Epsilon Archive for Student Projects

Abstract

(CFCs) as tracers in a well-characterised hillslope transect. CFCs are widely used as environmental tracers to estimate groundwater ages and recharge histories. However, their application in snowmelt-dominated catchments is complicated by strong seasonal variations in soil temperature, which affect CFC solubility, and by the dominance of spring snowmelt in driving groundwater recharge, both of which may introduce systematic biases in modelled recharge temperatures and CFC concentrations. A steady-state physically based flow model was applied to simulate tracer signals in the groundwater and stream. Once recharged, CFC-11 and CFC-12 showed little evidence of non-conservative behaviour, supporting their use as effective tracers for water that entered the subsurface between approximately 1960 and 1990. Furthermore, the findings integrate the measured groundwater CFC concentrations into the established process understanding of the site. While the model successfully reproduced observed flowpaths and transit times in the shallower subsurface (< 3 m depth), it significantly overestimated water ages below this depth, a finding consistent with earlier suspicions but only now corroborated with CFC data. These results suggest that the current parameterization of saturated hydraulic conductivity decline with depth requires revision. Future work should recalibrate and advance the model to reduce the rate of hydraulic conductivity decline below 1.5 m depth, potentially reconciling modelled and observed CFC concentrations across the full vertical profile.