BLM

MOUNT LEWIS FIELD OFFICE FIELD LEWIS MOUNT 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

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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

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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 ...... 2-13 Figure 2-10 Gold Acres Pit Partial Backfill Alternative – Mine Complexes ...... 2-21 Figure 2-11 Gold Acres Pit Partial Backfill ...... 2-22 Figure 2-12 Past and Present Actions and RFFAs ...... 2-29 Figure 3-1 Regional Hydrologic Features ...... 3-3 Figure 3-2 Geothermal Resources ...... 3-10 Figure 3-3 Seeps and Springs in the HSA ...... 3-13 Figure 3-4 FEMA Flood Hazard Areas ...... 3-17 Figure 3-5 Regional Geology ...... 3-27 Figure 3-6 Regional Geologic Map Units ...... 3-29 Figure 3-7 Regional Groundwater Elevations Prior to Pipeline Mine Dewatering (Pre-1996) ...... 3-33 Figure 3-8 Simulated Change in Groundwater Levels in the Central Part of the HAS, April 1996 to December 2015 ...... 3-34 Figure 3-9 Groundwater Sampling Locations ...... 3-37 Figure 3-10 Groundwater Sampling Wells Completed Below the 3,800-foot Elevation Level ...... 3-39 Figure 3-11 Private Active Water Rights ...... 3-47 Figure 3-12 Historic and Estimated Future Dewatering Requirements ...... 3-55 Figure 3-13 Predicted Change in Groundwater Levels – Proposed Action (End of Mining) ...... 3-60 Figure 3-14 Surface Water Resources Within Maximum Extent of 10-foot Drawdown Contour – Proposed Action versus No Action Alternative ...... 3-62 Figure 3-15 Private Water Rights Within Maximum Extent of 10-foot Drawdown Contour – Proposed Action versus No Action Alternative ...... 3-63 Figure 3-16 Predicted Change in Groundwater Levels - Proposed Action (500 Years Post-mining) ...... 3-64

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Figure 3-17 Rate of Pit Lake Development Under the Proposed Action ...... 3-66 Figure 3-18 Predicted Change in Groundwater Levels – No Action Alternative (End of Dewatering) ...... 3-89 Figure 3-19 Predicted Change in Groundwater Levels – Cumulative (End of Mining) ...... 3-94 Figure 3-20 Surface Water Resources Within the Maximum Extent of the 10-foot Groundwater Drawdown Contour - Proposed Action and Cumulative ...... 3-96 Figure 3-21 Private Water Rights Within the Maximum Extent of the 10-foot Groundwater Drawdown Contour -Proposed Action and Cumulative ...... 3-97 Figure 3-22 Predicted Change in Groundwater Levels – Cumulative (500 Years Post- mining) ...... 3-98

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Acronyms and Abbreviations

°C degrees Celsius °F degrees Fahrenheit µg/m3 micrograms per cubic meter µmhos/cm micromhos per centimeter ABA acid-base accounting AFY acre-feet per year AGP acid-generating potential amsl above mean sea level ANP acid-neutralization potential BCI Barrick Cortez Inc. BEA Bank Enabling Agreement BLM Bureau of Land Management BMRR Bureau of Mining Regulation and Reclamation BWQP Bureau of Water Quality Planning

CaCO3/t calcium carbonate per ton of rock CESA cumulative effects study area CFR Code of Federal Regulations cfs cubic feet per second CGM Cortez Gold Mines CR County Road CWA Clean Water Act EIS environmental impact statement FEMA Federal Emergency Management Agency Geomega Geomega Inc. gpm gallons per minute HA hydrographic area HC/CUEP Horse Canyon/Cortez Unified Exploration Project HCT humidity cell test HDR HDR Engineering, Inc. HGG HydroGeo Group HSA hydrologic study area IMP Integrated Monitoring Plan Itasca Itasca Denver, Inc.

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JBR JBR Environmental Consultants, Inc. kg kilogram MCL maximum concentration level mg/L milligrams per liter NAC Nevada Administrative Code NDEP Nevada Division of Environmental Protection NDWR Nevada Division of Water Resources NEPA National Environmental Policy Act NNP net neutralization potential NPR neutralization potential ratio NRS Nevada Revised Statutes RFFA reasonably foreseeable future action RIB rapid infiltration basin ROW right-of-way SEIS supplemental environmental impact statement SLERA Screening-level Ecological Risk Assessment SRK SRK Consulting, (U.S.) Inc. Stantec Stantec Consulting Services, Inc. SWPPP Stormwater Pollution Prevention Plan TDS total dissolved solids tpd tons per day tpy tons per year TU tritium unit USACE U.S. Army Corps of Engineers USEPA U.S. Environmental Protection Agency USGS U.S. Geological Survey WRCC Western Regional Climate Center WRMP Waste Rock Management Plan

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1.0 Introduction

Barrick Cortez Inc. (BCI), as manager of the Cortez Joint Venture, proposes modifications to BCI’s existing gold mining and processing operations within the Cortez Gold Mines (CGM) Operations Area, which is located approximately 24 miles south of Beowawe in Lander and Eureka counties, Nevada (Figure 1-1). On March 30, 2016, BCI submitted the Barrick Cortez Inc. (NVN-067575 (16-1A)) Deep South Expansion Project Amendment to Plan of Operations and Reclamation Permit Application #0093, which describes the proposed modifications, to the Bureau of Land Management (BLM) Battle Mountain District, Mount Lewis Field Office in compliance with 43 Code of Federal Regulations (CFR) Subpart 3809 and 3715. A revised plan amendment was submitted October 6, 2016 (BCI 2016).

The proposed modifications would result in new surface disturbance on private land owned by BCI and public lands administered by the BLM. The proposed mining activities on public and private lands are subject to review and approval by the BLM pursuant to the Federal Land Policy and Management Act of 1976 as amended, and the BLM’s surface management regulations (43 CFR Subpart 3809). The BLM’s review and approval of a mine plan of operations under the surface management regulations constitute a federal action that is subject to the National Environmental Policy Act of 1969 (NEPA). The BLM has determined that the project constitutes a major federal action and has determined that an environmental impact statement (EIS) must be prepared to fulfill NEPA requirements. The BLM is serving as the lead agency for preparing the Deep South Expansion Project EIS in compliance with all applicable regulations and guidance. The U.S. Environmental Protection Agency (USEPA), U.S. Fish and Wildlife Service, Nevada Department of Wildlife, and Lander and Eureka counties are serving as cooperating agencies for preparation and review of the EIS.

The EIS development is supported by supplemental environmental reports. This supplemental environmental report describes the potentially affected environment and the environmental consequences (direct, indirect, and cumulative) of implementing the Proposed Action or the alternatives, identifies monitoring and mitigation measures, as needed, and identifies the residual adverse effects for water resources and geochemistry.

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2.0 Alternatives Including the Proposed Action

2.1 Introduction This chapter summarizes the elements of the Proposed Action and other alternatives (including the No Action Alternative), and the past and present actions, as well as reasonably foreseeable future actions (RFFAs), considered in the cumulative impact analysis.

2.2 Existing Facilities Existing BCI mining and processing facilities are located in four mine complexes (Pipeline, Gold Acres, Cortez, and Cortez Hills) within the current CGM Operations Area boundary (Figure 2-1). The majority of the existing facilities would be used in support of the Proposed Action. Changes to existing facilities are summarized below.

2.3 Proposed Action 2.3.1 Project Overview BCI’s proposed Deep South Expansion Project (Proposed Action) would include modifications to existing facilities in the four existing mine complexes, construction of new facilities, modifications to overall operations, and expansion of the CGM Operations Area boundary (Figures 2-2 and 2-3). The proposed modifications and expansions are summarized below.

Pipeline Complex:  Deepen the existing Crossroads Pit (southeast portion of the Pipeline Pit Complex) by 200 feet and layback portions of the current Pipeline, Crossroads, and Gap pit walls.  Reconfigure the currently authorized backfill in the Pipeline and Gap pit portions of the Pipeline Pit Complex per one of three proposed backfill scenarios (Figures 2-4, 2-5, and 2-6), depending on the economic conditions at the time of mining.  Modify the existing Pipeline/South Pipeline Waste Rock Facility.  Expand the existing oxide ore stockpile.

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Gold Acres Complex:  Expand and deepen the existing Gold Acres Pit and develop three satellite pits (Alta, Bellweather, and Pasture) (Figure 2-7).  Expand the existing Gold Acres South Waste Rock Facility and combine the existing Gold Acres North and Gold Acres East waste rock facilities into one facility (Gold Acres North Waste Rock Facility).  Construct a new Class III-waivered landfill and close the existing landfill.  Construct a new refractory ore stockpile and a new growth media stockpile.  Construct or install additional ancillary support facilities (e.g., mine operations office, septic system, fuel skid, water pipeline, power infrastructure).

Cortez Hills Complex:  Expand existing underground operations by increasing the depth of mining by 1,300 feet and construct additional surface support facilities for underground operations.  Extend the Pediment portion (southern portion) of the existing Cortez Hills Pit to create the Pediment East and Pediment South extensions.  Potentially backfill the Cortez Hills Pit with approximately 63 million tons of waste rock (Figure 2-8).  Modify the existing Canyon Waste Rock Facility.  Construct a new water treatment plant and associated facilities.  Construct a new refractory ore/oxide ore stockpile and a new growth media stockpile.

Cortez Complex:  Expand and deepen the existing Cortez Pit by approximately 200 feet.  Backfill the northern portion of the Cortez Pit and the existing Ada 52 Pit with approximately 3 million tons of waste rock (Figure 2-9).  Expand the existing Cortez Waste Rock Facility and re-route the power infrastructure.  Construct or install additional ancillary support facilities (e.g., mine operations office, septic system, fuel skids, water pipeline, power infrastructure).

Water Management:  Continue dewatering to accommodate mining to lower elevations in the Pipeline and Cortez Hills complexes, with the maximum dewatering rate remaining below the currently authorized rate of 36,100 gallons per minute (gpm).  Construct additional rapid infiltration basins (RIBs) and associated infrastructure in Grass Valley, Pine Valley, and on private land outside of the CGM Operations Area in Crescent Valley.  Convert the two existing Grass Valley production wells to injection wells, and construct up to four additional injection wells in Grass Valley, to re-inject treated dewatering water into the aquifer.

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 Construct the proposed Rocky Pass Reservoir and associated infrastructure, if needed, and realign a segment of County Road (CR) 225 to provide public access around the reservoir.  Construct stormwater controls, as necessary.

General Site-wide Changes:  Expand the CGM Operations Area boundary from the current 58,093 acres to 62,372 acres to include the proposed Pediment East extension of the Cortez Hills Pit, the Pine Valley RIBs and associated infrastructure, and the Rocky Pass Reservoir and associated infrastructure.  Increase the off-site refractory ore shipment to the existing Goldstrike Mill for processing from the currently authorized rate of 1.2 million tons per year (tpy) to 2.5 million tpy. The additional ore would extend processing at the Goldstrike Mill by approximately 3 years.  Increase the backhaul of oxide ore from the Arturo Mine through the Goldstrike Mine to the Pipeline Complex for processing at the existing Pipeline Mill or heap leach facility from the currently authorized rate of 600,000 tpy to 2.5 million tpy. No associated change in the current mill throughput rate, increase in the existing Pipeline Tailings Impoundment, or expansion of the existing Pipeline South Area Heap Leach Facility would be required to accommodate the processing of Arturo Mine oxide ore.  Modify the site-wide surface mining rate from the currently authorized 580,000 tons per day (tpd) to a maximum of 600,000 tpd.

In addition to incorporation of the modifications outlined above, BCI proposes to modify the plan boundaries for BCI’s two existing exploration projects (Horse Canyon/Cortez Unified Exploration Project [HC/CUEP] [NVN-66621] and West Pine Valley Exploration Project [NVN-077213]) to eliminate overlap with portions of the expanded CGM Operations Area boundary.

The Proposed Action would result in a total proposed new surface disturbance of 4,380 acres, including 3,846 acres within the CGM Operations Area and 534 acres outside of the CGM Operations Area on private land owned by BCI. Approximately 2,779 acres of the total proposed new disturbance would be on BLM-administered public lands. The currently authorized and proposed new surface disturbance, as well as reallocation of use of currently authorized disturbance, at the site is summarized in Table 2-1.

No increase in BCI’s current work force (1,250 workers) would be required for the Proposed Action. It is anticipated that a contractor work force of approximately 350 workers also would be on site throughout the life of the project for construction of facilities and for other site preparation activities. Approximately 155 workers would be required for the final 3 years of ongoing ore processing, closure, and reclamation. The total BCI operations work force payroll/benefits is estimated to be approximately $628.8 million. The average annual contractor costs would be approximately $13.5 million.

If approved, the Deep South Expansion Project would extend the life of the mine by approximately 12 years, followed by approximately 3 years for site closure and final reclamation.

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Table 2-1 Currently Authorized Disturbance and Proposed New Disturbance under the Proposed Action

Proposed Action Proposed No Action Reallocation Alternative of Use of Total Proposed Currently Proposed Authorized Total Authorized New Surface Disturbance Disturbance Disturbance Disturbance by Facility by Facility (sum total by Facility Mine Complex Facility (acres) (acres) acres) (acres) Open Pits 2,752 3,411 474 185 Underground Operations 01 01 01 01 Waste Rock Facilities 5,393 5,685 -105 397 Heap Leach Facilities and Process Areas 1,933 2,049 116 0 Tailings Impoundments 1,416 1,208 -208 0 Ancillary Support Facilities 4,111 4,696 -336 921 Water Management Facilities 704 3,057 10 2,343 Exploration 391 391 0 0 Total Acres within CGM Operations Area2 16,700 20,498 -483 3,846 Proposed New Disturbance Outside CGM Operations Area4 534 Total Proposed New Disturbance 4,380 1 Disturbance associated with surface infrastructure for underground mining is accounted for in other currently authorized or proposed disturbance footprints. 2 Differences are due to rounding. 3 Reflects reallocation of undisturbed land that previously was authorized for disturbance. 4 Reflects surface disturbance associated with proposed RIBs and associated infrastructure northeast of the CGM Operations Area in Crescent Valley.

2.3.2 Dewatering, Water Management, and Hydrologic Monitoring Dewatering currently is and would continue at the Pipeline and Cortez Hills complexes. No additional dewatering would be required to facilitate mining of the Cortez Pit. No dewatering would be required for the proposed expansion of the Gold Acres Pit or development of the Gold Acres satellite pits. The dewatering rate for the Deep South Expansion Project would remain below the currently authorized maximum rate of 36,100 gpm.

Projected dewatering, consumption, and disposal rates and projected conveyance rates to the proposed Rocky Pass Reservoir are presented in Table 2-2. Prior to disposal or temporary storage in the reservoir, the dewatering water would be treated in the existing Pipeline water treatment facility or proposed Cortez Hills water treatment facility to reduce naturally occurring arsenic concentrations to meet Nevada Profile I reference values (Nevada Administrative Code [NAC] 445A).

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Table 2-2 Dewatering and Disposal Rates for the Proposed Action

Disposal Rates Rate to Rate to Mine/Milling Rate to Dean Grass Valley Rocky Dewatering Consumption Rate to Ranch for Injection Pass 1 2 3 Year of Rate Rate RIBs Irrigation Wells Reservoir Operation (gpm – annualized)

1 31,617 1,909 25,645 4,063 1,945 0

2 32,708 1,250 24,769 4,063 1,945 2,627

3 32,266 1,250 24,326 4,063 1,945 2,627

4 29,550 1,250 21,611 4,063 1,945 2,627

5 27,149 1,250 19,209 4,063 1,945 2,627

6 8,093 1,250 2,006 2,210 1,945 2,627

7 9,023 800 4,765 3,459 1,945 0

8 8,850 800 4,736 3,313 1,945 0

9 8,906 800 4,689 3,417 1,945 0

10 8,999 500 4,646 3,852 1,945 0 11 9,075 200 4,813 4,063 1,945 0 1 Includes dewatering for open pit and underground operations. 2 Water from the Pipeline and Cortez Hills dewatering systems would continue to be piped to the Dean Ranch as currently authorized (annualized average of up to 4,085 gpm). Under the Proposed Action, a portion of the water conveyed to the Dean Ranch for irrigation use may come from the Rocky Pass Reservoir in years 2 through 6. 3 Water sent to the Grass Valley injection wells (if used) would offset water sent to the Grass Valley RIBs. Source: BCI 2017a.

Hydrologic monitoring and reporting currently is conducted in accordance with existing permit requirements to measure the effects of the dewatering and discharge program on groundwater quantity and quality both locally in the CGM Operations Area and in southern Crescent Valley. The Integrated Monitoring Plan (IMP) (Itasca Denver, Inc. [Itasca] 2016) describes the monitoring requirements and discusses the annual recalibration of the groundwater model to incorporate the latest monitoring data. The existing monitoring program would be expanded in accordance with applicable federal and state permit requirements to measure the effects of the proposed Deep South Expansion Project pit dewatering and discharge program on groundwater quantity and quality.

2.3.3 Applicant-committed Environmental Protection Measures BCI’s committed environmental protection measures for operations in the CGM Operations Area are identified in the Barrick Cortez Inc. (NVN-067575 (16-1A)) Deep South Expansion Project Amendment to Plan of Operations and Reclamation Permit Application #0093 (BCI 2016b). These measures currently are, and would continue to be, implemented as standard operating procedures to mitigate potential impacts to environmental and human resources. The measures relative to water resources are presented below.

2.3.3.1 Water Resources  All heap leach, mill, and tailings facilities are designed and operated as zero discharge facilities, with a composite liner system in accordance with the BLM and Nevada

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Division of Environmental Protection (NDEP) criteria and the International Cyanide Code to minimize impacts to water resources.  Groundwater monitoring would be conducted in accordance with the IMP (Itasca 2016) to ensure compliance with Water Pollution Control Permit criteria and provide for early identification of potential impacts. If any monitoring wells go dry due to dewatering activities, the monitoring program would be reevaluated in coordination with the NDEP. The IMP would be reviewed and updated annually to include additional surface water and groundwater resources monitoring locations in the project vicinity.  All mineral exploration and development drill holes, monitoring and observation wells, and production dewatering wells would be properly abandoned following completion of their functions to prevent migration of potential contaminants to groundwater.  To minimize potential mine-related effects to perennial surface waters, the site-specific contingency mitigation measures developed for identified perennial waters within the currently authorized operations’ modeled groundwater drawdown area would be implemented if monitoring data indicate that an observed reduction in flow is attributable to mine-induced groundwater drawdown. If needed, one or more of the identified mitigation methods would be implemented per the site-specific mitigation plans presented in Table 3.2-1 of the Cortez Hills Expansion Project Final Supplemental EIS (SEIS) (BLM 2011a). Site-specific contingency mitigation measures identified in BCI’s proposed Contingency Mitigation Plans for Surface Waters (BCI and Stantec Consulting Services, Inc. [Stantec] 2018) would be implemented to minimize potential mine-related effects to perennial waters within, and within 1-mile of, the modeled maximum extent of the Proposed Action groundwater drawdown area not covered by the 2011 mitigation plan. In addition, BCI would continue to implement the existing and proposed contingency mitigation measures during the post- closure period and would include funding for this effort in the Long-term Contingency Fund for the project. Upon issuance of the Record of Decision for the Deep South Expansion Project by the BLM, BCI will begin installation of mitigation wells in the Horse Creek area within 1 year of receiving all necessary permits and authorizations to maintain baseflows as described in the proposed contingency mitigation plan. Mitigation of surface water resources would be implemented under the requirements of NDWR.  Waste rock characterization would continue to be conducted in accordance with the site's BLM waste rock characterization requirements and NDEP-Bureau of Mining Regulation and Reclamation (BMRR) Water Pollution Control Permit requirements.  Selective placement of waste rock, as needed, and routine monitoring of the waste rock disposal facilities during operations would be implemented during operations as identified in the Waste Rock Management Plan (Geomega Inc. [Geomega] 2016) to reduce the potential for acid rock drainage that does not meet applicable NDEP water quality standards.  To limit erosion and reduce sediment transport from project disturbance areas, erosion control measures as outlined in the site’s Stormwater Pollution Prevention Plan (SWPPP) (BCI 2016a) and Reclamation Plan would be installed, as needed, and maintained. Stormwater diversions would be installed around project facilities, as needed, to divert stormwater runoff around disturbance areas. Facilities would be monitored following spring snowmelt and intense rain events to ensure that drainage and sediment control measures are effective and operating properly. In addition, implementation of concurrent reclamation would further reduce erosion potential. The SWPPP would be amended as necessary to include the proposed project facilities. (The project is covered under the NDEP’s general stormwater permit [NVR300000].)

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2.3.4 Reclamation The proposed Reclamation Plan for the Deep South Expansion Project is summarized below.

2.3.4.1 Reclamation Overview With the exception of pit highwalls, ramps, and floors; post-reclamation stormwater control features; rerouted county roads (e.g., CR 225); and roads selected by BLM for post-mining use, all of the surface disturbance associated with the mine components would be reclaimed. Concurrent reclamation would be conducted to the extent practical to accelerate revegetation of disturbance areas. All sediment and erosion control measures and revegetated areas would be inspected periodically to ensure long-term erosion control and successful reclamation.

2.3.4.2 Growth Media Growth media replacement depths for the existing heap leach pads and tailings impoundments would be at least 18 inches and 12 inches, respectively. All other mine facilities (with the exception of the open pits) would be covered to a depth of at least 6 inches. Approximately 1.2 million cubic yards of growth media would be required to reclaim Proposed Action facilities. Approximately 1.6 million cubic yards of suitable growth media would be salvage, with up to approximately 190 million tons of alluvium/colluvium also available for reclamation use. The proposed growth media placement depths would be reviewed in coordination with the BLM and the NDEP for specification in the final closure plan for the project.

2.3.4.3 Seeding, Planting, and Noxious Weed Control Seeding would be conducted using the seed mixes that originally were developed by the BLM (BLM 2008a,b), as presented in the Barrick Cortez Inc. (NVN-067575 (16-1A)) Deep South Expansion Project Amendment to Plan of Operations and Reclamation Permit Application #0093 – Tables 3-2 and 3-3 (BCI 2016b). The seed mixes were based on the species’ effectiveness in providing erosion protection, the ability to grow within the constraints of the low annual precipitation experienced in the region, species suitability for site aspect, and the site elevation and soil type (BLM 2008a). In addition to seeding the waste rock facilities, BCI would evaluate planting of singleleaf pinyon seedlings in suitable areas as part of the reclamation program.

BCI’s Noxious Weed Control Plan (SRK Consulting, (U.S.) Inc. [SRK] 2014) would continue to be implemented at the site as a property-wide program.

2.3.4.4 Facility Reclamation Facility reclamation is summarized below.  Open Pits: Post-mining safety barriers (e.g., berms, fencing, or other appropriate barriers) would be installed peripherally to the crest of each pit, with pit ramps barricaded in a similar manner to prevent entrance. Pit lakes would form in the bottom of some pits after dewatering activities cease (i.e., portions of the Pipeline Pit Complex and Cortez Pit). Other pits would be completely or partially backfilled with waste rock material.  Underground Mine: Closure procedures would include: 1) construction of water-tight dams in select portions of the declines to re-establish pre-mining hydrologic conditions; 2) removal and salvage or disposal in an approved waste disposal facility of underground and surface piping, pumps, and equipment; 3) abandonment of surface dewatering wells and boreholes in accordance with applicable rules and regulations; 4) disposal of remaining fuels, lubricants, and explosives at a licensed off-site facility;

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and 5) installation of and earthen plug (minimum 30 feet long) in each decline to prevent access.  Waste Rock Facilities: Concurrent reclamation would be conducted to the extent possible using an interim reclamation seed mix (Barrick Cortez Inc. (NVN-067575 (16-1A)) Deep South Expansion Project Amendment to Plan of Operations and Reclamation Permit Application #0093 [BCI 2016] – Table 3-1). Lifts would be regraded to an overall average 2.5H:1V slope, growth media distributed to a depth of approximately 6 inches, areas reseeded, and erosion controls and storm diversions installed. Portions of pit backfill areas that would be above the projected groundwater table would be reclaimed in a manner similar to out-of-pit waste rock facilities.  Existing Heap Leach Facilities: A Final Plan for Permanent Closure detailing proposed closure technology (e.g., evaporation cells or evapotranspiration cells), management requirements for long-term effluent discharge, and closure would be developed 2 years prior to project closure pursuant to the requirements of the NDEP (NAC 445A.430 through 445.447) at the time of closure. An ecological risk assessment evaluating potential sodium (and other constituent) accumulation in the soils of the evaporation and evapotranspiration cells would be included.  Existing Tailings Impoundment: A Final Plan for Permanent Closure would be developed 2 years prior to project closure for submittal to BLM and NDEP. The plan would include tailings closure specifications, including draindown management, which would be similar to that for the heap leach facilities.  RIBs: The RIBs would be backfilled to grade and revegetated at closure. A detailed closure plan would be prepared at least 2 years prior to the anticipated closure date (NAC 445A.447) for submittal to BLM and NDEP. The closure plan would conform to the water pollution control regulations in effect at the time of closure.  Rocky Pass Reservoir: Water remaining in the reservoir would be pumped back to the Pipeline Pit. The material from the earthen embankment would be removed and placed in the impoundment footprint from where it was borrowed during construction. The pipelines and other equipment would be removed and properly disposed or reused at another Barrick site. The entire reservoir footprint would be scarified and seeded.  Roads: Some access roads would be maintained to provide access to monitoring sites following the completion of mining. As determined by BLM, any roads on public lands determined to be suitable for public access or which continue to provide public access consistent with pre-mining conditions would not be reclaimed. County roads also would be retained. Roads that potentially would support alternate land uses, as would be determined in coordination with agencies, local governments, and tribes, also may be retained. All other haul, access, and exploration roads would be recontoured and reclaimed.  Buildings and Ancillary Facilities: Disposition of buildings and ancillary facilities would be conducted as described in the Barrick Cortez Inc. (NVN-067575 (16-1A)) Deep South Expansion Project Amendment to Plan of Operations and Reclamation Permit Application #0093 (BCI 2016b). BCI would work with agencies, local governments, and tribes to evaluate alternative land uses that could provide long-term socioeconomic benefits from the mine infrastructure.  Drill Holes and Water Wells: All drill holes and water wells subject to Nevada Division of Water Resources [NDWR] regulations would be abandoned in accordance with applicable rules and regulations (NAC 534.425 through 534.428). Boreholes would be sealed to prevent cross contamination between aquifers, and the required shallow seal would be placed to prevent contamination by surface access.

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 Monitoring Wells: Monitoring wells around the heap leach facilities would be maintained until BCI is released from post-mining groundwater monitoring requirements by the NDEP. These wells then would be plugged and abandoned according to the requirements of the Nevada State Engineer.

2.3.4.5 Post-reclamation Monitoring and Maintenance Following mine closure, BCI would conduct maintenance, site inspections, and any other necessary monitoring for the period of reclamation responsibility. Post-mining groundwater quality would be monitored according to the requirements established by NDEP, with the goal of demonstrating non-degradation to waters of the state. Monitoring of revegetation success would be conducted annually for a minimum of 3 years or until the revegetation standards have been met, as determined by the jurisdictional agencies. In addition, noxious weed monitoring and control would be implemented for a period of 5 years. Post-mining monitoring and maintenance is provided for in BCI’s long-term contingency fund (BCI 2016b).

2.4 Alternatives to the Proposed Action Two alternatives to the Proposed Action were carried forward for analysis of impacts and are summarized below.

2.4.1 Gold Acres Pit Partial Backfill Alternative Project development, operation, and reclamation under the Gold Acres Pit Partial Backfill Alternative would be the same as under the Proposed Action, with the following exceptions.

 Expansion of the existing Gold Acres Pit would be completed prior to development of the proposed satellite pits (Alta, Bellwether, and Pasture), with the waste rock from the satellite pits (30 million tons) placed as backfill in the Gold Acres Pit (Figures 2-10 and 2-11).  Placement of backfill in the Gold Acres Pit would result in a 72-acre reduction in the proposed new disturbance for the Gold Acres North Waste Rock Facility (Table 2-3).

2.4.2 No Action Alternative Under the No Action Alternative, the existing mining and processing operations in the CGM Operations Area, the current off-site transport of refractory ore to the Goldstrike Mill for processing, the backhaul of Arturo Mine oxide ore to the Pipeline Complex for processing, and site reclamation would continue under the terms of current permits and approvals as authorized by the BLM and State of Nevada. Existing facilities in the four mine complexes in the CGM Operations Area and the authorized disturbance are shown in Figure 2-1 and presented in Table 2-1. The facilities and ongoing operations are summarized below.

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Table 2-3 Currently Authorized Disturbance and Proposed New Disturbance under the Gold Acres Pit Partial Backfill Alternative

Gold Acres Pit Partial Backfill Alternative Proposed No Action Reallocation Alternative of Use of Total Proposed Currently Proposed Authorized Total Authorized New Surface Disturbance Disturbance Disturbance Disturbance by Facility by Facility (sum total by Facility Mine Complex Facility (acres) (acres) acres) (acres) Open Pits 2,752 3,411 474 185 Underground Operations 01 01 01 01 Waste Rock Facilities 5,393 5,597 -121 325 Heap Leach Facilities 1,933 2,049 116 0 Tailings Impoundment 1,416 1,208 -208 0 Ancillary Support Facilities 4,111 4,696 -336 921 Water Management Facilities Water Management Facilities 704 3,057 10 2,343 Exploration 391 391 0 0 Total Acres within CGM Operations Area2 16,700 20,410 -643 3,774 Proposed New Disturbance Outside CGM Operations Area4 534 Total Proposed New Disturbance 4,308 1 Disturbance associated with surface infrastructure for underground mining is accounted for in other currently authorized or proposed disturbance footprints. 2 Differences are due to rounding. 3 Reflects reallocation of undisturbed land that previously was authorized for disturbance. 4 Reflects surface disturbance associated with proposed RIBs and associated infrastructure northeast of the CGM Operations Area in Crescent Valley.

Mine Facilities:  Open pit mining at the Pipeline Pit Complex and the Cortez Hills and Cortez pits would continue. Any additional mining at the Gold Acres Pit would be conducted in accordance with existing permit criteria.  Underground mining at the Cortez Hills Complex would continue, with mining conducted to the 3,800-foot elevation.  The following out-of-pit waste rock facilities would continue to be used: Pipeline/South Pipeline Waste Rock Facility, Gap Waste Rock Facility, Canyon Waste Rock Facility, North Waste Rock Facility, South Waste Rock Facility, and Cortez Waste Rock Facility.  Waste rock mined in the Pipeline Pit Complex alternately may be placed in the currently authorized backfill areas in the northeast and northwest portions of the pit complex (i.e., Pipeline Pit and Gap Pit, respectively).  The following heap leach facilities would continue to be used: Pipeline South Area Heap Leach Facility, the heap leach portion of the Pipeline Heap Leach/Tailings Facility, and the Grass Valley Heap Leach Facility.

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 The Pipeline Mill would continue to be used, and tailings would continue to be deposited at the tailings portion of the Pipeline Heap Leach/Tailings Facility.  Existing ancillary facilities would continue to be used.

Water Management:  Mine dewatering and disposal would continue through the completion of mining (early 2023). Dewatering water would be consumed, piped to the existing RIBs in Crescent Valley for infiltration, or piped to the Dean Ranch for seasonal irrigation purposes as currently authorized. Dewatering water would be treated at the Pipeline water treatment plant prior to disposal.

General Site-wide Operations:  Refractory ore would continue to be trucked off-site at a rate of up to 1.2 million tpy for processing at the Goldstrike Mill, with shipments and processing continuing through 2023.  Arturo Mine oxide ore would continue to be backhauled at a rate up to 600,000 tpy to the Pipeline Complex for mill and heap leach processing through 2023.

Approximately 1,250 workers currently are employed by BCI for open-pit and underground mining, heap leach and mill processing, and reclamation activities in the CGM Operations Area, with an on-site contractor work force of approximately 350 workers. Operations are anticipated to continue through approximately 2023. Approximately 155 workers would be required for the final 3 years (through 2026) of ongoing ore processing, decommissioning, and final reclamation. The average annual operations work force payroll for the remainder of the currently authorized project would be approximately $406 million.

2.4.2.1 Environmental Protection Measures BCI’s committed environmental protection measures for operations in the CGM Operations Area, as well as additional BLM-stipulated mitigation measures, were identified in the associated NEPA documents (BLM 2015a, 2014a, 2011a, 2008a) and decision documents (BLM 2015b, 2014b, 2011b, 2008b). These measures would continue to be implemented as standard operating procedures to mitigate potential impacts to environmental and human resources.

2.4.2.2 Reclamation Existing facilities would be closed and reclaimed in accordance with the currently approved reclamation plan, current permits, and applicable federal and state site closure and reclamation requirements. Final closure and reclamation of the mine site are discussed in previous NEPA documents (BLM 2015a, 2014a, 2008a) and generally would follow the procedures in Section 2.3.4, Reclamation. Post-mining pit lakes would develop in the Crossroads Pit and southern portion of the Gap Pit portions of the Pipeline Pit Complex, the Cortez Hills Pit, and the Cortez Pit as discussed in the Cortez Hills Expansion Project Final EIS (BLM 2008a).

2.4.2.3 Monitoring Under the No Action Alternative, monitoring would continue as described in the approved plans and the comprehensive Cortez IMP (BLM 2011a, 2008a).

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2.5 Past, Present, and Reasonably Foreseeable Future Actions The past and present actions, as well as the RFFAs, for the cumulative impact analysis are summarized below in Table 2-4, and the distribution of the primary surface-disturbing actions shown in Figure 2-12.

Table 2-4 Surface Disturbance Associated with Past and Present Actions and RFFAs

Past and Present Total Approved/ Approved RFFA Projected Projected Disturbance Disturbance Disturbance Action (acres) (acres) (acres) Mining Projects Black Rock Canyon Mine 117 0 117 Clipper Mine 400 0 400 BCI Buckhorn Mine 820 0 820 BCI CGM Operations Area 16,700 0 16,700 1 BCI Goldrush Project 0 1,102 1,102 BCI Horse Canyon Mine 425 0 425 BCI Mill Canyon 18 0 18 2 Cortez Silver Mining District 92 0 92 Elder Creek Mine 143 0 143 Fire Creek Mine 285 5 290 Fox Mine 4 0 4 Greystone Mine 242 0 242 Grey Eagle Project 5 0 5 Hot Springs Sulfur Mine 5 0 5 May Mine 1 0 1 Mud Spring Gulch 10 0 10 South Silicified Project 31 0 31 Utah Mine and Camp 6 0 6 3 Other Mining Projects 97 210 307 Subtotal 19,401 1,317 20,718 Exploration Notices BLM-Battle Mountain District Office: 265 0 265 4 118 expired, 8 pending, and 30 authorized 4 Plans (7) BLM-Battle Mountain District Office 306 0 306 4 Notices (10) BLM-Ely Field Office 50 0 50 5 BCI HC/CUEP 549 0 549 BCI West Pine Valley 150 0 150 BCI Hilltop Exploration/Mine 92 0 92 BCI Pipeline/South Pipeline/Gold Acres Exploration 50 0 50 Project BCI Robertson Project 12 0 12 6 BCI Robertson Exploration Project 294 0 294

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Table 2-4 Surface Disturbance Associated with Past and Present Actions and RFFAs

Past and Present Total Approved/ Approved RFFA Projected Projected Disturbance Disturbance Disturbance Action (acres) (acres) (acres) Dean Mine 67 0 67 Mud Springs 0 10 10 Mill Canyon Exploration 250 0 250 South Roberts 0 3 3 Toiyabe Project 40 0 40 Uhalde Lease 100 0 100 7 Other Mining Exploration 32 1,564 1,596 Subtotal 2,257 1,577 3,834 Utilities/Community State Route 306 and Roads in Northern Crescent 422 0 422 Valley (100 feet wide) Gravel Roads in Crescent Valley and Northern Carico 1,558 0 1,558 Lake Valley (50 feet wide) Dirt Roads in Crescent Valley and Northern Carico 776 0 776 Lake Valley (30 feet wide) Power lines in Crescent Valley (60 feet wide) 364 0 364 Wells Rural Electric Cooperative power line for 0 150 150 potential future Goldrush Project 8 BCI Fiber Optic Cable (20 feet wide) 53 0 53 BCI Jeremy’s Knob Communications Tower and 0.5 0 0.5 9 Right-of-Way (ROW) 10 Towns of Crescent Valley and Beowawe 900 0 900 Other ROWs (Roads, Mining) 27 161 188 Other Utilities (Electric, Communications, Federal 1,176 2 1,178 Aviation Administration) Subtotal 5,276 314 5,590 Other Development and Actions 1 BLM Fuels Reduction Projects1 5,641 900 6,541 2 Wildfires1 351,220 0 351,220 3 Recreation1 0 0 0 4 Livestock1 10 53 63 Wildlife 0 0 0 5 Agriculture Development1 9,750 0 9,750 6 BCI Additional Irrigation Pivots at Dean Ranch1 0 640 640 7 Lodge at Pine Valley1 30 0 30

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Table 2-4 Surface Disturbance Associated with Past and Present Actions and RFFAs

Past and Present Total Approved/ Approved RFFA Projected Projected Disturbance Disturbance Disturbance Action (acres) (acres) (acres) Crescent Valley Water Supply 2 0 2 6 BCI Cottonwood Infiltration Basins1 104 0 104 8 BCI Bank Enabling Agreement (BEA) Project Plans1 0 46,929 46,929 Subtotal 366,757 48,522 415,279 Total 393,691 51,730 445,421 1 Disturbance acreage from BCI’s Goldrush Mine Plan of Operations, Table 4-1 (BCI 2018); total disturbance of 1,724 acres less existing disturbance of 622 acres equals new disturbance of 1,102 acres. Existing disturbance is included in the disturbance for BCI’s HC/CUEP and West Pine Valley exploration projects. 2 Historic mining- and exploration-related disturbance first began in 1862, prior to the promulgation of surface land management laws and regulations governing mining activities on public lands (e.g., Federal Land Policy and Management Act of 1976 and 40 CFR 3809). Since there were no laws or regulatory programs in place at that time, there were no regulatory or administrative approvals granted. Therefore, the identified disturbance acreage does not include all historic mining-related disturbance in the area. 3 Includes gold and barium/barite mines. 4 Plans and notices outside of the general Crescent Valley area have not been quantified. 5 The approved plan provides for surface exploration activities and development of twin declines for underground exploration (BLM 2016b). 6 BCI’s Robertson Exploration Project boundary is located immediately north of, and partially within, the CGM Operations Area as shown in Figure 2-12. 7 Includes projects by Barrick Cortez Exploration, Nu Legacy Gold, and 777 Minerals Inc. 8 ROW runs from the Lodge at Pine Valley to the southeast boundary of the CGM Operations Area. 9 BCI facility located in T28N, R47E, Section 18 SESE just north of the CGM Operations Area; ROW N-092170. 10 Surface disturbance associated with the towns of Crescent Valley and Beowawe is assumed to be 640 and 160 acres, respectively, with approximately 100 acres of private developed land peripheral to the towns. 1 1 Inclusive of acreage associated with the Crescent Valley Wildland Urban Interface Fire Defense System, Tonkin Hazardous Fuels Reduction Project, and Red Hills Hazardous Fuels Reduction Project. Of the total acreage, planned prescribed burns would affect up to 2,537 acres of pinyon-juniper woodland, and 800 acres of pinyon-juniper woodland would be thinned. Also includes future treatment of 900 acres of encroaching pinyon-juniper woodland for enhancement of greater sage-grouse habitat in the approved HC/CUEP Plan of Operations (BLM 2016a,b). 2 1 Reflects acreage of vegetation affected by wildland fires from 1998 through 2017 within the vegetation cumulative effects study area (CESA). The acreage is inclusive of approximately 19,681 acres of fire-affected pinyon-juniper woodland. 3 1 Surface disturbance associated with recreation activities has occurred; however, the acreages have not been quantified. 4 1 Existing livestock-related surface disturbance is associated with water developments. The surface disturbance associated with the livestock RFFAs is based on 0.5 acre per water development activity and 43 acres for fencing and cattle guards. The 4,313 acres previously identified for RFFA activities (BLM 2015a) inadvertently included acreage of surface occupancy. Livestock-related activities outside of the Carico Lake Allotment have not been quantified. 5 1 Surface disturbance associated with agricultural development is based on the acreage under irrigation and assumes that a change in vegetation and habitat equates to surface disturbance. Acreage values were based on a February 15, 1998, special hydrographic abstract for Hydrographic Basin No. 054 from the NDWR. These values are based on permitted or authorized use of water and may not reflect actual use in a given year. 6 1 Surface disturbance located on private (Barrick-owned) land outside of the CGM Operations Area. 7 1 This facility is located on the JD Ranch Road approximately 4 miles west of State Route 278 at the BCI-owned JD Ranch. 8 1 Includes 37,006 acres for the BEA Public Lands Project Plan and 9,929 acres for the BEA Private Lands Project Plan. Conservation actions that would be implemented to restore and enhance greater sage-grouse habitat would include tree removal, seeding and planting, establishment of fuel breaks, and improving wet meadows (Barrick 2018). Source: BCI 2018; BLM 2017a,b, 2015a, 2008a; ESRI World Imagery 2017; U.S. Census Bureau 2017.

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3.0 Water Resources and Geochemistry

The CESA for water quantity and quality (herein referred to as the hydrologic study area [HSA]) encompasses the entirety of four hydrographic areas (HAs) (i.e., Crescent Valley, Carico Lake Valley, Pine Valley, and Grass Valley) (Figure 3-1) totaling approximately 2,725 square miles (Table 3-1). The project study area for direct and indirect impacts for water resources is defined as those areas within the four HAs where groundwater or surface water could be impacted by the proposed project. The project study area and CESA for wetlands and waters of the U.S. are described in the Deep South Expansion Project Supplemental Environmental Report for vegetation resources (BLM 2019a).

Table 3-1 Hydrographic Areas

Estimated Perennial Existing Basin Groundwater Groundwater NDWR Area Basin Yield Appropriations Designated Basin NDWR (square Area (acre-feet per (acre-feet per Groundwater HA Number Region miles) (acres) year) year) Basin Crescent 054 Humboldt 752 481,280 16,000 30,412 Y Valley River Basin Carico 055 Humboldt 376 240,640 4,000 4,015 Y Lake River Basin Valley Pine 053 Humboldt 1,002 641,280 20,000 16,541 Y Valley River Basin Grass 138 Central 595 380,800 13,000 13,161 Y Valley Region

Total 2,725 1,744,000 53,000 64,129 -- Source: NDWR 2017b.

3.1 Affected Environment 3.1.1 Hydrologic Setting The general topographic and physiographic features of the region are shown Figure 3-1 and described in the Deep South Expansion Project Supplemental Environmental Report – Geology and Minerals (BLM 2019b). The Crescent Valley, Carico Lake Valley, and Pine Valley HAs are within the Humboldt River Basin Region, and Grass Valley is within the Central Region as delineated by the NDWR (NDWR 2017a). All four HAs (or basins) have been designated as “Groundwater Basins” by the State Engineer; therefore, water rights are administered under the provisions of Nevada Revised Statute (NRS) 534.030 that provides the State Engineer with additional authority for administration of water resources within these basins. Crescent Valley is approximately 45 miles long and 20 miles wide and is bordered on the west by the Shoshone Range, on the east by the Cortez Mountains, and on the north by the Humboldt River. Carico Lake Valley is approximately 43 miles long and up to 15 miles wide and is bounded on the west by the Shoshone Range and on the east by the Toiyabe Range. This valley is semi-enclosed topographically with minor surface water outflow to Crescent Valley at Rocky Pass. Pine Valley is approximately 55 miles long and up to 30 miles wide and is bounded on the west by the Cortez Mountains, on the south by the Simpson and Roberts

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-2 mountains, on the east by the Sulphur Springs and Pinon ranges, and on the north by the Humboldt River. Pine Valley narrows northward to its intersection with the Humboldt River where the width is approximately 3 miles. Grass Valley is a closed topographic basin approximately 40 miles long and 18 miles wide bounded on the west and north by the Toiyabe Range and on the east by the Simpson Park Mountains.

Elevations across the HSA range from 10,134 feet above mean sea level (amsl) in the Roberts Creek Mountains in the southern end of Pine Valley to approximately 4,700 feet amsl in Beowawe in the northern end of Crescent Valley. Major topographic highs located within proximity to the project include Mount Tenabo (elevation 9,153 feet amsl) located approximately 1 mile east of the existing Cortez Hills Pit and Mount Lewis (elevation 9,680) located approximately 8 miles northwest of the CGM Operations Area in the northern Shoshone Range. In the project area, elevations range from approximately 6,800 feet amsl on the slopes of Mount Tenabo to approximately 4,760 feet amsl in the lower portions of Crescent Valley (Figure 3-1).

The climate in the HSA is arid with most precipitation occurring in the months of March through May. Throughout the region, precipitation varies widely between seasons and years as well as with elevation. The variation in average annual precipitation with elevation for weather stations in the region is summarized in Table 3-2. On the valley floor, the mean annual precipitation at the CGM Operations Area is approximately 7 inches, with the highest percentage of precipitation occurring in the winter and spring (Itasca 2016a). Similar data are reported by the Western Regional Climate Center for the Beowawe meteorological station north of the CGM Operations Area (Itasca 2016a). Regional data indicate that elevations below 6,500 feet amsl typically receive the 5 to 9 inches per year, and elevations above 6,500 feet amsl may receive 11 to 16 plus inches of precipitation annually (Western Regional Climate Center [WRCC] 2018).

Table 3-2 Mean Annual Precipitation at Selected Regional Sites

Approximate Approximate Measured Mean Distance/Direction from Elevation Annual Precipitation Station Location Project Boundary Center (feet amsl) (inches) Beowawe 27 miles, north-northeast 4,700 7.51 Beowawe-University of Nevada 18 miles, south 5,740 10.22 Ranch Eureka 45 miles, southeast 6,540 11.73 1 Period 1893-2012. 2 Period 1972-2012. 3 Period 1952-2010. Sources: Itasca 2016a; WRCC 2018.

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Evaporation rates vary with a number of factors, of which temperature, wind speed, relative humidity, and solar radiation are primary. Based on April through October data collected at the Beowawe University of Nevada Ranch station between 1972 and 2012, mean annual pan evaporation averaged 51.2 inches. Assuming evaporation during the winter months is 18 percent of the annual total, the mean annual pan evaporation is estimated to be 60.4 inches (Itasca 2016a). With a typical pan coefficient of 0.7, the mean annual evaporation from a free water surface would be approximately 42 inches. Based on pan evaporation measurements, U.S. Geological Survey (USGS) investigations estimated an open-water evaporation rate of 4.2 feet (50.4 inches) per year for the middle Humboldt River basin (Berger 2000a,b). Average annual evapotranspiration, which includes the effects of vegetation, the ground surface, and other factors, may differ substantially from this estimate as discussed in Section 3.1.3.

3.1.2 Surface Water Resources As is typical in the Basin and Range Province, the project region is dominated by mountain block watersheds that drain onto broad alluvial fans and valley fills. Perennial, intermittent, and ephemeral stream reaches occur in the bedrock-controlled mountain drainages, and flows typically dissipate into the fans along the valley margins or drain toward playas near the basin centers. Surface water features and major drainages in the HSA are presented in Figure 3-1.

Within Crescent and Grass valleys, surface water resources primarily consist of streams that generally drain from the mountain watersheds toward alkali flats (playas) in the lowermost valley areas. A few small artificial ponds are located along stream channels. On the valley floor, the playas are intermittently wet from occasional runoff and from natural fluctuations of groundwater levels beneath the playas. Most of the land area of Crescent Valley rarely, if ever, contributes surface water to the Humboldt River, due to a low topographic divide just south of Beowawe and other watershed divides near Iron Blossom Mountain. Pine Valley generally trends northeastward, paralleling Crescent Valley. The southwestern portion of Pine Valley includes headwater tributaries that drain the eastern slope of the Cortez Mountains near Mount Tenabo. The major channel in Pine Valley is Pine Creek, which is perennial over most of its length. Pine Creek drains to the Humboldt River at Palisade, west of Carlin, Nevada. The northern portion of Carico Lake Valley includes headwater tributaries that drain the southeastern slope of the Shoshone Range, two of which (Cooks and Elder creeks) are perennial in their upper reaches. Carico Lake Valley has minor surface water outflow to Crescent Valley at Rocky Pass.

3.1.2.1 Streams Precipitation and geologic conditions in the project study area limit perennial stream flows to only a few isolated channel reaches (Figure 3-1). Elsewhere, flows in the HSA occur as either intermittent or ephemeral discharges. Longer-duration intermittent flows originate from isolated springs or as short-term seasonal runoff from snowmelt and winter precipitation, whereas ephemeral flows result from infrequent, intense thunderstorms. Numerous drainages leave the mountain fronts and cross alluvial fans. Flows typically dissipate into deeper sediments on the fans or farther downslope on the valley floors. When water does reach the fans or valley floors during larger runoff events, it is soon taken up by evapotranspiration and seepage into the valley floor sediments.

Based on existing data, it is likely that isolated stream reaches are perennial during years of normal and above-average precipitation. A number of springs occur higher in the bedrock- controlled mountain watersheds, or where the mountain fronts transition onto alluvial fans, and also along the valley floors. Perennial flow and/or seasonally ponded water are most likely to occur over short stream reaches in the mountains or downstream of perennial springs. There are no perennial stream reaches within the CGM Operations Area boundary. To the west of the

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CGM Operations Area in the Shoshone Range, isolated perennial stream reaches occur in Carico Lake Valley along upper Cooks Creek and Elder Creek northwest of Rocky Pass, and in upper Indian Creek draining to Crescent Valley. Short perennial or intermittent stream reaches also drain to Crescent Valley from the Cortez Mountains (Figure 3-1). Based on aerial photography and a site visit in 2006, a perennial reach likely occurs on Mill Creek approximately 2.5 miles northeast of the Cortez Hills Complex (BLM 2008). Isolated perennial stream reaches also may occur in upper Brock Canyon, Cottonwood Creek, Hand Me Down Creek, and in other Crescent Valley side drainages well to the northeast of the project study area.

