Spokane will borrow more than $1 million from the state to help prevent untreated sewage from spilling into the Spokane River.

The City Council on Monday agreed to accept a low-interest loan from the state Department of Ecology to pay for a combined sewage overflow tank already under construction near the T.J. Meenach Bridge.

The project is one of many that that will add up to an estimated $300 million through 2017, the deadline that’s been set for the city to stop nearly all discharges of raw sewage into the river.

Much of Spokane’s south side has storm drains that flow into the sanitary sewage system. When it rains, that system becomes overburdened and sewage flows to the river without being treated. To prevent that from occurring, the city is installing a series of overflow tanks to capture excess sewage that can flow to the treatment plant as capacity allows.

City officials say they likely will seek a bond to pay for most of those projects. The construction of the tanks has been cited as a significant reason for recent and proposed sewage fee increases that could make monthly sewage bills hit $55 in 2013, up from about $33 in 2010.

John Mercer, Spokane’s capital projects manager, said the city applied for the loan in 2009 and was awarded it earlier this year.

Interest on the $1.2 million loan is set at 2.8 percent, about half as much interest as will be paid on the bond, Mercer said. It must be repaid within 20 years. Mercer said the city has worked to win grants and low-interest loans to lower the amount of money that the city will need to borrow through a bond.

“This is a really good deal,” Mercer said.

In the first three months of 2011, about 12 million gallons of untreated sewage flowed into the Spokane River as a result of rain or melting snow.

Dale Arnold, wastewater management director, said the combined sewage overflow tanks that the city has completed appear to have worked. Even with the extremely wet spring, none of the lines that now have overflow tanks have overflowed into the river, he said.

City Councilman Bob Apple, a critic of the state Department of Ecology, cast the lone vote against the loan. He said the public doesn’t understand the expense of the overflow tanks and said issue has been decided “behind closed doors.”

City Councilman Steve Corker, however, said decisions about the combined sewage overflow have been decided in a “very public process.”

Caption for above photo: Untreated sewage and storm water flow into the Spokane River under the Monroe Street Bridge on Dec. 15. The city has about 30 pipes that release sewage into the river during rain or snowmelt. (This overflow pipe won't be affected by the tank under construction that will be paid for with the state loan.)