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. Data summaries for the PWPS Project are included in the annual reports for the Monitoring and Assessment program.
Phase 1 Results (approximately 130 pesticides)
Approximately 5,700 wells were sampled in 50 counties between 2016 and the spring of 2021 (Table 1).
All samples were analyzed for at least 125 pesticide and pesticide degradates. Results indicate that pesticides or pesticide degradates were detected in 76% of the wells tested. There were 75 different pesticides and degradates found overall (Table 1).
Consistent with the MDA's ambient network monitoring, metolachlor ESA (a corn herbicide degradate) was the most frequently detected compound (Table 2). Table 2 also documents concentration statistics and health reference values for pesticide chemicals detected in greater than 14 percent of the samples analyzed between 2016 and the spring of 2021 during Phase 1 of the PWPS Project.
Based on sampling performed between 2016-2018 it was found that three wells exceeded a drinking water reference value (for diuron (herbicide), methyl parathion (insecticide), and cyfluthrin (insecticide)). Verification samples from the three wells with exceedances were found to be non-detect for those compounds.
Sampling performed in 2019- spring 2021 showed that 62 wells exceeded a drinking water reference value (primarily for total cyanazine (herbicide)). Verification sampling results also indicated that most of the water samples at these locations were above the reference value for total cyanazine.
Additional information can be found in the full Private Well Pesticide Sampling Project Phase 1 Summary Report located in the Minnesota Water Research Digital Library.
| County (years sampled+) | Number of Townships Sampled | Number of Wells Sampled | Number of Wells with a Pesticide Detection | Detection Frequency | Total Number of Pesticides & Pesticide Degradates Detected | Number of Pesticide Health Reference Value Exceedances |
|---|---|---|---|---|---|---|
| Becker (2017-2018) | 3 | 52 | 24 | 46% | 15 | 0^ |
| Benton (2017, 2020) | 4 | 144 | 117 | 81% | 31 | 0^ |
| Big Stone (2020) | 3 | 12 | 10 | 83% | 12 | 0 |
| Blue Earth (2019) | 5 | 43 | 20 | 47% | 12 | 0 |
| Brown (2020) | 2 | 4 | 2 | 50% | 3 | 0 |
| Carver (2019) | 1 | 27 | 19 | 70% | 7 | 0 |
| Chippewa (2019) | 3 | 46 | 23 | 50% | 20 | 2 |
| Chisago (2019) | 2 | 95 | 70 | 74% | 16 | 0 |
| Clay (2018) | 11 | 33 | 7 | 21% | 5 | 0^ |
| Cottonwood (2019) | 4 | 5 | 4 | 80% | 7 | 0 |
| Dakota (2016-2017) | 17 | 378 | 353 | 93% | 31 | 0^ |
| Dodge (2017-2018) | 8 | 112 | 80 | 71% | 25 | 0^ |
| Douglas (2017) | 9 | 134 | 46 | 34% | 15 | 0^ |
| Faribault (2019) | 2 | 6 | 1 | 17% | 1 | 0 |
| Fillmore (2018-2019) | 24 | 408 | 392 | 96% | 32 | 0^ |
| Freeborn (2020) | 1 | 1 | 1 | 100% | 5 | 0 |
| Goodhue (2018-2019) | 22 | 582 | 459 | 79% | 42 | 0^ |
| Houston (2019-2020) | 10 | 151 | 122 | 81% | 34 | 3 |
| Hubbard (2017-2018) | 6 | 279 | 158 | 57% | 31 | 0^ |
