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Subsidence Risk Assessment and Regulatory Considerations for the Brackish Jasper Aquifer

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Subsidence Risk Assessment and Regulatory Considerations for the Brackish Jasper Aquifer SUBSIDENCE RISK ASSESSMENT AND REGULATORY CONSIDERATIONS FOR THE BRACKISH JASPER AQUIFER Harris-Galveston and Fort Bend Subsidence Districts Final Report Prepared for: Harris-Galveston Subsidence District Fort Bend Subsidence District Prepared by: INTERA Incorporated 9600 Great Hills Trail Suite 300W Austin, TX 78759 512.425.2000 May 2018 This page intentionally left blank. SUBSIDENCE RISK ASSESSMENT AND REGULATORY CONSIDERATIONS FOR THE BRACKISH JASPER AQUIFER Harris-Galveston and Fort Bend Subsidence Districts Prepared By Van Kelley, P.G. Neil Deeds, Ph.D., P.E. Steve C. Young, Ph.D., P.G., P.E. James Pinkard INTERA Incorporated Contributors Dr. Zhuping Sheng, Ph.D., P.E., P.H.; Independent Consultant John Seifert, P.E., P.G.; WSP Scott Marr, P.E., HDR i This page intentionally left blank. ii Subsidence Risk Assessment and Regulatory Considerations for the Brackish Jasper Aquifer GEOSCIENTIST AND/OR PROFESSIONAL ENGINEER SEAL(S) Van A. Kelley (P.G. 4923) was the Project Manager and Principal Investigator for this study. All work performed was under the direct supervision of Van A. Kelley. It is not to be used for construction, bidding or any other purposes not specifically sanctioned by the authors. ___________________________________ __5/15/2018_____ Signature Date Neil Deeds was (P.E. 92741) was the technical lead for development of the Jasper Risk Model and he supervised all modeling associated with this report. Dr. Deeds also participated in the development of the conceptual model for prediction of compaction in the Jasper Aquifer. ___________________________________ __5/15/2018______ Signature Date Steve C. Young (P.G. 231) was the technical lead for the development of the conceptual model for prediction of compaction in the Jasper Aquifer and in that role Dr. Young reviewed available geotechnical data from cores taken from USGS boreholes in the Houston area in the Gulf Coast Aquifer. ___________________________________ __5/15/2018_____ Signature Date Zhuping Sheng (P.E. 87496) provided peer technical review for the study. Dr. Sheng supported the interpretation of geotechnical core analyses in the literature. Dr. Sheng also reviewed the conceptual model for prediction of compaction in the Jasper Aquifer and provided comment on the risk assessment and the relevant limitations and assumptions. ___________________________________ __5/15/2018_____ Signature Date iii Subsidence Risk Assessment and Regulatory Considerations for the Brackish Jasper Aquifer This page intentionally left blank. iv Subsidence Risk Assessment and Regulatory Considerations for the Brackish Jasper Aquifer Acknowledgments: The authors would like to acknowledge John Seifert (WSP) for improvement in our understanding of the Jasper Aquifer through his contribution of hydrogeologic data for the Jasper Aquifer and his review of the Jasper Risk Assessment Model. We would also like to acknowledge Scott Marr (HDR) for his support in understanding the historical application of PRESS in the Houston area to model compaction and for his review of the conceptual model for prediction of compaction in the Jasper Aquifer. Finally, we would like to thank Mike Turco (Harris-Galveston and Fort Bend Subsidence Districts) and his staff for supporting this project and providing feedback as the study progressed. We would finally like to thank Bill Mullican of Mullican and Associates who provided third party review during this project on behalf of the Harris-Galveston Subsidence District. The report has been much improved with these contributions. v Subsidence Risk Assessment and Regulatory Considerations for the Brackish Jasper Aquifer This page intentionally left blank. vi Subsidence Risk Assessment and Regulatory Considerations for the Brackish Jasper Aquifer TABLE OF CONTENTS 1.0 INTRODUCTION .......................................................................................................................... 1 2.0 CONCEPTUAL MODEL FOR PREDICTION OF COMPACTION IN THE JASPER AQUIFER..................... 3 2.1 Introduction to Compaction and Subsidence .................................................................... 3 2.2 Properties that Govern Compaction ................................................................................. 4 2.2.1 Ultimate Compaction: Overall Bed Thickness and Compressibility ...................... 4 2.2.2 Rate of Compaction: Individual Clay Bed Thickness and Vertical Conductivity .... 5 2.2.3 Stress at Which Compaction Begins: Drawdown at Preconsolidation Stress ....... 5 2.3 Compaction Properties in the Gulf Coast Aquifer System ................................................. 