Arsenic in Maine Well Water

Maine has one of the highest rates of arsenic in private well water in the United States. This is the complete guide for well owners.

The Scale of the Problem

Maine's arsenic problem is fundamentally geological. The arsenic isn't from pollution or contamination — it's been in the bedrock for hundreds of millions of years. This means it can't be avoided by drilling deeper, moving to a different part of your property, or waiting for it to go away. It's part of the landscape.

Where Does It Come From?

Bedrock Geology

Maine's bedrock is primarily granitic and metamorphic rock — the same geology that makes the state famous for its mineral specimens (tourmaline, beryl, garnets). These formations contain arsenic-bearing minerals, particularly arsenopyrite (iron arsenic sulfide).

When groundwater moves through fractures in this bedrock, it dissolves arsenic from the mineral surfaces. The longer the water is in contact with the rock, the more arsenic it picks up. This is why:

• Bedrock wells tend to have higher arsenic than wells in sand and gravel deposits
• Deeper wells don't necessarily have less arsenic — they may have more, because the water has had more contact time
• Arsenic concentrations vary dramatically from well to well, even on neighboring properties, because the fracture network is random

Geographic Hotspots

While arsenic can occur anywhere in Maine where wells tap bedrock, concentrations tend to be highest in:

• Central and southern Maine — along the granitic bedrock belt
• Oxford County — the pegmatite district
• Androscoggin County — documented arsenic hotspot
• Parts of Cumberland, York, and Kennebec counties

But any bedrock well in Maine could have arsenic. The only way to know is to test.

Health Effects

The International Agency for Research on Cancer (IARC) classifies arsenic as a Class I human carcinogen — the highest classification, meaning there is sufficient evidence that it causes cancer in humans.

At and Near the EPA Limit (10 µg/L)

• Even at 10 µg/L, lifetime cancer risk is approximately 1 in 300 (NRC estimate)
• Increased risk of heart disease and high blood pressure
• Possible developmental effects in children

Above 10 µg/L

• Increased risk of bladder, lung, skin, kidney, and liver cancers
• Skin changes — thickening, discoloration
• Peripheral neuropathy — numbness and tingling in hands and feet
• Cancer can appear up to 40 years after exposure

The Latency Problem

Arsenic's health effects are not immediate. Someone drinking arsenic-contaminated water today may not develop cancer for decades. This makes it easy to ignore — but the damage is accumulating with every glass of water.

Free Testing in Maine

See our complete testing guide for all testing options, labs, and costs.

Treatment Options

Treatment	Typical Cost	Notes
Point-of-use reverse osmosis	$200-$600 + installation	Treats one tap (kitchen sink). Most cost-effective first step. Removes arsenic, uranium, and most contaminants.
Whole-house reverse osmosis	$4,000-$15,000+	Treats all water. High upfront cost and maintenance.
Adsorptive media (iron-based)	$1,500-$4,000	Whole-house arsenic-specific treatment. Media replacement every 1-3 years. Works best at pH below 7.0.