FINAL CASE STUDY REPORT to the 60TH LEGISLATURE WATER POLICY INTERIM COMMITTEE (With Public Comments) by the Montana Bureau of M
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FINAL CASE STUDY REPORT TO THE 60TH LEGISLATURE WATER POLICY INTERIM COMMITTEE (with public comments) by the Montana Bureau of Mines and Geology September 11, 2008 WPIC members: Senator Jim Elliott, Chair Senator Gary L Perry, vice Chair Representative Scott Boggio Representative Jill Cohenour Representative Bill McChesney Representative Walter McNutt Senator Larry Jent Senator Terry Murphy HB 831 Report CONTENTS Recommendations to the Water Policy Interim Committee ..............................................1 SECTION 1: General Concepts of Stream–Aquifer Interaction and Introduction to the Closed Basin Area .......................................................................................................3 Introduction ...............................................................................................................5 Th e Hydrologic Cycle ............................................................................................5 Occurrence of Ground Water .................................................................................5 Stream–Aquifer Interaction ...................................................................................7 Closed Basin Regional Summary ...............................................................................10 Geology ....................................................................................................................18 Distribution of Aquifers ............................................................................................19 Ground-Water Occurrence and Movement ...............................................................22 Seasonal Water-Level Fluctuations ............................................................................22 Ground-Water Quality ..............................................................................................22 References .................................................................................................................25 SECTION 2: Case Studies ..........................................................................................27 Lower Beaverhead River Case Study ..........................................................................29 Summary ............................................................................................................29 Introduction .......................................................................................................32 Physiography .......................................................................................................32 Climate ...........................................................................................................32 Geology ..........................................................................................................34 Previous Investigations ........................................................................................35 Data Management ...............................................................................................38 Project Drilling ..................................................................................................38 Wells Drilled near the Beaverhead River .........................................................39 Wells Drilled in the Spring Creek Drainage ....................................................39 i Montana Bureau of Mines and Geology Wells Drilled to Monitor the Eff ects of a Nearby Irrigation Well ....................41 Aquifer Tests .............................................................................................................41 Methods ..........................................................................................................41 Water-Level Measurements ............................................................................41 Discharge Measurements ................................................................................43 Aquifer Test Results .......................................................................................43 Aquifer Test Analysis .......................................................................................45 Water Chemistry .......................................................................................................46 Hydrogeology ...........................................................................................................47 Ground-Water Flow Map ................................................................................47 Hydrogeologic Cross Sections .........................................................................49 Stream Depletion ......................................................................................................53 Methods of Determining Stream Depletion ....................................................53 Evaluation of Stream Depletion in the Lower Beaverhead River ................................55 Numerical Model Dimensions .......................................................................55 Numerical Model Calibration .........................................................................55 Steady-State Modeling ....................................................................................56 Stream Depletion Analyses ..............................................................................56 Near-Stream, Shallow Conditions ...................................................................56 Near-Stream, Deep Conditions .......................................................................56 Distal, Deep Conditions .................................................................................57 Basin Margin, Deep Conditions .....................................................................61 Cumulative Eff ects ..........................................................................................61 Transient Simulation of Cyclic Pumping .........................................................61 Analysis of Methods to Off set Stream Depletion .............................................64 Summary of Depletion Analyses .....................................................................66 References .................................................................................................................69 ii HB 831 Report Gallatin Valley Case Study—A Basin-Scale Ground-Water Model to Evaluate Ground- Water and Surface-Water Interaction .........................................................................73 Executive Summary .............................................................................................73 Introduction ........................................................................................................73 Approach.............................................................................................................73 Water Budget of the Gallatin Valley ....................................................................75 Geology ...............................................................................................................78 Steady-State Ground-Water Model ......................................................................78 Transient Modeling .............................................................................................84 Conclusion ..........................................................................................................89 References ...........................................................................................................93 Ground-Water Use and Development in the Bitterroot Watershed ............................95 Introduction ........................................................................................................95 Basefl ows over Time ............................................................................................95 Basefl ows and Well Development ........................................................................98 Basefl ows and Precipitation .................................................................................98 Ground-Water Storage .........................................................................................99 Changes in Ground-Water Storage ....................................................................100 Ground-Water Withdrawals ..............................................................................102 Conclusions ......................................................................................................102 References .........................................................................................................106 SECTION 3: Evaluation of Hydrologic Assessments ..................................................107 Executive Summary.................................................................................................109 Review of Application Process and Hydrogeologic Assessment Requirements ..........109 Components of a Hydrogeologic Assessment ................................................109 Part 1: Introduction ................................................................................109 Part 2: Physical Characteristics ...............................................................109 iii Montana Bureau of Mines and Geology Part 3: HB 831—Net Depletion Evaluation ............................................110 Part 4: HB 831—Net Depletion and Adverse Aff ect ...............................110 Part 5: HB 831—Water Quality .............................................................110 Part 6: Permit Application