Présentations Colloques

This research compares a range of fingerprinting techniques for identifying sources of private water well contamination. In particular the focus is to quantify the extent of the pollution from domestic wastewater treatment systems (DWWTS) as distinct from agricultural sources. In predominantly rural areas of Ireland approximately 438,000 dwellings use septic tank or other onsite wastewater systems. Often such rural areas are not connected to a public drinking water supply, and so many households obtain their drinking water from a private water well. Hydrogeologists are rarely involved in the siting or construction of these small private schemes, and therefore the wells are often located within relative close proximity to a DWWTS, a known source of microbial pathogens, and are often poorly constructed, with no sanitary seal around the wellhead. A total of 212 households dependent on private wells and DWWTS have been evaluated by site assessments and sampling of chemical and microbial parameters. A total of 15% of the wells were at least intermittently contaminated with E.coli. Subsequent monthly monitoring of 24 wells found 45% to be contaminated with E. coli at least once. These wells have been used to assess a range fingerprinting techniques, including fluorescent whitening compounds (FWC), faecal sterols, anion ratios and Bacteroidales faecal source tracking (FST). FST tests of 42 wells targeting regions of Bacteroidales 16S rRNA genes found 62% were positive for human specific Bacteroidales. However, no wells to date have tested positive for FWCs using fluorometry and UV degradation methods. The research has also evaluated faecal sterols, artificial sweeteners, caffeine and pharmaceuticals as tracers. With DWWTS effluent recognised as a major factor in the incidences of waterborne disease worldwide, accurate identification of private wells impacted by human effluent is required to help guide corrective action and protect householder health. **