When it comes to matters related to sewage, surprises aren’t usually welcome.

But Oak Harbor city officials were elated to learn the state approved a $42-million loan to help cover construction costs of the new sewage treatment plant incurred in 2017.

The money comes from the Clean Water State Revolving Fund, which provides low-cost financing for water quality infrastructure projects.

City Administrator Doug Merriman, who’s also finance director for now, said the low-interest loan will save residents millions over the length of the loans.

The city had estimated it would pay 4 percent interest on bonds; the revolving fund loans are at 1 percent.

In all, the city obtained $73 million in grants and loans for the project. Current estimates range from $91 million to $110 million in construction costs.

Merriman said all the grants and loans combined will save the city $52 million over a 30-year period in which the project is financed.

That will affect the rates sewer customers will have to pay.