GROUNDWATER FLOW OF A PROPOSED URANIUM IN-SITU RECOVERY MINE SITE AND SURROUNDING AREAS, WELD COUNTY, COLORADO MIORI YOSHINO B.A., University of Colorado at Boulder, 2006 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment Of the requirement for the degree of Master of Science Department of Geological Sciences 2011 This thesis entitled: Groundwater Flow of a Proposed Uranium In-Situ Recovery Mine Site and Surrounding Areas, Weld County, Colorado written by Miori Yoshino has been approved for the Department of Geological Sciences _________________________________ Shemin Ge _________________________________ Raymond Johnson _________________________________ Alexis Templeton Date______________________ The final copy of the thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. iii Yoshino, Miori (M.S., Geological Sciences) Groundwater Flow of a Proposed Uranium In-Situ Recovery Mine Site and Surrounding Areas, Weld County, Colorado Thesis directed by Professor Shemin Ge ABSTRACT With continued proposals for uranium in-situ recovery in northeastern Colorado, it is necessary to acquire a detailed understanding of background groundwater flow in order to estimate potential mining impacts. Groundwater studies for northern Denver Basin aquifers are limited. This study focuses on discerning in-situ recovery influences on groundwater flow in the Laramie-Fox Hills aquifer by using a steady state, regional scale groundwater flow model and a local scale model in the proposed mining zone. General stratigraphy of the study area includes, in ascending order, the Pierre Shale, the Fox Hills Formation, and the Laramie Formation. Data from public well records were used for hydraulic head mapping and calibrating the groundwater model. Slug and bail tests conducted in the Lower Laramie Formation yielded a hydraulic conductivity range between 9.2 x 10-7 m/s and 1.8 x 10-6 m/s. The Pierre Shale is considered less permeable with an assumed hydraulic conductivity of 1.0 x 10-8 m/s or less. MODFLOW, a finite-difference numerical model, was used to simulate the background steady state groundwater conditions. Groundwater generally flows south and slightly east. Model calibration achieved a correlation coefficient of 0.86 between model hydraulic head and observed water level data. The local scale model used two 7-spot pumping and injection well configurations to examine water level drawdown in response to long term pumping. For a given rate of pumping at 275.22 m3/d and injection at 54.5 m3/d at the pumping and injection wells respectively, drawdown effects iv were limited to a ~80 meter radius surrounding the well field in the proposed sandstone. MT3D, a three-dimensional solute transport model, was used for simulating solute transport in groundwater around the well field. Modeling results suggest that solute concentrations are generally confined by low-permeability shale layers under the given groundwater flow and pumping and injection scenarios. Lateral transport was limited to the radial extent of drawdown. Impacts of in-situ recovery on groundwater flow in areas overlying, underlying and downgradient of the Upper Fox Hills Formation can be minimized given an adequate understanding of the hydrogeologic conditions surrounding the recovery site. v ACKNOWLEDGEMENTS I would like to thank first and foremost my advisor, Shemin Ge, for taking a chance on me by accepting me into the program, for guiding me as I struggled through it, and for always encouraging me to answer my own questions. I am grateful to have trained under her instruction and received her advice, honesty, and support throughout this project. I am also grateful for her tolerance of my novice questions, for her patience as I came into a world unknown to me, and for always keeping her expectations of me just a little too high. I would like to extend my appreciation to researchers of the U.S. Geological Survey Uranium Energy Resources Team for providing me with unique training opportunities and for exposing me to broader research topics and new perspectives. I am especially thankful of my supervisor Raymond Johnson for not only offering guidance, but also for allowing me to make my own mistakes and making himself available when my efforts fell apart. Andrew Manning also provided much appreciated advice and support throughtout my time at the Denver Federal Center. Fellow students in the hydrogeology research group at the University of Colorado, Brent Aigler, Lyndsay Ball, Matthew Weingarten, Kali Abel, and Jessica King, provided valuable field assistance, support, advice, and friendship. I would like to extend many, many thanks to In Wook Yeo, whose timely visit to our research group helped me overcome large hurdles in the last months of the project, and whose constructive support and positive encouragement kept me going on my most challenging days. I would also like to thank my late-night comrades, Jeremy Ring and Gabriela Keeton for making nights in the office easier to endure. I am thankful of Alexis Templeton for her constant encouragement in geochemisty and for opening my eyes to new and exciting research in the field. My work in ArcGIS was greatly assisted by several peers and colleagues at various stages of my research—Kevin Befus, Evan vi Pugh, Lyndsay Ball, Matt Granitto and Stuart Giles. Valuable assistance with fossils was greatly appreciated; shell preparation was undertaken by Amanda Yoshino, and identification was generously provided by Talia Karim. I would like to thank my family and friends for their constant support throughout my graduate study. My most heart-felt gratitude is for Kelly Fenson-Hood for her companionship as a fellow graduate student, for her loving criticism when I was frustrated, and when I needed it, for convincing me there was always a reason to celebrate. I am thankful for William, who kindheartedly took care of me and offered generosity, wisdom, and compassion at a time when I had little to give in return. I would like to thank Matt Silverman for introducing me to geology so long ago, and for being a consistent source of wisdom and support throughout my graduate career. Similarly, I would like to extend my thanks to John Gustavson for offering his perspectives and for giving me truth when I needed to hear it. Finally, I would like to extend my appreciation to Powertech Uranium Corporation for both granting me access to two wells I used to conduct slug tests and for making their geologic and water level data publicly available. This research was supported by the Department of Geological Sciences, University of Colorado at Boulder and by the U.S. Geological Survey Energy Resources Program. vii CONTENTS Abstract..........................................................................................................................................iii Acknowledgements......................................................................................................................... v Chapter 1: Introduction.................................................................................................................. 1 1.1 Background: Uranium Roll-Front Deposits......................................................................... 6 1.2 Background: In-Situ Recovery ............................................................................................ 8 1.3 Purpose and Scope .............................................................................................................. 10 Chapter 2: Regional Hydrogeology ............................................................................................. 13 2.1 Regional Geology ............................................................................................................... 13 2.2 Groundwater Flow .............................................................................................................. 17 2.3 Existing Water Level Data.................................................................................................. 20 Chapter 3: Hydraulic Conductivity of Major Sedimentary Formations ...................................... 25 3.1 Slug Tests............................................................................................................................ 25 3.1.1 Background.................................................................................................................. 25 3.1.2 Analysis........................................................................................................................ 30 3.1.3 Results.......................................................................................................................... 40 3.2 Aquifer Pumping Test......................................................................................................... 41 Chapter 4: Regional Groundwater Modeling............................................................................... 43 4.1 Model Design...................................................................................................................... 45 4.2 Recharge and Evapotranspiration ....................................................................................... 47 4.3 Hydrologic Boundaries ....................................................................................................... 48 viii 4.4 Hydraulic Conductivity......................................................................................................