R. Gonzalez, Secretary/Treasurer Jaret Groth, President
Staff Report & Agenda Item Details
M. R. Gonzalez, Secretary/Treasurer Jaret Groth, President Date Approved . | D7. 4 TELE Page 8 of 8 Fees Minutes of 04-21-2026 Agenda Item 6: DFC Comparison Updated Calibration of Alternative GAM Updated GAM Simulations Draft Explanatory Reports and Non-Relevant Documentation Bill Hutchison GMA 3 and 7 Joint Meeting April 23, 2026 Topics • DFC Comparison • Updated Calibration of Alternative GAM • Updated GAM Simulations • Draft Explanatory Report and Non-Relevant Documentation Topics • DFC Comparison • Updated Calibration of Alternative GAM • Updated GAM Simulations • Draft Explanatory Report and Non-Relevant Documentation DFC Comparison (GMA 3) • Complete • GMA 3 Technical Memorandum 25-01 (Draft - September 5, 2025) • Presented results at GMA 3 meeting on October 22, 2025 • Summary of Findings: • Capitan Reef Complex Aquifer • Recommended classification as not relevant for purposes of joint planning • Dockum Aquifer • Recommended classification as not relevant for purposes of joint planning • Edwards-Trinity (Plateau) and Pecos Valley Aquifers • Recommended update to Alternative GAM calibration (Pecos and Reeves counties) • Rustler Aquifer • Recommended classification as not relevant for purposes of joint planning GMA 3 DFC Comparison Difference Number of Number of |Average Annual Average (Simulated ‘County Baseline Wells Annual Data | Data Points per Simulated Drawdown Points Baseline Well minus Actual 12.00 DFC Comparison (Phase 1 - GMA 7) (1) • Presented at GMA 7 meeting of August 14, 2025 • Summary of Findings • Capitan Reef Complex Aquifer • Recommended classification as not relevant for purposes of joint planning • Edwards-Trinity (Plateau), Pecos Valley, and Trinity Aquifers • Recommended Phase 2 (GCD data and interpolated baselines) • Recommended update of Alternative GAM • Recommended update of MAG approach for Kinney County • Recommended classification of Val Verde County as not relevant for purposes of joint planning DFC Comparison (Phase 1 - GMA 7) (2) • Presented at GMA 7 meeting of August 14, 2025 • Summary of Findings • High Plains Aquifer System (Dockum and Ogallala Aquifers) • Recommended classification as not relevant for purposes of joint planning • Llano Uplift Aquifers • Marble Falls Aquifer: recommended keeping classification as not relevant for purposes of joint planning • Ellenburger-San Saba and Hickory Aquifers: recommended Phase 2 (GCD data and interpolated baselines) • Rustler Aquifer • Recommended classification as not relevant for purposes of joint planning DFC Comparison (Phase 2 – GMA 7) • Complete • GMA 7 Technical Memorandum 26-01 (Draft – April 16, 2026) • Initial work presented at GMA 7 meeting of November 6, 2025 • Updated with GCD data (Irion and Sterling counties) • Work on Edwards-Trinity (Plateau), Pecos Valley, and Trinity Aquifers complete • Updated with GCD data (Irion and Sterling counties – 11/6/2025 GMA 7 meeting) • Updated with baseline interpolations (TWDB data) – 3/18/2026 GMA 7 meeting • Work on Llano Uplift (Hickory) complete • Updated with baseline interpolations (TWDB data) • No additional data from Hickory Aquifer available (City of San Angelo) Drawdown Comparison: Edwards-Trinity (Plateau), Pecos Valley, Trinity Aquifers Drawdown from 2012 (ft) Hydrograph of Average Drawdown (Actual and Simulated) GMA 7 - Edwards-Trinity (Plateau), Pecos Valley, Trinity Aquifer -4 Legend —— Actual Drawdown —— Simulated Drawdown Red Numbers = Number of Data Points Each Year 2012 2014 2016 2018 2020 2022 2024 Year Average Measured and Simulated Drawdown Ellenburger-San Saba Aquifer (GMA 7) “25 1a Table 10. Average Measured and Simulated Drawdown by GCD - Ellenburger-San Saba o4 Aquifer | Average Drawdown ft - 2010 = 7] . erage Drawdown ft - . = Groundwater Number of Base, 2011 to 2024 Data) Average oo] " . ctual Simulated a Conservation District . & 44 (GCD) ; ane N Measurements | Measured Simulated | Measured (ft) e | ickory UWCD No.1_| W 107