Mount Polley tailings dam failure
A tailings dam at the Mount Polley mine in British Columbia failed on 4 August 2014. In 2022 a court declared the limits of the operator's property insurance, and no criminal charges had been reported at the tenth anniversary.
Court-declared limits (C$10M + C$10M + C$0.5M, 2022) against the earth-movement limit Imperial Metals argued applied.
Status As of research dated October 2026: no criminal charges reported; the 2022 BC Supreme Court judgment set Factory Mutual's cover at the declared limits; the mine reopened in 2022.
- Imperial Metals — Received C$10M promptly from FM and won a C$108M settlement from its engineers in November 2018, in which FM was entitled to share. Supreme Court of British Columbia
- Imperial Metals (mine operations) — The mine reopened in 2022. The Narwhal
- Factory Mutual — Its exposure was declared at C$10M + C$10M + C$0.5M against an Imperial claim under a C$250M limit. Supreme Court of British Columbia
- Taxpayers — Paid $40 million of the cleanup, according to The Narwhal. The Narwhal
- The area affected by the release — About 25 billion litres of mud flowed out on 4 August 2014. The Narwhal
What happened
On 4 August 2014 the tailings dam at the Mount Polley mine in British Columbia, operated by Imperial Metals, failed. The Narwhal reported that about 25 billion litres of mud flowed out. At the time Imperial Metals was in the second year of its mining association's 'Towards Sustainable Mining' programme.
Imperial's property insurer was Factory Mutual (FM); its broker was Aon Reed Stenhouse. FM paid C$10 million promptly. Imperial argued that it could claim under a C$250 million earth-movement limit. In Imperial Metals v. Factory Mutual (2022 BCSC 73, 17 January 2022), the Supreme Court of British Columbia declared limits of C$10 million for property damage to the tailings facility, C$10 million for business interruption and C$0.5 million for claim-preparation costs. FM was also entitled to share in the C$108 million settlement Imperial had won from its engineers in November 2018.
A 2007 broker proposal, noted in the sources reviewed for the insurance case, estimated the maximum foreseeable loss from a tailings embankment failure at C$3 million for property damage and C$93.3 million for business interruption.
The Prince George Citizen reported in 2020 that no environmental charges had been laid by the sixth anniversary of the collapse. CBC reported that the province halted a private prosecution. The Narwhal's tenth-anniversary coverage, as reported, recorded an administrative penalty of $9,000 in 2020, $40 million of cleanup costs paid by taxpayers, and the reopening of the mine in 2022.
Several further findings about the cause of the failure and about professional discipline of engineers appear in the sources reviewed only. They are not stated here as fact; see Unknowns.
- 2007A broker proposal estimates the maximum foreseeable loss from a tailings embankment failure at C$3M (property) plus C$93.3M (business interruption)
- 20144 Aug: tailings dam fails, releasing about 25 billion litres of mud; FM pays C$10M promptly
- 2018Province halts a private prosecution (CBC); Nov: Imperial wins a C$108M settlement from its engineers, in which FM is entitled to share
- 2020No environmental charges six years after the collapse (Prince George Citizen); an administrative penalty of $9,000 is recorded
- 202217 Jan: BC Supreme Court declares insurance limits (C$10M + C$10M + C$0.5M); the mine reopens
- 2024Tenth-anniversary coverage by The Narwhal: no charges; $40M of cleanup paid by taxpayers
What was said
Where accounts differ
Each party's account, side by side, with its source. The record does not settle these points; it shows them.
Argued that it could claim under the C$250 million earth-movement limit.
Supreme Court of British ColumbiaPaid C$10 million promptly and was declared liable only up to the facility-specific limits (C$10M, C$10M, C$0.5M).
Supreme Court of British ColumbiaDeclared limits of C$10M for property damage to the tailings facility, C$10M for business interruption and C$0.5M for claim-preparation costs, and held FM entitled to share in the C$108M engineers' settlement.
Supreme Court of British ColumbiaHow it looked
Shown
- Imperial Metals was in the second year of its mining association's 'Towards Sustainable Mining' programme when the dam failed.Mining association programme, as described in the sources reviewed citing The Narwhal · The Narwhal
Recorded
- FM paid C$10 million promptly; the court declared limits of C$10M for property damage to the tailings facility, C$10M for business interruption and C$0.5M for claim-preparation costs.
- FM was entitled to share in the C$108 million settlement Imperial Metals won from its engineers in November 2018.
- A 2007 broker proposal estimated the maximum foreseeable loss from a tailings embankment failure at C$3M (property damage) and C$93.3M (business interruption).
- No environmental charges had been laid six years after the collapse (2020).
- The province halted a private prosecution over the spill (2018). The same note records that the permit to discharge into the lake was extended to 2025.
- An administrative penalty of $9,000 was imposed in 2020; $40 million of the cleanup was paid by taxpayers; the mine reopened in 2022.
