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.
Do you suspect a sinkhole on your property? Please fill out a small survey here
It is important that sinkholes are properly remediated because they act as direct conduits to groundwater which make it more vulnerable to contamination from the surface. 
More information about sinkholes: