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Home > Ag Chemicals & Fertilizers > Pesticides > Monitoring & Assessment for Agricultural Chemicals in the Environment > Groundwater Pesticide Water Quality Monitoring

Groundwater Pesticide Water Quality Monitoring

Map of Minnesota illustrating the monitoring sites for pesticides in groundwater.The Minnesota Department of Agriculture (MDA) is currently sampling over 160 monitoring wells, naturally occurring springs and private drinking water wells throughout the state. Although concentrations typically remain well below health risk levels, five pesticides have been detected frequently enough to be placed in "common detection" status. This list includes acetochlor, alachlor, atrazine, metolachlor, and metribuzin. These pesticides are being watched and alternative management practices are promoted whenever levels rise.


In 1987, the Minnesota Legislature amended the Minnesota Pesticide Control Law (Minnesota Statute 18B.04). It directed the Minnesota Department of Agriculture (MDA) to determine the impact of pesticides on the environment, including the impacts on surface water and groundwater.

In response to this charge, the MDA initiated a pesticide groundwater monitoring program in 1987 and in 1991, began surface water monitoring. The MDA has one of the most comprehensive pesticide monitoring programs in the country.


In 2015, 734 pesticide samples were collected from 167 sampling locations.

  • Thirty-six different pesticide compounds or pesticide degrades were detected in groundwater.
  • Metolachlor ESA was the most frequently detected analyte.
  • Nitrate was detected in 89 percent of the samples analyzed for nitrate.
  • One new monitoring well was installed and sampled.
  • Six neonicotinoids pesticides were analyzed in all of the groundwater samples.
    • There were no detections in urban areas or the private drinking water wells in southeast Minnesota.
    • Acetamiprid, dinotefuran and thiacloprid were not detected.
    • Clothianidin, imidacloprid, and thiamethoxam were detected in 6 to 15 percent of the samples collected. All detections were well below applicable reference values.
    Bar graph illustrating the number of pesticide target analytes and detections found from 2000 to 2015 in groundwater.
  • The number of pesticides analyzed in water samples has grown from 28 in 2000 to 138 in 2015 due to an increase in laboratory analysis capability.
  • Since 2010, the number of detected pesticide compounds in Minnesota groundwater has remained relatively stable.

View more detailed Water Monitoring Reports and Resources.

Graph illustrating the concentration (ng/L) of metolachlor ESA found from 2002 to 2016. The health risk limit for metolachlor ESA is 800,000 ng/L. Plotted values are below this value.

Most Frequently Detected - Metolachlor ESA

The graphic illustrates long term concentration of metolachlor ESA, a breakdown product of the pesticide metolachlor. It is the most frequently detected pesticide compound in groundwater in the state.

The data in the graphic is from the Central Sands Region, located in the central part of the state. Data indicates that in this area, the 75th percentile and 90th percentile metolachlor ESA concentration trends have been decreasing, while the median concentration trend has been increasing. The detected concentrations are well below any health reference values.




Future Work

The MDA is currently implementing a comprehensive groundwater monitoring initiative focused on sampling private wells for pesticides. It includes sampling thousands of wells in sensitive geologic conditions in the agricultural areas of the state.

The MDA is also evaluating changing groundwater conditions in areas undergoing conversion from forest to irrigated agriculture.

 MDA Contact

Bill VanRyswyk
Hydrologist Supervisor