Who gained
Reached nature or the ground
Gained elsewhere
Responses on record
- Imperial Metals (Judgment of 17 January 2022): Argued in court that it could claim under a C$250 million earth-movement limit. · Supreme Court of British Columbia
- Factory Mutual (Judgment of 17 January 2022): Paid C$10 million promptly. The court declared limits of C$10M (property damage to the tailings facility), C$10M (business interruption) and C$0.5M (claim-preparation costs). · Supreme Court of British Columbia
- Province of British Columbia (2018): Halted a private prosecution over the spill; the source headline gives the action but the sources reviewed give no statement of reasons. · CBC News
In court and with insurers
Lawsuits and rulings
- 2022-01-17Defendant wonCAD 20.5m Total of the three declared limits (C$10M + C$10M + C$0.5M), in millionsImperial Metals Corporation v. Factory Mutual Insurance Company, 2022 BCSC 73Supreme Court of British Columbia · Civil · Imperial Metals → Factory Mutual Insurance Company
Imperial Metals argued it could claim under a C$250M earth-movement limit. The court declared limits of C$10M for property damage to the tailings facility, C$10M for business interruption and C$0.5M for claim-preparation costs, and held FM entitled to share in the C$108M settlement Imperial won from its engineers in November 2018. Status is read from Imperial's side. Supreme Court of British Columbia
- 2018Outcome not on recordPrivate prosecution over the Mount Polley tailings spillNot stated in the source headline · Criminal · A private prosecutor (not identified in the cited headline) → Not stated in the cited headline
CBC reported that the province halted a private prosecution against the Mount Polley tailings spill. the sources reviewed does not record the forum, the prosecutor, the defendant or the reasons. CBC News
- 2020Claimant wonDollars (currency not specified) 0.01m Administrative penalty, in millionsAdministrative penalty relating to Mount PolleyNot stated in the source summary · Administrative · Authority not named in the source summary → Imperial Metals (recipient implied by the source summary; not stated explicitly)
The Narwhal, as reported, recorded an administrative penalty of $9,000 in 2020, with no charges laid. The Narwhal
Insurers
- 2022Partly paidCAD 10m Paid promptly, in millionsFactory Mutual Insurance Company (FM) → Imperial MetalsStated reason: Limit dispute: Imperial argued for a C$250M earth-movement limit; the court declared limits of C$10M, C$10M and C$0.5M. the sources reviewed describes this as a sublimit dispute, not a refusal based on the insured's knowledge.
FM paid C$10M promptly. On 17 January 2022 the BC Supreme Court declared the limits applying to the tailings facility and held FM entitled to share in the C$108M settlement Imperial won from its engineers. Supreme Court of British Columbia
What nature saw
Nature's report opens this page. Below: further outcomes measured on the ground.
What we don't know
Court
- Unclear Private prosecution over the Mount Polley tailings spill: outcome not on record.
Figures
- Insufficient Fines: Reported only: professional-body fine and costs for one registered engineer.
- Insufficient Fines: Reported only: professional-body fine and costs for the other registered engineer.
Accounts
- Disputed Which insurance limit applied to the tailings dam failure?
Record
- Insufficient Reported but not independently verified: an independent expert panel (January 2015) reportedly found the main cause was a design that did not account for the complex geology beneath the foundation.
- Insufficient Reported but not independently verified: the province's Chief Inspector of Mines (December 2015) reportedly wrote that the company and its registered engineers had not carried out adequate ground investigation, but that no specific rule governed this, so there was no breach.
- Insufficient Reported but not independently verified: the limitation period under provincial environmental law reportedly expired on 4 August 2017, and prosecutors reportedly halted a federal private prosecution brought by MiningWatch in 2017.
- Insufficient Reported but not independently verified: two registered engineers were reportedly fined and charged costs of C$94,000 and C$132,500 by their professional body and both gave up their licences.
- None on record The release volume is also given in one note as about 25 million cubic metres of tailings and water; that note says the volume came from general knowledge and was not re-verified.
Did the harm stop?
The failure was a single event on 4 August 2014. The mine reopened in 2022, and a permit to discharge into the lake was recorded as extended to 2025. The sources reviewed do not record an ecological recovery assessment.
Who paid?
According to The Narwhal, taxpayers paid $40 million of the cleanup. FM paid C$10 million of the insurance claim and the court declared limits of C$20.5 million in total across three heads.
Sources
Courts
- Imperial Metals Corporation v. Factory Mutual Insurance Company, 2022 BCSC 73Supreme Court of British Columbia · 2022-01-17
Press and investigations
- No environmental charges as 6th anniversary of Mt. Polley mine dam collapse loomsPrince George Citizen · 2020
- Mount Polley mining disaster tenth anniversaryThe Narwhal · 2024
Connected cases
- Five people to be prosecuted over Jagersfontein tailings dam failure South Africa · date not stated Related matter
- Insurers of the Carmichael coal mine Australia · 2015–2025
- Aon (Company) — here: Broker (Aon Reed Stenhouse); there: Broker asked to rule out the mine; says it provides no services to it
- Vale Brumadinho dam collapse Brazil · 2019–2027
- Aon (Company) — here: Broker (Aon Reed Stenhouse); there: Property insurance broker (press reports)