The discovery of a new bottom layer of sludge at Boat Harbour is being blamed for delaying Northern Pulp's cleanup of the effluent treatment facility in Pictou County.
The pulp mill said an independent assessment this summer detected a previously unknown layer of 194,000 cubic metres of sludge at the bottom of the aeration stabilization basin — a series of lagoons where mill effluent has been churned for decades.
"This discovery and additional sampling delayed our original fall 2020 cleanup plan for the ASB [aeration stabilization basin], which is now expected to start in spring 2021," the company said in a statement to CBC News.
The mill shut down earlier this year. The company is now insolvent and responsible for removing contaminated sludge accumulated in the aeration basin after it purchased the mill in 1997.
Northern Pulp said 81,000 cubic metres was deposited during its operations.
The Nova Scotia government is responsible for removing any sludge that existed prior to the arrival of Northern Pulp.
The company said the delay was caused because its sediment assessment was different from one done in 1997.
"A comparison on the two surveys identified a discrepancy in the amount of sediment in the ASB, which required further investigation before ASB decommissioning activities can begin," Northern Pulp said in its statement.
The discovery of the new bottom sludge was first revealed in a report filed in British Columbia by the court-appointed insolvency monitor on Oct. 30.
Province will investigate claim
"We're a bit puzzled by the assumption put forward in the monitor's report," said Ken Swain, project lead for the $292-million Boat Harbour remediation.
Swain said there is "a high probability" the bottom sludge is clean, pre-industrial sediment, but experts need to be brought in to determine what is there.
"At this point, we don't believe it impacts our cost or the operations of our remediation, although we do feel there needs to be a bit more study done on that," he said.
The monitor also reported the provincial Environment Department rejected Northern Pulp's initial Boat Harbour decommissioning plan submitted July 31.
On Oct. 7, the province outlined other requirements, including plans for soil sampling and secondary containment.
As of last week, the decommissioning plan was still a work in progress.
The monitor said the company is evaluating three bids to remove sludge from the aeration lagoons, which is expected to take three months once the work starts.