Massachusetts · 310 CMR 15.000
Septic system requirements in Massachusetts
Tank sizes, drainfield rules, setbacks, permits, and real costs — pulled from Massachusetts's own code rather than a national average.
- 3-bedroom tank
- 1,500 gal
- Design flow
- 110 gpd/BR
- Typical install
- $18,000–$45,000
- Permit fee
- $300–$1,500
- Well setback
- 100 ft
- Permitted by
- County / local
Septic tank sizes required in Massachusetts
Massachusetts sizes systems on a design flow of 110 gallons per day per bedroom, with every dwelling rated for at least 2 bedrooms. The tank must meet both the bedroom table below and a 2× daily-flow detention requirement — whichever produces the larger number governs.
| Bedrooms | Design flow | Code minimum | Recommended |
|---|---|---|---|
| 1 bedroom | 220 gpd | 1,500 gal | 1,500 gal |
| 2 bedrooms | 220 gpd | 1,500 gal | 1,500 gal |
| 3 bedrooms | 330 gpd | 1,500 gal | 1,500 gal |
| 4 bedrooms | 440 gpd | 1,500 gal | 1,500 gal |
| 5 bedrooms | 550 gpd | 1,750 gal | 2,000 gal |
| 6 bedrooms | 660 gpd | 2,000 gal | 2,000 gal |
Source: 310 CMR 15.000. The recommended column rounds the governing requirement up to a tank size manufacturers actually stock.Run your own numbers →
Drainfield size and cost by soil type
For a three-bedroom home in Massachusetts at 330 gpd. This single table explains most of the variation between quotes — the area scales inversely with how fast your soil accepts water, and the drainfield is the largest line item in the job.
| Soil | Loading rate | Absorption area | With reserve | Typical total install |
|---|---|---|---|---|
| Medium sand | 0.8 gpd/ft² | 413 ft² | 826 ft² | $13,100 |
| Sandy loam | 0.5 gpd/ft² | 660 ft² | 1,320 ft² | $15,700 |
| Loam | 0.4 gpd/ft² | 825 ft² | 1,650 ft² | $17,400 |
| Silt loam | 0.3 gpd/ft² | 1,100 ft² | 2,200 ft² | $20,400 |
| Clay loam | 0.2 gpd/ft² | 1,650 ft² | 3,300 ft² | $26,200 |
Estimates use Massachusetts's cost index of 1.18× the national average. Build a line-item estimate →
Permits and who issues them
Local Boards of Health issue Disposal Works Construction Permits under Title 5 (310 CMR 15.000); MassDEP oversees and handles variances.
| Permit required | Yes |
|---|---|
| Typical fee | $300 – $1,500 |
| Soil evaluation | Required before permit |
| Licensed installer | Required |
| Turnaround | 4–10 weeks |
| Ongoing inspection | Title 5 inspection required within 2 years before most property transfers |
| Reserve area | 100% replacement area required |
Minimum setback distances
Measured horizontally from the drainfield unless noted. Local rules are frequently stricter, and on a small lot these numbers — not the soil — often decide the layout.
| Private water well | 100 ft |
|---|---|
| Well (septic tank) | 50 ft |
| Property line | 10 ft |
| Surface water | 100 ft |
| Building foundation | 10 ft |
Regulatory contact
Massachusetts Department of Environmental Protection — Title 5
www.mass.gov · 617-292-5500
What makes septic hard in Massachusetts
Title 5 is among the strictest onsite codes in the country, and the mandatory inspection at property transfer means failures surface at the worst possible moment.
Cape Cod and the Islands are under nitrogen-loading watershed permits that increasingly require enhanced treatment, not just a conventional system.
Small older lots frequently cannot meet current setbacks, forcing variance applications.
Ledge is common across central and western Massachusetts.
Things that catch people out
- The tank minimum is 1,500 gallons — 50% higher than most states — and must also be at least 200% of design flow.
- A Title 5 inspection is valid for two years and is required before almost any sale. A failed system must be upgraded, typically within two years.
- A garbage grinder requires a two-compartment tank or two tanks in series on top of the 1,500 gallon floor.
Massachusetts septic questions
What size septic tank do I need in Massachusetts?
A three-bedroom home in Massachusetts requires a minimum 1,500 gallon tank under 310 CMR 15.000. Design flow is 110 gallons per day per bedroom, and the tank must also hold 2 times daily flow, so the practical recommendation is 1,500 gallons.
Do I need a permit for a septic system in Massachusetts?
Yes. Local Boards of Health issue Disposal Works Construction Permits under Title 5 (310 CMR 15.000); MassDEP oversees and handles variances. Fees typically run $300 to $1,500, with a turnaround of about 4–10 weeks. A soil evaluation or percolation test is required before a permit is issued.
How much does a septic system cost in Massachusetts?
A conventional system for a three-bedroom home typically runs $18,000 to $45,000 installed. Soil quality moves this more than anything else — on tight clay requiring a mound, budget two to three times the low end.
How far must a Massachusetts drainfield be from a well?
100 feet from a private water well, with the septic tank itself allowed at 50 feet. Local rules can be stricter.
Sources
Every figure on this page traces to one of these documents.
- 310 CMR 15.000 — Title 5 — The State Environmental Code · verified 2026-09-18
- 310 CMR 15.203 — Design flow and system sizing · verified 2026-09-18