North Dakota · North Dakota Administrative Code Article 33.1-03
North Dakota DEQ sets standards; local health units and district health departments handle permitting.
Minimum tank
One to three bedroom dwelling.
Design flow
Held two days for settling.
Cost index
Regional labour and permits.
Sets the design flow and the legal minimum.
Code sizes on bedrooms, not people.
Used to size the matching drainfield. Unsure? Sandy loam is the common default.
Glacial till with heavy clay across much of the state, lake plain clay in the Red River valley that is among the tightest soil in the country, and sandier ground in the west. Frost depth is severe.
Conventional trenches where soil permits, but the Red River valley clay frequently rules them out. Mounds and at-grade systems are common, and holding tanks appear on sites where nothing else is feasible.
| Dwelling | Design flow | Minimum tank | With disposal |
|---|---|---|---|
| 1 bedroom | 300 gpd | 1,000 gal | 1,250 gal |
| 2 bedrooms | 300 gpd | 1,000 gal | 1,250 gal |
| 3 bedrooms | 450 gpd | 1,000 gal | 1,250 gal |
| 4 bedrooms | 600 gpd | 1,250 gal | 1,500 gal |
| 5 bedrooms | 750 gpd | 1,500 gal | 1,750 gal |
Local health unit requirements govern the detail. Frost protection and deep burial are practical design considerations across the state.
The state sets a floor. These North Dakota counties are where the largest septic populations sit, and where local requirements most often exceed it.
| County | What makes it different |
|---|---|
| Cass | Fargo area; Red River valley clay is extremely tight |
| Burleigh | Bismarck; better soils on the Missouri terraces |
| Grand Forks | Lake plain clay |
| Ward | Minot area |
| Williams | Western oil country, sandier ground |
A three-bedroom home at 150 gallons per bedroom produces 450 gallons per day of design flow. On sandy loam that needs roughly 750 square feet of absorption area. On clay loam it rises to about 2,250 square feet, and on clay a conventional field is usually not permitted at all. Run your own soil class through the drainfield calculator.
No statewide mandated interval; cold soil slows digestion so intervals tend to shorten. Use the pump schedule calculator to work out the interval for your tank size and household.
Regional labour and permit costs in North Dakota run about 96% of the national baseline. Here is what typical installations land at for a three-bedroom home:
| System type | Typical installed cost in North Dakota | When it applies |
|---|---|---|
| Conventional gravity | $8,600 – $15,400 | Good soil, adequate depth to water |
| Chamber system | $9,500 – $17,700 | Alternative to gravel trenches |
| Mound system | $16,300 – $32,300 | Shallow water table or thin soil |
| Aerobic treatment | $13,800 – $27,700 | Clay soil or small lots |
| Tank pump-out (service) | $310 – $620 | Every 3–5 years |
Replacing an existing system costs more than these figures — old-system removal and re-permitting add to every line. The replacement cost calculator covers that case, and the cost estimator adjusts all of the above for your bedroom count and soil.
Verify before you build. The figures above are state minimums compiled for planning, drawn from North Dakota Administrative Code Article 33.1-03, Onsite Wastewater Treatment. County and health district rules routinely exceed them, code text changes, and only North Dakota DEQ — Onsite Wastewater or your local health department can confirm what applies to your parcel.
Send your sizing numbers to installers who work under North Dakota rules every day.