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 three-dimensional(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.
Highlights
IntroductionA number of low-enthalpy thermal springs were investigated using a multidisciplinary approach, integrating geophysical surveys, time-lapse measurements of hydrogeological parameters, and detailed hydrochemical analysis, with the aims of (1) identifying the source aquifer(s) for the thermal groundwater, (2) characterising the circulatory systems, and (3) assessing the potential for the existence of deeper, higher temperature, circulation patterns for future geothermal exploitation
Gorman’s Well, which is located in east-central Ireland in the limestones of the Carboniferous Dublin Basin
The dimensionality of the data was analysed by investigating the Z and T responses independently of each other, and the results indicate the existence of a 3D scenario beneath the survey area
Summary
A number of low-enthalpy thermal springs were investigated using a multidisciplinary approach, integrating geophysical surveys, time-lapse measurements of hydrogeological parameters, and detailed hydrochemical analysis, with the aims of (1) identifying the source aquifer(s) for the thermal groundwater, (2) characterising the circulatory systems, and (3) assessing the potential for the existence of deeper, higher temperature, circulation patterns for future geothermal exploitation. Two publications have been produced already from this project; Blake et al (2016a) present the results of a hydrochemical analysis of a set of Irish thermal springs, and Blake et al (2016b) describe a geophysical survey at one of Hydrogeol J the springs (Kilbrook spring, Co. Kildare). Gorman’s Well, which is located in east-central Ireland in the limestones of the Carboniferous Dublin Basin
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