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Our Environment

Water Management

Superfund legacy

Environmental contamination of surface water, groundwater, soil, and sediment occurred at the Site as a result of mining, milling, and smelting operations in the Silver Valley, including but not limited to, at the Bunker Hill Mining and Metallurgical Complex, of which the Bunker Hill Mine was a part.

The Bunker Hill Mining and Metallurgical Complex Superfund Site includes all areas of the Coeur d’Alene Basin where mining-related contamination occurred and encompasses a 21- square mile “Box” along Interstate 90 surrounding the former smelter complex. Operable Unit 1 (OU1) includes the populated areas and Operable Unit 2 (OU2) includes the non-populated areas within the “Box.” Operable Unit 3 (OU3) includes areas outside of the “Box” from near the Idaho-Montana border to the State of Washington where mining-related contamination is present. Bunker Hill Mine lies within OU2. Contaminants of concern in soil, sediments, surface water and groundwater are specific heavy metals which include arsenic, cadmium, lead, mercury and zinc. The 2001 OU2 Record of Decision (ROD) Amendment (also referred to as the Mine Water ROD Amendment) indicated that remediation would include acid mine drainage (AMD) source control, AMD collection, AMD storage, AMD treatment, sludge management and monitoring.

Figure 1: Superfund Timeline

The Bunker Hill Mining and Metallurgical Complex Superfund Site includes all areas of the Coeur d’Alene Basin where mining-related contamination occurred and encompasses a 21- square mile “Box” along Interstate 90 surrounding the former smelter complex. Operable Unit 1 (OU1) includes the populated areas and Operable Unit 2 (OU2) includes the non-populated areas within the “Box.” Operable Unit 3 (OU3) includes areas outside of the “Box” from near the Idaho-Montana border to the State of Washington where mining-related contamination is present. Bunker Hill Mine lies within OU2.

Contaminants of concern in soil, sediments, surface water and groundwater are specific heavy metals which include arsenic, cadmium, lead, mercury and zinc. The 2001 OU2 Record of Decision (ROD) Amendment (also referred to as the Mine Water ROD Amendment) indicated that remediation would include acid mine drainage (AMD) source control, AMD collection, AMD storage, AMD treatment, sludge management and monitoring.

Understanding the Water system of Bunker Hill Mine

Water infiltrates from the surface of Bunker Hill Mine on the east side of the mine in Wardner and on the west side of the mine in Deadwood Gulch.  Water entering the mine from Deadwood Gulch remains relatively clean in its journey from the upper levels of the mine until is flows out of the Kellogg Tunnel on the 9 Level.

Figure 1 shows the major events as water on the east side makes its way through the mine

Figure 1 shows the major events as water on the east side makes its way through the mine:

  1. Water enters through surface cracks and rock fissures in Wardner
  2. Water contacts sulfide ore bodies, mixes with oxygen and becomes highly acidic – Acid Mine Drainage (AMD)
  3. AMD pools under and around various structures in the upper levels of the mine (the greenhouse that reforested the Silver Valley is a good example)
  4. Pooled AMD sits for long periods and slowly degrades, dissolving greater and greater concentrations of metals and intensifying through evaporation
  5. Small volumes of intense AMD slowly move through chutes and raises making their way to the 9 Level
  6. The small volume of intense AMD enters the 9 Level and mixes with cleaner water on the East Drift where large volumes of sludge are created
  7. Sludge restricts flow of bad water on the 9 Level and further intensifies AMD in two drifts (Cherry Crosscut and Stanly Crosscut) – water in these drifts contains 90% of the metal leaving Bunker Hill Mine
  8. Bad water flows of approximately 20gpm combine with good water flows of approximately 1380 and flow out of the Kellogg Tunnel to the Central Treatment Plant (CTP)

Where we Started and Where We are Headed (water quality)

Where we started

When Bunker Hill started exploration in March of 2020, there had been very little rehabilitation and maintenance work performed in Bunker Hill Mine since 1991. However, Bunker Hill has taken action to change this for the better.

BEFORE March 2020: Ground Water Improvements
BEFORE March 2020: Ground Water Improvements

AFTER March 2020: Ground Water Improvement
AFTER March 2020: Ground Water Improvement

Activities in motion

In September 2020, Bunker Hill initiated a water management program that focuses on three main activities:

  1. Facilitating water flow through the mine’s system;
  2. Collecting and controlling the worst water in the mine and
  3. Treating the worst water flows so that mine effluent quality is improved significantly before it leaves the mine.

