Chlorofluorocarbons as tracers of groundwater transport processes in a shallow, silty sand aquifer
- Univ. of Waterloo, Ontario (Canada)
- Univ. of Utah, Salt Lake City, UT (United States)
- Geological Survey, Reston, VA (United States)
Detailed depth profiles of chlorofluorocarbons CFC-11 (CFCl{sub 3}), CFC-12 (CF{sub 2}Cl{sub 2}) and CFC-113 (C{sub 2}F{sub 3}Cl{sub 3}) have been obtained from a well-characterized field site in central Ontario. Aquifer materials comprise predominantly silty sands, with a mean organic carbon content of 0.03%. Nearly one-dimensional flow exists at this site, and the vertical migration of a well-defined {sup 3}H peak has been tracked through time. Detailed vertical sampling has allowed CFC tracer velocities to be estimated to within 10%. Comparison with {sup 3}H profiles enables estimation of chlorofluorocarbon transport parameters. CFC-12 appears to be the most conservative of the CFCs measured. Sorption at this site is low (K{sub d} < 0.03), and degradation does not appear to be important. CFC-113 is retarded both with respect to CFC-12 and with respect to {sup 3}H (K{sub d} = 0.09-0.14). CFC-11 appears to be degraded both in the highly organic unsaturated zone and below 3.5 m depth in the aquifer, where dissolved oxygen concentrations decrease to below 0.5 mg L{sup {minus}1}. The half-life for CFC-11 degradation below 3.5 m depth is less than 2 years. While apparent CFC-12 ages match hydraulic ages to within 20% (up to 30 years), apparent CFC-11 and CFC-113 ages significantly overestimate hydraulic ages at our field site. 37 refs., 9 figs., 3 tabs.
- OSTI ID:
- 81807
- Journal Information:
- Water Resources Research, Vol. 31, Issue 3; Other Information: PBD: Mar 1995
- Country of Publication:
- United States
- Language:
- English
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