It is clear from Principle 17 of the Rio Declaration, in addition to other international environmental instruments, that international law requires States to carry out an EIA when the proposed project is considered to have ‘significant adverse’ implications for the environment. A ‘project’ is gener­ally accepted to be the execution of construction works or other interven­tions in the natural surroundings and landscape (EIA Directive, 2009, Article 1(2)). The obligation to undertake an EIA will not apply where the potential environmental harm that may be caused by the project is slight. Therefore, the potential environmental harm must be significant. The legal terminology is similar at a European level, with EU Member States being required to carry out an assessment where a proposed project is likely to have ‘significant effects’ on the environment. It remains, however, the dis­cretion of the individual State to determine when the potential environ­mental impacts can be classed as ‘significant’. A key question, therefore, is whether there are parameters to this discretion — are there any types of activity that will necessarily cause environmental damage of the requisite significance so as to require a mandatory EIA?

The EIA Directive is of some assistance on this point. Annex 1 of the EIA Directive lists projects which, by their very nature, must be made subject to a mandatory EIA. ‘Nuclear power stations and other nuclear reactors’ and ‘installations solely designed for the permanent storage or final disposal of radioactive waste’ are expressly listed in Annex 1 and so development projects of this nature will always trigger the requirement for mandatory EIA. The European Court of Justice (ECJ) has recently ruled that Annex 1 activities carry with them a presumption of significant environmental damage or risk and therefore will always be subject to the ‘unequivocal obligation’ (Case C-431/92 Commission v Germany, para­graph 39) to carry out EIA, irrespective of whether the activity in question crosses the political boundaries of two or more Member States (Case C-205/08 Umweltanwalt von Kaernten).