The Pentwater River watershed, and the aquifer beneath it

In west Michigan there is a county that grows food for the whole country. Oceana, the asparagus capital of the world, with orchards of cherries, apples and peaches.

This is the watershed underneath it, the Pentwater River. One hundred sixty-six square miles, draining to Pentwater Lake.

And here is where all of this sits. Halfway up the west coast of the mitten. The Big Sable and the Pere Marquette to the north, the White River to the south, the big Muskegon basin inland, and Lake Michigan at the front door.

What makes it work starts with the rain, about nine hundred eighty-two millimeters a year.

The sandy ground drinks more than a third of it.

Thirty-four percent sinks straight down, into an aquifer beneath the whole watershed.

So where does all of that water go? Straight down, into this. Under every field and every town in this watershed lies a thick layer of glacial deposits, left behind by the ice. Here is a slice through it, from the lake in the west to the hills in the east.

Most people never see it, so here is what it is like. Across two and a half thousand well records, the water sits about thirty-one feet down, and most wells stop at seventy-eight. Ninety-nine percent of wells with a recorded aquifer draw from glacial deposits. It gives up water easily, which is why a single well can supply a whole farm. But open sand cuts both ways. Whatever soaks in at the surface has a short trip down.

And that water does two jobs. It feeds these streams all year, which is why they still run in a dry August. It also fills the wells, at about six per square kilometre, close to the west Michigan average.

So where does the drinking water come from? Not a river intake, not a pipeline, not Lake Michigan. Every drop is pumped out of that same aquifer. Two thousand three hundred homes on their own wells, two town systems, and a hundred and thirty-nine wells for irrigation. And they are not equal. The farms take about three quarters of all the water drawn here.

So can the aquifer keep up? Rain and snow put nearly a hundred and fifty million cubic metres back into it every year. Everything pumped out, farms, homes and towns together, comes to roughly four. That is three percent. Put another way, the recharge replaces a whole year of pumping in about ten days.

The river works for people too. Since 1927 the city of Hart has made its own electricity here, from a thirty-one foot dam and two small turbines.

But a dam is always a trade. The water it releases runs warmer than the trout stream below it, which is why taking it out has been discussed for years.

So the dam and the chemicals are things we do to this water. But what shapes it most is the land itself, and what is not average here is the farming. Thirty-seven percent of this watershed is cropland. Across west Michigan, the typical watershed is nine.

It is more farmed than ninety-two percent of the watersheds around it. Corn, soybeans and wheat, dairies, and those orchards.

With that much working land come the places where water is handled. Thirteen permitted sites, and the wastewater plants of Hart and Pentwater.

Each leaves a fingerprint. Fertilizer and manure carry phosphorus. Livestock, septic systems and wastewater carry bacteria.

And the rain that does not sink in carries them to the streams.

So people went out and measured. And in the summer of 2023, it showed up in the numbers. E. coli above twenty-four hundred in both branches, against a Michigan limit of one thousand for wading, and three hundred for swimming.

Source tracking looks for human, pig, cow and wildlife markers. In Village Creek, those tests found no human source. For the two branches, no result has been published yet.

And there is a newer question. PFAS, the forever chemicals. Michigan has sampled five streams here, and most of them are low.

The exception is a small tributary running into Pentwater Lake: six point six parts per trillion, above the EPA's drinking-water limit.

One sample, in a stream, not a tap. But it is a signal worth following, and the channel map shows which streams lead to it.

None of that is unusual for a farming watershed. What is unusual is being able to see it. The land, the crops, and the water above and below, as one connected system.

See how it fits, and you can see where to act.