New England Fractured Crystalline
The most uraniferous bedrock in the eastern US, drilled into by 40% of New Hampshire households
If you live north of Boston and drilled your own well, you are drilling into 400-million-year-old crystalline bedrock — granite, granitic gneiss, schist — that was glaciated, eroded, and partially overlain by glacial till during the Pleistocene. That geology gives New England well water its characteristic problem. It isn't one contaminant. It's three at once: arsenic, radon, and uranium. The same uraniferous minerals that produce radon by decay also dissolve directly into groundwater as uranium. The same fractured-rock pathways that pick up dissolved gas pick up dissolved metals from glacially crushed pyrite. New Hampshire is the worst-case overlay in the lower 48.
The geology, briefly
The bedrock of northern New England is a patchwork of plutons (granite intrusions) and metamorphic terrain (schist, gneiss) emplaced during multiple orogenies between 460 and 250 million years ago. Many of these plutons are uraniferous — they contain meaningful concentrations of uranium-bearing minerals, particularly in the White Mountain Magma Series (NH), the Conway Granite, and various pegmatites scattered across the region.
The Pleistocene glaciation left a layer of glacial till on top — a chaotic mix of crushed bedrock, including sulfide minerals like pyrite and arsenopyrite that, when weathered in oxygenated soil, release arsenic into shallow groundwater.
Wells in New England fall into two broad categories with very different chemistry:
- Bedrock wells — drilled deep into the crystalline rock, drawing from fractures. Higher radon and uranium. Lower bacteria risk. Variable yield (1-30+ gpm depending on fracture density).
- Dug wells / shallow wells — drawing from the glacial till or surface aquifer. Higher arsenic (from pyrite oxidation) and bacteria. Lower radon. More vulnerable to surface events.
The numbers, by state
Where this geology matters most:
- New Hampshire — about 40% of the population is on private wells. ~12% of NH wells exceed the EPA arsenic MCL of 10 μg/L. Radon levels in well water frequently 1,000-10,000 pCi/L, with hot zones in the south-central part of the state (Hillsborough, Merrimack counties).
- Maine — 10-12% of wells statewide above the arsenic MCL; up to 30% in southern Maine towns (parts of York, Cumberland counties). Maine has one of the most active state-level private-well testing programs because of this.
- Vermont — arsenic less common (different bedrock), radon and uranium common in the Green Mountains.
- Massachusetts (north and west of I-495) — radon and uranium common; arsenic in some Worcester County and Cape Ann wells.
- Connecticut and Rhode Island — patchier; some pegmatite-related uranium hotspots.
- Adirondack New York — similar to northern New England in chemistry.
Why the cocktail is the problem
One contaminant is a fixable problem. Three at once is a system. A well with 8 μg/L of arsenic, 4,000 pCi/L of radon, and 25 μg/L of uranium — not unusual in southern NH — needs three different treatment approaches that don't interfere with each other:
- Radon in water needs aeration (the right answer) or specialty GAC. Standard whole-house carbon doesn't address the radon-air handoff in the shower.
- Arsenic needs RO (point-of-use) or adsorptive media (whole-house). Speciation between As(III) and As(V) matters.
- Uranium needs RO or anion exchange. Not removed by aeration. Not reliably removed by standard carbon.
This is why the New England well-treatment market is more sophisticated than most regions and why New England homes commonly have multi-stage systems. A water softener alone is woefully inadequate.
What well owners should do
Test specifically for the New England triple: arsenic, radon-in-water, uranium. Not basic panels — those don't always include radon-in-water and may underreport arsenic if the lab doesn't acidify the sample. State health departments in NH and ME maintain certified-lab lists and recommended panels.
- NH Department of Environmental Services — recommended private-well panel
- Maine CDC — Be Well Informed program
- USGS New Hampshire-Vermont Water Science Center — bedrock arsenic risk maps
Known contaminant concerns
Communities on this aquifer
Sources
- USGS Open-File Report 2011-1235 — Arsenic, Iron, and Manganese in Drinking Water from Private Wells in New Hampshire
- Ayotte et al., USGS — Modeling the Probability of Arsenic in Groundwater in New England
- NH Department of Environmental Services — Private Well Testing recommended panel
- Maine CDC — Be Well Informed private well program
- USGS — Radon in Ground Water of New England
- Hall et al. — Lithology and Bedrock Arsenic Concentrations, Northern New England