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Home > Protecting Our Lands & Waters > Clean Water Fund > Groundwater & Drinking Water Protection > Private Well Pesticide Sampling Project > Results and Work Plans

PWPS Results and Work Plans


Pesticide Results
List of All Reports

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.


Homeowner Participation

Table 1: County Response Statistics for the Sampling Effort 2014-2016

Year County Nitrate Detections/ Letters Mailed Letters Returned Percent Response Total Wells Sampled Total Number of Samples
2014 Dakota Pilot Project 411 267 65.0% 256 280
2014 Total   411 267 65.0% 256 280
2015 Dakota - 2014 Carryover       11 11
  Benton 307 153 49.8% 145 160
  Dakota 461 268 58.1% 248 274
  Morrison 191 94 49.2% 91 99
  Olmsted 414 182 44.0% 183 208
  Sherburne 596 320 53.7% 301 342
  Stearns 905 443 49.0% 394 433
  Wadena 112 42 37.5% 39 43
  Washington 313 177 56.5% 173 194
2015 Total   3,299 1,679 50.9% 1,585 1,764
2016 Dakota - 2014/2015 Carryover   2   6 7
  Morrison - 2015 Carryover       2 3
  Sherburne - 2015 Carryover       2 2
  Stearns - 2015 Carryover       7 10
  Washington - 2015 Carryover       2 4
  Dakota - Resamples 496 372 75.0% 369 412
  Morrison 467 238 51.0% 230 256
  Otter Tail 1,009 451 44.7% 408 456
  Pope 67 29 43.3% 28 34
  Sherburne 249 118 47.4% 117 137
2016 Total   2,288 1,210 52.9% 1,171 1,321
2014-2016 Total   5,998 3,156 52.6% 3,012 3,365

Pesticide Results

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)

Pesticide Analyte Detection
Frequency
Median
(ng/L)
90th Percentile
(ng/L)
Maximum
(ng/L)
Health Reference Value
(ng/L)
Health Reference
Value Type
Metolachlor ESA 70% 69 870 6,900 800,000 HRL**
Alachlor ESA 55% 65 1,500 12,000 50,000 RAA***
Metolachlor OXA 45% <MRL* 420 12,000 800,000 HRL
Acetochlor ESA 21% <MRL 81 2,300 300,000 HRL
Desthylatrazine 19% <MRL 78 380 3,000 Parent HRL
Atrazine 19% <MRL 53 320 3,000 HRL
Bentazon 8% <MRL <MRL 2,900 30,000 HRL
Alachlor OXA 7% <MRL <MRL 5,300 50,000 RAA
Metribuzin DADK 6% <MRL <MRL 7,400 10,000 RAA

* <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


Reports

2016

2015


Additional Information

MDA Contact

Jeff Paddock
Hydrologist
jeff.paddock@state.mn.us
651-201-6560