Hydrogeology of the Ashland Ranger District, Custer National Forest, southeastern Montana Montana Bureau of Mines and Geology Open-File Report 570 2008 John Wheaton Jay Gunderson Shawn Reddish-Kuzara John Olson Licette Hammer TABLE OF CONTENTS ABSTRACT....................................................................................................................... 1 INTRODUCTION............................................................................................................. 3 Purpose and Scope ........................................................................................................ 3 Location and Description of Area ............................................................................... 3 Topography................................................................................................................. 5 Climate........................................................................................................................ 6 Previous Investigations................................................................................................. 9 Acknowledgements ....................................................................................................... 9 Methods........................................................................................................................ 10 GEOLOGY...................................................................................................................... 11 Regional Geological Setting ....................................................................................... 11 Stratigraphy................................................................................................................. 11 Fox Hills Formation (Cretaceous).......................................................................... 14 Hell Creek (Lance) Formation (Cretaceous).......................................................... 15 Fort Union Formation (Tertiary)............................................................................ 15 Tullock Member .................................................................................................... 15 Lebo Member ........................................................................................................ 15 Tongue River Member........................................................................................... 15 Wasatch Formation(Tertiary).................................................................................. 16 Clinker ...................................................................................................................... 16 Alluvium ................................................................................................................... 16 Mineral Resources ...................................................................................................... 16 Coal........................................................................................................................... 12 Gravel ....................................................................................................................... 12 Oil and gas................................................................................................................ 17 GROUND-WATER RESOURCES............................................................................... 14 Overview of the Hydrogeology of the Study Area ................................................... 14 Aquifers........................................................................................................................ 23 Fox Hills and Hell Creek formations...................................................................... 23 Fort Union Formation............................................................................................. 23 Tullock Member .................................................................................................... 23 Lebo Shale............................................................................................................. 24 Tongue River Member........................................................................................... 24 Clinker ...................................................................................................................... 31 Alluvium ................................................................................................................... 31 Springs ......................................................................................................................... 31 Occurrence of springs.............................................................................................. 33 Water quantity.......................................................................................................... 33 Inventoried Streams.................................................................................................... 42 Perennial stream flow .............................................................................................. 42 Water quantity.......................................................................................................... 43 Water quality ............................................................................................................ 44 i Inventoried Wells........................................................................................................ 47 Water quantity.......................................................................................................... 47 Water quality ............................................................................................................ 47 WATER SUPPLIES AND USES................................................................................... 49 VULNERABILITY TO COALBED-METHANE DEVELOPMENT....................... 51 ONGOING WORK......................................................................................................... 54 CONCLUSIONS ............................................................................................................. 54 REFERENCES................................................................................................................ 56 ii FIGURES 1. Location map of the study area...................................................................................... 4 2. Precipitation data for Broadus, MT ............................................................................... 7 3. Comparison of Broadus and Poker Jim monthly precipitation totals ............................ 8 4. Structural setting for Powder River Basin and the Ashland Ranger District................. 12 5. Generalized stratigraphic column for the Ashland Ranger District............................... 13 6. Conceptual ground-water altitudes for the Tullock Member and the Fox Hills Formation....................................................................................................................... 20 7. Conceptual ground-water altitudes for aquifers near the base of the Tongue River Member and for the Knobloch coal. .............................................................................. 21 8. Conceptual ground-water altitudes for the Canyon coal. .............................................. 22 9. Hydrograph for sandstone aquifer at Liscom well......................................................... 26 10. Hydrograph for sandstone aquifer at Tooley Creek well............................................... 26 11. Hydrograph for Anderson, Dietz and Canyon coals at CBM03-11 site ........................ 28 12. Geologic cross section for Otter Creek near well WO-1 ............................................... 29 13. Hydrographs for sandstone and Knobloch coal wells near WO-1 along Otter Creek.............................................................................................................................. 30 14. Hydrographs for Otter Creek alluvial wells near WO-10.............................................. 32 15. Total number of springs and cumulative spring discharge for stratigraphic units......... 35 16. Total number of springs and cumulative spring discharge for individual coal bed associations .................................................................................................................... 36 17. Average spring discharge rates for individual coal bed associations ............................ 37 18. Hydrograph for Bidwell North Spring........................................................................... 39 19. Hydrograph for Lemonade Spring................................................................................. 39 20. Hydrograph for North Fork Spring................................................................................ 40 21. Hydrograph for spring on lower Cow Creek ................................................................. 40 22. Hydrograph for Cow Creek Spring................................................................................ 41 23. Hydrograph for Alkali Spring........................................................................................ 41 24. Hydrograph and precipitation data for East Fork Hanging Woman Creek ................... 45 25 Specific conductance values measured in Cow Creek during October, 2004 ............... 46 26 Specific conductance values compared to flow rates at the East Fork Hanging Woman Creek weir .......................................................................................................