Pebble Mine Report

Bristol Bay Watershed, Alaska
Alaska’s Bristol Bay Watershed | © Ben Knight

Bristol Bay’s Wild Salmon Ecosystems and the Pebble Mine: Key Considerations for a Large-Scale Mine Proposal

In 2012 Wild Salmon Center and Trout Unlimited produced a report examining the proposed Pebble Mine and its potential impacts on the wild salmon fishery of Bristol Bay, Alaska. This report describes significant ecological, economic, and cultural concerns raised by proposed development of the Pebble copper, gold, and molybdenum deposit in the headwaters of the Bristol Bay basin, which is home to North America’s most abundant wild salmon fishery and the world’s largest wild sockeye salmon run.

The Threat: Pebble Mine

Pebble Mine Tailings Storage Facilities
How do you store 10.8 billion tons of waste? Click to view full size
Preliminary plans have proposed two tailings storage facilities (TSFs). Combined, these TSFs could store 2.5 billion tons of mine waste, less than a quarter of the estimated 10.8 billion tons of ore on site. The illustration above shows the height of the tallest of several dams initially considered to impound the tailings at one of the TSF’s (Site A). This dam would measure over four miles long and 740 feet high, taller than the Hoover Dam | © Wild Salmon Center
  • Based on preliminary plans, the proposed Pebble Mine project would be one of the largest mines in the world with a footprint that would cover 28 square miles of land.
  • The mine would produce up to 10.8 billion tons of waste rock. To put this number into perspective, if Pebble Limited Partnership used rail cars capable of carrying 100 tons each to transport the 10.8 billion tons of ore, the effort would require 108 million rail cars. Using standard 65-foot-long rail cars, the train would measure 1.33 million miles, long enough to  circle the Earth at its equator over 50 times.
  • Extraction of the ore could create an open pit up to 4,000 feet deep and 3.2 miles wide. Underground mining may limit the pit to about half this size but that could reach a depth of 5,000 feet.
  • Up to nine miles of dams reaching up to 740 feet high would be required to impound just 2.5 billion tons of the toxic waste produced (called tailings). These impoundments, known as tailings storage facilities, would be some of the largest in the world and must impound the tailings forever to protect the highly productive Nushagak and Kvichak Rivers.
  • The type of ore at Pebble is likely to produce acid mine drainage, which may lead to chronic contamination of surface and ground waters, having a severe detrimental impact on aquatic life.
  • The region’s seismic activity and extreme weather conditions could trigger dam failures, resulting in potentially catastrophic impacts to the Bristol Bay fishery.
  • The Pebble Mine’s infrastructure would include a network of roads, pipelines, a port, and an energy-generating station, which would pave the way for additional mining proposals in Bristol Bay.

Why are Bristol Bay Salmon so Important?

Bristol Bay Basin Map
© Wild Salmon Center
  • The Bristol Bay basin is one of the top producing wild Pacific salmon systems in the world, yielding up to 40 million mature salmon each year.
  • Bristol Bay is the most lucrative wild salmon fishery in Alaska, supporting nearly 5,000 full time equivalent jobs and generating an estimated $318 to $572 million annually.
  • Bristol Bay’s annual salmon migration provides essential dietary protein for both humans and numerous animal species, while depositing tons of marine-derived nutrients that are vital to the health and ecological function of the basin.

Key Report Findings

  • The Bristol Bay basin contains globally significant wild salmon populations of extraordinary abundance. These populations are highly vulnerable to even small changes in habitat and water quality.
  • The proposed Pebble Mine has the potential to permanently degrade Bristol Bay ecosystems and adversely impact its wild salmon populations.
  • If permitted, the Pebble Mine will enable the development of a mining district many times larger than the Pebble Mine lease, substantially increasing the likelihood that mining operations will adversely impact Bristol Bay ecosystems.
  • Economic evaluations promoting mine development do not adequately account for the value of healthy ecosystems or the long-term costs associated with large mine clean-up.
  • Alaska’s large mine permitting process may be inadequate to ensure the conservation of Bristol Bay’s wild salmon ecosystems; to date, the State of Alaska has never denied a permit for a large-scale mine.


Bristol Bay Sockeye
Bristol Bay: home of the world’s largest sockeye salmon runs | © Ken Morrish
Bristol Bay Smokehouse
Bristol Bay’s annual salmon migration provides essential dietary protein for First Nations, as well as the world | © Ben Knight

Based on the findings of the report, the Pebble Mine, as preliminarily proposed, will degrade the Bristol Bay basin’s aquatic and terrestrial ecosystems and adversely impact the region’s world class salmon fishery. While mine proponents will go to great lengths to assure the public that the mine will result in no net loss of salmon resources, no mine of Pebble’s massive scale has operated successfully in a sensitive aquatic ecosystem long enough to make this claim. There is too much at stake to conduct an experiment of this scale with a resource of Bristol Bay’s economic, ecological, and cultural value.

Additional Resources

Download a full copy of the report or review specific chapters listed below:

Executive Summary

Ch 1: The Bristol Bay Basin

Ch 2: The Pebble Project
2.1 Pebble Mine Project Overview
2.2 Mine Waste Facilities
2.3 Chemicals Used and Tailings Produced
2.4 The Pebble Mine and the Emergence of the Bristol Bay Mining District

Ch 3: Potential Sources of Contamination
3.1 Mine Rock-Water Interactions: Effluents
3.2 Waste Rock
3.3 Tailings
3.4 Process Water and Concentrates
3.5 Post-mining Pit Lake
3.6 Pipeline Failures
3.7 Tailings Dam Failures

Ch 4: The Salmonids of Bristol Bay
4.1 Habitat and Adaptation
4.2 Ecological Importance of Bristol Bay Salmon
4.3 Salmon Species of Bristol Bay

Ch 5: Potential Effects of the Pebble Mine on Salmon
5.1 Acid Mine Drainage and Changes in pH
5.2 Acid Mine Drainage and Copper Toxicity
5.3 Whole Effluent Toxicity and Community Effects
5.4 Water Appropriations
5.5 Sediment and Turbidity
5.6 Predictions versus Performance in Maintaining Water Quality

Ch 6: Pebble Mine Permitting Process
6.1 State Process and Regulatory Requirements
6.2 Federal Statutory and Regulatory Requirements
6.3 Additional Requirements for Pebble Mine Infrastructure
6.4 Other Considerations

Ch 7: Economic Valuations of a Wild Salmon Ecosystem
7.1 Comparing the Economic Values of a Wild Salmon Ecosystem and the Pebble Mine
7.2 Regional Economic Expenditures in Wild Salmon
7.3 Willingness to Pay
7.4 Non-market Passive Use Value
7.5 Taxation and Local Revenues
7.6 Local Employment and Native Communities
7.7 Potential Treatment Costs and Liabilities

Ch 8: Conclusions

Literature Cited

For additional references, see Bibliography.

Bristol Bay Sockeye Split Level
© Jonny Armstrong