GSNI GeoIndex Groundwater vulnerability screening layer

This map layer represents 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 -pdf document. Since this original layer production in 2005 some further modifications have been made to this regional layer, details of which can be obtained from the GSNI hydrogeologist if required. Five classes of vulnerability have been mapped: Highest:Five Lowest:One Class4 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 POINT RECHARGE SCENARIOS Within 30 m of mapped features of point recharge (e.g karst features and mine shafts), vulnerability is always category Five. The representation of vulnerability is intended to be used as a first pass assessment of relative vulnerability across the map layer area. It allows an understanding to be gained of where groundwater is more or less vulnerable to surface or near-surface activities where pollutants could be released and, as such, can help with strategic assessments as well as initial consideration of specific developments, activities or pollution events. Due to natural geological variability and data availability, this map cannot and is not intended to represent actual conditions on a site specific scale. Parameters used for determining vulnerability class are based on average values or broad ranges and local variation, which does commonly occur, is not represented. The Geological Survey of Northern Ireland (GSNI) makes no warranties on this map layers use for such more detailed assessments. The burden for determining fitness for such uses lies with the user. Where consideration of vulnerability of groundwater and the local groundwater resource is required for a specific site or location, then it is recommended that more detailed hydrogeological investigation be carried out. This will normally involve some form of intrusive investigation, such as trial-pitting or drilling. Information supplied is based on the material available to GSNI at the time of production and should not be regarded as complete data on the elements or areas being considered. Furthermore, uncertainty is an inherent element in drawing geological boundaries and local details are generalised in some cases. The nature of the receiving aquifer is not represented in the vulnerability class and as such, the significance with respect to potential impact on the groundwater resource is not addressed on this map layer. An aquifer map layer is also available for Northern Ireland at 1:250 000 scale and should normally also be consulted when using this map layer. The methodology used does not consider the physicochemical make up of any specific pollutant type, which will have an influence on how it is attenuated or otherwise along the pathway to the water table.

Tags: Geology, Ground water management, Groundwater, Hydrogeology, NERC_DDC
Organization: British Geological Survey (BGS)