Wider lessons of sewage shock for North West Water

North West Water is being forced to spend a further £100 million on improving sewage treatment in the Blackpool area to meet EC bathing water standards. The move follows the failure of modelling work to make accurate predictions of the fate of sewage effluent - a finding likely to add weight to a call by MPs this month for more precautionary standards of sewage treatment.

The House of Commons Environment Committee urged in February that all sewage should be fully treated and disinfected before discharge to inland or coastal waters (see pp 31-32 ). The water industry said this would have "enormous" funding implications - but North West Water's experience in attempting to improve bathing water quality suggests that a more precautionary approach may be wise in some areas at least.

The company's £500 million "Sea Change" programme was intended to deliver compliance with microbiological standards set by the 1976 EC Directive on bathing waters. It was completed in time for the 1997 bathing season - but 17 of the region's 34 designated waters still breached the standards. The failures prompted Environment Minister Michael Meacher to write to the company to express his "dismay" (ENDS Report 275, p 9 ).

The Government is anxious to avoid a second case before the European Court of Justice for non-compliance with the Directive. In 1993, the UK was ruled to be in breach of the rules - and the bathing waters off Blackpool and Southport were at the heart of the case (ENDS Report 222, p 47 ).

North West Water and the Environment Agency launched an investigation into the causes of the failures last year. Diffuse sources, such as run-off from farmland, were suspected to be significant causes. But an Agency spokesman told ENDS that it is now "very confident" that these are contributing only 10% of the problem. The main factors are storm sewage overflows and discharges from sewage works, including some inland on the Ribble estuary.

The findings are a serious embarrassment. Most of the modelling work on which the improvement schemes were based was carried out by the premier water consultancy WRc in the late 1980s and early 1990s. The work was audited by the former National Rivers Authority.

The modelling techniques were the "best available at the time", according to the Agency. The modelling was done on what was believed to be a "very conservative" basis, and those involved are "quite shocked" at its failure.

The Agency attributes the failure to a "fundamental lack of understanding in the scientific community" of some key issues. It was assumed, for example, that bacteria begin to die off as soon as they are discharged, but this has proved not to be the case. Reservoirs of bacteria in sediments were also not taken into account. And the finer grid models used today are much better at modelling local flow patterns, especially in shallower waters such as those in and around the Ribble estuary.

"It's a sorry tale, there's no getting away from that," the spokesman commented. "It's a salutary lesson that perhaps we don't understand the environment as well as we think we do."

North West Water will spend £3.5 million on interim measures to limit pollution before the 1998 bathing season. These include disinfection of storm water discharges in Blackpool and other coastal towns, together with chemical disinfection of discharges from five sewage works.

The rest of the £100 million will be spent on ultra-violet disinfection at six sewage works discharging to the river Douglas, the Wyre and Ribble estuaries, and to coastal waters at Southport. Storm water storage will be increased in three towns, and the closure of a small sewage works will be brought forward. Most of this work is due to be completed next year, although one scheme may take into 2000 to be completed.

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