POST FALLS - After years of argument over Spokane River water quality standards, taxpayers are starting to see bills for treatment plant upgrades to meet the federal mandate.

The cities of Post Falls and Coeur d'Alene and the Hayden Area Regional Sewer Board discharge treated wastewater to the river and must make facility improvements to meet the cleanup plan.

The Post Falls City Council has approved a $12.7 million contract with TML Construction of Hayden to make improvements to the headworks, equalization and sludge loading areas of its treatment plant off Seltice Way. Five bids were received.

The project will begin in June and is expected to last about 18 months.

"This is driven by the city's discharge permit from the EPA," said John Beacham, Post Falls environmental manager. "A primary focus of the current project is to invest in systems which will reduce the cost of the next phases of the compliance schedule by reducing peak flows into the plant."

Post Falls wastewater ratepayers - and those with the other dischargers - are feeling the pinch of the cost of the upgrades.

Post Falls rates for this fiscal year rose 14.5 percent to $38.69 per month. Rates are projected to increase 10 percent next year, followed by 9 percent and 7 percent for three consecutive years to $56.83 per month in fiscal 2020. The rates are not final until the council approves them by resolution each year.

A low-interest (2.25 percent) state loan funded by federal dollars will fund $10.8 million of the upcoming facility improvements.

"The fund is intended to provide cities with a way to finance projects required to meet requirements under the Clean Water Act," Beacham said. "The savings in interest over the 20-year life of the loan is expected to be around $3.3 million."

Beacham said the next major project on the wastewater compliance schedule will be the installation of tertiary treatment in the form of ultrafiltration membranes with chemical addition. Per the discharge permit, the installation must be made by November 2022.

"These will be capable of removing phosphorous down to the parts-per-billion levels mandated in our permit," Beacham said.

The city's facility plan estimated the cost for that phase of improvements at $19.23 million in 2012.