In 2017, Dakota County sampled 146 private wells as part of an ongoing County groundwater study. Owners of wells located where elevated levels of the herbicide cyanazine had previously been identified were invited to participate.
Untreated well water was collected and analyzed for triazine herbicides, nitrate, arsenic, manganese and chloride. Triazine herbicides are a category of weed killers predominantly used on crops.
Thirty-eight percent of the wells sampled exceeded one or more drinking water guidelines.
- Cyanazine breakdown products were detected in 91 well samples (62 percent); 12 wells (8 percent) exceeded the drinking water guideline of 1.0 µg/L (micrograms per liter equivalent to parts per billion).
- Atrazine and its breakdown products were detected in 83 well samples (57 percent) but none were over the drinking water guideline of 3.0 µg/L.
- Nitrate was detected in 85 well samples (58 percent); 41 well samples (28 percent) exceeded the drinking water guideline of 10 mg/L (milligrams per liter equivalent to parts per million).
- Arsenic was detected in 18 percent of samples and exceeded the drinking water guideline of 10 µg/L in one sample.
- Manganese exceeded the drinking water guideline of 0.100 mg/L for infants in 10 percent of samples.
- Chloride was detected in 69 percent of samples; all results were below 250 mg/L (the level where water may start to taste salty).
For more information, see the Targeted Drinking Water Quality Study Frequently Asked Questions.