Chlorofluorocarbons as tracers of groundwater transport processes in a shallow, silty sand aquifer

Water Resources Research
By: , and 

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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.

Additional publication details

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