FARMINGTON – Selectmen approved a plan to upgrade the gravity sewer main along Tannery Brook on Tuesday.

Dirigo Engineers detailed three options for making the long-needed repair to the 50-year-old line covering properties from Perham Street to Middle Street to Lincoln Street along Tannery Brook.

The other two options required building pumping stations on Perham and Middle streets that require more maintenance, electrical costs and replacement of major parts within 15 to 20 years.

The upgrade from the present 10-inch pipe to an 18-inch gravity sewer line would last 50 to 80 years, James Lord of Dirigo Engineering recommended. It’s estimated to cost $576,500, compared to $783,500 and $965,800 for the other options.

The town is applying for a rural development grant through the U.S. Department of Agriculture. Seventy-five percent of it will be considered a grant, and the town will borrow the rest at 2.5 percent interest over 30 years, Town Manager Richard Davis told the board. The work is expected to raise residential sewer rates slightly, he said.

Farmington will probably never see an opportunity like this again, Davis told the board at an earlier meeting.

During that meeting, Selectman Dennis Pike requested more information, including the option of pumping stations versus replacing the line.

In other sewer department business, the board unanimously approved a bid of $346,430 from Sargent Corp. of Stillwater to upgrade the influent pumps at the wastewater treatment facility. Sargent had the lowest of the six bids received, according to figures provided by engineers from Woodard & Curran Inc.

The work will be paid for with a rural development grant of $530,000, of which $387,000 would be considered a grant and $143,000 a loan by the town.

The grant is almost $200,000 more than needed, so about $100,000 would pay for engineering and legal costs, and the other $100,000 would pay off most of the loan on the gravity sewer line job.