No perennial stream reaches occur near the CGM Operations Area in Grass Valley. In the Pine Valley portion of the HSA, numerous headwater tributaries to Pine Creek form on the east and southeast-facing slopes of the Cortez Mountains. In Pine Valley, Willow Creek, Horse Creek, and tributaries east of the CGM Operations Area are steep channels fed by runoff and springflow. The results of the seep and spring monitoring conducted in September 2015 (HDR Engineering, Inc. [HDR] 2015) include a series of maps that distinguish perennial and ephemeral/intermittent stream reaches in western Pine Valley and southeast Crescent Valley. The HDR mapping was used to supplement existing data to identify perennial stream reaches within this portion of the HSA. Streams characterized as perennial include short isolated segments of Horse Creek and Willow Creek located on the east flank of the Cortez Mountains along the western-most portion of Pine Valley as shown in Figure 3-1. Horse Creek and Pine Creek are perennial immediately upstream of their confluence. Downstream, Pine Creek is generally perennial to its confluence with the Humboldt River, but has several branching intermittent reaches along wider parts of the valley floor where seepage into the valley floor sediments removes flow from the divided channels.

Elsewhere in the HSA, numerous channels extend from the mountain fronts at greater distances from the CGM Operations Area. Named streams are shown in Figure 3-1 and identified in Table 3-3. Where perennial stream reaches occur, most flows historically ranged from approximately 5 gpm to approximately 20 gpm (BLM 2008). In some streams, such as Indian Creek in Crescent Valley, greater flows ranging from approximately 150 to 1,000 gpm occur. Recent data for Horse Creek vary widely, but indicate a March monthly average high flow of approximately 50 gpm and a September monthly average low flow of approximately 4 gpm (USGS 2016). However, there was no measurable flow from July 2015 through January 2016. In the north central part of Pine Valley at the Modarelli Mine Road crossing, recent data for Pine Creek indicate an average monthly high flow in February of approximately 3,000 gpm (6.7 cubic feet per second [cfs]), and an average monthly low flow in October of approximately 1,660 gpm (3.7 cfs) (USGS 2017).

Table 3-3 Named Streams within the Hydrologic Study Area

NDWR Hydrographic Basin (Number) Range of Origin Stream Name Dominant Flow Duration1 Crescent Valley (054) Shoshone Range Coyote Creek Intermittent Fire Creek Intermittent Corral Canyon Perennial Indian Creek Perennial to intermittent Ferris Creek Perennial tributary to Indian Creek Cooks Creek Intermittent

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Table 3-3 Named Streams within the Hydrologic Study Area

NDWR Hydrographic Basin (Number) Range of Origin Stream Name Dominant Flow Duration1 Crescent Valley (054) Cortez Mountains Thomas Creek Perennial to intermittent (Cont.) Neil Creek Intermittent Coyote Creek Intermittent Frenchie Creek Intermittent Sod House Creek Intermittent Duff Creek Perennial to intermittent Dewey Dann Creek Perennial to intermittent Hand Me Down Creek Intermittent with isolated perennial reaches Little Cottonwood Creek Intermittent Cottonwood Creek Intermittent with isolated perennial reaches Brock Canyon Intermittent with isolated perennial reaches Mule Canyon Intermittent Fourmile Canyon Intermittent Mill Creek Perennial to Intermittent Cortez Canyon Intermittent Carico Lake Valley (055) Shoshone Range Elder Creek Perennial to intermittent Cooks Creek Perennial to intermittent Willis Creek Intermittent Toiyabe Range Iowa Creek Perennial to intermittent Hall Creek Perennial to intermittent Pine Valley (053) Cortez Mountains Horse Canyon/Horse Perennial to intermittent Creek Willow Creek Intermittent with isolated perennial reaches Dry Creek Intermittent Cottonwood Creek Intermittent Linka Creek Intermittent Doc Creek Intermittent Lamb Creek Intermittent Sheep Creek Intermittent

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Table 3-3 Named Streams within the Hydrologic Study Area

NDWR Hydrographic Basin (Number) Range of Origin Stream Name Dominant Flow Duration1 Pine Valley (053) (Cont.) Big Pole Creek Intermittent Little Pole Creek Intermittent Roberts Mountains/ Pine Creek Intermittent to Perennial Rocky Hills Grouse Creek Intermittent Denay Creek Intermittent Geyser Creek Intermittent Indian Creek Intermittent Pete Hanson Creek Intermittent with isolated perennial reaches Niel Creek Intermittent Kelley Creek Perennial Birch Creek Intermittent Willow Creek Perennial Dry Creek Intermittent Vinini Creek Perennial Henderson Creek Intermittent with isolated perennial reaches Sulpher Spring Range Edwards Creek Intermittent Pinon Range Dry Creek Intermittent Pony Creek Intermittent Hot Creek Perennial Willow Creek Intermittent with isolated perennial reaches Smith Creek Intermittent Trout Creek Perennial to intermittent Mill Creek Intermittent Front Creek Intermittent Ferdelford Creek Perennial to intermittent Webb Creek Perennial Cole Creek Intermittent Grass Valley (138) Toiyabe Range Dry Canyon Wash Intermittent with isolated perennial reaches Corral Canyon Creek Intermittent Cowboy Rest Creek Intermittent Rosebush Creek Intermittent Skull Creek Perennial Callaghan Creek Perennial to intermittent Ox Corral Creek Intermittent

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Table 3-3 Named Streams within the Hydrologic Study Area

NDWR Hydrographic Basin (Number) Range of Origin Stream Name Dominant Flow Duration1 Grass Valley (138) Simpson Park Crooked Canyon Creek Intermittent (Cont.) Mountains Steiner Creek Perennial Water Canyon Creek Intermittent Indian Creek Intermittent McClusky Creek Perennial to intermittent

1 Listed streams generally reflect those that emerge from the mountain fronts and maintain channels across alluvial fans and valley floors. A number of other canyons occur within the mountain blocks; however, their channels disperse on alluvial fans immediately upon leaving the ranges. Some of these are listed where they occur in or near the project area. Other channels, such as Corral Canyon and Indian Creek in Crescent Valley, persist for greater distances but disappear as flows seep into the valley floors or spread onto playas. Sources: BLM 2008; SRK 2016; TopoQuest 2017.

3.1.2.2 Seeps and Springs Numerous springs and seeps occur in or near the project area, as well as in the outlying HSA. Three of the spring systems in Crescent Valley have thermal springs; the remaining systems are cold springs (BLM 1996). In Crescent Valley, a large geothermal spring system is at Hot Springs Point north of the project area at the southern end of the Dry Hills (Figure 3-2). This system consists of five springs with temperatures ranging from 79 to 138 degrees Fahrenheit (°F) (26 to 59 degrees Celsius [°C]) (Water Management Consultants, Inc. 1992). The thermal springs at Hot Springs Point (Figure 3-2) issue from fault zones in the siliceous bedrock at the alluvium/bedrock interface (Muffler 1964; Water Management Consultants, Inc. 1992). Another hot spring occurs near the base of the Cortez Mountains west of Hand Me Down Creek (BLM 1996). Muffler (1964) mapped that hot spring (also known as the Dewey Dann spring), which is associated with the Hot Springs Point geothermal system, near the contact of the alluvium and the Pony Trail Group volcanic intrusions that occur along the Crescent Fault. The source of the hot spring is thought to be within the intrusions.

The Beowawe Geysers are surface features of a geothermal system in Whirlwind Valley to the north outside the HSA. This system (Figure 3-2) is located along a range-front normal fault associated with the Malpais fault system. Heated at great depths, water circulates upward along the fault system. A maximum downhole temperature of 415°F (213°C) has been recorded in the area. The hot water that vents continuously at the surface is not a natural geyser but a free-flowing uncapped geothermal well and its associated large sinter terrace (Struhsacker 1986). Maurer et al. (1996) reported that the source of thermal water at the Beowawe Geysers could be restricted to the area contained in Whirlwind Valley.

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Spring and seep surveys and related monitoring have been conducted by Barrick and its contractors since the early 1990s. In Crescent Valley, 68 seeps and springs were surveyed by JBR Environmental Consultants, Inc. (JBR) in 1993 (BLM 2008). These springs are located in the southern part of Crescent Valley. The survey did not locate all of the springs in the basin. Most were hillside seeps and springs associated with wet meadows and riparian areas below 6,000 feet amsl, and were classified as palustrine-type wetlands. Others were found emanating from the beds of drainages; these were classified as riverine-type wetlands. JBR reported on additional survey efforts in 2012, listing 100 seeps and springs in or near the project area and recommending 80 for monitoring (JBR 2012).

In 2013, HDR performed a spring and seep survey within a 10-mile radius of the Goldrush Project, and identified 61 new spring or seep features (HDR 2015). In addition, further southwest in Carico Lake Valley, Stantec surveyed 162 spring sites and sampled 87 of them (Stantec 2015c).

Inventoried springs and seeps located within the region that encompasses the proposed CGM Operations Area and surrounding areas of Crescent, Carico Lake, Grass, and Pine valleys are shown on Figure 3-3. A list of these inventoried springs, including their map identification number, site identification number, spring group designation, hydrographic basin, and if they are included in the current monitoring programs is provided in Appendix A, Table A-1.

For discussion purposes, all seep and springs sites are collectively referred to as “springs.” A total of 244 springs have been identified that includes 75 springs in Crescent Valley, 41 springs in Carico Lake Valley, 11 springs in Grass Valley, and 117 springs in Pine Valley. The spring group designations are used to define springs that occur in specific geographic areas within the region as shown in Figure 3-3. The numbers of springs identified within each geographic group are listed in Table 3-4.

HydroGeo Group [HGG] (2017a) compiled and evaluated the flow data for 196 springs that occur within the project region. The results of this study indicate that: 1) 90 percent of the sites have a history of going dry (i.e., at least one zero flow measurement); 2) 60 percent have a maximum discharge rate of 1 gpm or less; and 3) approximately one half of the springs that do not have recorded dry events have minimum measured flow rates of only 0.1 gpm. The fact that most of the springs go dry or have such low minimal flow rates suggest that most of the springs are not supported by discharge from the deep carbonate aquifer system (HGG 2017a).

HGG (2017b) also collected samples for determination of stable isotopes (140 springs) and radiogenic isotopes (tritium and carbon-14) (89 springs). The stable isotopic values of water are useful for distinguishing different groundwater types and evaluating recharge histories. Factors that affect the stable isotopic composition of water include recharge elevation, seasonal recharge, and climate variations (HGG 2017b). For these reasons, the stable isotopes of water can be used to characterize the recharge and flow history of the spring water. The stable isotopic data indicate that the composition of the spring water at many sites have been affected by excessive evaporation, which is consistent with the small discharge rates at most springs.

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Table 3-4 Summary of Springs and Seeps Identified within the Project Region

Number of Identified Springs Spring Group1 Hydrographic Basin and Seeps Brock Canyon Crescent Valley 3 Carico Lake North Carico Lake Valley 11 Carico Lake South Carico Lake Valley 25 Cortez Hills Crescent Valley 13 Cottonwood Canyon Crescent Valley 13 Dry Creek Pine Valley 6 Dry Hills Pine Valley 13 Fourmile Canyon Crescent Valley 6 Horse Creek Pine Valley 43 Mill Canyon Crescent Valley 6 North Toiyabe Range East Grass Valley 10 North Toiyabe Range West Crescent Valley 12 Peripheral Area Crescent Valley 1 Rocky Hills Grass and Pine Valleys 3 Rocky Pass Crescent and Carico Lake Valleys 4 Southeast Crescent Valley Crescent Valley 10 Shoshone Crescent and Carico Lake Valleys 12 Willow Creek Pine Valley 39 Willow Springs Pine Valley 14 TOTAL 244 1 As shown on Figure 3-3.

Tritium concentrations in groundwater are used as a tracer to identify relatively young water that originated through recharge of precipitation that occurred after the initiation of atmospheric testing of nuclear devises that began in 1952 and reached a maximum in 1963-1964 (USGS 2018). Samples of groundwater with tritium concentrations that are below the detection limit (0.3 tritium unit [TU]) indicate that the water originated from groundwater recharge that occurred prior to 1952. The average tritium content of the spring water was 4.3 TUs, indicating that most of the springs discharge relatively young water that originated during recharge over the past 50 years. However, a few springs have tritium concentrations that are less than the detection limit, indicating that groundwater recharge occurred prior to 1952.

For comparison to spring waters, tritium concentrations and carbon-14 ages were determined for 23 deep monitoring wells. The results indicate that 20 of the 23 wells had tritium concentrations less than 1.0 TU, and most of these had values of 0.3 TU or less (HGG 2017b), indicating that most of the well water reflects groundwater recharge that occurred prior to 1952. All of the wells had calculated carbon-14 ages ranging from 1,500 to 25,000 years, with the exception of one well completed in Tertiary sediment, one completed in Paleozoic sedimentary rocks, and one competed in Paleozoic carbonate. The differences between the stable and radiogenic isotopic contents between the spring and well waters indicate that most of the springs discharge from groundwater systems that are hydraulically separated from the deeper groundwater system (HGG 2017b).

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3.1.2.3 Floodplains Federal Emergency Management Agency (FEMA) has delineated flood hazard zones in the project locale as shown in Figure 3-4. A FEMA-designated floodplain (Zone A delineation for the 100-year flood hazard zones) follows Cooks Creek in a fairly narrow band through Rocky Pass into Crescent Valley. In Crescent Valley, the Cooks Creek floodplain widens downstream through the project study area and into Eureka County. A Zone A floodplain delineation also follows Indian Creek through the Dean Ranch, joining the widening Cooks Creek floodplain trending northward. The delineation substantially widens as it trends northward, becoming over a mile wide where it meets the Thomas Creek floodplain near Hot Springs Point at the southern toe of the Dry Hills (FEMA 2017).

3.1.2.4 Waters of the U.S. Clean Water Act (CWA) regulatory programs are administered at the federal level by the USEPA and the U.S. Army Corps of Engineers (USACE). Through Section 404 of the CWA, the latter has the authority to issue permits regulating the discharge of dredge or fill material into waterbodies that are determined to be within agency jurisdiction as waters of the U.S. Legal actions have further defined waters of the U.S. and the regulatory scope of the USEPA and USACE to administer Section 404. On June 29, 2015, a final “Clean Water Rule” was published jointly in the Federal Register by the USEPA and USACE. The Clean Water Rule has been subject to rulemaking and other efforts seeking to delay its implementation. In light of those efforts as well as the ongoing litigation challenging various aspects of the agencies’ approach to the waters of the U.S. rulemaking, the agencies generally have resumed nationwide use of their previous regulations defining the term “Waters of the United States” and are implementing programs and guidance that applied prior to the Clean Water Rule.

In September 2015, Stantec conducted waters of the U.S. investigations on the proposed Deep South Expansion Project area. Their overall approach for the delineation of stream channels first used a Geographical Information System to map channels that could potentially possess an ordinary high water mark, and then these features were inspected in the field (Stantec 2015a). Drainages were investigated, and any presence of diagnostic features was identified in accordance with applicable USACE regional guidance. Potential wetlands were identified prior to field surveys using aerial photography. Potential wetlands were then field- evaluated to determine if they met the wetland criteria using applicable USACE regional methods, criteria, and guidance (Stantec 2015a). Where wetlands were determined to occur, standard agency criteria and record-keeping were used to identify their boundaries. Once a wetland boundary was determined, the area was recorded with a Global Positioning System receiver to further document the location and extent (acreage) of the wetland (Stantec 2015a).

Stantec (2015a) identified a total of 3.14 acres of potential waters of the U.S, including a total of 2.95 acres of stream channel features having a total length of 37,533 feet (7.11 miles), and three wetlands with a total area of 0.19 acres. Survey results were submitted to the USACE Sacramento District for formal review and determination of regulatory jurisdiction as waters of the U.S. The agency officially determined that the identified resources are intrastate isolated waters with no apparent interstate or foreign commerce connection. As such, they are not currently regulated by the USACE (USACE 2016).

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3.1.2.5 Surface Water Quality Applicable surface water quality standards are promulgated by the NDEP, Bureau of Water Quality Planning (BWQP) (NDEP-BWQP 2016). The state has regulatory primacy to do so through the CWA. In Nevada, surface water quality standards (Table 3-5) apply to waters of the state. In most cases, waters that have been determined to be non-jurisdictional by the USACE are not required to be included under CWA sections 303(d) and 305(b) assessments and reporting requirements (Heggeness 2014a,b).

However, these waters still could be subject to other state water quality protection programs. State water quality standards typically apply (e.g., through application of the Tributary Rule) to waters located in watersheds with upgradient or downgradient waters subject to water quality standards regardless of any demonstrated hydrologic connection. “There are, however, some waterbodies in the state that do not have assigned uses and standards and are not located in a watershed with waters that do have standards. These waters generally flow out of the state or into a closed basin. The Tributary Rule does not apply and these waters are categorized as having no designated beneficial uses. Consequently these waters were not assessed and placed in Category 3 (Heggeness 2014a). Category 3 waterbody segments are those for which insufficient information exists to make a use support determination for any of the beneficial uses (NDEP-BWQP 2016).

On this basis, the only surface water bodies within the HSA with designated uses and corresponding surface water quality standards are the Humboldt River (which forms the northern boundary of the HSA), Pine Creek and its tributaries, and Coyote Creek and similar small tributaries draining to the river in the extreme northern end of Crescent Valley. All of these water bodies are distant from the CGM Operations Area and outside of the project study area. The remaining streams flow in closed basins or onto playas with no outlet to a designated stream segment. These streams, many of which are listed above in Table 3-3, have general narrative standards described in NAC 445A.121, “Standards applicable to all surface waters.” Portions of these general standards that may be of most interest to the proposed project are listed below (Nevada State Legislature 2016).

 Waters must be free from high temperature, biocides, organisms pathogenic to human beings, toxic, corrosive or other deleterious substances attributable to domestic or industrial waste or other controllable sources at levels or combinations sufficient to be toxic to human, animal, plant or aquatic life or in amounts sufficient to interfere with any beneficial use of the water.  Wastes from municipal, industrial, or other controllable sources containing arsenic, barium, boron, cadmium, chromium, cyanide, fluoride, lead, selenium, silver, copper, and zinc that are reasonably amenable to treatment or control must not be discharged untreated or uncontrolled into the waters of Nevada. In addition, the limits for concentrations of the chemical constituents must provide water quality consistent with the mandatory requirements of the 1962 Public Health Service Drinking Water Standards.  The specified standards are not considered violated when the natural conditions of the receiving water are outside the established limits, including periods of extreme high or low flow. Where effluents are discharged to such waters, the discharges are not considered a contributor to substandard conditions provided maximum treatment in compliance with permit requirements is maintained.

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Table 3-5 General Nevada Water Quality Standards

Groundwater Surface Water

Nevada Drinking Water Standards Municipal or Nevada Agriculture Constituent Primary Secondary Domestic Livestock Aquatic (mg/L)1 MCL2 MCL2 Supply Irrigation Watering Life Physical Properties Dissolved -- -- Aerobic -- Aerobic 5.0 Oxygen Color -- 153 75 ------(color units) Total Dissolved Solids (TDS) -- 5004; 1,0003 5004; 1,0003 -- 3,000 -- (at 180°C) Turbidity (NTU) ------Inorganic Nonmetals Ammonia (unionized) -- -- 0.5 ------(total NH3 as N) Chloride -- 2504; 4003 2504; 4003 -- 1,500 -- Cyanide 0.2 -- 0.2 ------(as CN) Fluoride 4.0 2.04 -- 1.0 2.0 0.00525 Nitrate 10 -- 10 -- 100 -- (as N) Nitrite (as N) 1.0 -- 1.0 -- 10 -- pH (standard -- 6.5-8.53 5.0-9.0 4.5-9.0 6.5-9.0 6.5-9.0 units) Sulfate -- 2504; 5003 2504; 5003 ------Metals6/Elements Aluminum -- 0.054 -0.23 ------Antimony 0.006 -- 0.006 ------Arsenic (total) 0.01 -- 0.01 0.10 0.20 0.185,7 Barium 2.0 -- 2.0 ------Beryllium 0.004 -- -- 0.10 -- -- Boron ------0.75 5.0 -- Cadmium 0.005 -- 0.005 0.01 0.05 0.00065,8 Chromium 0.1 -- 0.1 0.10 1.0 0.0155,8 (total) Copper 1.39 1.03 -- 0.20 0.50 0.00655,8 Iron -- 0.34; 0.63 -- 5.0 -- 1.0 Lead 0.0159 -- 0.05 5.0 0.10 0.00045,8 Magnesium -- 1254; 1503 ------Manganese -- 0.054; 0.13 -- 0.2 -- -- Mercury 0.002 -- 0.002 -- 0.01 0.000125

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Table 3-5 General Nevada Water Quality Standards

Groundwater Surface Water

Nevada Drinking Water Standards Municipal or Nevada Agriculture Constituent Primary Secondary Domestic Livestock Aquatic (mg/L)1 MCL2 MCL2 Supply Irrigation Watering Life Nickel 0.1 -- 0.134 0.20 -- 0.0875,8 Selenium 0.05 -- 0.05 0.02 0.05 0.0055 Silver -- 0.13 ------0.00145,8 Thallium 0.002 -- 0.013 ------Zinc -- 5.03 -- 2.0 25 0.5845,8 1 Units are milligrams per liter (mg/L) unless otherwise noted. 2 MCL = maximum contaminant level. Federal primary standards that existed as of July 1, 2009, are incorporated by reference in NAC 445A.4525. 3 Nevada secondary MCLs. 4 Federal secondary MCLs. 5 96-hour average. 6 The standards for metals and metalloids are expressed as total recoverable unless otherwise noted. 7 Standard for arsenic (III), trivalent (reduced) inorganic form of arsenic, which occurs as a water soluble form. 8 Standard is dependent on site-specific hardness; displayed value is based on a hardness of 60 mg/L as calcium carbonate. (See NAC 445A.144 for equations.) 9 Value is the action level for lead and copper as defined by USEPA regulation known as the Lead and Copper Rule (40 CFR Part 141 Subpart I). Sources: 40 CFR 141.51; 40 CFR 143.3; NAC 445A.119, 445A.144, 445A.453, and 445A.455.

Stream Water Quality In Pine Valley near the CGM Operations Area, the water quality in Willow Creek is impaired due to elevated concentrations of TDS (USEPA 2016). Lower Pine Creek downstream of Dry Creek is impaired due to elevated phosphorus and TDS concentrations in flows from the Pinon Range. Water quality standards for these stream reaches derive from the Tributary Rule (NAC 445A.097 and 445A.1239) and associated water quality standards (NAC 445A.1442 and 445A.1516) (NDEP-BWQP 2016).

Surface water quality data have been collected for years from perennial or intermittent streams in or near the CGM Operations Area, and along the Humboldt River both upstream and downstream of where it borders the HSA (Tetra Tech 2015; USGS 2017). Recent long-term surface water monitoring sites are located on:

 Mill Creek (BCI sites MIL-01 and MIL-02)  Ferris Creek (BCI site FER-01)  Indian Creek (BCI sites IND-01U and IND-01D)  Humboldt River at Palisade (USGS)  Humboldt River at the old Highway 40 bridge near Dunphy (USGS)

Another BCI monitoring location is on Fourmile Creek (site FOU-01); however, the stream did not have any observable surface water in 2015 during monitoring events. No in-situ field parameters or laboratory data are available (Tetra Tech 2015).

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Sampled surface water flows since 2007 were highly varied at site MIL-01 near the Cortez Pit, ranging from approximately 6.3 gpm (0.01 cfs) up to approximately 2,400 gpm (5.3 cfs). After June 2015, no water was present to allow sampling during the remaining 2015 field effort. Water temperatures ranged from approximately 5.6°C in January to 23.2°C in August. The maximum field conductivity value was 0.664 micromhos per centimeter (µmhos/cm). The maximum TDS concentration was 470 mg/L, with most samples having less than 400 mg/L. Field pH values ranged from 5.07 to 10.80; however, most were between 6.5 and 8.5 (Tetra Tech 2015). Since the winter of 2013, there appears to have been a decline in field pH readings at site MIL-01, and a slight increase in the TDS concentrations. However, the field pH declines were not evident in laboratory pH analyses, which ranged from 7.8 to 8.6 (Tetra Tech 2015).

Arsenic concentrations at site MIL-01 were generally less than 0.075 mg/L, well within NDEP standards for toxic materials, but above the municipal or domestic water supply standard (0.01 mg/L). Most arsenic concentrations at site MIL-01 range from approximately 0.06 to 0.075 mg/L, with a random few exceeding that range. These were typically well within state arsenic standards for irrigation (0.1 mg/L) or livestock watering (0.2 mg/L). Selenium concentrations were 0.003 mg/L or less, with selenium undetected in the vast majority of samples. Neither mercury nor cyanide was detected. The concentrations of these total and dissolved metals were not above the standards or criteria for existing local uses at any point in 2015 (Tetra Tech 2015).

Surface water quality at upper Mill Creek (site MIL-02), Ferris Creek, and Indian Creek was generally similar to that described above for lower Mill Creek. There were wide variations in flow; however, overall flow rates were fairly small. Water temperature ranges were similar. TDS concentrations typically were below 450 mg/L, with higher values occurring rarely during particularly low flows. Laboratory pH values were similar to those from lower Mill Creek. Arsenic concentrations were somewhat less in upper Mill Creek than in lower Mill Creek, ranging from approximately 0.04 to 0.06 mg/L. On Ferris and Indian creeks, arsenic concentrations were generally undetected, with a few detected values that were quite low (0.009 mg/L or less). Cyanide was not detected. Mercury and selenium were largely undetected; however, selenium values occasionally reached 0.002 or 0.003 mg/L. All these characteristics were within state standards for existing local uses.

On the Humboldt River, upstream water quality at Palisade (USGS gage 10322500) reflects conditions fairly similar to that in the mountain streams in the Crescent Valley basin. Specific conductance values were slightly higher, ranging from 435 to 526 microSiemens per centimeter (equivalent to µmhos/cm). Measured pH values ranged from 8.2 to 8.7 (USGS 2017). Other water quality data from the 1990s indicate TDS concentrations of approximately 300 mg/L, slightly lower than the monitored mountain streams in the Crescent Valley basin. Arsenic concentrations ranged from 7 to 9 micrograms per liter; approximately an order of magnitude less than the mountain streams. Selenium and mercury were undetected in river samples (USGS 2017).

Downstream river conditions at Dunphy (USGS gage 10323425) indicate pH and specific conductance values are somewhat greater than those upstream. Specific conductance ranged from 398 to 643 µmhos/cm, and pH ranged from 8.3 to 9.0 (USGS 2017). Other water quality data from the 1990s indicate that TDS concentrations ranged from 300 to 400 mg/L, slightly higher than upstream at Palisade. Arsenic concentrations ranged from 7 to 9 micrograms per liter, and neither selenium nor mercury was detected (USGS 2017). It is likely that flow contributions from the Beowawe geysers and nearby irrigation influence the pH, specific conductance, and TDS values at Dunphy.

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Spring Water Quality Approximately 200 pages of sample analyses present laboratory data from a 2015 spring monitoring program conducted in southern Crescent Valley in the vicinity of the Cortez Hills Complex, northern Grass Valley, and southwestern Pine Valley (HDR 2015). Also, 87 sites were monitored in Carico Lake Valley, with six field parameters recorded at each location during a 2015 spring and seep inventory (Stantec 2015c). Conditions at springs and seeps in previous years were documented by earlier JBR (2007) surveys and sampling.

In the northern portion of the survey area investigated by HDR (2015), most springs had pH values between 8.0 and 8.5. TDS concentrations typically were between 250 to 500 mg/L. Total recoverable arsenic, selenium, and mercury were rarely detected. In the few cases when total recoverable arsenic was detected, most concentrations ranged from 0.006 mg/L to approximately 0.016 mg/L; however, a maximum of 1.44 mg/L was recorded at one spring (27-48-34-322A) in the Willow Creek area in southwestern Pine Valley. Total recoverable selenium also was rarely detected; when detected, it ranged from approximately 0.005 to 0.008 mg/L (the latter at spring 27-48-21-421 in the Willow Spring area of southwestern Pine Valley). Total recoverable mercury was almost never detected.

One spring investigated by HDR (2015) is notable for water quality that substantially differs from the typical setting. Spring 27-49-31-244 in the Willow Creek area in southwestern Pine Valley had a low pH value of 3.7 and an elevated TDS concentration of 2,820 mg/L in early September 2015. The sulfate concentration was 1,570 mg/L (much greater than at other locations), and the bicarbonate alkalinity was not detected. At 66 mg/L, the chloride concentration was approximately an order of magnitude above typical values. Calcium was the dominant cation at 191 mg/L, followed by magnesium and sodium concentrations of 82 and 79 mg/L, respectively. Total recoverable concentrations for arsenic, mercury, and selenium were similar to the values common to other springs. However, the total aluminum concentration was 22.7 mg/L, and the total recoverable iron concentration was 301 mg/L. These are far greater concentrations of aluminum and iron than at other sites.

Spring 27-48-35-311 in the Willow Creek area of southwestern Pine Valley also had a higher TDS concentration (2,040 mg/L) in late September 2015 (HDR 2015). It had a sulfate concentration of 1,180 mg/L, pH of 7.7, and bicarbonate alkalinity of 108 mg/L. It had relatively high levels of calcium (267 mg/L) and magnesium (167 mg/L). Trace metal concentrations were low, similar to other common spring conditions.

Spring 27-48-34-322A in the Willow Creek area in southwestern Pine Valley had a higher TDS concentration (2,520 mg/L) in late September 2015 (HDR 2015). It had a sulfate concentration of 1,570 mg/L, pH of 7.6, and bicarbonate alkalinity of 135 mg/L. It had relatively high levels of calcium (322 mg/L) and magnesium (235 mg/L). The total aluminum concentration was 32.0 mg/L, and the total recoverable iron concentration was 50.1 mg/L. The total recoverable arsenic concentration was 1.44 mg/L, the highest recorded during the 2015 investigation. Mercury was detected at 0.003 mg/L, and selenium at 0.035 mg/L. Other trace metal concentrations also were elevated above other, more common spring conditions.

In Carico Lake Valley, the field pH at most springs ranged from 6.5 to 8.5. There were a few locations with higher or lower values. The minimum pH value (5.56) was recorded at Site IC-9 in the Iowa Creek sub-basin at the south end of Carico Lake Valley. The maximum pH value (9.46) was recorded in the Upper Hall Creek sub-basin at Site UHC-9 located in the southeastern portion of the Carico Lake Valley (Stantec 2015c). A wide range of specific conductance values were reported; however, they typically were between approximately 200 and 850 µmhos/cm. A wide range of TDS concentrations also were reported; however, most locations were approximately 200 to 700 mg/L. Lower TDS concentrations were 2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-23 measured in the Iowa Creek sub-basin and the headwaters of Hall Creek, with some exceptions. Dissolved oxygen concentrations generally were between 2 and 8 mg/L, with a few higher or lower. Water temperatures ranged from 7 to 22.5ºC; however, reading commonly were between approximately 10ºC and 18ºC (Stantec 2015c).

3.1.3 Groundwater Resources Baseline information for describing the hydrogeologic conditions in the HSA is presented in the Barrick Cortez Four-Basin (Carico Lake Valley, Crescent Valley, Grass Valley, and Pine Valley) Groundwater Flow Model Report (Itasca 2016a). Previous and more recent studies in the region have indicated a wide range of hydraulic properties of bedrock units and characterized the fault controlled and hydraulically isolated nature of the bedrock groundwater system as summarized by Geomega (2006) and Itasca (2016a).

3.1.3.1 Hydrogeologic Setting Recharge, storage, and movement of groundwater is dependent in part on the geologic conditions and the topography of a site. The general stratigraphic and structural framework of the study area is described in Deep South Expansion Project Supplemental Environmental Report – Geology and Minerals (BLM 2019b). For the purposes of characterizing the groundwater conditions in the area, the geologic formations have been grouped into six hydrogeologic units (Itasca 2016a). The physical characteristics of these units are summarized in Table 3-6; their general distribution is shown in Figure 3-5 with accompanying legend on Figure 3-6. These hydrogeologic units include fractured rock (carbonate, siliceous, intrusive, volcanic, and bedrock), and unconsolidated to poorly consolidated sediments (basin fill deposits). In the bedrock units, recharge, storage, flow, and discharge of groundwater primarily are controlled by the secondary features (fractures, faults, and solution cavities) that have enhanced the porosity and permeability of the rock. In the unconsolidated to poorly consolidated sediments, the groundwater is stored and transmitted through interconnected pores within the sediments.

Table 3-6 Summary of Hydrogeologic Units in the Study Area

Geologic Map Estimated Hydrogeologic Units (geologic Thickness Estimated Hydraulic Unit age) (feet) Lithology Properties Alluvium Quaternary 400 to 800 Alluvial fan and flood plain Horizontal hydraulic deposits, eolian sand, conductivity ranges from playa silt and clay, terrace 0.0001 to 430 feet per gravel, colluvium, day, vertical hydraulic landslide deposits. conductivity ranges from 0.007 to 15 feet per day, and specific yield ranges from 0.008 to 0.25. Older Basin Fill Quaternary and 0 to 9,000 Older alluvial sediments. Horizontal hydraulic Tertiary Poorly sorted to well conductivity ranges from sorted gravel, sand, silt, approximately 0.002 to and clay interbedded with 30 feet per day, vertical finer-grained sediments. hydraulic conductivity Partially consolidated at ranges from 0.002 to depth. Includes Tertiary 2 feet per day, and volcanic flows and ash- specific yield ranges from fall-sediments and 0.01 to 0.1. conglomerates in the Pediment area; gravel,

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Table 3-6 Summary of Hydrogeologic Units in the Study Area

Geologic Map Estimated Hydrogeologic Units (geologic Thickness Estimated Hydraulic Unit age) (feet) Lithology Properties stratified tuffaceous silt, and sand in the Horse Canyon area; and, tuffaceous limestone, vitric tuff, siltstone, and sandstone of the Hay Ranch Formation in Pine Valley. Volcanic Rocks Tertiary and 200 to >3,000 Basalt and andesite flows Horizontal hydraulic Jurassic in the in the Cortez Mountains conductivity ranges from Shoshone and Shoshone Range. 0.001 to 30 feet per day; Range Welded tuff, consisting of the upper value of the Up to 8,000 in dacitic ash flows and range corresponds to the Toiyabe volcanic debris with local locally fractured areas. Range quartz porphyry in the Vertical hydraulic 3,500 to Toiyabe Range. conductivity ranges from 10,000 in the Volcaniclastic rock, ash- 0.000004 to 0.6 feet per Cortez flow tuffs, and day. Specific yield ranges Mountains rhyolite/rhyodacite flow in from 0.005 to 0.04, and specific storage ranges the Cortez Mountains and -6 -3 Dry Hills. Ash-flow tuff from 3 x 10 to 1 x 10 flanking the southern part per foot. of Grass Valley in the Toiyabe Range. Andesite and intermediate flows and breccias flanking the southern part of Grass Valley in the Simpson Park Mountains. Interbedded basalt and gravel northeast of Horse Canyon in the southern Cortez Mountains. Intrusive Rocks Tertiary and -- Predominantly Horizontal hydraulic Jurassic granodiorite and quartz conductivity ranges from monzonite. 0.002 to 180 feet per day. The larger conductivity values correspond to locally fractured rock. Specific yield ranges from 0.005 to 0.01, and specific storage ranges from 3 x 10-6 to 1 x 10-3 per foot. Paleozoic Permian to 20,000 Quartzite, chert, siltstone, Hydraulic conductivity Siliceous Rocks Cambrian shale, sandstone, ranges from (Western conglomerate, and approximately 0.001 to Assemblage) argillite. Minor amounts of 100 feet per day. Most greenstone, dolomite, and values are between 0.01 limestone. and 0.5 for unfractured rock.

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Table 3-6 Summary of Hydrogeologic Units in the Study Area

Geologic Map Estimated Hydrogeologic Units (geologic Thickness Estimated Hydraulic Unit age) (feet) Lithology Properties Paleozoic Devonian to 6,000 in Limestone, dolomite, Horizontal hydraulic Carbonate Rocks Cambrian Crescent siltstone, claystone, chert, conductivity ranges from (Eastern Valley quartzite, and shale. 0.0004 to 2,700 feet per Assemblage) 20,000 to day, and vertical hydraulic 30,000 conductivity ranges from elsewhere 0.00005 to 0.5 feet per day. Permeability is mostly secondary due to fracturing and solution widening. Specific yield ranges from 0.003 to 0.05, and specific storage from 1 x 10-7 to 2 x 10-3 per foot.

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Bedrock Units. The Paleozoic carbonate hydrogeologic unit (herein, referred to as the carbonate unit) correlates to the eastern assemblage Paleozoic rocks discussed in Deep South Expansion Project Supplemental Environmental Report – Geology and Minerals (BLM 2019b). Although the carbonate unit consists mostly of carbonate rocks (i.e., limestone and dolomite), it also contains minor amounts of other rock types (i.e., quartzite and shale). The carbonate unit is exposed at the surface in “windows” where the Paleozoic bedrock was up-warped, and the upper plate (western assemblage) rocks were removed by erosion. Two “windows” have been identified in the project boundary (Figure 3-5): the Gold Acre window that encompasses the area that includes the Gold Acres and Pipeline complexes and the Cortez window that encompasses the area that includes the Cortez and Cortez Hills complexes.

The carbonate unit in the Cortez window within the project study area correlates with the carbonate unit encountered beneath the alluvium at the original Pipeline Project in the Gold Acres window. Therefore, it is reasonable to expect similar values of hydraulic properties for this same geologic unit within the two windows. The hydrologic properties of the carbonate unit in the Gold Acres window were evaluated from available aquifer test data and operational dewatering data collected during early stages of the Pipeline Project. Aquifer test data from the Pipeline Project area indicate that the local hydraulic conductivity for the carbonate unit ranges between 25 and 350 feet per day. These relatively high values are interpreted to result from localized secondary permeability associated with extensive fracturing along fault zones (Geomega 2006).

The carbonate aquifer is a regionally extensive hydrogeologic unit in large portions of eastern and central Nevada. Aquifer test results throughout the region indicate that the carbonate aquifer has a wide range of hydraulic conductivity. For example, in the Carlin Trend area located north of Crescent Valley, the hydraulic conductivity and storage coefficient of the carbonate aquifer unit are estimated to range from 0.1 to 150 feet per day and 0.00002 to 0.014, respectively (Maurer et al. 1996). At the Nevada Test Site, the carbonate aquifer has an estimated hydraulic conductivity that ranges from 0.7 to 700 feet per day (Winograd and Thordarson 1975). Harrill and Prudic (1998) and Plume (1996) reported values of hydraulic conductivity for eastern Nevada that range from 0.005 to 900 feet per day.

The siliceous hydrogeologic unit consists of the entire package of rocks included within the western assemblage as described in Deep South Expansion Project Supplemental Environmental Report – Geology and Minerals (BLM 2019b). This hydrogeologic unit is composed of chert, argillite, shale, siltstone, sandstone, conglomerate, and quartzite, with minor amounts of carbonate rocks. Within the project study area, siliceous rocks are exposed in the north Toiyabe Range immediately west of the Cortez window, and in the Cortez Mountains. Elsewhere they are largely covered by Tertiary volcanic rocks and alluvial deposits. Except in windows where these rocks have been removed by uplift and erosion, the siliceous hydrogeologic unit generally overlies the carbonate hydrogeologic unit.

Itasca (2016a) characterized the siliceous rocks as a confining unit that impedes groundwater flow. Other regional studies (Maurer et al. 1996; Stone et al. 1991) suggest that groundwater flow within siliceous bedrock of the mountain ranges is restricted and compartmentalized by geologic structures. Plume (1996) described the hydraulic conductivities of siliceous rocks as low and noted that this material tends to act as barriers to regional groundwater flow except where the permeability of the material has been enhanced along fault and fracture zones.

Rocks comprising the volcanic hydrogeologic unit include a variety of volcanic materials with variable lithologic and hydraulic properties (Itasca 2016a). This unit includes the Caetano Tuff, which crops out over most of the Toiyabe Range and has an estimated total thickness of approximately 8,000 feet (Gilluly and Mazursky 1965). The volcanic rocks typically are

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-31 confining units that impede groundwater flow (Itasca 2016a). Estimates of the hydraulic conductivity of volcanic rocks in Boulder Valley, just north of the Humboldt River, range from 0.01 to 10 feet per day (Maurer et al. 1996). At the Nevada Test Site, measured values of the hydraulic conductivity of volcanic rocks, consisting of lava flows and ash-flow tuffs, range from approximately 1.5 to 17 feet per day (Winograd and Thordarson 1975). Plume (1996) reported that 54 drill stem tests in volcanic rocks in the Railroad and White River Valleys in eastern Nevada produced hydraulic conductivity values that range from 0.000001 to 0.3 feet per day, with a mean value of 0.02 feet per day.

Intrusive rocks are exposed in the central and southern parts of the Cortez Mountains. Intrusive rocks in the southern Cortez Mountains primarily are composed of granodiorite and quartz monzonite (Muffler 1964). Results of aquifer tests in similar granodiorite intrusions near the Post-Betze Mine in Boulder Valley, north of the proposed project, indicate that the hydraulic conductivity of intrusive rocks is approximately 3 to 5 feet per day where the rocks are highly fractured (Maurer et al. 1996). However, where fracturing is less extensive, intrusive rocks generally have very low permeability and impede the movement of groundwater (Plume 1996). Belcher et al. (2001) report horizontal hydraulic conductivities from 0.002 feet per day to 3.3 feet per day for Jurassic- to Oligocene-age granodiorite, quartz monzonite, granite, and tonalite in southern Nevada and parts of California.

Basin Fill Deposits. Older basin fill consists of Tertiary- to Quaternary-age semi-consolidated deposits of conglomerate, sandstone, siltstone, claystone, freshwater limestone, and evaporite, with local interbeds of volcaniclastic rocks. Within the project study area, these deposits underlie younger alluvium throughout the valley floor areas in each of the hydrographic basins. The hydraulic conductivity of these older deposits is reported to range between 0.1 and 10 feet per day (Maurer et al. 1996). The depth of the contact between the younger alluvium and older basin fill deposits units is not well delineated except in the pit areas.

Recent basin fill deposits comprise an important aquifer in the Great Basin. Recent deposits of alluvial fans, landslides, stream floodplains, playas, and terrace deposits comprise the younger alluvium hydrogeologic unit. Based on the results of regional studies, the hydraulic conductivity of recent alluvial deposits is reported to range from 0.5 to approximately 2,000 feet per day, with many values between 3 and 74 feet per day. Specific yield of recent alluvial deposits ranges from approximately 1 percent to 25 percent (Itasca 2016a).

Hydrostructural Units. Groundwater flow pathways are influenced by major faults that offset and displace rock units and older alluvial deposits. Depending on the physical properties of the rocks involved, faulting may create either barriers or conduits for groundwater flow. For example, faulting of softer, less competent rocks typically forms zones of crushed and pulverized rock material that behave as a barrier to groundwater movement. Faulting of hard, competent rocks often creates conduits along the fault trace, resulting in zones of higher groundwater flow and storage capacity along the fault zone compared to the un-faulted surrounding rock.

Important fault zones identified in the project area are identified in Figure 3-5. Major hydrostructural features in the vicinity of the existing Pipeline and Gold Acres complexes include the Pipeline fault and faults that bound the Gold Acres window. The Pipeline fault zone is a northwest trending fracture zone with enhanced permeability. Faults that form the boundary of the Gold Acres window appear to restrict flow based on the contrast in groundwater elevations on either side of the faults (Itasca 2016a).

Major hydrostructural features identified in the vicinity of the Cortez window are the Crescent fault and Cortez fault. The Crescent fault also is a normal fault and major basin and range

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-32 structure that marks the western boundary of the Cortez window. The Cortez fault is a normal fault that dips steeply towards the west and forms the eastern boundary of the Cortez window. Variations in groundwater elevations on either side of the Cortez and Crescent faults suggest that both faults restrict the movement of groundwater across the faults and essentially compartmentalize the groundwater flow system within the Cortez window (Geomega 2006). The Cortez Hills 287 fault is a west-northwest trending fault located in the southern portion of the Cortez window. Pre-dewatering groundwater elevations dropped nearly 1,000 feet from south to north across the fault zone indicating that this structure is a substantial barrier to groundwater flow. Other important structures that also appear to restrict groundwater flow include the Roberts Mountain thrust fault forming the southwest boundary of the Cortez window, and the Oblique fault that intersects both the Roberts Mountain and Cortez Hills 287 faults (BLM 2008).

The Dry Hills fault is located along the east flank of the southern Cortez Mountains in the Pine Valley hydrographic basin. The Dry Hills fault is characterized as a wide (approximately 200 feet wide) fault zone with gouge that restricts groundwater flow. Several other faults and fault- block compartments have been identified in the Horse Canyon area of Pine Valley. Specifically, the Horse Canyon, Meadow, Double Cross, and Blue faults were identified as partial barriers to groundwater flow based on results from a 45-day aquifer pumping test (Itasca 2016a).

3.1.3.2 Groundwater Levels The simulated regional groundwater elevations prior to initiation of mine dewatering in the CGM Operations Area (i.e., prior to April1996) are shown on Figure 3-7. This represents the model simulated groundwater elevations across the HSA based on calibration to pre-mine dewatering groundwater levels at 108 well locations (SRK 2016). The regional flow system generally mimics the topography with steep gradients in the mountains and gentler gradients in the basins. The groundwater elevation contour pattern indicates that groundwater flow in the Crescent Valley and Pine Valley hydrographic basins generally is towards the Humboldt River that defines the northern boundary of the basins. Groundwater flow in the Carico Lake and Grass Valley hydrographic basins in the southern portion of the HSA is from the mountain blocks toward the central portion of the valleys.

The groundwater elevations for December 2015 represent the existing or baseline conditions for this EIS. The model simulated aggregate drawdown and mounding resulting from mine dewatering and re-infiltration activities that occurred between April 1996 and December 2015 are shown on Figure 3-8. The model simulation is based on transient calibration to observed groundwater levels in 182 monitoring wells within the HSA (SRK 2016). As shown on Figure 3-8, as of December 2015, drawdown associated with mine dewatering activities in the Pipeline Complex generally were restricted to areas in the southern Crescent Valley HA. Drawdown associated with dewatering activities in the Cortez/Cortez Hills complexes extends across an area in the southeast Crescent Valley HA, northern part of the Grass Valley HA, and in the Horse Canyon area of the western Pine Valley HA. Re-infiltration of mine water through the existing RIBs also has resulted in rising groundwater levels (i.e., mounding) in the basin fill aquifer in three areas in southern Crescent Valley (Figure 3-8).

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3.1.3.3 Aquifer Recharge and Discharge Inflow and outflow from the groundwater system were estimated by SRK (2016) to establish a baseline water balance for the HSA. The estimated average annual groundwater budget based on the simulated conditions in 2015 is presented in Table 3-7. Existing groundwater inflow components include precipitation recharge, infiltration of excess mine water at RIBs, and surface and subsurface inflow from adjacent areas outside the HSA. Groundwater outflow components include evapotranspiration from phreatophyte and playa areas, groundwater pumping for non-mining uses and for existing mine dewatering operations, discharge at springs and streams, and subsurface outflow to adjacent areas outside the HSA. A large percentage of the groundwater withdrawn for mine dewatering is re-infiltrated into the basin fill aquifer.

Table 3-7 Estimated Annual Groundwater Budget for the HSA (2015)4

Crescent, Carico Lake, Grass and Pine Valleys Groundwater System1,2 Budget Component (acre-feet per year) Groundwater Inflow Precipitation Recharge 71,300 Infiltration Recharge (RIBs) 26,100 Surface and Subsurface Inflow3 16,000 Total Inflow 113,400 Groundwater Outflow Evapotranspiration 55,500 Groundwater Pumping Non-mining 7,600 Mine Dewatering 27,500 Discharge to Surface Waters (springs and streams) 13,100 Subsurface Outflow3 14,400 Total Outflow 118,100 Net Results Inflow Minus Outflow -4,700 Storage Depletion (simulated by model) -4,500 1 Estimation based on results from the calibrated numerical groundwater model developed for the project. 2 Estimates provided in the source document were rounded to the nearest hundred for presentation in this EIS. 3 Values represent a summation of the inflows and outflows for each of the four basins included within the study area. As such, these summation values include both inter-basin flow between the four basins within the study area, and flow across the model boundary to basins located outside of the model area. 4 The flow rates for the groundwater inflow and outflow components provided in this table are based on a summation of the rates provided for each of the four basins included within the groundwater model. A detailed breakdown of the estimated groundwater inflow and outflow rates for each of the four basins within the study area is provided in a series of water balance tables for representative years provided in the referenced model report. Source: SRK 2016.

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The water balance values provided in Table 3-7 are based on the results of the groundwater model simulations developed based on available regional information (Itasca 2016a; SRK 2016). There is uncertainty regarding the actual flow rates, particularly the amount of recharge, evapotranspiration, and groundwater inflow and outflow that occurs at the boundaries of the HSA. These groundwater model simulation estimates indicate that the overall groundwater balance for the HSA is experiencing approximately 4 percent more outflow than inflow.

3.1.3.4 Groundwater Quality Waters of the State of Nevada are defined in NRS 445A.415 and include, but are not limited to: 1) all streams, lakes, ponds, impounding reservoirs, marshes, water courses, waterways, wells, springs, irrigation systems, and drainage systems; and 2) all bodies of accumulations of water, surface and underground, natural or artificial.

