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The PWPS Project is one component of the MDA's Monitoring and Assessment for Agriculture Chemicals in the Environment program. The larger program includes the monitoring of groundwater and surface water in the state.
Table 1: County Response Statistics for the Sampling Effort 2014-2016
During the 2014-2015 sampling, pesticides were detected above the Minnesota Valley Testing Lab method reporting limits in six of the private drinking water well samples (0.3%). The wells with pesticide detections were located in a single well from Benton, Olmsted, Sherburne, and Stearns County and two wells in Washington County. Complete pesticide results can be found in the 2014-2015 Private Well Pesticide Sampling Project Report (PDF: 321 KB / 14 pages).
Based on the results of the 2014-2015 sampling, the Minnesota Department of Agriculture contracted with a different laboratory capable of analyzing 126 pesticides and pesticide degradates at lower detection levels. Homeowners who had their well sampled from 2014-2015 will be given the opportunity to have their wells resampled using the new laboratory methods.
Approximately 1,171 wells were sampled in 2016 and were analyzed for 126 pesticide and pesticide degradates. Results indicate that pesticides or pesticide degradates were detected in 76% of the wells tested. Consistent with the MDA's ambient network monitoring, metolachlor ESA (a corn herbicide degradate) was the most frequently detected compound. Only one well exceeded a drinking water reference value (for diuron, a herbicide). Follow-up sampling from this well later in the year indicated lower levels, below the drinking water reference value.
The table below documents concentration statistics and health reference values for pesticide chemicals detected in greater than 5% of the samples analyzed in 2016. All concentrations are reported in ng/L, which is equivalent to parts per trillion (ppt).
Table 2: Concentration Statistics and Health Reference Values
(pesticide chemicals detected in >5% of samples analyzed in 2016)
* <MRL - concentration was below the method reporting limit from the laboratory;
** HRL - Health Risk Limit, a promulgated drinking water standard established by the Minnesota Department of Health
*** RAA - Risk Assessment Advice, a non-promulgated drinking water advice level established by the Minnesota Department of Health