APPENDIX A COMPREHENSIVE GEOCHEMICAL REPORT Lundin Minerals Engineering Report HTDF Geochemistry, Eagle Mine Civil Engineering H/353799 Comprehensive Report on the Chemistry of the Humboldt Tailings Disposal Facility (HTDF), Champion, Michigan Comprehensive Report on the Chemistry of the Humboldt Tailings Disposal Facility (HTDF), Champion, Michigan March 9, 2018 H349392-00000-22A-066-0006 2018-03-09 0 Final Devin Castendyk Siba Patnayak Chris Biederman As Required DATE REV. STATUS PREPARED BY CHECKED BY APPROVED BY APPROVED BY Functional Choose Discipline Lead Manager Approver H349392-00000-22A-066-0006, Rev. 0, 1 Ver: 04.03 © Hatch 2018 All rights reserved, including all rights relating to the use of this document or its contents. Lundin Minerals Engineering Report HTDF Geochemistry, Eagle Mine Civil Engineering H/353799 Comprehensive Report on the Chemistry of the Humboldt Tailings Disposal Facility (HTDF), Champion, Michigan Table of Contents Executive Summary .................................................................................................................................... 1 1. Introduction ........................................................................................................................................... 3 1.1 Overview ....................................................................................................................................... 3 1.2 Purpose ......................................................................................................................................... 4 1.3 Organization .................................................................................................................................. 5 2. Background ........................................................................................................................................... 6 2.1 History and Pre-Operations Conditions ........................................................................................ 6 2.2 Pre-operations Limnology and Terminology ................................................................................. 7 2.3 Tailings Disposal at the HTDF ...................................................................................................... 7 2.4 Challenges Associated with Total Dissolved Solids ..................................................................... 9 2.5 Sub-aqueous Tailings Disposal in North America ...................................................................... 10 3. Studies Submitted for Original Part 632 Permit .............................................................................. 11 3.1 Monitoring Data ........................................................................................................................... 11 3.2 Pre-operations Monitoring Results ............................................................................................. 13 3.3 Tailings Chemistry ...................................................................................................................... 14 3.4 Potential for Complete Mixing in the HTDF (L0) ......................................................................... 14 3.5 Depth of Oxidation of Sulfidic Tailings in a Fully Mixed HTDF (G0a) ......................................... 16 3.6 Water Quality in a Fully Mixed HTDF with Sulfide Oxidation (G0b) ........................................... 18 4. 97-Week Column Leachate Tests on Eagle Tailings ....................................................................... 21 4.1 Description .................................................................................................................................. 21 4.2 Objectives ................................................................................................................................... 21 4.3 Methods ...................................................................................................................................... 21 4.4 Results ........................................................................................................................................ 21 4.5 Integration into Predictive Modeling ............................................................................................ 23 5. HTDF Monitoring Program ................................................................................................................. 24 5.1 Ongoing Monitoring of the HTDF ................................................................................................ 24 5.2 Additional monitoring programs .................................................................................................. 25 5.3 Major Findings ............................................................................................................................ 27 5.4 Improvements to the Conceptual Model of the HTDF ................................................................ 30 H349392-00000-22A-066-0006, Rev. 0, Page i Ver: 04.03 © Hatch 2018 All rights reserved, including all rights relating to the use of this document or its contents. Lundin Minerals Engineering Report HTDF Geochemistry, Eagle Mine Civil Engineering H/353799 Comprehensive Report on the Chemistry of the Humboldt Tailings Disposal Facility (HTDF), Champion, Michigan 6. Predictive model of HTDF Limnology .............................................................................................. 33 6.1 Purpose and Overview ............................................................................................................... 33 6.2 Effect of Tailing Deposition on Lake Bathymetry ........................................................................ 33 6.3 Initial Conditions and Inflows ...................................................................................................... 36 6.4 Timing and Meteorological Inputs ............................................................................................... 36 6.5 Model limitations ......................................................................................................................... 37 6.6 Results and Discussion .............................................................................................................. 38 6.7 Sensitivity Analysis on Initial Chemocline Elevation ................................................................... 41 7. Predictive model of HTDF Water Chemistry .................................................................................... 45 7.1 Purpose and Overview ............................................................................................................... 45 7.2 Fundamental Assumptions ......................................................................................................... 45 7.3 Model Strategy Overview ............................................................................................................ 46 7.4 HTDF Inputs ................................................................................................................................ 47 7.5 HTDF Outputs ............................................................................................................................. 50 7.6 Model Results ............................................................................................................................. 51 7.7 Water Treatment Duration .......................................................................................................... 55 8. Model Sensitivity ................................................................................................................................ 56 8.1 Methods ...................................................................................................................................... 56 8.2 Results ........................................................................................................................................ 57 9. Conclusions ........................................................................................................................................ 58 10. References .......................................................................................................................................... 61 H349392-00000-22A-066-0006, Rev. 0, Page ii Ver: 04.03 © Hatch 2018 All rights reserved, including all rights relating to the use of this document or its contents. Lundin Minerals Engineering Report HTDF Geochemistry, Eagle Mine Civil Engineering H/353799 Comprehensive Report on the Chemistry of the Humboldt Tailings Disposal Facility (HTDF), Champion, Michigan List of Tables Table 2-1: Examples of Water Covers applied over tailings in North America ........................................... 10 Table 3-1: Monitoring conducted in 1984, 2008 and 2010 ......................................................................... 12 Table 3-2: Common parameters measured in HTDF water samples ......................................................... 13 Table 5-1: Recent Monitoring in the HTDF ................................................................................................. 24 Table 7-1: List of Dissolved Constituents Modeled in GoldSim .................................................................. 47 List of Figures Figure 1-1: Location map for the HTDF ........................................................................................................ 4 Figure 2-1: Present configuration of inputs and outputs