Deep South Expansion Project Final Supplemental Environmental
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BLM MOUNTLEWIS FIELD OFFICE Final Deep South Expansion Project Supplemental Environmental Report – Water Resources and Geochemistry Prepared in Support of: File Number: NVN-067575 (16-1A) DOI-BLM-NV-B010-2016-0052 EIS Bureau of Land Management Battle Mountain District Office Mount Lewis Field Office 50 Bastian Road Battle Mountain, NV 89820 2019 COOPERATING AGENCIES: U.S. Environmental Protection Agency U.S. Fish and Wildlife Service Nevada Department of Wildlife Lander County and Eureka County BLM Mission Statement The Bureau of Land Management’s mission is to sustain the health, diversity, and productivity of public lands for the use and enjoyment of present and future generations. Prepared in Support of: DOI-BLM-NV-B010-2016-0052 EIS Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry i Table of Contents 1.0 Introduction................................................................................................................... 1-1 2.0 Alternatives Including the Proposed Action .............................................................. 2-1 2.1 Introduction ........................................................................................................... 2-1 2.2 Existing Facilities .................................................................................................. 2-1 2.3 Proposed Action ................................................................................................... 2-1 2.3.1 Project Overview ..................................................................................... 2-1 2.3.2 Dewatering, Water Management, and Hydrologic Monitoring............... 2-15 2.3.3 Applicant-committed Environmental Protection Measures .................... 2-16 2.3.4 Reclamation .......................................................................................... 2-18 2.4 Alternatives to the Proposed Action ................................................................... 2-20 2.4.1 Gold Acres Pit Partial Backfill Alternative .............................................. 2-20 2.4.2 No Action Alternative ............................................................................. 2-20 2.5 Past, Present, and Reasonably Foreseeable Future Actions ............................. 2-25 3.0 Water Resources and Geochemistry .......................................................................... 3-1 3.1 Affected Environment ........................................................................................... 3-1 3.1.1 Hydrologic Setting ................................................................................... 3-1 3.1.2 Surface Water Resources ....................................................................... 3-5 3.1.3 Groundwater Resources ....................................................................... 3-23 3.1.4 Waste Rock Characterization ................................................................ 3-41 3.1.5 Water Rights ......................................................................................... 3-44 3.2 Environmental Consequences ........................................................................... 3-48 3.2.1 Evaluation Methodology ........................................................................ 3-49 3.2.2 Proposed Action .................................................................................... 3-59 3.2.3 Gold Acres Pit Partial Backfill Alternative .............................................. 3-87 3.2.4 No Action Alternative ............................................................................. 3-87 3.3 Cumulative Impacts ............................................................................................ 3-93 3.3.1 Proposed Action .................................................................................... 3-93 3.3.2 Gold Acres Pit Partial Backfill Alternative ............................................ 3-101 3.4 Monitoring and Mitigation Measures................................................................. 3-101 3.5 Residual Adverse Effects ................................................................................. 3-103 4.0 References .................................................................................................................... 4-1 2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry ii List of Tables Table 2-1 Currently Authorized Disturbance and Proposed New Disturbance under the Proposed Action .......................................................................................... 2-15 Table 2-2 Dewatering and Disposal Rates for the Proposed Action ................................. 2-16 Table 2-3 Currently Authorized Disturbance and Proposed New Disturbance under the Gold Acres Pit Partial Backfill Alternative .................................................... 2-23 Table 2-4 Surface Disturbance Associated with Past and Present Actions and RFFAs ............................................................................................................... 2-25 Table 3-1 Hydrographic Areas ............................................................................................ 3-1 Table 3-2 Mean Annual Precipitation at Selected Regional Sites ....................................... 3-2 Table 3-3 Named Streams within the Hydrologic Study Area ............................................. 3-6 Table 3-4 Summary of Springs and Seeps Identified within the Project Region ............... 3-12 Table 3-5 General Nevada Water Quality Standards ........................................................ 3-19 Table 3-6 Summary of Hydrogeologic Units in the Study Area ......................................... 3-23 Table 3-7 Estimated Annual Groundwater Budget for the HSA (2015) ............................. 3-35 Table 3-8 Summary of Background Groundwater Quality in the Vicinity of the Pipeline Pit Complex, Cortez Pit, Cortez Hills Pit, and Cortez Hills Underground Mine Operations .......................................................................... 3-40 Table 3-9 Summary of Acid-base Accounting Results ...................................................... 3-43 Table 3-10 Summary of Humidity Cell Tests ....................................................................... 3-43 Table 3-11 Private Active Water Rights .............................................................................. 3-45 Table 3-12 Summary of Historic and Model Simulated Future Dewatering Requirements .................................................................................................... 3-51 Table 3-13 Summary of Historic and Estimated Future infiltration Requirements ............... 3-53 Table 3-14 Potential Impacts to Perennial Water Resources Located Within the Projected Groundwater Drawdown Area .......................................................... 3-58 Table 3-15 Summary of Predicted Pit Lakes at 500 Years Post-mining under the Proposed Action ................................................................................................ 3-67 Table 3-16 Perennial Stream Miles Located within the Projected Drawdown Areas .......... 3-69 Table 3-17 Springs Located within the Projected Drawdown Areas ................................... 3-70 Table 3-18 Private Water Rights Located Within the Predicted Drawdown Area ............... 3-75 Table 3-19 Simulated Groundwater Budget Summary for the HSA Under the Proposed Action ................................................................................................ 3-76 Table 3-20 Model-predicted Pit Backfill Pore Water Chemistry at Approximately 100 Years ................................................................................................................. 3-80 Table 3-21 Summary of Predicted Pit Lakes at 200 Years Post-mining Under the No Action Alternative .............................................................................................. 3-90 Table 3-22 Simulated Groundwater Budget Summary for the HSA Under the No Action Alternative .............................................................................................. 3-92 Table 3-23 Simulated Groundwater Budget Summary for the HSA Under Cumulative .... 3-100 2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry iii List of Figures Figure 1-1 Project Vicinity .................................................................................................... 1-2 Figure 2-1 Existing Mine Facilities ........................................................................................ 2-3 Figure 2-2 Proposed Action .................................................................................................. 2-4 Figure 2-3 Proposed Action Mine Complexes ...................................................................... 2-5 Figure 2-4 Pipeline Pit Complex Backfill Scenario 1 ............................................................ 2-6 Figure 2-5 Pipeline Pit Complex Backfill Scenario 2 ............................................................ 2-7 Figure 2-6 Pipeline Pit Complex Backfill Scenario 3 ............................................................ 2-8 Figure 2-7 Gold Acres Pit and Satellite Pits ....................................................................... 2-11 Figure 2-8 Cortez Hills Pit Backfill ...................................................................................... 2-12 Figure 2-9 Cortez Pit and Ada 52 Pit Backfill ....................................................................