Water quality standards for state waters have been established by the State of Nevada under NAC. NAC 445A.453 establishes primary water quality standards, and NAC 445A.455 establishes secondary standards for water quality. General Nevada water quality standards are summarized in Table 3-5. Primary standards are based on the potential use of groundwater for drinking water and are established to protect human health; the secondary standards are for aesthetic qualities. These standards also are referred to as MCLs. Groundwater downgradient of the project has the potential to be used for drinking water, and therefore, Nevada drinking water standards would apply to mine-related activities that affect groundwater (NAC 445A.424). The NDEP BMRR has established reference values for use in compliance monitoring of groundwater quality downgradient of the mine facilities. The NDEP BMRR reference values are derived from (and equivalent to) the Nevada primary and secondary MCLs for drinking water as listed in Table 3-5.

Groundwater quality is monitored on a quarterly basis in an extensive network of monitoring wells and dewatering wells in the CGM Operations Area. The locations of wells used for water quality sampling are shown in Figures 3-9 and 3-10. The monitoring results are provided in quarterly reports, submitted as required under BCI’s Intergraded Monitoring Plan, and Quarterly Water Pollution Control Monitoring Reports. The monitoring results for the 4th quarter 2016 monitoring are provided in BCI (2017a). The results of groundwater monitoring for the 2011 through 2015 period are compiled in Appendix D of the Water Pollution Permit NEV00931019 Renewal Application (BCI 2016a). The general baseline groundwater quality for bedrock and basin fill aquifers located in Crescent Valley and Grass Valley adjacent to and downgradient from the mine complexes, and in the vicinity of the RIBs, were provided in the Cortez Hills Expansion Project Final EIS (BLM 2008).

A summary of the water quality in the vicinity of the open pit and underground mine areas that required dewatering is provided in Table 3-8. The background groundwater quality in the vicinity of the Pipeline Pit Complex is based on sampling through 2015 at nine wells located in the pit vicinity as reported by Geomega (2016b). The average chemistry for these wells indicates that the groundwater has a circum-neutral pH with abundant alkalinity (231 mg/L) and TDS concentration of 595 mg/L. All constituent concentrations were below their respective NDEP Profile II reference values with the exception of arsenic and manganese, which appear to be naturally elevated in this area.

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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

Cortez Hills NDEP Profile II Pipeline Cortez Pit Cortez Hills Underground Constituent Reference Complex Area Area Complex Area Mining Area (mg/L)1 Value2 (Average) (Average) (Average) (Average) pH (standard unit) 6.5-8.5 7.7 8.3 8.4 8.3 Total dissolved solids 1,000 594 415 299 323 Alkalinity (total) -- 231 180 149.5 190 Bicarbonate -- 272 218 175.2 225 Aluminum 0.2 0.01 0.01 0.01 0.016 Antimony 0.006 0.002 0.003 0.0015 0.014 Arsenic 0.01 0.013 0.03 0.016 0.08 Barium 2 0.05 0.05 0.075 0.11 Beryllium 0.004 0.001 0.001 0.001 0.001 Cadmium 0.005 0.001 0.001 0.001 0.001 Chloride 400 76 34 34.1 18 Chromium 0.1 0.005 0.005 0.005 0.005 Copper 1 0.005 0.005 0.005 0.005 Fluoride 4 2.2 1.2 0.26 0.85 Iron 0.6 3.0 0.01 0.037 0.25 Lead 0.015 0.001 0.001 0.001 0.03 Magnesium 150 21 16 21.4 17 Manganese 0.1 0.54 0.005 0.0055 0.015 Mercury 0.002 0.0005 0.0005 0.0005 0.0005 Molybdenum -- 0.01125 0.005 0.005 0.07 Nickel 0.1 0.005 0.005 0.005 0.005 Nitrate (as N) 10 2.7 1.6 1.035 0.07 Selenium 0.05 0.0025 0.0025 0.0025 0.0025 Silver 0.1 0.005 0.005 0.005 0.005 Sulfate 500 86.8 89 30.6 52 Thallium 0.002 0.0005 0.0005 0.0005 0.0005 Zinc 5 0.006 0.005 0.005 0.005 1 All values reported in mg/L except pH which is reported in standard units. 2 The NDEP reference values are used by the state for compliance monitoring and are based on the Nevada Primary and Secondary MCL’s for drinking water listed in Table 3-5. Note: Exceedances of NDEP Profile II reference values are highlighted. Source: Geomega 2016b,c.

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The background groundwater quality in the vicinity of the Cortez Pit was estimated using the average water quality from two wells located in the vicinity as reported by Geomega (2016b). The average chemistry of the groundwater is characterized as slightly alkaline (180 mg/L alkalinity), with a pH of 8.3 and a TDS of 415 mg/L. As shown in Table 3-8, all constituent concentrations were below the NDEP Profile II reference values except for arsenic that is naturally elevated in this region.

The background groundwater quality in the vicinity of the Cortez Hills Pit was estimated using the average groundwater quality from 10 wells located in the vicinity of the pit as reported by Geomega (2016c). The average chemistry of the groundwater is characterized as slightly alkaline (150 mg/L alkalinity), with a pH of 8.4 and a TDS of 299 mg/L. As shown in Table 3-8, all constituent concentrations were below the NDEP Profile II reference values except for arsenic.

In the vicinity of the Cortez Hills underground workings, the background groundwater quality was estimated using the average water quality from three wells as reported by Geomega (2016c). The average chemistry of the groundwater is characterized as slightly alkaline (190 mg/L alkalinity), with a pH of 8.3 water and a TDS of 323 mg/L. As shown in Table 3-8, all constituents concentrations were below the NDEP Profile II reference values except for arsenic, antimony, and lead, which are naturally elevated in this region (Geomega 2016c).

3.1.4 Waste Rock Characterization Mining operations bring mineralized rocks from depth, where they are stable, to the surface, where they react with air and water and potentially release metals and other solutes. Sulfide minerals, in particular, undergo oxidation reactions, resulting in acid sulfate and metal-bearing solutions commonly referred to as acid rock drainage. Acid generated by sulfide mineral oxidation and associated metals releases from waste rock can affect water quality. The potential of mined rock to affect contact water within the proposed project area was assessed by conducting standard geochemical tests on representative samples to evaluate both the acid rock drainage and metal leaching risk.

Extensive rock geochemical characterization sampling and analysis have been conducted to support the original and subsequent modifications to the water pollution control permit applications and NEPA analyses over the past two decades for mine operations in the CGM Operations Area. An earlier rock characterization study by Geomega (2007) (Cortez Hills Expansion Project Waste Rock Assessment) provides a comprehensive review of the available data at that time for the mine site. The Deep South Expansion Project, Waste Rock Management Plan (WRMP) (Geomega 2016d) presents updated characterization results that are specific to the proposed mine expansions included in the Proposed Action. Samples for geochemical testing were selected using a geochemical model of the site developed to represent the range in waste rock geology and geochemistry to be encountered across the proposed mine expansion areas. The updated WRMP includes samples distributed laterally and vertically across the proposed mine expansion areas in the Gold Acres, Pipeline, Cortez, and Cortez Hills complexes (Geomega 2016d).

A series of standard geochemical tests have been conducted on samples of waste rock material from the study area over the past two decades. These tests included multi-element analyses (i.e., whole-rock chemical analyses), acid-base accounting (ABA), meteoric water mobility procedures, and humidity cell tests (HCTs) and other column tests. Whole-rock chemical analyses measure the concentrations of constituents in the rocks and indicate potential sources of constituents of concern. ABA tests indicate whether waste rock is a likely net producer or consumer of acid that is generated by sulfide oxidation. The meteoric water

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-42 mobility procedures and HCT (and other column tests) are short-term and long-term tests, respectively, that are designed to evaluate constituent concentrations in leachate generated by water-rock interactions.

ABA testing is a widely used screening tool for distinguishing rocks with the potential to generate acid by reacting with air and water from rocks that have the potential to consume acid. Acid-base accounting is based on determinations of the acid-generating potential (AGP), which is a function of the amount of sulfide minerals in a rock, and the acid-neutralization potential (ANP), which is a function of the amount of carbonate minerals in a rock. The AGP and ANP are determined in static tests and expressed in terms of kilograms calcium carbonate per ton of rock (kg CaCO3/t).

The ratio of ANP to AGP (i.e., ANP/AGP) (also known as the neutralization potential ratio [NPR]) is commonly used to evaluate the acid generation potential of the material. If the NPR is 1 or less, the material is more likely to generate acid; if the ratio is 3 or greater, the material is unlikely to generate acid (USEPA 1994). NDEP-BMMR (2014) uses a NPR of less than 1.2 to define potential acid generating material that requires further evaluation using kinetic testing (i.e., HCT).

Another method to classify acid generating potential of rocks uses the net neutralization potential (NNP), which is the difference between the ANP and the AGP. Using this method, materials with NNP values greater than 20 kg CaCO3/t are considered non-acid generating, those with NNP values less than -20 kg CaCO3/t are considered acid generating, and materials with NNP values between +20 and -20 kg CaCO3/t are considered uncertain. To deal with the uncertainties of the static test, the BLM has required HCTs for any material where the NNP does not exceed +20 kg CaCO3/t and/or the NPR is 3 or less (BLM 2008).

The ABA database used to evaluate the waste rock that would be mined under the Proposed Action 2016 WRMP is summarized in Table 3-9. The database consists of 1,815 ABA analyses that indicate that most of the waste rock material is acid neutralizing. Geomega’s (2016d) evaluation included in the WRMP includes the following conclusion: “Comparing the ANP/AGP distribution in the proto-ABA models demonstrate that the waste rock from the Deep South Expansion is expected to be overwhelmingly neutralizing.”

The overall composition of the waste rock material from the Cortez Pit and Cortez Hills Pit (Pediment east and west extensions) are projected to have hundreds of times more ANP than AGP; while the waste rock material from the Cortez Hills underground mine expansion and Pipeline Pit Complex modifications are projected to have three orders of magnitude ANP than AGP. The waste rock generated from the Gold Acres Pit expansion and satellite pits is projected to generate the least neutralizing waste rock from the CGM Operations Area. The 110 ABA tests for the Gold Acres Complex indicate that the waste rock would be neutralizing with the ANP/AGP ratio distribution centered in the 2 to 20 range. Waste rock from this area would include skarn material that generally contains a higher percentage of sulfide mineralization than other waste rock materials on site. However, the higher sulfur values are offset by the substantial quantities of carbonate materials. Of the approximate 90 million tons of waste rock to be generated from the Gold Acres Complex, approximately 9 million tons (or 10 percent) of the material would have an ANP/AGP ratio of less than 1.2 (Geomega 2016d).

A total of 108 HCT have been completed for nine geologic units collected from within or near the mining areas at Gold Acres Complex (16 HCTs), Pipeline Complex (30 HCTs), Cortez Complex (17 HCTs), Cortez Hills Complex (open pit) (11 HCTs), and Cortez Hills Complex (underground expansion area) (34 HCTs) (Table 3-10). These kinetic tests include 75 new HCTs selected to supplement the existing dataset for characterizing the mining scenario

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-43 included under the Proposed Action. Of the 108 HCTs run beyond 20 weeks, four generated acid (one from the Gold Acres Complex [GAD-010] and three from the Cortez Hills Complex underground expansion area [CHUE-252_594-609; CHUE-282_563-583; DC-261_2230-2249]) (Geomega 2016d).

Table 3-9 Summary of Acid-base Accounting Results

NNP < 20 kg CaCO3/t; ANP/AGP or, < 1.21 ANP/AGP < 3 Total Number of Percent of Number of Percent of Mining Area Samples Samples Samples Samples Samples Open Pits Gold Acres Complex 110 3 2.7 27 24.5 Pipeline Complex 842 2 0.2 17 2.0 Cortez Complex (Cortez Pit) 21 0 0 2 9.5 Cortez Hills Complex 613 3 0.5 28 4.5 Underground Mine Cortez Hills Complex3 229 3 1.3 17 7.4 Total (or average) 229 3 (0.6) 17 (5.0) 1 NDEP-BMMR (2014) threshold for identifying acid generation potential that requires kinetic testing. 2 BLM (2008) criteria for identifying acid generation potential requiring kinetic testing to further evaluate AGP. 3 Proposed Deep South underground expansion area. Note: < = less than or equal to. Source: Geomega 2016d.

Table 3-10 Summary of Humidity Cell Tests

Samples Generating Mining Area New Samples1 Total Samples2 Acidic Leachate (pH<6) Open Pits Gold Acres Complex 16 16 1 Pipeline Complex 6 30 0 Cortez Complex (Cortez Pit) 17 17 0 Cortez Hills Complex 2 11 0 Underground Mine Cortez Hills Complex3 34 34 3 Total (or average) 75 34 4 1 Additional “new” samples collected specifically for development of the Proposed Action under the 2016 WRMP. 2 Total samples include combined historic samples and new samples that are representative of the waste rock materials to be generated during mining under the Proposed Action. 3 Proposed Deep South underground expansion area. Note: < = less than. Source: Geomega 2016d.

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The one sample from the Gold Acres Complex that generated acid (pH 4) was a high sulfide grab sample of upper skarn rock that represents the most mineralized material that would be encountered in the Gold Acres Complex. This sample produced initial leachate with elevated sulfate, aluminum, arsenic, copper, cobalt, cadmium, iron, manganese, and zinc (Geomega 2016d). The three samples from the Cortez Hills Complex underground expansion area that generated acid had low pHs that ranged between 2.5 to 3.8, and one or more of the samples produced leachate and had elevated arsenic, antimony, iron, and manganese levels (Geomega 2017a). Additional details regarding available waste rock geochemical data are provided in the WRMP (Geomega 2016d).

3.1.5 Water Rights An inventory of active water rights in the region surrounding the proposed project was used to identify the location and status of water rights within potentially affected areas. The inventory was based on water rights records on file with the NDWR (BCI 2018, 2017b; NDWR 2018). The inventory identified all active water rights located within and near the area potentially affected by groundwater drawdown in the HSA. For the purpose of the EIS analysis, all water rights owned by BCI were excluded from this summary. The locations of the points of diversion for these water rights are shown in Figure 3-11; the owners, beneficial use, and annual duty (acre-feet per year) for each water right are summarized in Table 3-11. Based on the NDWR database, there are a total of 22 active water rights in the inventoried area, which includes 5 surface water rights and 16 groundwater rights. The primary uses for water in the area are stock watering, irrigation, and mining and milling. Since water rights are not necessary for most domestic wells, this summary may not include all wells that exist within the inventoried area. No federally reserved water rights or Public Water Reserves were identified in the NDWR water rights database within the potentially affected areas (Resource Concepts Inc. 2018).

The State of Nevada started regulating water use through the enactment of the surface water code in March 1, 1905. Provisions related to artesian groundwater sources and percolating groundwater were passed March 22, 1913, and March 25, 1939, respectively. Water rights established prior to those dates are known as “vested water rights.” Any claimant of a vested water right is required to provide proof that the claimed water use began prior to the relevant water code date and that the use has been continuous. Historically, there were no deadlines to file a proof of appropriation to claim a vested water right unless the State Engineer initiated the process for adjudicating water rights for a specific stream or groundwater basin. However, recent changes to the state statutes now require that proof of any vested water right claim be filed by December 31, 2027 (NRS 533.087). The list of water rights provided in Table 3-11 does not include any vested water rights that have not yet been filed with the State Engineer.

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Table 3-11 Private Active Water Rights

Basin Map ID Basin No. Application Status Source Type of Use Priority Date Duty (AFY) Owner of Record Pine Valley 11 53 5100 Certificate Spring Irrigation 6/10/2018 - Isaac, Morris Crescent Valley 19 54 7095 Certificate Stream Irrigation 4/23/2024 - Dann, Mary Crescent Valley 20 54 6800 Certificate Stream Irrigation 10/19/2022 231 Dann, Mary Crescent Valley 17 54 31854 Certificate Groundwater Stock Watering 5/31/1977 4.48 Dann, Mary Crescent Valley 18 54 31855 Certificate Groundwater Irrigation 5/31/1977 1520 Dann, Mary Crescent Valley 16 54 18998 Certificate Groundwater Irrigation 7/11/1960 468.4 Dann, Mary Crescent Valley 21 54 15835 Certificate Spring Stock Watering 10/27/1954 2.36 Dewey Dann Crescent Valley 13 54 13343 Certificate Groundwater Mining-milling 3/29/1950 144.8 Little Gem Mining Company Crescent Valley 14 54 10071 Certificate Groundwater Mining-milling 11/11/1937 723.97 Mill Gulch Placer Mining Company Crescent Valley 12 54 V09040 Vested Stream Irrigation - - Wintle, Jay and Grace Crescent Valley 15 54 80138 Permit Groundwater Irrigation 2/9/1960 499.74 Zeda, Inc.; leased to Cortez Joint Venture Carico Lake 7 55 26872 Certificate Groundwater Mining-milling 8/7/1972 176.77 M-I LLC Valley Carico Lake 8 55 29694 Certificate Groundwater Mining-milling 10/8/1975 1074.11 M-I LLC Valley Carico Lake 10 55 35814 Certificate Groundwater Mining-milling 8/24/1978 1074.12 M-I LLC Valley Carico Lake 2 55 64260 Certificate Groundwater Mining-milling 4/14/1977 4.9 M-I LLC Valley Carico Lake 9 55 64261 Certificate Groundwater Mining-milling 8/24/1978 26.97 M-I LLC Valley Carico Lake 3 55 79547 Certificate Groundwater Mining-milling 8/24/1978 26.83 M-I LLC Valley

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Table 3-11 Private Active Water Rights

Basin Map ID Basin No. Application Status Source Type of Use Priority Date Duty (AFY) Owner of Record Carico Lake 4 55 80789 Certificate Groundwater Mining-milling 10/8/1975 200 M-I LLC Valley Carico Lake 1 55 81822 Abrogated by Groundwater Mining-milling 10/8/1975 200 M-I LLC Valley Permit 85868 Carico Lake 5 55 85868 Permit Groundwater Mining-milling 10/8/1975 200 M-I LLC Valley Carico Lake 6 55 17654 Certificate Groundwater Domestic 9/8/1958 2 Magnet Cove Valley Barium Corporation AFY = acre-feet per year. Sources: BCI 2018, 2017b; NDWR 2018.

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3.2 Environmental Consequences The primary issues related to water resources include: 1) reduction in surface and groundwater quantity for current users and water-dependent resources from pit dewatering and production well withdrawal; 2) impacts to groundwater and surface water quality from the construction, operation, and closure of waste rock facilities and underground mining operations; 3) impacts related to the water quality of the post-mining pit lakes; and 4) impacts from flooding, erosion, and sedimentation associated with mine construction, operation, or closure activities.

Impacts to water resources would be significant if the Proposed Action or other action alternatives result in the following:

Surface Water  Measurable reduction in the baseflow of perennial streams or perennial spring flows.  Degradation of the quality of surface water based on applicable state or federal regulations for designated or appropriate beneficial uses, including, but not limited to, municipal or domestic water supply; irrigation; livestock watering; or support of terrestrial, avian, and aquatic life.  Alteration of drainage patterns or channel geometry resulting in accelerated erosion and sedimentation.  Measurable reduction of seasonal surface flows caused by withdrawal of contributing watershed area or by channel blockages, if important for biological resources.  Damage to project facilities and on-site and off-site resources during operation or post- closure as a result of inadequate drainage control features. Groundwater  Reduction of static groundwater levels that could adversely affect water supply, agricultural, or industrial wells caused by project pumping, including dewatering, and post-mining pit lake development.  Degradation of groundwater quality downgradient from the project facilities such that one or more water quality constituents would exceed applicable Nevada or federal primary or Nevada secondary MCLs established to protect human health from potentially toxic or undesirable substances in drinking water, or where the quality of the groundwater already exceeds the MCLs for drinking water, the quality would be lowered such that it would render those waters unsuitable for other existing or potential beneficial use.

Potential impacts associated with dewatering-induced ground subsidence and earth fissure development are addressed in the Deep South Expansion Project Supplemental Environmental Report for Geology and Minerals (BLM 2019b). Other potential impacts to wetlands and riparian areas are discussed in the Deep South Expansion Project Supplemental Environmental Report for Vegetation (BLM 2019a). Potential impacts resulting from the transportation, storage, and use of hazardous substances are addressed in the Deep South Expansion Project Supplemental Environmental Report for Hazardous Materials and Solid Waste (BLM 2019c). Potential effects to Native American uses of streams and springs are addressed in the Deep South Expansion Project Supplemental Environmental Report for Native American Traditional Values (BLM 2019d).

The water resources and geochemistry analysis uses the following qualifiers to describe potential effects in terms of intensity, duration, and context:

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Intensity  Negligible: Effects to water resources could occur; however, they would be so slight as to not be measurable or distinguishable from natural fluctuations.  Minor: Effects to water resources would occur; however, they would be small and just measurable using normal methods. Effects would be unlikely to affect beneficial uses of the receiving water.  Moderate: Effects to water resources would occur, would be readily detectable, and could affect the beneficial uses of the surface water or groundwater resources.  Major: Effects to water resources would be large, measurable, and easily detected. They substantially would change beneficial uses of surface water or groundwater resources or the hydrologic regime over the area.

Duration  Short-term: 1 year or less.  Long-term: Greater than 1 year.

Context  Localized: Effects would occur at specific site(s), or within the project study area.  Regional: Effects would extend beyond the project study area.

3.2.1 Evaluation Methodology This section provides a summary of the methods used to evaluate: 1) changes in groundwater elevations (drawdown and mounding), 2) post-mining pit lake development, and 3) pit lake water quality.

3.2.1.1 Numerical Flow Modeling A calibrated three-dimensional numerical groundwater flow model was developed to estimate effects to groundwater and surface water resources from the Proposed Action and No Action Alternative, as well as the cumulative effects of historic dewatering and projected future dewatering and water management activities for this EIS. Specifically, the numerical model was used to evaluate or estimate: 1) mine dewatering rates required throughout the mine life; 2) areal extent, magnitude, and timing of drawdown and recovery of groundwater levels through the mining and post-mining periods; 3) development of post-mining pit lakes including groundwater inflow and outflow rates through the pits, and final surface water elevations of the pit lakes; 4) potential changes in the water balance in the Crescent Valley, Carico Lake Valley, Grass Valley, and Pine Valley hydrographic areas; and 5) potential changes in flow in the Humboldt River, Pine Creek, and Horse Creek, and selected regional springs.

The groundwater flow model for the proposed project, referred to as the “Four-Basin Model” (Itasca 2016a), represents an expansion of the previous model developed to simulate the dewatering and water management activities in the CGM Operations Area that have evolved since 1996. Earlier versions of the groundwater model for the Crescent Valley region were calibrated to evaluate potential effects to groundwater and surface water resources associated with mine dewatering and water management activities for the original Pipeline Pit (BLM 1996) and subsequent South Pipeline and Pipeline/South Pipeline Pit expansions (BLM 2004, 2000). This model was later expanded to include adjacent area of Grass Valley and Pine Valley to simulate the dewatering and water management activities associated with the Cortez Hills Expansion Project (BLM 2008; Geomega 2007). In addition, the groundwater model has been

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-50 updated and recalibrated on an annual basis since 1998 in accordance with BLM requirements for the existing project (Itasca 2016b).

The Four-Basin Model (Itasca 2016a) expands the previously modeled area to encompass the entirety of the Crescent Valley, Carico Lake Valley, Grass Valley, and Pine Valley hydrographic areas. It also incorporates updated data in the CGM Operations Area, northern portion of Grass Valley, and Horse Canyon area of western Pine Valley. Itasca (2016a) developed the Four-Basin Model using an enhanced version of the USGS groundwater flow program MODFLOW (McDonald and Harbaugh 1988) known as MODFLOW SURFACT (HydrogeoLogic 2011). MODFLOW-SURFACT contains many improvements over MODFLOW, including enhanced simulation capabilities for handling complex field conditions (including simulating large groundwater elevation fluctuations resulting in drying and wetting of grid cells). MODFLOW originally was designed to simulate flow through porous media. MODFLOW models have been used to simulate groundwater flow in bedrock aquifers where flow through the bedrock system is controlled by interconnected fracture networks that behave similarly to porous media flow.

The groundwater model domain encompasses the entire HSA shown in Figure 3-1. The numerical groundwater model consists of 28 horizontal layers to simulate the vertical range extending from above 10,000 feet amsl to 7,050 feet below mean sea level. In order to provide more detailed flow information in the project area, the grid cell dimensions vary horizontally from 10,000 feet by 10,000 feet at the outer margins of the model to 400 feet by 400 feet in the mine area. The more detailed discrete grid cells in the mining area allow the model to more accurately match observed hydrologic features (such as fault zones and steep hydraulic gradients, well locations, mine pit geometry, and groundwater levels) in the project vicinity.

The model was calibrated to measured groundwater elevations and estimated flow data for the Humboldt River, Pine Creek, and Horse Creek, as well as a set of reference springs included in the model. The model was calibrated to both steady-state (pre-mine dewatering) and transient (mining) conditions through 2014 (Itasca 2016a). The model subsequently was updated and re-calibrated by SRK using data through 2015 to simulate mining and post-mining conditions resulting from the dewatering and water management activities included in the Proposed Action and No Action Alternative, and cumulative scenario (SRK 2017, 2016). Details regarding the conceptual hydrogeologic model, modeling approach and setup, steady-state and transient calibrations, and simulations are presented in the groundwater model reports (Itasca 2016a; SRK 2017, 2016).

3.2.1.2 Pit Dewatering and Water Management Activities Historic dewatering and projected future dewatering requirements under the No Action Alternative, Proposed Action, and cumulative scenario are summarized in Table 3-12 and shown in Figure 3-12. Historic and projected future infiltration requirements under the No Action Alternative, Proposed Action, and cumulative scenario are summarized in Table 3-13. Active dewatering was initiated in 1996 and has continued uninterrupted through the present (end of 2016). The average annualized pumping rates for the CGM Operations Area has ranged from 3,700 to 25,067 gpm from 1996 through 2016.

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Table 3-12 Summary of Historic and Model Simulated Future Dewatering Requirements

Incremental Change In 1 6 Actual Model Simulated Dewatering Rates Pumping (from No Action) Historic No Action Proposed Cumulative Proposed Calendar Dewatering1,3 Alternative3 Action4 Scenario5 Action Cumulative Year2 (gpm) (gpm) (gpm) (gpm) (gpm) (gpm) 1996 3,700 * * * 1997 15,776 * * * 1998 21,011 * * * 1999 21,640 * * * 2000 20,558 * * * 2001 19,111 * * * 2002 18,643 * * * 2003 18,883 * * * 2004 22,081 * * * 2005 21,433 * * * 2006 22,236 * * * 2007 23,394 * * * 2008 22,123 * * * 2009 25,067 * * * 2010 22,144 * * * 2011 24,638 * * * 2012 21,838 * * * 2013 21,707 * * * 2014 21,034 * * * 2015 18,882 22,300 18,900 18,900 -3,400 -3,400 2016 21,994 19,300 21,300 21,300 2,000 2,000 2017 18,300 22,300 22,300 4,000 4,000 2018 23,800 26,400 26,400 2,600 2,600 2019 25,800 29,100 29,100 3,300 3,300 2020 26,600 31,600 31,600 5,000 5,000 2021 22,000 32,700 33,700 10,700 11,700 2022 20,400 32,300 33,400 11,900 13,000 2023 23,600 29,600 31,000 6,000 7,400 2024 27,100 28,400 27,100 28,400 2025 8,100 9,200 8,100 9,200 2026 9,000 10,500 9,000 10,500 2027 8,900 10,300 8,900 10,300 2028 8,900 10,200 8,900 10,200 2029 9,000 10,100 9,000 10,100 2030 9,100 17,900 9,100 17,900

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Table 3-12 Summary of Historic and Model Simulated Future Dewatering Requirements

Incremental Change In 1 6 Actual Model Simulated Dewatering Rates Pumping (from No Action) Historic No Action Proposed Cumulative Proposed Calendar Dewatering1,3 Alternative3 Action4 Scenario5 Action Cumulative Year2 (gpm) (gpm) (gpm) (gpm) (gpm) (gpm) 2031 9,100 15,100 9,100 15,100 2032 9,200 13,700 9,200 13,700 2033 3,700 3,700 2034 3,200 3,200 2035 2,700 2,700 2036 2,600 2,600 2037 2,500 2,500 2038 2,500 2,500 2039 2,400 2,400 2040 2,300 2,300 2041 2,300 2,300 2042 2,200 2,200 2043 2,200 2,200 1 Average annual flow rate. Model simulated rates were rounded to the nearest 100 gpm. 2 Calendar years used for numerical groundwater flow model simulations; actual startup dates for the Proposed Action would depend on BLM and NDEP authorizations. 3 Historic dewatering rates for 1996-2013; and No Action Alternative dewatering rates are based on estimates provided in Itasca (2016a) (Table 6-3); historic dewatering rates for 2014-2016 based on data provided in Integrated Monitoring Plan reports (BCI 2017c). 4 Estimated total future dewatering rates under the Proposed Action are based on model simulations provided in SRK (2016) (Appendix B). 5 Estimated total future cumulative dewatering rates are based model simulations that include the dewatering for both the Proposed Action and Goldrush Project (RFFA) provided in SRK 2017 (Appendix B). 6 Incremental increase in pumping required as compared to the No Action Alternative (currently authorized mining). * Historic dewatering rates for the 1996-2014 period included in each model simulation. Sources: BCI 2017c; Itasca 2016a; SRK 2017, 2016.

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Table 3-13 Summary of Historic and Estimated Future infiltration Requirements

Incremental Change In Infiltration Model Simulated infiltration Rates1 (from No Action)7 Historic No Action Proposed Cumulative Proposed Calendar Infiltration1,3 Alternative4 Action5 Scenario5 Action Cumulative Year2 (gpm) (gpm) (gpm) (gpm) (gpm) (gpm) 1996 4,026 * * * 1997 13,640 * * * 1998 20,585 * * * 1999 20,123 * * * 2000 19,661 * * * 2001 17,602 * * * 2002 15,835 * * * 2003 13,326 * * * 2004 16,155 * * * 2005 16,976 * * * 2006 17,070 * * * 2007 16,850 * * * 2008 15,189 * * * 2009 18,686 * * * 2010 15,893 * * * 2011 18,424 * * * 2012 15,426 * * * 2013 15,378 * * * 2014 14,492 * * * 2015 12,663 15,100 12,700 12,700 -2,400 -2,400 2016 15,776 12,100 15,300 15,300 3,200 3,200 2017 18,417 11,100 16,100 16,100 5,000 5,000 2018 16,600 20,400 20,400 3,800 3,800 2019 18,600 23,100 23,100 4,500 4,500 2020 19,400 25,700 25,700 6,300 6,300 2021 14,800 27,400 28,300 12,600 13,500 2022 13,200 27,000 27,000 13,800 13,800 2023 16,400 24,300 24,700 7,900 8,300 2024 21,800 22,100 21,800 22,100 2025 4,600 4,700 4,600 4,700 2026 4,800 5,300 4,800 5,300 2027 4,700 5,200 4,700 5,200 2028 4,700 5,000 4,700 5,000 2029 4,600 4,700 4,600 4,700 2030 4,800 12,600 4,800 12,600

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Table 3-13 Summary of Historic and Estimated Future infiltration Requirements

Incremental Change In Infiltration Model Simulated infiltration Rates1 (from No Action)7 Historic No Action Proposed Cumulative Proposed Calendar Infiltration1,3 Alternative4 Action5 Scenario5 Action Cumulative Year2 (gpm) (gpm) (gpm) (gpm) (gpm) (gpm) 2031 4,900 9,800 4,900 9,800 2032 4,900 8,400 4,900 8,400 2033 2,600 2,600 2034 2,200 2,200 2035 1,700 1,700 2036 1,600 1,600 2037 1,500 1,500 2038 1,400 1,400 2039 1,400 1,400 2040 1,300 1,300 2041 1,200 1,200 2042 1,200 1,200 2043 1,100 1,100 1 Average annual flow rate. Model simulated rates were rounded to the nearest 100 gpm. 2 Calendar years used for numerical groundwater flow model simulations; actual startup dates for the Proposed Action would depend on BLM and NDEP authorizations. 3 Historic infiltration rates for 1996-2006 based on BLM (2008) (Table 3.2-10); 2011-2016 based on data provided in Integrated Monitoring Plan reports (BCI 2017c). 4 No Action Alternative infiltration rates are based on Itasca 2016a (Table 6-3). 5 Total future infiltration rates under the Proposed Action based model simulations provided in SRK 2016 (Appendix B). 6 Total future infiltration rates based on the cumulative model simulations that include future infiltration requirements under both the Proposed Action and Goldrush Project (RFFA) provided in SRK 2017 (Appendix B). 7 Incremental change in estimated infiltration required as compared to the No Action Alternative (currently authorized mining activities). * Historic infiltration rates for the 1996-2014 period included in each model simulation. Sources: BCI 2017c; Itasca 2016a; SRK 2017, 2016.

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Under the currently permitted activities included in the No Action Alternative, dewatering is projected to continue through 2023 (Figure 3-12) to allow for mining to a target depth of 3,400 feet amsl at the Pipeline Pit Complex, and 3,800 feet amsl at the Cortez Hills underground mine. Compared to the pre-mining groundwater elevation, the dewatering required to allow mining to these target depths represent a maximum total drawdown of 1,400 feet at the Pipeline Complex and 2,000 feet at the Cortez Hills Complex (Itasca 2016a). Comparison of the simulated pumping and infiltration rates over the 2019 through 2023 period indicates that the dewatering system would remove approximately 190,968 acre-feet of groundwater; and the water management system would return approximately 132,903 acre-feet of water (or approximately 70 percent of the pumped water) to the groundwater system. The net amount that would be removed from groundwater storage is approximately 58,000 acre-feet which represents 30 percent of the total pumped water.

Under the Proposed Action, the active dewatering period would be extended approximately 9 years (through approximately 2032 depending on the actual start-up date), and the target dewatering elevations would be lowered from 3,400 to 3,200 feet amsl at the Pipeline Complex and from 3,800 to 2,500 feet amsl at the Cortez Hills Complex. The increased drawdown would be required to maintain “dry” conditions for the proposed expansions that include lowering the depth of open pit mining at the Pipeline Pit Complex and lowering the depth of underground mining at the Cortez Hills Complex (SRK 2016). As shown in Figure 3-12, the mine plan included under the Proposed Action would increase pumping over the 2019 through 2023 period compared to the No Action Alternative. The excess water that would not be used in the mine operations would be conveyed to existing and proposed RIBs in basin fill in Crescent, Grass, and Pine Valleys; to the Dean Ranch for ongoing irrigation use; to injection wells in Grass Valley; and to Rocky Pass Reservoir. Comparison of the simulated pumping and infiltration rates over the 2019 through 2032 period indicates that the dewatering system would remove approximately 409,194 acre-feet of groundwater; and the water management system would return approximately 302,097 acre-feet (or approximately 74 percent of the pumped water) to the groundwater system. The net amount that would be removed from groundwater storage is approximately 107,097 acre-feet which represents 26 percent of the total pumped water.

The cumulative impacts associated with mine dewatering and water management activities include an evaluation of the total drawdown (and infiltration) from all past, present, and reasonably foreseeable future mine dewatering and water management activities. This includes: 1) historic dewatering and infiltration activities initiated in 1996 and continuing through the present; 2) projected future total dewatering and infiltration activities required for the Proposed Action; and 3) projected dewatering and infiltration activities anticipated for the potential future Goldrush Project that is identified as a RFFA (see Section 2.5, Past, Present, and Reasonably Foreseeable Future Actions). The potential future Goldrush Project would be located east of the Cortez Hills Complex at the head of Horse Creek in Pine Valley. The Goldrush Project is anticipated to be an underground mine that would require dewatering and water management. For the numerical groundwater flow modeling cumulative simulations, mining for the Goldrush Project was assumed to extend from 2022 through 2043 (SRK 2017) (Figure 3-12). The historic dewatering and infiltration rates and projected future dewatering rates used in the cumulative analysis are presented in Tables 3-12 and 3-13, respectively. Comparison of the simulated pumping and infiltration rates over the 2019 through 2043 period indicates that the dewatering system would remove approximately 504,516 acre- feet of groundwater; and the water management system would return approximately 360,968 acre-feet (or approximately 72 percent of the pumped water) to the groundwater system. The net amount that would be removed from groundwater storage is approximately 143,548 acre-feet which represents 28 percent of the total pumped water.

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3.2.1.3 Evaluation of Impacts to Groundwater Levels For this impact analysis, the area that is predicted to experience a change (decrease or increase) in groundwater elevation of 10 feet or more is used for quantification and comparison of the maximum extent of drawdown (and mounding) effects between the various pumping and associated water management alternatives. The BLM does not believe that it is reasonable or appropriate to use the regional model to quantify changes in groundwater elevation of less than 10 feet considering the regional scale of the model, unavoidable uncertainty associated with regional groundwater flow models, and uncertainty associated from the use of the model to prediction conditions several hundred years into the future. The model is not designed to simulate seasonal or annual changes resulting from variations in groundwater recharge associated with variations in precipitation and groundwater recharge that would occur over the model simulation period. In addition, in many areas within the study area, changes in groundwater levels of less than 10 feet can be difficult to distinguish from natural seasonal and annual fluctuations in groundwater levels.

Impacts to groundwater levels were evaluated using the results of the numerical modeling for the different mine dewatering and infiltration scenarios discussed above. For the No Action Alternative, Proposed Action, and cumulative scenario, the projected changes in groundwater levels represent the difference between the model simulated groundwater elevations and simulated steady-state baseline groundwater elevations that existed in 1996 (prior to the initiation of major mine dewatering and water management activities) (Figure 3-7). As such, each of the model simulations simulate the total changes to groundwater elevations that have occurred in the project area due to the combined effects of historic and projected future pumping and water management activities that would have occurred since 1996.

Separate groundwater model simulations were conducted to evaluate the differences in drawdown at the end of mining and over the post-mining period for the three pit backfill scenarios (Scenarios 1, 2, and 3) included as options under the Proposed Action as described in Section 2.3. The model results predict changes in groundwater levels under backfill Scenarios 1, 2, and 3 for the Proposed Action (SRK 2016) and cumulative (SRK 2017) simulations. The results of these simulations conducted over the mining and post-mining period were used to define the maximum extent of the 10-foot drawdown contour for the Proposed Action and cumulative simulations. Comparisons of the maximum extent of the 10-foot drawdown contour for Scenarios 1, 2, and 3 for the Proposed Action (Figure 4-20, SRK 2016) and the cumulative model runs (Figure 4-23, SRK 2017) indicate that the predictions for each of the scenarios are very similar. Specifically, depending on location, the lateral extent of drawdown for the Scenario 3 simulations are either the same as, or slightly larger than, the drawdown areas defined for Scenarios 1 and 2. Therefore, the drawdown discussions provided in this section for the Proposed Action and cumulative model simulations conservatively are based on the Scenario 3 simulations.

3.2.1.4 Evaluation of Impacts to Surface Water Resources The use of the 10-foot drawdown contour to define the maximum extent of drawdown is described above (Section 3.2.1.3). Potential impacts to water resources are presented for the Proposed Action, No Action Alternative, and cumulative scenario. The impact assessment identifies and evaluates potential impacts to streams, springs, and seeps located: 1) within the maximum extent of the projected 10-foot groundwater drawdown contour and 2) outside of, but within 1-mile of, the maximum extent of the projected 10-foot groundwater drawdown contour. The area located outside of, but within 1 mile of, the maximum extent of the 10-foot drawdown contour is used as a “buffer” to identify surface water resources that may be affected as a result of drawdowns of less than 10 feet. For discussion purposes, these combined areas are

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-58 referred to in the remainder of the analysis for surface water resources as the “drawdown area.”

The springs and streams in the region can be characterized as either ephemeral, intermittent, or perennial. Ephemeral and intermittent springs and stream reaches flow only during or after wet periods in response to runoff events. By definition, these surface waters are not controlled by discharge from the groundwater flow systems. During the low-flow period of the year, ephemeral and intermittent springs and stream reaches typically are dry. In contrast, perennial springs and stream reaches generally flow throughout the year. Flows observed during the wet periods in perennial springs and streams include a combination of surface runoff and groundwater discharge, whereas flows observed during the low-flow period are sustained entirely by discharge from the groundwater system. If the flow from the perennial spring or stream is controlled by discharge from the aquifer affected by mine-induced drawdown, a reduction of groundwater levels could reduce the groundwater discharge to perennial springs or streams with a corresponding reduction in spring flows, lengths of perennial stream reaches, and their associated riparian/wetland areas.

In this region of north central Nevada, comparison of the average monthly precipitation at the Beowawe meteorological station indicates that higher precipitation occurs between November through June (with the highest precipitation in May), and lower precipitation occurs between July through October (WRCC 2018). Flows recorded in the late spring typically are influenced by stormwater runoff, whereas flows observed in the late summer and early fall typically are sustained by groundwater discharge. Therefore, for the purpose of this evaluation it was assumed that any surface water source observed to be flowing in most years (i.e., the majority of the years based on monitoring data) between August and mid-October is perennial and dependent upon groundwater discharge.

Hydrogeologic conditions that determine the risk of impacts to flow for perennial springs and streams from drawdown are summarized in Table 3-14. The relative risk of impacts to perennial water sources controlled by flow from perched or localized aquifer systems are assumed to be low, while those that are dependent on discharge from the regional groundwater system that would be targeted by proposed dewatering operations are assumed to be moderate to high depending on specific site conditions.

Table 3-14 Potential Impacts to Perennial Water Resources1 Located Within the Projected Groundwater Drawdown Area

Relative Risk of Impacts to Groundwater Flow Perennial Water System Controlling Resources within Discharge to Perennial the Drawdown Springs and Streams Area Explanation Local or Perched Low Impacts would be unlikely to occur at perennial water sources that are sustained by local or perched aquifers that are not hydraulically connected to the groundwater flow system that would be affected by mine-induced drawdown. Regional Moderate to High Impacts to perennial waters could occur where the water source is discharging from an aquifer that is hydraulically connected to the regional groundwater flow system that would be affected by mine-induced drawdown. 1 Includes the total surface water resources identified within: 1) the projected maximum extent of the 10-foot groundwater drawdown contour and 2) the 1-mile buffer zone located outside the 10-foot drawdown contour.

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The impact assessment for water resources is conservative in that it: 1) identifies all known surface water resources within the projected groundwater drawdown area; 2) provides site- specific mitigation triggers based on the monitoring of groundwater levels and surface water conditions; and 3) provides site-specific mitigation measures that would be implemented if ongoing monitoring identifies an exceedance of the mitigation trigger thresholds.

3.2.1.5 Pit Lake and Pit Backfill Water Quality Evaluation A hydrochemical evaluation of pit lake and pit backfill pore water quality under the Proposed Action was performed by Geomega (2016b). In this evaluation, the modeled processes incorporated estimates of the quality and quantity of groundwater inflow and outflow, pyrite oxidation rates in exposed pit wall rock, chemical releases from oxidized pit wall rock and pit backfill material (i.e., waste rock), with predictions of aqueous geochemical reactions in the pit lake (or pit backfill), evaporation from the pit lake surfaces, direct precipitation into the pit lakes, runoff from pit walls, and exchange of carbon dioxide between the pit lakes and the atmosphere.

A geologic model was used to define the lithology and geochemistry of the wall rock in the ultimate pit surface for each pit. Representative samples of the ultimate pit surface wall and backfill material were leached in the laboratory using HCT and column tests (Geomega 2016b). The leachate chemistry was used to define chemical release functions for use in predicting the water quality of the pit wall rock and pit backfill material. The oxidation rates of pyrite in the different geologic units in the wall rock were determined using the modified David- Ritchie modeling code. The model simulated sulfide oxidation reactions were based on the transport of oxygen and water within each of the geologic units accounting for macrofractures in the pit wall (Geomega 2016b).

The quantities of water entering the pit lakes were estimated from meteoric precipitation data and estimates of the volume of surface runoff from the pit walls, evaporative losses, and flow velocities, with pit lake water levels predicted by the groundwater flow model (SRK 2016). The chemical inputs to the pit lakes were predicted based on background groundwater chemistry, chemical release functions, amounts of waste rock placed as backfill in the pits, and estimated thicknesses of the oxidized wall rocks. These data were used to estimate the temporal evolution of the water quality of the pit lakes and pit backfill pore water over a 200-year post- mining simulation period. Details regarding the methodology used for the hydrochemical evaluation are provided in the pit lake and pit backfill pore water chemistry modeling report (Geomega 2016b).

3.2.2 Proposed Action 3.2.2.1 Water Quantity Impacts Impacts to Water Levels The model predicted changes in groundwater levels attributable to the Proposed Action at the end of dewatering and infiltration activities (Year 2032) are shown in Figures 3-13. The maximum projected drawdown is approximately 2,520 feet (SRK 2016) in the vicinity of the underground mine expansion area at the Cortez Hills Complex.

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At the end of dewatering, the simulated drawdown associated with the Pipeline Pit Complex and Cortez Hills Complex underground operations coalesce and form an elongate northwest- southeast oriented drawdown area that extends across southern Crescent Valley into northern Grass Valley and western Pine Valley. An isolated drawdown area is projected to develop in the Simpson Park Mountains in Pine Valley approximately 11 miles southeast of the Cortez Hills Complex. The isolated drawdown area in the Simpson Park Mountains occurs in a carbonate rock window that is hydraulically connected to the carbonate rock aquifer in the Cortez Hills Complex (Itasca 2016a). Projected mounding from infiltration activities in the basin fill aquifer is evident in areas developed around existing and proposed RIBs located in southern and east central margin of southern Crescent Valley, northern Grass Valley, and western Pine Valley. The overall impacts to groundwater elevations would be moderate to major, long term, and regional.

Modeling simulations were conducted for representative points in time over a 500-year post- mining period. The simulations indicate that after dewatering ceases, the depth of drawdown beneath the pumping centers diminishes, but the areal extent of the drawdown continues to expand laterally. Comparison of these simulations over the recovery period indicates that the maximum extent of the 10-foot drawdown contour continues to expand for up to approximately 170 years. However, the modeled lateral expansion reaches a maximum at different time periods in different areas and is controlled in large part by the modeled hydraulic parameters assigned for the different hydrogeologic units in different areas. The predicted long-term lateral expansion of the drawdown area results from continual inflow of groundwater from the surrounding area to fill the voids from the deep drawdown cone centered on the mine areas and filling of the pit lakes.

The maximum areal extent of the 10-foot drawdown contour attributable to the Proposed Action is presented in Figure 3-14. This figure shows the predicted outer limit of the 10-foot drawdown contour as determined by overlaying a series of 10-foot drawdown contours for representative points in time over the 500-year post-mining period (SRK 2016). The maximum area of drawdown (defined by the 10-foot contour) is predicted to extend across the southern portion of Crescent Valley and adjacent areas along the margins of Carico Lake Valley, northern Grass Valley, and western Pine Valley. Surface water resources and water rights identified within the maximum drawdown area for the Proposed Action are shown in Figures 3-14 and 3-15, respectively.

The simulated residual drawdown after 500 years of recovery is shown in Figure 3-16. The model results predict that residual drawdown would persist in areas surrounding the Pipeline and Cortez Hills complexes. Residual drawdown around the Pipeline Complex is predicted to extend up to several miles from the center of the Pipeline Pit Complex towards the northwest. Residual drawdown in the vicinity of the Cortez Hills Complex would extend up to a several miles to the west of the Cortez Hills Complex. The model simulations also predict that a groundwater mound would persist in the northern portion of Carico Lake Valley.

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The incremental changes in groundwater levels attributable to the Proposed Action are illustrated by comparison of the maximum extent of the model-simulated groundwater level changes for the Proposed Action and No Action Alternative as shown on Figure 3-14. The comparison indicates that the maximum extent of the drawdown area (defined by the 10-foot contour) for the Proposed Action is similar to, but covers a larger area than, the maximum extent of the predicted drawdown area under the No Action Alternative. This incremental change would result in a moderate, long-term, regional impact to groundwater levels. Based on the model results, impacts to groundwater levels are not projected to occur in the vicinity of the town of Crescent Valley or in the northern portion of Crescent Valley in the vicinity of the Humboldt River (SRK 2016).

The predicted drawdown associated with groundwater pumping under the Proposed Action would lower water levels in basin-fill sediments, particularly within the valley floor areas in the proposed pumping basins. Reduction of the groundwater level in the unconsolidated sediments essentially would dewater the portion of the basin-fill aquifer situated within the drawdown cone. The portion of the unconsolidated basin-fill sediments that would be dewatered would undergo compaction as the water is removed from the material. Compaction of these sediments would result in a permanent reduction of the water storage properties of the aquifer. However, the amount of compaction and reduction in storage properties would depend on the grain-size and texture of the layers within the basin-fill sedimentary sequence. For example, the reduction in storage properties for the fine-grained materials (i.e., clay beds or aquitards) would be much greater than the reduction in storage for the coarse-grained materials (sands and gravel or high transmissive aquifers) in the sequence. The potential impacts associated with groundwater pumping-induced ground subsidence are described in the Deep South Expansion Project Supplemental Environmental Report – Geology and Mineral Resources (BLM 2019b). Over the HSA, the potential reduction in the storage capacity of the basin-fill sediments (particularly the fine-grained materials) would represent a relatively minor but long- term, regional impact to the groundwater aquifer system.

Pit Lake Development As described in Section 2.3, Proposed Action, pit lakes are predicted to develop in the post- mining period in both the Pipeline Pit Complex, under all three partial pit backfill scenarios (Figures 2-4, 2-5, 2-6), and in the Cortez Pit (Figure 2-9). The predicted rates of pit lake development under the three pit backfill scenarios are shown in the graphs provided in Figure 3-17. As shown, the rate of pit lake development would be similar under all three partial backfill scenarios. In the Pipeline Pit Complex, the Crossroads Pit lake is predicted to start recovering in 2025 and reach 90 percent of full recovery within 52 to 55 years, depending on the backfill scenario. Under backfill Scenario 2, a separate pit lake is predicted to develop in the north end of the Pipeline Pit starting in 2038 and reach 90 percent of full recovery approximately 90 years after dewatering ceases. The Cortez Pit lake is projected to start to develop between 2040 to 2043, depending on the scenario, and reach 90 percent of full recovery within 88 to 100 years after dewatering ceases (SRK 2016).

