Tennessee · Tennessee Rules Chapter 0400-48-01
TDEC administers the program in most counties; a few counties operate their own delegated programs.
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.
Karst limestone through middle Tennessee with sinkholes and rapid groundwater movement, shale and sandstone on the Cumberland Plateau, and the west Tennessee coastal plain with loess and sandy soils.
Conventional trenches where soil depth allows. Low pressure pipe and drip distribution are used in shallow soils over rock. Middle Tennessee karst areas face significant restrictions.
| 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 |
TDEC issues subsurface sewage disposal permits and certifies installers. Soil maps and field evaluation determine suitability, and sites over shallow limestone can fail on depth to rock even with acceptable percolation.
The state sets a floor. These Tennessee counties are where the largest septic populations sit, and where local requirements most often exceed it.
| County | What makes it different |
|---|---|
| Rutherford | Fast growth on shallow limestone |
| Williamson | High-value development with karst constraints |
| Wilson | Rapid growth east of Nashville |
| Knox | Knoxville area; ridge and valley terrain |
| Sumner | Growth north of Nashville, shallow rock |
| Montgomery | Clarksville area with mixed soils |
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 residential interval. Use the pump schedule calculator to work out the interval for your tank size and household.
Regional labour and permit costs in Tennessee run about 92% of the national baseline. Here is what typical installations land at for a three-bedroom home:
| System type | Typical installed cost in Tennessee | When it applies |
|---|---|---|
| Conventional gravity | $8,300 – $14,700 | Good soil, adequate depth to water |
| Chamber system | $9,100 – $16,900 | Alternative to gravel trenches |
| Mound system | $15,800 – $30,900 | Shallow water table or thin soil |
| Aerobic treatment | $13,300 – $26,500 | Clay soil or small lots |
| Tank pump-out (service) | $290 – $600 | 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 Tennessee Rules Chapter 0400-48-01, Regulations to Govern Subsurface Sewage Disposal Systems. County and health district rules routinely exceed them, code text changes, and only Tennessee TDEC — Subsurface Sewage Disposal Systems or your local health department can confirm what applies to your parcel.
Send your sizing numbers to installers who work under Tennessee rules every day.