Uranium tailings ponds operators must double-check the safety of their facilities following the Mount Polley tailings pond breach and spill in B.C., Canada's nuclear regulator says.

The Canadian Nuclear Safety Commission regulates uranium mines and mills, including their waste. In a news release Monday, it said it sent a letter last week to seven companies that operate uranium tailings ponds in Ontario and Saskatchewan.

Uranium mine Key Lake Cameco

Cameco's Key Lake mine in northern Saskatchewan is seen in a 2007 photo. (Dave Stobbe/Reuters)

The ponds contained ground-up uranium ore stored underwater to minimize the escape of dust and radiation and to prevent it from oxidizing. According to the CNSC, they could contain significant concentrations of radioactive elements such as thorium-230 and radium-226, along with elements produced by their radioactive decay.

"The recent tailings dam breach that occurred at the Mt. Polley mine in British Columbia on Aug. 4, 2014 has raised awareness of issues associated with tailings impoundments," said the letter, dated Aug. 14.

"This is a reminder that vigilance must be maintained by ensuring that tailings dams continue to be properly  designed, constructed, operated, maintained and monitored to prevent such occurrences."

The letter asked the seven companies to review the causes of the breach of a dam at a tailings pond at the Mount Polley gold and copper mine in B.C. The incident spilled 10 million cubic metres of wastewater and more than four million cubic metres of sediment into nearby Hazeltine Creek. Following the breach, hundreds of people living downstream were temporarily ordered not to drink or bathe in the local water. Tests later showed that sediment at the mouth of Hazeltine Creek exceeded guidelines in contaminated site regulation standards for copper and iron.

Companies are also asked to:

  • Confirm the safety of their own tailings dam.
  • Confirm and demonstrate that they have conducted all operations, inspections and monitoring required by their operating license.
  • Confirm that measures are in place to mitigate a potential breach.
  • Report any "identified gaps" and "associated plans to address them."

Companies have until Sept. 15 to tell the agency when and how they will carry out the request.

The seven companies involved include:

  • Cameco Corporation
  • Rio Algom Limited
  • Willet Green Miller Ctr
  • P.J. Brugger and Associates
  • EWL Management Ltd.
  • Denison Mines Inc.

AREVA and Cameco operate three tailings ponds in Saskatchewan where tailings are still being deposited – McClean Lake, Key Lake and Rabbit Lake – along with some tailings ponds at closed or decommissioned uranium mines in the province.

The other companies operate tailings ponds at closed or decommissioned uranium mines in Ontario.

Several other uranium tailings ponds are operated by the federal government in the Northwest Territories and provincial governments in Ontario and Saskatchewan.