New septic system installation
Building outside sewer service? Here's how a new septic system goes from bare ground to final inspection in Flathead County.
A permit is required to install and operate a septic system in Flathead County, and the paperwork starts well before the excavator shows up. The county advises getting septic approval before you drill a well or build the house, because the drainfield location shapes where everything else can go.
What are the steps?
- Land research request. The county asks you to find out what the property is already approved for before applying. Lots under 20 acres often have a prior approval; larger parcels and replacement sites go through a full site evaluation.
- Site evaluation or review. Environmental Health checks the site against county and state rules. New development in Montana also needs a nondegradation analysis to show the system won't significantly pollute groundwater or surface water.
- Groundwater monitoring, if needed. Monitoring happens in spring, roughly mid-March through June, when groundwater peaks. Start early if you're hoping to build that year.
- Design. A designer or engineer certified by the county prepares the hydraulic design and drainfield layout.
- Permit and installation. Once the county approves the design and issues the permit, a licensed installer builds the system to match it. Any change needs county approval first.
- Final inspection. The installer attends, plus the engineer with as-built drawings if the system was engineered.
Gravity or pressure dosed?
From 2004 until 2026, Flathead County allowed only pressure-dosed drainfields. In March 2026 the commissioners approved amendments that permit gravity systems again, while the county still gives priority to pressure dosing. Your designer will recommend the approach that fits your soil, groundwater and site.
Near city or district sewer?
Under the county's rules, if an approved municipal or district sewer line is readily available within 200 feet, you're expected to connect rather than install septic, with some exceptions. Check this early if your land is on the edge of Kalispell, Whitefish, Columbia Falls or a sewer district.
Pricing comes from the septic company after it learns about your property and, for repairs or new systems, looks at the site and the county paperwork. We don't quote prices, and a figure given over the phone before anyone has seen the system is only a ballpark.
Where we connect you with help
Common questions
Should I drill the well or get septic approval first?
Septic approval first. Flathead County says site conditions can limit where a system can go, so it's best to have that settled before drilling.
Can a homeowner install their own septic system?
Flathead County offers a self-installer license for homeowners. Contact Environmental Health about the process before you plan on it.
Related services
More background: Flathead County septic guide.
Toilets slow, yard wet over the drainfield, or a pump alarm sounding?
Call and we'll put you in touch with a septic company that serves the Flathead Valley.