Dating groundwater with trifluoromethyl sulfurpentafluoride (SF5CF3), sulfur hexafluoride (SF6), CF3Cl (CFC-13), and CF2Cl2 (CFC-12)
Article first published online: 22 FEB 2008
Copyright 2008 by the American Geophysical Union.
Water Resources Research
Volume 44, Issue 2, February 2008
How to Cite
2008), Dating groundwater with trifluoromethyl sulfurpentafluoride (SF5CF3), sulfur hexafluoride (SF6), CF3Cl (CFC-13), and CF2Cl2 (CFC-12), Water Resour. Res., 44, W02431, doi:10.1029/2007WR006150., and (
- Issue published online: 22 FEB 2008
- Article first published online: 22 FEB 2008
- Manuscript Accepted: 30 OCT 2007
- Manuscript Revised: 3 OCT 2007
- Manuscript Received: 2 MAY 2007
- groundwater age;
- environmental tracers;
 A new groundwater dating procedure using the transient atmospheric signal of the environmental tracers SF5CF3, CFC-13, SF6, and CFC-12 was developed. The analytical procedure determines concentrations of the four tracers in air and water samples. SF5CF3 and CFC-13 can be used to date groundwaters in some environments where the CFCs and SF6 have previously failed because these new tracers have increasing atmospheric input functions, no known terrigenic source, and are believed to be stable under reducing conditions. SF5CF3 has a dating range from 1970 to modern; the mixing ratio (mole fraction) in North American air has increased from the detection limit of 0.005 parts per trillion (ppt) to the 2006 mole fraction of about 0.16 ppt. No evidence was found for degradation of SF5CF3 in laboratory anaerobic systems. The solubility of SF5CF3 was measured in water from 1 to 35°C. Groundwater samples that contained large amounts of terrigenic SF6 did not contain terrigenic SF5CF3. CFC-13 is a trace atmospheric gas with a dating range in groundwater of about 1965 to modern. CFC-13 has been used primarily in very low-temperature refrigeration; thus groundwater environments are less likely to be contaminated with nonatmospheric sources as compared to other widely used CFCs. Because of the low solubility of SF5CF3 and CFC-13 in water, an excess air correction must be applied to the apparent ages. The new dating procedure was tested in water samples from wells and springs from Maryland, Virginia, and West Virginia.