Opinion: About sulfate in the Antrim Shale geological formation

Chase

My lab does a variety of analyses for point-of-sale mortgages where we analyze for nitrate/nitrite most of the time.

Since 2009, I changed the method used so that it allowed me to see sulfate too, even when it was not asked for.

Gradually, over the years, I noticed high sulfate levels that had come from addresses within the Antrim Shale formation.

At first, it was a rare occurrence because the amount of mortgage samples, compared to today, was very low. As of 2023, the number of mortgage samples has increased substantially, including samples from southeastern Michigan and north middle Ohio. Sure enough, addresses within the Antrim Shale formation there had elevated sulfate.

So what’s going on in the Antrim Shale formation?

This formation is unique from its neighbors; it contains a large amount of pyrite (iron disulfide). When this comes into contact with water, the dissolved oxygen in the water turns it to hematite, or similar iron oxides, and releases sulfate. The amount of sulfate is varied over the formation.

There are obviously spots that are void of pyrite and/or lack of dissolved oxygen. Much more data is needed to pinpoint the hot spots’ boundaries.

Samples from the boundary of the formation are elevated, but under the MCL (Maximum Contaminate Level) of 250 ppm.

How bad is it? According to the EPA, elevated sulfate above the MCL of 250 ppm can cause diarrhea — that’s it.

But higher levels of sulfate mean higher levels of sulfuric acid, making the water acidic and dissolving heavy metals out of pipes.

Sulfate is naturally occurring in a certain geological formation that rings the state of Michigan. But sulfate at these higher levels is like diluted battery acid.

What can be done to treat this water?

Various Google searches suggest adding lime to neutralize the acid and filter, but within an industrial plant. Salt-water softeners will not stop sulfate from coming out. These only take out cations; sulfate is an anion. Commercial home filters will most likely fail quickly because there is too much sulfate. So there’s no good answer.

I am raising awareness about this. Even though I have been monitoring this for years, I did not have enough data until now to provide disclosure of it.

But I feel the general public, and those with wells in this area, should be informed.

About the author: Kirk Chase is an analytical chemist and part owner of Grand Traverse Analytical. He obtained a bachelor of science degree in chemistry/mathematics from Central Michigan University in 1984. He has 39 years of experience at a variety of environmental/drinking water labs.

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