SENECA - The Driftless Region in Southwest Wisconsin, Northwest Illinois, Northwest Iowa, and Southeast Minnesota is an ancient, intricately layered landscape that holds its treasure of clean, cold water deep within. Never run over by the glaciers that shaped the landscape in the rest of Wisconsin, its hydrogeology is made up of layers of different bedrock, many of which are riddled with cracks and fissures, caves, and underground rivers.
Dr. Kelvin Rodolfo, Professor Emeritus of Earth and Environmental Sciences, at the University of Illinois at Chicago, spoke to a group of 50 interested citizens on Saturday, July 28, at the Crawford County Highway Department building just south of Seneca. The participants gathered for a ‘Karst Geology Exploration and Sinkhole Verification’ event.
At the event, participants heard a presentation about Karst geology, and then went to look at two sinkholes in the Seneca area. One of the sinkholes was very new, and was actually a complex of sinkholes that had popped up in the last few years. The other was very old, about 25 feet in diameter, with walls about 12-15 feet high.
At the first sinkhole, the area was surrounded by bowl-shaped hills planted into prairie. At the second sinkhole, the area was a heavily wooded declivity, with old trees and forest undergrowth in it.
“The Earth is 4.65 billion years old, and 3.5 billion years ago is when the layers of rock that hold our aquifers in Southwest Wisconsin were laid down,” Rodolfo explained. “If you were to put the entire 4.65 billion years into a 24-hour movie, then humans would have come into existence 23:59 minutes ago and the first written history would have been created 10 seconds ago.”
Karst geology
Seneca has the most sinkholes in Crawford County, with some areas containing over 30 sinkholes per 100 km2. This has been demonstrated by the work of Crawford Stewardship Project to map the county’s sinkholes.
“Two of the rock formations in Crawford County are limestone and a similar rock called dolomite. Limestone, and dolomite to a lesser extent, can be slowly dissolved by the weak acid called carbonic acid that is present in all natural waters at the earth’s surface,” Rodolfo told the group. “The rocks have natural vertical cracks and fissures, as well as horizontal zones of weakness. Together, these function as direct conduits for groundwater to pass downward. The longer the water percolates through these cracks and fissures, the wider they get.”
Rodolfo went on to explain that underground, portions of the cracks and fissures can eventually widen into caves. When the roof of a cave collapses, a sinkhole is formed at the surface. Every sinkhole, of course, also serves as a funnel for passing groundwater down from the surface. The unique geology of limestone and dolomite, with underground passages and caves and sinkholes is called “karst” geology or topography.
“In some places, such as in Door and Brown counties of eastern Wisconsin, the karst rock may serve as an aquifer, or water-bearing rock. Water can pass quickly through it. If the karst aquifer is contaminated, it can be flushed out fairly quickly,” Rodolfo said. “But in Crawford County and the rest of the Driftless, the karst rocks are not aquifers. They only pass the rainfall water down into aquifers, which are several underground sandstone layers. These include the St. Peter, Jordan and Wonewoc formations.”
The experienced hydrogeologist told the group that the best sandstone aquifers are those made of well-rounded and sorted sand grains, because there is much pore space between the grains to hold water. Sandstone aquifers in Crawford County are exceptional because the sands were very well rounded and sorted over tens of millions of years long ago.
But groundwater can seep only very slowly through sandstone, only several inches, or at most a few feet per day. If the groundwater is polluted, the aquifer gets contaminated virtually forever.
“The round sand grains are also highly prized as “frac” sand used in oil and gas production,” Rodolfo explained. “Unfortunately, frac sand mining destroys and pollutes the landscape and must be avoided.”
All of the aquifers in the Driftless are very vulnerable to contamination because of the karst geology. In some areas in Kewaunee County in Northeast Wisconsin, which has shallow aquifers located in a Silurian dolomite bedrock layer, 60 percent of sampled wells contain unsafe levels of fecal material and other contaminants.
Water quality
Rodolfo explained that because of its fractured nature, a karst geologic bedrock can be a poor candidate for building very heavy manure impoundments or ‘lagoons. If the impoundment, for instance, were sited on top of a sinkhole or otherwise structurally weak area of the underlying bedrock, the weight of the impounded manure could cause the bedrock below to collapse.
“What the Crawford Stewardship Project has done here to map the sinkholes using LIDAR radar, is one of a handful of clues about what the underlying geology of an area is like,” Rodolfo explained. “Beyond that, it is very difficult and very expensive to precisely map the nature of underlying bedrock in a given area.”