The predicted physical conditions for the pit lakes under the three pit backfill scenarios are summarized in Table 3-15. After the pit lake stage levels reach approximate equilibrium, the modeling results predict that the Crossroads Pit lake (Scenario 2 and 3) and the Pipeline Pit lake (Scenario 2) would behave as sinks, with no through-flow to the groundwater system. However, under Scenario 1, as the Crossroads Pit lake stage approaches equilibrium, a small amount (3.7 gpm) of outflow to alluvium on the east side of the pit is predicted (SRK 2016). As the Cortez Pit lake stage reaches equilibrium, groundwater outflow is predicted to occur along the north side of the pit at rates ranging from 58 to 66 gpm depending on scenario (SRK 2016).

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Table 3-15 Summary of Predicted Pit Lakes at 500 Years Post-mining under the Proposed Action

Groundwater Outflow at 500 Final Pit Lake Pit Floor Net Years Post- Surface Pit Lake Pit Lake Elevation Maximum Pit Evaporative mining Backfill Mine Pit Lake Elevation Surface Area Volume (deepest) Lake Depth Loss2 (Yes/No) Scenario Complex Location (feet amsl) (acre) (acre-feet)1 (feet amsl) (feet) (gpm) (gpm) Scenario 1 Pipeline Crossroads 4,787 367 229,300 3,255 1,532 -340 Yes (3.7 gpm) Pit Scenario 2 Pipeline Crossroads 4,782 367 227,300 3,255 1,527 -442 No (<1 gpm) Pit and (4,200)3 Pipeline Pit (northern portion) Scenario 3 Pipeline Crossroads 4,771 713 338,000 3,255 1,516 -620 No (0 gpm) Pit and Pipeline Pit (east portion) Scenario 1 Cortez Cortez Pit 4,804 22 3,700 4,500 304 19 Yes (66 gpm) Scenario 2 Cortez Cortez Pit 4,802 22 2,700 4,500 302 19 Yes (63 gpm) Scenario 3 Cortez Cortez Pit 4,797 22 3,500 4,500 297 19 Yes (58 gpm) 1 Estimated pit lake volumes rounded to the nearest 100 acre-feet. 2 Net evaporative loss reflects evaporation minus direct precipitation and runoff. 3 Deepest pit floor elevation for the portion of the Pipeline Pit that would develop a separate pit lake. Source: SRK 2016.

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At 500 years after dewatering ceases, the combined estimated net evaporative loss for pit lakes under the Proposed Action is 321 gpm (518 acre-feet per year) for Scenario 1; 423 gpm (682 acre-feet per year) for Scenario 2; and, 601 gpm (970 acre-feet per year) for Scenario 3. These evaporative losses would result in a minor, long-term impact to the regional water balance.

The groundwater model simulations for the Proposed Action assume that backfill would be placed in the Cortez Hills Pit and preclude pit lake development (SRK 2016) as shown in Figure 2-8. However, as discussed in Section 2.3, Proposed Action, the final backfill design and elevations would be based on future hydrologic and geotechnical evaluations incorporating information gained during mining. As such, BCI may elect to backfill above the projected post- mining pit lake elevation to eliminate the pit lake as currently proposed, or a pit lake may be allowed to form as currently authorized. Predicted pit lake development for the currently authorized Cortez Hills Pit was evaluated in the Cortez Hills Expansion Project Final EIS (BLM 2008) and is briefly summarized in Section 3.2.4, No Action Alternative.

Impacts to Perennial Streams and Springs As described above, mine-induced groundwater drawdown resulting from the Proposed Action is predicted to result in a reduction in groundwater levels both during active dewatering and for an extended period after dewatering ceases. The methodology used to evaluate potential risk to perennial surface water sources within the projected drawdown area was described in the Evaluation of Impacts to Surface Water Resources subsection under Section 3.2.1. The impact evaluation identifies all springs, seeps, and perennial stream reaches identified within the drawdown area including those that were previously identified and addressed through mitigation in the Cortez Hills Expansion Project Final SEIS (BLM 2011 – Table 3.2-1). (It is important to note that the perennial surface water sites identified in Table 3.2-1 of the Cortez Hills Expansion Project SEIS [BLM 2011] occur within the modeled groundwater drawdown areas identified for both the Cortez Hills Expansion Project [BLM 2008] and the Proposed Action. Potential groundwater drawdown-related impacts under both the previously authorized activities and the Proposed Action would be the same [i.e., potential reduction in baseflow].) Unless otherwise noted, the spring and seep locations are referred to throughout the remainder of this section simply as springs.

Potential impacts to streams were evaluated by using available baseline data to estimate the length of perennial stream reaches located within the drawdown area. Potential impacts and site-specific mitigation measures previously were identified for Indian Creek and Ferris Creek, located on the east slope of the Shoshone Mountains northwest of the Pipeline Pit Complex, and Mill Creek, located in the Cortez Mountain northeast of the Cortez Complex (BLM 2011, 2008). The updated model simulations for the Proposed Action were used to reevaluate the perennial stream reaches located within the projected drawdown area.

The model-predicted groundwater drawdown resulting from the Proposed Action is projected to encompass three perennial streams located on the eastern slope of the Shoshone Mountains several miles west and northwest of the Pipeline Pit Complex (Figure 3-14): Indian Creek, Ferris Creek (a tributary to Indian Creek), and Elder Creek. The drawdown area also is projected to encompass the mapped perennial stream reaches of Horse and Willow creeks, located on the east slope of the Cortez Mountains, and Mill Creek, located on the west slope of the Cortez Mountains. The total perennial stream lengths located within the drawdown area are listed in Table 3-16.

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Table 3-16 Perennial Stream Miles Located within the Projected Drawdown Areas

Total Perennial Stream Miles Perennial Stream Miles Located within the Projected (baseline) Drawdown Areas1 Perennial Stream No Action Reach2 Alternative Proposed Action Cumulative Indian Creek 13.0 5.1 8.6 8.6 Ferris Creek 5.3 3.1 3.6 3.6 Elder Creek 6.3 1.4 1.6 5.9 Cooks Creek 5.1 0.0 0.0 5.1 South Fork Mill Creek 2.0 0.0 0.0 1.7 Mill Creek 4.7 4.7 4.7 4.7 Horse Creek 3.8 3.8 3.8 3.8 Willow Creek (tributaries) 5.2 1.5 1.5 2.4 Total 45.4 19.6 23.8 35.8 1 Includes the total miles of perennial streams identified within either: 1) the projected maximum extent of the 10-foot drawdown contour or 2) within the 1-mile buffer zone located outside of the 10-foot drawdown contour. 2 Based on drawdown results provided in Itasca (2016a) and SRK (2017, 2016) reports.

Comparison of the drawdown at the end of mining (Figure 3-13) with the maximum extent of the 10-foot drawdown contour (Figure 3-14) shows that the drawdown area is predicted to encroach into the Indian, Ferris, and Elder Creek areas during the post-mining period. However, the predicted drawdown at 500 years post-mining (Figure 3-16) indicates that the groundwater levels in the vicinity of the perennial stream reaches eventually would recover in the post-mining period. The model-predicted changes in groundwater discharge to Horse Creek are discussed below under the Impacts to the Regional Water Balance subheading.

If the perennial flow in the specific stream reaches identified above are controlled by discharge from the regional aquifer system that is projected to be affected by mine-induced drawdown, impacts to flows would likely occur. A reduction in flows could reduce the length of, or dry up, the perennial stream reaches. Potential flow reductions in perennial stream reaches attributable to mine-induced drawdown would be addressed through the implementation of BCI’s proposed Contingency Mitigation Plan for Surface Water Resources as identified in Section 2.3.3, Applicant-committed Environmental Protection Measures, and discussed below.

Spring sites that occur within the drawdown area under the Proposed Action are listed in Appendix A, Table A-2. As summarized in Table 3-17, there are a total of 141 spring sites identified within the Proposed Action drawdown area. The 141 sites exclude 27 spring sites that previously were addressed in the Cortez Hills Expansion Project Final SEIS (Table 3.2-1, BLM 2011).

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Table 3-17 Springs Located within the Projected Drawdown Areas1,2

No Action Proposed Category Alternative Action Cumulative Total Inventoried Springs within the Drawdown Area 144 168 188 Total Inventoried Springs within the Drawdown Area 122 141 161 (excluding sites identified in previous [BLM 2011] mitigation plan2) 1 Includes the total springs and seeps identified within either: 1) the projected maximum extent of the 10-foot groundwater drawdown contour or 2) within the 1-mile buffer zone located outside the 10-foot drawdown contour. 2 Excludes springs and seeps previously identified in Table 3.2-1 (Water Resources Mitigation Summary) in the Cortez Hills Expansion Project Final SEIS (BLM 2011). Sources: Based on drawdown results provided in Itasca (2016a) and SRK (2017, 2016) reports.

The actual impacts to individual seeps, springs, or stream reaches would depend on the source of groundwater that sustains the perennial flow (perched or hydraulically isolated aquifer versus regional groundwater system) and the actual extent of mine-induced groundwater drawdown that would occur in the area as described in Section 3.2.1. The interconnection (or lack of interconnection) between the perennial surface waters and deeper groundwater sources is controlled in large part by the specific hydrogeologic conditions that occur at each site. Considering the complexity of the hydrogeologic conditions in the region and the inherent uncertainty in numerical modeling predictions relative to the exact areal extent and magnitude of the predicted drawdown area, it is not possible to conclusively identify specific perennial stream reaches or springs that would or would not be impacted by future mine-induced groundwater drawdown. Potential flow reductions in springs or seeps attributable to mine-induced drawdown resulting from the Proposed Action would be mitigated through the implementation of the proposed Contingency Mitigation Plan for Surface Water Resources discussed below.

Contingency Mitigation Plans for Surface Water Resources A contingency mitigation plan previously was developed to identify and describe site-specific mitigation measures for perennial water sources identified within the projected maximum extent of the drawdown area for the currently authorized operations as described in the Cortez Hills Expansion Project Final SEIS (BLM 2011). A second proposed contingency mitigation plan (BCI and Stantec 2018) has been developed to address potential impacts to all additional perennial stream reaches, springs, and seeps identified within the Proposed Action drawdown area (defined previously as including the area located within, and within 1-mile of, the maximum extent of the 10-foot drawdown contour) that were not previously addressed in the Cortez Hill Expansion Project Final SEIS (BLM 2011). Potentially affected perennial surface water resources are listed in Tables A-2 and A-3 in Appendix A.

Contingency Mitigation Triggers. The combined site monitoring and groundwater monitoring results would be used to trigger the implementation of contingency mitigation measures to mitigate impacts to water resources. Mitigation triggers for each of the surface water features are listed in Table A-3 in Appendix A. Site-specific triggers are described in detail in the proposed Contingency Mitigation Plans for Surface Waters (BCI and Stantec 2018). The mitigation trigger depends on the observable flow and site characteristics of each individual surface water feature. For perennial springs, the mitigation trigger would be based on a reduction of baseflow below an established flow threshold. The baseflow threshold was determined by reviewing the flow variations from the quarterly monitoring results over the period of record. Mitigation triggers based on reductions in baseflow would be determined

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-71 using flow measurements from the low-flow period that typically occurs in late summer through early fall (August to October) and the results of the groundwater monitoring.

For perennial seeps characterized as wet soil or ponded areas that support vegetation with no measurable flow, the mitigation trigger would be based on a reduction in hydrophilic vegetation below an established threshold coincident with a reduction in groundwater levels in the area as determined by groundwater monitoring. As discussed in the proposed Contingent Mitigation Plans for Surface Waters (BCI and Stantec 2018), site-specific mitigation triggers would be used.

Monitoring and reporting would continue until impacts to water resources have been mitigated. The monitoring would provide for identification of potential flow impacts to perennial surface waters as a result of mine-related groundwater drawdown and trigger implementation of appropriate mitigation measures as identified below.

Contingency Mitigation Measures. If the monitoring results as identified in Contingency Mitigation Triggers indicate that flow reductions in perennial surface waters are occurring and that these reductions are likely the result of mine-induced drawdown, the monitoring results would trigger implementation of the site-specific mitigation measures identified in Table A-3 in Appendix A.

If mitigation is triggered, BCI would be responsible for implementing the site-specific mitigation measures identified in the proposed Contingency Mitigation Plans for Surface Waters (BCI and Stantec 2018) to enhance or replace the impacted perennial water resources. The mitigation plan would be submitted to the NDWR, Nevada Department of Wildlife (for mitigation involving guzzlers), and BLM identifying drawdown impacts to surface water resources. Mitigation would depend on the actual impacts and site-specific conditions and could include a variety of measures. Methods for providing a new water source or improving an existing water source as described in the proposed Contingency Mitigation Plans for Surface Waters may include, but are not limited to:

1. Installation of a water supply pump in an existing well; 2. Installation of a new water production well; 3. Piping from a new or existing source; 4. Installation of a guzzler; 5. Enhanced development of an existing seep to promote additional flow; or 6. Fencing or other protection measures for an existing seep to maintain flow.

A detailed description of each of these six methods is provided in the proposed Contingency Mitigation Plans for Surface Waters developed for the project.

An approved site-specific mitigation plan would be implemented followed by monitoring and reporting to measure the effectiveness of the implemented measures. If initial implementation is unsuccessful, the NDWR or BLM may require implementation of additional measures.

Effectiveness of Contingency Mitigation. Site-specific evaluations of the effectiveness of the proposed contingency mitigation measures for each of the identified perennial surface water resources that occur in areas where there is a potential risk of impacts resulting from the mine-induced groundwater drawdown are presented in Table A-3 in Appendix A. The site- specific measures include one or more of the six methods described below. Monitoring of the surface water resources would be used to document the effectiveness of the implemented 2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-72 measures. As noted above, the NDWR or BLM may require the implementation of additional mitigation measures if implementation of the initial measure is unsuccessful. Also note that Nevada Revised Statute NRS 533.367 requires a water right holder to ensure access to water for wildlife which customarily uses the water.

Methods #1 and #2. Use of an existing well or construction of a new well to supplement or replace baseflow affected by mine-induced groundwater drawdown are anticipated to be highly effective methods to maintain the identified use(s) over the period of impact that may occur, including providing a water supply for livestock and/or wildlife and maintaining hydrophilic vegetation for habitat diversity. Well pumping is expected to provide a long-term sustainable source of water to supplement or replace the loss of baseflow. There is some potential for the flow to be disrupted at times due to mechanical problems (including freezing pipes) or maintenance of the system. However, with appropriate maintenance and system monitoring, potential disruptions in flow likely would be of short duration (i.e., several days to several weeks).

Method #3. Piping water from a new or existing source also is anticipated to be an effective method to provide flow to supplement or replace baseflow to springs or seeps affected by mine dewatering. A sufficient upgradient source could provide a long-term sustainable water supply to provide water for livestock and/or wildlife and maintain hydrophilic vegetation for habitat diversity. This measure is considered to be moderately effective since the upgradient water source created by collecting water in a surface reservoir or pond could be depleted during drought conditions. If the water resource and site conditions are favorable, this type of flow augmentation could be installed within a short timeframe after mitigation is triggered. This type of system would require long-term maintenance, and flow disruptions could occur due to freezing pipes.

Method #4. Installation of a guzzler would be an effective method to replace a source of water for livestock and/or wildlife. If the original spring or seep only provided a seasonal or intermittent source of water, the guzzler would provide an improved sustainable perennial source of water for livestock and/or wildlife use. However, installation of a guzzler without other spring enhancements would not be effective at providing water to sustain a diversity of habitats (such as hydrophilic vegetation) that a spring or seep may have originally supported. Guzzlers would require periodic maintenance for the life of the system.

Method #5. Enhanced development of an existing spring or seep to promote additional flow may or may not be effective at increasing the flow available at the surface. This mitigation likely would be used in circumstances where there has been a decrease in the flow but not a complete loss of flow at the source. For this situation, the spring enhancement measures likely would be moderately effective at increasing flow and partially or completely effective at mitigating reductions in flow associated with mine-induced drawdown. However, for seeps or springs that have experienced a complete loss of flow due to mine-induced groundwater drawdown, these enhancement measures are not expected to be effective at mitigating reduction in flows.

Method #6. Eliminating grazing through installation of exclusionary fencing to keep livestock out but allow access for wildlife is an effective method of enhancing seep and spring flow along with hydrophilic vegetation if there has not been a complete loss of flow. However, if the flow of the spring or seep is completely lost due to a reduction in groundwater levels, then fencing alone is not expected to be an effective measure to mitigate impacts associated with mine-induced groundwater drawdown. If flow from a seep or spring is reduced but not completely lost, enhancement of the area through eliminating grazing likely would increase output of the spring.

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Environmental Impacts Associated with Implementation of Mitigation Measures. The estimated acreage of new disturbance associated with the implementation of the site-specific mitigation plans would range from 0.05 to 2.60 acres (as identified in the proposed Contingency Mitigation Plans for Surface Waters [BCI and Stantec 2018]) depending on the type of mitigation implemented and site-specific conditions. Any ground disturbance would be managed and reclaimed in accordance with BLM and State of Nevada requirements. Therefore, surface disturbance impacts associated with implementation of site-specific mitigation are assumed to be reclaimed within 2 to 3 years after disturbance. Potential impacts that would result from implementation of the site-specific mitigation measures are discussed in the following paragraphs.

Well Development. Ground disturbance impacts associated with piping water from an existing well would include new ground disturbance associated with installing a pumping system (either windmill or electric powered), a storage tank for maintaining consistent flow, and surface or buried piping from the well to the desired location. The most likely power source for pumping from an existing or new well would be solar-power cells (BCI and Stantec 2018). A new pipeline from an existing well would be placed in existing roadways if feasible; therefore, in this case, no new disturbance would be required for pipeline installation.

Ground disturbance activities associated with new well construction would include surface disturbance associated with the drill pad and sump, tank installation, and piping. A drill pad can range from several hundred square feet to several thousand square feet, depending on the size of the drill rig and ancillary facilities. Typical disturbance from the installation of a new production well would be approximately 0.2 acre. The pipelines would be placed in existing roadways to the extent practical. Pipelines installed along existing roadways are not expected to result in new ground disturbance; pipelines placed outside of existing roadways would result in new ground disturbance. For these locations, the distance between the proposed new wells and the spring and seep source areas would be less than 200 feet. Assuming a pipeline length of 200 feet and disturbance width of 6 feet, the total maximum new disturbance associated with pipeline installation would be approximately 0.03 acre.

The estimated pumping rates that could be required to augment flows to sustain the identified surface water resources are identified in Table A-3 in Appendix A. The flow augmentation rates range from 0.5 to 14.3 gpm for springs and 0.5 to 24.2 gpm for perennial streams. In the unlikely event that all of these wells were installed and pumped at the maximum rate to supplement a total loss of baseflow at all of the identified locations, the total combined pumping rate would be approximately 174 gpm. In comparison, dewatering associated with the Deep South Expansion Project would result in a total estimated annual average mine dewatering rate of 8,100 to 27,100 gpm over the 2024 through 2032 period (Table 3-12). Using these average annual mine dewatering rates, the maximum mitigation pumping rate of 173 gpm would represent an increase in the annual groundwater withdraw rate required for mine operations of approximately 2.1 and 0.6 percent, respectively. The maximum pumping rate that could be required for flow augmentation would represent a negligible increase in the total amount of groundwater withdrawal required for the proposed project.

As stated previously, new wells used to supplement or replace baseflow impacted by the mine- induced drawdown would be located in close proximity to the original water source as defined in the proposed Contingency Mitigation Plan for Surface Waters (BCI and Stantec 2018). Considering the close proximity of the new wells to the sources, it is likely that the well would intercept the same geologic formations that controlled discharge to the original spring. In this case, the water quality would be expected to have the same or similar geochemical characteristics as the original spring discharge.

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If all of the contingency mitigation measures that require groundwater pumping to augment surface flows were triggered, the total maximum groundwater production would require approximately 279 AFY (BCI and Stantec 2018). BCI currently holds water rights that include 4,998 AFY for mining and milling and 6,595 AFY for irrigation and stock watering (BCI 2018). It is anticipated that water rights for any new well production required for implementation of the mitigation plans would be addressed by transferring a portion of the existing water rights to the new points of diversion as required by the State Engineer. Other impacts to water rights associated with implementation of the site-specific measures are not anticipated.

Piping Water from a New or Existing Source. Disturbance associated with this measure would be limited to construction of a surface or buried pipeline from the source to the affected spring or seep. Assuming 0.5 mile of piping (a disturbance width of 6 feet along 2,640 feet of pipe), approximate disturbance associated with this mitigation measure would be 0.4 acre. It is anticipated that any water rights to capture and convey water to augment flows would be addressed by transferring a portion of the existing water rights to the new point of diversion, as discussed above for well development.

Installation of a Guzzler. Construction activities would include vegetation removal at the collection apron and tank locations; excavation for the tank (assuming below ground installation); installation of the apron, tank, piping, and trough; and installation of an exclusionary fence to prevent livestock from damaging the guzzler apron. The actual design (size, location, etc.) would be dependent on many variables including, but not limited to, annual precipitation, slope, and targeted wildlife (small game versus big game). Disturbance from a large game guzzler in this area would be up to 0.7 acre (assuming a disturbance area of approximately 150 feet by 200 feet).

Enhanced Development of an Existing Seep to Promote Additional Flow. The measures identified to enhance flow (i.e., installation of a spring box) at an existing spring would result in minimal (less than 0.1 acre) disturbance.

Fencing or Other Protection Measures for an Existing Seep to Maintain Flow. Installation of fencing around the water source would result in minimal (less than 0.05 acre) temporary disturbance for the duration of the mitigation.

Impacts to Water Rights For the purpose of this evaluation, all water rights owned by BCI (or Cortez Joint Venture or Barrick Gold) were excluded. Private water rights located within the predicted drawdown areas are shown in Figure 3-15 and listed in Table 3-18. There are five non-BCI owned or controlled water rights located within the predicted maximum extent of the of the 10-foot groundwater drawdown area under the Proposed Action. These include two surface water rights (one located at a spring source and one located at stream sources) and three groundwater rights. According to the State Engineer’s records, three of the water rights are used for irrigation and two are used for mining and milling.

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Table 3-18 Private Water Rights Located Within the Predicted Drawdown Area

Map Basin Type of No Action Proposed ID No. Basin Application1 Status Source Use Alternative Action Cumulative 1 55 Carico 81822 Abrogated Groundwater Mining- X Lake milling Valley 2 55 Carico 64260 Certificate Groundwater Mining- X Lake milling Valley 3 55 Carico 79547 Certificate Groundwater Mining- X Lake milling Valley 4 55 Carico 80789 Certificate Groundwater Mining- X Lake milling Valley 5 55 Carico 85868 Permit Groundwater Mining- X Lake milling Valley 6 55 Carico 17654 Certificate Groundwater Domestic X Lake Valley 7 55 Carico 26872 Certificate Groundwater Mining- X Lake milling Valley 8 55 Carico 29694 Certificate Groundwater Mining- X Lake milling Valley 9 55 Carico 64261 Certificate Groundwater Mining- X Lake milling Valley 10 55 Carico 35814 Certificate Groundwater Mining- X Lake milling Valley 11 53 Pine 5100 Certificate Spring Irrigation X X X Valley 12 54 Crescent V09040 Vested Stream Irrigation X X Valley 13 54 Crescent 13343 Certificate Groundwater Mining- X X Valley milling 14 54 Crescent 10071 Certificate Groundwater Mining- X X X Valley milling 15 54 Crescent 80138 Permit Groundwater Irrigation X X X Valley 1 Excludes water rights owned by BCI. Sources: Based on drawdown results provided in Itasca (2016a) and SRK (2017, 2016) reports.

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The actual impacts to individual surface water rights would depend on the site-specific hydrologic conditions that control groundwater discharge. Only those waters sustained by discharge from the regional groundwater system would likely be impacted. For surface water rights that are dependent on groundwater discharge, a potential reduction in groundwater levels could reduce or eliminate the flow available at the point of diversion for the surface water right. Impacts to wells (i.e., groundwater rights) could include a reduction in yield, increased pumping cost, or if the water level were lowered below the pump setting or the bottom of the well, make the well unusable. Specific impacts to wells would depend on the site-specific hydrogeologic conditions, well completion details, and timing of the drawdown. Potential effects to specific water rights would be localized, and impacts could range from negligible to major. Any measurable impact to a water right would likely be long term.

Impacts to the Regional Water Balance The water balance for the groundwater system within the HSA was estimated using the groundwater flow model (SRK 2016). Comparisons of the estimated annual groundwater inflow and outflow rates under the baseline condition (2015), end of dewatering under the Proposed Action (2032), and 500 years post-mining are summarized in Table 3-19. The water balance provides an estimate of the annual change in storage and fluctuations of the major inflow and outflow components over time resulting from the proposed mine dewatering and water management activities. The simulated groundwater outflow to the Humboldt River and Pine Creek are essentially the same for each period. The model simulations predict that groundwater discharge to Horse Creek would be reduced from an estimated 21 acre-feet per year in 2015 to approximately 1 acre-foot per year in 2032 (end of mining). These predictions indicate a substantial reduction in the baseflow to the perennial reach of Horse Creek. The post-recovery water budget (Year 2532) indicates that the groundwater discharge to Horse Creek eventually would return to pre-mining conditions during the post-mining period. The potential for impacts to Horse Creek is uncertain. If groundwater drawdown-related impacts to Horse Creek occur as simulated in the groundwater model, these impacts would be considered major, long-term, and regional.

Summary Table 3-19 Simulated Groundwater5 Budget for the HSA Under the Proposed Action 500 Years Pre-mining Baseline End of after Period Period Dewatering Dewatering (Pre-1996) (2015) (2032) (2532) Groundwater Budget Component (acre-feet per year)1,2 Groundwater Inflow Precipitation Recharge 71,300 71,300 71,300 71,300 Infiltration Recharge (RIBs) 0 26,100 8,000 0 Pit Lakes 0 0 0 100 4 Surface and Subsurface Inflow 12,100 16,000 16,100 12,300 Total Inflow 83,400 113,400 95,400 83,700 Groundwater Outflow Evapotranspiration 51,800 55,500 53,100 51,300 Groundwater Pumping Non-mining 8,100 7,600 6,900 7,500 Mine Dewatering 0 27,500 13,900 0 Pit Lakes 0 0 4,200 1,100

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Summary Table 3-19 Simulated Groundwater5 Budget for the HSA Under the Proposed Action 500 Years Pre-mining Baseline End of after Period Period Dewatering Dewatering (Pre-1996) (2015) (2032) (2532) Groundwater Budget Component (acre-feet per year)1,2 Discharge to Surface Waters (springs and 13,100 13,100 13,100 13,100 streams) (Humboldt River3) (300) (300) (300) (300) (Pine Creek3) (5,800) (5,800) (5,900) (5,800) (Horse Creek3) (29) (21) (1) (28) Subsurface Outflow 10,500 14,400 14,500 10,700 Total Outflow 83,500 118,100 105,700 83,700 Net Results Inflow Minus Outflow -100 -4,700 -10,300 0 Storage Change (model simulated) 0 -4,500 -10,500 100 1 Estimates based on results from the numerical groundwater model developed for the project (Scenario 3). 2 Estimates provided in the source document were rounded to the nearest hundred for presentation in this EIS. 3 Represent a breakdown of individual stream flows included under the “Discharge to Surface Waters (springs and streams).” Values in parentheses are positive values provided for comparison purposes. 4 Values represent a summation of the inflows and outflows for each of the four basins included within the study area. As such, these summation values include both inter-basin flow between the four basins within the study area, and flow across the model boundary to basins located outside of the model area. 5 The flow rates for the groundwater inflow and outflow components provided in this table are based on a summation of the rates provided for each of the four basins included within the groundwater model. A detailed breakdown of the estimated groundwater inflow and outflow rates for each of the four basins within the study area is provided in a series of water balance tables for representative years provided in the referenced model report. Source: SRK 2016.

3.2.2.2 Water Quality Impacts Pit Lake and Pit Backfill Water Quality A hydrochemical evaluation of pit lake water quality and pit backfill pore water quality under the Proposed Action was performed by Geomega (2016b). The Proposed Action includes three mining and backfill scenarios. The projected pit lake developments under the three scenarios at the mine complexes are summarized in Table 3-15. A brief overview of the methodology used to predict pit lake and pit backfill pore water quality is provided in Section 3.2.1, Evaluation Methodology. Details regarding the methodology used to evaluate pit lake and pit backfill pore water quality are provided in the geochemical investigating and modeling report: Cortez Deep South Expansion Pit Lake and Backfill Pore Water Chemistry (Geomega 2016b).

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To simplify the analysis, the most conservative pit lake and pit backfill scenarios (from a water quality standpoint) were evaluated (Geomega 2016b), including:

 Pit Lake Water Quality Evaluations  Pipeline Pit Complex  Crossroads Pit Lake (Scenario 2)  Pipeline Pit Lake (Scenario 2)  Crossroads-Pipeline Pit Lake (Scenario 3)  Cortez Pit Lake (Scenario 3)  Pit Backfill Pore Water Quality Evaluations  Pipeline Pit Complex  Pipeline Pit Backfill (Scenario 1)  Gap Pit Backfill (Scenario 1)  Cortez Hills Backfill (Scenario 1)

Pit Lake Water Quality Predicted pit lake water quality at selected time intervals over the 200-year post-mining period are provided in Table A-4a through Table A-4f in Appendix A. Under all of the scenarios evaluated for the Crossroads and Pipeline pits, the total pit lake water quality is predicted to be moderately alkaline, with pH increasing slightly within the 8.34 to 8.60 range (depending on scenario) over the 200-year simulation period. The modeling results indicate that with the exception of fluoride (all scenarios), and selenium (Pipeline Pit Scenario 2, only), all other chemical constituents are within the limits defined by the NDEP Profile III reference values. NDEP Profile III reference values are used to screen pit lake water quality for possible further evaluation for adverse impacts to avian or terrestrial life through ingestion (NDEP 2018). Fluoride is predicted to increase over time due to evapoconcentration. At 200 years, fluoride is predicted to range between 3.3- to 4.5-mg/L (depending on the scenario) which exceeds the 2 mg/L Profile III reference value. The selenium concentrations for the Pipeline Pit lake (Scenario 2) at 200 years (0.06 mg/L) slightly exceed the NDEP Profile III reference value (0.05 mg/L). Groundwater outflow is not projected to occur under Pipeline Pit lake Scenario 2.

The Proposed Action includes a plan to pump all the remaining water stored (and infiltrated beneath) the proposed Rocky Pass Reservoir into the Pipeline Pit Complex at the end of mining to accelerate pit lake formation. A hydrogeochemical evaluation was completed to evaluate the reservoir and groundwater quality that would be pumped into the pit (Geomega 2017c). The results of the study predict that with the exception of fluoride (3.06 mg/L) (compared to the 2.0 mg/L reference value), the reservoir water quality would not exceed the NDEP Profile III reference values.

Using the total chemistry, the Cortez Pit is predicted to be moderately alkaline (pH 8.31 to 8.46) over the 200-year simulation period. The modeling results indicate that with the exception of selenium, all other chemical constituents are within the limits defined by the NDEP Profile III reference values. After 200 years, selenium is predicted to be approximately 0.07 mg/L, which exceeds the 0.05 mg/L Profile III reference value.

A Screening-level Ecological Risk Assessment (SLERA) was used to evaluate risk to wildlife from consumption of the pit lake water quality. The results of the SLERA are provided in the

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Deep South Expansion Project Supplemental Environmental Report for Wildlife and Aquatic Biological Resources (BLM 2019e).

The predicted dissolved chemistry for the Cortez Pit lake used to evaluate outflow of pit water to groundwater indicates that the concentration of all chemical constituents except for arsenic and selenium would meet drinking water standards. At 200 years, the concentration of arsenic (0.017 mg/L) and selenium (0.07 mg/L) would exceed drinking water standards (arsenic 0.01 mg/L; selenium 0.05 mg/L). The arsenic exceedance would result from the naturally elevated concentrations in groundwater in the area. The elevated selenium concentration is an artifact of using a value of one half the detection limit for historic Cortez Pit leach samples and modeled evapoconcentration (Geomega 2016b). Arsenic is predicted to attenuate through absorption to the aquifer matrix material as pit lake water migrates into the formation as shown through field-scale leaching tests (Geomega 2016b). Therefore, groundwater outflow from the Cortez Pit lake is not expected to result in measurable impacts to groundwater quality downgradient from the pit. As a result, the localized, long-term effects would be negligible.

Pit Backfill Pore Water Quality Geochemical modeling was used to predict the backfill pore water quality after the groundwater table rebounds and saturates backfill material. The modeling predicts that the primary controls on the backfill pore water quality are the composition of the groundwater inflow and the reactivity of the submerged waste rock materials. The model results were validated against field-scale leaching tests on run-of-mine waste rock (Geomega 2016b).

All of the backfilled pits are predicted to behave as flow-through systems such that groundwater that enters the pit will move through and mix with groundwater downgradient of the backfilled pits. Predicted water chemistry of the backfill pit pore water for the pit backfill scenarios evaluated over an approximate 200-year post-mining period are provided in the pit lake and backfill pore water chemistry technical report (Geomega 2016b). The model predicted pit backfill pore water chemistry at the Gap, Pipeline, and Cortez Hills pits at approximately 100 years post-mining are listed in Table 3-20.

The modeling results indicate that chemical constituents of the Gap Pit backfill (Scenario 1) and Pipeline Pit backfill (Scenario 1) pore water would be below the Nevada Drinking Water Standards, with the exception of antimony. Antimony concentrations are predicted to be 0.006 mg/L (at the drinking water standard) at approximately 100 years, and 0.007 mg/L at approximately 200 years after backfilling. The Cortez Hills Pit backfill (Scenario 1) pore water quality would meet drinking water standards, with the exception of arsenic, antimony, mercury, and thallium. Fate and transport modeling was conducted to evaluate attenuation processes from solute dispersion and reactions. The results of the fate and transport modeling demonstrate that arsenic, antimony, and mercury would rapidly attenuate within 20 feet as groundwater moves through the bedrock aquifer downgradient of the Cortez Hills Pit. These results predict that these localized effects will be restricted to the immediate vicinity (i.e., within 20 feet) of the pit and are not predicted to impact downgradient groundwater quality located outside of the mapped footprint of the facility. Therefore, log-term groundwater outflow from the Cortez Hills Pit is not anticipated to impact the water quality downgradient from the mapped footprint of the facility.

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Table 3-20 Model-predicted Pit Backfill Pore Water Chemistry at Approximately 100 Years

Nevada NDEP Profile II Pipeline Pit Cortez Hills Pit Constituent Drinking Water Reference Gap Pit Backfill Backfill Backfill (mg/L)1 Standards2 Values (Scenario 1) (Scenario 1) (Scenario 1) Years Following 108 Years 98 Years 103 Years Completion of Backfill pH (standard 6.5 – 8.53 6.5-8.5 8.46 8.46 8.62 units) TDS 5004, 10003 1000 474 478 284 Alkalinity (total, -- -- 97 97 116 as calcium carbonate) Bicarbonate -- -- 117 117 140 Aluminum 0.054 – 0.23 0.2 0.03 0.03 0.02 Antimony 0.006 0.006 0.006 0.006 0.006 Arsenic (total) 0.01 0.01 0.002 0.002 0.08 Barium 2 2 0.027 0.03 0.083 Beryllium 0.004 0.004 0.000006 0.000006 0.003011 Boron -- -- 0.34 0.37 0.16 Cadmium 0.005 0.005 0.001 0.0009 0.004 Calcium -- -- 11 11 5 Chloride 2504, 4003 400 74 79 32 Chromium 0.1 0.1 0.006 0.007 0.009 (total) Copper 1.3, 1.03 1.0 0.001 0.001 0.012 Fluoride 2.04, 4.03 4 2.76 2.86 0.43 Iron 0.34, 0.63 0.6 0.00004 0.00004 0.00004 Lead 0.0157 0.02 0.00002 0.00002 0.00488 Lithium -- -- 0.2 0.2 0.1 Magnesium 1254, 1503 150 24 25 21 Manganese 0.054, 0.13 0.1 0.0000002 0.0000002 0.0000002 Mercury 0.002 0.002 0.001 0.001 0.004 Molybdenum -- -- 0.159 0.1 0.018 Nickel 0.1 0.1 0.004 0.004 0.011 Nitrate/Nitrite-N 10 10 2.6 2.8 1.2 Phosphorous -- -- 0.32 0.32 0.06 Potassium -- -- 21.5 22 12.8 Selenium 0.05 0.05 0.008 0.01 0.008 Silver 0.15 0.1 0.006 0.007 0.009 Sodium -- -- 90 90 36 Strontium -- -- 0.68 0.72 0.37

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Table 3-20 Model-predicted Pit Backfill Pore Water Chemistry at Approximately 100 Years

Nevada NDEP Profile II Pipeline Pit Cortez Hills Pit Constituent Drinking Water Reference Gap Pit Backfill Backfill Backfill (mg/L)1 Standards2 Values (Scenario 1) (Scenario 1) (Scenario 1) Years Following 108 Years 98 Years 103 Years Completion of Backfill Sulfate 2504, 5003 500 129 126 35 Thallium 0.002 0.002 0.0014 0.001 0.003 Tin -- -- 0.03 0.03 0.02 Uranium -- NA 0.003 0.004 0.009 Vanadium -- -- 0.0005 0.0004 0.01 Zinc 5.03 5 0.003 0.002 0.01 1 Units are milligrams per liter (mg/L) unless otherwise noted. 2 Maximum contaminant level. Federal primary standards that existed as of July 1, 2009, are incorporated by reference in NAC 445A.4525. 3 Federal secondary MCLs. 4 Nevada secondary MCLs. Note: Bolded text indicates concentrations at, or exceeding, standard or reference value. Source: Geomega 2016b.

Underground Water Quality Field and laboratory data combined with geochemical modeling were conducted to evaluate water chemistry in the underground workings of the Cortez Hills Underground Mine including the proposed expansion of the underground mining included under the Proposed Action (Geomega 2016c). The analysis used the average background groundwater quality as the starting composition for water discharging into the underground workings. Leachate chemistry results from samples of underground rock material were selected to represent the “worst-case” underground wall rock and backfill waste rock, and dissolution of concrete and shotcrete, to calculate their contribution to the total mass loading during underground mine flooding. The predicted total water quality of the flooded underground workings is circum-neutral (pH 7.3), and all analytes meet the NDEP Profile II reference values except for arsenic, antimony, and lead due to high concentrations in the background groundwater. The predicted dissolved chemistry has a pH of 8.2, and trace metal absorption controls the water chemistry due to iron dissolution from flow and wall rock leachate precipitating as ferrihydrite and sequestering arsenic and lead. The results indicate that all constituents except for arsenic (0.07 mg/L) and antimony (0.01 mg/L) would meet the drinking water standards and are below the background groundwater quality concentrations (0.08 mg/L and 0.014 mg/L, respectively) because of sorption (Geomega 2016c). After inundation of the underground mine, water that migrates into the surrounding bedrock is not predicted to degrade groundwater (Geomega 2016c). Therefore, long-term flow through the underground mine workings is anticipated to result in localized, negligible impacts to downgradient groundwater quality.

Waste Rock Facilities Characterization of the waste rock and waste rock leachate chemistry for the Proposed Action is described in Section 3.1.4, Waste Rock Characterization.

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Waste rock investigations for the proposed project have been conducted as discussed in the Waste Rock Management Plan (Geomega 2016d). Based on Geomega (2016d), the overall composition of the waste rock material from the Cortez Pit and the Pediment east and west extensions of the Cortez Hills Pit are projected to have hundreds of times more ANP than AGP, while the waste rock material from the Cortez Hills underground mine expansion and Pipeline Pit Complex modifications are projected to have three orders of magnitude more ANP than AGP. The waste rock generated from the Gold Acres Pit expansion and satellite pits although neutralizing, is projected to generate the least neutralizing waste rock from the CGM Operations Area.

The results of earlier infiltration and transport modeling through the Pipeline and Canyon waste rock facilities indicated that leachate that infiltrates out of the bottom of the facilities and migrates through the vadose (unsaturated) zone to the groundwater table would not exceed applicable water quality standards (BLM 2008, 2004). Infiltration and transport modeling was conducted for the proposed Gold Acres North Waste Rock Facility, which would receive the most mineralized waste rock under the Proposed Action (Geomega 2016d). Modeling for this waste rock facility was conducted for two reclamation scenarios: uncovered with no vegetation, and covered with 6-inches of growth media and revegetated. For the uncovered scenario, the modeling predicted that it would take 100 to 250 years for the draindown to reach groundwater. Also, leachate migrating from the base of the Gold Acres North Waste Rock Facility would not exceed applicable Nevada Profile I reference values, except for arsenic and antimony. However, these constituents would rapidly attenuate in the vadose zone (Geomega 2016d). For the second scenario (6 inches of cover, revegetated), the modeling results predict that there would be no draindown to groundwater, and minor toe seepage that would occur could be managed with an evaporation or evapotranspiration cell if necessary.

Geochemical testing indicates that site-wide, less than 2 percent of the waste rock has more AGP than ANP (Geomega 2016d). Based on the leachate test results, geochemical modeling, and implementation of the Waste Rock Management Plan (Geomega 2016d), significant impacts to surface or groundwater quality are not expected under the Proposed Action. As such, flow from the base of the waste rock facilities is anticipated over the long term. However, impacts to downgradient groundwater quality are anticipated to be localized and negligible.

Water Management Facilities As discussed in Section 2.3.2 , Dewatering, Water Management and Monitoring, excess dewatering water would be treated in the existing Pipeline water treatment facility or proposed Cortez Hills water treatment facility to reduce naturally occurring arsenic concentrations to meet Nevada Profile I reference values (NAC 445A) prior to being routed to the existing and proposed RIBs or injection wells for disposal, or conveyed to the Rocky Pass Reservoir or Dean Ranch for temporary storage or irrigation use, respectively.

Dewatering water temporarily stored in the reservoir would be routed to the RIBs, to the Dean Ranch for irrigation use, or to the Pipeline Complex pit lake following the completion of mining. The proposed RIB sites would be reviewed through the NDEP Water Pollution Control Permit process and would be constructed and operated as approved by NDEP. The proposed reservoir would be designed, constructed, operated, and closed in accordance with NAC 535. The final design plans would be submitted to NDEP, Division of Water Resources for approval prior to construction.

The water quality of the groundwater produced from the proposed expanded dewatering operations is expected to be similar to groundwater currently produced by existing dewatering operations (Geomega 2016a). Following treatment at the existing Pipeline or proposed Cortez Hills water treatment facility, the water quality is anticipated to be similar to that currently 2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-83 disposed of in existing RIBs or used for irrigation water at the Dean Ranch. Consistent with current operations of the water treatment facility, sediment from the proposed water treatment plant would be disposed of in the existing Pipeline Tailings Facility, a zero discharge facility.

Rapid Infiltration Basins (RIBs) Under the Proposed Action, excess dewatering water that meets the applicable Nevada water quality standards would be infiltrated into alluvial deposits at existing RIBs in Crescent Valley and in proposed new RIBs that would be constructed in Crescent Valley northeast of the CGM Operations Area, and in Grass Valley and Pine Valley. The infiltration of excess dewatering water would result in the development of groundwater mounds below and adjacent to the RIBs. Groundwater mounds are areas where the groundwater table rises above the pre-infiltration levels. The predicted location and extent of the groundwater mounds in Crescent, Grass, and Pine valleys at the end of mining and related water management activities under the Proposed Action are shown on Figure 3-13. These groundwater mounds are projected to dissipate in the post-mining period after infiltration activities cease.

Fennemore et al. (2001) described a rapid-screening technique to evaluate both basin infiltration rates and groundwater chemistry for the earlier Pipeline Project. Their results documented that mounding of groundwater in the alluvial basin sediments typically results in a short-term increase in solute concentrations. The increase in solute concentrations resulted from leaching of soluble minerals in the previously unsaturated zones and resulted in a transitory (less than 6-month) increase in solute concentrations followed by a decrease to baseline conditions. In addition, leaching of fine-grained deposits with evaporites produced higher solute concentrations than coarse-grained soils.

Site investigations have been conducted to characterize the conditions at the proposed RIB sites. These investigations included drilling, testing, and sampling (Barrick Nevada 2017). Geomega (2017b) conducted column tests on selected samples of the alluvium to estimate the rate and extent of solute release under conditions representative of the RIB operations. The results of this study identified nitrate and sulfate as the most likely solutes to be flushed from the alluvium during infiltration. Both nitrate and sulfate are elevated in the alluvium and generally decreased with depth.

Monitoring of the existing RIBs indicates that the rising groundwater has caused dissolution of naturally occurring salts present in the previously unsaturated alluvial materials. The salinity in the groundwater mounds is initially elevated as a result of dissolution of these soluble salts. However, the higher salinity is generally a transient event such that the soluble salts are dissolved in the first few pore volumes of infiltrating water; additional inputs of water do not cause dissolution of substantial additional amounts of soluble salts (Geomega 2017b).

The effects of the operation of the RIB’s on groundwater quality would be the same as discussed in prior NEPA for the CGM Operations Area including: the South Pipeline Project Final EIS (BLM 2000), Pipeline/South Pipeline Expansion Project Final SEIS (BLM 2004), and Cortez Hills Expansion Project Final EIS (BLM 2008). Construction of proposed RIBs would take into account site characteristics, including potential water quality considerations, and would be subject to review and approval through an NDEP permitting process. Monitoring would be conducted in accordance with the site’s IMP (Itasca 2016b).

In summary, based on the column test results and experience with the existing RIBs over the past two decades, operation of the proposed RIBs would likely result in short-term (generally less than 6 months), localized, elevated concentrations of nitrate and sulfate during the initial operation of the proposed RIBs as a result of the dissolution of naturally occurring minerals within the alluvium as the groundwater mound develops. However, mixing and dispersion 2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-84 would reduce the salinity as the groundwater moves downgradient. As a result, the increased salinity is not expected to result in exceedances of groundwater quality standards away from the immediate areas of the infiltration ponds. Therefore, impacts would be negligible.

Grass Valley Injection Wells Two existing Grass Valley production wells may be converted to injection wells, and up to four additional injection wells may be constructed in Grass Valley, to provide for re-injection of treated dewatering water into the alluvial aquifer in Grass Valley. These wells would be used, if necessary, as an option for water disposal operations. If constructed, the injection wells would be used to re-inject treated dewatering water at an estimated rate of 1,945 gpm (Table 2-2). All injection wells would be constructed in accordance with NAC 445A.842 through 445A.925.

The existing Grass Valley production wells (GVPW-01 and GVPW-02) are located on the valley floor in the northern portion of Grass Valley. These wells were constructed in the basin fill alluvial aquifer with a series of open louvered casing intervals situated between depths of 368 to 888 feet (GVPW-01) and 440 to 920 feet (GVPW-02). At the time the production wells were completed, the static water was recorded as 65 and 80 feet below ground surface, respectively, and the test pumping rates were 482 and 660 gpm, respectively. It is anticipated that the design and depth of any new injection wells would be similar to the existing production wells.

Any dewatering water re-injected into the basin fill alluvial aquifer would meet Nevada drinking water standards (NDEP Profile II reference values). Re-injection of dewatering water into the basin fill material would result in an increase in groundwater levels (i.e., groundwater mounding) around the well injection area. The groundwater mound would likely result in leaching of soluble minerals in the previously unsaturated zones and result in a transitory increase in solute concentrations followed by a decrease to baseline conditions as described above for the RIBs. As with the RIBs, the use of the injection wells would be subject to review and approval and groundwater monitoring requirements through an NDEP permitting process. Therefore, any impacts to water quality would be localized and short term such that downgradient water quality impacts are not expected.

Rocky Pass Reservoir A portion of the treated dewatering water would be stored in the proposed Rocky Pass Reservoir. The proposed reservoir site is located in a low-lying area in the northeast portion of Carico Lake Valley. Surface water streams in the footprint of the proposed facility are ephemeral. Seasonal surface water flow that occurs in this area of Carico Lake Valley is mostly lost to evapotranspiration, and the remainder seeps into groundwater (Zones 1961). The depth to groundwater at the reservoir site is relatively shallow (typically less than 40 feet) (Geomega 2017c).

Water uses assumed to occur at the proposed Rocky Pass Reservoir would include use as a livestock and wildlife water source, with irrigation use at the Dean Ranch. Water quality analyses from dewatering wells (Geomega 2016a) were reviewed as part of the surface water resources assessment for this EIS.

In general, existing constituent concentrations in the dewatering sources are well within the use standards in Table 3-5 for arsenic, boron, mercury, pH, selenium, sulfate, and TDS. Mercury and selenium were not detected in most dewatering well samples. Therefore, treated dewatering inflows would not generate surface water quality impacts at the proposed reservoir.

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Geomega (2017c) evaluated the surface water quality of the reservoir by testing the water quality of an analog reservoir constructed in the laboratory using water collected from the dewatering system and surface grab samples collected from across the reservoir footprint. The laboratory results indicated that the water quality of the top and bottom layer of the water column from the analog reservoir was similar, and there were no exceedances of the NDEP Profile III reference values except for fluoride (3.06 mg/L). The results of the analog reservoir indicated that the surface water in the proposed Rocky Pass Reservoir is expected to be of good quality compared to the NDEP Profile III reference values; therefore, adverse water quality impacts on livestock, wildlife, and irrigation are not anticipated.

Following the completion of mining, water remaining in the Rocky Pass Reservoir would be piped to the Pipeline Pit lake, the embankment removed, and the area reclaimed. As a result, no long-term surface water impacts would result from the proposed reservoir.

