Columbia Falls staff warns wastewater treatment allocation approaching limit; recommends planning limits and phased approvals

City Manager Eric Mulcahy told the Columbia Falls City Council that the city's wastewater treatment plant is nearing its allocated nutrient-removal capacity under Montana Department of Environmental Quality (DEQ) permits and urged a cautious approach to new large developments.

Mulcahy said staff and engineering models use a working baseline of 1,894 people — a model-derived, approximate figure approved in the city's 2023 engineering design — and that the city is approaching 100% of its permitted allocation for nutrient removal, not hydraulic flow. "Because we're approaching a 100% capacity allocation, that is not a it's a risk of regulatory noncompliance," Mulcahy said, distinguishing the regulatory limit from the plant's hydraulic capability. He added the facility can hydraulically handle significantly higher volumes but must meet concentration-based permit limits.

The manager explained the primary drivers of high peaks are inflow and infiltration (I&I) from manhole covers, groundwater and storm events (not a systemic failure of the treatment basins). He told the council Meadow Lake Water and Sewer District contributes a disproportionate share of I&I and said staff will address that through contract negotiations. Mulcahy also cited a June 2022 rain event and other engineering data used to derive design flows.

As guidance to the planning commission and council, Mulcahy recommended allocating up to 95% of current capacity (an additional roughly 1,500 people under the staff proposal) while leaving an operational margin of about 400 people. He recommended allowing permanent uses at the Lazydays Court site (hotel and commercial properties) based on prior allocations at that location, negotiating phased annexations for very large projects (for example, developers seeking hundreds of units), and considering a targeted moratorium on new very large construction applications until a fall restudy of bioreactor performance.

Councilors and residents asked whether allocations could be held for developers, how DEQ would respond if the city exceeded permitted nutrient levels and whether seasonal spikes from short-term rentals (VRBO/ADUs) had been analyzed. Mulcahy said developers who have completed engineering work often request and receive extensions; he acknowledged the 1,894 figure depends on modeling assumptions and can shift if variables change. On enforcement, he said the city has not violated DEQ permits to date and that staff will follow up with specifics on consequences and mitigation steps.

Mulcahy asked the planning commission to review staff recommendations at its Jan. 8 meeting and asked the council to provide guidance at its Jan. 20 meeting. He said longer-term fixes — including grant-funded projects to address I&I and a formal restudy after one year of new bioreactor operation — are part of the path to expand capacity. "We would qualify for a lot of those type of grants to help us with solving some of those problems to remove the barriers," he said.

No formal moratorium or binding allocation change was adopted at the meeting; staff framed the proposal as guidance and recommended next steps for the planning commission and subsequent council review. The council asked staff to return with clarifying information on DEQ consequences, seasonal-flow modeling and specific options for phased approvals.

Ending: The council did not take a final vote on capacity limits at this meeting. Planning commission review was scheduled for Jan. 8 and the council review for Jan. 20, when members may consider formal allocation limits or moratorium language.