Karst formations impact wells due to their ability to bypass much of the filtration and purification that occurs in other groundwater aquifers. Karst forms when bedrock is dissolved by groundwater, this dissolved bedrock expands to form underground streams, sinkholes and swallow holes. More information on karst can be found on the Kentucky Geological Survey website.
In the video above you can see a karst formation that was intersected by the well borehole, and below that is a pinhole leak in the bedrock which is shooting water across the well borehole.
The above video shows a verticle fracture leading to a large karst formation which the well borehole intersects.
This video shows a horizontal karst formation, along with a mirrored view of the formation.
This video shows the well borehole intersecting a large karst formation, so wide in fact that the walls of the formation can not be seen by the camera.
This video shows another karst formation, with water flowing through it.