How we did the irrigation well permit story

MPR News reporter Mark Steil is reporting today on Morning Edition and All Things Considered the results of a many-months-long look at state well and irrigation records. As crop irrigation has boomed, increasing yields and profits, hundreds of wells throughout Minnesota have been pumping tens of millions of gallons of public water without required state permits.

That means it's harder to know what exactly is going on with the state's groundwater, increasingly considered vulnerable and valuable.

The story is a great example of teasing something meaningful out of the reams of data the state collects. Mark's editor, Bill Catlin, did a lot of the heavy lifting, so we asked him to explain how they did it:

How did we do this?

The simple answer is we got a list of all irrigation wells and a list of irrigation wells with permits. That allowed us to identify wells that lacked permits using a database program.  Then we figured out where they were and zoomed in on them using Google Maps and Bing Maps to see whether there was visible evidence of irrigation.

The list of irrigation wells came from the Minnesota Department of Health, which keeps a registry of all wells drilled in Minnesota—permitted or not—for public health purposes.  Staff members there culled a list of wells whose purpose is identified in the well records as "irrigation."

The Department of Natural Resources is in charge of water permits and provides a list of permitted wells on the agency's website.

Each well drilled in Minnesota has a unique number, and this number is in both the DNR and MDH lists.

That unique identifier makes it possible to use a database program to quickly cull out wells that lack permits.

Steil acquired the paperwork for each well, and scoured through the documents to identify wells with sufficient capacity to feed a center pivot irrigator.

The DNR said its own enforcement standards involve looking at wells with a casing diameter of eight inches or more.  (Casing diameter basically identifies the size of the conduit through which water rises to the surface.)

Eventually we settled on a more conservative standard.

We included for examination wells documented as having 1) a casing diameter of at least 12 inches, or 2) the casing diameter is at least 6 inches and state records also indicate at least 150 gallons per minute pumping capacity or include a reference to an irrigator.

Wells that meet those criteria have a large capacity to move water above ground and therefore are likely to require a water permit. The pumping threshold for needing a permit is either 10,000 gallons in a day or 1 million gallons over a year.  Many wells we identified would cross the 10,000 gallons threshold in less than an hour of pumping at capacity.

To determine if these unpermitted wells were likely feeding high-volume irrigators (and therefore pumping water at volumes that would almost certainly require a permit), we converted two types of location data to formats that we could map with Google or Bing. Using their satellite imagery, we could then determine if wells were located close to an irrigator rig.  The mapping sites can zoom in close enough and with enough resolution that an irrigation rig is clearly identifiable.

The location data available was either pinpoint or a 40-acre square in which the well was located.   Once we converted the location data into GPS coordinates we were able to build a Google map showing the locations of all the high capacity wells we'd identified.  Google and Bing maps display satellite imagery from different sources, so in some cases an irrigator would be apparent on Bing but not on Google. ​

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