The Gowanus Canal cleanup, which is estimated to last two-and-a-half years, will get underway by fall. Photo: Rob Abruzzese/Brooklyn Eagle

The federal agency tasked with cleaning up the Gowanus Canal issued an order on Tuesday legally requiring six companies deemed responsible for the waterway’s pollution to start remediation efforts in September.

The Environmental Protection Agency’s order requires that the parties begin full scale dredging and capping of the upper portion of the canal from Butler to Third streets, as well as restoration of the former First Street Turning Basin, which will be converted into wetlands. This initial portion of the cleanup is expected to cost $125 million.

The order was addressed to National Grid, the City of New York, Con Edison, Hess Corp., Honeywell International, Inc. and The Brooklyn Improvement Co.

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EPA lawyer Brian Carr said on Tuesday at a Community Advisory Group meeting that his agency was required to give ample notice to the parties so that they could start hiring contractors, ordering materials from other countries and procuring barges so that there would be no delays come September.

“It takes lawyers an awfully long time to negotiate the heck out of a lot of those things and bill everyone inordinate amounts of money,” Carr said. “If we don’t give them months and months of a lead time, all of the contracting and things won’t be in place by the time we start that.

“Until we have that legal requirement for someone to do a particular thing, they’re not obligated to finish hiring their contractors or start paying for particular portions of the work.”

The entire dredging and restoration of the first third of the canal is expected to take two-and-a-half years. Carr said he hoped to have a detailed schedule of when each step will be completed by the end of February.

Carr once again referred to the massive amount of activity coming to the Gowanus Canal in the coming months as “D-Day,” as dormant bridges continue to be raised and numerous barges maneuver along the narrow waterway.

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There has already been a lot of preparation work along the canal in the past few months. Barges came in, one sunk, a soundproof wall was put up, ‘no fishing’ signs were installed and work began on an 880-foot steel wall along the waterway. A bulkhead (the border between the shore and the water) was also recently finished at Huntington Street.

Related: A new home for items found at the bottom of the Gowanus Canal

Cleaning of the canal involves maintaining combined sewer overflow — a mixture of storm runoff and raw sewage — with two massive $1.2 billion retention tanks, dredging contaminated deposit that has accumulated due to industrial and sewer discharge, and capping the bottom of the waterway.

In 2013, the cost of the entire cleanup was estimated at $506 million, a number the city has said was overly conservative. The EPA has not calculated an updated figure since then.

A review by the Brooklyn Eagle determined that the price of the two sewage retention tanks has ballooned from a projected $78 million to $1.2 billion — more than 15 times the initial figure and more than double the estimated cost of the Superfund cleanup in its entirety.

Related: The Gowanus Canal will never be clean

The city’s Department of Environmental Protection, which was named a potentially responsible party for the canal’s pollution, is tasked with covering the cost of the CSO tanks. The city and National Grid are on the hook for the majority of the cleanup, with more than 25 smaller private parties also contributing.

The cleanup will be split into three sections: north of Third Street, north of Ninth Street and north of 21st Street.

U.S Rep. Nydia Velázquez, whose district includes three federal Superfund sites, including the Gowanus Canal, called the order a “significant milestone.”

“We are on an ambitious timeline for cleanup as compared to other Superfund sites throughout the nation,” she said. “Most importantly, we are cleaning up Gowanus the right way, in a manner respectful of community needs, and responsible parties are shouldering the cost.”

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