The Governing Framework

New Hampshire regulates subsurface sewage disposal under:

• Env-Wq 1000 — New Hampshire subsurface rules. Codified under the NH Code of Administrative Rules, Chapter Env-Wq (Water Quality).
• NHDES (New Hampshire Department of Environmental Services) — state-level administrator. The Subsurface Systems Bureau within NHDES handles onsite wastewater.
• Approved designers and installers — NH requires specific state approval to design and install subsurface systems. Not every plumber or excavator qualifies.
• Local coordination — site plan, zoning, and shoreland protections at the municipal level layer on top of NHDES rules.

Design Flow and Tank Capacity

New Hampshire uses bedroom-based design flow for residential systems, with commercial and institutional systems sized by specific flow calculations per Env-Wq 1000. Typical residential sizing:

Your NH-approved designer will specify exact tank capacity and design flow based on Env-Wq 1000 tables and your specific site. Polyethylene tanks meeting IAPMO/NSF listings and NH construction requirements are accepted.

The 75-Foot Setback Radius — Systems Up to 750 gpd

One of the cleaner design envelopes in NH: for subsurface systems with design flow up to 750 gpd (which covers most single-family residential up to 5 BR), a 75-foot setback radius defines the minimum buffer from the system to various sensitive features. Larger systems have expanded setback requirements per Env-Wq 1000 tables.

This setback envelope means a typical 5-BR single-family residence needs roughly 75 feet of unobstructed buffer around the system footprint from wells, surface water, foundations, property lines (exact distances vary by feature). Plan parcel selection and house siting accordingly — small parcels may not physically accommodate setback compliance for larger residences.

Permit Process

1. Hire an NH-approved designer. NHDES maintains an approved designer list. Only approved designers can submit subsurface system plans to NHDES.
2. Site evaluation. Test pits, soil profile, percolation per Env-Wq 1000 methodology.
3. Design submission to NHDES. Application with plans, soil data, flow calculations.
4. NHDES review and approval. State-level approval, different from many states where permits are purely local.
5. Local coordination. Site plan, zoning, shoreland protection approvals at municipal level.
6. NH-approved installer construction.
7. Inspection before cover. NHDES-approved inspector.
8. Operational approval. System commissioning and approval to use.

Regional Considerations

• Seacoast (Rockingham, Strafford): Highest population density. Mix of municipal sewer (Portsmouth, Dover) and dense-septic suburbia. Coastal parcels face saltwater table and shoreland zoning. Great Bay watershed nitrogen concerns.
• Merrimack Valley (Hillsborough, Merrimack County corridor): Manchester and Nashua metro. Largely sewered; septic on exurban fringe.
• Lakes Region (Belknap, Carroll): Lake Winnipesaukee and neighbors. Shoreland protections and watershed phosphorus concerns layer on Env-Wq 1000 baseline.
• White Mountains (Coos, northern Grafton): Rocky bedrock, shallow soils, short construction season. Alternative systems common.
• Connecticut River Valley (western NH): Varied alluvial and glacial soils.
• Monadnock Region (Cheshire, Sullivan): Rural-estate and small-town parcels. Standard systems typical.

Alternative and Innovative Systems

Env-Wq 1000 provides for alternative system technologies where site constraints preclude conventional septic + absorption field. Alternative options include:

• Pressure distribution
• Mound systems (for high water table or shallow soil)
• Sand filters and peat biofilters
• Aerobic treatment units (ATUs)
• Cluster systems for small subdivisions

Alternative systems require additional engineering review, often ongoing O&M contracts, and higher upfront cost. Plan for $25,000–$65,000+ for I/A vs $12,000–$22,000 for conventional.

Frequently Asked Questions

Can I design my own system in New Hampshire?

No. NH requires a state-approved designer for subsurface system plans. NHDES maintains the approved designer list. Homeowner-designed systems are not accepted.

Why does NHDES review my permit instead of my town?

New Hampshire uses state-level NHDES review for subsurface systems, different from many states that delegate permits to local or county health. Municipal coordination (zoning, site plan, shoreland) still happens at town level but the subsurface permit itself is an NHDES document.

What are shoreland protections?

NH Shoreland Water Quality Protection Act imposes additional restrictions on land within 250 feet of designated waterbodies. Septic systems in shoreland have additional setbacks and sometimes nitrogen-reduction requirements on top of baseline Env-Wq 1000. Verify if your parcel falls within shoreland protection.

What happened at the October 2025 rulemaking hearing?

