A power generation unit at the facility has been shut down since late February.
Contractors have been working on rebuilding that element in order to integrate it into the burgeoning carbon capture system located at Boundary.
A SaskPower employee confirmed Thursday afternoon via email that contractors just informed management that the substance was present at the work site in the late evening of June 29.
The email indicates it was "pre-existing in the work area."
"There is no reason for SaskPower to believe that our employees or contractors were exposed to any asbestos-containing material prior to this discovery," said a further email statement released by media relations leader Tyler Hopson.
"At SaskPower, safety is as important as anything we do and part of everything we do. The safety of our employees and contractors is our priority, and, from the onset, we have handled this incident with their safety in mind."
The Crown power company said it's still working on verifying exactly what the substance is. The construction work has been called off for the time being. It also said the area is being roped off to make sure no one else is exposed to the material.
Occupational Health and Safety has been alerted and will be looking into the matter.