Emission standards may be set individually for each discharge, or uniform standards for a particular class of discharge may be applied across a whole area or country or even the Community. Directive 76/464 (see Section 4.8) requires all discharges to water of certain listed dangerous substances to be subject to emission standards but does not specify numerically what the emission standards are to be. Instead, limit values (upper limits) for these emission standards are to be laid down in subsequent (or daughter) Directives for certain particularly dangerous substances set out in a List I. For possibly less dangerous substances, set out in a List II, emission standards are the responsibility of the Member States and are to be set by reference to quality objectives. Since lead appears on List II and not on List I, the Community has no plans for setting emission standards for lead discharged to water, but this does not mean that Member States are not circumscribed by Community legislation. As we have seen, the Community has already laid down an environmental quality standard for surface water that is to be abstracted for drinking, and any emission standards laid down in Member States must be such that those quality standards are met at the abstraction points.

It is only for the List I substances that the Commission is to propose limit values which emission standards are not to exceed, but even here the Directive allows Member States the alternative of setting emission standards locally so long as environmental quality standards set by the Community are met. It is this alternative that Britain insisted upon and has chosen to follow (see Section 4.8). By following the alternative, the emission standard will depend on a number of factors including the capacity of the receiving environment to dilute the discharge, the environmental quality that will have been prescribed for it, and the quantity and quality of other emissions to it.

Emission standards may be set numerically (either in legislation or administratively) as so many parts of a substance per million of effluent or per unit of productive output. Alternatively an obligation may be placed on the discharger to use the ‘best available techniques’ (BAT) for reducing emissions, and as technology and management practices improve the emission standard will be progressively tightened, such as under the IPPC Directive (see Section 6.18). In the UK, for example, to make this system workable, the Environment Agency sets numerical emission standards which certain emissions to air are not to exceed, and these are revised from time to time. Such standards will need to take account of BAT References Notes produced under the IPPC Directive as EU wide guidance. EU wide emission standards are also set out in other Directives, such as those for incinerators (see Sections 6.11 and 6.16).