The challenge of interpreting environmental tracer concentrations in fractured rock and carbonate aquifers

摘要

Atmospheric environmental tracers are constituents and dissolved gases (e.g., chlorofluorocarbons, isotopes of hydrogen, helium, carbon, and oxygen) that are entrained in precipitation and recharged to groundwater. Often the time-varying atmospheric concentrations or processes affecting their evolution in groundwater are used with simplified conceptual models of groundwater flow to estimate residence times, which can then be used to infer velocity, recharge, and properties affecting chemical transport.For example, translating concentrations to residence time (measured in years) is often conducted using concepts of plug flow, binary mixtures of groundwater, and simple models of recharge and flow (Cook and Herczeg 2000).Successful interpretations of environmental tracer concentrations have been widely reported for unconsolidated,porous-media aquifers, and residence times have been introduced as calibration targets using particle-tracking methods in regional flow models (Sanford et al. 2004).