September 2018 Meeting

Monday, September 10, 2018
6:00 - 7:30 pm

Pellissippi State Technical Community College
10915 Hardin Valley Road, Knoxville
J.L Goins Administration Building
Faculty/Staff Dining Room


Tracing, Modeling, and Testing Assumptions Used in Dating Groundwater, and, Urban and Rural Impacts on Groundwater in the Woodville Karst Plain, North Florida

Presented By
Gareth Davies


The Woodville Karst Plain (WKP) of northwest Florida has formed in an Oligocene-Miocene carbonate terrane that includes the longest (~75 km explored and mapped) flooded cave system in the USA. Ground water tracing between swallets, sinks (flooded sinkholes and windows) and springs was done showing that velocities in conduits are near the global average of 1.7 km/day and discharge to large springs such as Wakulla Spring occurs in days to weeks along continuous conduit pathways, some dived nearly 20 km long and traced nearly 40 km long.

Urbanization is taking its toll on groundwater and this area of Florida is under increasing stress in that water quality is continuously declining and previously seen seasonal improvement is no longer happening. Wakulla Spring is a "Crown Jewell" natural wonder, and protection of it has suddenly become politically correct regardless of political persuasion. A battle emerged between a growing city and protecting natural water resources.

Difficult questions needed to be asked because of increased groundwater pumping and previous disposal of overcapacity sewage treatment plant effluent and a vast rural community hundreds of kilometers to the north, center-pivot pumping good quality groundwater out of wells and recharging nitrate-laden and poor-quality water. City of Tallahassee wells grab most of the rest. To the south natural swamp waters mix with fresh groundwater from springs, and toward the coast mix with both fresh groundwater and sea water. Fresh groundwater is being overwhelmed.

Calculated groundwater 3H/3He ages (apparently decades) suggests that there could be no immediate groundwater pollution risk. But, a no-mixing assumption is used in obtaining these specious ages and are used to determine modeling parameters used to delineate municipal well-protection and spring protection zones (if and when that is done). The extent of most groundwater basins is unknown.

A lot of disinformation has existed in Florida about whether young rocks produce different karst, etc, etc. We partially resolve this; there is no difference. It is a significantly vulnerable surface and subsurface. Florida exists on recreational springs and beautiful swimming holes, etc. and they are being destroyed, by non-native plants, nitrate and phosphate pollution, algal growths, and dark water. A lack of understanding of spring hydraulics between the coast and Wakulla Spring starkly illustrated by passage of tropical storms, means that fresh groundwater is disappearing fast from wells just north of the coast (Wakulla County) necessitating a ban on any future groundwater wells being drilled.

A series of injected tracer tests using fluorescent dyes established that Wakulla Spring, and other springs are connected to, among other locations, the City of Tallahassee Sewage Treatment Plant Sprayfield, and its elevated nitrate. This was a contributor to the spring, but with such huge groundwater basins, other areas of center-pivot irrigation and fertilizer use were overwhelming the good quality ground water, flowing south, then impacted by storm-related additions of black, tannic swamp waters near the spring vent.

I will show the results of testing the principal dating assumption (i.e., that there is no mixing of groundwater), and how a new numerical model builds on injected tracing data to accurately simulate tracing paths and diver-mapped conduit paths.


B.S. Millsaps College, Jackson, Mississippi, heavy emphasis in mineralogy and mining geology. M.S. University of Southern Mississippi, Thesis: Uranium Series Dates of Speleothems from Two Caves in the Southern Cumberland Plateau. Follow up work on speleothems from caves in the UK. Many years of work in karst under the classic tutelage of Jim Quinlan, subsequent work in many locations, countries, Caribbean islands, Puerto Rico, but most in hard rock mines in the Rockies, using multiple tracers, fluorescent dyes, but particularly natural isotopes, uranium, deuterium, oxygen and nitrogen.

Fellow, Geological Society of America.


Page updated September 12, 2018