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
SEPTEMBER PRESENTATION
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
Abstract
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.
Biography
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 |