The Kalispell City Council tonight will discuss a new interlocal agreement with the Evergreen Water and Sewer District.

The agreement would replace a deal that has been in place since 1990.

The agreement largely sets the cost for Kalispell’s wastewater treatment plant to handle Evergreen’s sewage.

It has taken years to reach the current proposal.

“The biggest hurdle was coming up with a way to calculate the rate,” said Roberta Struck, manager of the Evergreen district.

Household sewer rates in Kalispell take into account the collection, treatment and billing costs for the service. The Evergreen district handles its own billing as well as collection through its sewer lines.

In drawing up the new agreement, officials had to determine an equitable rate for Evergreen while extracting collection and billing costs. Kalispell then bills Evergreen for the treatment.

The latest estimate, based off the previous year’s sewage flow, is that it costs around $531,000 to treat Evergreen’s sewage.

“Basically, we wanted to get to where a household in Kalispell pays the same as a household in Evergreen,” Kalispell City Manager Doug Russell said.

What is not an immediate concern right now is capacity at the wastewater treatment plant. In previous years, the two entities negotiated the maximum amount of waste coming from Evergreen. Struck said Evergreen never reached the roughly 682,000 gallons-per-day limit.

But with the expansion of the treatment plant, capacity isn’t a concern at this time, Russell said.

Evergreen accounts for about 17 percent of the flow coming into the plant.

The current interlocal agreement expires this month. The council will not make a vote at the work session on Monday but is required to sign off on the deal eventually.

Reporter Matt Hudson may be reached at 758-4459 or by email at mhudson@dailyinterlake.com.