Catchment News

Groundwater source protection terminology used in Ireland

This article aims to explain and clarify technical terms used for groundwater source protection.

There are several terms used in Ireland for the areas around springs and wells, which can lead to a certain degree of confusion. The most widely used terms include catchments, zones of contribution, source protection areas, source protection zones, capture zones and safeguard zones, which are described as follows:

Zone of Contribution (ZOC) is the land area that contributes water to the well or spring (Misstear et al 2006). It is a simple, intuitive, basic hydrogeological definition that is considered to be the best term for general use.

Catchment is the land area that contributes water to the well or spring. Like surface water bodies, springs have natural catchment areas, whereas catchment areas to boreholes depend on a number of hydrogeological and meteorological factors plus the abstraction rate.

Capture Zone is a common term present in the scientific literature and is equivalent to the Zone of Contribution.

Safeguard Zone is a specific Water Framework Directive term that encompasses the same area as the Zone of Contribution.

Source Protection Areas: The Geological Survey of Ireland developed this terminology and the methodology for delineating the areas (DELG, EPA, GSI, 1999). Two Source Protection Areas (SPAs) are delineated which, when combined, are equivalent in area, shape and orientation to the Zone of Contribution:

• Inner Protection Area (SI), designed to give protection from microbial pollution.
• Outer Protection Area (SO), encompassing the remainder of the zone of contribution (ZOC).

Different methods can be used to map the entire Zone of Contribution to a spring, borehole or dug well, resulting in different degrees of confidence associated with the boundaries of the de-lineated area. To be able to specify the Inner Protection Zone within the entire Zone of Contribution, knowledge or estimates of groundwater travel time within the aquifer are required (e.g. from site-specific hydrogeological parameters or tracer tests).

The Zone of Contribution and the Source Protection Area account for the ‘horizontal’ movement of groundwater. Source Protection Zones are obtained by integrating the Source Protection Areas with the groundwater vulnerability categories, as shown schematically in Figure 1. An example of the Source Protection Zones defined for the Toberdaly source is provided in Figure 2.

The Source Protection Zone includes the complete pathway, both vertical and horizontal, for re-charge and any entrained contaminants to the abstraction point.

Whereas the objective of delineating ZOCs is to define approximate areas that contribute water to an abstraction point, the objective of SPZs is to geo-scientifically characterise the pathway and receptor elements of risk to groundwater within the ZOC of a given source (Kelly, 2010). EPA prepared an advice note on “Source Protection and Catchment Management to protect Groundwater Supplies” that outlines the key measures and policies in place in Ireland (EPA, 2011).

While these three terms essentially encompass the same total area, there are differences and they should be used appropriately. It is recommended that for general usage the simplest, most basic hydrogeological term “ZOC” is used. “SPA” and “SPZ” are appropriate when considering protection of groundwater sources and when a sufficiently detailed study has been undertaken in order to delineate the areas and zones. The term “Safeguard zones” is only used with reference to implementation of the WFD (Daly, 2009).

Other Related Terms

Drinking Water Protected Areas are a specific Water Framework Directive term and they encompass the same areas as Groundwater Bodies.

Groundwater Body is a specific Water Framework Directive term used to subdivide aquifers into effective management units, largely based on hydrogeological rules in relation to the boundaries, e.g. a ‘no flow’ boundary (GW WG, 2005).

Drinking Water Safety Plans is a risk assessment and risk management approach to ensure the ‘safety’ and ‘security’ of a water supply. In this context ‘security’ refers to the catchment to the supply and ‘safety’ refers to the quality of the treated water meeting drinking water standards. Further details are provided in an EPA Guidance Note on ‘Developing Drinking Water Safety Plans (EPA, 2011).

Setback Distances, Exclusion Areas/Zones are specific terms used to regulate the spreading of organic fertilisers and other farmyard activities around drinking water sources. The regulations (S.I. No 31, 2014) provide a range of setback distances from a water source depending on the daily abstraction or the number of people served. The regulations provide for alternate distances and/or zones to be proposed by a local authority or Irish Water subject to EPA approval for abstractions supplying 10m3 or more, of water per day, or serving 50 or more persons. Further details are given in the EPA advice note No. 11 (EPA, 2011). Distinguishing Zone of Influence and Zone of Contribution “Unless the water table is horizontal prior to pumping the Zone of Contribution is not the same as the zone of influence of the pumping well (the zone contained by the radius of influence of the well)” (Misstear et al., 2006).

The zone of influence (ZOI) is defined by the “radius of influence” of a pumping well, i.e. the area where drawdown occurs due to pumping. Therefore, the Zone of Influence boundary is where the drawdown is zero. The water table is unlikely to be flat in Ireland, therefore the Zone of Contribution and Zone of Influence areas and boundaries will never be the same for pumping wells. In most circumstances, the Zone of Contribution will be larger than the Zone of Influence. The difference between the zone of contribution (ZOC) and zone of influence (ZOI) is illustrated in Figure 3. As shown in Figure 3, the Zone of Contribution boundary will extend further up-gradient than the Zone of Influence but not as far down-gradient.

Summary

• Groundwater ‘Drinking Water Protected Areas’ comprise the entire land surface of the Republic of Ireland as all groundwater bodies are capable of yielding more than 10 m3 /day as an average. We recommend only using this term for WFD implementation purposes.

• The simplest and most intuitive term conceptually for the catchment area of a well/ spring is “zone of contribution (ZOC)”.

• ZOC area = SPA area (SI+SO) = SPZ area = safeguard zone area = capture zone. While these terms encompass the same total area, they have different purposes. It is recommended using ZOC for general usage as the most basic hydrogeological term; SPA and SPZ as appropriate when considering protection of groundwater sources; and only referring to “safeguard zones” when considering implementation of the WFD. Taly Hunter-Williams, Geological Survey of Ireland, Coran Kelly, Tobin Consulting Engineers , and Donal Daly, Environmental Protection Agency. This article originally appeared in the Geological Survey of Ireland’s Irish Groundwater Newsletter, which you can find at http:// www.gsi.ie/Programmes/Groundwater/ Groundwater+Newsletter.html

Resources

DELG/EPA/GSI, 1999. Groundwater Protection Schemes. Department of the Environment and Local Government, Environmental Protection Agency and Geological Survey of Ireland. Misstear, B. D., Banks, D., and L. Clark. 2006. Water Wells and Boreholes. Wiley & Sons Ltd. ISBN-13: 978-0- 470-87989-7.

EPA Guidance Note No. 7. 2011. Advice on Source Protection and Catchment Management to protect Groundwater Supplies.

EPA Guidance Note No. 8. 2011. Developing Drinking Water Safety plans.

EPA Guidance Note No. 11. 2011. Advice on Prior Investigations and Technical Assessments for Good Agricultural Practice Regulations.

European Union (Good Agricultural Practice for Protection of Waters) Regulations. S.I. No. 31 of 2014.

Groundwater Working Group. 2005. Water Framework Directive (WFD) River Basin District Management Systems: Approach to Delineation of Groundwater Bodies. Guidance Document No. 2. Available on the http://www.wfdireland.ie/ documents-wfd.html

Kelly, C. 2010. Delineating Source Protection Zones and Zones of Contribution for Monitoring Points. IAH (Irish Group) Annual Conference Proceedings. http://www.iah-ireland.org/ conference-proceedings/2010.pdf