MISSOULA — The state of Montana has blessed a proposal by the city of Missoula to eliminate some large septic systems on the south side of town.
The Montana Department of Environmental Quality (DEQ) last week published an environmental assessment of the City of Missoula’s plan to eliminate two septic tank effluent pumping systems, called STEP systems, and replace them with traditional sewer mains. The two STEP systems serve the Lamoreax and Birdie subdivisions and the Maloney Ranch subdivision along Lower Miller Creek Road, south of Brooks Avenue.
STEP systems represent a kind of halfway point between regular septic systems and city sewer systems. Each residence has a leak-proof septic tank, but unlike normal septic tanks, the liquid effluent is pumped to a large community tank and then to the city wastewater treatment plant via a sewer main. The solid waste that remains in the tank must eventually be pumped out, just like with a regular septic tank.
Based on the environmental assessment, DEQ found that eliminating the STEP systems would have no significant negative impact on the environment. In fact, it could benefit the environment because the two systems are aging out and tank failure would contaminate the groundwater, which is only 10 to 20 feet below the surface in the spring. In addition, the Bitterroot River is approximately 2,000 feet north of the
project areas.
The Lamoreax-Birdie STEP system was installed in 1993 and the Maloney Ranch system in 2003, according to the DEQ assessment. As a result, hydrogen sulfide gas is degrading the community tanks, and the pump and control parts are getting obsolete, thus reducing reliability during power outages. The Lamoreax-Birdie system has two 5,000-gallon community tanks and two 8,500-gallon tanks, while the Maloney system has eight 5,000-gallon community tanks.
The city plans to install 870 feet of new 8-inch PVC gravity line in the Lower Miller Creek Road to funnel effluent for the Lamoreax-Birdie system and 670 feet of line in Bigfork Road for the Maloney Ranch system. Both pipes would connect to the main sewer line. Then, community septic tanks would be pumped out and filled with gravel, and any cracks would be filled and pipes would be capped. Construction is expected to begin mid-June 2026 and should take around nine weeks.
The cost for decommissioning the community tanks and installing new pipe is estimated at more than $1,386,000. The City proposes getting a low-interest loan — 2.5% interest for 20 years — from the DEQ Water Pollution Control State Revolving Fund. The City is also increasing its wastewater collection rates by 9% annually in 2026 and 2027 as a result of a resolution passed in 2024.
The City of Missoula presented the 2019 Wastewater Facility Plan at a public city council meeting in November 2020. The facility plan included a list of proposed wastewater projects, including decommissioning STEP systems. More detailed STEP decommissioning projects were presented on June 25, 2025.
The DEQ is accepting public comment on the assessment and decision until March 13. Send comments to Rebecca Ridenour, Montana Department of Environmental Quality, PO Box 200901, Helena, MT 59620-0901 or email rridenour@mt.gov.
