Groundwater age dating with chlorofluorocarbons

Estimating the fate and mobility of CFC-113 in groundwater: results from the Gloucester Landfill Project.

Lesage (Editors), Groundwater Contamination and Analysis at Hazardous Waste Sites, Marcel Dekker, New York, pp.

Source of text: This review was assembled by Eric Caldwell, primarily from Solomon et al.

Comparison of Chlorofluorocarbon-Age Dating with Paticle-Tracking Results of a Regional Ground-water Flow Model of the Portland Basin, Oregon and Washington.

CFC concentrations in groundwater have been used as tracers and to estimate groundwater age (Thompson et al., 1974; Randall and Schultz, 1976; Schultz et al., 1976; Thompson and Hayes, 1979; Busenberg and Plummer, 1992; Dunkle et al., 1993; Plummer et al., 1993; Ekwurzel et al., 1994; Reilly et al., 1994; Hinkle and Snyder, 1997).

By measuring CFC concentrations in groundwater and determining or estimating the recharge temperature of the groundwater, a CFC-model age can be assigned to the sample.

CFCs have certain advantages over tritium because CFCs are detectable in lower concentrations than tritium, and are, therefore, more sensitive indicators of modern water where modern and old water mix. Apparent CFC ages are obtained by converting measured CFC concentrations in groundwater to equivalent air concentrations using known solubility relationships (Warner and Weiss, 1985; Bu and Warner, 1995) and the recharge temperature. Inferring shallow groundwater flow in saprolite and fractured rock using environmental tracers. Corrections for excess air are made if appropriate (Busenberg and Plummer, 1992). However, this is not always the case, particularly if the unsaturated zone is thick (Weeks et al., 1982; Severinghaus et al., 1994; Cook and Solomon, 1995). A time lag associated with gas diffusion through the unsaturated zone is strongly dependent on the soil water content and CFC solubility, and to a lesser extent on the recharge rate. Because the atmospheric concentration curve is approximately linear with time, dispersion has a minimal effect on concentration profiles.

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