Arsenic in Michigan Well Water: Testing Guide

While PFAS dominates Michigan water quality headlines, arsenic michigan well water contamination has quietly affected thousands of households for decades. Unlike PFAS, which comes from industrial pollution, arsenic in Michigan groundwater is naturally occurring — it leaches from geological formations that predate human activity. The Thumb region in eastern Michigan has some of the highest naturally occurring arsenic concentrations in the country, and many homeowners don't know their water exceeds safe limits until they test it.

The EPA drinking water standard for arsenic is 10 parts per billion (ppb). Some Michigan wells test at 50, 100, or even 200+ ppb — levels that pose serious health risks with long-term exposure. This guide covers where arsenic occurs in Michigan, how to test your well, and which treatment systems actually remove it.

Arsenic Michigan Well Water: Where It Comes From

Michigan's arsenic problem traces back millions of years to geological formations deposited during ancient sea and glacial periods. The Marshall Sandstone formation, which underlies much of central and eastern Michigan, contains naturally occurring arsenic minerals. As groundwater moves through these formations, it dissolves arsenic and carries it into the aquifer that feeds private wells.

The geological source means contamination patterns follow rock formations, not surface activity. A well drilled into the Marshall Sandstone at 80 feet may have elevated arsenic while a neighbor's well drilled into a different formation at 150 feet tests clean. Depth, geology, and local chemistry all affect concentration levels.

EGLE (Environment, Great Lakes, and Energy) has mapped arsenic occurrence across Michigan using data from thousands of well water tests. The data clearly shows concentration hotspots centered on the Thumb region and extending into parts of central Michigan.

Michigan Well Water Arsenic: The Thumb Region Hotspot

Huron, Sanilac, and Tuscola counties — the three counties forming Michigan's Thumb — have the highest rates of michigan well water arsenic contamination in the state. Studies estimate that 20 to 30% of wells in the Thumb region exceed the EPA's 10 ppb standard.

The Thumb region's geology creates a perfect storm for arsenic mobilization. The Marshall Sandstone sits at accessible well depths (60 to 150 feet), and local groundwater chemistry promotes arsenic release from rock into water. Homeowners in Huron, Sanilac, and Tuscola counties should consider arsenic testing mandatory, not optional.

Beyond the Thumb, elevated arsenic levels have been documented in parts of Shiawassee, Genesee, Ingham, and Washtenaw counties. The concentrations tend to be lower than the Thumb but still frequently exceed 10 ppb. Any Michigan well owner east of Lansing and south of Bay City should include arsenic in their water testing panel.

Arsenic Testing MI Wells: How and Where to Test

Testing your well for arsenic is straightforward and affordable. Arsenic testing MI wells require involves collecting a water sample and submitting it to a certified laboratory. Here's the process.

Collect the sample: Run cold water from your kitchen tap for 2 to 3 minutes before filling the sample container. Use a laboratory-provided bottle — not a random container from home. Follow the lab's instructions for preserving the sample (some require adding a few drops of acid preservative).

Submit to a certified lab: Michigan has dozens of labs certified for arsenic analysis. Your county health department can recommend local options. Many health departments also coordinate group testing events where residents can submit samples at reduced cost.

Cost: A standalone arsenic test costs $25 to $50 through most Michigan labs. A broader panel that includes arsenic, nitrates, bacteria, and other metals runs $75 to $150. EGLE occasionally offers free or subsidized testing in high-risk areas.

Interpreting results: The EPA maximum contaminant level (MCL) for arsenic is 10 ppb. Michigan follows this federal standard. Any result above 10 ppb means your water exceeds the safe drinking water limit and treatment is recommended. Results above 50 ppb warrant immediate action including using bottled water until a treatment system is installed.

Health Effects of Arsenic in Drinking Water

Long-term exposure to arsenic in drinking water increases the risk of several serious health conditions. The effects are cumulative — low-level exposure over years matters as much as high-level short-term exposure.

• Skin changes: Darkening, thickening, and small keratoses (rough patches) — often the first visible sign of chronic arsenic exposure
• Cancer risk: Increased risk of skin, bladder, lung, kidney, and liver cancers with long-term exposure above 10 ppb
• Cardiovascular effects: Higher rates of heart disease and circulatory problems
• Neurological effects: Numbness, tingling in hands and feet, cognitive effects in children
• Developmental concerns: Low birth weight and developmental delays associated with prenatal exposure

Children, pregnant women, and the elderly are most vulnerable. If your well exceeds 10 ppb, stop using untreated well water for drinking, cooking, and preparing infant formula immediately. Bathing in arsenic-contaminated water is generally considered safe because skin absorption is minimal at typical residential concentrations.

Thumb Region Arsenic Treatment Options

Three proven treatment technologies remove arsenic from well water. The best choice depends on your arsenic level, water chemistry, and budget.

