EU Water Framework Directive : groundwater-dependent rivers and lakes in Northern Ireland

The EU Water Framework Directive (WFD) requires that those rivers and lakes that are dependent on groundwater be identified and the pressures on these analysed such that the risk of not meeting their environmental objectives by 2015, as set out in Article 4, can be assessed. This report describes the methodology for identifying and carrying out risk assessments for groundwater-dependent rivers and lakes in Northern Ireland, as part of the initial characterisation process. The methodology reflects UK Technical Advisory Group (UKTAG) guidance. The report details those river water bodies and lakes that are groundwater dependent and assesses which of these are at risk of being significantly damaged as a result of groundwater abstractions and potentially polluting point sources; diffuse pollution is addressed elsewhere. The report does not address quantitative impacts on rivers and lakes from groundwater abstractions outside specified assessment zones; the study addressed localised impacts rather than those due to cumulative groundwater abstractions which affect the overall groundwater body water balance, and the ‘available groundwater resource’. This is reported elsewhere. The risk assessment for lakes has been restricted to those with an area greater than 50 hectares, these being the reporting units agreed for the UK for initial characterisation. Lough Neagh and Upper and Lower Lough Erne, whilst obviously falling within this category due to their significant scale, are reported elsewhere. Of the 673 river water bodies considered, 564 are classified as groundwater dependent. Of the 17 lakes assessed, 10 are classified as groundwater dependent. None of the groundwater-dependent lakes are assessed as being affected by groundwater abstractions. Flows in four river water bodies are possibly at local risk due to groundwater abstractions, and one, the Breckagh Burn, is probably at risk. All groundwater-dependent lakes have been classified as risk category 2b in relation to potentially polluting point sources. Using an approach that assesses the equivalent categories for river water bodies based on the sum of the number of sources within the surrounding assessment zones, regardless of type, 113 river water bodies were classified as risk category 2a and the remainder risk category 2b. The report details data limitations and gaps in knowledge affecting the initial characterisation process used

EU Water Framework Directive : groundwater-dependent terrestrial ecosystems in Northern Ireland

The EU Water Framework Directive (WFD) requires those terrestrial ecosystems dependent on groundwater be identified and the anthropogenic pressures acting on the ecosystems analysed. Where significant damage is occurring or could occur due to groundwater factors, then the associated groundwater body is considered to be at risk of not attaining ‘good status’ as defined in the Directive. This report describes the methodology for identifying and carrying out risk assessments for groundwater-dependent terrestrial ecosystems (GWDTEs) in Northern Ireland as part of the initial characterisation process of the WFD. The methodology is based on UK Technical Advisory Group (UKTAG) guidance. 22 designated sites, all Special Areas of Conservation (SACs), have been identified in Northern Ireland as GWDTEs. The report details the level of risk to these GWDTEs from groundwater abstractions and potentially polluting point sources. With one exception, the occurrence of both types of groundwater pressure within the assessment zones of the GWDTEs set by the UKTAG guidance is negligible and hence Risk Category 2b has been determined for initial characterisation. Murlough SAC has been given a Risk Category of 2a for potentially polluting point sources, i.e. it is not at significant risk but confidence that the available information is comprehensive and reliable is low. This is because there are a number of controlled point sources on or close to the GWDTE, on geology that is likely to be in hydraulic connection with it, and some of these sources are concentrated in a small area. It is suggested that improved monitoring of this site would be advisable to increase confidence in the risk assessment. The report highlights a number of aspects that could improve the methodology for identification and assessment of risk for GWDTEs

Improving the characterization of Quaternary deposits for groundwater vulnerability assessments using maps of recharge and attenuation potential

Assessing aquifer vulnerability is difficult for bedrock aquifers concealed by highly variable superficial deposits such as glacial till. Many current groundwater vulnerability maps, and the geological maps on which they are based, do not adequately account for regional and vertical variations in the characteristics of superficial deposits. A new method for characterizing recharge potential and contaminant retardation potential of superficial deposits is presented here, which captures primary geological and hydrogeological expert knowledge in a systematic manner. The method modifies existing superficial geology maps using Quaternary domains and their descriptions, bedrock lithology and thickness of superficial deposits, and applies additional information on superficial geology and bedrock lithology. Central to the method is a matrix that allows local geological and hydrogeological knowledge to be incorporated in a systematic and traceable manner. The scale-independent method has been piloted at 1:625 000 scale to produce maps of recharge and attenuation potential for Great Britain. Preliminary verification against several indicators (HOST data, the Scottish vulnerability screening tool, and nitrate data) has been encouraging. The method is being used by the Environment Agency as part of its vulnerability assessments for the characterization of groundwater bodies as required by the Water Framework Directive

Groundwater flow in the Antrim Lava Group and Ulster White Limestone Formation, Northern Ireland

The Antrim Lava Group (the ‘basalts’) and the underlying Ulster White Limestone Formation (the ‘chalk’) occupy a third of the land area of Northern Ireland. Neither sequence offers any significant groundwater resource potential but the basalt yields a baseflow contribution of 2630 Ml day–1 to the Lough Neagh catchment. Large spring discharges occur from the eastern outcrop of the chalk along the Antrim coast, giving the chalk a misleading reputation as a significant aquifer. These springs represent karstic risings from streams flowing off the basalt towards the sea, mixed with a small proportion of groundwater that has seeped through the basalt into the chalk below, although the concealed chalk aquifer is, for the most part, confined. Groundwater flow in the basalt is almost entirely of shallow catchment scale following preferred pathways within fossil soil horizons and other sub-horizontal discontinuities within the basalt sequence. Towards the periphery of the basalt some deeper circulation penetrates the chalk to discharge at outcrop. The main subcrop of the chalk is relatively impermeable with tighter jointing that is not favourable for transport or for storage. Available evidence indicates that little groundwater circulation in the chalk aquifer derives from direct rainfall recharge to the overlying basalts and that groundwater circulation is limited away from outcrop