DRAFT Groundwater Flow & Solute Transport Modeling Report Allen Fossil Plant Memphis, Tennessee July 12, 2019 Prepared for: Tennessee Valley Authority Chattanooga, Tennessee Prepared by: Stantec Consulting Services Inc. Revision Description Author Quality Check Independent Review DRAFT GROUNDWATER FLOW & SOLUTE TRANSPORT MODELING REPORT This document entitled DRAFT Groundwater Flow & Solute Transport Modeling Report was prepared by Stantec Consulting Services Inc. (“Stantec”) for the account of Tennessee Valley Authority (TVA). Prepared by Alexis Harkins, PG Joel RK Thompson, PG Hydrogeologist Senior Hydrogeologist Reviewed by John Griggs, PhD, TN PG No. 5966 John W. Jengo, TN PG No. Patrick Dunne Senior Principal Principal Senior Hydrogeologist Approved by Kim Kesler-Arnold, TN PG No. 5969 Vice President DRAFT GROUNDWATER FLOW & SOLUTE TRANSPORT MODELING REPORT Table of Contents ABBREVIATIONS ........................................................................................................................................ V 1.0 INTRODUCTION ........................................................................................................................... 1.1 1.1 SITE HISTORY ............................................................................................................................. 1.1 1.2 GROUNDWATER FLOW MODEL OBJECTIVES AND USAGE .................................................. 1.1 1.3 REPORT ORGANIZATION ........................................................................................................... 1.2 2.0 MODEL DEVELOPMENT APPROACH ....................................................................................... 2.1 2.1 HISTORICAL MODEL STUDIES .................................................................................................. 2.1 3.0 DATA COMPILATION .................................................................................................................. 3.1 4.0 HYDROGEOLOGIC CONCEPTUAL SITE MODEL .................................................................... 4.1 4.1 STUDY AREA DESCRIPTION ..................................................................................................... 4.1 4.2 REGIONAL STRATIGRAPHY AND GEOLOGY ........................................................................... 4.1 4.3 SURFACE WATER ....................................................................................................................... 4.2 4.4 STUDY AREA HYDROGEOLOGY ............................................................................................... 4.3 4.4.1 Fill ..................................................................................................................................... 4.3 4.4.2 Ash Disposal Areas .......................................................................................................... 4.3 4.4.2.1 Composition ...................................................................................................... 4.4 4.4.2.2 Extent and Structure ......................................................................................... 4.4 4.4.2.3 Hydraulic Properties ......................................................................................... 4.4 4.4.2.4 Water Quality .................................................................................................... 4.4 4.4.2.5 Sluiced Water ................................................................................................... 4.4 4.4.3 Alluvial Aquifer ................................................................................................................. 4.4 4.4.3.1 Composition ...................................................................................................... 4.4 4.4.3.2 Extent and Structure ......................................................................................... 4.5 4.4.3.3 Hydraulic Properties ......................................................................................... 4.5 4.4.3.4 Estimated Yields ............................................................................................... 4.6 4.4.3.5 Water Quality .................................................................................................... 4.6 4.4.3.6 Groundwater Flow ............................................................................................ 4.7 4.4.4 Terrace and Loess Deposits ............................................................................................ 4.7 4.4.4.1 Composition ...................................................................................................... 4.7 4.4.4.2 Extent and Structure ......................................................................................... 4.8 4.4.4.3 Hydraulic Properties ......................................................................................... 4.8 4.4.4.4 Estimated Yields ............................................................................................... 4.8 4.4.4.5 Groundwater Flow ............................................................................................ 4.8 4.4.5 Upper Claiborne Confining Unit ....................................................................................... 4.8 4.4.5.1 Composition ...................................................................................................... 4.8 4.4.5.2 Extent and Structure ......................................................................................... 4.9 4.4.5.3 Hydraulic Properties ......................................................................................... 4.9 4.4.5.4 Estimated Yields ............................................................................................... 4.9 4.4.5.5 Groundwater Flow .......................................................................................... 4.10 4.5 THREE DIMENSIONAL LITHOLOGIC MODEL ......................................................................... 4.10 3.0 COMPUTER CODE ...................................................................................................................... 3.1 5.1 MODFLOW ................................................................................................................................... 5.1 i DRAFT GROUNDWATER FLOW & SOLUTE TRANSPORT MODELING REPORT 5.2 MT3DMS ....................................................................................................................................... 5.1 6.0 MODEL CONSTRUCTION ........................................................................................................... 6.1 6.1 MODEL DISCRETIZATION .......................................................................................................... 6.1 6.1.1 Horizontal Discretization .................................................................................................. 6.1 6.1.2 Vertical Discretization ...................................................................................................... 6.1 6.2 TIME DISCRETIZATION ............................................................................................................... 6.2 6.3 PARAMETER DISTRIBUTION ..................................................................................................... 6.2 6.3.1 Hydraulic Conductivity ..................................................................................................... 6.2 6.3.2 Storage ............................................................................................................................. 6.3 6.3.3 Recharge .......................................................................................................................... 6.3 6.4 BOUNDARY CONDITIONS .......................................................................................................... 6.3 6.4.1 No Flow ............................................................................................................................ 6.3 6.4.2 Constant Head ................................................................................................................. 6.3 3.0 CALIBRATION ............................................................................................................................. 3.1 7.1 MODEL CALIBRATION APPROACH ........................................................................................... 7.1 7.2 SELECTION OF CALIBRATION DATA ........................................................................................ 7.1 7.3 CALIBRATION CRITERIA ............................................................................................................ 7.2 7.4 CALIBRATION RESULTS............................................................................................................. 7.3 7.5 CONVERGENCE CRITERIA ........................................................................................................ 7.4 8.0 SENSITIVITY ANALYSIS ............................................................................................................. 8.1 8.1 SENSITIVITY APPROACH ........................................................................................................... 8.1 8.2 DISCUSSION OF SENSITIVITY ................................................................................................... 8.1 8.2.1 Hydraulic Conductivity ..................................................................................................... 8.1 8.2.2 Storage ............................................................................................................................