Evaluation of Hydrochemical and Isotopic Data in Groundwater Management Areas 3 and 7 Prepared for: Texas Water Development Board May 2013 by Charlie W. Kreitler, Ph.D., P.G. James A. Beach, P.G. Leigh Symank Matt Uliana, Ph.D., P.G. Randy Bassett, Ph.D. John E. Ewing, P.E. Van A. Kelley, P.G. This page is intentionally blank. Evaluation of Hydrochemical and Isotopic Data in Groundwater Management Areas 3 and 7 Prepared for: Texas Water Development Board By: Charlie W. Kreitler, Ph.D., P.G. James A. Beach, P.G. Leigh Symank LBG-Guyton Associates Matt Uliana, Ph.D., P.G. Martin Geologic Consulting Randy Bassett, Ph.D. John E. Ewing, P.E. Van A. Kelley, P.G. INTERA Incorporated May 2013 This page is intentionally blank. ii Geoscientist and Engineering Seal This report documents the work of the following Licensed Texas Geoscientists and Licensed Texas Professional Engineers: Charlie W. Kreitler, Ph.D., P.G. Dr. Kreitler was the Project Manager for the study and was responsible for hydrochemical and isotope analysis and oversight of the project. James A. Beach, P.G. Mr. Beach was responsible for evaluating how the hydrochemical and isotope results affect conceptual models of the GAMs. Matthew M. Uliana, Ph.D., P.G. Dr. Uliana was responsible for the analysis and interpretations of the strontium isotope data for the Llano Uplift region and for all the analysis and interpretations for the Trans-Pecos aquifers. John E. Ewing, P.E. Mr. Ewing was responsible for performing GAM runs. Van A. Kelley, P.G. Mr. Kelley provided guidance and oversight of GAM runs. iii Table of Contents 1 Executive Summary ................................................................................................................. 1 2 Introduction ............................................................................................................................. 3 3 Approach for Evaluating Aquifers in the Study Area ............................................................. 7 3.1 Llano Uplift Aquifers .................................................................................................. 7 3.2 Aquifers of the Edwards-Trinity (Plateau) .................................................................. 9 3.3 Aquifers of the Trans-Pecos Region .......................................................................... 12 3.4 Limitations of the Data and Study ............................................................................. 12 4 Hydrochemical Approach Toward Understanding Aquifer Dynamics ................................. 13 4.1 Approach ................................................................................................................... 13 4.2 Pertinent Issues .......................................................................................................... 14 4.2.1 Defining Recharge Areas .......................................................................................... 14 4.2.2 Age of Groundwater .................................................................................................. 14 4.2.3 Mixing Between Aquifers or Aquifer and Surface Water ......................................... 14 4.3 Radioactive Isotopes .................................................................................................. 15 4.3.1 Carbon-14 .................................................................................................................. 15 4.3.2 Tritium ....................................................................................................................... 16 4.3.3 Chlorine-36 ................................................................................................................ 18 4.3.4 Radium-226 and Radium-228 ................................................................................... 18 4.4 Stable Isotopes ........................................................................................................... 18 4.4.1 Deuterium and Oxygen-18 ........................................................................................ 18 4.4.2 Strontium isotopic compositions ............................................................................... 21 5 Assimilation of Existing Data and Collection of New Data .................................................. 24 5.1 Data Sources .............................................................................................................. 24 5.1.1 Quality Control for TWDB data ................................................................................ 24 5.1.2 Previously Collected Data by Aquifer and by Region .............................................. 25 5.2 Newly Collected Data in the Llano Uplift Area ........................................................ 25 6 Regional Aquifer Isotope Analysis ........................................................................................ 28 6.1 Estimated Age of Groundwater from Aquifers ......................................................... 28 6.1.1 Assessment of Aquifers ............................................................................................. 28 6.2 Assessment of Individual Aquifers ........................................................................... 31 6.2.1 Ellenburger-San Saba Aquifer ................................................................................... 31 6.2.2 Hickory Aquifer......................................................................................................... 34 iv 6.2.3 Edwards-Trinity (Plateau) Aquifer ............................................................................ 37 6.2.4 Antlers Formation ...................................................................................................... 39 6.2.5 Edwards -Trinity (Plateau) Aquifer (Trans-Pecos Region) ....................................... 42 6.2.6 Pecos Valley Aquifer ................................................................................................. 44 6.2.7 Rustler Aquifer .......................................................................................................... 46 6.3 Hydrochemical Profiles ............................................................................................. 48 6.4 Discussion.................................................................................................................. 62 7 Llano Uplift Aquifers ............................................................................................................ 63 7.1 General Review of the Llano Uplift Aquifers ........................................................... 63 7.2 Northern Sub-Region (Mason and McCulloch Counties) ......................................... 66 7.2.1 Data Reviewed........................................................................................................... 66 7.2.2 Results for Hickory Aquifer ...................................................................................... 66 7.2.3 Critical Chemical Parameters .................................................................................... 75 7.2.4 Radiocarbon Age Corrections ................................................................................... 97 7.2.5 Discussion of the Hickory Aquifer Results ............................................................. 102 7.2.6 Results for Ellenburger-San Saba Aquifer .............................................................. 103 7.2.7 Critical Chemical Parameters .................................................................................. 106 7.2.8 Discussion of the Ellenburger-San Saba Aquifer Results ....................................... 109 7.3 Southern Sub-Region (Gillespie County) ................................................................ 109 7.3.1 Data Reviewed......................................................................................................... 109 7.3.2 Groundwater Hydrology .......................................................................................... 120 7.3.3 Hydrochemical Results ............................................................................................ 120 7.3.4 Discussion of Results .............................................................................................. 126 7.4 Eastern Sub-Region (Burnet County) ...................................................................... 132 7.4.1 Data Reviewed......................................................................................................... 132 7.4.2 Hydrogeologic, Chemical and Isotopic Results ...................................................... 137 7.4.3 Discussion of Results .............................................................................................. 150 7.5 Strontium Isotopic Compositions within Each Sub-Region .................................... 150 7.5.1 North Sub-Region (Mason and McCulloch Counties) ............................................ 152 7.5.2 South Sub-Region (Gillespie County) ..................................................................... 161 7.5.3 East Sub-Region (Burnet County) ........................................................................... 170 7.6 Conclusions ............................................................................................................. 178 8 Edwards–Tr inity (Plateau) Aquifer ..................................................................................... 179 8.1 Conceptual Groundwater Model ............................................................................