6 2.3.1 Inelastic and Elastic Specific Storage .................................................................. 6 2.3.2 Thickness of the Clay Beds ................................................................................. 8 2.3.3 Vertical Hydraulic Conductivity of Clays ............................................................. 8 2.3.4 Drawdown at Preconsolidation Stress ................................................................ 9 3.0 NUMERICAL MODEL FOR PREDICTION OF COMPACTION IN THE JASPER AQUIFER ..................... 17 3.1 Code Selection ............................................................................................................... 17 3.1.1 PRESS ............................................................................................................... 17 3.1.2 MODFLOW-SUB ............................................................................................... 18 3.2 Model Construction ....................................................................................................... 18 3.2.1 Extent and Grid ................................................................................................ 18 3.2.2 Boundary Conditions........................................................................................ 19 3.2.3 Parameterization ............................................................................................. 19 3.3 Compaction Simulation Approach .................................................................................. 21 3.3.1 Initial Conditions .............................................................................................. 21 3.3.2 Project Grid Domain......................................................................................... 21 3.3.3 Representative Jasper Aquifer Project .............................................................. 22 3.3.4 Compaction Simulation Sensitivity Cases .......................................................... 22 3.4 Compaction Simulation Results ...................................................................................... 23 3.4.1 Variation in Flow Rate ...................................................................................... 23 3.4.2 Rate of Compaction ......................................................................................... 24 3.4.3 Sensitivity Cases ............................................................................................... 24 4.0 JASPER AQUIFER SUBSIDENCE RISK ASSESSMENT APPROACH AND RESULTS ............................. 37 4.1 Risk Assessment Approach ............................................................................................. 37 4.1.1 Risk Categories and Performance Metrics ........................................................ 37 4.1.2 Normalized Risk Score Methodology ................................................................ 38 4.2 Jasper Aquifer Subsidence Risk Assessment Results ....................................................... 39 4.2.1 Performance Measure Normalized Risk Scores ................................................. 39 4.2.2 Total Subsidence Normalized Risk Score........................................................... 40 5.0 CONSIDERATIONS FOR BRACKISH GROUNDWATER DEVELOPMENT REGULATION IN THE JASPER AQUIFER ................................................................................................................................................ 47 5.1 Recommendations for Regulation and Monitoring ......................................................... 47 5.1.1 Well Design and Completion Documentation ................................................... 50 5.1.2 Geophysical Logs.............................................................................................. 51 5.1.3 Hydraulic Data ................................................................................................. 53 5.1.4 Geochemical Data ............................................................................................ 54 vii Subsidence Risk Assessment and Regulatory Considerations for the Brackish Jasper Aquifer 5.1.5 Geotechnical Core Data ................................................................................... 55 5.1.6 Modeling ......................................................................................................... 56 5.1.7 Monitoring....................................................................................................... 57 5.1.8 Subsidence Management Plan ......................................................................... 59 6.0 CONCLUSIONS AND LIMITATIONS ............................................................................................. 61 6.1 Study Summary of Findings and Recommendations ....................................................... 61 6.1.1 Conceptual Model and Parameterization of Compaction Properties in the Jasper Aquifer
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