This raises the interesting question of how EIA should be carried out where environmental consequences of a proposed nuclear installation may straddle political boundaries. Of particular relevance here is the concept of transboundary EIA, the process whereby States ‘take all appropriate and effective measures to prevent, reduce and control significant adverse trans­boundary environmental impact from proposed activities’ (United Nations, 1991, Article 2(1)). This is an express requirement of the EIA Directive, but is also an established principle of international law. The Convention on Environmental Impact Assessment in a Transboundary Context (the Transboundary EIA Convention) (United Nations, 1991) is the primary international agreement on the matter, and provided the basis upon which the EIA Directive was amended in 1997. The Transboundary EIA Convention has as its core the objective of enhancing international coop­eration in assessing and mitigating environmental impacts in a transbound­ary context, and addresses the situation where an activity proposed in a territory in one jurisdiction causes the risk of significant adverse environ­mental impacts in the jurisdiction of another State. The definition of ‘impact’ is drafted widely and includes ‘any effect on the environment. . . historical monuments or other physical structures’ and any resulting ‘effects on cul­tural heritage or socioeconomic conditions’ (United Nations, 1991, Article 1(vii)). Clearly, this threshold is deliberately set at a very low level so as to encourage active dialogue between States when the potential for trans­boundary environmental issues arises.

The process affords the affected State the right to participate in and, to a limited extent, influence the decision-making process in the State where the activity is proposed, principally by giving the affected State the right to be notified of the proposed activity and to receive certain documentation as regards environmental assessment. As with EIA at a national level, however, the transboundary EIA process does not give affected States(s) the right to ‘veto’ a proposed activity on the basis of transboundary envi­ronmental impacts.

Adopting an approach similar to that of the EIA Directive, Appendix 1 of the Transboundary EIA Convention identifies types of projects for which a transboundary EIA should always be carried out. This includes proposed development of installations for the ‘production or enrichment of nuclear fuels, for the reprocessing of irradiated nuclear fuels or for the storage, disposal and processing of radioactive waste’ (United Nations, 1991, Appendix 1, paragraph 3). In the early to mid-1990s, the British government listened closely to representations made by the Irish government when it was considering how to proceed with determining a licence application for a proposed nuclear waste disposal site at Sellafield in England. The Irish government produced strong scientific evidence that the storage of radioac­tive substances at the proposed disposal site could have significant adverse environmental impacts in Ireland, primarily as a result of Sellafield’s geo­graphical location on the Irish Sea coastline. This evidence ultimately played a significant part in the British government’s decision to not grant the licence.