Pool prevention / Reduce in-mine water retention time 

  • Greenhouse removal
  • Removal of crossbeams
  • Clearing cave-ins
  • Removing dams

Collect and control water streams

  • AMD collection system

    Pre-Treatment 9 Level Diagram
    Pre-Treatment 9 Level Diagram

    • Intense AMD flows from the 5, 6, 7, 8 levels flow into one pipe in the Cherry Raise, this enters the Cherry Crosscut on the 9 Level in a 4” pipe that connects to the pipe on the East Drift, this pipe connects with a pre-treatment system on the 9 Level
    • 1 gpm of the worst water in the mine flows from the Stanly Ore Chute on the 6 and 7 Levels into the Stanly Crosscut on the 9 Level where it is collected by a pipe that connects with the bad water pipe in the East Drift (which also contains the bad water flow from the Cherry Raise)
  • Clean water capture/control
    • Clean water flow from the East Reed and New East Reed Drift are being captured to prevent pooling and prevent mixing with bad water on the 5 level
  • Improve the water quality
    • Pre-treatment system – in development

Pre-Treatment System

Pre-Treatment System:

  • Bad water flows in the East Drift pipe to a lime treatment system
  • The system elevates pH and precipitates metals in a sludge
  • Sludge is piped as a slurry to a sealed area of the mine, where it remains alkaline
  • This system results in a 70% reduction in the metals that leave the mine
  • Performance testing results for the system will be available online starting in March 2021

Impact monitoring

We believe that providing access to information is essential for stakeholders and the general public to develop an adequate understanding of our environmental management program. Sharing a common understanding with our stakeholders is essential to meaningful and productive dialogue that leads to positive outcomes for the whole community.

Bunker Hill monitors 29 locations in and around Bunker Hill Mine on a continuous basis. This includes 10 surface locations and 19 locations inside the mine. Monthly samples are submitted to nearby a laboratory, Silver Valley Analytical (SVL). We collect additional information every two weeks. Water samples are collected in accordance with strict QA/QC protocols to ensure data integrity – our Quality Assurance Project Plan (QAPP).

  • Monthly lab testing
    • Time series for key locations (Sept – Dec 2020 so far)
      • Kellogg Tunnel (9 Level)
      • Greenhouse (5 Level)
      • Crusher Station (6 Level)
      • Flood Drifts (7 Level)
      • Cherry Drifts (7 Level)
      • Cherry Drifts (8 Level)
      • Cherry Raise (9 Level)
      • Stanly Ore Chute (9 Level)
    • Mass balance sheets
      • Monthly 2020 Sept – Dec (these need to be created)
    • Bi-weekly field parameter time series (Sept – Dec 2020 so far)
      • Kellogg Tunnel (9 Level)
      • Greenhouse (5 Level)
      • Crusher Station (6 Level)
      • Flood Drifts (7 Level)
      • Cherry Drifts (7 Level)
      • Cherry Drifts (8 Level)
      • Cherry Raise (9 Level)
      • Stanly Ore Chute (9 Level)

Future activities

Bunker Hill is committed to designing a project that will leave the environment in a better condition than when we found it.  We continue to develop future initiatives that will further improve the water quality of our community.

Clean water capture/control system

Preventing good water from mixing with bad water in the mine, has three main benefits:

  1. It allows for a smaller, more effective water treatment solution
  2. It allows the water to be used productively inside the mine and
  3. It allows for the possibility of productive use on the surface at the point of discharge.

We will develop a pipe system that captures and control good quality water in the mine in Phase 2 (started in August 2020).

Long-Term Water Treatment

We are working with environmental engineering firms and water treatment experts to determine the optimal long-term water treatment solution for Bunker Hill Mine. Active engagements involve:

  • Stantec
  • MineWater
  • Klepfer Mining Services

Source Control Research

Surface water above Bunker Hill Mine is very good quality water. It degrades quickly after entering the mine through thousands of fissures and fractures in near-surface rock. This is where we believe the best long-term water management system is source control. It is the process of preventing water from entering the mine in the first place.

Water quality has improved since the Phase 1 water management program began. The graphs below compare the water quality when in-mine research was last conducted by the EPA in 1998/9 versus when Bunker Hill initiated the water management program in Sept 2020.

Kellogg Tunnel Dissolved Zinc
Kellogg Tunnel Dissolved Zinc

Kellogg Tunnel pH Readings
Kellogg Tunnel pH Readings

While it isn’t feasible to seal all entry points, Bunker Hill will use studies conducted by the EPA as a starting point for water system modeling. We will also invest in additional studies to improve upon this understanding and engineer solutions that will reduce the volume of water entering the mine going forward. These studies will begin in August 2021:

Areas of Study for Reducing Water Entering Bunker Hill Mine

Beneficial Uses of Water

Once clean water in the mine is isolated and controlled, it may be of suitable quality for use in a range of activities that will be beneficial to the local economy.

  • Snowmaking
  • Agriculture
  • Municipal uses

Lake Coeur d’Alene

Bunker Hill will look for ways to improve fish habitat and water quality in Lake Coeur D’Alene in partnership with local stakeholders

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