NHDES held a public hearing on proposed Env-Wq 1000 revisions on October 24, 2025. The revisions update design methodology, alternative system provisions, and other technical standards. Adoption status and effective date should be verified at NHDES rulemaking portal. Projects in design should confirm which rule version applies.

Are polyethylene tanks accepted in New Hampshire?

Yes, when meeting IAPMO/NSF listings and NH construction requirements. Major OEM rotomolded polyethylene tanks from Norwesco, Snyder, and others are commonly approved. Your NH-approved designer will specify accepted models for your project.

Source Citations

• NHDES Subsurface Systems Bureau
• NHDES Rulemaking Portal
• Env-Wq 1000 (NH General Court rules portal)
• NHDES Subsurface Forms and Publications
• NHDES Shoreland Water Quality Protection Program

Agricultural Tank Regulations — NHDA & NHDES

The New Hampshire Department of Agriculture, Markets & Food (NHDA) and the New Hampshire Department of Environmental Services (NHDES) share agricultural-tank oversight under Revised Statutes Annotated (RSA) and New Hampshire Code of Administrative Rules:

• N.H. Admin. Rules Pes 301–1000 — NHDA Pesticide Control Division rules; applicator licensing, restricted-use pesticide (RUP) recordkeeping, bulk storage and repackaging, dealer licensing.
• RSA 430 — NH Pesticide Control Act and Fertilizer/Lime statutes (statutory authority).
• N.H. Admin. Rules Agr 1400 — Commercial Fertilizer registration, tonnage reporting, and labeling.
• N.H. Admin. Rules Env-Wq 1800–1900 — NHDES animal-waste and agricultural nonpoint-source management.

New Hampshire agriculture is dairy and maple in the North Country and Upper Valley (Coos, Grafton, Cheshire counties), apple and vegetable orchards and truck farms in the Merrimack Valley (Hillsborough, Merrimack, Rockingham), greenhouse/nursery operations statewide, and commercial blueberry on Monadnock-region uplands. Ag retailers with bulk liquid fertilizer and pesticide storage build secondary containment to 110% of the largest tank with impermeable liners, rinsate recovery, and NHDES-aligned spill plans. The state's tight lake-water-quality protections (Lakes Management and Protection Program) and the Great Bay nitrogen TMDL drive additional scrutiny on nutrient-bearing tank installations in the Seacoast and Lakes Region.

Oil & Gas Storage — Petroleum UST/AST Path

New Hampshire has no oil or gas production; there is no upstream operator framework. Petroleum storage is governed through a two-rule UST/AST system with a distinctively low AST threshold:

• Env-Or 400 — NHDES Underground Storage Facilities: design, installation, corrosion protection, spill/overfill prevention, release detection, operator training, closure, financial responsibility.
• Env-Or 300 — NHDES Aboveground Storage Facilities; notably, New Hampshire regulates AST facilities at a 660-gallon single-tank or 1,320-gallon aggregate threshold, significantly lower than the federal SPCC 1,320-gallon oil aggregate trigger, capturing many small commercial heating-oil and fleet-fueling sites that federal SPCC would exempt.
• RSA 146-A (Oil Discharge and Disposal Cleanup Fund) — statutory authority for the Oil Discharge and Disposal Cleanup Fund, which reimburses eligible corrective-action costs for registered tanks in good standing.
• RSA 146-C / 146-D / 146-G — petroleum fund statutes covering Oil Discharge, Motor Oil Discharge, and Gasoline Tank Fund programs.

The 660-gallon AST threshold is the headline difference between New Hampshire and neighboring states: a single 500-gallon heating-oil tank at a small commercial property avoids Env-Or 300 registration, but a single 1,000-gallon AST triggers state registration, secondary containment, overfill protection, and release-detection requirements. Offshore federal OCS leasing is outside state jurisdiction.

Septic System Sizing — Env-Wq 1000

NHDES regulates subdivision and individual sewage disposal under Env-Wq 1000. Residential design flow is 150 gpd per bedroom:

NHDES Subsurface Systems Bureau administers the statewide program; licensed Designers develop site-specific plans and licensed Installers construct. Soils run from glacial till across the White Mountains and Monadnock highlands (shallow bedrock, seasonal high water tables, and tight clay B-horizons requiring mound or pressure-dosed systems), stratified drift in the Merrimack and Connecticut River valleys (better perc), and sandy coastal plain near the Seacoast. Advanced-treatment systems (Presby, Eljen, Clean Solution, Orenco AdvanTex) are common on tight-soil parcels and increasingly in Great Bay watershed towns where NHDES applies tightened nitrogen-reduction requirements to protect the estuary. Shoreland Water Quality Protection Act (RSA 483-B) imposes additional setback and system-design constraints within 250 ft of public waters.

