Groundwater age dating with chlorofluorocarbons

05-May-2016 06:27 by 10 Comments

Groundwater age dating with chlorofluorocarbons - Adult Chat Rooms

Chloroflourocarbons (CFCs) are anthropogenic organic compounds that have been produced since the 1930s for a number of industrial and domestic purposes ranging from aerosol propellants to refrigerants. Decrease in growth rates of atmospheric chlorofluorocarbons 11 and 12. There is a short lag time between production and release to the atmosphere, where concentrations have been increasing steadily over the past 60 years.

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CFC-11 (CFCl) have relatively long residence times in the atmosphere (44, 180 and 85 years, respectively; Cunnold et al., 1994; Ko and Jackman, 1994), where they undergo equilibration with surface waters as a function of temperature. 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). These concentrations are compared with the atmospheric concentration curve to obtain an apparent CFC age. As a consequence, atmospheric concentrations show little spatial variation, with only 10% variation observed between average concentrations in Ireland, Oregon, Barbados, Samoa and Tasmania (Cunnold et al., 1994). Two CFCs that have gained recent attention as potential tracers and age-dating tools are trichlorofluoromethane (CCl).

CFCs and tritium can be used in a similar manner for tracing modern water.

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.

In addition to acting as tracers of modern water, CFCs can yield actual recharge ages when mixing and environmental contamination are significant (Hinkle and Snyder, 1997).

Concentrations of CFCs in ocean basins have been used to study mixing processes, and the movement of deep ocean currents (Trumbore et al., 1991; Wallace et al., 1992).

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.

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