At the event, Rodolfo went on to point out that despite the state standards, which, in theory should prevent it, a large confined feeder hog operation was recently granted a permit in Grant County. That operation is literally building a manure storage facility on top of a known sinkhole.
“Grant County has even more springs than Crawford County does,” Rodolfo explained. “In Grant, there are about two springs per square mile, meaning that their aquifers are likely even more vulnerable than those in Vernon or Crawford. The state law has tied local government’s hands. When the standards aren’t responsibly administered, then it leaves local communities with all the risk and none of the power.”
Farmers speak
Anne Marie Elwing and William Walleser of WallStone Holsteins attended the event. The two spoke up about some of the regulations already in place in Crawford and Vernon Counties which protect against larger-scale animal agriculture’s potential impacts on the area’s groundwater.
“Crawford and Vernon County both have enacted ordinances which require operations with more than 500 animal units to obtain a county permit,” Elwing explained. “This is more strict than the State Livestock Facility Siting Law, which only comes into play with more than 1,000 animal units. This means that whether or not USDA NRCS cost share dollars are utilized, the strict guidelines on siting and construction of a manure storage structure must meet the guidelines for the structure to be legal.”
At Wall-Stone Holsteins, a 500 animal unit dairy in Vernon County, the Wallesers employ strip cropping, with lots of terraces and grassed waterways. Walleser thinks that having animals in their rotation is of great benefit, along with the use of cover crops in building soil health.
“Because of our use of cover crops, we are able to apply manure on our sloped fields at an increased rate,” Walleser said. “Adding the manure does a lot for our soil health, and because of the conservation land use that we employ, we are able to keep the nutrients from running off and getting in the water.”
Walleser pointed out that despite the widely–debated pros and cons of manure storage facilities, the flip side are the guidelines which limit manure spreading at certain times of the year and in certain situations.
“There’s restrictions on when it is allowed or considered safe to be spreading manure,” Walleser pointed out. “If we were out there spreading every day, there would be increased risks to the water based on bad timing. Bad times to spread include during a spring melt, or at the time of a heavy rain event.”
Walleser reports that his family has also recently installed a new, all-concrete, manure pit, built to code. In the process, the family paid $30,000 to get engineers to survey the underlying bedrock 20 feet down with soil boring tests to determine the stability of the landscape underneath. This process was to ensure that the pit was not sited on top of any unstable, fractured karst geological features.
“The whole industry is moving away from clay-lined earthen lagoons, or pits constructed of concrete blocks,” the young dairyman observed. “Solid concrete pits, properly sited, are the way of the future.”
Contamination sources
Rodolfo pointed out that with the State’s ‘one-size-fits-all’ Livestock Facility Siting Law, siting decisions have been taken away from local government and made the sole province of the state. The only exception is in counties like Crawford and Vernon which took advantage of a historical window to enact ordinances which set the trigger for permitting, 500 animal units, lower than the state’s.
“And what we’ve seen in Kewaunee County is that conscientious farmers of large-scale operations can obtain a state permit, do everything they’re required to do, and still have a part in the adverse impacts on the crucial groundwater assets that they share with their neighbors,” Rodolfo said. “That’s why the state needs to basically set the minimum standards, and then let local government set higher standards based on their deep understanding about specific local conditions.”
In Kewaunee County, a study was conducted to verify sources and the specific nature of contamination of well water in Lincoln Township. The studies authors were Mark Borchardt and Susan Spencer of USDA, Agricultural Research Service. The two worked with the USGS Wisconsin Water Science Center in Marshfield, Wis.
The study, Sources of Fecal Contamination in Groundwater in Rural Northeastern Wisconsin, sampled 10 private wells in Lincoln Township, which had had brown water events. Of those 10 wells sampled, three were shown to contain contaminants from bovine sources, three from human sources. In all, it was determined that 60 percent of sampled wells contained water unfit for human consumption.
Since then, the State of Wisconsin has adopted ‘Sensitive Area’ additions to the Natural Resources administrative rule, NR151. These additions provide standards more stringent than the statewide standards for nutrient management in areas with karst geology overlain by shallow depths of soil for eleven Eastern Wisconsin counties. Since then, the State has also changed the language in the state statutes requiring compliance with private onsite waste treatment systems from “should” to “shall” to require private septic systems to be in compliance with state standards.
