Publication 180
Investigating the provenance of thermal groundwater using compositional multivariate statistical analysis:
a hydrogeochemical study from Ireland
Sarah Blake, Tiernan Henry, John Murray, Rory Flood, Mark R. Muller, Alan G. Jones, & Volker Rath
Abstract
Thermal groundwater is currently being exploited for district-scale heating in many locations
world-wide. The chemical compositions of these thermal waters reflect the provenance and
circulation patterns of the groundwater, which are controlled by recharge, rock type and
geological structure. Exploring the provenance of these waters using multivariate statistical
analysis (MSA) techniques increases our understanding of the hydrothermal circulation
systems, and provides a reliable tool for assessing these resources.
Hydrochemical data from thermal springs situated in the Carboniferous Dublin Basin in east
central Ireland were explored using MSA, including hierarchical cluster analysis (HCA) and
principal component analysis (P 24 CA), to investigate the source aquifers of the thermal
groundwaters. To take into account the compositional nature of the hydrochemical data,
compositional data analysis (CoDa) techniques were used to process the data prior to the
MSA.
The results of the MSA were examined alongside detailed time-lapse temperature
measurements from several of the springs, and indicate the influence of three important
hydrogeological processes on the hydrochemistry of the thermal waters: 1) salinity and
increased water-rock interaction; 2) dissolution of carbonates; and 3) dissolution of sulfides,
sulfates and oxides associated with mineral deposits. The use of MSA within the CoDa
framework identified subtle temporal variations in the hydrochemistry of the thermal springs,
which could not be identified with more traditional graphing methods, or with a standard
statistical approach. The MSA was successful in distinguishing different geological settings
and different annual behaviours within the group of springs. This study demonstrates the
usefulness of the application of MSA within the CoDa framework in order to better
understand the underlying controlling processes governing the hydrochemistry of a group of
thermal springs in a low-enthalpy setting.
Source
Applied Geochemistry, 75, 171-188, 2016.
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Alan G Jones / 19 April 2017 /
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