USDA: Many factors for Kewaunee Co. well contamination, including human and bovine waste

LUXEMBURG - A variety of natural and manmade factors appear to contribute to contamination of private water wells in Kewaunee County, and both bovine manure and human feces are to blame.

Those were among the conclusions of a report by the U.S. Department of Agriculture, which conducted a study on 138 water samples from 131 randomly chosen private wells in the county. USDA Research Microbiologist Mark Borchardt presented the findings to the county's Land and Water Conservation Committee in April and returned June 20 for a public presentation to about 50 citizens with a question-and-answer period in Exposition Hall at the county fairgrounds.

The presentation, "Risk Factors Associated with Private Well Contamination in Kewaunee County, Wisconsin," covered three objectives of research by Borchardt and his team on the county's well water: estimating contamination rates for nitrates and indicator bacteria, and relating those to depth to bedrock (how deep the soil goes before hitting bedrock, a particular concern in the shallow-depth Karst topography of the county); using viruses and fecal markers to determine the source of fecal contamination; and using statistical data to identify risk factors.

Borchardt said the reason is to not only understand what might cause contamination but also how a change in the magnitude of the risk factor might affect the magnitude of the contamination. Also, the results should give direction to policymakers to prevent contamination, such as regulating the number or density of its sources.

"If we had just stopped at the first two objectives, then we're done," Borchardt said after the program. "Now, we understand those factors, those related to contamination and, importantly, those things that don't relate to contamination, (so you can) focus on the things that are important."

The study identified microbes in the water that would come from human feces, bovine feces, and nonspecific fecal sources. It found 33 wells containing microbes with human-specific sources, including pathogens cryptosporidium and rotavirus A; 44 from bovine sources, including rotavirus A, and 79 from nonspecific sources, including cryptosporidium, E. coli, salmonella and rotavirus C.

"You can't conclude (from the data) that there's more bovine contamination than human," Borchardt said in his presentation. "You can conclude both are responsible."

Borchardt added that salmonella and rotavirus C are pathogens not normally found in water.

For the first study objective, the probability of total coliform and nitrate contaminations were charted against depth to bedrock. The results showed that wells located where depth to bedrock is less than 50 feet were more likely to be contaminated than the state average and vice versa. More than half — 2,687 — of the county's estimated 4,896 wells are under the 50-foot mark.

Risk factors considered were land use and bedrock features (including sinkholes and surface ledges) within certain distances from the wells, rainfall and groundwater levels and recharge (change in its levels) within certain days of sampling, and depth to bedrock at the wells.

The only significant factor for the probability of detecting microbes from bovine manure sources was groundwater recharge over the seven days prior to sampling — "When groundwater is rising, the surface water has less room to go into the soil," Borchardt said. He noted he was surprised to see that agricultural-related risk factors were not significant.

However, regarding concentration of microbes from dairy manure in wells, the top factor is the number of acres of agricultural field within 750 feet, with the concentration rising dramatically above 30 acres. 

The most significant factor for contamination from human fecal sources is the number of septic system drain fields within 750 feet of the well, according to the study. Borchardt said the probability in the county increases by about  2½ times the state average for each system within that distance. Other significant human-source factors noted are the amount of rainfall in the two days prior to sampling, depth to groundwater over the past 14 days, and depth to bedrock.

Agricultural factors pose higher risks for detecting both high levels of nitrates and coliform bacteria in wells, while septic system-related factors were not significant, the study showed.

For nitrates, the study determined the distance to the nearest agricultural field, distance to the nearest manure storage lagoon, distance to the nearest crop field and the size of a crop field within 750 and 1,500 feet were significant, along with depth to bedrock.

For coliform, distance to the nearest manure lagoon, distance to the nearest agricultural field and nearest crop field, and size of an ag field and crop field within 750 feet were significant factors, as well as depth to bedrock.

Borchardt said he couldn't determine whether the relationship to manure lagoons is because of possible leakage or other factors, such as larger applications of manure to ground closer to the lagoon.

Well construction factors other than location do not appear to significantly affect the risk of contamination, according to the study. That includes the depth of the well and depth of its casing, which is regulated by the Department of Natural Resources for new wells.

"A new well is unlikely to solve the problem (of contamination)," Borchardt said. "It's better to solve the land problem around the well.

"It's a very simple thing. What you do on your land ends up in your water."

FYI

To see the full report on "Risk Factors Associated with Private Well Contamination in Kewaunee County, Wisconsin," visit www.kewauneeco.org, then click on the Departments tab, then Land and Water Conservation, then the Website link, then the link to the report at the top of the page.

Contact Christopher Clough at 920-741-7952, 920-562-8900 or cclough@doorcountyadvocate.com.

RELATED: Kewaunee County Board passes resolutions related to water quality

RELATED: Study results discussed at  Midwest Manure Summit in Green Bay

This article originally appeared on Green Bay Press-Gazette: USDA: Many factors for Kewaunee Co. well contamination, including human and bovine waste