An investigation of uranium occurrence, sources and mobilization processes in selected Irish groundwaters

 

PhD Candidate: Fani Papageorgiou

Supervisors: Professor Frank McDermott (UCD), Dr Liam Morrison (NUIG), Dr Tiernan Henry (NUIG)

Funded by: Science Foundation Ireland through i-CRAG

Abstract:

This PhD project will investigate the occurrence, sources and processes responsible for geogenic uranium mobilisation in selected Irish groundwaters.  The main objective is to build on new low-blank analytical capabilities and on reconnaissance datasets for uranium in Irish groundwaters, to better characterise the sources, geochemical mobilisation processes and health risks posed by uranium chemical toxicity, particularly in private wells. In Ireland, some groundwaters from wells drilled into fractured Caledonian and Tertiary granites and in Carboniferous limestone-shale successions are known to contain levels of dissolved uranium close to or exceeding World Health Organisation (WHO) limits (RPII, 2013).  Reliable uranium data for Irish groundwater at the ppb level remain sparse however.  This project seeks to better understand and quantify the fundamental hydrogeological and hydrochemical processes that control uranium mobilisation and transport in these two distinct aquifer types.  In a recently published reconnaissance survey of 200 public groundwater samples from across the Republic of Ireland, dissolved uranium concentrations exceeded the 2 ?g/L WHO limit in 10% of the sampled wells.  However, almost no reliable data exist for much larger number of private wells (>100,000) that provide the main source of drinking water in several regions.  In regions where elevated concentrations have been demonstrated, the underlying geochemical processes responsible for uranium mobilisation and transport are currently not well characterised, and this will be a major focus of the PhD.  Three geographical areas linked to geological settings linked to Caledonian granites and Namurian shales have been selected for an initial focus in the PhD, based on pilot studies.  Analysis of mineralogical sources/sinks from selected field sites and from laboratory based leaching experiments will use X-Ray Diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometry (SEM-EDS), and Transmission Electron Microscopy (TEM).  U-series measurements (e.g. 234U/238U ratios) will also be undertaken at the National Centre for Isotope Geochemistry (NCIG) to constrain the nature of the sources (primary versus secondary remobilised) and the timescales of mobilisation processes.

References:

Nordstrom, K. (2002) Worldwide occurrences of Arsenic in Groundwater. Science 296, 2143-2145.

Ravenscroft, P., Brammer, H. and Richards, K. (2009) Arsenic Pollution: A Global Synthesis

ISBN: 978-1-405-18602-5