Different aquifers have differing abilities to store and transmit water. Based on the hydrogeological characteristics and on the value of the groundwater resource, GSI has classified Ireland’s land surface into aquifer categories.
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 sand and gravel aquifers classes. Scale: 1:40,000
Sand and gravel aquifers may be locally important (Lg) or regionally important (Rg).
Rg - A sand/gravel aquifer is classed as regionally important if it can supply regionally important abstractions (e.g. large public water supplies with ‘excellent’yields >400 m3/d). It is highly permeable, more than 10 m thick or has a saturated thickness of at least 5 m, and should extend over at least 5 km2, and usually over 10 km2.
Lg - Locally Important Sand/Gravel Aquifer: Similar to a Regionally Important Sand/Gravel Aquifer (Rg), but with a smaller continuous area (c.1-10 km2) and/or less consistent permeability. Although the aquifer may supply ‘excellent’ yields, the smaller size limits the amount of recharge available to meet abstractions.
Sand/gravel deposits have a dual role in groundwater development and supply. Firstly, in some cases they can supply significant quantities of water for supply and are therefore classed as aquifers, and secondly, they provide storage for underlying bedrock aquifers. A sand/gravel deposit is classed as an aquifer if the deposit is highly permeable, more than 10 m thick and greater than one square kilometre in aerial extent. The thickness of the deposit is often used rather than the more relevant saturated zone thickness as the information on the latter is rarely available. In many instances it may be assumed that a deposit with a thickness of 10 m will have a saturated zone of at least 5 m. This is not the case where deposits have a high relief (for example eskers or deposits in high topographic areas) as these gravels are often dry.
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.