Wastewater Directive implemented, but key issues unresolved

Regulations implementing the 1991 EC Directive on urban waste water treatment in Britain came into force at the end of last year.1 But the practical detail of how the Directive will be applied will not be clear until guidance notes are produced later in 1995. Finalisation of the guidelines awaits the results of a joint research project between the water industry and National Rivers Authority (NRA) into the Directive's monitoring requirements.

The regulations came into force on 30 November, but settled few of the outstanding questions on how the Directive will be implemented. The most cost-effective means of doing so remain to be agreed in negotiations between the Department of the Environment (DoE), the water industry and the National Rivers Authority (NRA).

One of the key areas to be decided is whether sewage works' performance will be assessed by fixed discharge limits or by percentage reductions in load, either of which is permitted by the Directive. Last year, the DoE made an about-turn in its established policy. Having originally favoured the fixed limit approach, it decided that the percentage reduction method would allow sewerage undertakers to achieve major savings (ENDS Report 228, pp 3-4 ).

However, the water industry has now underlined the disadvantages of the percentage reduction method - notably the higher investment required in monitoring. The percentage reduction approach demands the sampling of incoming sewage as well as of effluent discharges, and measurement of the flow through the treatment works. The method is also a departure from normal practice for the industry and could cause compliance difficulties at some works, particularly on COD.

The result is that the DoE is now expected to allow either approach to be used, leaving the decision essentially for water companies to agree with the NRA for individual discharges.

The type of works and its loading patterns will be crucial factors. For example, compliance with limit values could be threatened by occasional high loading rates, while the percentage reduction criteria could be difficult for a works to achieve if the influent sewage is very dilute.

The Directive requires monitoring on the basis of composite samples taken over a 24-hour period, with compliance being judged on a 95 percentile basis for the three key parameters - BOD, COD and suspended solids. The use of composite rather than spot samples is novel for both the industry and the NRA.

Finalisation of much of the detail for implementing the Directive hangs on a National Consents Translation Project managed by the Foundation for Water Research, due to be completed shortly. The project aims to examine the statistical relationship between composite and spot sampling of discharges.

One issue is whether the NRA will move to measuring compliance on a composite basis for all sewage works discharges, or whether the present spot system will be retained for measuring compliance with water quality objectives. The Directive allows alternative methods of monitoring to be used instead of 24-hour composite samples, provided that equivalent results can be demonstrated. The DoE has not ruled this out, but the decision will depend on the results of the consents translation project and the practicality of an equivalent spot sampling regime.

A further point under consideration in the research project is the relationship between standards for spot or composite samples and "upper tier" limits. The limits have been a cause of some disagreement between the NRA and water companies in recent years. The NRA believes them to be essential to protect the environment from occasional gross breaches of the 95 percentile standards, and has attempted to include them in existing sewage works consents. Water companies have generally appealed to the Secretary of State but the appeals have yet to be determined.

Although the DoE, NRA and water industry had reached an agreement on how to set upper tier limits, the current situation is that results from the consents translation project have highlighted problems with the proposed system.

The extent to which the Directive will impose an extra tier of water quality monitoring on the NRA and its Scottish counterparts remains to be seen. Where the Directive's requirements are more stringent than existing consents, it may be possible to combine the two if the composite sampling approach is adopted. But where existing consents are more stringent than the Directive, regulators will be required to operate both monitoring systems in parallel, with the objective of ensuring that failures to meet consents based on domestic water quality requirements do not jeopardise compliance with the Directive.

The regulations have been drafted to allow water companies to monitor their own discharges. The NRA will be required to assume a new role as auditor of their self-monitoring, which may involve a change from merely monitoring discharges to a more comprehensive responsibility for the design and maintenance of plant, akin to the current duties of HM Inspectorate of Pollution.

In Scotland, the prospect of self-monitoring by sewerage undertakers has raised legal questions due to the difficulties with self-incrimination in Scots law. In principle, a Scottish court requires independent corroboration of an offence, and monitoring data produced in-house by a sewerage undertaker would not provide this. According to a spokesman for the River Purification Boards, the principle is likely to mean that self-monitoring will not be an option for Scottish treatment works.

An important aspect of the regulations is the provision for prosecutions. The regulations go further than the Water Resources Act 1991 in allowing evidence gathered by recording apparatus to be presented as evidence in court. This will weaken the Act's requirements for "tripartite" samples, but this is any event being scrapped by the new Environment Bill (ENDS Report 239, pp 19-22 ).

The DoE now envisages that discharges from the industrial sectors covered by the Directive will be little affected. The European Commission has apparently accepted its argument that existing UK controls over direct industrial discharges based on water quality objectives satisfy the Directive's requirements, at least for the present. However, the Directive obliges the Commission to compare controls on industrial discharges in different Member States, and this may eventually give rise to new proposals.

Please sign in or register to continue.

Sign in to continue reading

Having trouble signing in?

Contact Customer Support at
or call 020 8267 8120

Subscribe for full access

or Register for limited access

Already subscribe but don't have a password?
Activate your web account here