Sinkhole Program

Sinkholes form when the ground collapses into cracks and caverns that have formed below the ground surface. The formation of sinkholes is common in western Wisconsin because of the presence of readily dissolvable limestone bedrock that is near the surface. Sinkholes can vary in size and depth from a few feet to hundreds of feet and can form slowly over hundreds to thousands of years. The central and eastern region of St. Croix County is especially vulnerable to the formation of sinkholes, as limestone is commonly the uppermost bedrock, and the bedrock is shallow. Shallow bedrock means that there is a thin layer (typically less than 50 feet) of sediment overlying the bedrock layer. In some areas of the County, there are only a few feet of sediment or even less than a foot of sediment covering the uppermost bedrock layer!

Sinkholes can be dangerous for citizen safety and for infrastructure. Along with the concern related to public safety, sinkholes also function as direct conduits from the ground surface to the water table. These conduits mean that the groundwater in these areas is extremely vulnerable to contamination from the surface. All of the citizens of St. Croix County rely on groundwater for drinking water through the use of private and public wells, so it is essential to ensure that sinkholes are properly remediated.

Program Background

St. Croix County is invested in protecting its citizens and water resources and has started a program to track and analyze the presence and severity of sinkhole locations so as to better assess their risks to public safety and water quality. This program involves using remote sensing data to help identify potential sinkhole locations and provide St. Croix County citizens with information about sinkhole remediation. Along with the remote sensing data tracking, St. Croix County’s Resource Management Division staff are also available to respond to citizen concerns related to sinkhole development. If you know of a sinkhole or suspect that a sinkhole is forming on your property, please fill out the online survey form located here. Include as much detail as possible. County staff will reach out further to set up a site visit. 

Sinkhole Remediation

Sinkholes can be difficult to remediate, as there is ultimately no way to completely stop the dissolution of the limestone bedrock, which is the cause of their development. However, proper remediation can significantly slow sinkhole development, lower the risk of sudden surface collapse, and reduce the risk of contaminated water quickly reaching the water table. Smaller sinkholes can be remediated by the landowner, and larger sinkholes should be remediated by experts, please utilize this list of contractors who offer excavation remediation services.

Related Links

Karst and Shallow Carbonate Bedrock in Wisconsin

Wisconsin Geological and Natural History Survey Karst and Sinkholes Webpage

U.S. Forest Service Caves and Karst Webpage

NRCS Karst Sinkhole Treatment