PORTSMOUTH, N.H. – Portsmouth officials are expected to vote on authorizing a $75 million bond toward an $84 million plan to upgrade the existing Peirce Island wastewater plant.

The Portsmouth Herald reports that if city council approves the resolution on Monday, the plant will become the biggest capital project in the city’s history.

Councilors last month passed the first reading of the request to borrow money toward the project. Officials say the city is trying to get the $75 million authorization to pay for the plant out of the state’s revolving fund loan program, which would be a 20-year term at 2.5 percent.

Officials say monthly sewer rates for city residents will increase from $59 in fiscal year 2016 to $87 in fiscal year 2026 if the bonding is approved.