Conduit Flow Paths and Conduit/Matrix Interactions Defined by Quantitative Groundwater Tracing in the Floridan Aquifer

Groundwater tracing and cave mapping conducted in the Woodville Karst Plain of north Florida have revealed an extensive dendritic network of saturated conduits, more than 70 km in total length, that convey water to Wakulla Spring from the northeast, north, northwest, and south. In some places, the conduits are known to connect to swallets and in others are known to extend up-gradient into the aquifer matrix. Two sets of tracer tests were performed in 2005 and 2006 to map groundwater flow pathways between the Ames Sink group of swallets, which receive approximately 60% of the City of Tallahassee's storm water runoff, and the City's wastewater spray field, and characterize groundwater velocities along those pathways. The results of these tests revealed that water flows rapidly from both locations to Wakulla Spring. Groundwater velocities through the swimmable portion of the conduit network range from ~1500 to >2000 m/day and velocities through the smaller conduit pathways range from 250 to >800 m/day. We have also compared the shape and timing of the tracer concentration recovery curves to groundwater levels and swallet stage during the tested periods. The results indicate that the aquifer is composed of conduits with varying capacities to convey water and that those capacities establish controls on local hydraulic gradients in the aquifer. More broadly, the results of these tracer studies indicate that tracer recovery curves can reveal significant and potentially quantifiable insights about the hydraulic dynamics of the aquifer when interpreted relative to continuously measured hydraulic data such as heads and flows within the region being tested.