May 2018 Montana Bureau of Mines and Geology Open-File Report 703 THREE-DIMENSIONAL HYDROSTRATIGRAPHIC MODEL OF THE SUBSURFACE GEOLOGY, FLATHEAD VALLEY, KALISPELL, MONTANA James Rose Montana Bureau of Mines and Geology Ground Water Investigations Program Cover image: Aerial view of the Flathead Valley looking northeast. Photo by Chris Saulit. THREE-DIMENSIONAL HYDROSTRATIGRAPHIC MODEL OF THE SUBSURFACE GEOLOGY, FLATHEAD VALLEY, KALISPELL, MONTANA May 2018 James Rose Montana Bureau of Mines and Geology Ground Water Investigation Program Montana Bureau of Mines and Geology Open-File Report 703 Montana Bureau of Mines and Geology Open-File Report 703 TABLE OF CONTENTS Preface ..................................................................................................................................................................1 Abstract ................................................................................................................................................................2 Introduction ..........................................................................................................................................................3 Project Background ........................................................................................................................................3 Purpose and Scope .........................................................................................................................................3 Project Location .............................................................................................................................................3 Previous Studies .............................................................................................................................................5 Geologic Setting .............................................................................................................................................5 Belt Supergroup Bedrock .........................................................................................................................6 Tertiary Sediments ..................................................................................................................................6 Quaternary Sediments ..............................................................................................................................6 Deep Alluvium System ......................................................................................................................8 Deep Alluvium .............................................................................................................................8 Troughs in the Deep Alluvium .....................................................................................................10 Silt, Clay, Gravel Alluvium of the Deep Alluvium System .........................................................10 Lacustrine and Till Deposits ..............................................................................................................11 Till Deposits .................................................................................................................................11 Lacustrine Sediments ...................................................................................................................11 Surficial Deposits ...............................................................................................................................12 Methods................................................................................................................................................................13 Overview ........................................................................................................................................................13 GMS Terminology .........................................................................................................................................13 Modeled Hydrostratigraphy ...........................................................................................................................13 Data Management ..........................................................................................................................................14 Well Selection Criteria ...................................................................................................................................14 Soil Identification Codes ................................................................................................................................14 Hydrostratigraphic Units ................................................................................................................................17 Bedrock Aquifer .......................................................................................................................................17 Tertiary Aquifer ........................................................................................................................................17 v James Rose, May 2018 Deep Aquifer System ...............................................................................................................................17 Deep Alluvial Aquifer .......................................................................................................................17 Silt, Clay, Gravel Zone of the Deep Alluvial Aquifer .......................................................................18 Lacustrine-Till Aquitard ...........................................................................................................................18 Shallow Aquifer .......................................................................................................................................18 Developing the Hydrostratigraphic Model ....................................................................................................18 Lacustrine-Till Aquitard Thickness Contour Map .........................................................................................19 Results ..................................................................................................................................................................19 Hydrogeologic Units ......................................................................................................................................19 Belt Bedrock Aquifer ...............................................................................................................................19 Tertiary Aquifer ........................................................................................................................................20 Deep Aquifer System ...............................................................................................................................21 Deep Alluvial Aquifer ........................................................................................................................21 Troughs in the Deep Alluvial Aquifer ................................................................................................21 Silt, Clay, Gravel Zone of the Deep Alluvial Aquifer ........................................................................24 Lacustrine-Till Aquitard ...........................................................................................................................26 Shallow Aquifer .......................................................................................................................................28 Alignment of Erosional Features ...................................................................................................................28 Southern Model Boundary .............................................................................................................................28 Discussion ............................................................................................................................................................30 Characteristics of the Lacustrine-Till Aquitard ..............................................................................................30 Implications for Drilling Water Wells ............................................................................................................31 Hydrostratigraphic Model ..............................................................................................................................31 GMS Project Files ..........................................................................................................................................33 Recommendations ................................................................................................................................................33 Acknowledgments ................................................................................................................................................33 References ............................................................................................................................................................34 Appendix A, available for download vi Montana Bureau of Mines and Geology Open-File Report 703 FIGURES Figure 1. The project study area is located in the Flathead Valley of northwestern Montana .............................4 Figure 2. Surficial geologic units in the Flathead Valley include Quaternary river alluvium in the north, river delta sediments in the south, and glacial deposits,