Ore Stockpiles As discussed in Section 2.3, the Proposed Action includes expansion of the existing oxide ore stockpile at the Pipeline Complex and construction of a refractory ore stockpile at the Gold Acres Complex and an oxide/refractory ore stockpile at the Cortez Complex. Both the refractory ore and oxide/refractory ore stockpiles would be designed and constructed to prevent potential degradation to surface or groundwater resources in accordance with the NDEP Water Pollution Control Permit requirements. The liner requirements for these two stockpiles would be determined based on ongoing rock characterization. Sampling and analytical testing of the refractory ore would be conducted in accordance with the BMRR waste rock, overburden, and ore evaluation guidelines (NDEP-BMRR 2014) to determine if the ore is considered a potentially acid generating material. Refractory ore materials characterized as potentially acid generating or that have the potential to generate leachate with elevated metals concentrations would be placed in a lined ore stockpile. Storm water would be diverted around the stockpiles as necessary to prevent run-on. The liner and storm water control designs for each lined stockpile would be submitted to NDEP for approval under the Water Pollution Control Permit requirements. Based on the: 1) requirements for geochemical characterization of the refractory ore materials; 2) NDEP procedure for review and approval of the final design of the refractory ore stockpiles; and 3) NDEP requirements for liners and storm water controls to prevent potential degradation to water quality, impacts to surface water or groundwater quality resulting from the proposed refractory ore and oxide/refractory ore stockpiles are not anticipated.

Under the Proposed Action, the existing Pipeline oxide ore stockpile would be expanded. Material characterization as outlined in the water pollution control permit would be used by the NDEP to determine the design and monitoring requirements for the ore stockpiles. Given existing authorizations and compliance with regulatory requirements for design, construction, and reclamation and closure, no significant impacts to surface water quality would occur under the Proposed Action.

3.2.2.3 Erosion, Sedimentation, and Flooding As shown in Figure 2-3 and indicated in Table 2-1, the proposed surface disturbance for waste rock facility and open pit modifications would affect a relatively small area. These permanent facilities would occupy approximately 0.1 percent of the Crescent Valley HSA. Facilities that would be removed and the associated disturbance areas reclaimed following the completion of mining (e.g., Rocky Pass Reservoir, RIBs, ancillary facilities) temporarily would occupy approximately 0.3 percent the Crescent Valley HSA, 0.7 percent of the Carico Lake Valley HSA, 0.1 percent of the Grass Valley HSA, and less than 0.1 percent of the Pine Valley HSA. Similar to existing waste rock facilities and open pits, stormwater diversions would be

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-86 designed, constructed, and maintained to route runoff around these areas in accordance with NDEP regulations and approved plans and permits. Consistent with the NDEP Water Pollution Control Permit and BCI’s Stormwater Pollution Prevention Plan (BCI 2016b), similar surface water management practices would be used to address additional surface disturbance under the Proposed Action. No alteration of drainage patterns or channel geometry resulting in accelerated erosion and sedimentation would occur. Given the arid setting and the ephemeral nature of the project area drainages involved, the temporary and permanent withdrawal of contributing watershed areas would not create a measurable reduction of seasonal surface flows. Therefore, no significant surface water quantity impacts would result.

Under the Proposed Action, part of the Cortez Waste Rock Facility expansion area would extend into a portion of the FEMA-delineated floodplain in Crescent Valley, and the proposed reservoir site would occupy a FEMA-delineated floodplain along Cooks Creek in Carico Lake Valley (Figure 3-4). The Cortez Waste Rock Facility expansion area is surrounded by existing facilities that currently occupy a portion of the floodplain as shown in Figure 3-4. As a result, impacts to the floodplain in Crescent Valley under the Proposed Action would be considered negligible. Construction of the Rocky Pass Reservoir and its embankment would be a significant impact to the existing delineated floodplain in Carico Lake Valley, which would be mitigated by Nevada dam safety requirements and the permitting process involving the Nevada State Engineer as described below.

The Rocky Pass Reservoir and its embankment would be subject to permit application review and approval by the Nevada Division of Water Resources, Dam Safety Program, and other requirements under NAC Chapter 535. The safety of dams permit is subject to specific permit terms, including design and construction requirements, an emergency action plan, authorization to impound (and associated water rights), monitoring, reporting, and other factors. As called for in the regulations and permit requirements, the State Engineer would determine the dam hazard classification and associated permit ramifications. Catastrophic breach conditions and related impacts would be included in that classification and related permit terms. In addition, design factors would be determined and reviewed for the inflow design flood, freeboard and surcharge, outlet capacity, spillway capacity, seismic and geotechnical factors, rapid fill and rapid drawdown, and other considerations. In addition, a formal dam decommissioning plan also would be required.

Assuming a thorough design and application review process on the part of BCI, its contractors, and the State Engineer, as well as construction, monitoring, and other compliance with a state- approved permit in accordance with NAC Chapter 535, no significant floodplain impacts would remain from the construction, operation, or decommissioning of Rocky Pass Reservoir. As discussed in Section 2.3.4, Reclamation, the reservoir embankment would be removed and the reservoir footprint would be recontoured and revegetate following the completion of mining. Implementation of these measures would mitigate the disturbance to the delineated floodplain.

The currently approved Water Pollution Control Plan for the CGM Operations Area is being updated. It includes an updated SWPPP (BCI 2016b) developed as part of the Proposed Action. Also, BCI has updated the sites’ reclamation plan to incorporate the Proposed Action. That plan is described in Section 2.3.4, Reclamation. All of these plans form critical parts of NDEP permit applications that will be reviewed by appropriate bureaus within the agency. NDEP reviews and approvals also involve BLM through various memorandums of understanding, particularly with respect to reclamation and water quality.

Best management practices to control runoff, erosion, and sedimentation have been, and would continue to be, employed as a result of agency permitting and approval processes. The best management practices are discussed in Section 2.3.3, Applicant-committed

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Environmental Protection Measures. Other design features, practices, and procedures implemented through the approved permits would address site drainage, good housekeeping and materials storage, staff responsibilities, monitoring and reporting, and other factors.

As discussed in Section 2.3.3, Applicant-committed Environmental Protection Measures, stormwater diversions would be constructed around project facilities, where needed, to divert stormwater around disturbance areas. These would be designed in accordance with NDEP regulatory programs. Aboveground fuel tanks would be provided with secondary containment equaling at least 110 percent of the maximum storage volume.

As a result of these practices and procedures, no significant water quality impacts from the construction, operation, or maintenance of project components would occur from the Proposed Action. At the end of the project, agency-approved reclamation and closure programs would restore site drainage and stability. These programs would prevent or mitigate long-term impacts to surface water resources.

Post-mining stormwater controls on the western and southern perimeters of the Gold Acres Pit and elsewhere would be modified to accommodate proposed pit expansions. These features would be maintained in accordance with NDEP requirements. Relatively small additional acreages would be diverted from ephemeral drainages of arid watersheds as a result of these features.

3.2.3 Gold Acres Pit Partial Backfill Alternative As per the Proposed Action, no dewatering would be required for the proposed expansion of open pit operations at the Gold Acres Complex under this alternative as the proposed pit bottom elevations would be above the groundwater table. Therefore, potential impacts to water resources under the Gold Acres Pit Partial Backfill Alternative would be the same as described under the Proposed Action.

3.2.4 No Action Alternative Under the No Action Alternative, the proposed Deep South Expansion Project would not be developed, and the associated impacts would not occur. Under this alternative, existing operations in the CGM Operations Area would continue to operate under the terms of current permits and approvals as authorized by the BLM and State of Nevada. The currently authorized dewatering and water management operations for existing operations are summarized in Section 2.4.2, No Action Alternative; annualized average dewatering and infiltration rates are summarized in Tables 3-12 and 3-13, respectively. Potential impacts to water quality from continued mining and the construction, operations, and closure of the currently authorized waste rock facilities, heap leach facilities, tailings impoundments, underground operations, and RIBs would be the same as described in the prior NEPA documents for the CGM Operations Area (BLM 2008, 2004, 2000, 1996). Impacts associated with mine-related groundwater drawdown and post-mining pit lake development under the No Action Alternative are described below based on updated modeling completed in support of the Proposed Action, which also included results for the No Action Alternative.

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3.2.4.1 Water Quantity Impacts Impacts to Water Levels Potential changes in groundwater levels under the No Action Alternative were evaluated using the methodology previously described in Section 3.2.1, Evaluation Methodology. The predicted changes in groundwater levels attributable to the No Action Alternative at the end of dewatering and infiltration activities (Year 2023) are shown in Figure 3-18. The maximum projected drawdowns are approximately 1,400 feet at the Pipeline Pit Complex and 2,000 feet at the Cortez Hills Complex (Itasca 2016a).

At the end of dewatering, three distinct drawdown areas are predicted to develop: one area centered on the Pipeline Complex, one area centered on the Cortez Hills Complex that extends to the southeast into northern Grass Valley and western Pine Valley, and an isolated area located in the Simpson Park Mountains in Pine Valley approximately 11 miles southeast of the Cortez Hills Complex. The isolated drawdown area in the Simpson Park Mountains occurs in a carbonate rock window that is hydraulically connected to the carbonate rock aquifer in the Cortez Hills Complex (Itasca 2016a). Mounding from infiltration activities is evident in three areas around existing RIBs located in southern Crescent Valley. Infiltration at RIBs located immediately to the northeast (Highway RIB) and south (Rocky Pass and Windmill RIBs) of the Pipeline Complex have limited mounding in the basin fill aquifer to the northeast and southwest of the Pipeline Pit Complex.

Modeling simulations were conducted by Itasca (2016a) for representative points in time over 200-year post-mining period. The results indicate that after dewatering ceases, the depth of drawdown beneath the pumping centers diminishes, but the areal extent of the drawdown continues to expand laterally. Comparison of these simulations over the recovery period indicates that the maximum extent of the 10-foot drawdown contour continues to expand for up to approximately 150 years. However, the lateral expansion reaches a maximum at different time periods in different areas and is controlled in large part by the modeled hydraulic parameters assigned for the different hydrogeologic units in different areas. The predicted long-term lateral expansion of the drawdown area results from continual inflow of groundwater from the surrounding area to fill the voids from the deep drawdown cone centered on the mine areas and filling of the pit lakes.

The predicted maximum areal extent of the 10-foot drawdown contour attributable to the No Acton Alternative is shown in Figure 3-14. This figure shows the predicted outer limit of the 10-foot drawdown contour as determined by overlaying a series of 10-foot drawdown contours for representative points in time over the 200-year recovery period (Itasca 2016a). The maximum area of drawdown (defined by the 10-foot contour) is predicted to extend across the southern portion of the Crescent Valley, and adjacent areas along the margin of Carico Lake Valley, northern Grass Valley, and western Pine Valley. The overall impacts to groundwater elevations would be moderate to major, long-term, and regional.

The simulated residual drawdown after 200 years of recovery predicts that residual drawdown would persists in areas surrounding the Pipeline and Cortez Hills complexes (Figure 6-15, Itasca 2016a). Residual drawdown around the Pipeline Complex is predicted to extend up to several miles from the Pipeline Pit Complex towards the north, west, and southwest. Residual drawdown in the vicinity of the Cortez Hills Complex would extend up to several miles focused towards the west, east, and southeast. This residual drawdown would represent a long-term, regional impact to the water table.

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As with the Proposed Action, the No Action Alternative is not predicted to impact groundwater levels in the vicinity of the town of Crescent Valley or in the northern portion of Crescent Valley in the vicinity of the Humboldt River (SRK 2016).

Pit Lake Development Pit lake development under currently authorized mining in the CGM Operations Area was evaluated in the Cortez Hill Expansion Project Final EIS (BLM 2008). Following the completion of the currently authorized mining and dewatering operations, groundwater elevations would rebound and eventually result in the development of pit lakes in both the Cortez Hills and Cortez pits. The predicted physical conditions of the pit lakes are summarized in Table 3-21. The predicted rate of pit lake development under the No Action Alternative was provided in Figure 3-15, in the Cortez Hills Expansion Project Final EIS (BLM 2008). Updated groundwater modeling predicts outflow from the Cortez Hills Pit lake to groundwater at a rate of approximately 174 gpm (280 acre-feet/year) after 200 years of recovery. A small amount of outflow (1.1 gpm or 1.7 acre-feet per year) is predicted to occur from the historic Cortez Pit. Groundwater flow in the vicinity of the Crossroads Pit is radially inward towards the pit in all direction except for a minor amount of outflow (0.3 gpm or 0.5 acre-feet per year) predicted to develop in the alluvial highwall on the east side of the pit as the lake stage approaches equilibrium (Itasca 2016a). In addition, at 200 years after dewatering ceases, the combined estimated net evaporative loss for pit lakes under the No Action Alternative is 527 gpm (851 acre-feet per year). These evaporative losses would be considered a minor but long-term impact to the regional water balance.

Table 3-21 Summary of Predicted Pit Lakes at 200 Years Post-mining Under the No Action Alternative

Pit Floor Lake Surface Elevation Maximum Groundwater Pit Lake Surface Area Volume Elevation (deepest) Depth Outflow Location1 (acre) (acre-feet) (feet amsl) (feet amsl) (feet) (gpm) Cortez Hills Pit 39 7,370 5,020 4,600 420 (174) Cortez Pit 5 355 4,801 4,770 31 (1) Crossroads Pit2 275 146,969 4,776 3,400 1,376 (0.3) Gap Pit2 35 5,524 4,776 4,400 376 No 1 Under currently authorized activities, the North Gap Pit expansion area of the Pipeline Pit Complex would be backfilled, precluding the development of a pit lake. 2 The approved Crossroads and Gap pits are part of the existing Pipeline Pit Complex. Source: Itasca 2016a.

Impacts to Perennial Streams and Springs Mine-induced groundwater drawdown under the No Action Alternative is predicted to result in a reduction in groundwater levels both during active dewatering and for an extended period after dewatering ceases. The methodology used to evaluate potential risk to perennial surface water sources within the projected drawdown area is described in Section 3.2.1, Evaluation Methodology. For purposes of this EIS, all spring and seep sites that previously were addressed in the Cortez Hills Expansion Project Final SEIS (Table 3.2-1, BLM 2011) were excluded from this evaluation. Unless otherwise noted, the spring and seep locations are referred to throughout the remainder of this section simply as springs.

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Potential impacts to streams were evaluated by using available baseline data to estimate the length of perennial stream reaches located within the projected drawdown area. Potential impacts and site-specific mitigation measures previously were identified for Indian and Ferris creeks, located on the east slope of the Shoshone Mountains northwest of the Pipeline Pit Complex, and Mill Creek, located in the Cortez Mountain northeast of the Cortez Complex. The updated model simulations for the No Action Alternative were used to reevaluate the perennial stream reaches located within the projected drawdown area. Perennial stream reaches located within the drawdown area are summarized in Table 3-16. There are an estimated 19.6 miles of perennial streams located within in the drawdown area.

Springs that occur within the project drawdown area under the No Action Alternative are identified in Appendix A, Table A-2. As summarized in Table 3-17, there are a total of 122 springs identified within the drawdown area, excluding the springs that previously were addressed in the Cortez Hills Expansion Project Final SEIS (Table 3.2-1, BLM 2011).

If the perennial flow in the specific stream reaches and springs identified above are controlled by discharge from the regional aquifer system that is projected to be affected by mine-induced drawdown, impacts to flows would likely occur. A reduction in flows could reduce the length of the perennial stream reaches or dry up a spring or seep. Reductions to flows along perennial stream reaches or at spring and seep sites within the drawdown area would be considered moderate to major, long-term, regional impacts to water resources.

As described for the Proposed Action, the actual impacts to individual seeps, springs, or stream reaches would depend on the source of groundwater that sustains the perennial flow (perched or hydraulically isolated aquifer versus regional groundwater system) and the actual extent of mine-induced drawdown that would occur in the area.

Impacts to Water Rights For the purpose of this analysis, all water rights owned by BCI (or Cortez Joint Venture or Barrick Gold) were excluded. Private water rights located within the predicted drawdown areas are shown in Figure 3-15. As listed in Table 3-18 there are four water rights located within the predicted mine induced drawdown area (i.e., areas where the groundwater levels are predicted to be lowered by 10 feet or more resulting from the mine groundwater pumping activities under the No Action Alternative). These include two surface water rights (one located at a spring source, and the other located at a stream source) and two groundwater rights. According to the State Engineer’s records, three of the water rights are used for irrigation and one is used for mining and milling. Potential impacts to individual water rights would be the same as described for the Proposed Action.

Impacts to the Regional Water Balance The water balance for the groundwater system within the HSA was estimated using the groundwater flow model (Itasca 2016a). Comparisons of the estimated annual groundwater inflow and outflow rates under the baseline condition (2014); end of dewatering under the No Action Alternative (2023); and 200 years post-mining for the No Action Alternative are summarized in Table 3-22. The water balance provides an estimate of the annual change in storage and fluctuations of the major inflow and outflow components over time resulting from the mine dewatering and water management activities. The simulated groundwater outflow to the Humboldt River and Pine Creek are essentially the same for each period. The model simulations predict that groundwater discharge to Horse Creek would be reduced from an estimated 21 acre-feet per year in 2015 to approximately 2 acre-feet per year in 2024 (end of mining). These predictions indicate a substantial reduction in the baseflow to the perennial reach of Horse Creek. At 200 years after mining, the post-recovery water budget indicates that

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-92 the groundwater discharge to Horse Creek eventually would return to approximately the pre- mining conditions.

Summary Table 3-22 Simulated Groundwater5 Budget for the HSA Under the No Action Alternative

Pre-mining End of Period Baseline Period Dewatering 200 Years after 2 Groundwater Budget (Pre-1996) (2014) (2023) Dewatering Component (acre-feet per year)1,2 Groundwater Inflow Precipitation Recharge 71,300 71,300 71,300 71,300 Infiltration Recharge (RIBs) 0 24,700 33,300 0 Pit Lakes 0 0 0 300 4 Surface and Subsurface Inflow 12,000 16,900 18,800 12,300 Total Inflow 83,300 114,300 123,400 83,900 Groundwater Outflow Evapotranspiration 51,800 55,600 56,800 50,300 Groundwater Pumping Non-mining 8,100 7,600 7,600 8,100 Mine Dewatering 0 32,600 38,300 0 Pit Lake 0 0 0 1,100 Discharge to Surface Waters 13,100 13,000 12,700 13,000 (springs and streams) (Humboldt River3) (300) (300) (300) (300) (Pine Creek3) (5,800) (5,800) (5,400) (5,800) (Horse Creek3) (28) (22) (2) (26) 4 Subsurface Outflow 10,400 15,300 17,200 10,700 Total Outflow 83,400 124,000 132,600 83,200 Net Results Inflow Minus Outflow -100 -9,700 -9,200 700 Storage Change (model 0 11,400 -9,200 -600 simulated) 1 Estimation based on results from the calibrated numerical groundwater model developed for the project. 2 Estimates provided in the source document were rounded to the nearest hundred for presentation in this EIS. 3 Represent a breakdown of individual stream flows included under the “Discharge to Surface Waters (springs and streams).” Values in parentheses are positive values provided for comparison purposes. 4 Values represent a summation of the inflows and outflows for each of the four basins included within the study area. As such, these summation values include both inter-basin flow between the four basins within the study area, and flow across the model boundary to basins located outside of the model area. 5 The flow rates for the groundwater inflow and outflow components provided in this table are based on a summation of the rates provided for each of the four basins included within the groundwater model. A detailed breakdown of the estimated groundwater inflow and outflow rates for each of the four basins within the study area is provided in a series of water balance tables for representative years provided in the referenced model report. Source: Itasca 2016a.

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3.2.4.2 Water Quality Impacts Pit Lake Water Quality Under the No Action Alternative, pit lakes are predicted to develop in the Cortez Hills and Cortez pits and in the Crossroads and Gap pits in the Pipeline Pit Complex as summarized in the Cortez Hills Expansion Project Final EIS (Table 3.2-11, BLM 2008). The predicted water quality for these pit lakes was described and evaluated as part of the Cortez Hills Expansion Project Final EIS (BLM 2008) Proposed Action. In summary, modeling results for these pit lakes and examination of water quality data from the historic Cortez Pit lake indicated that the pit lakes were expected to contain good quality water that would be reasonably similar to the background groundwater quality. The mature Gap and Crossroads pit lakes had predicted water chemistries that slightly exceeded some water quality standards. However, these pit lakes were predicted to act largely as terminal pit lake groundwater sinks; although a small amount of outflow (0.3 gpm) was predicted through the alluvium as the lakes approach equilibrium. The projected Cortez Hills Pit lake water quality did not exceed any water quality standards and was expected to have a steady-state flow-through of approximately 174 gpm. As a result, it is anticipated that the formation of these pit lakes would not affect the water quality of downgradient aquifers. The expected Cortez Pit lake water quality also was not predicted to exceed water quality standards and was not expected to affect the water quality of downgradient aquifers.

3.3 Cumulative Impacts The CESA for water resources is the HSA described for the project in Section 3.1.1, Hydrologic Setting, and shown in Figure 3-1, inclusive of the predicted maximum extent of the cumulative 10-foot groundwater drawdown contour. Past and present actions and RFFAs are identified in Table 2-4. Of those identified, the actions that have the potential to affect water resources within the HSA include the major groundwater development or dewatering operations that have occurred or are predicted to occur in the reasonably foreseeable future.

3.3.1 Proposed Action 3.3.1.1 Water Quantity Impacts Potential cumulative changes in water levels in the groundwater system were evaluated using the methodology previously described in Section 3.2.1, Evaluation Methodology. The average annual pumping and infiltration rates included under this cumulative modeling scenario are summarized in Table 3-12 and Table 3-13, respectively. The predicted cumulative changes in groundwater levels projected at the end of dewatering and infiltration activities are shown in Figure 3-19. The primary difference between the Proposed Action and the end of mining cumulative model scenarios is the addition of the dewatering and infiltration activities from the potential future Goldrush Project between model years 2022 through 2043 (Figure 3-12). By Year 2043, the maximum projected drawdown is approximately 1,815 feet in the vicinity of the Goldrush Project (SRK 2017).

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At the end of dewatering, the simulated drawdown associated with dewatering at the Pipeline and Cortez Hills complexes and the Goldrush underground mine coalesce and form an elongate northwest-southeast oriented drawdown area that extends across Crescent Valley into northern Grass Valley and western Pine Valley (Figure 3-19). An isolated drawdown area is projected to develop in the Simpson Park Mountains in Pine Valley approximately several miles southeast of the potential future Goldrush underground operations. The isolated drawdown area in the Simpson Park Mountains occurs in a carbonate rock window that is hydraulically connected to the carbonate rock aquifer in the Cortez Hills Complex (Itasca 2016a). Another isolated drawdown area located in the northern portion of the Carico Lake Valley HA results from pumping at the Greystone Mine (i.e., not resulting from BCI’s dewatering activities). Mounding from infiltration activities is evident in areas developed around RIBs located in the basin fill aquifers in the east central portion of Crescent Valley and western portion of Pine Valley. The overall impacts to groundwater elevations would result in moderate to major, long-term, regional impacts.

Modeling simulations were conducted for representative points in time over a 500-year post- mining period. After dewatering ceases, the depth of drawdown beneath the pumping centers diminishes, but the areal extent of the drawdown continues to expand laterally. Comparison of these simulations over the recovery period indicates that the maximum extent of the cumulative 10-foot groundwater drawdown contour continues to expand for up to approximately 260 years. However, the lateral expansion reaches a maximum at different time periods in different areas and is controlled in large part by the modeled hydraulic parameters assigned for the different hydrogeologic units in different areas. The predicted long-term lateral expansion of the drawdown area results from continual inflow of groundwater from the surrounding area to fill the voids from the deep drawdown cone centered on the mine areas and filling of the pit lakes.

The maximum areal extent of the cumulative 10-foot groundwater drawdown contour is presented on Figure 3-20. This figure shows the predicted outer limit of the 10-foot drawdown contour as determined by overlaying a series of 10-foot drawdown contours for representative points in time over the 500-year post-mining period (SRK 2016). The maximum area of groundwater drawdown (defined by the 10-foot contour) is predicted to extend across the southern portion of the Crescent Valley HA and adjacent areas along the margin of Carico Lake Valley HA, northern Grass Valley HA, and western Pine Valley HA. Surface water resources and water rights identified within the maximum cumulative drawdown area are shown on Figures 3-20 and Figures 3-21, respectively. The simulated residual drawdown after 500 years of recovery is shown in Figure 3-22. The model results predict that residual drawdown would persist in two areas: one surrounding the Pipeline Complex and another surrounding and extending across the combined Cortez Hills Complex and potential future Goldrush underground mine area. The model simulations also predict that a groundwater mound would persist in the northern portion of Carico Lake Valley.

As described above, mine-induced groundwater drawdown resulting from the cumulative scenario is predicted to result in a reduction in groundwater levels both during active dewatering and for an extended period after dewatering ceases. The methodology used to evaluate potential risk to perennial water sources within the projected cumulative drawdown area was described in Section 3.2.1, Evaluation Methodology. Unless otherwise noted, the springs and seeps are referred to throughout the remainder of this section as springs.

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Available baseline data and the model simulations for the cumulative scenario were used to evaluate the perennial stream reaches located within the projected cumulative drawdown area. Perennial stream reaches located within the cumulative drawdown area are summarized in Table 3-16. There are an estimated total of 35.7 miles of perennial streams located in the drawdown area. As shown in Figure 3-18, the predicted potential cumulative impacts to Indian and Ferris creeks are essentially the same as under the Proposed Action. The isolated drawdown associated with the Greystone Mine located in northern Carico Lake Valley is projected to encompass portions of the perennial reaches of Elder, Cooks, and South Fork Mill creeks. The residual drawdown at 500 years post-mining, as shown in Figure 3-22, indicates that the groundwater elevations in the vicinity of all of these perennial stream reaches would recover in the post-mining period.

As previously described, for the purposes of this EIS, all springs and seeps that previously were addressed in the Cortez Hills Expansion Project Final SEIS (Table 3.2-1, BLM 2011) were excluded from this evaluation. Springs that occur within the cumulative drawdown area are presented in Appendix A, Table A-2. As summarized in Table 3-17, there are a total of 161 springs identified within the cumulative drawdown area, excluding the 27 springs that previously were addressed in the Cortez Hills Expansion Project Final SEIS (Table 3.2-1, BLM 2011).

If the perennial flow in specific stream reaches and springs identified above are controlled by discharge from the regional aquifer system that is projected to be affected by cumulative mine- induced groundwater drawdown, impacts to flows would likely occur. A reduction in flows could reduce the length of the perennial stream reaches or dry up a spring or seep. Reductions to flows in the identified perennial stream reaches within the cumulative drawdown area would be considered a moderate to major, long-term, regional impact.

As described for the Proposed Action, the actual impacts to individual seeps, springs, or stream reaches would depend on the source of groundwater that sustains the perennial flow (perched or hydraulically isolated aquifer versus regional groundwater system) and the actual extent of mine-induced drawdown that would occur.

Private water rights located within the predicted drawdown areas are shown in Figure 3-21 and listed in Table 3-18. Water rights identified within the drawdown area under the cumulative scenario are the same as described for the Proposed Action, with the following exception. Under the cumulative scenario, there are 10 additional non-BCI owned or controlled water rights located within an isolated drawdown area in the Carico Lake Valley HA. All of these are listed as groundwater rights used for mining and milling and are associated with the Greystone (barite) Mine located in northern Carico Lake Valley. The Greystone Mine has operated nearly continuously since 1954 and pumps groundwater for production and dewatering purposes (Itasca 2016a). Potential cumulative effects to specific water rights would be localized, and impacts could range from negligible to major. Any measurable impact to a water right would likely be long term.

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The water balance for the groundwater system within the HSA was estimated using the groundwater flow model (SRK 2017) for the cumulative scenario. Comparisons of the estimated annual groundwater inflow and outflow rates under the pre-mining (Pre-1996), end of dewatering for the potential future Goldrush Project (2043); and at 500 years post-mining are summarized in Table 3-23. The water balance provides an estimate of the annual change in storage and fluctuations of the major inflow and outflow components over time resulting from cumulative mine dewatering and water management activities. The simulated groundwater outflow to the Humboldt River and Pine Creek are essentially the same for each period. The model simulations predict that groundwater discharge to Horse Creek would be reduced from an estimated 21 acre-feet per year in 2015 to approximately 0 acre-feet per year in 2043 (end of mining). These predictions indicate that baseflow to the perennial reach of Horse Creek would be eliminated from 2025 through 2121 (SRK 2017). If drawdown impacts to Horse Creek occur as simulated in the groundwater model, these impacts would be considered major, long term, and regional. At 500 years after mining, the post-recovery water budget indicates that the groundwater discharge to Horse Creek eventually would return to approximately the pre-mining conditions. After full development of the pit lakes in the CGM Operations Area, evaporation from the surface of the pit lakes is predicted to consume approximately 1,100 acre-feet per year of groundwater, which represents approximately 1.3 percent of the total groundwater outflow from the HSA.

Summary Table 3-23 Simulated Groundwater6 Budget for the HSA Under Cumulative

Pre-mining End of 500 Years after Period Dewatering2 Dewatering2 (Pre-1996) (2043) (2543) Groundwater Budget Component (acre-feet per year)1,3 Groundwater Inflow Precipitation Recharge 71,300 71,300 71,300 Infiltration Recharge (RIBs) 0 1,800 0 Pit Lakes 0 300 100 5 Surface and Subsurface Inflow 12,100 13,200 12,300 Total Inflow 83,400 86,600 83,700 Groundwater Outflow Evapotranspiration 51,800 49,500 51,300 Groundwater Pumping Non-mining 8,100 7,500 7,500 Mine Dewatering 0 3,500 0 Pit Lake 0 6,300 1,100

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Summary Table 3-23 Simulated Groundwater6 Budget for the HSA Under Cumulative

Pre-mining End of 500 Years after Period Dewatering2 Dewatering2 (Pre-1996) (2043) (2543) Groundwater Budget Component (acre-feet per year)1,3 Discharge to Surface Waters (springs and 13,100 13,100 13,100 streams) (Humboldt River4) (300) (300) (300) (Pine Creek4) (5,800) (5,900) (5,800) (Horse Creek4) (29) (0) (27) 5 Subsurface Outflow 10,500 11,600 10,700 Total Outflow 83,500 91,500 83,700 Net Results Inflow Minus Outflow -100 -4,900 0 Storage Change (model simulated) 0 -4,400 0 1 Estimation based on results from the calibrated numerical groundwater model developed for the project. 2 Results based on mining and closure Scenario 3 as described by SRK (2017). 3 Estimates provided in the source document were rounded to the nearest hundred for presentation in this EIS. 4 Represent a breakdown of individual stream flows included under the “Discharge to Surface Waters (springs and streams).” Values in parentheses are positive values provided for comparison purposes. 5 Values represent a summation of the inflows and outflows for each of the four basins included within the study area As such, these summation values include both inter-basin flow between the four basins within the study area, and flow across the model boundary to basins located outside of the model area. 6 The flow rates for the groundwater inflow and outflow components provided in this table are based on a summation of the rates provided for each of the four basins included within the groundwater model. A detailed breakdown of the estimated groundwater inflow and outflow rates for each of the four basins within the study area is provided in a series of water balance tables for representative years provided in the referenced model report. Source: SRK 2017.

3.3.1.2 Water Quality Impacts Water quality impacts are not anticipated under the Proposed Action. Therefore, the project would not contribute to cumulative water quality impacts.

3.3.2 Gold Acres Pit Partial Backfill Alternative As per the Proposed Action, no dewatering would be required for the proposed expansion of open pit operations at the Gold Acres Complex under this alternative as the proposed pit bottom elevations would be above the groundwater table. Therefore, potential cumulative impacts under this alternative would be the same as described for the Proposed Action.

3.4 Monitoring and Mitigation Measures Issue: Mine-induced drawdown of groundwater levels could impact flows in identified perennial stream reaches and springs located within the area affected by drawdown. Identified perennial surface water resources that potentially could be affected by mine-inducted drawdown if hydraulically connected to the affected aquifer are listed in Tables A-2 and A-3, Appendix A. The water sources include: 1) perennial surface water features that may or may

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 3-102 not be influenced by seasonal runoff, and 2) perennial wet soil or small ponded areas with no measurable flow (i.e., seeps) that support hydrophilic vegetation.

Monitoring Measure WR1: BCI would expand the monitoring included in the IMP, as necessary, to include all of the identified surface water sites and associated mitigation listed in Table A-3, Appendix A. A draft of the comprehensive water resources monitoring plan would be provided to both the BLM and NDWR for review and approval prior to implementation of any new dewatering activities associated with the project. A copy of the monitoring plan would be provided to Eureka County.

BCI would be responsible for continued monitoring and reporting of changes in groundwater levels and surface water flows prior to, and during, operation and for a period of time in the post-reclamation period.

BCI would provide the results of water level monitoring, describe any deviations from the original predictions, evaluate if changes in flow are attributable to mine-induced drawdown, and propose modifications to the monitoring plan, as necessary, in an annual report to the NDWR and the BLM. If the monitoring results identify changes in flow to perennial waters that are attributable to mine-induced drawdown, the network of monitored seeps, springs, and streams would be expanded to include all perennial surface water features located within 2 miles of the affected area.

Monitoring and reporting would continue over the mining and into the post-mining period until the risk of impacts to water resources have been determine by the BLM to be negligible and any impacts to surface water resources have been mitigated.

Effectiveness: This additional monitoring and mitigation measure would provide for identification of potential flow-related impacts to perennial surface waters as a result of mine- related groundwater drawdown and trigger implementation of appropriate mitigation measures as specified in the currently authorized and proposed Contingency Mitigation Plans for Surface Water Resources. Implementation of this mitigation measure in combination with the applicant committed Contingency Mitigation Plans is anticipated to mitigate adverse impacts to surface water resources resulting from mine induced drawdown during the mining and post-mining period.

Issue: Mine-induced drawdown potentially could reduce flow at the point of diversion for surface water rights, or reduce water levels in water supply wells.

Mitigation Measure WR2: BCI would be responsible for monitoring groundwater levels between the mine and water supply wells, groundwater rights, and surface water rights within the projected mine-related groundwater drawdown area as part of the water resources monitoring program (Mitigation Measure WR1). Adverse impacts to water wells and water rights would be mitigated, as required by the NDWR.

Mitigation for impacts to water rights would depend on the actual impact and site-specific conditions and could include a variety of measures. Methods for addressing impacts to water rights may include, but would not be limited to, the following: for wells, mitigation could include lowering the pump, deepening an existing well, drilling a new well, or providing a replacement water supply of equivalent yield and general water quality; for surface water rights, mitigation could require providing a replacement water supply of equivalent yield and general water quality.

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Effectiveness: Implementation of this mitigation measure is anticipated to mitigate adverse impacts to water rights.

3.5 Residual Adverse Effects Successful implementation of mitigation measures would minimize or eliminate most residual adverse effects to water resources. However, an area of residual mine-related groundwater drawdown is predicted to persist for the foreseeable future as shown in Figure 3-16.

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4.0 References

Chapter 1.0 Introduction

Barrick Cortez Inc. (BCI). 2016. Barrick Cortez Inc. (NVN-067575 (16-1A)) Deep South Expansion Project Amendment to Plan of Operations and Reclamation Permit Application #0093. Submitted to BLM Mount Lewis Field Office, Battle Mountain, Nevada, and Nevada Division of Environmental Protection, Carson City, Nevada. October 2016.

Chapter 2.0 Alternatives Including the Proposed Action

Barrick Gold of North America (Barrick). 2018. Bank Enabling Agreement 2017 Annual Report. February 2018.

Barrick Cortez Inc. (BCI). 2018. Barrick Cortez Inc. Goldrush Mine Plan of Operations and Reclamation Permit Application. Submitted to BLM Mount Lewis Field Office, Battle Mountain, Nevada, and Nevada Division of Environmental Protection, Carson City, Nevada. December 2018.

Barrick Cortez Inc. (BCI). 2017a. Supporting documentation provided for the Proposed Action. January 31 through June 12, 2017.

Barrick Cortez Inc. (BCI). 2016a. Stormwater Pollution Prevention Plan. Pursuant to Stormwater General Permit #NVR300000. Revised August 2016.

Barrick Cortez Inc. (BCI). 2016b. Barrick Cortez Inc. (NVN-067575 (16-1A)) Deep South Expansion Project Amendment to Plan of Operations and Reclamation Permit Application #0093. Submitted to BLM Mount Lewis Field Office, Battle Mountain, Nevada and Nevada Division of Environmental Protection, Carson City, Nevada. October 2016.

Barrick Cortez Inc. (BCI) and Stantec Consulting Services Inc. (Stantec). 2018. Technical Memorandum Contingency Mitigation Plans for Surface Waters Deep South Expansion Project Lander and Eureka Counties, Nevada. Stantec Project Number 203720412. March 27, 2018.

Bureau of Land Management (BLM). 2017a. Bureau of Land Management’s Land & Mineral Legacy Rehost 2000 System - LR2000. Internet website: http://www.blm.gov/lr2000/. Accessed January 27, 2017.

Bureau of Land Management (BLM). 2017b. GIS Shapefiles for Wildfire Affected Areas in Nevada. May 30, 2017.

Bureau of Land Management (BLM). 2016a. Environmental Assessment Barrick Gold Exploration, Inc. Horse Canyon/Cortez Unified Exploration Project Plan of Operations (NVN-066621 [16-1A]) and Reclamation Permit No. 0159 Plan Amendment – Twin Declines for Underground Exploration. Battle Mountain District Office, Mount Lewis Field Office. Battle Mountain, Nevada. July 20, 2016.

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 4-2

Bureau of Land Management (BLM). 2016b. Decision Environmental Assessment Barrick Gold Exploration, Inc. Horse Canyon/Cortez Unified Exploration Project Plan of Operations (NVN-066621 [16-1A]) and Reclamation Permit No. 0159 Plan Amendment – Twin Declines for Underground Exploration. Mount Lewis Field Office, Battle Mountain, Nevada. September 9, 2016. On file, Bureau of Land Management, Mount Lewis Field Office, Battle Mountain, Nevada.

Bureau of Land Management (BLM). 2015a. Environmental Assessment Barrick Cortez Inc. (NVN-067575 [14-1A]) Amendment 3 to Plan of Operations and Reclamation Permit Application. Battle Mountain District Office, Mount Lewis Field Office, Battle Mountain, Nevada. July 2015.

Bureau of Land Management (BLM). 2015b. Decision/Finding of No Significant Impact Barrick Cortez Inc. Amendment to the Plan of Operations Approval Determination of Required Financial Guarantee. Mount Lewis Field Office, Battle Mountain, Nevada. September 11, 2015.

Bureau of Land Management (BLM). 2014a. Environmental Assessment for Barrick Cortez Inc. (NVN-67575 [11-3A]) 2011 Amendment to Plan of Operations and Reclamation Permit Application Proposed North Waste Rock Facility Realignment/Rangeland Fence Addition/Stockpile Relocation/Ancillary Addition. Battle Mountain District, Mount Lewis Field Office, Battle Mountain, Nevada. February 2014.

Bureau of Land Management (BLM). 2014b. Decision/Finding of No Significant Impact Cortez Gold Mines Project Amendment to the Plan of Operations Approval Determination of Required Financial Guarantee. Mount Lewis Field Office, Battle Mountain, Nevada. February 24, 2014.

Bureau of Land Management (BLM). 2011a. Cortez Hills Expansion Project Final Supplemental Impact Statement. Battle Mountain District Office, Battle Mountain, Nevada. January 2011.

Bureau of Land Management (BLM). 2011b. Cortez Hills Expansion Project Record of Decision and Plan of Operations Amendment Approval. Battle Mountain District Office, Battle Mountain, Nevada. March 2011.

Bureau of Land Management (BLM). 2008a. Cortez Hills Expansion Project Final Impact Statement. Battle Mountain District Office, Battle Mountain, Nevada. September 2008.

Bureau of Land Management (BLM). 2008b. Cortez Hills Expansion Project Record of Decision and Plan of Operations Amendment Approval. BLM Battle Mountain District, Battle Mountain, Nevada. November 2008.

ESRI World Imagery. 2017. GIS Application for Satellite Imagery. May 17, 2017.

Geomega Inc. (Geomega).2016. Deep South Expansion Project Waste Rock Management Plan. Prepared for: Barrick Cortez Inc. August 1, 2016. In: Barrick Cortez Inc. (BCI). 2016. Barrick Cortez Inc. (NVN-067575 (16-1A)) Deep South Expansion Project Amendment to Plan of Operations and Reclamation Permit Application #0093, Appendix 2. October 2016.

Itasca Denver, Inc. (Itasca). 2016. 2016 Integrated Monitoring Plan. Prepared for Barrick Cortez Inc. #1912-16. April 2016. In: Barrick Cortez Inc. (BCI). 2016. Barrick Cortez Inc.

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 4-3

(NVN-067575 (16-1A)) Deep South Expansion Project Amendment to Plan of Operations and Reclamation Permit Application #0093, Appendix 6. October 2016.

SRK Consulting, (U.S.) Inc. (SRK). 2017. Deep South Expansion Project – Cumulative Effects, Groundwater Flow Modeling Report. Prepared for Barrick Cortez Inc. March 2017.

SRK Consulting (SRK). 2014. Noxious Weed Management Plan. Prepared for Barrick Cortez Inc. SRK Project Number 460100.020. July 2014. In: Barrick Cortez Inc. (BCI). 2016. Barrick Cortez Inc. (NVN-067575 (16-1A)) Deep South Expansion Project Amendment to Plan of Operations and Reclamation Permit Application #0093, Appendix 7. October 2016.

U.S. Census Bureau. 2017. TIGER/Line Shapefile, Roads-Lander County. Internet website: ftp://ftp2.census.gov/geo/tiger/TGRGDB13/. November 11, 2009. Accessed May 17, 2017.

3.0 Water Resources and Geochemistry

Barrick Cortez Inc. (BCI). 2018. BCI water rights information provided by S. Shoen, BCI, to D. Gregory, AECOM. April 4, 2018.

Barrick Cortez Inc. (BCI). 2017a. Integrated Monitoring Plan – 4th Quarter 2016. Prepared for Bureau of Land Management, Battle Mountain Field Office. January 2017.

Barrick Cortez Inc. (BCI). 2017b. Water rights information and GIS files and updated water rights table provided by S. Schoen, BCI, to D. Gregory, AECOM. January 26 and February 24, 2017.

Barrick Cortez Inc. (BCI). 2017c. Intergrated Monitoring Plan Reports extending from 1st Quarter 2011 through the 4th Quarter 2016 Report.

Barrick Cortez Inc. (BCI). 2016a. Barrick Cortez Inc. Water Pollution Control Permit NEV00931019 Renewal Application. September 2016.

Barrick Cortez Inc. (BCI). 2016b. Barrick Cortez Inc. (NVN-067575 (16-1A)) Deep South Expansion Project Amendment to Plan of Operations and Reclamation Permit Application #0093, Appendix 4. Submitted to BLM Mount Lewis Field Office, Battle Mountain, Nevada and Nevada Division of Environmental Protection, Carson City, Nevada. October 2016.

Barrick Cortez Inc. (BCI) and Stantec Consulting Services Inc. (Stantec). 2018. Technical Memorandum Contingency Mitigation Plans for Surface Waters Deep South Expansion Project Lander and Eureka Counties, Nevada. Stantec Project Number 203720412. March 27, 2018.

Barrick Nevada. 2017. 2015/2016 Cortez Rapid Infiltration Basin Investigations Summary. April 17, 2017.

Belcher, W. R., P. E. Elliot, and A. L. Geldon. 2001. Hydraulic-property Estimates for Use with a Transient Ground-water Flow Model of the Death Valley Regional Groundwater Flow System, Nevada and California Water-Resources Investigation Report 01-4210.

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 4-4

Berger, D. L. 2000a. Water Budgets for Pine Valley, Carico Lake Valley, and Upper Reese River Valley Hydrographic Areas, Middle Humboldt River Basin, North-Central Nevada – Methods for Estimation and Results. U.S. Geological Survey Water- Resources Investigations Report 99-4272. Prepared in cooperation with the Nevada Division of Water Resources.

Berger, D. L. 2000b. Water-Budget Estimates for the 14 Hydrographic Areas in the Middle Humboldt River Basin, North-Central Nevada. U.S. Geological Survey Water- Resources Investigations Report 00-4168. Prepared in cooperation with the Nevada Division of Water Resources.

Bureau of Land Management (BLM). 2019a. Deep South Expansion Project Supplemental Environmental Report – Vegetation. Prepared in support of: DOI-BLM-NV-B010-2016- 0052. Battle Mountain District Office, Mount Lewis Field Office, Battle Mountain, Nevada.

Bureau of Land Management (BLM). 2019b. Deep South Expansion Project Supplemental Environmental Report – Geology and Minerals. Prepared in Support of: File Number: NVN-067575 (16-1A) DOI-BLM-NV-B010-2016-0052 EIS. Battle Mountain District Office, Mount Lewis Field Office, Battle Mountain, Nevada. 2019.

Bureau of Land Management (BLM). 2019c. Deep South Expansion Project Supplemental Environmental Report – Hazardous Materials and Solid Waste. Prepared in Support of: File Number: NVN-067575 (16-1A) DOI-BLM-NV-B010-2016-0052 EIS. Battle Mountain District Office, Mount Lewis Field Office, Battle Mountain, Nevada. 2019.

Bureau of Land Management (BLM). 2019d. Deep South Expansion Project Supplemental Environmental Report – Native American Traditional Values. Prepared in Support of: File Number: NVN-067575 (16-1A) DOI-BLM-NV-B010-2016-0052 EIS. Battle Mountain District Office, Mount Lewis Field Office, Battle Mountain, Nevada. 2019.

Bureau of Land Management (BLM). 2019e. Deep South Expansion Project Supplemental Environmental Report – Wildlife and Aquatic Biological Resources. Prepared in Support of: File Number: NVN-067575 (16-1A) DOI-BLM-NV-B010-2016-0052 EIS. Battle Mountain District Office, Mount Lewis Field Office, Battle Mountain, Nevada. 2019.

Bureau of Land Management (BLM). 2011. Cortez Hills Expansion Project Final Supplemental Impact Statement. Battle Mountain District Office, Battle Mountain, Nevada. January 2011.

Bureau of Land Management (BLM). 2008. Cortez Hills Expansion Project Final Impact Statement. Battle Mountain District Office, Battle Mountain, Nevada. September 2008.

Bureau of Land Management (BLM). 2004. Pipeline/South Pipeline Pit Expansion Project Final Supplemental Environmental Impact Statement. Battle Mountain Field Office, Battle Mountain, Nevada. December 2004.

Bureau of Land Management (BLM). 2000. South Pipeline Project Final Environmental Impact Statement. Battle Mountain District, Battle Mountain, Nevada. February 2000.

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 4-5

Bureau of Land Management (BLM). 1996. Cortez Pipeline Gold Deposit, Final Environmental Impact Statement – Volume 1. U.S. Department of the Interior, Bureau of Land Management, Battle Mountain District, Shoshone-Eureka Resource Area. January 1996.

Federal Emergency Management Agency (FEMA). 2017. FEMA Flood Map Service Center, Floodzone Maps for Eureka and Lander Counties, Nevada, Unincorporated Areas. Eureka County Panels 32011C0550D and 32011C0675D; Lander County Panels 32015C1100G, 32015C1250G, and 32015C1275G. Internet website: https://msc.fema.gov/portal/advanceSearch#searchresultsanchor. Accessed January and February 2017.

Fennemore, G. G., A. Davis, L Goss, and A. W. Warrick. 2001. A Rapid Screening-Level Method to Optimize Location of Infiltration Ponds. Ground Water March-April 2003. Pp 230-238.

Geomega Inc. 2017a. Memorandum: Kinetic Test Program Results for the Deep South Expansion Project CHUE Project Through Week 116. February 15, 2017.

Geomega Inc. 2017b. Crescent-Grass-Pine Valley New RIB Material Characterization. Prepared for: Barrick Cortez, Inc. May 8, 2017.

Geomega Inc.2017c. Carico Valley / Rocky Pass Reservoir Material Characterization. November 10, 2017.

Geomega Inc. 2016a. Memorandum from A. Davis and M. Lengke, Geomega, to S. Schoen, N. Atiemo, and M. Miller, Barrick, regarding: Cortez Deep South Expansion – Sub- 3,800 ft Groundwater Characterization. February 23, 2016.

Geomega Inc. 2016b. Cortez Deep South Expansion Pit Lake and Backfill Pore Water Chemistry. Prepared for Barrick Cortez, Inc. September 15, 2016.

Geomega Inc. 2016c. Characterization, Reactivity and Tunnel Aqueous Geochemistry in the Deep South Expansion, Cortez Underground Mine, Nevada. October 18, 2016.

Geomega Inc. 2016d. Deep South Expansion Project Waste Rock Management Plan. Prepared for Barrick Cortez, Inc. August 1, 2016. In: Barrick Cortez Inc. (BCI). 2016c. Barrick Cortez Inc. (NVN-067575 (16-1A)) Deep South Expansion Project Amendment to Plan of Operations and Reclamation Permit Application #0093. Submitted to BLM Mount Lewis Field Office, Battle Mountain, Nevada and Nevada Division of Environmental Protection, Carson City, Nevada. Appendix 2. October 2016.

Geomega Inc. 2007. Cortez Hills Expansion Project Waste Rock Assessment. Report prepared for Cortez Gold Mines. February 20, 2007. In: Bureau of Land Management (BLM). 2008. Cortez Hills Expansion Project Final Impact Statement. Battle Mountain District Office, Battle Mountain, Nevada. September 2008.

Geomega Inc. 2006. Cortez Hills Expansion Project Baseline Characterization Report. Prepared for Cortez Gold Mines. September 12, 2006. In: Bureau of Land Management (BLM). 2008. Cortez Hills Expansion Project Final Impact Statement. Battle Mountain District Office, Battle Mountain, Nevada. September 2008.

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 4-6

Gilluly, J. and H. Masursky. 1965. Geology of the Cortez Quadrangle Nevada. U.S. Geological Survey Bulletin 1175. 117 p.

