Radon and arsenic in Massachusetts homes

Two in-home geologic exposures, estimated for the same Massachusetts ZIP codes: modeled indoor radon and modeled groundwater arsenic. This page is scoped to Massachusetts.

MassachusettsData release 2026Modeled inputs

Across parts of Massachusetts, two separate geologic exposures show up in the same ZIP codes — a modeled likelihood of elevated arsenic in groundwater, and modeled indoor radon. Here is exactly what each measurement is, and the federal reference each is measured against.

How we measure this →

Modeled indoor radonEPA action levelModeled · ZCTA-native

Where the modeled value crosses the line, this area's modeled radon runs above EPA's 4 pCi/L action level — the level at which the EPA recommends taking action to reduce indoor radon. It is an action level, a recommendation to act, never a regulatory limit.

EPA indoor-radon action level — 4 pCi/L. A recommendation to act, not a regulatory limit.

Modeled groundwater arsenicEPA public-water limitModeled likelihood

USGS models a high likelihood that groundwater arsenic here exceeds 10 µg/L — the level EPA sets as the limit for public water systems. Most private wells are federally unregulated, so this is a modeled likelihood, never a measured exceedance.

EPA drinking-water maximum contaminant limit — 10 µg/L. Applies to public systems; private wells are not covered.

What this is — and isn't. These are two exposures estimated for the same place. This page does not claim one causes the other, does not combine them into a single risk number, and does not link either to any health outcome. It reports where both figures are elevated together, and nothing more.

Massachusetts ZIP codes where both are elevated

The Massachusetts ZIP codes (ZCTAs) that rank among the highest 10% of US ZIP codes for both modeled exposures. The ranking is national; this list is Massachusetts only. How each area reads depends on whether its modeled radon actually crosses the 4 pCi/L action level — see the two labels below.

Above action levelmodeled radon crosses 4 pCi/L — the federal-reference sentence rendersElevated (top 10% in the US)in the top 10% of US ZIP codes but below 4 pCi/L — reads as a ranking, not the 4 pCi/L sentence

01501in AuburnElevated (top 10% in the US)
This area ranks among the highest 10% of US ZIP codes for both modeled radon and modeled groundwater arsenic.

Coverage & how to read this

Modeled, not measured. Indoor radon uses the Li national ZCTA-level model; groundwater arsenic uses the USGS private-well probability model. Neither is a reading from your home or tap. A ZIP with an unobservable leg is shown as not measured, never as "not impacted." Both references are federal: radon's 4 pCi/L is an action level (a recommendation to act), arsenic's 10 µg/L is the maximum contaminant limit EPA sets for public water systems. A ZIP reaches this list by ranking among the highest 10% of US ZIP codes for each exposure — the ranking is national, and this list is Massachusetts only. Read the full combined-exposure methodology →

Each ZIP links to its full ZipVitals page. Massachusetts only — the national list is on the explainer page.