National scale assessment of total trihalomethanes in Irish drinking water

Ireland reported the highest non-compliance with respect to total trihalomethanes (TTHMs) in drinking water across the 27 European Union Member States for the year 2010. We carried out a GIS-based investigation of the links between geographical parameters and catchment land-uses with TTHMs concentrations in Irish drinking water. A high risk catchment map was created using peat presence, rainfall (>1400 mm) and slope (<5%) and overlain with a map comprising the national dataset of routinely monitored TTHM concentrations. It appeared evident from the map that the presence of peat, rainfall and slope could be used to identify catchments at high risk to TTHM exceedances. Furthermore, statistical analyses highlighted that the presence of peat soil with agricultural land was a significant driver of TTHM exceedances for all treatment types. PARAFAC analysis from three case studies identified a fluorophore indicative of reprocessed humic natural organic matter as the dominant component following treatment at the three sites. Case studies also indicated that (1) chloroform contributed to the majority of the TTHMs in the drinking water supplies and (2) the supply networks contributed to about 30 μg L⁻¹ of TTHMs.