SAS Inside a Zone I Public Water Supply: The Title 5 Prohibition That Has No Variance

By The Complos Team. Last reviewed 2026-05-14.

TL;DR. Inspector and designer guide to 310 CMR 15.211 and the Zone I prohibition on soil absorption systems near public water supply wells. Map disagreements, redesign paths, and why MassDEP variances do not apply.

The property is a 1968 cottage in Carver. The well across the street is a public-water-supply well serving 240 connections. You overlay the parcel against the MassDEP Zone I map and the SAS — every trench of it — sits inside the 400-foot Zone I radius. The seller's agent is asking how big the variance hurdle is.

There is no variance hurdle, because there is no variance. 310 CMR 15.211 lists Zone I of a public water supply as a setback that is not waivable under 310 CMR 15.410 through 15.417. The 100-foot to 400-foot radius around a Class I public well, defined under 310 CMR 22.02, is an absolute prohibition on new SAS construction and on continued use of an SAS that has failed under 15.302. There is no path for an inspector, a designer, a homeowner, or the BOH to issue, request, or grant a variance for a SAS inside it.

This is the rule designers and inspectors confuse most often, because it does not behave like the other Title 5 setbacks. Here is what it actually requires you to do.

Part of the MA Title 5 Inspection Complete Guide guide.

What Zone I Is, in 310 CMR 22 Terms

310 CMR 22.02 defines Zone I as the protective radius immediately around a public-water-supply well: 400 feet for wells pumping 100,000 gpd or more, and a smaller radius (typically 100 to 250 feet, sized to the pumping rate) for wells under that threshold. The radius is set by MassDEP Drinking Water Program, not by the local BOH, and it is recorded in the MassDEP Source Water Assessment and Protection (SWAP) database.

310 CMR 15.211 then references those Zone I boundaries and prohibits SAS construction within them. The cross-reference is what trips designers up: the rule lives in 15.211 (Title 5 setbacks) but the boundary itself lives in 22.00 (Drinking Water). If the Drinking Water Program revises the wellhead radius — and they do, when pumping rates change — the Title 5 prohibition radius moves with it.

When the Town's Map Disagrees with MassDEP's

I see this on roughly one out of every fifteen Zone I overlays I check. The town's water-supply protection bylaw map shows a 200-foot radius around a particular well. The MassDEP SWAP database shows 400 feet. The seller's agent is pointing at the town map. The buyer's lender is pointing at the MassDEP map. Which one controls?

The MassDEP map controls for Title 5 purposes. The local map may be more restrictive (a town can write a wellhead protection bylaw that extends Zone I further than MassDEP requires, and that local rule then layers on top of state Title 5 like any other local bylaw overlay). The local map cannot be less restrictive than MassDEP for Title 5 setback purposes. If a town map shows a 200-foot radius but MassDEP's well classification puts it at 400 feet, the 400-foot prohibition under 15.211 still applies.

The practical test: pull the MassDEP SWAP record for the well's PWS-ID before you sign any Title 5 finding involving Zone I. The record will show the current pumping rate and the corresponding Zone I radius. That is the radius you measure against the SAS footprint.

What "No Variance" Actually Means for the Property Owner

The rule does not say the property is uninhabitable. It says you cannot have a soil absorption system there. The redesign paths are limited but real:

1. Tight tank with hauled-away pumping. A holding tank under 310 CMR 15.260 with no SAS at all. The waste is hauled by a licensed septage hauler under 310 CMR 15.340. Operating cost runs $2,400–$6,000 per year for typical residential occupancy, depending on pumping frequency. BOH approval still required, and many BOHs treat this as a stopgap rather than a permanent solution.

2. Connection to public sewer if available. If a sewer line is within reasonable distance (the threshold varies by town; commonly 200–500 feet), the BOH can require the connection regardless of cost. Connection costs in 2026 run $8,000–$30,000 depending on distance, paving restoration, and pump-station requirements.

3. Shared community system off the parcel. Multi-property shared systems located outside the Zone I boundary, treating waste from several parcels at a compliant SAS. This is rare, expensive ($60,000+ buy-in per parcel), and requires either a homeowners' association structure or a 310 CMR 15.011(2) approval pathway.

4. Sale of the land for non-residential use that does not generate sewage. Conservation, recreational easement, or agricultural use without dwelling. The rare practical outcome but a real one — I've seen two parcels inside coastal MA Zone I take this path in the last decade because no other option penciled.

What is not an option: an I/A OWTS unit inside Zone I. The treatment level of an I/A unit does not change the prohibition under 15.211. The rule is geographic, not performance-based.

What the MassDEP Variance Process Does and Does Not Cover

310 CMR 15.410 through 15.417 establish the variance process for Title 5 setbacks. That process explicitly carves out Zone I as non-variable. A homeowner petitioning for a Zone I variance will have the petition denied at intake; the BOH will not even forward it to MassDEP because the BOH lacks authority to entertain it under 15.410(2).

The one related process that does exist is a 310 CMR 22.04(2) modification of the well's Zone I radius, which is a Drinking Water Program action initiated by the public water supplier (not by the homeowner). It is rare, slow (12–24 months), and only applicable when the pumping rate or aquifer modeling supports a smaller Zone I. Do not advise a homeowner to pursue this as a path forward; it is the wrong agency, the wrong applicant, and the wrong timeline for a property transaction.

How Inspectors Should Document a Zone I Failure

If the SAS is within Zone I and is not failing under 15.302, the system continues to operate under the existing-system grandfathering language in 15.301(1). The inspector documents the Zone I location on Title 5 inspection report but does not call a failure on Zone I location alone.

If the SAS is within Zone I and is failing under any 15.302 criterion, the upgrade pathway is constrained. The inspector documents both: the 15.302 failure that triggers the upgrade, and the 15.211 Zone I location that prohibits a replacement SAS in the same footprint. The owner's design engineer then has to work the redesign paths above. Note both findings on Title 5 inspection report; the BOH order under 15.305 will need to address them together.

Frequently asked questions

What's the short answer to "SAS Inside a Zone I Public Water Supply: The Title 5 Prohibition That Has No Variance"?

Inspector and designer guide to 310 CMR 15.211 and the Zone I prohibition on soil absorption systems near public water supply wells. Map disagreements, redesign paths, and why MassDEP variances do not apply.

Who does this apply to?

NEIWPCC-certified Title 5 system inspectors in Massachusetts, FDEP-licensed septic contractors in Florida, SCDHS-permitted designers in Suffolk County NY, and the property owners these professionals serve.

Where can I read the underlying regulation?

Every Complos guide links to the source statute or rule in the body. MA Title 5: 310 CMR 15.000. FL HB 1379 / HB 1417. NY: Suffolk County Sanitary Code Article 19. Always confirm with mass.gov / flsenate.gov / suffolkcountyny.gov before acting.

How does Complos help with this?

Complos generates the regulator's exact PDF, validates the inspection against the local overlay, and tracks per-town submission methods so you don't ship the report into a black hole. Start a 14-day trial at complos.ai/signup.

How Complos helps

Complos's Title 5 compliance check overlays each property against the live MassDEP SWAP Zone I database and flags Zone I prohibitions before the inspector files the report, so the redesign-path conversation happens in week one instead of month four. Run the MA Title 5 compliance checker against any parcel near a public-water-supply well to catch the overlay before the inspection, and pair with the watershed lookup for nitrogen-sensitive-area overlays.

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