Vol. 513 No. 1
596 Mr. Durkan asked the Minister for the Environment and Local Government the investigation, if any, undertaken to evaluate the possible extent of water pollution arising from severe flooding at various locations; and if he will make a statement on the matter. [2025/00]
Statutory responsibility for monitoring water quality rests primarily with local authorities and the Environmental Protection Agency.
Flooding creates exceptional conditions which are not representative of water quality conditions generally and which are usually short-term. While I am not aware of any specific surveys to evaluate the impact of flooding on water quality, the effects of flooding in this regard have been documented on the basis of routine water quality surveys which coincided with flood conditions. In general, rivers in flood contain higher concentrations than normal of organic matter, nutrients, bacteria and other contaminants and may have high concentrations of suspended solids. Flooding in rivers is often accompanied by highly turbulent conditions leading to high aeration rates and, in general, the level of deoxygenation is moderate despite possibly high concentrations of biodegradable organic matter. In sluggish rivers or large lakes, some of the organic matter and nutrients may be incorporated in sediments and subsequently released to the overlying waters. The upper end of boreholes can be protected by sealing, and protection for groundwaters generally is provided by the passage of flood waters through soil layers which remove most contaminants. In some areas of karstic limestone, fissures may facilitate rapid movement downwards of contaminated water which may lead to pollution of groundwaters.
The conditions which may be generated by flooding are taken into account in the design, location and operation by local authorities of treatment plants for the production of drinking water. The operation of such plants is adjusted as necessary to respond to higher pollution loads which may be present in floodwaters and to counteract, for example, increased colour, bacterial matter and suspended solids. Where necessary, smaller treatment plants may be shut down on a precautionary basis for the duration of high water periods.
