Proposals for implementing EC rules on sewage, nitrate

Government proposals for the criteria which water pollution control authorities will use when identifying waters requiring special protection against sewage and nitrate pollution were issued for consultation on 11 March.1 The authorities' decisions will determine the size of the bill facing water undertakers in improving standards of sewage treatment and the scale of the land use restrictions which will have to be imposed on farmers to curtail nitrate leaching.

The proposals are part of the Government's plans for implementing two 1991 EC Directives. These deal with municipal wastewater treatment (ENDS Report 194, pp 34-5), and the control of nitrate pollution from agricultural sources (ENDS Report 205, p 35 ).

Both Directives impose general duties on Member States to control water pollution. The Directive on wastewater treatment requires secondary treatment as the norm at sewage works. And the nitrate Directive obliges Member States to issue voluntary codes of good agricultural practice to prevent undue nitrate leaching.

With both Directives, however, departures from these norms are required in prescribed cases. Higher standards of sewage treatment are required for sewage works discharging into "sensitive areas," and Member States may sanction only primary treatment at works discharging into "less sensitive areas". Similarly, catchments draining into waters suffering from more severe nitrate pollution or which are at risk of doing so must be designated as "vulnerable zones", and action programmes to curb nitrate leaching implemented within them.

General criteria for designating these zones are given in the Directives, and the consultation papers issued in March - one each for England and Wales, Scotland, and Northern Ireland - are intended to set more precise criteria for use by the regulatory authorities. Ministers claimed that the UK is the first Member State to consult publicly on this issue.

One of the EC criteria for designating both "sensitive areas" and "vulnerable zones" is whether the waters concerned contain or may contain nitrate at concentrations higher than 50mg/l. For surface waters, this applies where they are used for drinking water abstraction, while for groundwater there is no such restriction.

Surface waters to be designated under the Directives will be identified by a combination of nitrate monitoring over the next 12 months or more and, in cases where the 50mg/l threshold may be breached if protective measures are not taken, persual of historical data to identify any trends in nitrate levels. These have remained fairly constant in most waters in recent years due to changes in farming practices.

For groundwater, the approach will be to exclude from consideration any sources where nitrate levels are not expected, by linear extrapolation of any positive nitrate trend, to exceed 50mg/l by 2010. Land use, rainfall and other data will be examined for the remaining catchments in order to identify those where the predicted equilibrium concentration of nitrate is likely to exceed 45mg/l. These will be examined in more depth before a final selection of "vulnerable zones" is made.

Both "sensitive areas" and "vulnerable zones" will have to be designated where waters are affected by eutrophication or liable to become so. This could become the most controversial feature of the designation process, since perceptions of what constitutes eutrophication vary markedly.

As a House of Lords report on the nitrate Directive pointed out, the Department of the Environment claims that the phenomenon is restricted to a "few localised sites", while the former Nature Conservancy Council identified some 150 Sites of Special Scientific Interest alone which may be affected by eutrophication (ENDS Report 196, pp 29-30).

The consultation paper proposes that the regulatory authorities take into account a lengthy list of criteria in judging whether particular waters are eutrophic. These include different combinations of chemical, biological and physical parameters in different types of waters, and the importance of particular symptoms of eutrophication will vary with local circumstances, it says. Assessing the practical implications of the proposals is difficult for this reason.

The consultation period ends on 16 April. Further consultation papers on the methodology to be used in designating nitrate "vulnerable zones" and on defining their location and boundaries have been promised. The designation process under both Directives has to be completed by the end of 1993.

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