A multi-disciplinary investigation of Irish warm springs and their potential for geothermal energy provision (original) (raw)
Irish warm springs are one of several target types that are being evaluated for their geothermal energy potential during the course of the academia-government-industry, island-wide, collaborative assessment of the geothermal energy potential of Ireland under the IRETHERM project (www.iretherm.ie), funded by Science Foundation Ireland. Forty-two warm springs and warm shallow groundwater occurrences have been recorded to date in Ireland. Water temperatures measured in the springs (approximately 12 °C to 25 °C) are elevated with respect to average Irish groundwater temperatures (10 °C to 11 °C). This study focuses on warm springs in east-central Ireland, which are found in the Carboniferous limestone of the Dublin Basin. Geophysical methods (controlled source electromagnetics (CSEM) and audio-magnetotellurics (AMT)) have been utilised in conjunction with time-lapse hydrogeological and hydrochemical analyses to determine the source of the heated waters at depth and the nature of the geological structures that facilitate the upward movement of the water. This has provided the basis for an assessment of the source of these thermal waters as a potential geothermal energy reservoir. We present subsurface models derived from new geophysical data collected at St. Gorman's Well, Co. Meath in 2013. Highresolution AMT surveys at three warm spring locations in Leinster consisted of a grid of 40 soundings recorded at approximately 200 m intervals centred on each spring. A CSEM survey (25 sounding localities with 100 m spacings along two profiles) was also carried out at one of the locations in order to provide superior resolution of near-surface features. The aim of these surveys was to identify any (electrically conductive) fluid conduit systems that may be associated with the springs and to provide an understanding of the observed association of the springs with major structural lineaments, such as the Iapetus Suture Zone that bisects Ireland. Seasonal hydrochemical sampling of six warm spring locations commenced in July 2013. Data loggers were installed at each location to measure temperature and electrical conductivity (15-minute sampling intervals) throughout the sampling period (July 2013-early 2015). The hydrochemical results and the data from the logger at St. Gorman's Well are examined here in conjunction with regional rainfall and available hydrogeological information in order to establish the nature of the relationship between the hydrological cycle and fluctuations in the hydrochemistry of the spring. Further detailed hydrochemical analyses will be carried out in late 2014 to assess the age of the thermal waters. The combination of these separate strands of investigation will provide a better understanding of the location of the source aquifer for the heated waters.
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