Abstract - A hydrogeological conceptual model of the source, circulation pathways and temporal variation of a low-enthalpy thermal spring
in a fractured limestone setting is derived from a multidisciplinary approach. St. Gorman’s Well is a thermal spring in east-central
Ireland with a complex and variable temperature profile (maximum of 21.8 °C). Geophysical data from a threedimensional(3D)audio-magnetotelluric(AMT) survey are combined with time-lapse hydrogeological data and information from
a previously published hydrochemical analysis to investigate the operation of this intriguing hydrothermal system.
Hydrochemical analysis and time-lapse measurements suggest that the thermal waters flow within the fractured limestones of
the Carboniferous Dublin Basin at all times but display variability in discharge and temperature. The 3D electrical resistivity
model of the subsurface revealed two prominent structures: (1) a NW-aligned faulted contact between two limestone lithologies;
and (2) a dissolutionally enhanced, N-aligned, fault of probable Cenozoic age. The intersection of these two structures, which has
allowed for karstification of the limestone bedrock, has created conduits facilitating the operation of relatively deep hydrothermal
circulation (likely estimated depths between 240 and 1,000 m) within the limestone succession of the Dublin Basin. The results of
this study support a hypothesis that the maximum temperature and simultaneous increased discharge observed at St. Gorman’s
Well each winter is the result of rapid infiltration, heating and recirculation of meteoric waters within a structurally controlled
hydrothermal circulation system.
Hydrogeology Journal, doi.org/10.1007/s10040-021-02393-1, 2021.