Drainfield Repair & New Septic Systems in Flathead County

The drainfield (also called a leach field or absorption field) is where treated wastewater soaks back into the soil. When it fails, pumping the tank won't fix the problem. Whether you're replacing a failed drainfield, building on bare land, or upgrading an old cabin system, we'll connect you with a local installer who works in your area.

Call (406) 446-7883

Signs your drainfield may be failing

Wet, soggy or smelly ground over the drainfield, especially after heavy water use
Drains slow down again soon after the tank was pumped
Sewage surfacing in the yard
Repeated backups with no blockage found
The system is decades old and has never been evaluated

How new systems and replacements work in Flathead County

In Flathead County, septic systems are permitted through Flathead County Environmental Health. The general process looks like this (always confirm current requirements with the county):

Site evaluation — test holes are dug so the county sanitarian can evaluate soils, groundwater and bedrock.
Design — a system is designed for the site and the home's size. Many licensed installers are also certified designers; some sites need an engineer.
Permit — the permit application is submitted and approved before work begins.
Installation — the system is installed by a county-licensed installer (homeowners may self-install only after passing the county's competency test).
Final inspection — the installer must be present; engineered systems also need the engineer and as-built drawings.

High groundwater, shallow bedrock, and lake or river setbacks are common in parts of the valley. They can mean a larger, pressure-dosed, or engineered system — and a higher price. Plan for site evaluation before you budget.

Types of systems you may hear about

Conventional gravity system — tank plus gravity-fed drainfield; simplest where soils allow.
Pressure-dosed system — a pump spreads effluent evenly; common on tighter or slower soils.
Elevated sand mound — built up above grade where groundwater or bedrock is shallow.
Advanced treatment units — extra treatment before the drainfield, sometimes required near water.

What does a new system or drainfield cost?

Costs vary widely with soil, system type, access and permits — from several thousand dollars for a simple replacement to well over $20,000 for engineered systems. See our Flathead septic cost guide.

Drainfield and installation by area

Planning a new system or replacement?

Get connected with a licensed local installer.

Call (406) 446-7883 or request a quote →