While the federal environment minister says she found out only recently about Montreal's plan to dump eight billion litres of raw sewage into the St. Lawrence River, documents obtained by The Canadian Press show her department has known since 2014.

Leona Aglukkaq tweeted Wednesday that her office learned last week of the wastewater dump plan, which has become fodder in the federal election campaign and also been panned by environmental activist Erin Brockovich.

Last week my office learned of Montreal's plan to dump billions of litres of raw sewage into the St. Lawrence. 1/2 —@leonaaglukkaq

This plan is concerning and we have done the responsible thing by exploring options to prevent it while we get more information. 2/2 —@leonaaglukkaq

But documents show the federal Environment Department has been copied on correspondence since 2014, with full details and talking about an expected start date for the work in October 2015.

That is in line with the version of events Montreal Mayor Denis Coderre gave earlier this week.

In another document, an Environment Canada official confirms in an email the department was aware of the project in September 2014.

Ministry responds

Ted Laking, a spokesman for Aglukkaq, later maintained she was only told last week.

"Notwithstanding that it is clear officials knew as early as September 2014 about the city of Montreal's plans, the minister only learned of the plan last week," Laking wrote in an email.

"Upon hearing of this plan the minister instructed Environment Canada to explore options to prevent this sewage dump while we receive further science-based information and analysis on the environmental impacts of what Montreal is planning."

Laking said the immediate concern is ensuring the St. Lawrence is protected.

Coderre has accused the Conservatives of playing "cheap" politics after they called on the city to suspend the work, which is expected to start the day before the Oct. 19 election.

On Tuesday, he invited Environment Canada officials to meet with his administration by week's end to discuss the matter.

Coderre said initially there was a plan to streamline the process so that both provincial and federal environment departments wouldn't have to sign off on the plan.

Coderre reiterated on Wednesday that his invitation to meet remains on the table.

Dumping plan makes political waves

The sewage dump became a federal campaign issue this week when Conservative candidate Denis Lebel weighed in, prompting accusations from Coderre the federal politician was slinging political sludge.

On Wednesday, Prime Minister Stephen Harper entered the fray during a Saskatoon campaign stop.

"Obviously, a lot of concern has been expressed about this in Montreal and throughout Quebec and our ministers have already expressed their preoccupations," Harper said. "We are encouraging the city to meet Environment Canada and to consider other possibilities to settle this matter."

In Quebec City, Premier Philippe Couillard reaffirmed support for Coderre's plan, saying experts have gone over numerous scenarios and that he agrees with the mayor that, while unappealing, the short-term dump remains the best scenario.

"Mayor Coderre asked the federal representatives to come to the table right away and they should do this," Couillard said. "If somebody has an idea of genius that has not been mentioned until now, fine.

"But until now each time we've looked at this and Mayor Coderre and his team have looked at this, we always come to the same conclusion."

The provincial Environment Department approved the plan in February and Coderre has said it isn't the first time the city has proceeded in this manner — similar dumps were done in 2003 and 2007 — with federal blessing.

The story has made the rounds, with Brockovich contributing to the debate on her Facebook page on Tuesday.

"Montreal Mayor Denis Coderre wants to take a big dump in the Saint Lawrence River," she wrote, calling the plan "ridiculous and shameful" and urging people to call Montreal city hall.

The one-week sewage dump is aimed at relocating a snow chute that runs under a major downtown expressway that is being razed to build an urban boulevard.