Chlorofluorocarbons as tracers of groundwater transport processes in a shallow, silty sand aquifer
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Abstract
Detailed depth profiles of Chlorofluorocarbons CFC-11(CFCl3(, CFC-12 (CF2Cl2) and CFC-113 (C2F3Cl3) 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 3H peak has been tracked through time. Detailed vertical sampling has allowed CFC tracer velocities to be estimated to within 10%. Comparison with 3H 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 (Kd < 0.03), and degradation does not appear to be important. CFC- 113 is retarded both with respect to CFC-12 and with respect to 3H (Kd = 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−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.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Chlorofluorocarbons as tracers of groundwater transport processes in a shallow, silty sand aquifer |
| Series title | Water Resources Research |
| DOI | 10.1029/94WR02528 |
| Volume | 31 |
| Issue | 3 |
| Year Published | 1995 |
| Language | English |
| Publisher | American Geophysical Union |
| Contributing office(s) | Toxic Substances Hydrology Program |
| Description | 10 p. |
| First page | 425 |
| Last page | 434 |
| Google Analytic Metrics | Metrics page |