Oxidation Filtration (Iron-Based Media)

Iron-based adsorption media is the most common whole-house arsenic treatment. Brands like Bayoxide E33 and AdEdge use granular ferric oxide or hydroxide that binds with arsenic as water flows through the filter tank. These systems remove both arsenic III and arsenic V when paired with a pre-oxidation step (typically an air injection system or chlorination).

Cost runs $1,500 to $3,500 for a whole-house system. Media replacement every 3 to 5 years costs $400 to $800. The system handles the entire household water supply, which means arsenic is removed from every tap — drinking water, showers, laundry, and cooking.

Reverse Osmosis (RO)

Under-sink RO systems effectively remove arsenic at 90 to 99% efficiency. RO is more affordable as a point-of-use solution ($200 to $800 installed) but only treats water at a single tap. Most homeowners install RO at the kitchen sink for drinking and cooking water.

RO works best on arsenic V. Arsenic III removal requires pre-oxidation to convert it to arsenic V before the RO membrane. A water treatment professional can test your arsenic speciation and recommend whether pre-oxidation is needed.

Adsorption Media (Point-of-Use)

Specialty cartridge filters using iron-based adsorption media provide a lower-cost point-of-use option. These under-sink units cost $150 to $400 and remove arsenic effectively for 6 to 12 months per cartridge. They're a good interim solution while planning a whole-house system or for properties with moderately elevated levels (10 to 30 ppb).

Treatment Type	Coverage	Arsenic Removal	Cost	Maintenance
Oxidation filtration	Whole house	95–99%	$1,500–$3,500	Media every 3–5 years
Reverse osmosis	Single tap (POU)	90–99%	$200–$800	Filters/membrane annually
Adsorption cartridge	Single tap (POU)	85–95%	$150–$400	Cartridge every 6–12 months

EGLE Data and Resources on Michigan Arsenic

EGLE maintains the most detailed database of arsenic occurrence in Michigan groundwater. Their arsenic information page includes interactive maps, health guidance, and links to certified testing laboratories.

Key EGLE resources for Michigan well owners:

• Arsenic occurrence maps: County-level maps showing the percentage of wells exceeding 10 ppb
• Certified lab directory: List of laboratories approved for arsenic analysis
• Health advisories: Guidance on when to use bottled water and which activities are safe
• Treatment guidance: Technical fact sheets on treatment options for residential wells

Your county health department can also provide local data on arsenic prevalence in your specific area. Some Thumb region counties have conducted extensive well sampling campaigns and can tell you how common arsenic exceedances are in your township.

Geological Sources: The Marshall Sandstone Formation

The Marshall Sandstone is a geological formation deposited during the Mississippian period, roughly 340 million years ago. It forms a broad band across central and eastern Michigan from Saginaw Bay through the Thumb and south toward Lansing.

Arsenic in the Marshall Sandstone exists primarily as arsenopyrite — an iron-arsenic sulfide mineral. When groundwater contacts these minerals under the right chemical conditions (particularly low oxygen environments), arsenic dissolves into the water. The process is entirely natural and has been occurring for thousands of years.

Wells drilled into the Marshall Sandstone aquifer are most likely to contain elevated arsenic. However, not every well tapping this formation will have high levels — local chemistry, well depth, and micro-geology all influence concentration. This variability is why testing is essential regardless of where your well draws water.

Frequently Asked Questions

How common is arsenic in Michigan well water?

EGLE estimates that approximately 50,000 to 80,000 Michigan wells may exceed the 10 ppb EPA standard for arsenic. The Thumb region (Huron, Sanilac, Tuscola counties) has the highest rates, with 20 to 30% of wells exceeding safe limits. Testing is the only way to know your specific level.

Does boiling water remove arsenic?

No. Like PFAS, boiling does not remove arsenic — it concentrates it by evaporating water while the arsenic remains. Only filtration technologies (oxidation filtration, reverse osmosis, adsorption media) remove arsenic from drinking water.

How much does arsenic testing cost in Michigan?

A standalone arsenic test costs $25 to $50 at most certified Michigan labs. A broader water quality panel including arsenic, bacteria, nitrates, and other metals costs $75 to $150. Contact your county health department for local lab recommendations and possible group testing discounts.

Is it safe to shower in arsenic-contaminated water?

Generally yes. Arsenic absorption through skin is minimal at typical residential well concentrations (10 to 100 ppb). The primary health risk comes from drinking and cooking with contaminated water. However, a whole-house treatment system addresses all uses and provides full protection.

Can arsenic levels in my well change over time?

Yes. Arsenic concentrations can fluctuate seasonally and over longer periods due to changes in groundwater levels, pumping rates, and water chemistry. Test annually to track your levels. A sudden increase may indicate a change in well conditions that warrants investigation.

Get your Michigan well water tested today. Find well water testing providers serving your area, and explore water treatment options if your results show elevated arsenic. For PFAS testing information, read our Michigan PFAS well water testing guide and our Michigan well water testing guide.