The state Department of Natural Resources has released long-awaited proposed revisions to rules regulating runoff management, non-point source performance standards, and concentrated animal feeding operations.

Comments are being accepted through Aug. 7 on the economic impact of the proposed changes, said Kewaunee County Conservationist Davina Boness, who worked on the committee that is proposing updates to NR 151.

The rules package proposes standards that will apply to manure spreading and other agricultural practices in Silurian bedrock areas, which in Wisconsin exists most prominently under Door and Kewaunee counties.

Named for the Silurian geologic period for which it is believed to have been formed, dolomite

silurian dolomite model

A model of Silurian dolomite bedrock used in an educational talk Thursday at Farm Technology Days.

is a limestone-like rock that consists of calcium of magnesium, according to Ken Bradbury of the U.S. Geological Survey (USGS) during an educational presentation about the groundwater of Kewaunee County that he gave at Farm Technology Days on Thursday.

“It’s not very porous but it tends to crack,” and even dissolve under longtime exposure to water, he said, which allows water to travel more quickly to an underlying aquifer than other types of bedrock, he said.

The proposed DNR rules are designed to protect that groundwater; they set agricultural performance standards for practices such as manure spreading and fertilizer application on land with Silurian bedrock underneath.

In addition to Door and Kewaunee, 13 other counties are potentially affected – Brown, Calumet, Door, Fond du Lac, Kenosha, Manitowoc, Milwaukee, Outagamie, Ozaukee, Racine, Walworth, Washington and Waukesha.

“Within the Silurian bedrock area, the rule sets forth spreading rates and practices that vary according to the depth to bedrock,” states the preliminary economic impact analysis prepared by the state. The rules are most stringent when soil depth is 0-2 feet over bedrock, which is the case in parts of northern Kewaunee County and Door County, Boness said.

Concentrated animal feeding operations (CAFOs) will be required to comply with the standards through their pollution discharge permits that are renewed every five years, the analysis says. Farms that do not require such permits but operate in Silurian bedrock areas will also be required to follow the standards in areas of shallow (0-20 feet) surface-to-bedrock depths.

The results of a study of Kewaunee County wells conducted by the USDA, USGS and other agencies recently showed a relationship between well contamination and soil depth, with pollution levels that were especially high in areas with 5 feet or less of soil over bedrock, and to only a slightly lesser extent when the depth to bedrock was 5-20 feet.

NR 151 already has rules that limit agricultural practices to prevent pollution, including requirements for nutrient management plans.

“We’ve been able to prove that even with 80 to 100 percent (of farms adopting) nutrient management plans and the current NR 151 prohibitions, we’re still having trouble,” Boness said, leading to the rules specifically targeting Silurian bedrock areas.

This particular comment period is not about the rule language, Boness said. This phase seeks input for the final economic impact analysis on the question, “Would you, your business, your association, or your local unit of government be affected in a material economic way by the implementation of these targeted non-point performance standards?”

More general public hearings about the revisions to NR 151 are expected in the fall.

The proposed rules are very similar to the recommendations of DNR workgroups that studied groundwater issues last year, and therefore stand a reasonable chance of being adopted, Boness said.

The preliminary draft of the economic impact analysis and a draft of the rule order are available as a clickable link by going to and searching for the keyword phrase “Administrative Rules.”

Comments may be submitted electronically to or mailed to Mike Gilbertson, Water Resources Management Specialist, Wisconsin Department of Natural Resources, P.O. Box 7921 WT/3, Madison, WI 53707.