Any number of human activities can have adverse effects on groundwater quality.
Many times we consider groundwater the "hidden resource" because it is not readily seen - like a tree, bird, or river. It is often difficult for people to understand groundwater and why human action affects its quantity and quality so readily. What some people don't realize is that there is a way to see, study, and experience groundwater "up close and personal" - this geologic phenomenon is called karst. A karst landscape is mostly limestone and dolomite bedrock which will dissolve in slightly acidic rainwater. Over the years, the bedrock dissolves and creates conduits, or underground "pipes". Some components of a karst terrain are features many people have seen before such as caves, sinkholes, springs, and losing streams. Together these features form a sort of window to groundwater allowing us to see a "hidden resource".
A sinkhole is a basin that funnels water quickly into the earth. Sinkholes can range in size from a few inches to many feet.