Sinkholes can pollute groundwater

By Judy Brown

Regional Editor

HILBERT - For more than 50 years, Jerry Moehn and his family have piled rocks around a sinkhole on his Calumet County farm.

The sinkhole is part of the geological Niagara Escarpment formation, which begins near the Wisconsin-Illinois state line and ends up in New York.

The escarpment's most famous punctuation mark is Niagara Falls in New York and Canada.

"We want to know more how to manage it," Mr. Moehn said Oct. 4 at a sinkhole and well abandonment management workshop at his farm.

With limited soil over fractured bedrock, nature's filtering system doesn't get a chance to kick in. Mr. Moehn said he hasn't spread manure on the field for years and realizes even commercial fertilizer can be swept down the drain with rain.

Glacierland Resource Conservation & Development, Inc., in cooperation with several agencies, organizations and businesses, sponsored the workshop. It drew about 80 participants from northeastern Wisconsin, many of whom have had concerns about contaminated wells.

Earlier this year, well contaminations in southwestern Brown County drew attention to the karst features in the town of Morrison, said Bill Hafs, Brown County conservationist.

Specialists describe karst as an area where bedrock, such as limestone, is easily dissolved by water.

Karst features include cracks, fractures and sinkholes, all of which are direct conduits to groundwater and easily pollute groundwater. Sinkholes, shallow soils, sinking streams and springs all are found in karst bedrock.

Mr. Hafs said an inventory of the area turned up 200 karst features, which are potential groundwater contamination conduits.

"A lot of our water moves very quickly," said Amy Callis, a Calumet County Land and Water Conservation Department groundwater specialist. "That causes a lot of issues with our groundwater quality."

In some cases, surface water may reach groundwater in 24 hours, she said.

Water drains toward Lake Michigan from the escarpment.

"What happens here doesn't just affect local people, but those downstream," she said.

Greg Hines, Glacierland coordinator, said the Moehn farm workshop was aimed at educating landowners about how to manage sinkholes.

"They will not go away, so the only thing we will do is become more pro-active," Mr. Hines said.

Sinkholes, parts of the limestone dolomite landscape dominated by the Niagara Escarpment, have generated lore.

Some sinkholes are small, with farmers tilling fields and returning soil over the top, Ms. Callis said about a sinkhole that could be no larger than a gopher hole. Others are larger, some measuring more than 18 by 20 feet, she said.

Stories circulate about farmers pouring manure directly into sinkholes, using them as garbage collectors and even throwing in used farm equipment and machinery.

Besides traditional sinkholes, Ms. Callis said other karst features could be springs or disappearing streams or waterways.

"It just disappears," she said. "We found a few in the county where they enter a sinkhole."

Because sinkholes and shallow soils are poor pollutant filters, she suggested well owners test for nitrates and coliform.

A Calumet County well study from 2000 to 2005 found 36 percent of the water samples unsafe for bacteria and 55 percent unsafe or elevated for nitrates.

The state average for bacteria is 15 percent of the wells, Ms. Callis said, "so something is going on here."

Very shallow soils are defined as less than 20 inches, said Mark Krupinski, a soil scientist with the U.S. Department of Agriculture's Natural Resource Conservation Service.

Because there are limitations to soil surveys, he said site-specific investigations are necessary. He uses a Ground Penetrator Radar unit to probe up to 10 feet below the soil surface for cracks and fractures that could mainline water to groundwater.

Different management techniques are available, said Eugene McLeod, Calumet County conservationist. Some include diverting runoff and sealing the sinkhole.

The largest sinkhole sealed so far has been 18 feet deep, he said.

Conservation officials suggested rather than trying to seal a sinkhole of that scale, turning the land over to permanent vegetation should help filter water that goes to the sinkhole.

The Moehn farm has been in the family since 1851. Jerry and Patricia Moehn's son, John, operates the farm.

"We are always conservation-minded," Jerry Moehn said.

The Moehns receive cost sharing for the plan that takes three acres out of production.

The workshop also featured a demonstration on how to properly seal abandoned wells, which also can allow contamination because a direct path to groundwater.

Judy Brown may be reached at jlbrown@vbe.com.