Suffolk County will receive $388 million in state and federal recovery aid to extend sewers to 12,000 homes along the South Shore, Gov. Andrew M. Cuomo's office announced Saturday.

The money includes $24.2 million for an initial design and environmental review phase, which could take at least 18 months. The construction phase will use $364.3 million to improve sewer infrastructure in Suffolk in an effort to stem nitrogen pollution and bolster coastal protection.

The plan would hook up homes in North Babylon, Deer Park, Oakdale, Mastic, Mastic Beach and Shirley.

"This money allows us to take the first significant actionable step toward building the necessary waste water infrastructure," said Justin Myers, a spokesman for Suffolk County Executive Steve Bellone.

The money will pay for the construction of new collection systems in the Carlls, Connetquot and Patchogue rivers watershed areas that connect thousands of residential, commercial and nonvacant parcels to existing water conveyances and treatment systems, the governor's office said.

A new water collection and conveyance system also will be built in the Forge River watershed, linking even more residential, commercial and nonvacant parcels to a new wastewater treatment plant to be built on the site of the Calabro Airport in Brookhaven.

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The county had previously announced it was receiving the money.

Funding comes from the New York State Environmental Facilities Corporation's State Revolving Fund and the U.S. Department of Housing and Urban Development's Community Development Block Grant-Disaster Recovery Program, Cuomo's office said. The federal Hazard Mitigation Grant Program also is helping fund the construction phase.

Myers said the project is the "single largest sewer infrastructure project" to come to Suffolk in a generation.

Cuomo, in a news release, said: "This funding allows Suffolk County to improve and expand its sewer system in a way that not only reduces threats to water quality and contamination, but also strengthens Long Island's coast to better withstand future storms."

A large portion of nitrogen comes from outdated septic systems in a county where 74 percent of homes are not connected to sewage treatment plants. Of the 360,000 septic systems in Suffolk, more than 250,000 were built before 1972, when tanks were not required.

Excess levels of nitrogen have impaired waters, caused algae blooms, depleted oxygen levels and destroyed natural coastal barriers and storm buffers including marshland.

Completely bringing sewers to Suffolk would cost an estimated $9 billion and remove 70 percent of nitrogen seeping into bays and harbors.

Bellone has made stopping nitrogen pollution from septic tanks and cesspools his top priority.

Cuomo's office said the first phase of the project has already begun and the money for that portion is being doled out.