Harrill, J. R. and D. E. Prudic. 1998. Aquifer Systems in the Great Basin Region of Nevada, Utah, and Adjacent States – Summary Report. U.S. Geological Survey Professional Paper 1409-A.

HDR Engineering, Inc. (HDR). 2015. Goldrush Seep and Spring Monitoring Annual Report 2015 - Draft. Prepared for Barrick Gold of North America, Elko, Nevada. Eureka and Lander Counties, Nevada. December 9, 2015.

Heggeness, J. O. 2014a. Supervisor, Water Quality Standards and Monitoring, Bureau of Water Quality Planning, Nevada Division of Environmental Protection. Carson City, Nevada. Letter of April 7, 2014, to Melissa Barbanell, Barrick Gold of North America, Inc., regarding Comments of Barrick Goldstrike Mines, Inc. on the Draft Nevada 2012 Integrated Report

Heggeness, J. O. 2014b. Supervisor, Water Quality Standards and Monitoring, Bureau of Water Quality Planning, Nevada Division of Environmental Protection. Carson City, Nevada. Letter of April 7, 2014 to Tim Crowley, President, Nevada Mining Association, regarding Comments of the Nevada Mining Association on the Draft Nevada 2012 Integrated Report

HydroGeoLogic, Inc. 2011. MODHMS/MODFLOW-SURFACT: A comprehensive MODFLOW- based hydrologic modeling system, version 4.0 code documentation report. Reston, Virginia: HydroGeoLogic Inc.

HydroGeo Group (HGG). 2017a. Technical Memo from A. L. Mayo, HydroGeo Group, to S. Schoen, Barrick, Re: Springs Investigation. August 23, 2017.

HydroGeo Group (HGG). 2017b. Technical Memo from A. L. Mayo, HydroGeo Group, to S. Schoen, Barrick, Re: Isotopes Investigation. August 22, 2017.

Itasca Denver, Inc. (Itasca). 2016a. Barrick Cortez Four-Basin (Carico Lake Valley, Crescent Valley, Grass Valley, and Pine Valley) Groundwater Flow Model Report. Prepared for Barrick Cortez, Inc. January 2016.

Itasca Denver, Inc. (Itasca). 2016b. Barrick Cortez Inc. 2016 Integrated Monitoring Plan. Prepared for Barrick Cortez, Inc. Crescent Valley, Nevada. April 2016.

JBR Environmental Consultants, Inc. (JBR). 2012. Recommended Monitoring Locations Report, Goldrush Seep and Spring Project, Eureka County, Nevada. June. Elko, Nevada. In: HDR Engineering, Inc. (2015). Goldrush Seep and Spring Monitoring Annual Report 2015 - Draft. December 9, 2015.

JBR Environmental Consultants, Inc. (JBR) 2007. Cortez Gold Mines Pediment Project, Seep & Spring Monitoring, Fall Quarter 2006. October 28, 2005. In: Bureau of Land Management (BLM). 2008. Cortez Hills Expansion Project Final Impact Statement. Battle Mountain District Office, Battle Mountain, Nevada. September 2008.

Maurer, D. K., R. W. Plume, J. M. Thomas, and A. K. Johnson. 1996. Water Resources and Effects of Changes in Ground-Water Use Along the Carlin Trend, North-Central Nevada. U.S. Geological Survey Water-Resources Investigations Report 96-4134.

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 4-7

McDonald, M. G. and A. W. Harbaugh. 1988. A modular three-dimensional finite-difference ground-water flow model. In: Techniques of Water-Resources Investigations, Book 6. Washington, D.C.: U.S. Geological Survey/U.S. Government Printing Office. Internet website: http://pubs.usgs.gov/twri/index090905.html.

Muffler, L. J. P. 1964. Geology of the Frenchie Creek Quadrangle North-Central Nevada. Geological Survey Bulletin 1179, 99 p.

Nevada Division of Environmental Protection (NDEP). 2018. Pit Lake Water Quality Characterization Program NDEP Profile III. Internet website: https://ndep.nv.gov/uploads/documents/PIT_LAKE_WATER_QUALITY_SAMPLING_P ROGRAM.pdf. Accessed March 2018.

Nevada Division of Environmental Protection, Bureau of Mining Regulation and Reclamation (NDEP-BMRR). 2014. Waste Rock, Overburden, and Ore Evaluation. February 28, 2014.

Nevada Division of Environmental Protection, Bureau of Water Quality Planning (NDEP- BWQP). 2016. Water Quality Standards and Monitoring Branch, access to NAC 445A WQ Standards.

Nevada Division of Water Resources (NDWR). 2018. Hydrographic Abstracts (Water Rights Database) for Crescent Valley, Carico Lake Valley, and Pine Valley. Internet website: http://water.nv.gov/hydrographicabstract.aspx. Accessed January 2, 2018.

Nevada Division of Water Resources (NDWR). 2017a. Designated Groundwater Basins of Nevada, March 2017. Internet website: http://water.nv.gov/mapping/maps/designated_basinmap.pdf.

Nevada Division of Water Resources (NDWR). 2017b. Hydrographic Area Summaries for Crescent Valley, Carico Lake Valley, Pine Valley, and Grass Valley. Internet website: http://water.nv.gov/undergroundactive.aspx Accessed September 28, 2017.

Nevada State Legislature. 2016. Water Controls, Standards Applicable to all Surface Waters, Nevada Administrative Code (NAC) Chapter 445A.221. Revised June 2016. Internet website: www.leg.state.nv.us. Accessed December 28, 2016.

Plume, R. W. 1996. Hydrogeologic Framework of the Great Basin Region of Nevada, Utah, and Adjacent States. U.S. Geological Survey Professional Paper 1409-B.

Resource Concepts Inc. 2018. Email from K. Sylvia, RCI, to S. Schoen, BCI, regarding reserved water rights. April 24, 2018.

SRK Consulting, (U.S.) Inc. (SRK). 2017. Deep South Expansion Project – Cumulative Effects, Groundwater Flow Modeling Report. Prepared for Barrick Cortez Inc. March 2017.

SRK Consulting, Inc. (SRK). 2016. Groundwater Flow Model Report, Deep South Expansion Project, Crescent Valley, Nevada. Report prepared for Barrick Cortez, Inc. August 2016.

Stantec Consulting Services, Inc. (Stantec). 2015a. 2015 Waters of the U.S. Delineation Deep South Expansion Project, Lander and Eureka Counties, Nevada. Prepared for Barrick Cortez, Inc., Crescent Valley, Nevada. November 10, 2015.

2019 Deep South Expansion Project Supplemental Environmental Report Water Resources and Geochemistry 4-8

Stantec Consulting Services Inc. 2015b. Seep and Spring Quarterly Monitoring 2015 Fourth Quarter Barrick Cortez, Inc. Prepared for Barrick Cortez, Inc. November 16, 2015.

Stantec Consulting Services Inc. 2015c. 2015 Seep and Spring Baseline Survey Carico Valley Barrick Cortez, Inc. Prepared for Barrick Cortez, Inc. December 17, 2015.

Stone, W. T., T. Leeds, R. C. Tunney, G. A. Cusack, and S. A. Skidmore. 1991. Hydrology of the Carlin Trend, Northeastern Nevada – a preliminary report. Carlin, Nevada: Newmont Gold Company. In: Bureau of Land Management (BLM). 2008. Cortez Hills Expansion Project Final Impact Statement. Battle Mountain District Office, Battle Mountain, Nevada. September 2008.

Struhsacker, D. W. 1986. Geology and Mineralization of the Beowawe-White Canyon Area, Eureka and Lander Counties, Nevada. In: J. V. Tingley and H. F. Bonham, Jr., editors. Precious-metal Mineralization in Hot Springs Systems, Nevada-California, Report 41. Nevada Bureau of Mines and Geology, Reno, Nevada.

Tetra Tech. 2015. Cortez Pipeline/Pediment Surface Water Monitoring Annual Report – 2015. Prepared for Barrick Cortez, Inc., Crescent Valley, Nevada. December 2015. Tetra Tech Project No. 114-540368. Tetra Tech, Boise, Idaho.

TopoQuest. 2017. U.S. Geological Survey 15-minute or 7.5-minute topographic quadrangle images for Nevada, including the following quadrangles: Carico Lake North, Cortez, Ferris Creek, Pete Hanson Creek, Rocky Pass. Internet website: http://www.topoquest.com. Accessed January 13, 2017.

U.S. Army Corps of Engineers (USACE). 2016. Jurisdictional determination letter for the Deep South Expansion Project from J. Gipson, USACE, to M.Gili, Barrick Cortez Inc. SPK- 2015-01039, February 10, 2016.

U.S. Environmental Protection Agency (USEPA). 2016. Watershed Quality Assessment Report for Nevada, Pine Watershed. Internet website: https://iaspub.epa.gov/tmdl_waters10/attains_waterbody.control?p_list_id=NV04-HR- 83_00&p_cycle=2012&p_state=NV&p_report_type=T. Pine Creek Internet website: https://iaspub.epa.gov/tmdl_waters10/attains_watershed.control?p_huc=16040104&p_ cycle=&p_report_type=T. Accessed December 28, 2016.

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U.S. Geological Survey (USGS). 2018. The Reston Groundwater Dating Laboratory: 3H/3He Dating Background (Tritium). Internet website: https://water.usgs.gov/lab/3h3he/background/. Accessed February 3, 2018.

U.S. Geological Survey (USGS). 2017. Monthly Mean Discharge, USGS Gaging Station 10322800 - Pine Creek at Modarelli Mine Road near Hay Ranch, Nevada; and Available Data for USGS gaging stations 10322500 - Humboldt River at Palisade, Nevada; and 10323425 - Humboldt River at Old U.S. 40 Bridge at Dunphy, Nevada. USGS Water Data for the Nation, National Water Information Service, Surface Water, Nevada.

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U.S. Geological Survey (USGS). 2016. Monthly Mean Discharge, USGS Gaging Station 10322505 - Horse Creek at Horse Creek Canyon near Garden Gate Pass, Nevada. USGS Water Data for the Nation, National Water Information Service.

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2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources and Geochemistry

Appendix A

Water Resources

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources and Geochemistry

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2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-1

Table A-1 Inventoried Springs

Map BCI Monitoring Elevation Hydrographic Basin Spring Group1 ID Spring ID Type Program (feet amsl) Crescent Valley Brock Canyon 36 28-49-30-231 Seep/Spring Wetland Monitored 5,606 Crescent Valley Brock Canyon 37 28-49-30-443 Seep/Spring Wetland Monitored 5,550 Crescent Valley Brock Canyon 38 27-49-14-413 Seep/Spring Wetland Monitored 6,757 Carico Lake Valley Carico Lake North 14 WCCC-12 Spring Not Monitored 6,971 Carico Lake Valley Carico Lake North 15 WCCC-10 Spring Not Monitored 6,888 Carico Lake Valley Carico Lake North 16 WCCC-13 Spring Not Monitored 6,878 Carico Lake Valley Carico Lake North 17 WCCC-9 Spring Not Monitored 6,849 Carico Lake Valley Carico Lake North 18 WCCC-7 Spring Not Monitored 6,774 Carico Lake Valley Carico Lake North 19 WCCC-1 Spring Not Monitored 6,754 Carico Lake Valley Carico Lake North 20 WCCC-6 Spring Not Monitored 6,963 Carico Lake Valley Carico Lake North 21 WCCC-5 Spring Not Monitored 6,983 Carico Lake Valley Carico Lake North 22 WCCC-3 Spring Not Monitored 6,043 Carico Lake Valley Carico Lake North 23 WCCC-11 Spring Not Monitored 6,414 Carico Lake Valley Carico Lake North 24 WCCC-14 Spring Not Monitored 6,463 Carico Lake Valley Carico Lake South 71 WCCC-15 Spring Not Monitored 6,112 Carico Lake Valley Carico Lake South 72 WCCC-2 Spring Not Monitored 6,091 Carico Lake Valley Carico Lake South 73 WCCC-4 Spring Not Monitored 5,571 Carico Lake Valley Carico Lake South 74 WCCC-8 Spring Not Monitored 5,285 Carico Lake Valley Carico Lake South 75 CL-20 Spring Not Monitored 5,093 Carico Lake Valley Carico Lake South 76 CL-403 Spring Not Monitored 5,091 Carico Lake Valley Carico Lake South 77 CL-7 Spring Not Monitored 5,096 Carico Lake Valley Carico Lake South 78 CL-405 Spring Not Monitored 5,091 Carico Lake Valley Carico Lake South 79 CL-8 Spring Not Monitored 5,093 Carico Lake Valley Carico Lake South 80 CL-15 Spring Not Monitored 5,091 Carico Lake Valley Carico Lake South 81 CL-16 Spring Not Monitored 5,092

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-2

Table A-1 Inventoried Springs

Map BCI Monitoring Elevation Hydrographic Basin Spring Group1 ID Spring ID Type Program (feet amsl) Carico Lake Valley Carico Lake South 82 CL-1 Spring Not Monitored 5,091 Carico Lake Valley Carico Lake South 83 CL-2 Spring Not Monitored 5,090 Carico Lake Valley Carico Lake South 84 CL-9 Spring Not Monitored 5,093 Carico Lake Valley Carico Lake South 85 CL-21 Spring Not Monitored 5,091 Carico Lake Valley Carico Lake South 86 CL-404 Spring Not Monitored 5,093 Carico Lake Valley Carico Lake South 87 CL-3 Spring Not Monitored 5,095 Carico Lake Valley Carico Lake South 88 CL-17 Spring Not Monitored 5,103 Carico Lake Valley Carico Lake South 89 CL-401 Spring Not Monitored 5,103 Carico Lake Valley Carico Lake South 90 CL-4 Spring Not Monitored 5,103 Carico Lake Valley Carico Lake South 91 CL-5 Spring Not Monitored 5,104 Carico Lake Valley Carico Lake South 92 CL-13 Spring Not Monitored 5,103 Carico Lake Valley Carico Lake South 93 CL-18 Spring Not Monitored 5,103 Carico Lake Valley Carico Lake South 94 CL-402 Spring Not Monitored 5,103 Carico Lake Valley Carico Lake South 95 CL-14 Spring Not Monitored 5,103 Crescent Valley Cortez Hills 96 27-48-30-412 Spring Not Monitored 5,751 Crescent Valley Cortez Hills 97 27-48-30-421 Spring Not Monitored 5,767 Crescent Valley Cortez Hills 98 27-48-30-423 Spring Not Monitored 5,785 Crescent Valley Cortez Hills 99 27-48-30-44 Spring Not Monitored 6,068 Crescent Valley Cortez Hills 100 27-47-35-32 Spring Not Monitored 5,457 Crescent Valley Cortez Hills 101 27-47-35-324 Spring Not Monitored 5,498 Crescent Valley Cortez Hills 102 27-47-36-431 Spring Not Monitored 5,605 Crescent Valley Cortez Hills 103 27-47-36-433 Spring Not Monitored 5,641 Crescent Valley Cortez Hills 104 26-47-1-212 Spring Not Monitored 5,681 Crescent Valley Cortez Hills 105 26-47-1-214 Spring Not Monitored 5,718 Crescent Valley Cortez Hills 106 26-47-1-41 Spring Not Monitored 5,842

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-3

Table A-1 Inventoried Springs

Map BCI Monitoring Elevation Hydrographic Basin Spring Group1 ID Spring ID Type Program (feet amsl) Crescent Valley Cortez Hills 107 26-47-1-43 Spring Not Monitored 6,024 Crescent Valley Cortez Hills 108 26-47-12-21 Spring Not Monitored 5,937 Crescent Valley Cottonwood Canyon 25 28-49-20-241 Seep/Spring Wetland Monitored 5,527 Crescent Valley Cottonwood Canyon 26 28-49-21-314 Seep/Spring Wetland Monitored 5,689 Crescent Valley Cottonwood Canyon 27 28-49-20-442 Seep/Spring Wetland Monitored 5,959 Crescent Valley Cottonwood Canyon 28 28-49-28-123 Seep/Spring Wetland Monitored 5,988 Crescent Valley Cottonwood Canyon 29 28-49-35-311 Seep/Spring Wetland Monitored 6,497 Crescent Valley Cottonwood Canyon 30 28-49-36-322 Seep/Spring Wetland Monitored 6,950 Crescent Valley Cottonwood Canyon 31 28-49-36-323 Seep/Spring Wetland Monitored 6,872 Crescent Valley Cottonwood Canyon 32 27-49-12-112 Seep/Spring Wetland Monitored 6,950 Crescent Valley Cottonwood Canyon 33 27-49-12-114 Seep/Spring Wetland Monitored 7,016 Crescent Valley Cottonwood Canyon 34 27-49-12-122 Seep/Spring Wetland Monitored 7,002 Crescent Valley Cottonwood Canyon 35 27-49-12-141 Seep/Spring Wetland Monitored 7,074 Crescent Valley Cottonwood Canyon 245 CCCV-1 Spring Monitored 6,132 Crescent Valley Cottonwood Canyon 247 DCPC-1 Spring Monitored 6,692 Pine Valley Dry Creek 65 27-49-30-132 Seep/Spring Wetland Monitored 7,259 Pine Valley Dry Creek 66 27-48-24-421 Seep/Spring Wetland Monitored 7,485 Pine Valley Dry Creek 67 27-49-29-413 Seep/Spring Wetland Monitored 6,462 Pine Valley Dry Creek 68 27-49-32-111 Seep/Spring Wetland Monitored 6,565 Pine Valley Dry Creek 69 27-49-32-121 Seep/Spring Wetland Monitored 6,446 Pine Valley Dry Creek 70 27-49-31-244 Seep/Spring Wetland Monitored 6,541 Pine Valley Dry Hills 217 26-48-23-211A Seep/Spring Wetland Monitored 6,607 Pine Valley Dry Hills 218 26-48-23-211B Seep/Spring Wetland Monitored 6,592 Pine Valley Dry Hills 219 26-48-23-242 Seep/Spring Wetland Monitored 6,439 Pine Valley Dry Hills 220 26-48-24-133 Seep/Spring Wetland Monitored 6,403

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-4

Table A-1 Inventoried Springs

Map BCI Monitoring Elevation Hydrographic Basin Spring Group1 ID Spring ID Type Program (feet amsl) Pine Valley Dry Hills 221 26-48-24-134 Seep/Spring Wetland Monitored 6,394 Pine Valley Dry Hills 222 26-48-23-313A Seep/Spring Wetland Monitored 6,797 Pine Valley Dry Hills 223 26-48-23-313B Seep/Spring Wetland Monitored 6,794 Pine Valley Dry Hills 224 26-48-26-123B Seep/Spring Wetland Monitored 6,477 Pine Valley Dry Hills 225 26-48-26-123A Seep/Spring Wetland Monitored 6,477 Pine Valley Dry Hills 240 26-48-23-321 Spring Not Monitored 6,762 Pine Valley Dry Hills 241 26-48-26-111 Spring Not Monitored 6,557 Pine Valley Dry Hills 242 26-48-26-122 Spring Not Monitored 6,514 Pine Valley Dry Hills 243 26-48-26-132 Spring Not Monitored 6,575 Crescent Valley Fourmile Canyon 53 27-48-16-31 Spring Not Monitored 5,348 Crescent Valley Fourmile Canyon 54 27-48-14-313 Seep/Spring Wetland Monitored 5,781 Crescent Valley Fourmile Canyon 55 27-48-22-222A Seep/Spring Wetland Monitored 5,956 Crescent Valley Fourmile Canyon 56 27-48-23-244 Seep/Spring Wetland Monitored 7,039 Crescent Valley Fourmile Canyon 57 27-48-23-234 Seep/Spring Wetland Monitored 6,721 Crescent Valley Fourmile Canyon 58 27-48-35-112 Seep/Spring Wetland Monitored 7,775 Pine Valley Horse Creek 157 26-48-03-221 Seep/Spring Wetland Monitored 7,312 Pine Valley Horse Creek 158 26-48-03-213 Seep/Spring Wetland Monitored 7,208 Pine Valley Horse Creek 159 26-48-3-114 Spring Not Monitored 7,583 Pine Valley Horse Creek 160 26-48-03-134 Seep/Spring Wetland Monitored 7,289 Pine Valley Horse Creek 161 26-48-3-143 Spring Not Monitored 7,213 Pine Valley Horse Creek 163 26-48-02-322 Seep/Spring Wetland Monitored 7,515 Pine Valley Horse Creek 164 26-48-03-321 Seep/Spring Wetland Monitored 7,198 Pine Valley Horse Creek 165 26-48-03-413A Seep/Spring Wetland Monitored 7,034 Pine Valley Horse Creek 166 26-48-03-413B Seep/Spring Wetland Monitored 7,021 Pine Valley Horse Creek 168 26-48-02-423B Seep/Spring Wetland Monitored 7,395

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-5

Table A-1 Inventoried Springs

Map BCI Monitoring Elevation Hydrographic Basin Spring Group1 ID Spring ID Type Program (feet amsl) Pine Valley Horse Creek 169 26-48-02-423A Seep/Spring Wetland Monitored 7,397 Pine Valley Horse Creek 170 26-48-03-443 Seep/Spring Wetland Monitored 6,794 Pine Valley Horse Creek 171 26-48-03-444 Seep/Spring Wetland Monitored 6,739 Pine Valley Horse Creek 172 26-48-11-142 Seep/Spring Wetland Monitored 6,758 Pine Valley Horse Creek 173 26-48-10-142 Seep/Spring Wetland Monitored 7,022 Pine Valley Horse Creek 174 26-48-10-232 Seep/Spring Wetland Monitored 6,921 Pine Valley Horse Creek 175 26-48-11-144A Seep/Spring Wetland Monitored 7,050 (26-48-02-144A) Pine Valley Horse Creek 176 26-48-11-144B Seep/Spring Wetland Monitored 7,044 (26-48-02-144B) Pine Valley Horse Creek 177 26-48-11-312 Seep/Spring Wetland Monitored 6,720 Pine Valley Horse Creek 178 26-48-12-324 Seep/Spring Wetland Monitored 6,859 Pine Valley Horse Creek 179 26-48-12-341 Seep/Spring Wetland Monitored 6,852 Pine Valley Horse Creek 180 26-48-12-414 Seep/Spring Wetland Monitored 6,724 Pine Valley Horse Creek 181 26-48-12-432 Seep/Spring Wetland Monitored 6,743 Pine Valley Horse Creek 182 26-48-10-441 Seep/Spring Wetland Monitored 6,768 Pine Valley Horse Creek 183 26-48-11-422 Spring Not Monitored 6,633 Pine Valley Horse Creek 184 26-48-10-442 Seep/Spring Wetland Monitored 6,737 Pine Valley Horse Creek 185 26-49-18-331 Seep/Spring Wetland Monitored 6,486 Pine Valley Horse Creek 186 26-49-18-332 Seep/Spring Wetland Monitored 6,441 Pine Valley Horse Creek 187 26-48-10-444 Seep/Spring Wetland Monitored 6,678 Pine Valley Horse Creek 188 26-48-10-344 Seep/Spring Wetland Monitored 6,840 Pine Valley Horse Creek 189 26-48-10-433 Seep/Spring Wetland Monitored 6,831 Pine Valley Horse Creek 190 26-48-13-324 Seep/Spring Wetland Monitored 6,314 Pine Valley Horse Creek 191 26-48-13-323 Seep/Spring Wetland Monitored 6,310 Pine Valley Horse Creek 192 26-48-13-432 Seep/Spring Wetland Monitored 6,291

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-6

Table A-1 Inventoried Springs

Map BCI Monitoring Elevation Hydrographic Basin Spring Group1 ID Spring ID Type Program (feet amsl) Pine Valley Horse Creek 193 26-48-13-431 Seep/Spring Wetland Monitored 6,283 Pine Valley Horse Creek 194 26-48-13-342 Seep/Spring Wetland Monitored 6,283 Pine Valley Horse Creek 195 26-48-24-221 Seep/Spring Wetland Monitored 6,230 Pine Valley Horse Creek 236 26-48-12-323 Spring Not Monitored 6,870 Pine Valley Horse Creek 237 26-48-14-412 Spring Not Monitored 6,550 Pine Valley Horse Creek 238 26-48-14-424 Spring Not Monitored 6,523 Pine Valley Horse Creek 239 26-49-30-112 Spring Not Monitored 6,123 Crescent Valley Indian Creek 13 IC-1 Spring Not Monitored 5,158 Crescent Valley Mill Canyon 59 27-48-21-421 Seep/Spring Wetland Monitored 6,593 Crescent Valley Mill Canyon 60 27-48-28-211 Seep/Spring Wetland Monitored 6,129 Crescent Valley Mill Canyon 61 27-48-27-134A Seep/Spring Wetland Monitored 6,978 Crescent Valley Mill Canyon 62 27-48-27-134 Seep/Spring Wetland Monitored 7,059 Crescent Valley Mill Canyon 63 27-48-28-441A Seep/Spring Wetland Monitored 6,727 Crescent Valley Mill Canyon 64 27-48-28-441 Seep/Spring Wetland Monitored 6,764 Grass Valley North Toiyabe Range East 208 26-47-12-314A Seep/Spring Wetland Monitored 6,070 Grass Valley North Toiyabe Range East 209 26-47-11-433B Seep/Spring Wetland Monitored 6,387 Grass Valley North Toiyabe Range East 210 26-47-14-141 Seep/Spring Wetland Monitored 6,498 Grass Valley North Toiyabe Range East 211 26-47-23-314B Seep/Spring Wetland Monitored 6,223 Grass Valley North Toiyabe Range East 212 26-47-23-314A Seep/Spring Wetland Monitored 6,231 Grass Valley North Toiyabe Range East 213 26-47-23-344B Seep/Spring Wetland Monitored 6,086 Grass Valley North Toiyabe Range East 214 26-47-27-324 Seep/Spring Wetland Monitored 6,469 Grass Valley North Toiyabe Range East 215 26-47-35-134 Seep/Spring Wetland Monitored 5,845 Grass Valley North Toiyabe Range East 216 26-47-33-422 Seep/Spring Wetland Monitored 6,282 Grass Valley North Toiyabe Range East 248 HSCC-1 Spring Monitored 6,111

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-7

Table A-1 Inventoried Springs

Map BCI Monitoring Elevation Hydrographic Basin Spring Group1 ID Spring ID Type Program (feet amsl) Crescent Valley North Toiyabe Range 196 27-47-27-43 Spring Not Monitored 5,072 West Crescent Valley North Toiyabe Range 197 27-47-33-42 Spring Not Monitored 5,321 West Crescent Valley North Toiyabe Range 198 26-47-4-24 Spring Not Monitored 5,461 West Crescent Valley North Toiyabe Range 199 26-47-16-212C Spring Not Monitored 5,803 West Crescent Valley North Toiyabe Range 200 26-47-16-212B Seep/Spring Wetland Monitored 5,827 West Crescent Valley North Toiyabe Range 201 26-47-16-212D Seep/Spring Wetland Monitored 5,837 West Crescent Valley North Toiyabe Range 202 26-47-16-212A Seep/Spring Wetland Monitored 5,828 West Crescent Valley North Toiyabe Range 203 26-47-16-211 Seep/Spring Wetland Monitored 5,758 West Crescent Valley North Toiyabe Range 205 26-47-16-434 Seep/Spring Wetland Monitored 6,079 West Crescent Valley North Toiyabe Range 206 26-47-20-342 Seep/Spring Wetland Monitored 5,955 West Crescent Valley North Toiyabe Range 207 26-47-29-244 Seep/Spring Wetland Monitored 6,197 West Crescent Valley North Toiyabe Range 246 CSFAF-1 Spring Monitored 7,011 West Crescent Valley Peripheral Area 226 26-46-21-12 Spring Not Monitored 5,459 Grass Valley Rocky Hills 229 25-48-25-341 Seep/Spring Wetland Monitored 6,285 Pine Valley Rocky Hills 227 25-49-11-423 Seep/Spring Wetland Monitored 6,064 Pine Valley Rocky Hills 228 25-49-29-213 Seep/Spring Wetland Monitored 6,817 Carico Lake Valley Rocky Pass 49 27-46-16-11 Spring Not Monitored 5,231

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-8

Table A-1 Inventoried Springs

Map BCI Monitoring Elevation Hydrographic Basin Spring Group1 ID Spring ID Type Program (feet amsl) Carico Lake Valley Rocky Pass 52 27-46-28-11 Spring Not Monitored 5,022 Crescent Valley Rocky Pass 50 27-46-28-221 Spring Not Monitored 4,995 Crescent Valley Rocky Pass 51 27-46-28-224 Spring Not Monitored 4,993 Crescent Valley SE Crescent Valley 39 28-48-28-14 Spring Not Monitored 4,747 Crescent Valley SE Crescent Valley 40 28-48-28-342 Spring Not Monitored 4,771 Crescent Valley SE Crescent Valley 41 28-48-32-33 Spring Not Monitored 4,760 Crescent Valley SE Crescent Valley 42 28-48-32-34 Spring Not Monitored 4,760 Crescent Valley SE Crescent Valley 43 28-48-28-343 Spring Not Monitored 4,760 Crescent Valley SE Crescent Valley 44 28-48-28-43 Spring Not Monitored 4,768 Crescent Valley SE Crescent Valley 45 28-48-32-32 Spring Not Monitored 4,771 Crescent Valley SE Crescent Valley 46 28-48-32-24 Spring Not Monitored 4,772 Crescent Valley SE Crescent Valley 47 27-48-19-24 Spring Not Monitored 5,040 Crescent Valley SE Crescent Valley 48 HDR-27-48-19-24 Seep/Spring Wetland Monitored 5,050 Carico Lake Valley Shoshone 9 28-46-7-31 Spring Not Monitored 7,157 Carico Lake Valley Shoshone 10 28-46-17-11 Spring Not Monitored 6,718 Carico Lake Valley Shoshone 12 28-46-21-11 Spring Not Monitored 6,155 Crescent Valley Shoshone 1 29-46-29-22 Spring Not Monitored 6,295 Crescent Valley Shoshone 2 29-46-29-234 Spring Not Monitored 6,415 Crescent Valley Shoshone 3 29-46-29-31 Spring Not Monitored 6,631 Crescent Valley Shoshone 4 29-46-31-22 Spring Not Monitored 7,210 Crescent Valley Shoshone 5 29-46-31-434 Spring Not Monitored 7,251 Crescent Valley Shoshone 6 28-46-5-42 Spring Not Monitored 6,291 Crescent Valley Shoshone 7 28-46-4-33 Spring Not Monitored 6,226 Crescent Valley Shoshone 8 28-46-2-34 Spring Not Monitored 5,728 Crescent Valley Shoshone 11 28-46-15-32 Spring Not Monitored 6,226

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-9

Table A-1 Inventoried Springs

Map BCI Monitoring Elevation Hydrographic Basin Spring Group1 ID Spring ID Type Program (feet amsl) Pine Valley Willow Creek 109 27-48-25-244 Seep/Spring Wetland Monitored 7,238 Pine Valley Willow Creek 110 27-48-25-143 Seep/Spring Wetland Monitored 7,631 Pine Valley Willow Creek 111 27-48-25-411 Seep/Spring Wetland Monitored 7,448 Pine Valley Willow Creek 112 27-48-25-324A Seep/Spring Wetland Monitored 7,440 Pine Valley Willow Creek 113 27-48-25-324 Seep/Spring Wetland Monitored 7,412 Pine Valley Willow Creek 114 27-48-25-313 Seep/Spring Wetland Monitored 7,676 Pine Valley Willow Creek 115 27-49-31-344 Seep/Spring Wetland Monitored 6,808 Pine Valley Willow Creek 116 27-48-25-334 Seep/Spring Wetland Monitored 7,556 Pine Valley Willow Creek 117 26-49-06-211 Seep/Spring Wetland Monitored 6,620 Pine Valley Willow Creek 118 26-49-06-213 Seep/Spring Wetland Monitored 6,603 Pine Valley Willow Creek 119 27-48-35-234 Seep/Spring Wetland Monitored 7,317 Pine Valley Willow Creek 120 27-48-36-321A Seep/Spring Wetland Monitored 7,086 Pine Valley Willow Creek 121 27-48-35-311 Seep/Spring Wetland Monitored 7,477 Pine Valley Willow Creek 122 27-48-34-421 Spring Not Monitored 7,588 Pine Valley Willow Creek 123 27-48-34-322B Seep/Spring Wetland Monitored 7,648 Pine Valley Willow Creek 124 27-48-34-412 Spring Not Monitored 7,629 Pine Valley Willow Creek 125 27-48-34-322A Seep/Spring Wetland Monitored 7,681 Pine Valley Willow Creek 126 27-48-35-441B Seep/Spring Wetland Monitored 7,335 Pine Valley Willow Creek 127 26-49-05-324 Seep/Spring Wetland Monitored 6,239 Pine Valley Willow Creek 128 27-48-35-441 Spring Not Monitored 7,329 Pine Valley Willow Creek 129 27-48-35-442B Seep/Spring Wetland Monitored 7,321 Pine Valley Willow Creek 130 26-49-07-221 Seep/Spring Wetland Monitored 6,434 Pine Valley Willow Creek 131 26-49-07-111 Seep/Spring Wetland Monitored 6,824 Pine Valley Willow Creek 132 26-48-01-212B Seep/Spring Wetland Monitored 7,042 Pine Valley Willow Creek 133 26-48-02-224 Seep/Spring Wetland Monitored 7,506

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-10

Table A-1 Inventoried Springs

Map BCI Monitoring Elevation Hydrographic Basin Spring Group1 ID Spring ID Type Program (feet amsl) Pine Valley Willow Creek 134 26-49-07-222 Seep/Spring Wetland Monitored 6,358 Pine Valley Willow Creek 135 26-48-01-223 Seep/Spring Wetland Monitored 6,912 Pine Valley Willow Creek 136 26-49-07-114B Seep/Spring Wetland Monitored 6,699 Pine Valley Willow Creek 137 26-48-01-224 Seep/Spring Wetland Monitored 6,841 Pine Valley Willow Creek 138 26-48-01-241 Seep/Spring Wetland Monitored 6,834 Pine Valley Willow Creek 139 26-48-01-131 Seep/Spring Wetland Monitored 7,370 Pine Valley Willow Creek 140 26-49-08-114A Seep/Spring Wetland Monitored 6,284 Pine Valley Willow Creek 141 26-49-07-114 Seep/Spring Wetland Monitored 6,643 Pine Valley Willow Creek 142 26-48-01-141 Seep/Spring Wetland Monitored 7,166 Pine Valley Willow Creek 143 26-49-07-141 Seep/Spring Wetland Monitored 6,916 Pine Valley Willow Creek 144 26-48-01-234 Seep/Spring Wetland Monitored 6,917 Pine Valley Willow Creek 230 27-48-35-423 Spring Not Monitored 7,237 Pine Valley Willow Creek 231 26-48-01-142 Spring Not Monitored 7,033 Pine Valley Willow Creek 244 26-48-01-212 Spring Not Monitored 7,080 Pine Valley Willow Springs 145 26-48-01-313B Seep/Spring Wetland Monitored 7,284 Pine Valley Willow Springs 146 26-48-01-323 Seep/Spring Wetland Monitored 7,198 Pine Valley Willow Springs 147 26-49-07-331 Seep/Spring Wetland Monitored 6,678 Pine Valley Willow Springs 148 26-49-07-343 Seep/Spring Wetland Monitored 6,479 Pine Valley Willow Springs 149 26-49-18-111 Seep/Spring Wetland Monitored 6,672 Pine Valley Willow Springs 150 26-49-18-134 Seep/Spring Wetland Monitored 6,519 Pine Valley Willow Springs 151 26-49-18-423 Seep/Spring Wetland Monitored 6,161 Pine Valley Willow Springs 152 26-49-17-432 Seep/Spring Wetland Monitored 5,923 Pine Valley Willow Springs 153 26-49-20-122A Seep/Spring Wetland Monitored 5,937 Pine Valley Willow Springs 154 26-49-20-122 Seep/Spring Wetland Monitored 5,925 Pine Valley Willow Springs 155 26-49-20-122B Seep/Spring Wetland Monitored 5,928

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-11

Table A-1 Inventoried Springs

Map BCI Monitoring Elevation Hydrographic Basin Spring Group1 ID Spring ID Type Program (feet amsl) Pine Valley Willow Springs 156 26-49-20-213 Seep/Spring Wetland Monitored 5,918 Pine Valley Willow Springs 232 26-48-01-324 Spring Not Monitored 7,120 Pine Valley Willow Springs 233 26-48-01-313A Seep/Spring Wetland Monitored 7,315 1 Spring groups and map ID numbers are shown in Figure 3.2-3.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-12

Table A-2 Surface Water Sites within the Drawdown Area

Sites Within the Projected Drawdown Area (Maximum Extent of 10-foot Groundwater Drawdown Contour Plus 1-mile Buffer) Mitigation Plans Sites Included Proposed Action and in 2011 Final Sites Included in Map ID Spring or No Action Gold Acres Pit Partial SEIS Mitigation 2018 Contingent Spring Group1 Number1 Stream Site ID Alternative Backfill Alternative Cumulative (Table 3.2-1)2 Mitigation Plan3 Springs Rocky Hills 229 25-48-25-341 x x Rocky Hills 227 25-49-11-423 x x Rocky Hills 228 25-49-29-213 x x x x Peripheral Area 226 26-46-21-12 x x x x Cortez Hills 104 26-47-01-212 x x x x Cortez Hills 105 26-47-01-214 x x x x Cortez Hills 106 26-47-01-41 x x x x Cortez Hills 107 26-47-01-43 x x x x North Toiyabe Range West 198 26-47-04-24 x x x x North Toiyabe Range East 209 26-47-11-433B x x x x Cortez Hills 108 26-47-12-21 x x x x North Toiyabe Range East 208 26-47-12-314A x x x x North Toiyabe Range East 210 26-47-14-141 x x x x North Toiyabe Range West 203 26-47-16-211 x x x x North Toiyabe Range West 202 26-47-16-212A x x x x North Toiyabe Range West 200 26-47-16-212B x x x x North Toiyabe Range West 199 26-47-16-212C x x x x North Toiyabe Range West 201 26-47-16-212D x x x x North Toiyabe Range West 205 26-47-16-434 x x x x North Toiyabe Range West 206 26-47-20-342 x x x

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-13

Table A-2 Surface Water Sites within the Drawdown Area

Sites Within the Projected Drawdown Area (Maximum Extent of 10-foot Groundwater Drawdown Contour Plus 1-mile Buffer) Mitigation Plans Sites Included Proposed Action and in 2011 Final Sites Included in Map ID Spring or No Action Gold Acres Pit Partial SEIS Mitigation 2018 Contingent Spring Group1 Number1 Stream Site ID Alternative Backfill Alternative Cumulative (Table 3.2-1)2 Mitigation Plan3 North Toiyabe Range East 212 26-47-23-314A x x x x North Toiyabe Range East 211 26-47-23-314B x x x x North Toiyabe Range East 213 26-47-23-344B x x x x North Toiyabe Range East 214 26-47-27-324 x x x x North Toiyabe Range West 207 26-47-29-244 x x North Toiyabe Range East 215 26-47-35-134 x x x Willow Creek 139 26-48-01-131 x x x x Willow Creek 142 26-48-01-141 x x x x Willow Creek 231 26-48-01-142 x x x x Willow Creek 244 26-48-01-212 x x x x Willow Creek 132 26-48-01-212B x x x x Willow Creek 135 26-48-01-223 x x x x Willow Creek 137 26-48-01-224 x x x x Willow Creek 144 26-48-01-234 x x x x Willow Creek 138 26-48-01-241 x x x x Willow Springs 233 26-48-01-313A x x x x Willow Springs 145 26-48-01-313B x x x x Willow Springs 146 26-48-01-323 x x x x Willow Springs 232 26-48-01-324 x x x x Willow Creek 133 26-48-02-224 x x x x Horse Creek 163 26-48-02-322 x x x x

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-14

Table A-2 Surface Water Sites within the Drawdown Area

Sites Within the Projected Drawdown Area (Maximum Extent of 10-foot Groundwater Drawdown Contour Plus 1-mile Buffer) Mitigation Plans Sites Included Proposed Action and in 2011 Final Sites Included in Map ID Spring or No Action Gold Acres Pit Partial SEIS Mitigation 2018 Contingent Spring Group1 Number1 Stream Site ID Alternative Backfill Alternative Cumulative (Table 3.2-1)2 Mitigation Plan3 Horse Creek 169 26-48-02-423A x x x x Horse Creek 168 26-48-02-423B x x x x Horse Creek 160 26-48-03-134 x x x x Horse Creek 161 26-48-03-143 x x x x Horse Creek 158 26-48-03-213 x x x x Horse Creek 157 26-48-03-221 x x x Horse Creek 164 26-48-03-321 x x x x Horse Creek 165 26-48-03-413A x x x x Horse Creek 166 26-48-03-413B x x x x Horse Creek 170 26-48-03-443 x x x x Horse Creek 171 26-48-03-444 x x x x Horse Creek 173 26-48-10-142 x x x x Horse Creek 174 26-48-10-232 x x x x Horse Creek 188 26-48-10-344 x x x x Horse Creek 189 26-48-10-433 x x x x Horse Creek 182 26-48-10-441 x x x x Horse Creek 184 26-48-10-442 x x x x Horse Creek 187 26-48-10-444 x x x x Horse Creek 172 26-48-11-142 x x x x Horse Creek 175 26-48-11-144A x x x x (26-48-02-144A)

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-15

Table A-2 Surface Water Sites within the Drawdown Area

Sites Within the Projected Drawdown Area (Maximum Extent of 10-foot Groundwater Drawdown Contour Plus 1-mile Buffer) Mitigation Plans Sites Included Proposed Action and in 2011 Final Sites Included in Map ID Spring or No Action Gold Acres Pit Partial SEIS Mitigation 2018 Contingent Spring Group1 Number1 Stream Site ID Alternative Backfill Alternative Cumulative (Table 3.2-1)2 Mitigation Plan3 26-48-11-144B Horse Creek 176 (26-48-02-144B) x x x x Horse Creek 177 26-48-11-312 x x x x Horse Creek 183 26-48-11-422 x x x x Horse Creek 236 26-48-12-323 x x x x Horse Creek 178 26-48-12-324 x x x x Horse Creek 179 26-48-12-341 x x x x Horse Creek 180 26-48-12-414 x x x x Horse Creek 181 26-48-12-432 x x x x Horse Creek 191 26-48-13-323 x x x x Horse Creek 190 26-48-13-324 x x x x Horse Creek 194 26-48-13-342 x x x x Horse Creek 193 26-48-13-431 x x x x Horse Creek 192 26-48-13-432 x x x x Horse Creek 237 26-48-14-412 x x x x Horse Creek 238 26-48-14-424 x x x x Dry Hills 217 26-48-23-211A x x x x Dry Hills 218 26-48-23-211B x x x x Dry Hills 219 26-48-23-242 x x x x Dry Hills 222 26-48-23-313A x x x x Dry Hills 223 26-48-23-313B x x x x Dry Hills 240 26-48-23-321 x x x x

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-16

Table A-2 Surface Water Sites within the Drawdown Area

Sites Within the Projected Drawdown Area (Maximum Extent of 10-foot Groundwater Drawdown Contour Plus 1-mile Buffer) Mitigation Plans Sites Included Proposed Action and in 2011 Final Sites Included in Map ID Spring or No Action Gold Acres Pit Partial SEIS Mitigation 2018 Contingent Spring Group1 Number1 Stream Site ID Alternative Backfill Alternative Cumulative (Table 3.2-1)2 Mitigation Plan3 Dry Hills 220 26-48-24-133 x x x x Dry Hills 221 26-48-24-134 x x x x Horse Creek 195 26-48-24-221 x x x x Dry Hills 241 26-48-26-111 x x x x Dry Hills 242 26-48-26-122 x x x x Dry Hills 225 26-48-26-123A x x x x Dry Hills 224 26-48-26-123B x x x x Dry Hills 243 26-48-26-132 x x x x Horse Creek 159 26-48-03-114 x x x x Willow Creek 127 26-49-05-324 x x x Willow Creek 117 26-49-06-211 x x x x Willow Creek 118 26-49-06-213 x x x x Willow Creek 131 26-49-07-111 x x x x Willow Creek 141 26-49-07-114 x x x x Willow Creek 136 26-49-07-114B x x x x Willow Creek 143 26-49-07-141 x x x x Willow Creek 130 26-49-07-221 x x x x Willow Creek 134 26-49-07-222 x x x x Willow Springs 147 26-49-07-331 x x x x Willow Springs 148 26-49-07-343 x x x x Willow Creek 140 26-49-08-114A x x x x

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-17

Table A-2 Surface Water Sites within the Drawdown Area

Sites Within the Projected Drawdown Area (Maximum Extent of 10-foot Groundwater Drawdown Contour Plus 1-mile Buffer) Mitigation Plans Sites Included Proposed Action and in 2011 Final Sites Included in Map ID Spring or No Action Gold Acres Pit Partial SEIS Mitigation 2018 Contingent Spring Group1 Number1 Stream Site ID Alternative Backfill Alternative Cumulative (Table 3.2-1)2 Mitigation Plan3 Willow Springs 152 26-49-17-432 x x Willow Springs 149 26-49-18-111 x x x x Willow Springs 150 26-49-18-134 x x x x Horse Creek 185 26-49-18-331 x x x x Horse Creek 186 26-49-18-332 x x x x Willow Springs 151 26-49-18-423 x x x x Willow Springs 154 26-49-20-122 x x x Willow Springs 153 26-49-20-122A x x x Willow Springs 155 26-49-20-122B x x x Willow Springs 156 26-49-20-213 x x x Horse Creek 239 26-49-30-112 x x x Rocky Pass 49 27-46-16-11 x x x x Rocky Pass 52 27-46-28-11 x x x x Rocky Pass 50 27-46-28-221 x x x x Rocky Pass 51 27-46-28-224 x x x x North Toiyabe Range West 196 27-47-27-43 x x x x North Toiyabe Range West 197 27-47-33-42 x x x x Cortez Hills 100 27-47-35-32 x x x x Cortez Hills 101 27-47-35-324 x x x x Cortez Hills 102 27-47-36-431 x x x x Cortez Hills 103 27-47-36-433 x x x x

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-18

Table A-2 Surface Water Sites within the Drawdown Area

Sites Within the Projected Drawdown Area (Maximum Extent of 10-foot Groundwater Drawdown Contour Plus 1-mile Buffer) Mitigation Plans Sites Included Proposed Action and in 2011 Final Sites Included in Map ID Spring or No Action Gold Acres Pit Partial SEIS Mitigation 2018 Contingent Spring Group1 Number1 Stream Site ID Alternative Backfill Alternative Cumulative (Table 3.2-1)2 Mitigation Plan3 Fourmile Canyon 54 27-48-14-313 x x x x Fourmile Canyon 53 27-48-16-31 x x x x SE Crescent Valley 47 27-48-19-24 x x x x Mill Canyon 59 27-48-21-421 x x x x Fourmile Canyon 55 27-48-22-222A x x x x Fourmile Canyon 57 27-48-23-234 x x x x Fourmile Canyon 56 27-48-23-244 x x x x Dry Creek 66 27-48-24-421 x x x x Willow Creek 110 27-48-25-143 x x x x Willow Creek 109 27-48-25-244 x x x x Willow Creek 114 27-48-25-313 x x x x Willow Creek 113 27-48-25-324 x x x x Willow Creek 112 27-48-25-324A x x x x Willow Creek 116 27-48-25-334 x x x x Willow Creek 111 27-48-25-411 x x x x Mill Canyon 62 27-48-27-134 x x x x Mill Canyon 61 27-48-27-134A x x x x Mill Canyon 60 27-48-28-211 x x x x Mill Canyon 64 27-48-28-441 x x x x Mill Canyon 63 27-48-28-441A x x x x Cortez Hills 96 27-48-30-412 x x x x

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-19

Table A-2 Surface Water Sites within the Drawdown Area

Sites Within the Projected Drawdown Area (Maximum Extent of 10-foot Groundwater Drawdown Contour Plus 1-mile Buffer) Mitigation Plans Sites Included Proposed Action and in 2011 Final Sites Included in Map ID Spring or No Action Gold Acres Pit Partial SEIS Mitigation 2018 Contingent Spring Group1 Number1 Stream Site ID Alternative Backfill Alternative Cumulative (Table 3.2-1)2 Mitigation Plan3 Cortez Hills 97 27-48-30-421 x x x x Cortez Hills 98 27-48-30-423 x x x x Cortez Hills 99 27-48-30-44 x x x x Willow Creek 125 27-48-34-322A x x x x Willow Creek 123 27-48-34-322B x x x x Willow Creek 124 27-48-34-412 x x x x Willow Creek 122 27-48-34-421 x x x x Fourmile Canyon 58 27-48-35-112 x x x x Willow Creek 119 27-48-35-234 x x x x Willow Creek 121 27-48-35-311 x x x x Willow Creek 230 27-48-35-423 x x x x Willow Creek 128 27-48-35-441 x x x x Willow Creek 126 27-48-35-441B x x x x Willow Creek 129 27-48-35-442B x x x x Willow Creek 120 27-48-36-321A x x x x Dry Creek 67 27-49-29-413 x x Dry Creek 65 27-49-30-132 x x Dry Creek 70 27-49-31-244 x x Willow Creek 115 27-49-31-344 x x x x Dry Creek 68 27-49-32-111 x x Dry Creek 69 27-49-32-121 x x

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-20

Table A-2 Surface Water Sites within the Drawdown Area

Sites Within the Projected Drawdown Area (Maximum Extent of 10-foot Groundwater Drawdown Contour Plus 1-mile Buffer) Mitigation Plans Sites Included Proposed Action and in 2011 Final Sites Included in Map ID Spring or No Action Gold Acres Pit Partial SEIS Mitigation 2018 Contingent Spring Group1 Number1 Stream Site ID Alternative Backfill Alternative Cumulative (Table 3.2-1)2 Mitigation Plan3 Shoshone 8 28-46-02-34 x x x x Shoshone 11 28-46-15-32 x x x x Shoshone 12 28-46-21-11 x x x x SE Crescent Valley 39 28-48-28-14 x x x SE Crescent Valley 40 28-48-28-342 x x x SE Crescent Valley 43 28-48-28-343 x x x SE Crescent Valley 44 28-48-28-43 x x x x SE Crescent Valley 46 28-48-32-24 x x x x SE Crescent Valley 45 28-48-32-32 x x x x SE Crescent Valley 41 28-48-32-33 x x x SE Crescent Valley 42 28-48-32-34 x x x SE Crescent Valley 48 HDR-27-48-19-24 x x x x Carico Lake North 19 WCCC-01 x x Carico Lake North 22 WCCC-03 x x Carico Lake North 21 WCCC-05 x x Carico Lake North 20 WCCC-06 x x Carico Lake North 18 WCCC-07 x x Carico Lake North 17 WCCC-09 x x Carico Lake North 15 WCCC-10 x x Carico Lake North 23 WCCC-11 x x Carico Lake North 14 WCCC-12 x x

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-21

Table A-2 Surface Water Sites within the Drawdown Area

Sites Within the Projected Drawdown Area (Maximum Extent of 10-foot Groundwater Drawdown Contour Plus 1-mile Buffer) Mitigation Plans Sites Included Proposed Action and in 2011 Final Sites Included in Map ID Spring or No Action Gold Acres Pit Partial SEIS Mitigation 2018 Contingent Spring Group1 Number1 Stream Site ID Alternative Backfill Alternative Cumulative (Table 3.2-1)2 Mitigation Plan3 Carico Lake North 16 WCCC-13 x x Total Springs 144 168 188 27 161 Total springs excluding those covered in the 2011 Final SEIS mitigation2 122 141 161 -- -- Stream Sites Ferris Creek Stream S-07 FER-01 x x x Fourmile Canyon S-08 FOU-01-HDR x x x Fourmile Canyon S-09 FOU-01-JBR x x x Fourmile Canyon S-10 FOU-02 x x x Horse Creek S-11 HOR-01 x x Horse Creek S-12 HOR-02D x x x x Horse Creek S-13 HOR-05T x x x x Horse Creek S-14 HOR-05U x x x x Indian Creek 13 IC-1 x x x Indian Creek S-16 IND-01D x x x Indian Creek S-17 IND-01U x x x Mill Canyon S-18 MIL-01 x x x x Mill Canyon S-19 MIL-02 x x x x Mill Canyon S-20 MIL-02A x x x x Mill Canyon S-21 MIL-03 x x x x Willow Creek S-25 WIL-06D x x Total Stream Sites 7 14 16 5 11

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-22

Table A-2 Surface Water Sites within the Drawdown Area

Sites Within the Projected Drawdown Area (Maximum Extent of 10-foot Groundwater Drawdown Contour Plus 1-mile Buffer) Mitigation Plans Sites Included Proposed Action and in 2011 Final Sites Included in Map ID Spring or No Action Gold Acres Pit Partial SEIS Mitigation 2018 Contingent Spring Group1 Number1 Stream Site ID Alternative Backfill Alternative Cumulative (Table 3.2-1)2 Mitigation Plan3 Streams (Mapped Perennial Reaches) Cooks Creek x Elder Creek x x x Ferris Creek x x x Horse Creek x x Indian Creek x x x Mill Creek x x x South Fork Mill Creek x Willow Creek (tributaries) x x Total Streams 4 6 8 1 Spring groups and map ID numbers are shown in Figure 3.2-3. 2 Current mitigation presented in Table 3.2-1 in the Cortez Hills Expansion Project Final SEIS (BLM 2011). 3 Proposed contingent mitigation presented in Table 2 in the Contingency Mitigation Plan (BCI and Stantec 2018).

