River Alluvium Aquifer is a minor aquifer in central and east Texas under water table conditions. It is an underutilized resource and may be considered a supplemental water source. However, variability in salinity occurs throughout the Brazos River Alluvium Aquifer and the source of this variability is unclear. The objective of this study is to characterize the variability of salinity in the northern segment of the Brazos River Alluvium Aquifer and evaluate potential sources of elevated salinity. Three potential sources of elevated salinity were evaluated: Interactions between the aquifer and the river, concentration from irrigation, and brine contamination from historic oil and gas fields. Based on the ionic and isotopic composition of aquifer and river samples, in- situ water samples, core descriptions, batch leaching of sediment, and hydrographs, the Brazos River and historic oil and gas fields do not appear to be the source of elevated salinity for the aquifer; although, irrigation could impact aquifer salinity. Salinity in the Northern Segment of the Brazos River Alluvium Aquifer: A Hydro-Forensic Approach by Erin Noonan, B.S. A Thesis Approved by the Department of Geosciences Stacy Atchley, Ph.D., Chairperson Submitted to the Graduate Faculty of Baylor University in Partial Fulfillment of the Requirements for the Degree of Master of Science Approved by the Thesis Committee Joe C. Yelderman, Jr., Ph.D., Chairperson Steve Dworkin, Ph.D. Jack D. Tubbs, Ph.D. Accepted by the Graduate School August 2019 J. Larry Lyon, Ph.D., Dean Page bearing signatures is kept on file in the Graduate School. Copyright © 2019 by Erin P. Noonan All rights reserved TABLE OF CONTENTS LIST OF FIGURES ........................................................................................................... vi LIST OF TABLES ............................................................................................................. xi ACKNOWLEDGMENTS ............................................................................................... xiv DEDICATION ................................................................................................................. xvi CHAPTER ONE ................................................................................................................. 1 Introduction ..................................................................................................................... 1 Background ................................................................................................................. 1 Purpose ....................................................................................................................... 5 Study Area ................................................................................................................... 7 Climate ........................................................................................................................ 8 Geology ....................................................................................................................... 9 Hydrogeology ............................................................................................................ 13 Previous Works ......................................................................................................... 18 CHAPTER TWO .............................................................................................................. 22 Methods ........................................................................................................................ 22 Historic Brazos River Alluvium Aquifer and Brazos River Chemistry Data ............ 22 Brazos River Alluvium Aquifer and Brazos River Water Sampling .......................... 23 Coring and In-situ Water Sampling .......................................................................... 29 Batch Leaching ......................................................................................................... 30 Data Loggers ............................................................................................................ 31 CHAPTER THREE .......................................................................................................... 33 Results and Discussion ................................................................................................. 33 Specific Conductance and Ionic Composition of the Brazos River Alluvium Aquifer and Brazos River .................................................................................... 33 Land Use in the Northern Segment of the Brazos River Alluvium Aquifer ............... 62 Isotopic Composition of the Brazos River Alluvium Aquifer and Brazos River ....... 66 Coring and In-situ Water Sampling .......................................................................... 71 Batch Leaching Experiment ...................................................................................... 80 Comparison of In-situ and Batch Leaching Samples ................................................ 83 Hydrographs ............................................................................................................. 84 CHAPTER FOUR ............................................................................................................. 97 Summary and Conclusions ........................................................................................... 98 Variability of Salinity ................................................................................................ 98 iv Sources of Salinity ..................................................................................................... 99 CHAPTER FIVE ............................................................................................................ 102 Recommendations ....................................................................................................... 102 APPENDIX A ................................................................................................................. 105 Water Sampling Procedures ........................................................................................ 105 APPENDIX B ................................................................................................................. 108 Batch Leaching Procedures ........................................................................................ 108 Introduction ............................................................................................................. 108 Hypotheses .............................................................................................................. 108 Methods ................................................................................................................... 109 APPENDIX C ................................................................................................................. 111 2018 Brazos River Alluvium Aquifer and Brazos River Water Chemistry ............... 111 APPENDIX D ................................................................................................................. 115 Historic Brazos River Alluvium Aquifer and Brazos River Water Chemsitry ........... 115 APPENDIX E ................................................................................................................. 155 Isotopic Composition of the Brazos River Alluvium Aquifer and Brazos River ....... 155 APPENDIX F.................................................................................................................. 157 Core Descriptions ....................................................................................................... 157 APPENDIX G ................................................................................................................. 197 Ionic Chemistry of the Brazos River Alluvium Aquifer In-situ Water Samples ........ 197 APPENDIX H ................................................................................................................. 199 Well Diagrams ............................................................................................................ 199 APPENDIX I .................................................................................................................. 210 Batch Leaching Results .............................................................................................. 210 APPENDIX J .................................................................................................................. 215 Hydrographs ................................................................................................................ 215 Hydrographs for Well HDM ................................................................................... 215 Hydrographs for Well HDB .................................................................................... 217 Hydrographs for Well HDT .................................................................................... 220 Hydrographs for Well RP1 ..................................................................................... 222 Hydrographs for Well GM9M ................................................................................. 225 BIBLIOGRAPHY ........................................................................................................... 227 v LIST OF