The Columbia Falls City Council last week approved a $50,000 contract with HDR Engineering to develop a new sewage treatment capacity study that could boost the city’s ability to grow in the coming years.

The sewage treatment plant recently saw significant upgrades to its facility, most notably its bioreactor, which does biological treatment of the sewage.

Since the upgrades went online, the city has seen significant drops in nitrogen and phosphorous output, suggesting the plant could accommodate more capacity.

Here’s a look at some of the improvements in the plant’s operation, according to a report to Council by City Manager Eric Hanks:

• From November 2025 through September 2026, the upgraded bioreactor removed approximately 75% of total nitrogen, substantially exceeding the improvement assumed in the 2023 design model.

• Performance remains well below current nitrogen permit limits. The permit limits are 37.1 pounds per day monthly and 63.5 pounds per day weekly. Post-upgrade performance has averaged about 6.6 pounds per day monthly, with a peak-week value of roughly 14.5 pounds per day. 

• Post-upgrade effluent concentrations have substantially improved. Average monthly total nitrogen is about 1.84 mg/L, compared with roughly 7 mg/L during the period from pre-upgrade 2023-2025 performance. 

The city continues to have problems during high water events with inflow from stormwater. Much of that comes from the Meadow Lake community, which contracts with the city for sewer services.

Meadow Lake’s contract is coming up for renewal in the next few years and the city continues to have negotiations with the resort community’s water and sewer board.

Still, with the improvements to the existing plant, the city hopes that by doing the study, it can make a compelling argument to have its discharge permit from the state Department of Environmental Quality modified prior to renewal in 2030.

“Given these (performance) changes, staff believes a new engineering analysis based on demonstrated post improvement performance is appropriate. HDR will evaluate flow, organic and nutrient loading, seasonal and wet-weather conditions, and secondary-treatment performance; develop a capacity utilization analysis; identify treatment constraints and regulatory vulnerabilities; and recommend a revised (sewer) rated capacity if supported by the engineering analysis,” Hanks said in his report to Council.

Council agreed and approved the contract unanimously. HDR is the firm that designed the upgrades to the plant, which were financed through a federal grant.

The city is hoping for more federal dollars to further upgrade its plant into the future. 

Congressman Ryan Zinke garnered about $2.35 million for the city’s sewer plant for future upgrades in a rural infrastructure bill that passed the House back in June, but has yet to clear the Senate.

HDR’s report, per the contract, is due within six months.

The city’s sewer capacity is a significant issue, as without enough capacity, it could stymie future growth and housing. 

The city is also looking at needing to upgrade its water system in the future, with more storage capacity and now a new well, as one well was recently shut down as it was found to have what are colloquially known as forever chemicals that were above federal safe water drinking standards.