City eyes several $100 million in water, wastewater improvements
Martin Kidston
(Missoula Current) While the city's water and wastewater system is performing well and meets statutory requirements, the system will need several $100 million over the next 20 years to address issues around age and population growth.
And that could impact utility rates charged by the city in the coming years.
City officials on Wednesday said Missoula's population is expected to grow around 1.4% a year. The rate has been consistent over the past few decades and is expected to continue over the next 20 years – the life of the city's new water and wastewater facility plan.
The new plan took a deep look at the current system to identify growing pockets of the city and where the current wastewater system may have bottlenecks in the coming years.
Ross Mollenhauer, the city's utility engineer, said currently wastewater flows average around 7.6 million gallons per day, though the figure increases sharply during peak hours in the morning and evening.
Only two segments of gravity sewer mains are expected to be undersized through 2044, he said.
“One of those we're already working to fix,” said Mollenhauer. “That was really good news to hear. The lift-station work the city has done over the last 20 years has really made a difference. There's no lift-station work that's needed at the moment.”
But nearly 118 miles of existing sewer main is more than 50 years old. Much of that is vitrified clay pipe. Mollenhauer said it's not the strongest material and not what the city currently uses.
The study also found other issues with the wastewater system including the Clark Fork River sewer crossing and corroding concrete sewer mains in the Lincoln Hills area and pockets near Reserve and Brooks streets.
Mullenhauer attributed the issue to hydrogen sulfide gas. Step systems in other parts of the city are also aging.
The City Council authorized $11 million in the FY27 budget to address the Clark Fork crossing and to hire a utility engineer to head the city's sewer rehabilitation project. But the pace of work needs to increase, Mullenhauer said.
“We did recognize that other cities are being more proactive than the City of Missoula is,” he said. “It's something we want to get after. We set a goal of doing 1.3% of the sewer mains a year. That's about 4.3 miles a year. That would ramp up our sewer rehab system considerably.”
The utility service area currently serves a population of 80,000 people, though that's expected to reach 118,000 over the next 20 years. As a result, the new study also identified needs at the wastewater treatment plant.
Logan McGinnis, deputy director of Public Works, said the facility achieved 100% compliance in 2025 with the Montana Department of Environmental Quality by removing 99% of waste solids and 80% of nutrients from the wastewater.
“The plant is performing very well, but there are things we need to look at that drive that future performance,” said McGinnis. “The plant is generally in good condition. But there are condition-related improvements that will be needed over the 20-year planning horizon.”
That includes issues around grease, aging blowers and aeration control. An outfall pipe was found to be undersized and a new centrifuge and bioreactor are needed.
“The water quality in the Clark Fork has been improving,” McGinnis said. “We're permitted to discharge 900 pounds a day of total nitrogen. Our forecast is we're about to discharge 728 pounds. As we're growing, we're having to reduce even further the total nitrogen. It will be a challenge, but we think we can do it.”
The cost to upgrade the city's wastewater system is projected at $320 million over the next 20 years. McGinnis said that's a conservative estimate, with higher-end remedies running even more.
Water storage improvements will cost an additional $164 million over the same time period. The combined cost could impact utility rates down the road as the city looks for ways to fund the improvements.
“We know we need to spend a lot of money,” said McGinnis. “We're going to do a utility-rate study. Any future rate increases will be recommended through a utility-rate study.”