The increasing use of short outfall pipes to discharge effluent into the sea has brought attention to water companies' compliance with the tough effluent quality standards now prescribed. The standards are designed to ensure that bathing and shellfish waters meet microbiological standards laid down in EU Directives.
Companies are now turning to ultraviolet sewage disinfection to meet the standards. South West Water has the most UV plants in Britain, with 31 now in operation. But the quality of effluent that these produce is sometimes questionable.
Campaign group Surfers Against Sewage has complained that Trevaunce Cove, a prime surfing beach near St Agnes in Cornwall, failed to meet the EU guideline water quality standard in 2002. The beach met this standard in 2001 for the first time.
The group, suspecting that poor quality effluent from the nearby St Agnes sewage works is the cause, asked for clarification from the Environment Agency. "The public think that UV means clean waters, but at St Agnes this isn't the case. SWW are not delivering what we are expecting. You find a level of bacteria you might expect from a secondary treated effluent - not from UV," said Vicky Garner of SAS.
Peter Scott, an environmental lawyer and campaigner from law firm Toller Beattie, echoed these concerns. "The public should be given a health warning before visiting beaches which are affected by consistently poor South West Water sewage plants," he said.
Mr Scott singled out three plants for particular criticism based on SWW monitoring data submitted to the Agency: St Agnes, Perranporth and Newquay.
The performance of Perranporth was variable in 2001 but very poor in 2002, when it discharged up to 44 million faecal coliforms (fcs) per 100ml of effluent - the kind of levels present in raw sewage. St Agnes performed poorly in both years, discharging up to 9.3 million fcs/100ml.
While Newquay performed consistently well in 2001, a treatment problem in July 2002 led to a discharge containing over six million fcs/100ml.
South West Water commented that all of the works were performing satisfactorily and that local bathing waters had passed mandatory microbiological standards. Under the Agency's consenting rules, this effectively means that the works meet their consent conditions, since performance is judged by compliance with bathing and shellfish water quality standards rather than the quality of the discharge (ENDS Report 332, pp 41-42 ).
Agency marine policy advisor Keith Davis commented that the performance of works such as St Agnes and Perranporth was now recognised to be unsatisfactory. Both sites use chemically assisted settlement (CAS) instead of biological secondary treatment. The Agency now believes that CAS is unsuitable for use with UV disinfection.
South West Water has three sites using CAS, all of which are due to be replaced within the next few years. The Agency expects Perranporth and another works, Trecerus, to be refitted in the current investment period which ends in March 2005. It hopes that St Agnes will be refitted shortly afterwards.
Mr Scott was particularly interested in the poor quality discharge from Newquay because the company had noted in its submission to the Agency that it occurred when the works suffered an "unstable sludge blanket in final tanks".
The comment appears to imply that poor sewage treatment is predictable. "This turns out the proposition that people should be warned when there are sewage treatment failures. Plus all of [these sites] are linked by telemetry to South West Water's control centre. We must have a real-time response to these public health threats," Mr Scott said.
Mr Scott went on to suggest that failure to warn the public may be a breach of human rights under the Guerra principles - a 1998 judgement by the European Court in which it held that the Italian authorities infringed the rights of residents near an EniChem chemical factory. The court ruled that their rights to private and family life had been infringed because they were not warned of the health risks posed by emissions from the works.