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-23

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Springs Reduction of flow 1.0 Mitigation plan below established would be highly Spring source threshold coincident effective at developed with with a reduction in maintaining a Pipe from new or Rocky Hills 229 25-48-25-341 pipes; supports 6.068 groundwater levels in water supply for existing well. large wet the area as livestock, wildlife, meadow. determined from and habitat groundwater diversity. monitoring. Reduction of flow 0.5 Mitigation plan below established would be highly Spring source threshold coincident effective at flowing from a with a reduction in maintaining a Pipe from new or Rocky Hills 227 25-49-11-423 hillside and piped 0 groundwater levels in water supply for existing well. into a cattle the area as livestock and trough. determined from wildlife. groundwater monitoring. Reduction of flow 1.1 Mitigation plan below established would be highly threshold coincident effective at Spring pipe and with a reduction in maintaining a trough with fence Pipe from new or Rocky Hills 228 25-49-29-213 0.158 groundwater levels in water supply for surrounding main existing well. the area as livestock, wildlife, spring area. determined from and habitat groundwater diversity. monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-24

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of flow 0.2 Mitigation plan below established would be highly threshold coincident effective at with a reduction in maintaining a Developed source Pipe from new or Peripheral Area 226 26-46-21-12 0 groundwater levels in water supply for piped to trough. existing well. the area as livestock and determined from wildlife. groundwater monitoring. Basin seep on a None Not applicable. Not applicable. hillside; reported North Toiyabe as dry or no flow 209 26-47-11-433B 0 None Range East in 6 of 7 years during fall monitoring. Reduction of flow 0.3 Mitigation plan below established would be highly threshold coincident effective at Spring has a with a reduction in maintaining a North Toiyabe Pipe from new or 208 26-47-12-314A spring pipe and 0.024 groundwater levels in water supply for Range East existing well. trough. the area as livestock, wildlife, determined from and habitat groundwater diversity. monitoring. North Toiyabe Hillside seep with None Not applicable. Not applicable. 210 26-47-14-141 0 None Range East inconsistent flow.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-25

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at Two spring established threshold maintaining a discharge source coincident with a water supply for North Toiyabe Pipe from new or 203 26-47-16-211 areas feed into the 0.172 reduction in livestock, wildlife, Range West existing well. same wetland groundwater levels in and habitat complex. the area as diversity. determined from groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at established threshold maintaining a Seep associated coincident with a water supply for North Toiyabe Pipe from new or 202 26-47-16-212A with a larger 0.003 reduction in livestock, wildlife, Range West existing well. wetland complex. groundwater levels in and habitat the area as diversity. determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-26

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at established threshold maintaining a Seep associated coincident with a water supply for North Toiyabe Pipe from new or 200 26-47-16-212B with a larger 0.532* reduction in livestock, wildlife, Range West existing well. wetland complex. groundwater levels in and habitat the area as diversity. determined from groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at Seep with established threshold maintaining a standing water coincident with a water supply for North Toiyabe Pipe from new or 199 26-47-16-212C associated with a 0.333 reduction in livestock, wildlife, Range West existing well. larger wetland groundwater levels in and habitat complex. the area as diversity. determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-27

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at Seep associated established threshold maintaining a with a larger coincident with a water supply for North Toiyabe Pipe from new or 201 26-47-16-212D wetland complex. 0.0532* reduction in livestock, wildlife, Range West existing well. Heavy livestock groundwater levels in and habitat use observed. the area as diversity. determined from groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at Seep reported as established threshold maintaining a dry in 3 of 5 years coincident with a water supply for North Toiyabe Pipe from new or 205 26-47-16-434 during fall 0 reduction in habitat diversity. Range West existing well. monitoring. Noted groundwater levels in to support willows. the area as determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-28

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Site located in a hydrophytic would be highly heavily trampled vegetation below effective at drainage area. established threshold maintaining a Flow is coincident with a water supply for North Toiyabe Pipe from new or 206 26-47-20-342 inconsistent (i.e., 0.075 reduction in livestock, wildlife, Range West existing well. reported as no groundwater levels in and habitat flow or dry in 4 of the area as diversity. 5 years during fall determined from monitoring). groundwater monitoring. Reduction of 0.5 Mitigation plan Spring located on hydrophytic would be highly a side hill that vegetation below effective at flows down a established threshold maintaining a drainage. Flow is coincident with a water supply for North Toiyabe Pipe from new or 212 26-47-23-314A inconsistent (i.e., 0.017* reduction in livestock, wildlife, Range East existing well. no flow observed groundwater levels in and habitat in 4 of 7 years the area as diversity. during fall determined from monitoring). groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-29

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Spring located on vegetation below effective at a side hill and established threshold maintaining a flows down a coincident with a water supply for North Toiyabe drainage. Flow is Pipe from new or 211 26-47-23-314B 0.017* reduction in livestock, wildlife, Range East inconsistent (i.e., existing well. groundwater levels in and habitat reported as dry in the area as diversity. 4 of 5 years during determined from fall monitoring). groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at Seep associated established threshold maintaining with hydrophytic coincident with a habitat diversity. North Toiyabe vegetation. No Pipe from new or 213 26-47-23-344B 0.001 reduction in Range East flow has been existing well. groundwater levels in observed at this the area as site. determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-30

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located on a vegetation below effective at side hill above the established threshold maintaining channel. Flow is coincident with a habitat diversity. North Toiyabe inconsistent (i.e., Pipe from new or 214 26-47-27-324 0.58 reduction in Range East reported as no existing well. groundwater levels in flow in 3 of 5 the area as years during fall determined from monitoring). groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located on a vegetation below effective at side hill and flows established threshold maintaining down a drainage. coincident with a habitat diversity. North Toiyabe Flow is Pipe from new or 207 26-47-29-244 0.159 reduction in Range West inconsistent (i.e., existing well. groundwater levels in reported as dry in the area as 4 of 5 years during determined from fall monitoring). groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-31

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at Seep with established threshold maintaining standing water coincident with a habitat diversity. North Toiyabe that goes dry in Pipe from new or 215 26-47-35-134 0.001 reduction in Range East some years. Flow existing well. groundwater levels in has never been the area as recorded. determined from groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at established threshold maintaining Seep area defined coincident with a habitat diversity. by vegetation. Pipe from new or Willow Creek 139 26-48-01-131 0.75 reduction in Flow has never existing well. groundwater levels in been recorded. the area as determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-32

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at Seep area defined established threshold maintaining by vegetation. coincident with a habitat diversity. Monitoring from Pipe from new or Willow Creek 142 26-48-01-141 0.016 reduction in 2008 -2017 existing well. groundwater levels in indicates site is the area as typically dry. determined from groundwater monitoring. Seasonally None Not applicable. Not applicable. influenced site located in a drainage bottom. Monitoring data Willow Creek 231 26-48-01-142 indicate the site is 0 None consistently dry during the low flow period (late summer through fall).

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-33

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Seasonally Reduction of 0.5 Mitigation plan influenced site hydrophytic would be highly located in a rocky vegetation below effective at drainage bottom. established threshold maintaining Monitoring data coincident with a habitat diversity. Pipe from new or Willow Creek 244 26-48-01-212 indicate the site is 0.008 reduction in existing well. consistently dry groundwater levels in during the low flow the area as period (late determined from summer through groundwater fall). monitoring. Seasonally Reduction of 0.5 Mitigation plan influenced site hydrophytic would be highly located in a dry vegetation below effective at ephemeral established threshold maintaining channel that is coincident with a habitat diversity. tributary to Willow reduction in Pipe from new or Willow Creek 132 26-48-01-212B 0.014 Creek. Monitoring groundwater levels in existing well. data indicate the the area as site is typically dry determined from during the annual groundwater fall sampling monitoring. event.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-34

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Seasonally Reduction of 0.5 Mitigation plan influenced site hydrophytic would be highly located in a dry vegetation below effective at ephemeral established threshold maintaining channel that is coincident with a habitat diversity. Pipe from new or Willow Creek 135 26-48-01-223 tributary to Willow 0.015 reduction in existing well. Creek. Monitoring groundwater levels in data indicate the the area as site is typically dry determined from during the annual groundwater fall sampling. monitoring. Site located in a Reduction of 0.5 Mitigation plan dry ephemeral hydrophytic would be highly channel that is vegetation below effective at tributary to Willow established threshold maintaining Creek. Monitoring coincident with a habitat diversity. Pipe from new or Willow Creek 137 26-48-01-224 data indicate flow 0.098* reduction in existing well. has never been groundwater levels in recorded or the area as observed during determined from the annual fall groundwater sampling. monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-35

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Site located in a hydrophytic would be highly dry ephemeral vegetation below effective at channel that is established threshold maintaining tributary to Willow coincident with a habitat diversity. Pipe from new or Willow Creek 144 26-48-01-234 Creek. Monitoring 0.003 reduction in existing well. data indicate the groundwater levels in site is typically dry the area as during the annual determined from fall sampling. groundwater monitoring. Reduction of 0.5 Mitigation plan Site located in a hydrophytic would be highly dry ephemeral vegetation below effective at channel that is established threshold maintaining tributary to Willow coincident with a habitat diversity. Pipe from new or Willow Creek 138 26-48-01-241 Creek. Monitoring 0.098* reduction in existing well. data indicate the groundwater levels in site is typically dry the area as during the annual determined from fall sampling. groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-36

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Seep located in hydrophytic would be highly drainage channel. vegetation below effective at Monitoring data established threshold maintaining indicate flow has coincident with a habitat diversity. Pipe from new or Willow Springs 233 26-48-01-313A never been 0.014 reduction in existing well. recorded or groundwater levels in observed during the area as the annual fall determined from sampling. groundwater monitoring. Reduction of 0.5 Mitigation plan Seep located hydrophytic would be highly hillside east of vegetation below effective at Horse Canyon. established threshold maintaining Monitoring data coincident with a habitat diversity. indicate flow has Pipe from new or Willow Springs 145 26-48-01-313B 0.292 reduction in never been existing well. groundwater levels in recorded or the area as observed during determined from the annual fall groundwater sampling. monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-37

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Seep located hydrophytic would be highly hillside east of vegetation below effective at Horse Canyon. established threshold maintaining Monitoring data coincident with a habitat diversity. Pipe from new or Willow Springs 146 26-48-01-323 indicate flow has 0.152 reduction in existing well. never been groundwater levels in recorded or the area as observed at this determined from site. groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located in vegetation below effective at drainage channel. established threshold maintaining Monitoring data coincident with a habitat diversity. Pipe from new or Willow Springs 232 26-48-01-324 indicate the site is 0 reduction in existing well. typically dry during groundwater levels in the annual fall the area as sampling. determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-38

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located on a vegetation below effective at hillside above a established threshold maintaining drainage. Horses coincident with a habitat diversity. and cattle Pipe from new or Willow Creek 133 26-48-02-224 0.057 reduction in observed in area. existing well. groundwater levels in Flow has never the area as been recorded at determined from the site. groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located on a vegetation below effective at hillside adjacent to established threshold maintaining mine reclamation coincident with a habitat diversity. Pipe from new or Horse Creek 163 26-48-02-322 area. Flow has 0.014 reduction in existing well. never been groundwater levels in recorded at this the area as site. determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-39

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Perennial spring Reduction of flow 2.1 Mitigation plan located on a below established would be highly hillside at the top threshold coincident effective at of a wide channel with a reduction in maintaining a with an old cattle groundwater levels in water supply for trough. Monitoring the area as livestock and Pipe from new or Horse Creek 169 26-48-02-423A indicates flow is 0.612 determined from wildlife. existing well. seasonally groundwater influences but monitoring. persists during the low flow period (late summer through fall). Perennial spring Reduction of flow 0.5 Mitigation plan located on a below established would be highly hillside that flows threshold coincident effective at into a drainage with a reduction in maintaining a that supports a groundwater levels in water supply for large wet area. the area as livestock and Pipe from new or Horse Creek 168 26-48-02-423B Monitoring 0.314 determined from wildlife. existing well. indicates evidence groundwater of flow persists monitoring. during the low flow period (late summer through fall).

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-40

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at Seep located at established threshold maintaining the base of a coincident with a habitat diversity. small cliff in upper Pipe from new or Horse Creek 160 26-48-03-134 0.013 reduction in Horse Canyon. existing well. groundwater levels in Flow never the area as recorded. determined from groundwater monitoring. Reduction of flow 0.5 Mitigation plan Seasonally below established would be highly influenced spring threshold coincident effective at located on a steep with a reduction in maintaining a Pipe from new or Horse Creek 161 26-48-03-143 slope. Flow is 0.017 groundwater levels in water supply for existing well. typically dry during the area as livestock and the fall sampling determined from wildlife. period. groundwater monitoring. Spring located Reduction of flow 0.8 Mitigation plan within a wide below established would be highly channel in Horse threshold coincident effective at Canyon. Flow with a reduction in maintaining a monitoring groundwater levels in Pipe from new or water supply for Horse Creek 158 26-48-03-213 1.684 indicates strong the area as existing well. livestock and seasonal influence determined from wildlife. and spring groundwater reported dry in monitoring. some years.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-41

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at Spring located in established threshold maintaining a channel in upper coincident with a water supply for Horse Canyon. Pipe from new or Horse Creek 157 26-48-03-221 0.039 reduction in livestock and Flow has varied existing well. groundwater levels in wildlife. from 0.0 to over the area as 50 gpm. determined from groundwater monitoring. Reduction of flow Not applicable. Mitigation plan Perennial spring below established would be effective that emerges from threshold coincident at maintaining a a steep, rocky with a reduction in water supply for slope in upper Horse Creek 164 26-48-03-321 0.048 groundwater levels in Install guzzler. wildlife. Horse Canyon. the area as Flow has varied determined from from 0.45 to 450 groundwater gpm. monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-42

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Spring located Reduction of 0.5 Mitigation plan within the main hydrophytic would be highly channel of upper vegetation below effective at Horse Canyon. established threshold maintaining Flow has varied coincident with a habitat diversity. Pipe from new or Horse Creek 165 26-48-03-413A between 0.00 and 0.068 reduction in existing well. 27.01 gpm. Flows groundwater levels in reported as dry or the area as up to less than 1 determined from gpm since groundwater November 2010. monitoring. Reduction of 0.5 Mitigation plan Seep located on a hydrophytic would be highly hillside above the vegetation below effective at main channel of established threshold maintaining upper Horse coincident with a habitat diversity. Canyon. Typically Pipe from new or Horse Creek 166 26-48-03-413B 0.066 reduction in dry in the fall existing well. groundwater levels in monitoring period the area as except in determined from unusually wet groundwater years. monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-43

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Spring located Reduction of 0.5 Mitigation plan within a dry hydrophytic would be highly channel in the vegetation below effective at main Horse established threshold maintaining Canyon drainage. coincident with a habitat diversity. Pipe from new or Horse Creek 170 26-48-03-443 Highly variable 0.272 reduction in existing well. flow. Reported as groundwater levels in dry during the fall the area as monitoring determined from between 2012 and groundwater 2016. monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located vegetation below effective at within a dry established threshold maintaining meadow along the coincident with a habitat diversity. main channel of Pipe from new or Horse Creek 171 26-48-03-444 0.518 reduction in Horse Canyon. existing well. groundwater levels in Flow has never the area as been recorded at determined from this site. groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-44

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of flow 0.5 Mitigation plan Perennial spring below established would be highly locate within a threshold coincident effective at tributary on the with a reduction in maintaining a Pipe from new or Horse Creek 173 26-48-10-142 western side of 0.124 groundwater levels in water supply for existing well. Horse Canyon. the area as livestock, and Spring flow piped determined from wildlife. to a trough. groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located vegetation below effective at within a tributary established threshold maintaining on the west side coincident with a habitat diversity. Pipe from new or Horse Creek 174 26-48-10-232 of Horse Canyon. 0.033 reduction in existing well. Flow has never groundwater levels in been recorded at the area as this site. determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-45

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Spring located Reduction of 0.5 Mitigation plan within a tributary hydrophytic would be highly on the west side vegetation below effective at of Horse Canyon. established threshold maintaining Highly variable coincident with a habitat diversity. flow suggests reduction in Pipe from new or Horse Creek 188 26-48-10-344 0.568* spring is strongly groundwater levels in existing well. influenced by the area as seasonal runoff. determined from Dry during the fall groundwater sampling event monitoring. since 2013. Reduction of flow 0.2 Mitigation plan Spring located below established would be highly within a tributary threshold coincident effective at on the west side with a reduction in maintaining a of Horse Canyon. Pipe from new or Horse Creek 189 26-48-10-433 0.568* groundwater levels in water supply for Spring reported as existing well. the area as livestock and dry in 2 of 4 years determined from wildlife. during the fall groundwater sampling event. monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-46

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located vegetation below effective at within a tributary established threshold maintaining on the west side coincident with a habitat diversity. of Horse Canyon. Pipe from new or Horse Creek 182 26-48-10-441 0.02 reduction in Flow has never existing well. groundwater levels in been reported but the area as site is occasionally determined from wet. groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located vegetation below effective at within a tributary established threshold maintaining on the west side coincident with a habitat diversity. Pipe from new or Horse Creek 184 26-48-10-442 of Horse Canyon. 0.028 reduction in existing well. Flow has never groundwater levels in been reported at the area as this site. determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-47

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Seep located hydrophytic would be highly within a tributary vegetation below effective at on the west side established threshold maintaining of Horse Canyon. coincident with a habitat diversity. Pipe from new or Horse Creek 187 26-48-10-444 Flow (<1gpm) 0.016 reduction in existing well. reported in 2 of 10 groundwater levels in years in the late the area as summer-fall determined from sampling. groundwater monitoring. Reduction of 0.5 Mitigation plan Site located on a hydrophytic would be highly hillside on the vegetation below effective at eastern slope of established threshold maintaining Horse Canyon. coincident with a habitat diversity. Pipe from new or Horse Creek 172 26-48-11-142 Flow (<2gpm) 0.037 reduction in existing well. reported in 2 of 10 groundwater levels in years in the late the area as summer-fall determined from sampling. groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-48

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Seep located on hydrophytic would be highly the northern slope vegetation below effective at of Horse Canyon. established threshold maintaining Disturbed by fire coincident with a habitat diversity. 26-48-11-144A and cattle use. Pipe from new or Horse Creek 175 0.384* reduction in (26-48-02-144A) Flow (<~1gpm) existing well. groundwater levels in measured in 4 of the area as 10 years in the determined from late summer-fall groundwater sampling. monitoring. Seep located on Reduction of 0.5 Mitigation plan the northern slope hydrophytic would be highly of Horse Canyon vegetation below effective at and connected to established threshold maintaining water the same wetland coincident with a supply for complex as 26-48- reduction in livestock and 26-48-11-144B Pipe from new or Horse Creek 176 11-144A. 0.384* groundwater levels in wildlife and habitat (26-48-02-144B) existing well. Disturbed by fire the area as diversity. and cattle use. determined from Wet area or groundwater standing water monitoring. persists in most years.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-49

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at Seep located on established threshold maintaining water the northern slope coincident with a supply for of Horse Canyon. Pipe from new or Horse Creek 177 26-48-11-312 0.072 reduction in livestock and Flow or saturated existing well. groundwater levels in wildlife and habitat soil persists in the area as diversity. most years. determined from groundwater monitoring. Reduction of 0.5 Mitigation plan Seep with non- hydrophytic would be highly functioning trough vegetation below effective at and piping in established threshold maintaining heavily disturbed coincident with a habitat diversity. area. Fall Pipe from new or Horse Creek 183 26-48-11-422 0.214 reduction in monitoring data existing well. groundwater levels in indicates flow (<2 the area as gpm) in 2011 and determined from 2012; dry in 2013 groundwater and 2014. monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-50

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at established threshold maintaining Seep located on a coincident with a habitat diversity. slope. Flow never Pipe from new or Horse Creek 236 26-48-12-323 0.064 reduction in recorded at this existing well. groundwater levels in site. the area as determined from groundwater monitoring. Seep located on a Reduction of 0.5 Mitigation plan hillside above a hydrophytic would be highly tributary to Willow vegetation below effective at Creek. Area is established threshold maintaining disturbed by horse coincident with a habitat diversity. Pipe from new or Horse Creek 178 26-48-12-324 and cattle grazing. 0.168 reduction in existing well. Noted as wet area groundwater levels in or has measurable the area as flow (<0.5 gpm) determined from during the fall in groundwater most years monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-51

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Seep located on a hydrophytic would be highly hillside above a vegetation below effective at tributary to Willow established threshold maintaining Creek. Area is coincident with a habitat diversity. disturbed by horse Pipe from new or Horse Creek 179 26-48-12-341 0.047 reduction in and cattle grazing. existing well. groundwater levels in Noted as either the area as dry or wet area determined from during the fall groundwater sampling. monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at established threshold maintaining Seep located on a coincident with a habitat diversity. Pipe from new or Horse Creek 180 26-48-12-414 hillside that feeds 0.726 reduction in existing well. a larger wet area. groundwater levels in the area as determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-52

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located vegetation below effective at within a tributary established threshold maintaining channel to Willow coincident with a habitat diversity. Pipe from new or Horse Creek 181 26-48-12-432 Creek. Flow has 0.027 reduction in existing well. never been groundwater levels in recorded at this the area as site. determined from groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at Site is located established threshold maintaining a within a large wet coincident with a water supply for Pipe from new or Horse Creek 191 26-48-13-323 meadow with 15.720* reduction in livestock and existing well. highly variable groundwater levels in wildlife. flow. the area as determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-53

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of flow 14.3 Mitigation plan below established would be highly Site is located threshold coincident effective at within a large wet with a reduction in maintaining a Pipe from new or Horse Creek 190 26-48-13-324 meadow with 15.720* groundwater levels in water supply for existing well. highly variable the area as livestock and flow. determined from wildlife. groundwater monitoring. Reduction of flow 3.7 Mitigation plan below established would be highly Site is located threshold coincident effective at within a large wet with a reduction in maintaining a Pipe from new or Horse Creek 194 26-48-13-342 meadow with 15.720* groundwater levels in water supply for existing well. highly variable the area as livestock and flow. determined from wildlife. groundwater monitoring. Site is located on Reduction of 0.5 Mitigation plan the northern hydrophytic would be highly boundary of a vegetation below effective at large wet established threshold maintaining a meadow. Flow coincident with a water supply for Pipe from new or Horse Creek 193 26-48-13-431 data indicates that 1.288 reduction in livestock and existing well. the site persisted groundwater levels in wildlife. as a wet area the area as between 2008 and determined from 2011, and was dry groundwater in 2014-2017. monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-54

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Site is a seep None. Site is an Not applicable. Not applicable. Horse Creek 192 26-48-13-432 associated with an 0.426 existing well. None older well site. Site located in a None Not applicable. Not applicable. channel. No flow Horse Creek 237 26-48-14-412 0 None recorded; site consistently dry. Site located in a None Not applicable. Not applicable. channel. No flow Horse Creek 238 26-48-14-424 0 None recorded; site consistently dry. Reduction of 0.5 Mitigation plan Site is a dry rocky hydrophytic would be highly drainage vegetation below effective at southwest of established threshold maintaining Horse Canyon. coincident with a habitat diversity. Pipe from new or Dry Hills 217 26-48-23-211A Site is typically dry 0.015* reduction in existing well. but has flow groundwater levels in occasionally in the the area as spring-early determined from summer. groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-55

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at Site located just established threshold maintaining down channel coincident with a habitat diversity. from 26-48-23- Pipe from new or Dry Hills 218 26-48-23-211B 0.015* reduction in 211A and has existing well. groundwater levels in similar flow the area as characteristics. determined from groundwater monitoring. Reduction of 0.5 Mitigation plan Site is a dry hydrophytic would be highly channel southwest vegetation below effective at of Horse Canyon. established threshold maintaining Between coincident with a habitat diversity. Pipe from new or Dry Hills 219 26-48-23-242 9/23/2011 - 0.018 reduction in existing well. 9/08/2017 the site groundwater levels in was dry except for the area as 5/14/2016 (0.45 determined from gpm). groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-56

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Site is a dry hydrophytic would be highly channel southwest vegetation below effective at of Horse Canyon. established threshold maintaining Between coincident with a habitat diversity. Pipe from new or Dry Hills 222 26-48-23-313A 8/27/2008 - 0.012 reduction in existing well. 9/08/2017 the site groundwater levels in was dry except for the area as 5/05/2009 (1.93 determined from gpm). groundwater monitoring. Site is located just Reduction of 0.5 Mitigation plan down channel hydrophytic would be highly from 26-48-23- vegetation below effective at 313A at a cattle established threshold maintaining trough fed by a coincident with a habitat diversity. spring pipe. Flow reduction in Pipe from new or Dry Hills 223 26-48-23-313B 0.021 was recorded as groundwater levels in existing well. dry between the area as 9/16/2010 - determined from 09/08/2017 except groundwater for 5/16/2016 monitoring. (0.45 gpm). Site is located on None Not applicable. Not applicable. a hillside and not identified as a Dry Hills 240 26-48-23-321 0 None spring or seep in recent survey in 2018.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-57

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Site located within hydrophytic would be highly a drainage vegetation below effective at southwest of established threshold maintaining Horse Canyon. coincident with a habitat diversity. Pipe from new or Dry Hills 220 26-48-24-133 Site reported as 0.006 reduction in existing well. dry in the fall groundwater levels in monitoring the area as between 2011and determined from 2017. groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly Site is a dry vegetation below effective at channel established threshold maintaining downstream from coincident with a habitat diversity. 26-48-24-133. Site Pipe from new or Dry Hills 221 26-48-24-134 0.007 reduction in reported as dry in existing well. groundwater levels in the fall monitoring the area as between 2011 and determined from 2017. groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-58

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Site is located on Reduction of 0.5 Mitigation plan near the southern hydrophytic would be highly boundary of a vegetation below effective at large wet established threshold maintaining meadow. Flow coincident with a habitat diversity. Pipe from new or Horse Creek 195 26-48-24-221 data indicate that 3.87 reduction in existing well. the site persisted groundwater levels in as a wet area the area as between 2008- determined from 2011; and was dry groundwater in 2014-2017. monitoring. Reduction of 0.5 Mitigation plan Seep located in hydrophytic would be highly drainage channel. vegetation below effective at Monitoring data established threshold maintaining indicate flow has coincident with a habitat diversity. Pipe from new or Dry Hills 241 26-48-26-111 never been 0.007 reduction in existing well. recorded or groundwater levels in observed during the area as the annual fall determined from sampling. groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-59

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Seep located in hydrophytic would be highly drainage channel. vegetation below effective at Monitoring data established threshold maintaining indicates flow has coincident with a habitat diversity. Pipe from new or Dry Hills 242 26-48-26-122 never been 0 reduction in existing well. recorded or groundwater levels in observed during the area as the annual fall determined from sampling. groundwater monitoring. Site with cattle Reduction of 0.5 Mitigation plan trough located hydrophytic would be highly within a drainage vegetation below effective at south of Horse established threshold maintaining Canyon. Site coincident with a habitat diversity. reported as dry in reduction in Pipe from new or Dry Hills 225 26-48-26-123A the fall monitoring 0.020* groundwater levels in existing well. between 2008 and the area as 2017, with the determined from exception of 2011 groundwater when flow was monitoring. insufficient for sampling.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-60

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Seep located in hydrophytic would be highly drainage channel vegetation below effective at downstream from established threshold maintaining 26-48-26-123A. coincident with a habitat diversity. Monitoring data Pipe from new or Dry Hills 224 26-48-26-123B 0.020* reduction in indicate the site existing well. groundwater levels in was dry during the the area as annual fall determined from sampling (2008- groundwater 2017). monitoring. Reduction of Not applicable. Mitigation plan hydrophytic would be effective Seep located in vegetation below at maintaining the drainage channel. established threshold hydrophytic Monitoring data coincident with a vegetation. indicate the site is Dry Hills 243 26-48-26-132 0 reduction in Install guzzler. typically dry during groundwater levels in the annual fall the area as sampling (2008- determined from 2011). groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-61

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Site is a dry rocky hydrophytic would be highly drainage vegetation below effective at southwest of established threshold maintaining the Horse Canyon. coincident with a hydrophytic Pipe from new or Horse Creek 159 26-48-03-114 Site is typically dry 0.007 reduction in vegetation. existing well. but has flow groundwater levels in occasionally in the the area as spring-early determined from summer. groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at established threshold maintaining the Seep area defined coincident with a hydrophytic by vegetation. Pipe from new or Willow Creek 127 26-49-05-324 0.011 reduction in vegetation. Flow has never existing well. groundwater levels in been recorded. the area as determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-62

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep source area vegetation below effective at located above established threshold maintaining the retention basin. coincident with a hydrophytic Pipe from new or Willow Creek 117 26-49-06-211 Fall monitoring 1.549 reduction in vegetation. existing well. indicates site is groundwater levels in wet with no the area as measurable flow. determined from groundwater monitoring. Seep located Reduction of 0.5 Mitigation plan downstream of a hydrophytic would be highly retention basin vegetation below effective at that supports established threshold maintaining the vegetation. Fall coincident with a hydrophytic monitoring reduction in Pipe from new or vegetation. Willow Creek 118 26-49-06-213 0.469 indicates that groundwater levels in existing well. except for 2013 the area as (0.45 gpm), the determined from site is wet with no groundwater measurable flow monitoring. (2014-2017).

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-63

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep in wet vegetation below effective at drainage channel. established threshold maintaining the Fall monitoring coincident with a hydrophytic (2011-2017) Pipe from new or Willow Creek 131 26-49-07-111 0.215 reduction in vegetation. indicates site is existing well. groundwater levels in typically wet and the area as occasionally has determined from measurable flow. groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located in a vegetation below effective at dry rocky drainage established threshold maintaining the that is tributary to coincident with a hydrophytic Pipe from new or Willow Creek 141 26-49-07-114 Willow Creek. 0.005 reduction in vegetation. existing well. Flow never groundwater levels in recorded at this the area as site (2011-2017). determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-64

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located on a vegetation below effective at hillside above a established threshold maintaining the drainage. Site is coincident with a hydrophytic Pipe from new or Willow Creek 136 26-49-07-114B typically wet with 0.041 reduction in vegetation. existing well. no measurable groundwater levels in flow during fall the area as sampling. determined from groundwater monitoring. Reduction of 0.5 Mitigation plan Seep area located hydrophytic would be highly in a channel that vegetation below effective at is tributary to established threshold maintaining the Willow Creek coincident with a hydrophytic Pipe from new or Willow Creek 143 26-49-07-141 defined by 0.118 reduction in vegetation. existing well. vegetation. Flow groundwater levels in has never been the area as recorded (2011- determined from 2017). groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-65

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Seep area located Reduction of 0.5 Mitigation plan in a channel that hydrophytic would be highly is tributary to vegetation below effective at Willow Creek established threshold maintaining the defined by coincident with a hydrophytic vegetation. Flow reduction in Pipe from new or vegetation. Willow Creek 130 26-49-07-221 0.285 has never been groundwater levels in existing well. recorded (2011- the area as 2017); standing determined from water noted in fall groundwater sampling events in monitoring. 2012 and 2012. Seep area located Reduction of 0.5 Mitigation plan in a channel that hydrophytic would be highly is tributary to vegetation below effective at Willow Creek established threshold maintaining the defined by coincident with a hydrophytic Pipe from new or Willow Creek 134 26-49-07-222 vegetation. Small 0.031 reduction in vegetation. existing well. flows (<2gpm) groundwater levels in recorded in 3 of 7 the area as years fall sampling determined from events (2011- groundwater 2017). monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-66

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Seep area located Reduction of 0.5 Mitigation plan on a side hill that hydrophytic would be highly supports vegetation below effective at vegetation. Site established threshold maintaining the recorded small coincident with a hydrophytic Pipe from new or Willow Springs 147 26-49-07-331 flows (<4 gpm) or 0.224 reduction in vegetation. existing well. standing water in groundwater levels in pools in most the area as years during fall determined from sampling events groundwater (2011-2017). monitoring. Seep located on a Reduction of flow 1.1 Mitigation plan hillside at the below established would be highly head of a large threshold coincident effective at wet channel. Site with a reduction in maintaining a was noted to be groundwater levels in water supply for Pipe from new or Willow Springs 148 26-49-07-343 wet or had small 0.175 the area as livestock and existing well. measurable flows determined from wildlife. (<3.5 gpm) in all groundwater of the annual fall monitoring. sampling events (2011-2017).

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-67

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Seep in wet hydrophytic would be highly drainage channel vegetation below effective at that is tributary to established threshold maintaining the Willow Creek. Fall coincident with a hydrophytic monitoring (2013- Pipe from new or Willow Creek 140 26-49-08-114A 0.449 reduction in vegetation. 2017) indicates existing well. groundwater levels in site is typically wet the area as and occasionally determined from has measurable groundwater flow (<3 gpm). monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly vegetation below effective at established threshold maintaining the Seep area defined coincident with a hydrophytic by vegetation. Pipe from new or Willow Springs 152 26-49-17-432 0.036 reduction in vegetation. Flow has never existing well. groundwater levels in been recorded. the area as determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-68

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Spring area Reduction of flow 3.6 Mitigation plan located on a side below established would be highly hill that supports threshold coincident effective at vegetation. Spring with a reduction in maintaining a pipe with cattle groundwater levels in water supply for trough present. the area as livestock, and Site recorded determined from Pipe from new or wildlife. Willow Springs 149 26-49-18-111 0.39 variable flows up groundwater existing well. to 12.2 gpm or wet monitoring. conditions without measurable flow during fall sampling events (2011-2017). Spring / seep area Reduction of 0.5 Mitigation plan located on a side hydrophytic would be highly hill above tributary vegetation below effective at drainage. Site established threshold maintaining the recorded variable coincident with a hydrophytic flows up to 1 gpm reduction in Pipe from new or vegetation. Willow Springs 150 26-49-18-134 0.438 or wet conditions groundwater levels in existing well. without the area as measurable flow determined from during fall groundwater sampling events monitoring. (2011-2017).

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-69

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Seep located on a hydrophytic would be highly hillside that vegetation below effective at supports established threshold maintaining the vegetation. Fall coincident with a hydrophytic Pipe from new or Horse Creek 185 26-49-18-331 monitoring (2011- 0.065 reduction in vegetation. existing well. 2017) recorded groundwater levels in saturated soil with the area as no flow in most determined from years. groundwater monitoring. Spring area Reduction of flow 1.7 Mitigation plan located on a side below established would be highly hill that supports threshold coincident effective at vegetation. Site with a reduction in maintaining a recorded variable groundwater levels in water supply for Pipe from new or Horse Creek 186 26-49-18-332 flows up to 7.58 0.574 the area as livestock and existing well. gpm or wet determined from wildlife. conditions without groundwater measurable flow monitoring. most years (2008- 2017).

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-70

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of Not applicable. Mitigation plan hydrophytic would be effective Seep located in a vegetation below at maintaining the tributary channel established threshold hydrophytic to Willow Creek. coincident with a vegetation. Willow Springs 151 26-49-18-423 Site is typically 0.036 reduction in Install guzzler. wet without groundwater levels in measurable flow the area as (2011-2017). determined from groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly Site is a vegetation below effective at monitoring established threshold maintaining the location within a coincident with a hydrophytic Pipe from new or Willow Springs 154 26-49-20-122 wet meadow. Flow 0.08 reduction in vegetation. existing well. has never been groundwater levels in recorded at the the area as site (2011-2017). determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-71

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Site located within hydrophytic would be highly a dry water vegetation below effective at retention basin in established threshold maintaining the Willow Springs. coincident with a hydrophytic Pipe from new or Willow Springs 153 26-49-20-122A Fall monitoring 0.888* reduction in vegetation. existing well. data indicate site groundwater levels in was dry in 2 of 5 the area as years (2011- determined from 2015). groundwater monitoring. Site located within Reduction of 0.5 Mitigation plan a large wet hydrophytic would be highly meadow area that vegetation below effective at has been heavily established threshold maintaining the impacted by coincident with a hydrophytic cattle. Fall reduction in Pipe from new or vegetation. Willow Springs 155 26-49-20-122B 0.888* monitoring data groundwater levels in existing well. (2013-2016) the area as indicate wet determined from conditions with groundwater flow ranging from monitoring. 0.0 to 0.45 gpm.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-72

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Seep area located hydrophytic would be highly within a meadow. vegetation below effective at Fall monitoring established threshold maintaining the events (2011- coincident with a hydrophytic 2017) recorded Pipe from new or Willow Springs 156 26-49-20-213 0.116 reduction in vegetation. wet conditions existing well. groundwater levels in with no the area as measurable flow determined from or flow up to 0.75 groundwater gpm monitoring. Site located in a None Not applicable. Not applicable. broad flat area. Horse Creek 239 26-49-30-112 0 None Flow has never been recorded. Site is a dug-out None Not applicable. Not applicable. area in a hillside. Site was noted to have either a Rocky Pass 49 27-46-16-11 trickle of flow, or 0 None as wet area, or ponded area in most years (1996- 2017).

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-73

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Site is a disturbed None Not applicable. Not applicable. area immediately downstream of a Rocky Pass 52 27-46-28-11 culvert that is 0 None fenced off to prevent livestock use. Mitigation previously Not applicable. Not applicable. Spring source implemented (well Rocky Pass 50 27-46-28-221 0 None piped to a trough. drilled to supply water). Spring site altered Reduction of flow 0.5 Mitigation plan by prior below established would be highly construction threshold coincident effective at activities. Spring with a reduction in maintaining a developed as a groundwater levels in water supply for spring box the area as Pipe from new or livestock and Cortez Hills 100 27-47-35-32 0.066 upstream from determined from existing well. wildlife. original site. groundwater Variable flow or monitoring. saturated soil recorded (1996- 2017).

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-74

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Site located on a Reduction of 0.5 Mitigation plan steep, terraced hydrophytic would be highly slope adjacent to vegetation below effective at the county road. established threshold maintaining the Fall monitoring coincident with a hydrophytic Pipe from new or Cortez Hills 101 27-47-35-324 (2011-2017) 0.137 reduction in vegetation. existing well. indicates groundwater levels in consistent wet the area as conditions with determined from variable flow (0.0 - groundwater 5.26 gpm). monitoring. Large seep area Reduction of flow 0.5 Mitigation plan located within the below established would be highly main channel of threshold coincident effective at Fourmile Canyon. with a reduction in maintaining a Fall monitoring groundwater levels in water supply for Pipe from new or Fourmile Canyon 54 27-48-14-313 (2013-2017) 0.769* the area as livestock and existing well. indicates determined from wildlife. consistent wet groundwater conditions with monitoring. variable flow (0.0 - 0.5 gpm).

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-75

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Site located on hydrophytic would be highly hillslope and vegetation below effective at supports small established threshold maintaining the wetland. Fall coincident with a hydrophytic monitoring (2013- Pipe from new or Mill Canyon 59 27-48-21-421 0.118 reduction in vegetation. 2017) indicates existing well. groundwater levels in consistent wet the area as conditions with determined from variable flow (0.0 - groundwater 0.45 gpm). monitoring. Site located within Reduction of 0.5 Mitigation plan the main channel hydrophytic would be highly of Fourmile vegetation below effective at Canyon that feeds established threshold maintaining the a small wetland coincident with a hydrophytic area. Fall reduction in Pipe from new or vegetation. Fourmile Canyon 55 27-48-22-222A 1.039 monitoring (2013- groundwater levels in existing well. 2017) indicates the area as consistent wet determined from conditions with groundwater variable flow (0.0 - monitoring. 0.5 gpm).

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-76

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Site located within Reduction of 0.5 Mitigation plan and upper hydrophytic would be highly tributary to vegetation below effective at Fourmile Canyon established threshold maintaining the that feeds a small coincident with a hydrophytic wetland area. Fall reduction in Pipe from new or vegetation. Fourmile Canyon 57 27-48-23-234 0.259 monitoring (2013- groundwater levels in existing well. 2017) indicates the area as consistent wet determined from conditions with groundwater variable flow (0.0 - monitoring. 0.5 gpm). Seep located in Reduction of flow 0.5 Mitigation plan channel at the below established would be highly uppermost threshold coincident effective at reaches of a with a reduction in maintaining a tributary to groundwater levels in water supply for Fourmile Canyon. the area as livestock and Pipe from new or Fourmile Canyon 56 27-48-23-244 Fall monitoring 0.647 determined from wildlife. existing well. (2013-2017) groundwater indicates monitoring. consistent wet conditions with variable flow (0.0 - 3.0 gpm).

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-77

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Seep located at Reduction of 0.5 Mitigation plan the top of a long hydrophytic would be highly wet channel with a vegetation below effective at large wet established threshold maintaining the perimeter. Fall coincident with a hydrophytic Pipe from new or Dry Creek 66 27-48-24-421 monitoring (2013- 0.585 reduction in vegetation. existing well. 2017) indicates groundwater levels in consistent wet the area as conditions with determined from variable flow (0.0 - groundwater 0.5 gpm). monitoring. Reduction of 0.5 Mitigation plan Seep located hydrophytic would be highly within a tributary vegetation below effective at to Willow Creek. established threshold maintaining the Fall monitoring coincident with a hydrophytic (2013-2017) Pipe from new or Willow Creek 110 27-48-25-143 0.282 reduction in vegetation. indicates existing well. groundwater levels in consistent wet the area as conditions with determined from variable flow (0.0 - groundwater 0.45 gpm). monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-78

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Seep located at Reduction of flow 0.5 Mitigation plan the head of a long below established would be highly wetland area threshold coincident effective at adjacent to a with a reduction in maintaining a small reclaimed groundwater levels in water supply for mining area. Fall the area as Pipe from new or livestock and Willow Creek 109 27-48-25-244 1.738 monitoring (2013- determined from existing well. wildlife. 2017) indicates groundwater consistent wet monitoring. conditions with variable flow (0.0 - 5 gpm). Hillside seep that Reduction of 0.5 Mitigation plan supports a hydrophytic would be highly wetland complex. vegetation below effective at Fall monitoring established threshold maintaining the (2013-2017) coincident with a hydrophytic Pipe from new or Willow Creek 114 27-48-25-313 indicates 0.137 reduction in vegetation. existing well. consistent wet or groundwater levels in saturated soil the area as conditions with determined from variable flow (0.0 - groundwater 0.45 gpm). monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-79

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Small seep within hydrophytic would be highly a larger area of vegetation below effective at wetland established threshold maintaining the vegetation. Fall coincident with a hydrophytic Pipe from new or Willow Creek 113 27-48-25-324 monitoring (2013- 1.322 reduction in vegetation. existing well. 2017) has not groundwater levels in recorded the area as measurable flow determined from at this site. groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly Hillside seep that vegetation below effective at supports saturated established threshold maintaining the soil. Fall coincident with a hydrophytic Pipe from new or Willow Creek 112 27-48-25-324A monitoring (2013- 0 reduction in vegetation. existing well. 2017) indicates groundwater levels in flow not recorded the area as at this site. determined from groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-80

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Hillside seep that Reduction of 0.5 Mitigation plan supports a hydrophytic would be highly wetland complex. vegetation below effective at Fall monitoring established threshold maintaining the (2013-2017) coincident with a hydrophytic Pipe from new or Willow Creek 116 27-48-25-334 indicates 0.334 reduction in vegetation. existing well. consistent wet or groundwater levels in saturated soil the area as conditions with determined from variable flow (0.0 - groundwater 0.45 gpm). monitoring. Reduction of 0.5 Mitigation plan Hillside seep that hydrophytic would be highly supports a vegetation below effective at wetland area. Fall established threshold maintaining the monitoring (2013- coincident with a hydrophytic 2017) indicates Pipe from new or Willow Creek 111 27-48-25-411 0.197 reduction in vegetation. consistent wet or existing well. groundwater levels in saturated soil the area as conditions with determined from variable flow (0.0 - groundwater 0.5 gpm). monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-81

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Seep located side Reduction of 0.5 Mitigation plan slope within a hydrophytic would be highly tributary to Mill vegetation below effective at Canyon. Fall established threshold maintaining the monitoring (2013- coincident with a hydrophytic 2017) indicates reduction in vegetation. Pipe from new or Mill Canyon 62 27-48-27-134 variable conditions 0.23 groundwater levels in existing well. ranging from dry the area as (2016, 2017), to determined from no flow but groundwater saturated (2013, monitoring. 2015), to flowing (0.45 in 2014). Site located Reduction of 0.5 Mitigation plan downstream from hydrophytic would be highly 27-48-27-134. Fall vegetation below effective at monitoring (2013- established threshold maintaining the 2017) indicates coincident with a hydrophytic Pipe from new or Mill Canyon 61 27-48-27-134A generally wet 0.329 reduction in vegetation. existing well. conditions (except groundwater levels in for 2015 when it the area as was dry) with flow determined from ranging from 0.0 groundwater to 0.5 gpm. monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-82

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Side hill seep vegetation below effective at impounded by Mill established threshold maintaining the Canyon road that coincident with a hydrophytic supports a wet Pipe from new or Mill Canyon 60 27-48-28-211 5.245 reduction in vegetation. area. Fall existing well. groundwater levels in monitoring (2013- the area as 2017) had not determined from recorded flow. groundwater monitoring. Cherry Tree Reduction of flow 0.2 Mitigation plan Spring (noted on below established would be highly USGS topo map). threshold coincident effective at Fall monitoring with a reduction in maintaining a (2013-2017) groundwater levels in water supply for Pipe from new or Mill Canyon 64 27-48-28-441 indicates 0.009 the area as livestock and existing well. consistent wet or determined from wildlife. saturated soil groundwater conditions with monitoring. variable flow (0.0 - 1.5 gpm).

