Agency tightens policy on coastal sewage discharges

A new policy for consenting coastal sewage effluent discharges was published by the Environment Agency in July.1 It requires disinfected effluents discharged close to bathing waters to achieve tougher EC guideline values for water quality. The new standards will apply to only a few schemes but will add £30 million to investment costs.

The policy of the former National Rivers Authority (NRA) on coastal sewage discharges included a presumption in favour of preliminary settlement of sewage and discharge via long sea outfalls. The standards for bacterial and viral pathogens required by the 1976 EC Directive on bathing water quality were met by dispersion and attenuation in the sea. Several events in recent years have dictated a revision of that policy.

The 1991 EC Directive on urban wastewater treatment established secondary treatment as the norm for sewage works treating population equivalents of over 15,000. Water companies found that because they were obliged to install secondary treatment at some coastal sites, significant cost savings could be made by discharging effluent through shorter outfalls and using disinfection to achieve compliance.

The NRA expressed doubts about some schemes that relied on disinfection (ENDS Report 231, p 9 ). But experience with UV disinfection has shown it to be reliable in achieving compliance with bathing water standards. The Agency has also evolved a position to ensure that new-style sewage treatment schemes do not mean any reduction in quality for pathogens such as salmonellae and enteroviruses.

The 1976 Directive sets a zero standard for salmonellae and enteroviruses but only requires testing when inspection "shows that [they] may be present or that the water quality has deteriorated." The standards have been criticised as having little value in protecting public health, and a recent proposal to amend the Directive would entail replacement of the enterovirus standard with a standard for bacteriophages as soon as new research allows, as well as deletion of the salmonellae standard (ENDS Report 234, pp 17-21 ).

The Government has effectively ignored the standards for both salmonellae and enteroviruses by reporting compliance solely on the basis of coliform standards. Key evidence on its policy emerged in 1995 during a judicial review of an NRA decision to consent a sewage discharge at Tenby (ENDS Report 250, pp 43-44 ). The NRA indicated that it had been advised by the Government that viral standards should not be considered in the design of sewage schemes - an apparent breach of EC law.

The NRA won the Tenby case, but the case highlighted its difficult position. It was obliged to uphold the EC standards but unable to ensure adequate treatment or dispersion of sewage effluents because of a lack of adequate scientific data on the numbers of enteroviruses and salmonellae in sewage and their persistence in the environment.

The Agency's new policy evolved from this impasse. Pending the results of further research, it assumes that preliminary treatment and a long sea outfall designed to meet the Directive's faecal coliform standards will also achieve acceptable levels of other pathogens.

Dischargers proposing schemes involving enhanced treatment and discharge through a short outfall will be required to demonstrate that protection of bathing waters will be "at least equivalent to that gained by locating the discharge at the point required if only preliminary treatment were given in order to meet the bacterial mandatory standards." However, they will not be required to model hypothetical long sea outfall schemes. They will merely have to show that the standards achieved will be at least as good as those required by the Directive and no worse in terms of reliability and variability than a remote outfall.

An important proviso is that faecal coliforms are more readily removed by secondary treatment than enteroviruses or salmonellae. The Agency considers that secondary treatment is ten times less effective in removing enteroviruses and by implication salmonellae.

The policy takes the "precaution" of requiring secondary treatment schemes to comply with both the Directive's mandatory standards and the tougher "guideline" values for faecal and total coliforms "in order to aim to achieve equivalence to a long sea outfall."

This is a significant move towards full compliance with the EC requirements. Although the guideline limits are not mandatory, the Agency says it "will endeavour to respect" them in exercising its powers, echoing the Directive's requirement that Member States " observe them."

Where the guideline values are consistently met at bathing waters, the Agency's "no deterioration" policy will ensure that this continues. Where they are not always achieved, it "will seek to improve water quality where circumstances permit," the document says. In practice this may mean setting time-limited consents requiring improved standards to be met in future. However, the Agency "will not promote expenditure that is disproportionate to the expected degree of improvement."

The Agency's stronger line can be traced back to the Tenby judicial review. The NRA stated in evidence that guideline values were not applied by the Government, but it was reminded in the judgement that the Secretary of State had also directed it to put the Directive into effect - including the guideline standards.

The status of guideline values remains a key issue for the Agency because it faces a civil action over coliform standards at bathing waters in the Taw and Torridge estuary in Devon. The action is being brought by Barnstaple solicitor Peter Scott on behalf of a shellfisherman who alleges loss of livelihood following pollution of the estuary by South West Water's sewage effluent discharges. The plaintiff argues that achievement of guideline coliform standards at bathing waters would have protected the shellfish beds from pollution.

The new policy will apply only to planned sewage schemes which do not yet have discharge consents or letters setting out likely consent conditions. It therefore comes too late to affect the vast majority of schemes designed to achieve compliance with the 1976 Directive. A spokesman suggested that only "one or two" such schemes would be affected, but others designed to achieve compliance with the 1991 Directive on wastewater treatment would be caught. Such schemes may require the diversion of crude discharges not currently affecting bathing waters to areas where treatment can be provided. However, discharges made at new locations may influence bathing waters and therefore require additional treatment.

Other schemes coming under the new policy will be those associated with newly designated bathing waters and any additional programmes found necessary to ensure compliance at existing waters. The Agency says that the estimated cost of the new policy will be £30 million. The overall cost of achieving compliance with the 1976 Directive is put at £2 billion, the vast majority of which has either been spent or committed.

  • Wessex Water has announced that it will install the world's largest membrane filtration plant for treating sewage at Swanage. The plant will have a capacity of 20,000 population equivalents - five times larger than any other, the company says.

    The plant will be capable of removing at least 99.97% of viruses and 99.998% of bacteria. The supplier has not been finally selected but is likely to be the Japanese company Kubota, which supplied a smaller demonstration plant that Wessex is building at Porlock in Somerset.

    The Swanage plant is part of a £28 million sewerage improvement plan for the town. In 1996, Wessex promised to provide sewage disinfection at all of its coastal discharges before 2005 (ENDS Report 261, p 12 ). It intends to build a UV disinfection plant at Weston, but its intentions for its major Avonmouth discharge remain vague: "We are still at the planning and design stage," a spokesman said.

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