The geology of Kentucky varies dramatically depending on where you are in the state. Be it clay, sand and gravel in the Jackson Purchase Region, sandstone and coal in western and eastern Kentucky, or limestone in central Kentucky, the geology of the area can have a direct impact on the quality and quantity of groundwater.
Water-well and groundwater-quality data can be searched on the Kentucky Geological Survey's Groundwater Information page.
County Groundwater Resource Reports compiled by the Kentucky Geological Survey can also be downloaded there's one for every Kentucky county.  Additional information related to Kentucky groundwater and water wells can be found at the Kentucky Geological Survey's Water page.
Kentucky is well known for its karst features.  Approximately 55% of the state is underlain by rocks that could develop karst terrain (sink holes, sinking streams, caves, and springs). Water wells also intersect karst features.  Click here to view karst related videos.
Additional sources of information pertaining to water wells and groundwater have been developed by the United States Geological Survey (USGS).  Links are provided below:
USGS Groundwater Information
Ground Water Atlas of the United States
Why Some Public-Supply Wells are More Vulnerable to Contamination Than Others (YouTube Video)
Ground Water and the Rural Homeowner