Mapping and Drilling of Conduits within the Woodville Karst Plain of North Florida

The Woodville Karst Plain (WKP) is a complex hydrogeologic system characterized by major recharge areas, large conduits, cavities, caves, sinkholes, and karst windows along with an abundance of springs, some of which are recognized national treasures. A comprehensive surface and groundwater model for this system is currently being developed. Major efforts are being made to map existing features and their interconnection through cave diving, spring mapping and dye tracing. One of the many features being mapped is the extensive underwater cave and conduit system present within the WKP that have a significant impact to any groundwater model. While over 63 km (39 mi) of cave passages have been mapped using divers, it may only represent a small portion of what may exist within the entire WKP. Therefore, a non-invasive surface geophysical technique, microgravity, was used to provide an increased spatial sampling across the WKP. The microgravity method was selected based upon its ability to map low-density zones that may be due to a cave or conduit. A test project was completed over known conduits to evaluate the effectiveness of the method. This test of the microgravity method was quite successful and led to a production survey of over 43 line-km (27 line-mi) of data acquired across a large portion of WKP. Many low-density anomalies similar to those identified in the test phase were detected. A limited drilling and geophysical logging program of four borings were then completed as follow-up to the microgravity survey. Borings were located in areas corresponding to significant microgravity anomalies. While major conduits were not encountered, there were significant indications of secondary porosity, flow and interconnection such as flow carrying suspended particles up the borehole, turbulent flow indicated at selected fractures and the presence of a crawfish-like creature observed in one borehole. The drilling and geophysical logging program confirmed the significance of the microgravity anomalies and the complexity of the WKP system and reaffirmed that an integrated approach is required for karst investigations.