Dunn County water testing shows nearly 12 percent of wells at or above 10 mg/L for nitrate
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By LeAnn R. Ralph
MENOMONIE — Dunn County’s program to test nearly 1,000 water wells shows that nearly 12 percent of those wells are at or above 10 milligrams per liter for nitrate.
The average nitrate contamination in Dunn County is 4.1 mg/L, said Heather Wood, Dunn County water resources specialist, at the October 18 meeting of the Dunn County Planning, Resources and Development Committee.
Wood gave a preliminary report on the water testing results.
The full report will be written this winter, she said.
Dunn County paid for the water testing program with American Rescue Plan Act (ARPA) funds the county received from the federal government.
The goal was to test 1,000 wells. All together, 1,013 property owners signed up, and 977 samples were collected, with a final of 973 test results, Wood said, noting that some of the wells had to be retested.
The samples were collected over eight weeks by Dunn County Land and Water Conservation personnel and a university intern, Hunter Larson, she said.
At an earlier PR&D committee meeting, Chase Cummings, Dunn County conservationist, noted that Larson’s work had been very much appreciated.
Since Larson is from Colfax and knows Dunn County, he was particularly effective at collecting water samples and doing other work, Cummings said.
Larson showed a tremendous amount of initiative and was an asset to the land and water conservation department, he said.
Nitrates
The water testing checked for nitrates, hardness of the water and pH as well as metals, such as arsenic, lead and copper, and also screened for chemical compounds in herbicides and pesticides, Wood said.
One sample tested at 283 mg/L for nitrate, and when a lab representative called and asked what to do, Wood said the well obviously had to be retested.
After the second test, the nitrate level, thankfully, was much lower than the initial result, she said.
Dunn County’s average for nitrate was 4.1 mg/L, with the highest test coming in at 40.4 mg/L, Wood said.
Many wells had no detectable level of nitrate, and 113 wells were at or above 10 mg/L, she said.
If well water tests above 10 mg/L for nitrate, the property owner should have the well treated, Wood said.
The U.S. Environmental Protection Agency standard for public water supplies is a maximum of 10 mg/L.
Drinking water with nitrate below 10 mg/L is considered safe for everyone in the family to consume.
Water that is higher than 10 mg/L in nitrate can be harmful, especially for infants younger than six months. Seniors citizens and pregnant women also should not drink water that is higher than 10 mg/L for nitrate. Too much nitrate can affect how the blood carries oxygen and can cause methemoglobinemia, also known as “blue baby syndrome.”
Southeast corner
The southeast corner of Dunn County had the highest nitrate levels, Wood said.
The Town of Peru and the Town of Springbrook both had average levels of 8.1 mg/L of nitrate, she said.
The sandy soil types contribute to the higher nitrate levels because the water filters through faster, Wood said.
If a well has high nitrate, there is a state well compensation program. People can get financial assistance from the state to treat for high nitrates or to drill a new well, she said.
Here are the average nitrate levels in each township according to Wood’s presentation:
• New Haven — 3.1 mg/L.
• Sheridan — 3.4 mg/L.
• Wilson — 4.3 mg/L.
• Sand Creek — 3.6 mg/L.
• Tiffany — 2.1 mg/L.
• Hay River — 5.8 mg/L.
• Otter Creek — 2.2 mg/L.
• Grant — 1.8 mg/L.
• Stanton — 2.0 mg/L.
• Sherman — 2.9 mg/L.
• Tainter — 3.9 mg/L.
• Colfax — 4.1 mg/L.
• Lucas — 4.0 mg/L.
• Menomonie — 3.3 mg/L.
• Red Cedar — 5.6 mg/L.
• Elk Mound — 4.1 mg/L.
• Weston — 2.5 mg/L.
• Eau Galle — 5.2 mg/L.
• Dunn — 7.2 mg/L.
• Rock Creek — 7.0 mg/L.
Other testing
The well testing did not include bacteria, Wood said.
