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Note: This story has been updated to reflect the correct percentage of Town of Colfax wells testing above 10 mg/L for nitrate.
By LeAnn R. Ralph
TOWN OF COLFAX — Although agriculture is the primary land use in Dunn County, and agriculture is associated with nitrate contamination of water wells, whether an individual well is contaminated depends on the well’s location and a variety of other factors.
Heather Wood, Dunn County water resources specialist, and Chase Cummings, Dunn County conservationist, made a presentation about groundwater and test results at a meeting of the Town of Colfax Plan Commission September 22.
Of the wells tested in the Town of Colfax, 8.2 percent tested above 10 milligrams per liter for nitrate, with the highest test being 18.2 mg/L and an average of 3.97 mg/L, Wood said, who emphasized that not all of the wells in the Town of Colfax had been tested.
Based on 1982 nitrate data, the average level of nitrates in wells is increasing, Wood said.
The deeper the well, the lower the nitrate levels, which is not a “slam dunk,” but in general, it reduces the risk to dig deeper, she said.
Under the Safe Drinking Water Act, the federal maximum contaminant level for nitrate is 10 mg/L.
The Wisconsin Department of Health Services recommends that all persons should avoid long-term consumption of water with nitrate/nitrogen concentrations greater than 10 mg/L.
Pregnant women and infants should be especially careful about not drinking water with a high nitrate concentration.
“Water with greater than 10 mg/L of nitrate-nitrogen should not be consumed by infants less than six months of age, pregnant women and women who are trying to become pregnant. This includes baby formula made with this water … Some studies suggest that high nitrate water may be linked to birth defects and miscarriages,” according to “Interpreting Well Water Quality Results,” a publication by the Center for Watershed Science and Education, College of Natural Resources, UW-Stevens Point and Extension UW-Madison.
The depth of the well casing also figures into nitrate levels in well water. Deeper casing tends to have lower levels of nitrates, Wood said, adding that a deeper well casing is not a guarantee for avoiding all nitrate problems but that it reduces the risk.
The static water level (SWL) also is important in nitrate contamination, and if the well casing is below the SWL, that will help to reduce nitrates as well, she said.
In general, if the casing is above the SWL, there will be a higher nitrate level in the water, and if the casing is below the SWL, there will be lower nitrate levels, Wood said.
The primary nitrate loading will come from agriculture, particularly row crops and alfalfa, she said.
But nitrate loading also depends on where in the landscape the well is located, whether it is in a groundwater recharge area or a groundwater discharge area, Wood said.
If the well is located in a recharge zone, then the nitrate loading will be higher because the water is “newer” water, and if the well is in a discharge area, the water will be “older” and will have fewer nitrates because the nitrates have been filtered out, she said.
One individual well may have a low nitrate level, even though there is agricultural use upstream, because the well is deep enough, in a discharge area, and is drawing “older” water — perhaps water that came from a forested area years ago when the water was pulled into the system, Wood said.
Across Dunn County, wells are getting deeper, she noted.
Clay and other geologic layers can help filter out nitrates, Wood said.
Nitrate is water soluble, and if the weather is dry, nitrate/nitrogen will stay in the soil longer, and then if there is a heavy rain or snow melt, then the nitrogen can get into the wells, she said.
Land use control is important for controlling nitrates in well water, and farmers in Dunn County are doing good work, but they cannot fix what someone else did in 1985, Wood said.
Dunn County is working on developing a groundwater program. Sample kits are available from the Dunn County Health Department for expecting parents, and the testing is free, Wood said.
Sample kits also are available through Dunn County Land Conservation, but people must pay for the water testing themselves, and the cost is about $60 through UW-Stevens Point, she said.
The Commercial Testing Lab in Colfax also does water testing, but Wood said she was not sure of the cost through Commercial Testing.
Dunn County has a groundwater webpage in the works for Dunn County, too, that will have maps, general information and contact information, she said.
Well water should be tested every 15 months, or more often if problems are suspected or you notice changes in your water, such as an odor, Wood said.
Over time, testing well water every 15 months will provide test results during the spring, summer, winter and fall, and then the test results can be compared to see if there is in an increase or decrease in nitrate levels during certain seasons.
Well data that is provided to Dunn County is used in aggregate form for mapping, Wood said.
If a well is high in nitrates, the solution to bringing the nitrate level down will vary from well to well, and could include digging a deeper well, installing a deeper well casing or using a reverse osmosis system, she said.
Nitrate is an “indicator nutrient,” Cummings said.
If a well is contaminated with nitrate, there could be other contamination as well. The sources of contamination could be animal agriculture or commercial agriculture, he said.
The largest land use in Dunn County is agriculture, but contamination can come from industrial applications and septic systems, too, Cummings said.
The level of nitrates can fluctuate from well to well, and people often ask what they can do about a well that is already contaminated, he said.
The best course of action is to look at the individual well and then make recommendations specific to that well, Cummings said.
The solution could be installing a deeper well casing or drilling a deeper well that goes deeper into the water table, because older water has less nitrate, he said.
Nitrogen is a “leaky” nutrient. Farmers can apply nitrogen according to all of the rules, and a rain event can wash it away, Cummings said.
Agricultural performance standards can help mitigate the application of nitrates/nitrogen to help the groundwater overall, he said.
Land use management can be used to plan for the long term, so that clean water is there for future generations, Cummings said.
In the Colfax area, for example, the soil is sandy and the potential for leaching nutrients out of the soil is high, so nutrient management is especially important, he said.
Some money is available to help with well replacement, Cummings said.
The state Department of Natural Resources has a program to help people replace wells contaminated with nitrate, but applicants cannot have an income above $65,000 per year, and they must be seeking potable water for themselves as well as water for livestock, he said.
“If you don’t own livestock, you are out of luck,” Cummings said.
You must use 100 gallons per day for livestock to be eligible for well replacement for nitrate contamination, he said.
As for enforcing regulations that can affect groundwater, Dunn County’s authority may not be as strong as at the township level, where ordinances can be passed to achieve groundwater goals, Cummings said.
The county does have some authority, but it is limited to the authority granted by the state Legislature through NR-151. The DNR passes implementation of NR-151 to the county, he said.
The updated agricultural standards and manure management ordinance recently adopted by the Dunn County Board includes NR-151, but the land conservation department must offer cost-sharing in many instances. For manure storage structures existing prior to 2002, there must be a cost-share, and there is only so much money to go around, Cummings said.
At the conclusion of the presentations, the Town of Colfax Plan Commission recommended to the Colfax Town Board that the testing of wells continue and that the town’s website should contain information about water testing, the information presented by Wood and Cummings and a link to an online video of their presentation.