An environmental group says a coal company's application to deepen its open-pit mine shouldn't be considered while it's under investigation over wastewater releases into local rivers.

The Alberta Wilderness Association says CST Canada Coal in Grande Cache, Alta., must prove it can operate safely before the provincial regulator looks at its request. 

"Prior to any decisions on this application, the (association) respectfully requests (the Alberta Energy Regulator) complete the outstanding investigations of CST Canada’s operations and management," the group says in a statement to the regulator. 

CST Canada Coal operates open-pit coal mines in Grande Cache, about 430 kilometres northwest of Edmonton. In October, it applied for permits to deepen two of its pits by 155 and 210 metres. 

An approval would extend the mine's life by allowing it to reach about 3.3 million tonnes of steelmaking coal, company documents say.

But the wilderness association points out that three times within the last year, the CST mine has released large volumes of coal wastewater into the environment. 

On Dec. 29, 2022, more than 100,000 litres of coal wash water were released. On March 4, 2023, 1.1 million litres of tailings escaped into the Smoky River. And on June 19, heavy rains and regional flooding led to the release of an unknown amount of wastewater. 

Coal wastewater frequently contains selenium, a substance toxic to fish. 

The regulator has opened two formal investigations into CST, one for failing to meet the terms of its licence and one for failing to immediately report the release of a substance. 

"It is not environmentally responsible to approve further development of the No. 8 Mine until (the regulator) can enforce safe and efficient practices at CST Canada Coal," the association says. 

Inspectors from the regulator have also been on site this fall after three "rock-wall instabilities" in June, September and October — one of which partially buried a piece of heavy equipment and the operator inside it.

The association's statement concerns only the wastewater releases.

The regulator takes all factors into account when considering an application, said spokeswoman Teresa Broughton.

"All relevant operational performance and compliance history is considered during the application process," she said in an email. 

"We undertake a comprehensive administrative and technical review of all applications we receive to ensure the efficient, safe, orderly and environmentally responsible development of coal mining."

No representatives from CST responded to requests for comment. 

But the company has filed a response to the regulator over the association's concerns. 

"CST Coal takes matters such as these very seriously. However, CST Coal cannot comment on this matter as the investigation by the Alberta Energy Regulator into the alleged contraventions ... is ongoing," it says. 

The company added it is co-operating with the regulator's investigations and said the application is not connected to the wastewater releases. 

CST Coal is owned by CST Group, which is based in Hong Kong and incorporated in the Cayman Islands. It bought the mine in 2017 from the receiver after the previous owner, Grande Cache Coal, went bankrupt.

The mines are both open-pit and underground, company documents say. Most of its coal is exported to Japan, Korea and China.

CST employs about 300 people in Canada.

Its leases cover almost 30,000 hectares in the northwest Alberta foothills.