An investigation of Irish thermal springs: provenance, pathways and potential Sarah Blake

An investigation of Irish thermal springs: provenance, pathways and potential Sarah Blake IRETHERM Workshop, Dublin 1 st April 2016

Thermal springs in Ireland

Thermal springs in Ireland Springs range in temperature up to 25 C

Thermal springs in Ireland Springs range in temperature up to 25 C Irish groundwater typically 10 11 C

Thermal springs in Ireland Springs range in temperature up to 25 C Irish groundwater typically 10 11 C Located in S and E of island (ISZ)

Thermal springs in Ireland Springs range in temperature up to 25 C Irish groundwater typically 10 11 C Located in S and E of island (ISZ) Issue from Carboniferous strata

Thermal springs in Ireland Springs range in temperature up to 25 C Irish groundwater typically 10 11 C Located in S and E of island (ISZ) Issue from Carboniferous strata One example of small-scale utilisation of geothermal energy at Mallow swimming pool (19 C)

Geological setting

Geological setting Maximum temperature (red) and electrical conductivity in µs/cm (blue) for each spring.

Geological setting Six springs in Leinster chosen for detailed investigation Cold groundwater data supplied by EPA Maximum temperature (red) and electrical conductivity in µs/cm (blue) for each spring.

Project aims and methods

Project aims and methods Provenance: Pathways: Potential:

Project aims and methods Provenance: determine the source aquifers of the thermal waters Pathways: Potential:

Project aims and methods Provenance: Pathways: determine the source aquifers of the thermal waters characterise the nature of the warm water delivery system Potential:

Project aims and methods Provenance: Pathways: Potential: determine the source aquifers of the thermal waters characterise the nature of the warm water delivery system investigate the possibility of deeper water circulation patterns which might offer higher temperature waters

Project aims and methods AMT October 2013 AMT July 2012 Maximum temperature (red) and mean electrical conductivity in µs/cm (blue) for each spring.

Project aims and methods AMT October 2013 Hydrochemical study AMT July 2012 Maximum temperature (red) and mean electrical conductivity in µs/cm (blue) for each spring.

Project aims and methods AMT October 2013 Hydrochemical study AMT July 2012 Forthcoming paper: Blake, S., Henry, T., Murray, J., Flood, R., Muller, M., Jones, A.G., Rath, V. Investigating the provenance of thermal groundwater using compositional multivariate statistical analysis: a hydrochemical study from Ireland. Under review at Applied Geochemistry (Special Issue on Geochemical Statistics)

Hydrochemical study main findings

Hydrochemical study main findings Two endmember types of thermal spring

Hydrochemical study main findings Two endmember types of thermal spring Type 1: Na-Cl-type Steady temperature Little influence from seasonal recharge Longer residence times Louisa Bridge, St. Edmundsbury Type 2: Ca-HCO 3 -type Variable temperature (warmer after recharge) Strong influence from seasonal recharge Less evolved hydrochemistry St. Gorman s Well

Hydrochemical study main findings Time-lapse temperature (blue) and electrical conductivity (black) measurements (15 minute sampling interval).

Hydrochemical study main findings Most springs governed by carbonate dissolution

Hydrochemical study main findings Most springs governed by carbonate dissolution Na-Cl-type springs have a deep, non-carbonate source

Hydrochemical study main findings Most springs governed by carbonate dissolution Na-Cl-type springs have a deep, non-carbonate source Excess Cl from dissolution of evaporites

Electromagnetic imaging of thermal springs

Electromagnetic imaging of thermal springs AMT October 2013 AMT July 2012 Maximum temperature (red) and mean electrical conductivity in µs/cm (blue) for each spring.

Electromagnetic imaging of thermal springs Carboniferous limestones low 1 porosity fracture and conduit flow AMT October 2013 AMT July 2012 Maximum temperature (red) and mean electrical conductivity in µs/cm (blue) for each spring.

Electromagnetic imaging of thermal springs Carboniferous limestones low 1 porosity fracture and conduit flow Used AMT to identify (electrically conductive) fluid pathways in the bedrock AMT October 2013 AMT July 2012 Maximum temperature (red) and mean electrical conductivity in µs/cm (blue) for each spring.

Kilbrook spring

Kilbrook spring AMT July 2012 Maximum temperature (red) and mean electrical conductivity in µs/cm (blue) for each spring.

Kilbrook spring AMT survey layout and geological map of Kilbrook

Kilbrook spring 3-D electrical resistivity models of the subsurface beneath Kilbrook spring

Kilbrook spring 3-D inversion using ModEM code (Egbert and Kelbert, 2012; Kelbert et al., 2014) 3-D electrical resistivity models of the subsurface beneath Kilbrook spring

Kilbrook spring Estimated depth of circulation >> 560m assuming geothermal gradient of 25 C/km 3-D electrical resistivity models of the subsurface beneath Kilbrook spring

St. Gorman s Well

St. Gorman s Well AMT October 2013 Maximum temperature (red) and mean electrical conductivity in µs/cm (blue) for each spring.

St. Gorman s Well AMT survey layout and geological map of St. Gorman s Well

St. Gorman s Well 3-D electrical resistivity models of the subsurface beneath St. Gorman s Well

St. Gorman s Well 3-D resistivity model from ModEM inversion 3-D electrical resistivity models of the subsurface beneath St. Gorman s Well

St. Gorman s Well Estimated depth of circulation >> 500 m for maximum winter temperatures 3-D electrical resistivity models of the subsurface beneath St. Gorman s Well

Main conclusions

Main conclusions Provenance

Main conclusions Provenance Seasonally-driven hydrothermal circulation in limestone for Ca-HCO 3 springs

Main conclusions Provenance Seasonally-driven hydrothermal circulation in limestone for Ca-HCO 3 springs Evidence for evaporite dissolution for Na-Cl-type springs

Main conclusions Provenance Seasonally-driven hydrothermal circulation in limestone for Ca-HCO 3 springs Evidence for evaporite dissolution for Na-Cl-type springs Pathways

Main conclusions Kilbrook spring St. Gorman s Well

Main conclusions Provenance Seasonally-driven hydrothermal circulation in limestone for Ca-HCO 3 springs Evidence for evaporite dissolution for Na-Cl-type springs Pathways Structural control - karstification and conduit flow in limestone Cenozoic strike-slip faults NNW NNE oriented Carboniferous normal faults (NE, or NW for cross-faults) Estimated depths of circulation approx. 500 1,000 m Potential Thickness of Carboniferous basins limits hydrothermal circulation

Main conclusions Practical implications

Main conclusions Practical implications Seasonal variations in temperature affect how much energy is available for abstraction

Main conclusions Practical implications Seasonal variations in temperature affect how much energy is available for abstraction St. Gorman s Well

Main achievements Practical implications Seasonal variations in temperature affect how much energy is available for abstraction Highly transmissive structures are extremely localised hard to target

Main achievements Practical implications Seasonal variations in temperature affect how much energy is available for abstraction Highly transmissive structures are extremely localised hard to target Need to understand the structures and how they interact for the greatest yields

Main conclusions Practical implications Seasonal variations in temperature affect how much energy is available for abstraction Highly transmissive structures are extremely localised hard to target Need to understand the structures and how they interact for the greatest yields 1 m cavity 7,000 m 3 /d 16.3 C Huntstown Fault

Acknowledgements IRETHERM is funded by Science Foundation Ireland (grant no. 10/IN.1/I3022) All members of the IRETHERM team (www.iretherm.ie) Staff and students of DIAS and beyond who helped with data acquisition Landowners and tenants who kindly granted us access to their land My supervisors, co-authors and reviewers for their critical and constructive comments