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Missoula County adopts updated wastewater rule to allow engineered septic systems in fill
Summary
Missoula County commissioners adopted a resolution to replace Regulation 1 of the Missoula City-County Health Code to allow on-site wastewater systems in engineered fill consistent with Montana DEQ Circular 4, following a Health Board recommendation and no public opposition during the hearing.
Missoula County commissioners on July 30 adopted a resolution to replace the county—s Regulation 1, allowing on-site wastewater treatment and disposal systems to be installed in engineered fill when they meet Montana Department of Environmental Quality (DEQ) Circular 4 design standards.
Public health manager Charlie Shane told the board the DEQ revised Circular 4 after a 2023 legislative directive to allow certain new on-site systems in engineered fill. "DEQ recently changed their rules in that circular we just mentioned to allow new on-site wastewater systems in fill," Shane said, explaining the change gives property owners more flexibility on difficult sites while keeping public-health protections in place.
The Health Board approved the updated Regulation 1 on April 17, 2025, and recommended the county adopt it by reference. County counsel summarized the local action as bringing the county—s Regulation 1 into conformity with the DEQ circular: "It's essentially just bringing the health code regulation 1 in conformity with the state requirements in DEQ Circular 4," the attorney said during the hearing.
Under the new local rule, systems in fill must meet DEQ Circular 4—s design and construction requirements, including limits on the quality of fill material, prohibitions on using fill to overcome required horizontal and vertical setbacks (for example, setbacks from surface water, floodplains, steep slopes, bedrock or groundwater), engineered design reports, additional soil testing, lift placement and compaction, and submission of as-built certifications within 90 days of installation.
There was no public comment during the hearing held before the Board of County Commissioners. A commissioner made the motion to adopt the resolution to adopt the ordinance replacing the current Regulation 1 (the existing Regulation 1 was adopted under Ordinance 2022-003); another commissioner seconded. The motion carried by voice vote.
The revised Regulation 1 will be adopted by reference to the Health Board-approved text and replace the version adopted under Ordinance 2022-003. County staff said the change is intended to allow property owners and developers an additional engineered option on sites that otherwise cannot support conventional on-site systems, provided all DEQ design and construction safeguards are met.
