Groundwater is the water that soaks into the ground from rain and can be stored beneath the ground. An aquifer is a body of rock and/or sediment that holds groundwater. There are two main types of aquifer in Ireland – bedrock aquifers, and sand and gravel aquifers.

Bedrock is the solid rock at or below the land surface. Over much of Ireland, the bedrock is covered by materials such as sands and gravel. The sands and gravels occur naturally on top of the bedrock. They were laid down by meltwater from melting ice sheets, by rivers, or by wind.

There are two main types of bedrock aquifer. In most of them, groundwater flows through fractures and fissures. In about half of the limestone rocks, groundwater flows through cavities and caves. This type of limestone is called karst.

Not all sand and gravel layers are aquifers. This is because some of them are very thin or are dry. If the sands and gravels are saturated with water, they have the potential to supply large volumes of water through wells or springs.

The aquifer maps show the potential of areas in Ireland to provide water supplies. There are three main groups based on their resource potential:

Regionally important – the aquifers are capable of supporting large public water supplies sufficient to support a large town;

Locally important – the aquifers are capable of supporting smaller public water supplies or group schemes;

Poor – the aquifers are only capable of supporting small supplies, such as houses or farms, or small group schemes.

The three main groups are broken down into nine aquifer categories in total. Please read the lineage for further details.

Information used to assign bedrock aquifer categories include: rock type (Hydrostratigraphic Rock Unit Groups - simplified bedrock geology with similar hydrogeological properties), yield (existing wells and springs), permeability and structural characteristics. All of the information is interpreted by a hydrogeologist and areas are drawn on a map to show the aquifers.

This Bedrock Aquifer map is to the scale 1:100,000 (1 cm on the map relates to a distance of 1km).

It is a vector dataset. Vector data portray the world using points, lines, and polygons (areas).

The bedrock aquifer data is shown as polygons. Each polygon holds information on the aquifer code, description, rock unit name, rock unit description, Hydrostratigraphic Rock Unit Group Name, Hydrostratigraphic Rock Unit Group Changes, Bedrock Geology 100k newcode, stratigraphy code (rock layers with age profile), lithology code (rock type), Aquifer Category Original and Comments.

Geologists record information about how thick the sand and gravel layers on top of the bedrock are. They also note down how big the different grains of sand and gravel are. Information from quarries and deep pits is used. Information from boreholes (a deep narrow round hole drilled in the ground) is also used. All of the information is interpreted by a hydrogeologist and areas are drawn on a map to show the aquifers GSI Aquifer classes are divided into three main groups based on their resource potential (Regionally or Locally important, or Poor), and further subdivided based on the type of openings through which groundwater flows (through fissures, karst conduits or intergranular). There are nine aquifer categories in total.

This is a polygon dataset containing nine Bedrock Aquifer classes. Scale: 1:100,000

1) Regionally Important Aquifers: Regionally important aquifers are capable of supplying regionally important abstractions (e.g. large public water supplies), or excellent yields (>400 m3/d). Bedrock aquifer units generally have a continuous area of >25 km2 and groundwater predominantly flows through fractures, fissures, joints or conduits. Regionally important sand/gravel aquifers are >10 km2, and groundwater flows between the sand and gravel grains. This group is subdivided into the following types: Rk Regionally Important Karstified Bedrock Aquifer Rf Regionally Important Fissured Bedrock Aquifer Rg Regionally Important Sand/Gravel Aquifer Regionally important karstified aquifers may be further subdivided based on the whether groundwater flows mainly through conduits (Rkc) or more diffusely through solutionally-enlarged fissures (Rkd).

2) Locally Important Aquifers: Locally important aquifers are capable of supplying locally important abstractions (e.g. smaller public water supplies, group schemes), or good yields (100-400 m3/d). In the bedrock aquifers, groundwater predominantly flows through fractures, fissures, joints or conduits. Locally important sand/gravel aquifers are typically >1 km2, and groundwater flows between the sand and gravel grains. This group is subdivided into the following types: Lm Locally Important Bedrock Aquifer, Generally Moderately Productive Ll Locally Important Bedrock Aquifer, Moderately Productive only in Local Zones Lk Locally Important Karstified Bedrock Aquifer Lg Locally Important Sand/Gravel Aquifer

3) Poor Aquifers:

These bedrock aquifers are capable of supplying small abstractions (e.g. domestic supplies, small group schemes), or moderate to low yields (<100 m3/d). Groundwater predominantly flows through a limited and poorly-connected network of fractures, fissures and joints. This group is subdivided into the following types: Pl Poor Bedrock Aquifer, Generally Unproductive except in Local Zones Pu Poor Bedrock Aquifer, Generally Unproductive

The Aquifer maps along with the Groundwater Vulnerability map 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.