Arsenic in Michigan Well Water

Arsenic occurs naturally in Michigan's glacial deposits and is a documented concern across much of the state. This is the guide for private well owners.

Where It Comes From

Unlike some states where arsenic comes from volcanic geology, Michigan's arsenic is a product of glacial geology. The ice sheets that covered Michigan deposited layers of sand, gravel, clay, and till — and within those layers, arsenic-bearing minerals were concentrated in certain zones.

When groundwater contacts these arsenic-rich zones, it dissolves the arsenic and carries it into wells. This is completely natural — it has nothing to do with pollution or industrial activity. The arsenic has been there since the glaciers deposited it roughly 10,000 years ago.

Where in Michigan

Arsenic in Michigan groundwater is not uniformly distributed. The highest concentrations tend to occur in:

• Northeast Michigan — Alpena, Presque Isle, Alcona, Huron counties. This region has some of the highest naturally occurring arsenic in the Great Lakes region.
• The Thumb region — Huron, Tuscola, Sanilac counties
• Southeast Michigan — Parts of Livingston, Washtenaw, Jackson, and surrounding counties
• Central Michigan — Scattered detections in Gratiot, Isabella, and nearby counties

But arsenic can occur anywhere in the state where glacial deposits contain arsenic-bearing minerals. Location-based generalizations are useful but not definitive — the only way to know is to test your specific well.

The EPA Standard

The EPA maximum contaminant level (MCL) for arsenic is 10 parts per billion (ppb). This standard was lowered from 50 ppb in 2001, reflecting growing evidence of health effects at lower concentrations.

The National Research Council estimated that even at 10 ppb — the current legal limit — the lifetime cancer risk is approximately 1 in 300. That's far above the 1-in-10,000 risk level the EPA typically targets.

Health Effects

The International Agency for Research on Cancer (IARC) classifies arsenic as a Class I human carcinogen — the highest classification.

10-50 ppb

• Increased risk of high blood pressure and heart disease
• Skin changes — thickening, discoloration
• Effects may take years to decades to manifest

Above 50 ppb

• Cancer risk rises to 13 per 1,000 exposed over a lifetime
• Increased risk of bladder, lung, skin, kidney, and liver cancers
• Chronic poisoning: fatigue, numbness in hands and feet

The Latency Problem

Cancer from arsenic exposure can appear up to 40 years later. Someone drinking arsenic-contaminated water today may not develop cancer until decades later. This is why testing and prevention matter — you cannot wait for symptoms.

Testing for Arsenic

Every private well in Michigan should be tested for arsenic at least once. The test typically costs $40-$100 at certified labs.

If your area is known for elevated arsenic (Northeast Michigan, the Thumb), consider testing every few years, as concentrations can change as water levels fluctuate.

See our complete testing guide for labs and costs.

Treatment Options

Treatment	Typical Cost	Notes
Point-of-use reverse osmosis	$239-$600 + installation	Treats one tap. Most cost-effective first step. Effective for arsenic and most other contaminants.
Whole-house reverse osmosis	$4,500-$20,000+	Treats all water. High upfront and maintenance cost.
Adsorptive media (iron-based)	Varies; media replacement every 1-3 years	Whole-house arsenic-specific. Works best at pH below 7.0.