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New Septic System Design and Installation in Massachusetts and New Hampshire
A new system, whether for a house lot, an addition or a complete replacement, runs in a set order: test the soil, draw the plan, get it approved, build it, and have it inspected before anything is covered. Massachusetts runs that through your Board of Health; New Hampshire runs it through NHDES. Call (978) 486-7980 or send the form. A person reads every request and replies with what happens next.
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- Installer permits checked first
- State rules explained
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From soil test to sign-off
The order a new system follows
Soil first. The design depends on what the ground can absorb and how high the groundwater rises, so testing comes before drawing. In Massachusetts, percolation tests are done in the presence of the Board of Health or other Approving Authority (310 CMR 15.104).
A qualified designer. Massachusetts designs come from a registered sanitarian or a Massachusetts-registered professional engineer (310 CMR 15.002). New Hampshire plans must be prepared and signed by someone holding an NHDES permit for the work (RSA 485-A:35).
Approval before construction. Neither state lets construction start on an unapproved plan: Massachusetts requires a Disposal System Construction Permit (310 CMR 15.020), and New Hampshire requires NHDES approval of the plans and specifications (RSA 485-A:32).
Inspected before it's covered. In both states the open work is inspected before backfilling, and the system can't go into use until the final sign-off is issued.
Massachusetts
A new septic system in Massachusetts
Soil evaluators. Soil evaluation is done by an approved Soil Evaluator who has passed NEIWPCC's training course, classroom tests and field exams, and a soil evaluator may not act for both the Board of Health and the owner on the same site (MassDEP: inspectors and soil evaluators).
Two permits for new homes. New construction needs permits from the Board of Health and from the building department, separately, and MassDEP reviews only after the Board of Health's final decision (MassDEP: new construction). Your Board of Health must approve the design and the installation (MassDEP) and may have rules stricter than Title 5 (Title 5 FAQ).
Building and sign-off. The work must be finished, with a Certificate of Compliance, within three years of approval or the permit expires unless extended (310 CMR 15.020). Nothing may be backfilled before the Approving Authority's final inspection, the designer inspects before and during backfilling, and within 30 days of the final inspection the installer and designer certify that the system complies. No sewage may go into the system before the Certificate of Compliance issues, and on new construction you can't apply for a Certificate of Occupancy until it does (310 CMR 15.021).
Sewer nearby. A new system may not be built where connecting to sewer is feasible, subject to listed exceptions (310 CMR 15.004).
Accessory dwelling units. Under MassDEP guidance of April 7, 2025, an ADU that increases the design flow is New Construction, is figured at 110 gallons per day per bedroom; where the ADU shares the house's existing system, a multi-compartment tank or two tanks in series is generally required; adding ADU bedrooms to an existing system means meeting New Construction standards for the total bedroom count (MassDEP ADU guidance).
New Hampshire
A new septic system in New Hampshire
Two NHDES approvals. Before a system is used it needs both an Approval for Construction and an Approval for Operation (NHDES septic systems). It must be built in strict accordance with the approved plans and inspected before it is covered; NHDES inspects within seven business days of notice (RSA 485-A:29). Permitted designers, installers and surveyors file through NHDES's ePermit system (NHDES ePermit guidelines).
The application. The state fee is $450 per waste disposal system application, as of November 2026, and NHDES acts within 15 working days of receiving the plans and the fee (RSA 485-A:30 and 485-A:31). An approval for construction expires four years after it is issued if no inspection is requested (Env-Wq 1004.13).
Installers. Anyone in the business of installing septic systems needs an NHDES installer's permit, renewed every two years with continuing education (RSA 485-A:36, NHDES designers and installers).
Additions and camps. Before adding load to a system, for example by adding bedrooms, the owner must apply to NHDES and show the system meets the state's requirements or the town's minimum standards, whichever is stricter, or submit a new design (RSA 485-A:38). Converting a seasonal home to full-time occupancy also needs an approval for construction first (NHDES).
Near the water. Septic systems must sit 75 to 125 feet from the reference line of ponds, lakes, estuaries and the ocean depending on the soil, and 75 feet from rivers (RSA 483-B:9). Projects in the protected shoreland may also need an NHDES shoreland permit (NHDES protected shoreland).
New Hampshire septic rules and the towns we cover.
Last verified November 2026. Fees, restrictions and deadlines on this page are due for re-checking by November 2027. New England Septic Pros is a referral service. We don't design, install or file permits.
FAQ
New septic system questions
Who has to witness a perc test in Massachusetts?
Title 5 says all percolation testing must be done in the presence of the Approving Authority, usually your Board of Health. The test itself is done by a qualified person such as a Massachusetts professional engineer, a registered sanitarian or a MassDEP-approved soil evaluator.
How long does NHDES take to review a septic design?
State law gives NHDES 15 working days from receiving the plans and the fee to act. If it doesn't ask for more information in that time, the plans are deemed approved.
Can I put in a new septic system if sewer is in the street?
In Massachusetts, generally not: Title 5 bars building a new system, or upgrading or expanding an existing one, where connecting to sewer is feasible, with some listed exceptions. Ask your Board of Health how it applies to your lot.
Does adding an accessory apartment affect my septic system?
Often. In Massachusetts, MassDEP's ADU guidance treats an ADU that raises the design flow as New Construction under Title 5. In New Hampshire, adding load to a system requires NHDES approval first.
What does it cost me to use New England Septic Pros?
Nothing. The request and the referral are free; the contractor prices the work.
Town guides
Local rules for new septic systems by town
Each town page covers who permits septic work there, the town's own septic rules and where public sewer reaches. Towns with a local guide so far: Greater Lowell, MA (Lowell, Chelmsford, Dracut, Tewksbury, Billerica, Westford, Tyngsborough and Pepperell), Andover, Lawrence & Haverhill, MA (Methuen, Lawrence, Andover, North Andover and Haverhill), Woburn, Reading & Melrose, MA (Woburn, Lexington, Burlington, Wilmington, North Reading, Reading, Wakefield, Melrose, Stoneham and Winchester), Nashua Region, NH (Nashua, Hudson and Merrimack), Salem, Derry & Londonderry, NH (Pelham, Salem, Windham, Derry and Londonderry), Manchester & Bedford, NH (Manchester and Bedford) and Portsmouth, Dover & Rochester, NH (Portsmouth, Dover and Rochester). We add towns across New England as we can cover them properly.
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