The groundwater vulnerability concept is based largely on the question “can water and contaminants move in the subsurface materials (soil and subsoil) and/get down to groundwater easily?”

Groundwater is most at risk where the subsoils are absent or thin and in areas of karstic limestone, where surface streams sink underground at swallow holes. Groundwater vulnerability maps are based on the type and thicknesses of subsoils (sands, gravels, glacial tills (or boulder clays), peat, lake and alluvial silts and clays) and the presence of karst features.

Groundwater that readily and quickly receives water (and contaminants) from the land surface is considered to be more vulnerable than groundwater that receives water (and contaminants) more slowly and consequently in lower quantities.

Groundwater vulnerability is classified as follows: Rock near surface or karst (X) Extreme (E) High (H) Moderate (M) Low (L). Scale: 1:40,000

These data sources are used to classify groundwater vulnerability: Subsoil Permeability; Depth to Bedrock; Groundwater Karst DataSinking streams Teagasc subsoils

The Groundwater Vulnerability map along with the Aquifer maps and Source Protection Area maps are merged to produce Groundwater Protection Zones. Each zone enables an assessment of the risk to groundwater, independent of any particular hazard or contaminant type. The Groundwater Protection Zones form one of two components of Groundwater Protection Schemes.

A Groundwater Protection Scheme provides guidelines for the planning and licensing authorities in carrying out their functions, and a framework to assist in decision-making on the location, nature and control of developments and activities in order to protect groundwater. Use of a scheme will help to ensure that within the planning and licensing processes due regard is taken of the need to maintain the beneficial use of groundwater.

Groundwater Protection Schemes are county-based projects that are undertaken jointly between the GSI and the respective Local Authority.

The groundwater protection scheme comprises two components:A land surface zoning map (or maps) called the groundwater protection zone map, and Groundwater protection responses for existing and new potentially polluting activities. The role of the GSI is in the production of the land surface zoning map, whereas decisions on groundwater protection responses are the responsibility of the statutory authorities.