Chlorofluorocarbons as Tracers of Groundwater Transport Processes in a Shallow, Silty Sand Aquifer

P. G. Cook, D. K. Solomon, L. N. Plummer, E. Busenberg, S. L. Schiff

Research output: Contribution to journalArticlepeer-review

127 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)425-434
Number of pages10
JournalWater Resources Research
Volume31
Issue number3
DOIs
Publication statusPublished - Mar 1995
Externally publishedYes

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