This nitrate chart looks worrisome. Is it?

This bar graph looks ominous. But for the time being, put it in the “bears watching” category rather than push the panic button, the state Health Department says. It shows that a rising percentage of new wells in Minnesota hit nitrate-contaminated water.

You can find this on page 49 of a new report tracking what the Clean Water Fund is doing with sales tax dollars raised under Minnesota’s Legacy Amendment.

What it shows is this: Every year recently Minnesotans drill about 5,000 new wells for their houses, their cabins or other uses. (In fact, one out of five Minnesotans rely on private wells for their water.) The red bars represent the percentage of those new wells that hit water that violates federal and state standards for nitrate concentrations. If you’re concerned about the purity of Minnesota’s groundwater, that rising trend doesn’t  look so good.

Nitrates in groundwater, typically the result of fertilizer leaching into aquifers, are a growing concern. So if we’re seeing a steady increase, this chart would seem to be an indictment. Ten milligrams per liter is the level at which public health officials say the water should not be drunk by babies.

But Chris Elvrum, manager of the Minnesota Health Department’s well management section, offers several cautions in interpreting the numbers:

  • The percentage is really small — just over 1 percent in 2012.
  • In fact, 2013 numbers not included in the report show the percentage dipped that year to 0.8 percent, still historically high but not another increase. The total number, including the percentage of wells that measure between 5 and 10 milligrams per liter, dropped to 2.3 percent in 2013.
  • It’s not clear how good a statistical sample is represented each year. It’s possible that more wells are being drilled in sensitive areas in some years, throwing off what the numbers represent.

“Even 1 percent of our population, that’s something that needs to be considered,” Elvrum acknowledged. The state sends instruction about the safe use of water to anybody who drills a well and gets high nitrate levels, he said.

But perhaps most important is that it does put a spotlight on the plan launched by the Minnesota Department of Agriculture to test 70,000 existing private wells for nitrates over time. That effort got under way last year, and by the end of this year expects to have sampled wells in 60 townships in eight counties. Data from those wells eventually should be a much better barometer.