Kentucky · 902 KAR 10:085
The Kentucky Department for Public Health writes the regulation 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.
Karst limestone across much of central Kentucky — sinkholes, caves and rapid groundwater movement. Eastern Kentucky has steep slopes and thin soils over shale and sandstone. The western part of the state has better agricultural soils.
Conventional trenches where soil depth allows. Karst areas face strict groundwater protection requirements. Steep eastern slopes push designs toward contour trenches and, where nothing works, holding tanks.
| 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 |
Kentucky certifies installers and site evaluators. In karst areas, proximity to sinkholes and losing streams can disqualify a site outright regardless of percolation rate.
The state sets a floor. These Kentucky counties are where the largest septic populations sit, and where local requirements most often exceed it.
| County | What makes it different |
|---|---|
| Jefferson | Louisville metro fringe |
| Fayette | Lexington; bluegrass karst |
| Warren | Bowling Green; heavy karst with cave systems |
| Hardin | Growth around Elizabethtown |
| Pike | Eastern mountains, steep slopes and thin soil |
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 for conventional residential systems. Use the pump schedule calculator to work out the interval for your tank size and household.
Regional labour and permit costs in Kentucky run about 90% of the national baseline. Here is what typical installations land at for a three-bedroom home:
| System type | Typical installed cost in Kentucky | When it applies |
|---|---|---|
| Conventional gravity | $8,100 – $14,400 | Good soil, adequate depth to water |
| Chamber system | $8,900 – $16,600 | Alternative to gravel trenches |
| Mound system | $15,400 – $30,200 | Shallow water table or thin soil |
| Aerobic treatment | $13,000 – $25,900 | Clay soil or small lots |
| Tank pump-out (service) | $290 – $580 | 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 902 KAR 10:085, Kentucky On-Site Sewage Disposal Systems. County and health district rules routinely exceed them, code text changes, and only Kentucky DPH — Onsite Sewage Program or your local health department can confirm what applies to your parcel.
Send your sizing numbers to installers who work under Kentucky rules every day.