The Suffolk County Legislature on Tuesday set a Dec. 20 public hearing on the proposed hookup of the $538 million Ronkonkoma Hub to the Southwest Sewer District after county executive aides assured lawmakers there would be no fiscal impact on the 75,000 sewer district residents.

Public Works Commissioner Gilbert Anderson said confusing county documents stating the project will cost sewer district residents $11.42 a year will be revised to spell out that there would be “no cost to the district residents.”

Legis. Kevin McCaffrey, GOP caucus leader, said the vote only permits the hearing to go forward. McCaffrey said it was an “open question” whether there would be opposition to final approval of the project and the bond to pay for it.

The $26.375 million project would install two sewer lines for the 1,450-unit transit-related development next to the Long Island Rail Road station to handle 400,000 gallons of sewage daily.

The lines would have capacity for another 1.1 million gallons daily that could come from contracts with the Long Island MacArthur Airport, nearby industrial areas and potentially Islandia Village.

The developer, Tritec Real Estate, will be required to make a $7 million contribution to pay off the bonded debt for five years. Tritec also is responsible for $12 million in connection fees of its own, said Deputy County Executive Peter Scully. Suffolk has been awarded a $4 million state grant to help fund the project, Scully said.

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Those funds, he said, will give the county time to make agreements with town officials and other potential industrial users to complete financing of the remaining $3.75 million cost for the hookups. Tritec officials say their contributions will help the sewer district generate $33 million in new revenue from other connections that would yield them a $24 million net profit.

Several legislators expressed concern about the prospect of an increasing price tag and the project’s impact on the underground aquifer.

“These projects tend to become exorbitant,” said Legis. Thomas Barraga (R-West Islip).

Anderson said cost estimates are solid.

Legis. Leslie Kennedy (R-Nesconset) later questioned whether the administration of County Executive Steve Bellone was playing politics when, earlier in the day, his aides withdrew two resolutions to fund $6 million in improvements for the Hauppauge Sewer district.

“I’m suspect and concerned,” Kennedy said.

Scully said the Hauppauge resolutions need to be revised but had no connection to the hub issue.

“I still have questions,” said McCaffrey, referring to long-term funding of the project. “All the details are going to have to be flushed out before we vote on this.”