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-83

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Site located Reduction of 0.5 Mitigation plan downstream from hydrophytic would be highly 27-48-28-441 and vegetation below effective at is supported by established threshold maintaining the the same spring coincident with a hydrophytic Pipe from new or Mill Canyon 63 27-48-28-441A source. Fall 0.005 reduction in vegetation. existing well. monitoring (2013- groundwater levels in 2017) reports site the area as has no water with determined from no field groundwater measurements. monitoring. Spring located in a Reduction of flow 1.0 Mitigation plan drainage area in below established would be highly the upper reaches threshold coincident effective at of Willow Creek. with a reduction in maintaining a Fall monitoring groundwater levels in water supply for Pipe from new or Willow Creek 125 27-48-34-322A data (2008-2017) 0.032 the area as livestock and existing well. indicates site determined from wildlife. typically has groundwater measurable flow monitoring. (<2gpm) in most years.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-84

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Site located Reduction of 0.5 Mitigation plan downstream from hydrophytic would be highly 27-48-24-322A vegetation below effective at and is a fringe established threshold maintaining the wetland adjacent coincident with a hydrophytic Pipe from new or Willow Creek 123 27-48-34-322B to Willow Creek. 0.018 reduction in vegetation. existing well. Fall monitoring groundwater levels in (2008-2017) the area as indicates generally determined from wet or saturated groundwater soil conditions. monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep adjacent to vegetation below effective at drainage. Fall established threshold maintaining the monitoring (2008- coincident with a hydrophytic 2017) indicates Pipe from new or Willow Creek 124 27-48-34-412 0.011 reduction in vegetation. variable conditions existing well. groundwater levels in ranging from dry the area as to wet without determined from measurable flow. groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-85

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Seep located in Reduction of 0.5 Mitigation plan drainage channel. hydrophytic would be highly Fall monitoring vegetation below effective at data(2008-2014) established threshold maintaining the indicate the site coincident with a hydrophytic observations reduction in Pipe from new or vegetation. Willow Creek 122 27-48-34-421 0.002 ranged from damp groundwater levels in existing well. or "insufficient the area as water for determined from sampling" to low groundwater flow (0.10 gpm monitoring. recorded in 2011). Site located on a Reduction of Not applicable. Mitigation plan hillside just above hydrophytic would be highly a reclaimed road vegetation below effective at in the uppermost established threshold maintaining site reaches of coincident with a use by wildlife. Fourmile Canyon. reduction in Fall monitoring groundwater levels in Fourmile Canyon 58 27-48-35-112 (2013-2017) 0 the area as Install guzzler. indicates site is determined from typically wet or groundwater saturated soil monitoring. conditions with variable flow (0.0 - 0.5 gpm) were observed.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-86

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located in vegetation below effective at the main channel established threshold maintaining the of Willow Creek. coincident with a hydrophytic Fall monitoring Pipe from new or Willow Creek 119 27-48-35-234 0.162 reduction in vegetation. (2013-2017) existing well. groundwater levels in indicates site was the area as dry in 4 of the 7 determined from years. groundwater monitoring. Perennial spring Reduction of flow 1.3 Mitigation plan located adjacent below established would be highly to the upper threshold coincident effective at reaches of the with a reduction in maintaining a Willow Creek groundwater levels in water supply for drainage. Fall the area as livestock and monitoring (2013- determined from Pipe from new or wildlife. Willow Creek 121 27-48-35-311 0.036 2017) indicates groundwater existing well. site is typically wet monitoring. or saturated soil conditions with variable flow (0.0 - 0.5 gpm) were observed.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-87

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Seep area Reduction of 0.5 Mitigation plan adjacent to hydrophytic would be highly drainage. vegetation below effective at Monitoring data established threshold maintaining the (2008-2011) coincident with a hydrophytic indicates site is reduction in Pipe from new or vegetation. Willow Creek 230 27-48-35-423 0.239 strongly groundwater levels in existing well. influenced by the area as seasonal flow and determined from reported as dry groundwater during the fall monitoring. sampling events. Seep located on Reduction of 0.5 Mitigation plan steep side hill hydrophytic would be highly above the main vegetation below effective at channel of Willow established threshold maintaining the Creek. Monitoring coincident with a hydrophytic Pipe from new or Willow Creek 128 27-48-35-441 (2008-2014) 0.071 reduction in vegetation. existing well. indicates site is groundwater levels in typically dry in the area as most years during determined from the fall sampling groundwater events. monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-88

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Seep located on hydrophytic would be highly side hill above the vegetation below effective at main channel of established threshold maintaining the Willow Creek. Fall coincident with a hydrophytic monitoring (2011- Pipe from new or Willow Creek 126 27-48-35-441B 0.008 reduction in vegetation. 2017) indicates existing well. groundwater levels in site is typically wet the area as or has standing determined from water without groundwater measurable flow. monitoring. Reduction of 0.5 Mitigation plan Seep is a dry silty hydrophytic would be highly basin located vegetation below effective at above the main established threshold maintaining the channel of Willow coincident with a hydrophytic Pipe from new or Willow Creek 129 27-48-35-442B Creek. Fall 0.028 reduction in vegetation. existing well. monitoring (2011- groundwater levels in 2017) indicates the area as the site was dry determined from except for 2017. groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-89

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan Seep located hydrophytic would be highly within an vegetation below effective at ephemeral established threshold maintaining the channel. Fall coincident with a hydrophytic monitoring (2013- Pipe from new or Willow Creek 120 27-48-36-321A 0.026 reduction in vegetation. 2017) indicates existing well. groundwater levels in the site is typically the area as wet but no flow determined from has ever been groundwater recorded. monitoring. Reduction of Not applicable Mitigation plan Seep that feeds a hydrophytic would be highly small, hillside vegetation below effective at wetland. Fall established threshold maintaining the monitoring data coincident with a hydrophytic Dry Creek 67 27-49-29-413 (2013-2017) 0.87 reduction in Install guzzler. vegetation. indicates that flow groundwater levels in has not been the area as recorded at this determined from site. groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-90

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Spring site located Reduction of 0.5 Mitigation plan at the top of a hydrophytic would be highly large wet area. vegetation below effective at Fall monitoring established threshold maintaining the data (2013-2017) coincident with a hydrophytic Pipe from new or Dry Creek 65 27-49-30-132 indicates that the 0.661 reduction in vegetation. existing well. site is wet groundwater levels in although the area as measurable flow determined from was only reported groundwater in 2016. monitoring. Perennial spring Reduction of flow 2.8 Mitigation plan discharges from a below established would be highly spring pipe threshold coincident effective at downslope from with a reduction in maintaining a the old Buckhorn groundwater levels in water supply for Mine. Water the area as livestock and flowing from pipe determined from Pipe from new or wildlife. Dry Creek 70 27-49-31-244 2.215 supports a large groundwater existing well. wetland complex. monitoring. Fall monitoring data (2013-2017) recorded flows ranging from 0.75 - 7.17 gpm.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-91

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located on a vegetation below effective at hillside. Fall established threshold maintaining the monitoring data coincident with a localized Pipe from new or Willow Creek 115 27-49-31-344 (2013-2017) 0 reduction in hydrophytic existing well. indicates flow has groundwater levels in vegetation. never been the area as recorded. determined from groundwater monitoring. Reduction of 0.5 Mitigation plan Seep located on a hydrophytic would be highly hillside that vegetation below effective at supports established threshold maintaining the vegetation. Fall coincident with a hydrophytic Pipe from new or Dry Creek 68 27-49-32-111 monitoring (2013- 0.02 reduction in vegetation. existing well. 2017) recorded groundwater levels in saturated soil with the area as no flow in most determined from years. groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-92

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located on a vegetation below effective at hillside above a established threshold maintaining the shallow channel. coincident with a localized Fall monitoring Pipe from new or Dry Creek 69 27-49-32-121 0 reduction in hydrophytic data (2013-2017) existing well. groundwater levels in vegetation. indicates flow has the area as never been determined from recorded. groundwater monitoring. Perennial spring Reduction of 0.5 Mitigation plan source that hydrophytic would be highly emerges below a vegetation below effective at rock outcrop and established threshold maintaining a collects in a small coincident with a water supply for stock pond. Fall reduction in livestock and monitoring (1996- groundwater levels in wildlife. Pipe from new or Shoshone 12 28-46-21-11 2017) indicates 0.032 the area as existing well. the site conditions determined from typically vary from groundwater ponded area monitoring. without measurable flow to small recorded flows (<0.2 gpm).

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-93

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Perennial spring Reduction of flow 1.7 Mitigation plan that supports a below established would be highly large wetland area threshold coincident effective at at the toe of a with a reduction in maintaining a slope just west of groundwater levels in water supply for the entrance to the area as Pipe from new or livestock and SE Crescent Valley 48 HDR-27-48-19-24 0.379 Mill Canyon. Fall determined from existing well. wildlife. monitoring (2014- groundwater 2017) indicates monitoring. consistent flows ranging from 0.45 - 3.81 gpm. Reduction of 0.5 Mitigation plan Spring located on hydrophytic would be highly a hillside near the vegetation below effective at headwaters of established threshold maintaining the Cooks Creek. Fall coincident with a hydrophytic Pipe from new or Carico Lake North 19 WCCC-01 monitoring in 0.072 reduction in vegetation. existing well. 2016-2017 groundwater levels in indicates flows the area as ranging from determined from 0.125 - 4.76 gpm. groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-94

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located in a vegetation below effective at wide valley bottom established threshold maintaining the close to historic coincident with a hydrophytic Pipe from new or Carico Lake North 22 WCCC-03 mining. Flows 0.33 reduction in vegetation. existing well. recorded in 2016- groundwater levels in 2017 ranged from the area as 0.0 - 2.43 gpm. determined from groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly Bank seep vegetation below effective at adjacent to a dry established threshold maintaining the drainage bottom coincident with a hydrophytic north of Greystone Pipe from new or Carico Lake North 21 WCCC-05 0.008 reduction in vegetation. Mine. Flows existing well. groundwater levels in recorded in 2016- the area as 2017 ranged from determined from 0.0 - 3.24 gpm. groundwater monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-95

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep emerges in vegetation below effective at a drainage bottom established threshold maintaining the north of the coincident with a hydrophytic Greystone Mine. Pipe from new or Carico Lake North 20 WCCC-06 0.02 reduction in vegetation. Flows recorded in existing well. groundwater levels in 2016-2017 ranged the area as from 0.76 - 3.23 determined from gpm. groundwater monitoring. Reduction of 0.5 Mitigation plan Seep emerges hydrophytic would be highly from a hillside vegetation below effective at near the established threshold maintaining the headwaters of coincident with a hydrophytic Pipe from new or Carico Lake North 18 WCCC-07 Cooks Creek. 0.137 reduction in vegetation. existing well. Flows recorded in groundwater levels in 2016-2017 ranged the area as from 0.29 - 0.68 determined from gpm. groundwater monitoring.

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Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located at vegetation below effective at the headwaters of established threshold maintaining the Cooks Creek. coincident with a hydrophytic Pipe from new or Carico Lake North 17 WCCC-09 Flows recorded in 0.047 reduction in vegetation. existing well. 2016-2017 ranged groundwater levels in from 1.57 - 3.88 the area as gpm. determined from groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located at vegetation below effective at the headwaters of established threshold maintaining the Cooks Creek. coincident with a hydrophytic Pipe from new or Carico Lake North 15 WCCC-10 Flows recorded in 0.029 reduction in vegetation. existing well. 2016-2017 ranged groundwater levels in from 1.28 - 10.32 the area as gpm. determined from groundwater monitoring.

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Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located on a vegetation below effective at gentle slope that established threshold maintaining the drains towards coincident with a hydrophytic Cooks Creek. Pipe from new or Carico Lake North 23 WCCC-11 0.147 reduction in vegetation. Flows recorded in existing well. groundwater levels in 2016-2017 ranged the area as from 1.04 - 1.71 determined from gpm. groundwater monitoring. Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located at vegetation below effective at the headwaters of established threshold maintaining the Cooks Creek. coincident with a hydrophytic Pipe from new or Carico Lake North 14 WCCC-12 Flows recorded in 0.094 reduction in vegetation. existing well. 2016-2017 ranged groundwater levels in from 0.0 - 0.63 the area as gpm. determined from groundwater monitoring.

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Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Seep located at vegetation below effective at the headwaters of established threshold maintaining the Cooks Creek. coincident with a hydrophytic Pipe from new or Carico Lake North 16 WCCC-13 Flows recorded in 0.108 reduction in vegetation. existing well. 2016-2017 ranged groundwater levels in from 0.0 - 2.83 the area as gpm. determined from groundwater monitoring. Stream Sites Reduction of 0.5 Mitigation plan Located near the hydrophytic would be highly midpoint of vegetation below effective at Fourmile Canyon established threshold maintaining the immediately coincident with a hydrophytic upstream of a Pipe from new or Fourmile Canyon S-08 FOU-01-HDR 0.335 reduction in vegetation. major tributary. existing well. groundwater levels in Flow monitoring the area as (2013-2017) determined from indicates the site groundwater flow is ephemeral. monitoring.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-99

Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of 0.5 Mitigation plan hydrophytic would be highly Located at the vegetation below effective at mouth of Fourmile established threshold maintaining the Canyon. Flow coincident with a hydrophytic Pipe from new or Fourmile Canyon S-09 FOU-01-JBR monitoring (2013- 0 reduction in vegetation. existing well. 2017) indicates groundwater levels in the site flow is the area as ephemeral. determined from groundwater monitoring. Reduction of flow 0.4 Mitigation plan Site located below established would be highly downstream of threshold coincident effective at FOU-01. Flow with a reduction in maintaining a Pipe from new or Fourmile Canyon S-10 FOU-02 recording (2013- 0.769* groundwater levels in water supply for existing well. 2017) indicates the area as livestock and flow was generally determined from wildlife. perennial. groundwater monitoring.

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Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Stream site Reduction of 0.5 Mitigation plan located in Horse hydrophytic would be highly Creek. Flow data vegetation below effective at (2008-2017) established threshold maintaining the indicates flow was coincident with a hydrophytic perennial between reduction in Pipe from new or vegetation. Horse Creek S-11 HOR-01 0 2008 and 2012; groundwater levels in existing well. and ephemeral to the area as intermittent determined from between May groundwater 2013 and monitoring. December 2017. Reduction of flow 4.4 Mitigation plan Stream site below established would be highly located in Horse threshold coincident effective at Creek. Flow data with a reduction in maintaining a Pipe from new or Horse Creek S-12 HOR-02D (2008-2017) 0 groundwater levels in water supply for existing well. indicate flow was the area as livestock and typically determined from wildlife. ephemeral. groundwater monitoring. Reduction of flow 1.3 Mitigation plan Stream site below established would be highly located in Horse threshold coincident effective at Creek. Flow data with a reduction in maintaining a Pipe from new or Horse Creek S-13 HOR-05T (2008-2017) 0.017 groundwater levels in water supply for existing well. indicate flow was the area as livestock and typically determined from wildlife. ephemeral. groundwater monitoring.

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Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Stream site Reduction of flow 18.2 Mitigation plan located in Horse below established would be highly Creek. Flow data threshold coincident effective at (2008-2017) with a reduction in maintaining a indicate flow was groundwater levels in water supply for variable and the area as livestock and typically exhibited determined from Pipe from new or wildlife. Horse Creek S-14 HOR-05U 0.014 perennial groundwater existing well. characteristics monitoring. except for periods when the stream was reported dry in portions of 2008 and 2015. Reduction of 0.5 Mitigation plan Stream site hydrophytic would be highly located 0.75 mile vegetation below effective at upgradient from established threshold maintaining the the mouth of Mill coincident with a hydrophytic Canyon. Flow Pipe from new or Mill Canyon S-19 MIL-02 0.713 reduction in vegetation. data (2014-2017) existing well. groundwater levels in exhibited the area as ephemeral to determined from intermittent flow groundwater characteristics. monitoring.

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Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Reduction of flow 24.2 Mitigation plan Stream site below established would be highly located near the threshold coincident effective at mouth of Mill with a reduction in maintaining a Canyon. Flow Pipe from new or Mill Canyon S-20 MIL-02A 1.805 groundwater levels in water supply for data (2013-2017) existing well. the area as livestock and exhibited determined from wildlife. perennial flow groundwater characteristics. monitoring. Reduction of flow 7.0 Mitigation plan Stream site below established would be highly located within Mill threshold coincident effective at Canyon. Flow with a reduction in maintaining a Pipe from new or Mill Canyon S-21 MIL-03 data (2013-2017) 2.76 groundwater levels in water supply for existing well. exhibited the area as livestock and perennial flow determined from wildlife. characteristics. groundwater monitoring.

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Table A-3 Mitigation Triggers and Contingency Mitigation Measures for Drawdown Impacts to Surface Water Resources Not Covered by 2011 Final SEIS Mitigation1

Estimated Riparian/ Proposed Flow Hydrophytic Augmentation Effectiveness of 4 Map ID Spring or Stream Vegetation Mitigation Trigger Contingency Rates Site-specific Spring Group2 Number2 Site ID Site Description (acres) Type Mitigation Plan3 (gpm) Mitigation Plan Stream site Reduction of flow 13.6 Mitigation plan located at the below established would be highly upper confluence threshold coincident effective at of Willow Creek with a reduction in maintaining a and its first main groundwater levels in water supply for tributary. Flow the area as livestock and Pipe from new or Willow Creek S-25 WIL-06D data (2011-2017) 0.839 determined from wildlife. existing well. exhibited groundwater predominantly monitoring. perennial flow characteristics in 2013, 2014, 2016, and 2017. 1 Based on the Contingency Mitigation Plan (BCI and Stantec 2018). The 2011 Final SEIS mitigation is presented in the Cortez Hills Expansion Project Final SEIS (BLM 2011). 2 Spring groups and map ID numbers are shown in Figure 3.2-3. 3 New disturbance associated with mitigation implementation would range from 0.05 to 2.60 acres (as identified in the Contingency Mitigation Plan [BCI and Stantec 2018]) depending on the type of mitigation implemented and site-specific conditions. 4 Flow rates rounded to the nearest 0.1 gpm. Flow rate estimates per Table 2 of the proposed Contingency Mitigation Plan (BCI and Stantec 2018).

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Table A-4a Predicted Crossroads Pit Lake Scenario 2 - Total Pit Lake Chemistry

Pit Lake Chemistry NDEP Background Runoff Profile III 1 Year of 2 Years of 5 Years of 10 Years 25 Years 50 Years 100 Years 200 Years Groundwater Chemist Parameter Units Standard Infilling Infilling Infilling of Infilling of Infilling of Infilling of Infilling of Infilling Chemistry ry pH su1 6.5-8.5 8.34 8.34 8.35 8.35 8.36 8.38 8.41 8.47 7.68 8.45 Total dissolved solids mg/L 7,000 475 477 480 485 501 525 577 698 594 367 Alkalinity (total) mg/L -- 198 199 200 202 208 217 237 281 231 168.8

Bicarbonate (HCO3) mg/L -- 238 239 240 242 250 260 285 337 272 202.5 Aluminum mg/L 4.47 0.01 0.01 0.01 0.02 0.03 0.04 0.06 0.13 0.01 0.2 Antimony mg/L 0.29 0.002 0.003 0.004 0.004 0.004 0.004 0.004 0.01 0.002 0.002 Arsenic mg/L 0.2 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.03 0.01 0.005 Barium mg/L 23.1 0.05 0.05 0.05 0.05 0.06 0.06 0.07 0.09 0.05 0.06 Beryllium mg/L 2.83 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.002 0.001 0.001 Boron mg/L 5 0.3 0.3 0.3 0.3 0.3 0.33 0.36 0.44 0.3 0.16 Cadmium mg/L 0.05 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.002 0.001 0.001 Calcium mg/L -- 66.6 66.9 67.5 69 72 77 86 113 66 49 Chloride mg/L -- 75.7 76.0 76.6 77.4 79.6 83.6 92.5 112 76 33 Chromium mg/L 1 0.005 0.005 0.005 0.005 0.005 0.006 0.006 0.009 0.005 0.005 Copper mg/L 0.5 0.005 0.005 0.005 0.005 0.006 0.006 0.007 0.009 0.005 0.007 Fluoride mg/L 2 2.2 2.2 2.2 2.3 2.4 2.5 2.7 3.3 2.2 0.5 Iron mg/L -- 3.0 3.0 3.0 3.0 3.1 3.2 3.6 4.3 2.97 0.14 Lead mg/L 0.1 0.001 0.001 0.001 0.001 0.002 0.003 0.004 0.007 0.001 0.001 Lithium mg/L 40.3 0.21 0.21 0.21 0.21 0.22 0.23 0.26 0.31 0.21 0.005 Magnesium mg/L -- 21 21 21 21 22 23 25 30 20.9 20 Manganese mg/L 377 0.54 0.54 0.54 0.55 0.57 0.59 0.65 0.79 0.54 0.009 Mercury mg/L 0.01 0.0005 0.001 0.0005 0.0005 0.001 0.0006 0.0006 0.0008 0.0005 0.002 Molybdenum mg/L 0.6 0.011 0.011 0.012 0.012 0.021 0.023 0.027 0.037 0.011 0.005

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Table A-4a Predicted Crossroads Pit Lake Scenario 2 - Total Pit Lake Chemistry

Pit Lake Chemistry NDEP Background Runoff Profile III 1 Year of 2 Years of 5 Years of 10 Years 25 Years 50 Years 100 Years 200 Years Groundwater Chemist Parameter Units Standard Infilling Infilling Infilling of Infilling of Infilling of Infilling of Infilling of Infilling Chemistry ry Nickel mg/L 171 0.005 0.005 0.005 0.005 0.006 0.006 0.006 0.011 0.005 0.005

NO2/NO3-N mg/L 100 2.7 2.7 2.8 2.8 2.9 3.0 3.3 4.1 2.7 0.05 Phosphorous mg/L -- 0.05 0.05 0.05 0.05 0.05 0.06 0.06 0.08 0.05 0.05 Potassium mg/L -- 16.1 16.1 16.2 16.4 16.9 17.6 19.3 23.3 16 3.2 Selenium mg/L 0.05 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.008 0.003 0.003 Silver mg/L -- 0.005 0.005 0.005 0.005 0.005 0.006 0.006 0.008 0.005 0.005 Sodium mg/L 2,000 79 79 80 81 84 87 96 115 79 41.3 Strontium mg/L 1,127 0.6 0.64 0.64 0.65 0.67 0.7 0.77 0.93 0.64 0.005 Sulfate mg/L -- 87 88 88 89 92 96 106 125 87 79 Thallium mg/L 0.03 0.0005 0.0005 0.0005 0.0006 0.0007 0.001 0.001 0.002 0.0005 0.002 Tin mg/L 29 0.01 0.01 0.02 0.03 0.03 0.04 0.05 0.09 0.005 0.005 Uranium mg/L 6.995 0.003 0.003 0.003 0.003 0.003 0.004 0.004 0.005 0.003 0.001 Vanadium mg/L 0.1 0.006 0.006 0.006 0.006 0.007 0.007 0.008 0.01 0.006 0.005 Zinc mg/L 25 0.006 0.006 0.006 0.006 0.006 0.008 0.012 0.07 0.006 0.005

1 su = standard units. Note: Bold indicates values above the NDEP Profile III water quality standard. Source: Geomega 2016b.

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Table A-4b Predicted Crossroads Pit Lake Scenario 2 - Dissolved Pit Lake Chemistry

Pit Lake Chemistry NDEP NDEP Background Profile II Profile III 1 Year of 2 Years of 5 Years of 10 Years of 25 Years of 50 Years of 100 Years of 200 Years Groundwater Runoff Parameter Units Standard Standard Infilling Infilling Infilling Infilling Infilling Infilling Infilling of Infilling Chemistry Chemistry pH su 6.5-8.5 6.5-8.5 8.19 8.19 8.19 8.19 8.19 8.19 8.19 8.17 7.68 8.45 Total dissolved solids mg/L 1,000 7,000 464 465 467 470 479 493 527 597 594 367 Alkalinity (total) mg/L -- -- 137 137 137 137 137 136 137 133 231 168.8

Bicarbonate (HCO3) mg/L -- -- 165 165 165 165 164 163 164 160 272 202.5 Aluminum mg/L 0.2 4.47 0.01 0.01 0.01 0.02 0.02 0.02 0.02 0.02 0.01 0.2 Antimony mg/L 0.006 0.29 0.002 0.003 0.004 0.004 0.004 0.004 0.004 0.01 0.0022 0.002 Arsenic mg/L 0.01 0.2 0.00003 0.00003 0.00003 0.00003 0.00003 0.00005 0.00004 0.00006 0.01 0.005 Barium mg/L 2 23.1 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.03 0.05 0.06 Beryllium mg/L 0.004 2.83 0.000002 0.000002 0.000002 0.000002 0.000002 0.000003 0.000003 0.000009 0.001 0.001 Boron mg/L -- 5 0.30 0.30 0.303 0.31 0.31 0.33 0.36 0.44 0.30 0.16 Cadmium mg/L 0.005 0.05 0.0005 0.0005 0.0005 0.0005 0.0006 0.0007 0.0008 0.0015 0.0010 0.001 Calcium mg/L -- -- 41.1 41.2 41.2 41 42 43 44 48 66 49 Chloride mg/L 400 -- 75.7 76.0 76.6 77.4 79.6 83.6 92.5 112 76 33 Chromium mg/L 0.1 1 0.005 0.005 0.005 0.005 0.005 0.005 0.006 0.008 0.005 0.005 Copper mg/L 1.0 0.5 0.0004 0.0004 0.0004 0.0004 0.0005 0.0005 0.0005 0.0010 0.005 0.007 Fluoride mg/L 4 2 2.21 2.22 2.24 2.26 2.4 2.5 2.7 3.3 2.22 0.5 Iron mg/L 0.6 -- 0.00004 0.00004 0.00004 0.00004 0.00004 0.00004 0.00004 0.00004 2.97 0.14 Lead mg/L 0.02 0.1 0.000002 0.000002 0.000003 0.000003 0.000007 0.00002 0.00003 0.0003 0.001 0.001 Lithium mg/L -- 40.3 0.21 0.21 0.21 0.21 0.22 0.23 0.26 0.31 0.21 0.005 Magnesium mg/L 150 -- 21 21 21 21 22 23 25 30 20.9 20 Manganese mg/L 0.1 377 0.0000003 0.0000003 0.0000003 0.0000003 0.0000003 0.0000003 0.0000003 0.0000003 0.54 0.009 Mercury mg/L 0.002 0.01 0.0005 0.000 0.0005 0.0005 0.001 0.0006 0.0006 0.0008 0.0005 0.002 Molybdenum mg/L -- 0.6 0.011 0.011 0.012 0.012 0.021 0.023 0.027 0.037 0.011 0.005

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Table A-4b Predicted Crossroads Pit Lake Scenario 2 - Dissolved Pit Lake Chemistry

Pit Lake Chemistry NDEP NDEP Background Profile II Profile III 1 Year of 2 Years of 5 Years of 10 Years of 25 Years of 50 Years of 100 Years of 200 Years Groundwater Runoff Parameter Units Standard Standard Infilling Infilling Infilling Infilling Infilling Infilling Infilling of Infilling Chemistry Chemistry Nickel mg/L 0.1 171 0.003 0.003 0.003 0.003 0.003 0.003 0.004 0.008 0.005 0.005

NO2/NO3-N mg/L 10 100 2.7 2.7 2.8 2.8 2.9 3.0 3.3 4.1 2.7 0.05 Phosphorous mg/L -- -- 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.03 0.05 0.05 Potassium mg/L -- -- 16.1 16.1 16.2 16.4 16.9 17.6 19.3 23.3 16 3.2 Selenium mg/L 0.05 0.05 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.008 0.003 0.003 Silver mg/L 0.1 -- 0.005 0.005 0.005 0.005 0.005 0.006 0.006 0.008 0.005 0.005 Sodium mg/L -- 2,000 79 79 80 81 84 87 96 115 79 41.3 Strontium mg/L -- 1,127 0.6 0.64 0.64 0.65 0.67 0.7 0.77 0.93 0.64 0.005 Sulfate mg/L 500 -- 87 87 88 89 92 96 106 125 87 79 Thallium mg/L 0.002 0.03 0.0005 0.0005 0.0005 0.0006 0.0007 0.001 0.001 0.002 0.0005 0.002 Tin mg/L -- 29 0.005 0.01 0.02 0.03 0.03 0.04 0.05 0.09 0.005 0.005 Uranium mg/L NA 6.995 0.003 0.003 0.003 0.003 0.003 0.004 0.004 0.005 0.003 0.001 Vanadium mg/L -- 0.1 0.00003 0.00003 0.00003 0.00003 0.00003 0.00003 0.00003 0.00004 0.006 0.005 Zinc mg/L 5 25 0.001 0.001 0.001 0.001 0.002 0.004 0.006 0.05 0.006 0.005

Bold indicates values above the NDEP Profile III water quality standard. Shading indicates values above the NDEP Profile II water quality standard. Source: Geomega 2016b.

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Table A-4c Predicted Pipeline Pit Lake Scenario 2 - Total Pit Lake Chemistry

Pit Lake Chemistry NDEP Background Runoff Profile III 1 Year of 2 Years of 5 Years of 10 Years 25 Years 50 Years 100 Years 200 Years Groundwater Chemist Parameter Units Standard Infilling Infilling Infilling of Infilling of Infilling of Infilling of Infilling of Infilling Chemistry ry pH su 6.5-8.5 8.35 8.35 8.35 8.39 8.41 8.43 8.49 8.60 7.68 8.45 Total dissolved solids mg/L 7,000 529 522 552 616 661 711 841 1141 594 367 Alkalinity (total) mg/L -- 202 199 203 224 234 249 292 391 231 168.8

Bicarbonate (HCO3) mg/L -- 242 239 243 269 281 298 350 469 272 202.5 Aluminum mg/L 4.47 0.19 0.14 0.09 0.12 0.12 0.12 0.13 0.26 0.01 0.2 Antimony mg/L 0.29 0.004 0.004 0.005 0.006 0.011 0.015 0.021 0.03 0.002 0.002 Arsenic mg/L 0.2 0.03 0.03 0.03 0.03 0.04 0.05 0.04 0.05 0.01 0.005 Barium mg/L 23.1 0.07 0.06 0.06 0.07 0.08 0.09 0.10 0.14 0.05 0.06 Beryllium mg/L 2.83 0.002 0.002 0.001 0.002 0.003 0.004 0.004 0.005 0.001 0.001 Boron mg/L 5 0.26 0.25 0.28 0.30 0.33 0.36 0.43 0.60 0.30 0.16 Cadmium mg/L 0.05 0.001 0.001 0.001 0.002 0.003 0.004 0.004 0.005 0.001 0.001 Calcium mg/L -- 64.6 64.2 67.8 76 87 96 114 156 66 49 Chloride mg/L -- 59.6 58.9 68.3 75.2 82.5 90.4 108.5 149 76 33 Chromium mg/L 1 0.007 0.007 0.006 0.007 0.009 0.010 0.012 0.015 0.005 0.005 Copper mg/L 0.5 0.011 0.01 0.009 0.017 0.015 0.016 0.016 0.019 0.005 0.007 Fluoride mg/L 2 1.7 1.6 2 2.54 2.8 3.0 3.4 4.5 2.22 0.5 Iron mg/L -- 1.8 1.8 2.4 2.8 3.1 3.4 4.0 5.4 2.97 0.14 Lead mg/L 0.1 0.002 0.002 0.002 0.005 0.009 0.012 0.013 0.016 0.001 0.001 Lithium mg/L 40.3 0.12 0.12 0.17 0.21 0.25 0.28 0.34 0.44 0.21 0.005 Magnesium mg/L -- 22 22 22 23 25 27 32 44 20.9 20 Manganese mg/L 377 0.35 0.33 0.44 0.52 0.61 0.70 0.81 1.07 0.54 0.009 Mercury mg/L 0.01 0.0012 0.001 0.0009 0.0009 0.001 0.0009 0.0011 0.0015 0.0005 0.002 Molybdenum mg/L 0.6 0.025 0.023 0.023 0.075 0.074 0.063 0.060 0.278 0.011 0.005

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Table A-4c Predicted Pipeline Pit Lake Scenario 2 - Total Pit Lake Chemistry

Pit Lake Chemistry NDEP Background Runoff Profile III 1 Year of 2 Years of 5 Years of 10 Years 25 Years 50 Years 100 Years 200 Years Groundwater Chemist Parameter Units Standard Infilling Infilling Infilling of Infilling of Infilling of Infilling of Infilling of Infilling Chemistry ry Nickel mg/L 171 0.008 0.008 0.007 0.008 0.011 0.014 0.018 0.023 0.005 0.005

NO2/NO3-N mg/L 100 1.6 1.6 2.2 2.6 3.0 3.4 4.2 5.7 2.7 0.05 Phosphorous mg/L -- 0.08 0.06 0.06 0.09 0.15 0.13 0.13 0.17 0.05 0.05 Potassium mg/L -- 12.0 11.5 14.2 16.4 18.1 19.6 23.0 31.0 16 3.2 Selenium mg/L 0.05 0.008 0.008 0.01 0.01 0.08 0.06 0.048 0.06 0.003 0.003 Silver mg/L -- 0.006 0.006 0.006 0.007 0.009 0.010 0.011 0.015 0.005 0.005 Sodium mg/L 2,000 69 68 75 89 94 101 119 161 79 41.3 Strontium mg/L 1,127 0.4 0.38 0.52 0.63 0.71 0.8 0.91 1.23 0.64 0.005 Sulfate mg/L -- 93 92 93 102 109 116 137 188 87 79 Thallium mg/L 0.03 0.0012 0.0012 0.0010 0.0012 0.0015 0.002 0.002 0.003 0.0005 0.002 Tin mg/L 29 0.02 0.02 0.02 0.07 0.11 0.19 0.26 0.38 0.005 0.005 Uranium mg/L 6.995 0.002 0.002 0.003 0.004 0.005 0.005 0.007 0.008 0.003 0.001 Vanadium mg/L 0.1 0.007 0.007 0.007 0.010 0.011 0.011 0.012 0.016 0.006 0.005 Zinc mg/L 25 0.11 0.06 0.06 0.09 0.15 0.22 0.20 0.20 0.006 0.005

Bold indicates values above the NDEP Profile III water quality standard. Source: Geomega 2016b.

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Table A-4d Predicted Crossroads/Pipeline Pit Lake Scenario 3 - Total Pit Lake Chemistry

Pit Lake Chemistry NDEP Background Runoff Profile III 1 Year of 2 Years of 5 Years of 10 Years 25 Years 50 Years 100 Years 200 Years Groundwater Chemist Parameter Units Standard Infilling Infilling Infilling of Infilling of Infilling of Infilling of Infilling of Infilling Chemistry ry pH su 6.5-8.5 8.34 8.34 8.35 8.35 8.36 8.38 8.42 8.50 7.68 8.45 Total dissolved solids mg/L 7,000 552 552 557 563 586 622 704 886 594 367 Alkalinity (total) mg/L -- 198 198 200 202 208 220 246 301 231 168.8

Bicarbonate (HCO3) mg/L -- 238 238 240 242 250 263 295 361 272 202.5 Aluminum mg/L 4.47 0.01 0.01 0.01 0.02 0.04 0.07 0.13 0.26 0.01 0.2 Antimony mg/L 0.29 0.003 0.003 0.004 0.004 0.006 0.007 0.01 0.017 0.002 0.002 Arsenic mg/L 0.2 0.01 0.01 0.01 0.01 0.02 0.02 0.02 0.03 0.01 0.005 Barium mg/L 23.1 0.05 0.05 0.05 0.05 0.06 0.07 0.08 0.11 0.05 0.06 Beryllium mg/L 2.83 0.001 0.001 0.001 0.001 0.001 0.002 0.002 0.003 0.001 0.001 Boron mg/L 5 0.3 0.3 0.3 0.3 0.3 0.3 0.4 0.5 0.3 0.16 Cadmium mg/L 0.05 0.001 0.001 0.001 0.001 0.001 0.001 0.002 0.003 0.001 0.001 Calcium mg/L -- 66.5 66.5 67.1 68 73 80 93 127 66 49 Chloride mg/L -- 75 75 76 77 79 84 95 119 76 33 Chromium mg/L 1 0.005 0.005 0.005 0.005 0.006 0.006 0.008 0.01 0.005 0.005 Copper mg/L 0.5 0.005 0.005 0.005 0.005 0.006 0.007 0.009 0.01 0.005 0.007 Fluoride mg/L 2 2.2 2.2 2.2 2.2 2.3 2.5 2.8 3.5 2.2 0.5 Iron mg/L -- 2.9 2.9 2.9 3.0 3.1 3.2 3.6 4.4 2.97 0.14 Lead mg/L 0.1 0.001 0.001 0.001 0.001 0.002 0.003 0.004 0.01 0.001 0.001 Lithium mg/L 40.3 0.21 0.21 0.21 0.21 0.22 0.24 0.27 0.34 0.21 0.005 Magnesium mg/L -- 21 21 21 21 22 24 27 34 20.9 20 Manganese mg/L 377 0.53 0.53 0.53 0.54 0.57 0.60 0.68 0.85 0.54 0.009 Mercury mg/L 0.01 0.0005 0.001 0.0005 0.0005 0.001 0.0006 0.0007 0.0009 0.0005 0.002 Molybdenum mg/L 0.6 0.01 0.01 0.01 0.01 0.05 0.1 0.18 0.29 0.011 0.005

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Table A-4d Predicted Crossroads/Pipeline Pit Lake Scenario 3 - Total Pit Lake Chemistry

Pit Lake Chemistry NDEP Background Runoff Profile III 1 Year of 2 Years of 5 Years of 10 Years 25 Years 50 Years 100 Years 200 Years Groundwater Chemist Parameter Units Standard Infilling Infilling Infilling of Infilling of Infilling of Infilling of Infilling of Infilling Chemistry ry Nickel mg/L 171 0.005 0.005 0.005 0.005 0.007 0.007 0.01 0.014 0.005 0.005

NO2/NO3-N mg/L 100 2.7 2.7 2.7 2.8 2.9 3.1 3.5 4.6 2.7 0.05 Phosphorous mg/L -- 0.05 0.05 0.05 0.05 0.06 0.06 0.07 0.09 0.05 0.05 Potassium mg/L -- 15.8 15.8 16.0 16.2 16.9 17.8 20 24.7 16 3.2 Selenium mg/L 0.05 0.003 0.003 0.003 0.003 0.006 0.007 0.009 0.015 0.003 0.003 Silver mg/L -- 0.005 0.005 0.005 0.005 0.006 0.006 0.007 0.01 0.005 0.005 Sodium mg/L 2,000 79 79 79 80 83 88 99 124 79 41.3 Strontium mg/L 1,127 0.6 0.6 0.6 0.6 0.7 0.7 0.8 0.97 0.64 0.005 Sulfate mg/L -- 87 87 88 89 93 98 112 141 87 79 Thallium mg/L 0.03 0.0005 0.0005 0.0006 0.0006 0.0007 0.001 0.001 0.002 0.0005 0.002 Tin mg/L 29 0.009 0.009 0.019 0.028 0.04 0.05 0.08 0.17 0.005 0.005 Uranium mg/L 6.995 0.003 0.003 0.003 0.003 0.003 0.004 0.004 0.006 0.003 0.001 Vanadium mg/L 0.1 0.006 0.006 0.006 0.006 0.007 0.008 0.009 0.011 0.006 0.005 Zinc mg/L 25 0.006 0.006 0.006 0.006 0.03 0.04 0.07 0.09 0.006 0.005

Bold indicates values above the NDEP Profile III water quality standard. Source: Geomega 2016b.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-112

Table A-4e Predicted Cortez Pit Lake Scenario 3 - Total Pit Lake Chemistry

Pit Lake Chemistry NDEP Background Runoff Profile III 1 Year of 2 Years of 5 Years of 10 Years 25 Years 50 Years 100 Years 200 Years Groundwater Chemist Parameter Units Standard Infilling Infilling Infilling of Infilling of Infilling of Infilling of Infilling of Infilling Chemistry ry pH su 6.5-8.5 8.35 8.34 8.32 8.31 8.34 8.43 8.46 8.43 8.30 8.45 Total dissolved solids mg/L 7,000 462 456 448 444 463 583 648 601 415 367 Alkalinity (total) mg/L -- 198 193 185 182 192 242 268 245 180 168.8

Bicarbonate (HCO3) mg/L -- 238 232 222 219 230 291 322 294 216 202.5 Aluminum mg/L 4.47 0.2 0.1 0.1 0.1 0.1 0.2 0.2 0.1 0.01 0.2 Antimony mg/L 0.29 0.002 0.002 0.003 0.003 0.003 0.003 0.003 0.003 0.0028 0.002 Arsenic mg/L 0.2 0.01 0.01 0.02 0.02 0.02 0.02 0.02 0.02 0.03 0.005 Barium mg/L 23.1 0.07 0.07 0.38 0.72 1.01 1.00 2.14 6.17 0.05 0.06 Beryllium mg/L 2.83 0.001 0.002 0.002 0.002 0.002 0.002 0.004 0.002 0.001 0.001 Boron mg/L 5 0.18 0.19 0.21 0.22 0.21 0.26 0.28 0.27 0.24 0.16 Cadmium mg/L 0.05 0.001 0.001 0.002 0.002 0.001 0.002 0.003 0.002 0.001 0.001 Calcium mg/L -- 56.5 55.1 54.0 52 55 71 81 71 49 49 Chloride mg/L -- 38.7 37.7 35.8 35.5 37.5 47.9 53.2 49 34 33 Chromium mg/L 1 0.006 0.006 0.007 0.006 0.006 0.008 0.010 0.008 0.005 0.005 Copper mg/L 0.5 0.008 0.007 0.006 0.006 0.007 0.009 0.011 0.009 0.005 0.007 Fluoride mg/L 2 0.56 0.69 0.93 0.97 0.9 1.0 1.1 1.1 1.15 0.5 Iron mg/L -- 0.2 0.1 0.1 0.1 0.1 0.2 0.2 0.1 0.01 0.14 Lead mg/L 0.1 0.001 0.001 0.001 0.001 0.001 0.002 0.002 0.002 0.001 0.001 Lithium mg/L 40.3 0.01 0.04 0.11 0.13 0.10 0.09 0.17 0.18 0.14 0.005 Magnesium mg/L -- 23 22 19 18 20 27 30 26 15.5 20 Manganese mg/L 377 0.01 0.009 0.007 0.007 0.008 0.01 0.01 0.01 0.005 0.009 Mercury mg/L 0.01 0.0019 0.002 0.0010 0.0009 0.001 0.002 0.002 0.002 0.0005 0.002 Molybdenum mg/L 0.6 0.006 0.006 0.006 0.006 0.006 0.008 0.009 0.008 0.005 0.005

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-113

Table A-4e Predicted Cortez Pit Lake Scenario 3 - Total Pit Lake Chemistry

Pit Lake Chemistry NDEP Background Runoff Profile III 1 Year of 2 Years of 5 Years of 10 Years 25 Years 50 Years 100 Years 200 Years Groundwater Chemist Parameter Units Standard Infilling Infilling Infilling of Infilling of Infilling of Infilling of Infilling of Infilling Chemistry ry Nickel mg/L 171 0.006 0.006 0.006 0.005 0.006 0.008 0.009 0.007 0.005 0.005

NO2/NO3-N mg/L 100 0.1 0.4 1.0 1.1 0.8 0.8 0.7 1.0 1.6 0.05 Phosphorous mg/L -- 0.06 0.06 0.05 0.05 0.06 0.07 0.08 0.07 0.05 0.05 Potassium mg/L -- 3.8 4.7 6.4 6.7 6.1 6.9 7.3 7.6 8 3.2 Selenium mg/L 0.05 0.003 0.003 0.008 0.01 0.01 0.01 0.04 0.07 0.003 0.003 Silver mg/L -- 0.006 0.006 0.006 0.005 0.006 0.01 0.01 0.01 0.005 0.005 Sodium mg/L 2,000 48 50 55 55 55 67 73 70 59 41.3 Strontium mg/L 1,127 0.0 0.14 0.38 0.42 0.33 0.29 0.27 0.38 0.62 0.005 Sulfate mg/L -- 92 92 90 90 94 118 130 121 89 79 Thallium mg/L 0.03 0.0019 0.0016 0.001 0.001 0.001 0.0019 0.002 0.0017 0.0005 0.002 Tin mg/L 29 0.01 0.01 0.07 0.12 0.16 0.15 0.38 0.88 0.005 0.005 Uranium mg/L 6.995 0.001 0.001 0.002 0.002 0.002 0.002 0.002 0.003 0.003 0.001 Vanadium mg/L 0.1 0.006 0.006 0.006 0.005 0.006 0.007 0.009 0.007 0.005 0.005 Zinc mg/L 25 0.006 0.007 0.006 0.006 0.006 0.008 0.01 0.008 0.005 0.005

Bold indicates values above the NDEP Profile III water quality standard. Source: Geomega 2016b.

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-114

Table A-4f Predicted Cortez Pit Lake Scenario 3 - Dissolved Pit Lake Chemistry

Pit Lake Chemistry NDEP NDEP Background Profile II Profile III 1 Year of 2 Years of 5 Years of 10 Years 25 Years 50 Years 100 Years 200 Years Groundwater Runoff Parameter Units Standard Standard Infilling Infilling Infilling of Infilling of Infilling of Infilling of Infilling of Infilling Chemistry Chemistry pH su 6.5-8.5 6.5-8.5 8.23 8.22 8.22 8.22 8.22 8.25 8.25 8.25 8.30 8.45 Total dissolved solids mg/L 1,000 7,000 389 389 388 388 395 456 486 463 415 367 Alkalinity (total) mg/L -- -- 147 146 143 144 146 155 158 156 180 169

Bicarbonate (HCO3) mg/L -- -- 176 175 172 173 175 186 189 187 216 202.5 Aluminum mg/L 0.2 4.47 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.2 Antimony mg/L 0.006 0.29 0.002 0.002 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.002 Arsenic mg/L 0.01 0.2 0.002 0.007 0.018 0.020 0.014 0.012 0.012 0.017 0.03 0.005 Barium mg/L 2 23.1 0.04 0.04 0.04 0.04 0.04 0.03 0.03 0.03 0.05 0.06 Beryllium mg/L 0.004 2.83 0.0001 0.0002 0.0006 0.0005 0.0001 0.0002 0.0007 0.0003 0.001 0.001 Boron mg/L -- 5 0.18 0.19 0.214 0.22 0.21 0.26 0.28 0.27 0.24 0.16 Cadmium mg/L 0.005 0.05 0.001 0.001 0.0018 0.0015 0.0014 0.0019 0.003 0.002 0.001 0.001 Calcium mg/L -- -- 34.8 35.1 36.4 36 35 33 33 33 49 49 Chloride mg/L 400 -- 38.7 37.7 35.8 35.5 37.5 47.9 53.2 49 34 33 Chromium mg/L 0.1 1 0.006 0.006 0.007 0.006 0.006 0.008 0.010 0.008 0.005 0.005 Copper mg/L 1.0 0.5 0.006 0.006 0.006 0.006 0.006 0.008 0.009 0.008 0.005 0.007 Fluoride mg/L 4 2 0.6 0.69 0.93 0.97 0.89 1.0 1.1 1.1 1.15 0.5 Iron mg/L 0.6 -- 0.00004 0.00004 0.00004 0.00004 0.00004 0.00004 0.00004 0.00004 0.01 0.14 Lead mg/L 0.02 0.1 0.0005 0.0007 0.001 0.001 0.0007 0.001 0.001 0.001 0.001 0.001 Lithium mg/L -- 40.3 0.01 0.04 0.11 0.13 0.10 0.09 0.17 0.18 0.14 0.005 Magnesium mg/L 150 -- 23 22 19 18 20 27 30 26 15.5 20 Manganese mg/L 0.1 377 0.0000003 0.0000003 0.0000003 0.0000003 0.0000003 0.0000003 0.0000003 0.0000003 0.005 0.009 Mercury mg/L 0.002 0.01 0.0019 0.0016 0.001 0.0009 0.0012 0.0018 0.0021 0.0017 0.0005 0.002 Molybdenum mg/L -- 0.6 0.006 0.006 0.006 0.006 0.006 0.008 0.009 0.008 0.005 0.005

2019 Deep South Expansion Project Appendix A Supplemental Environmental Report Water Resources A-115

Table A-4f Predicted Cortez Pit Lake Scenario 3 - Dissolved Pit Lake Chemistry

Pit Lake Chemistry NDEP NDEP Background Profile II Profile III 1 Year of 2 Years of 5 Years of 10 Years 25 Years 50 Years 100 Years 200 Years Groundwater Runoff Parameter Units Standard Standard Infilling Infilling Infilling of Infilling of Infilling of Infilling of Infilling of Infilling Chemistry Chemistry Nickel mg/L 0.1 171 0.006 0.006 0.006 0.005 0.006 0.008 0.009 0.007 0.005 0.005

NO2/NO3-N mg/L 10 100 0.1 0.4 1.0 1.1 0.8 0.8 0.7 1.0 1.6 0.05 Phosphorous mg/L -- -- 0.06 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.05 0.05 Potassium mg/L -- -- 3.8 4.7 6.4 6.7 6.1 6.9 7.3 7.6 8 3.2 Selenium mg/L 0.05 0.05 0.003 0.003 0.008 0.013 0.015 0.014 0.04 0.07 0.003 0.003 Silver mg/L 0.1 -- 0.006 0.006 0.006 0.005 0.006 0.007 0.009 0.007 0.005 0.005 Sodium mg/L -- 2,000 48 50 55 55 55 67 73 70 59 41.3 Strontium mg/L -- 1,127 0.0 0.14 0.38 0.42 0.33 0.29 0.27 0.38 0.62 0.005 Sulfate mg/L 500 -- 92 92 90 90 93 117 129 117 89 79 Thallium mg/L 0.002 0.03 0.0019 0.0016 0.001 0.001 0.001 0.0019 0.002 0.0017 0.0005 0.002 Tin mg/L -- 29 0.006 0.011 0.067 0.124 0.162 0.155 0.380 0.879 0.005 0.005 Uranium mg/L NA 6.995 0.001 0.001 0.002 0.002 0.002 0.002 0.002 0.003 0.003 0.001 Vanadium mg/L -- 0.1 0.003 0.004 0.005 0.005 0.005 0.006 0.006 0.006 0.005 0.005 Zinc mg/L 5 25 0.006 0.006 0.006 0.006 0.006 0.008 0.009 0.008 0.005 0.005

Bold indicates values above the NDEP Profile III water quality standard. Shading indicates values above the NDEP Profile II water quality standard. Source: Geomega 2016b.

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