Jersey's UV disinfection system, the largest in Europe, was commissioned in mid-1992. The treated sewage effluent is far cleaner in microbiological terms than seawater must be to comply with the 1976 EC Directive on bathing water quality.
However, some areas of St Aubin's Bay, to which the effluent is discharged, have failed the EC bathing water standards in recent years. Some shellfish beds have also failed standards set by a 1991 Directive on shellfish contamination. To discover why, the States of Jersey funded an investigation of bacterial inputs to the coastal waters by researchers at Leeds University's Centre for Environment and Health.
The researchers fitted flow monitoring gauges on three key rivers on the island and monitored their bacteriological quality throughout the 1993 bathing season. Several seepages across local beaches were also sampled, as was the quality of the disinfected sewage effluent.
The results showed that rivers made a much bigger contribution to coliform and faecal coliform levels than the sewage effluent. Bacteria levels in the rivers were at least a factor of ten, and in some cases 10,000 times, higher. The quality of the rivers worsened considerably during storm flows, when mean counts of coliforms, faecal coliforms and faecal streptococci increased from three to 1,000 times.
The researchers concluded that the streams are likely to have a significant effect on coastal water quality and non-compliance with EC Directives, especially after heavy rain. The study has now been extended to a closer investigation of bacteriological contamination of river waters, with a view to managing their quality.
Professor David Kay, one of the scientists involved in the project, told ENDS that important sources of bacteria in the Jersey catchments appear to be faulty domestic sewage connections, farm drainage and poorly sited septic tanks. In contrast to many other areas in the UK, storm sewage overflows do not appear to be a significant problem.
Catchment controls to manage these sources of contamination appear to be a practical option. A further possibility is the use of UV treatment to disinfect storm flows. These may also be next on the agenda for many other parts of the UK once the £2 billion bathing water clean-up programme triggered by the EC Directive is completed.