Maryland · COMAR 26.04.02
The Maryland Department of the Environment sets standards and county 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.
Coastal plain sands on the Eastern Shore and southern Maryland, piedmont clay through the centre, and shallow rock in the west. Chesapeake Bay nitrogen loading dominates the regulatory conversation.
Conventional trenches and sand mounds. Best Available Technology for nitrogen removal is required in the Critical Area and in other designated zones — a defining feature of Maryland's program.
| 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 |
Maryland requires Best Available Technology nitrogen-reducing systems for new construction in the Chesapeake Bay Critical Area and in certain other circumstances. The Bay Restoration Fund has historically offered grants toward BAT upgrades.
The state sets a floor. These Maryland counties are where the largest septic populations sit, and where local requirements most often exceed it.
| County | What makes it different |
|---|---|
| Anne Arundel | Extensive Critical Area shoreline with BAT requirements |
| Baltimore County | Large septic population in the north |
| Harford | Suburban growth on piedmont soils |
| Calvert | Coastal plain with Critical Area coverage |
| Queen Anne's | Eastern Shore, sandy soils and Bay proximity |
| St. Mary's | Southern Maryland, extensive on-site use |
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.
BAT units require an operation and maintenance contract with reporting. Use the pump schedule calculator to work out the interval for your tank size and household.
Regional labour and permit costs in Maryland run about 118% of the national baseline. Here is what typical installations land at for a three-bedroom home:
| System type | Typical installed cost in Maryland | When it applies |
|---|---|---|
| Conventional gravity | $10,600 – $18,900 | Good soil, adequate depth to water |
| Chamber system | $11,700 – $21,700 | Alternative to gravel trenches |
| Mound system | $20,100 – $39,700 | Shallow water table or thin soil |
| Aerobic treatment | $17,000 – $34,000 | Clay soil or small lots |
| Tank pump-out (service) | $380 – $770 | 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 COMAR 26.04.02, Onsite Sewage Disposal Systems. County and health district rules routinely exceed them, code text changes, and only Maryland DOE — Onsite Systems Division or your local health department can confirm what applies to your parcel.
Send your sizing numbers to installers who work under Maryland rules every day.