HALIFAX -- Nova Scotia's environment minister has released new details of the long-awaited cleanup of Boat Harbour, calling the toxic lagoon one of the worst examples of environmental racism in the province and possibly the country.

Iain Rankin said Friday the cleanup of the Northern Pulp mill's wastewater site, on the edge of a First Nations reserve, will be Nova Scotia's biggest industrial remediation since the Sydney Tar Ponds.

"I don't think we can overstate the importance of this project," he said. "There are a lot of unknowns in terms of what contaminants have been in there. We're going back 50 years so some of the material was untreated."

Boat Harbour was a picturesque bay off the Northumberland Strait adjacent to the Mi'kmaq community of Pictou Landing First Nation until the pulp mill opened in the 1960s.

The site quickly turned into polluted lagoon. It was used by different industries to dump waste, including a chemical plant, and is now a toxic mess with "a myriad of different contaminants," Rankin said.

"I think it is one of the biggest examples of environmental racism in the province and probably in the country," he said.

The Nova Scotia government has committed to closing Boat Harbour by 2020 and restoring the waterway to a pristine tidal estuary.

It's part of the province's response to mounting controversy in recent years over the environmental impact of the pulp mill in Abercrombie Point, N.S.

Public outcry over air pollution and strong sulphur odours -- once shrugged off as "the smell of money" -- pressured the province to beef up emissions standards.

The government ordered the company to install new equipment to improve stack emissions and build a new effluent treatment plant.

But the Boat Harbour cleanup rests with the province.

In a bid to attract the pulp mill to Pictou County in the 1960s, the Nova Scotia government absolved the company from future cleanup costs.

The province has set aside $133 million and Ottawa is also expected to contribute through a federal infrastructure fund.

Ken Swain of Nova Scotia Lands, the provincial Crown corporation overseeing the cleanup, said the project will require more money.

"Until we get the results of the procurement, we won't know for sure what this is going to cost," said Swain, project leader for the Boat Harbour cleanup. But he added: "I think we'll need more."

The cleanup of the Sydney Tar Ponds -- a hazardous waste site near an old steel mill in Cape Breton -- cost $400 million and is what Swain referred to as an "in situ" cleanup. The contaminated sediments were mixed with cement and landscaped over.

However, in the case of Boat Harbour the sludge at the bottom of the lagoon will be removed. The mixture of the "fluffy wet contaminated layer" and some of the underlying harbour bottom that will be scooped up at the same time is expected to be about a million cubic metres, Swain said.

The material will be dried and stored or moved in about 18,000 truckloads off site to a nearby landfill or facility, he said.

Nova Scotia Lands will be launching pilot scale work in an isolated cove of Boat Harbour soon to determine the most effective cleanup method.

Given the scope and complexity of the work, however, it appears cost overruns could be inevitable.

Indeed, Rankin said his aim is to meet strict environmental standards -- not a set price tag.

"Price is not my concern, this clean up is too important," he said. "This needs to be done and needs to be done thoroughly."

The massive cleanup project will undergo a Class II environmental assessment, a rigorous process that evaluates human health, air, soil and water quality, the impact on nearby communities and other factors over 275 days.

The clock starts once the project is registered by Nova Scotia Lands, expected this August, Swain said.

The tender documents should be issued by late 2019, with construction starting in 2020 and taking five years to complete, he said.

The environment department will appoint an environmental assessment panel and hold public hearings or a public review of the project.

The federal Canadian Environmental Assessment Agency was unable to clarify Friday whether it would play a role in the project, though Rankin said he would welcome the federal agency's involvement.

Andrea Paul, chief of the Pictou Landing First Nation and a strong advocate for the Boat Harbour cleanup, did not respond to a request for comment.