Hydrogeology of Irish Poorly Productive Aquifers

Overview

The Griffith Geoscience Research Programme at QUB is focussed on understanding groundwater flow in poorly productive aquifers located in igneous and metamorphic bedrock units in Ireland. In spite of extending over 65% of the Irish land surface fluid movement in these aquifers, and the interaction between ground- and surface-water bodies, is only poorly understood. Their management and protection is required under the Water Framework Directive, yet there have been few studies to date and conceptual models have not been developed specifically for an Irish context.

Field Sites‌

Five contrasting type areas have been selected for investigation. Each catchment has existing borehole networks (developed by EPA and GSNI/NIEA) which are characterised using borehole geophysical techniques and used for pump tests to characterise the hydraulic properties of the units and as a basis for groundtruthing the geophysical investigations. The sites developed by the EPA in Donegal, Mayo, Louth and Galway typically consist of three nests of boreholes distributed linearly across a small catchment area with transition, shallow and deep wells in each. The Mountstewart site in Co. Down, developed by the NIEA/GSNI, consists of 8 borehole clusters distributed radially within an area of ~3 ha with 19 boreholes.‌‌

Approach

A multidisciplinary approach is applied to a 3D characterisation of each aquifer study site, incorporating traditional borehole hydrogeological and geochemical investigations with multi-scale geophysical surveys and geological mapping. These data provide input for producing conceptual models of groundwater flow in the catchments.

The methodology includes the following:

  1. Desk and field studies to determine/verify catchment boundaries, bedrock geology, overburden thickness and composition leading to development of a conceptual model landscape. A GIS has been developed for each site.
  2. Outcrop mapping of bedrock fracture characteristics to identify/constrain dominant and hydraulically active fracture sets.
  3. Mapping and sampling of the overburden to determine subsoil type, thickness and geomorphological origins.
  4. Geophysical characterisation working down from large scale surveys covering the entire area of each catchment (EM, ERT) to more localised investigations (2D/3D seismics, cross-hole/3D ERT, MRS, GPR, magnetometry, when applicable) at specific sub-scales.
  5. Geochemical analysis of bedrock and overburden.
  6. Borehole geophysical logging (temperature, conductivity, resistivity, natural gamma, High resolution acoustic televiewer (HiRAT), heat-pulse flow meter) is undertaken to map both bedrock structure and groundwater characteristics with depth and identify hydraulically active fractures. They also provide valuable data for ground truthing surface geophysical investigations.
  7. Hydraulic testing: pumping tests, slug tests, and packer tests.
  8. Geochemical sampling of surface water and groundwater with analysis being carried out at all sites for field hydrochemical parameters and major anions/cations, and for trace elements, and environmental isotopes in selected catchments.
  9. Data integration and groundwater modelling

Data integration and development of Conceptual models

Analysis and interpretation of the data from each catchment is undertaken during and following the field campaigns. Cross-comparison and integration of the different data sources is key to understanding the aquifers. Large-scale surveys (ERT and geological mapping) provide a basic structural framework in three dimensions which is refined using more local-scale surveys (seismic refraction/GPR/outcrop and borehole measurement) and integrated with the hydrochemical and hydraulic data.

Project Team

Dr Zuansi Cai

Dr Rachel Cassidy

Dr John Caulfield

Dr Merlyn Chelliah

Dr Jean-Christophe Comte 

Janka Nitsche 

Katarina Pilatova  

Chris Wilson

Selected  Publications:

Comte, J.C., Cassidy, R., Nitsche, J., Ofterdinger, U., Pilatova, K. & Flynn, R., 2012, The typology of Irish Hard-Rock Aquifers based on an Integrated Hydrogeological and Geophysical Approach, Hydrogeology Journal, doi:10.1007/s10040-012-0884-9

Comte, J.C., Cassidy, R. & Ofterdinger, U., A combined Dipole-Dipole/multi-Gradient ERT array optimized for hydrogeological modelling of hard rock aquifers, Int. Conference on Groundwater Flow in Fractured Rocks – GwFR 2012, Prague, May 2012

Cassidy, R., Comte, J.C., Nitsche, J. Pilatova, K., Flynn, R. & U. Ofterdinger, 2011, Towards conceptual models of flow and transport for Irish hard-rock aquifers: a multidisciplinary approach, European Geosciences Union General Assembly 2011, Austria, 03 – 08 April 2011, Vienna

Nitsche, J. & R. Flynn (2011) Investigating Hydraulically Active Fractures in a Shallow Meta-Sedimentary Bedrock Aquifer Using Single Well Tracer Testing, Mount Stewart, Northern Ireland, Hydrostratigraphy of Crystalline Rock Aquifers. NGWA Focus Conference on Fractured Rock and Eastern Groundwater Regional Issues Burlington, Vermont, September 26-27, 2011

Pilatova, K. & U. Ofterdinger, 2011, Hydrochemical case study of the poorly productive Irish bedrock aquifer, IAH International Conference - Groundwater: our source of security in an uncertain future, Pretoria (SA), September 2011

For further Information, please contact:

Dr Ulrich Ofterdinger or Dr Raymond Flynn

Groundwater Research Group

Environmental Engineering Research Centre (EERC)

School of Planning, Architecture and Civil Engineering

Tel: +44 (0) 28 9097 5633