Natural Sulfur Hexafluoride
(SF6) and Carbon Tetrachloride (CF4) in old
groundwater (update: 1/2009)
Recent studies have shown the natural abundance of sulfur hexafluoride (SF6)
and carbon tetrachloride (CF4) in fluorite-containing rocks (Harnisch and Eisenhauer, 1998).
Natural SF6 was also found in old groundwater
(Busenberg and Plummer, 2000) and our studies confirm these
findings. We have collected groundwater samples in the Mojave Desert (California) in 2000, 2002 and 2003
which I have analyzed for dissolved SF6. We have also discovered
the natural abundance of CF4 in these old groundwaters. The concentration of SF6 and CF4 in
the groundwater was found to exceed
several-fold the saturation level with respect to today's atmospheric concentrations of these extremely stable
compounds.
I studied this topic in collaboration with
Justin Kulongoski (US Geological Survey, USGS and Scripps
Institution of Oceanography, SIO), and with Dan Deeds (former SIO) who is working on the CF4 analysis
and who has published an interesting paper in 2008.
We combined the SF6/CF4 results with the work that
Justin Kulongoski has been doing on these groundwater systems. Using helium and carbon-14 chronology
he has found that some of these groundwaters are in excess of 40'000 years old. Interestingly, the
oldest waters are not the ones with the highest SF6 and CF4 concentrations...
