Septic system requirements in Missoula County, Montana
The septic rules landplan.io applies in Missoula County, what a septic tank costs there, and the parcel data we hold.
Updated
Design a septic system for an address in Missoula County
Montana's state rules apply in Missoula County: landplan.io has no county rules of its own here. State rules: Reviewed See Montana's rules
Septic systems allowed in Missoula County
The system types landplan.io permits in Missoula County:
- Elevated Sand Mound System
- Subsurface Pressure Trench System
- Subsurface Trench System
- Infiltrator Advanced Treatment Leachfield
- Infiltrator Advanced Enviro-Septic® (AES)
- Discharging System
Septic tank size in Missoula County
The daily design flow of a home: 150 gal/day per bedroom, at least 240 gal/day. The septic tank is sized from that flow:
| Daily design flow | Minimum tank |
|---|---|
| up to 240 gal/day | 1,000 gallons |
| 240 to 360 gal/day | 1,500 gallons |
| 360 to 600 gal/day | 2,000 gallons |
| 600 to 720 gal/day | 2,500 gallons |
| 720 to 840 gal/day | 2,750 gallons |
| 840 to 920 gal/day | 3,000 gallons |
| 920 to 1,040 gal/day | 3,250 gallons |
Septic setbacks in Missoula County
| From | To | Distance |
|---|---|---|
| Polygon | Existing Septic Component to be Abandoned | 5 ft |
These are the values the landplan.io design engine applies in Missoula County. Confirm a design with the Montana health department or your county's before you build.
Parcel data in Missoula County
landplan.io has parcel boundaries for Missoula County (100% of its area): type an address and the design starts from the parcel.
Septic companies, designers and jobs in Montana
- Septic companies and distributors in Montana
- Septic designers in Montana
- Septic design jobs in Montana
Where the rules come from
The regulations and documents landplan.io's Missoula County, Montana rules are read from:
- Subdivisions/On-Site Subsurface Wastewater Treatment Systems, Subchapter 3 (Subsurface Wastewater Treatment Systems) (Admin. R. Mont. (ARM) 17.36.301 - 17.36.343 (ch. 17.36, subch. 3))
- Circular DEQ-4: Montana Standards for Subsurface and Other Wastewater Treatment Systems (Circular DEQ-4 (2023), incorporated by reference in ARM 17.36.323)
Near Missoula County
- Lake County
- Powell County
- Granite County
- Mineral County
- Ravalli County
- Sanders County
- Lewis Clark County
- Deer lodge County
- All of Montana
Questions
What septic systems are allowed in Missoula County?
landplan.io designs by Montana's state rules there and permits: Elevated Sand Mound System, Subsurface Pressure Trench System, Subsurface Trench System, Infiltrator Advanced Treatment Leachfield, Infiltrator Advanced Enviro-Septic® (AES) and Discharging System.
What size septic tank do I need in Missoula County?
landplan.io sizes the septic tank in Missoula County from the daily design flow: up to 240 gal/day: 1,000 gallons; 240 to 360 gal/day: 1,500 gallons; 360 to 600 gal/day: 2,000 gallons; larger flows need larger tanks. A home's design flow is 150 gal/day per bedroom, at least 240 gal/day.
Does landplan.io have parcel data for Missoula County, Montana?
Yes: parcel boundaries cover Missoula County (100% of its area).