Well tests show high nitrates
By Kevin O’Brien
Nitrates topped the list of harmful contaminants found in private well tests conducted across Marathon County over the past two years, with over 100 wells showing elevated levels considered hazardous to human health.
Results from 1,001 well tests were reviewed Tuesday by the Environmental Resources Committee after a two-year effort to update groundwater data across the county. Samples collected from the western half of the county last year revealed some of the higher levels of various contaminants, including nitrates, manganese and arsenic.
Of the 111 wells that showed nitrate levels above the 10 mg/L threshold for safe consumption, a majority of them were concentrated in the rural areas west of Wausau. Drinking water with that amount of nitrates in it is considered unsafe for infants and pregnant women, as it has been linked to birth defects and miscarriages. Studies have also suggested that longterm exposure to nitrates at that level can possibly cause thyroid problems, diabetes and some forms of cancer in the general population, according to data provided to the county.
Well owners whose water samples revealed potentially dangerous levels of nitrates and other contaminants were notified by the county and given options for remediating their wells or drilling new ones. Laurie Miskimins, director of Conservation, Planning and Zoning (CPZ), said her staff also reached out to neighboring landowners about possibly getting their wells tested.
Kevin Masarik, director of the UWStevens Point’s Center of Watershed Science and Education, presented the testing results to ERC members and said the test data can be used to extrapolate predictive models for areas of the county where samples were not taken.
“Every well is a window into the groundwater, and we can use that information to paint a better picture of what we’re seeing throughout Marathon County,” he said.
Masarik said levels of nitrate over 1 mg/L indicate land-use impacts on groundwater, such as the application of fertilizers, leaking
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septic systems and animal waste. Over half of the 1,001 tested (55 percent) showed at least some evidence of land-use impacts.
In addition, he said the 11 percent of samples that exceeded safe drinking water standards is bit higher than the statewide average of 8 to 10 percent. The contamination is “not distributed equally” across the county, he noted, with clusters A data dashboard developed from the results showed that some of the highest nitrate averages appeared in the towns of Cassel, Marathon, Wien, Emmet, Cleveland, Eau Pleine, Rib Falls and Rietbrock. The town of Cassel, located between Edgar and Marathon City, had the highest nitrate average in the county, 8.7 mg/L, based on the 37 wells that were sampled in the town.
Four wells produced water with 20.1 mg/L of nitrates – twice the level considered safe.
Other findings
Besides nitrates, the well samples were also tested for chlorides, arsenic, manganese, DACT (atrazine pesticides) and hardness (a combination of calcium and magnesium).
Water hardness is associated with scaling and scum build-up, but it is not considered harmful to human health, according to data presented to the ERC. About a third of the wells tested (36 percent) fell within the “ideal” range, while another 26 percent of water samples were considered to have “hard” water.
Chlorides, which are known to come from fertilizers, septic systems and road salt, are not known to have any direct health impacts, but over the level of 250 mg/L, it cause to take on a salty taste. A vast majority of the county’s wells were either below the threshold considered to be naturally occurring, 10 mg/L, or not high enough to affect the taste.
Arsenic, which is known to cause a whole host of health problems, including various forms of cancer and circulatory problems, was not detected at all in 93 percent of the tested wells, but 18 wells registered levels above the safety standard.
Manganese, another naturally occurring element, can cause water to turn black or brown at levels above .050 mg/L, and anything above .300 mg/L may cause nervous system issues after longterm exposure. Eighty percent of the wells tested were below the levels that create discoloration or health issues, but 62 wells (6 percent) were above the safety threshold.
DACT levels from pesticides were nearly non-existent, with none detected in 99 percent of the wells.
For more information, search for “water testing at www.marathoncounty.gov.
NITRATES - The map above shows the different levels of nitrates found in private wells throughout Marathon County. The red dots with the letter E represent nitrate levels over 10 mg/L, which is considered unsafe for pregnant women and babies and is harmful for the general population to consume for long periods of time. The green, orange and dark blue dots indicate levels that are above what is considered naturally occurring, and the light blue A dots are wells where no nitrates were found.
