By LeAnn R. Ralph
MENOMONIE — Wells in areas where there is irrigated sandy soil are more vulnerable to fluctuations in nitrate levels, says Keith Bergeson, an environmental health specialist with the Dunn County Health Department.
Bergeson spoke about nitrate levels in Dunn County water wells at a meeting of the Dunn County Livestock Operations Study Group March 16.
The study group, which met for the first time November 30, is operating as part of a six-month moratorium in Dunn County on expanding or developing new Confined Animal Feeding Operations that would have 1,000 or more animal units.
The focus of LOSG is to evaluate the impact of CAFOs on the health, safety and welfare of Dunn County’s residents and resources, to report on the group’s findings and to make recommendations.
Elevated nitrate levels are a growing concern in areas with agricultural activity, such as large dairy farms or fertilized farm fields.
Dunn County has been tracking nitrate levels for more than 20 years and has 2,241 nitrate results.
A nitrate level of 10 parts per million is considered elevated, and pregnant women, women of child bearing age, infants, and people with low acid in their stomachs are advised to not drink the water.
If nitrate levels reach 20 parts per million, the Dunn County Health Department recommends that no one drink the water, Bergeson said.
Public wells that exceed 10 ppm but are less than 20 ppm must post a notice at all outlets. Public wells that exceed 20 ppm must take action to lower the level of nitrate by replacing the well, putting in a deeper well casing or installing a treatment system, such as reverse osmosis, he said.
No one option for dealing with elevated nitrate levels is best. Much depends on the location of the well and the sources of contamination, Bergeson said.
The problem with water treatment systems is that people often do not understand how to maintain them, he noted.
Elevated nitrate levels also can be an indicator of other contaminants in the groundwater, such as pesticides or herbicides, Bergeson said.
Karst and sandstone
Sandstone bedrock acts as “sponge” for groundwater, and Dunn County has sandstone bedrock.
Karst bedrock (limestone characterized by fissures and sinkholes) acts as a direct conduit to groundwater and can result in contaminants polluting the groundwater quickly.
St. Croix County has some areas of karst bedrock.
Well cap protection and well integrity is important, Bergeson said.
Properly abandoning unused wells also is important because the wells act as a direct conduit to groundwater and provide a channel for contaminants, he said.
Many of the townships in southeastern Dunn County have 20 percent of the wells exceeding 10 ppm for nitrate. Other townships in northern and central Dunn County have 10 to 20 percent of the wells that exceed 10 ppm, Bergeson said.
Areas in Dunn County that are susceptible to groundwater contamination include the Rusk Prairie, an area north of Wheeler and the area around Sand Creek, he said.
Although areas that are vulnerable to nitrate contamination can be predicted, local factors that might impact nitrate levels cannot be predicted, such as a change in land use in a small area, geological features that can be influenced by heavy precipitation or drought, and well integrity, including the depth of the well, the depth of the casing and the quality of the grouting, Bergeson said.
Trends toward nitrate contamination can be predicted in susceptible areas, but contamination can also come from a local source, he said.
Viking Bowl on the south side of Colfax has had some problems with elevated nitrate levels in the well water, Bergeson said, that could be attributed to a change in land use at a nearby farm.
Viking Bowl is located in the Town of Colfax and is not connected to the Village of Colfax’s water system.
Because the groundwater in Colfax flows toward the Red Cedar River, the well at the Viking Bowl was infiltrated with nitrate, Bergeson said.
Colfax’s municipal wells are deeper than most residential wells at 271 feet, 285 feet and 238 feet. The 2015 consumer confidence report for the Colfax Waterworks lists a nitrate level of .3 ppm.
Cedarbrook Church on Highway 25 near Menomonie also has had problems with elevated nitrate levels, and two other wells within a quarter of a mile are approaching 20 ppm, Bergeson said.
A farm was formerly located on the Cedarbrook Church site, and Bergeson said he wondered if the site had contained a well not properly abandoned that provided a conduit to the groundwater for nitrate contamination or some other geological formation that could be responsible.
Sandpoint wells in susceptible areas where there are irrigated farm fields also have had problems with elevated nitrate levels, such as the Sand Creek Cafe, Bergeson said.
One woman in the audience wondered if milk would have elevated nitrate levels if dairy cattle drank contaminated water.
Bergeson said he did not know about nitrate levels in milk but that elevated nitrates do create health problems in cattle, such as the spontaneous abortion of calves.
Anyone who is interested in obtaining more detailed information about nitrate levels in Dunn County water wells can contact the Dunn County Health Department at 715-232-2388 or by e-mail at email@example.com.
The Dunn County Health Department is located in the Dunn County Community Services Building on U.S. Highway 12 East (the former Dunn County Health Care Center).