Septic System Permitting Process

Applicant:  A permit is required to install and operate a sewage treatment system (septic system) in Flathead County.  Apply at Environmental Health.  It is extremely important to provide the property’s legal description.  Newly created property can get a physical address  from GIS Address Improvement at

Click here to view the septic system application process.

Site Review vs. Site Evaluation:

 Before a permit is issued, your property will be evaluated to determine if installing a septic system will comply with County and State regulations.

  1. PREAPPROVED: An EVALUATION may have been done when your property was created*   or prior to you owning the property. If this is the case and you are not relocating the septic system, a “SITE REVIEW” is required with a fee of $100.

  2. SITE REVIEW process: The applicant or their representative must physically stake and label 1) the 4 corners (~ 40’ x 100’) of the approved drainfield site, 2)  the well location, and 3) the proposed house site.  Contact Environmental Health when the staking is complete.

  3. NEVER APPROVED OR OLD APPROVAL: All other property must have a SITE EVALUATION which usually requires a soils determination (test hole), possible groundwater monitoring, and non-degradation analysis conducted to comply with the Montana Clean Water Act to protect surface and ground water.  The Site Evaluation fee is $225 and the Non-degradation fee is $200.

Department:  The applicant will receive a “Site Evaluation and Design Report” from Environmental Health after the Site Review or Site Evaluation has been completed which they  must provide to a designer (or engineer) certified by this office.

Applicant:  A completed Hydraulic Design (Pump or Siphon) and Detailed Drainfield Layout (i.e., site plan) must be prepared by the certified designer or professional engineer and returned to Environmental Health.

Department:  Upon approval of the design, a permit will be issued.

The permit fee will be dependent upon Class of System permitted.

  • Class 1 System– an individual or single family sewage treatment system–$300.00

  • Class 2 System- a shared, multi user or public sewage treatment system with design flow of less than 1000 gallons per day–$415.00

  • Class 3 System– a shared, multi-user or public sewage treatment systems with design flow of 1000 or more gallons per day–$475.00 +$0.15/gal over the first 1000 gallons.


In Montana when property is subdivided into lots less than 20 acres, an environmental review is required through the Montana Department of Environmental Quality (DEQ).  A consultant does the environmental work such as determining soil type, if groundwater quality will be excessively degraded (Non-degradation analysis), topography, limiting factors, storm water drainage, etc.   Once the State reviews and approves the environmental work a Certificate of Subdivision Approval (COSA) is issued describing specific requirements for the property and showing a site design where the sewage treatment system and well must be located.  This is different from Planning and Zoning or Homeowner’s Association rules.

  • New landowners should receive this documentation when they purchase the property.  If you have not received this documentation, contact your realtor or this office.

  • If the landowner wishes to alter the requirements stated in the COSA, they must contact a consultant to re-write the approval.