The use of dissolved constituents in precipitation, in streamwaters, and in ground waters to infer volumes and rates of water flows through catchments has been standard practice for some time (e.g., Pinder and Jones 1969; Pilgrim et al. 1979). With much emphasis placed recently on learning how the chemical composition of catchment waters evolve, the use of tracers of many types to understand hydrological and geochemical processes has burgeoned ( Hornberger 1991; Peters et al. 1993). Stable isotopes have been of particular usefulness in definition of conceptual models of water flows (e.g., Sklash et al. 1976; Maule and Stein 1990; Stewart and McDonnell 1991). Radiogenic isotopes, both natural and anthropogenic, have also been used as tracers ( Genereux et al. 1993; Rose 1992). Recently, chlorofluorocarbons have been used to trace flowpaths in shallow ground-water systems ( Dunkle et al. 1993).