Survey: Wells show ‘detectable’ pesticide levels

posted July 31, 2017 9:16 a.m. (CDT)
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by / Heidi Clausen, Regional Editor |

TOMAHAWK — A 2016 Wisconsin groundwater survey found “detectable” levels of a pesticide or pesticide metabolite in more than 40 percent of rural wells sampled throughout the state, according to information presented July 20 to the state Board of Agriculture, Trade and Consumer Protection.

While that’s up from 33 percent in 2007, when the last statewide groundwater survey was conducted, there’s reason for optimism as the compounds being detected generally are in low concentrations, according to Rick Graham, a hydrogeologist with the Wisconsin Department of Agriculture, Trade and Consumer Protection. He said the survey showed “no surprises,” as some level of agricultural chemicals can be expected in wells in areas under heavy cultivation.

“We’re finding pesticides in water and nitrates in wells, but generally, they’re in very low concentrations,” he said.

 The 2016 survey of agricultural chemicals in Wisconsin groundwater was conducted by the DATCP and the National Agricultural Statistics Service with funding from a federal Environmental Protection Agency grant. This is the fifth survey done since 1994; the last one was done in 2007. The survey focused on private water well samples in rural areas, and the purpose was to obtain a current picture of pesticides and pesticide breakdown products in groundwater and to compare the levels of those found in earlier surveys.

Of the approximately 750,000 wells in Wisconsin, 401 were sampled between March and August 2016. These were selected randomly based on the percentage of land under cultivation in the area. While about 200 wells were new to the study, about half also were sampled in the previous survey, allowing for a comparison.

Wells were analyzed for 102 compounds, including 70 herbicides, 26 insecticides, four fungicides, one pesticide safener and nitrate-nitrogen. That’s compared to just 32 compounds in the 2007 survey. Graham said this was a “very comprehensive” survey, and “it’s really gonna find what’s out there.”

Because it’s a more thorough review than in the past, the results can’t be directly compared to those of 2007, but the new data has been “normalized” so comparisons can be made “apples to apples,” said Lori Bowman, director of the DATCP Agrichemical Management Bureau.

The most commonly detected pesticide compound was the herbicide metabolite metolachlor ESA, found in an estimated 32 percent of wells. The second most commonly found pesticide compound was the herbicide metabolite alachlor ESA, found in some 21 percent of wells.

The statewide estimate of wells containing atrazine or one of its total chlorinated residues was almost 23 percent. Bowman said there has been a “statistically significant increase” in the percentage of wells containing TCR and metolachlor ESA. She said the rise in TCRs has largely been due to deethylatrazine.

“This is not the trend that we wanted to see,” she said, but levels are well below drinking water standards.

Half of the wells surveyed showed some presence of nitrate-nitrogen, but just 8 percent had more than 10 parts per million, which is the drinking water standard. That’s compared to 13 percent over 10 ppm in 1994. Graham said this downward trend is good news.

“It’s reassuring,” he said, because there a lot of good things happening that led to this, including better well building and nutrient-management planning.

The study also showed an increase in the number of pesticides found per well, with about 65 percent having one pesticide per well, compared to a little more than 60 percent in 2007. Forty percent of wells had three pesticides in 2016, compared to 22 percent in 2007.

Bowman said there was one detection of neonicotinoids, which are a concern for bees, at a southern Marathon County dairy farm.

She said the survey has left them with about as many questions as answers, and they’re trying to more actively engage the EPA on issues surrounding the presence of farm chemicals in wells, asking questions such as if the EPA is evaluating the “cocktail” of compounds and if there are synergistic effects, as well as how to go about performing a risk analysis on the infinite product combinations. They also wonder, she said, what homeowners need to know about the safety of their water supply.

“This is really a snapshot for us to look at what does groundwater look like in private drinking water wells,” she said.

To view complete results from the 2016 “Agricultural Chemicals in Wisconsin Groundwater” survey, visit https://​​Documents/​GroundwaterReport2017.pdf.

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