| Kanabec (2019) | 1 | 8 | 6 | 75% | 6 | 0 |
| Kandiyohi (2017) | 6 | 32 | 19 | 59% | 17 | 1**^ |
| Lac Qui Parle (2020) | 5 | 12 | 6 | 50% | 9 | 0 |
| LeSueur (2019-2020) | 2 | 38 | 23 | 61% | 13 | 0 |
| Lincoln (2019) | 1 | 1 | 1 | 100% | 1 | 0 |
| Lyon (2019) | 2 | 4 | 1 | 25% | 3 | 0 |
| Meeker (2019) | 2 | 19 | 3 | 16% | 6 | 0 |
| Morrison (2016- 2017, 2020) | 15 | 286 | 232 | 81% | 33 | 0^ |
| Mower (2020) | 12 | 173 | 166 | 96% | 36 | 3 |
| Nicollet (2019) | 1 | 4 | 3 | 75% | 6 | 0 |
| Nobles (2017) | 4 | 12 | 11 | 92% | 16 | 0^ |
| Olmsted (2019) | 11 | 123 | 103 | 84% | 26 | 4 |
| Otter Tail (2016-2017) | 31 | 431 | 242 | 56% | 44 | 0^ |
| Pipestone (2019) | 9 | 35 | 32 | 91% | 31 | 1 |
| Polk (2019) | 3 | 11 | 3 | 27% | 4 | 0 |
| Pope (2016) | 5 | 28 | 13 | 46% | 12 | 0^ |
| Redwood (2020) | 1 | 3 | 2 | 67% | 4 | 0 |
| Rice (2018) | 4 | 67 | 55 | 82% | 23 | 0^ |
| Rock (2017) | 7 | 60 | 51 | 85% | 25 | 0^ |
| Scott (2019) | 4 | 91 | 66 | 73% | 16 | 17 |
| Sherburne (2016, 2019-2020) | 6 | 309 | 262 | 85% | 35 | 1*^ |
| Stearns (2020-2021) | 17 | 249 | 190 | 76% | 34 | 1 |
| Steele (2019) | 4 | 21 | 8 | 38% | 14 | 0 |
| Swift (2020) | 8 | 25 | 11 | 44% | 16 | 2 |
| Todd (2017) | 9 | 74 | 46 | 62% | 27 | 0^ |
| Wabasha (2018-2019) | 14 | 476 | 389 | 82% | 35 | 0^ |
| Wadena (2018) | 4 | 26 | 22 | 85% | 20 | 0^ |
| Washington (2020) | 2 | 100 | 88 | 88% | 30 | 27 |
| Watonwan (2020) | 1 | 4 | 4 | 100% | 2 | 0 |
| Winona (2017) | 13 | 286 | 232 | 81% | 35 | 1**^ |
| Wright (2019-2020) | 5 | 180 | 116 | 64% | 29 | 2 |
| Total | 291 | 5,700 | 4,314 | 76% | 75 | 65 |
*Based on 2016 sampling, follow-up samples were non-detect. Initial detection was likely due to cross contamination.
**Based on 2017 sampling, follow-up samples were non-detect. Initial detection was likely due to cross contamination.
^The majority of sampling for this county occurred prior to 2019, before cyanazine degradates were analyzed.
+ Please note the year sampled for each county. Laboratory techniques changed in 2016 to include the analysis of additional compounds and lower detection levels. Additional compounds were added to the analytical list in 2019.
| 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 | 66% | 50 | 760 | 21,000 | 800,000 | HRL** |
| Alachlor ESA | 47% | <MRL* | 740 | 12,000 | 50,000 | RAA*** |
| †DEDI Atrazine | 33% | <MRL | 200 | 1,800 | 3,000 | Parent HRL |
| Metolachlor OXA | 28% | <MRL | 120 | 12,000 | 800,000 | HRL |
| Atrazine | 25% | <MRL | 66 | 1,400 | 3,000 | HRL |
| Desethylatrazine | 23% | <MRL | 120 | 1,500 | 3,000 | Parent HRL |
| Acetochlor ESA | 22% | <MRL | 100 | 2,500 | 300,000 | HRL |
| Hydroxyatrazine | 14% | <MRL | 11 | 560 | 20,000 | RA**** |
*<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;
****RA = Rapid Assessment, a non-promulgated value established by the Minnesota Department of Health.
†DEDI Atrazine, unlike the other pesticides in this table, was not tested for in 2016.
