Deep Background

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An interesting postscript to the devastating flooding that hit southeast Minnesota in August 2007: after the deluge, the Minnesota Department of Health tested 65 wells in the area for contamination. The good news is that most of the chemical pollution that may have been due to the flooding was short-lived. But, as is often the case, there’s a down side to this story.

Twenty-one of the wells contained at least one pesticide or pesticide breakdown product, mostly at levels too low to be considered a health risk by the government. (Respected scientists like Tyrone Hayes may disagree that even low levels are “safe.”) To no one’s surprise, the ever popular corn herbicide atrazine was the most common pesticide contaminant, showing up in 17 wells. If it can be found in the Boundary Waters, why not in farm wells?

And 21 of the wells also contained nitrate-nitrogen—a major crop fertilizer—at levels that exceeded more than one mg/L; four wells exceeded the state and federal drinking water standard for nitrate-nitrogen of 10 mg/L.

Re-samples two months after the initial testing showed pesticides and nitrate-nitrogen were still present in the wells where the chemicals were originally detected, and were there more or less at the same levels as before.

The researchers who conducted the testing concluded that: “Contamination levels that did not change significantly in the six to eight weeks between the initial and confirmation samples suggest background contamination of aquifers supplying water to the wells, rather than direct contamination of the wells by floodwaters.”

In other words, floods and other catastrophic weather events may come and go, but agrichemicals have infiltrated deep into aquifers that supply drinking water, and they aren’t going anywhere soon. It’s the difference between having the 24-hour flu, and cancer.

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