Utah · Utah Administrative Code R317-4
The Utah Division of Water Quality writes the rule and local health departments issue permits.
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.
Valley alluvium that can be very coarse and fast-draining, lake bed clays around the Great Salt Lake, and shallow rock in the mountain valleys. Groundwater depth varies sharply within short distances.
Conventional trenches and deep wall trenches. Where groundwater is shallow or soil is excessively permeable, alternative systems with enhanced treatment are required.
| 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 |
Utah requires a percolation test and a soil log with groundwater determination, and the local health department issues the permit. Groundwater separation requirements are strict given reliance on valley aquifers.
The state sets a floor. These Utah counties are where the largest septic populations sit, and where local requirements most often exceed it.
| County | What makes it different |
|---|---|
| Utah County | Rapid growth; variable alluvial soils |
| Salt Lake | Mostly sewered, on-site systems in canyon and fringe areas |
| Washington County | St George growth on desert soils |
| Wasatch | Heber valley; growth with groundwater concerns |
| Summit | Park City area, mountain terrain |
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.
Alternative systems carry maintenance requirements under permit. Use the pump schedule calculator to work out the interval for your tank size and household.
Regional labour and permit costs in Utah run about 102% of the national baseline. Here is what typical installations land at for a three-bedroom home:
| System type | Typical installed cost in Utah | When it applies |
|---|---|---|
| Conventional gravity | $9,200 – $16,300 | Good soil, adequate depth to water |
| Chamber system | $10,100 – $18,700 | Alternative to gravel trenches |
| Mound system | $17,500 – $34,200 | Shallow water table or thin soil |
| Aerobic treatment | $14,700 – $29,300 | Clay soil or small lots |
| Tank pump-out (service) | $330 – $660 | 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 Utah Administrative Code R317-4, Onsite Wastewater Systems. County and health district rules routinely exceed them, code text changes, and only Utah DEQ — Division of Water Quality, Onsite Program or your local health department can confirm what applies to your parcel.
Send your sizing numbers to installers who work under Utah rules every day.