Phase 2 (cyanazine only)
- From 2019 to 2024, the MDA tested 5,096 private wells across the state, and 238 of those wells had total cyanazine concentrations above the chronic health risk limit (HRL) of 1 microgram per liter (μg/L).
| County (years sampled) | Number of Wells Sampled | Number of Wells above the chronic HRL | Number of Wells above the acute HRL | Total Cyanazine Focus Report |
|---|---|---|---|---|
Benton | 118 | 0 | 0 | |
Carver | 27 | 0 | 0 | |
Chippewa | 50 | 2 | 1 | |
Chisago | 95 | 0 | 0 | |
Dakota (2019-2024) | 822 | 75 | 11 | |
Dodge (2021) | 14 | 0 | 0 | |
Douglas (2022) | 63 | 0 | 0 | |
Fillmore (2019-2023) | 184 | 2 | 1 | |
Goodhue (2019-2024) | 634 | 54 | 6 | |
Houston (2019-2024) | 162 | 3 | 1 | |
Kandiyohi (2022-2023) | 28 | 0 | 1 | |
Meeker (2019) | 19 | 0 | 0 | |
Morrison (2020-2023) | 152 | 0 | 0 | |
Mower (2020) | 173 | 2 | 0 | |
Olmsted (2019-2023) | 134 | 4 | 1 | |
Otter Tail (2023-2024) | 172 | 1 | 0 | |
Pipestone (2019-2022) | 36 | 1 | 0 | |
Polk (2019) | 11 | 0 | 0 | |
Pope (2023) | 13 | 0 | 0 | |
Rice (2019-2024) | 23 | 1 | 0 | |
Rock (2022) | 16 | 0 | 0 | |
Scott (2019-2024) | 409 | 29 | 6 | |
Sherburne (2019-2023) | 253 | 0 | 0 | |
Stearns (2020-2023) | 259 | 0 | 1 | |
Steele | 21 | 0 | 0 | |
Wabasha (2019-2023) | 170 | 6 | 1 | |
Washington (2020-2024) | 426 | 48 | 10 | |
Winona (2021-2022) | 115 | 4 | 0 | |
Wright (2019-2023) | 180 | 2 | 0 |
Phase 3 Monitoring
In the fall of 2025, the MDA continued to sample vulnerable private wells in the state, with the focus on total cyanazine (cyanazine plus the degradates of cyanazine) and 4-hydroxychlorothalonil (4-HDC) as the most likely pesticide compounds to be found above drinking water reference values. Additionally, a subset of wells monitored for 4-HDC were also analyzed for 2 neonicotinoid insecticide compounds, clothianidin and imidacloprid. A brief summary is below and more details can be found in the Private Well Pesticide Sampling Project Data summary Report, 2019-2025 located in the Minnesota Water Research Digital Library.
Total cyanazine (cyanazine and atrazine and their known degradates)
The MDA monitored 283 wells, primarily located in Dakota, Goodhue and Washington Counties, for total cyanazine in 2025. Of these, 41 had total cyanazine concentrations above the chronic HRL of 1,000 ng/L, including 3 wells that had total cyanazine concentrations above the acute HRL of 3,000 ng/L.
4-Hydroxychlorthalonil (fungicide degradate)
In 2025, the MDA monitored 208 wells, 14% of the tested wells had 4-HDC detected, and 2 wells had concentrations above the drinking water reference value of 2,000 ng/L.
Clothianidin and imidacloprid (neonicotinoid insecticides)
The MDA monitored 68 wells for clothianidin and imidacloprid in 2025. There were 17 detections of clothianidin and 2 detections of imidacloprid. None of these concentrations approached the respective HRLs of these 2 compounds. In 2026, thiamethoxam will be added to this neonicotinoid list.
