These data represent an assessment of the vulnerability of groundwater within the uppermost aquifer. This classification was initially undertaken to support groundwater assessments undertaken for the Water Framework Directive (2000/60/EC). The classification was produced on behalf of Northern Ireland Environment Agency (NIEA) (DoE, Northern Ireland) and is the standard classification currently used for assessing activities which may impact on groundwater resources.
Vulnerability has been primarily determined based upon the assumed permeability and thickness of geological deposits overlying the strata containing the upper, significant water table. Where these deposits are absent, the depth to water table can influence the vulnerability class. The methodology is described in Ball D, McConvey P and Campbell E 2005. A groundwater vulnerability screening methodology for Northern Ireland. British Geological Survey Commissioned Report CR/05/103N - http://maps.bgs.ac.uk/gsni_geoindex/LayerHelp/docs/CR_05_103N_NI_Groundwater_vulnerability_final_9_6_05.pdf
Five classes of vulnerability have been mapped.
5= highest, 1= lowest.
Class 4 can be further subdivided according to the nature of the pathway:
4a — sand and gravel cover (non-aquifer)
4b — moderate permeability cover
4c — low permeability cover
4d — thin soil over bedrock
4e — where superficial aquifers are present
This screening layer for groundwater ‘vulnerability’ does not take into account the nature of the underlying ‘receiving’ aquifer with respect to resource value or significance of pollution occurring. In this screening layer, the vulnerability class above a highly productive dual-porosity aquifer and a very limited productivity fracture flow aquifer may be the same but the consequences of pollution occurring may be quite different with respect to spread of pollutants along groundwater flowpaths and impacts on receptors such as abstraction boreholes and groundwater-fed surface waters. Hence the use of this screening layer within any regional or catchment analysis must be carefully considered.