S.S. Papadopulos & Associates, Inc. Environmental and Water Resource Consultants Development of a Transient Version of the Northeast Metro Lakes Groundwater-flow (NMLG) Model - with Simulation and Calibration from 1980 through 2016 Prepared For: Minnesota Department of Natural Resources October, 2017 Table of Contents Page List of Figures ................................................................................................................................. v List of Tables ................................................................................................................................. vi List of Appendices ........................................................................................................................ vii List of Acronyms ......................................................................................................................... viii Executive Summary ..................................................................................................................... 1-1 Introduction ............................................................................................................ 1-1 1.1 Background .......................................................................................... 1-1 1.2 Purpose ................................................................................................. 1-2 1.3 Objectives ............................................................................................ 1-2 1.4 Acknowledgements .............................................................................. 1-3 Study Area Hydrology and Hydrogeology ............................................................ 2-1 2.1 Ecology ................................................................................................ 2-1 2.2 Geomorphology, Surface Hydrology and Recharge Potential ............. 2-2 2.2.1 St. Croix Moraine ....................................................................... 2-2 2.2.2 Glacial Lake Hugo Plain............................................................. 2-2 2.2.3 Lake Elmo-Cottage Grove Outwash Plain ................................. 2-2 2.2.4 Denmark Dissected Plain............................................................ 2-2 2.2.5 St. Croix and Mississippi River Terraces ................................... 2-3 2.3 Stratigraphy and Groundwater Hydrology .......................................... 2-3 2.3.1 Quaternary Deposits ................................................................... 2-3 2.3.1 Bedrock Aquifers and Aquitards ................................................ 2-3 2.3.1.1 Decorah-Platteville-Glenwood Aquitard........................ 2-3 2.3.1.2 St. Peter Sandstone Minor Aquifer/Aquitard ................. 2-4 2.3.1.3 Prairie du Chien - Jordan Sandstone Aquifers ............... 2-4 2.3.1.4 St. Lawrence Formation – Tunnel City Aquifer and Aquitard .................................................................................................. 2-4 2.3.1.5 Wonewoc Sandstone Aquifer ......................................... 2-4 2.3.1.6 Eau Claire Formation Aquitard ...................................... 2-5 i 2.3.1.7 Mt. Simon Hinckley Formation Major Aquifer ............. 2-5 Steady-State NMLG Model Overview .................................................................. 3-1 3.1 Overview .............................................................................................. 3-1 3.2 Soil Water Budget (SWB) Model ........................................................ 3-1 3.2.1 Overview .................................................................................... 3-1 3.2.2 Input Grids .................................................................................. 3-2 3.2.3 Considerations for the Transition to a Transient Representation 3-2 3.2.3.1 Land Cover Representation ............................................ 3-2 3.2.3.2 Closed Depressions and Surface Run-off....................... 3-2 3.3 MODFLOW Groundwater Model ....................................................... 3-3 3.3.1 Overview .................................................................................... 3-3 3.3.2 Major MODFLOW Simulation Packages .................................. 3-4 3.3.2.1 Lake (LAK) Package ...................................................... 3-4 3.3.2.2 River (RIV) Package ...................................................... 3-4 3.3.2.3 Groundwater Pumping (WEL and MNW Packages) ..... 3-5 3.3.2.4 Unsaturated Zone Flow (UZF) Package......................... 3-5 3.3.3 Aquifer Properties....................................................................... 3-5 3.3.4 Considerations for the Transition to a Transient Representation 3-6 3.3.4.1 Lake Evaporation ........................................................... 3-6 3.3.4.2 Other Head-Dependent Boundaries ............................... 3-6 3.3.4.3 Unsaturated Zone Flow (UZF) ....................................... 3-7 Transient Model Development .............................................................................. 4-1 4.1 Simulation Period ................................................................................ 4-1 4.2 Extension of the SWB Model to Transient Conditions ....................... 4-1 4.2.1 Overview .................................................................................... 4-1 4.2.2 Computed Recharge ................................................................... 4-2 4.3 Extension of the MODFLOW Model to Transient Conditions ........... 4-2 4.3.1 Overview .................................................................................... 4-2 4.3.2 Considerations for Execution Time ............................................ 4-3 4.3.2.1 Time Discretization ........................................................ 4-3 4.3.2.2 Representation of Unsaturated Zone Flow ..................... 4-4 ii 4.3.3 Initial Conditions ........................................................................ 4-4 4.3.4 Peripheral Boundary Conditions ................................................ 4-4 4.3.5 Transient Groundwater Pumping ................................................ 4-4 4.3.6 Lakes Represented using the MODFLOW LAK Package ......... 4-6 4.3.7 Other Surface Water Bodies Represented using the MODFLOW RIV Package .................................................................................................... 4-7 Calibration Objectives and Data ............................................................................ 5-1 5.1 Overview .............................................................................................. 5-1 5.2 Quantitative Targets ............................................................................. 5-1 5.3 Qualitative Targets ............................................................................... 5-2 Calibration Procedure ............................................................................................ 6-1 6.1 Calibration of the SWB Model ............................................................ 6-1 6.1.1 Land Use ..................................................................................... 6-1 6.1.2 Curve Numbers ........................................................................... 6-1 6.2 Representing Stormwater Management Practices vis Interception ..... 6-1 6.2.1 Maximum Soil Infiltration .......................................................... 6-2 6.3 Calibration of the MODFLOW Model ................................................ 6-2 6.3.1 Peripheral Boundary Conditions ................................................ 6-2 6.3.2 Aquifer Parameters ..................................................................... 6-3 6.3.3 Surface Water Features not Represented using the LAK Package ......................................................................................................................... 6-3 6.3.4 Lakebed Conductance................................................................. 6-4 Calibration Results ................................................................................................. 7-1 7.1 Overview .............................................................................................. 7-1 7.2 Summary of Results ............................................................................. 7-1 Illustrative Predictive Scenarios ............................................................................ 8-1 8.1 Introduction .......................................................................................... 8-1 8.2 Simulated Scenarios ............................................................................. 8-1 8.2.1 Scenario 1 – Impact of Pumped Wells Tied Under a Single Permit Number ............................................................................................................ 8-1 8.2.2 Scenario 2 – Simultaneous Impact of Pumped Wells ................. 8-2 iii 8.2.3 Scenario 3 – Simultaneous Impact of Residential Irrigation Pumping ........................................................................................................... 8-2 8.3 Results .................................................................................................. 8-3 8.4 Conclusions .......................................................................................... 8-5 Assumptions and Limitations ................................................................................ 9-1 9.1 Overview .............................................................................................