Water samples tested for bacteria must be tested within 48 hours, and there was simply no way the lab could accomplish also testing for bacteria within 48 hours when the lab was receiving 150 to 200 samples per week from Dunn County, she said.
In addition, the testing flagged 128 participating wells for arsenic, Wood said.
The test was a screen for arsenic, so it picked up arsenic at a detectable level. The advice to those well owners was to have their wells tested to determine the level of arsenic, she said.
The testing also determined a “saturation index” which the lab listed as “corrosivity,” and that alarmed well owners, Wood said.
Certain water chemistry can corrode copper or cast iron piping on the high end of the scale or can result in lime-scale buildup on the lower end, she said.
The saturation index does not indicate that your water is going to eat holes in your pipes or anything else, simply that it can slightly corrode water pipes, Wood said.
Copper and iron that comes off water pipes can cause wastewater treatment facilities to exceed the limit set in the municipality’s Wisconsin Pollutant Discharge Elimination System (WPDES) permit.
Phosphorus
Phosphorus has both a surface water component and a groundwater component, Wood said.
The maximum phosphorus level was 2.065 mg/L, which is quite high, with an average of .25 mg/L, she said.
Phosphorus is a matter of concentration versus quantity. If one bottle of bleach is poured into Tainter Lake, “that’s not good” but it will not ruin the chemistry of the entire lake, Wood said.
Dunn County plans to work with Barron County to gain a better understanding of how phosphorus run-off can affect phosphorus levels in groundwater, she said.
According to a study by the U.S. Geological Survey in conjunction with the Red Cedar Lakes Association (northeast of Rice Lake), about 17 percent of the phosphorus load in the Red Cedar Lakes came from groundwater, while 80 percent of the phosphorus entered the lakes from tributaries. Septic systems and the Birchwood Sewage Disposal Pond only contributed minor amounts of phosphorus.
Next steps
One of the next steps will be to complete the final report this winter, Wood said.
Another step will be to determine secondary sampling, with the planning beginning soon, she said.
Secondary sampling will likely take place in the summer of 2024, but it will depend on the funds remaining, Wood said.
A report on the secondary sampling will follow, she said.
One consideration will be what does the data suggest is the next best course of action, such as considering nitrate levels in farm areas and around rural subdivisions, Wood said.
Gary Bjork, county board supervisor from Colfax and a member of the PR&D Committee, noted that soil type has an influence on nutrients in the groundwater.
Well casing depth and the depth of the well can impact the amount of nutrients as well, although soil type does have a large impact, Wood said.
Nitrate likes to bind to water, and phosphorus likes to bind to soil, she said.
Soil erosion contributes to phosphorus contamination, and water run-off contributes to nitrate contamination, Wood said.
If the water stays in the upper level of the soil where the plants can use it, then phosphorus and nitrate have less of an impact on groundwater, she said.
Soils that are porous, like the sandy soil in southeastern Dunn County, allow the water to reach the groundwater much more quickly and carry contaminants with it, Wood said.
High percentage
With 113 wells at or above 10 mg/L, that is a high percentage, over 10 percent, said Monica Berrier, county board supervisor from Menomonie and a member of the PR&D committee.
What can be done in sandy soil to mitigate the nitrate leaching into the groundwater? she asked.
Land use considerations, such as whether someone is over-applying soil nutrients or if there are nearby failing septic systems, can contribute to the problem, Wood said.
People should stand by their wellhead and look to see what is going on in the area that is in their control, she said.
If the well casing is below the static water level, then the nitrate level is lower, Wood said, adding that where a well is located in the water table will affect the amount of nitrate.
If people are over-applying fertilizer, the land conservation department can talk to them about not applying so much fertilizer or can encourage them to put in cover crops, Wood said.
A properly functioning drainfield will still not treat for nitrate, and nitrate will still leach from the system, Cummings noted.
Taking a look at rural subdivisions and considering where to place infrastructure will be helpful in the future to mitigate water quality problems, he said.
The data from the well water study can be used to inform and prioritize the land and water conservation department’s workload, and it can be used to inform us about where to put housing, Cummings said.
