Teck Resources says an incident at the Trail Smelter caused between 12,000 and 25,000 litres of sodium hydroxide to flow into a sewer line. That line leads to the Regional District sewage plant, which discharges into the Columbia River.
"Our initial information indicates that the sewage treatment plant process would have a limited effect on that solution as it passed through the plant and eventually discharged into the Columbia River," said Teck spokesperson Richard Deane.
The solution is usually treated on-site. The company is investigating how it could have drained into the sewer, but says it does not expect there to be any long-term impact on the river's aquatic life or surrounding environment.
"We are going to be having a third-party environmental impact assessment conducted to confirm whether there will be any impact as a result of this incident," Deane said.
The Ministry of the Environment, the Provincial Emergency Program and Environment Canada have been notified, he said.
This is not the first time Teck has had a major spill, whether intentional or unintentional.
In 2004, the company was sued by a the Colville Confederated Tribes — and later the U.S. Environmental Protection Agency — for environmental damage caused by operations at its Trail smelter dating back to 1896. Eight years later, Teck admitted in U.S. court to dumping millions of tonnes of slag into the river.
In 2008, the company accidentally dumped 1,000 kilograms of lead solution into the Columbia River. It was later fined $115,000 for what the judge called significant negligence.
In 2012, a Washington State judge ruled Teck is liable for intentionally discharging 9.97 million tonnes of slag into the Columbia River from 1930 and 1995, and that materials in the slag, including heavy metals were likely to cause harm.
Teck said it would appeal the decision.
In December, a Washington State woman, who lives 30 kilometres south of Teck's smelter in Trail, filed a class-action lawsuit against the company claiming pollutants from the plant caused her breast cancer and other ailments. Other people living downriver from the smelter have claimed high rates of disease which they attribute to pollution from the smelter.
Teck has already spent more than one billion dollars improving its operations in Trail, and remediating the surrounding area.