Chemical Storage Secondary Containment & Spill Reporting

Federal SPCC (40 CFR 112) applies at 1,320 gallons aggregate aboveground oil; New Hampshire tightens the framework through:

• Env-Or 300 — state AST rule at 660-gallon single-tank threshold capturing many sites below federal SPCC trigger.
• Env-Or 600 Hazardous Waste — RCRA generator requirements, accumulation limits, container management.
• NHDES 24-hour Spill Line — immediate reporting for petroleum and hazardous-substance releases.
• RSA 146-A — statutory strict liability for oil discharge response and cleanup.
• NFPA 30 / 30A — State Fire Marshal and local fire-code enforcement for flammable and combustible liquids.

Report federal-RQ releases to the National Response Center at 1-800-424-8802; report state releases immediately to NHDES. New Hampshire Oil Discharge and Disposal Cleanup Fund participation is contingent on registration and compliance status at time of discharge.

Permit Pathways at a Glance

• Residential septic: NHDES Subsurface Systems Bureau under Env-Wq 1000 (Designer + Installer licenses required).
• Shoreland Protection: NHDES under RSA 483-B for work within 250 ft of public waters.
• Fertilizer registration: NHDA under Agr 1400.
• Pesticide applicator license: NHDA Pesticide Control Division under Pes 301–1000.
• Petroleum UST: NHDES under Env-Or 400 with Oil Discharge/Disposal Cleanup Fund participation.
• Petroleum AST >660 gal: NHDES under Env-Or 300.
• SPCC > 1,320 gal oil aggregate: Federal SPCC plan; NHDES spill reporting; Env-Or 300 also applies.
• Flammable/combustible storage: State Fire Marshal / local fire under NFPA 30/30A.

Current fees change; verify with NHDES and NHDA before budgeting.

More New Hampshire FAQs

Why is New Hampshire's AST threshold 660 gallons?

Env-Or 300 sets the 660-gallon single-tank threshold for state AST registration to capture small commercial heating-oil and fleet-fueling sites below the federal SPCC 1,320-gallon aggregate trigger. New Hampshire's combination of dense residential development near surface water and historically severe heating-oil groundwater-contamination incidents drove the state to a lower threshold than most neighbors. Owners of single tanks 660 gallons and above must register, provide secondary containment, and follow state AST rules regardless of federal SPCC status.

Who issues my septic permit?

NHDES Subsurface Systems Bureau issues the statewide Approval for Construction and Approval for Operation for individual and subdivision systems under Env-Wq 1000. A state-licensed Designer prepares plans; a state-licensed Installer constructs. Some towns impose local setback or design overlays on top of the state approval.

Does the Shoreland Protection Act prohibit tanks near the lake?

RSA 483-B Shoreland Water Quality Protection Act does not outright prohibit tanks within the 250-ft protected shoreland but imposes setbacks, design constraints, and impervious-surface limits. Fuel-oil tanks, septic tanks, and chemical-storage tanks within the 250-ft zone require NHDES shoreland permit review in addition to any underlying UST/AST or septic approval.

What is the Oil Discharge and Disposal Cleanup Fund and does it pay for my spill?

RSA 146-A establishes the Oil Discharge and Disposal Cleanup Fund, financed by petroleum fees, that reimburses eligible corrective-action costs for registered tanks in good standing. Eligibility, caps, and deductibles are set by NHDES; confirm current parameters with the NHDES Oil Pollution Control Section before relying on fund coverage. Unregistered tanks or tanks out of compliance at the time of discharge may be ineligible.

Is the Great Bay nitrogen TMDL enforced on my septic project?

NHDES applies tightened nitrogen-reduction expectations within Great Bay estuary watersheds (Piscataqua River basin towns in Rockingham and Strafford counties). New construction and significant upgrades in sensitive sub-watersheds may require advanced nitrogen-reducing septic technology. Confirm watershed status during site evaluation.

Does NH regulate heating-oil tanks at a single-family home?

Residential heating-oil tanks at 1- to 4-unit dwellings have partial exemptions but still face NFPA 31 / 30 installation standards, local fire-code oversight, and strict Spill Act liability on any release. Tanks 660 gallons and above may cross the Env-Or 300 AST threshold even at residential sites. Insurance-driven tank-integrity programs are common.