Drainfield repair and replacement
When the soil under your drainfield stops taking water, wastewater has nowhere to go. Here's how a replacement works in Flathead County.
The drainfield, also called a leach field or absorption field, is where liquid from the tank soaks into the ground and the soil finishes treating it. Over years, solids that escape the tank and a slimy layer that forms in the trenches can seal the soil. When that happens, effluent surfaces in the yard or backs up into the house, and pumping the tank only buys a little time.
Signs the drainfield is failing
- Sewage surfacing over the field, especially after rain or snowmelt
- Lush, bright green strips over the trenches
- Odors outdoors near the field
- Backups that come back soon after a pump-out
How does a replacement get permitted?
The Flathead City-County Health Department puts properties that need a replacement system on its site evaluation path. Staff evaluate the property against county and state rules and issue a site evaluation and design report. A designer or engineer certified by the office then prepares the hydraulic design and drainfield layout, the county reviews it, and a permit is issued before work starts. A licensed installer has to attend the final inspection, along with the engineer and as-built drawings if the system was engineered.
Why groundwater matters so much here
Montana rules call for four feet of natural, undisturbed soil between the bottom of the drainfield and a limiting layer such as seasonal groundwater. In the Flathead, groundwater monitoring in spring, when levels peak, takes the place of the old perc test in deciding where a field can go. On a lot with shallow groundwater, that can mean a different location, a pressure-dosed design, an elevated sand mound or a system with added treatment.
Protect the new field
Keep vehicles, sheds and snow piles from the plow off it, aim downspouts and sump pump discharge away from it, and stay on a regular pumping schedule so solids never reach it again.
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
Can part of a drainfield be repaired instead of replaced?
Sometimes. A crushed line or a problem in one zone can be fixed. A field that's sealed off throughout usually needs to be replaced.
Why might my replacement need a mound or a pump?
If spring groundwater or shallow soil leaves less than the required separation, the design may need to raise the field or use pressure distribution to fit the site.
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.