DRIFTLESS - Wisconsin State Geologist Dr. Ken Bradbury spoke to about 50 people in Platteville about soils, geology and the movement of contaminants in groundwater. Bradbury appeared at the Rollo Jamison Museum on a beautiful 65-degree Sunday afternoon, March 8.

Bradbury gave meeting participants a primer on groundwater, karst geology, the soils of the region, the history of mining in Grant County, and the Southwest Wisconsin Groundwater and Geology Study (SWIGG) in Grant, Iowa and Lafayette counties.

Groundwater primer

Bradbury explained that groundwater is the water that fills the holes, pores, cracks and crevices in rock. The water held in the bedrock is known as an aquifer, which is recharged when water from the surface enters the landscape, and then discharges by draining into lakes and rivers.

“The nature of the underlying geology is what makes groundwater more or less vulnerable to contamination,” Bradbury said. “It will also affect the availability of the water.”

Different parts of the state are characterized by different bedrock geologies, and this can help to explain the groundwater challenges different regions experience. Much of the northeast part of the state has a hard, crystalline bedrock, and water tends to sit directly on top of this very old layer. In other parts of the state, there are many other layers laid over the older crystalline rock, which in those areas forms the bottom of the aquifer. 

The southern part of the state is characterized by a relatively young (Ordovician) layer of bedrock, which can be sandstone, limestone or dolomite. In the eastern part of the state, the aquifers tend to be located in Silurian dolomite. In southwest Wisconsin, the aquifers are located in layers of sandstone and limestone.

“In Grant County, the bedrock is near the surface,” Bradbury explained. “That bedrock is overlain by a very shallow layer of soil, so there is not much ability of those thin soils to inflitrate water from the surface before it reaches the fractured bedrock.”

Bradbury discussed how fractured karst geology is prone to erosion over time from carbonic acid in rainwater. He said that this can create underground caves, which can collapse and form sinkholes. These sinkholes, he said, are direct conduits to groundwater and should be protected through earthworks or plantings of deep-rooted perennial vegetation.

“Every year, someone calls us about a new sinkhole having formed,” Bradbury said. “This is happening all the time, particularly in the wetter weather we’ve been experiencing in recent years.”

History of mining

Bradbury also discussed how the history of mining in Grant, Iowa and Lafayette counties has created additional possibilities for contaminants from the surface to reach groundwater.

“There is lots of underground stuff that happened related to mining,” Bradbury said. “The whole landscape is dotted with vertical shafts, underground mines and bore holes. These are an open pipe to let contaminants into groundwater when they are not properly closed.”

Bradbury discussed how the State of Minnesota is lightyears ahead of Wisconsin in mapping of the geology and the aquifers in their state. He said that his team intends to provide a similar level of information for the counties in southwest Wisconsin.

Two employees of the Minnesota Geological and Natural History Survey were invited to make a presentation at the June 2019 meeting of the Wisconsin Speaker’s Task Force on Water Quality that took place in LaCrosse.

Runkel discussed the project Minnesota had undertaken to make a County Geologic Atlas for Water Resource Management. The project had first mapped the geology of the state, and then filled it in with information about the locations of the groundwater aquifers within the geologic formations. The resource is intended to be used by the DNR and county conservation departments in making land use and water resource management decisions.

The citizens of Minnesota voted to amend their state constitution in 1988 to create the ‘Environmental Trust Fund.’ This change earmarked 40 percent of the net Minnesota Lottery sales to fund the initiative, and has resulted in approximately $60 million annually that funds 60 projects per year. It funded about 65 percent of the cost of creating the groundwater atlas. 

In 2008, the Minnesota legislature also passed the Water and Land Legacy Act, which dedicated three-eights of one percent of the Minnesota sales tax (four cents of every $10) to resource conservation projects. This has resulted in about $250 million per year, with 33 percent of the money going to clean water projects, and the rest to outdoor heritage, parks, and arts/cultural heritage projects.

Ongoing research

Geologist Eric Stewart of WGNHS, according to Bradbury, is undertaking a new survey of the bedrock of Grant County. He will team up with another WGNHS researcher, Geomorplologist Eric Carson, who is surveying the soils of the county.

Stewart’s project will be conducted between 2019-2022. The project involves field work and compiling pre-existing data to map bedrock geology of Grant County at 1:100,000-scale. The publication will provide information on bedrock elevation, the thickness, distribution, and composition of bedrock units, and structures (folds and faults). 

Six 7.5’ quadrangles will also be mapped at 1:24,000 scale to provide a more detailed understanding of the relationship between structures, hydraulic conductivity, geomorphology, and mineralization.

In coordination with the southwest Wisconsin Geology and Groundwater (SWIGG) project, this mapping allows them to predict and identify patterns in the physical properties of the rocks that affect the area’s natural resources, including the aquifer system.

Stewart’s research of the bedrock will be paired with the research of his colleague Eric Carson, who is leading a project to survey the distribution of a layer of redclay in the soils of southwest Wisconsin known as the Rountree Formation.

This clay layer is formed as the carbonate bedrock chemically weathers over geologic time. Because the Rountree Formation is covered by younger sediment, very little is known about it. This project will evaluate the geographic distribution of this red clay layer across numerous counties; investigate its geologic and geochemical properties; and assess what—if any—role it plays in buffering the bedrock groundwater system from surface contamination. 

In 2019, Carson’s team completed mapping of Crawford, Vernon, and Richland counties. Those maps are currently undergoing peer review, and will be released in middle-to-late 2020 after that process is complete. He has begun Monroe County, but that work will be delayed in order to focus on Grant, Iowa and Lafayette counties. His team will have Grant County maps complete by summer 2020; Iowa County by summer 2021; and Lafayette County by summer 2022 or 2023.

New book

Dr. Eric Carson has recently completed a new book about the geology of the Driftless. The book’s title is, ‘The Physical Geography and Geology of the Driftless Area.’ Carson was involved in completing a book that was started through the research of one of his mentors, James Knox.

Over the course of his 43-year career, James C. Knox conducted seminal research on the geomorphology of the Driftless Area of southwestern Wisconsin. His research covered wide-ranging topics such as long-term landscape evolution in the Driftless Area; responses of floods to climate change since the last glaciation; processes and timing of floodplain sediment deposition on both small streams and on the Mississippi River; impacts of European settlement on the landscape; and responses of stream systems to land-use changes. 

The book presents the state of knowledge of the physical geography and geology of this unglaciated region in the otherwise-glaciated Midwest. The book includes contributions written by Knox prior to his passing in 2012, and by a number of his former colleagues and graduate students.

SWIGG Study

The SWIGG Study has been much in the news headlines in recent years. Residents of Grant, Iowa and Lafayette counties have received basic nitrate and coliform bacteria results about their private wells. Now, the study has almost completed the ‘phase two’ of four rounds of seasonal microbial source testing. 

From there, the study will proceed into its third and final phase, looking at underlying geology, land use and well construction characteristics. This will yield a correlational report on risk factors for groundwater and drinking water contamination in the three counties.

“The groundwater of southwest Wisconsin is made more vulnerable because of shallow layers of soil over a fractured bedrock, improperly abandoned wells and mines, and poorly designed wells,” Bradbury summed up. “In the future, after the study is complete, we will be faced with the need to better understand the fundamental hydrogeology, look at changes in well construction practices, explore how to manage nutrients from agriculture, and decide what the appropriate long-term groundwater quality goals should be.”